JP2007256678A - Liquid crystal display apparatus, method for driving the same, backlight device to be used for liquid crystal display apparatus, and method for driving backlight device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display apparatus, its driving method, a backlight device to be used for the liquid crystal apparatus, and a method for driving the backlight device, in which the generation of flickers can be prevented in the case of continuing the discharge of a vertical backlight even in a subframe period of dark display. <P>SOLUTION: The liquid crystal display apparatus is provided with a backlight driving part for turning on a backlight at the same peak luminance in both of a subframe period of dark display and a subframe period of bright display. The backlight driving part drives ON of the backlight so that the rate of an average ON time ratio of the vertical backlight in the subframe period of dark display to the average ON time ratio of the vertical backlight in the subframe period of bright display becomes ≤1/3. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  In the present invention, the luminance of the video signal corresponding to one frame is displayed by the sum of the luminance of the dark-displayed subframe and the luminance of the bright-displayed subframe which are time-divided, and is arranged in a direction parallel to the scanning line. The present invention also relates to a liquid crystal display device that sequentially lights a plurality of direct type backlights in synchronization with a scanning signal and a driving method thereof, and a backlight device used in the liquid crystal display device and a driving method thereof.

  In an active matrix liquid crystal display device, when attention is paid to a certain pixel, the color and brightness change by writing data, but the display is held and held constantly until the next data change. Device.

  Therefore, in the liquid crystal display device, not only the current frame but also the immediately preceding frame is recognized, leading to a reduction in the quality of moving image display due to “motion blur” or “edge blur”.

  In order to solve this problem, for example, in the active matrix type liquid crystal display device disclosed in Patent Document 1, a plurality of direct type backlights are arranged in a direction parallel to the scanning lines, and all the scanning lines are arranged. Within one field period to be scanned, each direct type backlight is controlled to blink sequentially in synchronization with the scanning signal.

  With this method, it is possible to improve the moving image display performance by shortening the apparent video signal hold period and apparently driving the liquid crystal display device in an impulse manner. That is, considering each pixel, in each frame period, the backlight is turned on only during a predetermined period after a certain delay time has elapsed since rewriting of the image signal. As a result, the progress of the change in the liquid crystal optical response is not easily seen by the viewer, and the light emission of each pixel becomes an impulse, so that the image quality in moving image display is improved.

  Further, Patent Document 1 discloses that when performing the pseudo impulse driving, the lighting period of the backlight is further time-divided into a lighting time and a light-off time. Thus, it is possible to control the luminance of the backlight, that is, the display panel by controlling the ratio of the lighting time and the light-off time. For example, the brightness of the backlight, that is, the display panel can be made the same.

  On the other hand, such a pseudo impulse drive is to flash (on / off) a linear lamp as a light source in synchronization with a frame cycle, and the linear lamp is completely turned off in an off state (discharge is not performed). Has stopped). Therefore, the brightness of the display screen is reduced by the extinguishing period, and the linear lamp starts the next discharge from the state where the discharge is stopped, so that the light emission efficiency is lowered and the rise of light emission is delayed. Therefore, it is difficult to ensure sufficient brightness of the screen during the lighting period of the linear lamp.

  Therefore, in Patent Document 2, in order to solve this problem, the linear lamp is driven by reducing the peak current even in the off period. Specifically, as shown in FIG. 12, in the past, the linear lamp was completely set to zero current during the off period as in IL2, whereas in the method of Patent Document 1, as indicated by IL1, Even during the off period, the discharge is continued by flowing through the linear lamp at 30% to 50% of the on period.

As a result, a difference can be provided between the on-time luminance and the off-time luminance, while pseudo-impulse driving is performed in order to continue the discharge of the linear lamp and perform illumination with low luminance even when off. Therefore, a decrease in luminance of the liquid crystal display panel can be suppressed.
JP 2002-207463 A (published July 26, 2002) JP 2004-252127 A (published September 9, 2004)

  However, in the above-described conventional pseudo-impulse drive liquid crystal display device using a scanning backlight, when the linear lamp is continuously discharged even when it is turned off to perform illumination at a low luminance, the luminance at the on time and the luminance at the off time are reduced. There is a problem that there is a difference in luminance and flickering occurs.

  This problem is thought to be because impulse stimuli are recognized as individual stimuli.

  The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a liquid crystal capable of preventing the occurrence of flicker when the discharge of a direct type backlight is continued even during a dark display subframe period. A display device and a driving method thereof, and a backlight device used in a liquid crystal display device and a driving method thereof.

  In order to solve the above problems, the liquid crystal display device of the present invention is provided with a switching element in the vicinity of the intersection of a plurality of data lines and a plurality of scanning lines provided so as to intersect with each other. The data line is connected to the pixel electrode in the form of a matrix, and the display is based on the sum of the brightness of the dark display subframe and the brightness of the bright display subframe obtained by time-dividing the brightness of the video signal corresponding to one frame. In addition, in the liquid crystal display device that sequentially turns on the plurality of direct type backlights arranged in the direction parallel to the scanning line in synchronization with the scanning signal, the direct type backlight is connected to the subframe period of the dark display. Backlight driving means for lighting at the same peak luminance is provided for both the bright display subframe period and the backlight driving means. Is a direct type backlight so that the average on-time ratio of the direct type backlight in the dark display subframe period is 1/3 or less of the average on time ratio of the direct type backlight in the bright display subframe period. It is characterized by driving the light.

  Further, in order to solve the above problems, the driving method of the liquid crystal display device according to the present invention includes a switching element provided in the vicinity of the intersection of the plurality of data lines and the plurality of scanning lines provided to intersect each other. The data lines are connected to the matrix pixel electrodes via the switching elements, and the luminance of the dark display sub-frame and the luminance of the bright display sub-frame are obtained by time-dividing the luminance of the video signal corresponding to one frame. In a driving method of a liquid crystal display device that sequentially turns on a plurality of direct type backlights arranged in a direction parallel to the scanning line in synchronization with a scanning signal, the direct type backlight is The dark display sub-frame period and the bright display sub-frame period are lit in a pulse shape with the same peak luminance, and the dark display sub-frame period is displayed. The direct type backlight is lit and driven so that the average on-time ratio of the direct type backlight in the period is 1/3 or less of the average on-time ratio of the direct type backlight in the brightly displayed subframe period. It is said.

  The backlight device of the present invention is a backlight device used in the above-described liquid crystal display device in order to solve the above problems, and each direct type backlight has a dark display period and a bright display period. The dark display period and the bright display period have the same peak luminance, and the dark display period and the bright display period have different light lighting periods.

  The backlight device of the present invention is a backlight device used in the above-described liquid crystal display device in order to solve the above problems, and each direct type backlight has a dark display period and a bright display period. The dark display period and the bright display period have the same peak luminance, and the bright display period is the same as or longer than the dark display period, and the dark display period and the bright display period are the same. The display period is alternately repeated.

  Further, in order to solve the above-described problem, the backlight device driving method of the present invention is a driving method of the backlight device used in the above-described liquid crystal display device, and each direct type backlight has a dark display period. The dark display period and the bright display period have the same peak luminance, and the dark display period and the bright display period have different light lighting periods. .

  Further, in order to solve the above-described problem, the backlight device driving method of the present invention is a driving method of the backlight device used in the above-described liquid crystal display device, and each direct type backlight has a dark display period. And the bright display period have the same peak luminance in the dark display period and the bright display period, and the bright display period is the same as or longer than the dark display period, In addition, the dark display period and the bright display period are alternately repeated.

  In the present invention, “lights up with the same peak luminance” is used. However, the same in a strict sense is not required, and a ratio of 0.8 to 1.3 is sufficient.

  According to the above invention, the backlight driving means turns on the direct type backlight with the same peak luminance for both the dark display subframe period and the bright display subframe period. Therefore, in the pseudo-impulse drive liquid crystal display device using the scanning backlight, the discharge of the direct backlight is continuously turned on at the same peak luminance even during the dark display subframe period. This eliminates the problem that the brightness at the time of turning on is reduced. Therefore, occurrence of flicker can be prevented.

  On the other hand, when the direct-type backlight is lit at the same peak luminance for both the dark-display subframe period and the bright-display subframe period, the direct-type backlight in the dark-display subframe period When the ratio between the total on-time and the total on-time of the direct type backlight in the bright-display subframe period is large, the luminance in the dark-display subframe period increases and the effect of the pseudo impulse drive is lost.

  In this regard, in the present invention, the average on-time ratio of the direct type backlight in the dark display subframe period is 1/3 or less than the average on-time ratio of the direct type backlight in the bright display subframe period. The direct type backlight is turned on.

  That is, it is generally said that the impulse effect in a moving image can be visually recognized if the brightness in the dark period is 1/3 or less with respect to the bright period. Moreover, this result is supported also by inventors' subjective evaluation.

  Therefore, if the direct type backlight is driven to light while maintaining this relationship, the effect of the pseudo impulse drive can be sufficiently maintained.

  As a result, a liquid crystal display device capable of preventing the occurrence of flicker when the direct type backlight continues to be discharged even during the dark display subframe period, a driving method thereof, and a backlight device used in the liquid crystal display device and the same A driving method can be provided.

  In the liquid crystal display device of the present invention, it is preferable that the backlight driving means sets the pulse interval of the off-time of the direct backlight in the subframe period for dark display to 3 msec or less.

  In the driving method of the liquid crystal display device of the present invention, it is preferable to set the pulse interval of the off time of the direct type backlight in the subframe period of the dark display to 3 msec or less.

  Here, the “pulse interval” will be described. As the light source of the backlight, any light source such as an LED or a cold cathode tube may be used. However, when a cold cathode tube or the like is used as a light source, an exact pulse in many senses such as light emission characteristics and electrical characteristics. It is rare to have a waveform. Accordingly, in the present invention, the meaning of “pulse” is, as a phenomenon, “a lighting state composed of a plurality (two or more times) of bright brightness periods and other periods darker than the bright brightness”. Shall be interpreted. That is, even if a peak occurs in a transient response or a round occurs, it is not relevant to the present invention.

  According to the above invention, since the pulse interval of the off-time of the direct backlight in the dark display subframe period is 3 msec or less, it is not recognized by the human eye as being turned off.

  That is, in the present invention, the direct-type backlight is driven to be lit so that the average on-time ratio is 1/3 or less of the average on-time ratio of the direct-type backlight in the brightly displayed subframe period. The ratio between the total dark period and the total light period in the best mode is 1: 4. In this case, for example, if the total period of the light period is 0.1 msec, the total period of the lighting period of the dark period is 0.025 msec, and the light and dark pulse periods of the light period at that time are conversely 0.1 msec. And 0.025 msec. In this case, since the dark period is 1/5 and the bright period is 4/5, an impulse of 4: 1 can be realized.

  However, such driving cannot be realized with a cold cathode tube. Therefore, for the purpose of improving flicker, the shorter the off-period pulse width, the better. However, actually, the light emission response characteristic of the backlight source (in the dark period, the on-period is even shorter than the off-period). The minimum value that can be set by itself is determined from the limit of. For this reason, the minimum pulse width capable of realizing the peak luminance may be set as the on-period pulse width in the dark period according to the light emission response characteristics of the light source to be used. Furthermore, considering the industrial effect, if the pulse width is made too short, the frequency increases, and many cost-up factors such as electromagnetic wave countermeasures, current efficiency, and reliability are generated, which is not preferable.

  As a result, in the present invention, it is preferable to set a maximum time during which a sufficient luminance ratio between the light period and the dark period can be obtained in 3 msec or less in which the extinction cannot be recognized.

  In the liquid crystal display device of the present invention, it is preferable that a plurality of row lighting driving means for lighting each of the plurality of direct type backlights among the plurality of direct type backlights is provided.

  Accordingly, when the plurality of direct type backlights are sequentially turned on in synchronization with the scanning signal, the light can be sequentially turned on for each of the plurality of direct type backlights.

  In the liquid crystal display device of the present invention, it is preferable that the direct type backlight is an LED.

  According to the above invention, by configuring the direct type backlight with LEDs, it is possible to easily perform arbitrary pulse driving without providing a complicated lighting driving circuit.

  In the liquid crystal display device of the present invention, the direct type backlight may be a cold cathode tube.

  According to the above invention, by constructing the direct type backlight with the cold cathode tube, the cold cathode tube that has been conventionally used as a backlight has been used, and the backlight can be used even during the subframe period of dark display. It is possible to provide a liquid crystal display device capable of preventing the occurrence of flicker when discharging is continued.

  As described above, the liquid crystal display device of the present invention and the driving method thereof, and the backlight device used in the liquid crystal display device and the driving method of the direct-type backlight are connected to the sub-frame period of the dark display and the sub-frame of the bright display. It is lit at the same peak luminance for both the frame period and the average on-time ratio of the direct type backlight in the dark display subframe period becomes the average backlight on-time ratio in the bright display subframe period. On the other hand, the direct type backlight is driven to turn on so that it becomes 1/3 or less.

  Therefore, when the discharge of the direct type backlight is continued even during the dark display subframe period, the liquid crystal display device capable of preventing the occurrence of flicker, the driving method thereof, the backlight device used in the liquid crystal display device, and the same The driving method can be provided.

[Embodiment 1]
An embodiment of the present invention will be described with reference to FIGS. 1 to 6 as follows. Note that in this embodiment, a liquid crystal display device using an LED (Light Emitting Diode) as a backlight will be described.

  In the liquid crystal display device 10 of the present embodiment, as shown in FIG. 2, an array substrate 1 made of a glass substrate and a counter substrate 2 are provided to face each other at a predetermined interval via liquid crystal. A common electrode (not shown) is formed on the entire surface of the counter substrate 2.

  On the array substrate 1, a plurality of data lines 3 and a plurality of scanning lines 4 are provided so as to intersect each other, and pixel electrodes 5 are provided in a pixel region partitioned in a matrix by both wirings. A TFT (Thin Film Transistor) 6 serving as a switching element is disposed in the vicinity of the intersection of both wirings. The source electrode of the TFT 6 is connected to the data line 3, the gate electrode is connected to the scanning line 4, and the drain electrode is connected to the pixel electrode 5 facing the storage capacitor 7 and the liquid crystal 8.

  Each data line 3 is connected to a source driver 11, and each scanning line 4 is connected to a gate driver 12. The source driver 11 and the gate driver 12 are connected to a control circuit 13 and controlled.

  Moreover, in this Embodiment, LED21 is laid by the back surface of the said array board | substrate 1 as the backlight 20 as a backlight apparatus.

  In the liquid crystal display device 10, the video signal is controlled as follows.

  First, an external data signal composed of an image data signal, a vertical / horizontal synchronization signal, and a power supply voltage is input to the control circuit 13, and a clock signal and scanning for capturing data into the source driver 11 based on the vertical / horizontal synchronization signal. A clock signal for switching the line 4 is generated. The source driver 11 starts the operation of the shift register simultaneously with the rising edge of the start pulse, and operates according to the clock. In the present embodiment, the frame period in the liquid crystal display driving is 60 Hz.

  Data input simultaneously with the clock is stored in the sampling memory selected by the shift register, and when display data for all one horizontal line is sent, a latch pulse is output from the control circuit 13. When the source driver 11 receives the latch pulse, the hold memory latches the data stored in the sampling memory all at once. The latched data is D / A converted and output to the data line 3, and an on-voltage is applied to one of the scanning lines 4 to turn on all the horizontal rows of the TFTs 6. Thereby, one line of data is displayed. By repeating the above operation in the same manner, all the scanning lines 4 are scanned in the vertical direction to drive all the lines. At this time, as the scanning line 4 is scanned from the top to the bottom, the direct type LEDs 21 are sequentially turned on. The backlight 20 is driven by the backlight driving unit 30.

  By the way, in the liquid crystal display device 10 according to the present embodiment, the video signal corresponding to one frame is divided into two subframes, and the video is displayed as the sum of the dark display subframe and the bright display subframe. In addition, the backlight 20 is controlled to be dark and bright in each subframe.

  Therefore, in the present embodiment, by controlling the backlight 20, the brightness of the backlight 20 is changed between the dark display subframe period and the bright display subframe period. There is a certain relationship between the number of pixels (particularly the number of pixels in the vertical direction) and the configuration of the backlight 20. In this embodiment, for example, the backlight 20 corresponds to a display panel conforming to the standard of full high vision having a pixel number of 1920 (horizontal) × 1080 (vertical) and an aspect ratio of 16: 9.

  By the way, in a conventional pseudo-impulse-driven liquid crystal display device using a scanning backlight, when the linear lamp discharge continues to be performed at low brightness even when it is off, the on brightness and the off brightness However, there is a problem that flicker occurs. This problem is thought to be because impulse stimuli are recognized as individual stimuli.

  In the liquid crystal display device 10 of the present embodiment, in order to solve this problem, as shown in FIG. Then, the peak luminance in the extinguishing period is made the same as the peak luminance in the lighting period, and the average on-time ratio of the backlight 20 in the dark display subframe period is the average on time of the backlight 20 in the bright display subframe period. The ratio is set to 1/3 or less, preferably 1/4 or less. As a result, flicker can be prevented. In FIG. 1, the vertical axis indicates the current value of the LED 21. That is, since the current value and the peak luminance are in a proportional relationship, the figure shows that the peak luminance in the extinguishing period and the peak luminance in the lighting period are the same.

  That is, when the backlight 20 is turned on, as shown in FIG. 3A, when the pulse of the lighting time T1 and the non-lighting time T2 is considered, the peak luminance is different as shown in FIG. 3B. It appears as flicker to the human eye. This phenomenon is the same even when the non-lighting time T2 is short when the peak luminance is different.

  On the other hand, as shown in FIG. 3C, when the peak luminance of the backlight 20 in the dark display period is the same as the peak luminance of the backlight 20 in the bright display period, the eyes are stimulated with the same intensity. Therefore, it has been medically found that flicker does not occur.

  Therefore, in the present embodiment, the backlight 20 is lit at the same peak luminance for both the dark display subframe period and the bright display subframe period, and the backlight 20 in the dark display subframe period is displayed. The lighting is driven so that the average on-time ratio of the light 20 is, for example, ¼ or less of the average on-time ratio of the backlight 20 in the brightly displayed subframe period. This driving is performed by the backlight driving unit 30 as a backlight driving means. As a result, flicker can be prevented.

  Specifically, it is preferable to set the pulse interval of the off-time of the backlight 20 in the dark display subframe period to 3 msec or less, and in this embodiment, for example, 1.6 msec.

  In the above description, the peak luminance during the extinguishing period is assumed to be the same as the peak luminance during the lighting period, but the exact same is not required.

  That is, in the backlight 20 according to the present embodiment, the ratio of the luminance of the backlight in the dark display subframe period to the luminance of the backlight 20 in the bright display subframe period is, for example, 1 to 0.8 to 1. .3 is enough. Furthermore, 1 to 0.9 to 1.2 is more preferable. If it is smaller than 1 to 0.8, the dark period may be recognized as being extinguished. On the other hand, if it is larger than 1: 1.3, it is recognized as a lighting period. In any case, flicker is easily recognized, which is not preferable. From the viewpoint of visual characteristics, it can be considered in the actual evaluation that the margin is somewhat large for a ratio larger than 1. However, in order to exceed the luminance in the bright period with an on-pulse having a shorter dark period, a circuit for increasing the luminance is particularly necessary, which is not preferable. Therefore, it is particularly preferably set between 1 and 0.9 to 1.0.

  The backlight 20 having the above configuration and the backlight drive unit 30 that drives the backlight 20 will be described in detail below with reference to FIG. FIG. 4 is a block diagram illustrating the arrangement of the LEDs 21 in the backlight 20 including the LEDs 21 according to the present embodiment and the configuration of the backlight driving unit 30 that drives the backlight 20.

  The LED 21 of the present embodiment is an LED 21 that emits white light, and is a direct type backlight 20. That is, the LED 21 is laid on the back surface of the array substrate 1 of the liquid crystal panel.

The size of the single LED21 is of the order of about ^{1cm 2 ~4cm} 2. The LEDs 21 are laid horizontally in k and l in length so as to be approximately the same size as the effective display portion of the liquid crystal panel. Specifically, for example, there are 40 horizontal LEDs and 27 vertical LEDs.

  The k horizontal lines are connected in series, and when the control signal Fcl becomes low level in accordance with a control signal Fcl from the backlight drive unit 30 described later, the LEDs 21 in the selected row are turned on. It has become.

  A configuration of the backlight driving unit 30 that drives the backlight 20 will be described.

  That is, the backlight drive unit 30 includes a DC / DC converter 31, a clock generation unit 32, a controller 33, and an output circuit 34.

  The DC / DC converter 31 is a power supply circuit that converts an input voltage Vin into an output voltage Vout. When the anode voltage of the backlight D (1, l) in the selected row is Va1, l by the DC / DC converter 31, each LED 21 in the selected row has (Vout−Va1, l) ÷ Rl = Il current flows, and the LED 21 emits light with a desired luminance determined by the current.

  The clock generator 32 generates a clock. The clock frequency generated by the clock generation unit 32 may be any frequency that can be counted by the controller 33 while sufficiently reducing the error of the horizontal synchronization signal, for example, 6.912 MHz or more. In this embodiment, for example, the frequency is 13.824 MHz.

  The controller 33 is provided with a counter 33a, a control signal generator 33b, and a delay circuit 33c, and generates various control signals in synchronization with the clock of the clock generator 32.

A plurality of counters 33a are provided. The second counter receives the V _D signal, counts the V _D signal, or an information which is a period as or second sub-frame period of the first subframe, the control signal generator 33b Send. The control signal generator 33b receives the information of the second counter, and switches between the control content corresponding to the period of the first subframe and the control content corresponding to the second period.

  The control operation of the controller 33 will be described with reference to FIG.

When the control signal generating section 33b is determined to be V _D signal period of the first sub-frame the V _D signals, to the first counter, it counts the H _D signals, to 40 counts the H _D signal The control signal generator 33b sets the control signal Fc1 to the high level (ts1 in FIG. 5). The meaning of ts1 means that the lighting of the backlight D (i, 1) (1 ≦ i ≦ k) in the first row starts scanning the 40th row of the corresponding display panel (the liquid crystal of each pixel in the 40th row). It is provided to delay until the writing of charges) is completed.

First counter and counts the 41 th H _D signal, the control signal generating unit 33b is a control signal Fc1 to a low level, a low level control signal Fc1 until counting 94 th H _D signal (54H) To do. (T1 in FIG. 5)
First counter and counts the 95 th H _D signal, the control signal generating unit 33b is a control signal Fc1 to high level, turns off the first line of the backlight D (i, 1), H _D signal The backlight D (i, 1) in the first row is extinguished until 162 are counted (t2 in FIG. 3). Here, if the first counter is a 217-digit counter from 0 to 216, the backlight D (i, 1) in the first row can be controlled to be turned on with a period of t1 + t2 and an on period of t1. become.

After V _D signal period of the first sub-frame is input, between the 40th and the 41 th H _D signal, the first counter is reset, the 54-th H _D signal input after reset between the 55th, the first counter is reset, between 162 th and 163 th H _D signal input after the reset, to reset the first counter, constituting the first counter You may do it. In any case, the counter 33a requires 7 bits.

The period of the second sub-frame, the first counter, the period in which V _D signals of the second subframe also continues counting of H _D signal after being inputted to count 40 a H _D signal (ts2) , the period of 162 amino counts _{H D} signal t3, t4 is set to a period for 162 pieces counting _{H D} signal. With this setting, the backlight D (i, 1) in the first row has an on / off ratio of 1: 3 in the first subframe period and in the second subframe period. Driving is performed with an on / off ratio of 3: 1. Thus, the luminance ratio of the backlight of the dark display subframe and the bright display subframe is set to 1: 3.

  The control signal generator 33b generates the control signal Fc1 as described above. Then, by inputting the control signal Fc1 to the delay circuit 33c, control signals Fc1, Fc3... Fc27 delayed by 40H from the control signal Fc2 are generated.

  If the frame discrimination signal can be directly input to the controller 33, the second counter may be omitted and the frame discrimination signal may be input directly to the control signal generator 33b.

  In the above configuration, for example, as shown in FIG. 6, a delay circuit 41 is provided outside the controller 33, and a multiplexer 42 as a multi-row lighting drive unit is provided between the delay circuit 41 and the output circuit 34. The backlight drive unit 40 can be used. With this configuration, the control signals Fc1, Fc2, and Fc3 are driven by the in-phase control signal delayed by 80H from Fc1, or are driven by the control signals Fc1, Fc2, and Fc3 delayed by 40H from the control signal Fc1. Thus, the driving method of the backlight 20 can be selected. That is, the present invention is not limited to a driving method for controlling the on / off phase of the backlight 20 one row at a time, and the plurality of rows of backlights 20 may be simultaneously driven in the same phase.

  As described above, in the liquid crystal display device 10 and the driving method thereof according to the present embodiment, and the backlight 20 and the driving method used in the liquid crystal display device 10, the backlight driving unit 30 causes the backlight 20 to perform dark display. It is lit at the same peak luminance for both the sub-frame period and the brightly displayed sub-frame period. For this reason, in the pseudo-impulse drive liquid crystal display device 10 using the scanning backlight, the discharge of the backlight 20 is continuously turned on at the same peak luminance even during the dark display subframe period. This eliminates the problem that the brightness at the time of turning on is reduced. Therefore, occurrence of flicker can be prevented.

  On the other hand, when the backlight 20 is lit at the same peak luminance for both the dark display subframe period and the bright display subframe period, the entire backlight 20 in the dark display subframe period is displayed. When the ratio between the on-time and the total on-time of the backlight 20 in the bright-display subframe period is large, the luminance in the dark-display subframe period increases and the effect of the pseudo impulse drive is lost.

  In this regard, in this embodiment, the average on-time ratio of the backlight 20 in the dark display subframe period is, for example, 1/3 or less of the average on-time ratio of the backlight 20 in the bright display subframe period. Thus, the backlight 20 is driven to turn on. That is, it is generally said that the impulse effect in a moving image can be visually recognized if the brightness in the dark period is 1/3 or less with respect to the bright period. Moreover, this result is supported also by inventors' subjective evaluation.

  Therefore, if the backlight 20 is driven to light while maintaining this relationship, the effect of the pseudo impulse drive can be sufficiently maintained.

  As a result, when the discharge of the backlight 20 is continued even during the dark display subframe period, the liquid crystal display device 10 capable of preventing the occurrence of flicker and the driving method thereof, and the backlight 20 used in the liquid crystal display device 10 and A driving method thereof can be provided.

  In addition, in the liquid crystal display device 10 and the driving method thereof according to the present embodiment, and the backlight 20 and the driving method used in the liquid crystal display device 10, the backlight driving units 30 and 40 are connected to each other during the subframe period of dark display. It is preferable to set the pulse interval of the off time of the light 20 to 3 msec or less.

  As a result, the pulse interval of the backlight off time in the dark display subframe period is 3 msec or less, and thus it is not recognized by the human eye as being turned off. That is, this period is recognized as being lit by human eyes, but indicates a dark display period.

  Here, in the present embodiment, the backlight 20 is driven at a double speed of 1/120 seconds in each subframe period of light and dark. Accordingly, the lighting pulse width in the dark display period (lighting period 54H≈0.43 ms, extinguishing period 162H≈1.3 ms), and the lighting pulse width in the bright display period (lighting period 162H≈1.3 ms, extinguishing period 54H≈0.43 ms). Since the backlight 20 is driven with an average on-time ratio of 1/3, the quality of moving image display can be improved. Further, since the extinguishing period (extinguishing pulse interval) of the dark display period is set to 1.3 ms <3 ms, the dark display period can also contribute to the display without causing flicker, and the display luminance of the liquid crystal display device 10 is improved. Can be made.

  As a result, in the present embodiment, it is preferable to set a maximum time during which a sufficient luminance ratio between the light period and the dark period can be obtained in 3 msec or less in which the extinction cannot be recognized.

  Moreover, in the liquid crystal display device 10 of this Embodiment, it is preferable that the multiplexer 42 which lights for every some backlight 20 of the some backlight 20 is provided.

  Accordingly, when the plurality of backlights 20 are sequentially turned on in synchronization with the scanning signal, the plurality of backlights 20 can be turned on sequentially.

  In the liquid crystal display device 10 and the driving method thereof according to the present embodiment, the backlight 20 is preferably an LED 21.

  Therefore, by configuring the backlight 20 with the LED 21, any pulse driving can be easily performed without providing a complicated lighting driving circuit.

[Embodiment 2]
The following will describe another embodiment of the present invention with reference to FIGS. Configurations other than those described in the present embodiment are the same as those in the first embodiment. For convenience of explanation, members having the same functions as those shown in the drawings of the first embodiment are given the same reference numerals, and explanation thereof is omitted.

  In the liquid crystal display device 10 of the present embodiment, instead of the backlight 20 of the LED 21 of the first embodiment, a backlight 50 as a backlight device including a cold cathode tube 51 is used.

  That is, the driving voltage of the backlight 50 composed of the cold cathode tube 51 is a value around 1000 V, and the cold cathode tube 51 is directly driven by a transistor like the backlight 20 composed of the LED 21 shown in the first embodiment. I can't. This is because the breakdown voltage of the transistor is equal to or lower than the driving voltage. Therefore, it drives using an inverter.

  A backlight 50 using the cold cathode tube 51 of the present embodiment will be described with reference to FIGS.

  As shown in FIG. 7, for example, the backlight 50 including the cold cathode tubes 51 is provided with 27 cold cathode tubes 51 in the column direction. Therefore, the timing relationship of the backlight drive unit 30 is configured such that the timing relationship of the backlight 20 including the LEDs 21 can be used as it is.

  Therefore, in the present embodiment, the output circuit 34 is changed to the output circuit 54 including the inverter 54a, and the cold cathode tube 51 is lit at a predetermined frequency while the control signal Fc1 is at a high level (selected row). A backlight using the LED 21 of the first embodiment except that the configuration is such that the buffer amplifier 43 in the subsequent stage of the multiplexer 42 is changed to the inverting buffer amplifier 53 in order to change the polarity (see FIG. 8). The configuration and timing relationship are the same as in the case of 20.

  The backlight 20 using the LED 21 described in the first embodiment is also set when the lighting period is set so that the controller 33 can be shared with the controller 33 of the backlight 50 using the cold cathode tube 51. Inverter 54a that oscillates at a frequency unique to the period is used.

For example, in FIG. 9, if the coils are L1, L2, the capacitor is C1, and L1 = L2,
Intrinsic oscillation frequency (f) = 1 ÷ 2π√L1C1
It becomes. In this embodiment, f = 30 KHz. However, if it is 20 KHz or more, it is possible to oscillate 10 times or more in one lighting period of the dark period (since this embodiment is a cold-cathode tube double-sided drive, discharge 20 times or more Current peaks). As a result, the dark / light luminance ratio can be accurately adjusted with less error.

  Note that the polarity of the control signal output in FIG. 7 may be switched. In this way, the controller 33 can share the backlight 20 of the LED 21 and the backlight 50 of the cold cathode tube 51.

  In the above configuration, the backlight 50 can be configured to be driven on one side.

  For example, as shown in FIG. 9, the number of the cold cathode tubes 51 in the backlight 60 as the backlight device using the cold cathode tubes 51 is 27 as described above, but the one-side drive configuration is adopted. The backlight 60 becomes the same.

  That is, as shown in FIG. 9, the control signal Fc1 is set to output a low level (set the multiplexer 42) with a delay of 40H (ts1) from the vertical synchronization signal. Specifically, the control for setting the control signal Fc1 of t1 = 27H and the subsequent 27H to the high level as one set is performed. In the dark display period, the backlight 60 is turned on once every 216 periods for 54H periods, and in the bright display period, the backlight 60 is turned on three times in 216 periods. The dark / light ratio is 1: 3.

  As described above, in the backlight 60 of the present embodiment, the pulse widths of the dark display period and the bright display period are fixed, and the lighting period (number of times) of the backlight 60 is controlled in a time-sharing manner. When such time division control is used, the backlight can be easily changed by switching the period during which the control signal Fc1 is at a low level during the 54H period without changing the output voltage Vout of the DC / DC converter 31. 60 brightness adjustments can be made. However, the period during which the control signal Fc1 is set to the low level is preferably 27H or less, and more than the period during which the backlight 60 is stably lit.

  Thus, in the liquid crystal display device 10 and the driving method thereof according to the present embodiment, and the backlights 50 and 60 used in the liquid crystal display device 10 and the driving method thereof, as shown in FIG. The backlight 50 is lit at the same peak luminance for both the dark display subframe period and the bright display subframe period. For this reason, in the pseudo-impulse drive liquid crystal display device 10 using the scanning backlight, the discharge of the backlight 50 is continuously turned on at the same peak luminance even during the dark display subframe period. This eliminates the problem that the brightness at the time of turning on is reduced. Therefore, occurrence of flicker can be prevented.

  On the other hand, when the backlight 50 is lit at the same peak luminance for both the dark display subframe period and the bright display subframe period, the entire backlight 50 in the dark display subframe period is displayed. When the ratio between the on-time and the total on-time of the backlight 50 in the bright-display subframe period is large, the luminance in the dark-display subframe period increases and the effect of the pseudo impulse drive is lost.

  In this regard, in this embodiment, the average on-time ratio of the backlight 50 in the dark display subframe period is 1/3 or less of the average on-time ratio of the backlight 50 in the bright display subframe period. The backlight 20 is turned on. That is, it is generally said that the impulse effect in a moving image can be visually recognized if the brightness in the dark period is 1/3 or less with respect to the bright period. Moreover, this result is supported also by inventors' subjective evaluation.

  Therefore, if the backlight 50 is driven to light while maintaining this relationship, the effect of the pseudo impulse drive can be sufficiently maintained.

  As a result, when the discharge of the backlights 50 and 60 is continued even during the dark display subframe period, the liquid crystal display device 10 capable of preventing the occurrence of flicker, the driving method thereof, and the backlight used in the liquid crystal display device 10 50.60 and its driving method can be provided.

  In the liquid crystal display device 10 of the present embodiment, the backlights 50 and 60 can be assumed to be the cold cathode tubes 51. As described above, the backlights 50 and 60 are constituted by the cold cathode tubes 51, so that the backlight 50 is also used in the dark display subframe period by using the cold cathode tubes 51 that have been conventionally used as backlights. The liquid crystal display device 10 that can prevent the occurrence of flicker when 60 discharges are continued can be provided.

  Further, in the driving method of the liquid crystal display device 10 of the present embodiment, the pulse interval of the off-time of the backlights 50 and 60 in the dark display subframe period is 3 msec or less, so that it is turned off to human eyes. It is not recognized as being.

  Here, the “pulse interval” will be described. As the light source of the backlight, any light source such as an LED or a cold cathode tube may be used. However, when the cold cathode tube 51 is used as a light source, an exact pulse in many meanings such as light emission characteristics and electric characteristics. It is rare to have a waveform. Therefore, in the present embodiment, as a meaning of “pulse”, a lighting state that is phenomenologically composed of a plurality of (two or more) bright bright luminance periods and other periods darker than the bright bright luminance. ". That is, even if a peak occurs in a transient response or a round occurs, it is not relevant to this embodiment.

  In addition, this invention is not limited to said embodiment, A various change is possible within the scope of the present invention. For example, in the above-described embodiment, the LED 21 or the cold cathode tube 51 is used as the backlight. However, the present invention is not particularly limited thereto, and for example, an EL (Electro Luminescence) element can be used. . For a backlight using such an EL element, any of the driving methods described above may be used as long as the driving voltage is taken into consideration (in combination with parallel series connection).

  In Embodiments 1 and 2, the backlight driving method corresponding to, for example, 40 rows of scanning lines 4 (pixels) has been described. However, the present invention is not limited to this, and for example, one row of scanning lines 4 (pixels). The backlight may be driven in response to the above, and the backlights of red (R), green (G), and blue (B) single colors may be turned on sequentially in the field.

  The present invention can be applied to a liquid crystal display device in which a direct backlight is sequentially turned on in synchronization with a scanning signal. As the backlight, an LED (Light Emitting Diode), an organic EL light emitting element, an inorganic EL light emitting element, or a cold cathode tube can be used.

FIG. 2 is a timing chart illustrating an embodiment of a liquid crystal display device according to the present invention and showing backlight lighting pulses in a dark display period and a bright display period. It is a block diagram which shows the whole structure in the said liquid crystal display device. (A)-(c) is explanatory drawing which shows the relationship between the lighting pulse of a backlight, and visual characteristics. It is a block diagram which shows the structure of the backlight drive part using the backlight which consists of LED in the said liquid crystal display device. It is a timing chart which shows the backlight drive method using the backlight which consists of LED in the said backlight drive part. It is a block diagram which shows the structure of the modification of the backlight drive part in the said liquid crystal display device. FIG. 6 is a block diagram illustrating another embodiment of the liquid crystal display device according to the present invention and illustrating a configuration of a backlight driving unit of a backlight including a cold cathode tube. It is a timing chart which shows the backlight drive method using the backlight which consists of a cold cathode tube in the said backlight drive part. It is a block diagram which shows the structure of the modification of the backlight drive part using the backlight which consists of cold cathode tubes in the said liquid crystal display device. It is a timing chart which shows the backlight drive method using the backlight which consists of a cold cathode tube in the said backlight drive part. It is a timing chart which shows the lighting pulse in the dark display period and bright display period of the backlight which consists of the said cold cathode tube. It is a timing chart which shows the backlight drive method in the conventional liquid crystal display device.

Explanation of symbols

1 Array substrate 3 Data line 4 Scan line 5 Pixel electrode 6 TFT
7 Retention Capacity 8 Liquid Crystal 11 Source Driver 12 Gate Driver 13 Control Circuit 20 Backlight (Backlight Device)
21 LED
30 Backlight drive unit (backlight drive means)
31 DC / DC converter 32 Clock generation unit 33 Controller 33a Counter 33b Control signal generation unit 33c Delay circuit 40 Backlight drive unit (backlight drive means)
42 Multiplexer (Multi-row lighting drive means)
43 Buffer amplifier 50 Backlight (Backlight device)
51 Cold Cathode Tube 54 Output Circuit 54a Inverter 60 Backlight

Claims (11)

A switching element is provided in the vicinity of the intersection of the plurality of data lines and the plurality of scanning lines provided to cross each other, and the data lines are connected to the matrix pixel electrodes through the switching elements. A plurality of pixels arranged in a direction parallel to the scanning line are displayed by the sum of the luminance of the dark-displayed subframe and the luminance of the bright-displayed subframe obtained by time-dividing the luminance of the video signal corresponding to one frame. In a liquid crystal display device that sequentially turns on a direct backlight in synchronization with a scanning signal,
Backlight driving means for lighting the direct type backlight with the same peak luminance for both the dark display subframe period and the bright display subframe period is provided,
In the backlight driving means, the average on-time ratio of the direct type backlight in the dark display sub-frame period is 1/3 or less than the average on-time ratio of the direct type backlight in the bright display sub-frame period. Thus, a liquid crystal display device is characterized in that the direct type backlight is driven to turn on.   2. The liquid crystal display device according to claim 1, wherein the backlight driving means sets the pulse interval of the off-time of the direct type backlight in the sub-frame period of dark display to 3 msec or less.   3. The liquid crystal display device according to claim 1, further comprising a plurality of row lighting driving means for lighting each of the plurality of direct type backlights out of the plurality of direct type backlights.   The liquid crystal display device according to claim 1, wherein the direct type backlight is an LED.   3. The liquid crystal display device according to claim 1, wherein the direct type backlight is a cold cathode tube. A switching element is provided in the vicinity of the intersection of the plurality of data lines and the plurality of scanning lines provided to cross each other, and the data lines are connected to the matrix pixel electrodes through the switching elements. A plurality of pixels arranged in a direction parallel to the scanning line are displayed by the sum of the luminance of the dark-displayed subframe and the luminance of the bright-displayed subframe obtained by time-dividing the luminance of the video signal corresponding to one frame. In a driving method of a liquid crystal display device in which a direct backlight is sequentially turned on in synchronization with a scanning signal,
The direct type backlight is lit at the same peak luminance for both the dark display subframe period and the bright display subframe period, and
The direct type backlight is adjusted so that the average on-time ratio of the direct type backlight in the subframe period of the dark display is 1/3 or less than the average on time ratio of the direct type backlight in the subframe period of the bright display A driving method of a liquid crystal display device, characterized by performing lighting driving.   7. The method of driving a liquid crystal display device according to claim 6, wherein a pulse interval of the off-time of the direct type backlight in the dark display subframe period is set to 3 msec or less. It is a backlight apparatus used for the liquid crystal display device of any one of Claims 1-5,
Each direct type backlight has a dark display period and a bright display period,
The backlight device characterized in that the peak luminance in the dark display period and the bright display period are the same, and the light lighting periods in the dark display period and the bright display period are different from each other. It is a backlight apparatus used for the liquid crystal display device of any one of Claims 1-5,
Each direct type backlight has a dark display period and a bright display period,
The peak luminance of the dark display period and the bright display period are the same, and the bright display period is the same as or longer than the dark display period, and the dark display period and the bright display period are alternately alternated. The backlight device is characterized by being repeated. A driving method of a backlight device used in the liquid crystal display device according to any one of claims 1 to 5,
Each direct type backlight has a dark display period and a bright display period,
A driving method of a backlight device, wherein the peak luminance of the dark display period and the bright display period are the same, and the light lighting periods of the dark display period and the bright display period are different from each other. A driving method of a backlight device used in the liquid crystal display device according to any one of claims 1 to 5,
Each direct type backlight has a dark display period and a bright display period,
The peak luminance of the dark display period and the bright display period are the same, and the bright display period is the same as or longer than the dark display period, and the dark display period and the bright display period are alternately alternated. A method for driving a backlight device, which is repeated.

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