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

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 degrees C with an accuracy better than 0.5 degrees 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.