Analysis of the dynamics of an active control of the surface potential in metal oxide gas sensors

•A sliding mode approach of the sigma-delta control of Surface Potential in MOX gas sensors has been made.•Constant Surface Potential Operation of MOX gas sensors alters the dynamics of the sensors,•The stability of the closed and open loop operation is analyzed for two rate equation models (for CO and NO2). Gas sensing is nowadays a key actor in pollution observation and detection of chemical toxic agents or explosives. All these applications require the shortest possible time response. Very recently, a control of the surface potential in gas sensors based on metal oxides has experimentally shown to dramatically improve the time response of metal-oxide gas sensors. The proposed control is inspired in sigma-delta modulators. This paper aims at studying the resulting dynamics in the sensor from a theoretical point of view. Using state space models, it is shown how the state variables, namely the concentrations of ionized species in the sensing layer, evolve with time in open and closed loop configuration. This analysis studies how it is possible to alter the dynamics of the overall system, while at the same time keeping some important characteristics of sigma-delta modulators, such as quantization noise-shaping. Numerical simulations validate the obtained results.