An event-driven and energy-efficient humidity sensor for environment detection and healthcare monitoring is presented. A differential CMOS-MEMS humidity device and proportion-based capacitance-to-digit readout circuit are proposed to overcome PVT variations, and in the meantime to improve sensitivity, response time, and conversion energy. This chip achieves 15.6b 20-90 %RH at 1KS/s, 6.1pJ per 0.02%RH of sensitivity, and 10ms fast response time in TSMC 0.35-m CMOS MEMS process. With variations in temperature and voltage, our proposal can minimize the errors from 40%RH to 0.2%RH and 50%RH to 0.1%RH, making it very suitable for wearable respiratory monitoring.

In this paper, we propose a power/area-efficient capacitive readout circuit for the Micro-Electro-Mechanical Systems (MEMS) sensor of 3-axis accelerometer. The proposed architecture is different from other traditional structures by exploiting true capacitive-to-digital converter (CDC) without Analog-to-Digital Converter (ADC). The proposed CDC can differentiate the bidirectional 125KS/s 80-level accelerations between 8g and support the 4-level adjustable resolutions of 0.1g/ 0.2g/ 0.4g/ 0.8g for each axis. The proposed readout circuit with 0.0354mm 2 area is fabricated in UMC 0.18um CMOS-MEMS process. Experimental results show power consumption is 50uW with 1.8V supply voltage for 1-axis (FOM=3.84pJ), 82uW for 3-axis (FOM=2.1pJ) under 125KHz of sampling frequency and 0.1g acceleration sensitivity for 0.2fF MEMS capacitance change.