Extended gate field effect transistor (EGFET) integrated readout interfacing circuit for pH sensing

This paper presents the integrated readout interfacing circuit (IROIC) for extended gate field effect transistor (EGFET) to be used as pH sensor. Development of IROIC for EGFET is for the creation of single chip for smart sensors with low cost. Implementation of constant voltage constant current (CVCC) technique to this architecture, resulted in the variation of electrochemical potential can be monitored via the output of IROIC. The design of IROIC was targeted to Silterra 0.13 μm CMOS technology with the size approximately 124 μm × 70 μm. The discrete level of single supply ROIC gave linear sensitivity to the measured pH values with range pH4-pH10 which was 46.9 mV/pH. This value was nearly to that the dual supply ROIC (45.3 mV/pH). The simulation result shows, Three Stage operational amplifier provided good characteristics for implementation of IROIC and produced minimal output voltage noise density which was 4μV/√(Hz) at 100Hz.