A Broadband Linearization Technique for Doherty Power Amplifiers Using Adaptive Impedance Compensation

This paper presents a novel adaptive impedance compensation technique for broadband linearity enhancement of Doherty power amplifiers. By incorporating a power-related tunable network with varactor-like behaviour, the Z-parameters of the input matching network could be adaptively adjusted according to the input power level, enabling compensation of the load modulation induced varying mismatch at the gate of the carrier transistor, and thus reducing amplitude-to-amplitude and amplitude-to-phase distortion. Applying a 80 MHz OFDM signal with 9 dB peak-to-average power ratio, the demonstrated Doherty power amplifier achieves a raw adjacent channel power ratio of -35 dBc to -40 dBc over a bandwidth of 1.5–2.6 GHz.