14.8 A 247-to-263.5GHz VCO with 2.6mW peak output power and 1.14% DC-to-RF efficiency in 65nm Bulk CMOS

Signal generation at mm-Wave-to-THz frequencies is attractive because of its applications in bio-sensing, spectroscopy, detection of concealed weapons, as well as high-data-rate communication. CMOS is considered a potential platform to implement a low-cost and high-yield signal generation solution at this frequency range. Despite continuous scaling, effective f
_max
of active devices is not high enough and hence either harmonic oscillators or frequency multipliers are employed for high-frequency signal generation. In recent CMOS VCO designs, reasonable power levels (~1mW) and tuning range (~10GHz) have been reported at around 300GHz but with very low DC-to-RF efficiency (<;0.4%), which is undesirable for portable applications [1,4]. Moreover, power-level fluctuation is more than 3dB across the frequency range [1]. In this work, we introduce a scalable VCO architecture that efficiently generates and extracts the 2
^nd
harmonic at 256GHz and hence simultaneously achieves high tuning range (16GHz), high output power (2.6mW), high DC-RF efficiency (1.14%), and low phase noise (-94dBc/Hz to -85dBc/Hz at 1MHz offset frequency across the tuning range). When compared to published state-of-the-art, this work demonstrates the highest output power, tuning range, and DC-to-RF efficiency, and the lowest phase noise among all CMOS VCOs above 200GHz.