Should I use Cgd or Cdg

[wangkes]

Cgd and Cdg is different in spice for mos device.

Should I use Cgd or Cdg such as in calculating miller cap in a CS stage?

And which does spice use with these cap ( Cgs, Csg ....), or it will not use these cap in calcutating some results, just do some iteration ?

Thanks!

 

[amir88]

The following paper is a good ref. for you:
A One-Step Input Matching Method for Cascode CMOS Low-Noise Amplifiers
**broken link removed**

 

[ic98]

According to HSpice manual CGD equals (-) derivative of gate charge to drain voltage, and CDG equals (-) derivative of drain charge to gate voltage, and are called Miller feedback and feedthrough.
Therefore when your see through the gate you must use CGD, CGS, and CGB. (the parameters cgs, cgd you give using .OP are the same CGD, and CGS)