Noisy noise generator

[Martin Czech]

:::I believe the reverse biased transistor junctions use the E-B breakdown
:::voltage as a zener diode. Most E-B breakdown voltages are around 5 volts for
:::a 2N3904. Presumably any semiconductor junction in a "trickle" current mode
:::will maximize the noise output of the junction.

Yes, the trick seems to be to starve the junction. I wonder if any
junction will give about tyhe same noise rms if the current could be
trimmed of a sufficient wide range.

What we call "Zener" diode should be better called "Z" Diode, because
of the Z-like VI plot and because Z-diodes really live from two effects: 

Zener (high field, heavy doping, short space charge zone tunneling,
negative breakdown voltage tempco, no destructive)

Avalanche(long space charge zone, moderate doping, positive breakdown
voltage tempco, can be destructive)

At Ub (breakdown voltage) about 8 V (from my head) both effects exists
in parallel and may lead to tempco canceling, below that (<5V) zener
tunneling is predominant, above 10V avalanche.

Emitter regions of transistor are heavy doped for good efficiency,
thus leading to low Ub, this is really zener effect.

Some z-diode from the shelf with Ub=10V is clearly avalanche.
Perhaps this is another reason for different noise output.


m.c.