Opamp input transistor gate parasitic capacitor

[iamxo]

We usually have to consider the input parasitic capacitor when the opamp is in closed loop, but i donot know how to calculate this parasitic capacitor.

is it only Cgs of the input transistor or Cgg ( Cgs + Cgd + others related to the gate)?? Anyone helps me.

 

[Jackon521]

if the input is CS stage, the Cgg is Cgs + A*Cgd, miller effect is considered.