A 9.1μW Capacitance-to-Digital Converter for Pressure Sensor Systems

This paper presents a capacitance-to-digital converter (CDC) for pressure sensor systems, which consists of a front-end circuit and a successive approximation register (SAR) ADC. The front-end circuit uses correlated double sampling technology to eliminate the impact of the low-frequency noise and offset voltage of the operational amplifier. The C DACP and C DACN in the SAR ADC can save power and area as the sampling capacitance of the front-end circuit. The SAR ADC uses bottom plate sampling to avoid various nonlinearities caused by top plate sampling, and a comparator with pre-amplification to reduce the impact of kickback noise. Adjustable reference capacitance (C REF ) is designed to expand the detection range of sensor capacitance. The circuit is designed and fabricated in 0.18μm standard CMOS process. While the power supply is 1.8V and the conversion time is 224μs, the power consumption is only 9.1μW. Capacitance resolution of 7.8fF is achieved with sensor capacitance (C SENS ) detectable in the range of 10.1pF-21.5pF.