JP2009109736A - Liquid crystal display device and driving method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device capable of suppressing an occurrence of uneven brightness distribution depending on the scan line by substantially uniforming the response attaining gradation of the liquid crystal in each scan line, and displaying an excellent moving image without increasing the circuit size or power consumption. <P>SOLUTION: In order to write an input video signal twice in one frame period, a frame memory part 1 converts the video signal to a high-speed video signal that has sped up the video signal. A drive circuit 3 divides one frame period into a first frame period and a second frame period, and drives a liquid crystal panel 4 by writing the high-speed video signal of the immediately preceding frame period in the first frame period, and writing in the high-speed video signal of the current frame period in the second frame period, to a pixel in the upper display region of the display screen of a liquid crystal panel 4. A backlight turning on/off control circuit 5 turns on a backlight 6 in the first frame period, and turns off the backlight 6 in the second frame period. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device that writes a high-speed video signal to a liquid crystal panel while intermittently turning on a light source provided on the back of the liquid crystal panel, and a driving method thereof. The present invention relates to a liquid crystal display device and a driving method thereof that make the liquid crystal response timing of the entire screen substantially uniform by writing the video signal twice.

  Conventionally, liquid crystal display devices have been widely used as display devices for computers because of their advantages such as light weight, thinness, and low power consumption. However, as the screen size increases, they are gradually used as general televisions. Is increasing. Since this liquid crystal display device is a hold-type display device that continues to display an image during one frame period, a motion blur phenomenon occurs in which the outline of the image blurs when a moving image is displayed, and a CRT (cathode ray tube) that is an impulse display device. Video display performance comparable to) is not obtained.

  For this reason, for example, scanning signal electrodes are sequentially selected, a voltage corresponding to the display image signal is applied to the data electrode, a display image signal for one image is written, and a voltage corresponding to the image signal applied to the liquid crystal panel is 1 The liquid crystal panel is not illuminated by the illumination power source during the period from the start of writing the display image signal for one image until the transmittance of the liquid crystal layer reaches a steady value from a transient value. After the transmittance of the layer reaches a steady value, the liquid crystal panel is illuminated by the illumination power source, and the transmittance of the liquid crystal layer reaches a steady value from a transient value from the start of writing the display image signal for one image. There has been proposed a liquid crystal display device in which the time until the start and the time from the start of illumination to the time when the illumination power source is turned off and the light from the illumination light source is added is within a frame period for displaying one image (for example, , Patent text Reference 1).

  In addition, in a liquid crystal display device that combines a liquid crystal panel in which a ferroelectric liquid crystal or antiferroelectric liquid crystal is sealed in a panel with a color filter, and a backlight that emits white light, the frequency at which data is written to the liquid crystal panel Is set to at least twice the frame frequency (120 Hz or more), the data writing process and the data erasing process on the liquid crystal panel are performed within one frame period, and the time for light to pass through the color filter is set to be less than half of the one frame period. A liquid crystal display device has been proposed (see, for example, Patent Document 2).

  Further, in other conventional liquid crystal display devices, backlight intermittent lighting is performed within one frame period in order to suppress motion blur of moving image display on the liquid crystal panel. FIG. 9 is a diagram illustrating video signal writing timing and backlight blinking timing in a conventional liquid crystal display device.

  In the example shown in FIG. 9, one frame period is divided into a previous frame period and a subsequent frame period, the backlight is turned off in the previous frame period, and the backlight is turned on in the subsequent frame period (hatched portion in the figure). The backlight is lit intermittently.

  Here, as a scanning line composed of pixels in one horizontal row of the liquid crystal panel, the uppermost first scanning line is P1, the intermediate scanning line at the intermediate position is PM, the lowermost final scanning line is PE, and the first A black level video signal (for example, 256 gray level 0 level) is written in the frame periods F1-F and F1-B, and a white level video signal (for example, 256th floor) is written in the second frame periods F2-F and F2-B. When the white level video signal is written in the third frame periods F3-F and F3-B, the white level video signal is intermediate from the first scanning line P1 according to the timing of the broken line DP in the figure. The data is sequentially written to the final scan line PE via the scan line PM, and the response waveform of each scan line is as shown in FIG.

That is, in the period when the backlight is lit, that is, in the subsequent frame period F1-B after the first frame period, black display is performed in all scanning lines, and in the subsequent frame period F3-B in the third frame period, all scanning lines are displayed. In the second frame period after the second frame period F2-B, the upper scanning line almost reaches the white level and the white display is performed.
JP 2001-125066 A JP 2001-343943 A

  However, since the liquid crystal is in a transient response state in the lower scanning line and there is a period in which the white level is not reached in the frame period F2-B after the backlight is turned on, the luminance of each scanning line is not good. It becomes uniform and motion blur occurs. Thus, when the display screen is rewritten, the upper part of the display screen has a faster video signal writing timing and the lower part has a slower writing timing, so even if the backlight is turned on after completion of the upper writing and liquid crystal response, the lower part Since the rewriting and the liquid crystal response are incomplete, the rewriting has not yet been performed, or the reached gradation is insufficient, and a double image or an edge blur occurs, thereby degrading the image quality.

  FIG. 10 is a diagram schematically showing motion blur when the liquid crystal panel and the backlight are driven at the drive timing shown in FIG. In the example shown in FIG. 10, as shown in (a-1), a black ellipse is written on the right side of the display screen in the first frame period, and then in the second frame as shown in (a-2). A black ellipse is written at the center of the display screen during the period, and finally, as shown in (a-3), the motion blur is schematically illustrated when the black ellipse is written at the left side of the display screen during the third frame period. It is shown in.

  In this case, in the first frame period, as shown in (b-1), a black ellipse that becomes whiter toward the lower side is displayed on the right side of the display screen, and in the second frame period, as shown in (b-2). In addition, a black ellipse that becomes whiter toward the lower side is displayed at the center of the display screen, and a black ellipse that becomes whiter toward the upper side as an afterimage of the first frame is displayed on the right side of the display screen. As shown in b-3), a black ellipse that becomes whiter toward the lower side is displayed on the left side of the display screen, and a black ellipse that becomes whiter toward the upper side as an afterimage of the second frame is displayed at the center of the display screen. When a moving image is displayed, the user perceives motion blur.

  As described above, when performing backlight intermittent lighting within one frame period, since the response arrival gradation of the liquid crystal at the time of backlight lighting is different for each scanning line, the luminance distribution becomes uneven depending on the vertical position of the display screen. The display image quality is impaired.

  Further, like the liquid crystal display device disclosed in Patent Document 1, the liquid crystal panel is illuminated by an illumination power source after the transmittance of the liquid crystal layer reaches a steady value, or the liquid crystal display device disclosed in Patent Document 2 Although it is conceivable that the liquid crystal response is completed in all the scanning lines when the backlight is turned on by writing the video signal at a high speed as described above, the slow response speed of the liquid crystal becomes a problem, which is not practical. In addition, a drive circuit for writing a video signal at a high speed is required, which increases the burden on the drive circuit and increases its power consumption.

  An object of the present invention is to suppress the occurrence of non-uniform luminance distribution by scanning lines by making the response arrival gradations of the liquid crystals in each scanning line substantially uniform, without increasing the circuit scale and power consumption. Another object of the present invention is to provide a liquid crystal display device capable of displaying a good moving image and a driving method thereof.

  The liquid crystal display device according to the present invention converts the video signal into a high-speed video signal with a high speed so that the liquid crystal panel including a plurality of pixels and the input video signal can be written twice within one frame period. Converting means to divide one frame period into a previous frame period and a subsequent frame period, and with respect to pixels in a predetermined display area of the display screen of the liquid crystal panel, a high speed of the immediately preceding frame period in the previous frame period By writing a video signal and writing a high-speed video signal of the current frame period in the subsequent frame period, panel driving means for driving the liquid crystal panel, a light source for illuminating the liquid crystal panel, and the light source in the previous frame period And a light source control means for turning off the light source in the subsequent frame period.

  In this liquid crystal display device, one frame period is divided into a previous frame period and a subsequent frame period, and a high-speed of the immediately preceding frame period in the previous frame period is applied to pixels in a predetermined display area of the display screen of the liquid crystal panel. The liquid crystal panel is driven by writing the video signal and writing the high-speed video signal of the current frame period in the subsequent frame period. At this time, since the light source is turned on in the previous frame period and the light source is turned off in the subsequent frame period, the high-speed video signal is first written in the subsequent frame period of the current frame period in which the light source is turned off. In addition, writing is performed again in the previous frame period of the next frame period in which the light source is turned on. Therefore, in the predetermined display area of the liquid crystal panel, a transient response of the liquid crystal is performed by the first writing of the high-speed video signal within the light source extinction period, so that the user visually recognizes the display screen at the time of the transient response of the liquid crystal After that, the second writing of the high-speed video signal is performed during the light source lighting period, and the liquid crystal has reached the target gradation during the light source lighting period, so only the display screen after completion of the liquid crystal response is visually recognized. can do. In this way, by making the response arrival gradation of the liquid crystal in each scanning line substantially uniform, it is possible to suppress the occurrence of non-uniform luminance distribution by the scanning line, without increasing the circuit scale and power consumption. A good video can be displayed.

  The panel driving unit divides the display screen of the liquid crystal panel into an upper display area and a lower display area, and writes a high-speed video signal in the previous frame period to the pixels in the upper display area. In addition, the high-speed video signal of the current frame period is written in the subsequent frame period, and the high-speed video signal of the current frame period is written to the pixels of the lower display area in each of the previous frame period and the subsequent frame period. Accordingly, it is preferable to drive the liquid crystal panel.

  In this case, the display screen of the liquid crystal panel is divided into an upper display area and a lower display area, and a high-speed video signal of the immediately preceding frame period is written to the pixels of the upper display area and the current image is displayed in the subsequent frame period. The liquid crystal panel is driven by writing a high-speed video signal in the frame period. Therefore, in the upper display area of the liquid crystal panel, a transient response of the liquid crystal is performed by the first writing of the high-speed video signal within the light source extinction period, so that the user visually recognizes the display screen at the time of the transient response of the liquid crystal. After that, the second writing of the high-speed video signal is performed during the light source lighting period, and the liquid crystal has reached the target gradation during the light source lighting period, so that only the display screen when the response of the liquid crystal is completed is visible. Can do.

  Further, since the liquid crystal panel is driven by writing the high-speed video signal of the current frame period in each of the previous frame period and the subsequent frame period to the pixels in the lower display area, in the lower display area of the liquid crystal panel, A transient response of the liquid crystal is performed by the first writing of the high-speed video signal during the light source lighting period, but the drive start timing of the scan line in the lower display area is sufficiently delayed from the drive start timing of the scan line in the upper display area. Therefore, the display due to the transient response is limited to only a part of the latter half of the light source lighting period, and most of the light source lighting period is written twice in the immediately preceding frame period, and the liquid crystal is in the target gradation. Has reached.

  As a result, the response arrival gradation of the liquid crystal in each scanning line can be made substantially uniform over the entire display screen, and the occurrence of non-uniform luminance distribution due to the scanning line is suppressed, and the circuit scale and power consumption are increased. It is possible to display a good video without having to do so.

  The panel driving unit preferably writes an overdrive video signal larger than the high-speed video signal in the current frame period in the subsequent frame period to the pixels in the upper lower region including the lowermost part of the upper display region.

  In this case, since the overdrive video signal larger than the high-speed video signal in the current frame period is written in the subsequent frame period to the pixels in the upper lower area including the lowermost part of the upper display area, the scanning line driving is started. A liquid crystal panel with a slow response speed that can reduce the time it takes for the liquid crystal to reach the target gradation in the upper lower area including the lowermost part of the upper display area with a slow timing and reach the target gradation within the light source extinction period. Even in the case where is used, the response arrival gradation of the liquid crystal in each scanning line in the upper display region can be made substantially uniform.

  The panel driving means preferably writes an underdrive video signal smaller than the high-speed video signal in the current frame period in the previous frame period to the pixels in the lower upper area including the uppermost part of the lower display area.

  In this case, since the underdrive video signal smaller than the high-speed video signal in the current frame period is written in the previous frame period to the pixels in the lower upper area including the uppermost part of the lower display area, the uppermost part of the lower display area In the lower upper area including the light source, the change in gradation due to the transient response of the liquid crystal during the light source lighting period can be reduced, and in the lower upper area including the uppermost part of the lower display area, the response reaching gradation of the liquid crystal in each scanning line can be reduced. It can be made substantially uniform.

  The light source control means turns on the light source in a pre-movement frame period in which the previous frame period has been moved by a predetermined movement time, and in the post-movement frame period in which the subsequent frame period has been moved by a predetermined movement time. Is preferably turned off.

  In this case, the light source is turned on in the pre-movement frame period in which the previous frame period is moved forward or backward by a predetermined movement time, and in the post-movement frame period in which the rear frame period is moved forward or backward by the predetermined movement time. Since the light source is turned off, the transient response period of the liquid crystal during the light source lighting period can be changed according to the response characteristics of the liquid crystal panel, and the response arrival gradation of the liquid crystal in each scanning line can be made substantially uniform.

  A driving method of a liquid crystal display device according to the present invention is a driving method of a liquid crystal display device including a liquid crystal panel including a plurality of pixels so that an input video signal can be written twice within one frame period. , Converting the video signal into a high-speed video signal, and dividing one frame period into a previous frame period and a subsequent frame period, and for the pixels in the upper display area of the display screen of the liquid crystal panel, The liquid crystal panel is driven by writing the high-speed video signal of the immediately preceding frame period in the previous frame period and writing the high-speed video signal of the current frame period in the subsequent frame period, and is provided on the back surface of the liquid crystal panel Turning on the light source in the previous frame period and turning off the light source in the subsequent frame period. That.

  According to the present invention, by making the response arrival gradation of the liquid crystal in each scanning line substantially uniform, it is possible to suppress the occurrence of non-uniform luminance distribution by the scanning line, and without increasing the circuit scale and power consumption. , Good video can be displayed.

  Hereinafter, liquid crystal display devices according to embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
First, the liquid crystal display device according to the first embodiment of the present invention will be described. FIG. 1 is a block diagram showing the configuration of the liquid crystal display device according to the first embodiment of the present invention. The liquid crystal display device shown in FIG. 1 includes a frame memory unit 1, a memory control circuit 2, a drive circuit 3, a liquid crystal panel 4, a backlight lighting control circuit 5, and a backlight 6.

  A video signal such as a television signal is converted into a video signal VS composed of image data suitable for the liquid crystal panel 4 by a predetermined process on the outside or inside, and the video signal VS is input to the frame memory unit 1 to be input to the video signal VS. A synchronization signal SS including a vertical synchronization signal, a horizontal synchronization signal, a pixel clock, and the like is input to the memory control circuit 2 and the backlight lighting control circuit 5. Normally, video signals VR, VG, and VB separated into three primary colors (RGB) are used. However, in order to facilitate the description, in the present embodiment, the following description will be given as one video signal VS. Do.

  The frame memory unit 1 includes first and second frame memories having a capacity capable of storing a video signal for one frame, and has a capacity capable of storing a video signal for two frames. The memory control circuit 2 switches the write start address and outputs the write address signal to the frame memory unit 1 every time the vertical synchronization signal of the synchronization signal SS is detected based on the synchronization signal SS, and outputs the first frame every frame. The frame memory unit 1 is controlled to perform double buffering for alternately writing to the memory and the second frame memory.

  Further, the memory control circuit 2 outputs a read address signal to the frame memory unit 1 at a predetermined timing based on the synchronization signal SS. The frame memory unit 1 alternately stores the input video signal VS in the first and second frame memories, and receives the video signal from the first and second frame memories at a predetermined timing described later based on the read address signal. By reading, the video signal VS is converted to a double-speed high-speed video signal (double-written video signal) so that the video signal can be written twice within one frame period and output to the drive circuit 3.

  The liquid crystal panel 4 includes a plurality of gate lines, a plurality of source lines, a switching element, and a plurality of pixel cells, and a plurality of pixels are arranged in a matrix at intersections of the plurality of source lines and the plurality of gate lines. One scanning line is composed of one line of pixels. A pixel signal is supplied from the driving circuit 3 to the plurality of source lines, and a gate pulse serving as a scanning signal is supplied from the driving circuit 3 to the plurality of gate lines to drive the pixels.

  The drive circuit 3 divides one frame period into a first frame period in the first half and a second frame period in the second half, and the display screen of the liquid crystal panel 4 is divided into an upper display area composed of an upper three-quarter area and a remaining lower side 4. The high-speed video signal of the immediately preceding frame period is written in the previous frame period and the current frame is written in the subsequent frame period. By repeating the operation of writing the high-speed video signal of the period and writing the high-speed video signal of the current frame period in each of the previous frame period and the subsequent frame period to the pixels (scanning lines) in the lower display area, The panel 4 is driven.

  The division ratio of the display screen of the liquid crystal panel 4 is not particularly limited to the above example, and various values can be used according to the response characteristics of the liquid crystal used in the liquid crystal panel 4, and the liquid crystal panel having a slow response. In the case of, the upper half of the upper display area is set as the upper display area and the lower half of the lower half is set as the lower display area. The lower eighth may be set as the lower display area.

  The backlight 6 is installed on the back surface of the liquid crystal panel 4 and illuminates the liquid crystal panel 4 from the back surface. Based on the synchronization signal SS, the backlight lighting control circuit 5 turns on the backlight 6 in the previous frame period, and turns off the backlight 6 in the subsequent frame period.

  FIG. 2 is a timing chart for explaining the write timing and read timing of the first and second frame memories of the frame memory unit 1 shown in FIG.

  First, the write timing will be described. As shown in the upper part of FIG. 2, the video signal V1 in the first frame period is written in the first frame memory over one frame period as the write data WA in the first frame memory. Next, as the write data WB for the second frame memory, the video signal V2 for the second frame period is written to the second frame memory over one frame period. Next, the video signal V3 in the third frame period is written as write data WA in the first frame memory in the first frame memory over one frame period. Next, the video signal V4 in the fourth frame period is written as write data WB in the second frame memory in the second frame memory over one frame period. Thereafter, the above operation is repeated.

  In this way, the frame memory unit 1 switches the write start address every time a vertical synchronization signal is detected, and alternately writes video signals to the first and second frame memories for each frame, thereby executing double buffering. Is done.

  Next, the reading timing will be described. Reading of the video signal from the frame memory unit 1 is performed twice during one frame period, and the high-speed video signal is read from the frame memory unit 1 at twice the writing speed. . Here, the read timing of the frame memory unit 1 starts at a timing delayed by half a frame from the write timing of the frame memory unit 1, and a period delayed by a half frame from the frame period at the write timing corresponds to the frame period at the read timing. In this embodiment, the first half of the frame period at the read timing is the previous frame period, and the second half is the subsequent frame period.

  In the above read operation, the memory control circuit 2 counts the horizontal synchronization signal to determine whether the current write scan line is the scan line of the upper display area or the scan line of the lower display area, According to the result, the read address of the frame memory unit 1 is generated as follows.

  First, when the current write scan line is the scan line of the upper display area, the first frame memory and the second frame memory in both the previous frame period and the subsequent frame period are faster from the frame memory in which writing is not performed. Read the image signal.

  Specifically, as shown in the middle part of FIG. 2, as the read data RAU of the first frame memory in the upper display area, the first frame period from the first frame period in the subsequent frame period of the first frame period at the read timing. The high-speed image signal HV1 obtained by reading out the video signal V1 at the double speed is output to the drive circuit 3. Next, in the frame period before the second frame period at the read timing, the high-speed image signal HV1 obtained by re-reading the video signal V1 of the first frame period at the double speed from the first frame memory is output to the drive circuit 3 again.

  Next, as the read data RBU of the second frame memory in the upper display area, the video signal V2 in the second frame period is read at a double speed from the second frame memory in the subsequent frame period of the second frame period at the read timing. The image signal HV2 is output to the drive circuit 3. Next, in the frame period before the third frame period at the read timing, the high-speed image signal HV2 obtained by re-reading the video signal V2 in the second frame period from the second frame memory at the double speed is output to the drive circuit 3 again. Thereafter, high-speed image signals are sequentially output from the first and second frame memories to the drive circuit 3 in the same manner as described above.

  On the other hand, when the current writing scanning line is a scanning line of the lower display area, in the previous frame period, the high-speed image signal is read from the frame memory currently being written out of the first frame memory and the second frame memory, and the subsequent frame period Then, the high-speed image signal is read from the frame memory that has not been written.

  Specifically, as shown in the lower part of FIG. 2, as the read data RAL of the first frame memory in the lower display area, the first frame period from the first frame period in the previous frame period of the first frame period at the read timing. The high-speed image signal HV1 of the first frame obtained by reading out the video signal V1 at double speed is output to the drive circuit 3. Next, in the frame period after the first frame period at the read timing, the high-speed image signal HV1 of the first frame obtained by re-reading the video signal V1 of the first frame period from the first frame memory at the double speed is again supplied to the drive circuit 3. Is output.

  Next, as the read data RBL of the second frame memory in the lower display area, the video signal V2 in the second frame period is read from the second frame memory at a double speed in the frame period before the second frame period at the read timing. The image signal HV2 is output to the drive circuit 3. Next, in the frame period after the second frame period at the read timing, the high-speed image signal HV2 obtained by re-reading the video signal V2 of the second frame period from the second frame memory at the double speed is output to the drive circuit 3 again. Thereafter, high-speed image signals are sequentially output from the first and second frame memories to the drive circuit 3 in the same manner as described above.

  FIG. 3 is a diagram showing video signal writing timing and backlight blinking timing of the liquid crystal display device shown in FIG. In the present embodiment, the first half of one frame period (the frame period at the read timing shown in FIG. 2) is the previous frame period, the latter half is the subsequent frame period, and the backlight 6 is turned on in the previous frame period (hatching in the figure). Part), the backlight 6 is turned off during the subsequent frame period, and the backlight 6 is turned on intermittently.

  Also, the upper three-quarters of the liquid crystal panel 4 are set as the upper display area and the lower quarter is set as the lower display area, and the uppermost part of the upper display area is formed as a scanning line consisting of one row of pixels in the horizontal direction. The first scan line is U1, the bottom last scan line is UE, the top first scan line in the lower display area is L1, and the bottom last scan line is LE.

  In the above setting, in the example shown in FIG. 3, a high-speed video signal of black level (for example, 0 level of 256 gradations) is written in the 0th frame period (not shown), and the high-speed video of black level is written in the first frame period. When a signal is written, a white level high-speed video signal (for example, 256 gradation 255 levels) is written in the second frame period, and a white level high-speed video signal is written in the third frame period, The high-speed video signal of the white level is sequentially written from the uppermost first scanning line U1 to the final scanning line UE in accordance with the timing of the broken line DU. Video signals are sequentially written from the uppermost first scanning line L1 to the last scanning line LE, and the response waveform of each scanning line is shown in FIG. Uninaru.

  That is, in the upper display area, the black level high-speed video signal in the 0th frame period is displayed in the period in which the backlight 6 is lit in the first frame periods F1-F and F1-B, that is, in the previous frame period F1-F. In the period in which black display is performed by writing to all the scan lines U1 to UE and the backlight 6 is turned off, that is, the post-frame period F1-B, the high-speed video signal of the black level in the first frame period is displayed on all the scan lines U1. ~ Written to UE.

  Next, in the second frame period F2-F, F2-B, in the period in which the backlight 6 is lit, that is, in the previous frame period F2-F, the high-speed video signal of the black level in the first frame period is transferred to all the scan lines U1. In the period when the black is displayed again by writing to the UE and the backlight 6 is turned off, that is, in the subsequent frame period F2-B, the high-speed video signal of the white level in the first frame period is fully scanned according to the timing of the broken line DU. Written on lines U1-UE.

  Next, in the third frame period F3-F, F3-B, in the period in which the backlight 6 is lit, that is, in the previous frame period F3-F, the white-level high-speed video signal in the second frame period is transferred to the entire scan line U1. In the period when the white display is performed by rewriting to the UE and the backlight 6 is turned off, that is, in the subsequent frame period F3-B, the high-speed video signal of the white level in the third frame period is applied to all the scan lines U1 to UE. Written.

  Therefore, in the upper display area, the transient response state of the liquid crystal is completed in the subsequent frame period F2-B, which is the period in which the backlight 6 is turned off, so the previous frame in which the backlight 6 is turned on. In the period F2-F, black display is performed in a state where the black level which is the target gradation is reached, and white display is performed in the state where the white level which is the target gradation is reached in the previous frame period F3-F. . As a result, in the upper display area, the response arrival gradation of the liquid crystal in each scanning line can be made uniform, the occurrence of non-uniform luminance distribution due to the scanning line is suppressed, and the circuit scale and power consumption are increased. And a good moving image can be displayed.

  The ratio of the upper display area to the entire display screen mainly depends on the response speed of the liquid crystal panel 4, but is 80% of the target gradation at the end of the previous frame period, preferably 90%, more preferably 95%. The ratio of the upper display area can be set so as to more preferably reach 98%.

  On the other hand, in the lower display area, in the first frame periods F1-F and F1-B, all the black level video signals in the first frame period are in the period in which the backlight 6 is lit, that is, the previous frame period F1-F. During the period when the black display is performed by writing to the scanning lines L1 to LE and the backlight 6 is turned off, that is, the post-frame period F1-B, the black level video signal of the first frame period is all the scanning lines L1 to LE. Will be written again.

  Next, in the second frame period F2-F, F2-B, in which the backlight 6 is lit, that is, in the previous frame period F2-F, the white level high-speed video signal in the second frame period is the timing of the broken line DL. Are written in all the scanning lines L1 to LE, but in most of the previous frame period F2-F, it is at the black level, black display is performed, and the backlight 6 is turned off, that is, the subsequent frame period F2-B. , The high-speed video signal of the white level in the first frame period is written again to all the scanning lines L1 to LE.

  Next, in the third frame period F3-F, F3-B, the period when the backlight 6 is lit, that is, the previous frame period F3-F, the high-speed video signal of the white level in the third frame period is transferred to the entire scan line L1. In the period in which white display is performed by writing in to LE and the backlight 6 is turned off, that is, in the subsequent frame period F3-B, the high-speed video signal of the white level in the third frame period is again applied to all the scan lines U1 to UE. Written.

  Therefore, in the lower display area, the liquid crystal transient response period is limited to only a part of the latter half of the previous frame period F2-F, which is the period during which the backlight 6 is lit, and most of the remaining part of the previous frame period. Black display is performed in a state where the black level which is the target gradation is reached. Further, the remaining transient response is executed in the subsequent frame period F2-B, which is a period during which the backlight is turned off, and then, in the previous frame period F3-F, during which the backlight 6 is lit, white is the target gradation. White display is performed when the level is reached. Thus, in the upper region of the lower display region, a part of the transient response state is located in the lighting period of the backlight 6, but the lower display region is sufficiently smaller than the upper display region, and most of the transient response states Since the response period is located in the backlight 6 extinguishing period, the response arrival gradation of the liquid crystal in each scanning line can be made substantially uniform also in the lower display area, and a non-uniform luminance distribution is generated by the scanning line. This can be suppressed and a good moving image can be displayed.

  FIG. 4 is a diagram schematically showing motion blur when the liquid crystal panel and the backlight are driven at the driving timing shown in FIG. In the example shown in FIG. 4, as in FIG. 10, as shown in (a-1), a black ellipse is written on the right side of the display screen in the first frame period, and then shown in (a-2). Thus, a black ellipse is written in the center of the display screen in the second frame period, and finally, as shown in (a-3), a black ellipse is written in the left side of the display screen in the third frame period. This is a schematic illustration of motion blur.

  In this case, in the present embodiment, in the previous frame period of the first frame period, as shown in (b-1F), the lower part of the black ellipse is written on the right side of the display screen only in the lower display area. In the subsequent frame period, as shown in (b-1B), a black ellipse is written on the right side of the upper display area and the lower display area, that is, the entire display screen.

  Next, in the previous frame period of the second frame period, as shown in (b-2F), most of the black ellipse excluding a part of the lower part is written on the left side of the display screen in the upper display area, and the lower part In the display area, a part of the lower part of the black ellipse is written in the center of the display screen. In the subsequent frame period, as shown in (b-2B), the upper display area and the lower display area, that is, the entire display screen are centered on the center. A black ellipse is written.

  Next, in the previous frame period of the third frame period, as shown in (b-3F), most of the black ellipse excluding a part of the lower part is written at the center of the display screen in the upper display area, and the lower part. In the display area, a part of the lower part of the black ellipse is written on the left side of the display screen, and in the subsequent frame period, as shown in (b-3B), on the left side of the upper display area and the lower display area, that is, the entire display screen. A black ellipse is written.

  As a result, in the first frame period, as shown in (c-1), only a part of the lower part of the ellipse (black that becomes whiter toward the lower side) needs to be displayed lightly in the lower display area. During the period, as shown in (c-2), only a part of the lower part of the ellipse (black that becomes whiter toward the lower side) is displayed as a thin afterimage of the first frame in the lower display area. A black ellipse is displayed on the right side of the lower display area, that is, the entire display screen. In the third frame period, as shown in (c-3), a part of the lower part of the ellipse is displayed in the lower display area as an afterimage of the second frame. It is only necessary to display lightly (black that becomes whiter toward the lower side), and a black ellipse is displayed at the center of the upper display area and the lower display area, that is, the entire display screen. As a result, in the present embodiment, the user can visually recognize a clear moving image with almost no perception of motion blur.

(Second Embodiment)
Next, a liquid crystal display device according to a second embodiment of the present invention will be described. FIG. 5 is a block diagram showing a configuration of a liquid crystal display device according to the second embodiment of the present invention. The difference between the liquid crystal display device shown in FIG. 5 and the liquid crystal display device shown in FIG. 1 is that an overdrive circuit 7 is added and the memory control circuit 2 is changed to a memory control circuit 2 a that also controls the overdrive circuit 7. Since the other points are the same as those of the liquid crystal display device shown in FIG. 1, the same portions are denoted by the same reference numerals, and the description thereof is omitted. Hereinafter, different portions will be described in detail.

  The overdrive circuit 7 includes a buffer memory 71 and a gradation conversion unit 72. The buffer memory 71 has a capacity capable of storing a high-speed video signal in an overdrive area among high-speed video signals for one frame. Here, the overdrive area is an upper lower area including the lowermost part of the upper display area. In the present embodiment, for example, the lower quarter of the upper display area is set as the upper lower area. ing. Accordingly, the buffer memory 71 stores a high-speed video signal of 3/16 of the display screen, that is, 3/16 of one frame, and the capacity thereof is reduced as much as possible. The upper lower region is not particularly limited to the above example, and the entire upper display region is set as the upper lower region or the lower half of the upper display region according to the response characteristics of the liquid crystal panel 4 or the like. Various areas such as 1 or lower 1/8 may be set.

  The frame memory unit 1 outputs the high-speed video signal created in the same manner as in the first embodiment to the buffer memory 71 and the gradation conversion unit 72. The memory control circuit 2a determines the timing at which the high-speed video signal in the upper lower region is input to the buffer memory 71 based on the synchronization signal SS, and stores only the high-speed video signal in the upper lower region. 71 is controlled. Further, the memory control circuit 2a determines the timing at which the high-speed video signal in the upper lower region is input to the drive circuit 3 based on the synchronization signal SS, and the period during which the high-speed video signal in the upper lower region is output. The gradation converter 72 is controlled so that an overdrive video signal larger than the high-speed video signal of the current frame period is generated in the subsequent frame period, and the high-speed video signal from the frame memory unit 1 is output as it is during this period. To do.

  The buffer memory 71 delays the high-speed video signal in the upper lower region by one frame period and outputs it to the gradation conversion unit 72. In the subsequent frame period of the period in which the high-speed video signal in the upper lower region is output, the gradation conversion unit 72 outputs the high-speed video signal in the current frame period output from the frame memory unit 1 and the buffer memory 71. Is compared with the high-speed video signal before one frame period, and if the current high-speed video signal is larger than the high-speed video signal before one frame period, an overdrive video signal larger than the current high-speed video signal is created, Conversely, if the current high-speed video signal is smaller than the high-speed video signal of one frame period before, an overdrive video signal smaller than the current high-speed video signal is created and output to the drive circuit 3. The high-speed video signal from the memory unit 1 is output to the drive circuit 3 as it is.

  Specifically, the gradation conversion unit 72 includes a lookup table, and the lookup table is determined in advance corresponding to the combination of the high-speed video signal of the current frame period and the high-speed video signal of one frame period before. Stored correction values are stored. In the upper lower region, the gradation conversion unit 72 refers to the lookup table from the high-speed video signal of the current frame period and the high-speed video signal of the previous frame period from the frame memory unit 1, and sets the corresponding correction value. An overdrive video signal is created by adding to the high-speed video signal in the current frame period. The configuration of the overdrive circuit 7 is not particularly limited to the above example, and various changes can be made.

  FIG. 6 is a diagram showing the write timing of the overdrive video signal and the flashing timing of the backlight of the liquid crystal display device shown in FIG. Here, a scanning line in the upper lower region of the liquid crystal panel 4 is defined as Un, a response waveform when no overdrive is performed is UnN, and a response waveform when overdrive is performed is UnO.

  As shown in FIG. 6, when the response characteristic of the liquid crystal panel 4 is slow, the response waveform UnN when the overdrive is not performed is within the frame period F2-B after the second frame period, which is the extinguishing period of the liquid crystal panel 4. The transient response state of the liquid crystal does not end, and the transient response of the liquid crystal continues in a part of the first half of the previous frame period F3-F of the third frame period which is the lighting period. And perceive motion blur.

  On the other hand, the response waveform UnO in the case of performing overdrive according to the present embodiment turns on when the transient response state of the liquid crystal ends in the second frame period F2-B after the second frame period, which is the extinguishing period of the liquid crystal panel 4. In the previous frame period F3-F of the third frame period, which is the period, white display is performed in a state where the white level that is the target gradation is reached.

  Thus, even if the response characteristic of the liquid crystal panel 4 is slow by overdriving the scanning lines in the upper lower region and writing a high-speed video signal with a gradation larger than the target gradation, the response of the liquid crystal The speed can be increased, and the transient response of the liquid crystal can be completed within the backlight extinguishing period. As a result, even when the response characteristics of the liquid crystal panel 4 are slow, the response arrival gradation of the liquid crystal in each scanning line can be made uniform in the upper display region, and a non-uniform luminance distribution is generated by the scanning lines. It is possible to suppress and display a good moving image.

  Various correction values can be used for overdrive. The same correction value is used for all scan lines in the upper lower region, or the upper scan line in the upper lower region is used. The overdrive amount may be increased as the lower scanning line is increased by increasing the correction value as the scanning line moves to the lower scanning line.

  Further, the upper lower area is not particularly limited to the predetermined area set in advance as described above, and the upper lower area is increased depending on the difference between the current high-speed video signal gradation and the high-speed video signal gradation one frame period before. Various changes such as changing the subordinate region are possible. For example, overdrive is performed only on a scan line whose gradation difference is equal to or greater than a predetermined threshold, or writing timing (the broken line DU in FIG. The threshold value may be reduced as the interval between the timing) and the lighting start timing of the backlight 6 becomes narrower, and overdrive may be performed only for scan lines where the gradation difference is equal to or greater than this threshold value.

  Here, the overdrive circuit 7 described above can function as an underdrive circuit that creates an underdrive video signal smaller than the high-speed video signal in the current frame period by changing the correction value of the lookup table. .

  In this case, for example, the upper 3/4 of the lower display area is set as the lower upper area, and the buffer memory 71 stores the high-speed video signal of 3/16 of the display screen, that is, 3/16 of one frame, Reduce that capacity as much as possible. The lower upper region is not particularly limited to the above example, and the entire lower display region is set as the lower upper region, or the upper half of the lower display region, depending on the response characteristics of the liquid crystal panel 4. Alternatively, various regions such as upper 7/8 may be set.

  At this time, the memory control circuit 2a determines the timing at which the high-speed video signal in the lower upper area is input to the buffer memory 71 based on the synchronization signal SS, and stores only the high-speed video signal in the lower upper area. The memory 71 is controlled. Further, the memory control circuit 2a determines the timing at which the high-speed video signal in the lower upper region is input to the drive circuit 3 based on the synchronization signal SS, and the previous period of the period during which the high-speed video signal in the lower upper region is output. The gradation conversion unit 72 is controlled so that an underdrive video signal smaller than the high-speed video signal of the current frame period is generated in the frame period, and the high-speed video signal from the frame memory unit 1 is output as it is during this period.

  The buffer memory 71 delays the high-speed video signal in the lower upper area by one frame period and outputs it to the gradation conversion unit 72. In the previous frame period of the period in which the high-speed video signal in the lower upper region is output, the gradation conversion unit 72 is output from the buffer memory 71 and the high-speed video signal in the current frame period output from the frame memory unit 1. If the current high-speed video signal is larger than the high-speed video signal one frame period before, an underdrive video signal smaller than the current high-speed video signal is created, and vice versa. If the current high-speed video signal is smaller than the high-speed video signal before one frame period, an underdrive video signal larger than the current high-speed video signal is created and output to the drive circuit 3. The high-speed video signal from the unit 1 is output to the drive circuit 3 as it is.

  Specifically, the gradation conversion unit 72 refers to the lookup table from the high-speed video signal of the current frame period from the frame memory unit 1 and the high-speed video signal of the previous frame period from the frame memory unit 1 in the lower upper region. The underdrive video signal is created by subtracting the correction value to be used from the high-speed video signal in the current frame period. The configuration of the underdrive circuit is not particularly limited to the above example, and various changes can be made.

  FIG. 7 is a diagram showing the write timing of the underdrive video signal and the blinking timing of the backlight of the liquid crystal display device shown in FIG. Here, a scanning line in the lower upper region of the liquid crystal panel 4 is Lm, a response waveform when the underdrive is not performed is LmN, and a response waveform when the underdrive is performed is LmU.

  As shown in FIG. 7, when the response characteristic of the liquid crystal panel 4 is fast, the response waveform LmN when the underdrive is not performed is the second half of the previous frame period F2-F of the second frame period that is the lighting period of the liquid crystal panel 4. The user starts to rise at the part, and the user visually recognizes the rising of the part and perceives motion blur.

  On the other hand, the response waveform LmU when underdrive according to the present embodiment starts to rise in the latter half of the previous frame period F2-F of the second frame period, which is the lighting period of the liquid crystal panel 4, but its amplitude is small. Therefore, the black display is performed in a state where it is in the vicinity of the black level which is the target gradation as a whole. Thereafter, in the second frame period F2-B after the second frame period, which is the turn-off period of the liquid crystal panel 4, the high-speed video signal of the current frame period is written as it is and reaches a substantially white level, and then the turn-on period of the liquid crystal panel 4 In the previous frame period F3-F of the third frame period, white display is performed.

  In this way, by under-driving the scanning line in the lower upper region and writing a high-speed video signal with a gradation smaller than the target gradation, even when the response characteristic of the liquid crystal panel 4 is fast, the liquid crystal rises. The transient response of the liquid crystal during the lighting period of the backlight 6 can be reduced. As a result, even when the response characteristics of the liquid crystal panel 4 are fast, the response arrival gradation of the liquid crystal in each scanning line can be made substantially uniform in the lower display area, and an uneven luminance distribution is generated by the scanning lines. Can be suppressed and a good moving image can be displayed.

  The above overdrive and underdrive may be used in combination, or only one of them may be executed.

  Various correction values can be used for underdrive. The same correction value can be used for all scanning lines in the lower upper area, or the lower scanning line can be used in the upper upper area. The amount of underdrive may be increased as the upper scanning line is increased by increasing the correction value toward the scanning line.

  Further, the lower upper area is not particularly limited to the predetermined area set in advance as described above, and the lower upper area depends on the difference between the gradation of the current high-speed video signal and the gradation of the high-speed video signal one frame period before. Various changes such as changing the area are possible. For example, underdrive is performed only on a scan line whose gradation difference is equal to or greater than a predetermined threshold, or writing timing (timing indicated by a broken line DL in FIG. 3). Alternatively, the threshold may be reduced as the interval between the turn-off start timing of the backlight 6 and the backlight 6 becomes narrower, and underdrive may be performed only for scan lines in which the gradation difference is equal to or greater than this threshold.

  Further, in each of the above embodiments, the lighting period and the non-lighting period of the backlight 6 are associated with the previous frame period and the subsequent frame period. However, the lighting period and the non-lighting period according to the response characteristics of the liquid crystal panel 4 and the like. May be moved back and forth by a predetermined time with respect to the previous frame period and the subsequent frame period.

  FIG. 8 is a diagram illustrating an example of video signal writing timing and backlight blinking timing when the backlight lighting period and extinguishing period are changed in the liquid crystal display device illustrated in FIG. 1. In the example shown in FIG. 8, the lighting period and the extinguishing period are advanced by a predetermined movement time T, for example, 1/16 of one frame period, and the backlight lighting control circuit 5 performs the previous operation based on the synchronization signal SS. The backlight 6 is turned on at a timing advanced by 1/16 of one frame period from the frame period (hatched portion in the figure), and the backlight 6 is advanced by 1/16 of one frame period from the subsequent frame period. Is turned off and the backlight is turned on intermittently. Note that, except for the blinking timing of the backlight 6, it is basically the same as FIG.

  In the above setting, in the example shown in FIG. 8, since the backlight 6 is turned off slightly before the end of the previous frame period F2-F of the second frame period, the response waveform of the liquid crystal is displayed in the upper part of the lower display area. Although it starts to rise, its amplitude can be reduced, so that the black display is performed in the vicinity of the black level that is the target gradation as a whole. As described above, by advancing the lighting period from the previous frame period, the transient response of the liquid crystal within the lighting period of the backlight 6 can be reduced even when the response characteristic of the liquid crystal panel 4 is fast.

  As a result, even when the response characteristics of the liquid crystal panel 4 are fast, the response arrival gradation of the liquid crystal in each scanning line can be made substantially uniform in the lower display area, and an uneven luminance distribution is generated by the scanning lines. Can be suppressed and a good moving image can be displayed. Since the backlight 6 is turned on slightly before the previous frame period F3-F of the third frame period, a part of the transient response state of the liquid crystal remains in the lower part of the upper display area, but the target gradation is white. If white display is performed in a state where the level is almost reached, the user hardly perceives motion blur.

  Further, the moving amount and moving direction of the lighting period and the extinguishing period are not particularly limited to the above example, and various moving amounts can be set according to the response characteristics of the liquid crystal, and the lighting period is delayed. Even when the response characteristic of the liquid crystal panel 4 is slow, it is possible to make the response arrival gradation of the liquid crystal in each scanning line substantially uniform in the upper display area and to generate a non-uniform luminance distribution by the scanning line. It is possible to suppress and display a good moving image.

  In each of the above embodiments, one frame period is equally divided to set the previous frame period and the subsequent frame period. However, the present invention is not particularly limited to this example, and various modifications can be made. The period may be longer than the previous frame period to increase the ratio of the upper display area.

  Moreover, although the lighting period and the extinguishing period are set for the entire display screen, the present invention is not particularly limited to this example, and various changes are possible. For example, the upper display area is divided into a plurality of upper display areas and displayed. Different lighting periods and extinguishing periods may be set for each region.

  The liquid crystal display device according to the present invention suppresses the occurrence of non-uniform luminance distribution by the scan lines by increasing the liquid crystal response arrival gradation in each scan line, thereby increasing the circuit scale and power consumption. Therefore, it is useful as a liquid crystal display device or the like that writes a high-speed video signal to the liquid crystal panel while intermittently lighting a light source provided on the back surface of the liquid crystal panel.

It is a block diagram which shows the structure of the liquid crystal display device by the 1st Embodiment of this invention. 3 is a timing chart for explaining write timings and read timings of first and second frame memories of the frame memory unit shown in FIG. 1. FIG. 2 is a diagram showing video signal writing timing and backlight blinking timing of the liquid crystal display device shown in FIG. 1. It is a figure which shows typically a motion blur at the time of driving a liquid crystal panel and a backlight with the drive timing shown in FIG. It is a block diagram which shows the structure of the liquid crystal display device by the 2nd Embodiment of this invention. It is a figure which shows the write-in timing of the overdrive video signal of the liquid crystal display device shown in FIG. 5, and the blink timing of a backlight. It is a figure which shows the write-in timing of the underdrive video signal of the liquid crystal display device shown in FIG. 5, and the blink timing of a backlight. FIG. 2 is a diagram illustrating an example of video signal writing timing and backlight blinking timing when a backlight lighting period and a light extinguishing period are changed in the liquid crystal display device illustrated in FIG. 1. It is a figure which shows the write-in timing of the video signal of the conventional liquid crystal display device, and the blinking timing of a backlight. It is a figure which shows typically a motion blur at the time of driving a liquid crystal panel and a backlight with the drive timing shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Frame memory part 2, 2a Memory control circuit 3 Drive circuit 4 Liquid crystal panel 5 Backlight lighting control circuit 6 Backlight 7 Overdrive circuit 71 Buffer memory 72 Gradation conversion part

Claims (6)

A liquid crystal panel including a plurality of pixels;
Conversion means for converting the video signal into a high-speed video signal that has been speeded up so that the input video signal can be written twice within one frame period;
One frame period is divided into a previous frame period and a subsequent frame period, and a high-speed video signal of the immediately preceding frame period is written to pixels in a predetermined display area of the display screen of the liquid crystal panel; Panel driving means for driving the liquid crystal panel by writing a high-speed video signal of the current frame period in the subsequent frame period;
A light source for illuminating the liquid crystal panel;
A liquid crystal display device comprising: a light source control unit that turns on the light source in the previous frame period and turns off the light source in the subsequent frame period.   The panel driving unit divides the display screen of the liquid crystal panel into an upper display area and a lower display area, and writes a high-speed video signal in the previous frame period to the pixels in the upper display area. In addition, the high-speed video signal of the current frame period is written in the subsequent frame period, and the high-speed video signal of the current frame period is written to the pixels of the lower display area in each of the previous frame period and the subsequent frame period. The liquid crystal display device according to claim 1, wherein the liquid crystal panel is driven.   The panel driving means writes an overdrive video signal larger than a high-speed video signal in a current frame period in the subsequent frame period to pixels in an upper lower area including the lowermost part of the upper display area. The liquid crystal display device according to claim 2.   The panel driving means writes an underdrive video signal smaller than the high-speed video signal of the current frame period in the previous frame period to the pixels in the lower upper area including the uppermost part of the lower display area. The liquid crystal display device according to claim 2.   The light source control means turns on the light source in a pre-movement frame period in which the previous frame period has been moved by a predetermined movement time, and in the post-movement frame period in which the subsequent frame period has been moved by a predetermined movement time. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is turned off. A method for driving a liquid crystal display device including a liquid crystal panel including a plurality of pixels,
Converting the video signal into a high-speed video signal that has been accelerated so that the input video signal can be written twice within one frame period;
One frame period is divided into a previous frame period and a subsequent frame period, and the high-speed video signal of the immediately preceding frame period is written to the pixels in the upper display area of the display screen of the liquid crystal panel, and The high-speed video signal of the current frame period is written in the subsequent frame period to drive the liquid crystal panel, the light source provided on the back surface of the liquid crystal panel is turned on in the previous frame period, and the light source in the subsequent frame period A method for driving a liquid crystal display device, comprising: turning off the light.