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How to decide the max sideband to get accurate pnoise simulation result (Read 134 times)
Homer
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How to decide the max sideband to get accurate pnoise simulation result
Aug 07th, 2015, 12:39pm
 
Hi,

I'm running pss+pnoise simulatoin for a big circuit. I use shooting method and the beat frequency is only 64K. The max sideband setting bother me a lot. I know the bigger the max sideband is, the more accurate the simulation result is. But big max sideband also leads to very long simulation time. Currentlly I have to increase the max sideband parameter step by step and check the difference of the simulation result to decide whether it's high enough. For example, at first run I set max sideband to 100 and the 1000 for the second run, and of course I also change harmonics correspondingly. I think 1000 is enough if the result difference is less than 5%. Or I may need to increase it further.

But this method means I need multi run to get one pnoise simulation result. And it take much long time because the circuit is big. Is there any method to decide max sideband without simulation? Can I calculated it from beat frequency?

Thanks!
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sheldon
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Re: How to decide the max sideband to get accurate pnoise simulation result
Reply #1 - Aug 7th, 2015, 6:57pm
 
Homer,

   Which version of Spectre are you using? If you are using a recent
version, you can review the full spectrum option for pnoise. In general,
it does not require tuning maxsideband and should also speed up the
simulation time significantly.

                                                                      Sheldon
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Frank Wiedmann
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Re: How to decide the max sideband to get accurate pnoise simulation result
Reply #2 - Aug 10th, 2015, 4:51am
 
I also would recommend that you use pnoisemethod=fullspectrum, which has been available since MMSIM 11.1. Please note, however, that this only applies to white noise, you still need to set maxsideband large enough to cover all the 1/f noise. In addition to this, you also need to set maxacfreq to a large enough value so that all the white noise is covered (also see http://support.cadence.com/wps/mypoc/cos?uri=deeplinkmin:ViewSolution;solutionNu...).
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Homer
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Re: How to decide the max sideband to get accurate pnoise simulation result
Reply #3 - Aug 10th, 2015, 8:12am
 
Hi, Sheldon and Frank,
Thanks for your reply.
I’m using 14.1 and I do have fullspectrum option. I’m trying it today. I checked it and it says “ Calculates noise contributions up to the frequency determined by PSS time point resolution”. Does it mean the accuracy is decided by PSS simulation? Do I need to do something to increase PSS resolution?

Another issue is about 1/f noise, in fact the major noise contribution in my circuit is 1/f noise. And I didn’t find a way to set maxsideband if I chose fullspectrum method. Does it mean I can’t use fullspectrum method if 1/f noise is the main concern? And the problem is come back to how to decide the maxsideband?

Homer
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Frank Wiedmann
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Re: How to decide the max sideband to get accurate pnoise simulation result
Reply #4 - Aug 11th, 2015, 6:59am
 
Regarding your first question: Yes, this is what the maxacfreq parameter is for.

Regarding your second question: In recent versions of Virtuoso, there is a field "Maximum sideband" even when fullspectrum is selected. If your version does not have this, you can always add any parameter by clicking the "Options..." button and writing it into the additionalParams field. The sidebands should cover the 1/f noise up to the corner frequency (or a little above).

Please also note that you have to use APS for pnoisemethod=fullspectrum.
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Homer
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Re: How to decide the max sideband to get accurate pnoise simulation result
Reply #5 - Aug 11th, 2015, 11:07am
 
Frank Wiedmann wrote on Aug 11th, 2015, 6:59am:
Regarding your first question: Yes, this is what the maxacfreq parameter is for.


For maxacfreq, normally I set it a little bit higher than the circuit BW. Is it OK?


Frank Wiedmann wrote on Aug 11th, 2015, 6:59am:
Regarding your second question: In recent versions of Virtuoso, there is a field "Maximum sideband" even when fullspectrum is selected. If your version does not have this, you can always add any parameter by clicking the "Options..." button and writing it into the additionalParams field. The sidebands should cover the 1/f noise up to the corner frequency (or a little above).

Please also note that you have to use APS for pnoisemethod=fullspectrum.


If the circuit BW is smaller than the corner frequency, can I just set max sideband to BW/Beat Frequency? Then save some simulation time?
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Frank Wiedmann
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Re: How to decide the max sideband to get accurate pnoise simulation result
Reply #6 - Aug 12th, 2015, 12:47am
 
Quote:
For maxacfreq, normally I set it a little bit higher than the circuit BW. Is it OK?

Yes, this should be ok.

Quote:
If the circuit BW is smaller than the corner frequency, can I just set max sideband to BW/Beat Frequency? Then save some simulation time?

Yes, this should be ok as well. However, in this rather unusual case where 1/f noise dominates over the entire circuit bandwidth, pnoisemethod=fullspectrum will not allow you to reduce maxsideband in order to speed up the simulation.
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Homer
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Re: How to decide the max sideband to get accurate pnoise simulation result
Reply #7 - Aug 14th, 2015, 6:08am
 
Thanks!  Now I understand how the simulator works.
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