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Simulators >> Circuit Simulators >> PSS and PAC Analysis
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Message started by Beginner on Dec 6^th, 2008, 2:48pm

Title: PSS and PAC Analysis
Post by Beginner on Dec 6^th, 2008, 2:48pm

Hi,

I'm currently designing a switched-capacitor (SC) filter. I try to run PSS and PAC analysis in SPECTRE to get the transfer function (H) to verify my gain and 3dB cut-off frequency.

However, the PSS analysis is failed with the following message:
"Attempt to generate initial guess for DC solver failed.
Zero diagonal found in Jacobian at ....."

I try to follow the guide from [http://www.designers-guide.org/Analysis/sc-filters.pdf] where I should set the initial condition of all the capacitors to ZERO & I also set the tstab parameter to 2us (fCLK=1MHz). I also disable the small signal at input (except PAC magnitude =0.1mV at Vin-)

Can anyone tell me what's wrong with my setup?

Thank you so much.

Title: Re: PSS and PAC Analysis
Post by Ken Kundert on Dec 7^th, 2008, 10:33pm

Zero diagonal is probably due to a floating node. You are probably using overly idealized switches.

-Ken