KR20090041029A

KR20090041029A - Backlight unit and driving method thereof

Info

Publication number: KR20090041029A
Application number: KR1020070106507A
Authority: KR
Inventors: 이태욱
Original assignee: 엘지디스플레이 주식회사
Priority date: 2007-10-23
Filing date: 2007-10-23
Publication date: 2009-04-28

Abstract

A backlight unit and a driving method thereof are disclosed.

The backlight unit is defined as a plurality of blocks, each LED array is arranged with a plurality of red, green and blue light emitting diodes in each block, and each block of the LED array and the red, green and blue light emitting diodes included in each block individually The LED driver generates a plurality of driving voltages reflecting the color temperature and the ambient temperature to drive the light, and generates a plurality of control signals reflecting the color temperature and the ambient temperature to control the LED driver, and selectively controls whether the color temperature is reflected. LED control unit.

Therefore, the present invention can improve image quality while keeping the white balance constant.

Description

Backlight unit and driving method thereof

The present invention relates to a backlight unit capable of improving image quality and a driving method thereof.

Due to the development of the information society, display devices capable of displaying information have been actively developed. The display device includes a liquid crystal display device, an organic electro-luminescence display device, a plasma display panel, and a field emission display device.

Among these, the liquid crystal display device has advantages such as light weight, small size, low power consumption, and full color video, and is widely applied to mobile phones, navigation, monitors, and televisions.

Since the liquid crystal display device is a light-receiving display device that does not emit light by itself, the liquid crystal display device uses a backlight unit that is provided on the rear surface of the liquid crystal panel for displaying an image to maintain uniform brightness of the entire screen.

The light source of the backlight unit includes a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp or a plurality of light emitting diodes (LEDs). There is.

Cold cathode fluorescent lamps and external electrode fluorescent lamps have a high power consumption, and it is difficult to cope with the increase in size. On the other hand, the LED array has low power consumption, easy to cope with the increase in size, and has the advantage of having a semi-permanent life, and has been widely developed recently.

However, the light emitting diode array has a disadvantage that it is difficult to maintain the white balance by each LED because the brightness is variable according to the temperature, and composed of red, green and blue LEDs. Therefore, the backlight unit having the conventional LED array has a problem in that the image quality of the LCD unit employing the backlight unit is deteriorated due to disadvantages such as variable brightness and weak white balance.

SUMMARY OF THE INVENTION An object of the present invention is to provide a backlight unit and a driving method thereof capable of maintaining white balance and improving image quality.

According to an embodiment of the present invention, a backlight unit may include: an LED array defined by a plurality of blocks, and a plurality of red, green, and blue light emitting diodes disposed in each block; An LED driver generating a plurality of driving voltages reflecting the color temperature and the ambient temperature to individually drive each block of the LED array and the red, green, and blue light emitting diodes included in each block; And an LED controller for generating a plurality of control signals reflecting the color temperature and the ambient temperature to control the LED driver, and selectively controlling whether the color temperature is reflected.

According to another embodiment of the present invention, a backlight unit including a LED array defined by a plurality of blocks and having a plurality of red, green, and blue light emitting diodes disposed in each block, and an LED driver for driving the LED array. The driving method includes: extracting data having maximum luminance from respective data pixels of one frame of video data; Calculating an average brightness of the data having the extracted maximum brightness; And comparing the average luminance of the data with a reference value and switching-controlling the supply of the color modulated signal according to the comparison result.

The present invention can control whether or not the color temperature is reflected to prevent deterioration of image quality that may occur when the luminance difference between blocks is large and maintain the white balance constant.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention.

1 is a block diagram schematically illustrating a backlight unit according to an exemplary embodiment of the present invention.

Referring to FIG. 1, the backlight unit 10 includes an LED array 20, an LED driver 30, and an LED controller 40.

In the present embodiment, the LED array 20 has a plurality of blocks (blocks 1 to 6) defined as shown in FIG. 2. The LED array 20 may have the same or similar size as the liquid crystal panel of the liquid crystal display device employing the backlight unit 10. The number of blocks (blocks 1 to 6) of the LED array 20 may vary according to its size. For example, as the size of the LED array 20 increases, the number of blocks may increase, and as the size of the LED array 20 decreases, the number of blocks may decrease.

In the LED array 20, a plurality of LEDs are arranged along a line for each block (blocks 1 to 6), and the lines may be arranged at regular intervals. The LEDs can be red, green and blue LEDs. LED pixels can be defined by red, green and blue LEDs. The LED pixel refers to a minimum unit capable of realizing white color by a red LED, a green LED, and a blue LED. The data pixel defined in the liquid crystal panel refers to a minimum unit that can implement full color by red, green, and blue color filters. Therefore, the definition of the LED pixel defined in the present embodiment is different from that of the data pixel of the liquid crystal panel. In addition, the LED pixels defined in the present embodiment are different in size or number from the data pixels of the liquid crystal panel. Since each LED emits light by diffusion, the LED pixels may have a larger size than the data pixels of the liquid crystal panel.

As shown in FIG. 3, for example, red, green, and blue LEDs may be disposed along a line in one direction in the first block (block 1). That is, red, green and blue LEDs are placed along the line, and this arrangement structure can be repeated repeatedly along the line. Thus, a number of LED pixels can be defined on the line, including red, green and blue LEDs. Here, the line may be interpreted as another meaning in one direction. Therefore, in the first block (block 1), a plurality of red, green, and blue LEDs arranged along a line may be arranged at regular intervals. For example, a plurality of red, green and blue LEDs may be disposed on the first line, second line, and third line.

In the first block (block 1), red LEDs may be electrically connected in common, green LEDs may be electrically connected in common, and blue LEDs may be electrically connected in common. Therefore, the red LEDs emit the red light having the same brightness at the same time by the red driving voltage, the green LEDs emit the green light having the same brightness at the same time by the green driving voltage, and the blue LEDs are the same at the same time by the blue driving voltage. Blue light having luminance may be emitted.

Each of the second to sixth blocks (blocks 2 to 6) may have the same or similar LED arrangement as the first block (block 1) described above.

However, the red, green, and blue driving voltages applied to the blocks (blocks 1 to 6) may be different. For example, red driving voltages Vr1 to Vr6 applied to the first to sixth blocks (blocks 1 to 6) are different, and green applied to the first to sixth blocks (blocks 1 to 6). The driving voltages Vg1 to Vg 6 may be different, and the blue driving voltages Vb1 to Vb6 applied to the first to sixth blocks (blocks 1 to 6) may be different.

As described above, since the driving voltages Vr1 to Vr6, Vg1 to Vg6, and Vb1 to Vb6 are applied to each of the blocks (blocks 1 to 6), the driving voltages Vr1 to Vr6 and Vg1 to Since the red, green, and blue LEDs of each of the blocks (blocks 1 to 6) emitted by Vg6 and Vb1 to Vb6) can be individually controlled for each block, image quality can be improved by maintaining white balance.

According to the present embodiment, each block (blocks 1 to 6) may be individually controlled in consideration of not only luminance but also color temperature and ambient temperature. Typically, each LED is different in brightness depending on the ambient temperature. For example, as the ambient temperature decreases, the brightness of each LED may decrease. In addition, a difference in color temperature of each of the red, green, and blue LEDs may occur. Accordingly, the present embodiment can improve image quality while maintaining white balance by individually controlling each block (block 1 to block 6) in consideration of the color temperature and the ambient temperature affecting the LEDs.

At least one temperature sensor capable of sensing the ambient temperature may be disposed on the upper side, the central one side, and the lower side of the LED array 20 to consider the ambient temperature. In addition, a color sensor capable of detecting a color temperature may be disposed on the lower side of the LED array 20. Since the color sensor must separately detect the red color temperature of the red LED, the green color temperature of the green LED, and the blue color temperature of the blue LED, the color sensor may be configured with three color sensors. Accordingly, the red, green, and blue LEDs of each block (blocks 1 to 6) may be driven in consideration of the temperature sensed by the at least one temperature sensor and the color temperature sensed by the color sensor.

The LED driver 30 generates a driving voltage for driving the LED array 20. As described above, since the LED array 20 is defined as six blocks (blocks 1 to 6) and red, green, and blue LEDs are disposed in each block (blocks 1 to 6), 16 driving voltages are provided. (Vr1 to Vr6, Vg1 to Vg6 and Vb1 to Vb6) may be generated. Each of the driving voltages Vr1 to Vr6, Vg1 to Vg6, and Vb1 to Vb6 may be generated by sixteen PWM signals supplied from the LED controller 40. Each PWM signal may consist of a pulse having an on duty ratio. Accordingly, PWM signals of pulses having different on duty ratios for each block (blocks 1 to 6) and for each LED are supplied from the LED controller 40 to the LED driver 30, and the LED driver 30 ) May generate 16 different driving voltages using PWM signals of pulses having different on duty ratios from each other. As the on duty ratio increases, the driving voltage generated by the LED driver 30 may increase.

4 is a block diagram illustrating the LED controller of FIG. 1.

Referring to FIG. 4, the LED controller 40 includes a luminance modulator 41, a switch controller 42, a color modulator 43, a switch 44, a temperature modulator 45, and a mixing unit 46. And a PWM generator 47.

The luminance modulator 41 generates optimal luminance for each block of the LED array 20 using video data. As illustrated in FIG. 5, the luminance modulator 41 includes a data region divider 111, an average luminance calculator 113 for each data region, and a luminance determiner 115.

The data region dividing unit 111 divides video data of one frame into a plurality of data regions so as to correspond to each block (blocks 1 to 6) defined in the LED array 20. One frame of video data refers to an image capable of displaying the liquid crystal panel for one frame. Since six blocks (blocks 1 to 6) are defined in the LED array 20, the video data may also be divided into six data areas. Each data area may include a plurality of red, green, and blue data.

The average brightness calculator 113 for each data area calculates an average brightness of each data area. The average luminance of all the red, green, and blue data included in each data area may be calculated. For example, when 20 red data, 20 green data, and 20 blue data are included in one data area, an average luminance of 60 red, green, and blue data may be calculated.

The luminance determiner 115 determines the luminance of each block (block 1 to block 6) of the LED array 20 based on the average luminance calculated in each data area, and the luminance modulated signal corresponding to the determined luminance. Create

The color modulator 43 adjusts color temperatures of red, green, and blue LEDs provided in each block of the LED array 20 based on color sensor signals detected from the color sensors disposed in the LED array 20. do. For example, when the color temperature of green is lowered from the color sensor signal detected by the color sensor, it may be corrected to have an optimal green color temperature.

As described above, as the color sensor is disposed on the lower side of the LED array 20, the distance between each block of the LED array 20 and the color sensor is different from each other. That is, the first to third blocks (blocks 1 to 3) of the LED array 20 are disposed on the lower side of the LED array 20 compared to the fourth to sixth blocks (blocks 4 to 6). Further away from the color sensor. Accordingly, the color sensor may generate a relatively accurate color sensor signal for the first to third blocks (blocks 1 to 3) of the LED array 20, but may not generate the color sensor signal. For the fourth to sixth blocks (blocks 4 to 6), a relatively inaccurate color sensor signal may be generated. In particular, the inaccuracy of the color processor is more severe when the luminance difference between the blocks of the LED array 20 is large.

Therefore, in the present embodiment, when the luminance difference between the blocks is large, the output of the color modulator 43 is cut off so that the color temperature is not temporarily considered in driving each block of the LED array 20. Of course, when the luminance difference between the blocks is small, the output of the color modulator 43 may be maintained to allow the color temperature to be taken into consideration when driving each block of the LED array 20.

To this end, a switch 44 is connected to an output terminal of the color modulator 43, and the switch 44 is switched and controlled by a switch control signal of the switch controller 42.

As illustrated in FIG. 6, the switch controller 42 includes a maximum luminance extractor 121 for each data pixel, a frame average luminance calculator 123, and a switching control determiner 125.

The maximum luminance extractor 121 for each data pixel extracts data having the maximum luminance among red, green, and blue data included in the data pixel. For example, when the red data is 140 gray, the green data is 230 gray, and the blue data is 79 gray, since the green data is the largest at 230 gray, the maximum luminance extractor 121 for each data pixel extracts the green data. Done. The luminance of the extracted data may be temporarily stored. Accordingly, the maximum luminance extractor 121 for each data pixel may temporarily store data having the maximum luminance from each data pixel included in the video data of one frame.

The one frame average luminance calculator 123 calculates an average luminance of the data having the maximum luminance based on data having the maximum luminance extracted from each data pixel of one frame supplied from the maximum luminance calculator for each data pixel. do. For example, red data having a maximum luminance of 180 gradations is extracted from the first data pixel, green data having a maximum luminance of 228 gradations is extracted from the second data pixel, and a maximum luminance of 178 gradations is extracted from the third data pixel. Green data may be extracted, red data having a maximum luminance of 238 grayscales may be extracted from the fourth data pixel, and green data having 78 grayscales may be extracted from the fifth data pixel. In this case, since the one frame average after calculation unit calculates an average luminance value of the data having the maximum luminance, an average gray scale value of (180 + 228 + 178 + 238 + 78) /5=902/5=180.4 is calculated. Can be.

The switching control determiner 125 controls the switch 44 based on the average luminance value of the maximum luminance extracted from each of the data pixels supplied from the one frame average luminance calculator 123. That is, by comparing the average luminance value of the maximum luminance extracted from each of the data pixels with a reference value, a switching control signal is generated according to the comparison result, the switch 44 can be controlled.

If the average luminance value of the maximum luminance extracted from each of the data pixels is larger than a reference value, the switching control determiner 125 generates a switching on signal, and thus the switch 44 is turned on by the switching on signal. Can be. Accordingly, the color modulated signal of the color modulator 43 may be supplied to the mixing unit 46.

If the average luminance value of the maximum luminance extracted from each of the data pixels is smaller than a reference value, the switching control determiner generates a switching off signal, and thus the switch 44 may be turned off by the switching off signal. have. Accordingly, the color modulated signal of the color modulator 43 is not supplied to the mixing unit 46.

The reference value may be an average luminance of blocks having a range of 30% to 40% of white among the blocks defined in the LED array 20. The reference value can be calculated experimentally. For example, if 100 blocks are defined in the LED array 20, the average brightness of the blocks having a range of 30% to 40% where white is possible can be obtained by measuring the 30 blocks among them in a white state. have.

When the luminance difference between the blocks of the LED array 20 is large from this, by driving the LED array 20 without considering the color temperature, it is possible to block the detection error of the color sensor to improve the image quality.

In this embodiment, the switch 44 is disposed at the output terminal of the color modulator 43, and the switch 44 is controlled based on the average of the maximum luminances of the data pixels extracted from each data region of one frame. In addition, even when the luminance difference between the blocks of the LED array 20 is large, the image quality may be improved while maintaining the white balance.

On the other hand, the temperature modulator 45 generates a temperature modulated signal according to the ambient temperature. That is, a temperature modulated signal in which a gain having a range of 0 to 1 may be adjusted according to the ambient temperature sensed by the temperature sensor. For example, the gain may be higher as the ambient temperature is lowered. Since the gain of the temperature modulated signal is reflected in the luminance modulation, the gain can be increased and the driving voltage supplied with the LED array 20 can be increased.

The mixing unit 46 is configured to output the temperature modulation signal output from the temperature modulation unit 45 and the color modulation unit 43 to each luminance modulation signal output from the brightness modulation unit 41. Reflects the signal and outputs it. Each of the luminance modulated signals is a signal outputted by the luminance modulator 41 to individually drive each block of the LED array 20 and the red, green, and blue light emitting diodes included in each block.

The PWM generator 47 generates a PWM signal corresponding to each signal output from the mixing unit 46 and supplies it to the LED driver 30. The LED driver 30 generates a driving voltage according to each PWM signal and is supplied to each block of the LED array and the red, green, and blue light emitting diodes included in each block. Accordingly, each block of the LED array 20 and the red, green, and blue light emitting diodes included in each block may individually emit light with different luminance.

7 is a flowchart illustrating a method of driving a backlight unit according to another embodiment of the present invention.

4, 6, and 7, video data of one frame is supplied to the maximum luminance extractor 121 for each data pixel (S 201). The maximum luminance extractor 121 for each data pixel extracts data having the maximum luminance from each data pixel of the video data of one frame (S203). The data having the extracted maximum luminance may be temporarily stored (S 205).

The switch controller 42 determines whether each data pixel is the last data pixel (S 207).

When the data having the maximum luminance is extracted from the last data pixel, the average luminance calculator of one frame average luminance value of the maximum luminance extracted from the respective data pixels (hereinafter referred to as 'average luminance value of one frame') To calculate (S 209).

The switching control determiner 125 compares the average luminance value of the one frame with a reference value and generates a switching control signal according to the comparison result (S 211). The reference value may be an average luminance of blocks having a range of 30% to 40% of white among the blocks defined in the LED array 20.

If the average luminance value of the one frame is larger than the reference value, the switching control determiner 125 generates a switching on signal (S213). Accordingly, since the switch 44 is turned on by the switching on signal, the color modulation signal of the color modulation unit 43 is supplied to the mixing unit 46 to drive the LED reflecting the color modulation signal (S). 215).

If the average luminance value of the one frame is smaller than the reference value, the switching control determiner generates a switching off signal (S217). Accordingly, since the switch 44 is turned off by the switching off signal, the color modulating signal of the color modulator 43 is not supplied to the mixing unit 46 and thus does not reflect the color modulated signal. Drive is made (S 219).

Therefore, in the present exemplary embodiment, since the LED can be driven with or without the color modulation signal based on the average luminance of the data having the maximum luminance extracted from the data pixels of one frame, the image quality due to the detection error of the color sensor is possible. The fall can be prevented.

1 is a block diagram schematically illustrating a backlight unit according to an embodiment of the present invention.

FIG. 2 shows blocks defined in the LED array of FIG. 1. FIG.

3 is a view showing light emitting diodes arranged in each block of FIG.

4 is a block diagram illustrating the LED control unit of FIG. 1.

FIG. 5 is a block diagram illustrating the luminance modulation of FIG. 4. FIG.

FIG. 6 is a block diagram illustrating the switch controller of FIG. 4. FIG.

20: LED array 30: LED driver

40: LED controller 41: luminance modulator

42: switch control section 43: color modulation section

44: switch 45: temperature modulator

46: mixing section 47: PWM generator

111: data area division unit 113: average luminance calculation unit for each data area

115: luminance determining unit 121: maximum luminance extraction unit for each data pixel

123: one frame average luminance calculator 125: switching control determiner

Claims

An LED array defined by a plurality of blocks, the plurality of red, green and blue light emitting diodes disposed in each block;

An LED driver generating a plurality of driving voltages reflecting the color temperature and the ambient temperature to individually drive each block of the LED array and the red, green, and blue light emitting diodes included in each block; And

And a LED controller for generating a plurality of control signals reflecting the color temperature and the ambient temperature to control the LED driver, and selectively controlling whether the color temperature is reflected.

The method of claim 1, wherein the LED control unit,

A luminance modulator for dividing video data of one frame into a plurality of data regions to determine luminance of each data division region and to generate a luminance modulated signal according to the determined luminances;

A temperature modulator for generating a temperature modulated signal according to the ambient temperature;

A color modulator for generating a color modulated signal according to the color temperature;

A mixing unit which reflects the temperature modulated signal and the color modulated signal to each luminance modulated signal and outputs the reflected signal;

A switch disposed between the color modulator and the mixing unit;

A switch controller which controls the supply of the color modulated signal by switching the switch based on an average luminance value of data having maximum luminance extracted from data pixels of the one frame of video data; And

And a PWM generator which generates a PWM signal corresponding to each signal output from the mixing unit and supplies the PWM signal to the LED driver.

The method of claim 2, wherein the luminance modulator,

An area divider dividing the video data of the one frame into a plurality of data areas;

A first average luminance calculator configured to calculate an average luminance of each of the divided data regions;

And a luminance determiner configured to generate a luminance modulated signal according to the average luminance of each of the calculated data regions.

The method of claim 2, wherein the switch control unit,

A maximum luminance extracting unit which extracts data having maximum luminance from respective data pixels of the video data of the one frame;

A second average luminance calculator configured to calculate an average luminance of the extracted maximum luminance data;

And a switching control determining unit for comparing the average brightness of the data with a reference value and generating a switch control signal for controlling the switch according to the comparison result.

The backlight unit of claim 4, wherein the reference value is an average luminance of blocks having a range of 30% to 40% of white among blocks defined in the LED array.

The backlight unit of claim 4, wherein the switch is turned on by the switch control signal when the average brightness of the data is larger than a reference value.

The backlight unit of claim 4, wherein the switch is turned off by the switch control signal when the average brightness of the data is smaller than a reference value.

A backlight unit defined by a plurality of blocks, each LED array having a plurality of red, green and blue light emitting diodes disposed in each block, and a LED driver for driving the LED array,

Extracting data having maximum luminance from respective data pixels of one frame of video data;

Calculating an average brightness of the data having the extracted maximum brightness; And

And comparing the average brightness of the data with a reference value and switching-controlling the supply of the color modulated signal according to the comparison result.

The method of claim 8, further comprising supplying a plurality of driving voltages reflecting the color modulation signal to each block of the LED array and each light emitting diode included in each block according to the switching control. A driving method of the backlight unit.

The method of claim 8, wherein the reference value is an average luminance of blocks having a range of 30% to 40% of white among blocks defined in the LED array.

The method of claim 8, wherein the switch is turned on by the switch control signal when the average brightness of the data is larger than a reference value.

The method of claim 8, wherein when the average luminance of the data is smaller than a reference value, the switch is turned off by the switch control signal.