[sdiy] Tunneldiodes...

[Alex Stettler]

Hi all,

> I figure you probably know more about tunnel diodes than I do,
> but it seems
> like they might be useful as the heart of a new VCO design?
>
> Yes, I know. They're expensive. Why use them when we already have good VCO
> designs using cheaper and perhaps better components? Quite simply, to
> expand our palette of sounds and circuit design options--and also because
> it's fun to go where angels fear to tread sometimes.  :)

Probably you could build a rather simple and compact VCO. I don't have any
idea about it's linearity and temperature dependet behaviour. With the
Tunneldiode as an element with a negative small-signal resistance (I don't
know, if this is the right term in English. Translated word by word, we call
it 'differential resistance' in German) you could compensate the damping of
a resonant circuit. So theoretically you should be able to build a very
simple VCO with a tunneldiode, a resonant circuit, a varactor to control the
frequency and a choke, to block off the generated AC signal from the supply
lines.

IMHO i see two reasons why tunneldiodes aren't that cheap:
1. The type I know is made like a normal Si-pn-Diode. Instead of silicon
it's made of germanium.
   Both, the n- and p-layer is heavily doped.
2. Probably tunneldiodes aren't needed it that large quantities. And every
semiconductor produced in smaller
runs is rather expensive.

Regards,
Alex