[sdiy] white noise from resistor?

Magnus Danielson magnus at rubidium.dyndns.org
Wed Nov 5 14:50:21 CET 2008


>
> 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..

The noise energy of a resistor is

e_n = 4*k*T*R*B

k = Boltzmans constant (1,3807E-23)
T = absolute temperature in Kelvin
R = resistance in Ohm
B = bandwidth in Hz

Consider that your amplifier will have both voltage and current noise,
which will be weigthed into the final noise by the resistor.

I am sure that with this formula in hand, and some rather simple formulas
like P=UI and U=RI you can figure out the rest with a pen and a piece of
paper.

Cheers,
Magnus




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