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Design >> Analog Design >> how to simulate this full differential OPA
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Message started by wjx197733 on Feb 5^th, 2006, 8:02pm

Title: how to simulate this full differential OPA
Post by wjx197733 on Feb 5^th, 2006, 8:02pm

Hi, all: I design a full differential OPA whose CMFB is switch capacitance circuit.
Because the switch capacitance circuit, I do not know how to process the ac analyse.

Title: Re: how to simulate this full differential OPA
Post by Paul on Feb 5^th, 2006, 10:55pm

Hi,

the easy solution is to replace the switched-cap part by its equivalent resistors, which then allows you to run a PAC simulation. If you have access to SpectreRF, you can alternatively run an analysis on your real schematic with the SC CMFB circuit. For more information on the second solution, have a look at Ken's paper in the analysis section:
http://www.designers-guide.org/Analysis/sc-filters.pdf

Paul

Title: Re: how to simulate this full differential OPA
Post by Andrew Beckett on Feb 7^th, 2006, 10:37am

Paul,

I assume you meant to say that if you replace the switch-cap parts with equivalent resistors you can then simulate using an AC analysis not a PAC analysis.

If you have SpectreRF (as you say), you can then simulate using PSS/PAC with the circuit as is (I expect).

I'm sure it was just a typo, but just thought I'd check (with my pedant's hat on).

Regards,

Andrew.

Title: Re: how to simulate this full differential OPA
Post by Paul on Feb 8^th, 2006, 7:36pm

Hi Andrew,

thanks for correcting my statement. Of course I wanted to say that the first option would be the replacement by resistors, which allows to run AC analysis, the second (and more elegant) option being the PAC analysis with SpectreRF.

Seems I'm still a little jet-lagged, or was that the wine at the social event??? ;)

Paul