Design Criteria of Low-Power Oscillators for Consumer-Grade MEMS Resonant Sensors

This paper discusses the constraints in the design of circuits for microelectromechanical systems (MEMS) resonant sensors in consumer applications, presents a novel integrated circuit implementation, and shows that this approach can be competitive with respect to the mostly used capacitive readout. From a circuit design perspective, it is shown how the large equivalent resistance typical of MEMS resonators, their operation close to mechanical nonlinearity, and the effect of feedthrough capacitances on the oscillating loop constrain the power requirements of the driving/readout electronics. As a case study, a resonant accelerometer built in an industrial process is coupled to a suitably designed transimpedance amplifier with a low-power “hard limiter.” The performance shown in terms of linearity across the measurement range (±8 g), minimum measurable acceleration (1 mg with a readout bandwidth of 100 Hz), and power consumption (≈ 100 μW per axis) is comparable to those of state-of-the-art capacitive inertial sensors.