5.1 A 1.5μW 0.135pJ·%RH² CMOS Humidity Sensor Using Adaptive Range-Shift Zoom CDC and Power-Aware Floating Inverter Amplifier Array

Capacitive sensors are widely deployed in low-power IoT nodes, where power consumption is stringently limited by the batteries or energy harvesters. Energy-efficient interface circuits that convert sensing information into digital code are important for successful application of such sensors. Two humidity sensors based on a frequency-locking loop (FLL) [1] and a delta-sigma modulator (DSM) [2] achieve high resolution, but at the expense of high power consumption of 10.32μW and 15.6μW, respectively. The Zoom-based humidity sensor in [3] and capacitor-to-digital converters (CDC) in [3,4] exhibit a significantly improved dynamic range (DR). However, the DSM in the Zoom scheme typically entails large redundancy to cover the SAR conversion error due to noise or interference. Further, the OTA current budget is set to drive the maximum input capacitance, thus wasting power when driving typically small capacitance in most cases.