A Novel – Pulsed Digital Oscillator (PDO) for MEMS

A novel digital oscillator topology for microelectromechanical systems (MEMS) based on bandpass sigma–delta modulation is presented. Short pulses of force of the same amplitude maintain the oscillation and the associated bit-stream output serves to know the oscillation frequency which, for low mechanical losses, is very close to the natural frequency of the MEMS resonator. Position-sensing requirements are extremely simplified because, at each sampling time, it is only necessary to know whether the resonator position is above or below the steady-state position. Continuous-time simulations are presented showing the behavior of the oscillator for different sampling frequencies and mechanical damping losses. Experimental results from an oscillator using a MEMS resonator with thermoelectric actuation and piezoresitive position sensing are presented. It is concluded that the quality of the oscillator response depends on the resonator damping losses and on the sampling frequency. The experimental results agree with the analytical and simulation results.