A low-power switched-capacitor humidity sensor interface

In this paper, a new switched-capacitor (SC) interface circuit for humidity sensor application is proposed. The sensing principle makes use of the difference between the thermal conductivity of air and water vapor at elevated temperatures. It causes a voltage difference between two isolated diodes. The reference diode is sealed and has a fixed thermal conductance, while the sensing diode is exposed to the environment having a humidity-dependent thermal conductance. The exposed diode is connected to the proposed SC circuit, which can be easily monolithically integrated using GlobalFoundries 0.18-μm CMOS process. The simulation results show that the humidity sensitivity of the sensor is 6.84, 12.44, 22.51mV/%RH for 20°C, 30°C and 40°C respectively. The key advantage is that the circuit operates across the full range of humidity levels for environment temperatures from 20°C to 40°C. The humidity sensing interface operates under a supply voltage of 3V and dissipates power as low as 400μW including the biasing circuits.