JP2004355017A - Liquid crystal display device and its driving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make display of high picture quality corresponding to a moving picture to be displayed. <P>SOLUTION: A signal line driving circuit can supply an image signal for (p) (p: an integer of ≥2) gradations and the image signal is turned to an image signal for displaying a picture with the (p) gradations, when a still picture is displayed, a multi-gradation display system is used which makes 2p-gradation display for a one-frame period and when a moving picture is displayed, one frame is divided into at least 1st and 2nd subfields to display the original image in the 1st subfield and an interpolated image in the 2nd subfield. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a liquid crystal display device and a driving method thereof.

  As a conventional image display device, an impulse-type display device (for example, a CRT) that emits light only for the afterglow time of the phosphor after writing an image, and keeps displaying the previous frame until a new image is written. Hold type display devices (for example, liquid crystal display devices (hereinafter, referred to as LCDs)) are roughly classified into two types.

  A problem with the hold-type display device is a blur phenomenon that occurs in displaying moving images. As shown in FIG. 20, when the eyes follow the motion of the moving object, the blur phenomenon occurs even when the picture of the previous frame is switched to the image of the next frame, and the image of the same previous frame is continuously displayed. Nevertheless, it occurs when the eye observes while moving on the previous frame image. In other words, the following movement of the eye is continuous and finely sampled, and as a result, the image is visually observed by the observer so as to fill the image between the previous frame and the next frame, and is observed as blurred.

In order to solve this problem, one frame is divided into two fields, that is, the first field is controlled by an analog control of light transmission with one polarity and the operation characteristics of a monostable liquid crystal material that does not transmit light with the other polarity. Canon has proposed a field inversion method in which the image is divided into a first field and a second field, and the first field is transparent and the second field is not transparent (for example, see Patent Document 1). Also, a display device of a liquid crystal panel using a bent alignment cell has been proposed by International Business Machines Corporation (for example, see Patent Document 2). In any of the proposals, a period for displaying an image and a period for displaying a black image are provided to approximate the impulse display.
JP 2000-10076 A JP-A-11-109921

  However, in the former proposal, the time required for both polarities must be made equal so that no DC component remains in the liquid crystal material, and the operation mode becomes 50% duty. Here, the duty ratio is defined as in the following equation.

Duty ratio = display period / (display period + non-display period) × 100-(1)
In the latter proposal, since the number of screen divisions must be increased in order to change the duty ratio, display unevenness due to variations in the signal line drive circuit (a luminance change such as joining occurs) or duty In order to change the ratio, the scanning line driving frequency must be changed, and it is difficult to set the duty ratio finely. For this reason, there is a problem that high-quality display cannot be performed according to the display image.

  In many liquid crystal display devices, the number of gradations of each color RGB (R = red, G = green, B = blue) for expressing colors is 64 gradations (6 bits). And the number of display colors is required to be large. Therefore, the number of colors is increased by using a frame rate control (hereinafter, also referred to as FRC) technique of performing display a plurality of times during one frame period. However, in experiments by the inventors, it was partially confirmed that even if the number of colors in a moving image was made smaller than that in a still image, the difference could not be recognized much.

  The present invention has been made in consideration of the above circumstances, and has as its object to provide a liquid crystal display device capable of performing high-quality display according to a display image and a driving method thereof.

A method for driving a liquid crystal display device according to a first aspect of the present invention includes: a scanning line formed on a first substrate; a signal line formed on the first substrate so as to intersect the scanning line; An array substrate having a plurality of pixels formed at each intersection of the scanning lines and the signal lines, and a plurality of switching elements that are opened and closed by a voltage of the scanning lines and transmit signals from the signal lines to the pixels; A counter substrate having a counter electrode formed on the substrate; a liquid crystal layer sandwiched in a gap between the array substrate and the counter substrate; and a signal for driving the signal line to supply an image signal to the signal line. A line driving circuit, and a driving method of a liquid crystal display device comprising the same,
The signal line drive circuit can supply the image signal for p (p is an integer of 2 or more) gradations, and displays the still image as the image signal for displaying an image for p gradations. In this case, a multi-gradation display method in which 2p gradation display is performed over one frame period is used, and when displaying a moving image, one frame is divided into at least first and second sub-fields. Displays an original image, and displays an interpolated image in the second subfield.

  The liquid crystal display device according to the second aspect of the present invention may further comprise a scanning line formed on the first substrate, a signal line formed on the first substrate so as to intersect the scanning line, and An array substrate having a plurality of pixels formed at each intersection of a signal line and the signal line, a switching element that opens and closes by a voltage of the scanning line, and sends a signal from the signal line to the pixel; A liquid crystal layer sandwiched in a gap between the array substrate and the counter substrate, and first to m-th (m is an integer of 2 or more) signals to the signal lines. A signal line driving circuit for driving the signal lines to supply the signals, a scanning line driving circuit for sequentially selecting and driving the scanning lines based on a scanning line signal and an output control signal, and a frame based on an image signal and a synchronization signal. Whether the image is a video or a still image A motion discrimination processing unit for discriminating, and generating the first to m-th signals, the scanning line signal, and the output control signal based on the image signal, the synchronization signal, and the output of the motion discrimination processing unit; A gate array unit that sends the first to m-th signals to the signal line driving circuit and sends the scanning line signal and the output control signal to the scanning line driving circuit.

  According to the present invention, as a display method of a liquid crystal panel using a high-speed response liquid crystal, image quality can be significantly improved by increasing the driving frequency of a signal line driving circuit. More specifically, means for changing the duty ratio between image display and black display according to the display image (still image and moving image), or multi-gradation display using FRC for still image and high refresh using interpolation image for moving image By using the display means, a high image quality display is provided in which color reproducibility is improved for a still image and sharpness is improved for a moving image.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to these embodiments.

(First Embodiment)
A first embodiment of the present invention will be described. The first embodiment is a liquid crystal display device, and FIG. 1 shows a configuration of the liquid crystal display device. FIG. 1 shows a configuration of a liquid crystal module (an array configuration of a liquid crystal panel and peripheral circuits) according to the liquid crystal display device. It is shown in FIG. The liquid crystal display device 1 according to the first embodiment includes a gate array 10, a motion determination processing unit 20, and a liquid crystal module 60.

  The gate array 10 receives the first to m-th signals, the scanning line signal, and the output control signal based on an image signal and a synchronization signal transmitted from the outside and a display method instruction signal transmitted from the motion determination processing unit 20. A signal is generated, the first to m-th signals are sent to the signal line driving circuit 80, and the scanning line signal and the output control signal are sent to the scanning line driving circuit 70. The motion determination processing unit 20 captures frame images at predetermined intervals based on the image signal and the synchronization signal, checks a correlation between two continuously captured frame images, and determines whether the two frame images are moving images. Or a still image. This determination result is sent to the gate array 10 as image information included in the display mode instruction signal.

The liquid crystal module 60 includes a liquid crystal panel 61, a scanning line driving circuit 70, and a signal line driving circuit 80. As shown in FIG. 2, the signal line driving circuit 80 and the scanning line driving circuit 70 are driven depending on the number of output pins (for example, 240 pin output) and the definition of the liquid crystal panel (for example, 640 × 3 × 480 in VGA). How many circuits are arranged (for example, eight horizontally and two vertically) is determined. In Figure 2, the liquid crystal module 60 includes a plurality of scan line driver circuits ₇₀ 1, 70 _2, and is configured with a plurality of signal line driving circuits ₈₀ 1, 80 _2. The liquid crystal panel 61 includes an array substrate (not shown), a counter substrate (not shown), and a liquid crystal layer sandwiched between these substrates. The array substrate includes a plurality of scanning lines 62 formed on a first transparent substrate (not shown) and a plurality of signal lines formed on the first transparent substrate so as to intersect the plurality of scanning lines. 63, a pixel electrode (also referred to as a pixel) 64 formed at each intersection of the scanning line and the signal line, and provided corresponding to the pixel electrode. A switching element (TFT (Thin Film Transistor)) 65 for transmitting an image signal from a line to a corresponding pixel electrode. The TFT 65 has a configuration in which the gate is connected to the corresponding scanning line 62, the source is connected to the corresponding signal line 63, and the drain is connected to the corresponding pixel electrode 64. In the counter substrate, a counter electrode is provided on the second transparent substrate so as to face the pixel electrode. Scan 62 is driven by the scanning line driving circuit ₇₀ 1, 70 _2, signal lines 63 are driven by the signal line driving circuit ₈₀ 1, 80 _2.

  The liquid crystal material in the liquid crystal panel 61 may be of any kind, but in the present invention in which the display is switched a plurality of times during one frame period, a high-speed responsive one is preferable. For example, a ferroelectric liquid crystal material, a liquid crystal material having spontaneous polarization induced by applying an electric field (for example, antiferroelectric liquid crystal (AFLC)), Iso. A liquid crystal material obtained by monostabilizing a ferroelectric liquid crystal material having a -Ch-SmC * layer transition series, an OCB (Optically Compensated Bend) mode, or the like is used. Further, depending on how the two polarizing plates are attached to the liquid crystal panel 61, a mode in which light is not transmitted when no voltage is applied (normally black) and a mode in which light is transmitted (normally white) can be set. 3 (a), 3 (b) and 3 (c) show alignment states when AFLC is used, and FIG. 4 shows a voltage-transmittance curve when two polarizing plates are arranged in crossed Nicols. Is shown. As shown in FIG. 3 (a), when no voltage is applied, the liquid crystal molecules are arranged alternately, canceling spontaneous polarization, and do not transmit light, resulting in a black display, but as shown in FIGS. 3 (b) and 3 (c). When the voltage is applied to the positive polarity side or the negative polarity side as described above, the liquid crystals are arranged in one direction, and the optical axis is rotated to be in the transmission mode. The difference between the TN modes is that the arrangement of the liquid crystal differs only depending on the polarity of the voltage, and there is no particular problem in the present invention. Further, depending on the intensity of the voltage applied between the electrodes, not only three orientations, that is, a no-voltage application state, a positive voltage application state, and a negative voltage application state, but also an intermediate orientation between them can be arbitrarily set.

As shown in FIG. 1, an image signal and a synchronization signal input from the outside are input to a gate array 10 and a motion determination processing unit 20 of the liquid crystal display device 1. The motion determination processing unit 20 determines whether the input image is a moving image or a still image. The motion discrimination processing unit 20 may be of any type. For example, a 5 as shown in the three frame memories _{23 1,} 23 2, 23 _3, the image from the first frame memory 23 ₁ Repeat third to the frame memory 23 ₃ through the input switch 21 is input May be adopted. For example, the first input to the frame memory 23 _1, after the input termination second to the frame memory 23 _2, the third frame memory 23 at the same time as ₃ going to enter the image into the first frame memory 23 within _one image The difference detection and determination unit 25 checks the correlation between the image and the image in the _second frame memory 232. A frame memory that is not selected can be determined by transmitting a frame memory selection signal indicating which frame memory is currently input with an image from the input changeover switch 21 to the difference detection and determination unit 25. Be eligible. The difference detection may be performed on the entire screen or on a block basis. Only the upper bits may be detected without checking all the bits of the red (R), green (G), and blue (B) pixels. If the obtained difference signal is larger than a certain threshold, it is determined as a moving image, and if smaller, it is determined as a still image. The determination result is sent to the gate array 10 as a display mode instruction signal. The gate array 10 receives the display mode instruction signal and receives the first to m-th signals (including an image signal, a horizontal synchronization signal (hereinafter also referred to as STH), and a horizontal clock (hereinafter also referred to as Hclk)), and scanning. A line signal (vertical synchronization signal (hereinafter also referred to as STV), a vertical clock (hereinafter also referred to as Vclk)) and an output control signal are transmitted to the liquid crystal module 60.

  Next, peripheral circuits in the liquid crystal module 60 will be described. Normally, the liquid crystal module 60 includes a liquid crystal panel 61 and its peripheral circuits. As the peripheral circuits, there are a signal line driving circuit 80 and a scanning line driving circuit 70. The scanning line driving circuit 70 has a shift register. As shown in FIG. 6, when the scanning line signal is input to the scanning line driving circuit 70, after the vertical synchronization signal STV is latched by the shift register in the scanning line driving circuit 70, the vertical synchronizing signal STV is latched according to the vertical clock Vclk. A signal having a pulse width equivalent to that of the synchronization signal STV (hereinafter referred to as a write signal) is sequentially shifted and transferred to the shift register.

  On the other hand, the output control signal controls the output of the scanning line driving circuit 70. When a write signal is input to the shift register when the output control signal is ON, writing of the scanning line is performed (see FIG. 6G), and when the output control signal is OFF, the write signal is shifted to the above-described shift register. The scanning line driving circuit 70 is configured so that when the data is input to the register, the writing of the scanning line is not performed (see FIG. 6F). The voltage waveform of the dashed line in FIG. 6F indicates a voltage waveform that will appear on the scanning line when the output control signal is ON.

Even if one scanning line driving circuit is divided into several blocks and output control is performed based on such a control method as a basic configuration, the same operation as described above can be performed. Further, by inputting a different output control signals for each scanning line driving circuit, the scanning line driving circuit 70 ₁ shown in FIG. 2, for example the OFF output, the scanning line driving circuit 70 ₂ may also be turned ON output . In the following embodiments, the writing of each scanning line is controlled using this control method.

  Next, a description will be given of a driving method for displaying 50% duty in a moving image and 100% duty in a still image when the liquid crystal display device of the present embodiment is normally black. When a backlight that is always lit is used, a voltage must be applied between pixels in order to display black. Therefore, as shown in FIG. 7 (a), when writing is completed up to the half scanning line on the screen, the first scanning line is selected, and the black signal as the second signal is connected to the first scanning line. Write to existing pixels. Similarly, as shown in FIG. 7B, when Gall is the total number of scanning lines, the first signal is written to the pixel on the Gall / 2 + 1st scanning line, and then the second signal is written to the pixel on the second scanning line. Write a signal. Subsequently, as shown in FIG. 7C, the first signal is written to the pixel on the Gall-th scanning line, and then the second signal is written to the pixel on the Gall / 2-1st scanning line. Next, as shown in FIG. 7D, the first signal is written to the pixel on the first scanning line, and then the second signal is written to the pixel on the Gall / 2nd scanning line. Then, as shown in FIG. 7E, the first signal is written to the pixels on the Gall-th scanning line, and the second signal is written to the pixels on the Gall-th scanning line. FIG. 7F shows a still image with 100% duty, and in this case, black display is not performed.

  Thus, the duty ratio can be changed by changing the timing at which the second signal is written. As shown in FIG. 8A, the signal waveform to the signal line when the duty is 50% is such that the first signal (image signal) and the second signal (black display signal) are alternately and periodically repeated. Is supplied to the wire. Further, since two types of video signals, the first signal and the second signal, are used, the video signal is supplied to the signal line at twice the frequency of the conventional display signal, but the frequency of the scanning line does not increase. The scanning lines are sequentially selected from the first scanning line to the Gall-th scanning line, and the first scanning line is selected after the Gall-th scanning line. . The same scanning line is selected twice in one frame period (see FIGS. 8B, 8C, and 8D), and the pixel connected to each scanning line is one frame. An image is displayed in the first half of the period, and black is displayed in the second half (see FIGS. 8E and 8F).

  Next, the variable ratio of the duty ratio will be described. The variable ratio of the duty ratio is determined by the number of scanning lines of the liquid crystal display panel 61. For example, when a VGA having 480 scanning lines is used, adjustment from 1/480% duty to 100% duty can be performed at 1/480% intervals (adjustment accuracy is 480), and the HDTV system having 1035 scanning lines is used. In this case, the duty can be adjusted from 1/1035% duty to 100% duty at intervals of 1/1035% (adjustment accuracy is 1035). FIG. 9 shows the relationship between the number of scanning lines, the adjustment accuracy, and the minimum duty. Although the adjustment accuracy is proportional to the number of scanning lines, the minimum duty is inversely proportional to the number of scanning lines.

  As described above, according to the present embodiment, the duty ratio can be easily changed according to the display image, and high-quality display can be achieved. Since a black image display period can be provided, it is possible to prevent blurring.

(Second embodiment)
Next, a second embodiment of the present invention will be described. This embodiment is a method for driving a liquid crystal display device, and the liquid crystal display device to be driven uses a liquid crystal material in which the writing period is reduced to half and a response shortage occurs as in the first embodiment. Except for this, the configuration is the same as that of the liquid crystal display device of the first embodiment.

  The driving method according to the second embodiment uses a third signal as a reset signal in addition to the first signal as an image signal and the second signal as a black display signal. The third signal is written as a high-potential-side reset signal (white display in AFLC) before the image signal as the first signal is written to the pixel as shown in FIG. In rare cases, this can increase responsiveness. The effect of the reset signal on the display is such that the white display is not visually recognized because the image signal is written in a short time after the reset. Further, in this embodiment, the writing period (width of the voltage waveform of the scanning line) is shortened to 1/3 of the conventional case, but the driving of this embodiment is performed within a range where the effect of the reset can improve the writing. The method is available. In the present embodiment, the first to third signals are supplied to the signal lines at a repetition period of three by three, and the driving frequency of the signal line driving circuit 80 is three times as large as that of the related art. The frequency of the driving circuit 70 does not increase. In this embodiment, one frame period of a pixel connected to each scanning line includes an image display period, a black display period, and a reset period (see FIGS. 10E and 10F). .

  According to the second embodiment, the duty ratio can be easily changed in accordance with the display image, and blur can be prevented from occurring. As a result, high-quality image display is possible. Further, the driving method of the second embodiment can be applied to a liquid crystal display device using a liquid crystal material in which a short response occurs due to a short writing period.

(Third embodiment)
Next, a third embodiment of the present invention will be described. When a large number of image signals are input as in the first and second embodiments, the power consumption of the signal line driving circuit increases accordingly. Therefore, a driving method with reduced power consumption will be described as a third embodiment. The liquid crystal display device using the driving method of the third embodiment has the same configuration as the liquid crystal display device of the first embodiment except that a blinking backlight is used.

  The driving method according to the present embodiment is also effective in oblique phenomena that can occur when the display method and the original image creation method are different. This oblique phenomenon appears particularly when the speed of the moving object is high. As shown in FIGS. 11A and 11B, consider a case where a white rectangular box 100 moves from the left to the right of the screen at high speed in the display screen. When the display method is a screen sequential method (displaying the screen collectively) and the original image is a line sequential method (an image captured by a CCD camera or the like), as shown in FIG. Since the creation time is different, the screen becomes oblique from the upper left to the lower right. On the other hand, when the display method is a line-sequential method (CRT or LCD) and the original image is a frame-sequential method (filming of a movie or the like or scenes are created frame by frame by CG (Computer Graphics) technology), the upper and lower sides of the screen are displayed. Even though the creation time is the same, there is a time difference between the top and bottom of the screen during display, so that the screen becomes oblique from the upper right to the lower left as shown in FIG. These phenomena become remarkable when the screen size is long in the horizontal direction and the moving body speed is high. For example, in a high-definition system, a moving body that moves from the left to the right of the screen in one second has a tilt of about 1.7 °. The above problem does not occur when the display method and the original image creation method are the same.

  Therefore, a driving method according to the present embodiment will be described with reference to FIG. 12 taking an example in which an original image is created by a frame sequential method.

  In the driving method according to the present embodiment, as shown in FIG. 12, one of the scanning lines (upper half of the screen) or lower half of the screen (the first subfield) in the first quarter of one frame period (the first subfield) is used. In 12, the first signal (image signal) is written to the pixels on the first to Gall / second scanning lines), and the other half of the screen is scanned in the next 期間 period (second subfield). The second signal (black display signal) is written to the pixels on the line (Gall / 2 + 1 to Gall-th scanning line in FIG. 12), and further in the next quarter period (third subfield). The first signal is written to the pixels on the scanning line of the other half of the screen, and the second signal is written to the pixels on the scanning line of the one half of the screen during the remaining 期間 period (fourth subfield). The writing is performed. Then, during the writing period of the first signal, the backlight is turned off to perform no display, and the backlight is turned on after writing to the pixels on the scanning lines in the upper half of the screen or the lower half of the screen is completed (FIG. 12 (i)). reference). In FIG. 12, the backlight is turned on in the second and fourth subfields within one frame period.

  In addition, the timing of the reset signal of the pixel, that is, the timing of the signal for displaying black in this embodiment mode may be the timing of turning on the backlight. The timing of turning on the backlight is preferably at the stage when the response of the liquid crystal is almost finished, but the timing of resetting is a black display, so there is not much problem.

  FIG. 13 shows an example of a display image displayed by the driving method according to the present embodiment, and FIGS. 13A, 13B, 13C, and 13D show first to third images shown in FIG. Screens corresponding to four subfields are shown. As can be seen from FIG. 13, since the in-phase screens are displayed collectively, no tilt phenomenon occurs. Further, in the present embodiment, the duty is 25%, which is effective when displaying a fast movement.

  FIG. 14 is a waveform diagram when a slow motion is displayed by the driving method of the present embodiment. In this case, one frame period is divided into first to fourth subfields, the first signal is written to the pixels on the first to Gall / 2nd scanning lines in the first subfield, and the first signal is written in the second subfield. Immediately before the end, the second signal is written to the pixels on the Gall / 2 + 1 to Gall-th scanning lines, and the first signal is written to the pixels on the Gall / 2 + 1 to Gall-th scanning lines in the third subfield. Immediately before the end of the subfield, the second signal is written to the pixels on the first to Gall / 2nd scanning lines. Even if driven in this manner, tilting the image does not pose a problem because the movement is slow. That is, it is difficult to visually recognize even if the screens whose phases are shifted by one frame are simultaneously displayed in a certain period of one frame period.

  FIG. 15 shows an example of a display image displayed by the above driving method. FIGS. 15A, 15B, 15C, and 15D show the first to fourth subfields shown in FIG. Each corresponds. In the second field, the image in the lower half of the screen is an image one frame before the image in the upper half of the screen, and is therefore displayed with a slight shift (see FIG. 15B). However, since the movement is slow, the phenomenon that the movement amount is small and tilts is difficult to be visually recognized. When the driving method according to this embodiment is used, the luminance can be increased with a duty of 50%.

  Thus, power consumption can be reduced by reducing the number of times of writing images in the signal line driving circuit 80 and blinking the backlight. In the driving method according to this embodiment, the duty ratio can be easily changed in accordance with the displayed image, and blur can be prevented from occurring. As a result, high-quality image display is possible.

(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described. This embodiment is a method for driving a liquid crystal display device. In the driving method according to the third embodiment, the above-mentioned reset signal is a signal of a halftone level, so that a grayscale is displayed instead of a black display. It is configured to use display. In the present embodiment, it is known that the contrast is reduced, but when the difference between the peripheral luminance and the display luminance increases, the contrast discrimination threshold decreases. In particular, when the peripheral luminance increases, the effect is great. For example, when the peripheral luminance becomes ten times as large as the display luminance, the human visibility (contrast discrimination value) drops to about 80%. However, since this depends on the absolute value of the display luminance, it cannot be uniquely determined. A liquid crystal display device to which the driving method of the present embodiment is applied has a configuration in which a user can adjust the brightness so that it is easy to see when priority is given to brightness over contrast. Therefore, as shown in FIG. 16, the display device 1A using the driving method of the present embodiment includes an insertion gray level image signal generation section 90 for creating a gray level image to be inserted, and a liquid crystal display shown in FIG. The device 1 is newly provided. Here, a halftone raster image is created, and this raster image is sent to the gate array 10 and sent to the liquid crystal module 60 as a third signal.

  As described above, the user may determine which halftone is to be selected, or a photodetector (for example, a signal can be taken out using a photodetector and a current-voltage converter) provided around the panel to provide a peripheral brightness. It may be adjusted accordingly.

  Also in the driving method of this embodiment, the duty ratio can be easily changed in accordance with the displayed image, and blur can be prevented from occurring. As a result, high-quality image display is possible.

(Fifth embodiment)
A fifth embodiment of the present invention will be described. This embodiment is a method for driving a liquid crystal display device, which utilizes a halftone display method. When a signal line driving circuit capable of displaying 64 gradations (6 bits) for each of the colors RGB (R = red, G = green, B = blue) for expressing the colors is used, a higher intermediate value is used. In order to display a key, FRC technology for displaying a plurality of times during one frame period is widely used. The driving method according to the present embodiment has a configuration in which the FRC technique is used for a still image and the refresh rate for rewriting the screen in a moving image is higher. In a still image, the image quality can be improved by increasing the number of halftones. However, in a moving image, it is more effective to improve the image quality by increasing the refresh rate for rewriting the screen than the number of gradations. Accordingly, in the present embodiment, as shown in FIG. 17, in the case of a still image, both the first signal and the second signal are inputted with a signal of 64 gradation levels to perform 128 gradation display, and in the case of a moving image, the first signal and the second signal are displayed. Although both the signal and the second signal are signals of 64 gradation levels, high refresh (120 Hz) display of 64 gradation levels is performed by transmitting images shifted in time phase. That is, one frame is composed of two subfield images, and an original image is displayed as a first signal in a first subfield, and an interpolated image is displayed as a second signal in a second subfield. Further, when the signal line driving circuit can perform high-speed writing up to 4 × speed, 256-gradation display as a still image and one frame as a moving image are divided into four sub-fields, and the first sub-field is used as the first signal. A 240 Hz refresh rate display may be used in which an original image is displayed, and interpolated images having different phases are displayed in the second, third, and fourth subfields. As shown in FIG. 18, the first subfield has the original image as the first signal, the third subfield has the interpolated image as the second signal, and the second and fourth subfields have the third image. By displaying a black image as a signal, a higher-quality moving image can be displayed at a refresh rate of 120 Hz.

  Here, creation of an interpolated image in a signal whose input signal source is a refresh rate of 60 Hz will be described. A method of extracting a changed area and changed image information from a motion vector in MPEG4, and replacing the changed area with image information in a frame memory (a frame memory shown in FIG. 5 can be used) (see Japanese Patent Application No. 11-89327). ) And interpolation methods (see Japanese Patent Application Laid-Open No. 7-107465). Although the detailed description is omitted here, the determination of the display method and the generation of the interpolation image are performed by the difference detection + determination + interpolation image generation unit 27 having the difference detection / determination function and the interpolation image generation function as shown in FIG. Do. The display mode instruction signal indicating the determined display mode and the generated interpolation image are sent to the gate array 10, and then sent to the liquid crystal module 60.

  Also in the fifth embodiment, high-quality display is possible.

  In the first to fifth embodiments, the signal line driving circuit is configured to supply the first to m-th (m is an integer of 2 or more) signals to each signal line. The display period of the first to m-th signals in each pixel will be described below.

  It is assumed that one frame period is from the writing of the first signal to writing of the first signal to the pixel, and the second to m-th signals are applied to the signal lines n times (n is an integer of 2 or more). . For example, if m = 3 and n = 4, there are first, second, and third signals as signal types, and the first signal (image signal) is a signal written for each pixel. The number of pixels arranged in the direction is input Pxv times, and the second signal and the third signal are input four times at an arbitrary interval. That is, the total number Sn of the signals supplied to the signal lines is represented by the following equation.

Sn = Pxv + 4 × 2 (2)
In this case, the number of times the second signal is input and the number of times the third signal is input may be different from n ₂ and n ₃ , in which case Sn is represented by (3).

Sn = Pxv + n ₂ + n ₃ (3)
The input timing of the second and third signals can be changed according to the image, and the number of signals after inputting the first signal is represented by k ₂ , k ₃ (subscripts indicate the second signal, respectively). , if the mean) a third signal, the display period T ₁ of the first signal in each pixel, the display period T ₃ of the second signal display period T _2, and the third signal of the following formula ( It is represented by 4) to (7). Here, T _total indicates one frame period.

T _total = T ₁ + T ₂ + T ₃ −−− (4)
T ₁ = T _total × (k ₂ / Sn) −−− (5)
T ₂ = T _total × ((k ₃ −k ₂ ) / Sn) −−− (6)
T ₃ = T _total × ((Sn−k ₃ ) / Sn) −− (7)
In the above example, the display method in which the third signal is written following the second signal is described.

In addition, as a method of changing a display method depending on an image, for example, when displaying a moving image with a 50% duty, a black display signal is input as a second signal. In the case where the liquid crystal display device used in this case is normally black, a voltage that does not apply a voltage to the liquid crystal material can be used as the reset signal. Although the driving method differs depending on the liquid crystal display device, when using a liquid crystal display device which always turns on the backlight, it is necessary to sequentially perform image writing and black display in each pixel. That is, the first signal is an image signal, the second signal is a black display signal, and the second signal is input between the first signals of the pixels. Looking at a certain pixel, after inputting the first signal, the second signal after T _total / 2 is written. In this case, Sn, K ₂ , and T ₁ are represented by equations (8) to (10), respectively.

Sn = Pxv + Pxv = 2Pxv-(8)
k ₂ = Pxv-(9)
T ₁ = T _total × (k ₂ / Sn) = T _total / 2 ---- (10)
In addition, when the displayed image is entirely dark, or when there is little external light from the periphery in the reflection type liquid crystal display device, in order to increase the brightness of the entire screen, grayscale display of halftone instead of black display is used as the second signal. May go.

In addition, in order to change the number of colors and the refresh rate between a still image and a moving image, in a still image, both the first signal and the second signal are 8-bit image signals, and T ₁ = T _total / 2, and are over one frame. In a moving picture, the first signal is an 8-bit image signal, the second signal is displayed in black, T ₁ = T _total / 2, and the display method is 50% duty. It is also possible to use a high refresh rate display method by using the first signal and the second signal as image signals whose phases are shifted in time.

  As described above, according to each embodiment of the present invention, the image quality can be significantly improved by increasing the driving frequency of the signal line driving circuit as the display method of the liquid crystal panel using the high-speed response liquid crystal. More specifically, means for changing the duty ratio between image display and black display according to the display image (still image and moving image), or multi-gradation display using FRC for still image and high refresh using interpolation image for moving image By using the display means, a high image quality display is provided in which color reproducibility is improved for a still image and sharpness is improved for a moving image.

FIG. 1 is a diagram illustrating a configuration of a liquid crystal display device according to a first embodiment of the present invention. FIG. 1 is a diagram illustrating an array configuration of a liquid crystal display device according to a first embodiment of the present invention. FIG. 4 is a diagram showing the orientation of an antiferroelectric liquid crystal material. The figure which shows the voltage-transmission curve of an antiferroelectric liquid crystal material. FIG. 3 is a diagram illustrating a configuration of a motion determination processing unit according to the first embodiment. FIG. 4 is a voltage waveform diagram illustrating an operation of the scanning line driving circuit according to the first embodiment. FIG. 7 is a diagram showing a display screen displayed by the operation of the scanning line driving circuit shown in FIG. 6. FIG. 3 is a signal waveform chart for explaining the operation of the first embodiment. FIG. 5 is a diagram illustrating a relationship between the number of scanning lines, adjustment accuracy, and minimum duty (%) according to the first embodiment. FIG. 9 is a signal waveform chart for explaining the operation of the second embodiment of the present invention. FIG. 7 is a diagram for explaining image quality deterioration (oblique phenomenon) due to a difference between an image creation method and a display method. FIG. 10 is a signal waveform diagram for explaining the operation of the driving method according to the third embodiment of the present invention. FIG. 13 is a view showing a display example displayed by the operation shown in FIG. 12. FIG. 14 is a signal waveform diagram illustrating an operation of the driving method according to the third embodiment. FIG. 15 is a view showing a display example displayed by the operation shown in FIG. 14. FIG. 13 is a diagram illustrating a configuration of a liquid crystal display device used in a driving method according to a fourth embodiment of the present invention. FIG. 14 is a signal waveform diagram for explaining the operation of the driving method according to the fifth embodiment of the present invention. FIG. 14 is a signal waveform diagram for explaining the operation of the driving method according to the fifth embodiment of the present invention. FIG. 14 is a diagram illustrating a configuration of a liquid crystal display device used in a driving method according to a fifth embodiment of the present invention. FIG. 4 is a diagram for explaining an image blur phenomenon due to a hold characteristic.

Explanation of reference numerals

Reference Signs List 1 liquid crystal display device 10 gate array 20 motion discrimination processing unit 60 liquid crystal module 61 liquid crystal panel 62 scanning line 63 signal line 64 pixel (pixel electrode)
65 switching element 70 scanning line driving circuit 80 signal line driving circuit

Claims (2)

A scanning line formed on a first substrate, a signal line formed on the first substrate so as to intersect the scanning line, a pixel formed at each intersection of the scanning line and the signal line, A switching element that opens and closes by the voltage of the scanning line and sends a signal from the signal line to the pixel;
A counter substrate having a counter electrode formed on the second substrate,
A liquid crystal layer sandwiched in a gap between the array substrate and the counter substrate,
A signal line driving circuit that drives the signal line so as to supply an image signal to the signal line;
In a method for driving a liquid crystal display device comprising:
The signal line drive circuit can supply the image signal for p (p is an integer of 2 or more) gradations, and displays the still image as the image signal for displaying an image for p gradations. In this case, a multi-gradation display method in which 2p gradation display is performed over one frame period is used, and when displaying a moving image, one frame is divided into at least first and second sub-fields. A display of an original image and an interpolation image in the second subfield. A scanning line formed on the first substrate, a signal line formed on the first substrate so as to intersect the scanning line, a pixel formed at each intersection of the scanning line and the signal line, A switching element that opens and closes by the voltage of the scanning line and sends a signal from the signal line to the pixel;
A counter substrate having a counter electrode formed on the second substrate,
A liquid crystal layer sandwiched in a gap between the array substrate and the counter substrate,
A signal line driver circuit for driving the signal line so as to supply first to m-th (m is an integer of 2 or more) signals to the signal line;
A scanning line driving circuit for sequentially selecting and driving the scanning lines based on a scanning line signal and an output control signal,
A motion determination processing unit that determines whether the frame image is a moving image or a still image based on the image signal and the synchronization signal,
The first to m-th signals, the scanning line signals, and the output control signal are generated based on the image signal, the synchronization signal, and the output of the motion determination processing unit, and the first to m-th signals are generated. A gate array unit that sends the signal to the signal line driving circuit and sends the scanning line signal and the output control signal to the scanning line driving circuit;
A liquid crystal display device comprising:

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