Digital platform for Sigma-Delta accelerometer assessment and test
A digital platform for fast assessment and testing of multiple order architectures of electromechanical Sigma-Delta modulators for MEMS capacitive accelerometers is introduced in this paper. It is well known that the introduction of a negative feedback loop on sensors presents significant advantages to improve important characteristics, such as precision, linearity, speed, and dynamic range over open-loop operation (Borovic et al. in J Micromech Microeng 15(10):1917–1924, 2005; Chen et al. in IEEE Sens J 16(17):6476–6495, 2016). In a closed-loop system, the controller is responsible for the aforementioned improvements, enabling the relaxation on the manufactured device specifications. Consequently, it demands better and more complex electronic circuits for the controller. A configurable multi-order (2nd, 3rd, 4th and 5th) ΣΔ module was developed in field-programmable gate array, along with the necessary signal acquisition and actuation modules, using a processor-centric approach, ensuring real-time performance, simple reconfiguration, and fast assessment of different orders and gains for the ΣΔ modulator with real MEMS devices. The system is capable of a measuring cycle lower than 100 ms. The platform was used to perform a comparison between two different types of MEMS accelerometers, evaluating the results obtained with second, third, fourth and fifth modulation orders for two bandwidth values—200 and 1000 Hz. The best noise figure achieved was 4.4 µg/√Hz, using a fifth order ΣΔ modulator and the device with the larger seismic mass. A comparison between three similar devices is also performed, as well as a comparison between simulated and experimental results.
The first and second authors are supported by FCT–Fundação para a Ciência e Tecnologia through the Grants PDE/BDE/114563/2016 and SFRH/BD/91806/2012 respectively.
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