In this letter, a novel predistortion topology using a tunable resonator is presented. The core of the circuit is a series tunable resonator employing a reverse biased varactor diode. The junction capacitance of the varactor diode increases with RF input power, effectively shifting the resonant frequency of the circuit. This results in the amplitude and phase deviations at the frequency of operation. A 1.8-GHz power amplifier (PA), with a gain of 9 dB and 21-dBm output power, is linearized based on this technique. A maximum of 11 dB improvement in adjacent channel power ratio and an increase in 1.8 dB for the compression point is measured for the linearized PA.

Operation and performance of a varactor diode based linearizer is investigated. This novel predistortion topology employs a series resonant circuit with a reverse biased varactor diode acting as a power dependant capacitor. The linearizer itself is both simulated and tested to display its nonlinear properties. In addition, a 1.8 GHz power amplifier is linearized based on this technique. An improvement of 11 dB in ACPR and an increase in 1.8 dB for the compression point is measured for the linearized PA.