Wide-range integrated gas sensor interface based on a resistance-to-number converter technique with the oscillator decoupled from the input device

In this paper an integrated wide-range gas sensor interface based on a resistance-to-number converter is presented. The circuit in transistor level simulations achieves a precision of about 0.5% over a range of 5 decades, i.e. [1kOmega-100MOmega] without requiring any calibration or autoranging, while reconfiguring the circuit and performing a limited calibration, the dynamic range is expected to rise up to 7 decades, e.g. [100Omega-1GOmega]. The presented technique exploits an integrator-based controlled oscillator, whose main time constant is function of the applied resistance value, named R_sens . The state of the art of this measurement method has been improved by separating the oscillator circuit from the sensing device, leading to higher linearity-speed response factor. The maximum conversion time is 5 seconds, when sensing the highest resistance values, i.e. R_sens=100MOmega, while for the lower half-range (R_sensles320kOmega) the conversion time is only 15ms