A 120-GHz Oversampling Digital-to-Phase Transmit Array for Integrated Sensing and Communications

Abstract

A digital transmit array technique is proposed using constant-envelope circuit architectures with state-of-the-art efficiency. Using 2-bit phase shifters that can oversample the signal at gigasample-per-second rates in each channel, the digital-to-phase modulation enables simultaneous beam-steering and waveform generation through spatial and temporal power combining. The prototype 4-channel transmitter (TX) is fabricated in a 22-nm FD-SOI CMOS technology, flip-chip mounted onto a Low-Temperature Co-fired Ceramic (LTCC) interposer with integrated Vivaldi antennas, and wire-bonded to a PCB. The TX array operates from 110 to 122 GHz and exhibits a measured peak effective isotropic radiated power (EIRP) of 29.5 dBm with $\pm$25^o of scanning range and 6.7% TX channel efficiency. Using a linear combinations of channels, a 250-Mbps, 32-QAM waveform is demonstrated with 13% EVM through oversampling and spatial calibration of the low-resolution phase shifters. Frequency-modulated continuous wave (FMCW) radar is demonstrated to realize a 3.1 cm range resolution. The oversampling digital-to-phase (ODP) architecture is a viable solution for scalable millimeter-wave (mm-wave) integrated sensing and communication (ISAC).