A High Performance InGaZnO Thin-Film Transistors Integrated Amplifier Circuit for Capacitance Sensing

An operational amplifier with indium-gallium-zinc oxide thin-film-transistors (InGaZnO TFTs) is proposed and investigated. The proposed amplifier features introduction of positive feedback with negative equivalent output resistance for high voltage gain. Biasing conditions for every TFTs and voltage gain are systematically discussed. In addition, influences of threshold voltage shift on both static and dynamic performances are discussed. Comparison results show that the voltage gain can be increased from 40 to 67 dB, and stability of the constant tail-current biasing is better than that of constant voltage biasing method. Further, an oscillating capacitance touch sensing circuit based on the proposed amplifier is shown, and sub-pF touching capacitance can be distinguished. The proposed InGaZnO TFTs integrated amplifier is promising for high performance system on panel designs.