A Low-Power Reflection-Coefficient Sensor for 28-GHz Beamforming Transmitters in 22-nm FD-SOI CMOS

Active load impedance variations in a phased array transmitter cause significant power amplifier (PA) performance degradation, in terms of output power, linearity, and power-added efficiency, which are key parameters to enable high-speed data throughputs using spectrally efficient modulation schemes. The system performance can be restored by using PAs having active or passive reconfigurability with the help of antenna impedance sensors. This article presents a low-power reflection-coefficient sensor for 5G millimeter-wave phased-array applications. The complex load impedance of the PA is determined based on the complex voltage over a sensing element, which can be integrated and co-designed with the PA output matching network, with minimal loss (<0.2 dB) and a negligible area penalty. A full-range phase detector with improved detection resolution is proposed, enabling an amplitude-insensitive phase detection. Fabricated in a 22 nm FD-SOI process, the sensor prototype occupies a silicon area of 0.024 mm² and consumes 13.2 mW power. The sensor demonstrates a wide detection range with |Γ | up to 0.7 (VSWR 5.67) in a load-pull test at 28 GHz. From Γ circle of 0.2 up to 0.7, the maximum detection errors in the magnitude and phase of the Γ are 0.14° and 40°, respectively.