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Re: [Help-gnucap] Time step control

From: a r
Subject: Re: [Help-gnucap] Time step control
Date: Mon, 3 Dec 2007 22:43:38 +0000

Thank you for detailed response.

On Dec 3, 2007 8:59 PM, al davis <address@hidden> wrote:
> It's not as bad as it looks.
> In a development snapshot, sometimes there are warnings for
> things that would be suppressed later.
> I do not have your models, so I am guessing here.

The models I am using were posted to the gnucap-dev list before:

(I have only changed level=49 to level=8 for evaluating bsim3 models).

I wished I could try Gnucap with "real" production models but for this
it would need to support at least expressions and including libraries
with sections. Preferably also verilog-a models.

> >
> > ^ ? bad parameter, ignored
> That is probably a bug.  I need to see the ".model".
> >
> > and then bunch of warnings:
> >
> > Warning: This model is BSIM3v3.3.0; you specified a wrong
> > version number.
> What version did you specify?  Maybe you don't want 330 ..

That's right. This should be bsim310 version.

> > [...]
> > initial step rejected:Mp.xi1
> > new=1.87716e-12 old=1e-11 required=5e-12
> [...]

Thank you for explanation.

> You say it works .... No trap ringing???

In fact, it is still ringing if I use trap method with default
options. However, dtmin=0.001 solves the problem for this circuit (for
larger circuits higher values are enough). Defaults are not very
suitable for simple logic or sampled circuits.

Regarding your next email:

> I need to reword that message.
> How would you like something of the form ...
> ===============
> C567: is too fast
> Required step for accuracy: 5.58e-18
> Min step per option dtmin:  1e-15
> Using Euler for this device.
> ===============

I tried that simulation with dtmin=1e-30:
storage element step control error:Mn.xi1 7.46722e-19
using Euler, disabling time step control

Interesting. The results are fine, though.


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