Low-Power High Sensitive Capacitance Read-Out Circuit Using a-InGaZnO TFTs

This paper presents a capacitance readout circuit with high sensitivity and low power consumption using amorphous-Indium-Gallium-Zinc-Oxide thin-film transistors (a-InGaZnO TFTs). A relaxation oscillator is proposed to convert the sensor output (capacitance) into frequency. The proposed circuit has bootstrapping load to improve the output voltage swing using unipolar transistors. A differential to single ended converter and a buffer are used to get rail to rail output voltage. Simulation results show an improvement in sensitivity (832Hz/pF) and power consumption (1.4mW) as compared to the conventional ring oscillator based designs (142Hz/pF, 1.9mW) when circuits are simulated with a power supply of 10V, without compromising voltage swing. Therefore, this circuit finds potential application to implement sensing systems with flexible electronics.