Patent ID: 6961051

Claim:
A circuit assembly for detecting a touch point within a display area, comprising: a plurality of light emitters disposed around a periphery of said display area; a plurality of detectors disposed around said periphery, each detector being opposed to a respective light emitter; and switching circuitry for connecting said light emitters and detectors in a switching matrix having a plurality of matrix rows and matrix columns, wherein said switching circuitry includes: a plurality of row lines, each row line corresponding to a respective matrix row; a plurality of column lines, each column line corresponding to a respective matrix column; a plurality of light emitter transistors each coupled between a respective light emitter and a respective row line, each light emitter transistor having a control input coupled to a respective column line and responsive to a respective column select signal for connecting its respective light emitter to said respective row line; a plurality of pull-up resistances each coupling a respective one of said row lines to a predetermined voltage; and a plurality of row transistors each coupled between a respective row line and ground, each row transistor having a control input coupled to a respective row line and responsive to a row select signal for selectably connecting its respective row line to ground.