A classic source of white noise is to reverse-bias a diode or the base-emitter junction of a transistor[1]. This produces shot noise[2] though, which is indepen

A classic source of white noise is to reverse-bias a diode or the base-emitter junction of a transistor[1]. This produces shot noise[2] though, which is independent of temperature, so I guess it's not what they are using. [1] http://darrenyates.com.au/electronics/archives/40 http://darrenyates.com.au/electronics/archives/40 [2] http://en.wikipedia.org/wiki/Shot_noise http://en.wikipedia.org/wiki/Shot_noise