JP2008268540A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device which reduces deterioration in luminance and the occurrence of coloring, then, more effectively remedies moving image blurring in moving image display. <P>SOLUTION: The liquid crystal display device includes: a liquid crystal panel 3 having a plurality of pixel electrodes arranged like a matrix, a plurality of switching elements provided in each of the pixel electrodes, gate lines and source lines connected to each of the switching elements; a back light part 4 which has a plurality of evenly spaced light sources and is disposed at the back surface of the liquid crystal panel 3; a black signal insertion part 2 which operates signals input in the gate lines to insert black signals different from video signals in one frame period; a back light driving part 7 which sequentially turns on or sequentially turns off the light sources according to insertion of the black signals into the black signal insertion part 2; and a back light current control part 6 which controls tube current flowing to the light sources according to insertion of the black signals into the black signal insertion part 2. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device that improves motion blur during moving image display.

  A liquid crystal display (LCD) is characterized by high-definition display, low power consumption, and space saving. In recent years, it has been used in various applications such as computer monitors and television display devices. Used as an alternative to Cathode Ray Tube). However, the liquid crystal display device does not have sufficient image quality in moving image display as compared with the CRT, and in order to further accelerate the replacement of the CRT, improvement of the moving image quality is required.

  One of the reasons why the liquid crystal display device is not superior in image quality of moving image display compared to the CRT is that the liquid crystal display device is a hold-type drive that maintains the display of the current frame until it is rewritten by the video signal of the next frame. to cause. In other words, in TFT-LCD (Thin Film Transistor-LCD), which is often used as a liquid crystal display device, the charge stored by the electric field applied to the liquid crystal is relatively high until a new electric field is applied in the next frame. In this driving method, the electric field applied in the current frame is maintained. Therefore, each pixel of the liquid crystal display device continues to display the same video until an electric field based on the video signal of the next frame is applied and rewritten.

  On the other hand, the CRT performs display by causing the phosphor to emit light by scanning an electron beam. For this reason, in the CRT, since the emission of the phosphor is completed before the electron beam based on the video signal of the next frame is scanned, the display at each pixel becomes an impulse shape. That is, the CRT is an impulse type drive.

  Therefore, the liquid crystal display device has a lower temporal frequency characteristic of image display light than a CRT, and a spatial frequency characteristic is also deteriorated, resulting in motion blur in moving image display. In order to improve the motion blur of the moving image display, in Patent Documents 1 and 2, a black insertion type liquid crystal display that shortens the hold period of the video signal by repeatedly writing the video signal and the black signal within one frame period. An apparatus is disclosed. In Patent Documents 3-6, a scanning backlight lighting type that performs pseudo impulse display by dividing a liquid crystal display panel into a plurality of display areas and sequentially turning on a light source of a backlight corresponding to the display areas. A liquid crystal display device is disclosed.

Japanese Patent Laid-Open No. 9-127717 JP-A-11-109921 JP-A-11-202286 JP 2000-321551 A JP 2001-296838 A JP 2005-128546 A

  However, in the black insertion type liquid crystal display devices disclosed in Patent Documents 1 and 2, the video signal display is held as much as the black signal is inserted (hold) compared to the liquid crystal display device that does not insert black. Period) is shortened. In the black insertion type liquid crystal display device, it is necessary to reach the gradation corresponding to the video signal input within the shortened hold period. In the black insertion type liquid crystal display device, for example, when the black signal insertion rate is 50%, a response speed twice that of a liquid crystal display device without black insertion is required.

  Note that the response speed is increased because the liquid crystal display panel obtains a predetermined transmittance corresponding to the written video signal, so that the gradation of the voltage higher than the gradation voltage corresponding to the input video signal. It can be improved to some extent by adopting the drive to convert to (overdrive drive). However, when the input video signal is a black signal, a high response speed is similarly required, but overdrive driving cannot be applied to a change to zero gradation. Therefore, even if the overdrive drive is adopted in the black insertion type liquid crystal display device, there is a problem that the effect of improving the motion blur is reduced when the black signal cannot be responded within the predetermined hold period. In addition, the black insertion type liquid crystal display device has a problem that the luminance is lowered in accordance with the black signal insertion rate.

  On the other hand, in the scanning backlight lighting type liquid crystal display device disclosed in Patent Documents 3-6, light from a light source that is turned on in a certain divided display region leaks to a display region that is originally intended to be turned off. For this reason, in the scanning backlight lighting type liquid crystal display device, it is impossible to completely suppress the light from the display area to be displayed in black, and as a result, there is a problem that the effect of improving the motion blur is reduced.

  Further, in the scanning backlight lighting type liquid crystal display device, there is a problem that the luminance decreases according to the lighting period of the light source. Furthermore, in the scanning backlight lighting type liquid crystal display device, the light emission (afterglow) characteristics of the light sources R, G, and B are different from each other. There was a problem that.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal display device that reduces a decrease in luminance and occurrence of coloring, and more effectively improves moving image blur during moving image display.

  The solution according to the present invention is a liquid crystal comprising a plurality of pixel electrodes arranged in a matrix, a plurality of switching elements provided on each of the pixel electrodes, and a gate line and a source line connected to each of the switching elements. A display panel, a plurality of light sources are arranged at equal intervals, a backlight unit provided on the back of the liquid crystal display panel, and a signal input to the gate line are operated to be separated from the video signal within one frame period. In accordance with the black signal insertion section for inserting the black signal, the backlight driving section for sequentially turning on or off the light source in accordance with the black signal insertion of the black signal insertion section, and the black signal insertion of the black signal insertion section And a backlight current control unit for controlling the tube current flowing through the light source.

  The liquid crystal display device according to the present invention includes a black signal insertion unit that inserts a black signal different from the video signal within one frame period, a backlight driving unit that sequentially turns on or off the light source, and a tube that flows through the light source. Since the backlight current control unit that controls the current is provided, it is possible to reduce the decrease in luminance and the occurrence of coloring, and more effectively improve the motion blur when displaying motion images.

(Embodiment 1)
First, as described in the background art, one of the factors causing motion blur is a hold-type drive in which the display of the current frame is maintained until the liquid crystal display device is rewritten by the video signal of the next frame. Here, the hold type driving is a driving method in which the electric field applied in the current frame is held at a relatively high rate until the electric field is applied in the next frame, as shown in FIG. On the other hand, the impulse type driving of the CRT is a driving method in which light emission ends before an electric field is applied in the next frame, as shown in FIG. The present invention improves the motion blur by performing a pseudo impulse type drive on a hold type liquid crystal display device.

  Next, the liquid crystal display device according to the present embodiment will be described with reference to FIGS. Here, FIG. 1 is a block diagram showing a configuration of the liquid crystal display device according to the present embodiment. FIG. 2 is a diagram illustrating the timing of the vertical synchronization signal, the video signal, and the black signal input to the liquid crystal display panel of the liquid crystal display device according to the present embodiment. FIG. 3 is a diagram showing the timing of a PWM (Pulse Width Modulation) waveform input to the backlight driving unit of the liquid crystal display device according to the present embodiment.

  The liquid crystal display device shown in FIG. 1 includes a scaling / signal processing unit 1, a black signal insertion unit 2, a liquid crystal display panel 3, a direct backlight 4, a PWM generation / control unit 5, and a backlight current control unit 6. And a backlight drive unit 7. The scaling / signal processing unit 1 performs scaling and necessary signal processing on the input video signal and synchronization signal. The black signal insertion unit 2 operates a control signal input to the gate line of the liquid crystal display panel 3 to repeatedly write the video signal and the black signal within one frame period, and inserts the black signal display into the video signal display. To do. Although not shown, the liquid crystal display panel 3 includes a plurality of pixel electrodes arranged in a matrix, a plurality of switching elements provided on the pixel electrodes, and a plurality of gate lines and sources connected to the switching elements, respectively. And display a video.

  The direct backlight 4 includes a plurality of first to n-th light sources (first direct backlight to n-th direct backlight) arranged at equal intervals, and is provided on the back surface of the liquid crystal display panel 3. The PWM generation / control unit 5 generates a PWM signal for driving the direct backlight 4 at the timing of inserting the black signal based on the output of the scaling / signal processing unit 1. The PWM generation / control unit 5 includes a first PWM generation / control unit to an n-th PWM generation / control unit corresponding to each of the first direct backlight to the n-th direct backlight.

  The backlight current control unit 6 controls the current value (tube current) that flows to each light source (first direct backlight to nth direct backlight) of the direct backlight 4 based on an instruction from the PWM generation / control unit 5. To do. The backlight current control unit 6 also includes a first backlight current control unit to an nth backlight current control unit corresponding to each of the first direct backlight to the nth direct backlight. The backlight drive unit 7 drives the direct backlight 4 based on the PWM signal. The backlight drive unit 7 also includes a first backlight drive unit to an nth backlight drive unit corresponding to each of the first direct backlight to the nth direct backlight.

  Next, the operation of the liquid crystal display device shown in FIG. 1 will be described. First, the scaling / signal processing unit 1 generates a vertical synchronization signal (hereinafter also referred to as a panel vertical synchronization signal) necessary for driving the liquid crystal display panel 3 based on an input video signal and a synchronization signal, and an image on the liquid crystal display panel 3. A control signal (hereinafter also referred to as a write video signal) necessary for writing the signal is generated. Then, the scaling / signal processing unit 1 supplies the panel vertical synchronization signal and the write video signal to the black signal insertion unit 2 and simultaneously supplies the panel vertical synchronization signal to the PWM generation / control unit 5.

  The black signal insertion unit 2 operates a control signal input to the gate line of the liquid crystal display panel 3 based on the panel vertical synchronization signal and the video signal, and generates a signal for repeatedly writing the video signal and the black signal within one frame period. The liquid crystal display panel 3 is supplied. That is, the black signal insertion unit 2 shortens the hold period (video display period) for displaying the video signal between the scanning of the frame of a certain video signal and the scanning of the next frame, and the liquid crystal display panel 3, a control signal (hereinafter also referred to as a writing black signal) necessary for writing a black signal is inserted.

  In the PWM generation / control unit 5, the first PWM generation / control unit to the n-th PWM generation / control unit correspond to the first direct backlight to the n-th direct backlight in synchronization with the input panel vertical synchronization signal. The generated PWM signal is generated. The generated PWM signal is supplied to the backlight current control unit 6. The backlight current control unit 6 supplies to the backlight drive unit 7 a tube current control signal for controlling the tube current that flows to each of the first direct backlight to the nth direct backlight according to the duty ratio of the PWM signal. .

  The backlight drive unit 7 drives the direct backlight 4 of the first direct backlight to the nth direct backlight according to the input PWM signal and tube current control signal.

  Next, the black signal insertion timing and direct backlight lighting timing of the liquid crystal display device according to this embodiment will be described with reference to FIGS. First, as shown in FIG. 2, the black signal insertion unit 2 supplies a writing black signal in addition to supplying a writing video signal to each gate line (G1 to Gn) within one frame period. In the liquid crystal display device according to the present embodiment, a video signal is supplied from the source line to each pixel electrode in response to a write video signal, and a black signal is supplied from the source line to each pixel electrode in response to a write black signal. Is supplied. Therefore, in the liquid crystal display device according to this embodiment, a period (black period) for displaying a black signal can be inserted into a period for displaying a video signal by performing the above-described series of operations within one frame period. it can.

  As shown in FIG. 2, the write video signal input to each gate line (G1 to Gn) is timed so that the write video signal is input to all the gate lines (G1 to Gn) during one frame period. Are entered with little by little. That is, the write video signal is input to all n gate lines and one frame period is completed. In the liquid crystal display device according to the present embodiment, in addition to the writing video signal, a writing black signal is sequentially input to each gate line (G1 to Gn) after a predetermined time has elapsed from the writing video signal. Note that the writing video signal and the writing black signal are synchronized with the panel vertical synchronization signal.

  Therefore, when the video period in which the video signal is displayed on the liquid crystal display panel 3 and the black period in which the black signal is displayed are schematically shown, the display of the liquid crystal display panel 3 in FIG. The liquid crystal display panel 3 displays an image while gradually shifting.

  Furthermore, in the liquid crystal display device according to the present embodiment, the PWM generation / control unit 5 generates n PWM signals (first PWM signal to n-th PWM signal) corresponding to n direct backlights at the timing shown in FIG. Generate. That is, the duty ratio and phase of the PWM signal are determined so that the direct backlight is turned off corresponding to the black period of the liquid crystal display panel 3 shown in FIG. Then, when the black signal is written in the liquid crystal display panel 3 by the writing black signal based on the PWM signal, the backlight driving unit 7 sequentially turns off the direct backlight 4 corresponding to the display area in which the black signal is written. Drive as you do.

  Note that the number of gate lines and the number of direct backlights are usually different, and the number of direct backlights is smaller than the number of gate lines. Therefore, since one direct backlight corresponds to a plurality of gate lines, the timing of turning on / off the direct backlight is one of the corresponding plurality of gate lines as shown in FIG. To match. Specifically, when one direct backlight corresponds to 10 gate lines (G1 to G10), the timing of turning on / off the direct backlight is, for example, the timing of the black period of the gate line (G5). To match. Therefore, there is a period in which the direct backlight is lit at the timing when the black signal is written to the gate lines (G1 to G4).

  Furthermore, in the liquid crystal display device according to the present embodiment, the backlight current control unit 6 changes the tube current flowing through the direct backlight 4 according to the duty ratio of the PWM signal. That is, when the duty ratio of the PWM signal is reduced in order to improve moving image blur, the backlight current control unit 6 increases the tube current, thereby reducing a decrease in luminance due to black signal insertion and backlight scanning.

  As described above, in the liquid crystal display device according to the present embodiment, a black signal is inserted within one frame period in order to improve motion blur. However, when the liquid crystal display device cannot respond to black within a specified time due to insufficient response speed of the liquid crystal. Then, the direct backlight 4 corresponding to the black display area is turned off. Thereby, in the liquid crystal display device according to the present embodiment, it is possible to more effectively improve the motion blur. Furthermore, in the liquid crystal display device according to the present embodiment, the reduction in luminance is reduced by controlling the tube current of the direct backlight 4 in accordance with the black signal insertion.

(Embodiment 2)
The liquid crystal display device according to the present embodiment will be described with reference to FIGS. Here, FIG. 4 is a diagram illustrating the timing of the vertical synchronization signal, the video signal, and the black signal input to the liquid crystal display panel of the liquid crystal display device according to the present embodiment. FIG. 5 is a diagram showing the timing of the PWM waveform input to the backlight drive unit of the liquid crystal display device according to the present embodiment. Note that the configuration of the liquid crystal display device according to the present embodiment is the same as the configuration shown in FIG.

  The black signal insertion unit 2 according to the present embodiment, as shown by an arrow a in FIG. 4, starts from the time when the gate line is written to write the video signal to the time when the gate line is raised to write the black signal. And the black insertion rate (ratio of black signals) can be arbitrarily changed.

  Further, the PWM generation / control unit 5 according to the present embodiment can arbitrarily change the duty ratio and phase of the PWM signal as shown in FIG. In FIG. 5, the lighting timing of the direct backlight 4 can be arbitrarily set by shifting the phase of the PWM signal as indicated by an arrow b. In FIG. 5, the lighting period of the direct backlight 4 can be arbitrarily set by changing the duty ratio of the PWM signal as indicated by an arrow c.

  Furthermore, the backlight current control unit 6 according to the present embodiment can arbitrarily change the tube current flowing through the direct backlight 4 within a range that the direct backlight 4 can tolerate, according to the duty ratio of the PWM signal.

  In the liquid crystal display device according to the present embodiment, the black insertion rate is increased and the duty ratio of the PWM signal is set to be small, which causes image degradation and luminance reduction due to flickering, but can increase the motion blur improvement effect. it can. On the contrary, in the liquid crystal display device according to the present embodiment, by reducing the black insertion ratio and setting the duty ratio of the PWM signal to be large, the effect of improving the motion blur is reduced, but the image deterioration and the luminance decrease due to flickering are reduced. It becomes possible to make it small, and the degree of freedom of the user increases. Further, in the liquid crystal display device according to the present embodiment, the tube current can be reduced by the backlight current control unit 6 when it is desired to reduce the luminance when used in an environment where the peripheral luminance is low.

  Furthermore, in the liquid crystal display device according to the present embodiment, for example, the user can freely set the black insertion rate, the duty ratio and phase of the PWM signal, and the tube current value by OSD (on-screen display). In addition, it is possible to achieve image quality that meets the characteristics of the liquid crystal display panel 3, the type of input video, user preferences, and the like.

(Embodiment 3)
A liquid crystal display device according to the present embodiment will be described with reference to FIGS. Here, FIGS. 6A and 6B are diagrams schematically showing the backlight emission waveform and the liquid crystal response waveform of the liquid crystal display device according to the present embodiment. Note that the configuration of the liquid crystal display device according to the present embodiment is the same as the configuration shown in FIG.

  As shown in FIGS. 6A and 6B, the direct backlight 4 has a light emission (afterglow) characteristic that the response of the green phosphor is slower than that of the red and blue phosphors. Therefore, as shown in FIG. 6A, magenta (RB color) coloring occurs when the writing of the video signal has started or the writing has been completed when the direct backlight 4 is turned on. Further, as shown in FIG. 6A, when the writing of the black signal starts when the direct backlight 4 is turned off or when the writing is completed, green (G color) coloring occurs.

  Therefore, in the liquid crystal display device according to the present embodiment, the PWM generation / control unit 5 controls the PWM signal, and the direct backlight 4 is turned on before the video signal writing starts as shown in FIG. The direct backlight 4 is turned off before writing of the black signal is started. That is, in the liquid crystal display device according to the present embodiment, unnatural coloring due to the light emission (afterglow) characteristics of the direct backlight 4 is reduced by controlling the black insertion rate and the duty ratio and phase of the PWM signal. be able to.

(Embodiment 4)
The liquid crystal display device according to this embodiment will be described with reference to FIGS. Here, FIG. 7 is a block diagram showing a configuration of the liquid crystal display device according to the present embodiment. FIG. 8 is a diagram for explaining the influence of the previous frame on the current frame when a black signal is inserted. Note that in the configuration of the liquid crystal display device according to the present embodiment, the same components as those illustrated in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  In addition to the liquid crystal display device shown in FIG. 1, the liquid crystal display device shown in FIG. 7 performs gradation conversion of the video signal so that the liquid crystal display panel 3 obtains a predetermined transmittance corresponding to the written video signal. An overdrive unit 8 to perform and a temperature detection unit 9 to detect the temperature of the liquid crystal display panel 3 are provided. Note that the gradation conversion of the video signal performed by the overdrive unit 8 converts the gradation of the current frame in accordance with the previous frame in order to obtain a target transmittance within a predetermined period.

  Here, the required response speed of the liquid crystal depends on the black insertion rate. Specifically, when the black insertion rate is set to 50%, the response speed of the liquid crystal needs to be twice as high as that of the normal liquid crystal in order to respond to achieve the target transmittance at least within the hold period of the video signal. Become. Furthermore, the response speed of the liquid crystal is highly temperature dependent. That is, when the temperature is low, the response speed of the liquid crystal is slow, and when the temperature is high, the response speed of the liquid crystal is fast.

  As shown in FIG. 2 of Embodiment 1 and FIG. 4 of Embodiment 2, in a liquid crystal display device into which a black signal is inserted, theoretically, writing of a video signal always changes from the black signal. However, in an actual liquid crystal display device, as shown in FIG. 8, since the arrival gradation of the written black signal differs depending on the gradation of the previous frame, the writing of the video signal is not always a change from the black signal. Furthermore, video signal writing does not always change from a certain gradation, and depends on the gradation of the previous frame.

  In addition, if the amount of gradation conversion is too large, the overdrive unit 8 generates an unnatural pseudo contour in the contour portion of the image when displaying a moving image. If the amount is too small, the overdrive unit 8 achieves a target transmittance within a predetermined time. Cannot be reached, resulting in motion blur. Further, even when the video signal is a still image, the writing of the video signal is not always changed from the black signal. In this case, when the overdrive unit 8 operates, the amount of gradation conversion is not optimal between the gradations. For example, when a gradation image is displayed, the display gradation is reversed and smooth display is not achieved. Further, when a natural image is displayed, coloring that is not present in the original video occurs.

  As described above, the gradation conversion by the overdrive unit 8 depends on the black insertion rate, the temperature of the liquid crystal display panel 3, and the gradation of the previous frame, so that optimization is very difficult. Therefore, in the liquid crystal display device according to the present embodiment, the black insertion rate is obtained from the scaling / signal processing unit 1 and the temperature of the liquid crystal display panel 3 is obtained from the temperature detection unit 9 as shown in FIG. Controls the amount of key conversion (overdrive amount). Further, in the liquid crystal display device according to the present embodiment, as shown in FIG. 7, the overdrive unit 8 is provided before the processing of the black signal insertion unit 2, and when the video signal is a still image, tone conversion of the video signal is performed. If the video signal is a moving image, the video signal is subjected to gradation conversion by comparing the video signal of the previous frame with the video signal of the frame.

  As a result, in the liquid crystal display device according to the present embodiment, an appropriate black insertion rate and the temperature of the liquid crystal display panel 3 are input, and not according to the black signal, but according to the gradation of the video signal of the previous frame. Optimal overdrive processing (gradation conversion) can be realized. In addition, in the liquid crystal display device according to the present embodiment, since the overdrive process is not performed in the case of a still image, a phenomenon that the display gradation is reversed when a gradation image is displayed, or a natural image is displayed. The effect that the coloring of the case does not occur is obtained.

(Embodiment 5)
A liquid crystal display device according to the present embodiment will be described with reference to FIG. Here, FIG. 9 is a block diagram showing a configuration of the liquid crystal display device according to the present embodiment. Note that in the configuration of the liquid crystal display device according to this embodiment, the same components as those illustrated in FIG. 7 are denoted by the same reference numerals, and detailed description thereof is omitted.

  The liquid crystal display device shown in FIG. 9 includes a light detection unit 10 that detects the intensity of light emitted from the liquid crystal display panel 3 in addition to the liquid crystal display device shown in FIG. As described in the first embodiment, it is necessary to optimally set the phase of the PWM signal for driving the direct backlight 4 with respect to the timing of the writing video signal and the writing black signal in order to improve the motion blur. Further, when the phase of the PWM signal is optimally set and the amount of gradation conversion (overdrive amount) is optimized as described in the fourth embodiment, the intensity of light emitted from the liquid crystal display panel 3 is as follows. Maximum.

  Therefore, in the liquid crystal display device according to the present embodiment, the light detection unit 10 that detects the light intensity is provided, and the light emitted from the liquid crystal display panel 3 is adjusted based on the detection result by adjusting the phase of the PWM signal. By maximizing the intensity of the image, it is possible to improve the motion blur more effectively.

(Embodiment 6)
A liquid crystal display device according to the present embodiment will be described with reference to FIG. Here, FIG. 10 is a block diagram showing a configuration of the liquid crystal display device according to the present embodiment. Note that in the configuration of the liquid crystal display device according to this embodiment, the same components as those illustrated in FIG. 7 are denoted by the same reference numerals, and detailed description thereof is omitted.

  The liquid crystal display device shown in FIG. 10 includes a chromaticity detection unit 11 that detects the chromaticity of light emitted from the liquid crystal display panel 3 in addition to the liquid crystal display device shown in FIG. As described in the third embodiment, unnatural coloring occurs due to the phase of the PWM signal that drives the direct backlight 4 with respect to the timing of the writing video signal and the writing black signal. If the unnatural coloring can be improved, the chromaticity emitted from the liquid crystal display panel 3 is equivalent to the case where the black insertion rate is 0% and the duty ratio of the PWM signal is 100%.

  As described above, the liquid crystal display device according to the present embodiment includes the chromaticity detection unit 11 that detects the chromaticity of the light emitted from the liquid crystal display panel 3, and the phase of the PWM signal is determined based on the detection result. By adjusting and optimizing the chromaticity of the light emitted from the liquid crystal display panel 3, it is possible to more effectively improve the motion blur.

(Embodiment 7)
A liquid crystal display device according to the present embodiment will be described with reference to FIG. Here, FIG. 11 is a block diagram showing a configuration of the liquid crystal display device according to the present embodiment. Note that in the configuration of the liquid crystal display device according to the present embodiment, the same components as those illustrated in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  The liquid crystal display device shown in FIG. 11 includes a video motion detection unit 12 that detects whether the video signal is a still image or a moving image in addition to the liquid crystal display device shown in FIG. When the video signal is a still image, image degradation due to flicker may occur when the video signal is subjected to the above-described control for improving the motion blur.

  Therefore, in the liquid crystal display device according to the present embodiment, the video motion detection unit 12 is provided, and the detection result is supplied to the black signal insertion unit 2 and the PWM generation / control unit 5. The black signal insertion unit 2 does not start a gate line for writing a black signal based on the detection result, and the PWM generation / control unit 5 sets the duty ratio of the PWM signal to 100% based on the detection result. To do. That is, in the liquid crystal display device according to the present embodiment, when the video signal is a still image, the black insertion rate is set to 0% and the scanning backlight is turned off, thereby displaying a flicker-free image on the still image. Yes.

  In the video motion detection unit 12 according to the present embodiment, the ratio of the black signal inserted by the black signal insertion unit 2 (black insertion rate) by delaying the timing for detecting whether the video signal is a still image or a moving image. Alternatively, the lighting time of the direct backlight 4 controlled by the backlight driving unit 7 is changed stepwise. Thereby, in the liquid crystal display device according to the present embodiment, it is possible to reduce a sense of discomfort when the video signal is switched from a still image to a moving image or from a moving image to a still image.

1 is a block diagram of a liquid crystal display device according to Embodiment 1 of the present invention. 3 is a timing chart of the liquid crystal display device according to Embodiment 1 of the present invention. 4 is a timing chart of PWM signals of the liquid crystal display device according to Embodiment 1 of the present invention. It is a timing chart of the liquid crystal display device which concerns on Embodiment 2 of this invention. It is a timing chart of the PWM signal of the liquid crystal display device which concerns on Embodiment 2 of this invention. It is a figure for demonstrating the timing of writing of the liquid crystal display device which concerns on Embodiment 3 of this invention. It is a block diagram of the liquid crystal display device which concerns on Embodiment 4 of this invention. It is a figure for demonstrating writing of the liquid crystal display device which concerns on Embodiment 4 of this invention. It is a block diagram of the liquid crystal display device which concerns on Embodiment 5 of this invention. It is a block diagram of the liquid crystal display device which concerns on Embodiment 6 of this invention. It is a block diagram of the liquid crystal display device which concerns on Embodiment 7 of this invention. It is a figure for demonstrating hold type drive and impulse type drive.

Explanation of symbols

  1 Scaling / Signal Processing Unit, 2 Black Signal Insertion Unit, 3 Liquid Crystal Display Panel, 4 Direct Backlight, 5 PWM Generation / Control Unit, 6 Backlight Current Control Unit, 7 Backlight Drive Unit, 8 Overdrive Unit, 9 Temperature Detection unit, 10 light detection unit, 11 chromaticity detection unit, 12 video motion detection unit.

Claims (12)

A liquid crystal display panel comprising a plurality of pixel electrodes arranged in a matrix, a plurality of switching elements provided on each of the pixel electrodes, and a gate line and a source line connected to each of the switching elements;
A plurality of light sources are arranged at equal intervals, a backlight unit provided on the back surface of the liquid crystal display panel,
A black signal insertion unit that operates a signal input to the gate line and inserts a black signal different from the video signal within one frame period;
In accordance with the insertion of the black signal of the black signal insertion unit, a backlight driving unit that sequentially turns on or off the light source;
A liquid crystal display device comprising: a backlight current control unit that controls a tube current flowing through the light source in accordance with the insertion of the black signal in the black signal insertion unit. The liquid crystal display device according to claim 1,
The liquid crystal display device according to claim 1, wherein the black signal insertion unit can arbitrarily change a ratio of the black signal inserted within one frame period. The liquid crystal display device according to claim 1 or 2,
The liquid crystal display device, wherein the backlight driving section can arbitrarily change the lighting timing of the light source. A liquid crystal display device according to any one of claims 1 to 3,
The liquid crystal display device, wherein the backlight driving unit can arbitrarily change a duty ratio of the light source. A liquid crystal display device according to any one of claims 1 to 4,
The liquid crystal display device, wherein the backlight current control unit changes the tube current based on a lighting period of the light source. A liquid crystal display device according to any one of claims 1 to 5,
The backlight driving unit turns on the light source corresponding to the pixel to which the video signal is written before the video signal is written within one frame period, and turns off the light source after writing the black signal. A liquid crystal display device characterized by the above. A liquid crystal display device according to any one of claims 1 to 6,
A temperature detector for detecting the temperature of the liquid crystal display panel;
Before writing the black signal within one frame period, an overdrive unit that performs gradation conversion of the video signal so that the liquid crystal display panel obtains a predetermined transmittance corresponding to the written video signal. In addition,
The liquid crystal display device, wherein the overdrive unit determines a value for gradation conversion of the video signal based on a result of the temperature detection unit and a ratio of the black signal. The liquid crystal display device according to claim 7,
The overdrive unit is provided before the processing of the black signal insertion unit, and when the video signal is a still image, gradation conversion of the video signal is not performed, and when the video signal is a moving image, one frame before A liquid crystal display device that performs gradation conversion of the video signal by comparing the video signal of the video signal with the video signal of the frame. The liquid crystal display device according to claim 7 or 8,
A light detection unit for detecting the light intensity emitted from the liquid crystal display panel;
The backlight driving unit controls the lighting timing and extinguishing timing of the light source so as to have a predetermined phase relationship with the writing timing of the video signal according to the light intensity detection result of the light detection unit. Liquid crystal display device. The liquid crystal display device according to claim 7 or 8,
A chromaticity detection unit that detects chromaticity of light emitted from the liquid crystal display panel;
The backlight driving unit controls lighting timing and extinguishing timing of the light source so as to have a predetermined phase relationship with the video signal writing timing according to a chromaticity detection result of the chromaticity detection unit. A liquid crystal display device. A liquid crystal display device according to any one of claims 1 to 6,
A video motion detector for detecting whether the video signal is a still image or a moving image;
When the video motion detection unit detects the video signal as a still image, the black signal insertion unit sets the ratio of the black signal to be inserted within one frame period to 0%,
The liquid crystal display device, wherein the backlight driving unit continues lighting the light source for one frame period. The liquid crystal display device according to claim 11,
The video motion detection unit delays the timing for detecting whether the video signal is a still image or a moving image,
The liquid crystal display device, wherein the ratio of the black signal inserted by the black signal insertion unit or the lighting time of the light source controlled by the backlight driving unit is changed stepwise.

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