Differential R-to-I conversion circuit for gas sensing in biomedical applications

In biomedical engineering specifically gas sensing applications, the concentration of the exhaled gas is converted to a variation in resistance, thus an electronic integrated interface circuit is required to analyze the exhaled gases, which are indications for many diseases. In this paper, a differential resistance to current conversion circuit for Electronic nose (E-nose) breath analyzer is presented. Over an input resistance range of more than 5-decades (500Ω to 100MΩ), a precision, less than 1%, required by novel gas sensing system in portable applications, is preserved. As a result, the proposed circuit obtains high accuracy under simulation. The outputs of the proposed Resistance to Current (R-to-I) conversion circuit achieve a percentage error below 0.25% under environment corners. The reliability of the proposed circuit is also investigated under the effect of process variations. In order to assess the correctness of the proposed architecture, the circuit was compared to similar solutions presented in literature. The proposed architecture attains a worst-case percentage error of 0.05%.