KR20080006116A - A driving circuit for electroluminescent displaying apparatus and a driving method thereof - Google Patents

Abstract

An electroluminescenct display device and a driving method thereof are provided to reduce power consumption by adjusting properly brightness based on the calculation of color data. An electroluminescenct display device includes a controller(100) and a driving current controller(200). The controller calculates color data transmitted from outside, predicts power consumption, and outputs a first control signal according to the prediction result. The driving current controller receives the first control signal and adjusts driving current based on the received signal. The controller predicts the power consumption for every color based on the weighted value of respective colors.

Description

A driving circuit for electroluminescent displaying apparatus and a driving method thereof}

1 is a cross-sectional view of a general organic EL device

2A and 2B are graphs illustrating a relationship between gray levels and luminance implemented on a screen in a general light emitting device.

3 is a circuit block diagram of an EL display device according to an embodiment of the present invention;

4A and 4B are graphs showing a plurality of step brightness curves used in the EL display device of the present invention.

<Description of Symbols in Drawings>

100: control unit 110: first operation unit

120: second calculation unit 130: third calculation unit

140: sub-control unit 200: drive current control unit

300: power control unit 400: memory unit

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit of an EL display device and a driving method thereof, and more particularly, to a driving circuit of an EL display device and a method of driving the same, which can drastically reduce power consumption of an EL display device without lowering contrast characteristics. It is about.

Recently, various flat panel displays capable of reducing weight and volume, which are disadvantages of cathode ray tubes (CRTs), have been widely used. Such flat panel displays include liquid crystal displays (LCDs), field emission displays (FEDs), plasma display panels (PDPs), and electroluminescent (EL) displays. have.

Among them, the EL element is a self-luminous element that emits a phosphor by recombination of electrons and holes. An inorganic EL element (also referred to as "LED") using an inorganic compound as the phosphor and an organic EL element using an organic compound (" Also referred to as "OLED". Such an EL element has an advantage that the response speed is remarkably faster than a passive light emitting element that requires a separate light source such as a liquid crystal display device. In addition, EL devices have many advantages such as low voltage driving, self-luminous, thin film type, wide viewing angle, fast response speed, and high contrast, and are expected to be the next generation display devices.

1 is a cross-sectional view of a general organic EL device for explaining the light emission principle of the EL device. As shown in FIG. 1, the organic EL device includes an electron injection layer 2, an electron transport layer 3, an emission layer 4, a hole transport layer 5, and a hole between the cathode 1 and the anode 7. The injection layer 6 has a laminated structure sequentially.

When a voltage is applied between the anode 7 as the transparent electrode and the cathode 1 as the metal electrode, electrons generated from the cathode 2 are transferred to the light emitting layer 4 through the electron injection layer 2 and the electron transport layer 3. Move. In addition, holes generated from the anode 7 move to the light emitting layer 4 through the hole injection layer 6 and the hole transport layer 5. Accordingly, in the light emitting layer 8, light is generated by collision between electrons and holes supplied from the electron transporting layer 6 and the hole transporting layer 10 and recombination. This light is emitted to the outside through the anode 7, which is a transparent electrode, so that an image is displayed.

There are two methods of driving such an organic EL device: a simple matrix method and an active matrix method using a thin film transistor (TFT). The simple matrix method is a method in which the anode and the cathode are formed to be orthogonal to each other, and the cathode line and the anode line are selected and driven. The active matrix method is a drive in which a thin film transistor and a capacitor are integrated in each pixel to maintain a voltage by capacitor capacity. That's the way. The simple matrix method is simple and inexpensive, but it is difficult to realize large or high precision panels. On the other hand, the active matrix method is possible to realize a large size and high precision panel, but the control method is technically difficult and relatively expensive.

Organic EL devices are also called OLEDs (organic light emitting diodes) because they are rectified in most cases. Since the display using such an organic EL element emits light using electric current, the amount of light emitted on the screen is proportional to the amount of current flowing through the element. Therefore, the higher the maximum amount of light emitted by the device, the greater the required current. In addition, if the maximum light emission amount of the device is suppressed, the whole screen becomes dark.

2A and 2B are graphs illustrating a relationship between gray levels and luminance implemented on a screen in a general light emitting device.

As shown in FIG. 2A, since the current driving the light emitting device is applied in proportion to the gray scale to be expressed, as a result, the brightness of the light emitting display element increases in proportion to the gray scale to be expressed, and the luminance curve is linear. Will have On the other hand, when the driving current is changed by gamma correction of each color data input from the outside, the luminance curve is not a straight line as shown in FIG. 2B because the driving current is not proportional to the gray level to be expressed. .

That is, in the conventional method of driving the light emitting device, since the current applied to each gray scale to be expressed in the image is specified, only one luminance curve according to the gray scale is provided as shown in FIGS. 2A and 2B.

In the case of the light emitting device driven by the conventional method, when the luminance is set low for all gray levels, that is, when the luminance curve is downwardly adjusted on the graph and applied uniformly, the entire screen becomes dark and the contrast characteristic is reduced. There is a problem of deterioration. On the other hand, when the luminance is set high for all the gray scales, that is, when the luminance curve is uniformly applied upwards on the graph, the entire screen is brightened and the contrast characteristic is improved, but the power consumption is increased. Problems will arise.

The present invention has been made to solve the above problems of the prior art, an object of the present invention is to calculate the data for each color input from the outside for each color to accurately predict the magnitude of power consumption and accordingly the luminance appropriately It is an object of the present invention to provide an EL display device and a method of driving the same, which can reduce power consumption due to driving without degrading the contrast characteristic.

The EL display device of the present invention for achieving the above object is a control unit for calculating the power consumption by calculating the data for each color transmitted from the outside for each color and outputting a first control signal according to the size; And a driving current controller configured to receive the first control signal and adjust a driving current.

As another aspect for achieving the above object, a driving method of the EL display device of the present invention comprises the steps of: receiving data for each color transmitted from the outside; Calculating data for each received color for each color to estimate the magnitude of power consumption; And adjusting the driving current by using the estimated power consumption for each color.

On the other hand, the EL element in the present invention is not limited to the organic EL element or the OLED, and includes any of them as long as the luminance is controlled by the amount of current flowing through the element. For example, it should be understood to include inorganic EL elements or LEDs.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 is a circuit block diagram of an EL display device according to an embodiment of the present invention.

As shown in Fig. 3, the EL display device of the present invention receives a data and color constant for each color input from the outside, and a controller 100 for outputting first and second control signals, and the first control. The driving current controller 200 may receive a signal to adjust the driving current, and the voltage controller 300 may receive the second control signal to adjust the driving voltage.

The controller 100 receives a data for a first color, for example, red, and calculates the amount of power consumption required by performing calculation on the first color, for example, red, for example, green. The second operation unit 120, which estimates the amount of power consumption required by receiving data for and performing calculation on the second data, for example, receives data for a third color, for example, blue and performs calculation on the same. The magnitude of the total power consumption is obtained by receiving and adding the magnitudes of the estimated power consumption from the third calculating unit 130 and the first to third calculating units 110, 120, and 130, respectively. And a sub-control unit 140 for outputting the first and second control signals.

Optionally, the first to third calculators 110, 120, and 130 estimate the magnitude of power consumption for each color by obtaining a gray level to be expressed in the image for each color using the data for each color received.

The first to third calculators 110, 120, and 130 respectively receive color constants, which are driving current values required for gradation, or reference values that are proportional thereto, in addition to data for each color, and then convert these color constants into the respective color constants. By multiplying the gradation to be expressed in the image for each color, the magnitude of power consumption according to the weight for each color can be estimated. In this case, the EL display device of the present invention may further include a memory unit 400 for storing the color constant for each color.

The sub-controller 140, which has received the power consumption estimates for each color obtained from the first to third calculators 110, 120, and 130, respectively, adds all of them to estimate the magnitude of the total power consumption. The first and second control signals are output according to the expected total power consumption.

Optionally, the sub-controller 140 may estimate the magnitude of the total power consumption every frame and output the first and second control signals. In this case, the power consumption required to display the entire screen is calculated as the magnitude of the total power consumption. In addition, since the first and second control signals are output every time the screen is changed, the luminance can be adjusted for each screen.

4A and 4B are graphs showing a plurality of stepwise luminance curves used in the EL display device of the present invention.

In the case of FIG. 4A, since the current driving the light emitting device is applied in proportion to the gray scale to be expressed, as a result, the brightness of the light emitting display element is increased in proportion to the gray scale to be expressed, and the luminance curve has a straight shape. Step-by-step brightness curves 1 ... N. On the other hand, in the case of FIG. 4B, when the driving current is changed by gamma-correcting each color data input from the outside, the luminance curves of each step (1 ... N) are straight because It is shaped like a curve.

The luminance curves 1 ... N mentioned below refer to the luminance curves shown in the graph of FIG. 4A, but the same may be applied to the luminance curves 1 ... N according to the graph of FIG. 4B. Of course.

The sub-controller 140 outputs first and second control signals for controlling the driving current controller 200 and the power controller 300, respectively, based on the expected total power consumption. At this time, when the estimated total power consumption is less than a predetermined reference, the first and second control signals are output in accordance with the luminance curve 1 applied in the conventional EL display device to prevent the contrast characteristics from being lowered. However, if the magnitude of the total estimated power consumption exceeds the predetermined criterion, it exceeds that of any one of the luminance curves (2 ... N) adjusted downward on the graph than the luminance curve (1) conventionally applied. Select according to the degree. Subsequently, the first and second control signals are output in accordance with the selected luminance curve (2 ... N) to lower the luminance of the entire screen.

As a result, according to the EL display device according to the present invention, when the overall display consumption is small and the expected total power consumption is small, the same luminance is displayed as on the other hand, while the display display volume is large as expected in full white. If the total power consumption is large, the luminance is lowered by selecting one of the down-adjusted luminance curves (2 ... N). This is possible because the user does not feel bright on a bright screen.

Hereinafter, the operation of the EL display device according to an embodiment of the present invention will be described in detail.

First, the controller 100 receives data for each color transmitted from the outside through an input unit (not shown) for displaying a screen. More specifically, the first calculating unit 110 of the control unit 100 receives red data, the second calculating unit 120 receives green data, and the third calculating unit 130 receives blue data.

The first to third calculators 110, 120, and 130 respectively receive data for each color, and at the same time, a color constant which is a driving current value required for expressing the gray level of each color from the memory unit 400 or a reference value proportional thereto. Receive each. That is, the first calculator 110 receives a red constant, the second calculator 120 receives a green constant, and the third calculator 130 receives a blue constant.

The first to third calculating units 110, 120, and 130 calculate the gray scales to be expressed in the image for each color by using the received color data, and then multiply the gray scales with the received color constants to generate power according to the weight for each color. Find the magnitude of the consumption or a value proportional to it. That is, the first to third calculators 110, 120, and 130 respectively calculate a magnitude or a value proportional to power consumption required to implement red, green, and blue in the image.

The sub-controller 140 receives the estimated power consumption for each color, or the value proportional thereto, from the first to third calculation units 110, 120, and 130, and adds them to the total power consumption or the value proportional thereto. Obtain Subsequently, the sub-controller 140 selects any one of the luminance curves 1... N after the expected total power consumption is calculated, and outputs first and second control signals accordingly. The selection of the luminance curve and thus the output of the first and second control signals are performed every frame.

In more detail, when the estimated total power consumption is less than a predetermined reference, the first and second control signals are output so that the luminance according to the first luminance curve 1 is displayed. If the estimated total power consumption exceeds the predetermined criterion, one of the rareness curves (2 ... N) is selected according to the excess amount. That is, the range of the excess amount is divided into the first range, ..., the N-th range in order of increasing magnitude, and when the excess amount is within the first range, the second luminance curve 2 and the second range The third luminance curve (not shown) in the range, the N-1 luminance curve N-1 in the N-2 range, and the Nth luminance curve N in the N-1 range Outputs first and second control signals such that luminance according to the &quot;

The driving current control unit 200 and the power control unit 300 receive first and second control signals from the sub-control unit 140 to adjust the driving current and the power supply voltage, respectively.

As described above, according to the EL display device and the driving method thereof of the present invention, the power consumption expected for each color is calculated by calculating data for each color input from the outside for each color. Based on the weight of the color, it is possible to estimate the magnitude of power consumption more accurately because the magnitude of the power consumption expected for each color or a value proportional thereto is obtained.

In addition, it is possible to lower the power consumption by adjusting the luminance according to the estimated total power consumption. That is, when the estimated total power consumption is less than a predetermined reference, the control unit may prevent the degradation of the contrast characteristic by controlling to have the same brightness as before, and when the estimated total power consumption exceeds the predetermined reference, By lowering the luminance in proportion to the excess amount, power consumption due to driving can be reduced.

As a result, the present invention has the effect of increasing the use time of a product to which the EL display device is applied, for example, a portable device, without deteriorating the contrast characteristic.

Claims (18)

A control unit for calculating a power consumption by calculating data for each color transmitted from the outside for each color and outputting a first control signal according to the size; And And a driving current controller for receiving the first control signal and adjusting a driving current. The method of claim 1, And the control unit estimates the amount of power consumption for each color based on the weight of each color. The method of claim 1, And the controller estimates the amount of power consumption for each color by multiplying the data for each color by the driving current value required for the gradation representation of that color. The method of claim 1, And the controller estimates the magnitude of total power consumption by adding up the magnitudes of the power consumption expected for each of the colors. The method of claim 1, And a memory unit which stores, for each color, a color constant which is a driving current value required for expressing a gray level of each color or a reference value proportional thereto. The method of claim 5, The control unit obtains the gradation to be implemented in the image from the data for each color, receives the color constant from the memory unit, and multiplies the gradation to be implemented in the image by the color constant received from the memory unit. An EL display device characterized by estimating the magnitude of power consumption for each color. The method of claim 1, And the control unit outputs the first control signal every frame. The method of claim 1, The control unit may be configured to calculate a magnitude of an expected power consumption for the first color by calculating data of the first color, and a second calculator to calculate an amount of expected power consumption for the second color by calculating data of the second color. A third calculating unit for calculating the magnitude of the expected power consumption for the third color by calculating data of the third color, and receiving and adding the magnitudes of the expected power consumption from the first, second, and third calculating units, respectively. And a sub-controller for estimating the magnitude of power consumption and outputting the first control signal accordingly. The method of claim 8, And the sub-controller estimates the magnitude of the total power consumption every frame and outputs the first control signal accordingly. The method of claim 8, The control unit outputs the first control signal according to a first luminance curve when the estimated total power consumption is less than or equal to a predetermined criterion. When the controller exceeds the predetermined criterion, the first control signal is output according to a second luminance curve. And an EL display device. The method of claim 1, And a power control section for receiving a second control signal according to the expected power consumption from the control section and adjusting a power supply voltage. Receiving data for each color transmitted from the outside; Calculating data for each received color for each color to estimate the magnitude of power consumption; And And adjusting a driving current by using the estimated power consumption for each of the colors. The method of claim 12, And calculating data for each color for each color based on the weight of each color. The method of claim 12, Computing the data for each color for each color, Obtaining a gradation to be implemented in an image for each color from the data for each color; And And multiplying a color constant which is a driving current value required for gradation representation of a corresponding color or a reference value proportional thereto and a gradation to be implemented in the image. The method of claim 12, The adjusting step of the drive current, Obtaining a magnitude of total power consumption by adding the magnitude of the expected power consumption for each color; And And adjusting the driving current according to the magnitude of the total power consumption. The method of claim 15, Adjusting the driving current according to the magnitude of the total power consumption, The driving current is adjusted according to a first luminance curve when the magnitude of the total power consumption is lower than or equal to a predetermined reference value, and the driving current is adjusted according to a second luminance curve when the magnitude of the total power consumption exceeds the predetermined criterion. A driving method of an EL display device, characterized by the above-mentioned. The method of claim 12, And the step of adjusting the driving current is performed every frame. The method of claim 12, And adjusting a power supply voltage by using the estimated power consumption for each of the colors.

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