Is there anybody who knows the equation for calculating Cds for a transistor?

[Alex Liao]

Hi, Cds stands for total drain to source capacitance.

I only know dQd/dVs. Is there any other ways of getting it?

Something like Cgs = Cox * Weff *Finger_Number *Leff * 2/3 + Cov*Weff*Finger_Number.

Thanks,

 

[dick_freebird]

This is going to depend on a lot of things. For the power MOSFET,
you're really talking Cdb as the dominant term because B=S by
close-in strapping. Then it's raw junction depletion capacitance
with Vds dependence (when off) or a pretty good D-S short and
not much use in figuring C, when on.

Short channel FDSOI MOSFETs, it's really the metallization and
S,D region fringing fields across the short L gap if the buried oxide
is thick. That's a nasty thing to try closed form analysis on;
TCAD with good EM tools is the best hope for accuracy in my
opinion.