Linearity investigations of continuous class-F power amplifier under multi-tone excitations

Radio frequency power amplifiers (RF PA) typically do not present true short circuit impedances at baseband frequencies inducing undesired ac voltages that overlay on to the dc voltage supply. This then introduces amplitude and phase modulation of the RF output signal. This paper investigates the effect of optimum broadband baseband load terminations on the linearity performance of high power amplifiers. The investigations are carried out on novel continuous class-F power amplifier under multi-tone excitations. It is shown that the GaN continuous class-F PA memory effects are dominated by baseband impedance variations. A digital predistortion based linearizer is used to improve the linearity performance of the class-F PA under a WCDMA excitation (PAPR=9.8dB). At a 10 dB output power back-off. In these conditions, a power added efficiency of 21% was measured along with 53dBc adjacent channel leakage ratio.