The variable-capacitance parametric amplifier

The physical principles involved in the operation of the major types of variable-capacitance parametric amplifiers are reviewed and a qualitative explanation is given of the variable-capacitance effect in semiconductor diodes. The utilization of these principles and also of these diodes in a number of experimental, low-noise amplifiers is described. A comparison is given of the best noise performance obtained to date with experimental vacuum-tube amplifiers with that of parametric amplifiers. This paper is directed primarily at nonspecialists who wish to acquire some familiarity with a new and fast-moving field.