[John Larkin]

On Sat, 22 Jul 2006 19:56:18 GMT, Phat Bytestard
wrote:

On Sat, 22 Jul 2006 11:48:12 +0100, Eeyore
m Gave us:

They fail to mention carbon film which is very widely used.

The entire selling point of the sheet was that they are very low
noise compared to other resistor manufacturing mediums.

Noise in a resistor occurs because resistance mediums are actually
heavily diluted semiconductors. The electrons bang around on their
way through. It's a loose lattice.


In a current flow in metals, electron-lattice interactions tend to
space electrons evenly, so their exit from the resistor is more
regular than a random (Poisson) distribution, so current-modulation
noise is far below the shot noise level you'd get for uncorrelated
conduction. The physically longer the resistor, the better the
smoothing effect. This works less well in non-metal conductors, with a
few exceptions.

That doesn't affect Johnson noise of course; that only depends on the
resistance and the temperature, as required by conservation of energy.

John