ISFET's Interface Circuit for Biomedical Applications Using Delta-Sigma Modulation

This paper presents a new ISFET's interface circuit for biomedical applications using delta-sigma modulation. The proposed design operates ISFET in the linear region so that an output current is linearly dependent on pH over a wide range (pH 2 to pH 14). Conversion to a digital output domain is done using a sigma-delta converter making the interface circuit very robust and reliable for most sensor applications. The proposed circuit is designed in a 0.18 μm technology. The supply voltage is 1.8 V and the total current drawn is 56 μA. The simulation results show that the proposed circuit can sense a pH with an error within the range of -0.2% to 0.3% for pH ranging from 2 to 14.