JP2004246064A - El display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an EL display device which can deter the temperature of an EL element from rising and reduce temperature unevenness among EL elements to reduce screen luminance unevenness. <P>SOLUTION: An STBV as a black write select pulse is supplied to a black vertical shift register 15, a 10H period before the point of time when a picture is written with an STV as an original video write select pulse. When the STBV is supplied to the black vertical shift register 15, a black write line is selected in every 1H. On the selected black write line, a black display switch 12 is turned ON and a capacitor C connected thereto is discharged, so a non-illumination state (black display state) is entered. On a line entering a black display state, a next picture is written a 10H period later. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
[Industrial applications]
The present invention relates to an EL (electroluminescence) device that drives an EL element based on a video signal.
[0002]
[Prior art]
As shown in FIG. 3, for example, the organic EL element has a structure in which an ITO transparent anode 12, a hole transport layer 13, an organic light emitting layer 14, an electron transport layer 15, and a cathode 16 are laminated in this order on a glass substrate 11. Have. When electrons and holes (holes) are respectively injected from the cathode 16 and the anode 12 by the power supply 17, these electrons and holes are recombined in the organic light emitting layer 14, whereby the organic molecules are excited and the original state is obtained. When returning to the (ground state), light is emitted from the organic light emitting layer 14. Not all of the energy when electrons and holes are recombined is emitted to the outside as light, but part of the energy becomes heat, raising the temperature of the organic EL element. When the temperature of the organic EL element increases, the mobility of electrons and holes decreases, and the luminance decreases.
[0003]
Organic EL displays using organic EL elements can be broadly classified into passive matrix drive types and active matrix drive types, like LCDs. The passive drive type has a simple matrix configuration in which a portion where an anode and a cathode cross can emit light, and is turned on only when a vertical line is selected. On the other hand, the active drive type is configured by arranging a switching TFT 31 in each organic EL element 30 as shown in FIG. 4, and a horizontal (H) shift register 21 for selecting a pixel (row) and a line (column). ) Is written to the organic EL element 30 selected by the vertical (V) shift register 22, and the video signal component (voltage) is held by the capacitor C attached to each organic EL element 30. Thus, each organic EL element 30 is turned on for a predetermined period (see Patent Document 1).
[0004]
Here, when displaying an NTSC image on an organic EL display having a horizontal pixel count of 320 and a vertical pixel count of 240, the vertical shift register 22 stores the line number 22 and the line number as shown in FIG. At the timing of a pulse CKV (vertical control clock) having a horizontal cycle corresponding to 285, an STV (vertical start signal) is input so that the top line of the display is selected. Assuming that the effective video period is 80% of the horizontal period, a pulse CKH (horizontal control clock) of 320 / 0.8 = 400 times the horizontal period is input to the horizontal shift register 21 and the display of the display is started immediately after the start of the effective video period. STH (horizontal start signal) is input so that the leftmost pixel of each line is selected.
[0005]
[Patent Document 1]
JP-A-2002-40963
[Problems to be solved by the invention]
If, for example, an image of a white lattice pattern is continuously displayed on a black background on the organic EL display driven as described above, the temperature does not rise because the organic EL element displaying black has not received any energy. The organic EL element displaying white always receives energy, and a part of the received energy becomes heat, so that the temperature continues to rise and the brightness decreases. Although there is no discomfort in terms of the image as it is, if an attempt is made to display, for example, a one-sided gray image after this image, the luminance of the organic EL element whose temperature has increased is lower than that of the organic EL element whose temperature has not increased. The black lattice pattern looks thin on a white background.
[0007]
The present invention has been made in view of the above circumstances, and has as its object to provide an EL display device capable of suppressing a temperature rise of EL elements, reducing temperature unevenness between EL elements, and reducing screen luminance unevenness.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, an EL display device of the present invention, in an EL display device that drives an EL element based on a video signal, extracts a charge of a capacitor provided in each pixel portion including the EL element, and A switch for turning on the pixel at a predetermined time before writing the next image to each pixel unit;
[0009]
According to the above configuration, the non-light emitting state (black display state) for a predetermined period can be formed in each EL element by turning on the switch for displaying black, so that a cooling period is given to all the EL elements. Will be done. Thereby, the temperature rise of each EL element is suppressed, the temperature unevenness between the EL elements is reduced, and the screen luminance unevenness of the display is reduced. Since the above-mentioned non-light emitting state is formed a predetermined time before the next image writing to each pixel portion, a constant cooling period and a certain image display time are given to any area on the display.
[0010]
In the EL display device having the above configuration, a black display vertical shift register may be provided, and a black writing start signal may be input to the black display vertical shift register at a predetermined timing.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an organic EL display device according to an embodiment of the present invention will be described with reference to FIGS.
[0012]
FIG. 1 is a circuit diagram showing an organic EL display device of this embodiment. In this organic EL display device, a switching TFT 11 is disposed in each organic EL element 10, and a horizontal (H) shift register 13 for selecting a pixel (row) and a vertical (V) shift for selecting a line (column). The video signal at that time is written to the organic EL element 10 selected by the register 14, the video signal component (voltage) is held by the capacitor C attached to each organic EL element 10, and each organic EL element 10 is held for a predetermined period. It has a lighting structure. As a feature of the present invention, a black display switch 12 is connected to each pixel portion in parallel with the capacitor C, and the black display switch 12 is ON / OFF controlled by a black vertical shift register 15. It has a configuration.
[0013]
CKH (horizontal control clock) and STH (horizontal start signal) are supplied to the horizontal shift register 13 and CKV (vertical control clock) and STV (vertical start signal) are supplied to the vertical shift register 14 from a timing controller (not shown). The black vertical shift register 15 is supplied with CKBV (vertical black control clock) and STBV (vertical black start signal).
[0014]
Here, when an NTSC image is displayed on an organic EL display having 320 pixels in the horizontal direction and 240 pixels in the vertical direction, the vertical shift register 14 stores the signals shown in FIGS. ), STV is input at the timing of the pulse CKV of the horizontal cycle corresponding to the line number 22 and the line number 285 so that the top line of the display is selected. Assuming that the effective video period is 80% of the horizontal period, a pulse CKH of 320 / 0.8 = 400 times the horizontal period is input to the horizontal shift register 21 and immediately after the start of the effective video period, each line of the display is input. STH is input so that the leftmost pixel is selected.
[0015]
Further, the timing controller supplies STBV to the black vertical shift register 15 at the timing shown in FIG. In the example shown in FIG. 2, the black write selection pulse STBV is given to the black vertical shift register 15 10H before the video is written by the original video write selection pulse STV. When this STBV is applied to the black vertical shift register 15, a black writing line is selected every 1H. In the selected black writing line, the black display switch 12 is turned on, and the electric charge of the capacitor C connected to the switch is removed, so that a non-light emitting state (black display state) is set. In the line where the black display is made, the next video is written after a period of 10H.
[0016]
As described above, black display for 10 H periods is performed in each pixel in one field. During this 10 H period, the organic EL element 10 has not received any energy, so the temperature has dropped and white has been continuously displayed. Since the temperature rise can be suppressed as compared with the case, it is possible to reduce luminance unevenness due to luminance decrease. In the above-described black display in the 10H period, the overall luminance of the organic EL display is 505/525 ≒ 96.2% as compared with the case where the black display is not performed, and the decrease in the luminance is hardly noticeable.
[0017]
In the above-described embodiment, an example is described in which an NTSC image is displayed on an organic EL display having a horizontal pixel count of 320 and a vertical pixel count of 240. However, the present invention is not limited to such a pixel count. , NTSC video display. In the above example, the black display is performed for a period of 10H, but the present invention is not limited to such a period.
[0018]
【The invention's effect】
As described above, according to the present invention, since a non-light emitting state is formed in all EL elements for a predetermined period, a cooling period is given to all EL elements, and a rise in the temperature of the EL elements is suppressed. This has the effect of reducing temperature unevenness between EL elements and reducing screen brightness unevenness of the display.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an organic EL display device according to an embodiment of the present invention.
FIGS. 2A and 2B are explanatory diagrams showing waveforms of respective drive signals to the organic EL display device of FIG.
FIG. 3 is a cross-sectional view showing an organic EL element.
FIG. 4 is a circuit diagram showing an organic EL display device of an active drive type.
FIG. 5 is an explanatory diagram showing waveforms of respective drive signals to a conventional organic EL display device.
FIG. 6 is an explanatory diagram showing a relationship between a video signal supplied to an organic EL display device for one horizontal period and each drive signal.
[Explanation of symbols]
10 Organic EL element 11 TFT
12 Black display switch 13 Horizontal shift register 14 Vertical shift register 15 Black vertical shift register

Claims (2)

In an EL display device that drives an EL element based on a video signal, a switch that extracts a charge of a capacitor provided in each pixel unit including the EL element and displays each pixel in black is provided. An EL display device, comprising: control means for performing an ON operation at a timing before a predetermined time before video writing. 2. The EL display device according to claim 1, further comprising a vertical shift register for black display, wherein a black write start signal is input to the vertical shift register for black display at a predetermined timing. EL display device.

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