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Design >> Analog Design >> OP phase margin in BPF?
https://designers-guide.org/forum/YaBB.pl?num=1357702787

Message started by kane on Jan 8^th, 2013, 7:39pm

Title: OP phase margin in BPF?
Post by kane on Jan 8^th, 2013, 7:39pm

Hi,
I am designing a BPF centered above 10MHz using OPAMP_RC,not GmC structure. and I have two questions about the design.
If the phase margin of the OP is poor, the OP will oscillate at GBW?
If the BPF has enough attenuate at GBW, then this oscillation will not happen?

Title: Re: OP phase margin in BPF?
Post by buddypoor on Jan 9^th, 2013, 12:16am

kane wrote on Jan 8^th, 2013, 7:39pm:

1) ..."phase margin of the OP": I suppose you mean the PM of the whole BP circuit, correct?
2) If the PM is "poor" - that means: small - the circuit will still be stable. The margin, of course, also depends on the band pass Q.
3.) If the margin is zero or even negative, the circuit is unstable. It most cases it will NOT oscillate but the output will be saturated, which means: The BP cannot be used.
4.) No - this is not the case. The PM depends on the open-loop response alone.