Gould Biomation K-105D Logic Analyzer Available

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Sat Dec 20 12:30:54 2003

> I can't say I have done it, but an alternative to using (and finding)
> TTL->ECL chips would be to use standard voltage comparators. Devices
> such as the LM319 (dual high speed (80nS) comparator) could be set up

80ns is nowhere near fast enough!. That's about 12MHz, the analyser is a
100Msample/second unit... You want a comparator that switches in about 5ns...

I did look into using analogue comparator chips, but at the time I did
this (which must be 10 years ago) I couldn't find any that were (a) fast
enough and (b) had enough input voltage range. I guess that's why the
original Gould pods had custom hybrid circuits in them.

> the threshold from the analyser). A resistor or two should should
> complete the interfacing between the comparator output and ECL input.

Actually, the input to the analyser is a differential pair of ECL
signals, but producing those is the easy part!

>
> This would have the added advantage of placing a far smaller load on
> the signal lines being tested. (A comparator input is a high impedance
> compared to the (rather large) load of a TTL input. (In the absence of
> ref data at hand I'm presuming TTL->ECL converter inputs are one TTL
> load.))

They are...

IIRC, I put some high-speed CMOS buffer chips between the
circuit-under-test and the level shifters. Probably something like
74ACT245s with the control inputs tied appropriately

-tony
Received on Sat Dec 20 2003 - 12:30:54 GMT