Talk:Negative feedback

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[edit] The link

The link:

has been moved here, this isn't an esoteric topic, it refers to the engineering term.. Perhaps there ought to be a Esoteric Negative Feedbak page??? Dominick 14:23, 13 Apr 2004 (UTC)

[edit] eBay in See Also??

Is this a typo or does eBay have something to do with negative feedback...? Rohitbd 09:28, 23 September 2005 (UTC)

[edit] Er, deleted text?

Does anyone care to explain why a bunch of the text I added about negative feedback in gaming was deleted, the remainder was commented out, and my reference was removed? I'm not making this stuff up, the book specifically used the term "negative feedback" and the examples seem to make it clear that this kind of cybernetic system responds in a way that tends towards equilibrium. Was it removed because the article is focusing on a narrower meaning of the term, or what? I'm just wondering. Deco 22:38, 30 November 2005 (UTC)

I would say the meaning of the term, as this is primarily a mathematical term. You need a loop, and then to show the response is subtracted from the input, and I think that man in the loop systems don't really count except in a narrow set of cases. I commented it out to see if I can come up with better text and examples. From where I sit, many examples of negative feedback are really examples of negative outcomes. When you put the man in the loop, they can choose to make this positive or negative feedback. If you can somehow show me how a loop is closed thats fine. Thanks for asking here, lets work on the article. Dominick (TALK) 01:05, 1 December 2005 (UTC)

Well, it is true that I was using it in a less rigorous/precise sense. Maybe it would help to have a more general informal article about positive and negative feedback loops as encountered in daily life and also more precise technical articles for the formal terms used in theory. I don't know. Deco 01:55, 10 December 2005 (UTC)
You encounter negative feedback loops every day in your life. Every second, in fact every keypress on your computer. All use amplifiers stabilized by negative feedback. There are few positive feedback loops. Generally if you can build a unstable amplifier, that is made to give outstanding gain, you can stablize it with a negative feedback loop. One application of positive feedback is an oscillator. Generally positive feedback amplifier techniques are only used where it is not possible to make a more stable circuit, like at extreme frequency. Dominick (TALK) 21:40, 10 December 2005 (UTC)

This information needs to be more specific. What about negative and positive feedback loops in environmental science? -Matt


[edit] Cleanup Tag

Can the original poster of the cleanup tag please give a cogent comment on what additional changes they want within 7 days, or I shall presume all is now well and remove the tag. Bob aka Linuxlad 14:03, 25 January 2006 (UTC)


[edit] NFB Section

Do we relly need the blow by blow account in developing the final equation?--Light current 17:37, 30 June 2006 (UTC)

Simplified it a bit--Light current 17:48, 30 June 2006 (UTC)

V' doesn't reproduce well on my Browser (Linux Firefox IIRC) - compared with V it looks very similar. Bob aka Linuxlad 20:28, 30 June 2006 (UTC)


[edit] Very narrow

Negative feedback happens in economics (scarcity causes prices to rise which chokes off demand) and in living systems. If it wasn't abundant in nature the world would fall apart. Yet this article confines itself to amplifiers and capacitors and suchlike. It misses the opportunity to explore a topic central to life itself. Or is that done in another article? David Colver 16:21, 30 August 2006 (UTC)

[edit] Component of a negative feedback loop

One of my teachers, in cell biology, mentioned the components of a negative feedback loop and I thought that it may be needed here.

Here are my note: Variable (measurable and changing) -> Change in variable (Stimuli) -> Negative Feedback Loop kicks in =

Receptor ("senses" the variable state) -> Control Center (can tell if the variable from the receptor is not in a good range and then decides and controls the responce) -> Effector (exerts the effect - effects the change) -> Responce (reaction of variable - opposite the stimulius) -> (which then goes back to variable)

[edit] feedback depends on what your talking about

In Ecology, Feedback, is when you have a state variable that is being affected by another variable that infact is the state variable it self, you get feed back, now negative feedback for instance would be competition which is a negative-negative interaction ( The species hurts its self more than it hurts its competator), and positive feedback would be mutualism a positive-positive interaction, ( species are mutualists for simply their own benefit, it just so happens that the service they are doing for themselves helps the other species, for instance bees and flowers," the bee benefits because it gets nectar, the flower benefits because it gets pollinated"). This is feedback only in terms of Ecology. These statements are fact based on Dr. Mike Rosensweig Phd at the University of Arizona, and Dr. Paveo-Zuckerman whom both work in the college of science in the department of ecology and evolutionary biology. Dr Rosensweigs research is known world wide as one of the key players in ecology, he is the student of the late Dr. McArther, he has worked with Gause', Kitchner, Jarred Diomond, and Huffacker. —The preceding unsigned comment was added by 69.252.128.148 (talk) 08:00, 15 December 2006 (UTC).

[edit] Fever

"I know right now you are thinking, "CAN I HAVE NON-CONFUSING FEEDBACK?!?!?" well if so, then think of it this way. If your body has a fever, your body will then try to make you have a normal temerature, so it fights it off."

This is not very encyclopedic. It uses the first person, contains a spelling mistake, and is completely inaccurate. Fever is not a disease that the body's thermostat attempts to 'fight off'. It is a change in the control temperature which makes the internal environment less hospitable to pathogens. Someone with a fever has a perfectly working thermostat that is 'intentionally' making them hotter. As the article on fever points out, it is completely distinct from hyperthermia, in which the thermostat mechanism fails or cannot cope.

I recommend immediate deletion.

--83.217.142.213 13:25, 29 March 2007 (UTC)

[edit] Negative feedback loops and feedback inhibition in biology

There seems to be little information on negative feedback loops and feedback inhibition in nature, e.g. in enzyme biochemistry. Negative feedback loop redirects here and feedback inhibition redirects to feedback. Neither article provide sufficient information for a topic that is covered in high school and intro bio classes. - tameeria 21:13, 5 May 2007 (UTC)

[edit] Guy who wrote under "Fever"

Fever guy, "you" is in the 2nd person not the 1st. For someone who sounds like they think rather a lot of themselves, you should know that.

[edit] Amplifier feedback isn't that simple

Most amplifiers aren't unilateral, so the simple feedback equation from control theory doesn't really apply. I think there should be an article dedicated just to negative feedback amplifiers covering the various methods of analysis. Roger 23:27, 11 May 2007 (UTC)

Really? Are you really claiming that most amplifiers have significant reverse gain - significant in the sense that the simple feedback equation doesn't apply? If you had said 'most RF amplifiers' aren't unilateral, I might not be so surprised. Please provide justification for this assertion, Roger. Do you have some citations to support this? Alfred Centauri 04:01, 13 May 2007 (UTC)
No, I mean most aren't perfectly unilateral, and yes, even less so at RF. Feedback circuits are certainly not unilateral (e.g. a resistive divider). Another problem is loading from the feedback circuit on the amplifier which makes it difficult to partition an amplifier according the ideal feedback model. Of course all of this is not normally significant in opamp circuits, but nevertheless it is in general. If you have "Analysis and Design of Analog Integrated Circuits, 4th Edition" by Gray and Meyer, check out page 499. He mentions this and gives a more complete block diagram for feedback amplifiers (its also here: http://ardem.com/images/NatBlockDiag+Adj.jpg). Roger 05:07, 13 May 2007 (UTC)
I have the 3rd edition of this book so please refer me to a chapter heading. At any rate, while I agree with you that the simple feedback equation is an approximation except in the limit of an ideal amplifier, is it reasonable to say that it doesn't apply? After all, aren't most equations in EE approximations? Alfred Centauri 13:14, 13 May 2007 (UTC)
Look in the chapter on feedback, right before the discussion of the return ratio method (if thats in your edition). If you have access to IEEE, find the follow paper: "Striving for Small-Signal Stability" by Tian, Visvanathan, Hantgan and Kundert. They say "It should be noted that the ideal single-loop feedback network shown in Fig. 1 is not an adequate representation of a practical feedback network. In practice, the active path may not be strictly unilateral; the feedback path is usually bilateral, and the input and output coupling networks are often complicated." Their Fig. 1 is the classical feedback block diagram. Anyway, I just thought feedback amplifiers deserved a more thorough coverage. I'll work on an article when I get a chance. Roger 00:20, 14 May 2007 (UTC)

[edit] Regarding "stability"

Hi Alfred,

You recently reverted my change regarding the phrase "improves gain stability" as an advantage of negative feedback, as I misinterpreted what was meant by "gain stability". Consequently, I think this could be clarified in the article. This article already talks about stability in the BIBO sense, and all mentions of stability in the Operational amplifier article also refer to the BIBO sense.

Given that there is currently no article on "gain stability", perhaps we could clarify what is meant by this phrase; most importantly, that it's not the same meaning of "stability" that was used a few paragraphs previously? Oli Filth 00:36, 14 May 2007 (UTC)

Good point. I think the word 'stability' shouldn't be used here for the reasons you mentioned. Maybe something like "reduces gain variations arising from component tolerances, changes in temperature and aging". I dunno, that sounds too long. See what you can come up with. Alfred Centauri 01:25, 14 May 2007 (UTC)