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Bode Plot stability analysis for nonminimum phase systems

Hi everyone,

It is well known that assessing the stability of a nonminimum phase feedback system (e.g., circuits with RHP zeros and time delays) may fail using the frequency analysis of the Bode plot. That's why many textbooks instead recommend the Nyquist test.
However, there is no Nyquist test available in Cadence.
Does this mean that the STB analysis from Cadence is insufficient to evaluate my circuit's relative stability?

I very much appreciate your taking the time to answer my question.

Frank Wiedmann over 2 years ago

You can access the (negative) loop gain with getData( "loopGain" ?result "stb" ) and you can for example plot it in a polar chart (see https://designers-guide.org/forum/YaBB.pl?num=1124688329 for the sign convention issue; make sure if you need to look for encirclements of -1 or of +1).
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Andrew Beckett over 2 years ago

If you go to the results browser, you can plot the loopGain (from the stb analysis results) on a polar plot, which will then give you a Nyquist plot. You can then look at the Nyquist criterion that way (including the angle at which it crosses the unit circle and the magnitude at which it crosses the x-axis - you can use the trace info assistant to show the gamma in dB to see that as you move along the trace). Is that what you want?

Andrew
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ronaldomponte over 2 years ago in reply to Andrew Beckett

Yes, that's it. Thank you very much for your time on this matter, Andrew.
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ronaldomponte over 2 years ago in reply to Frank Wiedmann

Many thanks, Frank.

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Arabic	Hebrew	Polish
Bulgarian	Hindi	Portuguese
Catalan	Hmong Daw	Romanian
Chinese Simplified	Hungarian	Russian
Chinese Traditional	Indonesian	Slovak
Czech	Italian	Slovenian
Danish	Japanese	Spanish
Dutch	Klingon	Swedish
English	Korean	Thai
Estonian	Latvian	Turkish
Finnish	Lithuanian	Ukrainian
French	Malay	Urdu
German	Maltese	Vietnamese
Greek	Norwegian	Welsh
Haitian Creole	Persian