In article , Arny
Krueger
wrote:
"Don Pearce" wrote in message


And of course the term jitter is used with cables - wrongly in my
view. Jitter is a random perturbation of the data edges caused by
noise events. The inaccuracies caused by cables are systematic and
identical on each data edge. This means that they can be corrected.
Either matching the cable better or using channel estimation (all
mobile phones have this and it is dirt cheap) to measure and cancel
the inaccuracies that shift the edges out of place.

The digital signal's edges tend to wander around because the cable is
ultimately a low pass filter and the spectral content of the digital
data passing through the cable varies as the data varies. So matching
the cable better can't be of much help.

Well a better match might improve things in principle. The snag is that
even trying to do this is questionably given the frequency range involved
as the cables don't necessarily have a frequency-independent impedance. :-)

And as you say, the real problem is the finite bandwith.

Yes. I think PM and others refer to it as 'data induced jitter' because it
depends on the details of the waveform. Generally tested using the 'J test'
waveform that toggles the LSB of an otherwise steady fs/4 waveform.

Slainte,

Jim

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