"John Larkin" wrote in message
...
Nonlinear transmission lines are cool. You can make them with
saturating inductors, ceramic capacitors, or varicap diodes, even
ordinary power diodes. You can get the risetime to go down as a step
propagates down the line.

I've been tempted to try that before -- a necklace of ferrite beads might
run you only a couple bucks per foot, and with the velocity factor so low,
that's enough to get something snappy with jellybean transistors (a few
nanoseconds' input edge). Downside is the impedance, which must be in the
kohms range (small signal). Hard to get much current into it like that.
Supposedly, ferrite has a high e_r as well, so the impedance probably isn't
*that* bad, but it's hard to ensure a consistent airgap (or lack thereof)
with loose beads.

I expect the pulse width is limited as much by geometry (ferrite beads being
a coax structure, periodically disturbed by the imperfect faces between
beads and imperfect spacing to the conductors) as by material dispersion
(losses, etc).

The not-even-ludicrous speed[1] generators do it with schottky junctions in
InP (like the LeCroy 200GHz scope) IIRC. With harmonics near the THz, there
isn't any physical length to spare before the signal dissipates, anyway.

Tim

[1]
"Aah! What the hell was that?!"
"Spaceball 1!"
"They've gone to plaid!"

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Deep Friar: a very philosophical monk.
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