Very high speed oneshot...

[M Gira]

Hi All,

I am hoping someone with with high speed experience could point me in the right direction.

My issue is that I have an ~850pS pulse (somewhat random pulse output) that I need to lengthen to 25nS. I have built many oneshot/timer circuits over the years but never this fast. My research seems to indicate that most timers (available ICs) need a minimum trigger pulse of several to ~ hundred nS.. Retrigger time doesn\'t seem to be an issue (yet).

Thanks in advance.
Martin


Martin Gira
Sr. Research Engineer
Center for Visual Science (CVS)
Center for Medical Technology & Innovation (CMTI)
Neurobiology and Anatomy
University of Rochester

 

[server]

On Tue, 1 Sep 2020 08:45:33 -0700 (PDT), M Gira <mgira53@gmail.com>
wrote:

Hi All,

I am hoping someone with with high speed experience could point me in the right direction.

My issue is that I have an ~850pS pulse (somewhat random pulse output) that I need to lengthen to 25nS. I have built many oneshot/timer circuits over the years but never this fast. My research seems to indicate that most timers (available ICs) need a minimum trigger pulse of several to ~ hundred nS. Retrigger time doesn\'t seem to be an issue (yet).

Thanks in advance.
Martin


Martin Gira
Sr. Research Engineer
Center for Visual Science (CVS)
Center for Medical Technology & Innovation (CMTI)
Neurobiology and Anatomy
University of Rochester

That might be too fast for even the fastest one-shot, like an
LVC1G123. But it would be easy to make a pulse stretcher. Assuming
your source has reasonable drive strength, a small schottky diode in
series, and an RC to ground would work.

You can use the Cin of the one-shot for the C. So, one diode and one
resistor. Optimize the time constant per your expected trigger
pattern.

I\'m doing that in some GHz-range signal detectors now and it works
fine with no discharge R at all. A little schottky like a BAT15 will
have maybe 0.25 pF capacitance and 100nA or so reverse leakage.

Where is that fast pulse coming from? What\'s the logic swing?



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[David Nadlinger]

Hi Martin,

I\'ve built something similar here together with a colleague recently,
using an MC100EP51 (a fast PECL FF). The input, from a fast photodiode
straight into an ADCMP582, clocks H to the output, which then triggers
the asynchronous reset some 10 ns later after a simple RC delay. This is
perhaps a bit crude, but worked well enough for the application, as we
didn\'t care about anything past the initial rising edge (provided the
pulse just stayed high long enough for a later, slower trigger to catch
it as well). Random jitter on the rising edge for the complete system
was a few ps, almost certainly dominated by the LVTTL output buffer.

Best,
David



On 01.09.20 4:45 pm, M Gira wrote:

Hi All,

I am hoping someone with with high speed experience could point me in
the right direction.

My issue is that I have an ~850pS pulse (somewhat random pulse

output) that I need to lengthen to 25nS. I have built many oneshot/timer
circuits over the years but never this fast. My research seems to
indicate that most timers (available ICs) need a minimum trigger pulse
of several to ~ hundred nS. Retrigger time doesn\'t seem to be an issue
(yet).

Thanks in advance.
Martin


Martin Gira
Sr. Research Engineer
Center for Visual Science (CVS)
Center for Medical Technology & Innovation (CMTI)
Neurobiology and Anatomy
University of Rochester

 

[server]

On Tue, 1 Sep 2020 17:36:07 +0100, David Nadlinger
<david@klickverbot.at> wrote:

Hi Martin,

I\'ve built something similar here together with a colleague recently,
using an MC100EP51 (a fast PECL FF). The input, from a fast photodiode
straight into an ADCMP582, clocks H to the output, which then triggers
the asynchronous reset some 10 ns later after a simple RC delay. This is
perhaps a bit crude, but worked well enough for the application, as we
didn\'t care about anything past the initial rising edge (provided the
pulse just stayed high long enough for a later, slower trigger to catch
it as well). Random jitter on the rising edge for the complete system
was a few ps, almost certainly dominated by the LVTTL output buffer.

Best,
David

An ECL-output comparator is an open emitter, so add a cap and a weak
pulldown to make a stretcher. Since the \'582 is a dual, use the other
half as a discriminator on the stretched pulse.

The 582 is expensive. One of the slower parts, like a 561, would work
at these speeds.


--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[David Nadlinger]

On 01.09.20 5:44 pm, jlarkin@highlandsniptechnology.com wrote:

An ECL-output comparator is an open emitter, so add a cap and a weak
pulldown to make a stretcher. Since the \'582 is a dual, use the other
half as a discriminator on the stretched pulse.

The 582 is expensive. One of the slower parts, like a 561, would work
at these speeds.

Well, the source pulses in our case were ~5 ps, and only some 100 ps (at
the trigger level) out of the photodiode. For a one-off lab gadget like
this, it seemed less complex to first square it up as faithfully as
possible while keeping the rising edge intact, and then manipulate the
cleanly driven logic signals. Parts cost is of less relevance than the
inelegance of my solution here.

Using a dual like the ADCMP561 (the ADCMP582 is a single) for a
stretcher is indeed a good suggestion, though. Speaking of which, what
actually happens in practice if you drive fast comparators like those
with a pulse shorter than the specified minimum pulse width? I\'ve never
tried…

— David

 

[server]

On Tue, 01 Sep 2020 09:44:03 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Tue, 1 Sep 2020 17:36:07 +0100, David Nadlinger
david@klickverbot.at> wrote:

Hi Martin,

I\'ve built something similar here together with a colleague recently,
using an MC100EP51 (a fast PECL FF). The input, from a fast photodiode
straight into an ADCMP582, clocks H to the output, which then triggers
the asynchronous reset some 10 ns later after a simple RC delay. This is
perhaps a bit crude, but worked well enough for the application, as we
didn\'t care about anything past the initial rising edge (provided the
pulse just stayed high long enough for a later, slower trigger to catch
it as well). Random jitter on the rising edge for the complete system
was a few ps, almost certainly dominated by the LVTTL output buffer.

Best,
David

An ECL-output comparator is an open emitter, so add a cap and a weak
pulldown to make a stretcher. Since the \'582 is a dual, use the other
half as a discriminator on the stretched pulse.

The 582 is expensive. One of the slower parts, like a 561, would work
at these speeds.

This should work:

https://www.dropbox.com/s/0h018di0qqk3m31/Pecl_Pulse_Stretcher.jpg?raw=1





--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[server]

On Tue, 01 Sep 2020 10:25:17 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Tue, 01 Sep 2020 09:44:03 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Tue, 1 Sep 2020 17:36:07 +0100, David Nadlinger
david@klickverbot.at> wrote:

Hi Martin,

I\'ve built something similar here together with a colleague recently,
using an MC100EP51 (a fast PECL FF). The input, from a fast photodiode
straight into an ADCMP582, clocks H to the output, which then triggers
the asynchronous reset some 10 ns later after a simple RC delay. This is
perhaps a bit crude, but worked well enough for the application, as we
didn\'t care about anything past the initial rising edge (provided the
pulse just stayed high long enough for a later, slower trigger to catch
it as well). Random jitter on the rising edge for the complete system
was a few ps, almost certainly dominated by the LVTTL output buffer.

Best,
David

An ECL-output comparator is an open emitter, so add a cap and a weak
pulldown to make a stretcher. Since the \'582 is a dual, use the other
half as a discriminator on the stretched pulse.

The 582 is expensive. One of the slower parts, like a 561, would work
at these speeds.

This should work:

https://www.dropbox.com/s/0h018di0qqk3m31/Pecl_Pulse_Stretcher.jpg?raw=1

U1A q-bar should have a pulldown.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[John Larkin]

On Tue, 1 Sep 2020 18:25:20 +0100, David Nadlinger
<david@klickverbot.at> wrote:

On 01.09.20 5:44 pm, jlarkin@highlandsniptechnology.com wrote:
An ECL-output comparator is an open emitter, so add a cap and a weak
pulldown to make a stretcher. Since the \'582 is a dual, use the other
half as a discriminator on the stretched pulse.

The 582 is expensive. One of the slower parts, like a 561, would work
at these speeds.

Well, the source pulses in our case were ~5 ps, and only some 100 ps (at
the trigger level) out of the photodiode. For a one-off lab gadget like
this, it seemed less complex to first square it up as faithfully as
possible while keeping the rising edge intact, and then manipulate the
cleanly driven logic signals. Parts cost is of less relevance than the
inelegance of my solution here.

Are you pulse picking? I developed a pretty cool Pockels Cell driver
for a biggish laser company who didn\'t buy many.

http://www.highlandtechnology.com/DSS/T850DS.shtml

Using a dual like the ADCMP561 (the ADCMP582 is a single) for a
stretcher is indeed a good suggestion, though. Speaking of which, what
actually happens in practice if you drive fast comparators like those
with a pulse shorter than the specified minimum pulse width? I\'ve never
tried…

Right, 582 is an expensive single. We use them when we absolutely have
to.

I wish Analog would add the ADCMP comparator models to LT Spice, so we
could simulate cases like the one you suggest.

 

[Steve Wilson]

M Gira <mgira53@gmail.com> wrote:

Hi All,

I am hoping someone with with high speed experience could point me in
the right direction.

My issue is that I have an ~850pS pulse (somewhat random pulse
output) that I need to lengthen to 25nS. I have built many
oneshot/timer circuits over the years but never this fast. My research
seems to indicate that most timers (available ICs) need a minimum
trigger pulse of several to ~ hundred nS. Retrigger time doesn\'t seem
to be an issue (yet).

Thanks in advance.
Martin


Martin Gira
Sr. Research Engineer
Center for Visual Science (CVS)
Center for Medical Technology & Innovation (CMTI)
Neurobiology and Anatomy
University of Rochester

two 100ep52 d-flops will capture this pulse with no problem. The first one
captures the pulse and signals the second to start the delay. When the
delay times out, it releases the first one so it is ready to find another
pulse.

 

[John Larkin]

On Tue, 01 Sep 2020 22:41:51 GMT, Steve Wilson <spam@me.com> wrote:

M Gira <mgira53@gmail.com> wrote:

Hi All,

I am hoping someone with with high speed experience could point me in
the right direction.

My issue is that I have an ~850pS pulse (somewhat random pulse
output) that I need to lengthen to 25nS. I have built many
oneshot/timer circuits over the years but never this fast. My research
seems to indicate that most timers (available ICs) need a minimum
trigger pulse of several to ~ hundred nS. Retrigger time doesn\'t seem
to be an issue (yet).

Thanks in advance.
Martin


Martin Gira
Sr. Research Engineer
Center for Visual Science (CVS)
Center for Medical Technology & Innovation (CMTI)
Neurobiology and Anatomy
University of Rochester

two 100ep52 d-flops will capture this pulse with no problem. The first one
captures the pulse and signals the second to start the delay. When the
delay times out, it releases the first one so it is ready to find another
pulse.

Most any flip-flop, CMOS or ECL, can be made to clear itself after
it\'s clocked high. You can do that with a delay line from Q to Clear
(PCB trace, or one R-L-C) but that has to clear out before the next
pulse can be accepted. That can be worked around.

Just an RC from Q to Reset works with some logic families, but some
don\'t like that, especially with long tau\'s.

 

[Steve Wilson]

John Larkin <jlarkin@highland_atwork_technology.com> wrote:

Just an RC from Q to Reset works with some logic families, but some
don\'t like that, especially with long tau\'s.

What logic families?

Increase the C.

 

[Bill Sloman]

On Wednesday, September 2, 2020 at 1:45:41 AM UTC+10, mgi...@gmail.com wrote:

Hi All,

I am hoping someone with with high speed experience could point me in the right direction.

My issue is that I have an ~850pS pulse (somewhat random pulse output) that I need to lengthen to 25nS. I have built many oneshot/timer circuits over the years but never this fast. My research seems to indicate that most timers (available ICs) need a minimum trigger pulse of several to ~ hundred nS. Retrigger time doesn\'t seem to be an issue (yet).

Ghiggino, K.P., Phillips, D., and Sloman, A.W. \"Nanosecond pulse stretcher\",Journal of Physics E: Scientific Instruments, 12, 686-687 (1979).

We didn\'t stretch the pulse to 25nsec - we only needed to get it long enough to trigger some ECL logic.

As is mentioned in the paper, the two transistors configured as an emitter-coupled monostable would probably have done a better job.

You probably can\'t now buy the broad-band (5GHz) PNP transistor we used but equivalent NPN transistors are widely available.

The BFR92 NPN transistor should work fine.

https://www.nxp.com/docs/en/data-sheet/BFR92A_N.pdf

Element 14 has 23,000 in stock , and they aren\'t expensive. It\'s surface mount part, but through the board mounting doesn\'t work well at this kind of speed.

You need to put a surface mount \"base-stopping resistor\" - something like 27R worked for me - right up against the base pin to prevent fast parasitic oscillations. There are better (but trickier) ways of doing this, but a base-stopper won\'t slow the circuit enough to stop it doing your job.

E-mail me with more detail, and I can probably whip up something in LTSpice that you could play with in simulation. I\'ve posted at least one .asc here recently that included an emitter-coupled monostable and the Spice model for a BFR92 (but I was exploiting the low collector capacitance of the BFR92 rather than its speed).

--
Bill Sloman, Sydney

 

[Bill Sloman]

On Wednesday, September 2, 2020 at 3:25:28 AM UTC+10, David Nadlinger wrote:

On 01.09.20 5:44 pm, jla...@highlandsniptechnology.com wrote:
An ECL-output comparator is an open emitter, so add a cap and a weak
pulldown to make a stretcher. Since the \'582 is a dual, use the other
half as a discriminator on the stretched pulse.

The 582 is expensive. One of the slower parts, like a 561, would work
at these speeds.

Well, the source pulses in our case were ~5 ps, and only some 100 ps (at
the trigger level) out of the photodiode. For a one-off lab gadget like
this, it seemed less complex to first square it up as faithfully as
possible while keeping the rising edge intact, and then manipulate the
cleanly driven logic signals. Parts cost is of less relevance than the
inelegance of my solution here.

Using a dual like the ADCMP561 (the ADCMP582 is a single) for a
stretcher is indeed a good suggestion, though. Speaking of which, what
actually happens in practice if you drive fast comparators like those
with a pulse shorter than the specified minimum pulse width? I\'ve never
tried…

Nothing much happens.

The difference between a fast op amp and a fast comparator is that the gain of a fast op amp drops as a linear function of frequency, and the gain of a fast comparator drops as the square or cube of frequency (two stage of gain, or three).

The small low frequency content in the pulse hitting the comparator does get amplified - so you might see a ripple on the output, but that\'s it.

Broad band transistors don\'t have a lot of gain, but what they have rolls down to 5GHz or higher.

http://www.farnell.com/datasheets/2615758.pdf

The BFU768F offers 110GHz for less than a dollar. Stopping it from self-oscillation might be tricky.

--
Bill Sloman, Sydney

 

[Jan Panteltje]

On a sunny day (Tue, 1 Sep 2020 08:45:33 -0700 (PDT)) it happened M Gira
<mgira53@gmail.com> wrote in
<cb23c2d6-e807-4f55-9414-d5e9c251399an@googlegroups.com>:

Hi All,

I am hoping someone with with high speed experience could point me in the right
direction.

My issue is that I have an ~850pS pulse (somewhat random pulse output) that
I need to lengthen to 25nS. I have built many oneshot/timer circuits over
the years but never this fast. My research seems to indicate that most timers
(available ICs) need a minimum trigger pulse of several to ~ hundred nS.
Retrigger time doesn\'t seem to be an issue (yet).

Thanks in advance.
Martin

Apart from the solutions like diode + RC time and D-flipflops
there is a simple circuit I used many times:
http://panteltje.com/pub/pulse_stretcher_IMG_0526.GIF

C1 R1 is a differentiator, C2 R2 sets the output pulse width,
you need to slice that somewhere.
Of course the Ccb and Cce of the transistor counts too.
Using 10 GHz transistors should work (have not tried that high).

If you bias the base just below Vbe it can work as pulse detector too.
May save components.

R2 will be low for short output pulses, could even be 50 Ohms perhaps.
Takes 5 minutes to test.

 

[Phil Hobbs]

On 2020-09-01 14:17, John Larkin wrote:

On Tue, 1 Sep 2020 18:25:20 +0100, David Nadlinger
david@klickverbot.at> wrote:

On 01.09.20 5:44 pm, jlarkin@highlandsniptechnology.com wrote:
An ECL-output comparator is an open emitter, so add a cap and a weak
pulldown to make a stretcher. Since the \'582 is a dual, use the other
half as a discriminator on the stretched pulse.

The 582 is expensive. One of the slower parts, like a 561, would work
at these speeds.

Well, the source pulses in our case were ~5 ps, and only some 100 ps (at
the trigger level) out of the photodiode. For a one-off lab gadget like
this, it seemed less complex to first square it up as faithfully as
possible while keeping the rising edge intact, and then manipulate the
cleanly driven logic signals. Parts cost is of less relevance than the
inelegance of my solution here.

Are you pulse picking? I developed a pretty cool Pockels Cell driver
for a biggish laser company who didn\'t buy many.

http://www.highlandtechnology.com/DSS/T850DS.shtml


Using a dual like the ADCMP561 (the ADCMP582 is a single) for a
stretcher is indeed a good suggestion, though. Speaking of which, what
actually happens in practice if you drive fast comparators like those
with a pulse shorter than the specified minimum pulse width? I\'ve never
tried…

Right, 582 is an expensive single. We use them when we absolutely have
to.

I wish Analog would add the ADCMP comparator models to LT Spice, so we
could simulate cases like the one you suggest.

Yeah, they\'ve been glacial about that stuff. They don\'t even add their
existing models to the library, e.g. ADA4899.

The selection dialogues for the built-in library are one of LTspice\'s
worst features. You have to run down the whole list using the arrow
keys to find such illuminating descriptions as

\"Voltage comparator\"
or
\"uPower dual comparator\"

Some of the newer parts actually have a good enough description that you
can tell whether it\'s worth looking at the datasheet, e.g.
LT6703-2 \"uPower, Low Voltage, SOT-23, Dual Comparator with 400mV Reference\"

Sure would be nice if there were a detailed list view available.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Chris Jones]

On 02/09/2020 04:17, John Larkin wrote:

On Tue, 1 Sep 2020 18:25:20 +0100, David Nadlinger
david@klickverbot.at> wrote:

On 01.09.20 5:44 pm, jlarkin@highlandsniptechnology.com wrote:
An ECL-output comparator is an open emitter, so add a cap and a weak
pulldown to make a stretcher. Since the \'582 is a dual, use the other
half as a discriminator on the stretched pulse.

The 582 is expensive. One of the slower parts, like a 561, would work
at these speeds.

Well, the source pulses in our case were ~5 ps, and only some 100 ps (at
the trigger level) out of the photodiode. For a one-off lab gadget like
this, it seemed less complex to first square it up as faithfully as
possible while keeping the rising edge intact, and then manipulate the
cleanly driven logic signals. Parts cost is of less relevance than the
inelegance of my solution here.

Are you pulse picking? I developed a pretty cool Pockels Cell driver
for a biggish laser company who didn\'t buy many.

http://www.highlandtechnology.com/DSS/T850DS.shtml


Using a dual like the ADCMP561 (the ADCMP582 is a single) for a
stretcher is indeed a good suggestion, though. Speaking of which, what
actually happens in practice if you drive fast comparators like those
with a pulse shorter than the specified minimum pulse width? I\'ve never
tried…

Right, 582 is an expensive single. We use them when we absolutely have
to.

I wish Analog would add the ADCMP comparator models to LT Spice, so we
could simulate cases like the one you suggest.

I\'m not sure that I would trust the models when used outside the
datasheet operating conditions. I\'m sure they have internal transistor
level ADICE models that would accurately predict behaviour in these
conditions, but then IIRC they tend to give some idealised model to
customers instead of the accurate transistor level model. I can\'t
understand the motivation for this. The idea that this would stop a
competitor from reverse-engineering it is silly - 1. any serious
competitor would easily be able to open one up and extract the schematic
and 2. they probably already bought the competitor anyway.

 

[server]

On Wed, 2 Sep 2020 08:27:49 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-09-01 14:17, John Larkin wrote:
On Tue, 1 Sep 2020 18:25:20 +0100, David Nadlinger
david@klickverbot.at> wrote:

On 01.09.20 5:44 pm, jlarkin@highlandsniptechnology.com wrote:
An ECL-output comparator is an open emitter, so add a cap and a weak
pulldown to make a stretcher. Since the \'582 is a dual, use the other
half as a discriminator on the stretched pulse.

The 582 is expensive. One of the slower parts, like a 561, would work
at these speeds.

Well, the source pulses in our case were ~5 ps, and only some 100 ps (at
the trigger level) out of the photodiode. For a one-off lab gadget like
this, it seemed less complex to first square it up as faithfully as
possible while keeping the rising edge intact, and then manipulate the
cleanly driven logic signals. Parts cost is of less relevance than the
inelegance of my solution here.

Are you pulse picking? I developed a pretty cool Pockels Cell driver
for a biggish laser company who didn\'t buy many.

http://www.highlandtechnology.com/DSS/T850DS.shtml


Using a dual like the ADCMP561 (the ADCMP582 is a single) for a
stretcher is indeed a good suggestion, though. Speaking of which, what
actually happens in practice if you drive fast comparators like those
with a pulse shorter than the specified minimum pulse width? I\'ve never
tried…

Right, 582 is an expensive single. We use them when we absolutely have
to.

I wish Analog would add the ADCMP comparator models to LT Spice, so we
could simulate cases like the one you suggest.

Yeah, they\'ve been glacial about that stuff. They don\'t even add their
existing models to the library, e.g. ADA4899.

The selection dialogues for the built-in library are one of LTspice\'s
worst features. You have to run down the whole list using the arrow
keys to find such illuminating descriptions as

\"Voltage comparator\"
or
\"uPower dual comparator\"

Yes, that\'s atrocious. Why isn\'t there a better description and a link
to the data sheet?

Some of the newer parts actually have a good enough description that you
can tell whether it\'s worth looking at the datasheet, e.g.
LT6703-2 \"uPower, Low Voltage, SOT-23, Dual Comparator with 400mV Reference\"

Sure would be nice if there were a detailed list view available.

Cheers

Phil Hobbs

--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[server]

On Wed, 2 Sep 2020 22:52:53 +1000, Chris Jones
<lugnut808@spam.yahoo.com> wrote:

On 02/09/2020 04:17, John Larkin wrote:
On Tue, 1 Sep 2020 18:25:20 +0100, David Nadlinger
david@klickverbot.at> wrote:

On 01.09.20 5:44 pm, jlarkin@highlandsniptechnology.com wrote:
An ECL-output comparator is an open emitter, so add a cap and a weak
pulldown to make a stretcher. Since the \'582 is a dual, use the other
half as a discriminator on the stretched pulse.

The 582 is expensive. One of the slower parts, like a 561, would work
at these speeds.

Well, the source pulses in our case were ~5 ps, and only some 100 ps (at
the trigger level) out of the photodiode. For a one-off lab gadget like
this, it seemed less complex to first square it up as faithfully as
possible while keeping the rising edge intact, and then manipulate the
cleanly driven logic signals. Parts cost is of less relevance than the
inelegance of my solution here.

Are you pulse picking? I developed a pretty cool Pockels Cell driver
for a biggish laser company who didn\'t buy many.

http://www.highlandtechnology.com/DSS/T850DS.shtml


Using a dual like the ADCMP561 (the ADCMP582 is a single) for a
stretcher is indeed a good suggestion, though. Speaking of which, what
actually happens in practice if you drive fast comparators like those
with a pulse shorter than the specified minimum pulse width? I\'ve never
tried…

Right, 582 is an expensive single. We use them when we absolutely have
to.

I wish Analog would add the ADCMP comparator models to LT Spice, so we
could simulate cases like the one you suggest.



I\'m not sure that I would trust the models when used outside the
datasheet operating conditions. I\'m sure they have internal transistor
level ADICE models that would accurately predict behaviour in these
conditions, but then IIRC they tend to give some idealised model to
customers instead of the accurate transistor level model. I can\'t
understand the motivation for this. The idea that this would stop a
competitor from reverse-engineering it is silly - 1. any serious
competitor would easily be able to open one up and extract the schematic
and 2. they probably already bought the competitor anyway.

Probably for simulation speed.

I\'ve seen some bizarre behavior. Sometimes an internal current source
makes an opamp into a perpetual atomic battery. One opamp and one
capacitor becomes a kilovolt (or teravolt) power supply.





--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[server]

On Wed, 02 Sep 2020 06:23:33 GMT, Jan Panteltje
<pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Tue, 1 Sep 2020 08:45:33 -0700 (PDT)) it happened M Gira
mgira53@gmail.com> wrote in
cb23c2d6-e807-4f55-9414-d5e9c251399an@googlegroups.com>:

Hi All,

I am hoping someone with with high speed experience could point me in the right
direction.

My issue is that I have an ~850pS pulse (somewhat random pulse output) that
I need to lengthen to 25nS. I have built many oneshot/timer circuits over
the years but never this fast. My research seems to indicate that most timers
(available ICs) need a minimum trigger pulse of several to ~ hundred nS.
Retrigger time doesn\'t seem to be an issue (yet).

Thanks in advance.
Martin

Apart from the solutions like diode + RC time and D-flipflops
there is a simple circuit I used many times:
http://panteltje.com/pub/pulse_stretcher_IMG_0526.GIF

C1 R1 is a differentiator, C2 R2 sets the output pulse width,
you need to slice that somewhere.
Of course the Ccb and Cce of the transistor counts too.
Using 10 GHz transistors should work (have not tried that high).

If you bias the base just below Vbe it can work as pulse detector too.
May save components.

R2 will be low for short output pulses, could even be 50 Ohms perhaps.
Takes 5 minutes to test.

At picosecond speeds, something like that would work with an
enhancement phemt.

And your graphics quality is much improved!



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[George Herold]

On Tuesday, September 1, 2020 at 11:45:41 AM UTC-4, M Gira wrote:

Hi All,

I am hoping someone with with high speed experience could point me in the right direction.

My issue is that I have an ~850pS pulse (somewhat random pulse output) that I need to lengthen to 25nS. I have built many oneshot/timer circuits over the years but never this fast. My research seems to indicate that most timers (available ICs) need a minimum trigger pulse of several to ~ hundred nS. Retrigger time doesn\'t seem to be an issue (yet).

Thanks in advance.
Martin

Is the pulse at the volt level or so?
For 0.8 ns to 25 ns I think you might be able to get by with
a fast comparator (from LT/ AD, If not at the volt level.)
And then a Schmitt trigger inverter with a diode and RC on the input.
something like the pulse stretchers here.
http://musicfromouterspace.com/analogsynth_new/ELECTRONICS/mickeymouselogic..html
But much smaller C\'s! (maybe the input C of the inverter is enough
as JL suggested.)

George H.

Martin Gira
Sr. Research Engineer
Center for Visual Science (CVS)
Center for Medical Technology & Innovation (CMTI)
Neurobiology and Anatomy
University of Rochester