Re: another fast one-shot

On Sat, 22 Jun 2024 13:13:44 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:

On 14/06/2024 1:31 am, john larkin wrote:

On Thu, 13 Jun 2024 16:03:04 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
 

On 13/06/2024 4:11 am, 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?

>
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>
It's just a two transistor emitter-coupled monostable, but with the two
transistors as BFR92's run at 10mA,  it produces 1nsec pulse without fuss.
>
Finding the broad-band PNPs to let you translate the output pulse to a
useful voltage level is tricky. Phil Hobbs has told us that there is a
least one still in production and available.

 
What a mess. The output pulse width just follows the input pulse
width. Unless you change C1, in which case it oscillates.

>
Actually, it doesn't. The input pulse has a full-width at half maximum
of 400psec, and the output pulse width is 1nsec, as intended

It's not a one-shot, it's a diffamp. Put in a 50 ns trigger and it
will make a 50 ns output.

And it makes the common beginner error of assuming that two
transistors are absolutely identical, and at the same temperature,
because Spice does that.

The critical 40 mV of diff offeset is derived by the diference between
the tweaked power supplies and, I suppose, two 1% resistors. That is
really weird. And unsafe.

The dangling wire scraps could roll around and short things.