Hi guys, I need a little digital pulse stretcher. I've got pulses that are 5ns to 25ns in width, and I'd like to bump them all up to all be at least 10ns. I've got a few spare 74HC14 inverters. I was thinking of just feeding one through a diode followed by an R/C to ground. Any other ways? There might be an extra AND gate too. (not my circuit so I'm not quite sure.)
Thanks
George H. (and who ordered the second t in stretcher)
Isn't 10ns width just a wee-bit tight for 74HC parts? ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
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I love to cook with wine. Sometimes I even put it in the food.
The diode thing is what I usually do. But 10nsec through a 74HC14? Now that's a strrrrretch.
-- Regards, Joerg http://www.analogconsultants.com/
...Jim Thompson | mens | | et | | |
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.
-- Regards, Joerg http://www.analogconsultants.com/
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.
-- 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
...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
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
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
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.
-- 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
-- "Pulse stretcher" implies that the leading edge of the source pulse should be presented at the input of the load simultaneously with its generation, and that its fall should occur after the desired delay. The former is, of course, unrealizable, while the latter is easy. How much delay can you tolerate between the generation of the leading edge of the source pulse and its presentation to the load?
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:
-- 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
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:
-- Regards, Joerg http://www.analogconsultants.com/
Just make sure the schottky has low c, a couple of pF or less.
-- 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
-- You've still got the initial gate delay from input to output, and the prop delay through the buffers isn't exactly precise...
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.
-- 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
and
-- Maybe not, but I posted a message to him asking for clarification, just to resolve the issue. You, on the other hand, opted to second-guess him and subjugate him to your will.
and
could trim >Vcc to tweak prop delay. There are lots of possibilities.
What a sad old dork.
-- 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
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