JP2000322029A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device excellent in animation display. SOLUTION: A liquid crystal display device is provided with a liquid crystal display panel, a liquid crystal drive circuit, and a light source providing an intensity modulation function, and irradiating an illumination light twice or more intermittently in a display period for one screen to allow a human eye to recognize the image. Flashing the light source reduces an effect of an afterimage of a previous displayed screen, thereby increasing the display quality of animation display. Flashing the light source at a high frequency provides a displayed screen without a flicker.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device in which the influence of an afterimage is reduced by intermittently irradiating illumination light a plurality of times during one screen display (frame) period.

[0002]

2. Description of the Related Art In recent years, display devices using liquid crystals have been widely used as monitors or projection devices. In particular, liquid crystal display devices for monitors have been widely used as the viewing angle of liquid crystals has been increased. For such a liquid crystal display device, a nematic liquid crystal having a relatively low operation speed is used. In general, a liquid crystal element has a size of 10 to 2 for binary display of black and white.
Although a response is made in a short time of 0 ms, a halftone (gradation) display requires a long response time, for example, a response time of about 100 ms is required. For this reason, conventionally, it has been difficult to display a moving image using a liquid crystal display device.

In recent years, a liquid crystal mode which responds relatively quickly has been researched and developed. An example of this is the document "Initialization of Optically Compensated Bend-Mode Elsidis", Nakamura et al., AMLC
D96 133 page, literature "Fast Response Liquid Crystal Display", flat, AM
LCD98 page 113 can be mentioned. In the liquid crystal display devices described in these documents, the liquid crystal element responds within a few milliseconds. The response time of this liquid crystal element is sufficiently fast in consideration of the fact that a screen is generally rewritten every 16.7 ms in a moving image.

However, even if the response speed of the liquid crystal element itself is increased, another problem still remains. This will be described with reference to FIGS. 15 and 16 in comparison with a CRT conventionally used for moving images. Generally, an afterimage occurs in human eyes during the display of a moving image. This afterimage is indicated by a dotted line in each of the following drawings. FIG. 15 shows a display on a CRT.
FIG. 3A shows a screen configuration when a white ellipsoid moves in a black screen from the first frame to the third frame, and FIG. The luminance signals at the display screen positions (points) A, B, and C in a) are represented by solid lines. In a CRT, fluorescence is generated immediately after scanning with an electron beam, and this fluorescence disappears quickly. Therefore, in the CRT, the display information of the first frame does not remain in the second frame.

FIG. 16 shows a display on the liquid crystal display device, similarly to FIG. FIG. 2B shows the amount of transmitted light at each of points A, B, and C, and the liquid crystal panel recognizes an image based on the amount of transmitted light. As can be understood from the figure, in the liquid crystal display device, the afterimage of the point A remains until the second frame, and in the second frame, the afterimage of the point A, the luminance signal of the point B, and the luminance signal of the point C overlap. I do.
As described above, in the liquid crystal display device, there is a problem that a moving image display is generated in which information of the previous frame is dragged and trailing.

The aforementioned document "Fast Response Liquid Crystal Display", Flat, AMLCD
On page 98, 113, the backlight is turned on only at the end of the frame to prevent the above problem. This is shown in FIG. 17 as a diagram similar to FIG. That is, in this liquid crystal display device, since the illumination light is emitted only at the end of each frame, the luminance signal characteristics as shown in FIG. In this case, the afterimages indicated by the dotted lines remain only when the illumination is not turned on, and are not recognized by human eyes. That is, in this liquid crystal display device, the information of the previous frame does not remain and the display does not have a trailing edge, so that a good moving image can be obtained.

[0007]

Generally, one frame period of the liquid crystal display device is 16.7 ms, and the screen is updated at a frequency of 60 Hz. Therefore, in the liquid crystal display device of the above document, the luminance is modulated by the flickering of the backlight at this frequency. This frequency is perceived as continuous by human vision, and it is considered that no flicker (ie, flicker) is perceived.

[0008] However, it is well known that the frequency at which flicker is perceived increases as the luminance increases as a characteristic of human vision. The visual sensitivity to this frequency is
Known as the DeLange function. Therefore, in the above-described method, if the screen luminance increases, flicker of 60 Hz is felt.

If the backlight emits exactly the same luminance when the backlight is blinking, the frequency characteristic of the luminance has a spectrum of 60 Hz or more. However, if the luminance at the moment of each blinking fluctuates, it will have a component below 60 Hz.
In this case, flicker is more easily felt.

As described above, the method described in the above-mentioned document does not perceive an afterimage, so that it is excellent in displaying a moving image, but has a problem that flicker easily occurs.

In view of the above, it is an object of the present invention to provide a liquid crystal display device suitable for displaying moving images by reducing afterimages and flicker perceived on a liquid crystal display panel.

[0012]

In order to achieve the above object, a liquid crystal display device according to the present invention comprises a liquid crystal display panel, a liquid crystal drive circuit for controlling display of a screen on the liquid crystal display panel, and the liquid crystal drive circuit. And a light source that modulates luminance in synchronization with the operation of the light source, wherein n is an integer of 2 or more,
The liquid crystal display panel is characterized in that illumination light is intermittently irradiated n times within one screen display period.

The operation of the liquid crystal display device of the present invention will be described with reference to FIG. In the liquid crystal display device of the present invention, the screen of the liquid crystal display panel is rewritten every frame period by the liquid crystal driving circuit. During this one frame period, the illumination light is emitted intermittently n times (n ≧ 2) from a backlight light source (hereinafter, also simply referred to as a light source). FIG. 1 illustrates a case where the illumination light is intermittently emitted twice for simplicity. In other words, by the illumination light, human eyes,
The display screen is recognized twice within one frame period. In the figure, the afterimages of the first frame and the second frame are indicated by dotted lines. Here, the afterimage of the point A lit in the second half of the first frame appears on the lit screen of the first half of the second frame. However, this afterimage appears only during one lighting period, and is extremely short. That is, it does not appear on the lighting screen in the latter half of the second frame. For this reason, the extent to which the image trails is reduced. Further, since the lighting cycle is twice the frame frequency, the luminance blinks at a high frequency. For this reason,
Even if there is some fluctuation in luminance, it is not easily recognized as flicker by human eyes.

In the liquid crystal display device of the present invention, one frame period includes a plurality of combinations of a non-irradiation period and an irradiation period of illumination. Therefore, how to set a combination of the non-irradiation period and the irradiation period is a practical problem. It is known that this setting generally depends on the screen luminance. On the other hand, the screen luminance is also determined by the luminance of a light source that performs irradiation multiple times. That is, the combination of the non-irradiation period and the irradiation period is determined in consideration of the screen luminance.

In the above-described example, illumination light irradiation is performed twice, that is, at an intermediate time and an end time of one frame period, and at the time of the irradiation, an image is recognized by human eyes. Here, in general, the liquid crystal display panel is scanned from the upper part to the lower part of the screen. Therefore, at the time of irradiation in the middle of each frame period, the upper screen is already rewritten and the lower screen is recognized in the previous display state. Next, at the time of irradiation at the end of the frame period, the upper and lower screens are recognized in a state in which rewriting has been completed. This situation will be described with reference to FIGS.

FIG. 2 shows a state in which an object moves in a direction opposite to the screen scanning (upward of the screen). In this case, as shown by the dotted line, the screen of the second half of the first frame is recognized as overlapping with the screen of the first half of the second frame due to the afterimage.
Therefore, the object looks long in the vertical direction. On the other hand, FIG. 3 shows a state in which the object moves in the same direction (downward of the screen) as the screen scan on the same liquid crystal display device. Also in this case, although the second half screen of the first frame is recognized as overlapping with the first half screen of the second frame due to the afterimage, the images of the point A and the point B do not overlap, and the object is recognized vertically, but FIG. 2 is better than 2. Thus, FIGS. 2 and 3
When compared with the above, there is asymmetry in which a difference occurs in the display screen depending on the order of the screen scanning direction and the object moving direction. FIG.
FIG. 3 shows how the scanning order is switched to alleviate the asymmetry when the object moves from the top to the bottom of the screen, as in FIG. In order to alleviate the asymmetry, the scanning direction is switched between upper and lower scanning of the screen and lower and upper scanning of the screen for each frame. in this case,
The image at the point A and the image at the point B do not appear to overlap, and the asymmetry is reduced.

As another method for reducing asymmetry, there is a method based on interlaced scanning in which scanning lines are thinned out for scanning. This is shown in FIG. In the figure, interlaced scanning is performed in which, for example, an odd-numbered frame scans an odd-numbered scanning line, and an even-numbered frame scans an even-numbered scanning line. In this case, the afterimage of point B in the second half of the first frame overlaps with the transmitted light of point A in the first half of the second frame, but the number of scanning lines in each scan is one.
/ 2, so that the amount of afterimages overlapping between the frames is also reduced to 緩和, thereby reducing the asymmetry that occurs on the display screen.

It is a preferred embodiment of the present invention that the light source is a light source group including a plurality of light sources having different wavelength bands. The plurality of light source groups are sequentially illuminated to perform color display, and preferably, each of the light sources is one light source within one screen display period.
Irradiation light whose luminance has been modulated is applied.

FIG. 6 shows an example of irradiation by a liquid crystal display device having a light source group composed of a plurality of light sources. In the example of FIG.
Lighting illumination is performed in each of R, G, and B colors. That is, three colors of illumination light having the same time width are sequentially emitted within one display period. FIG. 6 shows a state in which the white ellipse moves from the left to the right of the screen. At this time, as can be understood from FIG. 6, for example, the afterimage of the point A of the first frame overlaps with the display images of the points B and C of the second frame within the second frame period. However, in this case, since only the afterimage of any color of R, G, or B overlaps the display images of R, G, and B, the afterimage of white light overlaps with the display image. The effect is reduced. In the case of a liquid crystal display panel using a color filter, the number of R, G, or B display pixels is 1/3 of the whole, and in this sense, the afterimage is reduced.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail based on embodiments of the present invention. The liquid crystal display panel used in the present invention may be a simple matrix type liquid crystal panel or an active matrix type driving liquid crystal panel.
However, in any case, a liquid crystal element having a high response speed and capable of completing a response within one frame period is used.

FIG. 7 shows the configuration of the liquid crystal display device according to the first embodiment of the present invention. Here, a case where an antiferroelectric liquid crystal is used as a simple matrix type liquid crystal display panel will be described as an example. The response time of the antiferroelectric liquid crystal is 1 ms or less, and a sufficient response can be made within one frame period. Pixels in the liquid crystal display panel 17 are composed of scanning electrodes made of transparent electrodes, signal electrodes made of transparent electrodes, and antiferroelectric liquid crystals. As shown in FIG. 8, the voltage waveform applied to the scan electrode changes to a pair of negative and positive pulses during the selection period, a small positive holding voltage during the holding period, and zero voltage during the reset period. On the other hand, as shown in FIG. 8, a pair of positive and negative signal pulses or a pair of negative and positive signal pulses is applied to the signal electrode according to each of the bright and dark pixels. Is done. Each signal pulse is
It has an amplitude corresponding to the image to be displayed.

FIG. 7 shows a scan electrode drive circuit (scan drive circuit) 11 and a signal electrode drive circuit (signal drive circuit) 12 as drive circuits for generating the above voltage waveforms. The voltage supplied to the scan drive circuit 11 and the signal drive circuit 12 is generated by the control circuit 13 based on an externally input video signal. On the other hand, a synchronization signal synchronized with the video is sent from the control circuit 13 to the multiplication circuit 14, where the necessary synchronization signal having a frequency twice or three times the frame frequency is generated. This multiplied synchronization signal is sent to the backlight control circuit 15. The backlight light source 16 blinks in synchronization with the multiple synchronization signal. The backlight control circuit 15 controls a lighting period and a non-lighting (light-out) period of the backlight light source 16.

As described above, if the lighting period is extended, the luminance is improved, but it is necessary to set the light-off period according to the average luminance of the screen. Therefore, the sum of the lighting period and the turning-off period may not be equal to the frame period. In this case, the video signal is once sent to the frame conversion circuit to adjust the frame frequency. Such conversions are well known for video conversion between different television systems.

The above is an example employing an antiferroelectric liquid crystal display panel. In contrast, a thin film transistor (T
An active matrix type liquid crystal display panel using FT) can employ the same method. TFT
FIG. 9 shows a liquid crystal display device according to a second embodiment of the present invention using the above. In the liquid crystal display device of the present embodiment, the liquid crystal element in the liquid crystal display panel 17 is, for example, a twisted nematic liquid crystal having a gap of 2 μm or less, a ferroelectric liquid crystal having polarization,
Alternatively, an antiferroelectric liquid crystal or the like is used. Further, a nematic liquid crystal that has not been twisted can also be used. The configuration of FIG. 9 is the same as the liquid crystal display of FIG. 7 except for the configuration of the liquid crystal display panel 17.

FIG. 10 is a scanning timing chart of the liquid crystal display of FIG. Scanning is performed sequentially from the top to the bottom of the screen, illumination light is irradiated once at an intermediate point of the scanning, then scanning is continued to the bottom of the screen, and the second irradiation is performed at the end of one frame. The first embodiment and the present embodiment are examples in which the backlight light source 16 is directly turned on and off.

FIG. 11 shows a configuration of a liquid crystal display device according to a third embodiment of the present invention. In the present embodiment, the TFT substrate 18 of the liquid crystal display panel 17 and the backlight light source 16
, An optical shutter 19 is provided, and the optical shutter 19 is controlled by an optical shutter control circuit 20. FIG.
Is a timing chart of the present embodiment. The scanning drive circuit 11 sequentially scans each scanning line of the liquid crystal display panel 17 from the top to the bottom of the screen. The backlight light source 16 continues to emit a constant amount of light, and the optical shutter 19
In response to the opening / closing signal from 0, it opens once at an intermediate point in one display period, and opens again at the end point.

As the optical shutter, a film in which a polymer liquid crystal is sandwiched between polarizing plates can be used. As the polymer liquid crystal, a polymer ferroelectric liquid crystal is preferable from the viewpoint of high-speed operation.

A scan drive circuit 11 for scan electrodes
By devising, the scanning can be realized from the scanning from the top to the bottom of the screen, the scanning from the bottom to the top of the screen, or the interlaced scanning. FIG. 13 shows a liquid crystal display device according to a fourth embodiment of the present invention. In this embodiment, the backlight light source 1
As R6, R, G, and B are prepared and blinked by the color synchronization signal. Each light source is configured as a surface light source in which three cold cathode tubes are arranged on the end surface of the light guide plate 21. Each cold cathode tube is
The modulation light is irradiated once during each display period.

FIG. 14 shows a liquid crystal display according to a modification of the embodiment shown in FIG. In this example, instead of the three cold-cathode tubes 16 that are directly modulated, a light source that is arranged at an end of the light guide plate 12 and emits a constant amount of light, and a color light shutter 22 that is arranged immediately above the light guide plate 12 are provided. , The backlight light source 1
6 is an example. This makes it possible to obtain a surface light source in which the color of the transmitted light switches to R, G, and B in time series. The color light shutter 22 can be configured by stacking three liquid crystal layers and a plurality of retardation plates. A color light shutter formed by stacking such birefringent bodies can be designed by a conventionally known synthesis method. The three liquid crystal layers can be replaced with the above-mentioned polymer dielectric liquid crystal film.

As described above, the liquid crystal display device of the present invention can be realized by a liquid crystal element whose response time is shorter than the frame period. Further, it is preferable to use a liquid crystal display panel whose transmittance is kept constant during the frame period. This is shown in FIG.
6 can be understood from the description of the conventional liquid crystal display device. As an example of this, there is a liquid crystal display panel driven by a thin film transistor using a liquid crystal element which responds at a relatively high speed. This means that the thin film transistor maintains the voltage applied to the liquid crystal and keeps the transmittance constant during the frame period. Further, in the simple matrix type liquid crystal display panel, an antiferroelectric liquid crystal display panel can be particularly mentioned. This is because the transmittance of the liquid crystal is kept constant by the holding voltage applied to the scanning electrode. For this reason, the antiferroelectric liquid crystal provides a substantially constant transmittance except for the selection period and the reset period in the frame period.

[0031]

As described above, according to the liquid crystal display device of the present invention, the liquid crystal display panel is irradiated with the illuminating light a plurality of times during one frame period. Since afterimages recognized by human eyes can be reduced, there is an effect that moving images with reduced afterimages and flicker can be displayed.

[Brief description of the drawings]

FIGS. 1A and 1B are a plan view and a timing chart, respectively, for explaining image display in a liquid crystal display device according to an example of the present invention.

FIGS. 2A and 2B are diagrams illustrating a display state when an object moves in a direction opposite to a screen scanning direction in the liquid crystal display device of FIG.

FIG. 3 is a view similar to FIG. 2, showing a display when an object moves in the same direction as the screen scanning direction in the liquid crystal display device of FIG. 1;

FIG. 4 is a view similar to FIG. 1 in a liquid crystal display device of another example of the present invention.

FIG. 5 is a view similar to FIG. 1, illustrating a liquid crystal display device according to yet another example of the present invention.

FIG. 6 is a view similar to FIG. 1, illustrating a liquid crystal display device according to yet another example of the present invention.

FIG. 7 is a block diagram of a liquid crystal display device according to the first embodiment of the present invention.

FIG. 8 is a voltage waveform used in the embodiment of FIG. 7;

FIG. 9 is a block diagram of a liquid crystal display device according to a second embodiment of the present invention.

FIG. 10 is a timing chart showing timings of scanning and light source irradiation in the embodiment of FIG. 9;

FIG. 11 is a block diagram of a liquid crystal display device according to a third embodiment of the present invention.

12 is a timing chart showing timings of scanning and light source irradiation in the embodiment of FIG.

FIG. 13 is a block diagram of a liquid crystal display device according to a fourth embodiment of the present invention.

FIG. 14 is a block diagram showing a modification of the embodiment shown in FIG. 13;

FIG. 15 is a view similar to FIG. 1 of a conventional CRT.

FIG. 16 is a view similar to FIG. 1 of a conventional liquid crystal display device.

FIG. 17 shows a liquid crystal display device described in a document.
FIG.

[Explanation of symbols]

 Reference Signs List 11 scanning drive circuit 12 signal drive circuit 13 control circuit 14 multiplying circuit 15 backlight control circuit 16 backlight light source 17 liquid crystal display panel 18 TFT substrate 19 optical shutter 20 optical shutter control circuit 21 Light guide plate 22: color light shutter

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G09F 9/00 337 G09G 3/20 611E G09G 3/20 611 622J 622 660 V 660 3/36 3/36 G02F 1 / 1335 530 F term (reference) 2H091 FA23Z FA43Z FA50Z FD06 GA11 GA13 HA07 HA12 JA01 LA16 2H093 NA16 NA45 NA65 NC34 NC43 NC44 ND10 NE06 NE10 NF05 NF17 NF20 NH15 5C006 AA01 AA22 AC29 AC30 AF44 AF51 AF52 BB12 BA12 BC12 FA16 FA23 5C080 AA10 BB05 CC03 DD06 EE19 EE30 FF09 GG08 JJ02 JJ04 JJ05 5G435 AA01 BB12 BB15 CC09 CC12 DD13 EE25 EE27 FF08 FF11 FF13 FF15 GG26 GG27

Claims (8)

[Claims] 1. A liquid crystal display panel, comprising: a liquid crystal driving circuit for controlling display of a screen on the liquid crystal display panel; and a light source for modulating luminance in synchronization with an operation of the liquid crystal driving circuit.
The liquid crystal display device, wherein the light source irradiates the illumination light intermittently n times within one screen display period of the liquid crystal display panel, where n is an integer of 2 or more. 2. The liquid crystal display device according to claim 1, wherein scanning from the upper part to the lower part of the screen of the liquid crystal display panel and scanning from the lower part to the upper part of the screen are switched for each frame. 3. The liquid crystal display device according to claim 1, wherein the screen is interlaced scanned. 4. The liquid crystal display device according to claim 1, wherein the light source includes a constant light source that emits constant light, and a shutter that blocks the constant light source with a predetermined control signal. 5. The light source according to claim 1, wherein the light source comprises a plurality of light sources.
The liquid crystal display device according to claim 1, wherein each light source emits illumination light at least once during a screen display period. 6. The liquid crystal display device according to claim 5, wherein the plurality of light sources include R, G, and B. 7. The liquid crystal display device according to claim 5, wherein the plurality of light sources include one light guide plate and three cold cathode tubes arranged on an end face of the light guide plate. 8. The light source according to claim 5, wherein the plurality of light sources include one light guide plate, one cold cathode tube, and a color light shutter.
Or the liquid crystal display device according to 6.