From: Paul Levin ([email protected])
Date: Tue Sep 05 2000 - 12:19:39 PDT
I wanted to suggest another reference that might aid in your
of these two related phenomena - Ramo, Whinnery and VanDuzer, "Fields
and Waves in Electronic Communications."
The book explains that the skin effect resistance is mirrored by an
amount of inductive reactance. Since the resistance is increasing as
at least once the skin depth becomes a small portion of conductor depth,
this means that the equivalent inductance is dropping as a function of
Once this inductance is 'small enough,' the characteristic impedance
stabilizes at the nominal value; at low frequencies, this inductance,
adds to the line's geometric inductance, increases the characteristic
impedance and lowers the signal velocity.
Once upon a time (about two years ago,) I simulated some traces carrying
Fibre Channel's 'alternating disparity K28.5 pattern.' I did this by
fourier analysis of this 20-bit pattern and then applying the
phase delay predicted by Ramo, et al. to each harmonic. The resulting
eye pattern agreed with observed data, including a kink in the middle of
As I recall, the most significant Tpd changes for 1.4 mil trances and
conductors were in the first hundred MHz.
Happy reading and researching,
Senior Principal Engineer
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