Yuriy,
You cannot adjust the rise time since it is specified by the nominal
rise/fall time of the TX driver output (unless you are doing generic BERT
TX), de-embedded back to the TX output. Secondly, the channel losses
considering modern TX may have <10psec trise requires de-embedding. What
is a bit intense since Trise is sometimes faster than the TDR equipment we
often use to test and validate our test fixtures for signal integrity!
Our process when using WRT test fixtures is to determine rise time and rise
time characteristics de-embedded back to TX with high quality test fixture,
de-embedded back to TX. Capture that TX rise/fall in EDA tool, drive that
simulation into a controlled and pristine test channel, simulating eye
diagram and adjust things a bit to get the scope (time domain, eye), and the
simulation based on S-parameters in EDA tool to all correspond. We see
return loss margin at Fstop to be critical, sample with max VNA samples,
Fmin on the VNA at lowest frequency and a modern VNA with low phase noise
even with IF BW set to 1kHz. The scopes BW has an impact as well. The
above is also a good methodology for validating IBIS AMI model and reference
TX/RX. There is a lot of moving pieces and risk and the test fixturing
needs to be very pristine and the cables need to be good phase stability.
What we have not done, and wish someone would comment on is how Rational
Compact Modeling plays nicely with windows when doing the transform in the
EDA tool.
- Al Neves
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx <si-list-bounce@xxxxxxxxxxxxx> On Behalf
Of Yuriy Shlepnev
Sent: Monday, July 22, 2019 3:32 PM
To: farhilltramper@xxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Bandwidth of channel sparameter vs EH/EW
Hi Tramp,
There are three contributing factors that may explain the outcome.
First, the actual power spectral density of the signal you used in the
experiment. The spectrum will depend not only on the data rate, but also on
the rise time. If you set the rise time unrealistically small, it will
extend the signal spectrum and will create dependency on the bandwidth used
in the simulation.
Second, the channel losses. Shorter links with lower losses have more
dependency on the simulation bandwidth. If you are experimenting on a very
short of idealized link, the results will be very sensitive to the
bandwidth.
Third, algorithm used to compute the eye diagram. If it is based on DFFT,
the discretization as well as the extrapolation of S-parameters will affect
the result. You will never know what it is. If it is based on the rational
compact modeling, check the model quality and investigate how the rational
model behaves outside of the original bandwidth - resample it to higher
frequencies and see if it extracts the delay and attenuates the harmonics
(good) or not (bad).
Another important factor is the bandwidth of every component model that goes
into the channel model. Extending the simulation bandwidth beyond the
bandwidth of the component models does not make much sense.
Actually, if everything done properly, the investigation of the eye (or
single bit response) should be done to identify the simulation bandwidth.
The outcome may be not so obvious - see example at
http://www.simberian.com/Presentations/SLIDES_112G_Panel_EMAnalysis_rev3.pdf
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 to Design Predictable Interconnects!
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 Tramp
Sent: Sunday, July 21, 2019 12:29 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Bandwidth of channel sparameter vs EH/EW
Dear SI experts,
It seems that the bandwidth of channel sparameter has influence on the eye
result.Taking 10GKR for example, when comparing the eye obtained w/ the snp
of the BW of 50GHz, 60GHz, and 100GHz, the trend I observed so far is as
follows:
The 50GHz snp gets the smallest EH + largest EW, and vice versa for the
100GHz snp. The eye obtained w/ 60GHz has the mediate EH/EW in between,
Does that make sense? If, anyone can explain why?
--
Best Regards,
Tramp
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