Electroluminescent display device
AssigneeKoninklijke Philips Electronics N.V.
InventorMark J. Childs
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Abstract
An electroluminescent (EL) display device comprises an array of display pixels, each display pixel comprising an EL display element and a driving circuit. A digital pixel drive signal determines whether the pixel is on or off, and a selected one of a plurality of supply voltages is switched to the EL display element. This device enables a digital drive scheme to be implemented, but the provision of a plurality of different supply voltages enables a grey scale to be implemented without requiring time or area ratio systems to be employed. Alternatively, the device of the invention can allow time or area ratio techniques to be improved.
Claims20
An electroluminescent (EL) display device comprising an array of display pixels, each display pixel comprising an EL display element and a driving circuit, wherein the driving circuit comprises a switching device for selectively switching a supply voltage to the EL display element or else substantially isolating the display element from the supply voltage, in response to a pixel drive signal, wherein the driving circuit enables a selected one of a plurality of supply voltages to be switched to the EL display element.
A display device as claimed in any preceding claim, wherein the switching device comprises a thin film transistor coupled between supply voltage lines and the EL display element, the transistor being driven substantially fully on or off by the pixel drive signal.
A display device as claimed in any preceding claim, wherein there are three supply voltage lines.
A display device as claimed in any preceding claim, wherein each pixel comprises first and second pixel drive signal conductors, wherein the first pixel drive signal conductor is for operating the switching device, and the second pixel drive signal conductor is for selecting a one of the plurality of supply voltages.
A portable electronic device comprising a display device as claimed in any preceding claim.
A method of driving an electroluminescent (EL) display device comprising an array of pixels, each pixel comprising an electroluminescent (EL) display element and a drive circuit, the method comprising, for each pixel of the display, supplying a first drive signal to the pixel for selectively switching the pixel on or off so that a supply voltage is switched to the EL display element or else is substantially isolated from the EL display element, and wherein the method further comprises selecting the supply voltage level from a plurality of supply voltages levels.
Dependencies are inferred from the claim text.