Circuit for producing 10ns pulses of several amps

Run of the mill xenon or mercury thyratrons are typically slower than their silicon counterparts, with comparable risetime and deionization time in the ms. Hydrogen thyratrons are well renouned for their speed, however.

As circuits go with high current, fast risetime, and dreadful tails, there's this one. You still need a pulse generator, but that's easier than the current gain. Some TinyLogic would take care of that.

'Course, Jim would've been about the only person on Earth with a stash of stud type BJTs. YMMV.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

What's the actual specification of the pulse you're trying to generate? This is the first mention I've seen of 4ns risetime. falltime? How variable does the width need to be.

50KHz rep rate was mentioned, but not sure if the context was relevant. Do you care about jitter? How about life of the apparatus. Both are relevant for relays. Is it a current pulse or a voltage pulse? And what is required of the other? voltage compliance for current pulse or peak current available for voltage pulse? Does delay matter? Maybe something like a distributed amplifier made from smaller/faster devices.

I didn't catch whether this is a test fixture or a high volume device where cost matters a lot.

What's the actual specification of the pulse you're trying to generate into exactly what range of loads. LED is an ambiguous definition. The devil is in the details.

You can do some interesting things with avalanche transistors and/or snap diodes. I've never tried it at this power level, but you don't need much speed.

Common triacs won't do it, of course (the data sheet has a dI/dt limit, and there's a good reason for that). Phototriacs, on the other hand, DO turn on abruptly. They won't turn off so fast, but a Blumlein pulser might not care.

Jim Thompson schrieb:

Hello,

you closed and opened the same switch within some nanoseconds? Or did you close one switch and open another one within some nanoseconds?

Bye

You do it by connecting a charged, open-circuited coax stub via the relay. The coax empties itself out in a time t = 2L/sqrt(epsilon).

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

Talking to myself, it seems.

A quick LTspice simulation follows, using the cross-conduction alone.

RL

Version 4 SHEET 1 880 680 WIRE 192 64 64 64 WIRE 512 64 192 64 WIRE 16 80 -48 80 WIRE 512 160 512 64 WIRE -176 176 -192 176 WIRE -48 176 -48 80 WIRE -48 176 -96 176 WIRE 64 176 64 160 WIRE -192 240 -192 176 WIRE 64 256 64 240 WIRE 64 352 64 336 WIRE 192 352 192 128 WIRE 192 352 64 352 WIRE -48 432 -48 176 WIRE 16 432 -48 432 WIRE -192 480 -192 320 WIRE 64 480 64 448 WIRE 64 480 -192 480 WIRE 432 480 64 480 WIRE 512 480 512 240 WIRE 512 480 432 480 WIRE 432 496 432 480 FLAG 432 496 0 SYMBOL LED 48 176 R0 WINDOW 0 40 -8 Left 2 WINDOW 3 28 65 Left 2 SYMATTR InstName D1 SYMATTR Value QTLP690C SYMATTR Description Diode SYMATTR Type diode SYMBOL ind 48 240 R0 WINDOW 0 58 38 Left 2 WINDOW 3 48 70 Left 2 SYMATTR InstName L1 SYMATTR Value 5E-8 SYMBOL cap 176 64 R0 WINDOW 0 42 18 Left 2 WINDOW 3 23 53 Left 2 SYMATTR InstName C1 SYMATTR Value 300E-12 SYMBOL res -80 160 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R1 SYMATTR Value 10R SYMBOL nmos 16 352 R0 WINDOW 0 87 27 Left 2 WINDOW 3 57 56 Left 2 SYMATTR InstName M1 SYMATTR Value FDS6961A SYMBOL pmos 16 160 M180 WINDOW 0 82 68 Left 2 WINDOW 3 53 40 Left 2 SYMATTR InstName M2 SYMATTR Value Si9400DY SYMBOL voltage 512 144 R0 WINDOW 123 0 0 Left 2 WINDOW 39 24 132 Left 2 SYMATTR SpiceLine Rser=.01 SYMATTR InstName V1 SYMATTR Value 10 SYMBOL voltage -192 224 R0 WINDOW 0 -36 112 Left 2 WINDOW 3 -52 285 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V2 SYMATTR Value PULSE(10V 0V 1E-6 1E-8 1E-8 1E-5 2E-5 10) TEXT -248 528 Left 2 !.tran 0 11.2E-6 11E-6 1E-9 uic

Have you examined datasheet/appnotes for ZTX415 avalanch transistor - its all in the tuned co-ax line (apparently).

Phil Hobbs schrieb:

Hello,

ah, the length of the pulse is determined by the coax stub only. Pulses of some 100 ps should be possible too. But if you want periodic pulses with a period of some ms I would expect a jitter of some 100 ns even when the relay is driven with a good XTAL based clock.

Cheers

Relays will jitter many microseconds. The mechanical bits ring in a zillion modes, like a church full of bells, after every hit.

--

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

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME  analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

John Larkin schrieb:

Hello,

when I wrote of some 100 ns jitter, I already thought of several microseconds but I dont wanted to be too pessimistic.

Cheers

It's fun to look at the coil voltage of a regular or a reed relay, with a scope, after the drive device opens up. There's usually enough residual magnetism to make the various vibrations induce signals into the coil. It tends to be a frightful mess of superimposed mechanical resonances. Reeds are terrible for low-level signal switching for that same reason: long messy twangs.

I once designed a delay generator to replace a piezoacoustic delay line, a few microseconds delay as I recall. The piezo delay line worked, sort of, but it would twang for tens of milliseconds after generating that short delay. It cost $2000, too.

--

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

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME  analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

Does anyone know how fast they really switch, given a zero to 5V gate drive? The datasheets for those are rather paltry, not much info in them.

I've got a situation where even using several 7002 in parallel won't muscle around a few hundred pF of load capacitance fast enough. I am trying to get down to around a nanosecond.

--
Regards, Joerg

http://www.analogconsultants.com/

There's a fast LED driver described in there, without using a transmission line. 40 amps pulse, 10ns wide.

Don't believe the Spice model they supply, it's nowhere near the published datasheet figures. Or real life.

Nice device.

--
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)

By "they", do you mean the Tiny buffers? Figure about 600 ps rise/fall and, if you put three sections in parallel, maybe 8-10 ohms drive impedance. At 12 cents for a triple buffer, using several is feasible.

What are you driving the 2N7002 gates with? I can make a 2N7002 sink about an amp in under 1 ns, driving its gate hard.

--

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

mentioned.

The buffers can do it but can the EPC2012? I've looked up and down their site and none of the scope plots in switcher apps looked all that mouthwatering. No hard timing data that I could find either.

NL37WZ16. I'll have to see the layout, maybe something has gone wrong there (that art was out of my hands).

--
Regards, Joerg

http://www.analogconsultants.com/

I'd be very surprised if the jitter were better than tens of microseconds for a mercury relay. But that's what the sampling scope's delay line is for. ;)

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

mentioned.

Send me some screen snaps of the PCB layers, and I'll review it.

--

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

21A

mentioned.

Thanks. But I don't have them myself yet. It pretty much needs to follow RF design rules and usually they are pretty good at that.

--
Regards, Joerg

http://www.analogconsultants.com/

I think the usual way to shorten the pulses is to put a low value inductor in parallel with the LED. Therefore the current can only flow through the LED for a short while until the all the current available is shunted through the inductor instead.