Design of Tri-Band Doherty Power Amplifier Using Phase and Impedance Constrained Optimization

To realize the wideband and efficient operation of Doherty power amplifier (DPA) in multi-band mode, this paper proposes a tri-band DPA design method based on phase and impedance-constrained optimization. First, the phases required for impedance transformation networks across multi-band are determined based on the impedance required when the DPA operates at back-off power (BOP) and saturation. Then, the impedance judgment method using multiple impedance constraint circles was employed to determine the optimal load impedances. Finally, the phase and impedance constraints at multiple frequencies were used to optimize the carrier and peaking output matching networks. For verification, a tri-band DPA operating at 1.25−1.35, 1.9−2.1, and 2.75−2.85 GHz was designed and fabricated. Measured results show that, for the above three frequency bands, the drain efficiencies (DEs) at saturation reach 59.0%−61.7%, 59.5%−64.2%, and 52.4%−59.8% with corresponding output power exceeding 43 dBm. For 6 dB BOP, the DEs are 46.1%−54.2%, 50.4%−55.2%, and 44.8%−51.9%. Moreover, good linearity can be achieved after linearization for 20 MHz modulated signals.