A 105GHz VCO with 9.5% tuning range and 2.8mW peak output power using coupled colpitts oscillators in 65nm bulk CMOS

In this work, a loop of unidirectionally coupled oscillators to demonstrate high tuning range and output power is proposed. To achieve large tuning range, 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. The proposed system is designed and implemented using four coupled Colpitts VCOs in a 65nm bulk CMOS process. The VCO achieves continuous tuning range of 9.5% at the center frequency of 105GHz with the peak output power of 2.8mW. The circuit consumes 54mW from a 1.2V 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 100GHz.