A digital interface for gyroscopes controlling the primary and secondary mode using bandpass sigma–delta modulation

Abstract

This paper demonstrates a micro-electro-mechanical gyroscope system with extensive use of sigma–delta (ΣΔ) modulation in both, primary and secondary modes. Both control schemes are implemented digitally on a field programmable gate array (FPGA). The primary loop has a bandpass ΣΔ digital-to-analog converter (DAC) driving the primary mass into resonance using a two-level driver. With this strategy of replacing the discrete DAC of the primary oscillation control with a bandpass ΣΔ-DAC, the analog circuit complexity is enormously reduced. The Coriolis rate signal is converted into a bit stream with a new excess loop delay (ELD) compensated micro-electro-mechanical ΣΔ modulator (ΣΔM) incorporating the gyroscope in the loop with a second-order electrical bandpass filter (BPF). To investigate the ELD effect, this electro-mechanical ΣΔM is implemented on the FPGA emulating continuous-time (CT) behavior. Measurements show stable modulators, with an ELD of nearly one clock period of the sampled system, achieving in-band noise (IBN) below −60 dBFS. The full-scale (FS) is measured to 1019°/s. This paper demonstrates that the stability of ΣΔ modulators with large ELD can be ensured with the new ELD compensation technique.