A Capacitance-To-Digital Converter for MEMS Sensors for Smart Applications

Abstract

The use of MEMS sensors has been increasing in recent years. To cover all the applications, many different readout circuits are needed. To reduce the cost and time to market, a generic capacitance-to-digital converter (CDC) seems to be the logical next step. This work presents a configurable CDC designed for capacitive MEMS sensors. The sensor is built with a bridge of MEMS, where some of them function with pressure. Then, the capacitive to digital conversion is realized using two steps. First, a switched-capacitor (SC) preamplifier is used to make the capacitive to voltage (C-V) conversion. Second, a self-oscillated noise-shaping integrating dual-slope (DS) converter is used to digitize this magnitude. The proposed converter uses time instead of amplitude resolution to generate a multibit digital output stream. In addition it performs noise shaping of the quantization error to reduce measurement time. This article shows the effectiveness of this method by measurements performed on a prototype, designed and fabricated using standard 0.13 µm CMOS technology. Experimental measurements show that the CDC achieves a resolution of 17 bits, with an effective area of 0.317 mm2, which means a pressure resolution of 1 Pa, while consuming 146 µA from a 1.5 V power supply.

A Fully-Differential Switched-Capacitor Dual-Slope Capacitance-To-Digital Converter (CDC) for a Capacitive Pressure Sensor

“…A dashpot is used to represent a mechanical damping element. Considering that all these three elements share the same displacement x , and applying Newton’s second law of motion, the classical equation of motion can be derived [10].…”

Impact of Improved Design on Knudsen Force for Micro Gas Sensor

“…However, they have problems of large size, complicated structure, high price, and long response time [ 11 , 12 ]. There are commonly used chemiresistive, acoustic, optical, and capacitive gas sensors according to different working principles [ 13 , 14 , 15 , 16 ]. Chemiresistive gas sensors have advantages of easy fabrication, low cost, reuse ability, high stability, and sensitivity [ 17 , 18 ], however, the detecting properties are vulnerable to environmental factors such as humidity and temperature [ 17 , 18 ].…”

AC and DC Differential Bridge Structure Suitable for Electrochemical Interfacial Capacitance Biosensing Applications

“…For field deployment, a less complicated capacitance extraction method, operating at a single frequency, is required. One such method is with the use of a capacitance-to-digital converter (CDC) [12,13]. The readily available CDC integrated circuits are utilized in [14] for the readout system, but CDCs operate over a restricted range of full-scale capacitance that is not always compatible with the absolute capacitance value of custom-designed electrochemical capacitive electrode transducers which may range from tens to hundreds of nF.…”