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

This article presents the design and analysis of a millimeter-wave (mm Wave) four-way Doherty power amplifier (PA), aiming to enhance the PA energy efficiency when amplifying orthogonal frequency-division multiplexing (OFDM)-based5G 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 R(ANT )to R(OPT )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 demonstrations. 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 (P-SAT), 23.7-dBmoutput 1-dB compression point (P1 dB), 26.8% peak power-added efficiency (PAE(PEAK)), 26.3% PAE atP1 dB(PAE(12 dB)), 21.7% PAE at 6-dB back-off (PAE(6 dB)), and 13.1% PAE at 12-dB back-off (PAE(12 dB)), demonstrating state-of-the-art performance. In the modulation tests, the PA achieves 14.1-dBm average output power(P-avg) and 13.7% average efficiency (PAE(avg)) when amplifying a2000-MHz 5G NR 64-QAM OFDM signal. To the best of ourknowledge, this is the first silicon PA demonstration of 2000-MHzchannel modulation bandwidth for 5G NR OFDM along with back-off efficiency enhancement up to 12-dB back-off.