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The Designer's Guide Community Forum › Simulators › Circuit Simulators › how to simulate fully differential amp with switch cap CMFB?
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how to simulate fully differential amp with switch cap CMFB? (Read 3406 times)
alicia8283
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how to simulate fully differential amp with switch cap CMFB?
Dec 02nd, 2008, 7:27pm  
hi all,

i tried to simulate a fully differential amp which use switch cap as CMFB currently but i face trouble as the CMFB is timing dependant. i tried to connect the test circuit with ideal Balun as describe in "a test bench in differential circuits " which find in this forum but it seems have trouble. How should i test the differential amp with this switch cap?
thanks a lot.
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jbdavid
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Re: how to simulate fully differential amp with switch cap CMFB?
Reply #1 - Dec 18th, 2008, 8:25pm  
I would make a State average model of the switch cap circuit, and use that for the small signal analysies.
jbd
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jbdavid
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alicia8283
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Re: how to simulate fully differential amp with switch cap CMFB?
Reply #2 - Dec 18th, 2008, 11:57pm  
hi,

thanks a lot for your reply. Could you elaborate further on the method you mention?
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Ken Kundert
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Re: how to simulate fully differential amp with switch cap CMFB?
Reply #3 - Dec 19th, 2008, 8:23am  
He is just suggesting that you replace the SC resistors with real resistors. This of course is approximate. Another approach is to use SpectreRF, as described in http://www.designers-guide.org/Analysis/sc-filters.pdf

-Ken
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alicia8283
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Re: how to simulate fully differential amp with switch cap CMFB?
Reply #4 - Dec 22nd, 2008, 11:28pm  
hi guys,

thanks a lot for the replies. As my company do not have the license for spectreRF  :'( , so i unable to run the way according to the attachment.
Any other method? could you please specify more detail about the approximation method?

Thanks a lot
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