Simple pulse stretcher

Isn't 10ns width just a wee-bit tight for 74HC parts? ...Jim Thompson

The diode thing is what I usually do. But 10nsec through a 74HC14? Now that's a strrrrretch.

OK, maybe I should stretch to 20 ns.

George H.

OK thanks, I'll do 20ns then.

George H.

Still a bit of a stretch but if you need pulses this short there are faster versions of the HC14.

Why not use a one-shot? HC123 or the faster Tiny version of same, SN74LVC1G123.

The other way is to set a D-flop that resets itself. That can be a lot faster.

...Jim Thompson

What I was driving at was how can the 74HC do the stretch in the first place... reliably. Though I think I possibly see a way. ...Jim Thompson

Something like this:

You got the idea.

/* Placeholder for banal comments

Vladimir Vassilevsky DSP and Mixed Signal Designs

Yeah I was thinking of something like that too. The diode thing was an easy 'hack' and seems to be working just fine. (I stuck in 10k and 10pF and have about a 50ns minimum pulse.) Life is good.

George H.

I think that can double-glitch the output if you tease the input width just right.

The diode+RC thing is perfectly feasible with an HC14, likely at 20 ns out and certainly at 30.

A bit of inductance in series with the R would be interesting.

Here's a variation on Vlad's circuit:

Diode plus Schmitt is the better solution. The main reason is that doing it with piped-in gates relies on their prop delays. I have seen that blow up in production when people did it. All it takes is one or more manufacturers improving a semiconductor process, things become faster, suddenly the fix ain't working no more. Or only sometimes. Datasheets typically do not specify a guaranteed lower limit on prop delay. For example, there is no entry for it in the "min" column for the 74HC14 from TI:

Just make sure the schottky has low c, a couple of pF or less.

That's pretty much unavoidable. I doubt that it matters to George.

and the

How do you know that? I didn't specify the parts, other than max PD. They could be implemented as a tapped delay line, passive or silicon. Or one could trim Vcc to tweak prop delay. There are lots of possibilities.

Post something better.

and

and

could trim >Vcc to tweak prop delay. There are lots of possibilities.

What a sad old dork.