JP2003202549A - Liquid crystal display device and its driving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device capable of always displaying a video optimally without being affected by the change of the occurrence condition of reverse transition. <P>SOLUTION: In this liquid crystal display device, a detecting part 108 detecting the value of a parameter being the primary factor of the occurrence condition of the reverse transition, an arithmetic part 106 deciding at least one among the ratio of the applying time to one frame of a high voltage to be applied to a liquid crystal panel in order to prevent the reverse transition and the magnitude of the high voltage and an applying voltage corresponding to white display in accordance with the detection value of the detecting part 108 and a controller 104 driving the liquid crystal panel by a condition corresponding to the decision results of the arithmetic part 106 by outputting alternatively a video signal and a non-picture signal for applying the high voltage are provided. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to an OCB (optically self-C).
Opened Birefringence)
The present invention relates to a liquid crystal display device using a mode liquid crystal panel.

[0002]

2. Description of the Related Art Currently, liquid crystal display devices for displaying images are
A liquid crystal panel using an N (Twisted Nematic) mode is widely used. In recent years, a liquid crystal display device using an OCB mode liquid crystal panel developed to overcome the narrow viewing angle and poor response performance of the TN mode has been reported (Japanese Patent Laid-Open No. 7-8).
4254 (Patent Document 1), JP-A-9-96790.
Gazette (Patent Document 2)).

In the OCB mode liquid crystal panel, as disclosed in the above-mentioned Patent Document 2, a special process for transitioning the state of the OCB cell from the splay alignment to the bend alignment is required prior to the start of image display. (Hereinafter, such a transition from the splay alignment to the bend alignment is referred to as “transition”). However, since this processing is not directly related to the present invention, detailed description thereof will be omitted.

By the way, in the OCB mode liquid crystal panel, as shown in FIG. 14, even if the state of the OCB cell is changed to the bend orientation by the above treatment, the voltage applied to the OCB cell is less than a certain voltage Vc. Will continue to return to the splay orientation (hereinafter, such a transition from the bend orientation to the splay orientation is referred to as “reverse transition”). Therefore, in many liquid crystal display devices using the OCB mode liquid crystal panel, a voltage (Vc or more) within a range in which the bend alignment can be maintained is always applied to the OCB cell as shown by the characteristic a in FIG. In addition, the amplitude of the video signal is limited (in the case of normally white). However, if the amplitude of the video signal is limited in this way, the maximum transmittance of the liquid crystal panel becomes smaller accordingly (Ta in FIG. 14).
As a result, the maximum luminance of the liquid crystal panel (luminance during white display (bright display)) is reduced, and a desired luminance cannot be obtained.

However, if a high voltage is periodically applied to the OCB cell, the voltage applied to the OCB cell is temporarily V
Even if the value is less than c, the reverse transition does not occur. JP-A No. 11-109921 (Patent Document 3) and the April 25, 1999 issue of the Liquid Crystal Society of Japan (Vol.
2) P99 (17) to P106 (24) (Non-Patent Document 1). Utilizing this, when displaying an image of one frame, one frame period is divided into a period for displaying an image and a period for applying a high voltage.
As in the characteristic b of 4, the range of the voltage that can be applied to the OCB cell as the video signal can be expanded to Vw which is less than Vc. Hereinafter, such a driving method is referred to as "reverse transition prevention driving". In addition, a high voltage that is periodically applied to the OCB cell in order to prevent reverse transition is referred to as "reverse transition prevention voltage". The reverse transition prevention drive can increase the maximum transmittance of the liquid crystal panel (T in FIG. 14).
b) As a result, the maximum brightness of the liquid crystal display device can be increased. The larger the reverse transition prevention voltage is, and the larger the ratio of the application time to the one frame period (the ratio of the voltage holding time to the one frame period) is, the higher the reverse transition prevention effect is. It was confirmed by the inventors. It should be noted that the effect of preventing reverse transition referred to herein means that when a parameter (a ratio of the application time of the reverse transition preventing voltage to one frame period or the temperature of the liquid crystal), which will be described later, is a variable factor of the condition of occurrence of reverse transition. It represents the difficulty of occurrence of reverse transition.

[0006]

[Patent Document 1] JP-A-7-84254

[Patent Document 2] Japanese Patent Laid-Open No. 9-96790

[Patent Document 3] Japanese Patent Laid-Open No. 11-109921

[Non-Patent Document 1] Journal of the Liquid Crystal Society of Japan, April 25, 199 issue (Vol. 3, No. 2) P99 (17) to P106.
(24)

[0007]

However, in the case of performing the reverse transition prevention drive described above, the magnitude of the reverse transition prevention voltage necessary to prevent the reverse transition and the ratio of the application time to one frame period are, for example, It has been found that it changes depending on various factors such as the temperature of the liquid crystal panel (more accurately, the liquid crystal).

Therefore, as an example, the inventors investigated the relationship between the ratio of the application time of the reverse transition prevention voltage to one frame period and the temperature of the liquid crystal panel. As a result, in the OCB liquid crystal material used by the inventors, as the temperature of the liquid crystal becomes higher, the ratio of the application time of the reverse transition prevention voltage to one frame period becomes larger as shown by the dashed line in FIG. Do you get it. Therefore, if the ratio of the application time of the reverse transition prevention voltage to one frame period is, for example, the minimum required ratio at room temperature, the reverse transition occurs when the temperature of the liquid crystal becomes high, Image display becomes impossible. Therefore, the reverse transition prevention voltage is applied at a sufficiently large ratio so that the reverse transition does not occur even when the temperature of the liquid crystal panel is 80 ° C. so that the image can be displayed even when the temperature of the liquid crystal panel becomes high. It is possible to do it. However, when the ratio of the application time of the reverse transition prevention voltage (voltage corresponding to black display) to one frame period is increased, there is a problem that the maximum brightness is reduced. It should be noted that the brightness as used herein defines the brightness felt by humans, and it is nothing but the time integration of the transmittance within one frame period. It is for this reason that the maximum brightness is reduced when the ratio of the application time (black display) to one frame period is increased.

The inventors have also confirmed that the effect of preventing reverse transfer can be enhanced by increasing the magnitude of the reverse transfer preventing voltage. Therefore, as a reverse transition prevention voltage, for example, the temperature of the liquid crystal panel is 80 ° C., so that the image can be displayed even when the temperature of the liquid crystal panel becomes high.
It is conceivable to apply a sufficiently large voltage so that the reverse transition does not occur even at the time. However, when a voltage higher than the applied voltage (Vb in FIG. 14) corresponding to black display (dark display) is applied to the OCB liquid crystal, the O
Since the transmittance of the CB liquid crystal increases, there is a problem that the minimum luminance (luminance during black display) increases (that is, the contrast is impaired).

The inventors have also confirmed that the effect of preventing reverse transition can be enhanced by increasing the applied voltage (Vw in FIG. 14) corresponding to white display. Therefore, the applied voltage corresponding to the white display is set sufficiently so that the reverse transition does not occur even when the temperature of the liquid crystal panel is 80 ° C. so that the image can be displayed even when the temperature of the liquid crystal panel becomes high. It is possible to use a large voltage. However, when the applied voltage corresponding to the white display is increased, the transmittance of the liquid crystal during the white display is reduced, and thus there is a problem that the maximum brightness is reduced.

Therefore, an object of the present invention is to provide a liquid crystal display device capable of always displaying an image optimally regardless of the variation of the reverse transition generation condition.

[0012]

Means for Solving the Problems and Effects of the Invention In order to solve the above problems, the present invention adopts the following configurations.
The reference numerals and terms in parentheses show the correspondence with the embodiments described later in order to facilitate understanding of the present invention, and do not limit the scope of the present invention at all.
Liquid crystal display device of the present invention (100, 200, 300, 40
0,500) is an OCB mode liquid crystal panel (110)
Are displayed based on a video signal, and a detection unit (108, 408a to 408d, 516) that detects the values of parameters (temperature, frame frequency) that are factors that cause the reverse transition generation condition to change. ), And the ratio of the application time of the high voltage (reverse transition prevention voltage) applied to the liquid crystal panel to prevent the reverse transition to one frame period according to the detection value of the detector, the magnitude of the high voltage, And at least one of the applied voltage (Vw) corresponding to white display (106, 206, 306, 40)
6, 506) and a video signal and a non-image signal for applying a high voltage are alternately output, and a controller (104, 2) for driving the liquid crystal panel under the condition according to the determination result of the arithmetic unit.
04, 304). As described above, according to the present invention, the driving condition of the liquid crystal panel can be controlled in real time according to the fluctuation of the value of the parameter that is the fluctuation factor of the reverse transition generating condition. Video can always be optimally displayed. Note that examples of the “parameter that causes the reverse transition generation condition to change” include the temperature of the liquid crystal and the frame frequency of the video signal.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Various embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 shows the configuration of a liquid crystal display device according to a first embodiment of the present invention. In FIG. 1, the liquid crystal display device 100 includes a line memory 102, a controller 104, a calculation unit 106, a temperature sensor 108, a liquid crystal panel 110, a gate driver 112, and a source driver 114. The liquid crystal panel 110 is normally white.

A video signal and a sync signal are input to the liquid crystal display device 100. The video signal is written into the line memory 102 after being digitized as necessary. The image signal temporarily stored in the line memory 102 in this way is read at a speed (clock frequency) that is twice as high as that at the time of writing, and is input to the controller 104. The controller 104 alternately outputs the image signal for one line read from the line memory 102 and the non-image signal for one line (a signal for applying a reverse transition prevention voltage to the OCB cell) to the source driver 114. .

On the other hand, the controller 104 outputs a control signal to the gate driver 112. Gate driver 11
2 based on this control signal, the source driver 114
The gate lines to which the image signal or the non-image signal supplied to are written are sequentially selected. Thus, the liquid crystal panel 110
Image signal and non-image signal for each pixel of
It is written once in each frame period. The non-image signal is held in the pixel during the period from the writing of the non-image signal to the writing of the next image signal. By changing the writing timing of the image signal and the writing timing of the non-image signal, the holding time of the non-image signal in one frame period can be changed.

A temperature sensor 1 is provided near the liquid crystal panel 110.
08 is provided, and the calculation unit 106 uses the temperature sensor 1
Based on the temperature detected by 08, the ratio of the application time of the optimal reverse transition prevention voltage to one frame period is calculated.

FIG. 2 shows the input / output characteristics of the arithmetic unit 106. In FIG. 2, circles indicate the results of measuring the minimum value of the ratio of the application time of the reverse transition prevention voltage capable of preventing reverse transition to one frame period at each temperature. The alternate long and short dash line indicates the temperature sensor 10 estimated based on the measured values.
Detection result of 8 and 1 of reverse transition prevention voltage that can prevent reverse transition
The relationship with the minimum value of the ratio of the application time to the frame period is shown. However, the magnitude of the reverse transition prevention voltage is assumed to be constant. Note that, as will be described later, when the frame frequency of the video signal changes, the minimum value of the ratio of the application time of the reverse transition prevention voltage capable of preventing reverse transition to one frame period also changes, so here, the video signal It shows the input / output characteristics when the frame frequency is constant (60 Hz). The vertical axis on the right side of FIG. 2 indicates the application time of the reverse transition prevention voltage per frame when the frame frequency is 60 Hz. The calculation unit 106 uses the conversion table as shown by the solid line in FIG. 2 which is created in advance based on the relationship shown by the dashed-dotted line, and uses the four values corresponding to the application time of the reverse transition prevention voltage per frame. Any of (B1 to B4) is output according to the detection result of the temperature sensor 108. More specifically, the calculation unit 106
Indicates that the temperature detected by the temperature sensor 108 is 10 ° C.
B1 is output when it is less than 10 ° C, B2 is output when it is 10 ° C or more and less than 30 ° C, B3 is output when it is 30 ° C or more and less than 50 ° C, and B4 when it is 50 ° C or more and less than 70 ° C.
Is output. In this example, since the case of 70 ° C. or higher is not assumed, the output value corresponding to 70 ° C. or higher is not set. The values of B1 to B4 are set so that at least a time (a time longer than the time indicated by the alternate long and short dash line) does not cause reverse transition in each temperature range. The controller 104 causes the gate driver 112 to select a gate line at an appropriate timing based on the output of the arithmetic unit 106. Hereinafter, the gate line selecting operation will be described with reference to FIGS.

FIG. 3 shows an example in which the output of the calculation unit 106 is B1 (that is, when the temperature detected by the temperature sensor 108 is less than 10 ° C.). In FIG. 3, focusing on the first gate line G1, the gate line G1
The gate pulse becomes high at the timing T1 when the source driver 114 outputs an image signal, and a voltage corresponding to this image signal is applied to the pixels on the gate line G1. After that, the gate pulse of the gate line G1 is applied to the source driver 11
4 becomes high at the timing T2 at which the non-image signal is output, and the reverse transition prevention voltage is applied to the pixels on the gate line G1. Further, the gate pulse of the gate line G1 becomes high at the timing T3 when the source driver 114 outputs the image signal, and the voltage according to the image signal is applied to the pixel on the gate line G1. The time from the timing T2 when the reverse transition prevention voltage is applied to the timing T3 when the voltage according to the image signal is next applied is the application time B1 of the reverse transition prevention voltage output from the calculation unit 106 per frame.
Becomes The other gate lines G2 to Gn are similarly scanned, and the application time of the reverse transition prevention voltage per frame is B1 in all the gate lines G1 to Gn.

FIG. 4 shows an example in the case where the output of the arithmetic unit 106 is B2 (that is, the temperature detected by the temperature sensor 108 is 10 ° C. or higher and lower than 30 ° C.).
Similarly, FIG. 5 shows an example of the case where the output of the calculation unit 106 is B3 (that is, the temperature detected by the temperature sensor 108 is 30 ° C. or higher and lower than 50 ° C.), and FIG. If B4 (that is, temperature sensor 1
(When the temperature detected by 08 is 50 ° C. or higher and lower than 70 ° C.). For convenience of illustration, the ratio of the lengths of B1 to B4 in FIG. 2 and the ratio of the lengths of B1 to B4 in FIGS. 3 to 6 are not exactly matched, but this is not the case. It will not hinder the understanding of the invention. In this way, the reverse transition prevention voltage can be applied for an arbitrary time by changing the timing at which the gate pulse of each gate line becomes high.

As described above, the reverse transition prevention voltage is applied to each pixel on the liquid crystal panel 110 for an optimum time according to the detection result of the temperature sensor 108. Therefore, the reverse transition can be prevented even when the temperature of the liquid crystal rises, and when the temperature of the liquid crystal is low, the ratio of the application time of the reverse transition prevention voltage to one frame period is reduced, so that the reverse transition prevention voltage is applied. It is possible to suppress a decrease in the maximum brightness due to the above.

In the present embodiment, the arithmetic unit 106 uses a conversion table consisting of four steps.
The number of steps is not limited to four, and it goes without saying that more accurate control can be realized by appropriately increasing the number of steps. Further, by using a smoother conversion function instead of the conversion table, more accurate control can be realized.

Further, in this embodiment, the temperature sensor 108 is used.
Although the temperature near the liquid crystal panel 110 is detected by the above method, ideally, it is most preferable to detect the temperature of the liquid crystal itself. However, it is very difficult if not impossible to detect the temperature of the liquid crystal itself. Therefore, in reality, the influence of the heat of the backlight is exerted in the vicinity of the liquid crystal panel 110 without adversely affecting the display. It is preferably installed in a place that is difficult to receive (for example, near the edge of the glass substrate).

(Second Embodiment) In the first embodiment, the reverse transition prevention effect is controlled by controlling the ratio of the application time of the reverse transition prevention voltage to one frame period. It is also possible to control the reverse transition prevention effect by controlling the magnitude of the reverse transition prevention voltage.
As a second embodiment, a liquid crystal display device that controls the reverse transition prevention effect by controlling the magnitude of the reverse transition prevention voltage will be described below.

FIG. 7 shows the configuration of a liquid crystal display device according to the second embodiment of the present invention. In FIG. 7, the liquid crystal display device 200 includes a line memory 102 and a temperature sensor 108.
A liquid crystal panel 110, a gate driver 112, a source driver 114, a controller 204, and an arithmetic unit 206. 7, the same components as those in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted.

The calculation unit 206 calculates the optimum magnitude of the reverse transition prevention voltage based on the temperature detected by the temperature sensor 108.

FIG. 8 shows the input / output characteristics of the arithmetic unit 206. In FIG. 8, the alternate long and short dash line indicates the relationship between the detection result of the temperature sensor 108 and the minimum value of the reverse transition prevention voltage that can prevent reverse transition. However, it is assumed that the ratio of the application time of the reverse transition prevention voltage to one frame period is constant. Note that when the frame frequency of the video signal changes, the relationship between the detection result of the temperature sensor 108 and the minimum value of the ratio of the application time of the reverse transition prevention voltage capable of preventing reverse transition to one frame period changes, as described later. Therefore, here, the input / output characteristics are shown when the frame frequency of the video signal is constant. Note that the characteristics shown by the alternate long and short dash line in FIG. 8 differ depending on the liquid crystal material used for the liquid crystal panel 110, so only a general tendency is shown here. As is clear from FIG. 8, under the condition that the ratio of the application time of the reverse transition prevention voltage to one frame period is constant, the higher the temperature in the vicinity of the liquid crystal panel 110 is, the larger voltage is applied as the reverse transition prevention voltage. There is a need to. Therefore, the calculation unit 206 uses the temperature sensor 108.
Of the reverse transition prevention voltage based on the relationship shown by the solid line in FIG. More specifically, when the temperature detected by the temperature sensor 108 is less than 40 ° C., the calculation unit 206 notifies the controller 204 to apply the applied voltage Vb corresponding to black display as the reverse transition prevention drive voltage to the liquid crystal. To do. Further, for example, when the temperature detected by the temperature sensor 108 is 60 ° C., the controller 204 is notified to apply the voltage A as the reverse transition prevention drive voltage to the liquid crystal. Similarly, the temperature sensor 1
When the temperature detected by 08 is 80 ° C., the controller 204 is notified to apply the voltage B to the liquid crystal as the reverse transition prevention drive voltage. Note that the output corresponding to less than 40 ° C. is uniformly Vb because when a voltage less than Vb is used as the reverse transition prevention drive voltage, as shown in FIG.
This is because the minimum luminance (luminance during black display) increases (that is, the contrast is impaired) because the transmittance of the CB liquid crystal increases.

The controller 204 uses the line memory 10
The image signal for one line read from No. 2 and the calculation unit 2
The voltage notified by 06 is used as the reverse transition prevention voltage OC
The non-image signal for one line to be applied to the B cell is alternately output to the source driver 114.

As described above, an optimal voltage according to the detection result of the temperature sensor 108 is applied to each pixel on the liquid crystal panel 110 as the reverse transition prevention voltage. Therefore, even when the temperature of the liquid crystal rises, the reverse transition can be prevented, and when the temperature of the liquid crystal is low, the magnitude of the reverse transition prevention voltage is suppressed to Vb. Therefore, a voltage of Vb or more is applied as the reverse transition prevention voltage. It is possible to suppress the increase in the minimum luminance caused by the above.

In the present embodiment, the output of the arithmetic unit 206 corresponding to a temperature of 40 ° C. or higher is determined based on the smooth conversion function as shown in FIG. 8, but the conversion as shown in FIG. It may be determined based on the table.

(Third Embodiment) In the first and second embodiments, the reverse transfer prevention effect is controlled by controlling the ratio or magnitude of the application time of the reverse transfer prevention voltage to one frame period. However, instead of this, it is also possible to control the reverse transition prevention effect by controlling the applied voltage corresponding to white display. Hereinafter, as a third embodiment,
A liquid crystal display device that controls the reverse transition prevention effect by controlling the applied voltage corresponding to white display will be described.

FIG. 9 shows the configuration of a liquid crystal display device according to the third embodiment of the present invention. In FIG. 9, the liquid crystal display device 300 includes a line memory 102 and a temperature sensor 108.
A liquid crystal panel 110, a gate driver 112, a source driver 114, a controller 304, and an arithmetic unit 306. In FIG. 9, the same components as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

The calculation unit 306 calculates the optimum gain of the video signal based on the temperature detected by the temperature sensor 108.

FIG. 10 shows the input / output characteristics of the arithmetic unit 306. In FIG. 10, the alternate long and short dash line shows the relationship between the detection result of the temperature sensor 108 and the minimum value of the applied voltage corresponding to white display that can prevent reverse transition. However, it is assumed that the ratio and magnitude of the application time of the reverse transition prevention voltage to one frame period are constant. It should be noted that the characteristics shown by the alternate long and short dash line in FIG. 10 differ depending on the liquid crystal material used for the liquid crystal panel 110, and therefore only a general tendency is shown here. As is clear from FIG. 10, the liquid crystal panel 110
It is necessary to increase the applied voltage Vw corresponding to white display as the temperature in the vicinity of becomes higher. In the normally white liquid crystal panel 110, the higher the level of the video signal is, the smaller the voltage applied to each pixel of the liquid crystal panel 110 is. Therefore, increasing the applied voltage Vw corresponding to white display does not affect the video signal. This corresponds to reducing the gain (gain based on the signal level corresponding to black display). Therefore, the calculation unit 306 outputs the gain of the video signal according to the output of the temperature sensor 108 based on the relationship shown by the solid line in FIG. 10. More specifically, the calculation unit 306
Outputs to the controller 304 a gain such that the applied voltage Vw corresponding to white display becomes the voltage C when the temperature detected by the temperature sensor 108 is 20 ° C., for example. Similarly, when the temperatures detected by the temperature sensor 108 are 40 ° C. and 60 ° C., the controller 304 outputs gains such that the applied voltage Vw corresponding to white display becomes the voltage D and the voltage E, respectively.

The controller 304 uses the line memory 10
The non-image signal for one line for applying the reverse transition prevention voltage to the OCB cell is alternately output to the source driver 114 for the image signal for one line read from No. 2. At this time, the controller 304 adjusts the signal amplitude of the image signal based on the gain output from the calculation unit 306.

As described above, a video signal is applied to each pixel on the liquid crystal panel 110 such that the applied voltage Vw corresponding to white display has an optimum magnitude according to the detection result of the temperature sensor 108. Will be. Therefore, the reverse transition can be prevented even when the temperature of the liquid crystal rises, and when the temperature of the liquid crystal is low, the magnitude of the applied voltage Vw corresponding to the white display is suppressed, so that the applied voltage Vw corresponding to the white display is suppressed.
It is possible to suppress the decrease in the maximum brightness due to the w becoming larger than necessary.

In the present embodiment, the output of the calculation unit 306 is determined based on the smooth conversion function as shown in FIG. 10, but it may be determined based on the conversion table as shown in FIG. I do not care.

(Fourth Embodiment) Depending on the environment in which the liquid crystal panel is used, the temperature may be biased depending on the part of the liquid crystal panel due to the influence of, for example, sunlight irradiation. Therefore, in the fourth embodiment, a plurality of temperature sensors are installed in order to improve the accuracy of detecting the temperature of the liquid crystal. Hereinafter, a liquid crystal display device according to a fourth embodiment of the present invention will be described with reference to the drawings.

FIG. 11 shows the configuration of a liquid crystal display device according to the fourth embodiment of the present invention. 11, the liquid crystal display device 400 includes a line memory 102 and a controller 1.
04, the liquid crystal panel 110, and the gate driver 112.
, Source driver 114, and temperature sensors 408a-4
08d and the calculating part 406 are provided. In FIG. 11, the same components as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

The four temperature sensors 408a-408d are
They are arranged in the vicinity of the liquid crystal panel 110 and apart from each other. The calculation unit 406 includes the temperature sensors 408a to 408d.
The maximum value of the temperatures detected in 1 is extracted, and the ratio of the application time of the reverse transition prevention voltage to one frame period is calculated with reference to the conversion table shown in FIG. 2 based on the maximum value. Other processes are the same as those in the first embodiment.

As described above, according to this embodiment, even when the temperature of the liquid crystal panel 110 is uneven, the ratio of the application time of the reverse transition prevention voltage to one frame period is based on the temperature of the hottest part. So you can decide
It is possible to effectively prevent the reverse transition from locally occurring due to the temperature deviation of the liquid crystal panel 110.

In this embodiment, the number of temperature sensors is four.
However, the number of temperature sensors is not limited to this, and it is preferable to provide an appropriate number of temperature sensors in consideration of the size of the liquid crystal panel and the usage environment.

Further, in this embodiment, four temperature sensors 4 are used.
Although the ratio of the application time of the reverse transition prevention voltage to one frame period is controlled based on the maximum value of the detected values of 08a to 408d, the present embodiment is applied to the second and third embodiments, and four Based on the maximum value detected by the temperature sensors 408a to 408d, the magnitude of the reverse transition prevention voltage,
It is also possible to control the gain of the video signal.

(Fifth Embodiment) In the above-described first to fourth embodiments, the temperature of the liquid crystal is detected as a variable factor of the reverse transition generation condition, and the reverse transition prevention effect is controlled based on this. However, factors other than the temperature of the liquid crystal also exist as factors that cause the reverse transition to occur. From the results of the research conducted by the inventors, it is known that the reverse transition is less likely to occur as the OCB liquid crystal becomes unstable. That is, as the frequency of writing signals of different levels per unit time increases, the reverse transition is less likely to occur. Such a writing frequency per unit time changes according to the frame frequency of the input signal, for example. Hereinafter, as a fifth embodiment, a liquid crystal display device will be described in which a frame frequency of a video signal is detected as a variation factor of a reverse transition generation condition and the reverse transition prevention effect is controlled based on the detected frame frequency.

FIG. 12 shows the configuration of a liquid crystal display device according to the fifth embodiment of the present invention. In FIG. 12, the liquid crystal display device 500 includes a line memory 102 and a controller 1.
04, the liquid crystal panel 110, and the gate driver 112.
A source driver 114, a calculation unit 506, and a frame frequency detection unit 516. In FIG. 12, the same components as those in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted.

The frame frequency detector 516 detects the frame frequency of the video signal based on the synchronization signal. The calculation unit 506 calculates the ratio of the optimum application time of the reverse transition prevention voltage to one frame period based on the frame frequency detected by the frame frequency detection unit 516.

FIG. 13 shows the input / output characteristics of the arithmetic unit 506. In FIG. 13, the alternate long and short dash line shows the relationship between the detection result of the frame frequency detection unit 516 and the minimum value of the ratio of the application time of the reverse transition prevention voltage capable of preventing reverse transition to one frame period. As described above, if the temperature of the liquid crystal changes, the minimum value of the ratio of the application time of the reverse transition prevention voltage for one frame period that can prevent the reverse transition changes, so that the temperature of the liquid crystal is constant here. Shows the input / output characteristics in the case of. Note that the characteristics shown by the alternate long and short dash line in FIG. 13 differ depending on the liquid crystal material used for the liquid crystal panel 110, and therefore only a general tendency is shown here. By the way, when the frame frequency changes, it is easily conceived that the application time of the reverse transition prevention voltage per frame is changed accordingly (that is, the ratio of the application time to one frame period is constant). Although it may be, it was confirmed that it was not enough. That is, as is clear from FIG. 13, it is necessary to increase the ratio of the application time of the reverse transition prevention voltage to one frame period as the frame frequency of the video signal decreases. Therefore, the calculation unit 506 uses the conversion table as shown by the solid line in FIG. 13 created in advance based on the relationship shown by the one-dot chain line to apply the ratio (Br1 to Br1) of the reverse transition prevention voltage to one frame period. Br
4) is determined according to the detection result of the frame frequency detection unit 516, and the ratio is converted into the application time per frame (B1 to B4) based on the current frame frequency and output. Hereinafter, similarly to the first embodiment, the controller 104 outputs the output (B1 to B4) of the calculation unit 506.
Based on the above, the gate driver 112 is caused to select the gate line at an appropriate timing.

As described above, the reverse transition prevention voltage is applied to each pixel on the liquid crystal panel 110 for an optimum time according to the detection result of the frame frequency detection unit 516. Therefore, even when the frame frequency of the video signal is low, the reverse transition can be prevented, and when the frame frequency of the video signal is high, the ratio of the application time of the reverse transition prevention voltage to one frame period is reduced. It is possible to suppress a decrease in the maximum brightness due to the ratio of the application time becoming unnecessarily large.

In the present embodiment, the calculation unit 506 uses a conversion table consisting of four steps.
As with the first embodiment, the present invention is not limited to this.

Further, in the present embodiment, the ratio of the application time of the reverse transition prevention voltage to one frame period is controlled based on the detection result of the frame frequency detection section 516.
By applying the present embodiment to the second and third embodiments, the magnitude of the reverse transition prevention voltage and the gain of the video signal can be controlled based on the detection result of the frame frequency detection unit 516.

Furthermore, the first to fifth embodiments described above can be combined appropriately. For example, considering both the detection value of the temperature sensor and the detection value of the frame frequency detection unit, the ratio of the application time of the reverse transition prevention voltage to one frame period, the magnitude of the reverse transition prevention voltage, and the white display. The applied voltage (gain of the video signal) corresponding to the above may be controlled. In this case, the relationship between the input and output of the arithmetic unit is that the temperature is Tm.
When p is F and the frame frequency (frame rate) is Fr, it is represented by a function F (Tmp, Fr). For example, a method of approximately determining the output of the calculation unit as F (Tmp) × F (Fr) is also conceivable. At this time, considering that the alternate long and short dash line shown in FIG. 13 is close to a straight line, if F (Fr) is approximated by a linear function, the processing of the calculation unit can be simplified.

Two of the ratio of the application time of the reverse transition prevention voltage to one frame period, the magnitude of the reverse transition prevention voltage, and the applied voltage (gain of the video signal) corresponding to white display are used.
One or more may be controlled at the same time.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an input / output relationship of a calculation unit.

FIG. 3 is a diagram showing a gate line selecting operation when the output of the arithmetic unit is B1.

FIG. 4 is a diagram showing a gate line selecting operation when the output of the arithmetic unit is B2.

FIG. 5 is a diagram showing a gate line selecting operation when the output of the arithmetic unit is B3.

FIG. 6 is a diagram showing a gate line selecting operation when the output of the arithmetic unit is B4.

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

FIG. 8 is a diagram showing a relationship between inputs and outputs of a calculation unit.

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

FIG. 10 is a diagram showing a relationship between inputs and outputs of a calculation unit.

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

FIG. 12 is a block diagram showing a configuration of a liquid crystal display device according to a fifth embodiment of the present invention.

FIG. 13 is a diagram showing a relationship between inputs and outputs of a calculation unit.

FIG. 14 is a diagram showing voltage-transmittance characteristics of OCB liquid crystal.

FIG. 15 is a diagram showing the relationship between the temperature of the liquid crystal and the minimum value of the ratio of the application time of the reverse transition prevention voltage capable of preventing reverse transition to one frame period.

[Explanation of symbols]

100 liquid crystal display 102 line memory 104 controller 106 arithmetic unit 108 Temperature sensor 110 LCD panel 112 gate driver 114 source driver 200 LCD 204 controller 206 arithmetic unit 300 liquid crystal display 304 controller 306 Operation unit 400 liquid crystal display device 406 Operation unit 408a to 408d temperature sensor 500 liquid crystal display 506 operation unit 516 Frame frequency detector

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G09G 3/20 623 G09G 3/20 623C 623D 642 642C 642D 642E 650 650A 670 670E 3/36 3/36 (72 ) Inventor Yoshito Ota 1006 Kadoma, Kadoma-shi, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Takahiro Kobayashi 1006 Kadoma, Kadoma City Osaka Prefecture Matsuda Electric Industrial Co., Ltd. (72) Inventor Taro Funamoto Osaka F-Term (Reference) 2H088 GA02 HA03 HA06 JA04 MA01 MA20 2H093 NA16 NA43 NA44 NC13 NC15 NC16 NC21 NC29 NC49 NC57 NC63 ND02 ND60 NE04 NF04 NH13 NH14 NH15 5C006 AA16 AC13 AC51 AC21 AC21 AC21 AC21 AC21 AC21 AC21 AC21 AC21 AC21 AF53 AF62 AF71 BA15 BA19 BB16 BC03 BC11 BF05 BF15 BF26 BF38 BF42 FA 04 FA16 FA19 FA22 FA54 5C080 AA10 BB05 DD05 DD09 DD20 EE29 FF03 FF11 GG12 JJ02 JJ04 JJ05

Claims (20)

[Claims] 1. A liquid crystal display device for displaying an image by driving an OCB-mode liquid crystal panel based on an image signal, the detecting unit detecting a value of a parameter that causes a variation of a reverse transition occurrence condition. Depending on the detection value of the detection unit, the ratio of the application time of the high voltage applied to the liquid crystal panel to one frame period for preventing the reverse transition, the magnitude of the high voltage, and the application corresponding to the white display. An arithmetic unit that determines at least one of the voltages and a video signal and a non-image signal for applying the high voltage are alternately output, and the liquid crystal panel is driven under conditions according to the determination result of the arithmetic unit. A liquid crystal display device, comprising: 2. The liquid crystal display device according to claim 1, wherein the detection unit is a temperature sensor installed near the liquid crystal panel. 3. The calculating unit: a) determines the ratio of the application time of the high voltage to one frame period so as to have a relatively large ratio when the temperature detected by the temperature sensor is higher than a predetermined temperature. And b) when the temperature detected by the temperature sensor is lower than a predetermined temperature, the ratio of the application time of the high voltage to one frame period is determined to be a relatively small ratio. Item 3. The liquid crystal display device according to item 2. 4. The arithmetic unit determines a) the magnitude of the high voltage such that a) when the temperature detected by the temperature sensor is higher than a predetermined temperature, the voltage becomes a relatively high voltage, and b) the temperature. When the temperature detected by the sensor is lower than a predetermined temperature, the magnitude of the high voltage is determined to be a relatively low voltage.
The liquid crystal display device according to item 1. 5. The arithmetic unit: a) when the temperature detected by the temperature sensor is higher than a predetermined temperature, determines the applied voltage corresponding to the white display so as to be a relatively high voltage, and b). The liquid crystal display device according to claim 2, wherein when the temperature detected by the temperature sensor is lower than a predetermined temperature, the applied voltage corresponding to the white display is determined to be a relatively low voltage. . 6. The detection unit is a plurality of temperature sensors that are arranged in the vicinity of a liquid crystal panel and apart from each other, and the calculation unit is configured to detect a maximum value of the temperature detected by the plurality of temperature sensors. At least one of a ratio of an application time of a high voltage applied to the liquid crystal panel to one frame period to prevent a reverse transition, a magnitude of the high voltage, and an applied voltage corresponding to white display is determined. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is a liquid crystal display device. 7. The liquid crystal display device according to claim 1, wherein the detector is a frame frequency detector that detects a frame frequency of a video signal. 8. The arithmetic unit comprises: a) when the frame frequency detected by the frame frequency detecting unit is higher than a predetermined frequency, the application time of the high voltage for one frame period becomes relatively small. B) determining the ratio of the application time of the high voltage to one frame period so that the frame frequency detected by the frame frequency detector is lower than a predetermined frequency. The liquid crystal display device according to claim 7, wherein: 9. The computing unit a) determines the magnitude of the high voltage so that the voltage is relatively low when the frame frequency detected by the frame frequency detector is higher than a predetermined frequency, and b The liquid crystal according to claim 7, wherein when the frame frequency detected by the frame frequency detection unit is lower than a predetermined frequency, the magnitude of the high voltage is determined so as to be a relatively high voltage. Display device. 10. The arithmetic unit determines: a) an applied voltage corresponding to the white display so that the frame frequency detected by the frame frequency detection unit becomes a relatively low voltage when the frame frequency is higher than a predetermined frequency. B) When the frame frequency detected by the frame frequency detection unit is lower than a predetermined frequency, the applied voltage corresponding to the white display is determined so as to have a relatively high voltage. The liquid crystal display device according to item 1. 11. A driving method of a liquid crystal display device for displaying an image by driving an OCB mode liquid crystal panel based on an image signal, wherein a value of a parameter which is a factor of varying a reverse transition occurrence condition is detected, Depending on the detected value, the ratio of the application time of one frame of the high voltage applied to the liquid crystal panel to prevent the reverse transition, the magnitude of the high voltage, and the applied voltage corresponding to the white display. At least one of the image signal and the non-image signal for applying the high voltage are alternately output, and the liquid crystal panel is driven under the condition according to the determination result. Device driving method. 12. The temperature of the vicinity of a liquid crystal panel is detected as the value of the parameter.
7. A method for driving a liquid crystal display device according to. 13. A) When the detected temperature is higher than a predetermined temperature, the ratio of the application time of the high voltage to one frame period is determined so as to have a relatively large ratio, and b) the detected temperature is 13. The method of driving a liquid crystal display device according to claim 12, wherein the ratio of the application time of the high voltage to one frame period is determined so as to have a relatively small ratio when the temperature is lower than a predetermined temperature. 14. A) when the detected temperature is higher than a predetermined temperature, the magnitude of the high voltage is determined so as to be a relatively high voltage, and b) when the detected temperature is lower than the predetermined temperature. 13. The method of driving a liquid crystal display device according to claim 12, wherein the magnitude of the high voltage is determined so that the voltage is relatively low. 15. A) when the detected temperature is higher than a predetermined temperature, the applied voltage corresponding to the white display is determined so as to have a relatively high voltage, and b) the detected temperature is higher than the predetermined temperature. 13. The method for driving a liquid crystal display device according to claim 12, wherein the applied voltage corresponding to the white display is determined so that the voltage is relatively low when the voltage is low. 16. As the value of the parameter, the temperatures at a plurality of locations near each other in the vicinity of the liquid crystal panel are detected, the maximum values of the detected temperatures at a plurality of locations are extracted, and the reverse transition is performed according to the extracted maximum value. To prevent this, at least one of a ratio of an application time of a high voltage applied to the liquid crystal panel to one frame period, a magnitude of the high voltage, and an applied voltage corresponding to white display is determined. The method for driving the liquid crystal display device according to claim 11, wherein 17. The method of driving a liquid crystal display device according to claim 11, wherein a frame frequency of a video signal is detected as a value of the parameter. 18. A) when the detected frame frequency is higher than a predetermined frequency, the ratio of the application time of the high voltage to one frame period is determined so as to have a relatively small ratio, and b) the detected frame. 18. The method of driving a liquid crystal display device according to claim 17, wherein when the frequency is lower than a predetermined frequency, the ratio of the application time of the high voltage to one frame period is determined to be a relatively large ratio. . 19. When the detected frame frequency is higher than a predetermined frequency, the magnitude of the high voltage is determined so as to be a relatively low voltage, and b) the detected frame frequency is higher than the predetermined frequency. 18. The method for driving a liquid crystal display device according to claim 17, wherein the magnitude of the high voltage is determined so that the voltage is relatively high when the voltage is low. 20. When the detected frame frequency is higher than a predetermined frequency, the applied voltage corresponding to the white display is determined so as to be a relatively low voltage, and b) the detected frame frequency is predetermined. The applied voltage corresponding to the white display is determined so as to have a relatively high voltage when the frequency is lower than the frequency.
7. A method for driving a liquid crystal display device according to item 7.