RE: [SI-LIST] : Schottky diode termination

Andrew Ingraham (Andrew.Ingraham@digital.com)
Tue, 27 Oct 1998 18:38:58 -0500

John,

I first saw Schottky diode termination described in a rather old
Fairchild ECL book. Diode termination was not often used for ECL,
perhaps because the normal ECL parallel termination usually worked quite
well if you could afford the power dissipation.

The TTL logic families had clamp diodes in their input structures, and
one of their intended functions actually was to provide some amount of
diode termination. This is one of the reasons why TTL was easy to work
with, sometimes even when the wires got long compared to the falltimes.
Many people who have used TTL do not realize that they have been making
use of diode termination all along.

Most CMOS families also have input clamp diodes, and again they
generally work as both input protection and partial signal termination.

Those CMOS devices without input diodes tend to be SI nightmares.

In a multi-drop bus configuration, diode terminators may be needed at
several places, perhaps as many as one per input. For a daisy-chain
route, they may only be needed at the two ends. The best way to tell
what works is to try, preferably in simulation with GOOD models.

Regards,
Andy Ingraham

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