A W-Band RTWO-Based Digital Transmitter for PMCW Radar Achieving 14.9% Efficiency

This work presents a compact and highly efficient W-band digital transmitter for phase-modulated continuous-wave (PMCW) radar applications. A rotary traveling-wave oscillator (RTWO) with an embedded edge-combining upconverter simultaneously performs frequency quadrupling and BPSK modulation, eliminating the need for mm-wave LO buffers. Phase shifting (PS) is realized in the charge domain using a capacitive DAC within a charge-steering sampling (CSS) all-digital phase-locked loop (ADPLL), enabling a low-overhead and power-efficient path for phased-array operation. Fabricated in 22-nm CMOS, the transmitter occupies 0.144 mm² and delivers 18dBm peak output power with a maximum efficiency of 14.9%. PS is measured in both single- and dual-channel configurations, demonstrating a 409.7 fs (2.8°) step size and an RMS phase error of 55.6 fs (0.38°). In summary, the proposed architecture offers state-of-the-art TX efficiency and integration density for W-band radar transmitters, while providing intrinsic phase-shifting capability at the channel level for scalable PMCW radar arrays.