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Simulators >> Circuit Simulators >> vcvs feedback in PSS analysis with Spectre
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Message started by aaron_do on Aug 21^st, 2011, 7:38pm

Title: vcvs feedback in PSS analysis with Spectre
Post by aaron_do on Aug 21^st, 2011, 7:38pm

Hi all,

I am having some trouble with SpectreRF PSS anlaysis. I used a VCVS (voltage-controlled voltage source) in a negative feedback loop for DC biasing, but I found that although DC-analysis was able to find the correct solution, PSS anlaysis was not. In fact even DC analysis failed to find the correct solution when I switched the simulator to Turbo mode. Instead of forcing the two input terminal voltages of the VCVS to be equal, the negative input terminal just went to zero, and the output went to 1000V (my reference was 1 V, and the loop gain was 1000). I am sure it is negative and not positive feedback.

Has anybody experienced similar issues, and have a solution?

thanks,
Aaron

Title: Re: vcvs feedback in PSS analysis with Spectre
Post by Frank Wiedmann on Aug 22^nd, 2011, 12:46am

Seems like your feedback is not working correctly (how can the negative input be zero when the output is 1000 V?). When pss analysis does not converge, I usually do a tran analysis to see more clearly what is happening in the circuit.

Title: Re: vcvs feedback in PSS analysis with Spectre
Post by SoliS on Sep 28^th, 2011, 1:55pm

the manual of the pss simulator says it uses a special algorithm to calculate the steady-state of the circuit, which is less accurate than waiting for a transient sim to settle out. it could be that this special algorithm does not work well for your circuit for whatever reason - i second the opinion on running transient analysis to see whats going on.