Capacitor plate connection in feedback network

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Junus2012

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Hello,

consider please the image below for the fully differential filter, consider the case of using poly one-poly CAP or met2-met3.

I read that parasitic from one plate is different from the parasatic to the second plate, so what is the appropriate polarity connection regarding this circuit.

If you are not familer with this circuit you can refer your answer to the single ended sallen key low pass filter below it

'Thank you
Best Regards



 

Always drive the bottom plate if the cap is at lower
levels and C to substrate is the largest parasitic term.

But if you had (say) a 6LM process, routing power and
ground on M6 and the MIM cap is between M4 and M5,
you'd probably drive the M5 top plate (liable to be loaded
by bussing overflight) and take signal off M4.

As a rule you want to drive the more heavily loaded
plate, so that capacitive division and spurious coupling
is minimized on the "output" plate.
 

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