A 24-28-GHz Doherty Power Amplifier With 4-W Output Power and 32% PAE at 6-dB OPBO in 150-nm GaN Technology

A 24-28-GHz two-stage GaN Doherty power amplifier (PA) is designed and characterized. At millimeter-wave (mm-wave) frequencies, the low output impedance of the auxiliary transistor loads the Doherty combining network, which lowers the power added efficiency (PAE) in back-off. In this design, a small periphery auxiliary transistor is used to increase the output impedance of the auxiliary transistor. The periphery ratio of the auxiliary and the main transistors is 77%. Even though, compared to symmetric Doherty PAs, the load modulation of the main transistor is reduced, this amplifier still achieves 32% and 23% PAE at 6 and 9-dB output power back-off, respectively. Attributing to the small auxiliary transistor, the amplifier obtains a small signal gain of 19 dB. The maximum output power of the amplifier is 4 W with a peak PAE of 42%.