Patent ID: 9542039
Date: 2017-01-10
CPC Classifications: G06F

Claim:
1. A touchscreen apparatus comprising: a display screen having a plurality of pixels, a plurality of gate lines each being coupled to a respective group of the pixels, a plurality of data lines each being coupled to a respective group of the pixels, and a plurality of common electrode lines, each being coupled to a respective group of the pixels; a data driver circuit coupled to the plurality of pixels; a gate driver circuit coupled to the plurality of pixels; a touch sensor circuit coupled to the common electrode lines and the data lines, wherein the touch sensor circuit is to generate a touch stimulus voltage on and sense a touch event voltage on pairs of one of the common electrode lines and one of the data lines, during a blanking interval of a frame; a pixel compensation circuit coupled to the common electrode lines, wherein the pixel compensation circuit is to adjust voltage on the common electrode lines during a display interval of the frame to compensate for a pixel voltage shift, and wherein the common electrode lines are affected by both the touch sensor circuit and the pixel compensation circuit during the frame so as to exhibit unevenly distributed residual voltages when the touchscreen apparatus is turned off; a plurality of switch circuits, each having a conducting mode and an essentially non-conducting mode, wherein each switch circuit has (a) a control input, (b) a first carrier electrode, and (c) a second carrier electrode, wherein the first carrier electrode is coupled to a respective one of the plurality of common electrode lines, and the second carrier electrode is coupled to a known voltage node, and wherein each switch circuit automatically enters the conducting mode when voltage at its control input goes to zero; and a control circuit coupled to the control inputs of the switch circuits, wherein the control circuit only has a power supply input coupled to a power supply voltage and no control inputs, the control circuit to control the switch circuits only in response to its power supply input so as to equalize the voltages of the common electrode lines to a known voltage when the touchscreen apparatus is turned off and the power supply voltage to the control circuit goes to zero, so that the display screen exhibits less visual abnormalities when the touchscreen apparatus is turned on again.