WO2007108165A1

WO2007108165A1 - Liquid crystal display device

Info

Publication number: WO2007108165A1
Application number: PCT/JP2006/323021
Authority: WO
Inventors: Satoshi Sekido
Original assignee: Sharp Kabushiki Kaisha
Priority date: 2006-03-23
Filing date: 2006-11-17
Publication date: 2007-09-27

Abstract

It is possible to provide a liquid crystal display device capable of improving response speed as compared to the prior art. When a level of applied data signal voltage in one of the pixels of the liquid crystal display device is changed from a previous frame period, simultaneously with it, the luminance of the backlight device is temporarily increased or decreased. Thus, the light quantity of light passing through the liquid crystal layer per unit time is substantially constant before and after the transmittance of the liquid crystal layer reaches a set value and the apparent luminance on the display screen reaches the set value in a short time as compared in the prior art. This improves the response speed. The liquid crystal display device of the present invention can be applied to a mobile telephone, a television, and a display device of a computer.

Description

Specification

Liquid crystal display

Technical field

[0001] The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device including a backlight device.

Background art

In recent years, liquid crystal display devices are used in various fields such as mobile phones, televisions, and computers. The liquid crystal display device performs gradation display by adjusting the transmittance of the liquid crystal layer by changing the magnitude of the voltage applied to the pixel electrode for each pixel in accordance with the display image. In addition, a liquid crystal display device usually includes a backlight device that illuminates the liquid crystal display panel with a back surface power in addition to the liquid crystal display panel, except for some single-color display devices that do not perform power.

[0003] Liquid crystal display devices are inferior to CRT display devices in terms of force response speed, which has advantages such as power saving and space saving over CRT display devices. This point will be described with reference to FIG. FIG. 3 is an explanatory diagram for explaining the response speed in a conventional liquid crystal display device. FIG. 3A shows a change in the data signal voltage applied to the pixel electrode of one pixel, and FIG. Fig. 3C shows the change in the luminance of the backlight device, and Fig. 3D shows the change in the apparent luminance on the display screen in one pixel.

[0004] In addition, the liquid crystal display device shown in FIGS. 3A to 3D is configured to be capable of gradation display. The levels of “Data signal voltage”, “Transmittance of liquid crystal layer”, “Brightness of backlight device”, and “Luminance of appearance on display screen” showing the vertical axis of each of FIGS. 3A to 3D are gradation levels. The corresponding relative value is shown. 3A to 3D, the horizontal axis is time.

As shown in FIGS. 3A and 3B, due to the characteristics of the liquid crystal material, the transmissivity of the liquid crystal layer changes more slowly than the data signal voltage. Therefore, after the level of the data signal voltage is switched, There is a time lag until the transmittance of the light reaches the corresponding value (set value). In the example of FIG. 3, the response time of the liquid crystal layer is 16 ms (Typ). [0006] For this reason, as shown in FIG. 3D, the apparent luminance on the display screen also changes gradually, and until the apparent luminance reaches a value (set value) corresponding to the level of the data signal voltage. There is also a time lag. As a result, in particular, when a moving image is displayed on the display screen of the liquid crystal display device, an afterimage may be observed by the user of the liquid crystal display device. As shown in Fig. 3C, the brightness of the knocklight is constant regardless of the level of the data signal voltage.

In order to solve such a problem, for example, when the level of the data signal voltage is switched from “1” to “4”, a data signal voltage having a level greater than “4” is input at the initial stage of switching. As described above, a liquid crystal display device that corrects the data signal voltage has been proposed (see, for example, Patent Document 1.) o Since such a liquid crystal display device can quickly start up the liquid crystal, It is considered that the response speed can be improved.

Patent Document 1: Japanese Patent Application Laid-Open No. 2004-302160

Disclosure of the invention

Problems to be solved by the invention

However, in the liquid crystal display device described in Patent Document 1, there is still a time lag until the transmittance of the liquid crystal layer reaches the set value. For this reason, there is a time lag until the apparent luminance on the display screen reaches the set value, and there is a possibility that the user of the liquid crystal display device will observe the remaining.

[0009] An object of the present invention is to provide a liquid crystal display device that can solve the above-described problems and can improve the response speed as compared with the prior art.

Means for solving the problem

In order to achieve the above object, a liquid crystal display device according to the present invention is a liquid crystal display device including a liquid crystal display panel and a backlight device that illuminates the liquid crystal display panel, and the luminance of the backlight device A control unit that controls the brightness of the backlight device during a set time when the data signal voltage applied to any pixel electrode of the liquid crystal display panel changes. It is characterized by raising or lowering. The invention's effect As described above, in the liquid crystal display device according to the present invention, when the level of the applied data signal voltage changes from the level in the previous frame period at the pixel electrode of any pixel, the backlight is simultaneously generated. The brightness of the device temporarily increases or decreases. For example, when the level of the data signal voltage increases, there is a time lag until the transmittance of the liquid crystal layer reaches a set value, and conventionally, the amount of light passing through the liquid crystal layer is insufficient during this time. However, in the liquid crystal display device according to the present invention, in this case, the brightness of the knocklight device is increased, so that the shortage of light quantity is compensated. As a result, the apparent luminance on the display screen reaches the set value in a shorter period of time than in the prior art, and the liquid crystal display device according to the present invention can improve the response speed as compared with the prior art.

Brief Description of Drawings

FIG. 1 is a block diagram showing a schematic configuration of a liquid crystal display device according to an embodiment of the present invention.

2 is an explanatory diagram for explaining the response speed in the liquid crystal display device shown in FIG. 1. FIG. 2A shows a change in the data signal voltage applied to the pixel electrode of one pixel, and FIG. Fig. 2C shows the change in luminance of the liquid crystal layer in one pixel, Fig. 2C shows the change in luminance of the backlight device, and Fig. 2D shows the change in the apparent luminance on the display screen in one pixel.

FIG. 3 is an explanatory diagram for explaining the response speed in a conventional liquid crystal display device. FIG. 3A shows a change in the data signal voltage applied to the pixel electrode of one pixel, and FIG. FIG. 3C shows the change in luminance of the backlight device, and FIG. 3D shows the change in the apparent luminance on the display screen in one pixel.

BEST MODE FOR CARRYING OUT THE INVENTION

The liquid crystal display device according to the present invention is a liquid crystal display device including a liquid crystal display panel and a backlight device that illuminates the liquid crystal display panel, and includes a control unit that controls the luminance of the backlight device. The control unit increases or decreases the luminance of the backlight device during a set time when a data signal voltage applied to any pixel electrode of the liquid crystal display panel changes. To do. In the liquid crystal display device according to the present invention, the backlight device includes a light emitting diode as a light source, and the control unit controls the current value of the current supplied to the light emitting diode by controlling the current value of the current. It is preferable to adopt a mode for controlling the above. According to this aspect, the brightness of the knocklight device can be controlled easily and accurately.

[0015] In the liquid crystal display device according to the present invention, when the first change in the data signal voltage occurs in one frame period, the control unit changes the luminance of the backlight device during a set time. It is preferable to adopt a mode of raising or lowering. This aspect is particularly effective when the gradation of the entire display area of the liquid crystal display panel changes at once.

[0016] (Embodiment)

Hereinafter, a liquid crystal display device according to an embodiment of the present invention will be described with reference to FIG. 1 and FIG. First, a schematic configuration of the liquid crystal display device in this embodiment will be described with reference to FIG. FIG. 1 is a block diagram showing a schematic configuration of a liquid crystal display device according to an embodiment of the present invention.

As shown in FIG. 1, the liquid crystal display device in the present embodiment mainly includes a liquid crystal display panel and a backlight device 9 that illuminates the liquid crystal display panel. The liquid crystal display panel is configured by sealing a liquid crystal layer between an active matrix substrate 1 and a counter substrate. In FIG. 1, only the active matrix substrate 1 is shown, and the counter substrate and the liquid crystal layer are not shown. The liquid crystal display panel also includes a gate driver 2, a source dryer 3, and a control IC 4. Further, although not shown, the counter substrate is provided with a common electrode, a color filter corresponding to each pixel, and the like.

The active matrix substrate 1 includes a plurality of pixels A to A arranged in a matrix in an area corresponding to a display area (n and m are arbitrary integers). Pixel A

11 nm 11

... A each mainly includes a TFT 10 and a pixel electrode 11. Also active matri nm

On the task board 1, between the columns of the plurality of pixels A to A is along the vertical direction of the screen.

11 nm

A plurality of source lines X to X are arranged. Between each row of pixels A to A

1 m 11 nm

A plurality of gate lines Y to Y are arranged along the horizontal direction of the screen.

1 η

[0019] Each of the source lines X to Χ is connected to the source electrode and the source of the TFT 10 constituting the corresponding column.

1 m Connected to the source driver 3. Each of the gate lines Y to Y constitutes a corresponding row

1 η

The gate electrode of TFT10 and the gate driver 2 are connected. The gate driver 2 and the source driver 3 are connected to the control IC 4.

The control IC 4 receives an image signal, a synchronization signal, a clock signal, and the like from outside the liquid crystal display panel. When these signals are input, the control IC 4 generates a gate driver control signal and a source driver control signal at timings suitable for the gate driver 2 and the source driver 3 to drive the liquid crystal. The control IC 4 outputs an image signal, a source driver control signal, and a clock signal to the source driver 3, and outputs a gate driver control signal and a clock signal to the gate driver 2.

Although not shown in FIG. 1, the gate driver 2 and the source driver 3 are supplied with a power supply voltage from a power supply circuit (not shown). The source driver 3 is also supplied with a gradation reference voltage (V to V (1: integer)) from a gradation voltage circuit (not shown). Furthermore,

0 1

A counter electrode voltage (Vcom) is supplied to the counter electrode of the counter substrate from a counter electrode drive circuit (not shown). In this embodiment, the inversion driving method is employed, and the polarity of the voltage applied to the liquid crystal layer is inverted every frame or every horizontal period.

[0022] The gate driver 2 includes the gate lines Y to Y based on the gate driver control signal and the clock signal.

1 Sequentially supply signals to η. This selects the rows in order of up and down. When one row is selected, the source driver 3 generates an image signal and a gradation reference voltage (V

0

~ V) and the data signal voltage applied to each pixel electrode 11 of the selected row

1

Generated and output by source line X ~ Χ. This selects gate driver 2.

1 m

A data signal voltage is applied to the pixel electrode 11 of the pixel in the row.

[0023] Selection of a row (gate line) by the gate driver 2 and supply of a data signal voltage to the selected row by the source driver 3 are sequentially performed from the top to the bottom, and when all the rows are finished, The drawing of one frame ends. As a result, the transmittance of the liquid crystal layer corresponding to each pixel becomes a value corresponding to the image signal, and an image is displayed in the display area when the illumination light of the backlight device 9 passes through the liquid crystal layer.

As described above, the liquid crystal display device in the present embodiment is the same as the conventional liquid crystal display device. The power that has the configuration of is different from that in the following points. As shown in FIG. 1, the liquid crystal display device according to the present embodiment includes a backlight control unit 5 that controls the luminance of the backlight device 9. When the data signal voltage applied to any of the pixel electrodes 11 changes, the knock light control unit 5 increases or decreases the brightness of the knock light device 9 for a set time. In other words, in the conventional liquid crystal display device, the brightness of the knock device during drawing is constant (see FIG. 3C), but in this embodiment, the luminance of the backlight device during drawing is not constant. .

In the present embodiment, the knock light device 9 is an edge light type backlight device, and includes a light guide plate 8a and a plurality of light emitting diodes 8b arranged on one side surface of the light guide plate 8a. I have. In the example of FIG. 1, the light emitting diode 8b is disposed only on one side surface of the light guide plate 8a. The present embodiment is not limited to this. For example, the light emitting diode 8b may be disposed on two opposite side surfaces.

The backlight control unit 5 increases or decreases the luminance of the backlight device 9 by controlling the current value of the current supplied to the light emitting diode 8b. Further, in the present embodiment, the knock light control unit 5 increases or decreases the luminance of the backlight device 9 when the first change in the data signal voltage occurs in one frame period. Note that the “frame period” means the period from when all the gate lines are scanned sequentially from top to bottom until the display of one screen is completed once.

Specifically, the backlight control unit 5 includes a data operation circuit 6 and a current control circuit 7 that supplies current to the light-emitting diode 8b in response to an instruction from the data operation circuit 6. Similarly to the control IC 4, the data arithmetic circuit 6 receives image signals, synchronization signals, clock signals, and the like from the outside of the liquid crystal display panel. Based on these input signals, the data arithmetic circuit 6 first detects the timing at which the data signal voltage changes during the current frame period.

[0028] For example, when the gate line Y is selected, the data signal voltage output from the source lines X to X

1 1 m

If either changes compared to the previous frame period, the data arithmetic circuit 6 detects the output timing of the data signal voltage after the gate line Y is selected. And de

1

The data calculation circuit 6 sends a current control signal to the current control circuit 7 at the detected timing. Increase or decrease the current value. Specifically, when the data signal voltage increases, the data arithmetic circuit 6 increases the current value and increases the brightness of the knocklight device 9. On the other hand, when the data signal voltage decreases, the data arithmetic circuit 6 decreases the current value to decrease the brightness of the knock light device 9.

[0029] Further, the data calculation circuit 6 causes the current control circuit to increase or decrease the current value only during the set time for the detected time point. The setting time, current value increase and decrease ranges will be described later with reference to FIG.

Furthermore, in the present embodiment, information (luminance information) for specifying the luminance of the light source 8b is input to the current control circuit 7 from the optical sensor 12 disposed in the vicinity of the light emitting diode 8b. The current control circuit 7 controls the current value supplied to the light emitting diode 8b by feedback control based on luminance information. Specifically, the current control circuit 7 performs feedback control so that the target value of luminance given from the data calculation circuit 6 is achieved. In addition, the current control circuit 7 can obtain the current value of V, which is actually supplied to the light emitting diode 8b as the luminance information power, and can control the supplied current based on the obtained current value.

Here, the response speed of the liquid crystal display device in this embodiment will be described with reference to FIG. FIG. 2 is an explanatory diagram for explaining the response speed in the liquid crystal display device shown in FIG. 1. FIG. 2A shows a change in the data signal voltage applied to the pixel electrode of one pixel, and FIG. 2B shows one pixel. 2C shows the change in the transmittance of the liquid crystal layer, FIG. 2C shows the change in the brightness of the backlight device, and FIG. 2D shows the change in the apparent brightness of the display screen in one pixel.

[0032] In addition, the levels of "data signal voltage", "transmittance of the liquid crystal layer", "brightness of the backlight device", and "appearance brightness of the display screen" indicating the vertical axes of FIGS. 2A to 2D are as follows: It is shown as a relative value corresponding to the gradation level. 2A to 2D, the horizontal axis is time.

As shown in FIG. 2, as shown in FIGS. 2A and 2B, the transmittance of the liquid crystal layer also changes more slowly than the data signal voltage due to the characteristics of the liquid crystal material in this embodiment. There is a time lag between the time when the level of the data signal voltage is switched and the time when the transmittance of the liquid crystal layer reaches a corresponding value (set value). In the example of FIG. 2, the response time of the liquid crystal layer is 16 ms (Typ). However, in this embodiment, unlike the example shown in FIG. 3 in the background art, when the level of the data signal voltage is switched from “1” to “4”, it is shown in FIG. 2C. At the same time, the backlight control unit 5 (see FIG. 1) increases the brightness for the set time. As a result, the transmittance of the liquid crystal layer rises to the set value, and the amount of illumination light that passes through the liquid crystal layer increases as compared with the case where the luminance is constant (see FIG. 3C). As shown in 2D, the apparent brightness on the display screen reaches the set value in a short time. In the example of Fig. 2D, the time required for the apparent brightness on the display screen to reach the set value is only 0.1 μs or less.

Further, in the example of FIG. 2, the force for explaining the case where the data signal voltage is increased. The present embodiment is not limited to this example. For example, when the level of the data signal voltage is switched from “4” to “1” contrary to the example of FIG. 2, the backlight control unit 5 simultaneously decreases the luminance for the set time. As a result, the light intensity of the illumination light that passes through the liquid crystal layer when the transmittance of the liquid crystal layer does not decrease to the set value decreases compared to the case where the luminance is constant, so the apparent luminance on the display screen is Decrease to set value in a short time

As described above, according to the liquid crystal display device in the present embodiment, the apparent luminance on the display screen reaches the set value in a shorter period of time compared to the case where the luminance of the conventional knock light device is constant. . Therefore, according to the liquid crystal display device of the present invention, the response speed can be improved as compared with the conventional liquid crystal display device. Further, in the present embodiment, the increase and decrease in luminance occur over the entire light emitting surface of the knocklight device. Therefore, in the liquid crystal display device in this embodiment, in particular, the entire display area of the liquid crystal display panel is This is effective when the gradation changes at once.

[0037] In the present embodiment, the time to increase or decrease the luminance, the increase width and the decrease width of the luminance, in other words, the time to increase or decrease the current value supplied to the light emitting diode 8b, The descending width may be set according to the reaction rate of the liquid crystal material constituting the liquid crystal layer. However, in this embodiment, the time for raising or lowering the current value, the rise and fall width of the current value are the amount of light per unit time of light passing through the liquid crystal layer, and the transmittance of the liquid crystal layer is the set value. It is set to be almost constant before reaching and after reaching It is preferable.

Specifically, in the present embodiment, as shown in FIG. 2C, the time during which the current value is increased or decreased, the increase width and the decrease width of the current value, the current waveform is shown in FIG. 2B. It is preferable to set it so that a curve that reverses the waveform of the transmittance of the liquid layer is drawn. In this way, the apparent brightness on the display screen can be reliably reached to the set value in a short period of time.

In the liquid crystal display device according to the present embodiment shown in FIG. 1, the knock light device 9 is configured to uniformly illuminate the entire back surface of the liquid crystal display panel. It is not limited to. In the present invention, the knock light device may have a light emitting surface divided into a plurality of areas and capable of illuminating with different brightness for each area. Specifically, the backlight device may be capable of illuminating the back surface of the liquid crystal display panel with different luminance for each pixel (row) aligned in the horizontal direction, or the back surface of the liquid crystal display panel for each pixel. It may be one that can be illuminated with different brightness.

[0040] A specific example of such a backlight device is a direct type knock device in which a plurality of light emitting diodes are arranged in a matrix. In the former case, the same number of light emitting diodes as the number of rows of pixels are arranged. In the latter case, the same number of light emitting diodes as the number of pixels are arranged.

[0041] Further, in the former case, the knock light control unit determines whether a change in the data signal voltage occurs each time the data signal voltage is output as the source line force. When a change occurs in the data signal voltage, the backlight control unit supplies a current obtained by increasing or decreasing the current value to the light emitting diode that illuminates the corresponding row.

In the latter case, when the backlight control unit detects a change in the data signal voltage, the backlight control unit increases or decreases the current value with respect to the light emitting diode corresponding to the pixel in which the data signal voltage changes. Supply the lowered current.

In the present embodiment, the gate driver 2 and the source driver 3 can be provided by an IC chip. The IC chip that functions as the gate driver 2 and the source driver 3 is mounted in a peripheral area of the display area of the active matrix substrate 1 by COG (Chip On Glass), TCP (Tape Carrier Package), or the like. In addition, these IC chips are The active matrix substrate 1 is connected to source lines or gate lines formed on the active matrix substrate 1. In the present invention, the circuits constituting the gate driver 2 and the source driver 3 can be formed monolithically on the active matrix substrate 1.

Furthermore, in the present embodiment, knock light control unit 5 can also be provided by an IC chip. This IC chip can also be mounted in the area around the display area of the active matrix substrate 1 by COG, TCP, or the like. In the present invention, all or part of the data arithmetic circuit 6 and the current control circuit 7 constituting the backlight control unit 5 can be formed monolithically on the active matrix substrate 1.

Industrial applicability

The liquid crystal display device according to the present invention is effective as a display device for various devices such as a mobile phone, a television, and a computer. Therefore, the liquid crystal display device according to the present invention has industrial applicability.

Claims

The scope of the claims

[1] A liquid crystal display device comprising a liquid crystal display panel and a backlight device for illuminating the liquid crystal display panel,

A control unit for controlling the luminance of the backlight device;

The control unit raises or lowers the luminance of the backlight device for a set time when the data signal voltage applied to the pixel electrodes of the liquid crystal display panel changes. A liquid crystal display device.

[2] The backlight device includes a light emitting diode as a light source,

The liquid crystal display device according to claim 1, wherein the control unit controls the luminance by controlling a current value of a current supplied to the light emitting diode.

[3] The control unit according to [1] or [2], wherein when the first change of the data signal voltage occurs in one frame period, the control unit increases or decreases the luminance of the backlight device during a set time. Liquid crystal display device.