Circuit for producing 10ns pulses of several amps

[Uwe Hercksen]

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

Hello,

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

Cheers

 

[Joerg]

Nice part, 10 amps and 280 pF, maybe a little big for CRC's LED driver
requirement, but it would work fine. You could drive it from my
TinyLogic gates, or from some paralleled 74AC gates... it only needs
2-3 volts of gate drive. EPC2012 might be a better fit.

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.

There are PHEMTS with Idss in the amps, and they sometimes enhance
about 2:1 better than that. They can switch at sub-ns speeds with
fairly easy gate drive. Avago has some enhancement parts.

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.

 

[Fred Abse]

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

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.

 

[Joerg]

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.

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.

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.

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

 

[Joerg]

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

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.

 

[[email protected]]

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.

That's a pretty big inductor. Why would you burn power unnecessarily?

 

[Mr.CRC]

In case this has not already been cited, I have successfully used the
following circuit as the laser driver in a distance measuring
application

UHRING W., ZINT C.V., BARTRINGER J., A low-cost high-repetition-rate
picosecond laser diode pulse generator, Proc. SPIE 5452, 2004, pp.
583-590, Photonics Europe 2004, Strasbourg (France), April 26-30,
2004, edited by D. Lenstra, G. Morthier, T. Erneux, M. Pessa, ISBN
0-8194-5375-7. Lien

JohnR

Thanks. I'll try to get my hands on that. My work library should be
able to provide it.

I also have this bookmarked, but haven't gotten it yet:

http://ieeexplore.ieee.org/Xplore/l...643093.pdf?arnumber=5643093&authDecision=-203

 

[Mr.CRC]

Talking to myself, it seems.

Thanks for your reply. I saw it but the idea seemed a bit obscure for
my to spend time on. My limitation, not yours.

I'll have a look at your sim below, but it may take me a couple days...

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

RL

[edit]

Thanks for the consideration!