Method for driving liquid crystal device

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a method for driving a liquid crystal device.

【0002】

[Conventional technology]

Conventionally, a liquid crystal device that displays an image using a liquid crystal has been driven by various methods.

【0003】

FIG. 7 is a timing chart showing an example of a driving method of such a conventional liquid crystal device. In this driving method, Δt is set for a predetermined period.₂ A gate pulse is applied to the gate line of the liquid crystal panel in a line-sequential manner (see Fig. (B)), and when the line-sequential scanning is completed and a black-and-white gradation image is written on the liquid crystal panel t₁₀The backlight device is turned on to display the image (see the figure (c)).

【0004】

However, when the liquid crystal device is driven by the method shown in FIG. 7, it takes time to write the lines of the liquid crystal panel in sequence. Therefore, the illumination time by the backlight device is Δt.₃ There was a problem that the image became short and the image became dark.

【0005】

To solve such a problem, the liquid crystal panel is provided with two thin film transistors (TFTs) and data hold circuits for each pixel, and as shown in FIG. 8, while displaying one image, the following is performed. The voltage for the image data of is charged to the data hold circuit in line sequence (see Fig. 8 (c)), and the charged voltage is applied to each pixel in full screen batch instead of line sequence (Fig. (Fig. 8 (c)). b)), an image based on the voltage is proposed in Japanese Patent Application Laid-Open No. 08-95526. According to this method, batch writing of images is possible and the rewriting time Δt.₄ Is shortened and the lighting time by the backlight device Δt₅ Can be lengthened and the image can be brightened.

【0006】

[Problems to be Solved by the Invention]

By the way, when a moving image is displayed by sequentially rewriting a still image, a period during which no image is displayed is provided between the display of one still image and the display of the next still image, for example, like a CRT. It is known that the method (hereinafter referred to as "impulse type") has better image quality than the method of continuously displaying still images (hereinafter referred to as "hold type") without providing such a period. (See "Science Technical Report" EID 96-4 (1996) p.16).

【0007】

Here, in the case of the driving method shown in FIG. 8, Δt is displayed between displaying one still image and displaying the next still image.₄ Is close to the impulse type described above because the light irradiation is stopped, but during that time Δt₄ Was provided solely for image rewriting, and the image quality was not good.

【0008】

As a method of solving such a problem, the screen of the liquid crystal panel is erased every time a still image is displayed by alternately performing display scanning and erasing scanning, and the display is not held to approach the impulse type display. (See SID 97, p. 203). However, such a liquid crystal panel has a problem that light is unnecessarily irradiated even while the screen is erased and the power consumption is large.

【0009】

Therefore, an object of the present invention is to provide a method for driving a liquid crystal device that prevents deterioration of the image quality of a moving image.

【0010】

Another object of the present invention is to provide a method for driving a liquid crystal device that prevents an increase in power consumption.

【0011】

[Means for solving problems]

The present invention has been made in consideration of the above circumstances, and is connected to the first electrode and the second electrode, which are arranged in a matrix so as to face each other and constitute a plurality of pixels, and an arbitrary voltage connected to the second electrode. A voltage holding means for holding the voltage, a switching element interposed between the voltage holding means and the second electrode, and a liquid crystal element composed of liquid crystal arranged between the first electrode and the second electrode. In a method of driving a liquid crystal device that drives a liquid crystal device provided with a lighting means that is arranged so as to face the liquid crystal element and illuminates the liquid crystal element, the voltage holding means is used in a state where the switching element is off. Arbitrary voltages are applied in order, and when the application of the voltage is completed, the switching elements are collectively turned on and the voltage held by each of the voltage holding means is applied to the second electrode. , The liquid crystal is driven pixel by pixel by the potential difference between the first electrode and the second electrode to display one image on the liquid crystal element, and 30 to 70% while displaying the one image. It is characterized in that the illumination means is illuminated with the time opening ratio of the above, and the voltage for the next image data is sequentially applied to the voltage holding means with the switching element turned off.

【0012】

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 5.

【0013】

First, the structure of the liquid crystal device driven in the present embodiment will be described with reference to FIGS. 1 to 3. Here, FIG. 1 is a block diagram showing an overall configuration of a liquid crystal device to which the present invention is applied, FIG. 2 is a cross-sectional view showing an example of the structure of the liquid crystal element, and FIG. 3 is an example of the structure of the liquid crystal element. It is a top view which shows.

【0014】

The liquid crystal device driven in the present embodiment is arranged so as to face the liquid crystal element P and the liquid crystal element P and illuminate the liquid crystal element P, as shown by reference numeral 1 in FIG. And have.

【0015】

Of these, as shown in FIGS. 2 and 3, the liquid crystal elements P are arranged in a matrix so as to face each other to form a plurality of pixels, the first electrode 2 and the second electrode 3, and the second electrode 3. A voltage holding means 4 connected to and holding an arbitrary voltage (arbitrary voltage corresponding to image data), a switching element 5 interposed between the voltage holding means 4 and the second electrode 3, and It is composed of a liquid crystal 6 arranged between the first electrode 2 and the second electrode 3.

【0016】

By the way, the liquid crystal 6 described above includes a chiral smectic liquid crystal showing one stable state when no voltage is applied, for example, a monostable ferroelectric liquid crystal (monostable FLC) capable of high-speed response, and a thresholdless anti-threshold liquid crystal. Ferroelectric liquid crystal (TAFLC), OCB (Optically Compensated Bend) mode, etc. can be used. Here, the monostable FLC is obtained by injecting FLC showing a phase sequence of isotropic phase-cholesteric phase-chiral smectic C phase into a liquid crystal cell subjected to asymmetric orientation treatment on the upper and lower substrates, or by applying an electric field. It can be obtained by performing a reorientation treatment.

【0017】

Next, a method of driving the liquid crystal device according to the present invention will be described with reference to FIG. Here, FIG. 4 is a timing chart showing an embodiment of a method for driving a liquid crystal device according to the present invention.

【0018】

In this embodiment, First, with the switching element 5 turned off, an arbitrary voltage (voltage corresponding to image data) is sequentially applied to the voltage holding means 4. When the application of the voltage is completed, the switching elements 5 are turned on all at once, and the voltage held by each of the voltage holding means 4 is applied to the second electrode 3 (FIG. 4 (b)). reference). As a result, the liquid crystal 6 is driven pixel by pixel by the potential difference between the first electrode 2 and the second electrode 3, and one image is displayed on the liquid crystal element P. While displaying the one image in this way, the illumination means B was illuminated with a time aperture ratio of 30 to 70% (see FIG. 4D), and the switching element 5 was turned off. In this state, the voltages for the following image data are sequentially applied to the voltage holding means 4 (see FIG. 4 (c)).

【0019】

Here, the time aperture ratio is the time from when the switching element 5 is turned on until the end of illumination by the illumination means B is Δt.₀ Let, the time during which the illumination by the illumination means B is performed is Δt.₁ In the case of₁ × 100 / Δt₀ The value represented by. The time aperture ratio may be fixed to an arbitrary value of 30% to 70%, and may be adjusted by an external trimmer according to the displayed image within that range. For example, when displaying a still image or a slow-moving moving image, the time aperture ratio can be increased and the brightness of the lighting means B can be lowered to reduce power consumption without changing the brightness of the screen.

【0020】

By the way, a color image may be displayed by the liquid crystal device 1 described above, or a black-and-white image may be displayed. For example, when displaying a color image, * A color filter is placed on the liquid crystal element P described above, and a lighting means that irradiates white light is used. * A black-and-white image is sequentially displayed on the liquid crystal element P described above without arranging a color filter, and each color light (for example, each color light of the three primary colors) is sequentially irradiated in synchronization with the display of the black-and-white image as an illumination means. If you want to display a black-and-white image, you can mention how to do it (Fig. 5). * A method of irradiating white light as an illumination means without arranging a color filter on the liquid crystal element P described above (see FIG. 4) can be mentioned.

【0021】

Examples of the lighting means for irradiating white light include a single-color fluorescent tube and an LED light source, and examples of a lighting means for sequentially irradiating each color light of the three primary colors include those equipped with three RGB fluorescent tubes. Examples thereof include those in which a color filter is arranged in each of the three fluorescent tubes.

【0022】

Next, the effect of this embodiment will be described.

【0023】

According to the present embodiment, since the rewriting of the image is performed collectively for the entire screen instead of the line sequence, the writing time can be shortened, and the lighting time by the lighting means B can be lengthened to brighten the image.

【0024】

Further, since the lighting means B is not always lit, the power consumption can be reduced.

【0025】

Further, since the illumination by the illumination means B is performed with a time aperture ratio of 30 to 70%, the image quality of the moving image can be improved.

【0026】

[Example]

Hereinafter, the present invention will be described in more detail with reference to Examples.

【0027】

(Example 1) In this embodiment, the liquid crystal device 1 shown in FIG. 1 was created using the liquid crystal panel (liquid crystal element) P shown in FIGS. 2 and 3.

【0028】

First, the structure of the active matrix type liquid crystal panel P used in this embodiment will be described with reference to FIGS. 2 and 3.

【0029】

That is, as shown in FIG. 2, the liquid crystal panel P is composed of a pair of glass substrates 10a and 10b arranged at a predetermined distance, and the one glass substrate 10a has ITO (indium tin oxide). A first electrode (hereinafter referred to as opposite electrode) 2 made of the material is formed, and an alignment film 11a having a thickness of about 10 nm made of polyimide is formed on the surface of the counter electrode 2 and the surface of the alignment film 11a is formed. Was subjected to rubbing treatment.

【0030】

Further, on the other glass substrate 10b, as shown in FIG. 3, 160 × 120 transparent pixel electrodes (second electrodes) 3 made of ITO are arranged in a matrix, and these counter electrodes 2 and pixel electrodes 3 are arranged. The pixels were constructed by. Further, a batch write TFT 5 (source) as a switching element is connected to each pixel electrode 3, and a capacitor 4 as a voltage holding means or another TFT (hereinafter referred to as serial write TFT) is used as a drain of the TFT 5. ) 7 (source) was connected. Furthermore, a batch write TFT gate electrode 20, a serial write TFT gate electrode 21, and an earth line 22 are formed between the pixels in the X direction shown in the figure, and the batch write TFT gate electrode 20 is a batch write TFT 5. It was connected to the gate, the gate electrode 21 for the serial writing TFT was connected to the gate of the serial writing TFT 7, and the ground line 22 was connected to the other end of the capacitor 4. Further, a data electrode 23 was formed between the pixels in the Y direction shown in the drawing, and the data electrode 23 was connected to the drain of the serial writing TFT 7. Furthermore, an alignment film 11b was formed so as to cover these TFTs 5, 7 and the like.

【0031】

Further, spacer beads 12 were arranged in the gaps between the glass substrates 10a and 10b to define the substrate gaps, and the liquid crystal 6 was arranged in the substrate gaps.

【0032】

On the other hand, as the lighting means, a backlight device B that sequentially irradiates light of the three primary colors was used.

【0033】

Next, the peripheral devices for driving the liquid crystal panel P and the backlight device B described above will be described with reference to FIGS. 1 and 3.

【0034】

A signal driver 25 was connected to the data electrode 23 described above, and a scanning driver 26 was connected to the gate electrode 20 for batch writing TFT and the gate electrode 21 for serial writing TFT. Further, the ground line 22 was connected to the scanning driver 26 and grounded inside the scanning driver 26. The ground voltage is a reference voltage of the video signal applied to the data electrode 23, and is equal to the voltage applied to the counter electrode 2.

【0035】

Further, as shown in FIG. 1, a control circuit 27, an external signal processing memory 28, and a signal source 29 are connected to these drivers 25 and 26. Of these, the signal source 29 corresponds to a recording / playback device such as NTSC or PAL, a high-definition device, a personal computer (VGA, XGA, etc.), etc., and the external signal processing memory 28 is an image from the signal source 29. The signal is separated into an R color video signal, a G color video signal, a B color video signal, and a synchronization signal, and each video signal is supplied to the signal driver 25 according to the synchronization signal to supply the synchronization signal. It is supplied to the scanning driver 26 and the signal driver 25. Further, the control circuit 27 is composed of a timing generator or the like, and separates the synchronization signal from the signal source 29, and separates the synchronization signal from the signal source 29, the external signal processing memory 28, the drive pulse of the liquid crystal panel P, the voltage control pulse for illumination, and the system. It controls the power supply and the like.

【0036】

In this embodiment, the liquid crystal device 1 was driven by the method shown in FIG. Here, FIG. 5 is a timing chart showing an example of a driving method of the liquid crystal device according to the present invention.

【0037】

That is, t₁ At this point, charging of the data voltage for the R color to each capacitor 4 is completed. To charge this data voltage, a data signal for R color is applied from the signal driver 25 to each data electrode 23 in a state where the batch write TFT 5 is off and the connection between the pixel electrode 3 and the capacitor 4 is cut off. In addition, gate pulses are sequentially applied from the scanning driver 26 to the gate electrode 21 for serial writing TFT in line order, and batch writing TFT 5 is turned on in order.

【0038】

Then t₁ ~ t₂ A rewrite pulse is applied to all the batch write TFT gate electrodes 20 at the same time for the period of (see Fig. 5 (b)). As a result, the voltage held in each capacitor 4 is applied to the pixel electrodes 3 via the batch writing TFT 5, the liquid crystal 6 is driven for each pixel, and the liquid crystal panel P displays a black-and-white image for R color. The display of such a black-and-white image is t₂ It is maintained after the lapse of time.

【0039】

And the predetermined timing t₃ The R-color fluorescent tube is lit by the control circuit 27 (see FIG. 5 (d)), and the black-and-white image is recognized as an R-color image. In this example, the time aperture ratio was set to 30%.

【0040】

By the way, t₂ The batch write TFT 5 is turned off again at the timing of, the data signal for G color is applied to each data electrode 23 from the signal driver 25, and the gate pulse is sent from the scanning driver 26 to the serial write TFT gate electrode 21. The serial write TFT 7 is applied in sequence and turned on in order (see Fig. 5 (c)), and each capacitor 4 is charged with the data voltage for G color.

【0041】

And when the charging of the data voltage for this G color is completed, t₄ Then, all batch writing TFT5 is turned on again, and the liquid crystal panel P displays a black-and-white image for G color.

【0042】

As described above, in this embodiment, by rewriting the black-and-white image by the liquid crystal panel P and irradiating each color light as described above, each color image is sequentially displayed in a short time, and the afterimage phenomenon is used by the observer. Then, it is recognized as if a full-color image is displayed.

【0043】

Next, the effect of this embodiment will be described.

【0044】

According to this embodiment, since the image is rewritten collectively for the entire screen instead of line-sequentially, the writing time can be shortened, and the illumination time by the backlight device B can be lengthened to brighten the image. It was.

【0045】

In addition, the backlight device B was not always lit, and the power consumption could be reduced.

【0046】

Furthermore, since the time aperture ratio is set to 30%, the image quality of moving images can be improved. When a moving image (a moving image of a BTA high-definition standard image moved at a movement speed of 6.8 deg / sec) was actually displayed, no blurring around the screen was observed, and the image quality was sharp and good. It was confirmed. The movement speed of 6.8 deg / sec is a general movement speed of a television program.

【0047】

(Comparative Example) The present inventor displayed a moving image using the same liquid crystal panel P as in Example 1, changed the time aperture ratio in various ways, and examined the image quality and brightness. As shown in FIG. It was. In addition, the vertical axis in the figure shows the five-grade evaluation of the image quality of the moving image (the average value of the five-grade evaluation by 10 people). Scale 5; No blur around the screen is observed, and the condition is sharp. Scale 4; Bokeh around the screen is almost unnoticeable Scale 3; Bokeh around the screen is observed, and it is difficult to distinguish small characters. Scale 2; Bokeh around the screen becomes noticeable, making it difficult to distinguish large characters. Scale 1; No blur around the screen is observed, and the original image can hardly be discriminated. Is shown.

【0048】

When the time aperture ratio was 10%, the image quality of the moving image was good, but the screen became dark. Moreover, when the time aperture ratio was 80% or more, the screen became bright but the image quality was poor. In other words, it was found that the time aperture ratio must be 30 to 70% in order to obtain both the image quality of the moving image and the brightness of the screen.

【0049】

[Effect of the invention]

As described above, according to the present invention, since the rewriting of the image is performed collectively for the entire screen instead of the line sequence, the writing time can be shortened, and the lighting time by the lighting means can be lengthened to brighten the image. ..

【0050】

Further, since the lighting means is not always lit, the power consumption can be reduced and the life can be extended.

【0051】

Further, since the illumination by the illumination means is performed with a time aperture ratio of 30 to 70%, the image quality of the moving image can be improved.

[Simple explanation of drawings]

[Figure 1]

The block diagram which shows the whole structure of the liquid crystal apparatus to which this invention is applied.

[Figure 2]

The cross-sectional view which shows an example of the structure of a liquid crystal panel.

[Fig. 3]

The plan view which shows an example of the structure of a liquid crystal panel.

[Fig. 4]

The timing chart which shows one Embodiment of the driving method of the liquid crystal apparatus which concerns on this invention.

[Fig. 5]

The timing chart which shows one Embodiment of the driving method of the liquid crystal apparatus which concerns on this invention.

[Fig. 6]

The figure for demonstrating the effect of the driving method of the liquid crystal apparatus which concerns on this invention.

[Fig. 7]

The timing chart which shows an example of the driving method of the conventional liquid crystal apparatus.

[Fig. 8]

The timing chart which shows the other example of the driving method of the conventional liquid crystal apparatus.

[Explanation of symbols]

1 Liquid crystal device 2 Opposite electrode (1st electrode) 3-pixel electrode (second electrode) 4 Capacitor (voltage holding means) 5 Batch write TFT (switching element) 6 LCD B Backlight device (lighting means) P Liquid crystal panel (liquid crystal element)