JP2000122598A - Display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a display device emitting light with uniform brightness and keeping high display quality by correcting luminance unevenness due to initial and secular changes of a display element. SOLUTION: This display device is provided with a display part 4 having plural light emitting elements, a drive circuit 3 driving the light emitting elements of the display part 4, a command control circuit 1 controlling the drive circuit 3 and a correction value table 2 preserving the data operated based on the luminance information of the light emitting elements, and the command control circuit 1 corrects a light emission command value to control the drive circuit 3 by referring to the correction value table 2 corresponding to the light emitting element to be light emitted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device using, for example, a current drive type light emitting element (light emitting diode, organic electroluminescence element, field emission element).

[0002]

2. Description of the Related Art Conventionally, an organic EL device which emits light by passing a current through an organic film is known. FIG. 2 shows a schematic configuration diagram of the organic EL device. In FIG. 2, a transparent electrode 7 is formed on a glass substrate 8, and an organic layer 6 is formed on the upper surface of the transparent electrode 7. The organic layer 6 is laminated with a plurality of substances mainly composed of organic substances, and it is considered that light is emitted at a part or a boundary between the layers. The metal electrode 5 is formed on the organic layer 6.

In the organic EL element having such a configuration, light emission is generated by switching the switch 10 from the off state to the on state, applying a drive voltage from the drive source 9 and flowing a current.
This light emission is emitted outside through the transparent electrode 7 and the glass substrate 8.

An organic EL element is an element whose light emission intensity changes in proportion to a current flowing from an electrode to an organic layer. Therefore, the instantaneous light emission luminance of the element is proportional to the magnitude of the injected forward current, and the average light emission luminance of the element in a predetermined time is determined by the total charge injected within the time to be averaged. That is, the average light emission luminance of the element has two parameters, the magnitude of the applied current and the applied time. By controlling this parameter and controlling the integrated value of the current applied for a predetermined time, that is, the amount of current, it becomes possible to control the light emission luminance of the element.

FIG. 3 shows an example of a main part of a display device constituted by using the above-mentioned organic EL element as a light emitting element for display. Anode lines C1-Cm and cathode lines L1-
Ln are arranged in a lattice pattern, and the light emitting elements E1,1 to L1 are sandwiched between the intersections of the anode line and the cathode line arranged in the lattice form.
Connect En, m. The driving method is a simple matrix driving method, in which the cathode lines are sequentially selected at certain time intervals, and the anode lines are connected to the current sources 141 to 141 in synchronization with the selection.
By driving at 14 m, a light emitting element corresponding to an arbitrary intersection position emits light.

FIG. 3 shows the operation of each unit when emitting light at E1,1, E1,3 and E1, m. First, the cathode ray L1
Is selected and connected to the ground potential. Simultaneously with this selection, a driving source is connected to the anode lines C1, C3, Cm, and the corresponding light emitting elements emit light.

At this time, the anode lines other than the selected one are connected to the ground potential, and the reverse bias voltage Vcc is applied to the cathode lines other than the selected one to prevent erroneous light emission.

[0008]

The above display device can perform various displays as a dot matrix display device. At this time, if a constant current is applied to each light emitting element, the luminance of each element should basically be equal.

However, current-luminance characteristics may differ in a plane due to non-uniformity in a process such as a film forming process, and a luminance distribution may occur in the plane. Further, there are a case where the inside of the display device is divided into small regions (for example, about 64 × 64 pixels) and each is individually driven, or a case where panels of the small regions are attached to each other to form one display device.
At this time, a slight difference in light emission luminance appears as a linear streak at a joint between the small regions.

[0010] Even when there is no luminance distribution in the plane during the all white light emission (luminance command value 100%), luminance unevenness may occur when displaying a halftone. This means that the current-luminance characteristic curves of the light emitting elements vary, and that the characteristics in the halftone are not uniform only by correcting the peak value in the all white state.

As described above, even when driving is performed with a constant current, an in-plane luminance distribution occurs due to variations in light emitting elements.

Further, when the same information is displayed for a long time (for example, a total light emission time of 3000 hours), the element that emits light is more deteriorated than the element that does not emit light. Next, the display of certain information is terminated, and thereafter all the pixels are caused to emit light with the same luminance command (for example, the same current value). At this time, the place that should emit light with the same brightness on the entire surface is
Pixels displaying certain information have lower luminance than other elements because of deterioration. For this reason, there is a problem that a luminance difference occurs and certain information that has been displayed up to that point is seen as a phenomenon such as burn-in.

In view of the above problems, an object of the present invention is to provide a display device capable of maintaining high display quality without uneven light emission.

[0014]

In order to achieve the above object,
The present invention (claim 1) includes at least a display unit having a plurality of light emitting elements, a driving unit for driving the light emitting elements of the display unit, a control unit for controlling the driving unit, and a correction value table storing correction information. The control means refers to a correction value table corresponding to the light emitting element to emit light, and corrects the light emission command value to control the driving means.

Further, the correction value table stores data calculated based on luminance information of the light emitting element.

Further, the correction value table secures correction value data for each light emitting element.

Further, the correction value table stores correction value data for each small area of the display means.

Further, the correction value table stores correction value data corresponding to the number of gradations for each of the light emitting elements.

Further, the control means arbitrarily controls the drive current value of the drive means based on the correction value data.

Further, the control means arbitrarily controls the driving time of the driving means based on the correction value data.

Further, the control means arbitrarily controls the drive current value and the drive time of the drive means based on the correction value data.

Also, the present invention is characterized in that the correction value table of the display device is updated again after a fixed light emission time.

[0023]

Next, embodiments of the present invention will be described below.

FIG. 1 is a schematic block diagram of a display device according to a first embodiment of the present invention. In FIG. 1, 1
Is a command control circuit for controlling the drive circuit 3;
The light emission command value is corrected with reference to the correction value table 2 corresponding to the light emitting element to emit light, and the drive circuit 3 is controlled. Reference numeral 2 denotes a correction value table storing correction information, 3 denotes a drive circuit for driving the light emitting elements of the display unit 4, and 4 denotes a display unit having a plurality of light emitting elements.

Next, the operation will be briefly described. The command control circuit 1 fetches a value of the correction value table 2 corresponding to a pixel to be displayed according to the light emission command value, and raises the correction value as a gain to the light emission command value. The command control circuit 1 inputs the corrected light emission command value to the drive circuit 3. The drive circuit 3 changes an electric current value or a drive time width according to the input light emission command value, and causes any display element of the display unit 4 to emit light at a luminance corresponding to the light emission command value.

Next, a method of driving the display device according to the present embodiment will be described in detail with reference to FIG. FIG. 4 is a diagram illustrating a method of calculating and storing a correction value. This embodiment is obtained by adding a luminance correcting means 19 to the configuration shown in FIG. The brightness correction means 19 may be integrated with the display device or may be separated therefrom. For example, the luminance capturing means is C
A means for taking in information outside the display device such as a CD, or a drive voltage value or an element resistance value of an element may be detected inside the display device to take in information relating to luminance.

The display section 4 is made to emit light in all white (a luminance command value of 100%), and luminance data of the light emitting elements of the display section 4 is captured by the luminance capturing means 17. A correction value is calculated from the luminance data by the luminance correction calculator 18 and stored in the correction value table 2.

The brightness correction calculator 18 calculates, for example, the reciprocal of the brightness data of each pixel, and stores the calculated reciprocal in a predetermined location of the correction value table 2. Assuming that the correction value is stored in 8 bits, it becomes a two-digit number in hexadecimal notation as shown in FIG. FIG. 5 is a diagram schematically showing the correction value table 2, in which the number of stored data is the same as the number of light emitting elements.

For example, assuming that the display unit 4 forms a matrix of n rows and m columns (n and m are natural numbers) as shown in FIG. 3, the number of data is n × m. The correction values corresponding to the positions of the light emitting elements in the display unit are stored, and the correction values corresponding to the light emitting elements E1,1 in FIG.
Becomes

Thus, the brightness correction value calculator 18
Calculates a correction value from the luminance data obtained by the luminance capturing means 17 and stores it in the correction value table.

Next, the command control circuit 1 fetches correction value data corresponding to the pixel position to be displayed from the correction value table 2 according to the light emission command value. Then, the correction value data is multiplied by the light emission command value as a gain. After that, the corrected light emission command value is input to the drive circuit 3. The drive circuit 3 changes the current value or the drive time width according to the light emission command value, and drives the light emitting elements of the display unit at a specified luminance.

As described above, by calculating the correction data based on the light emission luminance information and correcting the light emission command value, it is possible to suppress the difference in light emission luminance and the light emission unevenness in the display unit 4 and to achieve uniform light emission. The display can be performed with a high brightness.

In the embodiment, the luminance correction is performed on all the light emitting elements. However, a certain small area (for example, an area of about several tens of pixels × several tens of pixels) is set as one unit, and the correction value data is set for each unit. May be provided to perform luminance correction. This can be applied when it is considered that the characteristics of adjacent pixels do not greatly change. In this case, it is possible to save memory and allow a margin for the resolution of the luminance capturing unit.

Further, the panels of the small area are joined together.
Alternatively, the display unit is divided and driven to form one image as a whole (for example, Japanese Patent Application No. 10-161837).
Prepares correction value data for each of the small region and the divided region, and corrects the light emission luminance. This makes it possible to improve the brightness unevenness between the small areas, to eliminate the streak caused by the brightness difference at the area boundaries, and to perform display with uniform brightness as a whole.

As a method of driving the drive circuit 3 in FIG. 4, there are a method of controlling the current value and a method of controlling the application time width while keeping the current value constant. In either method, the correction value table 2 may be a single sheet. For example, in a method in which both the current value and the application time width are simultaneously controlled,
What is necessary is just to prepare the correction value table (total 2 sheets) about each.

Next, a second embodiment according to the present invention will be described. As shown in FIG. 6, the correction value table 2 prepares data of the number of gradations for each pixel of the light emitting element of the display unit 4. For example, assuming that the number of gradations is 64, 64 correction value tables are prepared as shown in FIG. There are 64 data per pixel.

The basic operation is the same as in the first embodiment. In FIG. 6, the brightness correction means 19 performs the acquisition of the brightness information, the calculation of the correction value, and the storage of the correction value in the correction value table, and performs it for each gradation. The command control circuit 1 reads the element to emit light and its luminance information from the light emission command value, extracts the correction value from the corresponding correction value table 2, and uses the correction value as a gain to raise the light emission command value.

By performing the luminance correction for each gradation in this manner, uniform light emission can be obtained for all gradations from low luminance to high luminance, and luminance unevenness in halftone can be suppressed.

Further, since data for each gradation is held, γ can be obtained simply by changing the calculation method of the luminance correction value calculator.
The curve characteristics (the relationship between the input signal and the emission luminance) can be changed. For example, the relationship between the input signal and the light emission luminance can be variously changed, such as linear proportionality or power approximation. Since such a change can be made, fine adjustment of luminance when displaying an image is possible.

By having a plurality of tables as described above and performing luminance correction for each gradation, the display element can emit light uniformly even in a halftone. Further, since the input / output characteristics can be changed, it is possible to provide a wider range of adjustment when displaying an image.

Next, a third embodiment according to the present invention will be described. The first and second embodiments are methods for correcting uneven brightness in an initial state. Even if uniform display is possible without luminance unevenness in the initial state, for example, the same information can be displayed for a long time (emission time:
For example, when the display is performed for 3000 hours, the element that emits light is deteriorating as compared with the element that does not emit light. For example, an organic EL element has a characteristic that the luminance decreases with time even when driven at a constant current.
For this reason, when all the pixels are made to emit light at 100% luminance next time, even if the correction is performed by the gradation correction table, the light emitting elements in the portion where certain information is displayed are deteriorated. Luminance is lower than other parts. Therefore, a luminance difference occurs, and a phenomenon such as burn-in visually occurs.

In order to solve this phenomenon, in the present embodiment, for example, for a display device after a certain period of time (for example, 1000 or 2000 hours) has elapsed, the calculation is performed again using the brightness correction means 19 described above. Change the correction value table.

The brightness correction means 19 may be added to the outside of the display device, or may be integrated.

Even in the case where the characteristics of the light emitting elements have changed, the luminance unevenness can be eliminated by performing the luminance correction again after a certain period of time.

By performing such a correction, it is possible to suppress luminance unevenness in a form including the change with time of the element.
Uniform display becomes possible.

As the light emitting element, a field emission element, a light emitting diode element or the like can be used in addition to the organic electroluminescence element.

[0047]

As described above, according to the present invention, the luminance can be corrected for both the initial light emission unevenness of the display element and the light emission unevenness due to the temporal change. For this reason, light emission is displayed visually with uniform brightness, and high display quality can be maintained. In particular, it is suitable for a driving method of a current driven light emitting element such as an organic EL element. Further, since the values of the correction value table can be arbitrarily changed, it is possible to easily cope with characteristic variations between display elements, and there are few restrictions on the element configuration, which is practical.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a display device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a schematic configuration of a conventional organic EL element.

FIG. 3 is a diagram showing a main part of a display device using a conventional organic EL element as a light emitting element.

FIG. 4 is a block diagram showing a detailed configuration of a display device according to the first embodiment of the present invention.

FIG. 5 is a schematic configuration diagram of a correction value table of the display device according to the first embodiment of the present invention.

FIG. 6 is a schematic configuration diagram of a correction value table of the display device according to the second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Command control circuit 2 Correction value table 3 Drive circuit 4 Display part 17 Brightness acquisition means 18 Brightness correction value calculator 19 Brightness correction means

Continued on the front page (72) Inventor Hisanori Sugiura 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Tetsuya Sato 1006 Odaka Kadoma Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. Person Mikiko Matsuo 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture F-term in Matsushita Electric Industrial Co., Ltd.

Claims (13)

[Claims] 1. A display device comprising a plurality of light emitting elements, a driving means for driving the light emitting elements of the display means, a control means for controlling the driving means, and a correction value table storing correction information. A display device, wherein the control means refers to the correction value table corresponding to the light emitting element to emit light, and corrects a light emission command value to control the driving means. 2. The display device according to claim 1, wherein the correction value table stores data calculated based on luminance information of the light emitting element. 3. The display device according to claim 1, wherein the correction value table secures correction value data for each of the light emitting elements. 4. The display device according to claim 1, wherein said correction value table stores correction value data for each small area of said display means. 5. The display device according to claim 1, wherein the correction value table stores correction value data corresponding to the number of gradations for each of the light emitting elements. 6. The display device according to claim 1, wherein the correction value table secures correction value data for the number of gradations for each of the small areas of the display means. 7. The display device according to claim 1, wherein said control means arbitrarily controls a drive current value of said drive means based on said correction value data. 8. The display device according to claim 1, wherein said control means arbitrarily controls a driving time of said driving means based on said correction value data. 9. The display device according to claim 1, wherein said control means arbitrarily controls a drive current value and a drive time of said drive means based on said correction value data. 10. A display device comprising a plurality of light emitting elements, a driving means for driving the light emitting elements of the display means, a control means for controlling the driving means, and a correction value table storing correction information. A driving method of a display device, wherein the control unit refers to the correction value table corresponding to the light emitting element to emit light, and corrects a light emission command value to control the driving unit; And updating the correction value table of the display device again. 11. The display device according to claim 1, wherein said light emitting device is an organic electroluminescence device. 12. The display device according to claim 1, wherein said light emitting element is a field emission element. 13. The display device according to claim 1, wherein said light emitting element is a light emitting diode element.