Low-power and low-area CMOS quadrature RC oscillator with capacitive coupling

A quadrature oscillator based on two RC oscillators with capacitive coupling is proposed and analyzed. The capacitive coupling has the advantages of being noiseless and not increasing the power dissipation. Simulation results show that the oscillation frequency increases proportionally to the coupling capacitances, which is the opposite of what happens in capacitive coupled LC oscillators. Measurements on a 130 nm CMOS circuit prototype validate the theory of the coupling mechanism. The phase-noise is −115 dBc/Hz @ 10 MHz offset, and the FoM is −155.3 dBc/Hz, which is comparable to the best state-of-the art RC oscillators, yet the dissipated power is about four times less.