Modulated electro-mechanical continuous-time lowpass sigma-delta-modulator for micromachined gyroscopes

In this paper a novel system concept is presented for the implementation of lowpass sigma-delta (ΣΔ) modulators for micromachined gyroscopes. Within the electro-mechanical ΣΔ-modulator two modulation-stages are implemented, reducing the sampling frequency compared to bandpass- and conventional lowpass modulators by a factor of 4 and 100, respectively. By implementing two modulation-stages in the loop the frequency characteristic of the mechanical sensor is changed, thus it is possible to model the mechanical sensor as filter with lowpass-characteristic in the band of interest. Therefore the complete system functions with only one relevant frequency, namely the primary resonance frequency of the mechanical sensor. This concept enables the design of a continuous-time (CT) interface with an extremely low sampling frequency, hence the power dissipation is reduced enormously. A systematic design approach of this architecture is presented and simulation results are shown and discussed.