[sdiy] white noise from resistor?

Tom Wiltshire tom at electricdruid.net
Wed Nov 5 15:05:43 CET 2008


On 5 Nov 2008, at 13:33, Paul Perry wrote:

>
> I'm looking for a simple white noise source.
> The usual reverse breakdown transistor junction has a problem -  
> first, you
> need a fairly high voltage, and more importantly, level and quality  
> varies
> between transistors.
> In these days of very low leakage & high input impedance op amps,  
> could I
> get by with just amplifying the thermal noise of a high value  
> resistor?
> I know some of the EEs here can set me straight on this one..

Must it be an analogue noise source?

It seems to me that the significant problems that you mention with  
the usual reversed transistor junction technique make this a case  
where a digital solution is a clear favourite. The number of people  
that build various hardware shift-register sources suggests this too,  
although personally I'd favour software. I'm a recovering  
analogophile, so I don't say this lightly, but digital clearly has a  
place, and I think this is one of those occasions where a digital  
solution does a much better (cheaper/easier/more reliable) job than  
analogue.

I'll send you an 8-pin PIC that'll produce good quality white noise  
up to >40KHz for what it costs me if you can't find someone to  
program one up at your end.

Regards,
Tom




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