Transmit Efficiency Enhancement Using Over-the-Air Beamforming Phased Array for High PAPR Signals

This article presents a new transmitter phasedarray architecture for efficiency-boosting of a transmitter- receiver link for high peak-to-average power ratio (PAPR) signals. The phased array architecture utilizes sequential over-the-air combining of weighted power amplifiers (PAs) to increase the system efficiency without any die area nor antenna size penalties. The transmitted signal is decomposed into a low duty-cycle signal comprising only the signal peaks and a low PAPR signal containing the remaining envelope levels. The two signals are transmitted through different chains, each optimized for a different power level, and recombined over the air at the receiver side. A 5-GHz PA with a fast 2-ns ON/OFF switching time was designed in 0.18-μm CMOS process to demonstrate the efficiency boost technique. For a four-element array configuration, efficiency enhancement of 2.3× is demonstrated using an 80-MHz MSC9 802.11ac signal with 9-dB PAPR. The transmitter achieves efficiencies of 15% and 13% for 80and 160-MHz signals, respectively, at the error vector magnitude (EVM) of -32 dB.