[SI-LIST] Re: general belief about Xtalk

Mick,
The statements your colleagues made are in general true about printed 
circuit board striplines.  They are not true about microstrips.  They are 
not necessarily true about connectors.  Depending on the design of the 
connector, the electric and magnetic fields may not be well-balanced, 
leading to nonzero forward crosstalk.

The big difference between striplines and connectors is that the 
transverse electromagnetic mode is present in the stripline but typically 
breaks down when it encounters the connector.  In the transverse 
electromagnetic mode, the electric and magnetic field vectors are 
perpendicular to each other and to the direction of propagation.  When the 
TEM wave moves into the connector, the electric and magnetic field lines 
are not necessarily perpendicular to each other anymore, although each one 
by itself is still perpendicular to the direction of propagation.

Greg

Greg Edlund
Senior Engineer
Signal Integrity and System Timing
IBM Corporation
3605 Hwy. 52 N  Bldg 050-2
Rochester, MN 55901



Msg: #6 in digest
Date: Mon, 23 Feb 2009 16:58:47 -0700
Subject: [SI-LIST] general belief about Xtalk
From: Mick zhou <mick.zhou@xxxxxxxxx>

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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