An 82.2-to-89.3 GHz CMOS VCO with DC-to-RF Efficiency of 14.8%

In this paper, we present a 90-GHz CMOS voltage-controlled oscillator (VCO) that operates from 82.2 to 89.3 GHz. The proposed VCO utilizes a device-centric method to achieve a high-efficiency oscillator with DC-to-RF efficiency closer to the efficiency limits of the employed transistors. Using the swing-independent bias condition for the CMOS transistors at the frequency of interest, we incorporate an active feedback network with minimal power overhead to provide the maximum achievable swing at the gate terminal of the core transistor, thereby increasing the power added efficiency. Utilizing this method, a high-efficiency VCO with center frequency of 85.75 GHz is designed and implemented in a 65-nm CMOS process. In this VCO, the trade-offs among efficiency and tuning range are also considered and the VCO achieves a peak DC-to-RF efficiency of 14.8% at 89.3 GHz and a wide tuning range of more than 8.3% while consuming only 8.5 mW of dc power from a 1.2-V supply. Compared to the prior art, the proposed VCO demonstrates a DC-to-RF efficiency of more than 14% at frequencies up to 100 GHz. The fabricated circuit occupies a silicon area of less than 0.25 mm² including the pads.