Gain and noise figure of a variable-capacitance up-converter

The performance of a p-n junction nonlinear-capacitance diode as a low-noise, amplifying frequency converter is analyzed for the case in which the output signal frequency is many limes greater than the input signal frequency. The diode is represented by an equivalent circuit consisting of a time varying capacitance and a constant series resistance. Formulae for the maximum available gain and the noise figure of the circuit are obtained, and representative numerical values are given for the noise figures of systems incorporating such diodes as preamplifiers.