JP2002351403A - Image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the life of a light emitting element longer. SOLUTION: This organic EL(electroluminescence) display device is provided with a plurality of organic EL elements 16 constituting a display screen, driving circuits 14, 15, 31, 32 and 33 which drive the plurality of the organic EL elements 16 in accordance with a video signal. These driving circuits 14, 15, 31, 32 and 33 include control parts 20 and 34 which increase the luminance of the plurality of the EL elements 16 with respect to the reduction of luminous efficiency generated in the elements 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an organic EL (Ele)
The present invention relates to an image display device using a light emitting element such as a Ctro Luminescence element as a display pixel.

[0002]

2. Description of the Related Art In recent years, an organic EL display device has attracted attention as a monitor display of a portable information device such as a mobile phone because of its features of lightness, thinness, and high brightness. A typical organic EL display device is configured to display an image by a plurality of display pixels arranged in a matrix. In this organic EL display device, a plurality of scanning lines are arranged along a row of the display pixels, a plurality of signal lines are arranged along a column of the display pixels, and a plurality of pixel switches are connected to the scanning lines and the signal lines. Are arranged in the vicinity of the intersection of. Each display pixel includes an organic EL element, a driving transistor connected in series to the organic EL element between a pair of power terminals, and a capacitor for holding a gate voltage of the driving transistor. Each pixel switch becomes conductive in response to a scanning signal supplied from the corresponding scanning line, and applies a video signal supplied from the corresponding signal line to the gate of the driving transistor. The drive transistor supplies a drive current according to the video signal to the organic EL element.

An organic EL device has a structure in which a light emitting layer, which is a thin film containing a red, green, or blue fluorescent organic compound, is sandwiched between a cathode electrode and an anode electrode, and electrons and holes are injected into the light emitting layer. These are recombined to generate excitons, and light is emitted by light emission generated when the excitons are deactivated. The anode electrode is a transparent electrode made of ITO or the like, and the cathode electrode is a reflective electrode made of a metal such as aluminum. With this configuration, the organic EL
The device is 100-100,000 even with an applied voltage of 10 V or less.
A luminance of about cd / m ² can be obtained.

[0004]

By the way, the luminous efficiency of the organic EL element decreases depending on the luminous time (energization time) or the luminous amount. The conventional organic EL element has a short life until the luminance is reduced by half due to the decrease in luminous efficiency, and it has been difficult to continue using the display device for a long period of time.

An object of the present invention is to provide an image display device that can extend the life of a light emitting element.

[0006]

According to the present invention, there are provided a plurality of light emitting elements constituting a display screen, and a driving circuit for driving the plurality of light emitting elements in response to a video signal. An image display device is provided that includes a control unit that increases the luminance of these light-emitting elements in response to a decrease in luminous efficiency caused by the light-emitting elements.

In this image display device, when the luminous efficiency of a plurality of light emitting elements is reduced, the control unit increases the luminance of the light emitting elements. In this manner, the decrease in luminous efficiency is compensated, so that the life of the light emitting element can be extended until the decrease in luminous efficiency cannot be compensated. Therefore, the image display device can be used for a longer period.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an organic EL display according to an embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows the structure of the organic EL display device, and FIG. 2 shows a part of the structure of the organic EL display device shown in FIG. 1 in more detail. The organic EL display device is an organic EL panel 1.
0 and an external driving circuit 3 for driving the organic EL panel 10
0.

The organic EL panel 10 has a plurality of display pixels PX arranged in a matrix for displaying an image on an insulating substrate such as glass, and a plurality of scans arranged along the rows of the display pixels PX. Line 11, these display pixels PX
A plurality of signal lines 12, a plurality of pixel switches 13, which are respectively disposed near intersections of the scanning lines 11 and the signal lines 12, a scanning line driver 14 for driving the plurality of scanning lines 11, And a signal line driver 15 for driving the plurality of signal lines 12. Each display pixel PX
Denotes an organic EL element 16, a pair of power terminals DVDD, DVS
The drive transistor 1 which is connected in series to the organic EL element 16 between the S
7 and a capacitor 18 for holding the gate voltage of the driving transistor 17. Power supply terminal DV
DD and DVSS are set to potentials of, for example, +12.5 V and 0 V by the power supply voltage VEL supplied from the external drive circuit 30.

Each pixel switch 13 is formed of, for example, an N-channel thin film transistor, is controlled by a scanning signal supplied from the corresponding scanning line 11, applies a video signal supplied from the corresponding signal line 12 to the gate of the driving transistor 17, and Then, the video signal is written to the capacitor 18. The driving transistor 17 supplies a driving current Id corresponding to the video signal to the organic EL element 16. The organic EL element 16 has a structure in which a light emitting layer, which is a thin film containing a fluorescent organic compound, is sandwiched between a cathode electrode and an anode electrode.
An exciton is generated by injecting electrons and holes into the light emitting layer and recombining them, and light is emitted by light emission generated when the exciton is deactivated.

Here, for example, the N-channel thin-film transistor forming the pixel switch 13 and the P-channel thin-film transistor forming the driving transistor 17 are formed by using a polycrystalline silicon film for a semiconductor layer.

The scanning line driver 14 and the signal line driver 15 are composed of an N-channel thin-film transistor or a P-channel thin-film transistor using a polycrystalline silicon film formed in the same process as the pixel switch 13 and the driving transistor 17, and have the same insulation. It is formed integrally on the substrate.

The external drive circuit 30 is formed on a printed circuit board disposed outside the organic EL panel 10. The external drive circuit 30 converts a digital video signal into an analog signal and supplies the signal to a signal line driver 15. The controller 32 controls the scanning line driver 14, the signal line driver 15, and the DAC 31.
And a DC / DC power supply for generating and supplying each power supply voltage for driving the organic EL panel 10 from a DC power supply voltage supplied from the outside.
And a DC converter 33. The controller 32 receives a digital video signal and a synchronization signal via an arithmetic circuit 34 for correcting a digital video signal from the outside, and controls a vertical scanning control signal for controlling vertical scanning timing, a horizontal scanning control signal for controlling horizontal scanning timing, and A DAC control signal synchronized with the horizontal and vertical scanning timing is generated based on the synchronization signal, and the vertical scanning control signal, the horizontal scanning control signal, and the DAC control signal are respectively supplied to the scanning line driver 14, the signal line driver 15, and the DAC 31.
And supplies a digital video signal to the DAC 31 in synchronization with the horizontal and vertical scanning timings.

The DAC 31 converts the digital video signal into an analog format under the control of the DAC control signal and supplies the analog video signal to the signal line driver 15. The signal line driver 15 controls the DAC 31 in each horizontal scanning period by controlling the horizontal scanning control signal.
From the analog video signal Vsi
g is supplied to the plurality of signal lines 12 in parallel. The scanning line driver 14 sequentially supplies the scanning signals to the plurality of scanning lines 11 in each frame period under the control of the vertical scanning control signal. That is, each scanning line is driven by a scanning signal in one horizontal scanning period (1H) different from each other. The pixel switches 13 in each row are turned on for one horizontal scanning period by the scanning signal supplied from the corresponding scanning line 11, and are turned off until the scanning signal is again supplied one frame period later. The driving transistor 17 for one row supplies the driving current Id corresponding to the analog video signal Vsig supplied from the plurality of signal lines 12 by the conduction of the pixel switches 13 to the organic EL element 16.
Respectively. This video signal Vsig is written to the capacitor 18 and is updated for one frame period (1
F) It is updated every time.

The organic EL panel 10 further includes a plurality of dummy display pixels PX 'arranged in parallel to the columns of the display pixels PX in a light-shielding area outside the display area DA formed by a matrix array of the plurality of display pixels PX. It has. Further, the auxiliary signal line 12 'is arranged along the dummy display pixel PX' and is disposed near the intersection of one auxiliary signal line 12 ', a plurality of scanning lines 11, and the auxiliary signal line 12' for driving the dummy display pixel PX '. Multiple auxiliary pixel switches 1
3 ′, and a voltage detection unit 20 connected to the plurality of dummy display pixels PX ′. On the other hand, the external drive circuit 30 further receives a digital video signal and a synchronization signal obtained from an external computer or the like, performs an arithmetic operation on the video signal synchronized with the synchronization signal, and outputs the result to the controller 3.
And an arithmetic circuit 34 for supplying the data to the second circuit 2.

Each dummy display pixel PX 'has a structure equivalent to the display pixel PX, and is provided between the dummy organic EL element 16' and a pair of power terminals DVDD and DVSS.
A driving transistor 17 ', which is a P-channel thin film transistor, connected in series to an element 16', and a capacitor 1 for holding a gate voltage of the driving transistor 17 '
8 '. The scanning line 11 is connected to the gate of the auxiliary pixel switch 13 'corresponding to the display pixel PX, and the auxiliary signal line 12' is connected to the auxiliary pixel switch 13 '.
Are connected to the gates of the drive transistors 17 'of the plurality of dummy display pixels PX'.

Each of the auxiliary pixel switches 13 'is formed of, for example, an N-channel thin film transistor.
And a dummy signal VC supplied from the auxiliary signal line 12 'when driven by the scanning signal supplied through the gate of the driving transistor 17'. The driving transistor 17 'has a driving current Id' corresponding to the dummy signal VC.
Is supplied to the dummy organic EL element 16 '. For example, the dummy signal VC is a signal that causes the dummy organic EL element 16 ′ to emit light at the maximum gradation, and all the dummy organic EL elements 16 ′
Supplied to

The voltage detecting section 20 detects each dummy display pixel PX '
A plurality of voltage detectors connected to both terminals of the corresponding dummy organic EL element 16 ′ and detecting a terminal voltage generated between both terminals of the corresponding dummy organic EL element 16 ′ by the drive current Id from the corresponding drive transistor 17 ′. 20A. In the arithmetic processing of the arithmetic circuit 34, the gradation value of the digital video signal is corrected based on the average value of the detection results of the voltage detector 20A, and is supplied to the controller 32 together with the synchronization signal. The controller 32 controls the scanning line driver 14 and the signal line driver 1 in accordance with the video signal and the synchronization signal.
5 to control the driving transistors 1 of the plurality of display pixels PX.
7 adjust the drive current of the corresponding organic EL element 16.

FIG. 3 shows a temporal change of the luminous efficiency and the voltage between terminals of the organic EL element. The luminous efficiency of each organic EL element decreases with the passage of time, and the voltage between terminals of the organic EL element increases as the luminous efficiency decreases.

Since each dummy organic EL element 16 'has a structure equivalent to that of the organic EL element 16, the luminous efficiency of the dummy organic EL element 16' is reduced similarly to the organic EL element 16, and the dummy organic EL element 16 ' The terminal-to-terminal voltage increases as the luminous efficiency decreases.

Therefore, in the present invention, the voltage between the terminals of the dummy organic EL element 16 'is detected, and when the luminous efficiency is reduced, the video signal for driving the display pixel PX is corrected.

The voltages between the terminals of the dummy organic EL elements 16 'are respectively detected by a plurality of voltage detectors 20A. For example, the voltages between the terminals of the plurality of dummy organic EL elements 16' are reduced as the luminous efficiency is reduced as shown in FIG. , The gradation value of the digital video signal is corrected by the arithmetic circuit 34 so as to uniformly increase the drive current of the plurality of organic EL elements 16 in response to the increase of the average value of the inter-terminal voltage. . As a result, the brightness of each organic EL element 16 is increased so as to compensate for the decrease in luminous efficiency.

In the organic EL display device of the above embodiment,
The plurality of organic EL elements 16 are provided as a plurality of light emitting elements forming a display screen. Scan line driver 14, signal line driver 15, controller 32, DA converter 3
1, DC / DC converter 33, scanning line 11, signal line 1
2. The pixel switch 13, the drive transistor 17, and the capacitor 18 are provided as a drive circuit that drives a plurality of light emitting elements in accordance with a video signal. The drive circuit includes a dummy organic EL element 16 ′, a voltage detection section 20, and an arithmetic circuit 34 as a control section that increases the luminance of the plurality of organic EL elements 16 in response to a decrease in luminous efficiency caused by the plurality of organic EL elements 16. Having. The dummy organic EL element 16 ′ has a structure substantially equivalent to the plurality of organic EL elements 16 and is provided as a dummy light emitting element driven by a predetermined drive current. The arithmetic circuit 34 is provided to detect the voltage between the terminals of the dummy organic EL element 16 ′ which increases with the decrease in the luminous efficiency generated in the organic EL element 16 ′. Is provided in order to adjust the drive current of the plurality of organic EL elements 16 by correcting.

According to this configuration, even if the luminous efficiency of the organic EL element 16 decreases, the luminance of the organic EL element 16 is maintained by correcting the gradation value of the video signal. Organic E
The life until the luminance of the L element 16 is reduced by half is 3
If it is 000 hours, the half of the luminance can be delayed to about 7000 hours. The life of the organic EL element 16 can be extended more than twice as long as the case where the decrease in the luminous efficiency is not compensated. Therefore, the organic EL display device can be used for a longer period.

The present invention is not limited to the above-described embodiment, but can be variously modified without departing from the gist thereof.

In the above embodiment, a plurality of dummy organic
Although the L element 16 ′ is disposed on the organic EL panel 10, a single organic EL element 16 ′ is disposed and the gradation value of the video signal is corrected only by the voltage between the terminals of the single organic EL element 16 ′. You may do so.

In the above embodiment, the same dummy signal VC is supplied to all the dummy organic EL elements 16 '. However, the present invention is not limited to this.
6 ′ may be supplied with different dummy signals VC. For example, dummy signals VC corresponding to each gradation from the minimum gradation to the maximum gradation may be supplied.

An analog video signal supplied to an arbitrary signal line may be used as the dummy signal VC. For example, an analog video signal of the organic EL element 16 adjacent to the dummy organic EL element 16 'may be used. .

Further, a plurality of groups of organic EL elements in which the plurality of organic EL elements 16 are constituted by, for example, light emitting layers having different characteristics
In the case of being constituted by elements, a plurality of dummy organic EL elements 16 'corresponding to the characteristics of each group may be constituted. By making each of the dummy organic EL elements 16 'have a structure and a light emission characteristic substantially equivalent to those of the organic EL elements 16 of the corresponding group, it is possible to compensate for a decrease in light emission efficiency for each group according to the element characteristics of each group. That is, the dummy organic EL element 1
6 ′ is driven by a predetermined drive current, and the voltage detection unit 20 is configured such that the plurality of dummy organic EL elements 16 ′ increase in accordance with the decrease in luminous efficiency caused by each of the plurality of dummy organic EL elements 16 ′ similarly to the plurality of organic EL elements 16 The voltage between terminals of the EL elements 16 ′ is detected, and the current adjusting unit adjusts the drive currents of the organic EL elements 16 in a plurality of groups for correcting a video signal based on the detection result of the voltage detecting unit 20. Can be.

In particular, when the organic EL elements 16 of each group are configured to emit light of the corresponding emission color, dummy organic EL elements 16 'corresponding to the respective emission colors are formed, and the respective dummy signals correspond to these emission signals. The values may be set to different predetermined values depending on the luminance balance between colors. Organic EL
Since the luminous efficiency of the element 16 is not generally reduced uniformly between the material of the luminescent layer and the different luminescent colors, such a configuration is preferable to maintain the white balance.

In the above-described embodiment, the video signal is corrected based on the voltage between the terminals of the dummy organic EL element 16 ′ in order to increase the luminance of the plurality of organic EL elements 16.
For example, the power supply voltage VEL may be increased. Further, when desired luminance is obtained by limiting the light emission time of the dummy organic EL element in the initial state, it is possible to lengthen the driving time to increase the luminance.

Further, the above-described embodiments and modifications have been described using the organic EL element 16 and the dummy organic EL element 16 ′. It may be replaced with a light emitting element.

[0034]

According to the present invention, it is possible to provide an image display device which can extend the life of the light emitting element.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a configuration of an organic EL display device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a part of the organic EL display device shown in FIG. 1 in more detail.

FIG. 3 is a graph showing temporal changes in luminous efficiency and inter-terminal voltage of the organic EL element shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 16 ... Organic EL element 16 '... Dummy organic EL element 17 ... Driving transistor 17' ... Driving transistor 18 ... Capacitor 18 '... Capacitor 20 ... Voltage detection circuit 20A ... Voltage detector 31 ... DAC 32 ... Controller 33 ... DC / DC converter 34 arithmetic circuit PX display pixel PX 'dummy display pixel DVDD, DVSS power supply terminal

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // H05B 33/14 H05B 33/14 A

Claims (7)

[Claims] 1. A plurality of light-emitting elements constituting a display screen;
A driving circuit for driving the plurality of light emitting elements in response to a video signal, wherein the driving circuit controls the luminance of the plurality of light emitting elements to increase with respect to a decrease in luminous efficiency caused by the plurality of light emitting elements. An image display device comprising a unit. 2. A control device comprising: a dummy light emitting element having a structure substantially equivalent to the plurality of light emitting elements and driven by a predetermined drive current; a voltage detecting unit detecting a voltage between terminals of the dummy light emitting element; The image display device according to claim 1, further comprising a current adjustment unit that adjusts a drive current of the plurality of light emitting elements based on a detection result of the detection unit. 3. The image display device according to claim 2, wherein the current adjustment unit includes a signal correction unit that corrects the video signal based on a detection result of the voltage detection unit. 4. The image display according to claim 2, wherein the current adjustment unit is configured to correct a voltage between terminals of the plurality of light emitting elements based on a detection result of the voltage detection unit. apparatus. 5. The plurality of light emitting elements are constituted by a plurality of groups of light emitting elements, and the control unit has a structure substantially equivalent to that of the corresponding group of light emitting elements and is driven by a predetermined driving current with a plurality of dummy light emitting elements. A voltage detecting unit that detects a terminal voltage of the plurality of dummy light emitting elements, which rises with a decrease in luminous efficiency caused by each of the plurality of dummy light emitting elements, similarly to the plurality of groups of light emitting elements, and The image display device according to claim 1, further comprising a current adjustment unit that adjusts a drive current of each of the plurality of groups of light emitting elements based on a detection result. 6. The image display device according to claim 5, wherein the current adjustment unit includes a signal correction unit that corrects the video signal based on a detection result of the voltage detection unit. 7. A light emitting element of each group is configured to emit light of a corresponding light emitting color, and drive currents of the plurality of dummy light emitting elements are set to different predetermined values depending on a luminance balance between the light emitting colors. The image display device according to claim 5, wherein: