A Millimeter-Wave Four-Way Doherty Power Amplifier With Over-GHz Modulation Bandwidth

Abstract

This article presents the design and analysis of a millimeter-wave (mmWave) four-way Doherty power amplifier (PA), aiming to enhance the PA energy efficiency when ampli- fying orthogonal frequency-division multiplexing (OFDM)-based 5G new radio (NR) signals with a 10–12-dB peak-to-average power ratio (PAPR). We first introduce a systematic approach to extending a conventional two-way Doherty PA to N ways, followed by a new transformer-based N-way Doherty net- work synthesis flow. The proposed network synthesis achieves N-way Doherty load modulation using ( N −1) transformers, one fewer transformer and thus lower loss than conventional designs. In addition, it enables the desired impedance transformation from RANT to ROPT and effectively absorbs the parasitic capacitance of the power cells. Along with the Doherty network, we also introduce a high-speed adaptive biasing circuit, addressing the modulation bandwidth bottleneck in prior Doherty PA demon- strations. As proof of concept, a four-way Doherty PA prototype is implemented in the 47-GHz 5G band (band n262) using the GlobalFoundries 45-nm CMOS silicon-on-insulator (SOI) process. It achieves 24.0-dBm saturated power ( PSAT), 23.7-dBm output 1-dB compression point ( P1 dB), 26.8% peak power-added efficiency (PAEPEAK), 26.3% PAE at P1 dB (PAE1 dB), 21.7% PAE at 6-dB back-off (PAE 6 dB), and 13.1% PAE at 12-dB back-off (PAE12 dB), demonstrating state-of-the-art performance. In the modulation tests, the PA achieves 14.1-dBm ave