Noise generation under large signal conditions in the Read microwave avalanche diode†

Abstract

In this report the noise generation mechanism of the Read microwave avalanche diode is examined. Using a large signal approximation to the operation of the device as an oscillator, the current variation with time in the avalanche region is examined and an expression for the variance of this current, due to fluctuations in the ionization process, is obtained. The effect of this, current variance upon the output waveform of the device is then investigated It is found that as the bias current is increased the output waveform rapidly becomes very noisy. This is due to the build-up mechanism of the avalanche which tends to amplify the ionization fluctuations occurring while the current is small. Various means of reducing this effect are considered, the most promising of which seems to involve widening the avalanche region of the device. Finaly, expressions are derived for the F.M. and A.M. noise characteristics which would be obtained at the output of a microwave oscillator driven by a Head diode. The expected decrease of noise with increasing quality factor of the resonant circuit is obtained. It is concluded that the Road diode will be an extremely noisy device at high operating levels and that other avalanche diode configurations incorporating wider avalanche zones may prove better in this respect.