Patent ID: 7916127
Filing Date: 2011-03-29
Classification: G06F

Abstract:
1. A touch screen digitizing system including a touch screen assembly including a first resistive screen with opposed first and second terminals and a second resistive screen with opposed third and fourth terminals, and a touch screen controller circuit including an analog-to-digital converter (ADC) having first and second reference terminals, the improvement including self-test circuitry comprising: a first driver switch coupled between a first reference voltage and the first terminal, and a first test switch coupled between a second reference voltage and a first conductor connected to the second terminal to generate a test voltage on the first conductor indicative of the presence of any short circuit connection between the first and second resistive screens; means for coupling the first reference voltage to the first reference terminal of the ADC, and means for coupling the second reference voltage to the second reference terminal of the ADC; a second test switch having a first terminal connected to the first conductor and a second terminal coupled to an input of the ADC for coupling the test voltage to the input of the ADC; and a comparator having a first input coupled to receive an output of the ADC representative of the test voltage and a second input coupled to receive a predetermined reference signal for producing a pass/fail signal indicative of whether or not a short circuit exists between the first and second resistive screens, wherein the first input of the comparator receives a logical complement of the output of the ADC representative of the test voltage.