Distortion reduction of a GaN HEMT Doherty power amplifier with a series connected load

Doherty introduced two types of concepts for high-efficiency linear amplifiers in 1936. One has a shunt connected load and the other has a series connected load. We fabricated a 1.9 GHz GaN HEMT Doherty power amplifier with a series connected load using baluns. The amplifier realized high power efficiency with a wide dynamic range in comparison with a conventional push-pull amplifier. In this paper, we propose distortion reduction method for the amplifier and achieved reduction of the third-order intermodulation distortion (IMD3) more than 15 dB at the output power from 5 to 20 dBm. The amplifier realized power-added efficiency (PAE) of 31% at the output power of 24 dBm at 10 dB input backoff from the saturated output power of 31 dBm with PAE of 58%.