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stability criteria of system/circuit - quandary

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rover8898

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Hello all,

I have a question concerning the stability criteria of system/circuit that always bothered me.
Q:
A bode plot where the phase response toggles from 180 to -90 (or anything negative for that matter) while the gain response remains above 0dB is representative of an unstable/oscillating system. Does the same hold true if the phase response where to toggle from -180 to +90 (or anything positive) while the gain remained above 0dB ?

Thanks
-Rover
 

Re: stability criteria - quandary

Yes, what matters is phase shift.

However, I am still interested in asking other posters...how does Cadence or some other simulator determine what should be phase at s=0, ie +180 or -180.
 

Re: stability quandary

rover8898 said:
Hello all,
I have a question concerning the stability criteria of system/circuit that always bothered me.
Q:
A bode plot where the phase response toggles from 180 to -90 (or anything negative for that matter) while the gain response remains above 0dB is representative of an unstable/oscillating system. Does the same hold true if the phase response where to toggle from -180 to +90 (or anything positive) while the gain remained above 0dB ?
Thanks
-Rover
Click to expand...

Just to avoid misunderstandings:
Do you speak about the loop gain of a system with feedback?
The mentioned stability criterion applies to an open feedback loop whereas the normal operation is closed-loop.
 

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