A combined low power SAR capacitance-to-digital / analog-to-digital converter for multisensory system

A low power interface circuit for multisensory system is presented in this paper. A SAR capacitance-to-digital converter (CDC) and a SAR analog-to-digital converter (ADC) are combined together so that capacitance or voltage from different sensors can be measured by the same circuit and converted to digital signal directly. A dynamic comparator with self-calibration is designed to achieve zero-static power. Bootstrapped switches and bottom-plate sampling are used to reduce the non-idealities of sample/hold circuit. The 11bit converter is designed in 0.18um CMOS process with a core area of 0.1764 mm². It consumes 6.7μW and achieves an energy efficiency of 18.8 fJ/conversion-step as a CDC.