An interface circuit for temperature control and read-out of metal oxide gas sensors

Abstract

This paper presents a complete gas-sensing system. The latter consists of a high-efficiency temperature control loop with a switching heater based on a custom digital control logic and of a wide-dynamic-range interface circuit able to operate without calibration. The temperature control loop is driven by a digital set-point and the simulations results show that it controls the temperature of the sensor over a range of 250 °C with an accuracy better than 0.5 °C. The temperature control logic is reconfigurable and can be used to control the temperature of sensors with different baseline resistance value and different sensitivity. The gas-sensing interface circuit is based on a resistance to frequency conversion and achieves, without calibration, a precision in resistance measurements of 0.5% over a range of 5 decades (dynamic range, DR=146 dB). All voltage references are reconfigurable and on chip buffered.