[SI-LIST] Ansoft Q2D and Swept Impedance Parameters
- From: "Doug White" <dowhite@xxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Thu, 11 Dec 2003 11:38:41 -0500
All,
I have been using Ansoft Q2D to generate tabular w-element models for
lossy striplines. The geometries are fairly typical of what you might
see on a high-speed differential pair for a serial link on a backplane.
I'm doing an impedance-sweep up to 20GHz. For certain geometries, the
frequency-dependent resistance is incorrect. What I'm seeing when I
plot R(f) is that above some frequency, say
1GHz, the impedance curve begins to "flatten out", and no longer follows
the sqrt(f) relationship. The flattening is quite significant. Now,
for a subset of these problematic geometries, increasing the
# of iterations in the sweep mitigates the problem. For the others, it
appears that nothing can be done in the solution setup. Ansoft is aware
of the problem (they say that it is a numerical one), but have
not prioritized its resolution. There are some non-ideal workarounds
such as cutting the data off below some frequency and extrapolating from
there...but I was wondering if any of you have seen this problem
and if so, have you determined an effective solution?
Thanks,
Doug White
Cisco Systems
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