# The use of amplifier stages

You make vague statements that could mean any number of things, most of which are outright wrong. .
Since I am trying to improve my knowledge continuously, I would be very happy if you would direct my attention to the statements which are "outright wrong" (together with corresponding/necessary corrections).
Thank you again.

... I would be very happy if you would direct my attention to the statements which are "outright wrong" (together with corresponding/necessary corrections.
See my post #22. Depending on what you mean by 'dynamic stability' and what the feedback configuration is, that statement could mean any number of things. It certainly isn't true that negative feedback always reduces stability margins.

You could easily correct this by showing the math that supports your statement. If you're unwilling to, then I don't really see the point of a discussion.

milesyoung - may I ask you: Where are YOUR contributions resp. answers to the OPs problem?

Up to now, you have placed 5 responses within in this thread - without any reply to the OPs question.
Is it your only task to criticize other contributions without giving any substantial information?
Do you really think it helps anybody if you say that statements from others would be „most outright wrong“ - without being able to list those wrong statements?

Quote: "It certainly isn't true that negative feedback always reduces stability margins."

In this thread, we speak about amplifiers (one vs. several stages) - and in this context the term "stability" came up (it was NOT me who has brought this term into discussion, see post#2 and #4).
Do you agree that the classical methods for resistive amplifier feedback (emitter degeneration, opamp voltage divider as feedback path) will reduce the stability margin?
Yes or no?
For my opinion, it wouldnt help the OP (more than that: it would confuse him) to extend the discussion - as you did - to complex control systems with PID controllers etc. This has nothing to do with the problems described by the OP.

Averagesupernova
Gold Member
LvW. For the record, I am the one who mentioned PID controllers. Is this all attention you are paying here? It seems to me, and maybe my perception is off, that you are saying that in the following example...
If I can show you a system which, in open loop, has a highly oscillatory response to a step input, do you mean to tell me that it's impossible to improve upon its transient response using negative feedback?
...it would in fact be impossible to use negative feedback to tame the oscillations. Is one side of this discussion always assuming a zero phase margin and the other side not? I would like to resolve this.

I am sorry, but I do not want to continue this "discussion" - unless you answer my questions.
In particular, and If you want to be taken seriously, you should list all of my statements which - in your view - are "most outright wrong".

Averagesupernova
Gold Member
LvW, what makes you think your questions have more priority than anyone else? I don't believe you have asked me a direct question so it would be pretty hard for me to answer. I don't believe I ever said you are "most outright wrong". I have seen what I have seen and I know what I know. It would have been nice to resolve this with a simple admission from one side or the other that phase margin or something else is being considered by one side and not the other. What a waste this has turned into.
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Edit: I believe milesyoung was the first to ask a question besides the original poster. Wouldn't it be logical that his question is answered first?

Harrison G
Averagesupernova - please, excuse me. As far as the statement "most outright wrong" is concerned, I have I have mixed milesyoung`s answer (post#25) with one of your answers. I am sorry for that.
Nevertheless, I do not like to continue this (slightly aggressive) "discussion" - and it does not help the OP at all.
As far as the technical aspects are concerned, I just have said everything I wanted to say.
Bye bye.
LvW

Harrison G and Averagesupernova
My excuses about the late respond. I was away for a bit and couldn't chat back. My thanks to all of you who answered to this thread. Thank you!

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Tom.G