Noise Consideration of the Variable Capacitance Parametric Amplifier

This paper describes a model of the variable capacitance diode in which the spreading resistance is considered as the source of amplifier noise. Gain and noise figure calculations are made for this model and experimental results obtained at 5.84 kmc while pumping at 11.7 kmc are presented for gallium arsenide, silicon and germanium diodes. The qauntity 1/¿C0Rss defined as a quality factor" where Rs, is the spreading resistance and C0 is the static capacitance at zero bias point. Computations of minimum noise figure, optimum load admittance, optimum pumping factor, are all given in terms of the parameter ¿C0Rs. The essential differences between single- and double-sideband reception are discussed. Over a range of sufficiently large values of the parameter ¿C0Rs, there is a reasonable correlation of the theory developed with the measurements performed on most of the diodes. In the range of relatively small values of ¿C0Rs, the model proves inadequate to describe some diodes properly and suggests the need for introducing extra noise sources. These noise sources are also discussed. Of the experimental data obtained thus far, the best result has been with a gallium arsenide diode which yields a 0.9 db double-sideband noise figure and, equivalently, 3.9 db for single-sideband operation with 16 db gain and 25 mc of single-sideband frequency bandwidth.