Enhanced frequency stability in a non-linear MEMS oscillator employing phase feedback

Microelectromechanical system (MEMS) oscillators are conventionally designed so that the resonator is operated within the linear regime. This paper investigates an optimal low noise point for a nonlinear MEMS oscillator where phase noise to frequency noise conversion is minimized. A closed loop oscillator consisting of a digitally controlled phase shifter is implemented and measurements of frequency stability are conducted under varying phase feedback conditions. The measured results show that for a specific value of feedback phase, the oscillation frequency is independent of phase fluctuations. Enhanced frequency stability is achieved when the MEMS resonator is biased at the optimal phase feedback condition in the non-linear regime.