An Optimization Method for Load Modulation Trajectories in a Millimeter-Wave GaN MMIC Doherty Power Amplifier Design

The contribution of this brief is proposing an optimization method for load modulation trajectories of the Carrier and Peaking transistors based on shared load-pull contours. Firstly, theoretical analysis reveals that the load modulation trajectories can be expressed as a function of the back-off coefficient, the combining load and the output power. Taking the modulation interaction into consideration, the proposed method is then implemented in shared load-pull contours to demonstrate the optimization of load modulation trajectories. To validate the proposed method, a 25-26.5 GHz gallium nitride (GaN) microwave monolithic integrated circuit (MMIC) Doherty power amplifier (DPA) is realized by matching with the optimum load modulation trajectories. Measured results show that the DPA achieves saturated PAE higher than 29%, and 6 dB back-off PAE higher than 27%, with a saturated output power higher than 28.9 dBm across the band. To characterize the linearity, the DPA is measured using a 400 MHz modulated signal and digital predistortion (DPD).