Noise in IMPATT-diode oscillators at large-signal levels

A theory is formulated which describes the noise properties of IMPATT-diode oscillators operating at large-signal levels. This theory is based directly on the work of Convert [17] and Hines [18]. The theory takes into account the signal dependence of the noise generation process, and also the intermodulation effects occurring between the various frequency bands. The equations are conveniently arranged in matrix form; such a formulation provides physical insight and facilitates the obtaining of quantitative results in terms of measurable noise parameters. The AM, FM, and low-frequency noise of low-Q IMPATT-diode oscillators operating at high output power levels has been measured and compared with the values predicted by this theory. Si p⁺-n, Si n⁺-p, and n-GaAs S.B. IMPATT diodes have been used. Agreement between the measured and theoretically predicted values is good. Special experimental evidence for the signal dependence of the noise-generating mechanism is obtained by considering the ratio of the AM and FM noise. The Comparatively few measurements published on the correlation between AM, FM, and low-frequency noise have been compared with our theoretical results; as far as can be judged, the trends are similar. Finally, an experiment is described in which a Si n⁺-p diode was used in a high-Q Kurokawa circuit. The experimental value of the rms frequency deviation of 0.8 Hz in a 100-Hz bandwidth was found to be in reasonable agreement with the present theory, extended with an equivalent circuit describing the high-Q circuit.