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Simulators >> Circuit Simulators >> checking stability for a two stage fully differential simple OTA on cadence
https://designers-guide.org/forum/YaBB.pl?num=1483633619

Message started by ahmedhany_94 on Jan 5^th, 2017, 8:26am

Title: checking stability for a two stage fully differential simple OTA on cadence
Post by ahmedhany_94 on Jan 5^th, 2017, 8:26am

I made this circuit for a two stage fully differential OTA
I want to check its stability in a unity feedback but i have a version of cadence without the diffstbprobe

Title: Re: checking stability for a two stage fully differential simple OTA on cadence
Post by deba on Jan 6^th, 2017, 12:37am

You can apply a small step input and look for the number of rings or overshoot in your output. Or

you can break the loop using a large inductor and capacitor, if you want to look at the open loop gain in frequency domain. Take care of loading while breaking the loop.

Thanks

Title: Re: checking stability for a two stage fully differential simple OTA on cadence
Post by Andrew Beckett on Jan 6^th, 2017, 1:58am

If using an older version, you could use the older cmdmprobe component instead. This assumes that the two loops are balanced and that there's no significant CM to DM leakage (or vice versa), but is probably sufficient in this case.

Or you could use a more recent version. diffstbprobe has after all been there since IC614 (a hotfix of IC614 at least).

Regards,

Andrew.

Title: Re: checking stability for a two stage fully differential simple OTA on cadence
Post by Frank Wiedmann on Jan 10^th, 2017, 12:31am

You can also build your own diffstbprobe, see http://www.designers-guide.org/Forum/YaBB.pl?num=1190707743 (Reply #1) and https://community.cadence.com/cadence_technology_forums/f/33/t/27989 (my last reply).