MOSFET gate-drain capacitance calculation

[Elecemperor]

I'm looking for a creditable formula to calculate the gate-drain capacitance of a MOSFET. I've found a few equations online, but they are either too trivial (for example, Cgd=WCov) or too complicated (Cgd=Cgd,setup+WCgd,f+WLeffCgd,in). The first one doesn't seem to give very exact results, and the second one requires an expert in capacitance calculation to measure each parameter precisely, which is beyond my field of work. So, I'd be really grateful if anybody had any other equations that could help. (I compare my calculation results to the values I see in Cadence DC operating point).

There's also this formula for overlap capacitance whose image I've attached, and I wanna know if I can trust it or not? What does "edge" refer to?

 

[erikl]

There's also this formula for overlap capacitance whose image I've attached, and I wanna know if I can trust it or not? What does "edge" refer to?

"edge" refers to the gate width W , so Cov ≈ 0.2fF*W(in µm)/edge = 0.2fF*2W ( /edge means "per edge" ).