KR101282997B1 - Liquid crystal display device and backlight driving method thereof - Google Patents

Abstract

The present invention relates to a liquid crystal display and a backlight driving method of the liquid crystal display, wherein S (S is a natural number of two or more) LED arrays are divided into a plurality of groups, and each group has the same frequency but has a phase A backlight driving method of a liquid crystal display device and a liquid crystal display device employing the same are provided by applying a PWM signal having a difference to control the light emitting driving of the S LED arrays. It offers the advantage of improving wave noise in panels.

Description

Liquid crystal display device and backlight driving method thereof

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device and a backlight driving method of the liquid crystal display device, and more particularly, to a backlight driving method using an LED array mounted with a light emitting diode (LED) and a liquid crystal display device employing the backlight.

Liquid crystal display (hereinafter referred to as "LCD") is a plurality of liquid crystal cells arranged in a matrix form and for supplying the image data for controlling the light transmittance by controlling the rotation angle of the liquid crystal to each of these liquid crystal cells A desired image is displayed on a screen by transmitting light supplied from a backlight unit to a liquid crystal panel provided with a TFT (thin film transistor).

As a light source used in such a backlight unit, a cold cathode fluorescent lamp (hereinafter referred to as 'CCFL') is mainly used. Such a backlight unit has a trend of miniaturization, thinning, and weight reduction. In accordance with this trend, light emitting diodes (LEDs), which are advantageous in terms of power consumption, weight, and brightness, have been proposed instead of CCFLs used in backlight units.

FIG. 1 is a view schematically illustrating a configuration using LEDs as an edge type backlight unit of a liquid crystal display according to the related art, and includes a plurality of LED arrays 10 and an LED driver 20. It is composed.

The LED array 10 is composed of a plurality of LEDs 12 for emitting white light, the LED array 10 is generally composed of a plurality.

The LED driver 20 receives a pulse width modulation (PWM) signal from an external circuit unit, and supplies power in synchronization with an on period of the input PWM signal to turn on / off the plurality of LED arrays 10. / off).

The reason why the on / off state is repeated by using a PWM signal instead of maintaining the on state of the plurality of LED arrays 10 by using a DC voltage signal is because of the backlight. This is because the color characteristics of the backlight unit are better when the driving unit is advantageous in terms of power consumption of the unit and the on / off state is repeatedly driven due to the characteristics of the LED 12 itself.

However, the plurality of LED arrays 10 controlled by using one PWM signal input to the LED driver 20 are simultaneously controlled on / off because the same PWM signal is applied.

On the other hand, the TFT of the liquid crystal panel is made of amorphous silicon, which, when received, generates a photo leakage current corresponding to the intensity of the incident light when the light is received. current).

Therefore, when the LED array 10 is alternately driven in the on / off state using a PWM signal, the off current value of the thin film transistor of the liquid crystal panel is changed, and the off current variation of the thin film transistor is used to display an image on the liquid crystal panel. When displayed, it may cause defects, such as wavy noise, in which some areas become wavy and brighter.

The present invention has been made to solve the above problems, in the liquid crystal display device for driving the backlight unit using the LED wave noise generated on the liquid crystal panel by the on / off state alternate driving of the backlight unit using the PWM signal. It aims at improving defects, such as a phenomenon.

In order to achieve the above object, the present invention, S (S is a natural number of two or more) LED array is divided into a plurality of groups, and a plurality of PWM signals having the same frequency but phase difference with each other for the plurality of groups The backlight driving method of the liquid crystal display device is characterized by controlling the light emission driving of the S LED array by applying each.

In the driving method, the number of groups is determined to be one of 2 to S, and the number of S LED arrays belonging to the plurality of groups is the same.

In the driving method, the plurality of PWM signals are characterized by the same voltage level. In the driving method, the plurality of groups includes a first group and a second group, and the plurality of PWM signals A first and second PWM signal having a phase difference of 180 degrees with each other, wherein the first and second PWM signals each have a duty ratio of 1% to 99%, or the plurality of groups include first, second, and 3 groups, wherein the plurality of PWM signals include first, second, and third PWM signals having a phase difference of 120 degrees from each other, and the first, second, and third PWM signals each include 1% to 99% of each other. Or a plurality of groups including first to sixth groups, and the plurality of PWM signals include first to sixth PWM signals having a phase difference of 60 degrees from each other, and the first to sixth PWMs. The signals each have a duty ratio of 1% to 99%, or the plurality of groups are first to eighth. And a plurality of PWM signals including first to eighth PWM signals having a phase difference of 45 degrees from each other, and the first to eighth PWM signals each have a duty ratio of 1% to 99%. do.

The plurality of groups may include first to nth groups, and the plurality of PWM signals may include first to nth PWM signals having a phase difference of 360 degrees from each other, and the first to nth PWM signals may include: Each of them has a duty ratio of 100 / n%.

The plurality of groups may include first to nth groups, n may be an even number, and the plurality of PWM signals may include first to nth PWM signals having a phase difference of 360 degrees from each other. Each of the 1 st to n th PWMM signals has a duty ratio of 50%.

In addition, the present invention, the LED array unit having S (S is a natural number of two or more) LED array; An LED driver for outputting a plurality of PWM signals having phase differences from each other for driving control of the S LED arrays; A liquid crystal panel that receives light emitted from the S LED arrays and displays an image; A gate driver for outputting a scan signal to the liquid crystal panel; A source driver for outputting image data to the liquid crystal panel in synchronization with the scan signal; A liquid crystal display device including a timing controller for outputting a plurality of control signals for controlling the driving of the LED driver, the gate driver and the source driver.

In the liquid crystal display device, each of the S LED array is characterized by consisting of a plurality of LEDs.

In the liquid crystal display device, the plurality of PWM signals have the same frequency and the same voltage level.

In the liquid crystal display device, each of the plurality of PWM signals is applied to at least one LED array of the S LED arrays.

In the liquid crystal display device, the plurality of groups include first and second groups, and the plurality of PWM signals include first and second PWM signals having a phase difference of 180 degrees from each other. Each 2PWM signal has a duty ratio of 1% to 99%, or the plurality of groups include first, second and third groups, and the plurality of PWM signals have a phase difference of 120 degrees from each other. And a second and a third PWM signal, wherein the first, second, and third PWM signals each have a duty ratio of 1% to 99%, or the plurality of groups include first to sixth groups, The plurality of PWM signals include first to sixth PWM signals having a phase difference of 60 degrees from each other, and the first to sixth PWM signals each have a duty ratio of 1% to 99%, or the plurality of groups may be 1 to 8 group, wherein the plurality of PWM signals are the first to eighth PWM signal having a phase difference of 45 degrees from each other And the first to eighth PWM signals each have a duty ratio of 1% to 99%.

In the liquid crystal display device, the plurality of PWM signals are generated through a phase shifter.

The plurality of groups may include first to nth groups, and the plurality of PWM signals may include first to nth PWM signals having a phase difference of 360 degrees from each other, and the first to nth PWM signals may include: Each of them has a duty ratio of 100 / n%.

The plurality of groups may include first to nth groups, n is an even number, and the plurality of PWM signals may include first to nth PWM signals having a phase difference of 360 degrees from each other. Each of the 1 st to n th PWMM signals has a duty ratio of 50%.

According to the present invention, in a display device having a plurality of LED arrays and used as a backlight unit, the plurality of LED arrays are divided into a plurality of groups, and different PWM signals having a phase difference for each group are applied to each other. By reducing the number of LED arrays driven simultaneously through "group-specific parallax driving," the amount of light incident to the liquid crystal panel is reduced, thereby providing a method of improving wave noise.

According to this method, since the total amount of light incident on the liquid crystal panel is the same, there is an advantage of improving wave noise in the display panel while the viewer does not feel the luminance change.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings.

FIG. 2 is a configuration diagram briefly illustrating a configuration of a liquid crystal display device according to the present invention. The liquid crystal panel 50, the gate driver 60, the source driver 70, the LED array 80, and the LED driver ( 90 and the timing controller 100.

Briefly, although not illustrated, the liquid crystal panel 50 includes a thin film transistor TFT and a liquid crystal LC in each of a plurality of pixel regions divided by a plurality of data lines and a plurality of gate lines. The image is displayed by the data written into the liquid crystal LC through the switching control of the TFT.

The gate driver 60 outputs a scan signal to the gate wiring to control the switching of the thin film transistor TFT configured in the liquid crystal panel 50, and the data driver 70 synchronizes the scan signal. By outputting the image data through the data line and writing the image data into the liquid crystal LC, the image display on the liquid crystal panel 50 is performed.

The LED array unit 80 is a backlight unit, as shown in Figure 3, is composed of a plurality of LED arrays (80a ~ 80d) mounted with a plurality of LEDs emitting white light, it is easy to thin the product and control the light emission For this purpose, the LED array unit 80 may be configured at the edge (edge-type) of the liquid crystal panel 50, but in another embodiment, the LED array unit including a plurality of LED arrays that are components of the backlight unit is a liquid crystal. The present invention can also be applied to a direct-type liquid crystal display device disposed below the panel. In addition, the LED array unit 80 can be divided into a plurality of LED array (80a ~ 80d) configured in a group of 'group' which means a group of the LED array to which the same PWM signal is input, the group according to the circuit connection It is preferable to be divided into two or more, and the LED array is configured in the same number for each group. In addition, the PWM signals input to each group are different from each other, but the PWM signals input to one group are equally input to the entire LED array belonging to the group. In FIG. 3, four LED arrays 80a to 80d are divided into two groups A and B for illustrative purposes.

The LED driver 90 performs light emission driving control on the LED arrays 80a to 80d of the LED array unit 80. To this end, the LED driver 90 outputs a plurality of PWM signals received from an external circuit or generated within itself. do. In this case, the plurality of PWM signals output from the LED driver 90 are all the same frequency, each of which is output with a different phase, for example, 180 degrees or 120 degrees or 60 degrees, respectively, the LED driver 90 may include a phase shifter for generating a plurality of PWM signals having phase differences.

In addition, the timing controller 100 provides a plurality of control signals and image data for controlling the driving of the gate driver 60 and the source driver 70, and provides a control signal for driving control of the LED driver 90. to provide.

The liquid crystal display device according to the present invention comprises a LED array unit 80 including a plurality of LED arrays 80a to 80d as a backlight unit, and outputs a plurality of PWM signals having the same frequency but phase difference. The LED driving unit 90 is provided to perform light emission control of each LED array. In this case, the plurality of LED arrays 80a to 80d may be configured and driven in groups by electrical circuit connection.

Hereinafter, the backlight driving method of the liquid crystal display according to the present invention will be briefly summarized. In order to improve the wave noise phenomenon in the liquid crystal panel caused by the simultaneous light emission driving of the entire LED array, the present invention provides an LED array. The main concept is to improve the wave noise phenomenon by reducing the amount of instantaneous light generated by one PWM signal by dividing the light into a plurality of groups and driving light emission with a parallax. Hereinafter, the present invention will be described with various embodiments.

First Embodiment

4A and 4B are LED array circuit diagrams and PWM signal diagrams for explaining the backlight driving method of the liquid crystal display according to the first embodiment of the present invention, respectively. The configuration of a plurality of LED arrays of the array unit 80 will be described by combining the 24 LED arrays LA1 to LA24. The reason why the number of LED arrays is 24 is for convenience of comparison with the second to fourth embodiments described later.

As shown in FIG. 4A, the backlight driving method according to the first exemplary embodiment of the present invention performs a circuit connection so that the 24 LED arrays LA1 to LA24 are divided into two groups GR1 and GR2. Accordingly, the first PWM signal PWM1 and the second PWM signal PWM2 are respectively applied to the first group GR1: LA1, LA3, LA5, ..., LA23 and the second group GR2: LA2, LA4, LA6, ..., LA24. Apply.

In this case, the first PWM signal PWM1 and the second PWM signal PWM2 are signals having an on-duty of 50%, the same frequency, and a phase difference of 180 degrees, that is, inverted phases, as shown in FIG. 4B. . In addition, although the duty ratio, ie, on ?? duty is illustrated as 50% in FIG. 4B, the on ?? duty may be selected from a value between 1% and 99%.

When the plurality of LED arrays LA1 to LA24 are driven through the configuration and features as described above, the second and second LED arrays LA1, LA3, LA5,..., LA23 of the first group GR1 emit light. The LED arrays LA2, LA4, LA6, ..., LA24 of the group GR2 emit light and the driving is repeated. The plurality of LED arrays LA1 to LA24 are separated into two groups to be driven at different timings. As a result, the number of LEDs being turned on at the same time is reduced, thereby reducing the instantaneous amount of light incident on the liquid crystal panel. As a result, wave noise due to the off current variation of the thin film transistor of the liquid crystal panel is improved.

In addition, the instantaneous light amount is reduced to 1/2 level compared to when the 24 LED arrays LA1 to LA24 emit light at the same time, but since the entire LED arrays LA1 to LA24 emit light at different timings, Since the average total amount of light supplied to the liquid crystal panel is almost the same as before, there is no phenomenon such as a decrease in luminance.

Hereinafter, in the driving method according to the first embodiment of the present invention, an experimental result graph attached to a wave noise improvement effect according to various duty ratios of the first PWM signal and the second PWM signal PWM1 and PWM2 is applied. It demonstrates with reference.

5A and 5B illustrate the simultaneous light emission driving of the LED array according to the driving method of the comparative example and the driving method of the first embodiment of the present invention using a PWM signal having on-duty of 10%, respectively (phase difference between PWM signals: 180 degrees). Is a graph showing the input PWM signal of the split driving according to and the light quantity measurement result accordingly.

Referring first to FIG. 5A, which illustrates a backlight driving method according to the related art as a comparative example, the 24th LED array having the 0PWM signal PWM0 having an arbitrary frequency and an arbitrary voltage level of 10% on ?? In the case of simultaneous input to all of LA1 to LA24, the light amount is changed from 0 to 1 in synchronization with the 0th PWM signal PWM0 signal.

Here, the measurement of the amount of light can be measured by using an electrical signal generated in proportion to the amount of light by installing a photo diode (Photo diode), etc. In FIG. 5A, 24 LED arrays LA1 to LA24 using the 0th PWM signal PWM0 in FIG. The minimum value and the maximum value of the light quantity change for the simultaneous light emission drive of are set to '0' and '1', respectively, for convenience of comparison with the present invention.

5B illustrates a backlight driving method according to the first embodiment of the present invention, the first PWM signal PWM1 may be included in the LED arrays LA1, LA3, LA5,..., And LA23 of the first group GR1 of FIG. 4A. ) Is input and the second PWM signal PWM2 is input to the LED arrays LA2, LA4, LA6, ..., LA24 of the second group GR2, respectively.

The frequency, voltage level, and on-duty (10%) of the first PWM signal and the second PWM signal PWM1 and PWM2 are all the same as the zero PWM signal PWM0 of FIG. 5A, but the first PWM signal PWM1 And the second PWM signal PWM2 are input through a phase difference of 180 degrees with each other.

Accordingly, the LED arrays LA1, LA3, LA5,..., LA23 and the second group of the first group GR1 are input by the first PWM signal PWM1 and the second PWM signal PWMM2 having a phase difference of 180 degrees. The LED arrays LA2, LA4, LA6, ..., LA24 of GR2 alternately emit light, and the number of emission of the backlight by the first PWM signal PWM1 and the second PWM signal PWM2 of FIG. 5B is equal to that of FIG. 5A. The number of times of light emission of the backlight caused by the 0th PWM signal PWM0 is increased twice.

The number (12) of LED arrays emitted by each of the first PWM signal (PWM1) and the second PWM signal (PWM2) is greater than the number of LED arrays (24) emitted by the 0PWM signal (PWM0) of FIG. 5A. Since it is 1/2, the average instantaneous light amount at the time of one light emission is 1/2 level, but since the total number of light emission is doubled, the average total light amount of light supplied from the plurality of LED arrays to the liquid crystal panel (the sum of the total area of the light amount graph is The total amount of light) is substantially the same in the driving of FIGS. 5A and 5B.

6A and 6B are graphs identical to the above-described experimental settings of FIGS. 5A and 5B, but the on-duty of the 0th PWM signal PWM0 and the first and second PWM signals PWM1 and PWM2 is 50%. Simultaneous light emission driving of a plurality of LED arrays according to the driving method of the comparative example in the case of the present invention and input PWM signal of split driving according to the driving method (phase difference between PWM signals: 180 degrees) of the first embodiment of the present invention and the result of measuring the amount of light It is a graph shown.

FIG. 6A also shows the lowest and highest values of light quantity change for the total simultaneous light emission driving of 24 LED arrays (LA1 to LA24 of FIG. 4A) using the 0th PWM signal PWM0, respectively, for convenience of comparison with the present invention. Set to '1'.

6B illustrates a backlight driving method according to the first exemplary embodiment of the present invention, the first PWM signal PWM1 is included in the LED arrays LA1, LA3, LA5,..., And LA23 of the first group GR1 of FIG. 4A. ) Is input and the second PWM signal PWM2 is input to the LED arrays LA2, LA4, LA6, ..., LA24 of the second group GR2, respectively.

The frequency, voltage level, and on-duty (50%) of the first and second PWM signals PWM1 and PWM2 are all the same as the 0th PWM signal PWM0 of FIG. 6A, but the first PWM signal PWM1 and the first PWM signal PWM1 are The second PWM signal PWM2 is input with a phase difference of 180 degrees from each other.

Accordingly, the LED arrays LA1, LA3, LA5,..., LA23 and the second group of the first group GR1 are input by the first PWM signal PWM1 and the second PWM signal PWMM2 having a phase difference of 180 degrees. The LED arrays LA2, LA4, LA6, ..., LA24 of GR2 alternately emit light, and the number of emission of the backlight by the first PWM signal PWM1 and the second PWM signal PWMM of FIG. 6B is the same as that of FIG. 6A. The number of times of light emission of the backlight caused by the 0th PWM signal PWM0 is increased twice.

The number (12) of LED arrays emitted by each of the first PWM signal (PWM1) and the second PWM signal (PWM2) is greater than the number of LED arrays (24) emitted by the 0PWM signal (PWM0) of FIG. 6A. Since it is 1/2, the average instantaneous light quantity at the time of one light emission is 1/2, but since the number of light emission is doubled, the average total light amount of light supplied from the plurality of LED arrays to the liquid crystal panel (sum of the total area of the light intensity graph = total = The amount of light) is substantially the same in the driving of FIGS. 6A and 6B.

In particular, in this case, since the average instantaneous light amount by the first PWM signal and the second PWM signal PWM1 and PWM2 is the same at any point in time, the amount of light supplied to the liquid crystal panel from a plurality of LED arrays in the backlight is recognized as constant. As a result, the off current fluctuation of the thin film transistor of the liquid crystal panel is minimized, and the wave noise is further improved.

7A and 7B are graphs identical to those of the above-described experimental settings of FIGS. 5A and 5B, but the on-duty of the 0th PWM signal PWM0 and the first and second PWM signals PWM1 and PWM2 is 90%. Simultaneous light emission driving of a plurality of LED arrays according to the driving method of the comparative example in the case of the present invention and input PWM signal of split driving according to the driving method (phase difference between PWM signals: 180 degrees) of the first embodiment of the present invention and the result of measuring the amount of light It is a graph shown.

FIG. 7A also shows the lowest and highest values of light quantity change for all six LED arrays (LA1 to LA24 in FIG. 4A) using the 0th PWM signal PWM0, respectively, for convenience of comparison with the present invention. Set to '1'.

7B illustrates a backlight driving method according to the first exemplary embodiment of the present invention, the first PWM signal PWM1 is applied to the LED arrays LA1, LA3, LA5,..., And LA23 of the first group GR1 of FIG. 4A. ) Is input and the second PWM signal PWM2 is input to the LED arrays LA2, LA4, LA6, ..., LA24 of the second group GR2, respectively.

The frequency, voltage level, and on-duty (90%) of the first and second PWM signals PWM1 and PWM2 are all the same as the zero PWM signal PWM0 of FIG. 7A, but the first PWM signal PWM1 and the first PWM signal PWM1 are different from each other. The second PWM signal PWM2 is input with a phase difference of 180 degrees from each other.

Accordingly, the LED arrays LA1, LA3, LA5,..., LA23 and the second group of the first group GR1 are input by the first PWM signal PWM1 and the second PWM signal PWMM2 having a phase difference of 180 degrees. The LED arrays LA2, LA4, LA6, ..., and LA24 of GR2 alternately emit light, and the number of emission of the backlight by the first and second PWM signals PWM1 and PWM2 of FIG. 7B is 0PWM of FIG. 7A. The number of times of light emission of the backlight by the signal PWM0 is increased by two times.

The number (12) of LED arrays emitted by each of the first PWM signal (PWM1) and the second PWM signal (PWM2) is greater than the number of LED arrays (24) emitted by the 0PWM signal (PWM0) of FIG. 7A. Since it is 1/2, the average instantaneous light quantity at the time of one light emission by one PWM signal is 1/2, but the light is emitted twice by the first PWM signal PWM1 and the second PWM signal PWM2, so that the liquid crystal panel can be The average total light quantity (sum of the total area of the light quantity graph = total light quantity) of the light supplied to is substantially the same in the driving of Figs. 7A and 7B.

As a result, in the first embodiment of the present invention, by dividing a plurality of LED arrays into two groups, wave noise caused by variation of off current of a thin film transistor of a liquid crystal panel proportional to the intensity of light supplied from a backlight is generated. While improving, there is an advantage that no decrease in luminance occurs.

Second Embodiment

8A and 8B are an LED array circuit diagram and a PWM signal diagram for explaining a backlight driving method of a liquid crystal display according to a second embodiment of the present invention, respectively. The configuration of a plurality of LED array of the LED array unit 80 of the configuration according to the 24 LED array (LA1 ~ LA24) will be described.

As shown in FIG. 8A, the backlight driving method according to the second embodiment of the present invention performs circuit connection so that the 24 LED arrays LA1 to LA24 are divided into three groups GR1, GR2, and GR3. The first group (GR1: LA1, LA4, LA7, ..., LA22), the second group (GR2: LA2, LA5, LA8, ..., LA23) and the third group (GR3: LA3, LA6, LA9, ..., the first PWM signal PWM1, the second PWM signal PWM2 and the third PWM signal PWM3, respectively, are applied to LA24.

In this case, the first PWM signals to the third PWM signals PWM1 to PWM3 are signals having the same frequency and differing in phase by 120 degrees as shown in FIG. 8B. In addition, although FIG. 8B illustrates on-duty as about 33% in duty ratio, the on-duty may be arbitrarily selected from a value between 1% and 99%.

When the plurality of LED arrays LA1 to LA24 are driven through the exemplary configuration and features as described above, the LED arrays LA1, LA4, LA7,..., LA22 of the first group GR1 emit light, and then the second array. Sequential driving in which the LED arrays LA2, LA5, LA8, ..., LA23 of the two groups GR2 emit light and then the LED arrays LA3, LA6, LA9, ..., LA24 of the third group GR3 emit light. This is repeated, by separating a plurality of LED arrays (LA1 ~ LA24) into three groups and driving at different timings, respectively, to reduce the number of LEDs that are on at the same time, and thus the amount of instantaneous light incident on the liquid crystal panel And the wave noise due to the off current variation of the thin film transistor of the liquid crystal panel is improved.

 In addition, since each of the LED arrays LA1 to LA24 emits light once, the average of the total amount of light supplied from the plurality of LED arrays to the liquid crystal panel is almost different from the conventional one, so that a phenomenon such as luminance decrease does not occur.

Hereinafter, referring to a graph of an experimental result attached to the wave noise improvement effect according to the application of various duty ratios of the first PWM signals to the third PWM signals PWM1 to PWM3 in the driving method according to the second embodiment of the present invention. Will be explained.

9A and 9B show the simultaneous light emission driving of the LED array according to the driving method of the comparative example and the driving method of the second embodiment of the present invention (PWM signal: 120 degrees) using a PWM signal having on-duty of 10%, respectively. Is a graph showing the input PWM signal of the split driving according to and the light quantity measurement result accordingly.

Referring to FIG. 9A, which illustrates a backlight driving method according to the prior art as a comparative example, the 24th LED array (PWM0) having an arbitrary frequency and an arbitrary voltage level of 10% on ?? When the signals are simultaneously input to all of LA1 to LA24, the amount of light is changed from 0 to 1 in synchronization with the 0th PWM signal PWM0 signal.

In addition, as in the first embodiment, the measurement of the amount of light can be measured by using an electrical signal generated in proportion to the amount of light by installing a photodiode or the like. In FIG. 9A, 24 using the 0th PWM signal PWM0 is used. The minimum value and the maximum value of the light quantity change for the simultaneous light emission driving of the two LED arrays LA1 to LA24 are set to '0' and '1', respectively, for convenience of comparison with the present invention.

9B illustrates a backlight driving method according to the second embodiment of the present invention, the first PWM signal PWM1 may be included in the LED arrays LA1, LA4, LA7,..., And LA22 of the first group GR1 of FIG. 9A. ) Is input to the LED arrays LA2, LA5, LA8, ..., and LA23 of the second group GR2, and the second PWM signal PWM2 is input to the LED arrays LA3, LA6, and LA9 of the third group GR3. ..., ..., 3rd PWM signal PWM3 is input respectively, and this drive is repeated.

The frequency, voltage level, and on-duty (10%) of the first to third PWM signals PWM1 to PWM3 are all the same as the 0 PWM signal PWM0 of FIG. 9A, but the first PWM signal PWM1 The third to third PWM signals PWM2 are input to have a phase difference of 120 degrees. That is, the second PWM signal PWM2 has a phase delayed by 120 degrees from the first PWM signal PWM1 and the third PWM signal PWM3 has a phase that is delayed by 240 degrees from the first PWM signal PWM1.

Accordingly, the LED arrays LA1, LA4, LA7,..., LA22 of the first group GR1 are connected to the second group by the first to third PWM signals PWM1 to PWM3 having a phase difference of 120 degrees. The LED arrays LA2, LA5, LA8, ..., LA23 of GR2 and the LED arrays LA3, LA6, LA9, ..., LA24 of the third group GR3 are sequentially lighted, and the first through the first to the second ones of FIG. The number of light emission times of the backlight by the 3 PWM signals PWM1 to PWM3 has three times the light emission times of the backlight by the 0th PWM signal PWM0 of FIG. 9A.

The number (8) of LED arrays emitted by each of the first to third PWM signals (PWM1 to PWMM3) is 1 compared to the number of LED arrays (24) emitted by the 0PWM signal (PWM0) of FIG. 9A. Since the average instantaneous light amount at the time of one light emission by one PWM signal is 1/3, the number of light emission times is increased three times by each of the first to third PWM signals PWM1 to PWM3, so that the liquid crystal panel can be The average total light amount of the light supplied to (the sum of the total areas of the light quantity graphs becomes the total light amount) appears substantially the same in the driving of Figs. 9A and 9B.

The experimental result graphs of FIGS. 10A and 10B are the same as those of the above-described experimental settings of FIGS. 9A and 9B, but 50% of on ?? duty of the 0PWM signal PWM0 and the 1PWM to 3PWM signals PWM1 to PWM3 are 50%. The simultaneous PWM driving of the plurality of LED arrays according to the driving method of the comparative example in the case of and the input PWM signal of the split driving according to the driving method (phase difference between PWM signals: 120 degrees) of the second embodiment of the present invention and the result of measuring the amount of light Is a graph.

FIG. 10A also shows a minimum value and a maximum value of light quantity change of all 24 LED arrays (LA1 to LA24 of FIG. 8A) using the 0th PWM signal PWM0 for the convenience of comparison with the present invention. Set to '1'.

10B illustrates a backlight driving method according to the second embodiment of the present invention, the first PWM signal PWM1 is applied to the LED arrays LA1, LA4, LA7,..., And LA22 of the first group GR1 of FIG. 8A. In addition, the second array GR2 LED arrays LA2, LA5, LA8, ..., LA23 have a second PWM signal PWM2 and the third group GR3 has an LED array LA3, LA6, LA9, ..., ... The third PWM signal PWM3 is input to the LA24 respectively.

The frequency, voltage level, and on-duty (50%) of the first to third PWM signals PWM1 to PWM3 are all the same as the zero PWM signal PWM0 of FIG. 10A, but the first PWM signal to third PWM signal Signals PWM1 to PWM3 are input with a phase difference of 120 degrees from each other. That is, the second PWM signal PWM2 has a phase delayed by 120 degrees from the first PWM signal PWM1 and the third PWM signal PWM3 has a phase that is delayed by 240 degrees from the first PWM signal PWM1.

Accordingly, the LED arrays LA1, LA4, LA7,..., LA22 of the first group GR1 are connected to the second group by the first to third PWM signals PWM1 to PWM3 having a phase difference of 120 degrees. The LED arrays LA2, LA5, LA8,..., LA23 of GR2 and the LED arrays LA3, LA6, LA9,..., LA24 of the third group GR3 are sequentially lighted to emit the 0PWM signal of FIG. 10A. It has three times as many light emission times as the light emission number by PWM0).

The number (8) of LED arrays emitted by each of the first to third PWM signals (PWM1 to PWMM3) is 1 compared to the number of LED arrays (24) emitted by the 0PWM signal (PWM0) of FIG. 10A. Since the average instantaneous light amount at one light emission by one PWM signal is 1/3, the light is emitted three times by each of the first to third PWM signals (PWM1 to PWM3). The average total light quantity (sum of the total area of the light quantity graph = total light quantity) of light supplied is substantially the same in the driving of Figs. 10A and 10B.

The experimental result graphs of FIGS. 11A and 11B are the same as the experimental settings of FIGS. 9A and 9B described above, but 90% of the on-duty of the 0PWM signal PWM0 and the 1PWM to 3PWM signals PWM1 to PWM3 are 90%. The simultaneous PWM driving of the plurality of LED arrays according to the driving method of the comparative example in case of, and the input PWM signal of split driving according to the driving method (phase difference between PWM signals: 120 degrees) according to the second embodiment of the present invention and the result of measuring the amount of light Is a graph.

FIG. 11A also shows a minimum value and a maximum value of light quantity change for all the simultaneous light emission driving operations of 24 LED arrays (LA1 to LA24 of FIG. 8A) using the 0th PWM signal PWM0, respectively, for convenience of comparison with the present invention. Set to '1'.

11B illustrates a backlight driving method according to the second embodiment of the present invention, the first PWM signal PWM1 is applied to the LED arrays LA1, LA4, LA7,..., And LA22 of the first group GR1 of FIG. 8A. In addition, the second array GR2 LED arrays LA2, LA5, LA8, ..., LA23 have a second PWM signal PWM2 and the third group GR3 has an LED array LA3, LA6, LA9, ..., ... The third PWM signal PWM3 is input to the LA24 respectively.

The frequency, voltage level, and on-duty (90%) of the first to third PWM signals PWM1 to PWM3 are all the same as the zero PWM signal PWM0 of FIG. 11A, but the first to third PWM signals to third PWM Signals PWM1 to PWM3 are input with a phase difference of 120 degrees from each other. That is, the second PWM signal PWM2 has a phase delayed by 120 degrees from the first PWM signal PWM1 and the third PWM signal PWM3 has a phase that is delayed by 240 degrees from the first PWM signal PWM1.

Accordingly, the LED arrays LA1, LA4, LA7,..., LA22 of the first group GR1 are connected to the second group by the first to third PWM signals PWM1 to PWM3 having a phase difference of 120 degrees. The LED arrays LA2, LA5, LA8, ..., LA23 of GR2 and the LED arrays LA3, LA6, LA9, ..., LA24 of the third group GR3 are sequentially lighted to emit the 0PWM signal of FIG. 11A. It has three times as many light emission times as the number of light emission by (PWM0).

The number (2) of LED arrays emitted by each of the first to third PWM signals (PWM1 to PWMM3) is 1 compared to the number of LED arrays (6) emitted by the 0PWM signal (PWM0) of FIG. 11A. Since the average instantaneous light amount at one light emission by one PWM signal is 1/3, the light is emitted three times by each of the first to third PWM signals (PWM1 to PWM3). The average total amount of light supplied (sum of the total area of the quantity graph = total amount of light) is substantially the same in the driving of Figs. 11A and 11B.

As a result, in the second embodiment of the present invention, by dividing a plurality of LED arrays into three groups and simultaneously driving them, the number of LED arrays emitting simultaneously is further reduced than in the case of the first embodiment described above. The instantaneous light amount of the light supplied to is further reduced than in the case of the first embodiment. Accordingly, the wave noise improvement effect caused by the off current variation of the thin film transistor of the liquid crystal panel which is proportional to the intensity of light supplied from the backlight is also more pronounced than in the above-described first embodiment, but the luminance is not lowered. have.

Third Embodiment

12A and 12B are an LED array circuit diagram and a PWM signal diagram for explaining a backlight driving method of a liquid crystal display according to a third embodiment of the present invention, respectively, for convenience of description as in the first and second embodiments. In order to configure the configuration of a plurality of LED array of the LED array unit 80 of the configuration according to Figure 2 to 24 LED arrays (LA1 ~ LA24) will be described.

As shown in FIG. 12A, in the backlight driving method according to the third embodiment of the present invention, circuit connection is performed such that the 24 LED arrays LA1 to LA24 are configured into six groups GR1 to GR6. Accordingly, the first to sixth PWM signals to the sixth PWM signals PWM1 to PWMM6 are respectively input to the plurality of LED arrays LA1 to LA24.

At this time, the first to sixth PWM signals (PWM1 to PWM6), as shown in Figure 12b is a signal having the same frequency and the phase is different by 60 degrees. 12B illustrates an on-duty of about 16.7% in a duty ratio, but the on-duty may be arbitrarily selected from values between 1% and 99%.

When the plurality of LED arrays LA1 to LA24 are driven through the above example configuration and features, sequential light emission driving is repeated from the first LED array LA1 to the 24th LED array LA24, and the plurality of LED arrays is repeated. By separating LA1 to LA24 into six groups and driving them to emit light at different timings, the number of LEDs that are turned on at the same time is reduced, thereby reducing the amount of instantaneous light incident on the liquid crystal panel. The wave noise caused by the variation of the off current of the thin film transistor is improved. In addition, the third embodiment has a larger number of divided groups of a plurality of LED arrays LA1 to LA24 than the above-described first and second embodiments, and the number of LED arrays emitting at the same time is small, thereby improving wave noise. Provide a better way.

In addition, since the plurality of LED arrays LA1 to LA24 emit more numbers of times, the average total amount of light supplied from the plurality of LED arrays to the liquid crystal panel is almost different from the existing ones, and thus a phenomenon such as brightness reduction does not occur. .

Hereinafter, referring to a graph of an experimental result attached to the wave noise improvement effect according to the application of various duty ratios of the first to sixth PWM signals PWM1 to PWM6 in the driving method according to the third embodiment of the present invention. Will be explained.

13A and 13B illustrate the simultaneous light emission driving of the LED array according to the driving method of the comparative example and the driving method of the third embodiment of the present invention (phase difference between PWM signals: 60 degrees) using a PWM signal having on-duty of 10%, respectively. It is a graph showing the input PWM signal of the split driving according to the result and the light quantity measurement result.

Referring to FIG. 13A, which illustrates a backlight driving method according to the prior art as a comparative example, the 24th LED array LA1 includes the zero PWM signal PWM0 having an arbitrary frequency and an arbitrary voltage level of 10% on-duty. It is shown that the light amount is changed from 0 to 1 in synchronization with the 0th PWM signal PWM0 signal when all of them are input to LA24) at the same time.

In addition, as in the first embodiment, the measurement of the amount of light can be measured by using an electrical signal generated in proportion to the amount of light by installing a photodiode or the like. In FIG. 13A, 24 using the 0th PWM signal PWM0 is used. The minimum value and the maximum value of light quantity change by simultaneous light emission driving of two LED arrays LA1 to LA24 are set to '0' and '1', respectively, for convenience of comparison with the present invention.

13B illustrates the backlight driving method according to the third embodiment of the present invention, the first LED arrays 24 to 24 LED arrays LA1 to LA24 of FIG. 12A include the first PWM signals to the sixth PWM signals PWM1 to PWM6. Each is input and this drive is repeated. That is, the first PWM signal PWM1 is input to the first, seventh, thirteenth, and nineteenth LED arrays LA1, LA7, LA13, and LA19 of the first group GR1, and the second of the second group GR2 is input. The second, third, ninth, fifteenth, and twenty first LED arrays LA3, LA9, LA15, and LA21 are input to the eighth, fourteenth, and twentieth LED arrays LA2, LA8, LA14, and LA20. ), The third PWM signal PWM1 is input, and the fourth, tenth, sixteenth, and twenty-second LED arrays LA4, LA10, LA16, and LA22 are input with the fourth PWM signal PWM4, and the fifth, eleventh, The fifth PWM signal PWM5 is input to the seventeenth and twenty-third LED arrays LA5, LA11, LA17, and LA23, and the sixth PWM to the sixth, twelfth, 18th, and 24th LED arrays LA6, LA12, LA18, and LA24. The signal PWM6 is input.

The frequency, voltage level, and on-duty (10%) of the first to sixth PWM signals PWM1 to PWMM6 are all the same as the 0th PWM signal PWM0 of FIG. 13A, but the first PWM signals PWM1 to The sixth PWM signal PWM6 is input such that each has a phase difference of 60 degrees. That is, the second PWM signal PWM2 has a phase that is delayed by 60 degrees from the first PWM signal PWM1, and the third PWM signal PWM3 has a phase that is delayed by 120 degrees from the first PWM signal PWM1, and the fourth PWM signal PWM4. The signal PWM4 has a phase delayed 180 degrees from the first PWM signal PWM1, the fifth PWM signal PWM5 has a phase delayed 240 degrees from the first PWM signal PWM1, and the sixth PWM signal PWM6. Is a phase delayed by 300 degrees from the first PWM signal PWM1.

Accordingly, the first to 24th LED arrays LA1 to LA24 are sequentially lighted by the first to sixth PWM signals PWM1 to PWM6 inputted with a phase difference of 60 degrees. The number of light emission of the backlight by the 6PWM signals PWM1 to PWMM6 has 6 times as many light emission times as the number of light emission of the backlight by the 0th PWM signal PWM0 of FIG. 13A.

The number (4) of LED arrays emitted by each of the first to sixth PWM signals (PWM1 to PWM6) is 1 compared to the number of LED arrays (24) emitted by the 0PWM signal (PWM0) of FIG. 13A. Since the average instantaneous light amount at the time of one light emission by one PWM signal is 1/6, the total number of light emission is increased six times by each of the first to sixth PWM signals (PWM1 to PWM6). The average total light amount of the light supplied to the liquid crystal panel (sum of the total area of the light amount graph becomes the total light amount) appears substantially the same in the driving of FIGS. 13A and 13B.

14A and 14B illustrate the simultaneous light emission driving of the LED array according to the driving method of Comparative Example and the driving method of the third embodiment of the present invention (phase difference between PWM signals: 60 degrees) using PWM signals having 50% of on-duty, respectively. It is a graph showing the input PWM signal of the split driving according to the result and the light quantity measurement result.

Referring to FIG. 14A, which illustrates a backlight driving method according to the prior art as a comparative example, the 24th LED array LA1 includes the zero PWM signal PWM0 having on-duty 50% having an arbitrary frequency and an arbitrary voltage level. It is shown that the light amount is changed from 0 to 1 in synchronization with the 0th PWM signal PWM0 signal when all of them are input to LA24) at the same time.

In FIG. 14A, a minimum value and a maximum value of light quantity change for the simultaneous emission driving of 24 LED arrays LA1 to LA24 using the 0th PWM signal PWM0 are respectively referred to as '0' and '1' for convenience of comparison with the present invention. Set to.

Referring to FIG. 14B, the first to sixth LED arrays LA1 to LA24 of FIG. 12A receive first PWM signals to sixth PWM signals PWM1 to PWMM6, and the driving is repeated. That is, the first PWM signal PWM1 is input to the first, seventh, thirteenth, and nineteenth LED arrays LA1, LA7, LA13, and LA19 of the first group GR1, and the second of the second group GR2 is input. The second, third, ninth, fifteenth, and twenty first LED arrays LA3, LA9, LA15, and LA21 are input to the eighth, fourteenth, and twentieth LED arrays LA2, LA8, LA14, and LA20. ), The third PWM signal PWM1 is input, and the fourth, tenth, sixteenth, and twenty-second LED arrays LA4, LA10, LA16, and LA22 are input with the fourth PWM signal PWM4, and the fifth, eleventh, The fifth PWM signal PWM5 is input to the seventeenth and twenty-third LED arrays LA5, LA11, LA17, and LA23, and the sixth PWM to the sixth, twelfth, 18th, and 24th LED arrays LA6, LA12, LA18, and LA24. The signal PWM6 is input.

The frequency, voltage level, and on-duty (50%) of the first to sixth PWM signals PWM1 to PWM6 are all the same as the zero PWM signal PWM0 of FIG. 14A, but the first PWM signals PWM1 to The sixth PWM signal PWM6 is input such that each has a phase difference of 60 degrees. That is, the second PWM signal PWM2 has a phase that is delayed by 60 degrees from the first PWM signal PWM1, and the third PWM signal PWM3 has a phase that is delayed by 120 degrees from the first PWM signal PWM1, and the fourth PWM signal PWM4. The signal PWM4 has a phase delayed 180 degrees from the first PWM signal PWM1, the fifth PWM signal PWM5 has a phase delayed 240 degrees from the first PWM signal PWM1, and the sixth PWM signal PWM6. Is a phase delayed by 300 degrees from the first PWM signal PWM1.

Accordingly, the first to 24th LED arrays LA1 to LA24 are sequentially lighted by the first to sixth PWM signals PWM1 to PWM6 inputted with a phase difference of 60 degrees. The number of emission of the backlight by the sixth PWM signals PWM1 to PWMM6 has six times as many emission times as the number of emission of the backlight by the zeroth PWM signal PWM0 of FIG. 14A.

The number (4) of LED arrays emitted by each of the first to sixth PWM signals (PWM1 to PWM6) is 1 compared to the number of LED arrays (24) emitted by the 0th PWM signal (PWM0) of FIG. 14A. Since the average instantaneous light quantity at the time of one light emission by one PWM signal is 1/6, the total number of light emission times is increased six times by each of the first to sixth PWM signals (PWM1 to PWM6). The average total light amount of the light supplied to the liquid crystal panel (the sum of the total areas of the light quantity graphs becomes the total light amount) appears substantially the same in the driving of FIGS. 14A and 14B.

In particular, in this case, since the average instantaneous light amount of the first to sixth PWM signals (PWM1 to PWM6) is the same at any point in time, the amount of light supplied to the liquid crystal panel from the plurality of LED arrays of the backlight is recognized as being constant. As a result, the off current fluctuation of the thin film transistor of the liquid crystal panel is minimized, and the wave noise is further improved.

15A and 15B illustrate the simultaneous light emission driving of the LED array according to the driving method of Comparative Example and the driving method of the third embodiment of the present invention (phase difference between PWM signals: 60 degrees) using PWM signals having 90% on-duty, respectively. It is a graph showing the input PWM signal of the split driving according to the result and the light quantity measurement result.

First, as a comparative example, FIG. 15A illustrates a backlight driving method according to the related art. When the signals are simultaneously input to all of LA1 to LA24, the amount of light is changed from 0 to 1 in synchronization with the 0th PWM signal PWM0 signal.

In FIG. 15A, the lowest and highest values of light quantity changes for the simultaneous emission driving of 24 LED arrays LA1 to LA24 using the 0th PWM signal PWM0 are respectively referred to as '0' and '1' for convenience of comparison with the present invention. Set to.

Referring to FIG. 15B, the first to sixth LED arrays LA1 to LA24 of FIG. 12A receive first PWM signals to sixth PWM signals PWM1 to PWM6, and the driving is repeated. That is, the first PWM signal PWM1 is input to the first, seventh, thirteenth, and nineteenth LED arrays LA1, LA7, LA13, and LA19 of the first group GR1, and the second of the second group GR2 is input. The second, third, ninth, fifteenth, and twenty first LED arrays LA3, LA9, LA15, and LA21 are input to the eighth, fourteenth, and twentieth LED arrays LA2, LA8, LA14, and LA20. ), The third PWM signal PWM1 is input, and the fourth, tenth, sixteenth, and twenty-second LED arrays LA4, LA10, LA16, and LA22 are input with the fourth PWM signal PWM4, and the fifth, eleventh, The fifth PWM signal PWM5 is input to the seventeenth and twenty-third LED arrays LA5, LA11, LA17, and LA23, and the sixth PWM to the sixth, twelfth, 18th, and 24th LED arrays LA6, LA12, LA18, and LA24. The signal PWM6 is input.

The frequency, voltage level, and on-duty (90%) of the first to sixth PWM signals PWM1 to PWM6 are all the same as the 0th PWM signal PWM0 of FIG. 15A, but the first PWM signals PWM1 to The sixth PWM signal PWM6 is input such that each has a phase difference of 60 degrees. That is, the second PWM signal PWM2 has a phase delayed by 60 degrees from the first PWM signal PWM1, and the third PWM signal PWM3 has a phase that is delayed by 120 degrees from the first PWM signal PWM1. The 4PWM signal PWM4 has a phase delayed 180 degrees from the first PWM signal PWM1, the 5PWM signal PWM5 has a phase delayed 240 degrees from the first PWM signal PWM1, and the 6th PWM signal PWM6. ) Has a phase delayed by 300 degrees from the first PWM signal PWM1.

Accordingly, the first to 24th LED arrays LA1 to LA24 are sequentially lighted by the first to sixth PWM signals PWM1 to PWM6 that are sequentially input with a phase difference of 60 degrees. The number of emission of the backlight by the sixth PWM signals PWM1 to PWMM6 has six times as many emission times as the number of emission of the backlight by the zeroth PWM signal PWM0 of FIG. 15A.

The number (4) of LED arrays emitted by each of the first to sixth PWM signals (PWM1 to PWM6) is 1 compared to the number of LED arrays (24) emitted by the 0th PWM signal (PWM0) of FIG. 15A. Since / 6 is the average amount of light emitted by one PWM signal at 1/6, the total number of times of light emission is increased six times by each of the first to sixth PWM signals (PWM1 to PWM6). The average total light amount of the light supplied to the panel (sum of the total area of the light quantity graph becomes the total light amount) appears substantially the same in the driving of Figs. 15A and 15B.

Fourth Embodiment

16A and 16B are an LED array circuit diagram and a PWM signal diagram for explaining a backlight driving method of a liquid crystal display according to a fourth exemplary embodiment of the present invention, respectively, as in the first to third embodiments. To this end, the configuration of a plurality of LED array of the LED array unit 80 of the configuration according to Figure 2 will be described by combining the 24 LED array (LA1 ~ LA24).

As shown in FIG. 16A, in the backlight driving method according to the fourth embodiment of the present invention, circuit connection is performed such that the 24 LED arrays LA1 to LA24 are configured into eight groups GR1 to GR8. Accordingly, the first to eighth PWM signals PWM1 to PWMM8 are respectively input to the plurality of LED arrays LA1 to LA24.

At this time, the first to eighth PWM signals PWM1 to PWM8 are signals having the same frequency and differing in phase by 45 degrees as shown in FIG. 16B. 16B illustrates an on-duty of about 12.5% in a duty ratio, but the on-duty may be arbitrarily selected from 1% to 99%.

When the plurality of LED arrays LA1 to LA24 are driven through the above example configuration and features, sequential light emission driving is repeated from the first LED array LA1 to the 24th LED array LA24, and the plurality of LED arrays is repeated. By separating LA1 to LA24 into eight groups and driving them to emit light at different timings, the number of LEDs that are turned on at the same time is reduced, thereby reducing the amount of instantaneous light incident on the liquid crystal panel. The wave noise caused by the variation of the off current of the thin film transistor is improved. In addition, the fourth embodiment has a larger number of divided groups of a plurality of LED arrays LA1 to LA24 and a smaller number of LED arrays emitting at the same time than the first to second embodiments. Provide a better way.

In addition, since the plurality of LED arrays LA1 to LA24 emit more numbers of times, the average total amount of light supplied from the plurality of LED arrays to the liquid crystal panel is almost different from the existing ones, and thus a phenomenon such as luminance decrease does not occur. .

Hereinafter, referring to a graph of an experimental result attached to the wave noise improvement effect according to the application of various duty ratios of the first to eighth PWM signals PWM1 to PWM8 in the driving method according to the third embodiment of the present invention. Will be explained.

17A and 17B illustrate the simultaneous light emission driving of the LED array according to the driving method of the comparative example and the driving method of the fourth embodiment of the present invention (phase difference between PWM signals: 45 degrees) using PWM signals having on-duty of 10%, respectively. It is a graph showing the input PWM signal of the split driving according to the result and the light quantity measurement result.

Referring to FIG. 17A, which illustrates a backlight driving method according to the prior art as a comparative example, the 24th LED array LA1 includes the zero PWM signal PWM0 having on-duty 10% having an arbitrary frequency and an arbitrary voltage level. It is shown that the light amount is changed from 0 to 1 in synchronization with the 0th PWM signal PWM0 signal when all of them are input to LA24) at the same time.

In addition, as in the first embodiment, the measurement of the amount of light can be measured by using an electrical signal generated in proportion to the amount of light by installing a photodiode or the like. In FIG. 17A, 24 using the 0th PWM signal PWM0 is used. The minimum value and the maximum value of light quantity change by simultaneous light emission driving of two LED arrays LA1 to LA24 are set to '0' and '1', respectively, for convenience of comparison with the present invention.

17B illustrates the backlight driving method according to the fourth embodiment of the present invention, the first LED arrays 24 to 24 LED arrays LA1 to LA24 of FIG. 16A include the first to eighth PWM signals PWM1 to PWM8. Each is input and this drive is repeated. That is, the first PWM signal PWM1 is inputted to the first, ninth, and seventeenth LED arrays LA1, LA9, and LA17 of the first group GR1, and the second, tenth, and fifth pixels of the second group GR2 are input. The second PWM signal PWM2 is input to the 18 LED arrays LA2, LA10 and LA18, and the third PWM signal PWM1 is input to the third, eleventh and 19th LED arrays LA3, LA11 and LA19. The fourth PWM signal PWM4 is input to the twelfth and twentieth LED arrays LA4, LA12, and LA20, and the fifth PWM signal PWM5 is input to the fifth, thirteenth, and twenty first LED arrays LA5, LA13, and LA21. The 6th, 14th, 22nd LED arrays LA6, LA14, LA22 are inputted with the 6th PWM signal PWM6, and the 7th, 15th, 23rd LED arrays LA7, LA15, LA23 have 7th PWM signal PWM7 ) Is input, and the eighth PWM signal PWM8 is input to the eighth, sixteenth, and 24th LED arrays LA8, LA16, and LA24.

The frequency, voltage level, and on-duty (10%) of the first to eighth PWM signals PWM1 to PWM8 are all the same as the 0th PWM signal PWM0 of FIG. 17A, but the first PWM signals PWM1 to The eighth PWM signal PWM8 is input so as to have a phase difference of 45 degrees each. That is, the second PWM signal PWM2 has a phase delayed by 45 degrees from the first PWM signal PWM1, and the third PWM signal PWM3 has a phase that is delayed by 90 degrees than the first PWM signal PWM1, and the fourth PWM signal PWM4. The signal PWM4 has a phase delayed by 135 degrees from the first PWM signal PWM1, the fifth PWM signal PWM5 has a phase delayed by 180 degrees from the first PWM signal PWM1, and the sixth PWM signal PWM6. Has a phase delayed 225 degrees from the first PWM signal PWM1, the seventh PWM signal PWM7 has a phase delayed 270 degrees from the first PWM signal PWM1, and the eighth PWM signal PWM8 is the first PWM The phase is delayed 315 degrees from the signal PWM1.

Accordingly, the first to 24th LED arrays LA1 to LA24 are sequentially lighted by the first to eighth PWM signals PWM1 to PWM8 inputted with a phase difference of 45 degrees, respectively. The number of emission of the backlight by the 8 PWM signals PWM1 to PWM8 has eight times the number of emission of the backlight by the 0 PWM signal PWM0 of FIG. 17A.

The number (3) of LED arrays emitted by each of the first to eighth PWM signals PWM1 to PWMM8 is 1 compared to the number of LED arrays (24) emitted by the 0PWM signal PWM0 of FIG. 17A. Since the average instantaneous light amount at the time of one light emission by one PWM signal is 8/8, the total number of light emission is increased by 8 times by each of the first to eighth PWM signals (PWM1 to PWM8). The average total light amount of the light supplied to the liquid crystal panel (sum of the total area of the light quantity graph becomes the total light amount) is substantially the same in the driving of FIGS. 17A and 17B.

18A and 18B show the simultaneous light emission driving of the LED array according to the driving method of the comparative example and the driving method of the fourth embodiment of the present invention (phase difference between PWM signals: 45 degrees) using PWM signals having on-duty of 50%, respectively. It is a graph showing the input PWM signal of the split driving according to the result and the light quantity measurement result.

Referring to FIG. 18A, which illustrates a backlight driving method according to the related art as a comparative example, the 24th LED array (PWM0), which is on-duty 50% with an arbitrary frequency and an arbitrary voltage level, may be used. When the signals are simultaneously input to all of LA1 to LA24, the amount of light is changed from 0 to 1 in synchronization with the 0th PWM signal PWM0 signal.

In FIG. 17A, the lowest and highest values of light quantity changes for the simultaneous emission driving of 24 LED arrays LA1 to LA24 using the 0th PWM signal PWM0 are respectively referred to as '0' and '1' for convenience of comparison with the present invention. Set to.

17B, the first to eighth LED arrays LA1 to LA24 of FIG. 16A receive the first to eighth PWM signals PWM1 to PWM8, and the driving is repeated. That is, the first PWM signal PWM1 is inputted to the first, ninth, and seventeenth LED arrays LA1, LA9, and LA17 of the first group GR1, and the second, tenth, and fifth pixels of the second group GR2 are input. The second PWM signal PWM2 is input to the 18 LED arrays LA2, LA10 and LA18, and the third PWM signal PWM1 is input to the third, eleventh and 19th LED arrays LA3, LA11 and LA19. The fourth PWM signal PWM4 is input to the twelfth and twentieth LED arrays LA4, LA12, and LA20, and the fifth PWM signal PWM5 is input to the fifth, thirteenth, and twenty first LED arrays LA5, LA13, and LA21. The 6th, 14th, 22nd LED arrays LA6, LA14, LA22 are inputted with the 6th PWM signal PWM6, and the 7th, 15th, 23rd LED arrays LA7, LA15, LA23 have 7th PWM signal PWM7 ) Is input, and the eighth PWM signal PWM8 is input to the eighth, sixteenth, and 24th LED arrays LA8, LA16, and LA24.

The frequency, the voltage level, and the on-duty (50%) of the first to eighth PWM signals PWM1 to PWM8 are all the same as the zero PWM signal PWM0 of FIG. 18A, but the first PWM signals PWM1 to The eighth PWM signal PWM8 is input to have a phase difference of 45 degrees each. That is, the second PWM signal PWM2 has a phase delayed by 45 degrees from the first PWM signal PWM1, and the third PWM signal PWM3 has a phase that is delayed by 90 degrees than the first PWM signal PWM1, and the fourth PWM signal PWM4. The signal PWM4 has a phase delayed by 135 degrees from the first PWM signal PWM1, the fifth PWM signal PWM5 has a phase delayed by 180 degrees from the first PWM signal PWM1, and the sixth PWM signal PWM6. Has a phase delayed by 225 degrees from the first PWM signal PWM1, the seventh PWM signal PWM7 has a phase delayed 270 degrees from the first PWM signal PWM1, and the eighth PWM signal PWM8 is the first PWM The phase is delayed 315 degrees from the signal PWM1.

Accordingly, the first to 24th LED arrays LA1 to LA24 are sequentially lighted by the first to eighth PWM signals PWM1 to PWMM8 having a phase difference of 45 degrees. The number of light emission times of the backlight by the 8 PWM signals PWM1 to PWM8 has eight times the light emission times of the backlight by the 0th PWM signal PWM0 of FIG. 18A.

The number (3) of LED arrays emitted by each of the first to eighth PWM signals (PWM1 to PWMM8) is 1 compared to the number of LED arrays (24) emitted by the 0PWM signal (PWM0) of FIG. 18A. Since the average instantaneous light amount at the time of one light emission by one PWM signal is 1/8, the total number of times of light emission is increased by 8 times by each of the first to eighth PWM signals (PWM1 to PWM8), so that a plurality of LED arrays The average total light amount of the light supplied to the liquid crystal panel (the sum of the total areas of the light amount graphs becomes the total light amount) appears substantially the same in the driving of FIGS. 18A and 18B.

In particular, in this case, since the average instantaneous light amount by the first to eighth PWM signals PWM1 to PWM8 is the same at any point in time, the amount of light supplied to the liquid crystal panel from the plurality of LED arrays in the backlight is recognized as constant. As a result, the off current fluctuation of the thin film transistor of the liquid crystal panel is minimized, and the wave noise is further improved.

19A and 19B show the simultaneous light emission driving of the LED array according to the driving method of the comparative example and the driving method of the fourth embodiment of the present invention (phase difference between PWM signals: 45 degrees) using PWM signals having 90% on-duty, respectively. It is a graph showing the input PWM signal of the split driving according to the result and the light quantity measurement result.

Referring to FIG. 18A, which illustrates a backlight driving method according to the related art as a comparative example, the 24th LED array LA1 includes the zero PWM signal PWM0 of 90% on-duty having an arbitrary frequency and an arbitrary voltage level. It is shown that the light amount is changed from 0 to 1 in synchronization with the 0th PWM signal PWM0 signal when all of them are input to LA24) at the same time.

In FIG. 18A, the lowest and highest values of light quantity change for the simultaneous emission driving of 24 LED arrays LA1 to LA24 using the 0th PWM signal PWM0 are respectively referred to as '0' and '1' for convenience of comparison with the present invention. Set to.

Referring to FIG. 18B, the first to eighth LED arrays LA1 to LA24 of FIG. 16A are inputted with the first to eighth PWM signals PWM1 to PWM8, respectively, and the driving is repeated. That is, the first PWM signal PWM1 is inputted to the first, ninth, and seventeenth LED arrays LA1, LA9, and LA17 of the first group GR1, and the second, tenth, and fifth pixels of the second group GR2 are input. The second PWM signal PWM2 is input to the 18 LED arrays LA2, LA10, and LA18, and the third PWM signal PWM1 is input to the third, eleventh, and 19th LED arrays LA3, LA11, and LA19, and the fourth And the fourth PWM signal PWM4 is input to the twelfth and twentieth LED arrays LA4, LA12, and LA20, and the fifth PWM signal PWM5 is input to the fifth, thirteenth and twenty-first LED arrays LA5, LA13, and LA21. The sixth PWM signal PWM6 is input to the sixth, fourteenth, and twenty-second LED arrays LA6, LA14, and LA22, and the seventh PWM signal (7) is input to the seventh, fifteenth, and twenty-third LED arrays LA7, LA15, and LA23. PWM7) is input, and the eighth PWM signal PWM8 is input to the eighth, sixteenth, and 24th LED arrays LA8, LA16, and LA24.

The frequency, voltage level, and on-duty (90%) of the first to eighth PWM signals PWM1 to PWM8 are all the same as the zero PWM signal PWM0 of FIG. 19A, but the first PWM signals PWM1 to The eighth PWM signal PWM8 is input so as to have a phase difference of 45 degrees each. That is, the second PWM signal PWM2 has a phase delayed by 45 degrees from the first PWM signal PWM1, and the third PWM signal PWM3 has a phase that is delayed by 90 degrees than the first PWM signal PWM1, and the fourth PWM signal PWM4. The signal PWM4 has a phase delayed by 135 degrees from the first PWM signal PWM1, the fifth PWM signal PWM5 has a phase delayed by 180 degrees from the first PWM signal PWM1, and the sixth PWM signal PWM6. Has a phase delayed by 225 degrees from the first PWM signal PWM1, the seventh PWM signal PWM7 has a phase delayed 270 degrees from the first PWM signal PWM1, and the eighth PWM signal PWM8 is the first PWM The phase is delayed 315 degrees from the signal PWM1.

Accordingly, the first to 24th LED arrays LA1 to LA24 are sequentially lighted by the first to eighth PWM signals PWM1 to PWMM 8 sequentially input with a phase difference of 45 degrees. The number of emission of the backlight by the eighth PWM signals PWM1 to PWMM8 has eight times the number of emission of the backlight by the zeroth PWM signal PWM0 of FIG. 19A.

The number (3) of LED arrays emitted by each of the first to eighth PWM signals PWM1 to PWM8 is 1 compared to the number of LED arrays (24) emitted by the 0th PWM signal PWM0 of FIG. 19A. Since the average light quantity of one light emission by one PWM signal is 1/8, the total number of light emission is increased by 8 times by each of the first to eighth PWM signals (PWM1 to PWMM8), so that the liquid crystal from a plurality of LED arrays The average total light amount of the light supplied to the panel (the sum of the total areas of the light quantity graphs becomes the total light amount) appears substantially the same in the driving of Figs. 18A and 18B.

As a result, in the first to fourth embodiments of the present invention, by dividing the plurality of LED arrays into two or more groups, the number of LED arrays driven simultaneously in the backlight is reduced, and the light supplied from the backlight to the liquid crystal panel is reduced. Reduces the amount of instant light Therefore, by minimizing the off-current variation of the thin film transistor of the liquid crystal panel corresponding to the change in the intensity of light supplied from the backlight, there is an advantage that the decrease in luminance does not occur while maximizing the wave noise improvement effect.

In particular, when the backlight is driven with the first to n th PWM signals PWM1 to PWMM sequentially delayed by a phase value of 360 ° / n, the on-duty of each of the first to n th PWM signals PWM1 to PWMMn is At 100 / n%, the average instantaneous light quantity of a plurality of LED arrays in the backlight is the same at any point in time, so that the amount of light supplied from the backlight to the liquid crystal panel is recognized as unchanged. As a result, the thin film transistor of the liquid crystal panel Off-current fluctuations are also minimized and wave noise is further improved.

In addition, when n is an even number, even when the on-duty of each of the first to nth PWM signals PWM1 to PWMMn is 50%, the average instantaneous light quantity of the plurality of LED arrays of the backlight is the same at any point, and the wave Noise is further improved.

1 is a view briefly showing a configuration using LED as an edge-type backlight unit of a liquid crystal display according to the prior art;

2 is a configuration diagram briefly showing a configuration of a liquid crystal display according to the present invention.

3 is a view illustrating the LED array unit 80 of FIG.

4A and 4B are an LED array circuit diagram and a PWM signal diagram for explaining a backlight driving method of a liquid crystal display according to a first embodiment of the present invention, respectively.

5A and 5B illustrate the simultaneous light emission driving of the LED array according to the driving method of the comparative example and the driving method of the first embodiment of the present invention (phase difference between PWM signals: 180 degrees) using a PWM signal having on-duty of 10%, respectively. Graph showing the input PWM signal of the split driving according to the result and the light quantity measurement result

6A and 6B illustrate the simultaneous light emission driving of the LED array according to the driving method of the comparative example and the driving method of the first embodiment of the present invention (phase difference between PWM signals: 180 degrees) using PWM signals having on-duty of 50%, respectively. Graph showing the input PWM signal of the split driving according to the result and the light quantity measurement result

7A and 7B illustrate the simultaneous light emission driving of the LED array according to the driving method of the comparative example and the driving method of the first embodiment of the present invention (phase difference between PWM signals: 180 degrees) using PWM signals having 90% on-duty, respectively. Graph showing the input PWM signal of the split driving according to the result and the light quantity measurement result

8A and 8B are an LED array circuit diagram and a PWM signal diagram for explaining a backlight driving method of a liquid crystal display according to a second embodiment of the present invention, respectively.

9A and 9B illustrate the simultaneous light emission driving of the LED array according to the driving method of Comparative Example and the driving method of the second embodiment of the present invention (phase difference between PWM signals: 120 degrees) using PWM signals having on-duty of 10%, respectively. Graph showing the input PWM signal of the split driving according to the result and the light quantity measurement result

10A and 10B illustrate the simultaneous light emission driving of the LED array according to the driving method of the comparative example and the driving method of the second embodiment of the present invention (phase difference between PWM signals: 120 degrees) using PWM signals having on-duty of 50%, respectively. Graph showing the input PWM signal of the split driving according to the result and the light quantity measurement result

11A and 11B illustrate the simultaneous light emission driving of the LED array according to the driving method of Comparative Example and the driving method of the second embodiment of the present invention (phase difference between PWM signals: 120 degrees) using PWM signals having 90% on-duty, respectively. Graph showing the input PWM signal of the split driving according to the result and the light quantity measurement result

12A and 12B are an LED array circuit diagram and a PWM signal diagram for explaining a backlight driving method of a liquid crystal display according to a third embodiment of the present invention, respectively.

13A and 13B illustrate the simultaneous light emission driving of the LED array according to the driving method of the comparative example and the driving method of the third embodiment of the present invention (phase difference between PWM signals: 60 degrees) using a PWM signal having on-duty of 10%, respectively. Graph showing the input PWM signal of the split driving according to the result and the light quantity measurement result

14A and 14B illustrate the simultaneous light emission driving of the LED array according to the driving method of the comparative example and the driving method of the third embodiment of the present invention using a PWM signal having an on-duty of 50%, respectively (phase difference between PWM signals: 60 degrees). Graph showing the input PWM signal of split driving according to the signal and the light quantity measurement result

15A and 15B illustrate the simultaneous light emission driving of the LED array according to the driving method of Comparative Example and the driving method of the third embodiment of the present invention (phase difference between PWM signals: 60 degrees) using PWM signals having 90% on-duty, respectively. Graph showing the input PWM signal of the split driving according to the result and the light quantity measurement result

16A and 16B are an LED array circuit diagram and a PWM signal diagram for explaining a backlight driving method of a liquid crystal display according to a fourth embodiment of the present invention, respectively.

17A and 17B illustrate the simultaneous light emission driving of the LED array according to the driving method of the comparative example and the driving method of the fourth embodiment of the present invention (phase difference between PWM signals: 45 degrees) using PWM signals having on-duty of 10%, respectively. Graph showing the input PWM signal of the split driving according to the result and the light quantity measurement result

18A and 18B show the simultaneous light emission driving of the LED array according to the driving method of the comparative example and the driving method of the fourth embodiment of the present invention (phase difference between PWM signals: 45 degrees) using PWM signals having on-duty of 50%, respectively. Graph showing the input PWM signal of the split driving according to the result and the light quantity measurement result

19A and 19B show the simultaneous light emission driving of the LED array according to the driving method of the comparative example and the driving method of the fourth embodiment of the present invention (phase difference between PWM signals: 45 degrees) using PWM signals having 90% on-duty, respectively. Graph showing the input PWM signal of the split driving according to the result and the light quantity measurement result

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

50: liquid crystal panel 60: gate driver

70: source driver 80: LED array

90: LED driver 100: timing control unit

Claims (20)

S (S is a natural number of two or more) LED arrays are divided into a plurality of groups, and the plurality of PWM signals having the same frequency but having a phase difference from each other are applied to each of the LED arrays to emit light. To control driving, The plurality of groups may include first to nth groups, and the plurality of PWM signals may include first to nth PWM signals having a phase difference of 360 degrees from each other, and the first to nth PWM signals may each be 100. Back light driving method of the liquid crystal display device characterized in that it has a duty ratio of / n% The method according to claim 1, The number of the plurality of groups is determined to be one of 2 ~ S, the number of the LED array belonging to each of the plurality of groups is the same method for driving the backlight of the liquid crystal display device The method according to claim 1, And a plurality of PWM signals have the same voltage level. delete delete delete delete delete S (S is a natural number of two or more) LED arrays are divided into a plurality of groups, and the plurality of PWM signals having the same frequency but having a phase difference from each other are applied to each of the LED arrays to emit light. To control driving, The plurality of groups include first to nth groups, n is an even number, and the plurality of PWM signals include first to nth PWM signals having a phase difference of 360 / n degrees from each other. The n-PWM signal has a duty ratio of 50% each, the backlight driving method of the liquid crystal display device An LED array unit having S (S is two or more natural numbers) LED arrays divided into a plurality of groups; An LED driver applied to the plurality of groups for driving control of the S LED arrays and outputting a plurality of PWM signals having phase differences from each other; A liquid crystal panel that receives light emitted from the S LED arrays and displays an image; A gate driver for outputting a scan signal to the liquid crystal panel; A source driver for outputting image data to the liquid crystal panel in synchronization with the scan signal; It includes a timing controller for outputting a plurality of control signals for controlling the driving of the LED driver, the gate driver and the source driver, The plurality of groups may include first to nth groups, and the plurality of PWM signals may include first to nth PWM signals having a phase difference of 360 degrees from each other, and the first to nth PWM signals may each be 100. LCD having a duty ratio of / n% The method of claim 10, LCD array, characterized in that each of the LED array of S is composed of a plurality of LEDs The method of claim 10, And the plurality of PWM signals have the same frequency and the same voltage level. The method of claim 10, Each of the plurality of PWM signals is applied to at least one LED array of the S LED array, the liquid crystal display device delete delete delete delete The method of claim 10, The plurality of PWM signals are generated via a phase shifter delete An LED array unit having S (S is two or more natural numbers) LED arrays divided into a plurality of groups; An LED driver applied to the plurality of groups for driving control of the S LED arrays and outputting a plurality of PWM signals having phase differences from each other; A liquid crystal panel that receives light emitted from the S LED arrays and displays an image; A gate driver for outputting a scan signal to the liquid crystal panel; A source driver for outputting image data to the liquid crystal panel in synchronization with the scan signal; It includes a timing controller for outputting a plurality of control signals for controlling the driving of the LED driver, the gate driver and the source driver, The plurality of groups include first to nth groups, n is an even number, and the plurality of PWM signals include first to nth PWM signals having a phase difference of 360 / n degrees from each other. The nth PWM signal each has a duty ratio of 50%.

Images