Large-signal noise, frequency conversion, and parametric instabilities in IMPATT diode networks

A theoretical treatment is presented of some of the nonlinear properties of the IMPATT or Read avalanche diode, a negative-resistance semiconductor device that is now coming into wide-spread use for microwave oscillators and power amplifiers. Based upon the somewhat idealized Read model, this theory presents a qualitatively meaningful explanation of certain "parametric" effects that are often troublesome to the designers of amplifier and oscillator networks. First, an analytic treatment is given for frequency-conversion effects that appear when the device is strongly driven by one continuous signal, and simultaneously perturbed by a weak signal at another frequency or by noise. From this theory, stability criteria are derived for spurious oscillations of the "parametric" type which frequently appear in these devices under large-signal conditions. The noise-generation mechanism is reviewed, and it is shown that the noise is enhanced by strong signals and the spectral distribution is modified by frequency conversion. Some measurements of noise and frequency-conversion gain are presented which indicate substantial qualitative agreement with the theory.