JP2001282199A - Method for driving liquid crystal device and liquid crystal device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a driving method which increases the efficiency of a back light and achieves low power consumption when FMC is carried to by raster scan in HVFLC and is particularly effective for a small-sized direct viewing panel. SOLUTION: The back light is driven at a double speed to create a period when the back light is not lighted. The efficiency is increased to >=50% in spite of raster scan. The device is therefore driven in such a manner that the time when image signals are held is longer than the time for writing the prescribed primary color image signals among red, green and blue to the entire surface. In addition, the device is provided with black display sub-field period which is inputted with the entire surface black signal between sub-field periods when the prescribed primary color image signals among the red, green and blue are inputted and sub-field period when the other primary color image signals among the next red, green and blue are inputted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of driving a color liquid crystal device of a light source color switching type which does not require a color filter. Such a color liquid crystal device is used for a monitor of a PC (personal computer), a viewfinder of a video camcorder, a projector, and the like.

[0002]

2. Description of the Related Art A conventional color display device is provided with red (R), green (G), and blue (B) color filters as shown in FIG. The color display was performed by lighting. In this color filter type liquid crystal panel, the R, G, and B pixels are arranged at different positions in the panel. The drawback was that the rate was less than 1/3.

As a method of solving the above-described problem of the color filter, a method of sequentially inputting R, G, and B signals to a monochrome liquid crystal panel and switching and displaying a light source color in accordance with the color signal. (Japanese Patent Publication No. 63-41078).
FIG. 11 shows an explanatory diagram in the case of a light source color switching surface sequential method in which the light source color is switched over the entire panel in the light source color switching method. In the light source color switching plane sequential method, writing and display of three color signals are individually performed within one vertical scanning period. Therefore, the writing period did not contribute to the display, and the display efficiency was low.

A similar system applied to a ferroelectric liquid crystal display panel is described in Japanese Patent Publication No. Hei 8-27453. However, with such a configuration, the liquid crystal panel is scanned and driven sequentially from top to bottom for each horizontal line, so that the display time differs for each pixel, and the image quality is unfavorable. In order to solve this problem, as disclosed in Japanese Patent Application Laid-Open No. H10-254390, a subfield period for displaying R, G, B signals and another primary color of the next R, G, B are used. Has been proposed to provide a black display sub-field period between the periods indicating the period, thereby making the display period uniform in all pixels.

A brief description will be given with reference to FIGS. FIG. 12 shows a timing chart of the liquid crystal panel image display and the backlight. As shown in this figure, the backlight has a period of two subfields of black display by writing a black display signal to the liquid crystal display panel and the next primary color image display as one cycle, and in synchronization with this, the primary color image display is performed. The lighting color is sequentially switched so as to emit the same color as the primary color. In this example, the subfield period is set to a normal 60 Hz.
It is set to 360 Hz, which is six times as large as that of (ie, 1/360 sec). FIG. 13 is a timing chart showing the display state of each scanning pixel line. In other words, the display time of each primary color image is equivalent to one subfield at any pixel line position on the screen, and no crosstalk occurs between the primary color subfield images at all due to the presence of black display for one subfield. .

By displaying both the primary color image display and the black display by vertical scan writing in this manner, the display time of each pixel line at any position becomes equal, and the above-described brightness is obtained. Very good full color display without unevenness is formed.

[0007]

However, in the conventional liquid crystal device having such a configuration, the liquid crystal panel is generally scanned and driven from top to bottom for each horizontal line. Period) and the color signal writing period (black display period for preventing crosstalk) are equal, and only half of each RGB illumination light can be used effectively, causing a problem in that efficiency is wasted.

Accordingly, an object of the present invention is to solve the above-mentioned problems in a color liquid crystal display device of a light source color switching type, which is advantageous in terms of resolution, light transmittance, etc., with respect to a liquid crystal display device of a color filter type. It is an object of the present invention to provide a method of driving a color liquid crystal display device of a light source color switching type which has high power consumption and low power consumption.

[0009]

The above object of the present invention is attained by the following invention. That is, in the present invention, a liquid crystal panel having a plurality of pixels provided in a matrix and a light source capable of switching a plurality of colors to irradiate the liquid crystal panel are provided. An image corresponding to a lighting color is sequentially written, and a light source color switching method of performing color display with a temporal additive color mixture by lighting the light source with a lighting color corresponding to the image in synchronization with writing of each image. A method for driving a color liquid crystal device, wherein a time during which each pixel of the liquid crystal panel displays a state corresponding to each lighting color is sufficiently longer than a time during which the liquid crystal panel is raster-scanned, and A black table in which the entire black state is written between a subfield period in which an image according to the lighting color is written and a subfield period in which an image according to another lighting color is next written. And providing a sub-field period. The “sub-field period” in the present invention is a period in which a single or a plurality of continuous sub-fields corresponding to one color or black display are collected. For example, t in FIGS.
The period B is a “sub-field period”.

In order to maintain the display state of each pixel sufficiently longer than the time required for raster scanning of the entire liquid crystal panel as described above, for example, a subfield period in which an image corresponding to one lighting color is written is continuously provided. Raster scan is performed twice or more, and during the second and subsequent raster scans, writing of an image signal to each pixel is prohibited, so that the entire display surface of the liquid crystal panel is raster-scanned once for the equivalent display time of each pixel. Make it longer than twice the time. Alternatively, by performing raster scan twice or more consecutively in a subfield period in which an image corresponding to one lighting color is written, and writing the same image signal at each raster scan, the display time of each pixel is equivalently reduced. The time is sufficiently longer than twice as long as one raster scan of the entire liquid crystal panel.

[0011]

According to the present invention, the time for which the image signal is held in each pixel of the liquid crystal panel is sufficiently longer than the time for writing the image signal corresponding to each lighting color on the entire surface of the liquid crystal panel. A black signal is completely input between a subfield period in which an image signal corresponding to each lighting color is input and a subfield period in which an image signal corresponding to the next other lighting color is input. By providing a certain black display subfield period, the irradiation light from the light source can be used more efficiently. That is, it is possible to achieve power saving, long life, or high luminance by using the same liquid crystal panel and light source.

The present invention is effective for increasing the efficiency of the backlight and achieving low power consumption, especially when performing FSC by raster scanning in HVFLC. It is particularly effective for small direct-view panels.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a preferred embodiment of the present invention, a first substrate having a plurality of pixels provided in a matrix and a means for supplying a signal voltage to the pixels is opposed to a first substrate having a liquid crystal therebetween. And a backlight capable of illuminating the liquid crystal panel with red, green, and blue primary colors. The liquid crystal panel sequentially emits red, green, and blue primary color image signals for each of the subfields. When driving a liquid crystal device that switches and lights the backlight in synchronization with each of the primary color image signals, the red, green, and blue primary color image signals are written over the entire surface. The time during which the image signal is held is sufficiently longer than the time, and the red, green, and blue subfield periods in which the predetermined primary color signal is input, and the next red, green, and blue Horse And drives to provide a black display sub-field period in which the whole surface black signal is input between the subfield period other primary color signals is input.

According to the present embodiment, during the backlight lighting period, a black signal is written to the last pixel in the next black subfield from the time when each primary color image signal is written to the first pixel in one subfield. It is characterized by being up to time. Further, the present invention is characterized in that it has a holding period twice or more as compared with a time for writing the primary color image signal over the entire surface.

According to the present embodiment, the primary color image signal is repeatedly written at least twice. Further, a plurality of pixels provided in a matrix and a means for supplying a signal voltage to the pixels are active matrix elements formed on one substrate.

Further, the liquid crystal is a chiral smectic liquid crystal, and the phase transition series of the chiral smectic liquid crystal is isotropic liquid phase (ISO.)-Cholesteric phase (Ch) -chiral smectic C phase or the like from the high temperature side. It is characterized by being an isotropic liquid phase (ISO.)-Chiral smectic C phase.

According to this embodiment, the time for which the image signal is held is sufficiently longer than the time for writing the predetermined primary color image signal of red, green, and blue over the entire surface.
The red, green, and blue between a subfield period in which a predetermined primary color signal is input, and the next red, green, and a subfield period in which another primary color signal of blue is input. By having a black display subfield period in which a full black signal is input, the efficiency of the backlight can be greatly improved from 1/2. Preferably, the backlight lighting period is from the time when each primary color image signal is written to the first pixel in one subfield to the time when the black signal is applied to the last pixel in the next black subfield. If the response time of the liquid crystal is 0, the efficiency becomes maximum at this time. Strictly speaking, the liquid crystal response time and circuit delay are also taken into account,
It is preferable to set a lighting period of the backlight.

More specifically, for example, by driving at a double speed to create a period in which the backlight is not turned on,
Efficiency can be more than 50% even in raster scan.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. Embodiment 1 A first embodiment of the present invention will be described in detail with reference to FIGS. FIG. 1 shows a timing chart of a liquid crystal panel image display and a backlight. As shown in this figure, the backlight is lit for two subfields of primary color image display on the liquid crystal display panel and one subfield of black display by writing a black display signal. In synchronization with this, the lighting colors are sequentially switched so as to emit the same color as the primary colors of the primary color image display. In this embodiment, the subfield period is 72 times 3 × 4 times the normal 60 Hz.
It is set to 0 Hz equivalent (that is, 1/720 sec). FIG. 2 is a timing chart showing a display state of each scanning pixel line. The writing time is represented by tA, while the holding period is represented by tB. JP 1
In the conventional example shown by 0-254390, tA = tB, but in the present embodiment, 2tA = tB, which is 2 times of the writing time.
Long retention period. The display time of each primary color image is equivalent to two subfields at any pixel line position on the screen, and no crosstalk occurs between the primary color subfield images at all due to the presence of black display for one subfield. In addition, the efficiency is increased to 2/3 without changing the brightness as compared with the efficiency of 1/2 of the conventional example. That is, the lighting period 3
Two subfields are effectively used for display for the subfields.

FIG. 3 shows a specific circuit configuration of this embodiment. FIG. 3 is a configuration diagram of an active matrix type liquid crystal display device, wherein 1 is a horizontal shift register, 2 is a vertical shift register, 3 to 5 are transfer switches for sampling data signals Data to signal lines, and 6 is a pixel circuit. , 7 to 9 are output lines from the vertical shift register 2. First, the operation of the vertical shift register is started by φVs, and φV1, φV1
According to V2, output lines (gate lines) 7 to 9 from the vertical shift register are sequentially turned on. When the gate line 7 is first turned on, then the second of φHs and φH1
Transfer switches 3, 4, and 5 are sequentially turned on by two signals
Then, Data is transferred to the signal line, and further written to the pixel circuit 6. In a pixel circuit, a switching transistor generally has a storage capacitor and is connected to a pixel electrode, but is not particularly limited. Then, when the gate line 7 is turned off and the gate line 8 is turned on, the transfer switches 3, 4, and 5 are sequentially turned on again, and Data is written to the pixels in the next row. After writing to the last row, this operation is repeated again in order. Although an example of a 3 × 3 matrix is shown here, the number is usually large, for example, 640 × 480 pixels in VGA. The operation is basically the same.

The driving for realizing the timing chart shown in FIG. 1 will be described. FIG. 4 shows φVs, φV
1, φV2 and the potentials of the first written pixel and the last pixel (in the case of white display). To explain with the example of the first pixel, φVs enters, the vertical shift register starts operating, and the potential of the first pixel rises to a potential of, for example, 10 V (point A). The potential of the counter electrode is 5V, and a voltage of 5V is applied to the liquid crystal. When one subfield ends, a video signal is written to the last pixel, and the potential changes (point B). In the next subfield, the vertical shift register does not operate because φVs is not input, so that the pixel gate does not open and the pixel potential does not change. In the next subfield, φVs is input and a signal is input to the pixel so that black display is performed. First, at point C, the first pixel displays black, at point D, scanning from above ends, and the last pixel displays black. In the next subfield, φVs does not enter as before, and the pixel potential does not change. After black display for two subfields, a color signal is written again at point A '. The backlight starts when the first pixel potential becomes a video signal,
The backlight is turned on until the last pixel has a black potential, that is, only in three subfields from point A to point D, and is turned off from point D to point A.

However, in this example, as described above,
In the case where the liquid crystal response time is 0, that is, the change in the pixel potential is the response of the liquid crystal itself as it is, and it is impossible in reality. For example, the response time when the liquid crystal is ON is xμs,
Assuming that the response time is y μs, the backlight should be turned on with a delay of x μs from point A and turned off with a delay of y μs from point C. This is the drive corresponding to one color, and is similarly performed for the other colors.

According to this method, the frequency of the panel power consumption for driving is doubled, but the driving period is half, so that it is not different from the conventional example. On the other hand, the lighting period of the backlight is 3/4 of the conventional one, and the power consumption is 75%
Becomes Regarding brightness, R, G,
Each of the B colors corresponds to 1/6 field, which is not different from the conventional example. That is, a liquid crystal display device exhibiting good characteristics without changing brightness and without increasing power consumption including panel heat generation, while reducing the power consumption of the backlight which is most effective for power consumption by 25%, was realized.

The liquid crystal used in the present embodiment is a monostable mode ferroelectric liquid crystal. In the case of black display, a negative voltage having an absolute value equal to the voltage of white display is applied to obtain black display. And the DC component is cancelled. The monostable mode ferroelectric liquid crystal is described below. As a liquid crystal panel using such a monostable mode ferroelectric liquid crystal, an element described in Japanese Patent Application No. 10-177145 (hereinafter referred to as "prior application 1") has been proposed. In the prior application 1, for example, the isotropic liquid phase (ISO.)-Cholesteric phase (Ch) -chiral smectic C phase (SmC *)
) Or a phase series material showing an isotropic liquid phase (ISO.)-Chiral smectic C phase (SmC *), and is monostabilized at a position inside the edge of the virtual cone. Then, for example, a positive or negative DC voltage is applied between a pair of substrates at the time of Ch-SmC * phase transition or at the time of isotropic phase-SmC * phase transition, so that the layer direction is made uniform in one direction. Accordingly, a high-speed response and gradation control can be performed, and a high-brightness liquid crystal element excellent in moving image quality can be realized with high mass productivity. The device of the prior application 1 can reduce the spontaneous polarization value as compared with the various smectic liquid crystal modes described above.
This is an element having good matching with active elements such as.

Similarly, a liquid crystal panel using the above-mentioned monostable mode ferroelectric liquid crystal is disclosed in JP-A-2000-01076.
(Hereinafter referred to as "prior application 2") has been proposed. In the prior application 2, for example, the isotropic liquid phase (ISO.)-Cholesteric phase (Ch) -chiral smectic C phase (SmC *) or the isotropic liquid phase (ISO.)-Chiral smectic C phase from the high temperature side (SmC *)
Focusing on the phase-series material indicating the above, monostabilization is performed at the position of the virtual cone edge. And, for example, C
During the h-SmC * phase transition or during the isotropic phase-SmC * phase transition, a positive or negative DC voltage is applied between the pair of substrates, so that the layer direction is made uniform in one direction. A high-speed liquid crystal element capable of high-speed response and gradation control and having excellent moving image quality can be realized with high mass productivity. Also, the device of the prior application 2 can realize stable halftone display with small hysteresis and can reduce the spontaneous polarization value as compared with the other various smectic liquid crystal modes described above. Is a good element.

FIG. 5 is a timing chart when a voltage is applied to the circuit shown in FIG. 3 in a form of being held in a storage capacitor through a switching pixel. FIG. 5 (a)
Indicates a gate voltage, and FIG. 5B shows a potential of a signal line for a certain pixel. FIG. 5C shows the voltage value Vpix actually held in the liquid crystal capacitance and the storage capacitor of the pixel and applied to the liquid crystal layer as described above, and FIG. 5D shows the actual optical characteristics of the liquid crystal in the pixel. The response (optical response when a transmission type liquid crystal element is used) is schematically shown. As shown in FIG. 5 (c), the applied voltage is the same level (absolute value) V whose polarity is inverted only for two fields (1F and 2F).
x '. On the other hand, as shown in FIG. 5D, in the first field 1F, a gradation display state (light emission amount) according to Vx ′ is obtained, and in the second field 2F, a gradation display state according to −Vx ′. However, in the second field 2F, only a small amount of transmitted light is actually obtained, and the transmitted light amount is smaller than Tx and becomes Ty close to the 0 level.

In the active matrix driving as described above, when liquid crystal exhibiting a chiral smectic phase is used, gradation display based on good high-speed response can be performed, and at the same time, gradation display at a certain level can be performed by one pixel. , A first field for obtaining a high transmitted light amount and a second field for obtaining a low transmitted light amount are continuously performed.
% Or less, and the high-speed response characteristics of moving images perceived by human eyes are also improved. Further, since the voltage of the same level is inverted and applied to the liquid crystal layer in the first and second fields, the voltage actually applied to the liquid crystal layer is converted into an alternating current, so that the deterioration of the liquid crystal can be prevented.

In the present embodiment, as shown in FIG. 1, the white display subfield has two subfields and the black display subfield has two subfields.
It goes without saying that a larger number of subfields is acceptable. Further, in this case, the shift register is stopped and the write operation is not performed in the latter subfield of the two subfields, but this is not particularly limited.
For example, the same writing may be performed twice,
The number of times is not limited to three, but may be three or more. In the case of writing a plurality of times, the power consumption of the liquid crystal panel is twice the number of times, but is smaller than the reduction in power consumption of the backlight.
This is effective when the leakage of the switching element is large or when a liquid crystal material having the above spontaneous polarization is used.

[Embodiment 2] FIG. 6 is a timing chart showing an embodiment of the present invention. In this embodiment, the number of subfields corresponding to one color is two subfields for color display and one subfield for black display. As shown in this figure, the backlight is lit for two subfields of primary color image display on the liquid crystal display panel and one subfield of black display by writing a black display signal. In synchronization with this, the lighting colors are sequentially switched so as to emit the same color as the primary colors of the primary color image display. In this embodiment, the subfield period is set to 540H which is 3 × 3 times the normal 60 Hz.
z is set. FIG. 7 is a timing chart showing the display state of each scanning pixel line. That is, the display time of each primary color image is equivalent to two subfields at any pixel line position on the screen, and no crosstalk occurs between the primary color field images at all due to the presence of black display for one subfield. In addition, the efficiency is increased to 従 来 without changing the brightness as compared with the efficiency １ ／ of the conventional example (two subfields are effectively used for three subfields of the lighting period). Compared with the conventional example, the lighting period is 1/3 × 2/3 = 2/9 fields, which is more than 1/6 field of the conventional example. Therefore, by lowering the brightness of the backlight, the power consumption can be reduced. Can be dropped.

In contrast to the conventional example, in the first embodiment, the time used for lighting per pixel is the same as that of the conventional example. As a result, the backlight lighting time can be shortened, so that low power consumption is achieved. In Example 2, the lighting period of the backlight was the same, but the time used for lighting per pixel could be extended, so that low power consumption was achieved. In the second embodiment, in order to prevent burn-in, two sub-field displays of white display are performed with a pixel potential of a positive potential and a negative potential. For black display, normally black liquid crystal was used and the potential difference from the counter electrode was set to 0 for display. The liquid crystal used was an antiferroelectric liquid crystal.

In this example, a white display 2 subfield,
Although an example of one subfield for black display is shown, the present invention is not particularly limited. For example, if four subfields are used for white display, the efficiency becomes 4/5, and the driving frequency is increased to 900 Hz, but the efficiency of the backlight is further improved.

[Embodiment 3] FIG. 8 is a timing chart showing a third embodiment of the present invention. In this embodiment, the number of subfields corresponding to one color is set to two subfields for color display and four subfields for black display. As shown in this figure, the backlight 4 is lit for a period of four subfields of primary color image display on the liquid crystal display panel 2 and one subfield of black display by writing a black display signal. In synchronization with this, the lighting colors are sequentially switched so as to emit the same color as the primary colors of the primary color image display. In this embodiment, the subfield period is set to a normal 60 Hz 3 × 6.
It is set to 1080 Hz which is twice as large. FIG. 9 is a timing chart showing the display state of each scanning pixel line.
It becomes as shown in. In other words, the display time of each primary color image is equivalent to two subfields at any pixel line position on the screen, and there is no crosstalk between the primary color subfield images due to the presence of black display for four subfields. . In addition, the efficiency is increased to 従 来 without changing the brightness as compared with the efficiency １ ／ of the conventional example (two subfields are effectively used for three subfields of the lighting period). At this time, the display characteristic becomes a so-called impulse response, and a very clear image can be obtained even for a moving image.

According to the above embodiment, the liquid crystal panel is sequentially driven by the red, green, and blue primary color image signals for each of the subfields, and the backlight is switched on and off in synchronization with the primary color image signals. In the liquid crystal device to be turned on, the time during which the image signal is held is sufficiently longer than the time for writing the predetermined primary color image signal of the red, green, and blue over the entire surface, and the red, green, and , Between the subfield period in which the predetermined primary color signal of blue is input and the subfield period in which the other primary color signal of the next red, green, blue is input, By using the driving method of providing the input black display subfield period, a liquid crystal display device with high efficiency and low power consumption can be provided.

In the above embodiment, an example in which the present invention is applied to a device using a transmissive liquid crystal panel has been described. However, the present invention is applicable to a liquid crystal device using a reflective liquid crystal panel. Is also possible.

[0035]

As described in detail above, according to the present invention,
The time for which the image signal is held in each pixel of the liquid crystal panel is sufficiently longer than the time for writing the image signal corresponding to each lighting color on the entire surface of the liquid crystal panel, and the image corresponding to each lighting color is provided. A black display subfield period in which a full black signal is input is provided between a subfield period in which a signal is input and a subfield period in which an image signal corresponding to the next other lighting color is input. Thus, the irradiation light from the light source can be used more efficiently. That is, it is possible to achieve power saving, long life, or high luminance by using the same liquid crystal panel and light source.

[Brief description of the drawings]

FIG. 1 is a drive timing chart showing a first embodiment of the present invention.

FIG. 2 is a drive timing chart showing the first embodiment of the present invention.

FIG. 3 is a drive circuit diagram illustrating a first embodiment of the present invention.

FIG. 4 is a potential diagram showing a first embodiment of the present invention.

FIG. 5 is an explanatory diagram of a liquid crystal drive representing the first embodiment of the present invention.

FIG. 6 is a drive timing chart showing a second embodiment of the present invention.

FIG. 7 is a drive timing chart showing a second embodiment of the present invention.

FIG. 8 is a drive timing chart showing a third embodiment of the present invention.

FIG. 9 is a drive timing chart showing a third embodiment of the present invention.

FIG. 10 is an explanatory diagram of a conventional color filter system.

FIG. 11 is an explanatory diagram in the case of a conventional light source color switching surface sequential method.

12 is a driving timing chart of the conventional example shown in FIG.

FIG. 13 is a drive timing chart showing the conventional example shown in FIG.

[Explanation of symbols]

1: horizontal shift register, 2: vertical shift register, 3 to 5: transfer switch, 6: pixel circuit, 7 to 9: output line.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G09G 3/34 G02F 1/1335 530 F term (Reference) 2H091 FA41Z GA13 LA15 LA16 LA18 2H093 NA31 NA51 NB21 NB22 NC16 NC34 NC35 NC62 ND06 ND09 ND15 ND17 ND39 ND47 5C006 AA01 AA14 AA22 AC28 AF42 AF44 AF69 BA12 BB16 BB28 BB29 EA01 FA47 FA54 FA56 5C080 AA10 BB05 CC03 DD03 DD26 EE29 EE30 FF11 JJ02 JJ04 JJ05

Claims (13)

[Claims] 1. A liquid crystal panel having a plurality of pixels arranged in a matrix and a light source capable of switching a plurality of colors to irradiate the liquid crystal panel, and raster-scanning the panel to turn on each of the light sources A color of a light source color switching system for sequentially writing images corresponding to colors and lighting the light source with a lighting color corresponding to each image in synchronization with the writing of each image, thereby performing color display with a temporal additive color mixture. A method for driving a liquid crystal device, comprising:
The time during which each pixel of the liquid crystal panel displays a state corresponding to each lighting color is made sufficiently longer, and a subfield period in which an image corresponding to the lighting color is written, and then another lighting color A black display subfield period in which an entire black state is written between a subfield period in which an image corresponding to the above is written. 2. A raster scan is performed twice or more consecutively in a subfield period in which an image corresponding to one lighting color is written, and writing of an image signal to each pixel is inhibited during the second and subsequent raster scans. 2. The driving method for a liquid crystal device according to claim 1, wherein the display time of each pixel is equivalently set to be twice or more as long as the time required to perform one raster scan on the entire surface of the liquid crystal panel. 3. A raster scan is performed twice or more consecutively during a subfield period in which an image corresponding to one lighting color is written, and the same image signal is written at each raster scan, thereby reducing the display time of each pixel. 2. The method according to claim 1, wherein a time required for performing one raster scan on the entire surface of the liquid crystal panel is equivalently set to be sufficiently longer than twice. 4. The method according to claim 3, wherein the same image signal is written while inverting the polarity. 5. The transmittance characteristic of the pixel with respect to an applied voltage differs depending on the polarity of the applied voltage. When writing the same image signal while inverting the polarity, a voltage having a polarity capable of writing a high transmittance is written first. 5. The method according to claim 4, wherein the voltage is applied. 6. A liquid crystal panel having a plurality of pixels provided in a matrix, a first substrate having means for supplying a signal voltage to the pixels, and a transparent second substrate opposed to the liquid crystal, and The liquid crystal panel is provided with a backlight capable of emitting red, green, and blue primary colors to irradiate the liquid crystal panel. The liquid crystal panel is sequentially driven by red, green, and blue primary color image signals for each field, and synchronized with the primary color image signals. A driving method of a liquid crystal device for switching the backlight to a lit color and lighting the liquid crystal panel, wherein the image signal is longer than a time for writing a predetermined primary color image signal of the red, green, and blue over the entire liquid crystal panel. The time held in the liquid crystal panel is sufficiently longer, and the red, green, and blue subfield periods in which a predetermined primary color signal is input, and the next red, green, and blue home The driving method of a liquid crystal device and providing a black display sub-field period in which the whole surface black signal is input between the sub-field period other primary color signal is input. 7. The lighting period of the backlight is from when each primary color image signal is written to the first pixel to when the black signal is written to the last pixel in the next black subfield. The method for driving a liquid crystal device according to claim 5. 8. The driving of the liquid crystal device according to claim 5, wherein a holding period is at least twice as long as a time for writing the primary color image signal over the entire surface. Method. 9. The driving method for a liquid crystal device according to claim 5, wherein the primary color image signal is repeatedly written at least twice. 10. The active matrix element wherein the plurality of pixels provided in a matrix and a means for supplying a signal voltage to the pixels are formed on one substrate. A method for driving a liquid crystal device according to any one of the above. 11. The liquid crystal is a chiral smectic liquid crystal, and the phase transition series of the chiral smectic liquid crystal is isotropic liquid phase (ISO.)-Cholesteric phase (Ch) -chiral smectic C phase from a high temperature side. The method for driving a liquid crystal device according to any one of claims 5 to 10, wherein the liquid crystal device is an isotropic liquid phase (ISO.)-Chiral smectic C phase. 12. A liquid crystal panel having a plurality of pixels provided in a matrix, a light source capable of switching a plurality of colors and irradiating the liquid crystal panel, and a raster scan of the panel to provide each lighting color of the light source. Driving means for sequentially writing corresponding images and lighting the light source with a lighting color corresponding to each image in synchronization with the writing of each image, and a light source color switching system for performing color display with temporal additive color mixing Wherein the driving unit sets a time during which each pixel of the liquid crystal panel displays a state in which the pixel is written according to each lighting color, as compared with a time during which the liquid crystal panel is raster-scanned once. Between the subfield period in which an image corresponding to the lighting color is written and a subfield period in which an image corresponding to another lighting color is next written. A liquid crystal device characterized by providing the black display sub-field period is written. 13. A liquid crystal panel comprising a plurality of pixels provided in a matrix, a first substrate having means for supplying a signal voltage to the pixels, and a transparent second substrate opposed to a liquid crystal. A backlight capable of emitting red, green, and blue primary colors to irradiate the liquid crystal panel, and the liquid crystal panel is sequentially driven by red, green, and blue primary color image signals for each field, and in synchronization with the primary color image signals. A liquid crystal device comprising: a driving unit that switches the backlight to a lit color; wherein the red, green, and blue primary color image signals are written over the entire surface of the liquid crystal panel, The time held in the liquid crystal panel is sufficiently longer, and the red, green, and blue subfield periods in which the predetermined primary color signal is input, and the next red, green, and blue Chino liquid crystal device, characterized in that provided the black display sub-field period in which the whole surface black signal is input between the sub-field period other primary color signal is input.