Re: gEDA-user: TwoStageAmp example

[al davis <ad136@xxxxxxxxxxxxxxxx>]

On Monday 02 April 2007 16:42, Patrick Doyle wrote:
> Please forgive my ignorance, but how would I know if I can
> use the native models or not?  Similarly, when would I decide
> that I wanted BSIM models?

It depends what the fab gives you.  Your circuit is a simple BJT 
circuit.  There are some parameters that are designed for a 
particular commercial simulator, that gnucap ignores.  "bad 
parameter -- ignored"

To be truly accurate you need to find that model.  For what you 
are doing, the native ones are good enough.  Most of the time 
the native ones are good enough.  Unless you 
explicitly "attach" another one, you are using the built-in 
ones.

> Also, FWIW, the 3-29 snapshot crashes when I try to analyze
> the netlist from Stuarts TwoStageAmp example... at least it
> does when I try to run the version I built today.  I have,
> perhaps, attached the netlist for your review.  If it works
> fine for you, then I'll try rebuilding and paying more
> attention to what's going on.

Any crash is a bug, but it didn't crash for me.  Your commands 
are incorrect.  Mine acted as expected for the input you gave.

You did not supply "Simulation.cmd".  I made an empty one.
>
> Here's what crashes for me:
>
> $ ~/local/bin/gnucap spice.netlist.wpd
> gnucap> plot ac v(Vout)
> gnucap> ac dec 1Hz 1MegHz
>
> #Freq
> Segmentation fault

1.  You need to do "op" before "ac".  This is a difference 
between gnucap and spice.  If you don't your AC results will be 
an accurate representation of what the circuit does with the 
power off.  AC uses the last operating point from op, dc, or 
tran.  Spice always forces an op, and uses it to set up for AC.  
The gnucap way is more flexible.  It adds capabilities that are 
important to an analog designer.

To a beginner:  Always do "op" before "ac".

2. The AC line is incorrect.  The "Hz" is ignored, so you asked 
for 1 step per decade, with a start frequency of 1 meg, no stop 
frequency.  It assumes the stop frequency is also 1 meg, so you 
get a single point.

When I did an op first, then ac, I got reasonable results.


Gnucap really does have a problem with the lack of beginner 
documentation.


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