JP5249899B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device including a liquid crystal panel and a backlight light source, and more particularly to a technique for preventing motion blur and multiple contours in moving image display by intermittently lighting a backlight light source.

In recent years, a liquid crystal display device including a liquid crystal panel and a backlight light source has been widely used in applications such as a television receiver and a display device. In the liquid crystal display device, motion blur and multiple contours that occur during moving image display due to hold driving that always turns on the backlight light source are problematic.
For this reason, conventionally, there has been known a technique for preventing motion blur and multiple contours that occur during moving image display by intermittently lighting a backlight light source within one frame period (one vertical period) to approximate it to impulse driving. (For example, refer to Patent Document 1).
In particular, as disclosed in Patent Document 1, a backlight scan process in which a plurality of light sources corresponding to a plurality of display areas in the vertical direction of a liquid crystal panel are sequentially intermittently lit in synchronization with image writing in the display areas. May be executed. Specific examples will be described below.

FIG. 2 shows a schematic configuration of the backlight source 31 having a plurality of LED light source groups L1 to L12 corresponding to a plurality of display areas in the vertical direction of the liquid crystal panel. Each of the LED light source groups L1 to L12 of the backlight source 31 has a plurality of LED light sources 31a arranged in the horizontal direction.
FIG. 3 shows a specific example of the execution result of the backlight scan processing of the backlight light source 31. As shown in FIG. 3, in the backlight scanning process, the LED light source groups L1 to L12 are sequentially turned off and on within one frame. As a result, it can be approximated to impulse driving, and motion blur and multiple contours that occur during moving image display can be prevented.

By the way, the light from each of the LED light source groups L1 to L12 in the backlight light source 31 affects the luminance at the position of each of the other LED light source groups L1 to L12.
For example, FIG. 6 shows an example of the relationship of the luminance ratio between the LED light source group L1 and the other LED light source groups L2 to L12 when only the LED light source group L1 located at the upper end of the LED light source groups L1 to L12 is turned on. It is a graph which shows. As shown in FIG. 6, the luminance at each position of the LED light source groups L2 to L12 is affected by light leaked from the LED light source group L1. Therefore, in order to make the luminance of the illumination of the liquid crystal panel by the backlight light source 31 in one frame uniform, it is necessary to adjust the lighting rate of each of the LED light source groups L1 to L12.

Japanese Patent No. 3994997

However, when changing the lighting rate of each of the LED light source groups L1 to L12 in order to make the luminance of the illumination by the backlight light source 31 uniform, depending on the method of changing the lighting rate, the backlight scanning process of the backlight light source 31 may be performed. The effect of black insertion (intermittent lighting) may be reduced.
Specifically, FIG. 7 shows an example of a method for changing the lighting rate of the LED light source groups L <b> 1 to L <b> 12 of the backlight light source 31. Note that the shaded area in FIG. 7 is an extension of the lighting period.
In the example shown in FIG. 7, when changing the lighting rate of the other LED light source groups L1 to L6 and L8 to L12 based on the LED light source group L7 among the LED light source groups L1 to L12, the first half of the lighting period is extended. doing. In this case, in each of the LED light source groups L8 to L12, the simultaneous lighting period with the adjacent LED light source group is extended, but in each of the LED light source groups L1 to L6, the adjacent LED light source group is turned off. The lighting time in the period will be extended. Therefore, in each of the LED light source groups L1 to L6, there is a problem that light leaks from the lit LED light source group to the position of the unlit LED light source group, and the effect of black insertion is reduced. Conversely, when the latter half of the lighting period of each of the LED light source groups L1 to L6, L8 to L12 is extended, the adjacent LED light source group is turned off in each of the LED light source groups L8 to L12. A similar problem arises because the lighting time at is extended.
Conversely, when there is a light source group having a shorter lighting period than the reference LED light source group L7, the light source group is adjacent in the period when the light source group is turned off depending on the lighting timing of the light source group. The time during which the light source group is turned on becomes longer, resulting in a problem that the effect of black insertion is reduced.
Accordingly, the present invention has been made in view of the above circumstances, and an object of the present invention is to prevent black insertion caused by light leakage between light sources in a backlight light source (effect of preventing motion blur of moving image display and multiple contours). It is an object of the present invention to provide a liquid crystal display device capable of changing the lighting rate of each of the light sources while suppressing the reduction of the above.

To achieve the above object, the present invention provides a backlight light source having a plurality of light sources arranged in parallel corresponding to a plurality of display areas in the vertical direction of the liquid crystal panel, and each of the plurality of light sources in one frame period. The liquid crystal display device includes a backlight control unit that executes backlight scanning processing for sequentially intermittent lighting, and the backlight control unit has a lighting rate set in advance for each light source. One or a plurality of the light sources having a lighting rate set higher than that of the reference light source when the light source located in the center is used as a reference light source. The light source whose lighting order is earlier than the reference light source delays the end point of the lighting period when the light source is intermittently turned on at the same lighting rate as the reference light source. The light source whose lighting order is later than the reference light source changes the lighting rate by accelerating the start point of the lighting period when intermittent lighting is performed at the same lighting rate as the reference light source. It is comprised as a liquid crystal display device characterized by being.
Thereby, the lighting rate can be changed while suppressing the extension of the lighting time in the period in which the adjacent light source is turned off for any light source whose lighting order is before and after the reference light source. It is possible to change the lighting rate while suppressing a reduction in the effect of black insertion (effect of preventing moving image display motion blur and multiple contours) caused by light leakage between the light sources in the backlight light source.
Further, when the backlight control means has one or a plurality of the light sources having a lighting rate lower than that of the reference light source or the same lighting rate as that of the reference light source, the backlight control unit is turned on more than the reference light source among the light sources. It is conceivable that the light source with the earlier order delays the lighting start timing, and the light source with the lighting order later than the reference light source has an earlier lighting start timing.
As a result, the influence of light leakage between a light source having a lower lighting rate than the reference light source or having the same lighting rate as the reference light source and the other light source can be reduced, and the light source in the backlight light source It is possible to suppress a reduction in the effect of black insertion (effect of preventing motion display blur and multiple contours) caused by light leakage between each other.

By the way, the ratio of the lighting rates of the respective light sources is the inverse ratio of the luminance ratio obtained in each of the display areas corresponding to each of the light sources when all the light sources are turned on simultaneously or intermittently turned on at the same lighting rate. It is conceivable that they are preset in such a way.
Further, the backlight scanning process may be such that the plurality of light sources are sequentially intermittently turned on in synchronization with, for example, a vertical synchronizing signal and a horizontal synchronizing signal in one frame period.

According to the present invention, it is possible to change the lighting rate while suppressing the extension of the lighting time in the period in which the adjacent light source is turned off for any light source whose lighting order is before and after the reference light source. Therefore, it is possible to change the lighting rate while suppressing the reduction of the black insertion effect (the effect of preventing motion blur of moving image display and multiple contours) caused by light leakage between the light sources in the backlight light source.
Further, it is possible to reduce the influence of light leakage between a light source having a lower lighting rate than the reference light source or having the same lighting rate as that of the reference light source and the other light sources. It is possible to suppress the reduction of the effect of black insertion (the effect of preventing motion display blur and multiple contours) caused by light leakage between the two.

1 is a block diagram showing a schematic configuration of a liquid crystal display device according to an embodiment of the present invention. The schematic diagram which shows an example of the backlight light source provided in the liquid crystal display device which concerns on embodiment of this invention. The figure for demonstrating an example of the execution result of a normal backlight scan process. The figure for demonstrating an example of the execution result of the backlight scan process at the time of lighting rate change. The figure which shows the relationship of the luminance ratio at the time of the light source full lighting of the backlight light source in the liquid crystal display device which concerns on embodiment of this invention. The figure which shows the relationship of a luminance ratio when only one light source of a backlight light source is turned on. The figure for demonstrating an example of the change method of the lighting rate of each light source of a backlight light source.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
As shown in FIG. 1, a liquid crystal display device X according to an embodiment of the present invention includes a display control unit 11, a liquid crystal panel 21, a liquid crystal drive unit 22, a backlight light source 31, a backlight control unit 32 (backlight control means). Example).
The liquid crystal display device X is, for example, a display device used for a television receiver or a personal computer. Note that in this embodiment, description of other components included in a general television receiver or display device that does not directly affect the present invention is omitted.

The display control unit 11 receives a video signal included in a television broadcast received by an antenna (not shown) or a video content input from an external input terminal (not shown), and performs vertical synchronization based on the video signal. Signals and horizontal sync signals are generated. The video signal, the vertical synchronization signal, and the horizontal synchronization signal are input from the display control unit 11 to the liquid crystal driving unit 22. The display control unit 11 inputs the vertical synchronization signal and the horizontal synchronization signal to the backlight control unit 32.
Here, the display control unit 11 generates a vertical synchronizing signal having a driving frequency of 120 Hz, which is a double speed of 60 Hz, which is a frequency of a video signal of television broadcasting. Therefore, the display control unit 11 outputs one frame image in the video signal to the liquid crystal drive unit 22 twice, or generates an interpolated image from two consecutive frames in the video signal, Inserted and output to the liquid crystal drive unit 22.

The liquid crystal panel 21 is formed of a liquid crystal layer, a scan electrode and a data electrode for applying a scan signal and a data signal to the liquid crystal layer, and includes a plurality of liquid crystal elements whose transmittance varies depending on an applied voltage. This is an active matrix type liquid crystal panel.
The liquid crystal driving unit 22 applies scanning electrodes (gate electrodes) and data electrodes (source electrodes) of the liquid crystal panel 21 based on an image signal, a vertical synchronization signal, and a horizontal synchronization signal input from the display control unit 11. Drive. Specifically, after receiving the vertical synchronizing signal, the liquid crystal driving unit 22 outputs a gate signal to the scanning electrode in accordance with the horizontal synchronizing signal corresponding to the first line, and receives the image signal corresponding to the first line as data. Output sequentially to the electrodes. As a result, the first line image is displayed. Thereafter, when the horizontal synchronizing signal corresponding to the second line is input, the liquid crystal driving unit 22 outputs a gate signal to the scanning electrode of the second line, and sequentially applies the image signal corresponding to the second line to the data electrode. Output. Thereafter, the same processing is repeated to display an image on the full screen of the liquid crystal panel 21.

The backlight source 31 is disposed on the back surface of the liquid crystal panel 21 and illuminates the liquid crystal panel 21 from behind. FIG. 2 is a schematic diagram showing an example of the structure of the backlight light source 31. As shown in FIG.
As shown in FIG. 2, the backlight source 31 includes a plurality of LED light source groups L1 to L12 (an example of a plurality of light sources) arranged in parallel corresponding to a plurality of display areas in the vertical direction of the liquid crystal panel 21. Have. Each of the LED light source groups L1 to L12 includes a plurality of LED light sources 31a arranged in parallel in the horizontal direction of the liquid crystal panel 21. Each of the display areas corresponding to the LED light source groups L1 to L12 is an area including a plurality of lines of display pixels of the liquid crystal panel 21.
In response to a control instruction from the backlight control unit 32, the backlight light source 31 individually blinks a large number of the LED light sources 31a in units of the LED light source groups L1 to L12. The number of the LED light source groups L <b> 1 to L <b> 12 is not limited to this, and the design may be appropriately changed according to the size of the liquid crystal panel 21.
In addition, the light leakage that is a problem in the present invention appears more noticeably when the LED light source groups L1 to L12 having the LED light source 31a are used. However, in the present invention, the backlight light source 31 is the LED light source group. The present invention is also applicable to a case where a plurality of fluorescent tubes (an example of a plurality of light sources) arranged in parallel in the vertical direction of the liquid crystal panel 21 instead of L1 to L12.

The backlight control unit 32 performs a hold driving process for always lighting the backlight light source 31, and the LED light source 31a of the backlight light source 31 within the LED light source group L1 to L1 within one frame period (within one vertical period). Any one of the backlight scan processes in which intermittent lighting is sequentially performed every L12 is selectively executed.
Whether or not the backlight control process is executed by the backlight control unit 32 is switched by the display control unit 11 according to a user operation of an operation key provided on a remote controller (not shown) or the main body of the liquid crystal display device X, for example. It is done. The display control unit 11 may automatically switch the execution of the backlight scan process according to the content of the display video.
Here, one frame period is a period for displaying an image of one frame on the liquid crystal panel 21, that is, an interval of vertical synchronizing signals. Therefore, in the liquid crystal display device X in which the image writing speed (driving frequency) of the liquid crystal panel 21 is 120 Hz (so-called double speed liquid crystal), one frame period is about 8.3 ms. Of course, the driving frequency of the liquid crystal panel 15 may be 60 Hz or 240 Hz.

FIG. 3 is a schematic diagram for explaining an example of the execution result of the backlight scanning process.
As shown in FIG. 3, when the backlight scanning process is executed by the backlight control unit 32, each of the LED light source groups L1 to L12 is about 4.1 ms (1) from the start of image writing in the corresponding display area. After turning off (50% of the frame), the light turns on for about 4.1 ms (50% of one frame). As a result, pseudo impulse driving is realized, and motion blur and multiple contours in moving image display can be prevented. The time (ratio) during which the LED light source groups L1 to L12 are turned off or turned on is not limited to this.

Here, the backlight control unit 32 sequentially blinks each of the LED light source groups L1 to L12 in synchronization with the vertical synchronization signal and horizontal synchronization signal of the image signal displayed on the liquid crystal panel 21 in the backlight scanning process. Let
Specifically, the backlight control unit 32 turns off the LED light source group L1 in the first row for about 4.1 ms in response to reception of the vertical synchronization signal, and then turns it on for about 4.1 ms.
In addition, after receiving the vertical synchronization signal, the backlight control unit 32 receives a number of horizontal synchronization signals corresponding to the liquid crystal elements of a plurality of lines of the liquid crystal panel 21 corresponding to the LED light source group L1. The LED light source group L2 is turned off for about 4.1 ms, and then turned on for about 4.1 ms.
Similarly, after receiving the vertical synchronization signal, the backlight control unit 32 responds to reception of the number of horizontal synchronization signals corresponding to the liquid crystal elements of a plurality of lines of the liquid crystal panel 21 corresponding to the LED light source groups L1 and L2. Then, the LED light source group L3 is turned off for about 4.1 ms, and then turned on for about 4.1 ms.
Thereafter, the same processing is repeated, so that the LED light source groups L1 to L12 are sequentially blinked in synchronization with scanning of a plurality of liquid crystal elements of the corresponding liquid crystal panel 21. Note that the present invention can also be applied to the LED light source groups L1 to L12 of the backlight source 31 that are intermittently turned on sequentially from the lower end to the upper end.

As described above, the light from each of the LED light source groups L1 to L12 in the backlight light source 31 affects the luminance at the position of each of the other LED light source groups L1 to L12.
For example, FIG. 6 shows a luminance ratio between the LED light source group L1 and the other LED light source groups L2 to L12 when only the LED light source group L1 located at the upper end of the LED light source groups L1 to L12 is turned on. It is a graph which shows the example of a relationship. As shown in FIG. 6, the luminance at each position of the LED light source groups L2 to L12 is affected by light leaking from the LED light source group L1.
Therefore, as shown in FIG. 3, when the backlight scanning process is executed with all the lighting rates (50%) in one frame of the LED light source groups L1 to L12 set to be the same, the backlight in the one frame is executed. The luminance at the center of the light source 31 is increased due to the influence of light leaking from above and below. Therefore, in order to make the luminance of the illumination of the liquid crystal panel 21 by the backlight light source 31 in one frame uniform, it is necessary to previously adjust the lighting rate of each of the LED light source groups L1 to L12 at the time of executing the backlight scanning process. is there.
Therefore, in the liquid crystal display device X, as described below, the lighting rate of each of the LED light source groups L1 to L12 at the time of executing the backlight scan processing is set in advance, and the backlight control unit 32 The backlight scan process is executed based on the set lighting rate.

Here, FIG. 4 is based on the LED light source group L7 located at the center of the LED light source groups L1 to L12 when all the LED light source groups L1 to L12 of the backlight light source 31 are turned on (100%). The luminance ratio is shown.
As shown in FIG. 4, the luminance ratio of each of the LED light source groups L1 to L12 gradually decreases toward the upper end or the lower end with respect to the LED light source group L7 at the center.
Therefore, the lighting rate of the LED light source groups L1 to L12 of the backlight light source 31 in one frame of the backlight scan processing is set so that the LED light source groups L1 to L12 are turned on when all the LED light source groups L1 to L12 are turned on simultaneously. It is set to be the inverse ratio of the luminance ratio (see FIG. 4) obtained in each display area corresponding to each L12. That is, the lighting rate of each of the LED light source groups L1 to L12 is set to gradually increase toward the upper end or the lower end with respect to the LED light source group L7. For example, as shown in FIG. 4, since the luminance ratio between the LED light source group L1 and the LED light source group L7 is 85: 100, the lighting rate of the LED light source group L1 is the LED light source group L1 and the LED light source group. The lighting rate with the light source group L7 is set to be 100: 85, which is the inverse ratio of the luminance ratio.
Thereby, the luminance of the illumination of the liquid crystal panel 21 by the backlight light source 31 in one frame can be made uniform during execution of the backlight scanning process. Further, when all the LED light source groups L1 to L12 are intermittently lit at the same lighting rate, the luminance ratio is set to be an inverse ratio of the luminance ratio obtained in each display region corresponding to each of the LED light source groups L1 to L12. May be. The setting of the lighting rate may be performed as appropriate based on results obtained by experiments or simulations in advance, and is not limited to the method described here.

Then, as shown in FIG. 5, the backlight control unit 32 executes a backlight scan process based on a lighting rate set in advance for each of the LED light source groups L1 to L12.
Specifically, the backlight control unit 32 performs the LED scanning process in the backlight scanning process in which each of the LED light source groups L1 to L12 is intermittently turned on based on a lighting rate set in advance for each of the LED light source groups L1 to L12. When the LED light source group L7 that is located at the center and has the lowest lighting rate among the light source groups L1 to L12 is used as a reference light source, the LED light source groups L1 to L6 that are set to have a higher lighting rate than the LED light source group L7. Among the LED light source groups L7 to L12, the LED light source groups L1 to L6 whose lighting order is earlier than the LED light source group L7 are delayed in the end of the lighting period when intermittent lighting is performed at the same lighting rate as the LED light source group L7. As a result, the lighting rate is changed. On the other hand, the LED light source groups L8 to L12 whose lighting order is later than the LED light source group L7 are turned on by accelerating the start point of the lighting period when the LED light source group L7 is intermittently lit at the same lighting rate as the LED light source group L7. The rate is changing.
Thereby, in the liquid crystal display device X, the LED light source groups L1 to L6 whose lighting order is earlier than the LED light source group L7 and the LED light source groups L8 to L12 whose lighting order is later than the LED light source group L7. In any of the above, the lighting rate can be changed while suppressing the extension of the lighting time in the period in which the adjacent LED light source groups are turned off.
Therefore, in the liquid crystal display device X, the effect of black insertion due to light leakage between the LED light source groups L1 to L12 in the backlight light source 31 at the time of performing the backlight scan processing is reduced, that is, the motion blur of the moving image display. In addition, it is possible to adjust the lighting rate of each of the LED light source groups L1 to L12 while suppressing a reduction in the effect of preventing multiple contours.

By the way, in the backlight light source 31, there may be an LED light source group having a lower lighting rate than the LED light source group L7 as the reference light source, or an LED light source group having the same lighting rate as the LED light source group L7. Conceivable.
For example, in consideration of reflection from the casing of the backlight light source 31, the lighting rate of the LED light source groups L1 and L12 located at the upper and lower ends of the backlight light source 31 is the same as that of the LED light source group L7 or the LED It may be set lower than the light source group L7.
In such a case, the lighting start timing of the LED light source group L1 whose lighting order is earlier than the LED light source group L7 is delayed (the lighting period is shifted later), and the lighting order is higher than that of the LED light source group L7. By accelerating the lighting start timing of the LED light source group L12 later (shifting the lighting period forward), light leakage between the LED light source groups L1 and L12 and the other LED light source groups L2 to L11 is prevented. It is conceivable to reduce the influence.
Note that there is no LED light source group having a higher lighting rate than the LED light source group L7, which is a reference light source, and the LED light source group having a lower lighting rate than the LED light source group L7 or the LED light source group L7 is turned on. When there is an LED light source group with the same rate, the effect of black insertion can be enhanced by controlling the lighting timing as described above for the LED light source group having a lower lighting rate than the LED light source group L7. It is one form of invention. Of course, there is an LED light source group (the former) having a higher lighting rate than the LED light source group L7, and an LED light source group or the LED light source group L7 having a lower lighting rate than the LED light source group L7 as the reference light source. When there are LED light source groups (the latter) having the same lighting rate, the effect of black insertion may be enhanced by controlling the lighting timing as described above only for either the former or the latter.

  The present invention can be applied to a liquid crystal display device such as a television receiver or a display device.

DESCRIPTION OF SYMBOLS 11 ... Display control part 21 ... Liquid crystal panel 22 ... Liquid crystal drive part 23 ... Memory | storage memory 31 ... Backlight light source 32 ... Backlight control part 31a ... LED light source L1-L12 ... LED light source group X ... Liquid crystal display device

Claims (4)

A backlight light source having a plurality of light sources arranged in parallel corresponding to a plurality of display areas in the vertical direction of the liquid crystal panel and a backlight scanning process for sequentially intermittently lighting each of the plurality of light sources within one frame period are executed. A liquid crystal display device comprising a backlight control means,
The backlight control means intermittently lights each of the light sources based on a preset lighting rate for each light source, and when the light source located in the center among the plurality of light sources is a reference light source, Among the one or a plurality of the light sources set to have a higher lighting rate than the reference light source, the light source whose lighting order is earlier than the reference light source is turned on when intermittent lighting is performed at the same lighting rate as the reference light source. The lighting rate is changed by delaying the end point of the period, and the light source whose lighting order is later than the reference light source is advanced to the start point of the lighting period when intermittent lighting is performed at the same lighting rate as the reference light source. A liquid crystal display device characterized in that the lighting rate is changed by the above.   When the backlight control means has one or a plurality of light sources having a lighting rate lower than that of the reference light source or the same lighting rate as the reference light source, the lighting order of the light sources is higher than that of the reference light source. The liquid crystal display device according to claim 1, wherein the first light source delays the lighting start timing, and the light source whose lighting order is later than the reference light source has an earlier lighting start timing. The ratio of the lighting rates of the respective light sources is such that when all the light sources are simultaneously turned on or intermittently lit at the same lighting rate, the ratio is the inverse of the luminance ratio obtained in each of the display areas corresponding to each of the light sources. the liquid crystal display device according to claim 1 or 2, which has been preset in. The backlight scanning process, the liquid crystal display device according to any one of claims 1 to 3 in synchronization with those for sequentially intermittently turned the plurality of light sources to the vertical synchronizing signal and the horizontal synchronizing signal of one frame period .