Hybrid Asymmetrical Load Modulated Balanced Amplifier With Wide Bandwidth and Three-Way-Doherty Efficiency Enhancement

This letter presents a new active-load-modulation power amplifier (PA) architecture, i.e., hybrid asymmetrical load modulated balanced amplifier (H-ALMBA). It is discovered that the control amplifier (CA) of load modulated balanced amplifier (LMBA) can be set as the carrier amplifier and the balanced amplifier (BA) as the peaking amplifier with different threshold settings for two subamplifiers, BA1 and BA2. Through proper amplitude and phase control and cooperative alignment of the turning-on sequence of BA1 and BA2, the entire H-ALMBA can achieve enhanced efficiency overextended power back-off range, similar to a three-way Doherty PA. More importantly, this hybrid load modulation behavior can be replicated over a nearly unlimited frequency span. The theory is well validated by a prototype developed using GaN technology and commercial quadrature couplers, which experimentally demonstrates a 4:1 RF bandwidth from 0.55 to 2.2 GHz and high efficiency, i.e., 55%-82% at peak power, 51%-69% at 5-dB power back-off and 40%-61% at 10-dB power back-off.