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how to calculate the input capacitance of a circuit.

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wangkes9

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how to calculate input cap

as a simple common source CMOS circuit, how is the input cap value.
I think it will not be the Cox.

How to calculate or simulate it. Thanks.
 

calculate input capacitance

Read datasheet on actual CMOS circurit, try to find spice model on used circurit or last step - measure itself with network analyzer or simular measure bridge tools (need high skill measure knowledge)...

Cmos circurit exist in many generation (to speed increase over year) and you must read exact value from data sheet for used circurit, and in really high speed using, you must also calculate transmissionsline impedance and length between circurit, drivers impedace and inports impedance, matching, splitting and terminate properly if you not want reflection on line between units/ports...
 

circuit input capacitance calculation

hi wangkes9,

i think the input cap. includes cgs and miller cap. of cgd. in general the input transistor works in strong inversion region, so cgs is equal to 2/3*w*l*cox+cov, and the miller cap of cgd is cgd*(1-A).
 

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