Low frequency noise in oscillator with limited space-charge accumulation

Operation of a Gunn-diode microwave oscillator in the limited space-charge accumulation mode is analyzed for possible causes of low-frequency noise, such a noise also occurring but through different mechanisms in domain modes of operation. Calculations for a GaAs device with uniform doping over the active region and with uniform field distribution point to accumulation and propagation of space-charge perturbations by local inhomogeneities as the likely source of low-frequency fluctuations of the space-charge oscillation amplitude and frequency. A subsequent analysis of the fluctuation characteristics of such an oscillator, with flicker fluctuation of the initial concentrations of free charge carriers as the main source of noise which also modulates the induced current, reveals that limited accumulation and dissipation of space charge can cause frequency fluctuation of the output signal without pulling the oscillator out of synchronism.