John Popelish writes:


I think you could use an LM361 comparator in place of the front opamp.
It produces high going and low going digital outputs that you can
enable separately, so you can choose whether you want to sync on
positive going or negative going edges, without changing the switching
threshold.

It will also clock the flip flop a lot faster than an opamp will.

http://www.national.com/ds.cgi/LM/LM161.pdf

Yup, good call! I actually have a 361 based circuit I built a long time
ago. It works to about 50MHz. It is overkill for this purpose, but
would be the right choice, along with an HC4538, if someone wanted to
modify this and go to higher frequencies. You actually have to move
some pins around on the 4538 to make it non-retriggerable.

On the 361 board, I use long-tailed pair miller integrators to get near
perfect sweeps. But that was a complete homebrew scope I designed in 1978
or so.

Thanks.

Steve
--
Steven D. Swift, , http://www.novatech-instr.com
NOVATECH INSTRUMENTS, INC. P.O. Box 55997
206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA