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From: stevem@specialix.co.uk (Steven Murray)
Newsgroups: sci.electronics
Subject: Re: Pseudo-random numbers
Keywords: PRBS,m-sequence,random
Message-ID: <1991Apr8.130313.21130@specialix.co.uk>
Date: 8 Apr 91 13:03:13 GMT
References: <1991Mar27.101754.5326@specialix.co.uk> <1991Apr5.131838.10696@deeptht.santa-cruz.ca.us>
Distribution: sci
Organization: Specialix International, London
Lines: 35



RE:  Getting a decent source of Random Noise.

Has anyone got any comments on this circuit?  I've built it and checked
the output on the scope - it LOOKS like noise (I haven't got access to
anything flash like a spectrum analyser).  The source of noise (with
really good power supply filtering) is mostly the reversed biased NPN
transistor.  I've heard that thermal noise is pretty unpredictable (ie
it qualifies as a good source of noise) is the noise I see across a
reversed biased npn transistor B-E junction actually of thermal origin,
or something else ?? 

          ___+12v                          ___+5v  
           |                                |   
          < 1 megaohm             _         > 4.7 kilo-ohm  
           >                     | \       < 
          <            __________|   \      > 
           >   0.1uf   |         | +In \____|____  TTL Noise output     
           |____| |____|     ____| -In /           (sampled by micro)  
          e|    | |    |     |   |   / LM339   
   npn   ,/           <     <    |_/ 
     ___|        1 meg >     >
     | b|\            <     < 1 megaohm
     |   c\n.c.        >     >
     |                 |     |
   --|-----------------|-----|----- Gnd

Thanks for any comments received.

-- 
Steven Murray
uunet!slxsys!stevem  stevem@specialix.co.uk
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