The Elimination of Tuning-Induced Burnout and Bias-Circuit Oscillations in IMPATT Oscillators

The avalanche diode high-level microwave noise source

“…The existence of microwave-induced, low-frequency negative resistance effects in avalanche diodes is not a new phenomenon. It caused considerable difficulty to oscillator designers, particularly in regard to the generation of bias circuit oscillations, until the work of Brackett (1973) showed how this resistance could be quenched by stabilising resistors in the bias circuit. In the present paper an analytic theory for this negative resistance, starting from basic avalanche diode theory, has been developed.…”

“…a positive resistance arising from space charge effects in the diode. This is a similar representation to that deduced by Brackett (1973), except that there a frequency-independent negative capacitance was used. It is easily seen that if the magnitude of Rn is initially greater than that of the resistive component of the load impedance at the oscillator bias port, small perturbations in current and voltage will grow to non-linear levels.…”

“…In order to achieve microwave oscillations, the avalanche diode is placed in a microwave cavity which presents, after any transformation through diode package elements, an admittance YL across the diode chip. The oscillation condition at fixed DC bias, TdO, is then simply where The stability of oscillation has been analysed (Brackett 1973, Kurokawa 1969) by representing the total admittance YT for an oscillator of slowly changing microwave amplitude VI and phase C$ in the form…”

“…where V ~O and w1 are the steady-state microwave oscillation voltage amplitude and frequency. This leads to a differential equation describing the dynamic behaviour of VI (Brackett 1973) :…”