Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-09-08
2001-08-07
Hjerpe, Richard (Department: 2774)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S055000, C345S077000, C345S078000, C345S208000, C345S210000, C345S211000, C345S214000, C345S204000, C315S169100, C315S169200, C315S169400
Reexamination Certificate
active
06271812
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims benefit of priority of Japanese Patent Applications No. Hei-9-260636 filed on Sep. 25, 1997, and No. Hei-10-58185 filed on Mar. 10, 1998, contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electroluminescent display device in which residual images stored as electric charges in pixels are eliminated or made invisible on the display panel.
2. Description of Related Art
An electroluminescent (EL) display panel is generally composed of a pair of electrodes, a pair of insulation layers and a luminescent layer interposed therebetween. The display panel is driven by a driver including electrode driving circuits and a power source circuit.
It is known that polarized electric charges still remain in pixels after the panel is turned off. The relation between imposed voltages and electric charges in a pixel (Q-V characteristic) is illustrated in FIG.
15
. The voltage (V) imposed on a pixel is shown on the abscissa and the electric charge (Q) stored in the pixel on the ordinate. The Q-V relation in the pixel takes a position {circle around (
1
)} when no voltage is applied and no electric charge is stored. To drive the EL panel, a positive pulse voltage (Vth+Vm) is imposed on the pixel in a positive field and a negative pulse voltage −(Vth+Vm) in a negative field. The voltage Vth is a threshold voltage with which the pixel starts emitting light, and the voltage Vm is a modulation voltage representing an image datum. When the positive pulse voltage is imposed, the Q-V relation changes along a path {circle around (
1
)}-{circle around (
2
)}-{circle around (
3
)}-{circle around (
4
)}. This means that when the voltage becomes zero at the position {circle around (
4
)}, there still remains a certain electric charge. When the negative pulse voltage is imposed at that point {circle around (
4
)}, the Q-V relation changes along a path {circle around (
4
)}-{circle around (
5
)}-{circle around (
6
)}-{circle around (
7
)}-{circle around (
8
)}. When the positive and negative voltages are imposed alternatively after that point, the Q-V relation changes along a periphery of a parallelogram {circle around (
9
)}-{circle around (
3
)}-{circle around (
5
)}-{circle around (
7
)}. The EL pixel emits light on lines {circle around (
9
)}-{circle around (
2
)}-{circle around (
3
)} and {circle around (
5
)}-{circle around (
6
)}-{circle around (
7
)}.
To turn off the EL panel (to terminate light emission from the pixel), the voltage Vth is imposed in the positive field and the voltage −Vth in the negative field. If the voltage −Vth is imposed when a pixel is at the position {circle around (
4
)}, it returns to the position {circle around (
1
)} through the positions {circle around (
5
)} and {circle around (
6
)}. If the voltage Vth is imposed when a pixel is at the position {circle around (
8
)}, it returns to the position {circle around (
1
)} through the positions {circle around (
9
)} and {circle around (
2
)}. Therefore, no polarized electric charge is left in the pixel in both cases.
However, in actual use of the EL panel, some electric charges are left in the pixels after the panel is turned off. Under this situation, when the EL panel is turned on again and a voltage to make it dark is applied, the EL panel still emits light due to the electric charges remaining in the pixels. For example, if the EL pixel is at the position {circle around (
4
)} when the power is turned off, and the voltage −Vth which makes the pixel dark is imposed when the power is turned on again, then its position changes along a path {circle around (
4
)}-{circle around (
5
)}-{circle around (
6
)}-{circle around (
1
)}. The EL pixel emits light in a course of its position change from the point {circle around (
5
)} to the point {circle around (
6
)}. Similarly, if the EL pixel is at the position {circle around (
8
)} when the power is turned off, and the voltage Vth which makes the pixel dark is imposed when the power is turned on again, then its position changes along a path {circle around (
8
)}-{circle around (
9
)}-{circle around (
2
)}-{circle around (
1
)}. The El pixel emits light in a course of its position change from the point {circle around (
9
)} to the point {circle around (
2
)}. Therefore, an undesirable picture image is displayed on the panel due to the remaining electric charge when the power is supplied again after the power is once turned off. Actually, the image due to the remaining charge is mixed with an image to be first displayed, and the mixed image is displayed. Though this image is displayed only for a short time right after the power is turned on, it is still undesirable and uncomfortable for a viewer.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an electroluminescent (EL) display device, in which an undesirable picture image (a residual image) appearing when the device is turned on again is eliminated. The residual image can be eliminated by discharging electric charges stored in pixels when the display panel is turned off, or the residual image can be made invisible by activating all pixels storing residual images when the display panel is turned on again next time.
The electroluminescent display panel includes an array of scanning electrodes and another array of data electrodes. Both arrays are arranged to form a matrix, and an electroluminescent layer is interposed between both arrays. Picture elements or pixels are formed at each intersection of the scanning electrodes and the data electrodes. The electroluminescent panel is driven by imposing voltages on the picture elements by applying scanning voltages on the scanning electrodes and the data voltages on the data electrodes. When the EL panel is turned off, polarized electric charges are left in the pixels which have been activated. Those electric charges display residual images on the panel when the panel is turned on again next time. The residual images are undesirable and uncomfortable for a viewer.
To eliminate electric charges stored in the pixels, a voltage, a level of which is at a vicinity of scanning voltage, is applied on the scanning electrodes while applying a voltage to make the pixels inactive on the data electrodes, after the normal display on the panel is terminated. In other words, at the end of the normal display the EL panel is scanned at least one time to eliminate electric charges stored in the pixels which have been activated. Since the charge eliminating operation is performed upon turning off the EL panel, the residual images are not displayed when the panel is turned on next time.
Alternatively, upon turning on the EL panel, the pixels storing electric charges therein may be activated to emit light therefrom at least one time. By this operation the residual images are made invisible to a viewer. In this operation, all or substantially all the pixels are lit at least one time. This initial display may be designed to include some ornamental moving images. Further, the residual images can be made substantially invisible by delaying the normal display till the drive voltage reaches a predetermined level.
The EL panel according to the present invention may be suitably used as an instrument panel for an automobile. In this case, the EL panel is powered by a battery mounted on the automobile. When a key switch of the automobile is turned off, the process to eliminate the residual images is carried out by supplying power to the panel through a wired OR circuit, for example. Alternatively, the EL panel is lit at least one time before the normal display begins to make the residual images invisible.
This invention may also be applied to a segment-display type device in the same manner as in the matrix-display type device.
Other objects and features of the present invention will become more readily apparent fro
Kishita Hiroyuki
Ninoyu Toshinori
Nishioka Ken
Osada Masahiko
Saito Hideki
Denso Corporation
Hjerpe Richard
Pillsbury & Winthrop LLP
Zamani Ali
LandOfFree
Electroluminescent display device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electroluminescent display device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electroluminescent display device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2519141