The Designer's Guide Community
Forum
Welcome, Guest. Please Login or Register. Please follow the Forum guidelines.
Oct 24th, 2020, 1:46am
Pages: 1
Send Topic Print
Insufficient number of harmonics in pss affecting pnoise jitter (Read 2173 times)
manikanta
New Member
*
Offline



Posts: 1
Bangalore
Insufficient number of harmonics in pss affecting pnoise jitter
Sep 16th, 2016, 5:25am
 
Hi,

I am doing a simple experiment on pss and pnoise analysis.
My DUT is simple RC Low pass filter ckt where R=1 Ohm and C=1nF and BW = 159M Hz.
Input frequency of the ckt = 10M Hz(pss frequency).
I am measuring the jitter noise at the output across cap and it should be kT/C = 4.14pV
I have varied the number of harmonics from 20 to 1000 and no of sidebands = 2000.
Maxacfreq is set to default. Output noise numbers are in the image.

What is actually happening when there are insufficient number of harmonics in the pss simulation?
Why do the noise numbers go high when number of harmonics in pss are very low.


Note: I am aware that I need to set maxacfreq to no_of_sidebands*no_of_harmonics to get correct noise numbers. But trying to understand the working of pnoise on pss.

Back to top
 

psspnoise.png
View Profile   IP Logged
Ken Kundert
Global Moderator
*****
Offline



Posts: 2294
Silicon Valley
Re: Insufficient number of harmonics in pss affecting pnoise jitter
Reply #1 - Sep 16th, 2016, 2:24pm
 
You are chasing a side effect.
You only need to specify harmonics if you want to look at the PSS results in the frequency domain.
Spectre does not require you to set the number of harmonics, and generally you would only do it if you wanted to look at the spectra. However, for reasons I do not understand, ADE requires a value.

When you increase the number of harmonics, Spectre will shrink maxstep accordingly. Just as it does if you set maxacfreq. When you up the number of harmonics you see accuracy increasing because it is in effect increasing maxacfreq for you, but at the cost of computing more harmonics in the spectra of all the node voltages.

Just set maxacfreq.

-Ken
Back to top
 
 
View Profile WWW   IP Logged
sheldon
Community Fellow
*****
Offline



Posts: 751

Re: Insufficient number of harmonics in pss affecting pnoise jitter
Reply #2 - Oct 28th, 2016, 11:55pm
 
It also seems like you are using maxsidebands. If you use fullspectrum pnoise, this should not be required
Back to top
 
 
View Profile   IP Logged
Pages: 1
Send Topic Print
Copyright 2002-2020 Designer’s Guide Consulting, Inc. Designer’s Guide® is a registered trademark of Designer’s Guide Consulting, Inc. All rights reserved. Send comments or questions to editor@designers-guide.org. Consider submitting a paper or model.