Re: [SI-LIST] : the difference of far-end crosstalk between strip and microstrip line

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From: Doug Brooks (doug@eskimo.com)
Date: Wed Mar 14 2001 - 10:24:19 PST


It is better to use the term "Forward" and "Backward" crosstalk in this
context.

There are two forces at work that create crosstalk: inductive (magnetic)
coupling and capacitive (electric) coupling. Magnetic coupling induces a
signal in the opposite direction (i.e. backwards.) Capacitive coupling
induces a signal in BOTH directions. Picture an electron placed in the
middle of a trace. It repels electron(s) in the victim trace in both
directions (forward and backward.)

The forward coupling components are of opposite sign and tend to cancel ---
in fact they exactly cancel if the environment (read surrounding
dielectric) is homogeneous (stripline). They nearly cancel (but not exactly
so) if the surrounding environment is not homogeneous (microstrip.)

The backward components reinforce. That's why backwards crosstalk is
usually the problem in our circuits.

I will be giving a detailed seminar on crosstalk at PCB Texas in May if
people are interested.

Doug Brooks

t 09:22 AM 3/14/01 +0900, =?ks_c_5601-1987?B?sejB2Lno?= wrote:
>Hi, All
>
>I have a question about crosstalk.
>
>I knows the fact as follows.
>At microstrip txl (nonhomogeneous media), far-end crosstalk is nonzero.
>At strip txl (homogeneous media), far-end crosstalk is zero.
>
>Would you give me a explanation
>why the difference of far-end crosstalk between strip and microstrip
>line happen
>with physical meaning, without mathematical expression ?
>
>Best Regards
>
>Jun-Bae Kim

.
************************************************************
Doug Brooks' book "Electrical Engineering for the Non-Degreed
Engineer" is now available. See our web site for details.
.
Doug Brooks, President doug@eskimo.com
UltraCAD Design, Inc. http://www.ultracad.com

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