Simple pulse stretcher

Another one of JL's non-working "designs". A quick check of 74HC proves my supposition that a 5ns wide pulse goes nowhere... at least reliably... something JL never worries about... but that's what you get when you're pompously ignorant. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
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I love to cook with wine.     Sometimes I even put it in the food.

I think you're going to have a little problem with that inverter in regards to the speed you are referring to.

Jamie

I didn't say it was a 74HC, much less an HC14. Note that the delay elements are non-inverting.

Having no ideas of your own, you two old hens are naturally hostile to ideas.

Design an original pulse stretcher concept, if you can. Post it here.

This one makes pulses adjustable from 100 ps to 25 ns. How would you do that?

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John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators

The 5ns is way out of line for HC. You can apply the pulse directly to an e mitter follower loaded with parallel RC and then to HC to stretch it to any width you want. The BE junction is your diode. HC will not work reliably a cross VCC and temperature with anything less than about 25ns.

Yeah there's already ~20ns of latency between the input pulse and the output so a bit extra ain't too bad. I'll knock the 10pF down to 4.7

George H.

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.highlandtechnology.com  jlarkin at highlandtechnology dot com

Whee... fun!

George H.

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Yeah in this case there's certainly already some delay. But it doesn't really matter. OK it matters.. it all adds to the built in latency of the device. But at the moment there's some 'software' latency that's ~x10's as bad. So I can burn 10's of nanoseconds with abandon.

George H.

The 5...6 ns per gate is what you can practically expect from today's HC.

VLV

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      ...Jim Thompson         |    mens     |       |     et      |    |         |  |   |

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.highlandtechnology.com  jlarkin at highlandtechnology dot com

In this case I'm timing a pulse stream. But absolute time doesn't matter as much as relative time. So as long as the prop. delay doesn't stop more than one pulse from traveling down the signal chain, then it may not matter.

George H.

Please link to a datasheet- all I'm seeing is 20ns nominal performance on both Tpd's and minimum pulse widths into edge activated inputs like clk's, R's, and S's.

    ...Jim Thompson       |    mens     |     |     et      |  |       |

ide quoted text -

Yeah Jim the 5ns pulses weren't getting counted.... Sorry I missed a reply to you. There's a comparator on the input and I put the diode R/C thing between it and the first 74HC14 gate...

George H.

emitter follower loaded with parallel RC and then to HC to stretch it to a ny width you want. The BE junction is your diode. HC will not work reliably across VCC and temperature with anything less than about 25ns.

Cool 25 ns is just what I'd expect if I cut my C to 4.7pF

Thanks Fred.

George H.

Didn't Karl Marx teach you communists that practice is criterion of truth? Take a good scope, pulse generator and see for yourself.

VLV

Okay, you know what you measured, but you need to be real careful with layo ut using that parts family. It used to be a point of advantage for a logic family that it was unresponsive to full logic level transitions of duration less than the fastest edge rates in the system. Interwiring capacitive cou pling into a nice high impedance input converts the transition into a nice square pulse there. I think Lenin covered that one.

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That's not a pulse stretcher, cheater, that's a pulse _generator_.

A *triggered* pulse generator.

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Cheers, 
James Arthur

yout using that parts family. It used to be a point of advantage for a logi c family that it was unresponsive to full logic level transitions of durati on less than the fastest edge rates in the system. Interwiring capacitive c oupling into a nice high impedance input converts the transition into a nic e square pulse there. I think Lenin covered that one.

Hi Fred, As Vlad said the HC series was really doing just fine with

10ns pulses and perhaps only 'missing' 1% of the 5 or 6 ns ones. I don't have a commercial pulser that will do anything less than ~20ns, so it's hard to test. I had a pulse swallower circuit on a piece of copper clad, but I might have ripped it up to make something else... Anyway I don?t see any reason not to play it safe and make the minimum pulse 25ns.

My ?scope is only 200MHz, so I?m not really sure I even believe the

5ns... what?s that rule of thumb for ?scope bandwidth/ rise time? tau = 1/(3*BW) ?

George H.

using that parts family. It used to be a point of advantage for a logic family that it was unresponsive to full logic level transitions of duration less than the fastest edge rates in the system. Interwiring capacitive coupling into a nice high impedance input converts the transition into a nice square pulse there. I think Lenin covered that one.

The tinylogic one-shot that John mentioned is guaranteed to trigger off 2.5ns pulses (with a 5V 'Vcc'). Available in a nice friendly

0.65mm pitch 8-pin package (also a 0.5mm pitch or 1 x 2mm BGA if you are in need of pain).

It's a one-shot. It has no internal trigger. It generates no pulses.

And neither you nor Jim have a clue as to how this might be done.

We have a customer who wants us to take this down to 10 ps pulses. At that point, I'm not sure that I know how that might be done. We're thinking about it.

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John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators