A 2.92-$\mu$ W Capacitance-to-Digital Converter With Differential Bondwire Accelerometer, On-Chip Air Pressure, and Humidity Sensor in 0.18-$\mu$ m CMOS

Abstract

This paper presents a sensor front end for air pressure sensor, relative humidity (RH) sensor, and accelerometer in a standard CMOS process, equipped with a wide input range high-resolution capacitance-to-digital converter (CDC). For air pressure and RH, interdigitated top metals in air and polyimide are exploited, respectively, which exhibit the change in dielectric constant. For acceleration, separation among three bondwires is exploited. These sensing transducers induce capacitance change that is quantized by a CDC based on a dual-quantization architecture that employs a single-bit first-order $\Delta \Sigma $ modulator and a 7-bit SAR analog-to-digital converter (ADC). Implemented in 0.18- $\mu \text{m}$ CMOS, the air pressure sensor, RH sensor, and accelerometer achieve a noise floor of 0.14 psi/ $\sqrt {\textrm {Hz}}$ , 0.001 %RH/ $\sqrt {\textrm {Hz}}$ , and 4.6 mg/ $\sqrt {\textrm {Hz}}$ , respectively. The CDC achieves a resolution of 864 aF (minimum resolution of 116 aF) when the sensing capacitance is 10 pF and consumes $3~\mu \text{W}$ from 1.1-V supply.