A Wideband 65-nm 60-GHz Push-Push LC VCO using a Nonlinear Varactor Array

This work introduces a design technique to enhance the second-harmonic output in push-push LC VCOs through the use of a custom-engineered nonlinear varactor array. By leveraging the array nonlinearity, the amplitude of the second harmonic is significantly increased while care has been taken to maintain the spectral purity at the output. Post-layout simulation results confirm the boost in the second-harmonic amplitude, suggesting a promising approach for high-frequency CMOS VCO design. This technique can potentially simplify circuit design and improve efficiency in systems requiring enhanced harmonic signals. Using the proposed technique, a low-power LC-VCO is designed, laid out, and simulated in a 65-nm CMOS technology. Based on the post-layout simulation results, the VCO has a frequency tuning range of 17.7% centered at around 60 GHz. It exhibits a relatively large amplitude across the tuning range with a maximum of 130 m V pp at the highest frequency of operation while consuming 4.2 m W from a 1.2- V supply.