An Energy-Efficient Capacitance-to-Digital Converter With Top and Bottom Plate Sampling for Pressure Sensors

This brief presents a 12-bit low-power successive-approximation-register (SAR) capacitance-to-digital converter (CDC) for capacitive pressure sensors. It adopts a capacitance-to-voltage front-end (CVFE) scheme to decouple the capacitive digital-to-analog converter (CDAC) from the sensor capacitor, enabling a large swing of the SAR analog-to-digital converter (ADC) and a wide capacitance sensing range. To improve power efficiency, this brief proposed a top and bottom sampling (TBS) for CVFE circuit to achieve a single-ended sampling while differential conversion. The TBS includes only one sampling phase, which relaxes the amplifier’s bandwidth requirements, thereby reducing the power consumption of the CVFE. The prototype chip was fabricated using a 180-nm CMOS process. The measured capacitance resolution is 1.76 fF and the measurement capacitance range is from 0.63 pF to 38.37 pF. The proposed CDC consumes <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.90~\mu $ </tex-math></inline-formula>W with a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$128~\mu $ </tex-math></inline-formula>s conversion time, bringing a power efficiency of 80.6 fJ/conversion-step.