JP2006267303A - Display apparatus and driving method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display apparatus capable of preventing the reduction of luminance and the deflection of a black insertion period to one polarity of an AC driving cycle. <P>SOLUTION: A liquid crystal control part 15 controls the writing of a black picture in a backlight 18 or a liquid crystal module 16 so as to insert a black picture between moving picture frames. Consequently the number of times of inserting black pictures can be reduced as compared with a conventional apparatus and the reduction of luminance is prevented. Further the liquid crystal control part 15 controls the writing of black pictures in the liquid crystal module 16 equally on the positive (+) voltage side and the negative (-) voltage side of a moving picture cycle. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a display device and a driving method thereof, and more particularly to a liquid crystal display device used for a portable device and a driving method thereof.

  Insert a black screen between each frame to suppress the afterimage and the phenomenon that the moving image may appear blurred (so-called “moving image blur”) in a moving image display device used in a portable device, for example, a liquid crystal display device. Has been done. This speeds up the response speed of the eye by refreshing the afterimage of the human eye.

  FIG. 10 is a diagram showing a relationship between luminance and time of a conventional liquid crystal, and FIG. 11 is a diagram showing a relationship between luminance and time of a liquid crystal when a conventional black screen is inserted. FIG. 10 shows a case where a black screen is not inserted, and the luminance of the liquid crystal is constant for each frame. On the other hand, FIG. 11 shows a case where a black screen is inserted for a certain period between frames.

  The video screen brightness is higher when the area of the frame display period is wider. Therefore, the screen brightness of FIG. 11 with the black screen inserted is lower than that of FIG. 10 without the black screen inserted.

  In a portable device, a frame rate for performing AC driving of a liquid crystal display device (hereinafter referred to as “AC cycle”) is different from a frame rate of a moving image (hereinafter referred to as “moving cycle”). For example, whether the moving image cycle is 15 frames / second or 30 frames / second, the AC cycle is 60 frames / second. On the other hand, the conventional black screen is inserted between frames of the AC cycle. Therefore, a black screen is inserted 60 times per second.

  The insertion of the black screen is realized by controlling the lighting of the backlight or writing the black screen into the liquid crystal element.

  As an example of the prior art relating to the insertion of the black screen, a technique for reducing the charge / discharge current with respect to the device capacity by continuing black display in a normally black liquid crystal display device is disclosed (for example, Patent Document 1). reference).

  As another example, a liquid crystal display device is disclosed in which black lines are simultaneously written on two lines and a frame rate of 120 Hz secured by two-line interlaced scanning is assigned to black lines (see, for example, Patent Document 2). .

  As another example, the frequency of the video signal is doubled, the original video signal and the non-image signal are alternately output, and the non-image signal is a signal for applying a high voltage to the liquid crystal panel, A liquid crystal display device which is a signal corresponding to black display is disclosed (for example, see Patent Document 3).

  Further, as another example, the optical shutter corresponding to the display area in the upper half of the screen is in the reflection (light shielding) state so that the optical shutter corresponding to the display area in the lower half of the screen is in the reflection (light shielding) state. As described above, a liquid crystal display device is disclosed in which backlight light is irradiated only on the image display areas of the respective screen halves of the liquid crystal display panel so that the screen half of the liquid crystal display panel is the image non-display area. Further, this liquid crystal display device inserts a black display signal during the period in which writing scanning is performed with respect to the image non-display area of the liquid crystal display panel when reproducing a moving image with the image signal converted at the double speed by the frame frequency converter. Output to the drive unit is also disclosed (for example, see Patent Document 4).

  As another example, the image signal is repeatedly read twice with a double frame frequency (120 Hz), and the second, fourth, and sixth periods are divided among six equal periods of one frame period of the input image signal. By selecting an image signal and selecting a black display signal in the first, third, and fifth periods other than that, a period of 3/6 with respect to an image signal output twice within one frame period Discloses a liquid crystal display device that inserts and outputs a black display signal (see, for example, Patent Document 5).

JP 2001-290460 (paragraph 0029 and FIG. 1) Japanese Patent Laying-Open No. 2003-36056 (paragraph 0009 and FIG. 3) Japanese Patent Laying-Open No. 2004-4659 (paragraph 0016 and FIG. 2) Japanese Unexamined Patent Publication No. 2004-212489 (paragraphs 0034, 0036, 0083 and FIGS. 4, 5, 21, and 22) Japanese Unexamined Patent Publication No. 2004-233932 (paragraphs 0026 and 0027 and FIGS. 1 and 2)

  However, conventionally, since a black screen was inserted between frames of an AC cycle, the black screen was inserted 60 times per second, which was a factor of lowering the luminance more than necessary.

  In television and personal computer monitors, this decrease in brightness can be resolved by increasing the backlight brightness. However, in portable devices, the brightness of the backlight, which consumes a large amount of current, is increased due to battery life. It is not desirable to do so.

  As a black screen insertion method, there is a method of writing a black screen into a liquid crystal element. FIG. 12 is a diagram showing the relationship between the conventional liquid crystal AC drive voltage and time, and FIG. 13 is a diagram showing the relationship between the liquid crystal AC drive voltage and time during black screen writing.

  FIG. 12 shows a drive voltage waveform at an AC cycle of 60 Hz. In this case, the amount of applied voltage of the positive (+) voltage and the negative (−) voltage is equal. On the other hand, FIG. 13 shows drive voltage waveforms at the time of black screen writing in an AC cycle of 60 Hz and a moving image cycle of 30 Hz.

  Actually, the black screen exhibits its effect by being inserted when the image changes. That is, it is at least necessary to insert a black screen between frames of the moving image cycle.

  FIG. 13 shows a case where a black screen is written between frames of a moving image cycle. In this case, the positive (+) voltage is smaller than the negative (−) voltage, and the amount of applied voltage is reduced, and AC driving is disrupted. That is, there is a problem that the black insertion period is biased to one polarity of the AC driving cycle (positive (+) voltage side in the example of FIG. 13), whereby the AC driving of the liquid crystal is disrupted and the liquid crystal element is deteriorated. The same applies to the case of the AC cycle 60 Hz and the moving image cycle 15 Hz.

  Accordingly, an object of the present invention is to provide a display device and a driving method thereof capable of preventing a decrease in luminance and a black insertion period from being biased to one polarity of an AC driving cycle.

  In order to solve the above problems, a display device according to the present invention is a display device that displays a moving image by AC driving a display element, and includes a frame rate for AC driving the display element, and a frame rate of the moving image. And a black screen insertion means for inserting a black screen based on the frame rate of the moving image.

  The driving method according to the present invention is a driving method of a display device that displays a moving image by AC driving the display element, and the frame rate for AC driving the display element is different from the frame rate of the moving image. And a black screen inserting step of inserting a black screen based on the frame rate of the moving image.

  According to the present invention, since the black screen is inserted based on the frame rate of the moving image, the number of insertions of the black screen can be reduced as compared with the case where the black screen is inserted based on the frame rate for AC driving.

  According to the present invention, by inserting a black screen based on the frame rate of a moving image, the number of insertions of the black screen can be reduced as compared with the prior art, so that a reduction in luminance can be prevented. Further, since the writing of the black screen is performed equally on the positive (+) voltage side and the negative (−) voltage side of the moving image cycle, it is possible to prevent the display element from being deteriorated.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  1st Example has shown an example of the display apparatus which inserts a black screen by backlight control. FIG. 1 is a block diagram of a first embodiment of a display device according to the present invention.

  The display device 1 according to the present invention is a display device used for a portable device as an example, and has a telephone function. The display device 1 includes an antenna 11, an RF unit 12, a baseband processing unit 13, a CPU (Central Processing Unit) 14, a liquid crystal control unit 15, a liquid crystal module 16, an image memory 17, And a backlight 18.

  The antenna 11, the RF unit 12, and the baseband processing unit 13 process transmission / reception signals. This portion is, for example, a transmission / reception processing unit of a mobile phone device, and its operation is the same as that of the prior art and is not related to the present invention, so that description of the operation is omitted.

  The liquid crystal control unit 15 controls the liquid crystal module 16 using the image data signal 101, the horizontal synchronization signal 102, the vertical synchronization signal 103, and the pixel clock signal 104. The liquid crystal module 16 displays an image with liquid crystal.

  The image memory 17 stores moving image data and still image data. The backlight 18 is illumination that illuminates the liquid crystal module 16 from the back, and the liquid crystal control unit 15 controls the backlight 18 using the backlight control signal 105.

  The CPU 14 controls the baseband processing unit 13 and the liquid crystal control unit 15.

  Next, the operation of the first embodiment will be described. FIG. 2 is a diagram showing an example of black screen insertion timing in backlight lighting control, and FIG. 3 is a detailed timing diagram of an example of backlight control at a moving image frame rate of 30 Hz.

  First, a case where the moving image cycle is 30 Hz will be described. The AC cycle at this time is 60 Hz as an example. The following control is performed by the liquid crystal controller 15 on the liquid crystal module 16 and the backlight 18.

  In the case of the moving image cycle 30 Hz, two frames of the AC cycle 60 Hz (for example, (1) and (2) of the AC cycle (60 Hz) in FIG. 2) correspond to one frame of the moving image cycle 30 Hz.

  Assuming that the backlight control signal 105 is “H” (high level) when turned on and “L” (low level) when turned off, (1), (3), (5),. ), (59),..., (H) is output as the backlight control signal 105 (see the timing diagram of the moving image cycle 30 Hz in FIG. 2), and in each period, the liquid crystal module 16 displays an image of “1”. Data is output (see FIG. 3).

  On the other hand, the backlight control signal 105 during the periods (2), (4), (6),... (58), (60),. “L” is output (see the timing diagram of the moving image cycle 30 Hz in FIG. 2), and in each period, the liquid crystal module 16 is turned off after outputting “1” image data (see FIG. 3).

  That is, the insertion of the black screen is 30 times per second, which is reduced to half of the conventional 60 times.

  Next, a case where the moving image cycle is 15 Hz will be described. The AC cycle at this time is 60 Hz as an example. FIG. 4 is a detailed timing chart of an example of backlight control when the moving image frame rate is 15 Hz.

  In the case of a moving image cycle of 15 Hz, four frames of an AC cycle of 60 Hz (for example, (1) to (4) of the AC cycle (60 Hz) of FIG. 2) correspond to one frame of a moving image cycle of 15 Hz.

  If the backlight control signal 105 is “H” (high level) when turned on and “L” (low level) when turned off, the AC cycles (1) to (3), (5) to (7),. The backlight control signal 105 during the periods (57) to (59) outputs “H” (see the timing diagram of the moving image cycle 15 Hz in FIG. 2). 1 ″ image data is output (see FIG. 4).

  On the other hand, the backlight control signal 105 during the period (4), (8), (12),... (56), (60),. “L” is output (see the timing diagram of the moving image cycle 15 Hz in FIG. 2), and in each period, the liquid crystal module 16 outputs “1” image data and then turns off (see FIG. 4).

  That is, the insertion of the black screen is 15 times per second, which is reduced to a quarter of the conventional 60 times.

  As described above, according to the first embodiment of the present invention, since the black screen insertion timing is controlled in accordance with the moving image cycle, the number of black screen insertions can be reduced as compared with the conventional case. It is possible to prevent the decrease.

  The second embodiment shows an example of a display device that inserts a black screen under control of writing a black screen into a liquid crystal element. FIG. 5 is a block diagram of a second embodiment of the display device according to the present invention. In the figure, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.

  The display device 21 of the second embodiment is different from the display device 1 of the first embodiment in that the liquid crystal control unit 15 of the second embodiment further supplies an AC drive control signal 106 and a black screen write signal to the liquid crystal module 16. 107 is output. Others are the same as the first embodiment.

  When the control for writing the black screen into the liquid crystal element is applied, the liquid crystal control unit 15 manages the image data signal 101 and the horizontal synchronization signal 102 in order to manage and control the AC drive normally managed by the liquid crystal module 16 by the liquid crystal control unit 15. In addition to the vertical synchronization signal 103 and the pixel clock signal 104, an AC drive control signal 106 is required. The liquid crystal module 16 performs an operation of positive (+) driving when the AC drive control signal 106 is “H” and negative (−) driving when “L”.

  In addition to this, a black screen writing signal 107 is required for black screen writing control. When the black screen writing signal 107 is “L”, the liquid crystal module 16 performs black screen writing. The black screen is written during the black screen insertion period determined in advance according to the characteristics of the liquid crystal.

  Next, the operation of the second embodiment will be described. First, an example of black screen writing operation in the case of a moving image cycle of 15 Hz will be described.

  FIG. 6 is a diagram showing AC drive and black screen insertion timing when the moving image frame rate is 15 Hz, and FIG. 7 is a diagram showing black screen writing detailed timing when the moving image frame rate is 15 Hz.

  Referring to pattern A in FIG. 6, the liquid crystal control unit 15 sets the AC drive control signal 106 to “H” and the black screen write signal 107 to “H” during the AC cycle (1). In the period of the AC cycle (2), “L”, “H”, respectively, in the period of the AC cycle (3), “H”, “L”, respectively, in the period of the AC cycle (4), “L”, “L”.

  For the AC cycle (5) and thereafter, the same operation as in the AC cycles (1) to (4) is repeated.

  The liquid crystal module 16 performs AC driving and black screen writing according to this signal, whereby the control of the pattern A in FIG. 6 can be realized.

  That is, according to the present embodiment, the black screen is written equally on the positive (+) voltage side and the negative (−) voltage side of the moving image cycle. Accordingly, it is possible to prevent the liquid crystal element from deteriorating due to the AC driving of the liquid crystal being lost.

  In the pattern A in FIG. 6, black screen writing is performed at the end of each moving image frame (for example, refer to the waveforms in the AC cycles (3) and (4) of the pattern A in FIG. 6), but the pattern B in FIG. It is also possible to write a black screen between moving image frames (see, for example, the waveforms in the AC cycles (4) and (5) of pattern B in FIG. 6).

  Further, the black screen writing effect is improved by performing the backlight control together with the black screen writing. FIG. 7 shows waveforms of an AC cycle and a moving image cycle when black screen writing and backlight control are performed together in pattern A. Referring to the figure, by the AC drive control signal 106 and the black screen write signal 107, the black screen is written equally on the positive (+) voltage side and the negative (−) voltage side of the moving image cycle, and the backlight control signal. The backlight lighting control is performed by 105 (see waveforms in AC cycles (3) and (4) in FIG. 7).

  Next, an example of black screen writing operation in the case of a moving image cycle of 30 Hz will be described. FIG. 8 is a diagram showing AC drive and black screen insertion timing when the moving image frame rate is 30 Hz, and FIG. 9 is a diagram showing black screen writing detailed timing when the moving image frame rate is 30 Hz.

  Referring to pattern C in FIG. 8, the liquid crystal controller 15 sets the AC drive control signal 106 to “H” and the black screen write signal 107 to “H” during the AC cycle (1). In the period of the AC cycle (2), “L”, “L”, respectively, in the period of the AC cycle (3), “L”, “H”, respectively, in the period of the AC cycle (4), “H”, “L”.

  For the AC cycle (5) and thereafter, the same operation as in the AC cycles (1) to (4) is repeated. As shown in FIG. 6, the AC drive timing is different from that in FIG.

  The liquid crystal module 16 performs AC driving and black screen writing according to this signal, whereby the control of the pattern C in FIG. 8 can be realized.

  That is, according to this embodiment, the black screen is written equally on the positive (+) voltage side and the negative (-) voltage side of the moving image cycle. Accordingly, it is possible to prevent the liquid crystal element from deteriorating due to the AC driving of the liquid crystal being lost.

  In the pattern C of FIG. 8, black screen writing is performed between the moving image frames (for example, refer to the waveforms in the AC cycles (2) and (3) of the pattern C of FIG. 8). Thus, it is also possible to write a black screen at the end of each moving image frame (for example, refer to the waveforms in the AC cycles (2) and (3) of the pattern D in FIG. 8).

  Further, the black screen writing effect is improved by performing the backlight control together with the black screen writing. FIG. 9 shows waveforms of an AC cycle and a moving image cycle when black screen writing and backlight control are performed together in pattern C. Referring to the figure, by the AC drive control signal 106 and the black screen write signal 107, the black screen is written equally on the positive (+) voltage side and the negative (−) voltage side of the moving image cycle, and the backlight control signal. The backlight lighting control is performed by 105 (see waveforms in AC cycles (2) and (4) in FIG. 9).

1 is a configuration diagram of a first embodiment of a display device according to the present invention. It is a figure which shows an example of the black screen insertion timing in backlight lighting control. It is a detailed timing diagram of an example of backlight control when the moving image frame rate is 30 Hz. It is a detailed timing diagram of an example of backlight control at a moving image frame rate of 15 Hz. It is a block diagram of 2nd Example of the display apparatus which concerns on this invention. It is a figure which shows the alternating current drive at the time of a moving image frame rate 15Hz, and a black screen insertion timing. It is a figure which shows the black screen writing detailed timing at the time of moving image frame rate 15Hz. It is a figure which shows the alternating current drive at the time of a moving image frame rate 30Hz, and a black screen insertion timing. It is a figure which shows the black screen writing detailed timing at the time of moving image frame rate 30Hz. FIG. 11 is a diagram showing a relationship between luminance and time of a conventional liquid crystal, and FIG. 11 is a diagram showing a relationship between luminance and time of the liquid crystal when a conventional black screen is inserted. It is a figure which shows the relationship between the brightness | luminance of liquid crystal at the time of the conventional black screen insertion, and time. It is a figure which shows the conventional liquid crystal alternating current drive voltage and the relationship of time. It is a figure which shows the liquid crystal alternating current drive voltage at the time of black screen writing, and the relationship of time.

Explanation of symbols

1, 21 Display device 11 Antenna 12 RF unit 13 Baseband processing unit 14 CPU
15 Liquid Crystal Control Unit 16 Liquid Crystal Module 17 Image Memory 18 Backlight

Claims (14)

A display device that displays a moving image by AC driving a display element,
The frame rate for AC driving the display element is different from the frame rate of the moving image.
A display device comprising black screen insertion means for inserting a black screen based on a frame rate of the moving image. Including illumination for illuminating the display element from the back;
The display device according to claim 1, wherein the black screen insertion unit controls lighting of the illumination based on a frame rate of the moving image. The display device according to claim 1, wherein the black screen insertion unit writes the black screen into the display element based on a frame rate of the moving image. 4. The display device according to claim 1, wherein the black screen is inserted between frames of the moving image. 4. The display device according to claim 3, wherein the black screen is inserted equally on a positive (+) voltage side and a negative (-) voltage side of a moving image cycle. The display device according to claim 1, wherein the display device is used in a portable device. The display device according to claim 1, wherein the display device has a telephone function. A display device driving method for displaying a moving image by alternating-current driving a display element,
The frame rate for AC driving the display element is different from the frame rate of the moving image.
A driving method comprising a black screen insertion step of inserting a black screen based on a frame rate of the moving image. Including illumination for illuminating the display element from the back;
9. The driving method according to claim 8, wherein the black screen insertion step controls lighting of the illumination based on a frame rate of the moving image. 10. The driving method according to claim 8, wherein the black screen insertion step writes the black screen into the display element based on a frame rate of the moving image. The driving method according to claim 8, wherein the black screen is inserted between frames of the moving image. The driving method according to claim 10, wherein the black screen is inserted equally on a positive (+) voltage side and a negative (−) voltage side of a moving image cycle. The driving method according to claim 8, wherein the driving method is used for a portable device. 14. The driving method according to claim 8, wherein the driving method has a telephone function.

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