Re: gEDA-user: Problem with 2N3906 model in gnucap

[al davis <ad151@xxxxxxxxxxxxxxxx>]

On Wednesday 06 February 2008, gene wrote:
> Beta also varies with collector current, do the simulators
> (and these models) account for this behavior?  In fact, the
> curves for different transistors (beta vs. IC) are so
> incredibly different - some flat, some very peaky before
> rolling off.

Short answer:  Yes.

Long answer:  It depends on what model you use.  In older 
simulators, models are compiled into the core, so for a user to 
change them is difficult or impossible.  In most high end 
commercial simulators, and the development version of gnucap, 
models are not built in, but under complete control of the 
user.  As provided, one BJT model is compiled in, but there is 
nothing magic about it.

There are several models with varying degrees of accuracy and 
maturity.  As it stands now, there are 3 more as plugins.  For 
mosfets, there are 8 different models supplied with the core, 
and 53 more as plugins.  Some of these differ only trivially. 
Since models are plugins, you can use an old version of a model 
if you want.  There are more that are not currently available, 
many of which will become available when the Verilog-A model 
compiler works.

Some of these models are extremely accurate and complex.

The gnucap project does not develop models, but rather provides 
a way to use models developed by others as plugins, and 
provides the tools for developing models including interactive 
debugging.



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