Questions about Differential Line Receivers

[Paul Ciszek]

I have a detector with pairs of output lines: Q and Q NOT.
I am told that I need to look for a 5V difference between Q and Q NOT
in order to record an event; just watching for Q going high is not
good enough, Q NOT has to go low at the same time. This is in order
to separate signal from noise. These pulses should last for 2us give
or take a us.

I am told that a Differential Line Receiver should be able to do
this; however, the data sheet for one such:
http://focus.ti.com/lit/ds/symlink/sn75115.pdf
....leads me to believe that the output goes high whenever A goes
higher than B, not when A is some threshold higher than B. Can
one of these be jiggered to use a fixed voltage threshold, i.e.,
the output goes high only when A is 4 volts higher than B?

The other approach would involve op-amps used as a differential
amplifier and a schmidt trigger. Can anyone recommend an op
amp that would respond quickly enough? Single supply would be
nice, though not absolutely necessary.


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[Watson A.Name - \"Watt Su]

"Paul Ciszek" <nospam@nospam.com> wrote in message
news:dieug6$pdk$1@reader1.panix.com...

I have a detector with pairs of output lines: Q and Q NOT.
I am told that I need to look for a 5V difference between Q and Q NOT
in order to record an event; just watching for Q going high is not
good enough, Q NOT has to go low at the same time. This is in order
to separate signal from noise. These pulses should last for 2us give
or take a us.

I am told that a Differential Line Receiver should be able to do
this; however, the data sheet for one such:
http://focus.ti.com/lit/ds/symlink/sn75115.pdf
...leads me to believe that the output goes high whenever A goes
higher than B, not when A is some threshold higher than B. Can
one of these be jiggered to use a fixed voltage threshold, i.e.,
the output goes high only when A is 4 volts higher than B?

The other approach would involve op-amps used as a differential
amplifier and a schmidt trigger. Can anyone recommend an op
amp that would respond quickly enough? Single supply would be
nice, though not absolutely necessary.

The line receivers used in the boxes we used long ago at work were LM710
and Signetics NE529. They may be hard to come by today, so a more
recent substitute is probably better.

--
Please reply to: | "Mundus Vult Decipi"
pciszek at panix dot com | ("The world wants to be deceived")
Autoreply has been disabled | --James Branch Cabell