Abstract: A touch input device, suitable for use in detecting the presence of an opaque element within a display area bounded by light emitting elements and light detecting elements includes light emitter activating circuitry in which the light emitting elements are individually selectable. Each light emitting element is contained within a matrix and source drivers and sink drivers are effective to select a specific row and column address for each individual light emitter. Current for the light emitters is provided by a voltage source which is chosen for compatibility with the logic used in the touch input system. A charge pump operating sequentially with the selection light emitting elements is used to establish a voltage greater than the normal supply voltage to overcome the voltage drops of the source and sink driver and the activated light emitter to insure light emission greater than a minimum threshold.

Abstract: An edge linearization device for linearizing the electric fields in a resistive surface is described. A plurality of electrodes are disposed on the perimeter of an area on a surface having a substantially uniform resistivity. The device utilizes the geometry of the spaces between adjacent conductive elements to provide resistive elements. At least one of the electrodes has an extension. The extension or extensions of the electrodes are progressively inwardly displaced into the area from the perimeter so that there is at least one center-most extension on a first portion of said perimeter and also on a second, opposing portion of said perimeter. In a preferred embodiment, the invention utilizes a surface with a substantially rectangular area having four sides and four corners. Disposed along the sides are a plurality of electrodes and corner electrodes and disposed in the corners of the surface are corner connectors. The use of T-shaped extensions of the electrodes on such a surface is also disclosed.

Abstract: A touch input device having infrared light beams defined by a plurality of pairs of light emitters and phototransistors is disclosed. A feedback loop containing a programmable amplifier is employed to compensate for the effects of ambient light and for device irregularities. The phototransistor current is first converted to a signal voltage by an operational amplifier and then is input into a low pass filter. The output of the lowpass filter is input into a feedback loop containing a summing amplifier, a programmable amplifier and an integrator. As light emitters and phototransistors are sequentially activated, the feedback loop with the programmable amplifier compares outputs signals in the unactivated state with those input when the light emitters are activated to compensate for ambient conditions and errors.