Liquid crystal display device employing a guard plane between a layer for measuring touch position and common electrode layer

Abstract

The present invention provides for touch input functionality in a liquid crystal display having a plurality of cells each comprising a first substrate having a common electrode integrated thereon, a second substrate having a pixel electrode integrated thereon, and liquid crystal material disposed between the common electrode and pixel electrode. A first conductive layer (signal layer) and second conductive layer (guard plane layer) are integrated onto the first substrate and disposed between the first substrate and the common electrode. Contact position of a touch input device with the first substrate is determined by applying a first signal to the signal layer. A second signal is applied to the guard plane layer to thereby lower capacitive coupling between the signal layer and the common electrode. The second signal may be generated by scaling amplitude and/or phase shifting the first signal. Response to the first signal is measured to determine contact position of the touch input device. Preferably, the portion of the signal layer disposed opposite the pixel electrode is a patterned layer of black matrix material, and the guard plane layer may be a transparent ITO layer. Alternatively, portions of the signal layer and guard plane layer disposed opposite the pixel electrode may be a patterned layer of black matrix material. A resistor network may be coupled to the signal layer to linearize resistance of the signal layer in a horizontal and vertical direction. By lowering the capacitive coupling between the signal layer and the common electrode, the guard plane layer and signal applied thereto enables the determination of contact position of a portion of the human body (such as a finger or a toe) based upon the measured response to the source signal. The present invention may be in display systems wherein a matrix of display elements are viewed from above a first side of a substrate and the display elements are disposed on the second side (i.e., the opposite side) of the substrate.