RE: [SI-LIST] : **error**: internal timestep too small

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From: Mellitz, Richard (richard.mellitz@intel.com)
Date: Wed Jan 19 2000 - 16:26:14 PST


I know that one. However there are practices the seem to cause this (ITTS)
more than others. OOOH not another acronym! For example, using 0V DC
sources to short nodes is inherently more stable than lots of .00001 ohm
resistors. Once in a while if I'm not careful with W elements segmenting, I
get ITTS problems too.

For some reason, return path modeling quite susceptible to ITTS.

One key indicator is to look at the voltage change at the very first time
step of all "DC signals". If you get a spike then your very susceptible to
ITTS. Insuring a solution for all incantations of your design is a real art.

Rich Mellitz,
Intel

-----Original Message-----
From: Dmitri Kuznetsov [mailto:vdm@iname.com]
Sent: Wednesday, January 19, 2000 7:00 PM
To: si-list@silab.eng.sun.com
Subject: Re: [SI-LIST] : **error**: internal timestep too small

Interestingly, to get rid of the "internal timestep too small" error,
one needs to make the time step SMALLER.

The error is caused by nonconvergence due to previous time steps being
too large. SPICE tries to "backtrack" and redo the current time
iteration with subsequently smaller time steps, and when it fails, the
above error is generated.

I am sure you knew about that. But many novice SPICE users try to
increase the time step when they see the "timestep too small" error,
which makes the problem worse.

Dmitri Kuznetsov

 
Jim Freeman wrote:
>
> Haven't we all
>
> Jim Freeman
>
> "Mellitz, Richard" wrote:
>
> > I've got one thing to say about spice.
> >
> > I've grown to hate the following line:
> >
> > **error**: internal timestep too small in transient analysis
> >
> > Rich Mellitz
> > Intel
> >

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