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

This article presents a wideband 120-GHz CMOS polarization controllable I/Q transmitter for wireless short-range high-speed 6G Internet of Things (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 (LP) in a step of 22.5°. The transmitter was fabricated using a standard 40-nm CMOS process, and the chip size is 2.4 mm2 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 to 22 dB with the 3-dB baseband (BB) bandwidth of 12 GHz. The proposed work achieved the maximum data rate of 20 Gb/s for both quadrature phase shift keying (QPSK) and 16-QAM, and the corresponding error vector magnitudes (EVMs) were −13.4 and −19.1 dB, respectively.