[sdiy] Tunneldiodes...

[Czech Martin]

So called "Zener" diodes live from avalanche -
and from tunnel effect. Temperature compensated
zeners use the oposite tempco sign of both effects
to cancel.

Some low voltage zener diodes are fakes (several
diodes string in forward conduction).

If there are any heavy doped zeners, they should
exhibit some more pronounced tunnel effect.
But I don't know if the tunnel hump will be
visible...

For simple oscillators relaxation types with
bipolar snap back or SCR triggering seem
to be cheaper, and you can modulate the frequency
in a wide range,
which is not really possible (and wanted)
for a LC tank circuit.

m.c.

> -----Original Message-----
> From: Alex Stettler [mailto:alex at xatomic.ch]
> Sent: Mittwoch, 3. September 2003 12:09
> To: Glen; metasonix; synth-diy at dropmix.xs4all.nl
> Subject: RE: [sdiy] Tunneldiodes...
> 
> 
> 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
> 
>