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Design >> Analog Design >> mismatch problem in the filter
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Message started by James Bond on Oct 1^st, 2007, 12:48pm

Title: mismatch problem in the filter
Post by James Bond on Oct 1^st, 2007, 12:48pm

Hi,

I met a wierd problem, in my fully differential all pole chebyshev active filter, when I change one of the matched resistors 0.2%, system phase and frequency respond totally changed, it comes up zero and stop the attenunation in the stop band, which makes my filter away from the specification. Does anybody know the reason? why such small mismatch can affect that much ? and how to solve this problem?

Before mismatch:

Title: Re: mismatch problem in the filter
Post by James Bond on Oct 1^st, 2007, 12:48pm

with mismatch:

Title: Re: mismatch problem in the filter
Post by loose-electron on Oct 5^th, 2007, 4:19pm

it would be informative if you took and did the pole placements and how they shift due to mismatch.

Some pole-zero constellation placements are more robust (in spectral response) to shifts than others.

jerry

Title: Re: mismatch problem in the filter
Post by James Bond on Oct 6^th, 2007, 6:29am

Hi,

I will post the pole zero simulation diagram later. I am using vcvs from analoglib to model fully differential opamp, could that be a problem? it can not work as a real opamp to deal with the error input I think .

Thank you very much.