[SI-LIST] Re: general belief about Xtalk

The beliefs you give, below, come from the practical observation that,
for typical modern PCB designs, capacitive and inductive cross talk have
similar magnitudes. Consider:

For near end crosstalk:
- the capacitive and inductive components reinforce each other, but
- the received energy observed at the victim driver is spread out in
time,
  due to the fact that the crosstalk induced energy is traveling in a
  direction opposite that of the advancing wave in the aggressor.

For far end crosstalk:
- the capacitive and inductive components cancel each other, but
- the received energy observed at the victim receiver is localized in
time,
  because the crosstalk induced energy is traveling along with the
advancing
  aggressor wave.

So, to know whether a larger magnitude of crosstalk will be observed at
the near or far end requires knowing something about the relative
significance of the inductive/capacitive cancelling effects vs. the
spreading and localizing effects. In typical modern PCB designs, the
inductive and capacitive components of crosstalk cancel rather well and,
so, the cancelling ends up being more significant than the spreading,
and we get larger magnitude at the near end.

-db


> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of Mick zhou
> Sent: Monday, February 23, 2009 3:59 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] general belief about Xtalk
> 
> Hi,
> Recently, I run into some basic beliefs about Xtalk from my
colleagues.
> They
> seem match intuiations but may not be right.
> 
> Statement 1: Single-ended near-end Xtalk is always greater than
far-end
> Xtalk, both in f and t domains.
> Statement 2: Differential/Common near-end Xtalk is always greater than
the
> far-end, both in f and t domains.
> 
> I do not remember any general proofs of the above statements. They may
be
> true for many practical cases but may not be generally true. One
example
> in
> S. H. Hall's book, p.50. disproves the statement 1 in t-domain.
> 
> Any more helps?
> 
> Mick
> 
> 
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