A predistortion linearizer using a tunable resonator

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.