[SI-LIST] Re: hspice convergence problem
- From: "Andrew Ingraham" <a.ingraham@xxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Mon, 21 Aug 2006 11:26:31 -0400
Leo,
Convergence problems are as old as SPICE itself.
There are books written about SPICE that devote chapters to helping solve
convergence problems.
You need to understand ... SPICE is not an authority and there is no right
or wrong method to using it. There are countless choices you can make with
the options and all of them result in a simulation which is only an
approximation to reality. There is no one combination that could be called
"correct". (Though there may be some options that your vendor who gave you
their SPICE models says you should use for their models.) Electronic
circuit simulation is sometimes more art than science, despite decades of
work since it was created.
Some things that may or may not help:
SPICE has two solution algorithms: TRAPezoidal and GEAR. Occasionally it
helps to change to the alternate method.
Making RMIN smaller probably makes SPICE more likely to get stuck. Going in
the other direction may help, but eventually this affects accuracy, so try
several values and see how it affects your results.
Play with increasing the various tolerances (anything with "TOL" in the
name), but again keep in mind that the things you do to improve convergence,
tend to decrease accuracy by letting SPICE be more sloppy.
If you have no luck with the other options, you can try simulating only
portions of your netlist. Sometimes there is a bad model in there which is
causing all the trouble. The trick is locating it! Often problems only
show up when elements are combined. Also don't try simulating more than you
really need to.
Regards,
Andy
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