Load-Mismatch Tracking Digital Predistortion Technique for Mobile-Terminal Power Amplifiers

The power amplifiers (PAs) often suffer from load mismatch in mobile terminals due to the complicated working environments, making linearizing those PAs a challenging task. This article proposes a novel load-mismatch tracking digital predistortion (LMT-DPD) technique for linearizing mobile-terminal PAs under varying load-mismatch conditions. The time-domain polyharmonic distortion (TD-PHD) model is discussed first for the behavioral modeling and linearization of PA under mismatch, followed by a practical model construction method. Then, the proposed LMT-DPD technique is derived based on the superposition principle. According to the real-time load reflection coefficients, the LMT-DPD enables automatic and fast adjustments of the predistorter to adapt to the PA’s nonlinear distortion under different load-mismatch conditions without coefficient recalibration. Experimental validations are carried out on a mobile-terminal PA module at 4.6 GHz with a 100-MHz 5G new radio (NR) signal. The test results show that the proposed LMT-DPD technique can significantly reduce the update frequency of predistorter while realizing excellent linearization performance.