Noise Sources

Resistance noise is an expression of the coupling of thermal and electrical fluctuations. The saturated vacuum diode can be used as a noise source for measurement purposes. The derivation of the Nyquist formula for the thermal noise of resistors from the RC circuit is a simple plausibility consideration, not a physically strict procedure. The question of frequency limitation is clarified by the connection with Planck's radiation formula. In non-metallic conductors, there is additional noise caused by the current flow. The current noise is related to another noise source, which is extremely important in active electronic components. It is the shot noise. Closely related to the physics of thermal noise of resistors is the noise of the positive column of a gas discharge plasma. Inadequate contacts of semiconductor laser diodes are detected by the noise of the operating current.