A Closed-Loop Digitally Controlled MEMS Gyroscope With Unconstrained Sigma-Delta Force-Feedback

Abstract

In this paper we describe the system architecture and prototype measurements of a MEMS gyroscope system with a resolution of 0.025The architecture makes extensive use of control loops, which are mostly in the digital domain. For the primary mode both the amplitude and the resonance frequency are tracked and controlled. The secondary mode readout is based on unconstrained Σ∆ force-feedback, which does not require a compensation filter in the loop and thus allows more beneficial quantization noise shaping than prior designs of the same order. Due to the force-feedback, the gyroscope has ample dynamic range to correct the quadrature error in the digital domain. The largely digital set-up also gives a lot of flexibility in characterization and testing, where system identification techniques have been used to characterize the sensors. This way, a parasitic direct electrical coupling between actuation and readout of the mass-spring systems was estimated and corrected in the digital domain. Special care is also given to the capacitive readout circuit, which operates in continuous time.

1-Bit processing based model predictive control for fractionated satellite missions

“…Incorporating the Δ∑ modulator to the gyroscope sensing element is one of the most promising approaches to implement the MEMS gyroscope due to the circuit simplicity and the benefits of incorporating the sensing component in a feedback control loop (Kraft and Ding, 2009). The Δ∑ modulation embedded MEMS gyroscope was first introduced in (Jiang, et al, 2000), and ever since became a popular research topic in literature (Petkov and Boser, 2006;Raman, et al, 2009;Antonello and Oboe, 2012).…”

“…Due to the non-linear nature of the quantizer, the extra integrators in the gyroscope transfer function may cause stability issues in the control loop. Moreover, the compensator will also introduce extra poles in the control loop and consequently affect the noise-shaping performance of the system (Raman, et al, 2009). Additional integrators, serving as usual noise shaping solutions, will be adopted in the feedback loop to attenuate the magnitude of the impulse response of the NTF at low frequencies (see e.g.…”

A virtually floating dual-mass accelerometer

“…For this, a quantizer is added after the loop filter, before applying the digital feedback. With a proper designed loop filter [16][17][18], the added quantization noise can be made negligible and the performance will be further enhanced.…”

“…Due to the 180 • phase shift in the mechanical part, the force-feedback will only be stable for a dominant pole sufficiently lower in frequency than the mechanical resonance frequency. The system bandwidth could be increased by using a more advanced filter with frequency compensation [17,18], but this is beyond the scope of this prototype. The complete system level diagram for the differentialmode is then shown in Fig.…”

A dual-mass capacitive-readout accelerometer operated near pull-in

“…The loop uses an unconstrained architecture, negating the requirement of a compensator for stability [8], [9]. Two poles result from M (s); two additional electric integrators from the electrical loop filter H(z) shape the quantisation noise further.…”