Fast, Versatile, and Low-Cost Interface Circuit for Electrochemical and Resistive Gas Sensor

Chemical sensors for gas detection nowadays are widely used in several applications; basically, electrochemical sensors and semiconductor devices are used for this purpose. In both cases, the sensor value estimation is usually implemented as a current measurement and they are often referred as current-output sensors. In this paper, a versatile and low-cost interface circuit for such kind of sensors is presented. The proposed solution is characterized by a wide measurement range, yielding flexibility of use with sensors showing different baseline values. In addition, the fast readout time, on the order of tens of milliseconds, guarantees an accurate acquisition of the sensor data even in presence of fast transients, for example when using sensors operated in pulsed thermal regimes. The front-end works with a single-voltage power supply and furnishes a time-coded digital output signal, thus it is suitable to be directly interfaced to a microcontroller for the management of the measurement process, data elaboration, and presentation. Simplicity and compactness of the electronic interface make possible the integration in a single-chip solution, together with the digital electronics. Reproducibility of the circuit, for applications requiring the simultaneous acquisition of multiple sensors, is furthermore facilitated. The proposed approach has been validated with experimental tests conducted on a discrete component prototype. The system characterization has shown a maximum linearity error in the estimation of the sensor current or resistance of ~ 5% over a measurement range of seven decades; the measurement time is in all the considered input range. Fast thermal transients of different semiconductor sensors for gas sensing have been successfully acquired, demonstrating the validity of the proposed approach. Power dissipation ( at 3.3 V) and the front-end cost ( ~ 10 $) make the presented solution suitable for the employment in low-cost and low-power gas detection systems.