A 28GHz Dual-Mode Power Amplifier for Enhanced Load Resiliency or Back-Off Efficiency Enhancement in 22nm FDSOI Process

This paper presents a dual-mode power amplifier (PA) with configurable gate biases, optimized for large-scale antenna array system (LSAAS) front-ends. In the first mode, the VSWR resiliency mode, the PA is configured to maximize resiliency to high load variations caused by antenna cross-coupling in LSAAS, by maintaining consistent power, linearity, and efficiency. In the second mode, the back-off (BO) efficiency enhancement mode, the PA is configured to improve BO efficiency when driven by complex modulated signals with high peak-to-average power ratio (PAPR), during minimal load variation. A 28 GHz circuit demonstrator is implemented using the 22 nm fully-depleted silicon-on-insulator (FD-SOI) CMOS process. Under a 50-ohm load, the VSWR resiliency mode achieves 16.5 dB gain, 13 dBm output power, and 18% peak power-added efficiency (PAE), while the BO efficiency enhanced mode delivers 14 dB gain, 13 dBm output power, with 17.5% and 11% PAE at peak and 6 dB back-off, respectively. When tested against a varying load with VSWR 2.5:1 over a 360° range, the VSWR resiliency mode shows an average saturated power loss of 0.5 dB, while the BO efficiency enhanced mode shows a 1 dB average loss. Modulated signal measurements further confirm the superior performance of the VSWR resiliency mode under load variation compared to the BO efficiency enhanced mode.