A low-phase-noise wide-tuning-range quadrature oscillator in 65nm CMOS

In this paper, we present a low-phase-noise wide-tuning-range quadrature oscillator using an LC-ring resonator. It achieves low phase noise by employing passive coupling between multiple stages and at the same time it covers a wide tuning range by switching between two resonant modes. Furthermore, the problem of oscillation frequency uncertainty which is a common issue in oscillators with multiple oscillation modes is addressed by the novel mode switching method. The proposed design is verified by a four-stage LC-ring prototype in a 65nm CMOS process, which covers 2.78GHz-5.00GHz with phase noise FoM of 186dB at 3.66GHz and >;180dB across the entire tuning range. This demonstrates the best performance among wide-tuning-range quadrature VCO's at this frequency range.