Electroluminescent display devices
First Claim
Patent Images
1. An active matrix electroluminescent display device comprising an array of display pixels, each pixel comprising:
- an electroluminescent (EL) display element;
a drive transistor for driving a current through the display element;
a current sampling resistor, wherein the EL display element, the drive transistor and the current sampling resistor are in series between first and second power lines;
circuitry comprising at least one sampling transistor for providing one or more feedback signals representing the voltage drop across the current sampling resistor to at least one feedback line, wherein the circuitry comprises a first sampling transistor connected between one terminal of the current sampling resistor and a first said feedback line; and
an address transistor, connected between a data input line and the gate of the drive transistor, the gates of the address transistor and the or each sampling transistor being controlled by a shared address line,wherein the display device further comprises processing means for processing pixel drive signals in dependence on the feedback signal or signals.
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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.
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Citations
15 Claims
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1. An active matrix electroluminescent display device comprising an array of display pixels, each pixel comprising:
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an electroluminescent (EL) display element; a drive transistor for driving a current through the display element; a current sampling resistor, wherein the EL display element, the drive transistor and the current sampling resistor are in series between first and second power lines; circuitry comprising at least one sampling transistor for providing one or more feedback signals representing the voltage drop across the current sampling resistor to at least one feedback line, wherein the circuitry comprises a first sampling transistor connected between one terminal of the current sampling resistor and a first said feedback line; and an address transistor, connected between a data input line and the gate of the drive transistor, the gates of the address transistor and the or each sampling transistor being controlled by a shared address line, wherein the display device further comprises processing means for processing pixel drive signals in dependence on the feedback signal or signals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. 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, a drive transistor for driving a current through the display element and a current sampling resistor in series with the EL display element and the drive transistor, the method comprising, for each pixel:
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applying a drive signal to the pixel representing a desired current; switching a shared data line to control sampling of a voltage on the terminals of the resistor in series with the EL display element to obtain a feedback signal representing the current flowing through the display element; switching a feedback line to control the sampling of the voltage on the terminals of the resistor in series with the EL display element to obtain the feedback signal representing the current flowing through the display element; and using the drive signal and the feedback signal to generate a modified pixel drive signal such that the current flowing is equal to the desired current. - View Dependent Claims (10, 11, 12)
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13. 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, a drive transistor for driving a current through the display element and a current sampling resistor in series with the EL display element and the drive transistor, the method comprising, for each pixel:
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driving a desired current through the current sampling resistor and not through the display element; switching a shared data line to control sampling of a voltage on one or more terminals of the current sampling resistor to obtain a feedback signal representing the voltage drop across the current sampling resistor; switching a feedback line to control the sampling of the voltage on one or more terminals of the current sampling resistor to obtain the feedback signal representing the voltage drop across the current sampling resistor; and 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. - View Dependent Claims (14, 15)
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Specification