A High-Dynamic-Range Switched-Capacitor Sigma-Delta ADC for Digital Micromechanical Vibration Gyroscopes

Abstract

This paper presents a multi-stage noise shaping (MASH) switched-capacitor (SC) sigma-delta (ΣΔ) analog-to-digital converter (ADC) composed of an analog modulator with an on-chip noise cancellation logic and a reconfigurable digital decimator for MEMS digital gyroscope applications. A MASH 2-1-1 structure is employed to guarantee an absolutely stable modulation system. Based on the over-sampling and noise-shaping techniques, the core modulator architecture is a cascade of three single-loop stages containing feedback paths for systematic optimization to avoid deterioration in conversion accuracy caused by capacitor mismatch. A digital noise cancellation logic is also included to eliminate residual quantization errors in the former two stages, and those in the last stage are shaped by a fourth-order modulation. A multi-rate decimator follows the analog modulator to suit variable gyroscope bandwidth. Manufactured in a standard 0.35 μm CMOS technology, the whole chip occupies an area of 3.8 mm2. Experimental results show a maximum signal-to-noise ratio (SNR) of 100.2 dB and an overall dynamic range (DR) of 107.6 dB, with a power consumption of 3.2 mW from a 5 V supply. This corresponds to a state-of-the-art figure-of-merit (FoM) of 165.6 dB.

A Self-Oscillating Driving Circuit for Low-Q MEMS Vibratory Gyroscopes

“…The closed-loop drive mode is commonly utilized in micromechanical gyroscopes. After undergoing processes such as peak detection and variable gain, the driving electrode’s vibration signal is fed back to the driving electrode to create a closed-loop drive signal [ 21 ].…”

“…The vibration of the micromechanical gyroscope on the x -axis results in the generation of Coriolis force acceleration on the y -axis via the angular velocity in the z -axis. When the sense combs vibrate on the y -axis, the equivalent capacitance changes [ 21 ]. The principle underlying the detection of angular velocity is based on the detection of alterations in the equivalent capacitance on the y -axis.…”

An Interface ASIC for MEMS Vibratory Gyroscopes with Nonlinear Driving Control

“…This work employs a 6-bit SAR ADC for hardware consumption economy and rapid reference interval confirmation to provide for subsequent ΣΔ conversion, during which further process of oversampling and noise shaping is accomplished [19]. Furthermore, the elementarily locked references allow a single-bit quantizer which is equipped with inherent linearity [20]. Besides, the quantizer output is scaled independently of the output of the preceding loop filter.…”