Super Diodes and detectors

I think the best low-level detector diode is a germanium back diode, essentially a tunnel diode with very low peak point current. People still make them.

John

Thanks John,

Yes, Tunnel diodes have a sharp knee and can work well with apropriate bias.

There are many other tricks, such as using as high impedance as possible (to get higher voltage swing) and a Schottky (eg HP 5082-2835).

The best "normal" diode so far seems to be the rather obscure ITT FO-215

some info on the FO-215 at

The FET idea can be seen at:

........... Zim

..as visions of a straw covered alpine shack floor, with a germanium spinning wheel in the corner come to mind. Outside, the dark and foreboding clouds of the impending Silicon invasion are gathering. A silence has filled the Valley.

mike

Would not a crystal headset be better for matching and sensitivity?

Yes, they are often used. No nearly as efficient as good dynamic headsets however.

The best are the old Navy "Sound Powered" Headsets. If you can find them

................... Zim

Ah... Germanium Valley was never as popular and successful as Silicon valley, it never really had the same potential.

Back to the original point though, JFETs with source & drain connected together are one thought. The silicon Schottky CDSH270 (replacement for the

Using a JFET (or pentode?) as an infinite impedance detector (which I think was what was meant in the first post) is pretty good (tends to be a bit fussy about the resistor value, but only a bit fussy). I have used them at

I recall "super diode" being used to describe transistors with base to collector, used as a diode (e.g. thermal compensation in output stages), but they aren't great at low signal levels... pretty good at higher currents though. Now "super diode" is used only to mean "precision rectifier circuit" in many web pages.

--------------------------------------- Posted through

Areoflex, among others

A back diode is the only germanium IC-like (planar, passivated, wire bonded) process I've heard of. Too bad they don't make serious switching-type TDs this way.

The best silicon RF detectors are low-barrier schottky diodes. SMS7621 is nice... 2 volts reverse rating, 0.26 pF junction capacitance.

Jfets used as diodes are pretty horrible. Lots of capacitance, lots of series resistance. Even the leakage is mediocre compared with what you can do with the c-b junction of a good transistor.

John

Here are some Russian Back Diodes. I've had good luck with their TDs.

tm