SC interface and calibration circuit for a CMOS humidity sensor

This paper describes a switch-capacitor interface and calibration circuit that has been co-integrated with a CMOS humidity sensor to achieve a cost-effective solution for accurate and reliable humidity measurements under wide variation of the operating temperature. The calibration circuit is based on a switched-capacitor front-end, featuring high linearity, insensitivity to temperature, as well as low power consumption. The humidity sensing property on-chip is obtained by a post-processing step after the standard CMOS fabrication and whereby a non-photosensitive polyimide is deposited on the packaged chip. The measured results show that, the offset and the sensitivity of the sensor can be precisely calibrated by the integrated circuit which also provide a readable output. The sensor has a linear function with relative humidity in the range of 10% RH to 90%RH and a negligible hysteresis.