[SI-LIST] Re: HSPICE S-element with a large number of ports
- From: "Hassan O. Ali" <hassan@xxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Wed, 30 Mar 2005 18:11:10 -0500 (EST)
Hi All,
Thanks to all who have provided me with various suggestions on trying to solve
the
HSPICE transient convergence problem. The suggestion I received from Jason
Pritchard
<pritchard_jason@xxxxxxx> (thanks again Jason) turned out to be the best in my
case.
He suggested that I reduce the port numbers of my 36-port S-parameter file to
remain
with only the ports I was interested in driving or probing. Please find below
his
suggestion (which I think should be captured in the SI-list FAQ archive):
On Mar 30, "pritchard, jason" <pritchard_jason@xxxxxxx> wrote:
>
> Hi Hassan,
>
> If you only want to look at a diff pair then convert the 36 port to a 4
> port. Tie off all the other nodes with 50 ohms to ground.
>
> p1,p2,p3,p4 are the nodes of interest in the s-parameter model you want to
> reduce. I use p1 and p2 as my input nodes and p3,p4 as output.
>
> This creates a new 4 port touchstone file......
>
> .ac LIN 1601 0 10G
>
> .LIN sparcalc=1 modelname="NEW model name" filename="NEW file name"
> + format=touchstone noisecalc=1 gdcalc=1
>
> P1 p1 0 dc 0 ac 1 port=1 z0=50
> P3 p3 0 dc 0 ac 1 port=3 z0=50
>
> P2 p2 0 dc 0 ac 1 port=2 z0=50
> P4 p4 0 dc 0 ac 1 port=4 z0=50
>
> Overlay the s-parameters to make sure you set it up correctly and that
> hspice converged on all nodes. This approach almost always works for me.
>
> NOTE: When you start cascading s-parameters together you will run into
> more problems. Use this approach to combine s-parameter blocks together which
> will help with convergence in HSPICE too...
>
> -Jason
The 1601 number appearing above in Jason's message is the number of frequency
points in
the new S-parameter file - it can be different or same as in the original
s-parameter
file. In the example above the frequency range is DC (0) to 10GHz - it should
preferably
be same as in the original S-parameter file.
Another thing to consider while making S-parameter port number reduction: If
the
actual loads tied to the ports you wish to eliminate are other than 50-ohm,
and you would like to include the effects of those loads in the new s-parameter
file, then you should not terminate those ports with 50-ohm loads while making
port
number reduction. You should instead terminate them with the actual loads. The
new S-
parameters of the remaining ports will be different from the original ones.
Hassan.
>-----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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