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receiver gm-c filter question

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liletian

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Hi Guys
In the attached pic, the two filters are suppused to be the same. One uses gm-c gyrator to replace big inductor in another pic. What are the four cap in the elleptical circles corresponds to?
I was thinking they correspond to the cap 1.23p and 3.29 p in passive filter. But why do you need four of them?
It is a IF filter in GPS application? Can anyone comments on it?
Thanks,
 

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enjunear

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The upper circuit looks like a balanced implementation. The lower appears to be single-ended, so by using image theory you could equate the two (draw a line across the middle of the upper circuit and "fold" the components over onto their counterparts... the two capacitors should double in value, IIRC).
 

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