A digitally controlled MEMS gyroscope with unconstrained sigma-delta force-feedback architecture

In this paper we describe the system architecture and prototype measurements of a MEMS gyroscope with a resolution of 0.055 degrees/s/root Hz. Two innovations are presented. The first is the complete migration of control and demodulation tasks to the digital domain. For this purpose, interfacing circuits based on Sigma Delta techniques are introduced for both primary and secondary mode. The advantage is that complex analog electronics for tracking the resonant frequency, stabilizing the amplitude of the primary mode oscillation and phase-sensitive demodulation can be replaced by their digital Counterpart. A second innovation relates to the Sigma Delta force-feedback loop. In previously reported structures a compensation filter is introduced for stabilizing the loop [1-3]. Unfortunately, the compensation filter introduces extra poles and influences the noise-shaping characteristic, which makes the loop difficult to design and optimize. We demonstrate the possibility of obtaining a stable Delta Sigma force-feedback loop without an explicit compensation filter