A High Efficiency Dual-Band Outphasing Power Amplifier Design

This article proposes a novel design methodology for dual-band outphasing power amplifiers (PAs) with back-off efficiency enhancement. While satisfying load modulation requirements of the Chireix outphasing PA, this work replaces the quarter-wavelength impedance inverter in the classical structure with a dual-band impedance inverter. In addition, two dual-band reactance compensation networks that absorb the transistor parasitic capacitance are strategically placed. This mitigates the intrinsic reactive loading problem of the outphasing PA and also reduces circuit complexity. A comprehensive theoretical formulation of the proposed design is described and verified through the implementation of a dual-band (2.6 and 3.5 GHz) PA prototype intended for LTE and 5G applications. This amplifier is built upon two 10-W GaN HEMTs, and achieves a maximum power of 44.6 and 43.5 dBm with over 71% and 64% associated drain efficiencies at 2.6 and 3.5 GHz, respectively. At the 6 dB output back-off points, corresponding efficiencies reached 58.4% and 50.1%, respectively. According to the best of authors' knowledge, this is the first dual-band outphasing PA work with comparable performances to other load modulation type PA such as the Doherty.