JP2009175346A - Liquid crystal display device and method for driving the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device for suppressing the reduction of luminance. <P>SOLUTION: An illumination means has: a first illumination part for emitting light in a first direction; and a second illumination part for emitting light in a second direction. A control means has: a time sharing writing part for setting a first subframe period and a second subframe period in one frame period and setting a first period, a second period and a third period in each of the first and second subframe periods to write a video signal corresponding to the first direction in the first and second periods of the first subframe period write a black image signal in the third period, write a video signal corresponding to the second direction in the first and second periods in the second subframe period, and write a signal corresponding to the black image in the third period; and an illumination means control part for turning on the first illumination part in the first subframe period and turning on the second illumination part in the second subframe period. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device and a driving method of the liquid crystal display device, and more particularly to an active matrix liquid crystal display device and a driving method thereof.

  Liquid crystal display devices are widely used as display devices for personal computers, car navigation systems, television receivers, and the like by taking advantage of features such as light weight, thinness, and low power consumption.

  Conventionally, there has been proposed a liquid crystal display device capable of displaying not only one two-dimensional information but also a three-dimensional display or a plurality of screens simultaneously on the same screen. For example, a two-screen display device in which the images seen in the driver's seat and the passenger's seat are different for in-vehicle use, and a three-dimensional display device that performs stereoscopic display by displaying a right-eye image and a left-eye image, respectively, have been proposed. ing.

  As a technique that enables such display, a parallax barrier method and a time-division driving method have been proposed (see Patent Document 1 and Patent Document 2). When the parallax barrier method is adopted, it is difficult to prevent a decrease in the aperture ratio. Therefore, a time-division drive method has been proposed as a method for preventing a decrease in the aperture ratio.

  When the time-division driving method is adopted, for example, a first subframe period and a second subframe period following the first subframe period are set within one frame period for displaying one screen, and the first subframe is set. Then, the first image is presented on the display unit during the second subframe period.

Then, using a backlight that can switch the directivity of the emitted light between two directions, the first direction and the second direction, in this backlight, the first direction (for example, the right direction) during the first subframe period, In the second subframe period, light is emitted with directivity in the second direction (for example, the left direction). By doing so, it is possible to display different images corresponding to the first direction and the second direction, respectively.
Japanese Patent Laid-Open No. 10-161061 JP 2004-258596 A

  When the time-division driving method as described above is adopted, it is necessary to perform scanning at least twice in one frame period (about 1/60 sec), and in some cases, four times. Need to be done. However, there is an upper limit on the signal transfer speed of the source driver, and it is necessary to secure time for charging the pixels via the pixel switching elements of the liquid crystal display panel, so that it is difficult to set the scanning speed to a desired speed. there were. In addition, when the scanning speed cannot be sufficiently increased, it is difficult to obtain a desired luminance because a sufficient time for the liquid crystal to be in a display state cannot be secured.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a liquid crystal display device in which a decrease in luminance associated with a decrease in light utilization efficiency is suppressed.

  A liquid crystal display device according to a first aspect of the present invention includes a pair of substrates disposed to face each other, a liquid crystal layer sandwiched between the pair of substrates, and a plurality of display pixels arranged in a matrix. And a control means for controlling the liquid crystal display panel and the illuminating means. The first sub-frame period of one frame period is a first sub-frame period. A liquid crystal display device that displays an image and displays a second image in a second sub-frame period following the first sub-frame period, wherein the illuminating means includes a first illuminating unit that emits light in a first direction; A second illuminator that emits light in a second direction different from the first direction, and the control unit sets the first subframe period and the second subframe period within one frame period. The first In each of the second subframe period, a first period, a second period following the first period, and a third period following the second period are set, and the first period within the first subframe period In the second period, a video signal corresponding to the first image is written to the display pixel, and in the third period, a signal corresponding to a black image is written to the display pixel, and the video signal in the second subframe period is written to the display pixel. A time division writing unit that writes a video signal corresponding to the second image to the display pixel in the first period and the second period and writes a signal corresponding to a black image to the display pixel in the third period; And an illuminating means control section that turns on the first illumination section during the first subframe period and turns on the second illumination section during the second subframe period.

  A liquid crystal display device according to a second aspect of the present invention includes a pair of substrates disposed to face each other, a liquid crystal layer sandwiched between the pair of substrates, and a plurality of display pixels arranged in a matrix. And a control means for controlling the liquid crystal display panel and the illuminating means. The first sub-frame period of one frame period is a first sub-frame period. A liquid crystal display device that displays an image and displays a second image in a second sub-frame period following the first sub-frame period, wherein the illuminating means includes a first illuminating unit that emits light in a first direction; A second illuminator that emits light in a second direction different from the first direction, and the control unit sets the first subframe period and the second subframe period within one frame period. The first A first period during which a video signal corresponding to the first image or the second image is written to the display pixel within the subframe period and the second subframe period, and after the first period, the display A time-division writing unit that sets a second period in which a signal corresponding to a black image is written to a pixel; and the first illumination unit is lit during the first subframe period, and the second period during the second subframe period. An illuminating means control unit that turns on the illuminating unit, and the second period is shorter than the first period.

  The driving method of the liquid crystal display device according to the third aspect of the present invention sets a first subframe period and a second subframe period within one frame period, and each of the first and second subframe periods includes: A step of setting a first period, a second period following the first period, and a third period following the second period; and the first period and the second period within the first subframe period A video signal corresponding to an image is written to a display pixel, a signal corresponding to a black image is written to the display pixel in the third period, and the first period and the second period in the second subframe period are changed in the second period. A time division writing step of writing a video signal corresponding to two images to a display pixel and writing a signal corresponding to a black image to the display pixel in the third period; Turns on the first lighting part, having an illumination means controlling step of turning on said second illuminating portion in the second sub frame period.

  ADVANTAGE OF THE INVENTION According to this invention, the liquid crystal display device with which the fall of the brightness accompanying the fall of light utilization efficiency was suppressed can be provided.

  Hereinafter, a liquid crystal display device according to a first embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, in the liquid crystal display device according to the present embodiment, a transmissive liquid crystal display panel DP, a backlight BL as illumination means arranged on the back side of the liquid crystal display panel DP, and the liquid crystal display panel DP. And a display control circuit CNT for controlling the backlight BL.

  The liquid crystal display panel DP includes an array substrate 1 and a counter substrate 2 which are a pair of electrode substrates, and a liquid crystal layer 3 sandwiched between the array substrate 1 and the counter substrate 2. The liquid crystal layer 3 uses, as a liquid crystal material, a liquid crystal that is previously transitioned from a splay alignment to a bend alignment for a normally white display operation and blocked by a voltage to which a reverse transition from the bend alignment to the splay alignment is applied. Including. In the liquid crystal display device according to the present embodiment, a pixel voltage corresponding to a black image is applied to the liquid crystal layer as a voltage for preventing reverse transition of the liquid crystal.

  The array substrate 1 is formed by laminating a pixel electrode PE and an alignment film (not shown) on a transparent insulating substrate (not shown). The counter substrate 2 is configured by sequentially laminating a common electrode CE and an alignment film (not shown) on a transparent insulating substrate (not shown). The array substrate 1 and the counter substrate 2 are arranged so that the pixel electrode PE and the common electrode CE are opposed to each other. The alignment film of the array substrate 1 and the alignment film of the counter substrate 2 are rubbed so that the rubbing directions are substantially parallel to each other.

  In the array substrate 1, a plurality of pixel electrodes PE are arranged in a substantially matrix shape on the transparent insulating substrate. In addition, a plurality of gate lines Y (Y1 to Ym) are arranged along the rows of the plurality of pixel electrodes PE, and a plurality of source lines X (X1 to Xn) are arranged along the columns of the plurality of pixel electrodes PE. .

  A plurality of pixel switching elements W are arranged in the vicinity of the intersection position of the gate line Y and the source line X. Each pixel switching element W includes, for example, a thin film transistor having a gate electrode connected to the gate line Y and a source-drain path connected between the source line X and the pixel electrode PE, and is driven through the corresponding gate line Y. Is conducted between the corresponding source line X and the corresponding pixel electrode PE.

  Each pixel electrode PE and common electrode CE is made of a transparent electrode material such as ITO, for example, and is covered with an alignment film, and is controlled by a liquid crystal molecular arrangement corresponding to the electric field from the pixel electrode PE and common electrode CE. A display pixel PX is configured together with a pixel region that is a part of the display pixel PX.

  Each of the plurality of display pixels PX has a liquid crystal capacitance between the pixel electrode PE and the common electrode CE. The plurality of auxiliary capacitance lines C1 to Cm constitute auxiliary capacitances Cs that are capacitively coupled to the pixel electrodes PE of the display pixels PX in the corresponding rows. The auxiliary capacitance Cs has a sufficiently large capacitance value with respect to the parasitic capacitance of the pixel switching element W.

  The display control circuit CNT controls the transmittance of the liquid crystal display panel DP by the liquid crystal driving voltage applied from the array substrate 1 and the counter substrate 2 to the liquid crystal layer 3. The transition from the splay alignment to the bend alignment can be obtained by applying a relatively large electric field to the liquid crystal by a predetermined initialization process performed by the display control circuit CNT when the power is turned on.

  The display control circuit CNT includes a gate driver YD, a source driver XD, a backlight driving unit LD, a driving voltage generation circuit 4, and a controller circuit 5. The gate driver YD sequentially drives the plurality of gate lines Y1 to Ym so that the plurality of pixel switching elements W are conducted in units of rows. The source driver XD outputs the pixel voltage Vs to the plurality of source lines X1 to Xn in a period in which the pixel switching elements W in each row are turned on by driving the corresponding gate line Y.

  The backlight driver LD is driven by the controller circuit 5 to drive the backlight BL. The driving voltage generation circuit 4 generates a driving voltage for the liquid crystal display panel DP. The driving voltage generation circuit 4 includes a compensation voltage generation circuit 6 that generates a compensation voltage Ve applied to the auxiliary capacitance line C, a gradation reference voltage generation circuit 7 that generates a predetermined number of gradation reference voltages VREF, and a common electrode. A common voltage generation circuit 8 that generates a common voltage Vcom applied to CE is included.

  The controller circuit 5 controls the gate driver YD, the source driver XD, and the backlight driver LD. The controller circuit 5 includes a control circuit 10, a vertical timing control circuit 11, a horizontal timing control circuit 12, an image data conversion circuit 17, and a backlight control circuit 14. The control circuit 10 generates a new synchronization signal SYNC based on the synchronization signal SYNC 'input from the external signal source SS, and generates a signal for controlling the operation of each part of the display control circuit CNT.

  The vertical timing control circuit 11 generates a control signal CTY for the gate driver YD and the like based on the synchronization signal SYNC input from the control circuit 10. The control signal CTY includes, for example, a vertical synchronization signal VSYNC and a clock signal VCLK. The horizontal timing control circuit 12 generates a control signal CTX for the source driver XD based on the synchronization signal SYNC input from the control circuit 10. The control signal CYX includes, for example, a horizontal synchronization signal HSYNC and a clock signal HCLK.

  The control signal CTY is used for causing the gate driver YD to sequentially drive the plurality of gate lines Y as described above, and the control signal CTX is used for assigning the pixel data DO to the plurality of source lines X, respectively. .

  The gate driver YD is configured using, for example, a shift register circuit (not shown) in order to select the gate line Y. The source driver XD refers to a predetermined number of gradation reference voltages VREF supplied from the gradation reference voltage generation circuit 7, converts the pixel data DO into pixel voltages Vs, and is parallel to the plurality of source lines X1 to Xn. To output automatically.

  The pixel voltage Vs is a voltage applied to the pixel electrode PE with reference to the common voltage Vcom of the common electrode CE. For example, the polarity is inverted with respect to the common voltage Vcom so as to perform frame inversion driving and line inversion driving.

  For example, when the gate driver YD drives the gate line Y1 with an on-voltage to make all the pixel switching elements W connected to the gate line Y1 conductive, the pixel voltage Vs on the source lines X1 to Xn is switched to these pixels. The corresponding pixel electrode PE and one end of the auxiliary capacitor Cs are supplied through the element W, respectively.

  The gate driver YD outputs the compensation voltage Ve from the compensation voltage generation circuit 6 to the auxiliary capacitance line C1 corresponding to the gate line Y1. The compensation voltage Ve reduces the charge drawn from the pixel electrode PE by these parasitic capacitances when the pixel switching element W becomes non-conductive, thereby substantially canceling the fluctuation of the pixel voltage Vs, that is, the penetration voltage.

  As shown in FIG. 2, the source driver XD includes a shift register 21, a sampling / load latch 22, a digital / analog (D / A) conversion circuit 23, and an output buffer circuit 24.

  The control signal CTX includes a horizontal synchronization signal HSYNC, a horizontal start signal STH for controlling the start timing of fetching pixel data for one row, and a horizontal clock signal HCLK for shifting the horizontal start signal STH in the shift register 21. .

  The shift register 21 shifts the horizontal start signal STH in synchronization with the horizontal clock signal CKH, and controls the timing at which the pixel data DO is sequentially serial-to-parallel converted. The sampling / load latch 22 sequentially latches the pixel data DO for the display pixels PX for one line under the control of the shift register 21 and outputs them in parallel. The D / A conversion circuit 23 converts the pixel data DO into an analog pixel voltage Vs. The output buffer circuit 24 outputs the analog pixel voltage Vs obtained from the D / A conversion circuit 23 to the source lines X1 to Xn. The D / A conversion circuit 23 is configured to refer to a plurality of gradation reference voltages VREF generated from the gradation reference voltage generation circuit 7.

  In the liquid crystal display device according to the present embodiment, as shown in FIGS. 1 and 3, the video signal DI corresponding to each of the A direction image and the B direction image is transmitted from the external signal source SS to the liquid crystal display panel DP within one frame period. Sent to the side.

  In the liquid crystal display device according to the present embodiment, as shown in FIG. 3, the image data conversion circuit 17 has a frame memory MA for the A direction image and a frame memory MB for the B direction image, and each frame memory MA. , Pixel data DO corresponding to the A direction image and the B direction image temporarily stored in the MB is transferred to the liquid crystal display panel DP at a predetermined timing.

  In the liquid crystal display device according to this embodiment, the pixel data DO is pixel data DOK for black image display, pixel data DOA for A-direction image display, or pixel data DOB for B-direction image display.

  As shown in FIG. 3, the backlight BL includes a first illumination unit BLA that emits light in the A direction and a second illumination unit BLB that emits light in the B direction different from the A direction. The first illumination unit BLA includes a light source LA and a light guide LGA that guides light emitted from the light source LA. The second illumination unit BLB includes a light source LB and a light guide LGB that guides light emitted from the light source LB.

  Here, when the light source LA is turned on, the light emitted from the light source LA is guided in the direction A in the figure by the light guide LGA. That is, the light emitted from the light source LA passes through the liquid crystal display panel DP and is viewed from the A direction side of the front surface of the liquid crystal display panel.

  When the light source LB is turned on, the light emitted from the light source LB is guided by the light guide LGB in the direction B in the drawing. The light emitted from the light source LB passes through the liquid crystal display panel DP and is viewed from the B direction side of the front surface of the liquid crystal display panel.

  Next, a method for driving the liquid crystal display device in the present embodiment will be described. The liquid crystal display device according to the present embodiment employs a time division drive method. In the following description, a case where the lower limit of the scanning time determined by driving restrictions is 39% of one subframe period will be described.

  The drive timing of the liquid crystal display device according to this embodiment is shown in FIG. Here, the horizontal axis shown in FIG. 4 corresponds to the time axis, and the vertical axis corresponds to the vertical position in the screen. As shown in FIG. 4, in the driving method of the liquid crystal display device according to the present embodiment, one frame period includes a first subframe period FLA and a second subframe period FLB following the first subframe period. The first illumination unit BLA and the second illumination unit BLB of the backlight BL are turned on and off corresponding to the respective subframe periods FLA and FLB.

  At the drive timing of the liquid crystal display device according to the present embodiment, signal writing scanning is performed twice within each subframe period. That is, in the liquid crystal display device according to the present embodiment, the first period, the second period following the first period, and the third period following the second period are set for each of the subframe periods FLA and FLB. Yes.

  First, the display operation of the A direction image will be described. In the first period of the first subframe period FLA, the gate driver YD sequentially selects the gate lines Y1 to Ym by the control signal CTY, and turns on the pixel switching elements W of each row for one horizontal scanning period. The A-direction image display pixel data DOA is serially supplied from the image data conversion circuit 17 to the source driver XD.

  The source driver XD refers to a predetermined number of gradation reference voltages VREF supplied from the gradation reference voltage generation circuit 7 to convert the A-direction image display pixel data DOA into pixel voltages Vs, respectively. Output in parallel to the lines X1 to Xn. The pixel voltage Vs output to the plurality of source lines X1 to Xn is supplied to the pixel electrode PE via the pixel switching element W.

  In the second period of the subsequent first subframe period FLA, the same operation as that in the first period is performed. That is, the gate driver YD sequentially selects the gate lines Y1 to Ym from the upper end of the screen to the lower end of the screen by the control signal CTY, and turns on the pixel switching elements W of each row for one horizontal scanning period.

  The A-direction image display pixel data DOA is serially supplied from the image data conversion circuit 17 to the source driver XD. The source driver XD refers to a predetermined number of gradation reference voltages VREF supplied from the gradation reference voltage generation circuit 7 described above, converts each of the A-direction image display pixel data DOA into a pixel voltage Vs, and outputs a plurality of pixel voltages Vs. Are output in parallel to the source lines X1 to Xn.

  In the liquid crystal display device according to the present embodiment, the pixel voltage Vs applied by the source driver XD to the plurality of source lines X1 to Xn in the first period and the source driver XD in the second period are the plurality of source lines X1 to Xn. The pixel voltage Vs applied to is the same signal.

  In the subsequent third period of the first subframe period FLA, the gate driver YD sequentially selects the gate lines Y1 to Ym for A-direction image display by the control signal CTY, and the pixel switching elements W in each row are set for one horizontal scanning period. Conduct.

  The image data conversion circuit 17 forms black image display pixel data DOK. The black image display pixel data DOK is output in series from the image data conversion circuit 17 to the source driver XD. The source driver XD converts the black image display pixel data DOK into a pixel voltage Vs, and outputs the pixel voltage Vs in parallel to the plurality of source lines X1 to Xn.

  The vertical timing control circuit 11 outputs a light on / off signal to the backlight control circuit 14 at a predetermined timing in accordance with the subframe period FLA in which the A direction image is displayed. In the liquid crystal display device according to the present embodiment, the backlight control circuit 14 drives the backlight driving unit LD to turn on the first illumination unit BLA and turn off the second illumination unit BLB in the subframe period FLA.

  Next, the B direction image display operation will be described. In the first period, the second period, and the third period of the second subframe period, the gate driver YD moves the gate lines Y1 to Ym from the upper end of the screen to the screen in accordance with the control signal CTY as in the above-described A-direction image display operation. The pixels are sequentially selected to the lower end, and the pixel switching elements W in each row are made conductive for one horizontal scanning period. The source driver XD applies the pixel voltage Vs corresponding to the B direction image to the pixel electrode PE in each of the first period and the second period of the subframe period FLB, and applies the pixel voltage Vs corresponding to the black image in the third period. Applied to the pixel electrode PE.

  In accordance with the subframe period FLB, the vertical timing control circuit 11 outputs a light on / off signal to the backlight control circuit 14 at a predetermined timing. For example, in the liquid crystal display device according to the present embodiment, the backlight control circuit 14 drives the backlight driving unit LD to turn on the second illumination unit BLB and turn off the first illumination unit BLA during the subframe period FLB.

  As described above, in the liquid crystal display device according to the present embodiment, by writing the pixel voltage corresponding to the black image at the end of one subframe period, the signal held in the panel is once reset, and the A direction image, B Mixing (crosstalk) of each direction image is suppressed.

  In a liquid crystal display device that employs the time-division driving method as described above, the response speed of the liquid crystal is sufficient to reliably perform resetting by writing the pixel voltage Vs corresponding to a black image (hereinafter referred to as black insertion scanning). It needs to be fast. For this reason, the OCB liquid crystal having a high response speed is the most suitable liquid crystal material for the time division driving method.

  In the OCB liquid crystal, in order to prevent so-called reverse transition in which the liquid crystal alignment state returns from the bend state to the splay state, for example, a high voltage equal to or higher than the threshold voltage is applied at a certain time ratio during one frame period, for example, black image display is performed. There is a need. For this reason, it is necessary to perform at least one black insertion scan and at least one video signal writing (hereinafter referred to as signal scanning) within one frame period. Therefore, by performing black insertion scanning as described above, reverse transition of the OCB liquid crystal is also prevented.

  Here, for example, in the driving method in which the video signal is written only once in each subframe period, when the lower limit of the scanning time determined by driving restrictions is, for example, 39% of one subframe period, the liquid crystal is in the display state. The time ratio within one subframe period is 100% −39% = 61%.

  On the other hand, in the case shown in FIG. 4, the signal writing scanning time for one time is 22%, which is shorter than the lower limit value of the scanning time. That is, the video signal writing to the display pixel PX is performed twice within one subframe period to prevent the video signal from being insufficiently written to the display pixel PX, and the scanning time for one time is shortened accordingly.

  In the liquid crystal display device according to the present embodiment, the time ratio in one subframe period in which the liquid crystal is in the display state is 100% −22% = 78%. Strictly speaking, the video signal writing is completed when the second signal writing is completed. However, since the video signal is written in the first signal writing scan, this time is displayed. Can be the beginning of

  That is, according to the liquid crystal display device according to the present embodiment, the time ratio in one subframe period in which the liquid crystal is in the display state can be increased from 61% to 78%, thereby improving the light use efficiency and the luminance. Can be increased. Therefore, according to the liquid crystal display device according to the present embodiment, it is possible to provide a liquid crystal display device that suppresses a decrease in luminance accompanying a decrease in light utilization efficiency.

  Next, a liquid crystal display device according to a second embodiment of the present invention will be described below with reference to the drawings. In the following description, the same components as those of the liquid crystal display device according to the first embodiment described above are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIG. 5, a parasitic capacitance Csd exists between the display pixel PX and the signal line X adjacent thereto. Accordingly, when driven as in the liquid crystal display device according to the first embodiment, during the second period in which the video signal is written for the second time in each subframe period FLA, FLB, it is retained by coupling via the parasitic capacitance Csd. The pixel potential in the state varies. For this reason, vertical crosstalk may occur in the liquid crystal display device according to the first embodiment.

  The liquid crystal display device according to the present embodiment is driven as shown in FIG. 6 in order to prevent the occurrence of the above-described crosstalk. That is, as shown in FIG. 6, as in the case of the liquid crystal display device according to the first embodiment, the first period and the second period of the first subframe period FLA and the second subframe period FLB The video signal corresponding to the A direction image or the B direction image is written in, and black insertion scanning is performed in the third period.

  In the liquid crystal display device according to the present embodiment, after the video signal writing corresponding to the A direction image or the B direction image is finished in the second period of the first subframe period FLA and the second subframe period FLB, the gate Without scanning the lines Y1 to Ym, only the signal line potential is changed in a pattern obtained by inverting the video signal.

  That is, in the second period of the first subframe period FLA and the second subframe period FLB, a signal obtained by inverting the video signal is output from the source driver XD after the video signal is written.

  By driving the liquid crystal display device as described above, fluctuations in the pixel potential due to coupling of the parasitic capacitance Csd and potential fluctuations in a completely reverse pattern can be applied to the pixel potential, thereby canceling out the potential fluctuations. Thus, the occurrence of vertical crosstalk can be suppressed.

  Here, the pattern in which the video signal is inverted is specifically a pattern in which the polarity of the video signal is simply inverted, or a pattern in which only the black and white (gradation) of the video is inverted without inverting the polarity ( This includes a negative image pattern).

  When the pattern in which the video signal is inverted is a pattern in which the polarity is inverted, for example, in the subframe period in which the positive video signal is applied, the source driver XD has the positive polarity in the video signal writing period in the second period. After outputting the video signal, the polarity is inverted and the video signal with only the polarity changed is output.

  When the pattern in which the video signal is inverted is a pattern in which the black and white of the video is inverted, for example, in the subframe period in which the positive video signal is applied, the source driver XD is positive in the video signal writing period of the second period. After a negative video signal is output, a negative video pattern is output with a positive polarity.

  The pattern obtained by inverting the video signal is not limited to the above signal. For example, the column average value of the video signal may be calculated, and a constant voltage value obtained by inverting the average value may be output from the source driver XD.

That is, for example, in a liquid crystal display panel DP having the number of pixels M (vertical) × N (horizontal), pixels (m, n) (m = 1, 2,..., M, n = 1, 2,..., N) When the video signal output to V (m, n) is
Vave (n) = (1 / M) ΣV (m, n) [m = 1, 2,..., M]
And a voltage corresponding to −Vave (n) may be output for a period equal to the video signal writing period in the second period.

  Even with this method, it is possible to suppress vertical crosstalk by the same principle as described above. Further, when the output voltage value is constant as described above, the power consumption of the source driver XD can be reduced.

  In this case, it is not necessary to make the time for outputting the constant voltage equal to the video signal writing period in the second period. Even if the time to output a constant voltage is short, if the correction coefficient of (video signal writing period in the second period) / (time to output a constant voltage) is applied to the output constant voltage value, the effect of suppressing vertical crosstalk Is obtained.

  That is, according to the liquid crystal display device according to the present embodiment, the same effect as that of the liquid crystal display device according to the first embodiment described above can be obtained, and the occurrence of vertical crosstalk can be suppressed and the display quality can be improved. Can be provided. In short, it is only necessary to apply a potential that cancels the variation in pixel potential to the signal line.

  Next, a liquid crystal display device according to a third embodiment of the present invention will be described below with reference to the drawings. In the liquid crystal display device according to the present embodiment, it is assumed that the lower limit of the scanning time determined by the constraint of the driving condition is 39% of one subframe period, and the description of the second signal writing is omitted. .

  In the liquid crystal display device according to the present embodiment, the first subframe period FLA and the second subframe period FLB are set within one frame period, and each of the first subframe period FLA and the second subframe period FLB is set. A first period in which a video signal corresponding to the first image or the second image is written to the display pixel PX and a third period in which a signal corresponding to a black image as a non-display image is written to the display pixel PX are set. Yes.

  As shown in FIG. 7, in the liquid crystal display device according to the present embodiment, the first period is the first of the first subframe period FLA and the second subframe period FLB, and is set to 25% of one subframe period, for example. A second period (not shown) is set subsequent to the first period, and a third period is set at the end of the first subframe period FLA and the second subframe period FLB.

  In the liquid crystal display device according to the present embodiment, for example, as shown in FIG. 7A, the third period is set to 20% of one subframe period FLA, FLB that is shorter than the first period. That is, the period during which black insertion scanning is performed (hereinafter referred to as black insertion scanning period) is shortened to 20% of one subframe period FLA, FLB.

  Regarding black insertion scanning, the signal output level from the source driver XD is a constant value corresponding to the black image, and there is no particular limitation due to the transfer speed of the source driver XD. Further, the limitation on the scanning time for preventing the pixel charge shortage on the liquid crystal display panel DP side can be eliminated by measures such as turning on the pixel switching element W over a plurality of horizontal periods. For this reason, the black insertion scanning period can be set to a value that is sufficiently lower than the lower limit value of the scanning time determined by the constraints of the driving conditions.

  At the drive timing shown in FIG. 7A, the time ratio at which the liquid crystal is in the display state within the first subframe period FLA and the second subframe period FLB is the first subframe period FLA and the second subframe at the upper end of the screen. 80% of each period FLB, 77.5% at the center of the screen, and 75% at the bottom of the screen.

  As shown in FIG. 7C, at the driving timing of the liquid crystal display device when the black insertion scanning period is set to 25% of one subframe period FLA, FLAB, which is equivalent to the first period, the liquid crystal is in the display state. Assuming that the time ratio is 75% of the first subframe period FLA and the second subframe period FLB in the entire screen, driving at the timing as shown in FIG. Furthermore, it becomes possible to increase the brightness, and the luminance will also increase.

  If the black insertion scanning period is 20% of one subframe period FLA, FLB as described above, a slight luminance gradient occurs between the upper end and the lower end of the screen, but the time ratio at the upper end of the screen / the lower end of the screen. The time ratio of 80 (%) / 75 (%) = 1.067 indicates that the relative error is only 6.7%, which is hardly recognized by the observer's eyes.

  In addition, the shorter the black insertion scanning period is shortened in the first subframe period FLA and the second subframe period FLB, the greater the luminance improvement effect. However, if the black insertion scanning period is too short, particularly at the upper edge of the screen, The ratio of the time during which the pixel voltage corresponding to the black image is applied to the liquid crystal layer 3 within the frame period (hereinafter referred to as the black insertion rate) decreases, and the OCB liquid crystal alignment state returns from the bend state to the splay state. This causes a shift and causes a display defect.

  FIG. 7B shows drive timings for preventing the occurrence of display defects as described above and further increasing the luminance. In the case shown in FIG. 7B, the scanning directions in the subframe periods FLA and FLB are opposite to each other. That is, in the case shown in FIG. 7B, in the first subframe period FLA, both black insertion scanning and signal scanning are performed from the upper end to the lower end of the screen, and in the second subframe period FLB, both black insertion scanning and signal scanning are performed. It goes from the bottom of the screen to the top.

  For example, if the lower limit value of the black insertion rate at which reverse transition does not occur is 20% of one frame period, the black insertion scanning period at the upper end of the screen is exactly 1 at the drive timing shown in FIG. If it is 20% of the subframe periods FLA and FLB and the black insertion scanning period is further shortened, reverse transition occurs.

  On the other hand, in the driving timing shown in FIG. 7B, when the black insertion scanning period is shortened to 15% of the first subframe period FLA and the second subframe period FLB, it is regarded as an average of one frame period. The black insertion scanning period at that time is equal to 20% of one frame period on the entire screen.

  Further, in FIG. 7B, the time ratio at which the liquid crystal is in the display state in each of the first subframe period FLA and the second subframe period FLB is equal to one subframe period at the upper end of the screen of the first subframe period FLA. 85%, 75% at the bottom of the screen, 75% of one subframe period at the top of the screen in the second subframe period FLB, and 85% at the bottom of the screen. When viewed as an average of one frame period, the liquid crystal is in the display state. The time ratio is 80% of one frame period.

  That is, when driven as shown in FIG. 7B, the time ratio during which the liquid crystal is in a display state within one frame period is further improved from the case shown in FIG. 7A (77.5%). . Therefore, by driving as shown in FIG. 7B, it is possible to prevent the occurrence of display defects due to the reverse transition of the OCB liquid crystal, and to further improve the light utilization efficiency and luminance as the screen average. .

  That is, according to the liquid crystal display device according to the present embodiment, similarly to the liquid crystal display devices according to the first embodiment and the second embodiment described above, a liquid crystal display device that suppresses a decrease in luminance due to a decrease in light utilization efficiency. Can be provided.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. For example, in the liquid crystal display device according to the above embodiment, the video signal DI corresponding to each of the A direction image and the B direction image is transmitted from the external signal source SS to the liquid crystal display panel DP side within one frame period, and the image data Although the conversion circuit 17 converts the pixel data DO, the pixel data DO may be transmitted from the external signal source SS to the liquid crystal display panel DP. Even in that case, the same effect as the liquid crystal display device according to the above-described embodiment can be obtained.

  Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine the component covering different embodiment suitably.

4A and 4B are diagrams for describing a configuration example of a liquid crystal display device according to an embodiment of the present invention. FIG. 3 is a diagram for describing a configuration example of a source driver of the liquid crystal display device illustrated in FIG. 1. FIG. 4 is a diagram for explaining a configuration example of a backlight of a liquid crystal display device according to an embodiment of the present invention. The figure for demonstrating the drive timing in the drive method of the liquid crystal display device which concerns on 1st Embodiment of this invention. The figure for demonstrating the parasitic capacitance which arises between a display pixel and a signal line. The figure for demonstrating the drive timing in the drive method of the liquid crystal display device which concerns on 2nd Embodiment of this invention. The figure for demonstrating the drive timing in the drive method of the liquid crystal display device which concerns on 3rd Embodiment of this invention.

Explanation of symbols

  DP ... Liquid crystal display panel, BL ... Backlight, CNT ... Display control circuit, PX ... Display pixel, LD ... Backlight drive unit, FLA ... Subframe period, FLB ... Subframe period, 1 ... Array substrate, 2 ... Counter substrate 3 ... Liquid crystal layer, 4 ... Driving voltage generation circuit, 5 ... Controller circuit, 14 ... Backlight control circuit

Claims (7)

A liquid crystal display panel having a display portion in which a plurality of display pixels each having a liquid crystal layer sandwiched between a pair of electrodes are arranged in a matrix;
Illuminating means for illuminating the display unit;
Control means for controlling the liquid crystal display panel and the illumination means,
A liquid crystal display device that displays a first image in a first subframe period of one frame period and displays a second image in a second subframe period following the first subframe period,
The illumination means includes a first illumination unit that emits light in a first direction, and a second illumination unit that emits light in a second direction different from the first direction,
The control means sets the first subframe period and the second subframe period within one frame period, and each of the first and second subframe periods includes the first period and the first period. A second period that follows and a third period that follows the second period are set, and a video signal corresponding to the first image is displayed in the display pixel in the first period and the second period within the first subframe period. And a signal corresponding to a non-display image in the third period is written to the display pixel, and an image corresponding to the second image in the first period and the second period in the second subframe period. A time division writing unit for writing a signal to the display pixel and writing a signal corresponding to a non-display image in the third period to the display pixel;
A liquid crystal display device comprising: an illuminating means control section that turns on the first illumination section during the first subframe period and turns on the second illumination section during the second subframe period. The display unit includes a scanning line arranged along a row where the display pixels are arranged, and a signal line arranged along a column where the display pixels are arranged,
The time division writing unit is an inverted signal applying unit that changes the potential of the signal line with an inverted signal pattern obtained by inverting the video signal applied to the signal line at the time of signal writing after writing the video signal in the second period. The liquid crystal display device according to claim 1. The display unit includes a scanning line arranged along a row where the display pixels are arranged, and a signal line arranged along a column where the display pixels are arranged,
The time division writing unit calculates an average value of the video signal written to each display pixel at the time of signal writing after writing the video signal in the second period, and calculates the average calculated The liquid crystal display device according to claim 1, further comprising a reverse polarity column average signal applying unit that applies a reverse polarity column average signal in which the polarity of the value is inverted to a signal line corresponding to the column of the display pixels.   The liquid crystal display device according to claim 1, wherein the third period is shorter than the first period or the second period. A liquid crystal display panel including display pixels each having a liquid crystal layer sandwiched between a pair of electrodes, arranged in a matrix, and a display portion on which scanning lines for scanning the display pixels are arranged;
Illuminating means for illuminating the display unit;
Control means for controlling the liquid crystal display panel and the illumination means,
A liquid crystal display device that displays a first image in a first subframe period of one frame period and displays a second image in a second subframe period following the first subframe period,
The illumination means includes a first illumination unit that emits light in a first direction and a second illumination unit that emits light in a second direction different from the first direction,
The control means sets the first subframe period and the second subframe period within one frame period, and applies the display pixel to the display pixel within the first subframe period and the second subframe period. A first period in which a video signal corresponding to the first image or the second image is written and a second period after the first period in which a signal corresponding to a non-display video is written to the display pixel are set. A time division writing unit;
An illumination means controller that turns on the first illumination unit during the first subframe period and turns on the second illumination unit during the second subframe period;
The liquid crystal display device in which scanning directions of the scanning lines are opposite to each other in the first subframe period and the second subframe period.   The liquid crystal display device according to claim 1, wherein the liquid crystal layer includes OCB liquid crystal. A first subframe period and a second subframe period are set within one frame period, and in each of the first and second subframe periods, a first period, a second period following the first period, and a second period Setting a third period following the two periods;
The video signal corresponding to the first image is written to the display pixel in the first period and the second period within the first subframe period, and the signal corresponding to the black image is written to the display pixel in the third period. The video signal corresponding to the second image is written to the display pixel in the first period and the second period in the second subframe period, and the signal corresponding to the black image is written to the display pixel in the third period. Write time division writing step;
A method of driving a liquid crystal display device, comprising: illuminating means control steps for turning on the first illumination section in the first subframe period and turning on the second illumination section in the second subframe period.

Images