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[SI-LIST] Re: Question on 2D field solver
- From: "Craig Clewell" <cclewell@xxxxxxxxx>
- To: <ray.anderson@xxxxxxxxxx>
- Date: Thu, 11 Nov 2004 06:07:22 -0800
Hi Ray,
I have used this tool extensively and it does perform quite well.
However, there is some error in the W element that it exports. I sent
the errors to the "Clinic" and they addressed them, but when you
generate a W element you will still need to tweak the Ro value and the
Rs value a bit. The Ro value is off on the last 3 decimal places from
what the solver gives you. The Rs value is off a bit more. You can
use the formulas in the help file to calculate the values.
I think that 1% error isn't bad for a piece of software that never read
Grover :>). Actually, I haven't really used to the tool for round
conductors, but have had good success with the "rectangles".
I did speak with Robert Techentin at the clinic when I reported some
errors that I found. He gave me some pointers on the software which
included using the sweep function to generate values for the C-seg and
D-seg. This helps to dial in the asymmetry in the C and L matrices.
Sometimes one value must be different than the other in order to obtain
the lowest asymmetry in the matix. Perhaps you have a small error in
the asymmetry and this is what is contributing to your 1% error.
Depending on the application 1% may not really mean too much. Another
thing was that sometimes you can reduce the asymmetry by lowering the
values of C and D seg as opposed to raising them.
I also did what you have done comparing the results from TNT to other
methods using "rectangles". I used Linpar, Agilent, Ansoft, and AWR's
tool. I found that the results were about the same as what you have
obtained using your tools. I took the results one step further and ran
a frequency sweep up to about 4GHz on all the values I exported. I was
within a couple of tenths of a dB on the insertion loss and return loss
with values similar to those you show below. In most cases I believe
this to be an acceptable error.
Craig
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Raymond Anderson
Sent: Wednesday, November 10, 2004 3:25 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Question on 2D field solver
Here's a question for the field solver guru's on the list:
I'm currently taking a critical look at the Mayo MMTL BEM 2D field
solver (TNT 1.2.2) that the developers at Mayo have so graciously made
freely available under the GNU GPL to the world. See the si-list
message announcing it for download links:
(http://www.freelists.org/archives/si-list/07-2004/msg00311.html)
In preparation for doing a series of simulations on some via geometries
in packages I decided to validate the accuracy of the MMTL program on
some simple geometries that independent high accuracy answers were known
for.
I first tried the zero thickness stripline benchmark suggested by Dr.
Rautio at Sonnet Software.
(http://www.sonnetusa.com/products/benchmarking/eval_ch3.asp). The
results were about -0.4% low at 49.8002 ohms. This compares
comparably with a selection of other solvers I've had access to (but on
the low end of the range).
Mayo MTTL 49.8002
Polar CITS25 49.96
Agilent Appcad 3.0.2 49.8
AWR TXLINE 50.0346
LINPAR 2.0 50.03
LINPAR 1.0 50.027
Next I selected the case of a pair of parallel round elements as a test
case. The analytical solution for the inductance of this geometry is
given by Grover in chapter 5 of "Inductance Calculations". His formula
is an analytic solution based on first principles.
Using a test case of conductors 150 microns in diameter on a 500
micron pitch, Grover's equations yields a loop inductance of
758.84797 nH for 1 meter long conductors. The same problem modeled in
the MMTL field solver gives an answer of 749.4645 nH. I'm trying to
understand why the field solver answer is about 1.2% low. Is this
reasonable for a 2D MOM BEM solver using quasi-TEM assumptions? I've
tried modeling it several ways (as a pair of parallel circular
conductors far from ground and as a single circular conductor with it's
image reflected across a ground plane) and am getting the same answer
out to at least 2 decimal places. I've also tried upping the density of
the meshing with little real improvement.
Comments, suggestions and ideas solicited. Thanks!
-Ray Anderson
Senior Signal Integrity Staff Engineer
Advanced Packaging R&D
Xilinx Inc.
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