Low-power humidity read-out circuit in CMOS 180-nm for RFID sensors

The manuscript describes the design and implementation of a read-out circuit for the measurement of the Relative Humidity by means of an external capacitive sensor. The circuit is based on a timer oscillator and a digitally calibrated resistor which are available in an integrated circuit implementing the functions of sensing and data logging. Thanks to the reusing concept low power consumption and small silicon area are achieved. An accuracy of a few percent is obtained by means of a relatively inexpensive one-point calibration. In addition a circuit interfacing between the oscillator and the external capacitor sensor is proposed.