Hi Gert,
Thanks for the advice. I will definitely try your suggestion.
Cheers,
Tramp
On Thu, Oct 17, 2019 at 2:52 PM Havermann, Gert <Gert.Havermann@xxxxxxxxxxx>
wrote:
Todd,
it would be great If I would be in the position to demand good
S-Parameters, but the regular way is still that I have to live with what I
get.
Mit freundlichen GrüÃen / Kind regards.
Gert Havermann
Signal Integrity Engineer
Dept.: Corporate Technology Services
HARTING Stiftung & Co. KG
MarienwerderstraÃe 3
D-32339 Espelkamp
Phone +49 (0)5772 47 857
Fax +49 (0)5772 47 90857
mailto:gert.havermann@xxxxxxxxxxx
http://www.HARTING.com
----------------------------------------
HARTING Stiftung & Co. KG | Postfach 11 33, 32325 Espelkamp |
www.HARTING.com
Persönlich haftende Gesellschafterin:
HARTING Führungsstiftung | Amtsgericht München | HRA 108479 | München
Vorstand: Dipl.-Kfm. Philip F. W. Harting (Vorsitzender), Dipl.-Kffr.
Maresa W. M. Harting-Hertz, Dipl.-Kfm. Dr.-Ing. E. h. Dietmar Harting,
Dipl.-Hdl. Margrit Harting, Dipl.-Ing. (FH) Dipl.-Wirtsch.-Ing. (FH)
Andreas Conrad, Dr. iur. Michael Pütz
Sitz der Gesellschaft: Espelkamp | Amtsgericht Bad Oeynhausen | HRA 9021 |
UST-ld Nr. DE812136745
-----Ursprüngliche Nachricht-----
Von: Westerhoff, Todd <Todd_Westerhoff@xxxxxxxxxx>
Gesendet: Donnerstag, 17. Oktober 2019 15:42
An: Havermann, Gert <Gert.Havermann@xxxxxxxxxxx>; si-list@xxxxxxxxxxxxx
Betreff: RE: [SI-LIST] AW: impact of sparam's DC value &violations on HS
signal performance
Gert,
I think your point gets glossed over often.
Let's look at it this way - most of us would agree that IBIS-AMI models
have portability problems, but how many of us would say that S-parameters
have the same issue? I maintain that they do.
There are a number of aspects to S-parameter portability, but the most
important is probably the DC point. When it's missing, a time-domain
simulator is *forced* to create one and that process is highly tool
dependent. Add the issues associated with obtaining / extracting accurate
low frequency data, and the variance between tools and results gets even
larger.
The fallback - the safety net that we all want to rely on - is that most
tools can "correct S-parameters for missing DC points, passivity, symmetry
and causality". Which sounds great, right? Because how many of us can
really tease those problems out of tabular frequency-domain data, much less
do anything about it? We all want the "Easy" button that will take bad data
and make it good, without out having to really understand what was going on.
I maintain that's a trap. Fixing small causality and passivity issues is
fine - *but you need to know the problems were small in the first place*,
such that automated correction is even appropriate. Automated correction of
significantly bad data is just a bad idea.
My point - we should be striving to create (or demand) s-parameter data
with DC points that passes appropriate quality checks. Automated
extrapolation and correction is really just a crutch - for a problem that
shouldn't have existed in the first place.
That's my $0.025 (you get an extra half cent on Thursdays).
Todd.
Todd Westerhoff
High-Speed Design Product Marketing | Electronic Board Systems
300 Nickerson Rd, Marlboro, MA 01752
todd_westerhoff@xxxxxxxxxx | office: 508-303-5821 | cell: 978-846-0203
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Havermann, Gert
Sent: Thursday, October 17, 2019 2:04 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] AW: impact of sparam's DC value &violations on HS
signal performance
Hi Tramp,
the correct DC point is the key to correct domain transformation. If you
need time domain data (like eye or impedance plot) from S-Parameters then
the DC point is very important as it affects the reference impedance and
the causality. Extrapolation works ok if the extrapolated DC point is still
"passive", but especially for measurements this isn't always the case
because VNAs trend to have problems with the accuracy of the lowest
frequency points. Thatâs why it sometimes helps for you if you clip below
60MHz.
Just for the fun of it, take a set of S-Parameters and add two slightly
different DC points and compare the results after transforming it to time
domain. And add an "active" DC point (+0.3dB or similar) and then compare.
And check all those files for causality. You can also transform all these
files using the passivity and causality enforcement. This gives a very nice
overview about the importance of the DC point.
Mit freundlichen GrüÃen / Kind regards.
Gert Havermann
Signal Integrity Engineer
Dept.: Corporate Technology Services
HARTING Stiftung & Co. KG
MarienwerderstraÃe 3
D-32339 Espelkamp
Phone +49 (0)5772 47 857
Fax +49 (0)5772 47 90857
mailto:gert.havermann@xxxxxxxxxxx
http://www.HARTING.com
----------------------------------------
HARTING Stiftung & Co. KG | Postfach 11 33, 32325 Espelkamp |
www.HARTING.com Persönlich haftende Gesellschafterin:
HARTING Führungsstiftung | Amtsgericht München | HRA 108479 | München
Vorstand: Dipl.-Kfm. Philip F. W. Harting (Vorsitzender), Dipl.-Kffr.
Maresa W. M. Harting-Hertz, Dipl.-Kfm. Dr.-Ing. E. h. Dietmar Harting,
Dipl.-Hdl. Margrit Harting, Dipl.-Ing. (FH) Dipl.-Wirtsch.-Ing. (FH)
Andreas Conrad, Dr. iur. Michael Pütz Sitz der Gesellschaft: Espelkamp |
Amtsgericht Bad Oeynhausen | HRA 9021 | UST-ld Nr. DE812136745
-----Ursprüngliche Nachricht-----
Von: si-list-bounce@xxxxxxxxxxxxx <si-list-bounce@xxxxxxxxxxxxx> Im
Auftrag von Tramp
Gesendet: Donnerstag, 17. Oktober 2019 00:09
An: si-list@xxxxxxxxxxxxx
Betreff: [SI-LIST] impact of sparam's DC value &violations on HS signal
performance
Hi experts,
As we know the DC value of PDN is critical in PI simulations. But for
10Gbps+ SI sim, how much impact an inaccurate DC value of the sparam can
produce?
and, quite often we see the extracted sparam has passivity and/or
causality issue at LF and DC, due to extrapolation or other reasons. So the
same question comes again: for 10G+ sim, how much impact on the eye such
violation can pose? Is it ok to simply cut out the part below 60MHz? In my
experience for most cases clipping this band of freq eliminates the
majority of passivity and causality violations.
--
Best Regards,
Tramp
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