problem:switch cap filter

[wjlzhx]

swich cap filter




it is a switch cap filter ,I conversion the circuit in z field by allen's book ,but i do not know how deal witch the R1,C1,and R2,C8,C9,R7.
Could anyone can help me?

R1 = R2 = 225K,C1 = C8 = 20P,R7 = 22K

input signal 's frequency is audio
and swtich frequency is 200k.

 

[LvW]

Hi wjlzhx !

It is not possible - or in some cases possible, but not wise - to convert each active RC circuit into an equivalent S/C circuit. In detail, you can convert a resistor into a switched capacitor only if this resistor is located between "signal input, ground, or virtual ground (negative opamp input)". For example, you cannot convert resistors of a voltage divider or a passive RC combination.
As a consequence, only some active RC filters are suitable to be converted to S/C circuits.
More than that, it is best not to convert each R separately, but complete active units - preferrably integrator stages (inverting, noninverting or difference).
Therefore, I´m afraid you have to start with another active RC circuit (Integrator filter like Tow-Thomas or KHN, or Leapfrog structures).
Regards
LvW

 

[wjlzhx]

Dear LvW
thanks for your help
now i converter the circuit in z filed like that.except res



but now i have anothe idea,look at the picture below



In my circuit my input signal is audio frequency,so the RC filter is no attenuation to the input signal ,just a delay ,R3 is small ,so i delete it.so i do the job like this .
Am i right.

and how can i simulate the circuit in cadence to validate my idea?