breadboarding picosecond stuff

Nice. Might want to spend a low-ESR electrolytic since those Lascar supplies are switchers AFAIR.

Did ya hafta show off that 11802?

He who does not try will not win ;-)

The "drool", as you call it, is probably due to the chip using resistors instead of current mirrors... ala VERY OLD style ECL.

...Jim Thompson

On a sunny day (Wed, 09 Jan 2008 13:44:52 -0800) it happened John Larkin wrote in :

Hey, I had not seen those little vertical wire strips in many years :-)

This is an ONsemi EclipsPlus, silicon-germanium part, pretty recent stuff. The drool could be skin effect on wirebonds and leads maybe? Just running out of Ft on the output transistors? This usually happens on rising edges when the ecl emitter is sourcing a lot of current into a termination.

The circuit is roughly....

Vcc-------------+-------+ | | Rup | | | | c +------b | e | | c | --b | e +---------- out | | | Rterm = 50r | | | gnd

Where Vcc = +2.5, Vee = -2.5. The lower npn turns off, and Rup pulls the output gadget base up to about Vcc, and "out" jumps up to about Vcc-0.8 maybe. The output transistor is almost saturated (Vce = 0.8) and it's driving the termination resistor hard, it's running out of Ft, and Ccb is max'd out. No wonder it drools; I sure would.

Why didn't they put an inductor in series with Rup? Lazy bums, a mere

John

Hurrumph! A typical wirebond is only about 1.55nH. Spiral inductors on a chip take up lots of silicon area.

...Jim Thompson

It never really saturates. Could be the rapidly rising capacitance of the output transistor. Hey, can't you scope that out with your Aade meter? Hang a 0402 size C in series and keep the output high.

That would make the die a few hundred milli-cents more expensive ...

Nah, use nano tubes :-)

Who makes those cute bench supplies in that first pic?

One time I searched Digikey for those "old tv" (phenolic?) solder strips. No luck..

Why the "Y" connection off the chip capacitors to the ground plane?

Neat. I didn't spot bypass capacitors on the 317 ? .

Funky bench meters... :)

Relative to the Tek 11802...I use sticks and stones to test electronics. :P

D from BC British Columbia Canada.

Lascar. They're pretty nice, switchers. My only gripes is that they don't go down to zero volts, and the voltage knob is a little stiff, hard to set very precisely.

John

I think Mouser still has them. They're great for stuff like this.

Less inductance. I think.

There's a tantalum hidden behind the terminal strip, on the +5 input, and the tiny ceramics are OK on the output side.

Are not!

That's an ebay find, $600 or so for the mainframe. It's the sampling heads that are expensive, $750 to $2K or more. That head is on an extender cable, which is really handy at these speeds; a pair of short hardlines run a few inches, straight into the head. That head is 20 GHz sampling and TDR.

John

Switchmode bench supplies should have the lowest shipping costs. Less weight and size. There's no giant lump of silicon steel.

D from BC British Columbia Canada.

Looks super. Have you tried using two resistors in parallel to ground, "Y"ed at about 30 degrees to 45 degrees?

Yes...about 40 or so years...

The "Y" connection is a simple and effective way of reducing inductance to near zero. That is why i asked about doing the same for the resistors.

Darn, my 'Google books'* electronics education failed me again. :P I think that page was missing :)

• Google books are previewable books however pages are missing to deter copying.
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D from BC British Columbia Canada.

A little L in series with things like ecl pulldowns doesn't matter much. Two resistors, like you suggest, would probably help if termination were critical. I'll TDR some examples and see how much difference it makes.

We sometimes use two surface-mount resistors in parallel, on superfast signal terminations, to reduce component and via inductance.

The cheap axial carbon-film resistors are actually pretty good in the roughly 1 GHz sort of area.

John

Near zero? Does it really give more than a factor of 2 or so reduction in inductance? If so, _that_'s a trick I'm glad to know about. How does it work?

Cheers,

Phil Hobbs

I like how they're under the "home improvement category." "Honey, can I get some home improvement items fro Amazon?" "Thanks!"