Active matrix display devices
AssigneeKoninklijke Philips Electronics N.V.
InventorDavid A. Fish
Life of this patent
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Abstract
An active matrix display device stores a transistor drive voltage on a storage capacitor (24; Cs). A light-dependent device (27) effects discharge of the storage capacitor in dependence on the light output of the light emitting display element (2). Power is provided to each pixel from a first power line (26), and one of the light dependent device and the storage capacitor is coupled to a second power supply line (50), to which a varying voltage is provided during a pixel illumination period. By varying the voltage on one of the power supply lines, the discharge characteristics of the capacitor by the optical feedback system are altered to provide compensation for the light-dependent device leakage currents.
Claims16
An active matrix display device comprising an array of display pixels, each pixel comprising:
- a current-driven light emitting display element;
- a drive transistor for driving a current through the display element;
- a storage capacitor (Cs) for storing a voltage to be used for addressing the drive transistor;
- and
- a light-dependent device for effecting discharge of the storage capacitor in dependence on the light output of the light emitting display element,
- wherein power is provided to each pixel from a first power line, and wherein one of the light dependent device and the storage capacitor is coupled to a second power supply line, and wherein the device further comprises means for varying the voltage on the second power supply line during a pixel illumination period, and
- wherein the voltage on the second power supply line is ramped during a pixel illumination period to cancel a leakage current IL at a gate node of the drive transistor by creating a current of opposite magnitude of the leakage current IL.
A method of driving an active matrix display device comprising an array of display pixels each comprising a drive transistor and a current-driven light emitting display element, the method comprising, for each addressing of the pixel:
- applying a drive voltage to an input of the pixel;
- storing a voltage derived from the drive voltage on a discharge capacitor;
- driving the drive transistor using a voltage on a storage capacitor;
- discharging the storage capacitor using a light sensitive element, at a rate or time dependent on the light output of the display element, and
- varying a voltage on a terminal of the light sensitive element or the storage capacitor thereby to compensate for leakage currents of the light sensitive element
- wherein the voltage on the terminal of the light sensitive element or the storage capacitor is ramped during a pixel illumination period to cancel a leakage current IL at a gate node of the drive transistor by creating a current of opposite magnitude of the leakage current IL.
Dependencies are inferred from the claim text.