KR100541830B1 - Driving apparatus and method of a display device for automatically adjusting the optimum brightness under limited power consumption - Google Patents

Abstract

A driving device of a display element that automatically adjusts an optimum brightness under a limited power consumption aims to obtain respective brightness ratios for image data values under respective image loadings. If the photographic image loading is larger, the driving device of the present invention automatically lowers the luminance ratio to the image data value, thereby lowering the power consumption of the display panel below the design value. When the photographic image loading is small, the driving apparatus of the present invention automatically increases the luminance ratio with respect to the image data value, thereby increasing the display luminance of the panel image and improving the contrast ratio.

Description

DRIVING APPARATUS AND METHOD OF A DISPLAY DEVICE FOR AUTOMATICALLY ADJUSTING THE OPTIMUM BRIGHTNESS UNDER LIMITED POWER CONSUMPTION}

1 is a diagram showing a relationship between luminance (X axis) and image data (Y axis) emitted by each pixel of the prior art.

2 is a diagram showing a relationship between luminance (X axis) and image data (Y axis) emitted by each pixel according to the present invention.

3 is a schematic representation of the apparatus of the present invention.

4 is a view showing the relationship between the maximum current (X axis) and image loading (Y axis) of the OLED panel according to the present invention.

5 is a diagram showing the relationship between the voltage drop (X axis) applied to the resistance according to the present invention and the image loading (Y axis).

6 is a diagram illustrating a relationship between power consumption (X axis) and image loading (Y axis) according to the present invention.

<Description of the symbols for the main parts of the drawings>

20: pixel 21: switching unit

22: driver unit 23: storage unit

24: OLED 30: data driver

31: data line 40: scanning driver

41: scanning line 50: resistance

60: power supply line 61: common cathode connection line

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a driving device of a display element that automatically adjusts an optimum brightness under a limited power consumption. The present invention relates to a device for automatically adjusting an optimal display brightness under a limited power consumption according to different photographic image loading conditions and to improve image brightness. Increase

Organic light emitting diodes (OLEDs), also called organic electroluminescent (OEL), are a new generation technology and other flat panel display device technologies are difficult to match. This gives a brighter, clearer full color image and has a faster response.

The basic structure of an OLED includes an organic material layer and an anode made of thin and transparent indium tin oxide (ITO) having semiconductor properties, with a layer of organic material interposed therebetween. The glass material layer includes an electric hole transport layer (HTL), a light emitting layer (EL), and an electron transport layer (ETL). When the battery provides a suitable voltage (with low voltage characteristics), the charge injected into the electrical holes of the anode and the charge from the cathode combine in the light emitting layer to generate an electroluminescence in the organic material layer. The structure of the organic layer and the design choice of the anode and the cathode are important factors for the OLED device to fully deliver the luminescent effect.

OLEDs have many features, such as being able to emit light alone. It does not require a backlight module. It can be driven at low voltages (less than 10 V) to save power, provide high energy efficiency (16 mA / W), greater luminance (100,000 mA / m2 or more), and faster response times ( <2 kW), high contrast ratio, wide viewing angle (up to about 180), light weight, thin thickness, simple configuration, lower manufacturing cost, flexible (plastic based) and full color enablement.

Therefore OLEDs have been used extensively. This is a huge potential market for display devices or lighting devices such as mobile phones, game consoles, audio system panels, digital cameras, personal digital assistants (PDAs), car navigation systems, electronic books, information appliances, notebook computers, monitors, TVs, etc. Have

When OLEDs are used as elements of portable or pocket electronics such as cell phones, PDAs, digital still cameras (DSCs), digital video cameras (DVCs), there are basic and important requirements for their properties, namely low power consumption. . Therefore, producers generally require these elements to operate within a limited power consumption range. As far as mobile display devices are concerned, the power consumption of the OLED panel should be lower than the design value when displaying any image photograph.

OLEDs are self-luminous display devices, so OLED panels are expected to consume the most power when displaying all white images. This is because image loading is the maximum value in that case (image loading is the sum of the image data values of all the pixels of the display panel). That is, the image data values of all the pixels are the maximum (the maximum value is 255 if the image data is 8 bits). Therefore, in order to limit the power consumption below the design value, the conventional method requires that the image data values of all pixels be the maximum so that when the OLED panel displays all white image photographs, the panel's power consumption is exactly the same as the limited power consumption value. Adjust the brightness when Reference is made to FIG. 1 regarding the relationship between image data and luminance of each pixel of the prior art. If the power consumption of the OLED panel for displaying all white image photographs is adjusted to be equal to the limited power consumption value, the intensity of light emitted by each pixel is the luminance (Lmax) of each pixel when the image data value is the maximum value. Is defined. If the pixel displays another image data value such as n, the luminance is Ln and Ln = nx (Lmax / 255).

Moreover, the image contrast ratio CR is basically the ratio of the maximum luminance value of the image display to the minimum luminance of the image display. The formula is CR = Lmax / Lmin. Thus, the above-described conventional method allows the OLED panel to keep the power consumption below the design value even when displaying any image photograph, while the contrast ratio of the image to be displayed is limited.

U.S. Patent No. 6,380,943 entitled "Color Display Apparatus" discloses image data processing technology applied to self-luminous flat panel display devices such as OLEDs, PDPs and the like. The purpose is to increase the display brightness within the limited power consumption by automatic modulation according to each image loading state, while satisfying the requirements of power consumption and picture quality.

The patent utilizes the following principle, which first divides the image loading into five regions according to light and heaviness; Five areas are displayed on the panel using each parameter and curve to adjust the original image data values to the image data of each image loading controlled by each parameter and curve. Thereby, no matter what image picture is displayed, the power consumption is lower than the design value. The optimum luminance can be adjusted and displayed according to each image loading state. This satisfies the requirements of power consumption and image quality.

However, it also has the disadvantage of requiring a large number of digital image processing units and complicated mathematical processes. This can achieve improved picture quality, but at a high cost. This does not meet the low cost requirements for small AMOLEDs.

Japanese Patent 2002-251167 entitled "Display element" discloses a current control circuit arrangement. It detects the current flowing from the power supply to the power line of the AMOLED panel. If the detected current increases and is greater than the rated value, the output voltage of the power supply decreases, lowering the voltage on the power line of the AMLOED panel, allowing the AMOLED panel to operate within limited power consumption.

It is therefore a first object of the present invention to solve the above problems and to eliminate the disadvantages of the cited prior art. An object of the present invention is to automatically adjust an optimal display brightness according to each image loading state under a limited power consumption, improve image contrast to improve contrast ratio, and satisfy power consumption and image quality requirements. .

According to the present invention, all the pixels of the display element have an OLED element which is connected to each other in a common cathode manner. The common cathode is connected to a resistor with the other end grounded. In addition, the anode of the OLED element of each pixel is connected to a power supply line (Vdd supply line) through a driver portion. As a result, the larger the image loading of the photograph, the larger the sum of the current flowing through the OLED in each pixel of the panel, i.e., the larger the total current I _total flowing out to the common cathode. However, since a larger voltage drop occurs when a larger current flows through the resistor, all driver portions on the panel have a smaller Vsd (voltage of the source electrode and the drain electrode) during operation. Each gray scale luminance ratio value for the image data value is automatically lowered, so that the panel's power consumption is lower than the design value.

If the photographic image loading is small, the sum of the current flowing through the OLED in each pixel of the panel is expected to be smaller, i.e., the total current I _total flowing out to the common cathode is smaller. However, because a smaller voltage drop occurs when a smaller current flows through the resistor, all driver portions on the panel have a larger Vsd during operation. Each gray scale luminance ratio value with respect to the image data value is automatically increased, so that the luminance of the image displayed on the panel is increased to improve the contrast ratio.

The above as well as further objects, features and advantages of the present invention will become more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.

Reference is made to FIG. 2 for the relationship between luminance emitted by a pixel according to the invention and image data input to the pixel. The principle of the present invention is that the luminance ratio with respect to the image data value changes with image loading. If the photographic image load is greater (transmission curve 10 for the larger image loading shown in Fig. 2), the driving device of the present invention automatically lowers the luminance ratio to the image data value to reduce the power consumption of the display element to the design value. Lower. If the photographic image loading is smaller (transmission curve 12 for the smaller image loading shown in FIG. 2), the driving device of the present invention automatically increases the luminance ratio to the image data value to increase the maximum luminance of the display panel. Therefore, the contrast ratio of the display panel is improved.

Referring to FIG. 3, the apparatus of the present invention includes a data driver 30 and a scan driver 40. The above driver drives electronic components in all the pixel 20 circuits of the display device. The electronic component includes at least two input terminals connected to the data line 31 and the scan line 41 and a switching unit 21 having one output terminal, and one terminal connected to the power supply line 60 (voltage ( Vdd) for supply) and a storage unit 23 having another terminal connected to the output terminal of the switching unit 21, an output terminal of the switching unit 21 and an input terminal of the storage unit 23; And a driver portion 22 having one input terminal connected to the junction of and a second input terminal connected to the power supply line 60, and an OLED 24. The OLED elements 24 of each pixel 20 are connected to each other in a common cathode manner via a common cathode connection line 61. The common cathode connection line 61 is connected to a resistor 50 having the other terminal grounded. The anode of the OLED element 24 of each pixel is connected to the power supply line 60 (for supply of voltage Vdd) via the driver unit 22.

The present invention operates as follows: If the photographic image loading is large, the sum of the currents flowing through the OLEDs 24 of each pixel 20 of the panel will be larger, i.e., the total current flowing out to the common cathode connection line 61. I _total is expected to be larger. However, since a larger voltage drop occurs when a larger current flows through the resistor 50, all the driver portions 22 on the panel have a smaller Vsd (voltage between the source electrode and the drain electrode) during operation. . Since the luminance ratio to image data value is automatically lowered, the panel's power consumption is limited below the design value.

When the photographic image loading is small, the sum of the currents flowing through the OLEDs 24 of each pixel 20 of the panel will be smaller, i.e., the total current I _total flowing out to the common cathode connection line 61 is smaller. It is expected to lose. However, since a smaller voltage drop occurs when a smaller current flows through the resistor 50, all the driver portions 22 on the panel have a larger Vsd (voltage between the source electrode and the drain electrode) during operation. . Since the luminance ratio with respect to the image data value is automatically increased, the luminance of the image displayed on the panel is increased to improve the contrast ratio.

Reference is made to FIG. 4 regarding the relationship between the maximum current and image loading of an OLED according to the invention. Since the driving apparatus of the present invention can automatically adjust the luminance ratio with respect to the image data value in each image loading state, the luminance of the maximum gray scale is different in each image loading state. In FIG. 4, the Y axis represents the maximum current I _oled-max of the OLED (ie, corresponds to the maximum gray scale of the image data), and the X axis represents image loading (0% -100%). If the photographic image loading is large, the maximum current I _oled-max of the OLED is automatically reduced, i.e., the maximum gray scale luminance of the OLED 24 is automatically lowered to lower the power consumption of the display panel below the design value. When the photographic image loading is small, the maximum current I _oled-max of the OLED 24 is automatically increased, that is, the maximum gray scale luminance of the OLED 24 is automatically increased to increase the display luminance of the panel image, thereby increasing the contrast ratio. To improve.

Reference is made to FIG. 5 regarding the relationship between the voltage across the resistor 50 of the drive device according to the invention and the image loading. As shown in the figure, under each image loading, the total current I _total flowing out to the common cathode connection line 61 will produce a different voltage drop while flowing through the resistor 50, so the panel at each image loading The operating points of the gray scales of the driver section 22 are different. The voltage drop across the resistor 50 (V _cv ) is constantly changing depending on the image loading state. Thus, the present invention can result in continuous adjustment without creating a flickering image caused by discontinuous adjustment.

Reference is made to FIG. 6 regarding the relationship between power consumption and image loading of a display panel according to the invention. As shown in the figure, at each image loading the OLED display panel has a respective power consumption. In the conventional method, in order to lower the power consumption below the power design value 15, the OLED display panel is designed such that the power consumption is exactly the same as the limit value of the power consumption value 15 when displaying all white image photographs. Therefore, the power consumption of the display panel of the OLED 24 is entirely proportional to the image loading (as indicated by the power consumption curve 13 in FIG. 6).

In contrast, the driving apparatus of the present invention can automatically adjust the luminance ratio with respect to the image data value in each image loading state. When photographic image loading is small, the maximum gray scale luminance is automatically increased to increase the display luminance of the panel and to improve the image contrast ratio. As such, the power consumption of the OLED 24 display panel is not linearly proportional to the image loading (as shown by the power consumption curve 14 of the present invention in FIG. 6). Thus, the power consumption of the display panel can meet the requirements of the power consumption limit value.

In summary, the present invention provides the following advantages.

1. Improved image contrast ratio. The present invention can improve the contrast ratio by automatically adjusting to achieve the optimum brightness and increase the image brightness according to each photographic image loading within the power consumption limit, while satisfying the requirements of the power consumption limit and the image quality. have.

2. Continuous automatic adjustment. The technique provided by the present invention can automatically adjust the luminance ratio value of each gray scale related to the image data value under each image loading. Adjustments are made in this way, and under each image loading the total current (I _total ) flowing through the resistor 50 to the common cathode generates a respective voltage drop, so that the driver portion of the panel at each image loading ( The operating point of each gray scale in 22) is different. The voltage drop across the resistor 50 is constantly changing depending on the image loading state. In contrast, conventional techniques, such as US Pat. No. 6,380,943 (April 30, 2002), use built-in look-up tables and complex mathematical processes, and adjustments include image flicker (ratio of relative image data ratios of two different gray scale luminances). Caused by a photograph in the middle blur area).

3. Low cost. The panel according to the invention only needs extra passive resistance. Conventional techniques, such as US Pat. No. 6,380,943 (April 30, 2002), require the use of a large number of digital image processing units and expensive complex mathematical processes, and are cost effective for small, low cost AMOLEDs. not.

While the preferred embodiments of the invention have been described for purposes of disclosure, variations of the embodiments of the invention disclosed, as well as other embodiments, may occur to those skilled in the art. Accordingly, the appended claims cover all embodiments without departing from the spirit and scope of the invention.

Claims (5)

A display element driving device for automatically adjusting an optimum brightness under a limited power consumption, A data driver and a scan driver, wherein each pixel is A switching unit having two input terminals and one output terminal respectively connected to the data line and the scan line; A storage unit having one terminal connected to a power line and another input terminal connected to an output terminal of the switching unit; A driver section having one input terminal connected to the junction of the output terminal of the switching section and the input terminal of the storage section and another input terminal connected to the power supply line; And An organic light emitting diode element having a cathode and an anode connected to the power line through an output of the driver unit, And the organic light emitting diode elements are connected to each other in a common cathode manner through a common cathode connection line connected to a resistor having the other terminal grounded. The display element driving apparatus of claim 1, wherein the switching unit is a thin film transistor. The display element driving apparatus of claim 1, wherein the driver unit is a thin film transistor. The display element driving apparatus of claim 1, wherein the storage unit is a capacitor. A method of driving a display element each comprising a plurality of pixel elements each having a driver portion for driving an organic light emitting diode to emit light, wherein the display element automatically adjusts an optimum luminance under a limited power consumption. Interconnecting the organic light emitting diodes of each pixel in a common cathode manner through a common cathode connection line; Connecting the common cathode connection line to a resistor; Grounding the other terminal of the resistor; And Connecting an anode of an organic light emitting diode of each pixel to a power line through the driver; The amount of change in the total current I _total flowing out to the common cathode connection line is used to generate different voltage drops across the resistance and to adjust Vsd (voltage between the source electrode and the drain electrode) of the driver section, respectively, for each image data value. A display element driving method for changing a gray scale luminance ratio value of a.

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