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I am not familiar with ADS - however, using a universal simulation program like PSpice it is possible to adjust a certain part within a circuit with feedback for a desired phase margin. This (new) method is described in the following document (chapt. 4)...
Let me repeat again: The keypoint for the two alternatives for the stability criterion is the question: Is the necessary phase inversion (by design !) for negative feedback inluded in the loop gain- yes or no?
1,) In the avove figure, the loop gain phase starts at 0 deg. If this would be the...
The stability criterion requires that at 0dB loop gain the phase must be still slightly negative (because for negative feedback the phase starts at -180deg).
So it must not cross the 0 deg line for loop gains still above 0db.
When the stability margins are found by simulation, the calculation...
Yes - that`s how I have interpreted your wording.
More than that, it is also interesting that even an ac analysis (simulation program) shows a frequency-dependent gain response that will look as expected from a stable system. This is because the DC operational point is calculated before based on...
No - I don`t think so. A positive voltage at the inverting input causes a positive output. Is this logical?
However - I can imagine what you mean: Applying the known mathematical tools and rules seem to confirm this result - however, it is not logical.
By the way: Even simulation programs (DC...
Yefj - I recommed to study in detail the concept and the effects of/on negative feedback.
For my opinion, it does not make much sense to describe all these effects in the time domain because it takes a certain (pretty small) time until the steady state (feedback active) will be reached. This...
1) Closed loop: The "spike" in the region of the pole frequency is called "frequency peaking". It is an indication for a phase margin that could be app. 30 deg.
(for a second-order response there is a fixed and known relationship between phase margin and gain peaking).
This value should be...
I think that such a danger does not exist.
The larger the feedback capacitor, the lower the "cross-over frequency" (with unity closed-loop gain) - and the smaller the probability that the additional opamp induced phase shift will lead to instabilities. Typical example: Miller intergator.
Klaus - I rather think that the effect of limited slew rate is caused by saturation of the opamps input stage - until the delayed feedback brings the unit back to linear operation. During this very short time of saturation the input stage acts as a current source which loads the Miller...
The answer to your question was given already in post#10:
"Both cases represent the most critical application as far as stability is concerned (maximum feedback)."
That means: An opamp that is stable for closed-loop gain values of "+1" resp. "-1" wil also be stable for all other gain values...
The following comment is intended to avoid confusing the questioner with the different terminology and to clear up any misunderstandings.
1) The best-known stability criterion is that of H. Nyquist, which consists of feeding a test signal into the feedback loop, which must be broken for this...
1) It seems that you have applied a stabiliy criterion on the closed-loop gain response. That is not correct.
Instead, the well-known stability criteria are based on the loop gain - that is the gain of the complete loop when it is broken at a sitable node.
(By the way: A "Barkhausen instability"...
Explanation:
1.) For a non-inverting amplifier with a closed-loop gain Acl=+1 the loop gain is identical to the opamps open-loop gain Aol (very large)
2.) For an inverting amplifier with Acl=-1 the loop gain is identical to Aol/2 (Ao-3 db).
Both cases represent the most critical application as...
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