FM noise in a Gunn-effect oscillator

FM noise in a cavity-controlled Gunn oscillator is investigated both theoretically and experimentally. The susceptance of a GaAs Gunn diode fluctuates following velocity fluctuations of high field domains. This results in FM noise. The fluctuations of the velocity are considered to be due mainly to those of carrier concentration fluctuations. Measured FM noise is in good agreement with the model, verifying that fluctuations of carrier concentration result in FM noise in the oscillator. When the quality factor Q
ex
of the resonant cavity used becomes large, the FM noise characteristic deviates from the theoretical one based on the fluctuations of carrier concentration. The fluctuations of the voltage across the diode in the resonant cavity also influence the domain dynamics and hence the diode susceptance. These seem to be causes of the deviation.