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 (Ca
²
+) 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 Ca
²
+ EGFET sensors consist of a thin film of SnO2/ITO/Glass and the immobilized Ca
²⁺
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, CaCl
2
buffer concentrations of 0.1m–1 Mol also confirm the functionality of the fabricated Ca
²⁺
biosensors. An on-chip version of the AFE using TSMC 0.35μm CMOS 2P4M Technology the circuit is also presented.