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From: "Helmut Sennewald"
Subject: Re: SwCADIII
Date: Sun, 5 Jan 2003 01:16:14 +0100
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
"mmormota" schrieb im Newsbeitrag
> Hello Helmut,
> Thank you for the fast reply.
> > > - Sometimes the starting voltage of a capacitor seems to be 0,
> > It happens often that especially large circuits make problems with
> > convergence.
> > Sometimes the circuit itself is wrong. You could send me your circuit to
> > take a look at it.
> Thank you. I am trying to find a simple and clean situation, a twin
> with a small modification but with different starting behaviour.
> > That happens if the circuit simulation has problems. The time step will
> > be reduced automatically to very slow values in this case. If this
> > help, the simulation aborts after a while.
> Ones I just modified the Vcc/2 source from 1.5V to 1.501V and it runs
> again... :-)))
> The device was rather simple without tricky loops, so it seemed to be a
> I dont know nothing about the SPICE calculations, maybe the opamp models
> the problems... Usually I am using slow, low voltage, low power cmos
> like the mcp609.
that sounds indeed interesting and could be worth some investigation.
Can you send me the circuit and model files for some testing?
I am shure Mike E. will improve SwitcherCAD if there is really a weakness
> Do you use a SPICE program for noise analysis too? A tricky feature could
> very useful: somehow converting the usual frequency domain noise (1/f
> to time domain and make it visible in a transient analysis.
I have never seen that feature on any simulator. As far as I know it is
impossible to exactly calculate the time domain noise distribution
from the frequency noise density.
> It could be more
> informative to see it "as on the scope" rather then thinking about the
> of a frequency domain diagram... And much more fun... :-))) If the
> circuit is highly nonlinear, it could be the only useful examination. Is
> this feature available in one of those many spice variants?
You could try to make time domain noise with B-sources using the rand()
Doing some noise additional summing and shaping with filters could make it
possible to get Gaussian noise in time domain. I have never tried that.
PS: I am not an employee of Linear Technology if that matters for you.
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