Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-04-06
2001-02-20
Shalwala, Bipin (Department: 2778)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S077000, C313S504000, C315S169300
Reexamination Certificate
active
06191764
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a self lighting display device, and, more particularly, to an organic electroluminescent display device and a method of driving such a display device.
2. Description of the Related Art
An ordinary organic electroluminescent display device has a matrix of segment electrodes and common electrodes respectively formed in X and Y directions on the respective sides of an organic electroluminescent layer which emits light in accordance with the applied voltage. While the organic electroluminescent layer of such a simple matrix drive type of display device is excellent in luminescent response with respect to the applied voltage, it hardly has a luminescent memory property with respect to the applied voltage so that it merely emits light line by line only in the scan period. This requires that the luminescent luminance in the scan period should be increased. Increasing the voltage for that purpose results in an increased burden on the organic electroluminescent layer and accelerates the degradation of the organic electroluminescent layer. When this display device is driven at a high duty ratio to match with the high resolution, a crosstalk occurs, which provides displayed images with a low contrast ratio.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a display device which has a memory property and presents image display with a high contrast ratio, and to provide a method of driving such a display device.
To achieve the above object, a display device according to this invention comprises an electroluminescent address panel including an address electroluminescent layer for emitting light in accordance with injected carriers, first address electrodes provided on one side of the address electroluminescent layer and second address electrodes provided on the other side of the address electroluminescent layer; and
an electroluminescent display panel including a first display electrode, a phototransistor provided on the first display electrode, showing a conductivity according to incidence of light emitted from the address electroluminescent layer and having a non-linear light vs. conductivity characteristics, a display electroluminescent layer, provided on the phototransistor, for emitting light as carriers are injected inside, and second display electrodes provided on the display electroluminescent layer.
In this invention, as address light is generated from the electroluminescent address panel and comes into the phototransistor, the phototransistor is optically excited to be turned on, allowing carriers to be injected into the display electroluminescent layer. Because of the non-linear light vs. conductivity characteristics, the phototransistor does not show a conductivity with respect to outside light or minute incident light produced by the crosstalk of the address electroluminescent layer. When the address light from the electroluminescent address panel is not incident to the display electroluminescent layer, the display electroluminescent layer does not emit light, thus ensuring display with a high contrast ratio.
The address electroluminescent layer and the display electroluminescent layer may contain organic electroluminescent materials. The electroluminescent layer containing an organic electroluminescent material, even if formed very thin, can emit light with a sufficient luminance and can secure a shorter distance for the address light to reach the phototransistor. It is thus possible to minimize the diffusion of the address light within the phototransistor, address a small area in the phototransistor and allow just the corresponding area of the display electroluminescent layer to emit light. This can lead to high-resolution display.
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Kono Ichiro
Shioya Masaharu
Yamada Hiroyasu
Casio Computer Co. Ltd.
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Kovalick Vincent E.
Shalwala Bipin
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