A 105-GHz VCO With 9.5% Tuning Range and 2.8-mW Peak Output Power in a 65-nm Bulk CMOS Process

To demonstrate high tuning range and large output power, we propose a loop of coupled oscillators in this work. Two different tuning mechanisms are simultaneously exploited. First, each core oscillator is tuned using a variable capacitor. Next, by controlling the phase/delay between the coupled oscillators, the entire loop dynamics, and hence, its frequency is tuned. In this paper, we analyze a loop of “n” coupled oscillators using Adler´s equation and derive the expression for the maximum tuning range. Perturbation analysis is used to study the stability conditions of the loop of coupled system. The analysis is extended toward a nested loop of coupled oscillators. The activity condition from two-port theory is used to squeeze maximum power out of active devices. The proposed system is designed and implemented using four coupled Colpitts voltage-controlled oscillators (VCOs) in a 65-nm bulk CMOS process. The VCO achieves continuous tuning range of 9.5% at the center frequency of 105 GHz with the peak output power of 2.8 mW. The circuit consumes 54 mW from a 1.2-V supply. To the best of our knowledge, this VCO has the highest output power and tuning range among all the CMOS oscillators at or above 100 GHz.