A 28-GHz 26.8-dBm Doherty Power Amplifier With Four-Way Differential Hybrid Load- Modulated Combiner in 55-nm CMOS

This letter presents a 28-GHz high-power four-way differential Doherty power amplifier (PA) in 55-nm bulk CMOS technology. A transformer-based hybrid load-modulated combiner (HLMC) (i.e., a parallel combined series-load-modulated Doherty output network) is proposed to simultaneously achieve high output power, low-loss power combining, and a true-Doherty load modulation. Meanwhile, the closed-form expressions of the proposed combiner are derived. The measured results of the proposed Doherty PA demonstrate a
$P_{\mathrm {sat}}$
of 26.8 dBm, an output 1-dB compression point (OP1dB) of 25.2 dBm, a peak power added efficiency (PAE) of 26.7%, and 19.2% PAE at 6-dB power back-off (PBO) at 28 GHz. The PA is also tested with 400-MSym/s 64-quadrature amplitude modulation (QAM) signals, and it achieves 17.9-dBm average output power with 14.1% average PAE at −26.2-dB error vector magnitude (EVM).