#### A 3.1-51GHz, Sub-8mW, Single-Core LC VCO Based on a Novel Compact Tunable Transmission Line (CTTL) Resonator in 28nm FDSOI CMOS

The adoption of 5G standards requires new wireless devices to support not only traditional RF bands, but also mmW frequencies up to and beyond 40GHz. Such mmW hardware typically requires narrowband LC resonant circuits for efficient, low-noise operation. For widely-tuned software-defined systems, multi-octave LC tuning is not achievable due to the lack of a practical, solid-state tunable inductive element, limiting the mmW performance of software-defined radios. In this paper, we present a novel, compact, lumped/distributed LC-equivalent resonator capable of continuous tuning over more than four octaves in frequency while maintaining a practical quality factor in an unmodified 28nm FDSOI CMOS for the first time. This resonator is used to implement a cross-coupled LC VCO tunable from 3.1 to beyond 51GHz requiring less than 0.208$\text{mm}^2$ of area, less than 8mW of power, and achieving a state-of-the-art peak $\text{FOM}_\text{T}$ for multi-octave tunable mmW VCOs of -197.9dBc/Hz.