JP2007108288A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that an image is seen possibly double when an outline having discriminating light and shade moves during scanning of a back light synchronized with vertical synchronism for improving moving picture responding performance of a liquid crystal display device. <P>SOLUTION: A phase shift of a scan is made small in width under a certain condition. In concrete, the width of the phase shift in a light-off period within a driving cycle is less than one frame period×display area rate and not less than one frame period×display area rate×(N-1)/N-(light-off period of one area). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device, and more particularly to a lighting control technique for a lamp that functions as a backlight of a liquid crystal panel.

  A CRT often used in an image display device emits light by applying an electron beam to a phosphor screen. When measured in a very short time, each point on the screen is displayed only in a very short time consisting of phosphor afterglow. In the CRT, this point emission is sequentially scanned to display one frame image using the afterimage effect of the eyes. Such a display element is called an impulse type.

  On the other hand, in recent years, the demand for liquid crystal display devices is increasing not only as a personal computer monitor but also as a television application, and accordingly, opportunities for displaying moving images are also increasing. However, with regard to the moving image quality of the liquid crystal display device, the display performance is insufficient, such as motion blur being perceived.

  The motion blur is caused by poor response characteristics of the liquid crystal material itself and a system in which the same display is continued over one frame period (so-called hold type display). That is, in a liquid crystal display device, display data is generally written once per frame using data lines (source lines) and address lines (gate lines) for pixels arranged in a matrix. Each pixel keeps (holds) display data for one frame. That is, in the liquid crystal display device, the screen is always displayed even if measurement is performed in a minute time compared to one frame period.

  Note that the “frame” in this specification refers to a video signal in a period in which all the pixels constituting one screen are scanned in the liquid crystal panel. For example, in a display device that performs display by scanning all the pixels constituting one screen for each field of a television signal, one field of the television signal and one frame referred to in this specification are regarded as being equal. It is not necessarily the same as the “frame” generally used in the signal.

  In such a hold-type image display device, a phenomenon that the outline of a moving image is blurred visually occurs. An explanation of the principle of occurrence of the phenomenon and a proposal of an improvement method have been made (see Non-Patent Document 1). According to this document, it is understood that the quality of moving image display can be greatly improved by setting the display period in the frame time direction to half or less of one frame.

  As a method for solving the problem caused by the liquid crystal display device being a hold-type display device, for example, sequential field display information of a video signal is written in a liquid crystal panel in a period sufficiently shorter than one field period, and a fluorescent lamp is connected to the video signal. The LCD is turned on during a part of the time interval in which the video signal is not written and is turned off in part of the time interval in which the video signal is written, so that an effect equivalent to the impulse driving of the CRT is simulated in the LCD. There is also a thing (refer patent document 1).

  As a conventional technique for improving the response characteristics of the liquid crystal, the backlight has a plurality of areas that emit light in a strip shape in the scanning direction, and when a video signal or a synchronization signal is input, the plurality of light emission areas turn on the liquid crystal panel. Means for sequentially scanning and lighting in synchronization with a vertical synchronizing signal for this purpose is known (see, for example, Non-Patent Document 2).

  In this case, in general, scanning lighting is sequentially performed from the top to the bottom in synchronization with the vertical synchronization signal, and the phase of the flashing control signal for the uppermost strip-like light emitting area and the lowermost strip-like light emitting area. The phase difference from the phase of the flashing control signal for the panel is one frame period of panel driving or one frame period of panel driving × display area ratio. Here, the display area ratio indicates a time ratio necessary for writing a video signal from the uppermost line to the lowermost line of the liquid crystal panel in one frame period.

In general, the effective display range of the basic video signal is almost the same, and is generally about 0.91 to 0.96. However, in the case of writing time compression as disclosed in Patent Document 1, the display area ratio is, for example, 0. .5 or less.
JP-T 8-500915 Yashiro Kurita: Image quality of video display on hold-type display, IEICE Technical Report, EID99-10 (1999-06) Toshiba Technical Disclosure Vol. 15-78 P.I. 45-49 1997

  However, in the prior art as described in the above-mentioned Patent Document 1, since the lighting device is turned on after the entire surface of the liquid crystal panel is scanned and the liquid crystal on the entire panel responds, the scanning time and the response time of the liquid crystal are significantly increased. There is a need. In addition, since the lighting time of the lighting device is short, it is necessary to increase the emission intensity in order to achieve the same luminance as the conventional one. For this purpose, there has been a problem that the tube current is increased and the life of the lighting device is shortened.

  Further, in the method of sequentially scanning the backlight as described in Non-Patent Document 2, even if an area with N divided backlights is in the extinguishing period, one of the other areas is simultaneously used. Since the above is a lighting period, the backlight of the display area of the liquid crystal panel corresponding to the area | region which is a light extinction period will shine a little by the scattered light from another area | region. For this reason, when a moving image is projected, there is a problem in that the light image, which is shifted by one frame in the image, appears to overlap, looks like a double image, and the quality of the moving image deteriorates.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a liquid crystal display device that improves image quality without sacrificing the quality of moving images.

In order to solve these problems, the first invention of the present application is provided with a backlight having a turn-on and turn-off period by pulse width modulation corresponding to the period in which the liquid crystal panel is driven, Divided into N regions, and the extinguishing periods of the respective regions have the same period and different phases, and the deviation width of the extinguishing period in the driving cycle is
1 frame period of panel drive x smaller than display area ratio, and
1 frame period of panel drive × display area ratio × (N−1) / N− (light-out period of one area)
It is characterized by the above.

  According to the present invention, the overlapping width of the double images becomes small, and the double becomes inconspicuous. Also, since the phase of the extinguishing period of each area of the backlight is within the range, it is possible to maintain the video response performance by scanning, so the image quality is improved without sacrificing the video image quality. The remarkable effect of being able to do is acquired.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  FIG. 1 shows a block diagram of a main configuration of an image display apparatus according to the present invention. In FIG. 1, reference numeral 1 denotes a liquid crystal module as an image display element. The liquid crystal module 1 includes a liquid crystal panel 2, a backlight 3, It comprises a driver circuit unit 4 for driving the liquid crystal panel 2 and other optical and mechanism members.

  The backlight 3 is composed of a large number of lamps and the like, and can be controlled to blink by dividing it into a plurality of N areas. In the present invention, the backlight area (corresponding to four image display areas ( In this specification, an example in which “bands”) can be individually controlled is shown.

  FIG. 3 is a diagram showing the relationship between the backlight band and the corresponding image display area of the liquid crystal panel. When the backlight is divided into four bands in the vertical direction, the image display area of the liquid crystal panel corresponding to each band. Is divided into four as shown by the broken lines in FIG.

  However, although the plurality of lamps constituting the backlight are divided into four sections, the image display area corresponding to each band may not be clear due to light diffusibility. Even in such a case, the present invention is effective.

  As the light source of the backlight 3, a fluorescent tube, an LED, or the like is used. In the case of blinking, it is easy to obtain the ON / OFF switching characteristics of the LED, but a fluorescent lamp is often used. The backlight 3 may or may not include the light source and the light source driving circuit. Hereinafter, an example including the light source driving circuit will be described.

  Reference numeral 6 denotes a video signal processing unit which adjusts the gain and color density of the video signal, performs scaling to change the number of lines and dots of the video signal, and performs processing such as γ correction.

  A control pulse generation circuit 5 generates a timing signal for blinking the backlight 3 from a synchronization signal or an enable signal for a video signal input to the liquid crystal module 1.

  The operation will be described below with reference to FIG.

  Note that there may be further preprocessing of the video signal in the former stage of FIG. 1, but this time, the configuration and illustration are omitted.

  First, the video signal input to the video signal processing unit 6 is subjected to processing such as gain and color density adjustment, scaling for changing the number of lines and dots, and γ correction.

  The signal output from the video signal processing unit 6 is input to the liquid crystal module 1. The operation of the driver circuit unit 4 in the liquid crystal module 1 is omitted.

  On the other hand, the operation of blinking the backlight in the configuration of FIG. 1 will be described with reference to FIGS.

  FIG. 2 is an explanatory diagram for explaining the operation until the backlight is blinked after the synchronization signal is input to the control pulse generation circuit 5 of FIG.

  A synchronization signal synchronized with the output signal is output from the video signal processing unit 6 in FIG. 1 and input to the control pulse generation circuit 5. As shown in FIG. 2A, the control pulse generation circuit 5 counts the horizontal synchronization signal (HSYNC) using the vertical synchronization signal (VSYNC) as a starting reference, and generates backlight control signals s1 to s4.

  In FIG. 2, the timing signals s1 to s4 for blinking the backlight 3 are generated based on the synchronization signal, but may be generated based on the enable signal as described above.

The backlight control signals s1 to s4 are slightly different in phase as shown in FIG. 2B, and the phase difference between s1 and s4 is
1 frame period of panel drive x smaller than display area ratio, and
1 frame period of panel drive × display area ratio × (N−1) / N− (light-out period of one area)
As described above, the control is performed by setting the count number to the control pulse generation circuit 5. The count number is set from a microcomputer, for example.

  The generated backlight control signals s 1 to s 4 are transmitted from the control pulse generation circuit 5 to the backlight 3 in the liquid crystal module 1. The backlight 3 is divided into four bands in the vertical direction. Each band flickers according to the backlight control signal, and the luminance of the backlight repeats light and dark.

  As a result, the overlap width of the double image, which was a problem at the time of backlight scanning, becomes small, and the double becomes inconspicuous. Also, since the phase of the extinguishing period of each area of the backlight is within the range, it is possible to maintain the video response performance by scanning, so the image quality is improved without sacrificing the video image quality. The remarkable effect of being able to do is acquired.

  The reason why the effect is obtained will be described again in detail below.

  In a conventional liquid crystal display device that sequentially drives a backlight, when a moving image is projected as described above, it may look like a double image, but the maximum of the blinking control signal of each band that is driven sequentially. It has been found through experiments by the present inventors that the phase difference is made smaller than (one frame period of panel drive × display area ratio) and approaches the same as much as possible to eliminate double images.

  However, if it is made to blink completely at the same time, that is, all the screens simultaneously, the video signal to the liquid crystal panel is driven sequentially on the panel, so the video response performance cannot be improved in the vertical direction of the panel, and it deteriorates conversely. The part comes out.

  In order to align the backlight blinking phase while improving the moving image response performance, the phase range is limited.

  The present inventors have made the range clear through simulation experiments.

  First, the relationship between the turn-off control phase of the backlight control signal and the moving image response performance will be described with reference to FIG.

  FIG. 4 is a relational diagram between the phase of the backlight control signal extinguishing control and the moving image response performance, and shows the simulation result in the upper stage when there are two types of response times (separate from the moving image response) of the liquid crystal panel. Although there are various ways of thinking as an index of moving image response performance, the present inventors used MPRT, which is currently being standardized, as an index. The lower the moving image response performance MPRT value is, the less blur is displayed when displaying a moving image, and the better the performance.

  In FIG. 4, it can be seen that the phase range in which turning off the backlight is effective for improving the moving image performance is limited to a certain range. The middle stage of FIG. 4 shows the first and last backlight control signal waveforms in the effective range. The backlight control signal waveform indicates that the control is turned on at High and turned off at Low. Furthermore, the response waveform of the liquid crystal panel used for the simulation is shown below.

  As can be seen from these figures, the phase range of the backlight control signal turn-off control, which is effective for improving the video performance, is approximately half the response of the liquid crystal from the timing when the turn-off control ends when the liquid crystal response is almost half. It was a range up to the timing at which the turn-off control was started at that time, and it was found that the width of the range hardly depends on the response speed of the liquid crystal panel. However, the degree of the effect depends on the response speed of the liquid crystal panel.

  Next, the phase range in which the backlight blinking phase difference can be reduced while improving the moving image response performance on the entire display screen of the liquid crystal module will be described with reference to FIG. When the liquid crystal panel sequentially drives the video signal from the top to the bottom, the backlight scanning direction is also from the top to the bottom. As an example, if the backlight is divided into four bands in the vertical direction, the image display area of the liquid crystal panel corresponding to each band is divided into four as shown by broken lines in FIG.

  FIG. 5 shows the slowest extinguishing control timing at which the effect of improving the moving image response performance in the first band is obtained when the backlight is divided into N bands. Furthermore, the earliest extinguishing control timing at which an effect for improving the moving image response performance in the Nth band is shown. It is an important condition that each of the turn-off control phase differences is equal to or greater than the timing difference in order to improve the moving image response performance over the entire screen.

  The slowest extinguishing control timing that is effective for improving the video response performance in the first band is almost half of the average response of the liquid crystal panel of the image display portion corresponding to the first band (example of rising in FIG. 5). This is the timing at which the turn-off control starts at the time (A in FIG. 5). The earliest turn-off control timing that is effective in improving the video response performance in the Nth band is almost half of the average response of the liquid crystal panel of the image display portion corresponding to the Nth band (example of rising in FIG. 5). This is the timing when the turn-off control ends at the time (B in FIG. 5).

  The time difference between A and B in FIG. 5 is substantially equal to the time for which the liquid crystal panel sequentially drives the video signal from the top of the panel to the bottom for N-1 bands, assuming that the bands are substantially equally spaced. That is, since it takes time for one frame period of the panel drive × display area ratio for the liquid crystal panel to drive the video signal for one frame full screen, one frame period of the panel drive × display area ratio × (N−1). ) / N.

  The timing at which the light turns off at B in FIG. 5 is the timing at which the light turns off at C in FIG.

That is, the minimum phase difference that can align the backlight blinking phase while improving the video response performance on the entire display screen of the liquid crystal module is the difference between A and C.
1 frame period of panel drive × display area ratio × (N−1) / N− (light-out period of one area)
It becomes.

In the present invention, the phase shift width of the off period of each area of the backlight is
1 frame period of panel drive x smaller than display area ratio, and
1 frame period of panel drive × display area ratio × (N−1) / N− (light-out period of one area)
Since the backlight control pulse is generated so as to be in the range, as a result, it is possible to maintain the video response performance by scanning, so that the image quality can be improved without sacrificing the image quality of the video. The remarkable effect is obtained.

  The liquid crystal display device of the present invention has a remarkable effect that the image quality can be improved without sacrificing the image quality of moving images, and particularly as a display device of a television receiver in which moving image display is important. Useful.

The block diagram of the principal part structure of the image display apparatus of this invention Explanatory drawing explaining operation | movement until blinking a backlight. The figure which shows the relationship between the band of a backlight, and the image display area of a corresponding liquid crystal panel Relationship diagram between backlight control signal extinction control phase and video response performance Explanatory drawing explaining the phase range of a backlight control signal

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid crystal module 2 Liquid crystal panel 3 Backlight 4 Driver circuit part 5 Control pulse generation circuit 6 Video signal processing part

Claims (5)

Corresponding to the period in which the liquid crystal panel is driven, a backlight having a lighting period and an extinction period by pulse width modulation is provided, and the backlight is divided into a plurality of N areas for driving, and the extinction period of each area is , The timing is the same and the phase is different, the phase shift width of the extinguishing period within the driving cycle is smaller than one frame period of panel driving × display area ratio, and one frame period of panel driving × display A liquid crystal display device characterized by having a ratio of (N-1) / N- (one region extinction period) or more. The liquid crystal display device according to claim 1, wherein the driving cycle is a vertical synchronization cycle to the liquid crystal panel or a vertical cycle of an enable signal. 3. The liquid crystal according to claim 1, wherein a phase control signal during the extinguishing period of each region divided into a plurality N of the backlight is generated from a synchronization signal or an enable signal to the liquid crystal panel. Display device. The phase control signal during the extinguishing period of each region divided into a plurality N of the backlights, and each region divided into the plurality N of backlights has a phase control signal phase corresponding to that region, The range from the timing at which the extinction control is substantially completed at a time point substantially half of the average response of the liquid crystal panel of the image display portion corresponding to 1 to the timing at which the extinction control is started The liquid crystal display device described. Each phase control signal in the extinguishing period of each of the regions divided into a plurality of N of the backlight is in a range between the phase of the phase control signal for the first region and the phase of the phase control signal for the Nth region. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is a liquid crystal display device.

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