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resetting a filter

I have a cmos logic signal that I want to delay a few ns. So I figure I'll just run it through a 2 or 3-pole Bessel lowpass filter into the next gate. I'd like it to recover quickly, so I figure I could discharge the cap/caps in the filter. I could do that with schottky diodes, but a transistor would discharge them better.

How about this?

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(Of course, it leaves a little current circulating in the inductor.)

I'm not sure how well it will work, so of course I'll simulate it.

But what's interesting is that I think the transistor doesn't saturate once it's discharged the cap. Ic goes to zero, so there's base current but no steady-state c-b junction current. No saturation, right?

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John Larkin                  Highland Technology Inc
www.highlandtechnology.com   jlarkin at highlandtechnology dot com   

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Reply to
John Larkin
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Saturation is about nonequilibrium charge density in the base region, which shields out the E field in the junction. It's the collector current that scavenges all the injected carriers from the base, so I would think that your situation would have all the nasty charge storage problems of recovery from saturation.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

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Reply to
Phil Hobbs

How about a little piece of coax? Or wind the pcb trace around the board?

or lumped element delay?

George H.

So I figure

.highlandtechnology.com=A0 jlarkin at highlandtechnology dot com

Reply to
George Herold

Somewhere there is a famous video of a presentation by a older female military officer (Navy?) where she holds her fingers about

12" apart and says that's about one nanosecond.

Ahh, I found a link, not the one I remember, but good.

Her name Grace Hopper.

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Mikek

Reply to
amdx

Grin, yeah I was looking at an Ortec delay generator 425A the other day.

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George H.

Reply to
George Herold

what is a "few"? 3, 6, 22? How accurate of a delay?

If it's less than 15 or so take a 74lvc04 running at 3.3 will give you a tpd typical of 2.5ns per gate. Wire 2,4 or 6 to get 5, 10 or 15ns.

--
Chisolm
Republic of Texas
Reply to
Joe Chisolm

It's hard to pick-and-place two feet of coax!

Or wind the pcb trace around the

That would take a couple feet of trace, and it's not tunable. The board will be pretty small.

This *is* lumped element delay!

--

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro   acquisition and simulation
Reply to
John Larkin

Oh well, I guess I'll use diodes.

--

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro   acquisition and simulation
Reply to
John Larkin

She is also the one who introduced "bug" into our language for a problem in the equipment.

Reply to
John S

3 maybe.

10% or so would do, but I'd like it to be fairly stable with temperature and I don't want to add much jitter.

It would be good if I could change parts values to tweak the delay to sub-ns resolution. I can do that with an RLC circuit.

--

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro   acquisition and simulation
Reply to
John Larkin

What does "recover quickly" mean? After a positive-going transition how soon does a negative-going transition occur? ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

ge

a

vary the supply voltage?

or maybe a single gate with a resistor in the supply? might make pull up slower than pull down

-Lasse

Reply to
langwadt

Now, I'm really confused. If coax would meet the electrical requirement, why do you need to reset your filter??? Sounds like you want to shorten the pulse by delaying the front edge.

More info about the range of pulse rates and widths might be relevant.

Reply to
mike

IIRC her notebook says something like "First actual bug found in logic system", because there was a moth or something stuck in there. That remark seems to show that the phrase "getting the bugs out" was already in use.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net
Reply to
Phil Hobbs

Farnell in Europe is still selling Filotex 1.22mm OD 75R coax. You could wind a metre or so of that onto a RM core former and place it like any other component.

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Newark doesn't seem to stock it, so you'll have to go a different distributor

Not if you are planning to use active parts to "reset" it (which seems like a very bad idea).

-- Bill Sloman, Nijmegen

Reply to
Bill Sloman

That would more than fill up the entire volume of the instrument I have in mind.

Why is it a bad idea? It will certainly work, namely give me a delay that resets quickly.

--

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro   acquisition and simulation
Reply to
John Larkin

Ancient problem, ancient solution. Just use a stupid RCD delay. (R || D) + C, use a schottky if your V_IL is tight.

Tim

-- Deep Friar: a very philosophical monk. Website:

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Reply to
Tim Williams

My thoughts exactly.

Proper selection of the DIODE and R type (not value) is key though.

Jamie

Reply to
Jamie

Yes, Adm Grace used to hand out "nanoseconds" (a foot long piece of wire) when she gave presentations. A former boss had one of hers.

Reply to
krw

How do you figure there's no c-b current. The path from /Q thru b-c and back to Q looks like a forward biased c-b current path?

Reply to
bloggs.fredbloggs.fred

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