Display device and display driving method

Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix

Reexamination Certificate

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Details

C345S081000

Reexamination Certificate

active

06215462

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a display device and a method for driving the same, and more particularly to a spontaneous light emission type display device with pixels having a high aperture ratio and a method for driving the display device.
2. Description of the Related Art
Of late, organic electroluminescent display devices have received attention as flat-panel electroluminescent display devices having a large viewing angle. Some organic electroluminescent dot-matrix display devices are active-matrix drive type, and others are simple-matrix drive type.
A conventional organic electroluminescent display device
350
is active-matrix drive type, and has organic electroluminescent elements
351
, a plurality of drive transistors
352
for applying voltages to the electroluminescent elements
351
, a plurality of capacitors
353
for retaining the applied voltages, and a plurality of selection transistors
354
for selectively writing image signals into the capacitors
353
, as illustrated in
FIG. 17
which is a diagram showing an equivalent circuit (corresponding to one pixel). The gates of the selection transistors
354
are connected to a gate driver via gate lines GL, while the drains of the selection transistors
354
are connected to a drain driver via drain lines DL.
When driving the organic electroluminescent elements
351
, the selection transistors
354
are selected line by line in accordance with selection signals supplied from the gate driver. The drain driver writes image signals into the capacitors
353
in a currently selected line through the drain lines DL and the selection transistors
354
. The drive transistors
352
drive the organic electroluminescent elements
351
in accordance with the magnitudes of the image signals written into the capacitors
353
. Voltages according to gradations are applied to the organic electroluminescent elements
351
, thereby making the display device display desired images. Thus, in the case of the organic electroluminescent display device
350
, the selection transistors
354
are selected line by line, in which case there is no possibility of an unintended voltage being applied to the organic electroluminescent elements
351
in lines other than the currently selected line. This enables the display device to display images without the crosstalk occurring.
According to the organic electroluminescent display device
350
of the active-matrix drive type, however, the drive transistors
352
, the capacitors
353
and the selection transistors
354
have to be formed in addition to the organic electroluminescent element
351
constituting each pixel. This entails a problem in that the area (aperture ratio) of the organic electroluminescent element
351
forming each pixel is small.
As shown in
FIG. 18
, an organic electroluminescent display device of the simple-matrix drive type includes a substrate
360
, anode electrodes
361
, an organic electroluminescent layer
362
and cathode electrodes
363
, which are all laminated on the substrate
360
. The anode electrodes
361
are perpendicular to the cathode electrodes
363
. The intersections of the anode electrodes
361
and the cathode electrodes
363
are pixels. In the organic electroluminescent display device of the simple-matrix drive type, the aperture ratio of the pixels is higher than the aforementioned case.
According to the organic electroluminescent display device of the simple-matrix drive type, however, there is the possibility of a voltage being applied also to those parts of the organic electroluminescent layer
362
which are located on the anode electrodes
361
of the pixels in lines other than the currently selected line. Thus, when an unintended voltage is applied, crosstalk occurs due to the voltage-luminance characteristic of the organic electroluminescent layer
362
, resulting in a low contrast ratio.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above problems, and it is an object of the present invention to provide a display device, whose pixels have a high aperture ratio and which performs display with suppressed crosstalk, and a method for driving such a display device.
According to one aspect of the present invention having the aforementioned object, there is provided a display device comprising;
first light emission elements which emit light in a predetermined range of wavelengths when a predetermined voltage is applied to the first light emission elements;
light waveguides, each of which guides the light emitted from a corresponding one of the first light emission elements;
active elements, each having a first end and a second end and in each of which a carrier occurs upon incidence of the light emitted from a corresponding one of the first light emission elements and guided by a corresponding one of the light waveguides;
data electrodes to which a voltage is applied in accordance with image data, the first end of each of the active elements being connected to a corresponding one of the data electrodes; and
second light emission elements which emit light in a predetermined wavelength range when currents flow in the second light emission elements, each of the second light emission elements being connected to the second end of a corresponding one of the active elements.
According to the above-described display device, when the first light emission elements are made to emit light, the light emitted therefrom enters the corresponding active elements through the light waveguides such that carriers occur in the active elements, rendering the resistance of the active elements low. While the first light emission elements are emitting no light, no carriers occur in the active elements, and consequently the resistance of the active elements remains high. When the resistance of the active elements is satisfactorily low, the voltage between each of the data electrodes and the second light emission elements is applied substantially to the second light emission elements. On the other hand, when the resistance of the active elements is satisfactorily high, the voltage between each of the data electrodes and the second light emission elements is applied substantially to the active elements. This eliminates the problem that due to the voltage applied to the data electrodes, an unintended voltage is applied to those ones of the second light emission elements which correspond to the non-selected first light emission elements which are emitting no light. The above-described display device can therefore display a high-quality image without crosstalk occurring.
Stacking the waveguides, the data electrodes, the active elements and the second light emission elements on the substrate in the described order ensures an improved aperture ratio to the second light emission elements.
According to another aspect of the present invention having the aforementioned object, there is provided a method for driving a display device including:
light waveguides which guide incident light,
electroluminescent address elements formed on the light waveguides and from which light to be guided by the light waveguides is emitted in a predetermined range of wavelengths in accordance with an applied voltage,
data electrodes provided on the light waveguides, and having light transmission parts which the address light passes through, a voltage being externally applied to the data electrodes in accordance with image data,
active elements provided on the data electrodes, each of the active elements having a base in which a carrier occurs when the address light emitted from a corresponding one of the electroluminescent address elements enters the base, and
electroluminescent display elements provided on the active elements, each of the electroluminescent display elements including an anode electrode, an organic electroluminescent layer and a cathode electrode,
the method comprising steps of:
having the electroluminescent address elements sequentially emit the address light in order to selectively drive th

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