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Simulators >> Circuit Simulators >> Question about bisim3v3 parameters
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Message started by kiran123 on Jun 11^th, 2007, 1:19am

Title: Question about bisim3v3 parameters
Post by kiran123 on Jun 11^th, 2007, 1:19am

Hi
i am using BISIM3v3 level -11 model parameters and i could not find parameter "phi" which is useful for below equation ,

VTH = VT0 + gamma * ( sqrt(phi - VBS) - sqrt(phi) )

can anyone help me on how to get this

gamma is declared as k1 in models statement

Thanks & Regards
Kiran

Title: Re: Question about bisim3v3 parameters
Post by Geoffrey_Coram on Jun 11^th, 2007, 4:12am

The Berkeley code for BSIM3 has:

pParam->BSIM3phi = 2.0 * Vtm0
* log(pParam->BSIM3npeak / ni);

where Vtm0 is kT/q (for T=tnom) and BSIM3npeak is entered as the parameter NCH. ni is the intrinsic carrier concentration of Si.

Title: Re: Question about bisim3v3 parameters
Post by kiran123 on Jun 12^th, 2007, 12:50am

Geoffrey_Coram wrote on Jun 11^th, 2007, 4:12am:

Geoffrey,

what is this "pParam->" declaration ? where should i mention this to get "phi" value ?
i understood that the above equation is looks like
"phi" = 2 * kt/q * log( ni / NA)
can i take kT/q = 26mV at 300k
& ni = 1.45* 10^10 cm^-2 otherwise where from i should get ?
NA = nsub or nch ?

Thanks
Kiran

Title: Re: Question about bisim3v3 parameters
Post by Geoffrey_Coram on Jun 12^th, 2007, 4:14am

kiran123 wrote on Jun 12^th, 2007, 12:50am:

what is this "pParam->" declaration ? where should i mention this to get "phi" value ?
i understood that the above equation is looks like
"phi" = 2 * kt/q * log( ni / NA)
can i take kT/q = 26mV at 300k
& ni = 1.45* 10^10 cm^-2 otherwise where from i should get ?
NA = nsub or nch ?

pParam is a data structure in the BSIM3 source code (having to do with sharing values for devices with the same L and W).

You inverted the division in the log, it's log(NCH/ni), and NCH is the parameter.

ni = 1.45e10 * (Tnom / 300.15) * sqrt(Tnom / 300.15) * exp(21.5565981 - Eg0 / (2.0 * Vtm0));

You should double-check that Tnom in the model card is 27.0 C (which would be 300.15 K), else you'll have to adjust ni and kT/q from what you are using; then again, you may not care to be all that exact.

Title: Re: Question about bisim3v3 parameters
Post by kiran123 on Jun 21^st, 2007, 12:05am

Geoffrey_Coram wrote on Jun 12^th, 2007, 4:14am:

kiran123 wrote on Jun 12^th, 2007, 12:50am:

Geoffrey,
Thanks a lot for sharing helpful information on this , if possible can you tell me why should NCH is to be consider instead of nsub, some text boox says it is nsub i.e equivalent SPICE parametr name is NSUB
from the model file information i found below definition for them
NCH: Peak Channel doping concentration
Nsub : substrate doping concentration

thanks
Kiran

Title: Re: Question about bisim3v3 parameters
Post by Geoffrey_Coram on Jun 21^st, 2007, 10:18am

Have you tried reading the appropriate section of the BSIM3 manual? I assume it's explained there.