[sdiy] analog vs digital noise generators

[James Patchell]

Which one you use depends on what you require and your tastes.

A biased semiconductor junction will give you real noise.  However, you 
have to contend with unwanted signal intrusions, such as power supply junk 
(hum, ripple, etc), and the fact that the white noise may also be 
contaminated with a bit of 1/f type noise.  Generally, these are not a big 
problem.

PNR type noise generators (using shift registers) have predictable 
performance.  You will always get the same amount of noise.  One bad 
attribute is that a PNR repeats.  If the sequence is long enough, you will 
not even notice...(32 bits is what I use).  And like I said, it is 
predictable.  I use one to produce random voltages.  All I have to do is 
hit the reset, and I get those same voltages again.  You can't do that with 
a real source.

It depends on what I am doing on which one I choose....

At 07:58 AM 9/20/2005 +0000, Sumanth Peddamatham wrote:
>hello all,
>
>could someone explain to me the differences between analog and digital
>noise generators, besides the obvious, of course. :-)
>
>i'm mainly interested in adding more noise sources to my fatman, and
>stringing together a bunch of shift registers seems to be much more of
>a pain than biasing a transistor and amping the output.  are there
>subtleties that i am missing?
>
>sumanth peddamatham

         -Jim
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