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Simulators >> Circuit Simulators >> How can I get the position of poles and zeros of loop gain after stb analysis?
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Message started by frozenduck on Sep 16^th, 2010, 8:33pm

Title: How can I get the position of poles and zeros of loop gain after stb analysis?
Post by frozenduck on Sep 16^th, 2010, 8:33pm

Hi,

I'm using stability analysis (Spectre) to get loop gain plot(magnitude, phase, Nyquist plot) to check stability.

When I want to check stability through Nyquist plot, the number of encirclement of (-1,0) equals
P(RHP poles of loop gain also RHP poles of (1+loop gain)) - Z(RHP zeros of (1+loop gain )).

If there are RHP poles, the number of encirclement of (-1,0) will not be zero to make sure there are no RHP zeros(stable system).

"How can I get the position of poles and zeros of loop gain after stb analysis?"
I tried to recognize them from bode plot, but failed(it's too complicated).

Otherwise, if using pole-zero analysis in Spectre, the loop needs to be broken. As I know, it's not a good idea to do so in a closed loop system.(that's why we are using stb analysis)

Thanks.

Title: Re: How can I get the position of poles and zeros of loop gain after stb analysis?
Post by Andrew Beckett on Jan 2^nd, 2011, 8:41am

You probably need to contact Cadence to request this. There are some existing enhancement requests asking for the poles and zeros of a specific loop - currently the pz analysis gives you the poles and zeros of the entire circuit, whereas stb gives you the loop gain of a specific loop (but does not decompose this into poles and zeros). To do so is not entirely straightforward.

Anyway, you should register your interest in developing a solution for this by requesting such an enhancement via Cadence Customer Support at http://support.cadence.com .

Best Regards,

Andrew.