Re: gEDA-user: TwoStageAmp example

[al davis <ad136@xxxxxxxxxxxxxxxx>]

On Monday 02 April 2007 14:05, John Doty wrote:
> Sounds wonderful. Is it sufficiently compatible with SPICE
> that I can   feed it an HSPICE netlist to describe the
> circuit itself? 

Parts of it are closer to HSPICE than NGspice, and have been for 
a long time.  Gnucap has HSPICE compatible VCR and similar 
devices, binning, .param .

The plugins allow it to be customized.  The core will have no 
devices, no commands, and no languages.  It's all in plugins.  
You attach what you want to use.  The default will be 
Verilog-AMS all the way.

One big problem with spice is the conflict between compatibility 
and progress.  Anything added breaks compatibility in some way.  
Again, plugins to the rescue.  There will be "language plugins" 
that will customize the language.  With that, there can be one 
for HSPICE compatibility, another for PSPICE compatibility, and 
so on.  With Verilog-AMS as the language for moving forward, 
there is no longer a need for extensions to Spice that could 
cause compatibility problems.

Most new models are coming out in Verilog-A (subset of 
Verilog-AMS) first.

> I don't care about commanding the simulation 
> in some other language, but I've been working with a VLSI
> layout contractor that uses HSPICE netlists as an interchange
> format and a fab house that distributes BSIM parameters in
> HSIPCE format. 

That's one of the reasons the model plugins are so important.  
One fab give you parameters for BSIM420.  Another gives you 
parameters for BSIM440.  The latest is BSIM460.  There are 28 
official BSIM (3, 4, soi) variants from Berkeley alone.  How do 
you deal with that?  The answer is plugins.  If you want 
BSIM420, that's the one you attach.

Minor compatibility issues can be handled thorough a wrapper.  
If BSIM440 is almost what you want, there will be a simple way 
to wrap it to make it look like something else.

> I generate HSPICE netlists from the schematic, 
> check them in simulation, and submit them to the contractor.
> I get back huge, flat "parameter extraction" HSPICE netlists
> for more simulation. I've been using ngspice with a
> customized spicepp.pl successfully, but there are issues. The
> bigger transient simulations bring ngspice to its knees
> without careful tuning, and noise simulations produce
> nonsense.

Gnucap doesn't have noise simulation yet.  The transient 
analysis has some of the improvements you see in 
the "fast-spice" tools, the ones that do not cost accuracy.

There is also a way to trace what is happening, so you can 
better tell what is going wrong when things go wrong.



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