Author Topic: Capacitor Tee: can the capacitory be all different  (Read 1111 times)

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Offline Bigman

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Capacitor Tee: can the capacitory be all different
« on: June 04, 2015, 02:42:45 pm »
Hi,
in a book I came across the attached circuit. In order to fine-tune the capacitor in the feedback loop, this book suggest a tee-network with a trimmer.
I am wondering: can the capacitors C1 and C2 have a different capacity or should C1=C2 ?
 

Online TimFox

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Re: Capacitor Tee: can the capacitory be all different
« Reply #1 on: June 04, 2015, 03:23:38 pm »
They can all be different.
Typically, to obtain the effect of a small feedback capacitance, C1 is the smallest.
If C1 << C2, C3, then the effective feedback is less than C1, and there is an additional input capacitance of approximately C1.
The tee network is exactly equivalent to a pi network (using those equations) and independent of frequency if all impedances are the same type (capacitor, inductor, or resistor).
Also note that the op amp must be happy driving the series combination of C2 and C3 to ground (not too huge).
 

Offline Bigman

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Re: Capacitor Tee: can the capacitory be all different
« Reply #2 on: June 04, 2015, 03:35:11 pm »
@TimFox: Thanks for your nice reply.  :-+
 


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