An Analog Predistorter for Doherty Power Amplifiers Based on Minimum Gain and Phase Deviation

This brief presents a design method of analog predistorter (APD) for Doherty power amplifiers (DPAs) based on minimum gain and phase deviation to improve the output adjacent channel leakage power (ACLR). To prove this method, the normalized deviation is formulated based on the non-linear analysis of DPAs' gain and phase, which is a new joint design indicator between DPAs and APDs. Then an APD design and linearisation performance prediction platform is constructed using this indicator as the core. An APD consisting of two T-networks in series is designed as an example of an existing DPA. It has low circuit complexity and low power consumption, which can effectively improve the AM-AM and AM-PM of the DPA after optimization. Under the excitation of a 40 MHz, 64-QAM modulated signal, the results show that the ACLR of the DPA output is improved by nearly 10 dB with the proposed APD, from -34.4/-34.3 dBc to -43.9/-45.6 dBc. In case of constant output ACLR, the application of the APD also increases the output power and efficiency. Moreover, the proposed APD still has good linearization performance under the excitation of 80 MHz, 64-QAM modulated signal.