Interface circuit for an ultra low power gas sensor

An electronic system based on a microcontroller architecture devoted to interfacing an Ultra Low Power (ULP) Metal OXide (MOX) gas sensor is presented. The circuit controls the operating temperature and manages the acquired data. A Pulse Width Modulation (PWM) signal with variable duty cycle is used to provide power to the heating resistor in order to set the desired operating temperature. The heating resistance value is measured in the range [100 Omega - 500 Omega] with a relative error less than 1%. The circuit devoted to measure the gas concentration is based on a logarithmic amplifier which measures the current flowing in the sensing layer of the sensor. The measurand range is [30 nA - 60 mu A] and the relative error on the measured current is less than 0.6%.