[SI-LIST] Re: Touchstone vs. "txt" file output
- From: "Yuriy Shlepnev" <shlepnev@xxxxxxxxxxxxx>
- To: "'Ralph Wilson'" <wilson@xxxxxxxxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Tue, 6 Jul 2010 15:56:13 -0700
Hi Ralph,
Take a look into the generated Touchstone file - most likely it is written
in the original Touchstone format that does not support the mixed-mode
S-parameters. Mixed mode requires different normalization impedances for
differential, common and single-ended ports that is supported only by the
new Touchstone version 2.0.
After reading data from the older Touchstone file with the single-ended
S-parameters, you have to transform them into the mixed-mode to see SDD11 or
SDD12. Free software Simbeor 2008.01 L0 can help you to do such
transformations and in addition to estimate quality of the computed
S-parameters (passivity, causality, reciprocity, symmetry). The software is
available at
www.simberian.com/Downloads.php (requires registration).
Best regards,
Yuriy Shlepnev
www.simberian.com
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Ralph Wilson
Sent: Tuesday, July 06, 2010 9:49 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Touchstone vs. "txt" file output
All,
I am using CST Microwave Studio for via investigation at high speed
SERDES rates. After
a simulation I am able to view various plots, including "magnitude (dB)"
vs. frequency. If I
export this as a "txt" file and convert it to csv, I can see the same
curves when I plot them in
Excel. However, if I export these same results as a "Touchstone file",
when I open the resulting
.s4p file in a Touchstone viewer many of the curves are different (some
of the S parameters
seem to be very similar, many are significantly different). To the best
of my knowledge, I am
keeping the port(s) and modes(s) straight - at least based on the
documentation provided on
exporting such files. I have also tried to make sure I'm looking at
"magnitude" and not simply
the real / imaginary parts. Based on the way I read the export
documentation, I do not think the
tool is doing a mode conversion.
Is there any reason I should NOT expect these plots to be identical? Is
there any "math magic"
that would manipulate an "SDD21 magnitude in dB" plot (for example) as
it is exported to a
Touchstone file?
Thanks!
Ralph Wilson
Alcatel-Lucent
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