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Greg

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GP2 BJT Model - nonlinear caps charge conservation
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

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Geoffrey_Coram

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Re: GP2 BJT Model - nonlinear caps charge conserva
Reply #1 - 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.

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If at first you do succeed, STOP, raise your standards, and stop wasting your time.

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Greg

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Re: GP2 BJT Model - nonlinear caps charge conserva
Reply #2 - 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

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Greg

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Re: GP2 BJT Model - nonlinear caps charge conserva
Reply #3 - 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

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Ken Kundert Global Moderator Offline Posts: 2384 Silicon Valley	Re: GP2 BJT Model - nonlinear caps charge conserva Reply #4 - 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
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Greg New Member Offline Posts: 4	Re: GP2 BJT Model - nonlinear caps charge conserva Reply #5 - 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
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Ken Kundert Global Moderator Offline Posts: 2384 Silicon Valley	Re: GP2 BJT Model - nonlinear caps charge conserva Reply #6 - Jan 26^th, 2006, 8:01am That is quite understandable. Here is the relavent section of the book.
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