An energy-efficient 17-bit noise-shaping Dual-Slope Capacitance-to-Digital Converter for MEMS sensors

A noise-shaping Dual-Slope (DS) Capacitance-to-Digital Converter (CDC), specifically designed for interfacing capacitive MEMS sensors, is presented. In particular, this work proposes a design with a MEMS sensor built with a bridge of capacitors. In this bridge, some capacitors are function of the pressure in order to obtain a variation in the output of the bridge related with the change of 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 time domain noise-shaping Dual-Slope ADC is used to digitalize the magnitude of the capacitive bridge. The use of time instead of amplitude resolution leads to the following strengths: 1) intrinsically small sensitivity to temperature and process variations; 2) simplicity of trimming offset and gain to correct the sensor parameter spread; and 3) area and energy efficient implementation. The effectiveness of the method is demonstrated by measurements performed on a prototype, designed and fabricated using standard digital 0.13µm CMOS technology. Experimental results show that it achieves a resolution of 17-bit, which corresponds to a capacitive resolution of 5.4aF, while consuming only 146µA from a 1.5V power supply, with an effective area of 0.317mm 2 .