JP2004333570A - Display driving device and method for performing automatic regulation to optimum luminance under limited power consumption - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display driving device and method for performing the automatic regulation to the optimum luminance under limited power consumption. <P>SOLUTION: An organic light emitting diode display is formed in such a manner that respective pixel devices of the display are provided with drive units for driving organic light emitting diode and emitting light, the organic light emitting diode in respective pixels are communicated one another on the basis of a shared cathode system and are connected to a resistive element by shared cathode connecting lines and the other end of the resistive element is grounded. Therein, a voltage of the resistive element is changed in accordance with the change of a total current (Itotal) flowing through the shared cathode connecting line, a source-drain voltage of the drive unit is adjusted and the value of the ratio of each gray scale luminance to an image data value is changed. As a result, the picture contrast is enhanced. That is, in the display driving device and method, both of power consumption limitation and picture quality requirement can be achieved by performing automatic regulation to the optimum display luminance in accordance with different circumstances of screen image loads under limited power consumption, enhancing the image luminance and enhancing the contrast. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display driving apparatus and method for automatically adjusting a display brightness to an optimal level under a limited power consumption. The present invention relates to a display driving apparatus and method for increasing contrast by increasing the contrast.
[0002]
[Prior art]
2. Description of the Related Art Organic light emitting diode display panels (OLEDs), also called organic electroluminescence (OEL), are a new era of technology that achieves bright and clear full-color images and agile reaction speed that are difficult to achieve with other flat display technologies. .
The basic structure of an OLED is a thin transparent ITO-based material with a positive electrode, and together with a metal cathode, an organic material layer such as a hole transport layer (HTL), a light emitting layer (EL), and an electron transport layer (ETL) like a sandwich. It is a structure sandwiched between. When the battery provides an appropriate voltage (low volt number characteristic), when the holes injected into the positive electrode and the charges from the cathode combine in the light emitting layer, the organic material is excited to generate light (electroluminescence). I do. The structure of the organic layer and the selective design of the positive electrode and the negative electrode are the keys to the OLED device to sufficiently exhibit the light emitting function.
Features of an OLED self-luminous, a backlight module required, low voltage (less than 10V), and power-saving, high energy efficiency (16lm / W), (it can reach 100,00cd / ^{m 2} or more) high-intensity, short response Time (less than 2 μs), high contrast, wide vision (close to 180 °), light weight, thin shape, simple structure, low manufacturing cost, flexibility (plastic substrate) and full color capability. Therefore, the operation range of the OLED is wide, and the potential in the market is high regardless of whether the display or the lighting equipment is used. For example, it can be used in mobile phones, game machines, acoustic panels, digital cameras, PDAs, car navigation systems, digital books, information appliances, notebook computers, monitors, television receivers, and the like.
The above-mentioned OLEDs are applied to portable or hand-held electronic products, such as mobile phones, PDAs, digital cameras, digital video cameras, etc., and the components of these products have certain important characteristics, that is, Due to the demand for low power consumption, manufacturers usually require the components of such devices to operate within a limited power consumption range. As for the display device, taking a self-luminous OLED as an example, when the OLED panel displays an image screen, it is necessary to ensure that the power consumption thereof is lower than a standard value.
Since the OLED belongs to the self-luminous type, it is expected that the power consumption when the OLED panel displays the full white image screen is the largest, because at this time, the image loading is maximized (image loading). Is the sum of the image data values of the pixels of the display panel), that is, the image data of each pixel is the maximum value (if the image data is 8 bits, the maximum value is 255) Therefore, in order to reduce the power consumption below the requirement of the standard value, a well-known processing method adjusts the brightness when each pixel displays the maximum value of the image data, so that the OLED panel can display the full white image. The power consumption when displaying the screen is set equal to the power consumption limit value. FIG. 1 is a diagram showing the relationship between luminance and image data generated by each known pixel. When the power consumption when the OLED panel displays a full white image screen is adjusted to be equal to the power consumption limitation value, The luminance generated by each pixel is defined as Lmax of the luminance when the image data displayed by each pixel is the maximum, and when displaying other image data values, for example, n, the luminance Ln is Ln = n × (Lmax / 255) It becomes.
Further, the basic definition of the image contrast ratio (Contrast Ratio; CR) is a ratio of the maximum value of the image display luminance to the minimum value of the image display luminance, and its display formula is CR = Lmax × Lmin. Although the above-described known method can ensure that the power consumption of the OLED panel when displaying the image screen is lower than the standard value, the displayed image contrast ratio is limited.
Also, Patent Document 1 provides an image data calculation device, which is applied to a self-luminous flat display such as an OLED or PDP, the purpose of which is to automatically display the display under limited power consumption based on different image load conditions. The purpose of the present invention is to modulate the display brightness so as to meet power consumption and image quality requirements.
The principle used in Patent Document 1 is as follows. First, the image load is divided into five areas according to the degree of lightness, and the five areas use different coefficients and curves to adjust the original image data values. After the adjustment, the display is further performed on the OLED panel, so that the power consumption is lower than the standard value when any image screen is displayed, and the optimum luminance display can be performed based on different image load conditions. In addition to the adjustment, the power consumption and the image quality need to be met.
Further, Patent Document 2 provides a current control circuit device, detects a magnitude of a current flowing from a power supply to an active matrix organic light emitting display panel power supply line, and detects that a current increase is larger than a set value. , Thereby reducing the power supply line voltage of the active matrix organic light emitting display panel so that the operation of the active matrix organic light emitting display can be performed within a limited power consumption.
[0003]
[Patent Document 1]
US Patent No. 6,380,943 [Patent Document 2]
JP-A-2002-251167
[Problems to be solved by the invention]
The main object of the present invention is to solve the above-mentioned drawbacks of the prior art and to eliminate the drawbacks, and the present invention provides an optimum display brightness under limited power consumption according to different screen image load conditions. Automatically adjust to enhance image brightness and contrast while meeting power consumption and image quality requirements.
The present invention connects the organic light emitting diode elements in each pixel in the display to each other in a shared cathode manner, connects the shared cathode to a resistance element, grounds another end of the resistance element, and connects the organic light emitting diode in each pixel. The anode of the diode element is connected to a power supply line (Vdd Supply Line) via a drive unit. When the screen image load is large, the sum of the currents passing through the organic light emitting diodes of each pixel on the panel becomes large, that is, the total current (Itotal) flowing from the common cathode to the common cathode connecting line also increases. When a large current passes through the resistive element, it may have a large voltage drop, at which time all the drive units on the panel work with a relatively small source-drain voltage (Vsd), and the image data of each gray scale luminance The value of the ratio to the value is automatically reduced, thereby fulfilling the requirement that the power consumption of the panel be lower than the specified value.
When the screen image load is small, the sum of the currents passing through the organic light emitting diodes of each pixel of the panel is also small, that is, the total current (Itotal) flowing from the common cathode to the common cathode connecting line is also small. When passing through the resistive element, the voltage drop is also small, so that at this time all the drive units of the panel work with a relatively large source-drain voltage (Vsd) and the value of the ratio of each gray scale luminance to the image data value Automatically increases, thereby increasing the displayable brightness of the panel image and increasing the contrast.
[0005]
[Means for Solving the Problems]
The invention according to claim 1 includes a data driver (30) and a scan driver (40) for driving a circuit in each pixel (20) of the display, wherein the circuit in the pixel (20) is a switch unit (21). It comprises a storage unit (23), a drive unit (22), an organic light emitting diode (24), the switch unit (21) has two input terminals and one output terminal, and these two input terminals are respectively connected to data lines ( 31) and the scanning line (41), one end of the storage unit (23) is connected to the power supply line (60), and the other end is connected to the output end of the switch unit (21). The input end of the unit (22) is connected to the connection between the output end of the switch unit (21) and the input end of the storage unit (23), and another input end of the drive unit (22). The anode of the organic light emitting diode (24) connected to the power supply line (60) and having an anode and a cathode is connected to the output terminal of the drive unit (22) via the power supply line (60). ), A display driving device that automatically adjusts to the optimum brightness under limited power consumption,
The organic light emitting diode (24) is connected to the resistance element (50) by a shared cathode connection line (61), and the other end of the resistance element (50) is grounded. The display drive device automatically adjusts the brightness.
According to a second aspect of the present invention, there is provided a display driving apparatus for automatically adjusting to an optimum luminance under a limited power consumption according to the first aspect, wherein the switch unit (21) is a TFT.
According to a third aspect of the present invention, there is provided the display driving apparatus according to the first aspect, wherein the driving unit (22) is a TFT.
According to a fourth aspect of the present invention, there is provided the display driving apparatus according to the first aspect, wherein the storage unit (23) is composed of a capacitor.
The invention according to claim 5 is composed of a plurality of sets of pixel devices, each pixel device comprising a driving unit (22) for driving and emitting an organic light emitting diode (24), and an organic light emitting diode in each pixel (20). (24) is connected to each other in a shared cathode system and connected to a resistance element (50) by a shared cathode connection line (61), and is used for a display formed so that another end of the resistance element (50) is grounded. In a display drive method that automatically adjusts to the optimal brightness under limited power consumption
The source-drain voltage (Vsd) of the drive unit (22) is adjusted by changing the voltage of the resistance element (50) according to the change of the total current (Itotal) flowing out of the shared cathode connecting line (61), and each gray scale luminance is adjusted. Wherein the value of the ratio to the image data value fluctuates, and the display driving method automatically adjusts to the optimum luminance under the limited power consumption.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 2 is a diagram showing the relationship between the luminance (X axis) generated by each pixel and the image data (Y axis) according to the present invention. As shown, the principle of the present invention is as follows. When the screen image load is large (large load 10 in the figure), since the image data value of each gray scale luminance can have a different ratio value under different image loads, the driving device of the present invention uses each gray scale luminance. When the demand for lowering the panel power consumption below the standard value is achieved by automatically reducing the ratio value of the scale luminance to the image data value, and the screen image load is small (medium load 11 or small load 12 in the figure). The driving apparatus of the present invention automatically increases the ratio of each gray scale luminance to the image data value, enhances the luminance that can display a panel image, and increases the contrast.
[0007]
FIG. 3 is a diagram showing a device according to the present invention. As shown, the present invention comprises a data driver (30) and a scan driver (40), the data driver (30) and the scan driver (40) being electronic devices of circuits in each pixel (20) of the display. The electronic device comprises at least a switch unit (21), a storage unit (23), a drive unit (22), an organic light emitting diode (24), and the switch unit (21) has one input terminal and one input terminal. It has two output terminals, and these two input terminals are connected to the data line (31) and the scanning line (41), respectively, and one end of the storage unit (23) is connected to the power supply line (60) (supply voltage Vdd). The other end is connected to the output end of the switch unit (21), and the input end of the drive unit (22) is connected to the output end of the switch unit (21). (23), the other input end of the drive unit (22) is connected to the power supply line (60), and the organic light emitting diode (24) is connected to the shared cathode connection. The common cathode connecting line (61) is connected to the resistance element (50) by a line (61) in the form of a shared cathode, and another end of the resistance element (50) is grounded. The anode of the organic light emitting diode (24) in each pixel (20) is connected to the power supply line (60) (supply voltage Vdd) via the drive unit (22).
[0008]
The operation of the present invention is as follows. When the screen image load is large, the sum of the current passing through the organic light emitting diode (24) of each pixel (20) on the panel becomes large, that is, the total current flowing from the shared cathode to the shared cathode connecting line (61). (Itotal) can also be large, but large currents can have large voltage drops as they pass through the resistive element, at which time all drive units (22) on the panel have relatively small source-drain voltages (Vsd ), The value of the ratio of each grayscale luminance to the image data value is automatically reduced, thereby fulfilling the requirement that the power consumption of the panel be lower than the standard value.
[0009]
When the screen image load is small, the total current flowing through the organic light emitting diode (24) of each pixel (20) of the panel is also small, that is, the total current (Itotal) flowing from the shared cathode to the shared cathode connecting line (61). ) Is small, but when a small current passes through the resistance element (50), the voltage drop is also small. Therefore, at this time, all the drive units (22) of the panel are driven by a relatively large source-drain voltage (Vsd). In operation, the value of the ratio of each grayscale luminance to the image data value is automatically increased, thereby increasing the displayable luminance of the panel image and increasing the contrast.
[0010]
FIG. 4 is a diagram showing the relationship between the maximum current and the image load of the organic light emitting diode of the present invention. As shown, the present invention automatically adjusts the value of the ratio of each grayscale luminance to the image data value according to different image load conditions, so that the maximum grayscale luminances are all different under different image load conditions. sell. The Y-axis in FIG. 4 is the maximum current (Ioled-max) of the organic light emitting diode (representing that the image data is the maximum value, that is, 255), and the X-axis is the image load (0% to 100%). ), When the image load on the screen is large, the maximum current (Ioled-max) of the organic light emitting diode is automatically reduced. In other words, the maximum gray scale luminance of the organic light emitting diode is automatically reduced, and the panel power consumption is reduced. The requirement to be below specification is achieved. When the screen image load is small, the maximum current (Ioled-max) of the organic light emitting diode (24) automatically increases, that is, the maximum gray scale luminance of the organic light emitting diode (24) also increases automatically. As a result, the brightness at which a panel image can be displayed is enhanced, and the contrast is enhanced.
[0011]
FIG. 5 is a diagram showing the relationship between the voltage across the resistor element of the present invention and the image load. As shown in the figure, the total current (Itotal) flowing from the common cathode to the common cathode connecting line (61) at different image loads. Have different voltage drops as they pass through the resistive element (50). Accordingly, when the image load is different, the operating point (Operating Point) of each gray scale Isd-Vsd (the relationship between the source-drain current and the voltage) of the drive unit (22) on the panel also differs, and the resistance element (50) ) Causes a change in continuity according to the image load condition, and therefore the present invention generates an automatic adjustment of the continuity, causing a situation in which the image screen flickers due to a discontinuous change in voltage. do not do.
[0012]
FIG. 6 is a diagram showing the relationship between power consumption and image load according to the present invention. A known method for lowering the power consumption of the organic light emitting diode panel to a power specification value of 15 under different image loads is to reduce the power consumption when the organic light emitting diode display panel displays a full white image screen to the power specification. The power consumption of the organic light emitting diode display panel was absolutely directly proportional to the image load by making the value equal to the limit value of 15 (like the well-known power consumption curve 13 in FIG. 6).
[0013]
In contrast, the present invention automatically adjusts the value of the ratio of each grayscale luminance to the image data value under different image load conditions, and when the screen image load is small, automatically increases the maximum grayscale luminance, The displayable brightness of the panel image is increased to enhance the contrast of the image, so that the power consumption of the organic light emitting diode (24) panel is not directly proportional to the image load (see the power consumption curve 14 of the present invention in FIG. 6). ), The power consumption meets the requirement of the power consumption limit value.
[0014]
【The invention's effect】
Taken together, the present invention has the following advantages.
(1) Enhance image contrast. In other words, the present invention automatically adjusts the display brightness to the optimum according to the different screen image load conditions under the limited power consumption, increases the image brightness to increase the contrast, and achieves both the limitation of the power consumption and the requirement of the image quality.
(2) Automatic continuity adjustment is performed. That is, the technique of the present invention automatically adjusts the value of the ratio of each grayscale luminance to the image data value under different image loads. The current system uses a different voltage drop when the total current (Itotal) flowing out of the shared cathode passes through the resistance element (50) at different image loads, so that the driving unit (22) of the panel at different image loads is changed. This causes a difference in each grayscale Isd-Vsd operating point. According to the present invention, the voltage drop across the resistive element (50) produces a continuity change depending on the image load situation. On the other hand, in the well-known patent document 1, a built-in look-up table (Look-UP TABLE) and a considerably complicated mathematical operation are required, and the adjustment method has a drawback of discontinuous alteration, and a flickering image screen. A situation has formed (because these screens are in the middle of a fuzzy zone in the middle of the ratio value step for two grayscale luminance image data).
(3) The manufacturing cost is low. While the present invention requires only one extra passive resistor per panel, Patent Document 1 requires the use of a large number of digital image processing units and rather complicated mathematical operations, resulting in a cost reduction. Do not meet the low cost requirements of small sized active organic light emitting displays.
The above is only a description of preferred embodiments of the present invention, and does not limit the scope of the present invention, and any modification or alteration of details that can be made based on the present invention shall fall within the scope of the claims of the present invention. I do.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a relationship between luminance (X axis) generated by each known pixel and image data (Y axis).
FIG. 2 is a diagram illustrating a relationship between luminance (X axis) generated by each pixel and image data (Y axis) according to the present invention.
FIG. 3 is a view showing a device according to the present invention.
FIG. 4 is a diagram showing the relationship between the maximum current (X-axis) and the image load (Y-axis) of the organic light emitting diode of the present invention.
FIG. 5 is a diagram showing the relationship between the voltage (X-axis) and the image load (Y-axis) across the resistance element according to the present invention.
FIG. 6 is a relationship diagram between power consumption (X axis) and image load (Y axis) according to the present invention.
[Explanation of symbols]
Reference Signs List 20 pixel 21 switch unit 22 drive unit 23 storage unit 24 organic light emitting diode 30 data driver 31 data line 40 scan driver 41 scan line 50 resistor element 60 power supply line 61 shared cathode connecting line

Claims (5)

The display includes a data driver (30) and a scan driver (40) for driving a circuit in each pixel (20) of the display. The circuit in the pixel (20) includes a switch unit (21), a storage unit (23), and a drive unit. The switch unit (21) has two input terminals and one output terminal, and the two input terminals are a data line (31) and a scanning line (41), respectively. ), One end of the storage unit (23) is connected to the power supply line (60), the other end is connected to the output end of the switch unit (21), and the input end of the drive unit (22). Is connected to a connecting portion between the output terminal of the switch unit (21) and the input terminal of the storage unit (23), and another input terminal of the drive unit (22) is connected to the power supply line. The organic light emitting diode (24) having an anode and a cathode is connected to the power supply line (60) through a connection with the output terminal of the drive unit (22). In a display drive device that automatically adjusts to the optimal brightness under limited power consumption,
The organic light emitting diode (24) is connected to the resistance element (50) by a shared cathode connection line (61), and the other end of the resistance element (50) is grounded. Display drive that automatically adjusts to brightness. 2. The display driving device according to claim 1, wherein the switch unit is a TFT. The display driving apparatus according to claim 1, wherein the driving unit (22) is a TFT. 2. The display driving apparatus according to claim 1, wherein the storage unit is formed of a capacitor. A plurality of pixel devices, each pixel device including a driving unit (22) for driving and emitting an organic light emitting diode (24), and an organic light emitting diode (24) in each pixel (20) being a shared cathode type , And connected to a resistor element (50) by a shared cathode connection line (61), under limited power consumption used in a display formed so that another end of the resistor element (50) is grounded. In a display driving method that automatically adjusts to the optimal brightness,
The source-drain voltage (Vsd) of the drive unit (22) is adjusted by changing the voltage of the resistance element (50) according to the change of the total current (Itotal) flowing out of the shared cathode connecting line (61), and each gray scale luminance is adjusted. A display driving method for automatically adjusting to an optimum luminance under limited power consumption, wherein a value of a ratio with respect to the image data value is varied.

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