Electroluminescent display devices
AssigneeKoninklijke Philips Elecronics N.V.
InventorWilliam Steer
Life of this patent
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Abstract
An active matrix electroluminescent display device has a current sampling resistor within each pixel in series with the display element. A feedback signal represents the voltage drop across the current sampling resistor and the pixel drive signals are modified in dependence on the feedback signal to control the current driven through the display element. In this way, threshold compensation is provided, whilst enabling a single voltage-driven drive transistor to be employed.
Claims17
An active matrix electroluminescent display device comprising an array of display pixels (1), each pixel comprising:
- an electroluminescent (EL) display element (2);
- a drive transistor (22) for driving a current through the display element;
- a current sampling resistor (30), wherein the EL display element (2), the drive transistor (22) and the current sampling resistor (30) are in series between first and second power lines (26;
- 32);
- and
- circuitry (38, 40) for providing a feedback signal or signals representing the voltage drop across the current sampling resistor (30) to at least one feedback line (34, 36),
- wherein the display device further comprises processing means for processing pixel drive signals (52) in dependence on the feedback signal or signals.
A method of addressing an active matrix electroluminescent display device comprising an array of display pixels, in which each pixel comprises an electroluminescent (EL) display element (2), a drive transistor (22) for driving a current through the display element and a current sampling resistor (30) in series with the EL display element and the drive transistor, the method comprising, for each pixel:
- applying a drive signal (52) to the pixel representing a desired current;
- obtaining a feedback signal representing the current flowing through the display element by sampling a voltage on the terminals of the resistor (30) in series with the EL display element;
- and
- using the drive signal (52) and the feedback signal to generate a modified pixel drive signal such that the current flowing is equal to the desired current.
A method of addressing an active matrix electroluminescent display device comprising an array of display pixels, in which each pixel comprises an electroluminescent (EL) display element (2), a drive transistor (22) for driving a current through the display element and a current sampling resistor (30) in series with the EL display element and the drive transistor, the method comprising, for each pixel:
- driving a desired current through the current sampling resistor and not through the display element;
- obtaining a feedback signal representing the corresponding voltage drop across the current sampling resistor;
- storing the feedback signal;
- and
- using the stored feedback signal as a feedback control signal for subsequently driving current through the display element by applying a voltage to the gate of the drive transistor, the feedback control signal being used to determine the gate voltage.
Dependencies are inferred from the claim text.