Hi, all,

I have questions about Cdb and Cjd.

If my understanding is correct, in saturation, Cjd is roughly Cdb.
(Cjd = drain-bulk junction capacitance (drain bottom plate and sidewall capacitance, Cdb = dQd/dVb - transconductance)

In spectre op values, Cjd and Cdb are different in saturation region. Do you guys know why? (Cjd is several order bigger than Cdb)
I believe that Cdb in op values in spectre is in F, not F/m^2..or so.

Since Cdb is defined as dQd/dVb, it is small signal capacitance. What about Cjd?
Is it small signal capacitance too? (I named small-signal capacitance, do you have better name and explanation? - Is it capacitance load at the drain while it is being biased?)

If I want to account drain load capacitance of a transistor, do I have to consider Cdb or Cjd?


(Bottom line: How does Cdb we see in analog books differ from Cdb in spice?)

Thanks in advance!!
PS: Any references are welcome!! (Easy to read ones..^^)