A 24-31GHz Compact Low-Power Complex Impedance Sensor for Beamforming Transmitters in 22nm FD-SOI

We present a complex impedance sensor to measure the impedance variations at the output of a (phased-array) transmitter (TX) operating around 28 GHz. Based on complex voltage sensing of the output balun in a transmitter, the envelope detectors and injection-locked ring oscillators (ILRO) split the amplitude and phase sensing of voltages for computing the complex impedance. With a bandwidth spanning from 24 GHz to 31 GHz and an input power dynamic range of 7 dB, this circuit can sense reflection coefficients up to 0.74 with a maximum magnitude error of 0.14 and a maximum phase error of 12.8°. It consumes 8 mW of power and occupies only 0.0043 mm2.