Junction Noise

[Martin Czech]

This noise is mainly shot noise, the granularity of
charge is audible when it is transfered over the 
junction. Like peas on a tin plate.

Larger voltage breakdown is avalanche (low voltgae is tunnel effect).
Now, avalanche is extremely sensitive to "crap", ie.
impurities, crystal deformation etc. etc.
So I'd say that the noise depends a lot on the individual
diode and the actual reverse current yoiu are are running it.

Even a vacuum tube diode can be used, and was used as standard noise
element. So I don't think that the Ge bandgap difference to Si
would make much difference, but the impurities level will.
Ge transistors were always noted as noisy, perhaps because Ge does
not behave so well when melting and so on.

Low noise zeners habe burried layers thus avoiding surface dirt effects.
Cheap zeners are quite noisy, because they don't have that feature.

I think you should try a few diodes (the transistors proposed
actually run as zener diodes, emitter breakdown) and see what
sounds best.

Good means hissing noise without large fluctuations or
even popcorn effects.

Generating ideal noise is absolutely no easy task, for 
example the random variables needed in communication theory
traffic simulation...

m.c.


:::Date: Tue, 29 Aug 2000 20:25:41
:::From: Scott Gravenhorst <chordman at earthlink.net>
:::To: synth-diy at node12b53.a2000.nl
:::Subject: Junction Noise
:::X-Mail-Agent: RedStarWare SMTP Emailer v0.03
:::X-MDaemon-Deliver-To: synth-diy at node12b53.a2000.nl
:::
:::I'm playing with reverse bias junction noise.  Will a germanium 
:::diode (1N34) reverse biased, be noisier than a small signal 
:::silicon transistor BE junction?
:::
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