Quote:when you guys say "breaking the loop" you mean breaking by inserting an "AC CUT" ?
Yes.
Quote:cant i put an AC cut in both positive and negative feedbacks, and then insert an AC source at the negative feedback input and measure the frequency response will be M2's drain minus M1's drain.
No , i dnt think so.
Placing a separate ac cut in the other loop(one in which ac test src has nt been inserted) will not allow that loop's effect to show up in the plot because you broke the second loop, but you are not feeding the test voltage into that loop at exactly the same pt where you are placing it in the first loop.
This scheme can provide you the LGs of both loops separately, but combined effect cannot be analysed.
Breaking the loop at the common pt. & inserting a test ac src there will give you common injection.
Thus, you can test the return voltage at opamp output & be worried about the overall stability of this dual-feedback architecture instead of probing both loops separately.
--M