Talk:Negative feedback/Archive 3

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Please cool it

@Brews, I am sure you mean well, and some of your suggestions definitely are useful, but your style is combative rather than collaborative and the sheer volume of your input is overwhelming and counter-productive. You have made about 1500 edits running to thousands of words in the last few months, almost all of them here or in related discussions. And to be frank, some of your ideas are misconceived and some of them are downright eccentric.

When I suggested recently that you step back for a bit your feelings were hurt (and I'm genuinely sorry for that, I had no intention of being offensive), but you said you would give it a break; this lasted a few days and then you were back, and with the same patterns of behaviour. Please, please, leave this topic alone for a few weeks. Maybe edit a bunch of completely different subjects, or just get some exercise. But try to cultivate a less combative style and a more succinct expression when you do. DaveApter (talk) 10:57, 23 September 2014 (UTC)

Dave: In almost all editors' contributions, your own being an exception, sources do not come up, and the introduction of them is considered offensive. For example, the actions above by Dicklyon & GliderMaven, and I regret, yourself, indicate an amazing disparagement of the widely published arenas of social dynamics and complex adaptive systems, which includes the application of feedback in education, management, and psychology, described above by GliderMaven as cargo cult science, and according to Dicklyon my desire to mention it is 'a stupid thing'. The sources cited, including even Wiener's cybernetics, and scientific application to neural networks, are not paid any attention. You have suggested that the mere mention of this work is so far off-topic (despite published opinion to the contrary) that it should be made a separate article and omitted here entirely. This shared hostility to a recognized field is contrary to WP policy and common sense.

I have raised the issue of using sources repeatedly here, and so far the only discussion of sources beyond my own is to ignore or to disparage them, and direct attention elsewhere, mostly as complaints that I am interfering with consensus. Whatever consensus that might be, it has nothing to do with sources.

This intolerance of sources and obsession with personal beliefs is inadvisable. Brews ohare (talk) 12:56, 23 September 2014 (UTC)

This kind of continuing misrepresentation of my attitudes and positions is one reason I am unable to participate productively in discussions with you, Brews. Anyone who knows my editing style knows that I very much seek out, value, and respect good references. You just have no idea what is going on with you. Dicklyon (talk) 17:31, 23 September 2014 (UTC)

Misrepresentation?

While I agree that negative feedback is important both in systems with identifiable setpoints and errors and in systems without, I do not agree that the kind of parameter insensitivity that those guys talk about is the first-order way to look at negative feedback; it's a secondary effect, and applies to both types system with and without setpoints and errors. You have jumped to an odd interpretation of those sources that makes it impossible for you to converge with others. And I though you said you were going to go away and let it get worked out... Dicklyon (talk) 05:25, 2 September 2014 (UTC)

My reasoning is this: when you say stupid things, it is impossible to talk you out of your odd way of thinking, so I give up. Dicklyon (talk) 19:11, 22 September 2014 (UTC)

Anything else? Brews ohare (talk) 17:53, 23 September 2014 (UTC)

Of course, this point, obvious to me, is no less obvious than the impossibility of conveying it to those assembled. I understand your difficulty to some degree, as my thought originally was like yours that error-controlled regulation was the paradigm. That meant that the negative feedback amplifier was outside the paradigm unless the concept was widened. Unfortunately, instead of that widening, you all have decided that willy-nilly the negative feedback amplifier will be forced into the Procrustean bed of error-correction, even if no gospel can be found advocating this faith.

That is why I changed my attention to other fields of scholarship that employ the term 'negative feedback'. This topic is refused as well, not on the basis of sources, but as before, based upon the personal belief of those assembled. The belief in this case is that these other uses of the term 'negative feedback' are either like cargo cult science, or far off-topic using 'negative feedback' only in the loose everyday sense of unwanted rejection. That belief is erroneous, and readily disproven by reading the sources instead of assuming what they say. Brews ohare (talk) 21:02, 23 September 2014 (UTC)

I have never taken the position you ascribe to all of us here. I disagree with both Trevithj and GliderMaven on various points. Yet we have several times been close to converging on a compromise, until you torpedoed it. Go away, as you said you would, and maybe we'll work it out. Dicklyon (talk) 02:16, 24 September 2014 (UTC)

Back to amplifiers

I have moved contributions by Trevith j above that were injected into the above thread that concern the subject of the negative feedback amplifier.

[Deleted]

Please don't be concerned about giving offense, Trevith. I do agree that when the textbook analysis does not mention error correction in discussing the negative feedback amplifier, that is not to say that it is absent. However, as their discussion does not use this idea, we can definitely say that their discussion of negative feedback does not need this idea. Accordingly, if the negative feedback amplifier in fact does incorporate some form of 'gap' that is reduced, this point is not part of the standard discussion. We therefore need some basis for bringing it up in this context, which obviously is not supplied by stating that it is the consensus of editors here present, sans sources. There is no logical fallacy in this argument that I can see. Brews ohare (talk) 21:02, 23 September 2014 (UTC)

I believe you can't see it. But it is there. "Textbook analysis" either refers to a standard and widely-held analysis of the subject, or it refers to your analysis of two textbooks. Then there is that false premise: "does not mention error correction". Actually, Bhattacharya devotes much of the introductory chapter to exactly that. Trevithj (talk) 02:18, 24 September 2014 (UTC)

Trevith, Amplifiers are not control systems, but Battacharya's book is about control systems. Its relevance to the negative feedback amplifier is found in his discussion of the effect of feedback upon sensitivity, which is for our purposes indistinguishable from that of Kal, who addresses directly the negative feedback amplifier. So, for example, Bhattacharya's introductory chapter is about control systems, not the negative feedback amplifier, and he describes things like comparators and set points typical of control systems that have nothing to do with the negative feedback amplifier, and refers to comparators, set points, and errors that are found only in control systems.

Naturally the way to get to the bottom of these things is to examine the sources carefully and identify exactly what portions we might interpret differently. The sensitivity analysis of both Bhattacharya and Kal are basically identical and do not require any of these ideas that describe control systems. Both are based upon the figure in the lede (mathematically identical to this figure in the feedback amplifier section), while the figure for a system involving set points, 'gaps' and regulators is like the figure found in the error-control section. If you wish to assert that the negative feedback amplifier, whatever one cares to say about its sensitivity, is at bottom a control system like that of this figure, then you will have to support that assertion with a source. No source making such an assertion will be found. Brews ohare (talk) 04:29, 24 September 2014 (UTC)

Negative feedback amplifier using ideal unilateral elements. The feedback is negative if βA_OL> 0.

What do you regard as evidence that you are wrong? Bhattacharya includes the negative feedback amplifier in a book about control systems. Trevithj (talk) 04:53, 24 September 2014 (UTC)

Argument from authority is the only VALID form for Brews Ohare; even though argument from authority is a well-known fallacy. Mere logic based on facts need not apply. I'm with the WP:SHUN camp. If Brews can't sort his head out, we certainly can't.GliderMaven (talk) 13:27, 24 September 2014 (UTC)

My argument is that the figure at the right is used by both Kal and Battacharya to establish the traditional argument as to why feedback renders this circuit insensitive to variations in the open loop gain A_OL, and this argument does not make use of any ideas from control theory about measurement of the value of an essential variable, measurement of a 'gap', use of a comparator, or regulator, or minimizing a 'gap'. So, I believe, you two have at least two possible positions to take, namely that this block diagram does not represent a negative feedback amplifier, or the traditional analysis of this circuit is mistaken. You have both made version of these arguments in the past, and you both have not provided any source that suggests either of these possibilities is held to be valid. Showing comendable creativity, you two have now converged upon a different kind of objection:1,2:

"So let me get this straight, you are claiming that a negative feedback amplifier is not an example of an error-controlled regulator, and you are basing this on something that a textbook did not say, and then writing it into Wikipedia as true?."GliderMaven (talk) 17:33, 30 August 2014 (UTC)

[Deleted]

I believe that the logic of this argument as a rebuttal to my own is of the same ilk as saying just because a theorem about the angles of a triangle doesn't involve pentagrams, doesn't mean that pentagrams are unimportant to all theorems about triangles. Now that is a true statement, but it doesn't dispute the statement that the theorem in question has no need of pentagrams. It does, however, leave open the possibility that some theorems about triangles employ pentagrams.

With this context in mind, it is your responsibility to show that some aspects of feedback in the negative feedback amplifier cannot be demonstrated using this figure, and the reality of the negative feedback amplifier transcends this figure. (Dicklyon also supports this view, also without sources to date.) If you can do that, it then remains to flesh out whatever these newly discovered sources have to offer about feedback that is missing from that based upon the traditional argument. Until you succeed, you are in the wilderness of personal assertions and beliefs that, so far as is known here, have no basis in published work.

I add that, whatever new may be discovered about feedback in the negative feedback amplifier during your researches, it remains the case that the traditional argument succeeds in demonstrating feedback provides insensitivity without any need for these newly discovered features, whatever the nature of the amazing new features you may find for it.

Do you agree? Brews ohare (talk) 15:29, 24 September 2014 (UTC)

You seem to be repeatedly arguing that negative feedback amplifiers aren't feedback loops and don't use negative feedback.GliderMaven (talk) 15:43, 24 September 2014 (UTC)

"It is your responsibility": No, WP does not work like that. It works by consensus. Consensus is against you, has been against you again and again. Repeatedly ignoring it is simply disruptive, and was a long time ago. Just stop.--JohnBlackburne^words_deeds 16:26, 24 September 2014 (UTC)

GliderMaven: I have not argued any point of view other than that expressed by the traditional argument. I have suggested that if you and Trevithj wish to supplement that argument in some way, you should source it and not rely upon your own opinions. Brews ohare (talk) 17:20, 24 September 2014 (UTC)

Blackburne: Reporting what sources say is indeed a responsibility of WP editors, although you may not think so by looking at this talk page. Consensus among WP editors concerning their personal opinions about content is meaningless without the support of sources, unless that consensus is about how sourced material is to be organized and summarized; matters of presentation are entirely within editor discretion and subject to their consensus. This sensible use of consensus is not what is seen at the moment. Brews ohare (talk) 17:20, 24 September 2014 (UTC)

I have removed some of my comments, since I object to them being placed in a context other than the original one. Trevithj (talk) 19:14, 24 September 2014 (UTC)

Regards the rest of this section: I agree with the other editors that the burden of proof falls on Brews to show that the negative feedback amplifier is not a control system, when both the primary authors he has cited clearly treat it as though it is a control system. If the conclusion is true, this shouldn't be much of a burden. Trevithj (talk) 19:28, 24 September 2014 (UTC)

Tevithj: The diagram used in the traditional argument is not that of a control system. Should it devolve that you consider that it is the diagram of a control system, that implies that some control systems do not use a 'gap', a set point, and neither do they attempt to regulate by minimizing a 'gap'. On the other hand, there are control systems that do all those things, and their analysis is based upon a different block diagram that incorporates those features.

We are now back at square one, with the words "control system" expanded to include the negative feedback amplifier, but with this new member of the set "control system" exhibiting insensitivity according to an analysis without employing a 'gap', a set point, or regulation by minimizing an error. So where does that leave you? Nowhere. The traditional argument stands and does not use any of these features of feedback you wish to invoke. Brews ohare (talk) 20:15, 24 September 2014 (UTC)

No, we're back further than that. We're already reverting most of your edits, but I think we're pretty much at the stage where we'll have to go through the entire history of the feedback articles and remove all of your edits, one by one, or at least look at them. We just can't trust somebody in this much denial about simple, basic facts about the topic.GliderMaven (talk) 20:50, 24 September 2014 (UTC)

What do you regard as evidence that you are wrong? We are back to square one because of the basic form of your arguments. The diagram referred to is clearly that of a control system. Trevithj (talk) 21:07, 24 September 2014 (UTC)

Your link to the table of contents of Battacharaya's contribution to CONTROL SYSTEMS, ROBOTICS, AND AUTOMATION is insufficiently detailed to establish anything. If you look at his Figure 2: A feedback control system, you will notice 'reference inputs' that provide set points, 'disturbances' that represent upsets from status quo, and a controller that compares the monitored plant variables with the reference inputs and feeds back a regulatory signal to the plant. On the other hand, his Figure 4: A feedback system depicts a feedback loop, which is only a simplified part of a control per se, the same loop he uses in the traditional argument. There is nothing there to suggest he thinks this represents a complete control system.

None of this matters of course, Whether you call the negative feedback amplifier a 'control system' or not, the traditional argument is based upon this figure and that analysis does not depend in any way upon a set point, a measured 'essential variable', or regulation by minimizing a 'gap'. Don't you agree with that much? The analysis of the figure makes no use of the elements found in Figure 2 and missing in Figure 4.

I fail to see any 'circular reasoning' here, or in the presentations of Kal or Bhattacharya, or in the summary of their argument. If there is circularity, please identify it rather than refer to what is, for me, a chimera. Brews ohare (talk) 23:36, 24 September 2014 (UTC)

The traditional argument based upon the block diagram of the lead remains an accurate analysis of the mathematical implications of this figure, which makes no use of a 'performance gap' or regulation by reduction of such a 'gap'. So far editors on this page refuse to acknowledge the connection between the diagram and the math associated with it described in the traditional argument, preferring to drag up red herrings to avoid direct discussion of these sources.

By the 'traditional argument' linked here, in case there is any confusion, is meant simply the unadorned summary of the Kal - Bhattacharya analysis, see Kal and Bhattacharya. The original sources are linked, so anyone dissatisfied with this summary can read the original arguments for themselves. Brews ohare (talk) 12:45, 25 September 2014 (UTC)

Discussion between Dicklyon and brews_ohare

I don't think anyone has expressed any doubt about the advantages of feedback as expressed by those two refs. Why do you keep bringing them up as if someone was disagreeing with them? Dicklyon (talk h) 04:06, 26 September 2014 (UTC)

A regulator R adjusts the input to a system T so the monitored essential variables E are held to set-point values S that result in the desired system output despite disturbances D.

Dick: I take it that you would agree that this summary is an accurate description of the textbook approach to the analysis of amplifier desensitivity. If so, you and I are pretty much on the same page about the textbook approach, but you seem to entertain the idea that any real-world amplifier, and not some idealization like that of the figure, enjoys aspects of feedback not described by this analysis, that are in fact more significant than the factors involved in this insensitivity analysis. GliderMaven and also Trevithj go even further to suggest (but do not attempt to substantiate) that this summary is a defective presentation on my part that doesn't capture the work of Kal and Bhattacharya at all, and according to Trevithj is in essence a ploy on my part to gain acceptance of my own weird ideas. Where do you actually stand, Dick? Brews ohare (talk) 14:45, 26 September 2014 (UTC)

For example, we have this remark by GliderMaven that this summary is about a stability point. Further, both editors hold the view 1 2 that the fact that this summary doesn't need any ideas like a 'performance gap', a set point, or regulation to minimize a 'gap' doesn't mean that these ideas are not pertinent to this analysis, even though not employed by it. These two also seem to think that the standard diagram does not uniquely determine the Kal-Battacharya analysis based upon it, but that the Kal-Battacharya analysis is related to some emasculated view of this diagram that ignores its 'deeper' meaning that is buried in a realistic understanding of what these blocks actually contain and stand for, a point of view they have yet to substantiate. Brews ohare (talk) 15:02, 26 September 2014 (UTC)

In essence, they believe that a more refined understanding of the feedback amplifier diagram would demonstrate its equivalence to some version of the diagram for an error-controlled regulator, perhaps the one shown with this comment. For example, Trevithj claims, his second point, that he can see no essential difference between them. Brews ohare (talk) 15:10, 26 September 2014 (UTC)

Among the differences between these diagrams that makes it impossible to reconcile them is the fact that the error-controlled regulator deals with external disturbances D, while the negative feedback analysis deals only with internal disturbances generated within the open-loop amplifier, that the error-controlled regulator uses an externally supplied set point, not found in the negative feedback amplifier, and that the error-controlled regulator employs a measurement of some internal variable E and a comparator that determines a 'performance gap' or error that is used to calculate the feedback response intended to drive the error to zero, none of which elements appear in the negative feedback amplifier. Brews ohare (talk) 16:49, 26 September 2014 (UTC)

To state my own position about these matters in terms of these diagrams, I'd agree that the desensitivity analysis is not everything that is going on, that some more complicated diagram would be more accurate and could account for other kinds of disturbances. But what the idealized Kal-Battacharya analysis does show is that immunity to internal disturbances can be achieved using feedback without the apparatus of error-controlled regulation, by simpler means. That means the definition of negative feedback used in this article should be extended to go beyond any limitation to error-controlled regulation, because the negative feedback amplifier demonstrates that alternatives are available. Brews ohare (talk) 17:42, 26 September 2014 (UTC)

My agreement with the sources, and maybe even with your analysis of the "primary advantage of negative feedback", should not be taken as an indication that we "are on the same page" about this. Go back a few pages in those sources and you'll find out what feedback is; advantages, even primary ones, are secondary to the fact that negative feedback reduces gain, or output fluctuation per input fluctuation. Dicklyon (talk) 18:05, 26 September 2014 (UTC)

Dick: I assume your reference to gain reduction is the reduction from A_OL to 1/β. Of course, that means that any input variation δI produces the output variation δI /β. But of course also the input signal I also produces an output reduced to I /β, so the noise is the same percentage as before. The same result is achieved by simply dropping the feedback and using an open-loop amplifier with a reduced gain to start with. Maybe you can clarify? Brews ohare (talk) 18:46, 26 September 2014 (UTC)

Kal, p. 194 makes the same point. Brews ohare (talk) 18:58, 26 September 2014 (UTC)

BTW, this is not "my analysis". It is the desensitivity analysis of the negative feediback amplifier found in every electronics text of the last 40 years. Here are some of them: Kandaswamy, Chen Choudhury. The most famous of them, Sedra & Smith, § 8.2.1 Gain Desensitivity, p.795 and Gray & Meyer, §8.2 Gain Sensitivity are not on-line accessible. There seems to be a bootleg copy of S&S here, and possibly of G&M here. Brews ohare (talk) 20:53, 26 September 2014 (UTC) Brews ohare (talk) 19:08, 26 September 2014 (UTC)

That's right. Dicklyon (talk) 23:50, 26 September 2014 (UTC)

Cute respose, Dick, but unhelpful. So now tell me why a lower gain is an advantage for input noise when it doesn't improve the signal-to-noise ratio? Please. Brews ohare (talk) 00:47, 27 September 2014 (UTC)

In response to the question in your edit summary, yes, it is my considered opinion that if would withdraw we could work this out. But if you keep trying to put words into my mouth, I'm not going to engage. With respect to your query re advantages and SNR, I didn't bring those up; why did you? It just shows your inability to listen to what is actually being said. Dicklyon (talk) 01:12, 27 September 2014 (UTC)

Dick: You said:

"advantages, even primary ones, are secondary to the fact that negative feedback reduces gain, or output fluctuation per input fluctuation"

Now I interpreted this as saying the output fluctuation is reduced if the gain is reduced compared to what it would be if the gain weren't reduced. That seems like the only thing you could mean. However, because the signal is also decreased the S/N ratio is not improved. My observation, as you say, not yours. So the query is, what is the advantage of reducing the output fluctuation if the output signal is reduced proportionally? I see no inability to listen on my part. I simply saw that this conclusion of mine would render your comment meaningless, and so I asked for an interpretation that would provide some sense. Brews ohare (talk) 01:41, 27 September 2014 (UTC)

Perhaps you were not referring to input noise, but to internal noise? That is what the insensitivity analysis is about, and reduction of internal noise according to the standard analysis has to do with βA >> 1. If this is your meaning, the standard analysis covers the situation and you are not identifying new factors, but those already handled in the standard analysis. Brews ohare (talk) 01:45, 27 September 2014 (UTC)

I didn't bring up noise. I thought the point of my comment was clear, not meaningless: the primary effect of negative feedback is to reduce the gain. That's what I meant when I said "advantages, even primary ones, are secondary to the fact that negative feedback reduces gain". I clarified gain as "output fluctuation per input fluctuation", which as you noted doesn't depend on any distinction of signal from noise. I complained that in trying to say what feedback is, you jumped over that to advantages, focusing on pages in sources that are several pages past where feedback and its primary effects are explained. That's what I meant by "advantages, even primary ones, are secondary ...". I don't know a way to express myself more clearly, or get my content to break through your filter that interprets everything through your idiosyncratic lens. And that's why I usually don't try. It's a waste of time. Dicklyon (talk) 02:22, 27 September 2014 (UTC)

OK, so I guess you are saying noise (and fluctuations) are not the point; the point is that a lower gain is desirable in itself. One might ask what feedback has to do with that, as low gain is easy to find by many methods. So, I'll surmise further. One situation where high gain is a problem is when the output signal, due to high gain, is so large that it drives the amplifier into saturation. Now, Dick, you haven't brought this up either. So as part of this guessing game about what exactly is on your mind, is this it? And if it isn't amplifier saturation, and it isn't noise, perhaps you could actually come right out and say why low gain is an advantage and why achieving low gain by using feedback is the method of choice? Brews ohare (talk) 03:14, 27 September 2014 (UTC)

Listen to yourself! Putting words in my mouth again. I didn't express any opinion about what's desirable, or why feedback might be chosen. Nothing. Nada. Dicklyon (talk) 03:21, 27 September 2014 (UTC)

Well, Dick you say you have nothing to say and that is what I have got from these attempts to draw out what you want to contribute to this discussion. It's pretty clear that I want to understand your views, and you don't really want to explain them. You blame my lack of listening, but that seems to be an excuse to avoid being pinned down to anything specific about the role of feedback in the negative feedback amplifier. Brews ohare (talk) 03:36, 27 September 2014 (UTC)

I'm sorry you refuse to hear what I have to say, which is that we need to start with what negative feedback is, before we get to discussing its potential advantages. Your confusion on that point seems to be driving your walls of text on this page. I do not disagree with you or with the sources about what the advantages typically are (in amplifiers at least). Dicklyon (talk) 03:41, 27 September 2014 (UTC)

I thought the subject was the idea of GliderMaven and Trevithj that the negative feedback amplifier is not fundamentally different from an error-controlled regulator. In my opinion, the implementation of negative feedback in the circuit for the negative feedback amplifier and the analysis of that circuit is completely different from its implementation in the circuit for the error-controlled regulator and the analysis of that circuit. One is not a version, or simplification, or whatever of the other. The circuits for these two types of circuit are known, and it really is an issue of how the circuits and their analyses relate to one another. Have you anything to say about this subject? Brews ohare (talk) 04:03, 27 September 2014 (UTC)

The underlying problem is that if the two circuits are fundamentally the same, then any definition of negative feedback that fits the error-controlled regulator applies to both. If they are different, the definition has to be broader in order to include them both. Brews ohare (talk) 04:07, 27 September 2014 (UTC)

I think I don't really know what their sticking points are because whenever I get something started with them you jump in and squash it. I do agree that they are "fundamentally" the same, but that doesn't mean it's easy to find a definition that applies equally well to both. Dicklyon (talk) 04:15, 27 September 2014 (UTC)

One doesn't have to 'opine' that the two circuits are 'fundamentally the same'. One has to compare the analyses for the two only to find they use different concepts. Or one can look at the two circuits and see they involve different inputs and different components and incompatible topologies. If instead one relies upon intuition or vague verbalizations, one can go round and round as has been happening. Brews ohare (talk) 04:59, 27 September 2014 (UTC)

Typically both amplifiers and control systems are analyzed as linear systems (at least approximately), with transfer function equal to the forward gain divided by one minus the loop gain. Slightly different arrangements of components around the loop, or labels on components, or what path you take to be "forward" don't make a fundamental difference. This is the sense in which (linear) feedback systems are all "fundamentally the same". I'm not denying that the differences in viewpoints are also important, which is why it's not so easy to find a definition that applies well to both. In particular I agree that a definition involving a "gap" or a "reference" or "target" is probably too control specific, even though it is easy enough to augment an amplifier diagram to treat input as target (appropriately scaled), or to add a zero target and treat the input as a disturbance. It's not a matter of fundamentals, but of finding a best way to treat the multiple viewpoints. For nonlinear systems, it's more complicated. Log amplifiers (op amps with diode in feedback, for example) have the feedback path more nonlinear than the forward path, unlike your "standard" amplifier analysis; nonlinear control systems do all kinds of things. In many cases, however, they still get analyzed as linearized about an operating point, so that their dynamics can be described conventionally at least for small deviations. Maybe we need to start by describing what negative feedback is just in respect to a loop, with no inputs, outputs, targets, gaps, etc., and then explain separately how that applies to the two main cases. But we've also had some simple definitions that might be OK to cover both, I think, except that we didn't far enough to see what others thought because you already shot them down with a wall of text before anyone had a chance. Dicklyon (talk) 16:13, 27 September 2014 (UTC)

Happy to see signs of discussion from you Dick. The simple definitions are OK, and can be specialized to illustrate application to error control and to the negative feedback amplifier. Already tried in an earlier attempt proposing the 'opposition-to-change' formulation widely used in the literature and examples using error control and the negative feedback amplifier. Maybe GliderMaven and Trevithj are ready to consider this now? I'll watch developments. Brews ohare (talk) 19:08, 27 September 2014 (UTC)

Or you could go back and support one proposed by someone else. Dicklyon (talk) 00:35, 28 September 2014 (UTC)

Remember this?. Brews ohare (talk) 03:03, 28 September 2014 (UTC)

New examples section

I've added a new section at the top with some brief descriptions of various examples of negative feedback in practice. I've call this new section 'Examples', and re-named the one which was previously called that. I feel this will give the reader a quick general idea of the concept before moving on to the more detailed exposition. DaveApter (talk) 14:52, 30 September 2014 (UTC)

Those are nice concise understandable examples, spanning considerable ground. Thanks. Dicklyon (talk) 17:45, 30 September 2014 (UTC)

I like the text, and the examples you've chosen, but I have some reservations about the structure. You've created a section called 'examples' but there's already a section called 'Some specific implementations' which is an examples section in all but name.GliderMaven (talk) 19:32, 30 September 2014 (UTC)

These examples are good - they avoid details of implementation, and simply talk about the effect. Nice. While I have some reservations, they aren't about the specific examples. My concern is that the focus of the examples is on the term "negative feedback", rather than the concept.

Thinking about the examples with the overall concept of negative feedback in mind, they do seem to have a strong emphasis on electrical engineering. Understandable given the origin of the term, but the concept is of course much older: James_Clerk_Maxwell's work on governors (1868); Adam Smith's "invisible hand" (1776); Cornelis_Drebbel's thermostat (1600). We could go right back to the Golden_Rule (1700 BCE)!

I believe there is a basic confusion in this subject between term and concept. It may make sense to treat this page as term-centric, and focus on electrical engineering. But if not, the examples should perhaps be given a historical sequence, and have more non-electronic examples. Trevithj (talk) 19:56, 30 September 2014 (UTC)

Never, never, never base an encyclopedia article on terms.GliderMaven (talk) 21:10, 30 September 2014 (UTC)

I did think I was illustrating the concept by means of these, broadly drawn, examples; that was the intention at any rate. The objective is to get the reader rapidly to a general intuitive understanding by these examples in various different fields, so that the rest of the article becomes accessible to them. No problem about adding more, or changing the order. I put the electronic ones first because that's the area where the wording was first commonly used (or so I think), or maybe it's just because that's the area I'm personally most acquainted with! DaveApter (talk) 21:44, 30 September 2014 (UTC)

Sure, electronics was my introduction to the concept too. The wording/term "negative feedback" was popularized by Black, according to several sources. (There doesn't seem any usage prior to 1920.) I suggest the historical sequence, simply because it is (hopefully) a less controversial framework. And as per GliderMaven's hint, it avoids putting focus on the term.

Mind you, we don't want to clutter the section with lots of examples either: perhaps 'classical' examples by key authors? Trevithj (talk) 22:39, 30 September 2014 (UTC)

Okay, I have added a few mechanical examples, and reordered in (rough) historical sequence. I've tried to keep the wording similar to the existing examples. Trevithj (talk) 01:09, 1 October 2014 (UTC)

Perhaps I wasn't totally clear. Right now the article actually has two different examples sections. IMO this is a fairly horrible idea. The reason it probably seems to work is because the history section is so bad. If the history section was better, the examples would be the historical ones and the reader would be more naturally drawn into the topic. At least, that's what I think.GliderMaven (talk) 01:51, 1 October 2014 (UTC)

Okay, historical examples are kind of where I was headed with these. History does give a natural progression to the development of the concept, so should we look at merging examples with history?

BTW, GliderMaven - not sure if you reverted the right version. I have undone change because there were a group of other edits involved. I am not sold on the content though, so please critique. Trevithj (talk) 06:04, 1 October 2014 (UTC)

OK, I think the article is much improved - now someone who is new to the subject can get a pretty good idea of what it's about by the time they've read the lead and the first section, and they can go further in to build more detail. I'm somewhat with GliderMaven's reservations about the fact that we now have two "examples" sections. The old one (now re-named "Some specific implementations" - and I'm open to other suggestions for the title) was too detailed to serve to give a quick general understanding, but it has plenty of useful information. Any suggestions for a more comfortable structure? DaveApter (talk) 17:42, 1 October 2014 (UTC)

The Reinforcement page takes an interesting approach to dealing with confusion of terms. Perhaps we could follow suit: rename Examples to Brief History, and move the History section to a sub-heading History of the term, where origin/mis-use can be directly discussed. Trevithj (talk) 22:55, 2 October 2014 (UTC)

It would be easy to recast the Examples section as Historical examples by adding a date for the introduction of each example. History could be renamed Background. Brews ohare (talk) 04:30, 3 October 2014 (UTC)

Removal of unsubstantiated statements

The following paragraph:

"Harold Stephen Black detailed the use of negative feedback in electronic amplifiers in 1934, where he defined negative feedback as a type of coupling that reduced the gain of the amplifier, in the process greatly increasing its stability and bandwidth.[9][10] Nyquist and Bode built on Black’s work to develop a theory of amplifier stability, but chose to define "negative" as applying to the polarity of the loop (rather than the effect on the gain), which gave rise to some confusion over basic definitions."

asserts that the attention given to 'polarity of the loop' by Nyquist and Bode, led to confusion over 'basic definitions' of the term negative feedback. This claim is unsupported and historically incorrect. The work of Nyquist (1932) and Bode (1940) led to the ideas of the Nyquist stability criterion and of gain margin that occurred much later than Black's idea of the negative feedback amplifier (1927). An extensive historical account is provided by Bennett, CHapter 3, pp. 70 ff. There is no evidence that the different emphasis, Black upon gain and Bode/Nyquist on polarity, caused any confusion. The Mindell source cited in support of this statement juxtaposes a sentence about Nyquist/Bode with a conclusion about 'confusion', but does not make the historically impossible claim of the WP sentence that this 'confusion' was occasioned by the differences between the Nyquist/Bode analysis and that of Black. I replaced the Mindell source with Bennettt, who supplies a more detailed history without Mindell's claims of confusion.

Accordingly, I have removed this last portion of the last sentence. Brews ohare (talk) 16:38, 5 October 2014 (UTC)

The lower sections involving Ashby and Skinner now don't follow on from the previous section.

Going back to an earlier point that seems to have been glossed over - when Black says "negative feed-back reduces [the gain]", is he defining negative feedback, or is he describing its effect? Trevithj (talk) 18:18, 5 October 2014 (UTC)

I suppose the interest in this question is historical: what does the record indicate Black thought was the definition? Evidence on this point might be found in his writings and patents. The possible significance of this point to this WP article has not been made clear. Brews ohare (talk) 01:00, 6 October 2014 (UTC)

This seems like it belongs in an earlier section; why the loss of context? Dicklyon (talk) 03:27, 6 October 2014 (UTC)

Second paragraph of lede

The second paragraph of the lede presently reads:

Whereas positive feedback tends to lead to instability via exponential growth or oscillation, negative feedback generally promotes stability. Negative feedback tends to promote a settling to equilibrium, and reduces the effects of perturbations. Negative feedback loops in which just the right amount of correction is applied in the most timely manner can be very stable, accurate, and responsive.

There are some problems with this paragraph. The first sentence should be rewritten more accurately as:

Whereas positive feedback tends to lead to instability via exponential growth or oscillation, negative feedback can promote stability.

The words 'generally promotes' suggests that negative feedback as a general statement promotes stability. Of course, that is not the case, as negative feedback results in greater stability only under well-known circumstances.

The second sentence:

Negative feedback tends to promote a settling to equilibrium, and reduces the effects of perturbations.

makes sense for things like thermostatic control of house temperature (assuming an extended idea of 'equilibrium' to include 'steady-state'), but is inapplicable to the negative feedback amplifier (illustrated in the lede) where issues of "settling to equilibrium" play no role whatsoever. This sentence should be replaced by:

Negative feedback tends to reduce the effects of disturbances, in some cases external disturbances, and in other cases, internal.

Brews ohare (talk) 14:07, 3 October 2014 (UTC)

It is not unusual to look at amplifiers in terms of their step response. Negative feedback helps the output settle rapidly and smoothly to a new equilibrium after a step. Dicklyon (talk) 02:10, 4 October 2014 (UTC)

Oh baloney. It "is not unusual" to look at amplifiers in terms of lots of things. Brews ohare (talk) 02:46, 4 October 2014 (UTC)

The baloney was your statement that the second sentence "is inapplicable to the negative feedback amplifier (illustrated in the lede) where issues of 'settling to equilibrium' play no role whatsoever". I'm just pointing out that settling to equilibrium does play a role, sometimes. Surely you recall characterizing amplifiers by their step responses? Like here? Dicklyon (talk) 03:09, 4 October 2014 (UTC)

Dick, you are right, of course, that feedback does control some aspects of the step response of the negative feedback amplifier, although the settling time or damping is related to the open-loop amplifier time constants. I just doubt that will come to reader's mind when they read "Negative feedback tends to promote a settling to equilibrium". They are more likely to think of homeostasis, and it would be desirable for the reader to be nudged toward a broader view rather than reinforce a widely prevalent myopia. Brews ohare (talk) 15:35, 4 October 2014 (UTC)

Brews, you should realize that negative feedback will result in a corner frequency much higher than the one of the open-loop high-gain amplifier, no? That is, it promotes fast settling to a new equilibrium after an input step. It's hard to tell from your analysis in Step response, as that analysis assumes so much feedback that the second pole is what matters, rather than looking first at the simpler system with less feedback such that the forward amplifier's dominant pole is what matters; the feedback makes a faster closed-loop pole, and more feedback makes it even faster, up to the point that the second pole makes it start to ring, which is not where you want to be because that's where the net feedback is phase shifted enough to be positive it high frequencies; stop short of there, and negative feedback speeds up settling. However you look at, negative feedback usually promotes stability and fast settling, as in homeostasis and also in amplifiers. I see it as the opposite a positive feedback pushing toward ringing and singing and slow settling. Dicklyon (talk) 22:30, 5 October 2014 (UTC)

If you want to support your ideas about settling time, the place for that is Talk:Step response. I don't agree with you, and the analysis there doesn't either. However, here all this is digression and the point is: what is the likely inference of the general reader? I seriously doubt step response is on their short list.

The main problem throughout the various discussions on this Talk page is the unwavering belief that the negative feedback amplifier implements some variant of error-controlled regulation. This forced-fit is imbedded in the minds assembled here, and underlies your support for references to 'settling to equilibrium' as this choice of words satisfies your love for the simplicity of one universal approach. Brews ohare (talk) 02:37, 6 October 2014 (UTC)

I have updated Step_response#Step_response_of_feedback_amplifiers to include the simple case; please verify that I got it right. I'm not sure what you mean by "If you want to support your ideas about settling time"; I'm not interested in supporting any particular ideas here; I was just explaining why your claim is wrong, when you said that the statement about promoting settling is "inapplicable to the negative feedback amplifier (illustrated in the lede) where issues of 'settling to equilibrium' play no role whatsoever." Just trying to clarify the role so that you can get off this and do something else, perhaps more useful. Dicklyon (talk) 03:22, 6 October 2014 (UTC)

And just for the record, as I have said before, I am not at all in favor of an alleged "unwavering belief that the negative feedback amplifier implements some variant of error-controlled regulation". One does not need to believe that to see that negative feedback promotes stability and quick settling. Dicklyon (talk) 03:25, 6 October 2014 (UTC)

Dick: I've agreed with you that negative feedback affects step response; my reservation is simply that the wording involving equilibrium isn't likely to start the reader thinking about step response. Instead, they are going to think about homeostasis or the like. IMO that is too narrow a view of negative feedback. Brews ohare (talk) 04:45, 6 October 2014 (UTC)

I agree with your single-pole analysis. However, a reservation is that no real amplifier is single pole. If there are two poles then, for a normal amplifier design, the shorter time constant of the open-loop amplifier will determine the damping, and this will be in fact faster than τ/(1+βA) because stability and step response considerations force such a requirement. Brews ohare (talk) 04:58, 6 October 2014 (UTC)

Inaccurate version of Black's definition of negative feedback

In the History subsection the sentence occurs:

" Harold Stephen Black came up with the idea of using negative feedback in electronic amplifiers in 1927, submitted a patent application in 1928,[9] and detailed its use in his paper of 1934, where he defined negative feedback as a type of coupling that reduced the gain of the amplifier, in the process greatly increasing its stability and bandwidth.[10][11] "

Black's BSTJ paper is the primary source for the assertion that Black's definition of negative feedback was a 'form of coupling that reduced the gain of the amplifier'. In actual fact, Black (p. 5) in the section titled Change of Gain Due to Feedback following his derivation of the gain as

$G_{CF}=20log_{10}\left|{\frac {1}{1-\mu \beta }}\right|$

says:

"1/(1-μβ) will be used as a quantitative measure of the effect of feedback and the feedback referred to as positive feedback or negative feedback according as the absolute value of 1/(1-μβ) is greater or less than unity."

Now, of course, one implication of Black's definition is that negative feedback reduces the gain, but his definition is more general than this single implication, and implies many other matters, among them an increase in bandwidth and certain stability implications.

In view of the concern expressed on this page that Black's definition did not match Nyquist and Bode's interest in the sign of μβ:

"Nyquist and Bode built on Black’s work to develop a theory of amplifier stability, but chose to define "negative" as applying to the polarity of the loop (rather than the effect on the gain), which gave rise to some confusion over basic definitions" (See this).

the accurate statement of Black's definition assumes importance, to some WP editors at least. Brews ohare (talk) 15:11, 7 October 2014 (UTC)

It should be noted that Black does not refer to 'cause and effect' nor to the concept of error-controlled regulation where feedback reduces a measured performance discrepancy. Brews ohare (talk) 17:11, 7 October 2014 (UTC)

Where does this leave us?

If we can't talk about cause and effect, then how can we generalize Nyquist's "loop polarity" definition to examples that don't involve an electronic signal?

If we can't talk about measured performance discrepancy, then how can we generalize Black's "effect of feedback" to examples that don't involve reducing some "absolute" value?

Trevithj (talk) 22:19, 7 October 2014 (UTC)

Exactly: Black's approach is different, and does not use the ideas of error-controlled regulation, such as 'performance discrepancy'. It also does not involve 'cause and effect'. None of Black's works use these ideas, which at a minimum shows they aren't necessary to Black's work. Brews ohare (talk) 23:30, 7 October 2014 (UTC)

The suggested generalization that includes both approaches is 'opposition to change' discussed already . In the case of the amplifier opposition to change is reduction of output swing that reduces gain. In the homeostatic case opposition is to an increase in performance gap leading to a reduction in the gap. Brews ohare (talk) 23:34, 7 October 2014 (UTC)

More fundamentally, Black's approach lives with disturbances and works around them to render them uninfluential, while the other approache is to fight the disturbance and directly oppose it, thereby reducing its influence. It's the difference between avoiding flat tires by driving on roads free of debris and making tires tougher. Brews ohare (talk) 00:13, 8 October 2014 (UTC)

No, it's not. Those analogies make no sense at all. Dicklyon (talk) 03:59, 8 October 2014 (UTC)

Well. Dick, don't try to explain yourself. The analogy, whether it succeeds with you or not, has this going for it: it points out that Black's feedback circuit makes zero attempt to counteract variations internal to the open-loop amplifier (walks around the puddle), but makes the closed loop amplifier gain the same no matter what the open-loop amplifier does. In contrast, the error-controlled approach determines how far the open-loop amplifier has strayed and tries to correct this discrepancy by returning it to its 'normal' state (drains the puddle and walks straight through). Brews ohare (talk) 05:05, 8 October 2014 (UTC)

Your claim, or interpretation, that "Black's feedback circuit makes zero attempt to counteract variations internal to the open-loop amplifier" is nonsense. Negative feedback DOES counteract any such variations, by feeding some of the output back to the input with a negative sign. See Negative feedback. Dicklyon (talk) 06:09, 8 October 2014 (UTC)

Dick, it's not nonsense. Perhaps you have not understood my meaning? It's what Black's gain formula says, as pointed out repeatedly in discussion of Kal's gain desensitivity analysis. The open-loop gain can change by a relative amount ΔA/A and the open loop gain change is lowered in the closed-loop gain to (ΔA/ A) / (1+βA), by virtue of the circuit feedback. The change ΔA is not affected in any way; it is not counteracted or reduced. But it's influence on the closed-loop gain is small.

Error-controlled regulation, in contrast, confronts the variation ΔA head on and tries to reduce it to zero. Brews ohare (talk) 15:08, 8 October 2014 (UTC)

I understand that Black's gain formula only talks about the gain. But the same formula can be applied to show the the gain to a disturbance anywhere inside the forward path is reduced by the same factor. The fact that that fact is not explicit in one formula is not a reason to assert the nonsense that ""Black's feedback circuit makes zero attempt to counteract variations internal to the open-loop amplifier". Dicklyon (talk) 15:13, 8 October 2014 (UTC)

Apparently your goal is to entertain yourself by jeering rather than trying to understand what is said. It is very very clear that the internal workings of the open-loop amplifier play no role in the negative feedback amplifier. To attempt complete clarity, the focus is not upon the reduction of ΔA, not upon dealing with the fundamental origins of ΔA and fixing them. Historically that is the key point motivating Black who observed the frustrating failures of the technology of the day to succeed in countering the gain fluctuations of high-gain amplifiers. Black's solution was instead of fighting these fluctuations, to render them unimportant. The question of other noise sources inside the feedback loop (a topic not under discussion here) is treated exactly like those disturbances introduced by the open-loop amplifier, and in Kal's analysis, the closed-loop amplifier is desensitized in exactly the same way, by the desensitivity factor (1+βA). Brews ohare (talk) 15:35, 8 October 2014 (UTC)

It is unclear why this is relevant. The internal workings of the steam engine play no role in the centrifugal governor either. Nor does the workings of the furnace play a role in the thermostat. What exactly is the point of making the above distinction? Trevithj (talk) 18:35, 8 October 2014 (UTC)

I don't quite understand Brews either, as he points out. He seems to be arguing that since Black was more concerned about keeping the gain constant, it is no longer fair to note that the closed-loop ampifier "counteracts variations internal to the open-loop amplifier" or "reduces fluctuations in the output". This seems to be motivated by him wanting to prove that these concepts that apply to control systems do not also apply to negative feedback amplifiers. But they do. So he's wrong, and going off on an odd tangent for an odd reason, I think. Dicklyon (talk) 19:31, 8 October 2014 (UTC)

I guess this all really doesn't matter. The sections on error-controlled regulation and on the negative feedback amplifier are pretty clear and nobody (more accurately, not everybody) who reads them will confuse these different applications of feedback as being somehow the same. The leading sentence is not wrong. The second paragraph is a bit screwy, but WP has worse problems to deal with.

I do regret being unable to get through to you two, but unreasoned convictions are hard to overcome, and even appeal to the objective of reporting what sources say carries no weight.. Brews ohare (talk) 20:47, 8 October 2014 (UTC)

I do agree with his last sentence, in a pot-to-kettle sort of way. Trevithj (talk) 01:44, 9 October 2014 (UTC)

Exactly. From a person with a long history of idiosyncratic interpretations of sources. Dicklyon (talk) 02:26, 9 October 2014 (UTC)

Thanks for including me out of this love fest. It would help WP if talk pages weren't used for personal innuendo and instead focussed on presentation of sources. I have taken that route. Brews ohare (talk) 02:46, 9 October 2014 (UTC)

In reply to Trevith's remark that 'internal workings' play no role in error-controlled regulation, it may be noted that such regulation is predicated upon assessing the internal state of the system by monitoring selected 'essential variables', for example, temperature, or angular velocity. In the negative feedback amplifier no essential variable is selected to monitor the status of the open-loop amplifier. Perhaps Trevith regards the gain A of this amplifier as such a variable, but in the negative feedback amplifier the open-loop gain is not monitored, nor is it compared with a desired value or set point, nor is any attempt made to adjust its value in any way. Rather, the closed-loop gain is set at 1/β independent of A, so long as A is large. There is no candidate for an essential variable other than A, because this variable is the only role for the open-loop amplifier in the analysis.

It is doubtful that Trevith or Dick are unaware of these points, and their misunderstanding and their distorted summary of them is due, not to the error of these arguments, but to their impatience with them. This hostility toward obvious facts is born largely of their personal prejudice that this argument cannot possibly be correct if it concludes error-controlled regulation actually differs from what happens in the negative feedback amplifier. Brews ohare (talk) 15:36, 9 October 2014 (UTC)

Because directly confronting the obvious objections above to their prejudices is uncomfortable, Trevith and Dick resort to repackaging these objections in wrong or very muddy versions that they then can mock. This approach to protection of an idée fixe is common. Brews ohare (talk) 15:45, 9 October 2014 (UTC)

It is certainly common to this idea.

For the record, the "muddy" version is that a negative feedback amplifier monitors the output amplitude, compares it to the input amplitude, and processes the difference.[1] It therefore is a control system. Trevithj (talk) 23:30, 9 October 2014 (UTC)

The actual statement of the linked source is

""A fraction of φ_o [the output signal] is fed back to the input and added with externally applied input signal φ_S"

There is no mention of a 'monitor', of 'comparing', or of a 'control system'. I believe the main connection between amplifiers and control systems is the use of op amps in control system comparators, which is not a role for the negative feedback amplifier.

Apparently, for you, this linked statement means the negative feedback amplifier is a 'control system'. I guess you think every control system is an error-controlled regulator, so QED? Else, if control systems come in various flavors, e.g. op amps, regulators, servos, whatever, then this linked statement with your extrapolation to 'control systems' doesn't support this contention of yours that the negative feedback amplifier works the same way as an error-controlled regulator. Both fire hoses and fire extinguishers are fire equipment, but they don't work the same way. Or, perhaps you would like to restate your contention about the similarities? Brews ohare (talk) 00:17, 10 October 2014 (UTC)

In the amplifier, the "essential variable" that is monitored and fed back is the output. To me, that doesn't make it a control system, but with minor contortions it can be cast as one. I'm not sure why Trevithj wants to do that, but it doesn't make what you've been saying any more sensible. Dicklyon (talk) 04:26, 10 October 2014 (UTC)

To be facetious, I don't think Trevith or you are trying to make more sense of these views. More seriously, if the output serves as the 'essential variable' here, how does it fit the definition of an essential variable? To what set point is it compared? What is the performance gap? How is this gap reduced? The lack of any answers to all these questions means 'output' cannot play this part. Brews ohare (talk) 04:43, 10 October 2014 (UTC)

Maybe a contender for 'essential variable' is the closed-loop gain? One might argue that the feedback loop sets β, which is the desired value of the closed-loop gain. If the output is not the input/β, the closed-loop gain is in error. Somehow one has to argue that the process of feeding back βO is some analog of regulation based upon the performance gap in the closed-loop gain. Could that be made plausible, at least? Brews ohare (talk) 04:59, 10 October 2014 (UTC)

Similarities between the negative feedback amplifier and error-controlled regulation

Taking the earlier questions in turn:

1. It depends on what definition of 'essential variable' you are referring to. V_out is a variable, and it is essential to the operation of an amplifier, since it is the obvious sign that the amplifier is working.
2. The set point is V_in.
3. The performance gap is (of course) the difference between actual and desired V_out.
4. The signal to the amplifier element is modified as required.

Maybe "control system" isn't exact terminology, but negative feedback involves some sort of comparison/difference. That is its salient point, IMO. Trevithj (talk) 05:08, 10 October 2014 (UTC)

These points reflect several misunderstandings.

1. An essential variable is a variable that has to be kept within assigned limits to achieve a particular goal.1

2. V_in cannot serve as a set point because the output is V_in/β, which is by design not at this set point.

3. There could be a performance gap of this kind, that is: error = V_out–V_in/β

4. The signal to the open-loop amplifier is modified as I–βO. However, it is uncertain just how this modification is achieved as a regulation of the error, although perhaps some argument can be devised to make the analogy.

A remaining issue is that this is all original research as no source has been found that uses this approach. Brews ohare (talk) 05:28, 10 October 2014 (UTC)

If β=1 then this would be error-regulation. Are you arguing that an amplifier can't be error-regulation because β<1? Trevithj (talk) 06:31, 10 October 2014 (UTC)

OK, given the strict definition of "essential variable", it would be best to say that doesn't apply in the case of the amplifier. When I said it was the output, I was speaking by analogy; it's the thing being monitored and fed back, not that it needs to be kept within certain bounds or compared to a reference. I also don't agree with Trevithj that negative feedback necessarily requires "some sort of comparison/difference", though it can often be cast that way, as with an op-amp which is a lot like a comparator. I prefer to just think of linear systems with adders combining input and feedback paths, where the notion of comparison or difference does not come up. Casting control systems into this form is more natural (to me) than going the other way. It's all in your POV, I think. As your assertion, Brews, that "Vin cannot serve as a set point", I think that's just wrong; control systems very often have indirect comparisons, so that the setpoint doesn't have to be specified in the physical domain of the output; there is usually an analog, or analogical, relationship between the setpoint signal and the actual monitored variable, is there not? If you made a system to compare by taking the difference Vout/beta - Vin, perhaps with another negative on Vin, and you amplified that error and used it to drive Vout to close the gap, you'd have a feedback amplifier, wouldn't you? Not that that's the only kind of feedback amplifier. But making up weird shit like trying to make the gain be the essential variable isn't making any useful point. Dicklyon (talk) 06:46, 10 October 2014 (UTC)

I'm afraid that Brews seems to have an obsession with the completely erroneous notion that there is some kind of fundamental distinction between the concept of negative feedback in the instance of a control system and the concept in the instance of, say, an audio amplifier. Let's take three examples: 1) a room thermostat; 2) the power steering system in a car; 3) an audio amplifier.

1. For the thermostat the system input is the desired temperature setting and is static (of course it may be adjusted from time to time), and the output is the room temperature.
2. For the steering system, the system input is the position of the steering wheel and it changes slowly, and the output is the direction of the car wheels.
3. For the amplifier, the system input is an audio signal (eg from a microphone) changing rapidly at up to 70 radians/sec, and the output is generally a larger (more "ample") replica of that waveform (eg to drive a loudspeaker).

In each case any tendency of the output to deviate from the desired value generates a corrective signal which is fed back to the input in such a way as to restore it to an accurate tracking of the system input (as processed by the designed transfer function). Is this clear, or do we need to work through these examples in more detail to make the point? DaveApter (talk) 09:51, 10 October 2014 (UTC)

@Trevithj: You ask: "Are you arguing that an amplifier can't be error-regulation because β<1?" Yes, that is true for the negative feedback amplifier of Black. Because β=1 (the unity gain buffer) is a special case where the output and the input are the same, so the input can serve as a set point. See Friedland, Figure 1.2. This circuit can enforce a gain of β=1, but won't work when β<1 because then the input is no longer a set point. Brews ohare (talk) 15:45, 10 October 2014 (UTC)

A voltage amplifier using an operational amplifier to set the voltage across R₁ to V_in.

@Dicklyon: Regarding the use of V_in as the set point of the negative feedback amplifier: it doesn't work because the output is V_in/β which is not V_in, and so V_in is not the output's set point. You go on to say:

"If you made a system to compare by taking the difference Vout/beta - Vin, perhaps with another negative on Vin, and you amplified that error and used it to drive Vout to close the gap, you'd have a feedback amplifier, wouldn't you? Not that that's the only kind of feedback amplifier. But making up weird shit like trying to make the gain be the essential variable isn't making any useful point."

Yes, the system you describe would be an error-controlled regulator. It might be the op-amp version in the figure. This op amp circuit takes the difference between its inputs 'V_in–βV_out' and drives this error toward zero. It is not Black's negative feedback amplifier, and although it also amplifies with gain 1/β, it doesn't work like Black's amplifier, because the negative feedback amplifier does not take the difference 'V_out/β–V_in' and does not use this error to drive the error toward zero. Obviously, the discussion is not about whether different ways to make amplifiers can be found. The discussion is about how the way Black's amplifier works differs from the way you describe. You also say:

"But making up weird shit like trying to make the gain be the essential variable isn't making any useful point."

My purpose, unlike yours, was not to change the subject. It was to suggest a way of looking at Black's amplifier that resembles an error-controlled regulator. This suggestion is almost the same as your own, although you don't seem to realize it. The weak link is pointed out, that of finding the explanation of how this error is monitored and used in Black's amplifier, as it isn't at all clear that this happens. Brews ohare (talk) 14:50, 10 October 2014 (UTC)

@DaveApter: It isn't helpful to label the sourced views I am attempting to bring to your attention as an obsession. And the idea is that the same negative feedback applies to both amplifiers and error-controlled regulators. But, it is implemented in different ways. The governing 'negative feedback' is stated in your first sentence of the lede although, because of your second paragraph, I doubt you see the ambiguity in that first sentence that allows it to cover both applications. Your first two examples, the thermostat and the steering control are both well understood as instances of error-controlled regulation. Why you bring them up is unclear. The third example, an audio amplifier, could be implemented in many ways, and that makes the discussion vague because here the subject is Black's amplifier, not audio amplifiers in general. Your new definition of 'negative feedback' is a system in which any "tendency of the output to deviate from the desired value generates a corrective signal which is fed back to the input in such a way as to restore it to an accurate tracking of the system input" This new definition is inferior to the existing one in the lede, as it doesn't apply to Black's amplifier, where there is not present any attempt at "accurate tracking of the system input". The goal instead is the creation of an enlarged image of the input where the degree of enlargement is held constant despite disturbances.

@All: One missing item in all three of your expositions here is any specification of a disturbance that has to be minimized, which is the point of the feedback. In Black's work, the disturbance whose influence he is reducing is any undesirable variation in the open-loop gain. That goal has not come up in your presentations. Brews ohare (talk) 15:09, 10 October 2014 (UTC)

A few points arising from this latest batch of exchanges:

1. I didn't explicitly mention resilience to "disturbances" because dealing with them is a natural by-product of the operation of the feedback that has been described.
2. There is no difference in principle between disturbances (ie factors that would tend to move the output of the system away from the desired value) that arise externally and those that arise internally. Examples of external disturbances - for the three examples above - would be: a) heat leaving or entering the room being regulated; b) the road wheels being jolted by bumps and contours; c) the loading on the output of the amplifier being altered, eg by extra speakers being switched in or out. Examples of internal disturbances would be: a) The heating element becoming more or less efficient; b) the hydraulic steering pump becoming less efficient over time due to wear; c) changes in the open-loop gain of the amplifier stage due to, for example, changes in semiconductor characteristics because of temperature drift. In all of these cases the feedback operation will cause the desired output to be maintained regardless.
3. My reference to the 'transfer function' above was intended to cover all cases, whether it is positive amplification, fractional amplification (normally called attenuation of course), unity gain, and whether inverting or non-inverting, as well as the implementation of other mathematical functions. The principles apply in all cases.
4. I've been designing with op-amps for decades - for audio amplification, audio signal processing, control systems, and analog computation. I see no difference in principle between any of these. Since the original purpose of op-amps was as building blocks for modelling physical processes, I see the same basic ideas in play however they are implemented (and this is a key theme in Ashby's book). Prior to that, I built amplifiers with discrete transistors and earlier still with valves. I see no difference in the fundamentals in any of these. I'm not acquainted with Black's amplifier but I'll look inot it, but I'll be astonished if it deviates in any essential regard from the fundamentals that apply to all of these examples. DaveApter (talk) 17:06, 10 October 2014 (UTC)

A voltage amplifier with gain 1/β when the open-loop gain A is large

Dave: The idea that the op-amp amplifier of the figure immediately above and Black's amplifier are'fundamentally' the same is bound to be true at some level of abstraction. However, that is not at stake here, where the issue is how they differ. Obviously, they do differ. The difference is that the op amp circuit uses a performance gap and its reduction, while Black's amplifier does not, at least as its operation is described in textbooks like that of Kal. Brews ohare (talk) 17:28, 10 October 2014 (UTC)

The figure at right shows a voltage amplifier with gain A/(1+βA) ≈ 1/β for discussion. I think it's an example of Black's amplifier. The error is V_in–βV_O. The circuit drives this error toward zero. These aspects of operation seem clear, and similar to error-controlled regulation. However, in error-controlled regulation the 'error' is an actual deviation of the disturbed system (i.e. A, which has become A+ΔA) from its 'normal' state, and the return of A to its normal state by regulation, by driving ΔA→ 0. That is not what happens here. Instead, the gain is set up by the feedback to be 1/β whether or not A remains at its deviant value A+ΔA. Brews ohare (talk) 18:52, 10 October 2014 (UTC)

In candor, my understanding has evolved, and I think this figure and the op-amp figure are basically identical. The key distinction of both circuits from error-controlled regulation is the last sentence above: neither of these circuits drive the disturbance ΔA→ 0. Brews ohare (talk) 19:01, 10 October 2014 (UTC)

That distinction brings to mind an earlier analogy. Is the process of keeping a car in the center of the lane the same if the road is straight as it is when the road is curved? One requires occasional correction, the other requires continuous correction. Does this matter?

BTW, looking at the diagram above - why can't βV_out be an essential variable? Trevithj (talk) 01:24, 11 October 2014 (UTC)

Can you address the point raised that the difference to be noted is that ΔA is not driven to zero when V_in-βV_out is driven to zero, but when a performance gap based upon an essential variable is driven to zero, the system governed by that variable is returned to its normal state that prevailed before the disturbance occurred? In Black's amplifier, the disturbance is ΔA in the open-loop amplifier, but this disturbance remains despite the feedback. Brews ohare (talk) 02:23, 11 October 2014 (UTC)

To me, this difference indicates different ways of using feedback operating differently. Brews ohare (talk) 03:12, 11 October 2014 (UTC)

I thought I was addressing the point. But since you ask: V_out is returned to its normal state (or near enough if A is large) that prevailed before the disturbance occurred. If the disturbance remains, that means continuous correction is required - like the car on the curved road. Does this matter?

Also, why can't βV_out be an essential variable? Trevithj (talk) 04:09, 11 October 2014 (UTC)

Trevith: We don't understand the 'disturbance' the same way. Assuming A is large, in Black's amplifier the disturbance ΔA has no effect upon V_out. That is because ΔA changes the open-loop gain A but doesn't change the closed loop gain 1/β so V_out remains V_in/β whether ΔA takes place or it doesn't. That desensitivity results because the percentage change in closed loop gain is reduced from that in the open loop gain by the feedback factor (1+βA) which in principle is as large a reduction as one can imagine if A is large enough. Brews ohare (talk) 05:02, 11 October 2014 (UTC)

We also understand 'normal state' differently. A variable may have a normal value, but only a system (a complicated entity) has a normal state. This state may be identified by the values of certain essential variables. For example, the state of an ideal gas can be identified by specifying two of the variables pressure, temperature and volume, with the three interrelated by an equation of state. The state of an amplifier involves a myriad of transistor parameters and bias voltages and temperatures that are only hinted at by the single gain parameter A.

I am unclear what your interest is in deciding whether βV_out is identifiable as an essential variable. Whether the answer is yes or no doesn't seem to play a role in the present discussion. In any event, the state of the open-loop amplifier, the system whose state variations cause ΔA, has nothing to do with βV_out, which is not an essential variable of the open-loop amplifier and has no influence over ΔA. One type of change ΔA, one type of variation among those envisioned by Black, is caused by things like aging of the transistors or heating of components, or fading of battery voltages; nothing to do with the input signal or the feedback loop. Brews ohare (talk) 05:02, 11 October 2014 (UTC)

Black also was interested in reproducibility of manufacture, where he wanted to be able to make amplifiers with a specified gain 1/β despite poor reproducibility of high-gain amplifiers. (One application to telephony he was involved in incorporated the combined use of many amplifiers that had to have identical gains.) In this case ΔA is a manufacturing variation and despite this variation, the closed loop amplifiers regardless of their different values of A, all will have the specified gain 1/β. 1 Brews ohare (talk) 14:44, 11 October 2014 (UTC)

This is all very interesting, professor, but you still haven't addressed either of my questions.

1. I assume that you believe that βV_out can not be an essential variable. My question is: why not? It fits the definition you provided earlier.1
2. I accept that Black's amplifier does not directly influence ΔA. My question is: does it matter? A car doesn't directly influence the curve of a road either, but stays in its lane. Trevithj (talk) 22:37, 12 October 2014 (UTC)

1. It makes no sense to suggest that βV_out is an essential variable without specifying what system you are talking about for which it serves that purpose. If we are talking about the open-loop amplifier, I answered your question in detail: No. A possible exception would appear to be a signal so large as to saturate the amplifier, but that circumstance would not be an exception in fact, because it would drive the gain A to a small value, violating the assumption that A is large.

2. Does it matter that Black's amplifier does not affect ΔA? It does if you believe that Black's amplifier is a form of error-controlled regulation that opposes ΔA. And as far as I can determine, it is your belief that Black's circuit does employ error-controlled regulation. If this emphasis upon error control isn't your position, then we have nothing to discuss: Black's amplifier uses feedback in a different fashion than error controlled regulation. If error control is your position, then you must specify what performance gap it is that Black's circuit opposes; obviously it is not ΔA. Brews ohare (talk) 23:26, 12 October 2014 (UTC)

1 We agree that the open-loop amplifier doesn't include the feedback signal βV_out. That is why it is called open-loop, I guess. I am talking about the closed-loop amplifier, since βV_out is the feedback signal that forms the closed loop in question. So in this system (the one with negative feedback) can βV_out be an essential variable?

2 To clarify: It is my position that Black's amplifier is a form of error-controlled regulation. It is not my position that Black's amplifier is a form of error-controlled regulation that opposes ΔA. As you have correctly pointed out, nothing opposes ΔA. So it follows that I don't think it matters. Do you think it matters? Trevithj (talk) 19:50, 13 October 2014 (UTC)

OK, you propose that βV_out is an essential variable of the open loop amplifier, suggesting that the open-loop system maintains its normal operation by comparing the value of βV_out with some set point value, say V_in, and forcing this variable toward its set point. That is how it operates. However, that is its normal operation, and there is no regulation going on here, no overcoming of a disturbance from normal operation. This point of view does nothing to explain why one would choose to use feedback in this way rather than simply to directly amplify the input signal with an open-loop amplifier of gain 1/β and be done with it. Any explanation? Brews ohare (talk) 21:51, 13 October 2014 (UTC)

Given that one could simply use an open loop amplifier, why introduce feedback? Recognized explanations for using feedback include benefits other than desensitivity to gain variations, such as increased bandwidth, greater linearity and so forth. But these last have nothing to do with coping with disturbances and provide no opening for the justification that feedback is introduced to provide error-controlled regulation. Rather, feedback is introduced for these other benefits unrelated to regulation. Brews ohare (talk) 22:12, 13 October 2014 (UTC)

Historically, Black was very concerned with gain variations, and they were a major impetus for his use of feedback. Perhaps you will recognize that a comparison of how feedback deals with disturbance by desensitization shows a departure from the approach of homeostasis? Brews ohare (talk) 22:31, 13 October 2014 (UTC)

Black's amplifier compared

Thanks Brews for providing the link to Black's paper. The two things I notice immediately are: a) The equation he gives for the closed-loop gain is exactly the same as the equation for a standard op-amp implementation of a positive gain non-inverting amplifier; and b) The conceptual diagram he gives is exactly as we would draw the schematic for an op-amp implementation. This is even thhough op-amp modules did not exist as available building blocks at that time! This would seem to indicate that the underlying principles are common. Designing with op-amps is so much simpler because the signal paths and feedback paths can be dealt with conceptually, whereas in discrete valve or transistor designs, the feedback mechanism is often not obvious without a thorough circuit analysis. In some ways it's analagous to the difference between programming in say Java and in assembler - in Java you can just concentrate on the algorithm but in assembler you have to deal with the details of registers, opcodes, addressing modes etc.

The short conclusion is that I can't see that it's been established either that Black's original design differs in principle from modern op-amp implementations, or that either differ in principle from control-system feedback applications. And I can't see that any of the sources that Brews has cited say otherwise. Also that with about 35 refs to the article, that it is inadequately supported by citations. DaveApter (talk) 09:47, 13 October 2014 (UTC)

Hi Dave: I agree with you about the equivalence in principle between op-amp amplifiers and Black's circuit. The difference between them is the implicit summer in the op amp and the explicit summer in Black's circuit. In transistor amps realizing Black's circuit, this summer is built in by such subtleties as the sign-flip of a single transistor stage, or feeding back to the emitter of the input transistor in a two-stage amplifier. In the op amp the summer is incorporated as a differential pair. These different ways of achieving the subtraction of the feedback from the input are not essential.

However, it does not follow that there is "no difference in principle from [other] control-system feedback applications". First, "control systems" is a broad category that includes both error-controlled regulators and Black's circuits, and these two both are in this category but are not alike. Second, as pointed out above, the feature distinguishing between them is how they approach undesirable disturbances. In error-control the effect of the disturbance is countered by bringing the disturbed system back into normal operation. In Black's approach the disturbance ΔA is not corrected and the open- loop amplifier is not brought back. Instead the open-loop amplifier is allowed to do its thing, but the closed-loop amplifier is rendered insensitive to this behavior. This achievement of desensitivity to disturbances without their correction is very well documented by numerous sources linked above. Brews ohare (talk) 15:30, 13 October 2014 (UTC)

These two classifications of control systems use fundamentally different ways of approaching disturbances. Brews ohare (talk) 13:48, 13 October 2014 (UTC)

Reverted addition of new figure

Negative feedback amplifier using ideal unilateral elements

A negative feedback amplifier with gain 1/β when the open-loop gain A is large

A voltage amplifier using an operational amplifier to set the voltage across R₁ to V_in.

I reverted this edit in which Brews added the figure above, with an amplifier and an abstract adder. It seems to obscure, rather than clarify, the conditions under which the op amp circuit behaves approximately ideally, since the abstract adder gives no indication of where current might flow, or what it adds even, so it's hard to interpret much from it that would be different from the op-amp idealization; just say the op-amp has a finite gain if that's the point. And it's not clear what the goal of another figure there would be anyway. Dicklyon (talk) 22:36, 12 October 2014 (UTC)

Hi Dick: It's my understanding that the adder combines the voltage inputs, just as it does in the ideal negative feedback amplifier circuit assuming voltage input and voltage output. In both, the adder combines its inputs, producing V_in–βV_out. The only difference between these two circuits is that the lower one provides a voltage divider for the network that feeds back the voltage βV_out.

Perhaps it needs to be clarified that a voltage amplifier is modeled here, as the general negative feedback amplifier circuit of the top diagram is vague on this point, and could have any combination of current and voltage inputs and outputs provided β incorporated the appropriate dimensions (V/V. V/A, A/A, A/V) to convert the output to the same form as the input.

The goal of the center figure is, of course, to clarify the connections between the negative feedback voltage amplifier and the op amp voltage amplifier (bottom diagram). I believe it is well-known that op-amps ideally admit no current, and that the summer likewise deals only with its voltage inputs. To clarify the confusions that plague you about this comparison, perhaps you could suggest some rewording? Brews ohare (talk) 23:58, 12 October 2014 (UTC)

In the event that the algebra behind the negative feedback amplifier circuit escapes you, for both negative amplifier circuits the output is given in terms of the input by:

$V_{out}=A\left(V_{in}-\beta V_{out}\right)$

$V_{out}(1+\beta A)=AV_{in}$

${\frac {V_{out}}{V_{in}}}={\frac {A}{1+\beta A}}\approx {\frac {1}{\beta }}$

where, of course, in the lower circuit:

$\beta ={\frac {R_{1}}{R_{1}+R_{2}}}.$

Brews, the top and bottom pictures are clear and unambiguous. The top is abstract, and the bottom is a circuit with inputs and outputs being voltages. The one in the middle is a muddled mix, using an abstraction of a voltage adder and amplifier with a voltage divider circuit. With the op-amp circuit, one can talk about near-infinite input impedance not loading the voltage divider. With your new diagram, it's less clear what is circuit and what is abstract idealization, or how it is intended to help with the understanding. Dicklyon (talk) 00:49, 13 October 2014 (UTC)

Dick: I am not sure I understand the 'muddled mix' description. It's clear that voltages are used for input and output, so that's not an issue. My best guess is that the replacement of the β-block by a voltage divider has derailed you because this is a very particular example of such a β-block and not an abstract version that could be represented in many different ways. Is that the issue? Brews ohare (talk) 02:35, 13 October 2014 (UTC)

To my mind the op-amp circuit has done the same thing. What is the difference in your mind? Brews ohare (talk) 02:40, 13 October 2014 (UTC)

A second point you raise is that it is not clear that the summer is assumed to draw no current from the divider, which loading would alter the value of β from the simple resistor ratio. If that is a probable concern of readers, it is avoidable by simply pointing out the assumption that, like the ideal op amp, the summer draws no current. Brews ohare (talk) 17:21, 13 October 2014 (UTC)

As a real example, if I used this figure and replaced the dashed block enclosing the transistors with the triangular designation of this amplifier, that figure would be equivalent to the one I have used here. Brews ohare (talk) 02:58, 13 October 2014 (UTC)

As indicated in the discussion above with Dave, the only difference between the center and the bottom figures is making the summer explicit in the center circuit that is implicit in the op amp. This equivalence might seem more transparent if the summer were simply moved to the right and stuck inside the amplifier triangle? The center circuit is possibly more general in not assuming a particular implementation of the summer, while the op amp almost always uses a differential pair as the input stage that differences the signals at its two inputs. Of course, the op amp summer might be achieved differently. Brews ohare (talk) 14:01, 13 October 2014 (UTC)

I believe this discussion demonstrates your reservations about the center figure are groundless, and the discussion above with Dave shows the comparison between op-amp circuits and Black's serves a useful purpose in demonstrating their fundamental equivalence. However, the presentation of these points could benefit from your attention, so please look into that. Brews ohare (talk) 14:43, 13 October 2014 (UTC)

I can only agree with Dicklyon, the picture was a weird mishmash of a system diagram and a circuit diagram.GliderMaven (talk) 19:10, 13 October 2014 (UTC)

Your endorsement of Dicklyon's characterization contains nothing to explain your reasons for it. This figure, as has been carefully pointed out, is no more a 'mishmash' with its idealization of a summer that draws no current from the resistor divider than is the idealized op amp with its differencing at its input that acts exactly the same way. Without any comment on this point, GliderMaven, your support is simply a "me too" with all the weight that mindless effort deserves. Brews ohare (talk) 21:16, 13 October 2014 (UTC)

This talk page has had 1375 edits since 6 June 2014—just over 10 edits per day for 130 days. No amount of talking is going to persuade a passionate editor that their interpretations are unhelpful, as shown in each of the previous cases. Chatting here is a pretty minor problem on Wikipedia's scale of badness, but a less time-consuming arrangement would be to work out what the consensus is, then revert to it, and close attempts to re-negotiate settled issues. Re the new figure: I am another "me too" mindless commentator, albeit one with a good understanding of negative feedback principles. Johnuniq (talk) 06:00, 14 October 2014 (UTC)

Agreed. No big deal that all this time and talk space is being wasted. When Brews eventually goes away, we can talk it out and settle it. Dicklyon (talk) 06:12, 14 October 2014 (UTC)

A feedback voltage amplifier using an op amp with finite gain but infinite input impedances

It's remarkable that you two cannot reply to the suggestion that the summer implicit in the input of the ideal op-amp circuit is no different from the one explicit in the identical circuit using a high-gain amplifier. If you were to provide a schematic for an op amp that broke out its input summer the two circuits would be the same, although you don't think so. Brews ohare (talk) 12:35, 14 October 2014 (UTC)

To drive the point home, I have added a figure employing the traditional representation of an ideal op amp with finite gain {see, for example, Figure 1.4, p. 7 Ideal op amp model in Sergio Franco (2002). Design with operational amplifiers and analog integrated circuits (3rd ed.). McGraw-Hill. ISBN 978-0078028168.) For Dicklyon, this representation has an infinite input impedance summer. If there is any difference at all from Black's negative feedback voltage amplifier using the same feedback circuit, please point it out. Brews ohare (talk) 14:07, 14 October 2014 (UTC)

I am unsympathetic with those that would describe this circuit as a "muddled mix" or a "weird mishmash" as it represents standard diagram practice in all circuit textbooks. Brews ohare (talk) 14:31, 14 October 2014 (UTC)

The new diagram is certainly an improvement; it's more clear what it means. It's less clear now that there's any point in keeping the one without the finite gain A if we include the one with. Trevithj will probably like it, too, since it's more explicitly in for form of error-controlled regulation. Dicklyon (talk) 15:33, 14 October 2014 (UTC)

The new figure is no different from its predecessor except it is sourced. As for error-controlled regulation, I'd love to know what that means to you in the context of this circuit. As I pointed out to Trevith, it is true that in this circuit you can view V_in as a set point for βV_out, and the circuit drives the difference to V_in/(1+βA), which is small if A is large. However, there is no analogy here to error-control in the sense of homeostasis, that is, defending the status quo against disturbances by driving the disturbance-induced departures to zero. The error V_in/(1+βA) is designed in, in advance of operation, and is not adjusted to improve upon how well we're doing. The error V_in/(1+βA) is selected to obtain a desired bandwidth, desensitivity, step response, in advance, and isn't adjusted in process if the goals aren't being realized. The signal is throughput in an amplifier, not a disturbance in the sense of error-controlled regulation. The feedback is not introduced here to "protect" the circuit from the input signal, but because of the advantages of gain desensitivity and other things (bandwidth etc.). All these advantages that motivate the use of feedback are totally unrelated to error-control so error-control is not the reason for using feedback. Brews ohare (talk) 17:14, 14 October 2014 (UTC)

Consider input as setpoint and it may become clear. The error is the difference that the amplifier amplifies. Dicklyon (talk) 01:29, 15 October 2014 (UTC)

Dick: Thanks for the suggestion. I hoped that reading what I have said immediately above and to Trevith would have made clear that I am fully aware of this point. I've tried very hard to explain why 'error control' is not the reason for using feedback in Black's circuits. If we agree that we can interpret Black's circuit using V_in as a set point, and the input V_in-βV_out as an error, the possibility of such an interpretation does not mean that the purpose for feedback in Black's circuit is 'error control'. No more than the purpose of eating is to put on weight. Please take a look at the next thread headed Overview. Brews ohare (talk) 03:07, 15 October 2014 (UTC)

You've made this point so very many times, and yet you've been wrong every single time. But you continue to spam the talk page and waste everyone's time with your misunderstanding of the topic.

The error can be generated by external perturbations to the loop, but also by non linearities.

Your error is not going away because you are open loop. We explain to you in many different ways why all negative feedback loops operate by what can be referred to as error control, but you repeatedly do not understand. Given that you are spamming the talk page so very much, if you mention this again, I will be looking to get you banned. This is a waste of your time as well as our time, and it will be better for you when you go somewhere else.GliderMaven (talk) 15:19, 17 October 2014 (UTC)

GliderMaven your intemperate responses are largely the result of your failure to read what is said and attacking straw-man positions of your own invention. Your crossover distortion example of nonlinearity is discussed in detail below and shown to have no bearing upon the issues under discussion here. It would behoove you to address what actually is said there instead of fantasies. Brews ohare (talk) 17:27, 18 October 2014 (UTC)

Mindell's "confusion"

We have in the text, "Nyquist and Bode built on Black’s work to develop a theory of amplifier stability, but chose to define "negative" as applying to the polarity of the loop (rather than the effect on the gain), which gave rise to some confusion over basic definitions.[7]" But I don't understand this. Aren't these essentially equivalent? Does anyone other than Mindell find a confusion or difference between the definitions that these guys used? If this concept is unique to Mindell, perhaps we should dismiss it? Dicklyon (talk) 06:09, 1 October 2014 (UTC)

I think the definitions are operating in the same direction in that particular case. The value being controlled is assumed to be higher than the desired value, so control is always reducing the value. That's a bit like steering a car around a circular track: to stay in the lane, you only have to turn one way. But Black's version doesn't generalize to the case where the actual value is lower than the desired value. Likewise, you can't control a car on a straight road by only turning one way.

Ramaprasad mentions at least one other author who uses a definition like Black's. Berrien (1968,1976) apparently talks about thermostats as using positive feedback if the heat is increasing! Trevithj (talk) 07:59, 1 October 2014 (UTC)

OK, I can see that you are confused; but that's because you're not understanding Black's definition. The negative loop gain doesn't affect what sign of error can be corrected. What's lowered is the gain from input to output, the close-loop gain, relative to the open-loop gain (e.g. from disturbance to effect, without and with the negative feedback loop closed). The loop gain is the forward gain divided by one minus the loop gain, which is less than the forward gain when the loop gain is negative. That what negative feedback is, and does. The polarity of the loop and the effect on the gain are strongly linked this way, and it doesn't matter which one you take to be defining (at least to the extent that the loop can be treated in an approximately linearized way). Dicklyon (talk) 18:04, 1 October 2014 (UTC)

I see. The troublesome text seems to be:

... the feed-back referred to as positive feed-back or negative feed-back according as the absolute value of 1/(1-μβ) is greater or less than unity. Positive feed-back increases the gain of the amplifier; negative feed-back reduces it.

(from H.S. Black, "Stabilized feed-back amplifiers") It isn't immediately clear if Black called the feedback "negative" because it reduced the gain, or saying that it reduced the gain because it is negative. Trevithj (talk) 18:29, 1 October 2014 (UTC)

There's no real distinction of cause and effect between the loop gain μβ and the closed-loop gain 1/(1-μβ); they are just algebraically equivalent descriptions of the feedback loop. When μβ is negative, 1/(1-μβ) is less than unity. No conflict or confusion here that I can see. I think Black understood this, but chose to focus on the gain, since that was what he wanted good control of. But when he says, "Positive feed-back increases the gain of the amplifier; negative feed-back reduces it", I presume he means "Positive μβ increases 1/(1-μβ); negative μβ reduces it [relative to the no-feedback case]." Dicklyon (talk) 04:19, 2 October 2014 (UTC)

Well, that's the confusion - we have to presume his meaning. I suspect Black pushed the gain aspect because he had such trouble with the patents. He doesn't seem to use "negative feedback" as a term until some of the later submissions (around 1934). And when he does, he either talks in terms of gain-reduction, or refers to the "prior art". It is easy to assume that his definition is "negative = reduction". I'll re-read Mindell, to see the exact quote. (Mindell 2002). Trevithj (talk) 07:53, 2 October 2014 (UTC)

Mindell says:

In Black’s time, however, the definition of this specific-sounding term, “negative feedback,” had yet to be settled. The idea of positive feedback had become current in the 1920s with the introduction of the regenerative amplifier. Positive feedback, or regeneration, in a radio amplifier increased the sensitivity of a receiving tube by sending a wave back through an amplifier many times. Black insisted that his negative feedback referred to the opposite of regeneration: gain was reduced, not increased. Yet, to return to the analogy of the steam engine governor, Black’s use of “negative” means the energy required to spin the balls reduces the energy output of the engine, not that the balls trigger an action that slows it—hardly a significant effect for a steam engine. In their 1924 paper Friis and Jensen had made the same distinction Black had between positive feedback and negative feedback, that is, distinguishing one from the other not by the sign of the feedback itself but rather by its effect on the amplifier’s gain.39 In contrast, Nyquist and Bode, when they built on Black’s work, referred to negative feedback as that with the sign reversed. Black had trouble convincing others of the utility of his invention in part because confusion existed over basic matters of definition.

But this is just Mindell. Personally, I don't understand his point, since the two concepts (e.g. Black's versus Bode's) are completely equivalent. It didn't bother Nyquist and Bode, so why does it bother Mindell? His going off on "energy" here strongly suggests that Mindell is not reasoning clearly about these engineering concepts. This "confusion" is Mindell's invention, unsupported by anyone else, as far as I know. Hence we have a primary source issue in assigning this novel thesis any weight in the article. Dicklyon (talk) 05:12, 3 October 2014 (UTC)

I looked up some of the citing works. Aström and Murray (2008) make this point in their introduction:

The term feedback refers to a situation in which two (or more) dynamical systems are connected together such that each system influences the other and their dynamics are thus strongly coupled. Simple causal reasoning about a feedback system is difficult because the first system influences the second and the second system influences the first, leading to a circular argument.

— KJ Aström, RM Murray., Feedback Systems: An Introduction for Scientists and Engineers

That's the confusion - circular definitions. Is it negative feedback because it reduces the gain, or does it reduce the gain because it is negative feedback? Black's description is ambiguous, but strongly implies the former. The views aren't equivalent: Black defined the term based on its effect; Nyquist defined it as a cause. I think Mindell makes a valid point, and other authors echo it. Perhaps it could be better worded in the article though. Trevithj (talk) 08:05, 3 October 2014 (UTC)

The real confusion here is using words of vague content to replace mathematical argument. While some philosophers support ideas like emergence on the basis that our present theory of complex feedback and feed-forward systems is inadequate, for a simple case like the negative feedback amplifier the math is perfectly clear and logical, and makes the quote from Aström important if interpreted (as a reading of his work suggests) as saying causal reasoning is inapplicable and circular here. The notion of 'causality' is not used by the math, and is completely irrelevant to an understanding of this amplifier. Brews ohare (talk) 13:43, 3 October 2014 (UTC)

On the one hand, we could avoid circular definitions by using a mathematical approach. On the other hand, we could keep the article broadly accessible by using a narrative approach. How do we keep the article broadly accessible while avoiding circular definitions?

I suspect it might be true that Black wasn't defining negative feedback, so much as describing its effect. If so, it seems to have confused Mindell (among others) that the guy who popularized the term didn't define it. Does that imply there is an earlier source to be found? Trevithj (talk) 00:25, 5 October 2014 (UTC)

It would be helpful to define the objective here. At the moment the sentence under discussion occurs in the History subsection:

"Harold Stephen Black detailed the use of negative feedback in electronic amplifiers in 1934, where he defined negative feedback as a type of coupling that reduced the gain of the amplifier, in the process greatly increasing its stability and bandwidth.[9][10] Nyquist and Bode built on Black’s work to develop a theory of amplifier stability, but chose to define "negative" as applying to the polarity of the loop (rather than the effect on the gain), which gave rise to some confusion over basic definitions."

This statement is an attempt to summarize remarks by Mindell, p. 121. The point of Mindell's discussion is to say that the term 'negative feedback' evolved over time. Personally I find that an unremarkable observation and also that Mindell has not made its historical background clear, but muddy.

One of Mindell's problems is that he suggests that "Black's sense of 'negative' [in 'negative feedback'] means that the power required to spin the balls [in a flyball governor] reduces the power output of the engine." One problem with this idea is that it equates an erroneous idea about how the governor works to Black's conception of feedback, which proposes mistakes Black would never make.

And Mindell does not understand that the steam-engine governor is a form of error-controlled regulation, which is unrelated to the idea behind the negative feedback amplifier, and has nothing to do with gain. The spinning balls of the governor control the throttle just like a cruise control keeps a car's speed constant. The negative feedback amplifier doesn't work that way - the circuit does not use feedback to 'regulate' the gain by adjusting the operation of the open-loop amplifier, in the manner of how a throttle control adjusts the power input to an engine. If one thinks of the input to the open-loop amplifier as an analog of fuel input to an engine, we then have the odd situation where the engine (open-loop amplifier) runs exactly the same way regardless of how much fuel is sent to it. Unless Mindell's ridiculous assessment of Black's concepts can be traced directly and verbatim to Black, I'd call this a gross misconception by Mindell.

Given that Mindell has introduced a mistaken comparison without adequate sourcing, why elevate this confusion to the level of a metaphysical argument over cause and effect unrelated to the accuracy of Mindell's historical account? Brews ohare (talk) 04:44, 5 October 2014 (UTC)

Mindell's unsupported historical assertion is that "Black had trouble convincing others of the utility of his invention in part because confusion existed over basic matters of definition" I am with Dicklyon on this one: if there was any historical confusion, Mindell has failed to identify it, and has failed to establish any historical importance for it. Brews ohare (talk) 05:42, 5 October 2014 (UTC)

The present text in the WP article suggests that the 'confusion' is exemplified by the difference in approaches of Black and the later work by Nyquist and Bode. However, this later work had no historical role in the acceptance of Black's ideas, and is not indicative of an earlier confusion. The Nyquist/Bode analysis was of amplifier stability in the sense of immediate response to electrical inputs, unlike Black's objective which was the long-term service stability of the amplifier over its service life to aging of components and power supplies. As Dicklyon says, there is no conflict between their views, only a matter of emphasis. Brews ohare (talk) 15:17, 5 October 2014 (UTC)

While I agree the Mindell's mention of the centrifugal governor is muddled, one can hardly conclude that "Mindell does not understand that the steam-engine governor is a form of error-controlled regulation." I think your analysis here goes way too far, but I'll agree that we should just leave out mention of the "confusion" that seems to only be discussed my Mindell, without much support or impact. Dicklyon (talk) 22:56, 5 October 2014 (UTC)

Going back to an earlier point, there is an earlier source that defines negative feedback:

Use of a common grid battery ... introduces a small feed-back from the second stage to the first. This feed-back may be either positive or negative, depending upon the phase relations in the intermediate transformer and may be eliminated by placing a condenser across the grid battery terminals.

— Robert W. King, Thermionic Vacuum Tubes and their Applications page58 (1923)

Clearly "negative" refers to out-of-phase signals "negating" each other.

BTW: I'm not sure if Mindell is referring to an "earlier" confusion - rather a subsequent one, especially when applying this term to the overall concept outside the context of electronic signals. Ashby and Ramaprasad mention this too. Trevithj (talk) 21:30, 5 October 2014 (UTC)

That is not my reading of the passage examined here. In any event, unless it can be demonstrated that this 'confusion' is important to history by finding some other sources that think so, it is not worth mentioning here. Brews ohare (talk) 02:44, 6 October 2014 (UTC)

The role of a 'confusion' of definition outside electronics is not germane to Mindell's claims about Black's difficulties 'selling' his idea. I believe that the primary evidence for the existence of any such difficulty is the nine years it took to get the patent granted. However, another explanation I have read is that the patent was enormously long and included a great many claims that had to be evaluated. Brews ohare (talk) 03:00, 6 October 2014 (UTC)

In any event, Black had lab prototypes that demonstrated the principle that negative feedback made overall gain independent of changes in the gain of the open-loop amplifier. This was not just a debate over terms. And Nyquist and Bode were entirely persuaded that Black's feedback circuit was working, regardless of any putative confusion over definitions. Brews ohare (talk) 03:11, 6 October 2014 (UTC)

Reviewing Black's paper again, I see why he said it the way he did. It's because he is working the general complex transfer function. He says "absolute value of 1/(1-μβ) is greater or less than unity" because that's how he chose to generalize from the sign of μβ in the real case to its effect on gain in the complex case, where μβ does not have a sign because it's not real. So I think it's not so much that the definition was not settled, but that he had moved beyond the simple definition to a closely related generalization where one could work real engineering problems, like frequency dependence and stability analysis. Dicklyon (talk) 03:17, 19 October 2014 (UTC)

Steering a car

By this argument, steering a car along a straight road is "fundamentally different" to steering a car along a curved road. How is that a useful distinction? Trevithj (talk) 19:56, 13 October 2014 (UTC)

Trevith: Perhaps you could explain where the analogy is here that you find so compelling? Brews ohare (talk) 21:08, 13 October 2014 (UTC)

What analogy? Trevithj (talk) 00:38, 14 October 2014 (UTC)

OK, Trevith, there is no analogy and you just felt like steering cars was a fun topic. . Bye. Brews ohare (talk) 01:49, 14 October 2014 (UTC)

Oh, you thought the steering cars reference is an analogy? No, it is a counter-example. I'm applying your distinction to a different situation. Do you find it useful? Trevithj (talk) 05:13, 14 October 2014 (UTC)

I don't follow you. Brews ohare (talk) 05:44, 14 October 2014 (UTC)

I tracked down an old edit in which you discuss steering a car. To reprise your comment:

[deleted as per my original objection to change of context edits.] Trevithj (talk) 06:48, 19 October 2014 (UTC)

You do use the word analogy here, not counterexample. It seems here that you are trying to point out a fundamental difference between the cases, as the second requires both continuous input to hold to the curve and a continuous minor adjustment while the first only requires minor steering adjustment. You have apparently changed your view and now think that the two cases are not fundamentally different.

It seems you originally wished to say that the negative feedback amplifier uses feedback to "stay on the curve" (achieving a gain 1/β, I suppose) and ignores minor adjustments (countering ΔA, I suppose). That is a poor description, because the negative feedback amplifier does deal with the fluctuations ΔA as a general issue, independent of their exact form or occurrence, by rendering the system insensitive to them whatever their nature and whether or not they occur. On the other hand, you see error-controlled regulation as focused upon minor adjustments (minimizing real-time upsets like ΔA) and not forced to deal with "staying on the curve". However, homeostasis or thermostatic control of house temperature is all about maintaining equilibrium, even against steady disturbances.

I confess to confusion about what this analogy/counterexample means to you. Brews ohare (talk) 16:29, 18 October 2014 (UTC)

To clarify:

The goal of steering a car is to keep it in the lane. A curve in the road is a disturbance to that goal. The act of steering in no way changes the curve of the road.

Given that your proposed distinction is based on whether or not the disturbance is corrected, is steering a car around a curve an example of error-control? Trevithj (talk) 06:48, 19 October 2014 (UTC)

Your clarification includes no identification of how this comparison of steering examples compares to that between the negative feedback amplifier and an error-controlled system.

To address your point within the context of steering a car, it is hard to say whether a curve is a disturbance without having some idea of the control mechanism. So, for example, imagine a control mechanism that is focused upon following the yellow line dividing a highway. (Here is a line-following system. The Google driverless car has a more complicated system.) I would imagine that such a system sees no difference between the problems of following this line around a curve or on a straight line. Both are examples of error-controlled regulation that could be based upon a performance gap measured as the difference between the position of the yellow line and the monitored position of the car. Arguably, in normal driving the decisions of a human driver act as the comparator in such a system, the same role as a thermostat. The driver's steering adjustments are the commands to the effector in this system, the complex of steering box, tie rods, tires, etc. resulting in redirection of the car. Brews ohare (talk) 17:13, 19 October 2014 (UTC)

You are being disingenuous. It is very easy to say whether a curve is a disturbance - one only has to let go of the steering wheel while driving around a curve. The fact that you shy away from the obvious comparison is not adding any support to the argument regards "fundamental differences". I say the same concepts you outline in the context of steering a car also apply in the context of maintaining the amplifier output. Regardless of where the disturbance comes from, the output is controlled with respect to the input. Trevithj (talk) 03:35, 20 October 2014 (UTC)

Overview

The overview of this article is this: Negative feedback, as it is used in biology and in management and education, is about setting a goal and monitoring a performance gap in achieving that goal with the aim of keeping on track toward the objective by reducing this gap. On the other hand, in the negative feedback amplifier, negative feedback is used for achieving goals as well, but not by using a performance gap but by designing the system so the goals are implicit in the design. So closed-loop gain, bandwidth, gain desensitivity, step response etc. all go into the up front design of the feedback network. They are fixed in advance of operation. They are not adjusted during operation by observing how far the goals are from being met. For example, the overshoot in step response is designed in, not monitored and adjusted in real time. There are many such design goals to consider, not just one or two, and none involve real-time monitoring of performance gaps. There are, therefore, two different approaches to using feedback, the designed in advance approach versus the correction while we're in progress approach. Trying to lump these disparate methodologies together in the lede is where all this trouble began. Brews ohare (talk) 16:57, 14 October 2014 (UTC)

@Brews - I really can't follow any argument that you've put forward which demonstrates any essential difference between the amplifier exemplar and control-system examples such as thermostats or power steering. Neither can I find any clear statement to that effect in any of the references that you have provided. The only difference I can see is in the speed of the response and possibly in the degree of hysteresis that is acceptable. I don't see anything you've said that refuted the analysis of these examples I gave above.

In the case of the amplifier the set-point is the instantaneous value of the input voltage V, and the effect of the feedback is to reduce to negligible quantity any deviation from the output from the "desired" value of βV. Obviously it's desirable that this happens as nearly instantaneously as possible (although a finite time is necessary because of propagation delays, and for stability considerations). This is regardless of whether the deviation is due to (i) a change in the "set point" - ie input voltage; (ii) a change in the open-loop gain - eg because of temperature drift; or (iii) a change in the output drive required - eg because of alteration of loading. On the other hand a thermostat will generally allow for a certain deviation to build up before the heating or air-conditioning is switched in, and it may take a while to correct the "error". But of course in the case of body temperature regulation in warm-blooded animals, the correction normally achieves near-constant results.

If you do have a valid point, you may be obscuring it by the sheer volume of your posts - hundreds a week. Can you please at least be more concise? And perhaps develop your arguments offline first and then post them when you are satisfied that they are clear, rather than working them out on this page? Thanks. DaveApter (talk) 16:39, 15 October 2014 (UTC)

Dave: You have not responded to the points raised in this thread. They are (1) Yes, the circuit can be seen as pushing the output toward V_in/β. (2) Why use feedback to do this? One could just use an open-loop amp with gain 1/β (3) The reason for using feedback is the advantages like insensitivity to gain variations ΔA, control of step response, etc. These objectives of feedback are the reason for its adoption, nothing else. These objectives are designed into the feedback in advance. They are not monitored and enforced in real time. (4) So, why stress the 'error control' aspect? It is not a focus like it is in error-controlled regulation where the entire design philosophy is aimed at implementing real-time monitoring and reduction of a performance gap. For Black's use of feedback, error control is not a design issue and bringing it up is just a distraction from understanding real concerns. Brews ohare (talk) 18:02, 15 October 2014 (UTC)

First let me apologise for any confusion I caused by my treating β as the closed-loop gain above rather than the feedback ratio which is its reciprocal - I've corrected that now. To answer your points: (1) yes, agreed; (2) one couldn't "just use an amp with open-loop gain of 1/β" because these are impossible in practical realisation. They would suffer from distortion due to non-linearities, gain drift due to component changes with temperature etc, and variations in performance from one item to the next due to manufacturing tolerances; (3) agreed; (4) the reason why I'm stressing on the error control aspect is to underline the fundamental congruence of all examples or negative feedback instances - which after all is the topic of this article. DaveApter (talk) 18:53, 15 October 2014 (UTC)

Good. We agree on everything but the last line. Fundamental congruence. From an economy of thought standpoint that would be great. But it's not accurate. I've pointed out the question: "Why do we use feedback to achieve Black's goals?" We seem to agree upon what these goals are: gain desensitivity, linearity, bandwidth, step response etc. And error-control is not on his list, and he never brought up things like Sperry's PID control as a possible progenitor or patent conflict. By error-control I refer to the analysis described in Negative feedback#Error-controlled regulation involving minimization of measured performance gaps.

So in discussing why Black uses feedback, error control did not and does not come up, neither in textbooks nor in Black's work. Wouldn't it be clearer and more real to broadly outline at the outset the objectives of feedback as used in Black's circuits, and indicate that when feedback is employed toward these objectives it is possible (though not at all a concern of design practice) to look at the input signal as a set-point and the feedback βV_out as an "essential" variable, a parallel with error control. But that one should not get bamboozled into thinking there is some profound insight here into why Black chose feedback to achieve his objectives, and that Black's approach uses feedback to build in his goals as a property of circuit architecture, and not to achieve them by real-time monitoring and regulation of performance gaps. Brews ohare (talk) 23:25, 15 October 2014 (UTC)

First off, kudos for making the argument clearer. I also largely concur with the first three points, and strongly agree with DaveApter's point (4). This leaves me with two main reservations with the proposed distinction. If these could be resolved, I would be much more sympathetic towards the proposal.

1. The argument rests on the assumption that a built-in goal necessarily excludes real-time monitoring and regulation of performance gaps. In other words, there is no such thing as error-control with a "built in goal". Given that a performance gap is defined in terms of a goal, this seems unlikely.
2. If we do accept the distinction, we have the difficulty of explaining why something so different from error-control (Black's negative feedback) has nonetheless given its name to the earlier concept of error-control, without raising any objections in the literature.

I do have other reservations, but those are the big ones. Trevithj (talk) 00:49, 16 October 2014 (UTC)

It's not really all that different. The main difference is in what part of the loop you call the system and what part you call the feedback. In the op-amp, the system is essentially the voltage divider. It's output is compared with a reference (the amplifier input), and then the amplifier works as the controller to reduce the error (the difference). In the control viewpoint, the op-amp is part of the feedback or control path. In the amplifier viewpoint, it's the forward path, and the divider is the feedback path. Either way, it's the same loop, the same analysis, and the same name. Dicklyon (talk) 03:01, 16 October 2014 (UTC)

That would seem to be the simpler explanation. Trevithj (talk) 04:09, 16 October 2014 (UTC)

No-one seems to pick up on the simple point: Black never referred to error control. It was not that he was unaware of it. And he worked for decades in this area without bringing it up. So it's pretty obvious even just on that basis that error-control is not the essence of Black's use of feedback. Can you all face this point? The second point is that an engineer designing a negative feedback amplifier never uses the concept of error control. Look at Gray & Meyer or Sedra & Smith or ... So how important can it be to the negative feedback amplifier? As pointed out, the concept of error-controlled regulation is about real-time minimization of a performance gap. Negative feedback amplifier designers don't think about real-time gap minimization at all. Brews ohare (talk) 05:52, 16 October 2014 (UTC)

Granted that Black didn't mention error correction, or apparently notice any parallels with PID control, and that error control is not generally foremost in the minds of audio amp designers, I don't concede that any of these observations detracts from the point I am making [in (4) above].

Let me illustrate it by the case of a unity gain buffer op-amp circuit (and similar reasoning applies when any other gain configuration). Let us suppose that initially the input is at 0V, and that it steps up to 1V. Supposing the open-loop gain is say 80dB (x 10,000 voltage gain), the output will start to head off in the direction of + 10,000V. Of course it would never get there because it would saturate somewhere around the rail voltage of 15V or so. But long before it gets even to there it would stop moving because the output is connected to the inverting input, and when that reaches approximately 1V (0.9999V in this case) it will stabilise. Depending on the output slew rate and the propagation delay it might of course overshoot, then reverse direction and overshoot in the opposite direction and oscillate or “ring” with a gradually decreasing amplitude until it settles at the new value. Alternatively, if the slew rate is too low, it will slow down before reaching the final value and have a rounded corner to the rising edge. These two deviations from the ideal are exactly similar to the behaviour of a servomechanism which is either underdamped or overdamped. DaveApter (talk) 12:01, 16 October 2014 (UTC)

We already do have a line in the first ('Examples') section which says "In audio amplifiers, negative feedback reduces distortion, minimises the effect of manufacturing variations in component parameters, and compensates for changes in characteristics due to temperature change." Would it satisfy everyone if we included that - or a precis of it - in the lead? DaveApter (talk) 12:12, 16 October 2014 (UTC)

It's agreeable to see it has been heard that if the feedback article were written by Black or by Gray & Meyer or by Sedra & Smith or by any amplifier designer no connection would be drawn between the negative feedback amplifier and error-correcting regulation exampled, for example, by the PID controller. It is not a solid argument for flying against such authorities to say that because feedback in both amplifiers and servos combats saturation, ergo both involve error control, or even that feedback plays essentially the same role in both. Error control is described in Negative feedback#Error-controlled regulation. The considerations entering design of such systems, which include thermostatic controls, homeostasis, cruise controls and so forth all involve real time correction of performance gaps that plays no part in Black's negative feedback amplifier design. Brews ohare (talk) 15:23, 16 October 2014 (UTC)

Continued

Look, absolutely no provably correct conclusion can be drawn from someone not using a particular phrase. You've tried to use this stupid argument before and it's total garbage. And how do you even know he never used the phrase 'error controlled regulator', are we to believe you've read everything he ever wrote to check??? No. And even if he didn't it doesn't prove anything at all. We don't want to know whether he said that we want to know whether it really is.

And they are error controlled regulators. Some types of type 0 servos are mathematically exactly the same as a negative feedback amplifier. So the claim that 'it's not an error controlled regulator' is, for the purposes of this article, false; since it's completely isomorphic with one.

Cross over distortion removal using negative feedback

And even if we ignore servos and restrict ourselves to amplifiers, note that performance gaps form in real time due to nonlinearities. In a common audio amplifier design, the two push-pull stages run at offset voltages so they cannot switch on together. Negative feedback is specifically used to deal with the error that this introduces, the loop measures the error and increases the voltage until the output is the correct ratio of the input voltage and the cross-over distortion, for practical purposes, vanishes. And it does so specifically because the loop detects the error gap due to the nonlinearity and corrects for it.

Personally, I'm sick of Brews Ohare's utter stupidity on this, and I'm hereby calling for Brews Ohare to be completely banned from editing this page and the article, and all the other feedback articles and talk pages. How many times do we have to put up with him making and remaking and making again and remaking again and making again and again the same completely flawed argument that has been debunked over and over again????

He is SPAMMING the talk page. He makes dozens of edits a day, and says the same bullshit over and over again. His edits to the main article cannot be trusted, and we are having to proof read each one incredibly carefully. I have never seen anyone's edits being so massively reverted over such a sustained period. This has got to stop now.GliderMaven (talk)

GliderMaven: The argument is that the established sources do not connect the negative feedback amplifier with error-controlled regulation. Your long reply here misstated the point and makes use of your assertions (a nonstarter on WP), not sources. Brews ohare (talk) 14:26, 17 October 2014 (UTC)

You do not use the term 'performance gap' as it is commonly understood and as defined in this article. Your discussion of correcting for cross-over distortion appears to have changed the subject from Black's negative feedback amplifier to the use of negative feedback in general. Brews ohare (talk) 14:44, 17 October 2014 (UTC)

Absolutely NOT. The cross over distortion introduces an error by anyone's definition, and the cross over distortion is explicitly reduced by the negative feedback. It is absolutely exactly the same thing as the speed error used in a cruise control. If cruise control is an error controlled feedback system, then so is the servo and so is a negative feedback amplifier. They are exactly isomorphic; there is a one-to-one correspondence between the components and their mathematical behaviour is the same.GliderMaven (talk) 14:53, 17 October 2014 (UTC)

@GliderMaven: Your op-amp circuit for crossover control is discussed in this WP article. The comparison of the amplifier with a cruise control might be argued as follows:

System Feature	Cruise control	Power amplifier
Set point	Target speed	Input waveform
Essential variable	Measured speed	Output voltage
Disturbance	Road grade	Nonlinear gain
Performance gap	Measured – target	Output - input

This power output stage is an example of a nonlinear unity gain buffer that enables a load to draw a large current that the originating signal source cannot supply. It has already been pointed out that the unity gain buffer can be seen as an example of error-control, because the input is the desired output. See Friedland, Figure 1.2. In Black's more general case, the output is an enlarged version of the input, and the amplifier sets the gain at 1/β. Therefore, the difference between input and output, I–O, has to be replaced by I–βO. It still is a possible interpretation that I–βO is a 'performance gap', and I is a set point, but unlike the gap in an error-controlled regulator, this 'error' is built-in (not measured; it simply is the value I/(1+βA), all variables that are known in advance of performance, especially when I is viewed as a given set point) and the circuit makes no attempt to measure and minimize it, which is different from the basis for operation in error-controlled regulation. Brews ohare (talk) 16:54, 17 October 2014 (UTC)

The interpretation of the negative voltage amplifier using I as a set point and I–βO as an essential variable is (so far anyway) WP:OR because the authoritative sources like S&S] and G&M do not use this interpretation in their (traditional) analysis of this amplifier. Brews ohare (talk) 17:21, 17 October 2014 (UTC)

To be charitable, the most valid form of this argument I can come up with is:

• If the concepts (Black's feedback amplifier/error-controlled regulation) were the same then the terminology would be the same.
• The terminology is not the same.
• Therefore the concepts are not the same.

But the first premise is very weak. A concept can have different terms. For example: psi and Pa are very different units, but they measure the same thing. Likewise, return difference and error signal are different terms that describe the same concept.

We agreed earlier that the article is about the concept, not the terminology. If Black's negative feedback is really a different concept to the wider sense of correcting or balancing something, then it should have its own page. Black's only significance to this article is that he popularized the term. Trevithj (talk) 08:42, 18 October 2014 (UTC)

Trevith: I see no need to be "charitable" about this. The table shows the comparison very clearly. The use of I-βO, an error calculable in advance of performance (evaluated as I/(1+βA), all known parameters), is a contrast with that of minimizing a performance gap created by an unpredictable outside upset and measured during operation as done in Negative feedback#Error-controlled regulation. The concept of performance gap by any name is not used by S&S and G&M or Kal, so this approach has as yet no basis in sources, making it WP:OR. The way around this situation is to find pertinent sources and present it as an alternative to the textbook view. Brews ohare (talk) 14:17, 18 October 2014 (UTC)

The proposal for a separate page Negative feedback (error controlled regulation) to complement Negative feedback amplifier is one way to go if sources cannot be found that connect these usages of feedback. Another is to use a broad definition that can include error-correction and design for desensitivity. Dave's introductory sentence: "a function of the output of a system, process, or mechanism is fed back in a manner that tends to reduce the fluctuations in the output, whether caused by changes in the input or by other disturbances" does that, although his second paragraph shows he didn't mean to do that. Brews ohare (talk) 14:29, 18 October 2014 (UTC)

These concepts are either "fundamentally different" or they are not. If they are, create another page. Trevithj (talk) 21:00, 18 October 2014 (UTC)

This either-or is artificial. If the goal is to counter fluctuations, there are at least two ways to go about it. Make the system impervious to fluctuations ( wear a bullet-proof vest) or counter the fluctuations (duck). With Dave's definition, negative feedback can work either way. Brews ohare (talk) 22:04, 18 October 2014 (UTC)

If the concepts are not fundamentally different, then we can talk about negative feedback in terms of closing a measurement gap, like several cited sources already do. Trevithj (talk) 01:55, 19 October 2014 (UTC)

That's also not a justified conclusion. The concepts are similar, but a "measurement gap" need not always be part of the concept. Many uses of negative feedback have nothing resembling an error signal being minimized or driven toward zero, even though high-gain op-amp feedback circuits do. Dicklyon (talk) 02:47, 19 October 2014 (UTC)

I'm surprised to hear that, since I couldn't come up with counter-examples without something like a measurement gap. Can you give an instance? Trevithj (talk) 06:54, 19 October 2014 (UTC)

Consider an audio compressor. The detected output level is fed back to a gain control, with higher outputs causing lower gain. There is not one particular desired output level being compared. If the gain is controlled to be reciprocal of detected output level, you get a 2:1 Input:Output level compression (aka square-root compression). No gap; no error, just negative feedback. Similarly, with low-gain amplifier systems, unlike op amps and high-gain ones, the notion of an error or a gap is not usually relevant. Dicklyon (talk) 19:28, 19 October 2014 (UTC)

Trevith: Dick has pointed out that a performance gap plays a different or perhaps no role in different systems. That difference is illustrated in the comparison above of a power amplifier and a cruise control. The performance gap is defined in both cases as the difference between a set point and the actual value of some essential parameter.

The way the gap is found differs in the two systems. In Black's negative feedback amplifier for a general choice of gain 1/β, the performance gap can be identified as I–βO but this quantity has a value I/(1+βA) that can be calculated from the set point I and the known parameters βA without any need to measure or monitor system behavior, while in error-controlled regulation the gap is not known separately from performance and depends upon measurement of actual real time behavior.

Dick's point also is illustrated: that the use of a performance gap may differ from case to case. In the negative feedback amplifier there is no attempt to modify the gap based upon how things are working out, the gap is 'designed into' the system independent of its working environment, not measured, while in error-controlled regulation, as the name implies, the error is used to control system response to its environment by minimizing a measured performance gap. Brews ohare (talk) 16:09, 19 October 2014 (UTC)

Trevith, I see resistance on your part to directly addressing three things: (i) that there is a difference between systems in how the gap is found, (ii) that there is a difference in how the gap is used, and (iii) that there are no sources discovered as yet that treat the negative feedback amplifier as an example of error-controlled regulation. Brews ohare (talk) 19:08, 19 October 2014 (UTC)

Please don't try to say what my point is when you don't understand me. And where you say "this quantity has a value I/(1+βA) that can be calculated from the set point I and the known parameters βA without any need to measure or monitor system behavior", that's nonsense. The whole point of Black's scheme is that by monitoring the actual output, the feedback corrects for things like distortion and noise and gain fluctuations; the error signal might be close to I/(1+βA), but if you're going to ignore fluctuations from that, you might as well design a feed-forward system. Dicklyon (talk) 19:28, 19 October 2014 (UTC)

As I is a set point, and the open loop gain A and the feedback fraction β are given in advance, it hardly is surprising that the "performance error" can be calculated with no knowledge of what the system actually is doing, without any need to monitor or to measure. Not nonsense, Dick, Brews ohare (talk) 21:28, 19 October 2014 (UTC)

Gain A is given by whom? If your amplifier is ideal, and you can know or control its gain accurately, and it doesn't distort and has no noise, then yes, you're right. But a better idea is to monitor its output using negative feedback, as Black showed, and as you well know. So what are you saying here? Dicklyon (talk) 00:27, 20 October 2014 (UTC)

Dick: If we look at Kal's analysis (or that S&S or G&M) they treat the open-loop gain A as a given, known quantity. Where they wish to examine variations in A, they use the notation A+ΔA. To follow your catchy phrase "as you well know" the treatment of amplifier variations and desensitivity depends upon A being large, and the analysis never calls upon 'monitoring' output using negative feedback. Percentage fluctuations in the closed-loop gain are reduced relative to those in the open-loop gain by the feedback factor 1+βA no matter their size or other characteristics, and the size of ΔA is not diminished by the feedback. What is reduced is the influence of ΔA, simply because the closed loop gain is A/(1+βA)≈1/β, to all intents independent of variations ΔA in A. Please re-read the sources. Brews ohare (talk) 00:58, 20 October 2014 (UTC)

Hi Dick. Getting back to the audio compressor example: I get that there are cases where a measurement gap may be implied rather than explicit. Isn't this a case in point? Output-level can't be related to gain without an input-level as a reference - by definition.

To clarify, this is not about debating exact terminology so much as getting at a unifying principle of some sort. Trevithj (talk) 04:53, 20 October 2014 (UTC)

In the negative feedback amplifier, no source uses the term measurement gap. Rashid and some other authors use the term error signal] for I/(1+βA), which is a fixed quantity for any given set point I, feedback factor β, and open-loop gain A. Brews ohare (talk) 05:31, 20 October 2014 (UTC)

I partially agree with Brews in this case (I don't agree that the error signal is "fixed" by these things, as that ignores the important things about feedback paying attention to the output). Trying to unify around a concept that is foreign to engineers familiar with feedback amplifiers does not seem like a good direction. And I don't see what "gap" you believe might be implied in the example I cited. Dicklyon (talk) 05:36, 20 October 2014 (UTC)

Hmm. Trying to unify around a concept that is foreign to non-engineers unfamiliar with feedback amplifiers seems like a poor direction also. I'm not sure what level of understanding biologists or economists would be required to have in order to read this article.

Regards the "gap" (or whatever term you prefer) I mean that gain is input:output. If gain is constant, the output must change if the input changes. It follows from that in my mind that the input is the reference for the gain. Reference implies gap. Trevithj (talk) 08:17, 20 October 2014 (UTC)

Trevith: Yes, gain is output/input. Yes, if gain is fixed, that means output increases with input as in O=I /β. No, it doesn't follow that input is 'reference' for the gain. For instance, β is set by the feedback network. In the op-amp voltage amplifier example, it is R₁/(R₁+R₂). No, reference doesn't imply 'gap'. A gap is the difference between a measured value for an essential variable and a set point. Nothing is gained by loosening definitions to avoid the established terms used in sources. Brews ohare (talk) 14:56, 20 October 2014 (UTC)

Nothing is gained by tightening definitions to avoid generalization either. A set point is a specific type of reference.

However, I stand corrected: the input (times the desired gain) is the "set point" for the output. Trevithj (talk) 18:20, 20 October 2014 (UTC)

No, the input I is the "set point" for βO, I–βO is the 'gap'. Brews ohare (talk) 18:57, 20 October 2014 (UTC)

Reverting Op-amp POV/bloat

In this revert I tried to make sense of Brews's recent bloat to the op-amp section. It seems to have been intended to support some kind of point he has been trying to make here, perhaps. But the use of two essentially equivalent op-amp circuit figures has no support, and the many words to say it's just like the amplifier analyzed in the previous section seem unnecessary. So I tried to simplify. Dicklyon (talk) 02:57, 16 October 2014 (UTC)

What is omitted is the equivalence between the depicted op amp circuit and the negative feedback amplifier that results if the triangular box outlining the op amp part of the figure (which is purely decorative and non-functional) is removed. This is an important point that was not immediately recognized by Dick or myself. Brews ohare (talk) 06:10, 16 October 2014 (UTC)

I don't understand that point. The triangle obviously has no functional role, and removing it obviously does nothing. Dicklyon (talk) 16:07, 16 October 2014 (UTC)

That is the point: the op amp circuit is the same as a voltage amplifier based on Black's circuit. This point is obvious looking at this circuit, but is not obvious without it. That is why the point is worth making. Brews ohare (talk) 19:20, 16 October 2014 (UTC)

Circuit with general op-amp symbol

The deletion of the original circuit is somewhat inadvisable for the same reason. This circuit is the typical form used as a circuit diagram, and a reader is more likely to encounter this version than the less general representation of the op-amp of the other figure. It might be noted that the general op-amp symbol need not represent the more detailed figure, and even the ideal op amp has Figure 16.2 four different internal interpretations. Brews ohare (talk) 17:56, 17 October 2014 (UTC)

Only one of those four is the infinite-input-impedance zero-output-impedance device under discussion. Dicklyon (talk) 05:21, 18 October 2014 (UTC)

Dick: You don't seem to have in mind presenting matters so the novice reader can make sense of the literature. Presenting the reader with the op amp symbol most often found is to begin with the prevalent and familiar and then to proceed with a particular simplification to provide the connection with a simple version of Black's amplifier. Presenting matters briefly, assuming context known to the initiated while incurring opacity for general readership, is not the goal of WP. Brews ohare (talk) 06:33, 18 October 2014 (UTC)

If anyone besides Brews sees a reason for two drawings of the op amp with feedback, I'll let it be. But without that, it seems clear that the consensus is that we don't need it. So I took one out again. Dicklyon (talk) 02:44, 19 October 2014 (UTC)

The reason for two diagrams is obvious: one involves the symbol for the general op amp and the other does not. Brews ohare (talk) 04:50, 19 October 2014 (UTC)

The reverted version of this subsection has a number of improvements over the existing misleading version. The reverted version derives the gain for the ideal circuit using the ideal op amp properties (infinite gain) and derives the gain for the simplified finite gain op amp circuit based upon its properties instead of mixing the two up. It also makes clear that there is a connection to the negative feedback voltage amplifier based upon their having the same gain, instead of a confusing abridged derivation that seems to suggest that voltage division is all that is involved.

Dick, you have a well-established desire to keep WP down to some bare-bones near dictionary-like collection of entries. That is your personal aesthetic and in many cases, this being one example, this aesthetic impedes transparency of presentation by combining ideas best separated, and eliminating context. Brews ohare (talk) 16:44, 19 October 2014 (UTC)

Circuit with general op-amp symbol

Please do not pretend to understand my aesthetic. Dicklyon (talk) 19:30, 19 October 2014 (UTC)

Not an understanding so much as a description. Brews ohare (talk) 21:22, 19 October 2014 (UTC)

Please address the several approaches to this circuit that are based upon different models: (1) the real op amp with non-ideal and finite gain, various impedances, offsets, etc., (2) the ideal model used in virtually all first-cut op-amp circuit design with infinite gain, zero output impedance, infinite input impedance, no offsets, etc. (3) the ideal op amp with finite simple gain but no other complications that is used to make contact with Black's circuit. Brews ohare (talk) 16:05, 21 October 2014 (UTC)

It's my contention that the usual gain derivation based upon zero difference between the op amp inputs should be presented because it employs the standard zero-order approach to analyzing op amp circuits. It does not make contact with Black's circuit. The finite gain ideal circuit does connect with Black's and leads to Black's formula for the gain, A/(1+βA). Then voltage division provides β. Of course, β plays no role whatsoever in the zero-order approach.

Apparently you feel no remorse in failing to provide connection to standard op-amp analysis, nor in mashing together the two gain calculations based upon different assumptions. I think that is a disservice to the general reader. Brews ohare (talk) 16:27, 21 October 2014 (UTC)

Is the error signal fixed?

Dicklyon has objected that the error signal in the negative feedback amplifier is not 'fixed', as that would imply we "ignore the important things about feedback paying attention to the output".Dicklyon

I'd like to engage in some discussion of this point, as it is at the crux of the views held by Trevithj, GliderMaven, and DaveApter. First, some terminology:

The term 'error' here is short for 'error signal' as defined by Rashid, for example.1. It refers to the signal entering the open-loop amplifier of nominal gain A and its mathematical expression is:

$I-\beta O={\frac {I}{1+\beta A}}\ .$

The quantity β is the feedback fraction, set for example as β = R₁/(R₁+R₂) in the simple op-amp voltage amplifier of the article. The quantity I is the input signal, identified by Rashid as the 'input or reference signal', and O is the output.

If I is a reference signal, we may suppose that it is a given, provided by some signal source. The feedback factor β also is a given, set by the feedback network. I assert that the nominal gain A also is a given (pretty much what I mean by 'nominal'), which means that the nominal error signal can be calculated in the abstract, in advance of operation, without reference to what the amplifier actually is doing. Perhaps Dicklyon is right that the 'error' is not fixed, if that means it is independent of fluctuations in A, but that is not the point. More clearly, the point is that whatever the value of A, the error signal is calculable without need to monitor system behavior: the error signal is calculable independent of a measurement of system performance.

The role of the nominal open-loop gain A appears to be a bone of contention:

"If your amplifier is ideal, and you can know or control its gain accurately, and it doesn't distort and has no noise, then yes, you're right. But a better idea is to monitor its output using negative feedback, as Black showed" Dicklyon

Now, I think my nominal A almost corresponds with Dick's 'if' above. I refer to a nominal open loop gain that is known. That hypothetical knowledge does not require that A doesn't distort or that A can be controlled, which are practical issues that may interfere with knowing how the real A in an actual amplifier compares with its nominal A, but that does not enter this determination of the nominal error signal, a calculation in principle.

The contention seems to be that this calculation of the nominal error signal does in fact show that the nominal error has nothing to do with monitoring of how the amplifier actually works in the field. But in practice the real A differs from the nominal A, one can never have exact knowledge of the real A, so such a demonstration based upon a nominal A is meaningless.

It is asserted that the 'real' operation of this circuit involves a fluctuating real A, and the circuit feedback as it really works, automatically deals with these fluctuations and is the true meaning of Black's circuit.

To this assertion I have agreed that, yes indeed, Black stressed the independence of his closed-loop gain from fluctuations, say ΔA, away from the nominal value A, and this independence is indeed a key motivation behind his invention. But the standard textbook discussion of this gain desensitivity is built around the closed-loop gain expression:

${\frac {O}{I}}={\frac {A+\Delta A}{1+\beta (A+\Delta A)}}\approx {\frac {1}{\beta }}\ ,$

which shows that so long as A+ΔA is large, there is no effect of ΔA.

Another key point is that this analysis in no way suggests that the feedback reduces ΔA. What it does do is make the closed-loop gain insensitive to ΔA. But ΔA is left free to do its own thing unaffected by the feedback. This freedom seems to be a point those assembled find hard to face. In my opinion, this reluctance is due to a background in error-controlled regulation that, if it were at work here, would counteract the variations ΔA, and attempt to reduce them to zero.

What is the opinion of those assembled as to the meaning of these textbook analyses? Is the nominal error analysis meaningless? Is the desensitivity analysis inadequate? Can you all address these analyses directly and identify what is missing, rather than simply asserting your own intuitive understandings without identifying their point of departure from the textbook approach? Brews ohare (talk) 16:30, 20 October 2014 (UTC)

And, if possible, can you source your reservations so that they can be put into the WP article without incurring a charge that they are unsourced and so WP:OR? Brews ohare (talk) 17:10, 20 October 2014 (UTC)

"What it does do is make the closed-loop gain insensitive to ΔA. But ΔA is left free to do its own thing unaffected by the feedback."

Yes. We all know.

"This freedom seems to be a point those assembled find hard to face."

The loop is insensitive to the open loop gain. We know. I've been formally taught feedback theory, much more than you have. I've actually been taught how to build negative feedback amplifiers, I know how to analyse, design and test them for stability. I've actually implemented negative feedback loops on many occasions. You're the one that hasn't been taught this. Reading your posts is like reading the thoughts of a slow child.GliderMaven (talk) 03:46, 21 October 2014 (UTC)

May I take it that you read the above carefully enough to understand that the closed-loop gain is insensitive not only to A, but also to its fluctuations ΔA; and moreover, that according to the textbook analysis, the feedback exerts no reduction upon ΔA? If so, perhaps you can help the others to understand this too? Brews ohare (talk) 05:20, 21 October 2014 (UTC)

You did not comment upon the topic giving this thread its name. In summary it says the 'error signal' amplified by the open-loop amplifier can be calculated in advance of operation (in principle), with no need to monitor how the operation is going, a contrast with error-controlled regulation which (in principle) measures and corrects a gap calculated as operation takes place. This difference separates the conceptual basis of the negative feedback amplifier from error-controlled regulation, a point denied by those assembled here. Brews ohare (talk) 14:38, 21 October 2014 (UTC)

Perhaps this way of arguing a distinction is redundant for someone who accepts that the negative feedback amplifier operates in a manner unaffected by fluctuations ΔA, and without affecting these fluctuations. Brews ohare (talk) 14:44, 21 October 2014 (UTC)

What nonsense. Feedback is a monitoring of the output because the open-loop gain, the distortion, the noise, and other oddities of the amplifier are not known or calculable in general. The feedback reduces these things by striving to keep the error small. Dicklyon (talk) 02:59, 22 October 2014 (UTC)

Dick: You have chutzpah to say the above summary of textbook results is 'what nonsense'. Your own view is that in the negative feedback amplifier, "feedback reduces these things [the distortion, the noise, and other oddities of the amplifier] by striving to keep the error small". This remark is (1) not sourced, and (2) contrary to sources so far presented.

One could say that feedback reduces the influence of these things, but it does not reduce them, as the desensitivity analysis shows. Feedback also accomplishes this desensitivity without reducing the error I/(1+βA). SO for example, if ΔA is negative, feedback actually increases the error.

Dick you have reiterated this point of view of yours several times, and as yet have not a shred of source support for your opinion. You also have not addressed the sourced views presented at the outset of this thread to indicate any reservations you may have about them. In fact, you are on record as saying (i) they are correct within their imposed limitations and (ii) they treat only matters of secondary importance. When challenged on this last, you came up with the nonsensical view that the main role of feedback in the negative feedback amplifier was to reduce input noise by lowering the gain, directly contradicting sources.

To proceed you could (i) find some sources to support your views, and (ii) explain what it is you object to in the standard textbook analysis showing desensitivity is the key feature, and rejecting any role for reduction of fluctuations. Brews ohare (talk) 03:56, 22 October 2014 (UTC)

Yes, sorry, when I said "reduces these things" I meant "reduces the influence of these things" on the output (not the input). I have no objection to any standard textbook analyses; not sure why you think I have. Dicklyon (talk) 04:02, 22 October 2014 (UTC)

It could be because you referred to the above outline with the reaction "what nonsense" and now you are agreeing with it. That is a bit confusing. Brews ohare (talk) 04:05, 22 October 2014 (UTC)

No, I am not agreeing with you that the error is "fixed" or that the output does not need to be monitored. The error is in fact obviously computed by using the output. If you try to compute it from the input, and feed that into the amplifier, you'll just have a noisy uncertain-gain distorting feed-forward system. Dicklyon (talk) 04:08, 22 October 2014 (UTC)

I assume we agree that the error is what Rashid calls the 'error signal' I/(1+βA)? If so, you will notice that this quantity does not involve the output. Brews ohare (talk) 04:17, 22 October 2014 (UTC)

The 'error signal' goes into the open-loop amplifier of gain A to produce the output AI/(1+βA). The input is considered to be a signal, and if it contains noise, that is treated as part of the signal - the amplifier doesn't filter that out. The gain may have fluctuations ΔA, but they don't affect the output, and they are not reduced in magnitude by the feedback. I gather that you agree with the textbooks on that. Brews ohare (talk) 04:40, 22 October 2014 (UTC)

That is exactly what I disagree with: expressing the error as a function of input alone, ignoring output. The error is $I-\beta O$. The equality you wrote at the outset is either an approximation, or a definition of an instantaneous A, but not a statement that the error doesn't require monitoring the output. I haven't seen anything to disagree with in books about this. Rashid's figure 10.3 and text seem pretty explicit about needing to monitor the output. Actually, I disagree with Rashid that this formulation makes much sense in the case of positive feedback; or that it is a great way to conceptualize negative feedback; but it's the error-controlled regulation view that Trevithj likes. Dicklyon (talk) 04:59, 22 October 2014 (UTC)

Dick, I think we should look at this carefully. I'd guess you do not doubt that the math produces an error signal of I/(1+βA). And I imagine you agree the input is some known quantity. Likewise the feedback factor β is known from the feedback network. And the gain A is determined by its construction and components. So the parameters I, A, and β are what we would agree are independent variables. The error signal is a dependent variable determined by these independent variables. The output is also a dependent variable determined by these independent variables. These are the mathematics of the amplifier. Now math is not necessarily the intuitive way to look at things, but it is hard to argue with it. How would you go about squaring your intuition with the math? Brews ohare (talk) 05:34, 22 October 2014 (UTC)

Rashid

By consensus, further discussion here would not be helpful for the article. Johnuniq (talk) 23:41, 24 October 2014 (UTC) & GliderMaven (talk) 03:54, 25 October 2014 (UTC)
The following discussion has been closed. Please do not modify it.
General feedback configuration Rashid, Microelectronic circuits: Analysis & Design, and his Fig. 10.3 in particular, is cited by Dicklyon as "pretty explicit about needing to monitor the output." Rashid's Fig. 10.3 is equivalent to that shown at the right, and the caption is his. He denotes the input signal by Si, the output signal by So, the feedback return signal by Sf, the input (error signal) to the open-loop amplifier of gain A by Se = Si–Sf and the feedback factor by β. This is the extent of Rashid's description so far as I can see, and there is no reference to "monitoring" other than the fact that a fraction of the output is fed back to the input summer. Dicklyon also says that: "it's the error-controlled regulation view that Trevithj likes". Yet, there is no reference here to error-controlled regulation and there is no 'gap' or 'set point' mentioned, so I do not follow this conclusion. My query for Dick is - what is there in Rashid's treatment that (i) supports these remarks, or that (ii) is in any way different from the treatment of S&S or G&M? Brews ohare (talk) 16:16, 22 October 2014 (UTC) In his equation 10.7 Rashid derives the error signal as: $S_{e}=S_{i}-S_{f}=S_{i}-\beta S_{o}=S_{i}-{\frac {\beta AS_{i}}{1+\beta A}}={\frac {S_{i}}{1+\beta A}}\ .$ Regarding this final form of expression for the error signal, Dicklyon writes: "The error is I–βO. [In Rashid's notation, this error is Si–βSo]. The equality you wrote at the outset [In Rashid's notation, this equality is to Si./(1+βA)] is either an approximation, or a definition of an instantaneous A, but not a statement that the error doesn't require monitoring the output." The first option, that this final expression for Se is an approximation, is incorrect because it follows directly from the definitions supplied in the figure and listed in Equations 10.1-10.3 by Rashid. The second option, that this relation is a definition of the open-loop gain is also incorrect, as this gain is defined as the amplification provided by the open-loop amplifier of its input in order to form its output. This amplification could be an instantaneous value, but it isn't necessarily so. It doesn't matter. This gain A is determined by the amplifier construction, components, voltage supplies, temperatures and so forth, that make A a property of the open-loop amplifier unaffected by its insertion into the negative feedback circuit. We may not have practical knowledge of what the value of A is, but for the purpose of this abstract analysis, we assume omniscience. Dicklyon provided an earlier description of the problems with Rashid's formulation as: "The error is in fact obviously computed by using the output. If you try to compute it from the input, and feed that into the amplifier, you'll just have a noisy uncertain-gain distorting feed-forward system." This remark seems to suggest that the equation for the error Se involving the output signal explicitly: $S_{e}=S_{i}-\beta S_{o}$ is somehow superior to that based upon the independent variables Si, A, and β (the values of which are independently set by the construction of the signal source, the amplifier and the feedback network): $S_{e}={\frac {S_{i}}{1+\beta A}}\ .$ This form for the error signal shows that it is determined by the independent variables Si, A, and β all of which have values known from considerations related to their independent construction (signal source, amplifier components, feedback network parameters), values that are unaltered by the incorporation of these parts in the feedback network. Looking at Rashid's derivation, it would seem that Dicklyon believes Rashid's equations are not entirely accurate, allowing an incorrect algebraic conclusion that these two equations for Se are equivalent. That claim would seem to require a different formulation using different definitions that no source has provided. Brews ohare (talk) 16:16, 22 October 2014 (UTC) Summary I am sympathetic to Dick's efforts to generalize the standard treatment of the negative feedback amplifier to bring it more in line with error-controlled regulation, but so far that has yet to be accomplished, or sourced. It would seem that something like Dick's perspective would require some way to model how the operation of the open-loop amplifier changes when it is inside the feedback circuit, affecting its gain A. An example of such a model would calculate the state of the open-loop amplifier, its internal temperatures, voltages etc. as a function of the signal it is processing. Nothing this ambitious is attempted in the standard analysis. Brews ohare (talk) 16:16, 22 October 2014 (UTC) It may be noted that the standard analysis avoids any attempt to understand the operation of the open-loop amplifier, and treats its variations ΔA as a deus ex machina that has no effect on the operation of the closed-loop amplifier (if A is large enough) and vice versa. Brews ohare (talk) 16:27, 22 October 2014 (UTC) It is likely that a more sophisticated modeling of the open-loop amplifier would also be accompanied by a treatment of known non-ideal behaviors of the feedback amplifier, such as bilateral components, parasitic feed back and feed forward, and so forth. Brews ohare (talk) 17:38, 22 October 2014 (UTC) I'm not actually interested in trying to "generalize the standard treatment of the negative feedback amplifier to bring it more in line with error-controlled regulation." In answer to some of your questions, I believe the subscript "e" in Rashid is for "error", in the feedback regulation sense; so yes he has an error signal, dependent not just on the input but on the monitored (fed back) output. The equation that puts it into an input-only form is only applicable when there is no noise in the amplifier, no distortion in the amplifier, and A is known. Feedback is used when A is unknown or a random variable, as Rashid makes clear. I haven't checked to see what he says about noise and distortion, but Black certainly does not omit those, even if some simple algebraic treatments approximation those as zero. Dicklyon (talk) 01:10, 23 October 2014 (UTC) (1) Rashid's notation Se for 'error signal' is introduced in the first paragraph above along with his other notation. (2) Rashid's equation 10.7 is quoted above: $S_{e}=S_{i}-S_{f}=S_{i}-\beta S_{o}=S_{i}-{\frac {\beta AS_{i}}{1+\beta A}}={\frac {S_{i}}{1+\beta A}}\ .$  Rashid's Eq. 10.7 The first form, Se=Si–βSo is what you call the input-output form, and the last form Se=Si./(1+βA) is what you call the input-only form. (3) You say the: "input-only form is only applicable when there is no noise in the amplifier, no distortion in the amplifier, and A is known". This remark is vague, and possibly erroneous. I don't know what kind of noise you refer to - the equation works regardless of possible fluctuations in A. I don't know what kind of distortion you are referring to - the equation works regardless of possible nonlinearities in A. (4) You say that the "input-only form" works only when A is known. Of course, A is known in the sense of being knowable in principle. There is no claim that it has been measured exactly, and that isn't a requirement of a theoretical analysis. I don't know why this is an objection. It also works only when β is known. That these variables are known is the presumption of the formulation. You cannot do a gain analysis of the closed-loop amplifier without these values. (5) You say "Feedback is used when A is unknown or a random variable, as Rashid makes clear." Perhaps you can link the remarks by Rashid that present this limitation of feedback. I think this idea is incorrect, or at least out of context, and makes Rashid's entire feedback chapter incomprehensible. What do you actually mean here? Dick, your remarks appear to confuse Rashid's presentation and do not address the issues raised. You seem to imply that Se=Si/(1+βA) is a limited expression while Se=Si–βSo is more general. But they are equivalent according to Rashid's equation 10.7 quoted above. Brews ohare (talk) 03:38, 23 October 2014 (UTC) Please see Rashid's section 10.3.2, which treats A as an unknown and fluctuating quantity. It is therefore not possible to treat the error signal as "fixed" or a function of system constants. The feedback ratio Beta is more often treated as a constant, because it is created by stable passive components, but Rashid also looks at that as fluctuating or unknown, in 10.3.3. And it doesn't really work in general to treat A as the instantaneous ratio of output to input in such a way as to include noise, since the input may be zero. Distortion perhaps one could fold into gain fluctuation, as Rashid does in 10.3.5, but that's not usually how it's handled (especially not workable for crossover distortion). Rashid pretty much ignores noise in his feedback treatment. He certainly never treats the A as fixed when showing how the error signal relates to the feedback factor, nor suggests that the error signal count be generated any way other than by monitoring the output. Dicklyon (talk) 03:55, 23 October 2014 (UTC) As to Se=Si–βSo being more general than Se=Si/(1+βA), yes, it is clear especially if you look at special cases such as when Si is zero but So is nonzero, as can happen with noise or offset of the amplifier. If your model does not contain any noise or offset, and you're using the instantaneous ratio of output to input to define A, you still have the problem that when both the input and output are zero you have undefined A, so the latter form remains undefined rather than zero. So even as algebraic abstractions from too-simple model, the former is more generally correct than the latter. Dicklyon (talk) 04:05, 23 October 2014 (UTC) Dick, I'll look at your remarks about Rashid's discussion tomorrow. As for your last paragraph, it is clear from Rashid's equations 10.1-10.3 defining his notation that within his formulation there is no difference at all between the forms for the error signal of his Eq. 10.7. So for your claim that the 'input-output form' is more general to hold true, a formulation more general than this one of Rashid's is necessary, one in which the input-output form holds, but the 'input-only' form is inadequate or more limited. Where is that more general set-up for the analysis? Brews ohare (talk) 05:05, 23 October 2014 (UTC) Dicklyon's comments on Rashid According to Dick: 1. "Please see Rashid's section 10.3.2, which treats A as an unknown and fluctuating quantity. It is therefore not possible to treat the error signal as "fixed" or a function of system constants." Dicklyon (talk) 04:05, 23 October 2014 (UTC) Section 10.3.2 Gain Sensitivity is not different from other standard treatments of gain fluctuations in which A may become (A+δA). The desensitivity analysis proceeds using the same formulation identified in Rashid's Eqs. 10.1-10.3 that lead to his Eq. 10,7: $S_{e}=S_{i}-S_{f}=S_{i}-\beta S_{o}=S_{i}-{\frac {\beta AS_{i}}{1+\beta A}}={\frac {S_{i}}{1+\beta A}}\ .$  Rashid's Eq. 10.7 Rashid's fluctuation analysis uses the formulation in which A is known and the gain subject to departure (A+δA) also is known in order to find how much such a change in A affects the standard closed-loop gain expression A/(1+βA). The variation in gain is found using the d/dA derivative of the standard gain expression and therefore assumes the the standard gain expression holds for all values of A., including (A+δA). Nothing here suggests that "it is therefore not possible to treat the error signal as "fixed" or a function of system constants." That is exactly what Rashid (and every other source) does. The change δA is attributed by Rashid to "changes in temperature and operating conditions of active devices". These changes result in a gain (A+δA) that is determined, just as is A, by the system components at their new bias points and temperatures. That means A changes, not in a manner affected by feedback considerations, but for reasons that are equally applicable when the open-loop amplifier is not in the feedback circuit at all. 2. "The feedback ratio Beta is more often treated as a constant, because it is created by stable passive components, but Rashid also looks at that as fluctuating or unknown, in 10.3.3. Dicklyon (talk) 04:05, 23 October 2014 (UTC) Section 10.3.3 Feedback Factor Sensitivity, proceeds in the same fashion as the treatment of gain variation, calculating the d/dβ derivative of the standard gain expression. The analysis therefore assumes the the standard gain expression holds for all values of β. 3. "And it doesn't really work in general to treat A as the instantaneous ratio of output to input in such a way as to include noise, since the input may be zero." Dicklyon (talk) 04:05, 23 October 2014 (UTC) Dick, you appear to be thinking of the noise generated by the open-loop amplifier itself independent of any input signal. That is, A fluctuates to become (A+δA). This situation is described by Kal, §6.3.1 Gain Stability and employs the standard formulation of Rashid's Eqs. 10.1-10.3. Even if the input signal actually is zero, the amplifier gain does not depend upon the physical presence of a signal but is the gain that would be seen if there were a signal, no matter how small. It is defined as A = output/input regardless of the actual physical presence of an input signal. 4. "Distortion perhaps one could fold into gain fluctuation, as Rashid does in 10.3.5, but that's not usually how it's handled (especially not workable for crossover distortion). Dicklyon (talk) 04:05, 23 October 2014 (UTC) Section 10.3.5 treats a nonlinear open-loop transfer characteristic, an S-shaped curve of output versus input depicted in Rashid's Figure 10.5. He breaks the curve up into approximate straight line segments and shows that the standard gain expression applied in each region with gains A1, A2... leads to a closed loop gain of 1/β in each segment provided the gains all are large, and renders the closed-loop gain independent of the nonlinearity in A. Again it therefore assumes the the standard gain expression holds for all values of A. 5. "Rashid pretty much ignores noise in his feedback treatment. He certainly never treats the A as fixed when showing how the error signal relates to the feedback factor, nor suggests that the error signal count be generated any way other than by monitoring the output. Dicklyon (talk) 04:05, 23 October 2014 (UTC) To see the standard treatment of noise reduction for noise introduced (like δA) inside the feedback loop, look at Kal, §6.3.2 Noise Reduction. It also uses the standard formulation. The remark: "He certainly never treats the A as fixed when showing how the error signal relates to the feedback factor" contradicts Rashid's derivation of the error signal. What Rashid and everybody else does is to use A as an algebraic variable that takes on the value of the open-loop gain defined as the gain relating the input to this amp to its output when the amp is considered in isolation. This approach leads to the relation between the error signal and the feedback factor given by Se = Si./(1+βA). See Rashid's Eq. 10.7 reproduced above. And Dick's remark: Rashid "certainly never suggests that the error signal cou[ld] be generated any way other than by monitoring the output." is vague indeed. Rashid 'never suggests' a great many things. However, it is clear that the standard gain expression A/(1+βA) results because feedback is present. It is equally clear that the output is a consequence of amplifying the error signal Se = Si./(1+βA) that is determined by the three parameters: Si., β, and A; all of which have values set (respectively) by the operation of the signal source, the feedback network, and the open-loop amplifier, just as they would perform in isolation, outside the feedback amplifier. Summary Although I have dealt in detail with Dicklyon's commentary here, the basic issue remains as stated in the thread above: Using Rashid's formulation of his Eqs. 10.1-10.3 leads to his Eq. 10.7 (reproduced above) stating the equivalence of all forms for the error signal Se. Therefore, a justification of Dicklyon's claim that the input-output form of the error signal Se=Si–βSo is more general than the input-only form Se=Si./(1+βA) requires a formulation different from Rashid's (and every other textbook) using different definitions that no source has provided. Brews ohare (talk) 17:01, 23 October 2014 (UTC) Almost everything you are saying is either nonsense or a misinterpretation of what I've said. Go back to what started this discussion. You claimed that the 'error signal' amplified by the open-loop amplifier can be calculated in advance of operation (in principle), with no need to monitor how the operation is going, a contrast with error-controlled regulation which (in principle) measures and corrects a gap calculated as operation takes place. This is still nutty, to claim to be able to characterize a feedback amplifier without feedback from the output, which is where the unknowns and non-idealities show up, just as in the systems that feedback controllers control. Your disclaimer of "in principle" really means if you ignore noise and distortion and unknown fluctations. OK, fine, if you there's no noise, no distortion, and no uncertianty in the forward gain, then you can calculate the error signal without monitoring the output. So what? Anyway, have fun going on about it; I'm going to be off the grid for a three weeks, so someone else might want to play. Dicklyon (talk) 04:51, 24 October 2014 (UTC) Dick: Calling my remarks nonsense is not helpful and is itself nonsense. Here are the facts as simply as they can be stated: Rashid's formulations is his Eqs. 10.1-10.3. They state: $S_{o}=AS_{e}\ .$   (1) $S_{e}=S_{i}-S_{f}\ .$   (2) $S_{f}=\beta S_{o}\ .$   (3) Now simple algebraic manipulation leads to: $S_{e}=S_{i}-S_{f}=S_{i}-\beta S_{o}=S_{i}-{\frac {\beta AS_{i}}{1+\beta A}}={\frac {S_{i}}{1+\beta A}}\ .$   Rashid's Eq. 7 Your statement is that Se=Si–βSf is a more generally valid statement than Se=Si./(1+βA). Inasmuch as Rashid's formulation shows them to be equivalent, your remark is not compatible with Rashid's formulation (or, you don't understand algebra, if that is your preference). Brews ohare (talk) 05:17, 24 October 2014 (UTC) The algebra is fine. The formulation (equation 1) is limited to the no-noise, no-distortion case. Equation 2 is valid more generally than that. And your interpretation of not needing to monitor the output relies on A being known exactly. I still don't see why you're trying to describe feedback while pretending you don't need to feed back the output. Dicklyon (talk) 06:03, 24 October 2014 (UTC) Yes, the algebra is fine. The rest of your remarks are incorrect. You have no source for any of them. Without sources to back up your formulation of operation, which directly contradicts the traditional textbook approach as itemized in my comments above, these ideas of yours remain your own. Brews ohare (talk) 13:03, 24 October 2014 (UTC) Your remark upon the limitations of Eq. 1 is unsourced imagination that would seem to apply equally to Eq. 3 and invalidate your (erroneous) claims for the greater generality of the input-output formulation of the error signal. Your remark that Eq. 2 has greater generality than Eq. 1 also is unsupported. It could be taken as the definition of a summer, just as Eq. 1 is the definition of gain. Hard to argue over definitions. Eh? And your interpretation of my comments is wrong, a strawman portrayal. Brews ohare (talk) 13:19, 24 October 2014 (UTC) Look, basically, so far as I am, or as far as I can tell, everyone else is concerned, you've misunderstood this class of circuit. Your rants on the talk page are not persuading anyone. Given that, we are not letting you write any of your non consensus views into the article, and if you do so, they will be reverted without mercy. Given that, you are completely wasting your time on the talk page, nobody buys a word you say. Please stop wasting your own, and everyone else's time.GliderMaven (talk) 20:23, 24 October 2014 (UTC) GliderMaven: There are 3 equations here defining gain A, feedback factor β, and the difference or 'error signal'. These 3 equations are combined by Rashid to provide several equivalent forms for the error signal. But you find this simple matter too complex and prefer to rant that "nobody buys a word" of it. Too complex, too well referenced, and too contrary to your unsourced and incorrect prejudices. The issue, as Dick sees it, is that Rashid's (and every other textbook's) 3 definitions don't apply to the 'real' negative feedback amp, but only to a severely compromised abstraction of it. There is no doubt that it is an idealization, but Dick's notions about a better model are not supported by sources. Your approach to resolving this matter is simply to spit. Brews ohare (talk) 22:17, 24 October 2014 (UTC)

Collapsing discussions

I collapsed this section, and was reverted:

• Johnuniq 23:41, 24 October 2014 close discussion: this is a gentle hint; we can take it for admin attention if you want
• Brews ohare 02:00, 25 October 2014 This action is not necessary: things have crystallized

What do others think? Of course it is unusual to collapse discussions, but the activity on this talk page is already unusual. At 06:00, 14 October 2014 above, I noted that this talk page has had 1375 edits since 6 June 2014—just over 10 edits per day for 130 days. There have been 248 edits since then—over 20 edits per day for 11 days. Here are some numbers:

Edits to talk page since 6 June 2014

Editor	Number of edits	Percentage
Johnuniq	10	0.6%
Lowercase sigmabot III	11	0.7%
JohnBlackburne	21	1.3%
Nigelj	24	1.5%
DaveApter	31	1.9%
GliderMaven	78	4.8%
Trevithj	114	7.0%
Dicklyon	153	9.4%
Brews ohare	1181	72.8%
Total	1623	100%

If anyone wants to collapse the parent section, including this subsection, please do so. Or, should there be a meta-discussion about how discussions should occur? There is no reason this topic should require this much discussion that I can see. Do people want this much talk? Is there any likelihood it will conclude in a reasonable time? Johnuniq (talk) 03:21, 25 October 2014 (UTC)

I completely agree, and I intend to collapse any further pointless discussion by Brews Ohare or anyone else for that matter, unless more than one person complains.GliderMaven (talk) 03:54, 25 October 2014 (UTC)

I would object if there was any sign that the discussions were converging towards any sort of consensus. But they clearly aren't. So I also support the collapse. Trevithj (talk) 09:31, 25 October 2014 (UTC)

The discussion of Rashid is between Dicklyon and myself as others here have not participated. So this action is really just a closing of discussion with no attempt at clarification. The issue involved is the simple one of Dicklyon's unsourced challenge to the generality of Rashid's approach, which happens to be the universal approach of all textbooks. Apparently all but Dicklyon and myself feel unmoved to comment upon his original research, and consensus is to collapse this discussion as a substitute. Brews ohare (talk) 14:24, 25 October 2014 (UTC)

The purpose of the talk page is to discuss things that may actually make a contribution to the article. Where any discussions are clearly not reaching consensus, as here, they will be collapsed.GliderMaven (talk) 15:49, 25 October 2014 (UTC)

It is not WP policy for non-administrators to collapse discussions, whether or not it is the supposed consensus of non-contributing bystanders that a discussion is pointless. I don't agree that it is pointless to emphasize the universal textbook view of the negative feedback amplifier in the face of WP:OR, and oppose the disdain of the those present for sources in favor of personally held intuitions. Brews ohare (talk) 17:23, 25 October 2014 (UTC)

On the contrary, we're all over those sources; we just don't agree with your interpretation of them. We can certainly get an administrator here if you prefer. The likely outcome will be you getting blocked. I'd like to remind you that this is not a WP:FORUM. If you prefer we could refactor the discussion to a subpage off your own user page where you can continue it (if anyone else wants to, which I doubt), but I think, without wishing to put words in anyone else's mouth, that everyone else is agreed drawing a line under this here.GliderMaven (talk) 17:46, 25 October 2014 (UTC)

Recent suppression of Talk page contributions

By consensus, further discussion here would not be helpful for the article.GliderMaven (talk) 03:54, 25 October 2014 (UTC)
The following discussion has been closed. Please do not modify it.
The Wikipedia:Talk page guidelines cited in connection with collapse of talk-page discussion by Johnuniq contains the paragraph Off-topic posts, which does not suggest deletion, but collapse of off-topic material with a show/hide facility. That approach was used by Johnuniq to collapse two entire sehctions of Talk-page discussion of Rashid's derivation of the 'error signal' in the negative feedback amplifier, with the reason By consensus, further discussion here would not be helpful for the article Whether or not these editors think discussion of Rashid's formulation (typical of all textbooks on the subject) is 'not helpful', there is no doubt that it is on topic, and its collapse is unwarranted according to the guidelines. The same applies to the repeated collapse of this discussion by GliderMaven, another violation of WP policies and guidelines. The purpose of these actions, IMO of course, is that these two editors, who have not contributed to the content of the discussion of Rashid, wish either to suppress this examination or possibly just to interfere with my attempts. Brews ohare (talk) 18:52, 31 October 2014 (UTC) In essence, the issue that these editors do not wish to see discussed is the interpretation of Rashid's Eqs. 10.1-10.3. They state: $S_{o}=AS_{e}\ .$     (10.1) $S_{e}=S_{i}-S_{f}\ .$   (10.2) $S_{f}=\beta S_{o}\ .$     (10.3) and their simple algebraic manipulation leads directly to: $S_{e}=S_{i}-S_{f}=S_{i}-\beta S_{o}=S_{i}-{\frac {\beta AS_{i}}{1+\beta A}}={\frac {S_{i}}{1+\beta A}}\ .$   Rashid's Eq. 10.7, p. 645 Eqs' 10.1-10.3 are definitions of gain A (Eq. 10.1), the error signal Se input to the open-loop amplifier (Eq. 10.2) and the definition of the feedback fraction β (Eq. 10.3). They lead in Eq. 10.7 to several equivalent forms for the error signal Se. Brews ohare (talk) 18:54, 31 October 2014 (UTC) Some controversy has arisen here on this Talk page over the interpretation of the "input-only" form (the last version in 10.7). This form of the error signal shows that it is determined by the input signal Si from the external signal source, the open-loop gain A determined by the amplifier construction, and by the feedback factor β determined by the feedback network, all of which parameters are therefore fixed by their own stand-alone construction, entirely apart from their incorporation in the feedback amplifier. The formula for the error signal depends upon the presence of feedback, of course, but its value is set by external parameters and is not changed during operation. This fact is found disturbing by some assembled here, who hold the (unsourced) belief (contrary to Rashid's Eq. 10.7) that the 'error signal' is not set by external parameters that are determined apart from, and independent of, feedback operation. Rather, these editors believe, the error signal plays the role of a 'performance gap' that is measured and minimized by feedback during operation, as occurs within error-controlled regulation, a different use of feedback integral to the operation of such error-minimization systems. Brews ohare (talk) 18:55, 31 October 2014 (UTC) Dicklyon has proposed that various considerations result in "Se=Si–βSo being more general than Se=Si./(1+βA)", limiting the generality of the 'input-only ' form of the formula and potentially undermining the conclusion that outside parameters fix the value of the error signal. As no-one denies that Rashid's 'input-only' form for the error signal is equivalent to all the other forms as is shown by Rashid's Eq. 10.7 displayed above, such controversy is resolved by establishing under just what circumstances the defining equations 10.1-10.3 are suitable. In particular, Dicklyon has suggested that Eq. 10.1 defining the gain is unsuitable in the presence of noise, making the various forms of the error signal in Rashid's 10.7 equivalent only under restrictive conditions (that remain to be elaborated upon and sourced). Although Dicklyon has not suggested it, his ideas seem to fit a modified version of Black's circuit proposed by Marc Thompson that includes an external noise disturbance inside the feedback loop. Brews ohare (talk) 18:57, 31 October 2014 (UTC) Rather than engage in this discussion, GliderMaven and Johnuniq wish to cut this examination short. These editors may have missed the point of this discussion, or perhaps they are uncomfortable with its implications for their own views of the negative feedback amplifier as a form of error-controlled regulation. In either eventuality, the high-handed interference with a discussion pertinent to the literature on negative feedback is out of place and not suggested by WP:TPG: Off-topic posts . Brews ohare (talk) 16:29, 27 October 2014 (UTC) This and the other use of collapse above both are actions contrary to WP guidelines. Brews ohare (talk) 16:48, 27 October 2014 (UTC) In view of the simplicity of the item under discussion as explained above, it is no longer possible to think these editors have missed the relevance of this issue, which puts their actions in suppressing its discussion beyond the rational. Brews ohare (talk) 16:59, 27 October 2014 (UTC)

Reverts by Dicklyon

Dicklyon has said in other remarks that the feedback amplifier is a form of feedback control. However, contrary to Dicklyon's own expressed view, in this massive revert Dicklyon removed material that supports and sources this claim. This removed material outlines the key difference between this type of control and the more elaborate methods identified by the sources. The deleted explanation is as follows:

When a system, sometimes called a load or a plant, is characterized by a simple input/output model, it can be controlled by a single variable like the output of a negative feedback amplifier.¹ Then the negative feedback amplifier can be used as a type of feedback control, maintaining a stable control signal for the load or plant.² Such a controller is more rudimentary than those that employ measurements of the internal variables governing the plant, the so called full-state feedback or state-space approach.^3,4,5

Notes

¹Boris Lurie, Paul Enright (2000). Classical feedback control with MATLAB. CRC Press. p. xiii. ISBN 9780824703707.

²A simple example from Lurie & Enright cited below (their Figure 1.5 a) is the case where the 'plant' presents itself as a load resistor and the input signal to the amplifier is a voltage. The feedback amplifier then serves as an interface between the input signal source and the load that tends to keep the voltage across the load constant (presumed to be a 'plant' requirement). If the feedback amplifier were not present the voltage across the load would vary with changes in either the load resistance or in the output impedance of the signal source because they would constitute a simple voltage divider.

³Boris Lurie, Paul Enright (2000). Classical feedback control with MATLAB. CRC Press. p. xiii. ISBN 9780824703707.

⁴Shimon Y. Nof (2009). "§4.7: The emergence of modern control theory". Springer handbook of automation. Springer Science & Business Media. pp. 63 ff. ISBN 9783540788317.

⁵D Roy Choudhury (2005). "Chapter 11: State-variable formulation". Modern control engineering. PHI Learning Pvt. Ltd. pp. 522 ff. ISBN 9788120321960.

Dicklyon has removed this material with the one-line Edit Summary: Tangential bloat, not supported by the cited sources. It is obvious that the material is sourced and is hardly tangential. At a minimum, Talk-page explanation of this peremptory action is needed. Brews ohare (talk) 18:30, 30 November 2014 (UTC)

How do you separate an application of negative feedback from an approach that could be applied to it?

unproductive discussion collapsed
The following discussion has been closed. Please do not modify it.
This question posed by Dicklyon about the distinction between the negative feedback amplifier and state-space control is followed by this remark: The meaning and logic there escape me; no source supports these conclusions. The confusion here is born of impatience interfering with understanding. The logic of Dicklyon's remark is that "modern" control theory could be applied to the negative feedback amplifier, so how can it be a separate matter? That seems to be so. But the meaning of my remark, which is perhaps badly expressed in this one sentence, is very clear from what is said in the material Dicklyon reverted: the meaning is that the negative feedback amplifier belongs to the "classical" approach that ignores the internal variables determining the state of the controlled object, while the "modern" approach to control employs these variables. This division is remarked upon by all three of the state-space sources. To quote two of them: As linked above, Lurie & Enright define the "classical" approach as one where the object of control is characterized by "a rather simple input/output mathematical model." In particular, in their Figure 1.5(a) they show a negative feedback amplifier controlling the voltage across a resistor, which obviously fits the "classical" model where the controlled object is described by the input/output equation of Ohm's law: I=V/R. The same point is made by Choudhury who divides the evolution of controls between the "classical approach (up to 1956) and the "state variable approach" (post 1956). He characterizes the "classical" approach as one based upon using transfer functions for the system components, and the negative feedback amplifier falls into this category. About the comparison with the state-space approach he says: "The transfer-function approach confines to input-output behavior of linear systems only. On the contrary the state-space representation gives information about the internal behavior of the system as well as information about its input-output behavior." I think with this in mind it is clear that what I am trying to express is that the negative feedback amplifier, in its focus entirely upon single-variable external control of its controlled object, is to be distinguished from state-variable control that uses information about the internal state of the controlled object. That claim is supported by both these sources, and is obvious. Brews ohare (talk) 15:04, 4 December 2014 (UTC) The amp is a simple case of state-variable control. But what does this distinction that you want to draw have to do with the topic of the article? Dicklyon (talk) 02:13, 5 December 2014 (UTC) What makes it a simple example? It doesn't use internal variables of the controlled system. Different controllers do.See this. What are the consequences? It can control only systems governed by simple input/output models. Different controllers can control more complex objects and can control them more precisely.See this. Why should these differences be part of this article? Because the article is about negative feedback, and hence about how it is put to use. An article about motor vehicles might point out differences between cars and trucks. Brews ohare (talk) 03:10, 5 December 2014 (UTC)