Closed-loop silicon accelerometers

The control-system structure and behaviour are considered for an analogue and a digital servo-accelerometer having a dynamic range from mg to several g (1g = 9.81 ms(-2)), for use in low-frequency applications. The paper emphasises the derivation of mathematical models, which are presented together with simulated and test results obtained from the implementation of these strategies on a bulk-micromachined silicon sensing element employing capacitive signal pick-off. The digital device, which is based upon oversampling conversion, proved to have superior stability compared to the analogue accelerometer. Furthermore, it has the advantages of producing a direct digital output signal and an inherent self-test feature.