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Measurements >> Phase Noise and Jitter Measurements >> Floquet eigenspace error during pnoise sims
https://designers-guide.org/forum/YaBB.pl?num=1211819357

Message started by aval on May 26^th, 2008, 9:29am

Title: Floquet eigenspace error during pnoise sims
Post by aval on May 26^th, 2008, 9:29am

I am running pss+pnoise analysis on LDO + VCO (LDO being the power supply for the VCO). The VCO is a ring oscillator. All bondwire models are included and so are external capacitances on the LDO.

I get the following warning from pnoise:

"The Floquet eigenspace computed by spectre PSS analysis appears to be ill-defined. PNOISE computations may be inaccurate. Consider re-running the simulation with smaller reltol, different tstab(s), and method=gear2only. Check the circuit for unusual components."

I have tried out the suggestions (smaller reltol, increased tstab, gear2only). The warning does not go away. The warning does go away if the bondwire inductances are taken out. I would however like to simulate the noise with the bondwire inductances.

Any ideas on what could be going wrong here?

thanks in advance,
Aarathy

Title: Re: Floquet eigenspace error during pnoise sims
Post by didac on May 26^th, 2008, 9:55am

Hi,
Time ago I find a similar problem with pss(I don't remember the error message), in my case was caused by bondwires without real part, adding a small amount of series resistance helped to solve this issue.
Hope it helps,

Title: Re: Floquet eigenspace error during pnoise sims
Post by aval on May 27^th, 2008, 12:46am

Thanks! That did work!!

I had missed the series resistance for ground and substrate connections. Once I included those, the problem went away.

thanks once again!
Aarathy