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From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design
Subject: Re: The emitter-coupled monostable as slow differential amplifer
Date: Sun, 21 Jul 2024 13:22:55 +1000
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On 21/07/2024 7:04 am, john larkin wrote:
> On Sat, 20 Jul 2024 15:29:58 +1000, Bill Sloman <bill.sloman@ieee.org>
> wrote:
> 
>> About a month ago John Larkin dismissed the emitter coupled monostable
>> with "It's really a slow diffamp, not a one-shot."
>>
>> If you feed a really slow pulse into it, it can look that way.
>> The 3.3pf capacitor at C1 doesn't feed through much current if you drive
>> the input with a slow edge
>>
>> The simulation below demonstrates it working exactly that way.
>>
>> No sensible circuit designer would deliberately drive it with a very
>> slowly rising and falling pulse  - if you want it to work as a
>> monostable pulse stretcher, you have to drive it with a pulse that is
>> narrower than the one you want to get out.
>>
>> Integrated circuit monostables don't have that limitation, but they are
>> more complicated, and slower. There was an ECL monostable that went down
>> to 10nsec, but the emitter-coupled monostable lets you get down to
>> 1nsec, if you use it right.
>>
> 
> That wasn't my point. My comment wasn't about the trigger risetime but
> that if you put in a long trigger, you get a long output. It's hardly
> a one-shot.  The input and output levels are weird too.

The emitter-coupled monostable has been around for ages, and it's 
limitations have been well-known for just as long.

> If course a proper one-shot should fire cleanly on a fast or slow
> rising edge.

Sadly, proper one-shots can't produce a 1nsec wide pulse. If you need 
that, you have to settle for a less-than-proper one-shot.

Skilled circuit designers know about those kinds of compromises, and 
find work-arounds.

<snipped the elaborate - if totally unjustified - circuit diagram.>

John Larkin seems to confuse discussion and willy-waving.

-- 
Bill Sloman, Sydney

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