JP3717894B2 - EL display drive device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a drive device for driving a display composed of EL (electroluminescence) elements based on a video signal.
[0002]
[Prior art]
For example, as shown in FIG. 4, 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 on a glass substrate 11 in this order. Have When electrons and holes (holes) are respectively injected from the cathode 16 and the anode 12 by the power source 17, the electrons and holes are recombined in the organic light emitting layer 14, whereby the organic molecules are excited, and the original state Light is emitted from the organic light emitting layer 14 when trying to return to the (ground state). Not all of the energy when electrons and holes are recombined is released to the outside as light, but part of it becomes heat and raises 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, similar to LCDs. The passive drive type has a simple matrix configuration in which light can be emitted at a portion where the anode and the cathode intersect, and is lit only when a vertical line is selected. On the other hand, as shown in FIG. 5, the active drive type is formed by disposing a switching TFT 31 in each organic EL element 30, and a horizontal (H) shift register 21 for selecting a pixel (row) and a line (column). The video signal at that time is written in the organic EL element 30 selected by the vertical (V) shift register 22 for selecting the video signal), and the video signal component (voltage) is held by the capacitor C attached to each organic EL element 30. Each organic EL element 30 is lit for a predetermined period (see Patent Document 1).
[0004]
Here, when an NTSC image is displayed on an organic EL display having 320 horizontal pixels and 240 vertical pixels, the vertical shift register 22 includes a line number 22 and a line number as shown in FIG. An STV (vertical start signal) is input so that the top line of the display is selected at the timing of a horizontal period pulse CKV (vertical control clock) corresponding to 285. Assuming that the effective video period is 80% of the horizontal period, the horizontal shift register 21 receives a pulse CKH (horizontal control clock) 320 / 0.8 = 400 times the horizontal period as shown in FIG. STH (horizontal start signal) is input so that the leftmost pixel of each line of the display is selected immediately after the start of the effective video period.
[0005]
[Patent Document 1]
JP-A-2002-40963 [0006]
[Problems to be solved by the invention]
For example, when an image of a white lattice pattern on a black background is continuously displayed on the organic EL display driven as described above, the temperature does not increase 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 the temperature continues to rise and the luminance decreases. If the image is left as it is, there is no sense of incongruity in the image, but if, for example, a gray image is displayed after this image, the organic EL element whose temperature has risen is lower in brightness than the organic EL element whose temperature has not increased. As a result, the black lattice pattern appears thin on a white background.
[0007]
In view of the above circumstances, the present invention provides a drive device for an EL display capable of suppressing temperature rise of EL elements to reduce temperature unevenness between EL elements and thereby reducing screen brightness unevenness of a display composed of EL elements. The purpose is to provide.
[0008]
[Means for Solving the Problems]
In order to solve the above-described problems, an EL display driving apparatus according to the present invention is a driving apparatus that drives a display composed of EL elements based on a video signal. Means for forming a non-light emitting state in the element, and correcting means for correcting the luminance of the video signal so that the input image luminance is higher as the EL element has a shorter video display time to form the non-light emitting state. It is characterized by having.
[0009]
With the above configuration, since a non-light emitting state is formed in all EL elements using the vertical blanking period, a cooling period is given to all the EL elements, and the temperature rise of the EL elements can be suppressed, The temperature unevenness between the EL elements is reduced, and the screen brightness unevenness of the display is reduced. A change in display luminance between display areas on the display due to the video display time of each EL element being different by forming the non-light emitting state is eliminated by the correcting means.
[0010]
The correction means may comprise an A / D conversion circuit that converts the video signal into a digital video, and an arithmetic unit that executes arithmetic processing for brightness correction on the digital video.
[0011]
The correction means includes a variable gain amplifier that inputs the video signal, amplifies the video signal with an arbitrary gain, and outputs the amplified video signal. The variable gain amplifier changes the gain based on a vertical synchronization signal of the video signal. It may be configured.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
(Embodiment 1)
Hereinafter, an EL display driving apparatus according to an embodiment of the present invention will be described with reference to FIGS. Note that the organic EL display to be driven by the drive device of this embodiment has the same configuration as that shown in FIG.
[0013]
As shown in FIG. 2, the driving apparatus of this embodiment includes an A / D conversion circuit 1 that inputs a video signal (in this embodiment, an NTSC video signal) and generates digital video data. A digital signal processor (DSP) 2 that performs correction processing on the digital video data, a D / A converter 3 that converts the corrected digital video data into an analog video signal, an organic EL display 4, and a timing controller 5 are provided.
[0014]
The timing controller 5 controls the output of STV and CKV of the vertical shift register 22 (see FIG. 5) in the organic EL display 4. As shown in FIGS. 1A and 1B, the timing controller 5 inserts a 20H-width pulse into the STV corresponding to the vertical blanking period (21H period). The speed is increased to 12 times over the 21H period (21H period × 12 = 252). Since the video signal in the vertical blanking period is at the black level, black is written in all the organic EL elements during this period, and the organic EL display 4 is in the period until the next video is written by the original line selection pulse (STV). It will continue to display black. That is, since all the organic EL elements do not receive any energy during the vertical blanking period, the temperature falls, and the temperature rise can be suppressed compared with the case where white is continuously displayed, and thus the brightness unevenness due to the brightness drop can be reduced. .
[0015]
However, in this state, the video signal is displayed on the top line in one frame period at 483/525 (21H period × 2 (field) = 42 is subtracted from 525, 483 is obtained). The video signal is displayed at the bottom line of 44/525 ((21H period + 1 (own period)) × 2 (field) = 44). turn into.
[0016]
The digital signal processor (DSP) 2 makes the luminance uniform by correcting the video signal input to the organic EL panel 4 at the input stage in order to eliminate the lowering of luminance toward the lower side of the screen. Specifically, when k is a correction coefficient, arithmetic processing is performed by multiplying the video signal written in the top line by k · 525/483 (≈k · 1), and the result is written in the bottom line. The video signal is corrected to an appropriate luminance by multiplying each line by the reciprocal of the luminance reduction degree so as to be multiplied by k · 525/44 (≈k · 12). More specifically, in the case of a video signal corresponding to an intermediate line, correction by multiplying by about k · 6 is performed.
[0017]
(Embodiment 2)
Another embodiment of the present invention will be described with reference to FIG. The circuit shown in FIG. 3 shows an analog circuit example in which a video signal is passed through the variable gain amplifier 6 and the gain of the variable gain amplifier is controlled by a vertical sawtooth wave. That is, the period of the vertical sawtooth wave corresponds to the pixel writing period of the organic EL display 4, and the voltage value change of the vertical sawtooth wave corresponds to the pixel position of each organic EL element of the organic EL display 4 (luminance reduction degree). Therefore, by adjusting the gain of the variable gain amplifier with such a vertical sawtooth wave, the organic EL element whose video display time is shortened becomes higher in input video luminance, and the display luminance between the display areas on the organic EL display 4 is increased. The change can be eliminated.
[0018]
In the above embodiment, the case where an NTSC image is displayed on an organic EL display having 320 horizontal pixels and 240 vertical pixels is described. However, the present invention is not limited to this. It is not limited to the display of NTSC video.
[0019]
【The invention's effect】
As described above, according to the present invention, since the non-light emitting state is formed in all the EL elements using the vertical blanking period, the cooling period is given to all the EL elements. An increase in temperature is suppressed, temperature unevenness between EL elements is reduced, and display screen brightness unevenness is reduced.
[Brief description of the drawings]
FIGS. 1A and 1B are explanatory diagrams showing waveforms of signals to an EL display in an EL display driving apparatus according to an embodiment of the present invention.
FIG. 2 is a block diagram showing a driving device composed of a digital circuit.
FIG. 3 is a block diagram showing a driving device configured with an analog circuit.
FIG. 4 is a cross-sectional view showing an organic EL element.
FIG. 5 is a circuit diagram showing an active drive type organic EL display;
FIG. 6 is an explanatory diagram showing waveforms of drive signals to an organic EL display in a conventional drive device.
FIG. 7 is an explanatory diagram showing a relationship between a video signal in one horizontal period supplied to the organic EL display and each drive signal.
[Explanation of symbols]
1 A / D conversion circuit 2 Digital signal processor (DSP)
3 D / A conversion circuit 4 Organic EL display 5 Timing controller 6 Variable gain amplifier

Claims (3)

In a driving device for driving a display composed of EL elements whose luminance is lowered due to a temperature rise based on a video signal, the frequency of a vertical control clock given to the display during a vertical blanking period of the video signal is written into an effective video signal A means for forming a non-light emitting state in all the EL elements by writing a black level video signal in the vertical blanking period to all the EL elements higher than the frequency of the vertical control clock at the time, and for forming the non-light emitting state And a correction means for correcting the luminance of the video signal so that the input video luminance becomes higher as the EL element has a shorter video display time.   2. The EL display driving apparatus according to claim 1, wherein the correction means includes an A / D conversion circuit for converting the video signal into a digital video, and an arithmetic operation for performing luminance correction on the digital video. And an EL display driving device.   2. The driving device for an EL display according to claim 1, wherein the correction means includes a variable gain amplifier that inputs the video signal, amplifies the video signal with an arbitrary gain, and outputs the amplified video signal. An EL display driving apparatus configured to change the gain based on a synchronization signal.

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