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. [1k Omega-100M Omega] 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. [100 Omega-1G Omega]. The presented technique exploits an integrator-based controlled oscillator [1], whose main time constant is function of the applied resistance value, named The state of the art of this measurement method has been R, 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)100M Omega, while for the lower half-range (R-sens < 320k Omega) the conversion time is only 15ms