[SI-LIST] Re: HSPICE S-element with a large number of ports
- From: "lei luo" <lluo3@xxxxxxxx>
- To: <hassan@xxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Tue, 29 Mar 2005 20:28:32 -0500
Hassan:
I met the "internal time step too small" problem in my spice simulations
too, although it's nothing to do with the S-element.
Most cases, I find it is because I didn't provide DC paths between some
nodes. I had several global power supply nets and ground nets and there are
many capacitors and inductors in the package model and it is easily just
forget to provide DC paths for some nodes.
Three notes:
1. Although in most cases, spice will notify you "no dc path" error, in some
cases, you have to find them out by yourself. And this hidden "no dc path"
error will cause you problems.
2. Adding some models will bring in the "internal time stop too small
problem". I had an experience: without a W-model in my circuit, I don't have
"interal time step too small" problem, but after I add a W-model, the
problem happens. Then I find it's due to the hidden "no DC path" error.
After I provided DC path, this "internal time step too small" problem were
solved.
3. You may need to set the initial conditions for those nodes associated
with the S-element, I am not sure about this, maybe some guru can provide
some information on that,
Hope this helps,
-- Lei Luo
NC State University
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Hassan O. Ali
Sent: Tuesday, March 29, 2005 3:05 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] HSPICE S-element with a large number of ports
I'm trying to perform a very simple (or so I thought) HSPICE simulation with
a 36-port S-
element for 18 coupled package lines. Only one port is driven with a pulse,
the rest are
terminated with RC loads.
The simulation fails with the dreaded "internal time step too small in
transient
analysis" error message.
I don't use any fancy options in my S-element model line. Just:
.model s-para-line18 s tstonefile='../s-parameter/line18.s36p'
Could any one share tricks for better transient convergence with large
S-elements?
Thanks.
Hassan.
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