RE: XAUI receiver characteristics
From: Kesling, Dawson W [mailto:dawson.w.kesling@xxxxxxxxx]
Sent: Tuesday, October 17, 2000 5:52 PM
Subject: RE: XAUI receiver characteristics
...<PAT> stuff deleted...
>An eye diagram builds up an aggregate picture over many thousands of
>bits. If in that sample size, one bit stretched and another bit shrunk
>by half pk-pk jitter, it would result in an eye opening of 0.35 UI. It
>would not necessarily mean however that any bit had shrunk by 0.65 UI.
Right. This is the intent of the receive eye.
>A jitter mask describing amplitude of jitter versus frequency from 100hz
>to 3.125G/2 would be helpful.
There is some desire to avoid a full jitter immunity plot verses frequency
if possible due to the compliance testing burden. Even a SONET-like immunity
plot has a flat tolerance out to the baud rate and doesn't eliminate the
112ps pulse scenario.
If the intent is to avoid a misinterpretation of receive eye compliance
requirements, then I would prefer to see a statement such as, "The source
for receiver compliance testing must comply with the transmit
specifications. A linear filter can be used between this source and the
receiver for compliance testing purposes." I haven't thought enough about
how to word and incorporate this into the standard, but the purpose is to
prevent someone from generating a 112ps pulse and expecting the receiver to
comply. In effect, it limits random jitter to 0.35UI (plus a little for
noise) and budgets the rest to DJ. This is more like the real world
situation. Any thoughts?
<PAT> This has come up before though I don't think we have implemented a
solution for it. We've counted on people applying some sense when generating
a jittered signal for receive jitter tolerance testing (or perhaps counted
on the unrealistic signal being too difficult to actual generate). I think
the direction you are heading in would be useful, but some definition of
the filter would need to be supplied. It may need to say something about
the signal resulting from the source plus the filter.