From: freeman@MasPar.COM (Jay R. Freeman)
Date: Thu, 16 Sep 93 08:30:46 PDT
To: yerazunis@aidev.enet.dec.com
Subject: Re:  Digital noise
Message-ID: <9309161529.AA05681@cleo.MasPar.Com>
MIME-Version: 1.0
Content-Type: text/plain


> To get real random noise, try using a transistor "backwards", as a
> zener diode.  Then look at the voltage- it's quite "noisy", esp. if you
> use a decent-sized series resistor (try 100Kohms).

When I was in graduate school, a colleague built a gadget based on this
principle as a source of Poisson-distributed pulses for testing the
post-detector electronics of X-ray and extreme-ultraviolet astronomical
instruments.  I don't remember the precise source of the noise, but it
was similar to the "zener" trick cited in that it was based on quantum
phenomena rather than a mathematical generator.  The idea was to get
random pulses of varying amplitudes, amplify them up and use only those
bigger than a threshold to generate output pulses.  The instrument
also averaged the output rate and used it via feedback to adjust the
amplifier, so as to obtain a desired average rate of outputs.

I think that for a while at least there was a commercial random-noise
generator available that used this principle, though I don't remember
whose (and it's been long enough that it probably doesn't matter).
Try scientific-instrument catalogs, et cetera.

                                            -- Jay Freeman