JP2003131265A - Driving method of liquid crystal display device - Google Patents

Abstract

(57) [Problem] To drive a video signal and an initialization signal for initializing the state of the liquid crystal, the video signal is surely written to the liquid crystal, and the deterioration of the display image quality is reduced. To suppress. A pixel writing step of a pixel state initialization signal is performed a plurality of times. Even if writing is not enough with one writing of the initialization signal, the writing is complemented by the second writing and thereafter. Writing the initialization signal, thereby improving the initialization effect.

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 liquid crystal display device, etc., and more particularly to an optically compensated birefringence (Optical) method.
y Compensated Birefringenc
e (OCB)) A liquid crystal mode or other active matrix type liquid crystal display device utilizing a liquid crystal mode in which a signal different from the video signal for maintaining the video display state is written in the liquid crystal and held. The present invention relates to a driving method.

[0002]

2. Description of the Related Art Liquid crystal display devices are widely used as screen display devices for computer devices and the like, but in the future, their use in TV applications is expected to expand. However, the TN liquid crystal mode which is widely used at present has a narrow viewing angle and an insufficient response speed, which causes a big problem in display performance when used as a TV such as a reduction in contrast due to parallax and blur of a moving image. .

In recent years, OC has replaced the above-mentioned TN liquid crystal mode.
Research on B liquid crystal mode is in progress. It can be said that the OCB liquid crystal mode is a liquid crystal cell which has characteristics of wider viewing angle and faster response than the TN liquid crystal mode and is more suitable for displaying a natural moving image.

As shown in FIG. 14, the OCB liquid crystal mode has a bend orientation (b), which is in a state capable of displaying an image,
(C) and a splay orientation (a) that is in a state that cannot be displayed. In order to shift from the bend alignment state to the splay alignment state (hereinafter referred to as transition), unique driving such as applying a high voltage for a certain period of time is required. However, since the driving related to this transition is not directly related to the present invention, further description will not be given.

In addition, in the OCB liquid crystal mode, even if a transition is made to bend alignment due to this unique driving, the bend alignment cannot be maintained and the splay alignment is not maintained if a voltage above a predetermined level is not applied for a certain period of time. (Hereinafter, this phenomenon is referred to as reverse transition), and it is necessary to write a signal of a predetermined voltage or more at a constant cycle separately from the video signal and hold the signal.

The drive required to maintain the liquid crystal in a displayable state is called initialization drive, and the signal applied to the liquid crystal in the initialization drive is called the initialization signal.

Of the conventional driving methods for the liquid crystal display device requiring the above-mentioned initialization driving, as an example,
A driving method of a liquid crystal display device using the OCB liquid crystal mode will be described with reference to the drawings.

FIG. 11 is a timing chart of a driving method of a liquid crystal display device using a conventional OCB liquid crystal mode, FIG.
2 is a block diagram showing a configuration of a liquid crystal display device used in the driving method, and FIG. 13 is a diagram illustrating an operation of a frequency conversion unit forming a part of the liquid crystal display device.

In FIG. 12, X_1, X_2, ..., X
_N is a gate line, Y_1, Y_2, ..., Y_p is a source line, 107 is a thin film transistor (hereinafter referred to as TFT) as a switching element, and the drain electrode of each TFT is connected to the pixel electrode 109 in the pixel 106. There is.

Each pixel 106 has a pixel electrode 109.
And a counter electrode 105 which is a transparent electrode, and a liquid crystal 108 held between both electrodes.

The counter electrode 105 is driven by the voltage supplied by the drive controller 102.

The gate driver 104 has a gate line X_.
, X_n is an IC for applying a voltage for turning on the TFT or a voltage for turning off the TFT. That is, the gate driver 104 is the source driver 1
, 03, in synchronization with the data supply to the source lines Y_1, Y_2, ..., Y_p by the gate lines X_1, X_2 ,.
The ON potential is sequentially applied to X_n. The source driver 103 is an IC that outputs a voltage supplied to the pixel 106 to the source lines Y_1, Y_2, ..., Y_p. The voltage supplied to the counter electrode 105 and the source lines Y_1, Y
The difference from the voltage applied to each pixel electrode 109 via _2, ..., Y_p is the voltage applied to both ends of the liquid crystal 108 in the pixel 106, and this determines the transmittance of the pixel 106.

In order to write the initialization signal separately from the writing of the video signal, the frequency conversion unit 101 is provided with the configuration shown in FIG.
As shown by 3, frequency conversion is performed on the input video signal. Here, a case is shown in which the frequency is doubled. In this case, the video writing period of each line of the liquid crystal panel is half the horizontal synchronizing period of the input video signal.

FIG. 11 shows the timing for driving the liquid crystal display device. The gate lines X_1, X_2,
, X_n are controlled by the gate driver 104 at the timings X_1, X_2, ..., X_n, respectively. Therefore, in the first line on the liquid crystal panel, the image 1 which is a part of the source input image signal frequency-converted by the frequency conversion unit 101 at the timing T1 of X_1 is written. Also, the timing T2 after a predetermined time
In addition, the initialization signal output separately from the video signal is written by the frequency conversion unit 101. These writings are performed in a period that is half the horizontal synchronizing period of the input video signal. The period from the writing of the video signal to the writing of the initialization signal, that is, the period from timing T1 to timing T2 is the video display period, and conversely,
The period from T2 to T1 is the holding period of the initialization signal. The timing of T2 with respect to the timing T1 is determined depending on the characteristics of the liquid crystal used, and when a liquid crystal having a long holding period of an initialization signal necessary for maintaining a normal display state is used, the above image display period is It gets shorter.

[0015]

Generally, in a liquid crystal display device, when liquid crystal is driven by direct current, polarization occurs, and afterimages remain even when the screen is switched, a so-called burn-in state occurs. It is driven by an AC voltage that is inverted with respect to the reference potential. Therefore, even in a liquid crystal display device that needs to write such an initialization signal,
Although it is necessary to perform such AC driving, conventionally, there has been a problem that AC driving of such a liquid crystal display device causes a reduction in contrast of a displayed image.

Therefore, an object of the present application is to investigate the cause of this decrease in contrast and to provide a driving method of a liquid crystal display device capable of improving the contrast of a display image.

[0017]

In order to solve the above-mentioned problems, the inventors of the present application have considered that the AC drive is not performed in consideration of the initialization signal, and that it takes time to write the video signal in the pixel. Be shorter than the horizontal synchronization period of the video of
Furthermore, as a result of repeated experiments and studies, it is assumed that the reason for the decrease in contrast is that the writing time becomes shorter with the need for higher resolution, and the inability to completely write the video signal is the cause of the decrease in contrast. In particular, when an initialization signal of opposite polarity is written to the written video signal, the initialization signal is not sufficiently written due to the delay in the response of the liquid crystal, and the initialization effect is reduced. . Therefore, it has been found that the video signal cannot be written sufficiently and the contrast of the displayed video is lowered.

The method of driving a liquid crystal display device invented by the inventors of the present invention includes a pixel writing step of a video signal and a plurality of pixel writing steps of a pixel state initialization signal.

Further, the plurality of pixel state initialization signals have the same polarity with respect to a predetermined reference potential.

Further, the polarity of the video signal with respect to a predetermined reference potential and the polarity of the plurality of pixel initialization signals with respect to a predetermined reference potential are opposite polarities.

The present invention is also characterized in that the active matrix type liquid crystal display device uses OCB liquid crystal.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION A method of driving a liquid crystal display device according to an embodiment of the present invention will be described in detail below with reference to the drawings.

(First Embodiment) FIG. 1 is a diagram showing a timing of driving a liquid crystal display device by using a driving method of a liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing the structure of an active matrix liquid crystal display device driven by the driving method.

In FIG. 2, the liquid crystal display device according to the first embodiment has a frequency converter 101 and a drive controller 202.
And a source driver 103, a gate driver 204, and a pixel cell 106. The pixel cell 106 also includes a switching element 107 and a liquid crystal 108.

The liquid crystal display device shown in FIG. 12 includes a conventional liquid crystal display device shown in FIG. 12 and a drive controller 202 (10 in FIG. 12).
2) and the gate driver 204 (104 in FIG. 12)
The operation is different in.

The other configurations of the liquid crystal display device according to the first embodiment are the same as the respective configurations of the conventional liquid crystal display device described above. Omit it.

In FIG. 1, "video 1" in the input video signal indicates a video signal written in the first line by the signal X_1 output to the output line X_1 of the gate driver 204. Other video signals n are also signal X
_N means a video signal written in the nth line. As shown in FIG. 1, the video signal is written once and the initialization signal is written twice for each line of the liquid crystal panel. For example, for the first line controlled by the signal X_1 output to the output line X_1 of the gate driver 204, after the video signal is written at the timing T1, the first initialization signal of the first initialization signal is given at the timing T2. Writing is performed, and at timing T3, the second initialization signal is written.

The writing of the initialization signal for the second time is also the timing of writing the initialization signal to the second line controlled by the signal X_2 output to the output line X_2 of the gate driver, that is, the first line and the second line. Initialization signals of the two lines are written simultaneously.

By thus writing the initialization signal twice, even if the initialization signal cannot be written sufficiently by one writing, the writing can be surely performed by the second writing of the initialization signal. Therefore, it is possible to improve the problems in the conventional driving method such as the reduction of the initialization effect and the contrast of the display image.

In the above embodiment, the case where the initialization signal is written twice has been described.
The same effect can be obtained by writing the initialization signal more than once.

The case where the second writing is synchronized with the initialization signal writing timing for the adjacent line has been described. For example, the second initialization for the first line controlled by the output line X_1 of the gate driver is performed. The same effect can be obtained when the signal writing timing is delayed at timing T4 or further.

(Embodiment 2) When the liquid crystal is driven by direct current, polarization occurs, and afterimages remain even when the screen is switched to a so-called burn-in state. Therefore, the liquid crystal is driven by an AC voltage that is inverted with respect to the reference potential at the frame frequency. Furthermore, from the viewpoint of display performance such as flicker performance and crosstalk performance, and the ability to write a voltage to the liquid crystal, paying attention to the polarity with respect to the reference potential between adjacent pixels,
Drives such as column inversion drive, line inversion drive, and dot inversion drive are performed as shown in FIGS. When line inversion drive or dot inversion drive is performed, considering the above AC conversion timing, if the initialization signal is not written, the written initialization signal is
When writing the initialization signal of the opposite polarity, the intended writing improvement effect cannot be obtained due to the delay of the response of the liquid crystal.

Therefore, in the second embodiment of the present invention, the drive is performed by paying attention to the polarity so that the initialization signal having the same polarity as the previously written initialization signal is written.

FIG. 3 is a diagram showing the timing of driving the liquid crystal display device by using the driving method of the liquid crystal display device according to the second embodiment of the present invention.

FIG. 4 is a block diagram showing the structure of a liquid crystal display device driven by the driving method.

FIG. 5, FIG. 6, FIG. 7 and FIG. 8 are views for explaining AC driving of liquid crystal.

In FIG. 4, the liquid crystal display device according to the second embodiment has a frequency converter 101 and a drive controller 402.
And a source driver 103, a gate driver 404, and a pixel cell 106. The pixel cell 106 also includes a switching element 116 and a liquid crystal 126.

As shown in FIG. 3, the liquid crystal display device according to the second embodiment includes the conventional liquid crystal display device shown in FIG. 12, a drive control unit 402 (102 in FIG. 12), and a gate driver 404 (FIG. 12). Then, the operation is different in 104).

The other configurations of the liquid crystal display device according to the second embodiment are the same as those of the conventional liquid crystal display device described above, and the same configurations are denoted by the same reference numerals and described. Omit it.

Here, the alternating drive will be described. FIG. 5 shows the correspondence between the brightness displayed by a pixel and the voltage written in the pixel at that time and held for one frame period in synchronization with the frame. It can be seen that even when the same brightness is displayed, a voltage whose polarity is inverted is written centered on the reference potential VCOM for each frame. This is called AC drive. In FIG. 5, the display brightness is higher as the voltage applied to the liquid crystal is smaller, that is, the case of so-called normally white is shown as an example. On the contrary, the lower the voltage applied to the liquid crystal is, the lower the display brightness is. Also in the case of so-called normally black, the drive for inverting the polarity in synchronization with the frame is the same, only the relationship between the display brightness and the writing voltage is reversed.

As shown in FIGS. 6, 7 and 8, as a concrete method of this AC driving, depending on the AC timings and polarities of the peripheral pixels, column inversion driving, line inversion driving and dot inversion driving are largely performed. Can be separated.

However, in the column inversion drive shown in FIG. 6, it is possible to invert the polarity every two lines, and there is no clear distinction from the dot inversion drive shown in FIG.
In the various types of driving shown in FIGS. 6, 7, and 8, depending on the polarity of the pixel from the gate driver with respect to the reference potential, “+
It is defined as "line" or "-line".

In FIG. 3, "+" and "-" are shown below the source input video signal and below the drive waveform of the gate line to show the polarities of the lines. For example, the gate line X_
The first line is written at the timings T2 and T3 by the signal X_1 output to 1 and the initialization signal indicates that the polarity of the pixel closest to the gate driver is “−” with respect to the reference potential. There is.

As shown in FIG. 3, by making the polarity of the initialization signal written twice the same with respect to the reference potential,
Even if the writing of the initialization signal is insufficient once, the writing can be improved and the sufficient initialization effect can be obtained by the second writing.

In the second embodiment of the present invention, the case where the initialization signal with the same polarity is written twice has been described, but the same effect can be obtained by performing the writing three times or more. Can be obtained, and the first time
Increase the write interval of the second initialization signal, for example, the first
It is also possible to write the initialization signal to the line for the first time at the timing T2 and then write the second time at the timing T5 instead of the timing T4.

Further, in FIG. 3, the polarity of the initialization signal is inverted for each line, but it is not always necessary, and it may be inverted in several line cycles or in frame cycles.

(Third Embodiment) Writing of a video signal
It is affected by the polarity of the initialization signal written in the liquid crystal at the time of writing. If the initialization signal held by the liquid crystal and the video signal to be written have the opposite polarities, the video signal cannot be written sufficiently and the image quality is impaired.

Therefore, the third embodiment of the present invention takes into account the correlation between the polarity of the video signal and the polarity of the initialization signal so that the video signal can be surely written like the initialization signal.

FIGS. 9A and 9B are diagrams showing the timing of driving the liquid crystal display device using the driving method of the liquid crystal display device according to the third embodiment of the present invention. FIG.
It is a block diagram showing a configuration of a liquid crystal display device driven by the driving method.

In FIG. 10, the liquid crystal display device according to the third embodiment has a frequency converter 101 and a drive controller 10.
02, source driver 103, gate driver 100
4 and the pixel cell 106. Also, the pixel cell 106
Includes a switching element 116 and a liquid crystal 126.

As shown in FIG. 10, the liquid crystal display device according to the third embodiment includes a conventional liquid crystal display device shown in FIG. 12, a drive controller 1002 (102), and a gate driver 1.
The operation is different at 004 (104).

The other configurations of the liquid crystal display device according to the first embodiment are the same as the respective configurations of the conventional liquid crystal display device described above. Omit it.

As shown in FIG. 9A, from the viewpoint of AC driving, the polarities of the video signal written in the first line at timing T1 and the video signal written at timing T6 in the next frame with respect to the reference potential are different. It has opposite polarity. The polarity of the initialization signal written at timing T2 is the same as the polarity of the video signal written at timing T6. At this time, the polarity of the video signal written at the timing T1 and the polarity of the initialization signal written at the timing T2 are opposite polarities, the writing of the initialization signal is disadvantageous as a condition, and the writing may not be performed sufficiently. Therefore, at timing T4, an initialization signal having the same polarity as the previously written initialization signal is rewritten to improve the writing. In addition, by performing writing with such a polarity, the polarity of the initialization signal held by the pixel at the time of writing the video signal becomes the same as the polarity of the video signal to be written, which facilitates the writing and the display. Image quality improves.

Although the third embodiment of the present invention has been described with respect to the case where the initialization signal is written twice with the same polarity, it is also possible to write the initialization signal three times or more. It is also possible to write the initialization signal for the second time at timing T5 or the like instead of timing T4.

Further, in FIG. 9A, the polarity of the video signal is inverted line by line, line inversion or dot inversion drive is premised, and correspondingly the polarity of the initialization signal is also inverted line by line. However, it is not always necessary to perform such driving, and it is also possible to invert the polarities of the video signal and the corresponding initialization signal in units of a plurality of lines. FIG. 9B shows, as an example, a drive waveform when the polarities of the video signal and the initialization signal are inverted every two lines. As is apparent from FIG. 9B, for example, the write timing of the second initialization signal to the first line is changed from the timing T4 in FIG. Will be exactly the same.

[0057]

According to the present invention, it is possible to surely write a video signal in the liquid crystal and suppress the deterioration of the display image quality and the initialization effect.

[Brief description of drawings]

FIG. 1 is a diagram showing a timing of a driving method according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a liquid crystal display device to which the driving method according to the first embodiment of the present invention is applied.

FIG. 3 is a diagram showing a timing of a driving method according to a second embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of a liquid crystal display device to which a driving method according to a second embodiment of the present invention is applied.

FIG. 5 is a diagram illustrating AC driving of liquid crystal.

FIG. 6 is a diagram illustrating AC driving of liquid crystal.

FIG. 7 is a diagram illustrating AC driving of liquid crystal.

FIG. 8 is a diagram illustrating AC driving of liquid crystal.

9A is a diagram showing timings of a driving method according to a third embodiment of the present invention. FIG. 9B is a diagram showing timings of driving methods according to the third embodiment of the present invention.

FIG. 10 is a block diagram showing a configuration of a liquid crystal display device to which a driving method according to a third embodiment of the present invention is applied.

FIG. 11 is a diagram showing a timing of a driving method of a conventional liquid crystal display device.

FIG. 12 is a block diagram showing a configuration of a conventional liquid crystal display device.

FIG. 13 is a diagram for explaining the operation of the frequency conversion unit.

FIG. 14 is a diagram showing an alignment state of OCB liquid crystal.

[Explanation of symbols]

101 Frequency converter 102, 202, 402, 1002 Drive control unit 103 Source driver 104, 204, 404, 1004 Gate driver 105 Counter electrode 106 pixels 107 TFT 108 LCD 109 pixel electrode

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G09G 3/20 670 G09G 3/20 670K 3/36 3/36 (72) Inventor Takahiro Kobayashi Kadoma City, Osaka Prefecture Daiji Kadoma 1006 Matsushita Electric Industrial Co., Ltd. (72) Inventor Katsuyuki Arimoto Osaka Kadoma City Kadoma 1006 Matsushita Electric Industrial Co., Ltd. (72) Inventor Taro Funamoto Kadoma City Osaka 1006 Sangyo Co., Ltd. F term (reference) 2H088 HA03 HA06 JA09 JA28 2H093 NA32 NA33 NC09 NC11 NC16 NC32 ND04 ND12 5C006 AC27 AC28 AF42 AF43 AF44 AF71 BB16 BC03 BC11 FA34 FA54 5C080 AA10 BB05 DD03 DD29 EE28 FF11 JJ02 JJ04

Claims (4)

[Claims] 1. A method of driving a liquid crystal display device, comprising a step of writing a pixel of a video signal and a step of writing a pixel of a pixel state initialization signal a plurality of times. 2. The method of driving a liquid crystal display device according to claim 1, wherein the pixel state initialization signals of a plurality of times have the same polarity with respect to a predetermined reference potential. 3. The liquid crystal according to claim 1, wherein the polarity of the video signal with respect to the predetermined reference potential and the polarity of the pixel initialization signals with respect to the predetermined reference potential are opposite polarities. Driving method of display device. 4. The active matrix type liquid crystal display device uses OCB liquid crystal.
4. The method for driving the liquid crystal display device according to any one of items 1 to 3.