A Sub-THz Dual-Tank VCO Using Active Negative-Conductance Boosted Architecture in 28-nm CMOS

Abstract

This paper proposes a sub-THz voltage-controlled oscillator (VCO) employing an active negative-conductance boosted architecture. The proposed architecture contributes to relaxing start-up conditions, improving tuning linearity, and increasing swing. A triple-coil coupled transformer is introduced as the tail resonator, simultaneously providing the broadband frequency selectivity of the feedback loop and further achieving conductance enhancement. The head resonator further improves phase noise (PN) performance while efficiently extracting second-harmonic components without requiring additional structures. And filtered output is achieved by a compact coupled-line-based buffer. Fabricated in 28nm CMOS process, the proposed VCO achieves a frequency tuning range (FTR) of 7.1% while operating at a center frequency of 109.6 GHz. At a 10 MHz frequency offset, the measured PN is -112.8 dBc/Hz, corresponding to a figure of merit (FoM) of -180.4 dBc/Hz. The VCO operates under a 0.5-1 V supply and occupies a core chip area of 0.035 mm².