Hi Weston,
The unit for the incoming and reflected waves related by S-parameters are
usually sqrt(Watt) - not voltage or current unit. Square of wave magnitude
is the power. See definition of S-parameters for Touchstone models for
instance. This is because of the normalization with sqrt(Zo). Though, there
are definition of S-parameters with voltage or current waves and even
un-normalized S-parameters - they are rarely used, due to practically
complete equivalency to the power definition. Also, the waves can be
converted back into voltages and currents without any loss of information
about the multiport (it not applicable to degenerate descriptors of
multiport).
Best regards,
Yuriy
Yuriy Shlepnev, Ph.D.
President, Simberian Inc.
www.simberian.com
Simbeor - Accurate, Productive and Cost-Effective Electromagnetic Signal
Integrity Software to Design Predictable Interconnects!
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Beal, Weston
Sent: Sunday, December 8, 2019 6:26 PM
To: farhilltramper@xxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Serdes RX: Power based or voltage based?
Tramp,
Why do you say that we all know that S parameters are power based? The
definition of S parameters is entirely in terms of voltage. I suppose that
if you consider the voltages in S parameters you can answer your own
question.
Regards,
Weston
On Dec 8, 2019 3:38 AM, Tramp <farhilltramper@xxxxxxxxx> wrote:
Hi experts,
We all know sparam is power based. But when it comes to the RX sampler, it
seems to be voltage based to me. This is bcs that the slicer doesnt care if
the voltage it is sampling is inphase w/ time, or out of phase since it can
shift its time base to locate the peaks of incoming voltage. In other
words, what is cared for is the apparent power rather than the effective
power.
is my understanding correct?
Best Regards,
Tramp
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