Theory and Design Methodology for Reverse-Modulated Dual-Branch Power Amplifiers Applied to a 4G/5G Broadband GaN MMIC PA Design

This article presents a generalized theory and new design methodology for reverse-load-modulated dual-branch (RMDB) power amplifiers (PAs), which uses a current-biased transistor in the main branch to realize optimal load modulation without using the impedance transformers at the output of the PAs. Consequently, this topology offers a proper load modulation mechanism over a wider frequency bandwidth. Besides, smaller output matching network (OMN) footprint and lower loss are suitable features for monolithic microwave integrated circuit (MMIC) designs. The proposed theory can be applied for symmetrical and asymmetrical designs to realize different output power back-off (OPBO) ranges. The theory and design methodology were used to design the first MMIC RMDB PA. The broad bandwidth of this design (2.6-3.8 GHz) allows it to cover multiple bands in 4th-generation (4G) Long Term Evolution (LTE) and 5th-generation (5G) New Radio (NR) standards. Under continuous wave (CW) excitation, the experimental results show a drain efficiency (DE) higher than 58% at peak output power (POP) and 37% at 9 dB OPBO, over the whole frequency band.