typically stupid ED article

For a one-off, just using something like an LMC660CN (quad, 14-pin DIP) mounted dead bug will make a pretty decent femtoammeter. You get 14 low-leakage standoffs for free, and you can use the other sections to bootstrap the input protection circuitry.

Cheers

Phil Hobbs

Insect abuse. I solder a few pins to the copperclad, or use bypass caps as standoffs, and bend the signal pins out.

(RCA gate. That pic must be pretty old.)

I can still see the part number and count in the usual direction.

Agree that air is the best insulator, and there's nothing wrong with mid-air junctions. Plastic DIP packages seem to have fA surface leakage.

At least I put them out of their misery, unlike _some_ people. ;)

The pins get weakened a lot when you do that, though. In their natural state they can handle a lot of torque from bending resistor leads and stuff.

You probably open boiled eggs from the small end, too. That would figure.

I just put a gouge in the pin 1 end of the package using dikes, and sometimes scribble the P/N on the copper with a fine-point Sharpie.

Yeah, they're surprisingly good. Of course you can't make a fA op amp with a leaky package.

Cheers

Phil "the only good bug is a dead bug" Hobbs

_some_people just get everything right first time.

Boiling eggs is too much trouble, and I get burned handling them. I have a new egg cooking technique that I will reveal if enough people beg.

I was shocked when I tested that ACT04. I was used to CMOS being slow, and its edges were as fast as 10K ECL. And a lot bigger.

Call the SPCI.

Plus the shoot-through and asymmetry teaches you a lot about bypassing.

Society for the Promotion of Cool Inventions? Bring 'em on.

Cheers

Phil Hobbs

ECL was always designed to drive 50R transmission lines.

A 1.2V swing into 50R is 24mA, and that's enough to get the driver warm.

National Semiconductors LVDS uses the same voltage swing for the same reason. Most of us have known about this for some forty years now, but John gets shocked when he runs into it.

what are you on about? John saw that an ATC04 was just as fast with a bigger swing

and LVDS isn't some National Semiconductors special it is a standard and the swing is only 450mV or 4.5mA

And standard ECL swings about 0.8, not 1.2. The voltage across a pulldown resistor could be anything.

A few ECL parts, like EL89, swing close to 2 volts. That can be handy.

CML usually swings about 0.4 at the termination. I haven't tried them unterminated; I should.

We're playing with the idea building a distributed amplifier with discrete fets; I have an EE prof doing the math. The arbitrary goal is to make 50 volt pulses with 50 ps edges. If the output stage works, the next problem will be to come up with a fast gate-line driver with sufficient swing. The problem keeps moving left.

The Tek 545 used a distributed amp made from tubes. We should be able to do that with fets.

Hopefully with fewer tweaks. Some of those distributed-deflection tubes were monsters.

Cheers

Phil Hobbs

I remember chasing the ripples down the line in Tek 551 distributed amplifiers. Pain in the whatsit to get right and very time consuming. Varied with temperature and tube (12BH7 ?) life as well...

Chris

The 545 also had a differential signal delay line that was made of tunable t-coils. The tuning procedure was iterative. Must have taken hours. I think the 585 had two cascaded banks of distributed amps.

The 519 managed 1 GHz, with no amps at all. The deflection plates were distributed, vaguely the same idea.

The early Tek stuff was hand-wired and had selected parts and lots of tuning. Labor intensive.

There are lots of IC distributed amps around now, mostly to drive telecom fiber modulators. They are fairly expensive ($200 range) and have wimpy voltage swings.

I remember seeing a 519 around 1966-67. It was being used for laser research fwir. 1 Ghz real time bandwidth, but as you say, not that sensitive with y input direct to the plates. The bandwidth was revolutionary for it's time though. Scope camera on it as well. Yes, am that old but try to stay awake :-).

I think some of HP kit was the same and can be very difficult to restore because of the hand selected parts. Can't just replace with a stock 2n part number and get the same results.

Still not trivial to design and build a very high speed, high voltage amplifier...

Chris

Los Alamos used many 519s with cameras to record certain one-shot events. They also had a home-made scope that recorded longish transients on eight stacked scan lines of a pretty big CRT. Recording one DHART shot was a massive project.

Los Alamos Sales had a bunch of 519s out in the rain in the parking lot. I didn't want to lug one home, so they let me have a CRT for $20 or something.

It's single-ended distributed-deflection on the vertical axis. The screen was tiny.

I like the tube but the scope itself was really ugly. It used some big ole transmitting tube in the horizontal sweep.

We recently released this:

The output stage baby board took me lots of simulation and three official PCB iterations. Tiny things start to matter below 1 ns. Spice stops being believable down there.

Kurt Rosenfeld of TekWiki found a whole box of vintage internal documents a while back, including factory cal procedures. The original procedures are probably buried in there somewhere:

-- john, KE5FX

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eason. Most of us have known about this for some forty years now, but John gets shocked when he runs into it.

ger swing

But you can't send it anywhere and expect the signal to retain the fast edg es without pushing it into a transmission line.

the swing is only 450mV or 4.5mA

It's a standard now, but it started off as a range of National Semiconducto r parts. At the time there were several back-plane standards that didn't wo rk well for rack-length back planes and fast signals. I'd been using ECL fo r that kind of job, but it meant a -4.5V negative rail, and a -2V rail for the terminating resistors. When LVDS became widely available life got quit e a bit easier.

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reason. Most of us have known about this for some forty years now, but John gets shocked when he runs into it.

gger swing

But didn't seem to be aware that terminating that larger swing at the other end of a transmission line was going to be tricky.

the swing is only 450mV or 4.5mA

If the resistor is being used to terminate a transmission line there's a b ig temptation to return it to a -2V rail.

There are all sorts of ways of skinning that particular cat

It's a very specialised part designed to drive lines that are driven from a resistance equal the cables' characteristic impedance, and terminated at t he receiving end another such resistance, halving the signal swing at the r eceiving end

"The device is especially useful in Digital VideoBroadcasting applications ; " which tend to involve rather long cables and don't tolerate much in the way of reflection.

It might be educational. You should have got that bit of education at Tulan e, but it was probably covered in one the lectures you skipped.

Bill Percival invented - and patented - the distributed amplifier in 1936. I met him once when I was working at EMI Central Research.

I did it with broad-band transistors in 1983. It sort of worked - we got tw o 800psec wide complementary pulses swinging through 7V out of a string of three long-tail pairs of cheap 5GHz broad band transistors, but two bigger

- and much more expensive - HP rf transistors eventually got us to 500psec with a much simpler circuit.

You can now buy cheap 110GHz bipolar broad-band transistors, which might ge t you down to 50psec but they won't do 50V, unless you stack up a few trans mission line transformers. Exotic FETs are a different ball game.