Linearisation of RF PA by even-order nonlinear baseband signal processed in digital domain

Abstract

ABSTRACTThis paper represents, for the first time, the linearisation method of RF power amplifiers, which is based on using the second- and fourth-order nonlinear signals shaped by digital signal processing in a baseband domain. The linearisation signals are generated by the second- and fourth-order nonlinear modifications of the baseband signal in the proposed manners. The composite second- and fourth-order linearisation signals modulate carrier second harmonics, and the modulated signals are then driven to the gate and drain of the amplifier transistor. The linearisation effects of the proposed method are evaluated on a single stage power amplifier for the simulated QAM and OFDM digitally modulated signals at diverse input power levels up to the 1 dB compression point. Moreover, the FPGA implementation of a system for the generation and processing of the fundamental signal, and the second-order linearisation signals is presented in the paper, and the proposed technique is verified for the generated QAM signal. In addition, the linearisation of the two-way asymmetrical Doherty amplifier is performed in the experiment by using software defined radio platforms for synthesising the fundamental signal and the second-order linearisation signals.