Patent ID: 8094135
Filing Date: 2012-01-10
Classification: G06F

Abstract:
1. A touch screen digitizing system, comprising: a touch screen unit including a first resistive sheet with opposing first and second terminals and a second resistive sheet with opposing third and fourth terminals; a first switch coupled between a first reference voltage and the first terminal, and a second switch coupled between the second terminal and a second reference voltage for energizing the first resistive sheet; an analog to digital converter comprising: a first input coupled to the third terminal when the first resistive sheet is energized and the second resistive sheet is not energized, the first resistive sheet capable of touching the second resistive sheet at a contact point; a first reference terminal coupled to the first reference voltage during a sampling phase of the analog to digital converter and being floating and held at a first voltage level thereon during a conversion phase of the analog to digital converter; a second reference terminal coupled to the second reference voltage during the sampling phase and being floating and held at a second voltage level thereon during the conversion phase; and an output terminal providing digital output data; and a third switch coupled between the first reference voltage and the third terminal, and a fourth switch coupled between the fourth terminal and the second reference voltage for energizing the second resistive sheet; and a voltage drop generator coupled between the third switch and the third terminal, wherein the voltage drop generator is a diode, and wherein: the first input of the analog to digital converter is coupled to the first terminal when the second resistive sheet is energized and the first resistive sheet is not.