XAUI skew
Dawson,
Clause 47 has specifications on differential skew both for the
transmitter and receiver. There is however no definition for
differential skew, or method given for measuring it. In paragraph
47.3.4.1 the differential skew is said to include the effects of
intersymbol interference, ISI. I would think the main effect of ISI is
deterministic jitter, which is part of the jitter specifications. To
define and measure skew, we would probably have to relate it to rise and
fall times and define a common mode load and load balance with
tolerances. The transmitter skew and possible crosstalk along the line
is filtered by the channel common mode transmission magnitude and group
delay, which falls outside the channel model work done to date.
In the receiver compliance test some additional sinusoidal jitter is
applied to ensure some margin for effects otherwise not accounted for.
How about lumping skew into this, to avoid going into specifying enough
parameters and conditions to take measurements on skew and related
parameters? That would mean the skew limits could be removed from the
spec. Comments?
Tord.
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