From: Paul Levin (firstname.lastname@example.org)
Date: Thu Apr 12 2001 - 16:31:49 PDT
To all concerned,
Besides the attenuation effects on PCB traces, don't forget that the
delay is a function of frequency EVEN IF EPSILON-R IS CONSTANT.
Few people realize that skin effect resistance is only a portion of the
impedance. The Rs figure must really be multiplied by (1+j). This
reactance means that there is a bit more inductance (diminishing as the
increases.) Because of this, lower frequencies propagate more slowly
This effect has nearly disappeared by the time one gets to 1 GHz, but 1
Gbps data signals have frequency components much lower than a GHz.
Fibre Channel's "alternating disparity K28.5 pattern." This 20 bit
quite a bit of energy at 1/20th of the data rate. Some others have told
they have been able to create some (admittedly pathological) data
that resulted in even lower frequency content.
Some years ago I computed the Fourier transform of the entire pattern
ran the harmonics through both the attenuation and phase characteristics
microstrip. It surprised people how well I could simulate the
eye pattern. The analysis worked for shielded, twisted pair, too.
Senior Principal Engineer
Logic Innovations, Inc.
A Xyratex Company
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