Super duper hype fast FET driver?

The rise/fall times are mediocre. A little series inductive peaking would help.

Gate driver chips are cool, though. They have lots of off-label uses.

What's the load? Need DC coupling/long pulses?

I know how to get 6 or 7 volts of brutal sub-ns swing cheap, at zero Iq. Could be doubled, depending. Not for public release.

John

Mediocre? At high capacitive load maybe but at low loads I think they are amazing for a 25c part. Most others including its other ZXGD300x brethren peter out towards 10nsec for one of both slopes towards zero capacitance.

Oh yeah :-)

Pulses are under 100nsec length and duty cycle is well under 5%. Getting DC across would be great but I am afraid I'll have to clamp that ... somehow ... because it's a high voltage I'll have to move with that. Or I'll let this whole thing ride on the rail. Woe to dose who toucha wid da fingahs :-)

Are Zetex parts OK nowadays. I now a biggish business who wont take those because of reliability problems. The case was too small for the chip inside, or something like that, I was told.

Folks,

Have to drive around a hundred pF or so in parallel with maybe a few hundred ohms blazingly fast. 10-12V amplitude, transitions ideally sub-nanosecond from 10-90% both directions. Not too boutiquish or unobtanium (which excludes certain companies ...) and not more than a few Dollars. Shouldn't introduce noise when low. Low quiescent current, preferably under 20mA.

Looked around and the fastest one I could see is this dude:

Not too much data but it gets into the 2nsec range. Anyone aware of a driver with even more testosterone?

Of course the ideal scenario would be a push-pull MMIC with 15V or more supply voltage but that ain't going to happen. Same with RF switches, even if they could take 12V they are surprisingly slow in switch action.

Ok, could roll my own, of course. But that gets to be involved and a bit too big for this project.

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Have you thought about precharging the gates? Does the fets need to turn of completely to be effective?

If you need high-side drive, a pair of my drivers could feed opposite ends of a 1:1 transmission line transformer (or maybe a balun) to double the swing. 12 volts for 100 ns would be no problem, edges well below a ns.

At below 5% duty cycle, you probably don't need to DC restore.

It'll cost you a burger and a couple of beers. Zeitgeist has about 40 on tap.

If pulse width is fixed, there's another way to do it: a really fast open-drain mosfet feeding a 1:1 transformer, 12 volts or whatever you like. The magnetizing current powers the falling edge. Also cheap.

John

I've done that, biased a gate just below threshold, to optimize a driver that had limited swing. The total gate charge doesn't change much, but sometimes a couple of volts of additional enhancement can help a lot.

John

RF parts such as baluns or obscure directional couplers with a voodoo coefficient never scared me.

Not sure yet if I do. This high voltages acts as kind of a reference somewhere. It's one of those circuits that most people won't even touch with a 10ft pole.

I am game. But I have no idea when I get to S.F. the next time. A lot of my clients are no longer in California, for reasons we all know, and Villaraigosa has just made that loud and clear to companies once more :-(

Now if you ever get into this area we have a very nice Japanese restaurant. Blue Moon and Sapporo on tap.

It must remain adjustable.

This isn't a gate but another capacitive load. The goal is to make the pulse waveform look as perfectly square as can be.

Wish I could find something like the NE3509 that can take 15-20V instead of just 4V.

Never turn down an offer from Larkin. He's promised you a half-fast solution, and I'm sure he can deliver ;-) ...Jim Thompson

How's this?

Transformer isolated 100 volt pulses into 50 ohms with rise and fall below 1 ns. That's over 1e11 volts per second. Got any idea how to do this?

John

They are actually happy to run around 8 volts. Lovely part. But heck, a 2N7002 can switch 15 or 20 volts in under a ns... if you bang the gate hard enough.

Some of the mesfets can be run at 12 or even 15 volts. But the bees knees these days is GaN fets, which work in the 40-200 volt range, need tiny gate drives, and switch insanely fast. But not cheap.

We blew up about a kilobuck worth of Nitronex fets one afternoon. They claim they have the process down now.

John

The 2N7002 or BSS123 plus some magnetics would be kind of my last resort if none of the ICs can do that. And it looks like none can. No market I guess.

Doesn't have to be cheap, but my definition of expensive is everything north of $5 :-)

I'll have to see what CEL has to offer. Paralleling European dual-gates for UHF tuners might also work but that gets old.

Ouch!

I am sure he can. Fast stuff is what his company mostly does and if they didn't earn megabucks per year with this they would hardly be able to buy a large building smack dab in the middle of a metropolis.

It was a working fortune cookie factory. 1930's (ie, terrible) concrete side walls, wooden floors and roof, a perfect candidate for pancaking in the next good earthquake. It's sitting on sand, at the edge of a liquefaction zone. We added a bunch of concrete footings and steel frames and plywood and bolts.

You can see our place in the default Google Earth view of San Francisco. For some odd reason, Google thinks "San Francisco" is in the middle of the interesction of Market and Van Ness, one block away.

And we haven't had a sandstorm for as long as we've been here.

John

solution,

Those cherubim were on there before you bought it? They are amazingly well preserved. I can't imagine the salty air down there to be too friendly to concrete and plaster. The almond below probably has some cultural meaning as well.

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Almond? I thought it was a tamale.

Cheers

Phil Hobbs

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They are original, and we just cleaned them up and repainted. No architect would dare do anything this cool any more.

The salty fog is out west, near the ocean. Everything rusts out there.

The bummer is that it's a wooden building that looks up at Sutro Tower, 22 megawatts of AM/FM/TV/whatever. The EMI is ghastly.

John

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Look at the bright side: If you'd need a sensor somewhere out of reach of power you can just add a loop, some diodes, and it'll be supplied with power until Sutro Tower keels over :-)

If I'd needed a quiet lab place I'd find something in the outbacks of Alabama or similar states. Then you are neither bothered by RF fields nor by biz-hostile politicians.

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On the other hand, the chances of being able to hire locally resident expert help wouldn't be that great. And they are Baptists - perhaps not as sincerely Baptist as the inhabitants of Urk are Calvinist, but still pretty inflexible - so you'd run the risk of being rejected as a schismatic Lutheran.