Hybrid Analog/Digital Linearization of GaN HEMT-Based Power Amplifiers

In this paper, we describe a hybrid analog/digital linearization scheme for GaN high-electron-mobility transistor (HEMT)-based power amplifiers that consists of a novel analog feedforward circuit and a conventional generalized memory polynomial (GMP) digital predistorter (DPD). The analog circuit implements a nonlinear filter that compensates the long-term memory effects observed in GaN HEMTs due to the self-biasing behavior caused by electron-trapping phenomena. Experimental tests demonstrate that this linearization scheme achieves a level of intermodulation distortion 6.8 dB better than what can be achieved with just the use of the GMP DPD. This level of distortion is in compliance with the linearity specifications for multicarrier Global System for Mobile communications base station transmitters.