JP2004020738A - Liquid crystal display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display that is free from nonuniformity in display brightness in the display screen, where the nonuniformity is caused by the delay of liquid crystal response in a liquid crystal display element for which a liquid crystal panel and a flickering light emitting back light are combined. <P>SOLUTION: To the liquid crystal, there is applied a corrected voltage with the voltage value adjustably varied depending on a display area where time to take is comparatively long from the rewriting of a display signal until the emission of a back light and a display area where it is comparatively short. Consequently, nonuniformity of the display due to the response speed of the liquid crystal is improved as the characteristic of this display element. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a liquid crystal display device, and more particularly to an improvement in display uniformity of a liquid crystal display device using a backlight that emits light by blinking.
[0002]
[Prior art]
A liquid crystal display element is used as a display element for displaying a color image. In general, a combination of a white backlight that is always lit, a liquid crystal that performs light switching, and color filters of three primary colors of red, green, and blue is used. Performs color display. On the other hand, in order to improve the productivity and display performance of the liquid crystal display device, there has been proposed a liquid crystal display device using a blinking backlight that periodically turns on and off light emission.
[0003]
For example, Japanese Patent Application Laid-Open No. 2000-147454 discloses a method of blinking a white backlight in order to improve the visibility of a liquid crystal display element when displaying a moving image. In this method, the procedure of rewriting the display content of the screen while the backlight is off, turning on the backlight for a certain short period of time, then turning off the backlight, and then rewriting the display content of the moving image is repeated. .
[0004]
Japanese Patent Application Laid-Open No. H5-40260 proposes a liquid crystal display device that uses a backlight that emits light by blinking three primary colors of red, green, and blue and that uses a three-primary-color sequential lighting method without using a color filter. The liquid crystal display device based on the sequential lighting method of three primary colors is composed of a black and white liquid crystal display device that does not use a color filter and a backlight of three primary colors of red, green, and blue that can independently emit light. Are sequentially turned on for a certain short period of time to perform display.
[0005]
These blinking light emitting type liquid crystal display elements rewrite the display content of the liquid crystal element and emit the backlight when the response of the liquid crystal is almost completed.
[0006]
[Problems to be solved by the invention]
FIG. 6 shows a configuration of a display portion of a general liquid crystal display element. In FIG. 6, reference numeral PS denotes a video signal, SS denotes a synchronizing signal, ICd denotes a signal wiring driving IC, ICs denotes a selection wiring driving IC, SL denotes a signal wiring, L denotes a selection wiring, and P denotes a liquid crystal panel. As shown in FIG. 6, many liquid crystal display elements use a matrix type liquid crystal panel P on which signal lines SL are formed vertically and horizontally. The horizontal wiring is called a gate wiring or a selection wiring L, and selects a line for rewriting display. The vertical wiring is a wiring called a source wiring or a signal wiring SL, and supplies a display content to be rewritten by a voltage. At the intersection of the signal line SL and the selection line L, a pixel electrode for applying a voltage to the liquid crystal is formed. In a TFT (Thin Film Transistor) liquid crystal display element, a TFT is further formed at the intersection. The selection lines L are sequentially turned on one by one, and a voltage corresponding to the selected row of display content is supplied to the pixel electrode from the source line SL, and a voltage is applied to the liquid crystal.
[0007]
As described above, in the general liquid crystal display device, the display contents on the screen are not rewritten at once, but the selection lines L are selected one by one in order from the top of the display screen in the downward direction (or the upward direction from the bottom) and the scanning is performed. While the screen is being rewritten. When such a liquid crystal display element is combined with a blinking backlight, the timing at which the display is rewritten differs between an area where scanning is performed first in the display screen and an area where scanning is performed with a delay. There is no problem when the response to the voltage change of the liquid crystal is infinitely fast, but the response of the liquid crystal is generally tens to several tens ms and cannot be ignored. FIG. 7 shows the influence of the response speed of the liquid crystal. 7A is a graph showing an optical response waveform at the top of the screen, FIG. 7B is a graph showing an optical response waveform at the bottom of the screen, and FIG. 7C is a light emitting (ON) state of the light source. 7 is a graph showing the timing of the light-off (OFF) state. In FIG. 7, reference numeral T1 1 display period, the bright _{levels Lb 10} is to be displayed, dark level _{Ld 10} is to be displayed, _{Lb 11} bright levels to be displayed is, _{Ld 11} is a dark level to be displayed, respectively Is shown. In the part of the display screen where scanning is performed first, sufficient time is required for the liquid crystal response from the point of screen rewriting to the emission of the backlight. In some cases, sufficient time cannot be taken for light emission, and the response of the liquid crystal may not be in time. For example, FIGS. 7A to 7C show an example in which scanning starts from the upper part of the screen and ends at the lower part of the screen. In the example shown in FIG. In the upper part of the screen, the time from the change of the signal applied to the liquid crystal to the light emission (ON) of the backlight is long, and the response of the liquid crystal is sufficient, and a predetermined display Br ₁ is obtained. On the other hand, at the lower part of the screen where scanning is performed slowly, the time from the change of the signal applied to the liquid crystal to the light emission of the backlight is short, and the backlight is turned on in a state where the response of the liquid crystal is insufficient, and the display is Br _2. , And the predetermined display is not obtained. For the reasons described above, the liquid crystal display device using the blinking backlight has a problem that the brightness is different between, for example, the upper part and the lower part of the screen. SUMMARY OF THE INVENTION It is an object of the present invention to improve non-uniformity of display on a screen due to a response speed of a liquid crystal and to obtain a uniform display in a liquid crystal display device using a blinking backlight.
[0008]
[Means for Solving the Problems]
The present invention includes a transmissive liquid crystal panel capable of controlling the amount of light, and a backlight disposed on the back of the liquid crystal panel and capable of blinking and emitting light, the timing corresponding to a display rewriting cycle of the liquid crystal panel. In a matrix type liquid crystal display element in which a backlight emits light, different voltages are applied to a display area in which a relatively long time from rewriting of a display signal to emission of the backlight can be obtained, and an area in which the time is relatively short. By applying a voltage to which the correction voltage is applied to the liquid crystal, display non-uniformity caused by the response speed of the liquid crystal is improved.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiment 1
First Embodiment A first embodiment of the present invention will be described with reference to FIGS. 1A is a graph showing an optical response waveform at an upper portion of the screen, FIG. 1B is a graph showing an optical response waveform at a lower portion of the screen, and FIG. 1C is a light emitting (ON) state and a light OFF (OFF) state of a light source. (D) is a graph showing a voltage waveform applied to the liquid crystal at the top of the screen, and (e) is a graph showing a voltage waveform applied to the liquid crystal at the bottom of the screen. That is, FIG. 1 illustrates an optical response waveform of a liquid crystal of a matrix type liquid crystal display element in which a backlight emits light at a timing corresponding to a display rewriting cycle of a liquid crystal panel, and a backlight emission timing. T1 is one display period in FIG. 1, Lb ₁ is bright level to be displayed, Ld ₁ is dark level, Lb ₂ is bright levels to be displayed to be displayed, Ld ₂ dark level to be displayed, Vb ₁ is bright level applied voltage corresponding to, Vd ₁ is applied voltage corresponding to the dark level, Vb ₂ is applied voltage corresponding to the bright level, Vd ₂ applied voltage corresponding to the dark level, the applied voltage waveform before Wf1 is being corrected Is shown.
[0010]
In this liquid crystal display device, the brightness increases as the voltage applied to the liquid crystal increases, and the rewriting of the display is performed by scanning from the top to the bottom of the screen. The optical response waveform of the liquid crystal is shown in two cases, upper and lower portions of the screen (FIGS. 1A and 1B).
[0011]
When the display is switched from a low voltage to a high voltage, display rewriting is performed in the upper part of the screen, and the backlight is lit when the response of the liquid crystal is almost completed. After display rewriting the screen bottom is performed, the compensated voltage as predetermined brightness at the time the backlight emits light is obtained by applying a high voltage V'b ₂ than the predetermined voltage in this example The brightness of the upper part of the screen and the lower part of the screen at the time of backlight emission are the same (see FIG. 1 (e)).
[0012]
When the display is switched from a high voltage to a low voltage, a voltage V′d ₂ lower than a predetermined voltage is applied to the lower part of the screen, so that the brightness of the upper part and the lower part of the screen become the same at the time of backlight emission. (See FIG. 1 (e)).
[0013]
Embodiment 2
The first embodiment is effective when the contents of the display are binary values of ON and OFF, but may cause a problem when the contents of the display include halftones. For example, FIG. 2 shows the relationship between the correction voltage and the optical response when the display method changes from off to on and when the display changes from an intermediate level between on and off, using the correction method of the first embodiment. . FIG. 2A shows an optical response waveform when the display changes from off to on at the bottom of the screen, and FIG. 2B shows an optical response waveform when the display changes from the intermediate level to on. (C) corresponds to (c) in FIG. 1, and (d) in FIG. 2 is a graph showing a voltage waveform applied to the liquid crystal at the bottom of the screen.
[0014]
T1 is one display period in FIG. 2, Lb ₃ is bright levels to be displayed, Ld ₃ dark level, Lb ₄ is bright levels to be displayed to be displayed, Ld ₄ dark level to be displayed, Vb ₃ is bright levels applied voltage corresponding to, Vd ₃ is applied voltage corresponding to the dark level, CWf1 is corrected applied voltage waveform, Wf2 shows the applied voltage waveforms before being corrected.
[0015]
When setting the correction voltage at the lower part of the screen, assuming that the previous screen is at a dark level, if the same correction voltage is applied to the liquid crystal when the previous screen is at an intermediate level between on and off, The correction is too strong, and the display may be higher than a predetermined brightness (arrow H2 in FIG. ₂ ). As described above, when the display content includes a halftone, it is necessary to perform a correct display by determining the correction voltage in accordance with the display of the previous screen. FIG. 3 shows an example in which the correction voltage is determined according to the display of the previous screen. 3 (a) to 3 (c) correspond to FIGS. 2 (a) to 2 (c), but FIG. 3 (d) is applied to the liquid crystal at the bottom of the screen as in FIG. 2 (d). 4 is a graph showing a voltage waveform to be applied.
[0016]
3. In the drawing T1 is 1 display period, Lb ₅ Ming level to be displayed, Ld ₅ dark level to be displayed, Lb ₆ is bright level to be displayed, Ld ₆ dark level to be displayed, Vb ₄ Ming applied voltage corresponding to the level, Vd ₄ is applied voltage corresponding to the dark level, CWf2 the applied voltage waveform display of the previous screen is corrected in the case of dark level, CWf3 the previous screen of the display is dark preparative Ming intermediate level 3 shows the corrected applied voltage waveform in the case of FIG.
[0017]
When setting the correction voltage at the lower part of the screen, if the previous screen is at a dark level, a voltage CWf2 having a waveform obtained by adding a relatively large correction voltage is applied to the liquid crystal. If applied when turning on from an intermediate level, an overshoot of the optical response waveform occurs. To prevent this, a voltage CWf3 having a waveform obtained by adding a relatively small correction voltage is applied to the liquid crystal. By performing the correction corresponding to the display level of the previous screen as described above, it is possible to perform the display at the same display level at the lower part of the screen as at the upper part of the screen, regardless of the display level of the previous screen. .
[0018]
Embodiment 3
In the second embodiment, since the correction voltage at the lower part of the current screen is determined according to the contents of the display of the previous screen, it is necessary to compare the contents of the display between the previous screen and the current screen. FIG. 4 is a block diagram of a circuit configuration of a means for comparing the contents of display between the previous screen and the current screen and determining a correction voltage. In FIG. 4, reference numeral FM is a frame memory, TM is a reference table memory, P is a liquid crystal panel, IS is an image signal, SS is a synchronization signal, D1 is current display data, D2 is display data of the previous screen, and D3 is corrected. FIG.
[0019]
In FIG. 4, the frame memory FM is for storing image data for one display screen, and sends out the stored image data to the reference table memory TM with a delay of one display cycle. In the reference table memory TM, a correction voltage determined by comparing the current image with the image of the previous screen is stored in advance. The reference table memory TM calculates a correction voltage by comparing the current display data D1 with the previous display data D2 output from the frame memory FM, and adds or subtracts the correction voltage from the current display data D2 to the liquid crystal panel P as correction data. send. The correction amount is also changed between the upper part and the lower part of the liquid crystal panel P, and the contents are also stored in advance in the reference table memory TM so that the lower part and the upper part of the screen and the correction by the previous screen and the current screen are corrected. Both can be implemented.
[0020]
Instead of searching the table memory TM, a calculation (digital) may be performed by substituting the data D1, D2 and the vertical position on the screen into a response equation solution based on the response characteristic of the liquid crystal. .
[0021]
An analog signal can be used for the image signal and the memory. However, since the memory is generally digital, it is preferable to use a digital signal for the image signal in terms of cost and circuit scale.
[0022]
Embodiment 4
Embodiment 4 of the present invention will be described with reference to FIGS. 5A is a graph showing an optical response waveform, FIG. 5B is a graph showing the timing of a light emitting (ON) state and a light OFF (OFF) state of the light source, and FIG. 5C is a voltage waveform applied to the liquid crystal at the bottom of the screen. FIG. 5, reference numeral T1 is one display period, Lb ₇ Ming level to be displayed, Ld ₇ dark level to be displayed, Vb ₅ is applied voltage corresponding to the bright level, Vd ₅ corresponds to the dark level applied The voltage, Wf3 indicates the original voltage waveform, and CWf4 indicates the corrected voltage waveform.
[0023]
In the fourth embodiment, one display period is divided into two, a voltage corresponding to black is applied to the liquid crystal during the first half display period, and a predetermined display voltage is applied to the panel during the subsequent half display period. And a voltage obtained by adding or subtracting a voltage for correcting the response speed according to the display location. Since black is always displayed before the predetermined display, it is not affected by the display before that. Therefore, it is not necessary to perform the correction corresponding to the display content of the previous screen as described in the second embodiment, but only the correction corresponding to the display location as in the first embodiment.
[0024]
The ratio of dividing the display period is generally half, but may be divided at other ratios according to the response speed of the liquid crystal from light to dark and from dark to light.
[0025]
【The invention's effect】
According to the liquid crystal display device of the present invention, the display non-uniformity caused by the response speed of the liquid crystal generated in the rewriting scanning direction of the display of the liquid crystal panel is corrected by the voltage applied to the liquid crystal. In the liquid crystal display element used, the non-uniformity of the display on the screen due to the response speed of the liquid crystal can be improved, and a uniform display can be obtained.
[Brief description of the drawings]
FIG. 1 is a timing chart showing the operation of the liquid crystal display device of the present invention.
FIG. 2 is a timing chart illustrating a display of a defect of a liquid crystal display element.
FIG. 3 is a timing chart showing the operation of another embodiment of the liquid crystal display device of the present invention.
FIG. 4 is a block diagram illustrating a configuration of a liquid crystal display element according to an embodiment of the present invention.
FIG. 5 is a timing chart showing the operation of another embodiment of the liquid crystal display device of the present invention.
FIG. 6 is a diagram illustrating a configuration of a liquid crystal display element.
FIG. 7 is a timing chart showing the operation of a conventional liquid crystal display element.
[Explanation of symbols]
P Liquid crystal panel D1 Current display data D2 Display data D3 of previous screen Corrected display data FM Frame memory IS Image signal SS Synchronization signal TM Table memory

Claims (4)

A transmissive liquid crystal panel capable of controlling the amount of light,
A backlight that is arranged on the back of the liquid crystal panel and that can emit light by flashing light;
A matrix type liquid crystal display element in which a backlight emits light at a timing corresponding to a display rewriting cycle of a liquid crystal panel,
A liquid crystal display device wherein a display non-uniformity caused by a response speed of a liquid crystal generated in a rewriting scanning direction of a display of a liquid crystal panel is corrected by a voltage applied to the liquid crystal. A transmissive liquid crystal panel capable of controlling the amount of light,
A backlight that is arranged on the back of the liquid crystal panel and that can emit light by flashing light;
A matrix type liquid crystal display element in which a backlight emits light at a timing corresponding to a display rewriting cycle of a liquid crystal panel,
The current display content and the display content one display cycle before are compared, and if the voltage applied to the liquid crystal is higher in the current display content than in the previous display content, it is higher than the voltage corresponding to the current display content. When the voltage corrected as described above is applied to the liquid crystal, and the voltage applied to the liquid crystal is lower in the current display content than in the previous display content, the voltage corrected so as to be lower than the voltage corresponding to the current display content. Has a function of applying liquid crystal, and the correction amount is reduced in a portion where the display rewriting scanning is started in the display area of the liquid crystal panel, and is increased in a portion where the display rewriting scanning is completed. A liquid crystal display device characterized by the above-mentioned. A transmissive liquid crystal panel capable of controlling the amount of light,
A backlight that is arranged on the back of the liquid crystal panel and that can emit light by flashing light;
In a matrix type liquid crystal display element in which a backlight emits light at a timing corresponding to a display rewriting cycle of a liquid crystal panel,
The LCD panel displays the display contents and turns off the display in a specific cycle.
In the case of a liquid crystal element in which the display becomes darker as the higher voltage is applied, a voltage corrected so as to be lower than the voltage corresponding to the display content is applied at a portion where the display rewriting scan is completed, and the higher the voltage is applied, A liquid crystal display element characterized in that a voltage corrected so as to be higher than a voltage corresponding to display contents is applied to a portion where display rewriting scanning is completed in a liquid crystal element having a structure in which display becomes brighter. The liquid crystal display device further comprises means for storing correction data in advance so that the display on the entire display screen of the liquid crystal display becomes uniform, and means for applying a voltage based on the stored correction data to the liquid crystal. 4. The liquid crystal display device according to claim 1, wherein:

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