Yuriy,
WRT has been using 3X round trip delay (lowest sample wavelength needs to be
<3X length of DUTX3) versus the 90degree rule you discussed.
My thinking is that both of these rules provide same result to get the first
S-parameter sampled frequency point to be low enough base on sample points.
The rule you stated would be equivalent to 4X delay. Do you agree?
- Al
Products for the Signal Integrity Practitioner
Alfred P. Neves
Chief Technologist
Office: 503-679-2429
www.wildrivertech.com <http://www.wildrivertech.com/>
2015 Best In Design&Test Finalist
On Jun 25, 2017, at 1:00 PM, Yuriy Shlepnev <shlepnev@xxxxxxxxxxxxx> wrote:
Hi Chetan,
I think the extrapolation can be done under some conditions:
1. The measurement quality is good at the lowest frequency points - this is
not always the case.
2. No skin effect at the lowest measurement frequencies (it looks like is
satisfied in your case).
3. To make the extrapolation simpler, the electrical length of the cable
should be below 90 degrees at the first frequency point:
2*pi*L/lambda<=pi/4, where lambda=c/(frq*sqrt(eps)).
Optionally, you can use Ohm-meter to measure signal and reference conductors
resistance, compute S-parameters from the measurements and add zero
frequency point into Touchstone model - that turns the uncertain
extrapolation problem into an easier interpolation problem.
You can find description of some extrapolation technique in the upcoming
IEEE P370 standard (TG3).
Best regards,
Yuriy
Yuriy Shlepnev, Ph.D.
President, Simberian Inc.
2629 Townsgate Rd., Suite #235, Westlake Village, CA 91361, USA
Office +1-702-876-2882; Fax +1-702-482-7903
Cell +1-206-409-2368; Virtual +1-408-627-7706
Skype: shlepnev
www.simberian.com
Simbeor - Accurate, Productive and Cost-Effective Electromagnetic Signal
Integrity Software
2010 and 2011 DesignVision Award Winner, 2015 Best In Design&Test Finalist
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of chetan reddy
Sent: Saturday, June 24, 2017 3:32 AM
To: si-list
Subject: [SI-LIST] Signal quality: 100Khz square wave signal sending into a
channel with S parameter model from 300KHz to 5Ghz
Hi All,
I am trying to run a transient simulation for checking the signal quality on
one of the low speed interface, which runs at 100 Khz (Square wave). The
topology is shown below:
(TX ibis)---> (board trace S parameter model)--->(Cable S parameter
model)--->(board trace S parameter model)--->(RX ibis).
The Vendor has provided the S parameter model for the cable, but they have
extracted it from 300Khz to 5Ghz but my square wave signal operating
frequency is 100Khz. When i have asked them to extract from DC to 5Ghz, they
replied like that their VNA is not capable to extract from DC (0Hz), minimum
it works from 300Khz to 25Ghz.
Signal logic is 3.3V. I have used the same cable S parameter into my
transient SI simulation. At the output side i could see only a Square wave
with ampliture 1.2V. This is because the fundamental component is being
filtered by the channel.
In this case, how should i get a cable model which is from 100Khz to 5Ghz or
DC to 5Ghz?
Can we do extrapolation to generate the model from DC to 5Ghz?
I have tried to extrapolate in Ansys Designer, but i could not see any
improvement in the output.
Please kindly suggest what needs to be done?
Regards
Chetan.
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