pulse width limiter

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An ideal pulse-width limiter has zero rising-edge delay, programmable
width, and zero recovery time. This isn't too bad:

https://dl.dropboxusercontent.com/u/53724080/Circuits/Fast_Stuff/PW_Lim_1.JPG

The first gate is acting like a line receiver, so doesn't count
against my prop delay; so delay = 1 ns.

Recovery time should be pretty good, under 10 ns maybe. If I tease the
exponential a bit, I could reduce the cap and improve recovery.




--  

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement  

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Re: pulse width limiter
Hmm, two gate delays?  I guess you're discounting the first one, fair  
enough.

Could use a diode gate, or a series resistor and a somewhat beefier  
transistor, to shunt the input after the delay.

To do any less than what you've shown, you've got to incur some sort of  
quirkiness, such as sensitivity to load, which the above strategy will have.  
(Hopefully, the diode gate or resistor feeds a minimal load, like a single  
logic pin and no trace length.)  The sensitivity could be further  
worsened\optimized by adding a peaking coil or two...

Tim

--  
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
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Re: pulse width limiter
On Thu, 6 Jul 2017 20:05:08 -0500, "Tim Williams"

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A series L in the discharge path would help, make the discharge
critically damped instead of exponential. I'll probably have 30 or 40
ns minimum low time, so may not benefit from an L just now.



--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: pulse width limiter
John Larkin wrote:
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   Feed an open transmission line for fixed time period, trombone  
assembly for adjustable..


Re: pulse width limiter
On Fri, 07 Jul 2017 01:46:19 -0800, Robert Baer

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Not in roughly 1/4 of a square inch.

And something would have to discharge that line, no?


--  

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement  

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Re: pulse width limiter
On Thu, 06 Jul 2017 19:20:26 -0700, John Larkin

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If I use both switch sections in parallel, that's below 2 ohms
discharge resistance. The critical inductor value would be a couple of
nH, and I probably have that just in wirebonds and strays. It will
probably ring on the discharge with no added L.


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: pulse width limiter
On Thursday, July 6, 2017 at 8:40:27 PM UTC-4, John Larkin wrote:
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OK, does the circle on the fet input mean an inverter?  
So the fet is normally on, closed, then open when the pulse comes?

George H.
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Re: pulse width limiter
On Thu, 6 Jul 2017 18:43:55 -0700 (PDT), George Herold

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That NC7 analog switch (actually sold as a bus switch) is
active-low-on. It's a dual, so I may as well use both sections in
parallel to discharge my cap.

Oh, the part number is typo'd. It should be NC7WB3306.


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: pulse width limiter
On Thu, 06 Jul 2017 17:40:15 -0700, John Larkin wrote:

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PW_Lim_1.JPG
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You haven't really explained anything about your application.  It seems
like you're making (almost) a low-prop-time programmable one-shot.  Are  
there any of those that might work?

  -F

Re: pulse width limiter
On Fri, 7 Jul 2017 21:24:11 -0000 (UTC), Frank Miles

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It's not a one-shot, it's a pulse width limiter. I'm ultimately going
to drive a transmission-line transformer, and I don't want the user's
input pulses to be allowed to be wide enough to saturate the core.

Narrow pulses pass right through with 2 ns delay. Longer pulses get
truncated to a programmable width.




--  

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement  

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Re: pulse width limiter
On Friday, July 7, 2017 at 5:57:05 PM UTC-4, John Larkin wrote:
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Ah, Thanks I had the same question.  

I wish more people would post circuit questions.  

I've been thinking about measuring heat capacity.  
Maybe a FET to give a  heat pulse and then measure  
temperature change. (with the body diode)  
Sample attached to the fet and some thermally
'driven shield' around the sample space.  
A pulse and response system.

George H.  

  


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Re: pulse width limiter
On Fri, 7 Jul 2017 17:41:47 -0700 (PDT), George Herold

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I suppose that most people have, or think they have, personal or
business reasons why they can't show their work. Or don't design
circuits at all.

  
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I've pulsed one transistor of a dual, and used the other to measure
temperature vs time. That's sort of fun. The temperature measurement
is continuous, not time-shared with the heating pulse.









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--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: pulse width limiter
On Friday, July 7, 2017 at 9:57:46 PM UTC-4, John Larkin wrote:
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Yeah, or they don't want to appear like an idiot.  
(which never stops me.)
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Right a dual might be better.  
I think I saw Fets that had a built in diode for temperature sensing.
I should look at those.

George H.  
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Re: pulse width limiter
On Sat, 8 Jul 2017 06:58:33 -0700 (PDT), George Herold

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I have seen this phenomenon with several times with communications
protocols.

Some companies demand NDAs to get access to their protocol
specifications.While in some cases, this might be a commercial
interest of keeping competitors out of their product family,  but in
many cases, their protocol specification is so dumb that detecting bad
specification only takes 5 minutes.

It is understandable that the companies  
try to hide such embarrassing protocol specifications or device
designs :-)


Re: pulse width limiter
On Sat, 08 Jul 2017 18:07:10 +0300, snipped-for-privacy@downunder.com wrote:

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They probably think it's great.


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: pulse width limiter
On Friday, July 7, 2017 at 5:41:53 PM UTC-7, George Herold wrote:

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That's good if you want to probe a  noisy system, because you can send
a large number of pulses in, and sum all the noisy responses in memory.
There's a lovely system called a 'hammer seismometer' that uses some
percussor (anything from a sledge hammer up to a one-piston internal
combustion gizmo) and a triggered receiver.   Signal averaging and
patience go in, rewarding data comes out.

Re: pulse width limiter
wrote:

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Even cheap scopes usually do signal averaging these days.


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: pulse width limiter
On Saturday, July 8, 2017 at 4:40:02 PM UTC-4, John Larkin wrote:
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Poor man's spectrum analyzer;
Normal trigger at the top (~5%) of your noise waveform.
Average for max number,  adjust time base, press FFT function.

(Does anyone beside me do this?)

George H.  
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Re: pulse width limiter
On Sat, 8 Jul 2017 14:16:15 -0700 (PDT), George Herold

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Sure.   Been doing it for forty years, with a few more twists, even.


Re: pulse width limiter


  

Scope FFTs in 1977? Do tell.  

Cheers

Phil Hobbs

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