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Modeling >> Semiconductor Devices >> Reverse diode voltage
https://designers-guide.org/forum/YaBB.pl?num=1208810360

Message started by Godfrey on Apr 21^st, 2008, 1:39pm

Title: Reverse diode voltage
Post by Godfrey on Apr 21^st, 2008, 1:39pm

Is there a parameter for modelling the junction to substrate diode?

So if I take the drain of an nmos transistor below Vss, at some voltage the reverse diode of N diff to substrate should conduct. Same for a PMOS, if I take the drain above Vcc, at some voltage the P diff to N well diode must conduct.

Title: Re: Reverse diode voltage
Post by Geoffrey_Coram on Apr 22^nd, 2008, 8:05am

Godfrey wrote on Apr 21^st, 2008, 1:39pm:

Is there a parameter for modelling the junction to substrate diode?

Generally, yes.

Are you using a BSIM3/4 or PSP model? Do you have a 4-terminal model? I've seen some 3-terminal discrete component models that don't have a substrate terminal. I've also seen some MOS models that don't include the diodes, because they expect you to put them in a subckt that contains the diode.

Title: Re: Reverse diode voltage
Post by Godfrey on Apr 24^th, 2008, 2:02pm

Its BSIM 3.3 with four terminal devices.

The only parameter I can see which looks about the right value is Dvt1 which also sounds like it might be diode Vt?

Title: Re: Reverse diode voltage
Post by Geoffrey_Coram on Apr 25^th, 2008, 5:27am

No, Dvt1 is an offset to the threshold voltage of the mos.

For BSIM3/4, you need to have JS and/or JSW specified non-zero for the model card, and these are then multiplied by AD/AS or PD/PS to get the total diode saturation current (JS*AD + JSW*PD). PB is the parameter for the built-in potential. CJ, CJSW, CJSWG are the capacitance parameters (something like CJ*AD, CJSW*(PD-W), CJSWG*W).