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Simulators >> RF Simulators >> warning message in PNOISE
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Message started by City on Nov 1^st, 2004, 3:05am

Title: warning message in PNOISE
Post by City on Nov 1^st, 2004, 3:05am

Hi,

I believe this is a common question so sorry if this was asked before. I am simulating a low noise oscillator using spectre RF PSS/PNOISE analysis a warning message I have is :

Warning from spectre during PNoise analysis `pnoise'.
The Floquet eigenspace computed by spectre PSS analysis appears to be inaccurate. PNOISE computations may be inaccurate. Consider re-running the simulation with smaller reltol and `method=gear2only'.

Can simebody explain me what it is about ?
I have tried simulating again with smaller reltol and the recommended integration method but still get a wrong
output phase noise result !

thanks for any help ?

City

Title: Re: warning message in PNOISE
Post by Frank Wiedmann on Nov 2^nd, 2004, 12:49am

You can find a pretty detailed explanation of the Oscillator Noise Analysis in Appendix A of the SpectreRF User Guide, see http://sourcelink.cadence.com/docs/files/Release_Info/icoa5033/spectreRF/appA.html (access to SourceLink requires registration). There you can also find details about the Floquet eigenspace that is mentioned in the warning message as well as tips for troubleshooting.

Another possible method to improve the accuracy of the PSS solution might be to increase the value of the PSS option maxacfreq beyond its default value of 40*fundamental, which will force a smaller timestep. This was suggested as a solution to a somewhat similar problem, see http://sourcelink.cadence.com/docs/db/kdb/2002/Feb/11009978.html. You might want to try if it helps in your case.

Title: Re: warning message in PNOISE
Post by City on Nov 3^rd, 2004, 7:28am

Thank you Frank,

I'll try this out.

City