JP4157240B2 - OCB type liquid crystal display element driving method and OCB type liquid crystal display element - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for driving a liquid crystal display element used in a liquid crystal television or the like and a liquid crystal display device.
[0002]
[Prior art]
As a liquid crystal display element characterized by high-speed response, an OCB type display element has been studied. For OCB type liquid crystal display elements, please refer to “The Institute of Electrical Communication, IEICE Technical Report EDI98-144, page 199”.
[0003]
In this OCB type liquid crystal display element, a liquid crystal is sandwiched between substrates, and a transparent electrode is formed on the substrate as a voltage applying means. In the state before the power is turned on, the alignment state of the liquid crystal is a state called splay alignment. When this apparatus is turned on, a relatively large voltage is applied to the voltage applying means in a short time to shift the alignment of the liquid crystal to the bend alignment state. It is a feature of the OCB type liquid crystal display mode that display is performed using this bend alignment state.
[0004]
If the voltage applied here is lowered, the bend alignment state partially returns to the splay alignment state, so it is necessary to continue to apply a voltage higher than a certain voltage. This is because the splay alignment state is stable at a voltage lower than a predetermined voltage, but the bend alignment state is stable at a voltage higher than the predetermined voltage.
[0005]
Japanese Patent No. 2678591 describes an example in which a voltage for turning on all the pixels is applied in order to compensate for the occurrence of spraying in a voltage OFF period.
[0006]
[Problems to be solved by the invention]
As described above, the OCB type liquid crystal display element needs to keep applying a voltage of a certain value or more. In the normally white mode of this element, there is a characteristic that the transmittance becomes higher and brighter as the voltage is lower. For this reason, continuing to apply a voltage of a certain value or more means that the brightness cannot exceed a certain value. That is, there is a problem that sufficient brightness cannot be obtained.
[0007]
Further, the method of turning on all pixels has a problem that the screen flickers.
[0008]
An object of the present invention is to provide a driving method capable of obtaining sufficient brightness with an OCB type liquid crystal display element.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, a display device of the present invention, liquid crystal interposed between the substrates, has a voltage applying means for applying a voltage to the liquid crystal, the bend state formed after the power is turned on, the bend state The OCB-type liquid crystal display element that performs display as a display state and has a splay state different from the bend state in the display state in a state where the voltage of the voltage application unit is equal to or lower than a predetermined voltage, the voltage of the voltage application unit a voltage but corresponding to the display data, OCB type liquid crystal display element characterized by having two when the voltage in the case of performing white display is larger than said predetermined voltage falls below the predetermined voltage It is.
[0010]
Further, the present invention is characterized in that a period during which the voltage is not more than the predetermined voltage is 100 ms or less.
[0011]
Further, the present invention is characterized by having means for adjusting a signal voltage in order to apply a voltage equal to or lower than the predetermined voltage.
[0012]
Further, it is characterized by having means for adjusting the voltage of the counter substrate in order to apply a voltage equal to or lower than the predetermined voltage.
[0013]
The present invention also includes a voltage applying means for sandwiching a liquid crystal between the substrates and applying a voltage to the liquid crystal, forming a bend state after turning on the power, displaying the bend state as a display state, and displaying the display state. the I bend state different from splay state is the driving method der the OCB type liquid crystal display device voltage of said voltage applying means is present in the predetermined voltage or less in the state, the voltage which the voltage of the voltage applying means corresponding to the display data in The OCB type liquid crystal display element driving method is characterized in that there are two types of cases where the voltage for performing white display is lower than the predetermined voltage and when the voltage is higher than the predetermined voltage .
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a display device according to an embodiment of the present invention will be described with reference to the drawings.
[0015]
(Embodiment 1)
In a general liquid crystal display element, a liquid crystal is sandwiched between substrates, and voltage applying means for applying a voltage to the liquid crystal is formed. In many cases, a transparent electrode is formed as the voltage applying means, and an active matrix substrate such as a TFT is often used as one substrate. A voltage value corresponding to the display data is applied to the voltage application means.
[0016]
In general, a voltage applied to a liquid crystal layer in a liquid crystal display element using an active matrix such as a TFT has a positive / negative polarity changed for each field of a video signal. This is to prevent the accumulation of ions due to application of a direct current component by alternating current for the entire period. Although depending on the period of the video signal, one field for displaying 60 images per second is normally driven for 16 ms. Here, the period for displaying the one-sided polarity is referred to as one field.
[0017]
In the OCB type liquid crystal display mode, a bend state is formed by applying a relatively large voltage after power-on, and display is performed using this alignment state. Here, when the voltage is equal to or lower than the predetermined voltage, a splay alignment state is generated. This splay alignment state appears as a display defect because it looks different from the bend state. Therefore, it is necessary to drive the OCB type liquid crystal display element without generating this splay alignment state.
[0018]
FIG. 2C shows a time series of voltages applied to the liquid crystal layer when white display is performed by the conventional OCB type liquid crystal display element. This is an example of normally white. In the conventional OCB type liquid crystal display device, voltages of the same magnitude are applied with positive and negative polarities in each field. In this example, since a splay state occurs at a voltage of 2v or less, a voltage of 2v is applied to display white. That is, the predetermined voltage described above was 2v.
[0019]
FIG. 1 shows the relationship between the luminance and the applied voltage of this OCB type liquid crystal display element. In the OCB type liquid crystal display element, the slope is steep in a low voltage region, and the brightness changes abruptly with only a slight difference in voltage. FIG. 1B conceptually shows a driving method of a conventional OCB type liquid crystal display element. In the conventional OCB type liquid crystal display element, both positive and negative polarities are driven with a symmetrical voltage. At this time, a splay state occurred when the voltage amplitude was 2 v or less. Therefore, 2v is applied when performing white display to obtain the maximum brightness. At this time, utilization efficiency indicating brightness was as low as 60%.
[0020]
The present invention realizes a bright OCB type liquid crystal display element by applying a low voltage only for a short time, instead of continuously applying a low voltage constantly.
[0021]
(Example 1)
We have found that it takes time to generate the splay state, and if it is a short time, no spray will occur even if the voltage is lowered to 2 V or less. The inventors have invented a method of extending the driving voltage range to the spray generation region in a short time.
[0022]
In OCB type liquid crystal display device of this example was set low voltage side polarity only as in FIG. 2 (a). That is, the voltage in the spray generation voltage region and the voltage with stable bend orientation were applied in alternating frames. In this embodiment, when white display is performed, the positive voltage is set to 2.2 v and the negative voltage is set to 1.5 v. Shown the relationship of the luminance and the applied voltage at this time is shown in FIG 1 (a). When the voltage is 1.5v, the luminance increases, and when the voltage is 2.2v, the luminance slightly decreases, but overall, the luminance obtained by averaging the two fields becomes brighter than that of the conventional method. In this example, the utilization efficiency indicating brightness was 75%, which was higher than the conventional value.
[0023]
In order to set the voltage applied to the liquid crystal in this way, a method was adopted in which the center voltage of the counter electrode is shifted to the minus side by 0.35v from the normal value. Further, the source amplitude may be adjusted in a positive / negative field.
[0024]
The present invention is characterized in that the voltage waveform itself for displaying white has two types of voltage, that is, a voltage in a spray generation voltage region and a voltage in a bend alignment region. Here, there is no problem in the case of the black display or the halftone display that does not cover the voltage region where the splay occurs. This is different from the method of inserting the entire surface ON.
[0025]
(Example 2)
In Example 1, the positive voltage was excessive in the long term, and the problem of burning was generated. In this example, the waveform of FIG. 2B was applied. After displaying a positive / negative 2 field with a voltage of 2.2 v having a relatively large amplitude, a positive / negative 2 field was displayed with a low voltage of 1.5 v. Thereafter, the 2.2v field was repeated alternately with two positive and negative fields, and the 1.5v field was alternately repeated with two positive and negative fields.
[0026]
Thus, the problem that the DC voltage is applied as in the first embodiment was solved by changing the amplitude every two fields. However, since the time for applying the low voltage is doubled, the possibility of occurrence of splay alignment is increased, but no particular problem was found in this example.
[0027]
In order to realize this voltage waveform, the potential of the counter electrode was varied at a period of 4 fields. Further, the source amplitude may be changed for each field.
[0028]
The present invention is not limited to a field frequency of 60 Hz. Rather, driving at a high frequency of 60 Hz or more is more effective because the spray state is less likely to occur. In addition, the high frequency driving of 120 Hz or higher is more effective because the effect that the splay state does not occur is high and at the same time the effect of appearing at a higher speed is seen.
[0029]
The present invention is not limited to the OCB type liquid crystal display element. It is a technique that can be used for general purposes in display elements such as liquid crystal displays in which problems occur when the voltage is lowered below a certain voltage and kept for a certain period of time.
[0030]
Note that the present invention is based on the finding that even if a voltage is originally generated by splay alignment, the splay alignment does not occur in a short time and does not cause a display defect. The upper limit of the time during which no defect occurs on the display was 100 ms. In terms of the driving method, it is effective to change the voltage for each field, and it was effective to apply a low voltage equal to or lower than a predetermined voltage for a period of 6 fields at a field frequency of 60 Hz. In order to display stably, it is better to make the length of the field to which the low voltage is applied equal to the length of the field to which the voltage higher than the predetermined value is applied. In this method, it was good to make it not more than twice the field frequency as in the first and second embodiments.
[0031]
【The invention's effect】
As described above, according to the present invention, a bright liquid crystal display element can be provided.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing a relationship between drive voltage and luminance according to an embodiment of the present invention. FIG. 2 is a conceptual diagram showing a drive waveform according to an embodiment of the present invention.

Claims (13)

Sandwiching a liquid crystal between the substrates, has a voltage applying means for applying a voltage to the liquid crystal, the bend state is formed after power, it performs display the bend state as the display state, the bend state in the display state The OCB type liquid crystal display element in which a different spray state exists in a state where the voltage of the voltage applying means is a predetermined voltage or less,
The voltage of the voltage applying means is a voltage corresponding to display data, and there are two types of cases where the voltage when displaying white is less than or equal to the predetermined voltage and larger than the predetermined voltage. OCB type liquid crystal display element. 2. The OCB type liquid crystal display element according to claim 1, wherein a period during which the voltage is less than or equal to the predetermined voltage is 100 ms or less. 2. The OCB type liquid crystal display element according to claim 1, wherein the period during which the voltage is less than or equal to the predetermined voltage is not more than six times the field display period. 2. The OCB type liquid crystal display element according to claim 1, wherein the period during which the voltage is equal to or less than the predetermined voltage is not more than twice the field display period. 2. The OCB type liquid crystal display element according to claim 1, further comprising means for adjusting a signal voltage in order to apply a voltage equal to or lower than the predetermined voltage. 2. The OCB type liquid crystal display element according to claim 1, further comprising means for adjusting a voltage of the counter substrate in order to apply a voltage equal to or lower than the predetermined voltage. 7. The OCB type liquid crystal display element according to claim 6, wherein the means for adjusting the voltage of the counter substrate is means for adjusting a center voltage. 7. The OCB type liquid crystal display element according to claim 6, wherein the means for adjusting the voltage of the counter substrate is means for periodically adjusting a voltage amplitude. 9. The OCB type liquid crystal display element according to claim 8, wherein the means for periodically adjusting the voltage amplitude is a four field period. 2. The OCB type liquid crystal display element according to claim 1, wherein a field frequency of the liquid crystal display element is twice or more a video frequency. Sandwiching a liquid crystal between the substrates, has a voltage applying means for applying a voltage to the liquid crystal, the bend state is formed after power, it performs display the bend state as the display state, the bend state in the display state What driving method der the OCB type liquid crystal display device voltage different splay state is the voltage applying means is present in the following states predetermined voltage and,
A voltage which the voltage of the voltage applying means corresponding to the display data, and characterized by having two when the voltage in the case of performing white display is larger than said predetermined voltage falls below the predetermined voltage Of driving an OCB type liquid crystal display element. 12. The OCB according to claim 11, wherein the polarity of the voltage corresponding to the display data is reversed for each field, and a voltage when displaying either positive or negative white is equal to or less than the predetermined voltage. Type liquid crystal display element driving method. The polarity of the voltage corresponding to the display data is reversed for each field, and white is displayed. 12. The method of driving an OCB type liquid crystal display element according to claim 11, wherein the voltage in the case of positive and negative is equal, and the period during which the voltage equal to or lower than the predetermined voltage is applied is 100 ms or shorter.

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