A low-power bio-sensor interface with wide measurement range

A new low-power high dynamic range conductance-to-frequency converter, using relaxation oscillator approach, is proposed for bio-sensor interfacing applications. Enhanced by a leakage current compensation technique, the interface has immunity against input pad ESD leakage current as well as hum noise. The output frequency is linear with respect to sensor conductance, with the maximum systematic error of 0.58% and average error of 0.46% for nanowire sensor resistance from 100 MOmega ~ 1 GOmega. For 2% systematic error, the resistance range of the interfacing system can attain from 5 MOmega to 5 GOmega. The bio-sensor interface is designed using CSM 0.18 mum CMOS technology, which dissipates 37.2 muW at a single supply of 1.8 V and the maximum sensor current.