Cgs and Cgd for balanced MOS Mixers

How can we set up a simulation to find the Cgs or Cgd of a balanced MOS Mixer?

(single-balanced and double-balanced).

Hspice can simulating the transistor work condition.

You can get them by your device size
and parameters(cgxo) from model file.
For hand calculation such results are acceptable, however, if you don't satisfy such accuracy, you need know
much on Cap modeling which is complicated in modern device models
such as bsim3.