[SOLVED] Cgd and Cgd Overlap - check the results of my AC simulation

[MohEllayali]

Hello
I want to check the results of my AC simulation.
so i try to have the capacitance and what this will give as results
I use the dc op point simulation, and with the results displayer I see the capacitances
so I have 2 questions, if somebody can give me answers or clues , I zill save a lot of time

my first question is , from a pole/ zero point of view is there a difference between cgdoverlap and cgd ? to calculate the transmnission zero of a simple common source stage do I need to sum this capacitors ?

my second question is about the bsim model, there is a lot of capacitances , cbb cgd, cdg , .... can somebody please give me the formulas giving the cgd for instance as a function of all these frightnings capacitances


thanks a lot

 

[erikl]

Re: Cgd and Cgd Overlap

is there a difference between cgdoverlap and cgd ? to calculate the transmnission zero of a simple common source stage do I need to sum this capacitors ?

Sure: cgd is the voltage-dependent gate-drain junction capacitance, whereas cgdoverlap is the fixed physical capacitance from the gate's overlapping part over the drain. But beware: cgd is given as absolute value (Farad), whereas cgdoverlap (usually named cgdo) is given in capacitance/(gate)length (F/m).

my second question is about the bsim model, there is a lot of capacitances , cbb cgd, cdg , .... can somebody please give me the formulas giving the cgd for instance as a function of all these frightnings capacitances.

You may find these relationships in the BSIM manuals or in the C@dence Verilog-A Language Reference (available somewhere here on the EDAboard forums).

 

[MohEllayali]

Cgd and Cgd Overlap

Tnak you erikl