A predistortion linearizer for a class-F GaN HEMT power amplifier using two independently controlled diodes

A novel pre-distortion technique using two independently bias-controlled Schottky diodes is proposed to compensate the complicated nonlinear characteristics of the AlGaN/GaN HEMT microwave class-F amplifier, in which inferior intermodulation distortions are often observed for an output power range of large back-off. The newly developed technique has made it possible to achieve both high drain efficiency and low intermodulation distortion simultaneously. The developed linearizer was fabricated in MMIC form and applied to a one watt AlGaN/GaN HEMT class-F amplifier operating at 1.9 GHz, where harmonic frequencies up to the fifth higher order were controlled. With the diode predistortion linearizer, the third-order intermodulation distortion ratio (IMD3) of the 1.9-GHz class-F GaN HEMT power amplifier was improved over power output from 0 to 18 dBm. The IMD3 was under -40 dBc at output powers lower than 10 dBm. The amplifier had a maximum drain efficiency of 70.6 % at output power of 27 dBm.