[SI-LIST] Re: S-par to Spice
- From: Kim Helliwell <kimgh@xxxxxxxxxxx>
- To: Saoer Sinaga <saoer.sinaga@xxxxxxxxx>, si-list@xxxxxxxxxxxxx
- Date: Mon, 2 Jun 2008 08:12:40 -0700 (PDT)
My experience is that if you take due care in creating your S-parameter
model in HFSS, you can almost always generate a passive model. The
current version of HFSS has a built-in passivity checker with an
adjustable tolerance, which you can use to good effect.
My technique is to do an interpolating sweep over the range of
interest, with extrapolation to DC. If there are non-passive points at
the low end, I do an interpolating sweep over a smaller
range including the non-passive points, and another sweep for the
remaining portion of the full range, and then combine those two sweeps
for output. Usually, this is enough to create a passive model that
HSPICE can accept. There were only a couple of times that I had to create
several sweeps before achieving passivity over the whole range, out of
dozens of package models that I created while working at my former
employer.
The technique is based on the observation that the calculated points are almost
never nonpassive; it's only the interpolated (or extrapolated) points that
might be nonpassive. So the described technique makes the interpolation more
accurate in difficult ranges by forcing the calculation of more points in that
region. If the actual calculated points are nonpassive, this technique will
obviously not help. But I've never seen that happen so far.
This technique is not my invention, by the way: it was suggested by one of the
CAEs at Ansoft. I have found it to work very effectively. I never found it
necessary to do my own curve fitting and interpolation; just take advantage of
the built-in interpolation in HFSS itself.
Kim Helliwell
----- Original Message ----
From: Saoer Sinaga <saoer.sinaga@xxxxxxxxx>
To: si-list@xxxxxxxxxxxxx
Sent: Monday, June 2, 2008 12:53:22 AM
Subject: [SI-LIST] S-par to Spice
Dear all,
As you all might know, the S-parameter produced by HFSS is not always
passive, especially when you extrapolate to DC.
Is there any tool that can generate a passive spice file (spectre
compatible) out of a non-passive S-par? Preferably a freeware that I can use
immediately.
many thanks,
Saoer Sinaga
NXP Semiconductors.
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