Abstract
Controls of surface potential have been proposed to accelerate the time response of MOX gas sensors. These controls use temperature modulations and a feedback loop based on first-order sigma-delta modulators to keep constant the surface potential. Changes in the surrounding gases, therefore, must be compensated by average temperature produced by the control loop, which is the new output signal. The purpose of this paper is to present a second order sigma-delta control of the surface potential for gas sensors. With this new control strategy, it is possible to obtain a second order zero of the quantization noise in the output signal. This provides a less noisy control of the surface potential, while at the same time some undesired effects of first order modulators, such as the presence of plateaus, are avoided. Experiments proving these performance improvements are presented using a gas sensor made of tungsten oxide nanowires. Plateau avoidance and second order noise shaping is shown with ethanol measurements.
Highlights
Interest in metal-oxide (MOX) gas sensors has grown significantly during the recent years.Different materials, such as SnO2, WO3, or ZnO, and specific fabrication techniques have been developed to form the sensing layers of such sensors, often structured as nanoneedles, nanotubes, nanorods, etc
This paper introduces a new second-order sigma-delta strategy to control the chemical resistance of MOX gas sensors
For by changes in the average temperature generated by the control. As it has been mentioned before, this paper presents a second order sigma-delta topology for. As it has been mentioned before, this paper presents a second order sigma-delta topology for surface potential control in MOX-based gas sensors
Summary
Interest in metal-oxide (MOX) gas sensors has grown significantly during the recent years.Different materials, such as SnO2 , WO3 , or ZnO, and specific fabrication techniques have been developed to form the sensing layers of such sensors, often structured as nanoneedles, nanotubes, nanorods, etc. Good stability, reduced cost, low power consumption, and compatibility with semiconductor fabrication processes are other advantages of this type of sensors [1,2,3,4,5]. All this makes them excellent candidates in applications such as detection of hazardous gases, pollution observation, or detection of gas leaks [6,7,8]. The mode of operation of the MOX gas sensors usually consists of monitoring the conductivity of the sensing layer Since this layer is a semiconductor, its conductance strongly depends on the temperature and on the chemical reactions involved in the gas adsorption and ionization processes [9]. MOX sensors are usually operated in open-loop at constant-high temperature, of 100 ◦ C
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