A modified compact broadband asymmetric Doherty power amplifier design for 5G applications

This paper presents a modified compact broadband asymmetric Doherty power amplifier (DPA) with a 10-dB output back-off (OBO) range for 5G applications. A modified transformer-less load-modulated (TLLM) asymmetric DPA architecture and its reflection coefficient (RC) design theory are proposed. The proposed architecture eliminates the additional quarter-wavelength (λ/4) post-matching impedance transformer used in conventional DPAs, which simplifies the output network and facilitates broadband operation. The carrier output matching network and the 50 Ω output offset line are co-optimized. At OBO, the carrier maximum-efficiency impedance is matched to the system impedance 50 Ω without an additional post-matching network, while the peaking PA presents an approximate open circuit. As the peaking PA turns on, the carrier load is driven toward the maximum‑power impedance region. To verify this design, an asymmetric device configuration is employed to extend the OBO range to 10 dB. A prototype operating from 3.3 to 3.8 GHz is implemented using CGH40010F and CGH40025F GaN HEMTs. Under pulsed-CW excitation, the measured saturated output power is 46.0–46.7 dBm with a drain efficiency (DE) of 64.7%-74.5%, while the DE at 10-dB OBO is 41.0%-47.5%. With digital pre-distortion (DPD), ACPR values below −44.0 dBc are achieved using a 5 × 20 MHz signal with a 10-dB peak-to-average power ratio (PAPR). The fabricated DPA occupies only 4.5 cm × 3.2 cm.