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I’m been lurking on the reflector without
following closely so I apologize if what I say is not relevant. 1010 patterns
are a disaster for EMI if they persist for long periods of time. If the 1010
content is only sent 1% or some other low percentage of the time in any normal
operating situation it won’t matter. (eg if the pre-amble is only at
the front of a data block that is always longer than 100 times the length of
the 1010 pattern even in idle situations with the rest of the data block being
scrambled or PRBS like.) From: Jaime
Kardontchik [mailto:jaime@xxxxxxxxxx] Dear
Task Force members, Recently
it has been proposed to change the sync pattern (Preamble) from the periodic
101010 … pattern to a non-periodic “data-like” pattern.
I am afraid that this might affect negatively one of the main purposes of
having a preamble, clock recovery, as well as its associate parameter:
the locking time. As
was pointedly stated in 3av_0805_effenberger_3.pdf, the periodic 101010…
pattern is the “golden” pattern for clock recovery and it
also has the advantage that it does not discriminate between any specific
implementations, neither present nor future, which is a very good feature for a
Standard. Changing
to a “data-like” pattern preamble will clearly affect the locking
time which will become longer, since the number of transitions (or updates for
the phase-locked-loop) will be less. In some situations, where the BER
(before FEC) might be marginal, it might even lead to catastrophic failure of
the clock recovery system. Regards, Jaime
Kardontchik |