A 3.7GHz GaN HEMT Doherty power amplifier using digital predistortion linearization

In this study, we implemented a 3.7 GHz band Doherty amplifier based on GaN HEMTs which was linearized using a digital predistortion method. The forward and reverse models of the predistortion consist of simple polynomials whose coefficients are extracted using a conventional LMSE algorithm. Using two carrier signals based on IEEE 802.16e, whose PAR is 9.44 dB, an ACLR improvement of 10.74 dB was achieved to give an ACLR level of 41.74 dBc at an offset of 4.79 MHz. The overall efficiency of the Doherty power amplifier is 13.74% which represents a 2.44% improvement compared to that of a balanced class-AB power amplifier at an average power of 36 dBm.