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Hi Brian I under that different
group delays at different critical frequencies directly effects jitter (eye
closure and distortion) on a specific channel. It is also a sensitive
measure of one of component of jitter. I tied to make this work before for
compliance channel on another project but discovered you can’t add derivatives.
I can loosely bound a system loss by combination of losses of the components.
However, I found many cases where the group delay of chain of channels wasn’t
even close to a sum of the component channels. So I agree the Group delay
should be deemed questionable at best. Have you done
a similar analysis for Phase Delay? Is the sum of the parts equal to the whole? Just for kicks
I plotted Phase delay (-phi/omega) for two radically different channels. You
can see the mag il response of the two channels in the attachment as well as
the PD. I was trying to get feel how we used group delay. Could you help
me here? … Rich
Mellitz, Intel Corporation Ad hoc
meeting attendee From: owner-stds-802-3-blade@listserv.ieee.org
[mailto:owner-stds-802-3-blade@listserv.ieee.org] On Behalf Of Brian Brunn Hi All, Attached is my recommendation that we
look at changing our quantity of interest from Group Delay to Phase Delay. The criticality of delay distortion is
debatable. However, I want to get this out quickly because switching
to Phase Delay may be the right thing to do *and* help eliminate some of the
repeatability problems people are seeing when taking channel
measurements. Someone on the call mentioned that magnitude repeatability
was fine and that the phase was the problem.. Regards, Brian Brunn |