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Approaching the Cliff: Measured crosstalk on a large
backplane
This measurement comes from one of the 350 data channels
held in a physical library of backplanes by Accelerant Networks.
We've been cataloging backplane performance there for
some time. The pictures always look like this.
The signal amplitude (in dB) falls off in proportion to
frequency. That means the signal amplitude in volts falls off
exponentially
with frequency.
The crosstalk amplitude generally grows in proportion to
frequency.
Between the two effects, the usable channel bandwidth is
severely pinched.
In this example, binary operation at 3.125 Gb/s (which
yields a Nyquist rate, or maximum alternation rate, of 1.565 GHz), can
reliably take place with a signal to crosstalk ratio (SCR) of about 20
dB.
All Publications by Dr. Howard Johnson except as noted.
Signal Integrity Training Classes taught exclusively by Dr. Howard Johnson -
for full schedule, see www.sigcon.com
© 2003 Signal Consulting, Inc., Dr. Howard
Johnson. All rights reserved.
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