A 4.2-W 10-GHz GaN MMIC Doherty Power Amplifier

This paper describes the design and performance of an X-band GaN monolithic microwave integrated circuit (MMIC) Doherty power amplifier (DPA) in a 0.15 μm gate length GaN on SiC process. The measured output power is greater than 36dBm at peak PAE of 47% at 10 GHz. Gain flatness of ±0.1 dB around 9.2 dB is obtained at up to 25dBm input power. The PAE at 6 and 10 dB backoff is 41% and 31% respectively. For a 10-Mbps OQPSK signal, the ACPR at 10MHz is >30 dBc at maximum output power and >33 dBc at 10 dB backoff. This combination of linearity and efficiency at backoff represents state of the art for an X-band DPA. Limitations of supply modulation in DPAs to further extend output power back-off are highlighted in the discussion.