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NNTP-Posting-Date: Wed, 12 Jun 2024 21:21:13 +0000
From: john larkin <jl@650pot.com>
Newsgroups: sci.electronics.design
Subject: Re: another fast one-shot
Date: Wed, 12 Jun 2024 14:21:13 -0700
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On Wed, 12 Jun 2024 16:44:14 -0400, bitrex <user@example.net> wrote:

>On 6/12/2024 2:11 PM, john larkin wrote:
>> On Wed, 12 Jun 2024 17:22:49 -0000 (UTC), Cursitor Doom
>> <cd999666@notformail.com> wrote:
>> 
>>> On Wed, 12 Jun 2024 09:33:17 -0700, john larkin wrote:
>>>
>>>> Here's another idea for a fast one-shot. This is the just-apply-money
>>>> version and should get close to 1 ns pulse width and should easily
>>>> trigger at 150 MHz.
>>>>
>>>> https://www.dropbox.com/scl/fi/1okfo8964bw5m53mjmxs6/
>>> Pecl_One_Shot_1.jpg?rlkey=dwus6qjyqsynl2rv6uje2xxtj&raw=1
>>>>
>>>> I can use the other half of the dual comparator elsewhere. This one has
>>>> programmable hysteresis too.
>>>
>>> Exposing my contemptworthy ignorance here no doubt, but what exactly is it
>>> that is fast about this design, John? And what would its application be?
>> 
>> It would have a leading-edge prop delay of 350 ps, a minimum pulse
>> width just over 1 ns, and would easily trigger at 150 MHz. Integrated
>> one-shots, xxx123 types, are always terrible, even the obsolete ECL
>> ones.
>> 
>> It would be a programmable delay in a number of possible products,
>> including some optical modulators. Just playing right now.
>> 
>> More dollars could certainly do something faster, but as long as
>> customers connect boxes with cables, faster isn't worth a lot. Light
>> just moves too slow.
>> 
>> Any suggestions for a faster one-shot?
>> 
>
>What about connecting the + of the RC to Q to speed up the discharge

Pecl only swings about 0.8 volts, up close to Vcc, so it wouldn't help
much. That phemt turns on pretty hard, maybe 100 mA with Rds-on a
couple of ohms.

Speeding up the discharge would improve rep-rate but wouldn't affect
minimum pulse width. I'd need a faster comparator for that, or some
different architecture.

The phemt gate driver is a little scary but will work if done
carefully.

I could give up a bit of speed and do this in CMOS. There's a 1 ns
TinyLogic flop that's 36 cents.