XAUI receiver characteristics
Dawson,
I think the distribution of the jitter budget with 35% for the
transmitter and 30% for line does not reflect what can be
achieved in a given technology. The transmitter jitter should
be limited to 0.1UI to allow more headroom for the receiver.
The far end template of figure 47.4 does not say much about
the difficulty of data recovery unless accompanied by a jitter
frequency distribution limit.
The receiver input parameter limits given in table 47.2 is a mixture of
requirements on the receiver and on the input signals to the receiver.
For ease of use that should be changed requirements on the specification
of a compliant receiver.
Thus we should have an upper limit for the minimum input amplitude
specification of a compliant receiver (e.g. 175mV). To be meaningful, this
requirement must be supplemented by time domain conditions on the
input signal and some criterions for receiver function. The requirements
on the receiver would be unnecessary high if the far end template of
figure 47.4 would be interpreted as demanding the receiver to handle
0.65UI high frequency jitter (112ps symbols)
Likewise, there should be a lower limit for the spec point for maximum input
amplitude of a compliant receiver. It would be advantageous to increase this
limit from 1V to 1.5V.
For ease of implementation the upper limit on differential input impedance
can
be increased quite a lot without significant impact on the jitter. At least
to
the geometrically symmetric 125 ohm level (relative to 80 ohms).
Proposal: use 130 ohm as an upper limit.
In clause 47.3.4.2 the return loss is required to be less than -10dB but in
table it is given as a minimum requirement.
Is the input differential skew parameter really needed, or covered by other
spec points?
While working with the standard, it would be good to have a couple of more
columns in the specification tables. One with a justification for the spec
point,
and one with reference to related spec points. This will make it easier to
make
a consistent spec and to keep track of the implications of proposed changes.
Best regards Tord.
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Optillion
Tord Haulin Ph: +46 8-477-4192
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