A 10 ms-readout Interface For Experimental Resistive Sensor Characterization

Metal oxide gas sensors exhibit resistance values varying over a wide range, from tens of kilohms to tens of gigohms, depending on the chosen oxide and on the excitation parameters (voltage, temperature, gas exposure). Resistance-to-time converters (RTC) are widely used in electronic interfaces to such sensors thanks to the low-cost, low-noise and high-range characteristics. RTC main limit is in the variable and long measuring time, ranging from microseconds (tens of kilohms) to several seconds (tens of gigohms), impeding a fine analysis of fast transients. This work proposes a new approach based on combination of the RTC method with a new technique based on the least means square algorithm. The implemented prototype allows the sensor resistance estimation with 100 sample/s (T-meas = 10 ms) over the range 10 k Omega divided by 10 G Omega with relative estimation error below 10% (below 1% in the range 47 k Omega divided by 2 G Omega). Fast thermal transients of a SnO2 nanowire sensor have been finely analyzed thanks to the new interface system.