Asymmetric Doherty power amplifier with optimized characteristics in output power back-off range between 6 dB and 10 dB

This paper presents an asymmetric Doherty power amplifier for improving the efficiency under the linearity specifications in output power back-off (OPBO) range between 6 dB and 10 dB. The OPBO determines several design parameters for the asymmetric Doherty power amplifier: the peak power ratio of main to peaking amplifiers based on the wanted OPBO and the characteristic impedance of 90-degrees impedance transformer in a peaking amplifier. The power-dividing ratio of the unequal power divider in an input port is calculated for transferring the maximum power to the load. Experiments under a test signal with peak-to-average power ratio of 7 dB were performed on the proposed Doherty power amplifier. The experimental results demonstrate that the proposed asymmetric Doherty power amplifier achieves the optimized efficiency, and is also appropriate for the digital pre-distortion linearization.