A Compact 321–343-GHz Integrated CMOS Radiator by Co-Designing Ring Oscillator and Multifunctional Antenna

This work presents a compact integrated CMOS radiator with a tuning range of 321-343 GHz. The miniaturization and enhanced performance of the radiator is achieved through co-designing a ring oscillator and a multifunctional antenna. The multi-stage ring oscillator features a variable common-source (CS) stage, which is proposed to achieve a broad frequency tuning range. To enhance the performance of the proposed variable CS stage for terahertz (THz) oscillator, wideband load impedances for all harmonics are theoretically analyzed and recursively optimized. The multifunctional antenna integrates six key functions into a simple compact structure: 1) inherently embedding the ring oscillator within a symmetric layout to ensure uniform operation, 2) directly combining the desired third harmonic signals without bulky and lossy passive networks, 3) radiating the desired third harmonic, 4) suppressing unwanted even harmonics, 5) providing fundamental inductance for the ring oscillator, and 6) supplying DC bias at virtual ground. For experimental validation, a THz radiator including a four-stage ring oscillator and a multifunctional antenna, is co-designed and fabricated in 40 nm CMOS process. The total chip area is as compact as 0.12 mm ${}^{\mathbf {2}}$ . The measured output power and EIRP are −3.6 dBm and −9 dBm at 343 GHz, respectively, with a low DC power consumption of 46 mW. Moreover, the CMOS THz radiator is with a measured frequency tuning range of 6.7%, and DC-to- $P_{\mathbf {out}}$ efficiency of 0.95%. This compact radiator demonstrates promising potential for wideband and high-efficiency THz applications.