A General Purpose Single-Slope MEMS Capacitive Sensors Interface Circuit For IoT Applications

Abstract

A new energy-efficient single-slope capacitance-to-digital interface circuit is proposed. The proposed interface circuit is a general purpose interface that can be adapted for multi-sensors IoT applications. This interface utilizes a new iterative charge sharing technique, which can be easily configures for different capacitive sensor ranges. The interface employs a switched capacitor circuit followed by a low-power dynamic comparator and a digital controller with a counter to generate the digital output, corresponding to the input capacitance of the sensor. The simplicity of the proposed capacitance-to-digital converter (CDC) architecture leads to an energy efficient interface. Detailed analysis of the proposed CDC architecture with emphasis on the linearity, conversion time, and noise are presented and verified by the simulation. The proposed CDC achieves a resolution of 8.4 bit and a figure-of-merit (FoM) of 1.56pJ for a capacitor sensor range of 8pF and a supply voltage of 1.2V in $0.18\mu \mathrm{m}$ CMOS technology node.