A 10 ms-readout interface for the characterization of high-value wide-range experimental resistive sensors

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 as electronic interfaces for 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 One 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 mean square (LMS) algorithm. The implemented prototype allows the sensor resistance to be estimated with a fixed measuring time of 10 ms over the range 10 k Omega-10 G Omega with relative estimation error below 10% (below 1% in the range 47 k Omega-2 G Omega). It can Furthermore estimate the parasitic capacitance of the sensor (in parallel with the resistive component), on the order of few picofarads with a linearity error less than 0.5% full scale (FS). Fast thermal transients of a SnO2 nanowire sensor have been finely analyzed using the new interface system, demonstrating the suitability of the proposed method for accurate analysis of new experimental resistive sensors. (C) 2009 Elsevier B.V. All rights reserved.