previous    The Torches and the Hair    next

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.

Signal Integrity Training Classes taught exclusively by Dr. Howard Johnson
for full schedule, see www.sigcon.com

© 1993-2007 Signal Consulting, Inc. All rights reserved.