ISFET Readout Circuit using Flipped Voltage Follower with Temperature Compensation

摘要

Sensors and devices dependent in temperature variations can present significant problems that may lead to incorrect analysis of results. Ion-Sensitive Field Effect Transistors are sensors that can measure the pH level of a solution. A low-power flipped voltage follower readout circuit was used to acquire the corresponding voltage level output. However, the output changes as temperature varies, resulting to a proportional-to-absolute-temperature output voltage. A diode-connected MOSFET was used to provide a complementary-to-absolute-temperature voltage along with the flipped voltage follower to construct a circuit with temperature compensation. The proposed circuit was simulated from a temperature range of 0 °C to 70 °C, and pH levels of 4, 7, and 10. Temperature coefficient with a 91.8% improvement was obtained from an uncompensated average of 685.47 ppm/°C to a compensated 6.29 ppm/°C output. The circuit was designed in 0.18 µm technology with a supply voltage of 1.8V and an overall power consumption of 27.76 µW.