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CJPAT for testing XAUI receiver and transmitter?



XAUI folks -

I have had a long-standing action to initiate discussion of the item that Anthony listed, per his email dated 2/20/01 (re-listed below):

Section 6.5.1; Use of CJPAT for compliance testing of (XAUI) receiver and transmitter.
           1.  Does this requirement create too much restriction on the implementor and testor?
           2.  Is this requirement necessary to guarantee interopability between devices?
           3.  Is the current jitter specification correct, for CJPAT or K28.5 compliance testing?
To begin, let's go back to some Fibre channel history.

Fibre channel (FC) understood that CDRs track low frequency jitter, and that including this effect in the specifications could ease requirements on clock oscillators (lower cost designs tend to exhibit low frequency random jitter), serializer (serdes, same advantage) designs, and switching power supplies, layouts, bypassing, etc. With all this in mind, all FC jitter output specifications include the effects of a high-pass filter (to suppress the significance of low frequency jitter) to emulate CDR tracking.

FC also realized that, due to frequency content, long complex patterns cause phenomena that are not observed with short patterns - data dependent jitter (DDJ, a form of deterministic jitter) can have extreme ranges of frequency content from well below to well above the CDR corner frequency. Effects are usually seen in both transmitters and receivers. Since such long complex patterns (such as CJPAT) can exist in real systems, they must be included somewhere in a set of specifications for a standard.

Some observations:


Now, for the debate - assuming that HPF is used (do we want to debate this one?), data pattern options are:

4 combinations exist from above. My opinion is probably obvious: use long patterns for ALL jitter budgeting and specifications in the standards. My opinion deals with the first 2 questions under Anthony's listing above. The 3rd question is yet another topic for the group.

I encourage the debate to continue.

Thanks, Tom Lindsay
Vixel
425/806-4074