Super fast sample & hold under $10?

Came also per PM :-)

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That was the reason I didn't consider it. If I had to build something like the Bay Bridge a 6x cost overrun would not be a problem, but here it would be.

Schottky diodes don't leak badly. You have to read it out in a few us after the sample.

There is also "blow-by", which is capacitive feedthrough of the diodes. That is easily compensated with an opamp.

Sampling efficiency of a fast sampler (the output voltage over the input voltage) is low, a few per cent maybe, but gain is cheap.

The classic HP 2-diode feedback sampler is well documented.

That's what I meant, the capacitance. Even at 0.3pF or so that doubles to 0.6pF for a 2-diode sampler. If you have a lot of clanging or a major step going on in the source after the sampling that feeds through and can mess up the reading.

That's not a problem as long as one doesn't use this as a sensitive receiver.

I've got some papers about it that were hand-typed. From the days when HP was really HP, the founders were still alive and the Beatles played on the radio.

That's how I have done it until now, mostly. But yeah, above a GHz it becomes tough.

I like that...

The 7S14 got 2 GHz typical bandwidth from a 4-diode sampler driven by an avalanche transistor! Most of the HP and Tek 4-diode samplers were spec'd at 1 GHz.

Tek published "Sampling Oscilloscope Circuits", part of their Tek Concept series of white paperbacks. It's probably online somewhere, or I could loan you mine with a suitably huge security deposit.

I actually own an HP185 sampling scope, mostly tubes, early 60's monster. It was the first modern 2-diode feedback sampler gadget.

It would take a little fiddling, but a 2-GHz sampler could be done for $10, maybe for $5. I don't know anything about your specific application, but if you email me privately I could deliver any number of wild opinions.

If you use the pHEMTs in cascode, you can get the effective C_dg way down.

Cheers

Phil Hobbs

But their budget was "the sky is the limit", probably all gold-plated on alumina and hand-signed by Agoston Agoston.

I guess my wooden beer Dollar won't count as collateral. Plus you gave that to me.

Seems this Concept Series never made it onto the web. I do have tons from HP though so I am pretty well covered for samplers. Over the years I've built/designed several so I am fairly aware of the trade-offs. That is one area where there seriously are no free lunches.

That sure is a piece of history. My GHz workhorse here is a HP-54110D. Not comparable to very fast sampling scopes but has four HP-samplers in there. It is remarkable how easy such vintage HP equipment can be operated. I haven't ever pulled out the manual, not once. Looks like new.

Thanks. Can't reveal all that much at this point though.

Looks like a good copy here:

--sp

Yes, the "Miller" effect goes way down to the point where it's hardly existing anymore. But in a sampler one has to connect and disconnect from the sampling capacitor somehow. That's where even very few tenths of pF begin to hurt.

Thanks! That is a reallynice blast from the past. Haven't heard the word snap-off diode in a long time.

Sure, but if it's independent of the input, you can fix it afterwards, as with blow-by in a diode sampler.

An ordinary dual gate Si MOSFET, circa 1975, has a typical C_dg1 of something like 0.02 pF. I used to use 3N201s for samplers back in the day. They worked great.

Cheers

Phil Hobbs

Like this:

We have a bunch of (about a dozen) Tek 11801s, ca early 90s. Big, nice scopes. I have some 20 GHz TDR heads, and a 50 GHz single-channel sampling head with funny connectors. Picoseconds are fun.

Harumph.

Nice scan. Thanks.

They were first called Boff Diodes.

It's out there. See e.g.

Cheers

Phil Hobbs

An OTA might be the right kind of gated gizmo; TI's OPA860 has a buffer/ follower and the OTA, and at least some response out at that frequency (gain of 5 at 80 MHz is claimed).

Thanks - this looks like interesting reading!

That was a whole series of books: probes, timebases, CRT circuits, vertical amplifiers. Ten-ish books? I have them at home.

I have scans of all of them, I think. The TV, CRT, and horizontal circuits are pretty much historical interest only.

Cheers

Phil Hobbs