JPH0854605A - Driving method for anti-ferroelectric liquid crystal display - Google Patents

Abstract

PURPOSE:To attain an excellent display with less fluctuation at the time of non- selection, to attain a gradation display without changing a voltage level of an applied voltage and to attain the gradation display even using an inexpensive IC by changing a pulse width of a voltage waveform applied for a selection period of a drive voltage waveform, that is, adjusting the period when the voltage of a threshold value voltage or above of a liquid crystal is applied. CONSTITUTION:The drive waveform consists of four phases of selection period, the first half of the phases, that is, a first phase and a second phase, is used for a reset period, and the second half of the phases, that is, a third phase and a fourth phase, is used for a selection period. The voltage of OV is applied for the reset period of a scan electrode waveform, 30V is applied for the selection period and 6V is applied for the non-selection period. Further, the voltage of OV is applied for first three phases of a signal electrode waveform, 30V is applied for the final fourth phase when an ON display is performed, and OV are applied for the four phases also when an OFF display is performed. Thus, synthesis voltage waveforms of which pulse widths of a voltage value applied for the selection period are different from each other in the cases of the ON display and the OFF display, and a transmission light quantity is controlled.

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 an antiferroelectric liquid crystal display such as a liquid crystal display panel having a matrix of pixels having an antiferroelectric liquid crystal as a liquid crystal layer or a liquid crystal optical shutter array. is there.

[0002]

2. Description of the Related Art A liquid crystal panel using an antiferroelectric liquid crystal is
JP-A-2 of Nippon Denso Co., Ltd. and Showa Shell Sekiyu Co., Ltd.
-173724 has been vigorously studied since it was reported that it has a wide viewing angle, that it can respond at high speed, and that it has good multiplex characteristics.

FIG. 6 is a block diagram of a liquid crystal cell when an antiferroelectric liquid crystal is used as a display. A liquid crystal cell 62 is placed between the polarizing plates 61 aligned with crossed Nicols so that the polarization axis of either one of the polarizing plates is parallel to the long axis direction of the molecule when no electric field is applied. White is displayed when a voltage is applied. When a voltage is applied to the liquid crystal cell in such a cell structure, a change in transmittance with respect to the voltage is plotted in a graph, and a hysteresis curve as shown in FIG. 7 can be drawn. In the conventional driving method, the first stable state is selected and black display is performed or the second and third stable states are selected depending on the magnitude of the voltage value applied during the selection period on the signal electrode side. I had decided whether to display white. For example, when performing black display, the applied voltage value is set between the voltage values V1 to V3 in FIG. 7, and when performing white display, the threshold voltage of the antiferroelectric liquid crystal | V2 | It has been set to | V4 | or higher. Also, when performing gradation display, the amount of transmitted light has been controlled by the magnitude of the voltage value applied during this selection period.

FIG. 2 shows a conventional drive waveform and a corresponding amount of transmitted light. In this way, when the voltage value applied during the selection period on the signal electrode side is changed, that is, the peak value of the pulse is changed to control the amount of transmitted light, the voltage is applied during the selection period even during the non-selection period. Since the pulse having the same length as the existing pulse width is applied, the fluctuation of the transmitted light amount becomes large and the display quality is impaired. Further, in order to perform gradation display, it is necessary to apply pulses with different voltage values,
Since the output level of the driving IC has to be increased, there has been a problem that the cost of the IC increases.

[0005]

SUMMARY OF THE INVENTION According to the present invention, an antiferroelectric device which can maintain good display quality with little fluctuation during the non-selection period and can easily perform gradation display without increasing the number of voltage levels of applied pulses. It is intended to provide a driving method for a liquid crystal display.

[0006]

In order to achieve the above object, according to the present invention, the anti-ferroelectric liquid crystal cell has an anti-ferroelectric liquid crystal cell with an anti-ferroelectric liquid crystal cell having a threshold voltage or more. It controls the transmission of the ferroelectric liquid crystal display. Also, as one of the means to change the length of this period,
The pulse width of the pulse applied to the signal electrode side during the selection period is changed.

When a pulse is applied to the antiferroelectric liquid crystal to switch it to the second or third stable state and then the value of the applied voltage is set to 0V, the second or third stable state is changed to the first stable state. As a result of detailed measurement of the time to return to the state, if the length of the period (pulse width) exceeding the threshold voltage of the applied pulse is reduced as shown in FIG.
It was revealed that the response time for returning from the stable state to the first stable state was shortened. By using this phenomenon, it is possible to control the state of liquid crystal molecules in the subsequent non-selection period by controlling the length of the period exceeding the threshold voltage of the pulse applied in the selection period. It becomes possible to control. Also, if the period when the voltage value applied to the antiferroelectric liquid crystal cell is equal to or higher than the threshold voltage of the antiferroelectric liquid crystal is sufficiently short, liquid crystal switching does not occur, and liquid crystal molecules respond to the pulse within the non-selection period. It is possible to realize good display without preventing the display quality from being impaired and not impairing the display quality such as display fluctuation. Here, the relationship between the pulse width and the response time shown in FIG. 8 has a different slope of the graph depending on the antiferroelectric liquid crystal material used, so it is necessary to select the liquid crystal material according to the target grayscale display. is there.

[0008]

The gray scale display can be realized because the response time of the liquid crystal is different by arbitrarily changing the period in which the voltage equal to or higher than the threshold voltage is applied within the selection period for each liquid crystal pixel, and the application is performed within the non-selection period. If the applied voltage is within the response time, good display can be performed without any influence on the liquid crystal switching. Further, since gradation display can be performed without changing the level of the voltage value of the applied voltage, it is possible to perform gradation display even by using a highly versatile IC with a small number of input levels.

Generally, in order to perform switching of the antiferroelectric liquid crystal, the threshold voltage varies depending on the state immediately before switching (first stable state, second stable state or third stable state). Therefore, when the display is performed by actual driving, the writing state in the selection period is affected by the display state immediately before the selection period. Therefore, immediately before the selection period, by applying a reset pulse so that the display state is always constant, the threshold voltage is always kept constant, and a new display voltage does not depend on the display state of the pixel before the display information is written. The display can be performed, and the reliability of the display is improved.
Further, since the reset pulse is not provided in the selection period but as the reset period immediately before the selection period, the number of pulses in the selection period is not increased, so that the entire writing time is not affected.

[0010]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 9 is a cell configuration diagram of the liquid crystal panel used in this example. The liquid crystal panel used in this embodiment has a pair of glass substrates 93 having an antiferroelectric liquid crystal layer 96 having a thickness of about 2μ.
a, 93b. Electrodes 94a and 94b are formed on the opposite surface of the glass substrate, and polymer alignment films 95a and 95b are applied thereon and subjected to rubbing treatment. Further, a first polarizing plate 91a is provided outside one glass substrate so that the polarization axis of the polarizing plate and the rubbing axis are parallel to each other, and the first polarizing plate 91a is provided outside the other glass substrate. The second polarizing plate 91b is installed so as to be different from the polarization axis by 90 °. The threshold voltage for switching the liquid crystal material used from the first stable state to the second or third stable state is about 30 V, and the response speed is about 90 μs.

<Embodiment 1> FIG. 1 is a diagram showing a drive voltage waveform according to an embodiment of the present invention and a change in the amount of transmitted light in accordance therewith. The pulse width was set to 30 μs, one frame was composed of two scanning periods, and the driving waveforms in the preceding and following scanning periods were symmetrical with respect to 0V. Each scanning period is composed of a selection period for determining the amount of transmitted light for performing the desired display and a non-selection period for holding the amount of transmitted light. Further, the selection period is composed of a reset period and a select period. In the reset period, the liquid crystal molecules are switched to the first stable state (black display) regardless of the display contents, and in the select period, this state is maintained or the second or Select whether to switch to the third stable state (white display). In the drive waveform of the present invention, the selection period has four phases, the first phase and the second phase in the first half of the selection period are used as the reset period, and the third phase and the fourth phase in the latter half are used as the selection period. . The reset period of the scan electrode waveform was 0 V, the voltage value of the pulse applied during the select period was 30 V, and the voltage of 6 V was applied during the non-select period. When the signal electrode waveform is displayed as ON, the first 3 phases are 0 V, the last 4 phases are 30 V, and OF
When F display was performed, a voltage waveform of 0 V was used for all four phases. Therefore, in the combined voltage waveform applied to the pixel, the pulse width (hatched portion) of the voltage value applied in the selection period is different between the ON display and the OFF display, and the transmitted light amount can be controlled, which is excellent. It was possible to display. Further, since the pulse width of the pulse applied in the non-selection period is 30 μs, which is sufficiently shorter than the response speed of this liquid crystal material, the fluctuation of molecules due to this pulse could be considerably reduced.

<Example 2> The same liquid crystal material and cell structure as in Example 1 were used. FIG. 3, FIG. 4, and FIG. 5 are diagrams showing drive waveforms of the second embodiment and changes in the amount of transmitted light corresponding to the drive waveforms. The pulse width of the drive waveform used here was set to 20 μs, and one frame was composed of two scanning periods. Each scanning period is composed of a selection period and a non-selection period, the selection period is composed of 8 phases, and is composed of a reset period and a selection period. In the reset period, the liquid crystal molecules are switched to the first stable state (black display) regardless of the display content, and in the select period, the amount of transmitted light in this state is maintained, or in accordance with the target display gradation state. Select the amount of transmitted light. In the drive waveform of the present invention, the first four phases of the selection period are used for the reset period and the last four phases are used for the selection period. The voltage value during the reset period of the scan electrode waveform is 0V, and the voltage value during the select period is 30V.
Then, a voltage of 6 V was applied during the non-selection period. The four phases of the first half of the signal electrode waveform were set to 0 V, and the phases of the latter half of the four phases were changed according to the target gradation state of the display. In this embodiment, three gradation display with different amounts of transmitted light were performed (level 1, level 2, level 3). The signal electrode waveform for level 1 gradation display has a voltage value of 25 V at the 8th phase (FIG. 3), and the signal electrode waveform for level 2 gradation display is at the 7th and 8th phases. The voltage value was set to 25 V (FIG. 4), and the voltage values at the sixth, seventh, and eighth phase of the signal electrode waveform when performing gradation display of level 3 were set to 25 V. (FIG. 5) As a result, the composite voltage waveform applied to the pixel is different for each gradation display, and the pulse width (hatched portion) applied during the select period of the selection period can be changed, that is, above the threshold voltage. Over a certain period of time, we were able to obtain the amount of transmitted light required for each. The pulse width of the pulse applied at the time of non-selection is 60 μs at the maximum, which is smaller than the response speed of this liquid crystal material, and the voltage value is 25 V, which is smaller than the threshold voltage of this liquid crystal material. Was able to be reduced considerably.

[0013]

EFFECTS OF THE INVENTION By changing the pulse width of the voltage waveform applied during the selection period of the drive voltage waveform, that is, by adjusting the period during which a voltage equal to or higher than the threshold voltage of the liquid crystal is applied, there is little fluctuation during non-selection. Can be displayed. Further, since gradation display can be performed without changing the voltage level of the applied voltage, gradation display can be performed even by using a versatile and inexpensive IC having a small number of input levels.

[Brief description of drawings]

FIG. 1 is a diagram showing a drive waveform used in a first embodiment of the present invention and a corresponding amount of transmitted light.

FIG. 2 is a diagram showing a conventional drive waveform and a corresponding amount of transmitted light.

FIG. 3 is a diagram showing a level 1 drive waveform used in Example 2 of the present invention and a corresponding amount of transmitted light.

FIG. 4 is a diagram showing a level 2 drive waveform used in Example 2 of the present invention and a corresponding amount of transmitted light.

FIG. 5 is a diagram showing a level 3 drive waveform used in Example 2 of the present invention and a corresponding amount of transmitted light.

FIG. 6 is a configuration diagram of an antiferroelectric liquid crystal cell and a polarizing plate of the present invention.

FIG. 7 is a diagram showing a hysteresis curve of the antiferroelectric liquid crystal display of the present invention.

FIG. 8 is a diagram showing the relationship between pulse width and response time.

FIG. 9 is a cell configuration diagram of an antiferroelectric liquid crystal display of the present invention.

[Explanation of symbols]

 61a, 61b Polarizing plate 62 Liquid crystal cell 91a, 91b Polarizing plate 92a, 92b Sealing material 93a, 93b Glass substrate 94a, 94b Polymer alignment film 95a, 95b Electrode 96 Antiferroelectric liquid crystal

Claims (3)

[Claims] 1. An antiferroelectric liquid crystal is sandwiched between a pair of substrates each having a plurality of scanning electrodes and signal electrodes on opposite surfaces,
In an antiferroelectric liquid crystal cell having liquid crystal pixels in a matrix, the amount of transmitted light of the antiferroelectric liquid crystal cell is a period during which a voltage applied to the antiferroelectric liquid crystal cell is equal to or higher than a threshold voltage of the antiferroelectric liquid crystal. A method for driving an anti-ferroelectric liquid crystal display, which is controlled by the length of the liquid crystal display. 2. The drive voltage waveform applied to the antiferroelectric liquid crystal cell is composed of two or more scanning periods, and the drive voltage waveforms in the preceding and following scanning periods are symmetrical with respect to 0 V, and each scanning period is There is at least a selection period and a non-selection period, and the length of the period in which the voltage applied to the antiferroelectric liquid crystal cell is equal to or higher than the threshold voltage of the antiferroelectric liquid crystal is applied to the signal electrode side within the selection period. The method for driving an antiferroelectric liquid crystal display according to claim 1, wherein the antiferroelectric liquid crystal display is controlled by the pulse width of the pulse. 3. The method for driving an antiferroelectric liquid crystal display according to claim 2, wherein a reset period in which at least liquid crystal molecules are reset to a black state or a white state within a scanning period, and a transmitted light amount in the reset period are set. A method of driving an anti-ferroelectric liquid crystal display including a select period for deciding whether to maintain or set to a different transmitted light amount.