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Modeling >> Semiconductor Devices >> GP2 BJT Model - nonlinear caps charge conservation
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Message started by Greg on Jan 11^th, 2006, 1:29am

Title: GP2 BJT Model - nonlinear caps charge conservation
Post by Greg on Jan 11^th, 2006, 1:29am

Hi,

I have the problem that the nonlinear simulation of BJT amplifier does not match reality, especially impedance matching at harmonics.
Could this be because the nonlinear junction capacitors are simulated as nonlinear c(v) and not as q(v)?
Could a solution for that be possible if I set the junction capacitors to zero and ad some q(v) modelled caps with the appropriate c(v) values?

Regards,
Greg

Title: Re: GP2 BJT Model - nonlinear caps charge conserva
Post by Geoffrey_Coram on Jan 12^th, 2006, 5:58am

Is "GP2" a proprietary extension to Gummel-Poon? I'm not familiar with it.

Most modern transistor models have learned the problems with c(v); I know it was an issue with early MOS levels, but I don't recall reading anything about problems for BJTs. In particular, most BJT models compute the base charge and use this to determine other quantities, so I'd be surprised if there were c(v) formulations.

Title: Re: GP2 BJT Model - nonlinear caps charge conserva
Post by Greg on Jan 15^th, 2006, 10:58pm

GP2 is a Gummel-Poon model in Tekspice, a spice simulator from Tektronix.

How about the other caps, like collector-base?
Is there a way one could test if it is simulated correctly? Like a testcircuit that is especially sensitive to the c(v) errors and where there are known results with correct and with wrong implementation?

Greg

Title: Re: GP2 BJT Model - nonlinear caps charge conserva
Post by Greg on Jan 25^th, 2006, 11:32pm

Greg wrote on Jan 15^th, 2006, 10:58pm:

Is there a way one could test if it is simulated correctly? Like a testcircuit that is especially sensitive to the c(v) errors and where there are known results with correct and with wrong implementation?

Is there no easy circuit to test the simulation for correct simulation of those capacitances?
Greg

Title: Re: GP2 BJT Model - nonlinear caps charge conserva
Post by Ken Kundert on Jan 26^th, 2006, 12:42am

Check out section 4.2.5 of the Spice and Spectre book (designers-guide.org/Books/dg-spice), which starts on page 167.

-Ken

Title: Re: GP2 BJT Model - nonlinear caps charge conserva
Post by Greg on Jan 26^th, 2006, 7:51am

Ken,

not that I would not want to pay for valuable information, but more than $100 is a bit too much for me (privately based, radio amateur).
I will try to persuade my boss at work to buy this book for the company, but we are very small company and at the moment we arevery narrow on money.

Greg

Title: Re: GP2 BJT Model - nonlinear caps charge conserva
Post by Ken Kundert on Jan 26^th, 2006, 8:01am

That is quite understandable. Here is the relavent section of the book.