An analysis of nonlinear terms in capacitance-voltage characteristic for anti-series-connected varactor-diode pair

Abstract

A variable-capacitance (varactor) diode is widely applied in microwave devices, which utilize the characteristic property that the junction capacitance is varied by an externally applied voltage. In applications of capacitance-controlled devices, such as voltage-controlled oscillators, the capacitance is varied by the control-bias voltage, whereas the variation in capacitance for microwave RF-signal voltages should be minimized in order to suppress higher-order distortions in the output signal. The capacitance-voltage characteristic of a varactor diode is characterized by a slope exponent γ. This article discusses the slope exponent that gives a minimum of variation in capacitance for the microwave excitation in the circuit in which diodes are connected in anti-series. The analysis is based upon a time-domain-oriented method, in which we first obtain the voltage and current waveforms by solving differential equations with respect to time and then calculate the frequency-domain quantities by Fourier analysis of voltage and current waveforms. © 2004 Wiley Periodicals, Inc. Int J RF and Microwave CAE 14: 274–282, 2004.