JP2003280590A - Organic el display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL (electroluminescence) display device capable of preventing degradation of brightness or unevenness of luminance from being caused by a voltage drop in a power supply line. <P>SOLUTION: The organic EL display device provided with a color organic EL display comprises a mean brightness calculation means for calculating mean brightness of an input video signal for each vertical period, a voltage drop calculation means for calculating a power source voltage drop in a power supply line at each pixel position in the color organic EL display based on the mean brightness calculated by the mean brightness calculation means, and a correction means for correcting the input video signal so as to supplement the degradation of brightness due to the power supply voltage drop based on the power supply voltage drop at each pixel calculated by the voltage drop calculation means. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic EL display device having an organic electroluminescence (EL) display.

[0002]

2. Description of the Related Art Organic electroluminescence (EL) devices are used in what are expected as next-generation flat panel displays because they have various advantages over liquid crystal displays (LCD) which are the mainstream of flat panel displays at present. There is an organic EL panel.

As is well known, the structure of an organic EL element is a structure in which a hole transport layer, a light emitting layer, an electron transport layer and a cathode are sequentially laminated on a glass substrate on an anode (ITO). Further, the organic EL display can be roughly classified into a passive matrix type and an active matrix type, depending on the driving method, like the LCD.

The passive matrix type is composed of a simple matrix in which the portion where the anode and the cathode intersect can emit light. On the other hand, the active matrix type has a switching TFT arranged in each pixel.

Since the organic EL display is a self-luminous type, it does not require a backlight and has an advantage that it can realize lower power consumption than the LCD as a whole. However, regardless of whether it is a passive matrix type or an active matrix type, the organic EL element itself is current driven,
A relatively large amount of current is required during driving as compared with a liquid crystal element. Therefore, there is a problem that a pixel located farther from the current (voltage) supply source has lower brightness due to a voltage drop due to the power supply line.

It is assumed that the organic EL display power supply line having 320 horizontal pixels and 240 vertical pixels is wired as shown in FIG.

In FIG. 1, W1 indicates a range of 200 pixels in the horizontal direction from the left end of the organic EL display, and W3 indicates a range of 100 pixels in the horizontal direction from the right end of the organic EL display. It is assumed that the power supply line for the range W2 of 20 pixels in the horizontal direction between the range of W1 and the range of W3 is directly connected to the power supply source 100.

It is assumed that the resistance of the power supply line is uniform. That is, the resistance of the wiring for one pixel distance is r. If the same amount of current i is consumed in each organic EL element (pixel), it is a position within the range W1 and
The voltage drop (horizontal voltage drop) Vn1 at the point E, which is n pixels in the horizontal direction from the left end of the display and is closest to the power supply source 100 in the vertical direction, is expressed by the following equation (1).
It is represented by.

[0009]   Vn1 = {240ri ・ W1 (W1-1) / 2}-{240ri ・ n (n-1) / 2} (1)

{240ri · W1 (W1-1) in the above formula (1)
/ 2} indicates the voltage drop due to the wiring of the power supply line in the entire range W1, and {240ri · n (n-1) / 2} is the range from the left end of the organic EL display to n pixels in the horizontal direction. The voltage drop due to the wiring of the power supply line is shown.

The position within the range W3, which is the organic E
The voltage drop (horizontal voltage drop) Vn3 at a position horizontally n'pixels away from the right end of the L display and closest to the power supply source 100 in the vertical direction is expressed by the following equation (2).
It is represented by.

[0012]   Vn3 = {240ri ・ W3 (W3-1) / 2}-{240ri ・ n '(n'-1) / 2} (2)

{240ri · W3 (W3-1) in the above equation (2)
/ 2} indicates the voltage drop due to the wiring of the power supply line in the entire range W3, and {240ri · n '(n'-1) / 2} is from the right end of the organic EL display to the n'pixel in the horizontal direction. It shows the voltage drop due to the wiring of the power supply line in the range.

In the range W2 between W1 and W3,
The voltage drop Vn2 in the horizontal direction becomes zero. Therefore, the voltage drop at each horizontal position and the position closest to the power supply source 100 in the vertical direction is as shown in FIG.

The voltage drop (vertical voltage drop) Vm at a point F at an arbitrary position in the horizontal direction and at a distance of m pixels in the vertical direction from the upper end of the organic EL display is expressed by the following equation (3).

[0016] Vm = {240 (240-1) ri / 2}-{m (m-1) ri / 2} (3)

{240 (240-1) ri / 2} in the above equation (3)
Indicates the voltage drop due to the wiring of the power supply line in the vertical direction at any position in the horizontal direction, and {m (m-1) ri / 2} is the organic E
It shows the voltage drop due to the wiring of the power supply line in the range from the upper end of the L display to m pixels in the vertical direction.

That is, the voltage drop due to the power supply line at each vertical position at any horizontal position is as shown in FIG.

Therefore, in the range W1, G which is n pixels in the horizontal direction and m pixels in the vertical direction is separated from the upper left corner of the screen.
The voltage drop Vnm1 at the point is expressed by the following equation (4).

[0020]   Vnm1 = Vn1 + Vm = {240ri ・ W1 (W1-1) / 2}-{240ri ・ n (n-1) / 2}                 + {240 (240-1) ri / 2}-{m (m-1) ri / 2}… (4)

Further, within the range W3, the voltage drop Vnm3 at the point separated from the upper right end of the screen by n'pixels in the horizontal direction and m pixels in the vertical direction is expressed by the following equation (5).

[0022]   Vnm3 = Vn3 + Vm = {240ri ・ W3 (W3-1) / 2}-{240ri ・ n '(n'-1) / 2}                 + {240 (240-1) ri / 2}-{m (m-1) ri / 2}… (5)

In the range W2 between W1 and W3,
Voltage drop V at the point m pixels vertically from the top of the screen
nm2 is represented by the following equation (6).

[0024]   Vnm2 = Vn2 + Vm = {240 (240-1) ri / 2}-{m (m-1) ri / 2} (6)

As shown in FIGS. 2 and 3, the horizontal direction
The maximum value of voltage drop is 4.8 × 10 ⁶Even though it is ri
However, the maximum vertical voltage drop is 2.8 × 10^Fourri
Therefore, the uneven brightness due to the vertical position is notable
However, the uneven brightness due to the horizontal position is
There was a problem of being conspicuous.

[0026]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an organic EL display device capable of preventing a decrease in brightness and uneven brightness due to a voltage drop due to a power supply line.

[0027]

According to a first aspect of the present invention, in an organic EL display device having a color organic EL display, an average luminance calculating means for calculating an average luminance of an input video signal every vertical period, Based on the average brightness calculated by the average brightness calculation means, a voltage drop calculation means for calculating a power supply voltage drop due to a power supply line for each pixel position in the color organic EL display, and each calculated by the voltage drop calculation means It is characterized in that a correction means is provided for correcting the input video signal so as to complement the luminance decrease due to the power supply voltage drop based on the power supply voltage drop for each pixel.

According to a second aspect of the invention, in the color organic EL display according to the first aspect, the correction means is
The video input signal for each pixel is characterized in that the input video signal is corrected such that the larger the power supply voltage drop calculated for that pixel, the higher the light emission luminance of that pixel.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

FIG. 4 shows the configuration of a signal processing circuit provided in an organic EL display device having an organic EL display.

The input video signal is digitized by the A / D converter 1 and then input to the DSP 2. DSP2
Performs a correction process for preventing uneven brightness in order to prevent uneven brightness from occurring due to a voltage drop due to the power supply line. Video data corrected by DSP2 is A / D
After being converted into an analog signal by the converter 3, the organic E
It is sent to the L display 4.

A correction process for preventing uneven brightness will be described. In the following description, it is assumed that the gradation of white is 0 and the gradation of black is 255.

Assuming that the wiring of the power supply line of the organic EL display 4 is as shown in FIG. 1, the voltage drop at the point A is the largest and the luminance drop is the largest at the point A. When the voltage drop Va from the voltage V0 of the power supply source 100 to the point A is subtracted from the video signal component Vsa at the point A, the power supply voltage (V0-Va) at the point A and the signal voltage (Va).
s-Va) is equal to the difference (V0-Vsa) between the power supply voltage and the signal voltage when there is no voltage drop.

V obtained by the above equations (4), (5) and (6)
Since nm1, Vnm3, and Vnm2 are voltage drops when it is assumed that the current consumption in each pixel is the same, ri
If the average luminance level k is used instead of / 2, the above equations (4), (5), and (6) become the following equations (7), (8), and (9), respectively.

[0035]   Vnm1 = {240 W1 (W1-1) −240 n (n-1) +240 (240-1) −m (m-1)} k… (7)

[0036]   Vnm3 = {240 W3 (W3-1) -240 n '(n'-1) +240 (240-1) -m (m-1)} k (8)

Vnm2 = {240 (240-1) -m (m-1)} k (9)

Vnm1, Vnm2 and Vnm3 are collectively referred to as Vnmk
Then, for the pixels within the range of W1, the above equation (7)
Of the above formula (8) for pixels within the range of W3, and Vnm2 of the above formula (9) for pixels within the range W2 between W1 and W3. By performing correction such as subtracting from the video signal Vs of
The difference between the actual power supply voltage (V0-voltage drop) and the corrected signal voltage (Vs-Vnmk) in each pixel is the difference (V0-V) between the power supply voltage and the signal voltage when there is no voltage drop.
s) is approached.

The average brightness level k is obtained by adding the signal components of each pixel for one vertical period and dividing the addition result by the total number of pixels.

By performing the above-described correction processing on the input video signal, a current proportional to the difference voltage between the power supply voltage and the signal voltage flows through each organic EL element in the organic EL display 4. Since each organic EL element emits light with a brightness proportional to the current, the influence of the power supply voltage drop due to the wiring in each pixel is reduced, and the uneven brightness is improved.

FIG. 5 shows a configuration (functional block) of a correction processing circuit for preventing uneven brightness in the DSP 2.

In FIG. 5, V is a vertical synchronizing signal of the input video signal, H is a horizontal synchronizing signal, and D is a dot clock signal.

The correction processing circuit for preventing uneven brightness includes an average brightness level calculating section 11, a voltage drop calculating section 12 and a subtracting section 13.

The average brightness level calculator 11 calculates the average brightness level for each vertical period based on the input video data. The voltage drop calculation unit 12 includes the average brightness level calculation unit 1
The average luminance level calculated by 1 and the above equation (7),
Voltage drop Vnmk for each pixel based on (8) and (9)
To calculate. The subtraction unit 13 subtracts the voltage drop Vnmk corresponding to the pixel position from the input video data.

[0045]

According to the present invention, it is possible to prevent the decrease in brightness and the uneven brightness due to the voltage drop due to the power supply line.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing wiring of a power supply line of a color organic EL display.

FIG. 2 is a graph showing a voltage drop at each horizontal position and in a position closest to the power supply source 100 in the vertical direction.

FIG. 3 is a graph showing a voltage drop due to a power supply line at each vertical position at an arbitrary horizontal position.

FIG. 4 is a block diagram showing a configuration of a signal processing circuit provided in a display device including a color organic EL display.

FIG. 5 is a block diagram showing a configuration (functional block) of a correction processing circuit for preventing uneven brightness in the DSP 2.

[Explanation of symbols]

1 A / D converter 2 DSP 3 A / D converter 4 Organic EL display 11 Average Brightness Level Calculation Unit 12 Voltage drop calculator 13 Subtraction unit

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H05B 33/14 H05B 33/14 A

Claims (2)

[Claims] 1. In an organic EL display device having a color organic EL display, an average luminance calculating means for calculating an average luminance of an input video signal for each vertical period, and based on the average luminance calculated by the average luminance calculating means. A voltage drop calculation means for calculating a power supply voltage drop due to a power supply line for each pixel position in the color organic EL display, and a power supply voltage drop based on the power supply voltage drop for each pixel calculated by the voltage drop calculation means An organic EL display device comprising: a correction unit that corrects an input video signal so as to complement the decrease in brightness due to. 2. The correcting means corrects the video input signal for each pixel such that the larger the power supply voltage drop calculated for that pixel, the higher the emission brightness of that pixel. 2. The method according to claim 1, wherein
The organic EL display device described in 1.