JP4086462B2 - Liquid crystal display device and liquid crystal display method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a liquid crystal display device.And liquid crystal display methodIn particular, an active drive type liquid crystal display device using a liquid crystal having spontaneous polarizationAnd liquid crystal display method using the liquid crystal display deviceAbout.
[0002]
[Prior art]
With the recent development of so-called office automation (OA), OA devices represented by word processors, personal computers, PDAs (Personal Digital Assistants), etc. are widely used. Furthermore, with the spread of office automation equipment in offices, there is a demand for portable office automation equipment that can be used both in the office and outdoors, and there is a demand for reduction in size and weight. Liquid crystal display devices are widely used as one of means for achieving such an object. The liquid crystal display device is an indispensable technology for reducing the power consumption of not only a small size and light weight but also a battery-driven portable OA device.
[0003]
By the way, liquid crystal display devices are roughly classified into a reflection type and a transmission type. The reflective liquid crystal display device is configured to reflect light incident from the front surface of the liquid crystal panel on the back surface of the liquid crystal panel and visually recognize the image, and the transmissive type is a light source (backlight) provided on the back surface of the liquid crystal panel. The image is visually recognized by the transmitted light from (). The reflective type is inferior in visibility because the amount of reflected light is not constant depending on the environmental conditions, but is inexpensive. Therefore, the reflective type is widely used as a display device of a single color (for example, white / black display) such as a calculator and a clock. It is not suitable as a display device for a personal computer that performs color or full color display. Therefore, a transmissive liquid crystal display device is generally used as a display device for a personal computer that performs multi-color or full-color display.
[0004]
On the other hand, current color liquid crystal display devices mainly use STN (Super Twisted Nematic) type with a simple matrix electrode configuration and TN (TFT) using switching elements such as TFT (Thin Film Transistor) in terms of the liquid crystal material used. Generally classified as Twisted Nematic) type. Although the STN type is relatively inexpensive to manufacture, there is a problem that it is not suitable for displaying moving images because crosstalk is likely to occur and the response speed is relatively slow. On the other hand, the TN type driven by TFT has higher display quality than the STN type, but the light transmittance of the liquid crystal panel is as low as 4%, and a high-brightness backlight is required to obtain high screen brightness. become. For this reason, the TFT type has problems such as high power consumption, response speed, particularly slow response speed in halftone, and narrow viewing angle.
[0005]
Under the circumstances as described above, the present inventors have proceeded with the development of a liquid crystal display device using a ferroelectric liquid crystal material having spontaneous polarization and a response speed to an applied voltage as high as several hundreds to several μs. ing. When a ferroelectric liquid crystal having spontaneous polarization is used as the liquid crystal material, the liquid crystal molecules are always parallel to the substrate regardless of the presence or absence of the applied voltage, and the refractive index changes depending on the viewing direction. , Much smaller than TN type. Therefore, it is possible to obtain a wide viewing angle.
[0006]
Thus, a liquid crystal display device using a ferroelectric liquid crystal material is superior to a conventional liquid crystal display device in terms of response speed and viewing angle. The driving method is also possible with a simple matrix electrode configuration as in the STN type, but the selection period per line for writing display data is as long as several hundred μs, so the response speed of the ferroelectric liquid crystal However, even if it is as fast as several hundreds to several μs, it takes a long time to rewrite one screen (number of lines × several hundreds μs). Moreover, there is also a problem that halftone display is difficult due to its principle.
[0007]
The present inventors drive a liquid crystal display device using a ferroelectric liquid crystal material (hereinafter also simply referred to as a ferroelectric liquid crystal display device) with a switching element such as a TFT to display a moving image display and a halftone display. (Japanese Patent Laid-Open No. 11-119189, Japanese Patent Laid-Open No. 2000-180827, etc.).
[0008]
[Problems to be solved by the invention]
However, in such a ferroelectric liquid crystal display device driven by a switching element such as a TFT, the ferroelectric liquid crystal has spontaneous polarization, and in principle, the distance between the substrates is set to a conventional liquid crystal display. There is a problem that the power consumption required for driving is large because the device must be narrower than the device. This is a problem that goes against lower power consumption of a battery-driven portable OA device. For example, a ferroelectric liquid crystal display device driven by a TFT is used for a portable OA device. There is a point that should be improved.
[0009]
  The present invention has been made in view of such circumstances, and is a liquid crystal display device that uses a liquid crystal substance such as a ferroelectric liquid crystal having spontaneous polarization and is driven by a switching element such as a TFT, and has low power consumption. LCD device that can be realizedAnd liquid crystal display method using the liquid crystal display deviceThe purpose is to provide.
[0010]
[Means for Solving the Problems]
  In the liquid crystal display device according to claim 1, a liquid crystal material having spontaneous polarization is sealed in a gap formed by at least two substrates, and the light transmittance of the liquid crystal material is controlled corresponding to each pixel. In a liquid crystal display device provided with a switching element for controlling on / off of voltage application as much as possible,A first display mode for rewriting a display image by alternately applying a positive voltage and a negative voltage to the liquid crystal substance at a predetermined period;All voltages applied to the liquid crystal material are removed, and the display before the removalimageMaintainMeans for switching between the second display form and the second display form when moving from the second display form to the first display form.All the pixels are displayed in black.
[0011]
  In the liquid crystal display device according to the first aspect, after all the voltages applied to the liquid crystal substance are removed by the switching elements such as TFTs, the display state immediately before removing the applied voltage is substantially maintained. Therefore, an image can be displayed without applying a voltage to the liquid crystal substance, and the power consumption can be greatly reduced. Therefore, application to a portable device is also possible, and in particular, the effect of reducing power consumption for a portable device having many still screens is increased. When resuming the voltage application to the liquid crystal material, all the pixels are first displayed in black, and then a voltage corresponding to the display data is applied to the liquid crystal material. Therefore, a black base display is always obtained after resumption of application, and a clear display can be obtained.
  Then, a display mode in which the display image is rewritten by applying a voltage to the liquid crystal material at a constant period and a display mode in which the voltage application to the liquid crystal material is removed and the display image before the removal is maintained are arbitrarily switched. Can do. Therefore, when switching from video display to still image display, or switching from still image display to video display, it is possible to adjust the presence or absence of voltage application according to whether or not display rewriting is necessary, reducing image quality. It is possible to reduce power consumption without causing it to occur.
[0012]
  The liquid crystal display device according to claim 2 is the liquid crystal display device according to claim 1,A light source for display is provided, and the luminance of the light source in the second display mode is lower than the luminance of the light source in the first display modeIt is characterized by that.
[0013]
  In the liquid crystal display device according to claim 2,The brightness of the light source in the display form that maintains the display image by removing the voltage application,Display form that rewrites display image by applying voltageSince it is lower than the brightness of the light source inReduction of power consumptionIs achieved.
[0014]
  A liquid crystal display device according to claim 3 is the claim1 or2There is no period in which the voltage is maintained at the ground level between the application period of the positive voltage and the application period of the negative voltage.It is characterized by that.
[0016]
A liquid crystal display device according to a fourth aspect of the present invention is the liquid crystal display device according to any one of the first to third aspects, wherein a voltage corresponding to an image to be displayed after the voltage application is removed before the voltage application to the liquid crystal material is removed. It is characterized by being applied to.
[0017]
  In the liquid crystal display device according to the fourth aspect, before removing the voltage application to the liquid crystal substance, a voltage corresponding to an image to be displayed next is applied. Therefore, the next desired image can be displayed without applying a voltage, and power consumption can be reduced.
  In the liquid crystal display method according to claim 5, a liquid crystal material having spontaneous polarization is enclosed in a gap formed by at least two substrates, and the light transmittance of the liquid crystal material is controlled corresponding to each pixel. In a liquid crystal display method for performing liquid crystal display using a liquid crystal display device including a switching element that controls on / off of voltage application, positive and negative voltages are alternately and repeatedly applied to the liquid crystal material at a predetermined period. By switching between the first display mode for rewriting the display image and the second display mode for removing all voltages applied to the liquid crystal substance and maintaining the display image before the removal, the second display mode is switched. When shifting from the display mode to the first display mode, all the pixels are displayed in black.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings showing embodiments thereof. Note that the present invention is not limited to the following embodiments.
(First embodiment)
FIG. 1 is a schematic cross-sectional view of the liquid crystal panel 1 and the backlight 30 of the liquid crystal display device according to the first embodiment, and FIG. 2 is a schematic diagram showing an overall configuration example of the liquid crystal display device.
[0019]
As shown in FIGS. 1 and 2, the liquid crystal panel 1 includes a polarizing film 2, a common electrode 3, and a color filter 4 arranged in a matrix form from the upper layer (front surface) side to the lower layer (back surface) side. A glass substrate 5 having a pixel electrode 6 arranged in a matrix, and a polarizing film 8 are laminated in this order.
[0020]
A drive unit 20 having a data driver, a scan driver (not shown) and the like is connected between the common electrode 3 and the pixel electrode 6. The data driver is connected to the TFT 21 via the signal line 22, and the scan driver is connected to the TFT 21 via the scanning line 23. The TFT 21 is on / off controlled by a scan driver. Each pixel electrode 6 is ON / OFF controlled by the TFT 21. Therefore, the transmitted light intensity of each pixel is controlled by a signal from the data driver given via the signal line 22 and the TFT 21.
[0021]
An alignment film 9 is disposed on the upper surface of the pixel electrode 6 on the glass substrate 7, and an alignment film 10 is disposed on the lower surface of the common electrode 3. The alignment films 9 and 10 are filled with a liquid crystal substance that is a ferroelectric liquid crystal. Thus, the liquid crystal layer 11 is formed. Reference numeral 12 denotes a spacer for maintaining the layer thickness of the liquid crystal layer 11.
[0022]
The backlight 30 is located on the lower layer (rear) side of the liquid crystal panel 1 and is provided with an LED array 32 that emits white light in a state of facing the end face of the light guide and light diffusing plate 31 constituting the light emitting region. Yes. The LED array 32 has a wide brightness adjustment range, and brightness adjustment is easy. The light guide and light diffusion plate 31 functions as a light emitting region by guiding the white light emitted from each LED of the LED array 32 to the entire surface and diffusing it to the upper surface. The luminance of the backlight 30 (LED array 32) is adjusted by the backlight control circuit 33.
[0023]
Here, a specific example of the liquid crystal display device in the first embodiment will be described. First, the liquid crystal panel 1 shown in FIGS. 1 and 2 was produced as follows. After washing the TFT substrate having the pixel electrode 6 (640 × 3 (RGB) × 480, diagonal 3.2 inches) and the common electrode substrate having the common electrode 3 and the RGB color filter 4, polyimide is applied. By baking at 200 ° C. for 1 hour, a polyimide film of about 200 mm was formed as alignment films 9 and 10.
[0024]
Further, these alignment films 9 and 10 were rubbed with a cloth made of rayon and overlapped with a gap maintained by a silica spacer 12 having an average particle diameter of 1.6 μm between them to produce an empty panel. This empty panel is filled with a ferroelectric liquid crystal material mainly composed of naphthalene-based liquid crystal (for example, a material disclosed in A. Mochizuki, et.al .: Ferroelectrics, 133, 353 (1991)) to form a liquid crystal layer 11. . The magnitude of spontaneous polarization of the encapsulated ferroelectric liquid crystal material is 6 nC / cm.²Met.
[0025]
The produced panel is sandwiched between two polarizing films 2 and 8 in a crossed Nicol state so that the liquid crystal layer 11 is in a dark state when the major axis direction of the ferroelectric liquid crystal molecules inclines to one side. It was. The liquid crystal panel 1 and the backlight 30 were overlapped to constitute a liquid crystal display device.
[0026]
Next, the operation of the present invention will be described. First, the memory function of the ferroelectric liquid crystal will be described.
[0027]
The voltage applied is to apply a voltage to the liquid crystal panel 1 having the above-described configuration, then stop the application and remove the voltage, and measure the transmittance when the voltage is applied and the transmittance after 60 seconds of voltage removal. We went while changing the value of. The measurement result at that time is shown in FIG. In FIG. 3, the measurement result is shown by taking the voltage (V) applied on the horizontal axis and the transmittance (%) on the vertical axis, where ◯-○ is the transmittance during voltage application, and Δ-Δ is the voltage removal 60. The transmittance after 2 seconds is shown respectively. Even after the applied voltage is removed, the correspondence characteristic between the applied voltage and the transmittance does not change, and even if the voltage applied to the liquid crystal panel 1 is removed, the transmittance according to the display state when the voltage is applied. It can be seen that Further, the black display (transmittance: approximately 0%, applied voltage: approximately 0 V) did not change between the voltage application and the voltage application, and the display state was maintained.
[0028]
Further, the temporal change of the transmittance after removing the voltage was measured for the liquid crystal panel 1 having the above-described configuration. The measurement results are shown in FIG. As shown in FIG. 4A, a voltage having a pulse waveform of 5 V and 5 μs was applied to the liquid crystal panel 1, and the transmittance was measured over time. In FIG. 4B, the transmissivity measured with time (ms) on the horizontal axis and transmissivity (arbitrary unit) on the vertical axis is shown. It can be seen that the transmittance suddenly rises at the moment when the voltage is applied and then gradually attenuates, but no attenuation is observed after the voltage removal of 100 ms and the constant transmittance is maintained.
[0029]
From the above, the ferroelectric liquid crystal has a memory function, and even when the applied voltage is removed, the liquid crystal molecules move from a stable position before removing the applied voltage to another stable position. It can be seen that the previous state is maintained without doing. Therefore, in the liquid crystal display device using the ferroelectric liquid crystal having such a memory function, the display information on the next screen is obtained by applying the applied voltage corresponding to the display information for one screen once. Even if the voltage is not continuously applied until the applied voltage corresponding to is applied, a constant display according to the applied voltage can be maintained. Therefore, it is possible to maintain the screen display without applying a voltage, and power consumption can be reduced when the application is unnecessary.
[0030]
Next, a specific operation example of the present invention will be described. FIG. 5 is a timing chart showing an example of a driving sequence in the operation example. (A) The magnitude of the signal voltage applied to the ferroelectric liquid crystal to obtain a desired display, (b) The gate voltage of the TFT 21, (C) Transmittance, (d) Luminance of the backlight 30, and (e) Screen luminance are shown.
[0031]
In the liquid crystal display device of the present invention, the first display mode (period A in FIG. 5) in which the display image is rewritten by applying a voltage to the ferroelectric liquid crystal at a predetermined cycle, and the voltage application to the ferroelectric liquid crystal is removed. Thus, the second display mode (period B in FIG. 5) for maintaining the display image before the removal can be switched.
[0032]
A voltage is applied to the ferroelectric liquid crystal for each line by switching of the TFT 21 (gate-on voltage), and the time until a certain line is selected and the same line is selected again is 1/120 s. FIG. 5 shows a driving sequence in a selected line.
[0033]
After a voltage corresponding to a desired image is applied to the ferroelectric liquid crystal for each line at a gate-on voltage timing at a period of 1/120 s, the voltage application of the final line is finished and the first line is applied. Immediately before is selected, all the voltages applied to the liquid crystal panel 1 are turned off (timing C in FIG. 5). However, in the write scan immediately before turning off all the voltages, a voltage (signal voltage D in FIG. 5) corresponding to desired image data to be maintained and displayed when no voltage is applied is applied.
[0034]
In the period in which no voltage is applied (period B in FIG. 5), the transmittance is maintained based on the memory function of the ferroelectric liquid crystal, and the display image is displayed according to the voltage applied immediately before (signal voltage D in FIG. 5). Is maintained.
[0035]
Thereafter, in order to display a different image, voltage application to the ferroelectric liquid crystal was resumed (timing E in FIG. 5). At this time, the display corresponding to the desired display data was applied after the display on the liquid crystal panel 1 was all black. That is, when voltage application to the ferroelectric liquid crystal is started again, first, a voltage corresponding to black display (signal voltage F in FIG. 5) was applied.
[0036]
FIG. 6 is a diagram for explaining the change in transmittance of the black base. The liquid crystal molecules 40 are initially positioned along the polarization axis as shown in FIG. 6A (the position of the black display indicated by the solid line). ), The direction is changed between the position and a position shifted from the polarization axis (a white display position indicated by a broken line) according to voltage application. An example of the transmittance change at this time is shown in FIG. On the other hand, FIG. 7 is a diagram for explaining the white-based transmittance change, and the liquid crystal molecules 40 are initially positioned so as to deviate from the polarization axis as shown in FIG. 7A (white display indicated by a solid line). The position is changed between the position and a position along the polarization axis (a black display position indicated by a broken line) according to voltage application. An example of the transmittance change at this time is shown in FIG.
[0037]
When resuming the voltage application, as shown in FIG. 6, when the voltage corresponding to the desired display data is applied after the display of the liquid crystal panel 1 is set to all black display as in the present invention. A black-based display is always obtained, and a clear display can be obtained. On the other hand, when the voltage application is resumed, inconvenience arises if the display of the liquid crystal panel 1 is not temporarily displayed in all black. For example, if the display maintained in the state where no voltage is applied is a display other than black, in particular, white display, when the voltage application is started, the display is white based as shown in FIG. Cannot get the display.
[0038]
Next, the adjustment of the luminance of the backlight 30 will be considered. During normal voltage application (first display mode in period A in FIG. 5), positive and negative voltages are alternately applied to the liquid crystal. In the case of a ferroelectric liquid crystal, light is transmitted only when a voltage of one polarity is applied. Therefore, when the ratio applied by the positive voltage and the negative voltage is 1: 1, the average brightness is about half that of the light transmitted. become. On the other hand, the brightness when no voltage is applied is always constant. Therefore, the time when no voltage is applied may be brighter than when the voltage is applied.
[0039]
In order to solve such a problem, as shown in FIG. 5D, in the present invention, the brightness of the backlight 30 when no voltage is applied is reduced to about 70% in synchronization with the removal of the applied voltage, Adjust the brightness. Even if it does in this way, as shown in FIG.5 (e), a screen brightness | luminance does not fall. This reduction in the luminance of the backlight 30 also leads to a reduction in power consumption, and is significant. Note that the luminance of the backlight 30 when no voltage is applied may be arbitrary, and the luminance of the backlight 30 may be reduced to about 70% or less in order to further reduce power consumption when no voltage is applied. Of course. After resuming voltage application, the brightness of the backlight 30 was also restored.
[0040]
As described above, the same image display can be realized when the voltage is applied and when no voltage is applied. At this time, the power consumption when a voltage was applied was 600 mW, and the power consumption when no voltage was applied was 320 mW, so that the power consumption was reduced.
[0041]
Although the transmissive liquid crystal display device has been described in the first embodiment, the present invention can of course be applied to a reflective liquid crystal display device, and this example will be described below.
[0042]
(Second Embodiment)
The liquid crystal display device in the second embodiment was produced as follows. Similar to the first embodiment, after cleaning the TFT substrate having the pixel electrode (640 × 480, diagonal 3.2 inches) and the common electrode substrate having the common electrode, polyimide is applied at 200 ° C. By baking for 1 hour, a polyimide film of about 200 mm was formed. These polyimide films were rubbed with a rayon cloth, and were laminated with a gap maintained between them by a silica spacer having an average particle diameter of 1.6 μm to produce an empty panel. A ferroelectric liquid crystal material (for example, a material disclosed in A. Mochizuki, et.al .: Ferroelectrics, 133, 353 (1991)) containing naphthalene-based liquid crystal as a main component was encapsulated in this empty panel. The magnitude of spontaneous polarization of the encapsulated ferroelectric liquid crystal material is 6 nC / cm.²Met.
[0043]
The produced panel is sandwiched between two polarizing films in a crossed Nicol state (one with a reflector) so that the liquid crystal molecules are in a dark state when the major axis direction of the ferroelectric liquid crystal molecules is tilted to one side. It was. The reflection type ferroelectric liquid crystal panel thus fabricated was combined with a front light using R, G, and B LEDs as light sources to constitute a liquid crystal display device capable of color display by a field sequential color system.
[0044]
In contrast to the liquid crystal display device according to the second embodiment, as in the first embodiment, according to the driving sequence shown in FIG. Voltage was applied. The time from when a certain line is selected until the same line is selected again is set to 1/360 s.
[0045]
Immediately before the voltage application for the last line was completed and the first line was selected, all the voltages applied to the liquid crystal panel were turned off (timing C in FIG. 5). However, in the write scan immediately before turning off all the voltages, a voltage (signal voltage D in FIG. 5) corresponding to desired monochrome image data to be maintained and displayed when no voltage is applied is applied.
[0046]
Next, when resuming voltage application to the liquid crystal panel, the display on the liquid crystal panel was set to all black display, and then a voltage corresponding to display data was applied to the liquid crystal panel.
[0047]
As for the front light control, R, G, and B LEDs are time-division light emission when voltage is applied (first display mode), and white light emission is adjusted when voltage is removed (second display mode). .
[0048]
In this way, when applying voltage, it is possible to obtain color display using a field sequential color display method for high-quality images including moving image display, and to obtain monochrome display with low power consumption when voltage is removed. I was able to. In addition, when the front light was switched to green display and the luminance was further adjusted, a green / black monochrome color display could be obtained. Similarly, a single color display of blue / black, a single color display of red / black, and a single color display of mixed colors synthesized by R, G and B light sources could be obtained.
[0049]
Furthermore, even when the front light was turned off during voltage removal, monochrome display was possible in the reflection mode. In this case, the power consumption can be extremely low.
[0050]
The power consumption in each display mode in this second embodiment is 450 mW when displaying moving image color, 70 mW when displaying monochrome (however, the front light is turned on), and approximately 0 mW when displaying reflected monochrome (where the front light is turned off). There was a significant reduction in power consumption.
[0051]
(Third embodiment)
The liquid crystal display device in the third embodiment was produced as follows. As in the first embodiment, after cleaning the TFT substrate having the pixel electrode but the Al reflective electrode (640 × RGB × 480, diagonal 3.2 inches) and the common electrode substrate having the color filter and the common electrode A polyimide film of about 200 mm was formed by applying polyimide and baking at 200 ° C. for 1 hour. These polyimide films were rubbed with a rayon cloth, and overlapped with a gap held between them by a silica spacer having an average particle diameter of 0.8 μm to produce an empty panel. A ferroelectric liquid crystal substance (for example, a substance disclosed in A. Mochizuki, et.al .: Ferroelectrics, 133, 353 (1991)) containing naphthalene-based liquid crystal as a main component was encapsulated in this empty panel. The magnitude of spontaneous polarization of the encapsulated ferroelectric liquid crystal material is 6 nC / cm.²Met.
[0052]
A polarizing film was pasted on the surface of the produced panel to produce a single polarizing film type reflective ferroelectric liquid crystal panel. The produced single-polarized film type reflective ferroelectric liquid crystal panel was combined with a front light having an LED as a light source to constitute a liquid crystal display device capable of color display by a color filter method.
[0053]
For the liquid crystal display device according to the third embodiment, as in the first embodiment, the ferroelectric liquid crystal is applied to each line by switching the TFT (gate on voltage) in accordance with the driving sequence shown in FIG. Voltage was applied. The time from when a certain line is selected until the same line is selected again is set to 1/120 s.
[0054]
All voltages applied to the liquid crystal panel were turned off immediately before the application of the voltage on the last line was completed and the first line was selected. However, in the write scan immediately before turning off all the voltages, a voltage corresponding to desired image data to be maintained and displayed when no voltage is applied is applied. Next, when resuming voltage application to the liquid crystal panel, the display on the liquid crystal panel was set to all black display, and then a voltage corresponding to display data was applied to the liquid crystal panel.
[0055]
As for the control of the front light, as in the first embodiment, the luminance was lowered at the time of voltage removal (second display mode) than at the time of voltage application (first display mode).
[0056]
By doing so, it was possible to obtain color display of a high quality image including moving image display at the time of voltage application, and color display with low power consumption at the time of voltage removal. Furthermore, even when the front light was turned off during voltage removal, color display was possible in the reflection mode. In this case, the power consumption can be extremely low.
[0057]
The power consumption in each display mode in the third embodiment is approximately 550 mW when displaying moving image color, 100 mW when displaying still color (however, the front light is turned on), and approximately when displaying reflected color (the front light is turned off). The power consumption was 0 mW, and the power consumption was greatly reduced.
[0058]
Although the transmissive and reflective liquid crystal display devices have been described in the above-described embodiments, it is needless to say that the present invention can achieve the same effect with a transflective liquid crystal display device.
[0059]
Further, in the present invention, a material having a good correlation between the transmittance at the time of voltage application and the transmittance at the time of voltage removal is used, but there is a high correlation between the transmittance at the time of voltage application and the transmittance at the time of voltage removal. It goes without saying that the same effect can be obtained even if a material having such characteristics as shown in FIG. 8 is used.
[0060]
【The invention's effect】
As described above in detail, in the present invention, since all the voltages applied to the liquid crystal substance are removed by the switching elements such as TFTs, the display image immediately before removing the applied voltage is maintained. Display can be achieved, and power consumption can be significantly reduced. As a result, the range of use for portable devices can be expanded. In addition, when voltage application to the liquid crystal material is resumed, the voltage corresponding to the display data is applied to the liquid crystal material after all pixels have been displayed in black, so a black-based display is always required after the application is resumed. Thus, a clear display can be obtained.
[0061]
In the present invention, a display form in which a display image is rewritten by applying a voltage to the liquid crystal substance at a constant period and a display form in which the voltage application to the liquid crystal substance is removed and the display image before the removal is maintained are arbitrarily selected. When switching from moving image display to still image display, or switching from still image display to moving image display, it is possible to adjust the presence or absence of voltage application according to the necessity / requirement of display rewriting. It is possible to reduce power consumption without degrading image quality.
[0062]
In the present invention, the luminance of the display light source is made different between the display form in which the display image is rewritten by voltage application and the display form in which the display image is maintained by removing the voltage application. In the latter display form, the luminance of the display light source can be made lower than that in the former display form, and the power consumption can be further reduced.
[0063]
In the present invention, the image data to be displayed next is written before removing the voltage application to the liquid crystal substance, so that the next desired image can be displayed with low power consumption.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a liquid crystal panel and a backlight of a liquid crystal display device according to a first embodiment.
FIG. 2 is a schematic diagram showing an example of the overall configuration of the liquid crystal display device according to the first embodiment.
FIG. 3 is a graph showing an example of transmittance when a voltage is applied and when no voltage is applied.
FIG. 4 is a graph showing an example of applying a pulse voltage and a temporal change in transmittance accompanying therewith.
FIG. 5 is a timing chart showing an example of a driving sequence in the liquid crystal display device of the present invention.
FIG. 6 is a diagram for explaining a black base transmittance change;
FIG. 7 is a diagram for explaining a white-based transmittance change;
FIG. 8 is a graph showing another example of transmittance when a voltage is applied and when no voltage is applied.
[Explanation of symbols]
1 LCD panel
11 Liquid crystal layer
21 TFT
30 Backlight
33 Backlight control circuit

Claims (5)

A liquid crystal material having spontaneous polarization is sealed in a gap formed by at least two substrates, and voltage application is controlled on / off to control the light transmittance of the liquid crystal material corresponding to each pixel. In a liquid crystal display device provided with a switching element,
A first display mode for rewriting a display image by alternately applying a positive voltage and a negative voltage to the liquid crystal material at a predetermined period, and removing all voltages applied to the liquid crystal material, Means for switching between the second display mode for maintaining the display image before the removal and that the display of all the pixels is set to the black display when moving from the second display mode to the first display mode. A liquid crystal display device. The liquid crystal display device according to claim 1 , further comprising a light source for display, wherein the luminance of the light source in the second display mode is lower than the luminance of the light source in the first display mode . The liquid crystal display device according to claim 1, wherein there is no period in which the voltage is maintained at a ground level between the application period of the positive voltage and the application period of the negative voltage.   The liquid crystal display device according to claim 1, wherein a voltage corresponding to an image to be displayed after removing the voltage application is applied to the liquid crystal material before removing the voltage application to the liquid crystal material. . A liquid crystal material having spontaneous polarization is sealed in a gap formed by at least two substrates, and voltage application is controlled on / off to control the light transmittance of the liquid crystal material corresponding to each pixel. In a liquid crystal display method for performing liquid crystal display using a liquid crystal display device including a switching element,
A first display mode for rewriting a display image by alternately applying a positive voltage and a negative voltage to the liquid crystal material at a predetermined period, and removing all voltages applied to the liquid crystal material, A liquid crystal display method characterized by switching to a second display mode for maintaining a display image before removal thereof, and displaying all pixels in black when moving from the second display mode to the first display mode. .

Images