Temperature Compensation Circuit for ISFET based pH Sensor

Abstract

The ion sensitive field effect transistor (ISFET) are being utilized in pH sensor technology to sense pH values. However, it is highly sensitive to temperature and may introduce variations in the output resulting into errors in the reading. This paper proposes a readout integrated circuit (ROIC) for temperature compensation of an ISFET based pH sensor. The resistor present in the bridge works as a thermistor and helps in stabilizing the output. The test circuit is simulated using LTSpice. The analysis is done for a temperature range of 0 − 50°C and pH range of 5.5 to 14 respectively. The performance analysis has been presented with four different type of sensing films i.e. SiO2, Al2O3, Ta2O3 and Si3N4. The proposed circuit gave optimum results, wherein a constant output voltage is achieved throughout the temperature range 0 − 50°C with sensitivity less than 56.33mV/pH. The proposed circuit has been briefly compared with the existing circuits.