High Order Bandpass Sigma Delta Interface for Vibratory Gyroscopes

Abstract

Previous work on sigma delta (SigmaDelta) interfaces for micromachined vibratory gyroscopes were based on lowpass SigmaDelta modulators. However, for a lowpass SigmaDelta interface the signal band is a relatively small fraction of the sampling frequency fs , which increases the noise aliasing and result in a relatively high noise floor in the signal band. Due to the characteristic of narrowband amplitude-modulated signals of vibratory rate gyroscopes, a bandpass SigmaDelta interface is more attractive. A bandpass SigmaDelta interface is superior as it is relatively immune to 1/f noise compared to a lowpass SigmaDelta interface. To achieve a similar noise floor with a given oversampling ratio (OSR), the sampling frequency of a bandpass SigmaDelta interface can be much lower than that of a lowpass SigmaDelta interface. Furthermore, some high order SigmaDelta loop topologies have favorable noise shaping characteristics for electronic noise originating from the pickoff circuit and signal anti-aliasing. Therefore, the requirements for the electronic circuits can be considerably relaxed