A Wideband 120-GHz Polarization Controllable I/Q Transmitter Front-end

Abstract

This paper presents a wideband 120-GHz CMOS polarization controllable I/Q transmitter for wireless short-range high-speed 6G IoT. The transmitter consists of an I/Q modulator with a quadrature injection-locked oscillator (QILT) for 16-quadrature amplitude modulation (QAM) and a polarization controller for mismatch reduction between TX and RX antennas. An I/Q calibration is applied to QILT to reduce the I/Q imbalance, and a 1-bit phase shifter and a variable-gain amplifier (VGA) with 8 dB gain control are used to control the linear polarization in step of 22.5°. The transmitter was fabricated using a standard 40-nm CMOS process and the chip size is 2.4mm2 including pads with a total power consumption of 378 mW. The measured 3-dB bandwidth was 20 GHz with a peak gain of 13 dB, and the image rejection ratio (IMRR) was improved up to 37.8 dBc by applying the I/Q calibration. From the over-the-air (OTA) test, the measured isolation of the dual-polarized antenna was varied from 9 dB to 22 dB with the 3-dB baseband (BB) bandwidth of 12 GHz. The proposed work achieved the maximum data rate of 20 Gbps for both quadrature phase shift keying (QPSK) and 16-QAM and the corresponding error vector magnitudes (EVMs) were -13.4 dB and -19.1 dB, respectively. IEEE