The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Simulators >> Circuit Simulators >> Distortion (THD) for switched-cap filter
https://designers-guide.org/forum/YaBB.pl?num=1050170824

Message started by pwm on Apr 12^th, 2003, 11:07am

Title: Distortion (THD) for switched-cap filter
Post by pwm on Apr 12^th, 2003, 11:07am

Hi,
Currently I am using Spectre simulation for switched-cap filter (4th order, 13MHz clockrate with 1kHz input sine wave). I heard of fantastic tools like Pdisto and PSS can help to speed up the sims (or maybe there are other tools ?) for getting THD (distortion). Could anyone advise me whether Pdisto or PSS would be the best tool ? and if there is a step-by-step guide for getting the THD ? If there is also step-by-step guide for Pnoise and PAC, that would be great too ! :D
Thanks ! ::)

Title: Re: Distortion (THD) for switched-cap filter
Post by August West on Apr 22^nd, 2003, 9:30pm

Whether you use PSS or QPSS (aka PDisto) depends on the frequencies you are using. Generally, the time required for PSS (like transient) depends strongly on the frequency ratios, but only weakly on the number of harmonics requested. Conversely, the time required for QPSS does not depend on the frequency ratios, but does depend strongly on the number of harmonics requested (except for harmonics of the clock, which like with PSS are largely free). Generally you want to use QPSS if the frequencies are such that either transient or PSS analyses will be really expensive.

There is a relatively new document in the Analysis section that attempts to lead people through a complete simulation of SC filter-like circuits. You can find it at http://www.designers-guide.com/Analysis/sc-filters.pdf.

Have you looked at it? If so, maybe you can describe where the explaination it gives is lacking.

August