An implementation of an electronic tongue system based on a multi-sensor potentiometric readout circuit with embedded calibration and temperature compensation

We present an Electronic Tongue system composed of an analog front-end (AFE) with embedded calibration and temperature compensation for interfacing with an array of ISFETs (Ion-Sensitive FETs) or EGFETs (Extended Gate FETs). The AFE consists of a floating bridge type constant voltage constant current (CVCC) structure, and transmission gates as sensor enable. The calibration algorithm is synthesized into a Field Programmable Gate Array (FPGA). The system shall be used to measure the pH and ionized Calcium (Ca²⁺) of a solution and forms part of a urine stone prediction platform. The ISFETs used are from ITE-Poland and shall be used to measure pH; while the Ca²⁺ EGFET sensors consist of a thin film of SnO₂/ITO/Glass and the immobilized Ca²⁺ ionophore on polyvinyl chloride (PVC). Performance verifications using known pH buffer solutions of 4-10 confirm the functionality of the system using both FET sensors along with the AFE´s sensor enable and disable. Furthermore, CaCl₂ buffer concentrations of 0.1m-1 Mol also confirm the functionality of the fabricated Ca²⁺ biosensors. An on-chip version of the AFE using TSMC 0.35μm CMOS 2P4M Technology the circuit is also presented.