JPH05158018A - Driving method for ferroelectric liquid crystal panel - Google Patents

Abstract

PURPOSE:To provide a driving method by which display having stable contrast is performed for a long time without changing the oriented state of the liquid crystal molecule of the liquid crystal layer of a ferroelectric liquid crystal panel in comparison with the initial oriented state even when the liquid crystal panel is driven for a long time. CONSTITUTION:In a non-selection period, a signal impressed on a scanning electrode has the equal voltage value of a signal impressed on a signal electrode, and at least two or more pulses of signals having the same polarity are continuously impressed. Thus, a dormant period is set in the non-selection period whatever data is inputted in the signal electrode, so that the ferroelectric liquid crystal panel is stably driven for a long time.

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 ferroelectric liquid crystal panel such as a liquid crystal display panel having a matrix of pixels and a liquid crystal optical shutter array having ferroelectric liquid crystal as a liquid crystal layer.

[0002]

2. Description of the Related Art A liquid crystal panel using a ferroelectric liquid crystal has been reported in U.S. Pat. No. 4,367,924 to Clark, et al. Since then, research has been done vigorously.

The switching of the ferroelectric liquid crystal occurs only when a voltage above a certain threshold is applied to the liquid crystal molecules, and the first stable state (ON state) or the second stable state depends on the polarity of the applied voltage. Any of the stable states (OFF state) of is selected. FIG. 4 shows an electrode structure of a matrix type liquid crystal panel including the ferroelectric liquid crystal. In order to drive the matrix type liquid crystal panel, a selection voltage is applied to the scan electrodes X1 to X4 periodically and in sequence, and a predetermined information signal is applied to the signal electrodes Y1 to Y4 in parallel in synchronization with the scan electrode signals. However, time-division driving is used in which liquid crystal molecules of the selected pixel are switched according to display information.

Various methods have been proposed as time-division driving methods. FIG. 5 shows a driving method disclosed in JP-A-62-150334, in which (A) shows an ON state and (B) shows O.
7 shows changes in voltage waveform and pixel transmittance when setting the FF state. The signals applied to the scan electrodes are shown in FIG.
As shown in (a) of (A) and (B), it consists of four phases,
The first phase and the second phase and the third phase and the fourth phase respectively form a positive and negative pulse pair, and the polarities of the two pulse pairs are opposite to each other. The signal applied to the signal electrode is also 4
It is composed of phases, and it is possible to select either the ON state or the OFF state by combining four pulses of the scanning side voltage applied in one scanning period and the signal side voltage synchronized with the four pulses. For example, when a signal voltage as shown in (b) of FIG. 5A is applied, the composite voltage waveform applied to the pixel becomes as shown in (c) of FIG.
Since the pulse exceeds the threshold voltage and the latter two pulses are below the threshold voltage, the ON state is set and held by the pulse of the second phase. Further, when a signal voltage waveform as shown in (b) of FIG. 5B is applied due to the difference in the combination of the signal voltages, the combined voltage waveform applied to the pixel is as shown in (C) of FIG. ), The two pulses in the first half of the selection period are below the threshold voltage, and the two pulses in the latter half exceed the threshold voltage value. Therefore, by the pulse in the fourth phase of the selection period,
The OFF state is set.

[0005]

However, when the liquid crystal panel is driven for a long time by this driving method, the alignment state of the liquid crystal molecules in the liquid crystal layer of the liquid crystal panel changes to an alignment state different from the initial alignment state. As a result, there is a problem that the display contrast deteriorates. Therefore, the present invention solves such a problem, and the ferroelectric liquid crystal panel can be stably driven without changing the alignment state of the liquid crystal molecules of the liquid crystal layer of the liquid crystal panel even if it is driven for a long time. The purpose is to provide a driving method.

[0006]

In order to achieve the above-mentioned object, according to the present invention, a ferroelectric liquid crystal is sandwiched between a pair of substrates each having a scanning electrode and a signal electrode on opposite surfaces to form pixels in a matrix. In the method for driving a ferroelectric liquid crystal panel in which the above-mentioned ferroelectric liquid crystal panel is time-divisionally driven, a period in which the voltage applied to the pixel is zero is provided in the non-selection period of each pixel.

[0007]

When the voltage applied to the pixel is 0 V, the electric field direction due to the spontaneous polarization of the ferroelectric liquid crystal molecules is parallel to the normal direction of the glass substrate and does not appear in the vertical direction, but has a certain value. When the voltage is applied to the pixels and the liquid crystal molecules start moving, an electric field due to spontaneous polarization appears perpendicular to the normal direction of the glass substrate. If this electric field exists in the cell for a long time, it causes a change in the alignment state of the liquid crystal molecules, and the display contrast also drops. Therefore, by providing a rest period in which the voltage is 0 V in the non-selection period so as to prevent continuous application of an electric field in the direction perpendicular to the substrate normal direction, the above phenomenon is mitigated.

[0008]

Embodiment 1 An embodiment of the present invention will be described in detail below with reference to the drawings. The liquid crystal panel used in this example is composed of a pair of glass substrates having a ferroelectric liquid crystal layer having a thickness of about 2 μm. The electrodes shown in FIG. 4 are formed on the facing surface of the glass substrate, and a polymer alignment film is applied on the electrodes and subjected to rubbing treatment. Further, a first polarizing plate is installed on the outside of one glass substrate such that the polarizing axis of the polarizing plate is 22.5 ° with the rubbing axis, and the first polarizing plate is on the outside of the other glass substrate. The second polarizing plate is installed so as to be different from the polarization axis by 90 °.

FIG. 1 shows a drive voltage waveform according to the first embodiment of the present invention. (A) is the scanning side voltage waveform,
(B) is a signal side voltage waveform, (C) is a composite voltage waveform applied to the selected pixel, and X1, X2 and Y1 correspond to the scanning side electrodes and the signal side electrodes of the matrix electrode shown in FIG. , A and b correspond to the pixels a and b in FIG. The drive waveform in the present invention is composed of four pulses in one selection period. The scanning-side voltage waveform in the non-selection period has the same polarity in the first phase and the fourth phase, the same polarity in the second phase and the third phase, and the opposite polarity to the first phase and the fourth phase in the previous period. Is. In the non-selection period immediately after the selection period, the 4 pulses of the first block and the 4 pulses of the second block have opposite polarities to each other, and then 4 pulses of the odd-numbered block and 4 pulses of the even-numbered block in that order. Have opposite polarities. In FIG. 1, the voltage of the first phase and the fourth phase of the scanning side voltage waveform in the selection period is + 12V, the voltage of the second phase and the third phase is -12V, and the scanning side voltage waveform of the non-selection period is The first and fourth phases of the first block are −4V, the second and third phases are 4V, the first and fourth phases of the second block are 4V, and the second and third phases are −4V. It is 4V. The voltage waveform on the signal side when the ON state is selected is 4 V for the first phase and the third phase, and the fourth phase for the second phase.
The phase is -4V. In addition, the signal electrode waveform when selecting the OFF state has the opposite polarity to the signal electrode voltage waveform when selecting the ON state. The pulse width of all phases was 100 μs.

In FIG. 1C, a indicates a case where an ON-state voltage is applied to the signal electrode during the selection period, and b indicates a case where an OFF-state voltage is applied to the signal electrode during the selection period. Both a and b show a composite voltage waveform applied to a pixel when a signal voltage in the ON or OFF state is applied to the signal electrode. Regardless of whether the signal electrode ON or OFF is applied during the non-selection period, a pause period in which the voltage value is always 0 is formed during the non-selection period. When this liquid crystal panel was continuously driven for 24 hours, the alignment state of the liquid crystal molecules in the liquid crystal layer of the liquid crystal panel did not change compared to the alignment state at the beginning of driving, and as a result, as shown in Table 1, long-term driving was performed. Even if the above was performed, good display could be performed without lowering the display contrast as compared with the conventional driving method.

[0011]

[0012]

Second Embodiment FIG. 2 shows a drive voltage waveform according to the second embodiment of the present invention. (A) is the scanning side voltage waveform,
(B) shows a signal-side voltage waveform, and (C) shows a composite voltage waveform applied to the selected pixel. X1, X
2, Y1 correspond to the scanning side electrodes and the signal side electrodes of the matrix electrode shown in FIG. 4, and a and b correspond to the pixels a and b in FIG. The drive waveform in the present invention is 1
The selection period is composed of four pulses. The scanning-side voltage waveforms in the non-selection period have the same polarity in the first phase and the second phase, the same polarity in the third phase and the fourth phase, and the first phase.
The phase and the third phase have opposite polarities. Further, each block composed of 4 pulses in the non-selected period has the same polarity. In FIG. 2, the voltage of the first phase and the fourth phase of the scanning side voltage waveform in the selected period is + 12V, and the voltage of the second phase and the third phase is -12V. Further, the first phase and the second phase of each block of the voltage waveform on the scanning side in the non-selection period are -4V, and the third phase and the fourth phase are + 4V. The voltage waveforms on the signal side when the ON state is selected are 4V for the first phase and the third phase, and -4V for the second phase and the fourth phase. In addition, the signal electrode waveform when selecting the OFF state has the opposite polarity to the signal electrode voltage waveform when selecting the ON state. The pulse width of all phases was 100 μs.

In FIG. 2C, "a" indicates that the signal electrode is O during the selection period.
When an N-state voltage is applied, b is when an OFF-state voltage is applied to the signal electrode during the selection period, and both a and b are applied with an ON-state or OFF-state signal voltage during the non-selection period. The combined voltage waveform applied to the pixel in the case is shown. Regardless of whether an ON signal or an OFF signal is applied to the signal electrode during the non-selection period, a non-selection period has a pause period in which the voltage value is always 0. When this liquid crystal panel was continuously driven for 24 hours, the alignment state of the liquid crystal molecules in the liquid crystal layer of the liquid crystal panel did not change as compared with the alignment state at the initial stage of driving, and the length as shown in Table 1 was the same as in Example 1. We were able to obtain stable display contrast over time.

[0014]

[Embodiment 3] FIG. 3 shows a drive voltage waveform according to another embodiment of the present invention. (A) is the voltage waveform on the scanning side, (b)
Shows a signal-side voltage waveform, and (c) shows a composite voltage waveform applied to the selected pixel. X1, X2, Y1
Corresponds to the scanning side electrode and the signal side electrode of the matrix electrode shown in FIG. 4, and a and b are the pixels a and b in FIG.
It corresponds to. The drive waveform in the present invention consists of two frames, and ON or OFF is selected by the first two pulses of each frame. The scanning-side voltage waveform in the non-selection period is the first voltage immediately after the selection period in the first frame.
The first phase and the second phase of the block have the same polarity, and the first phase and the second phase of the second block have the same polarity. Further, the two pulses of the first block and the second block of the non-selection period immediately after the selection period have mutually opposite polarities, and thereafter, the two pulses of the even-numbered block and the two pulses of the odd-numbered block are sequentially arranged.
The pulses have opposite polarities. Immediately after the selection period of the second frame, the first phase and the second phase of the first block have the same polarity, and the first phase and the second phase of the second block have the same polarity. In the non-selection period immediately after the selection period, the two pulses of the first block and the second block have opposite polarities, and the two pulses of the even-numbered block and the two pulses of the odd-numbered block have opposite polarities in that order. It has become. In FIG. 1, the voltage of the first phase of the scanning side voltage waveform in the selected period is + 12V, the voltage of the second phase is -12V, and the first phase of the first block of the scanning side voltage waveform in the non-selected period is The second phase is 4V, and the first and second phases of the second block are -4V. In the signal side voltage waveform when the ON state is selected, the first phase is 4V and the second phase is -4V.
The signal electrode waveform when selecting the OFF state is ON
All have opposite polarities to the signal electrode voltage waveform that selects the state. The pulse width of all phases was 100 μs.

In FIG. 3C, a indicates a case where an ON-state voltage is applied to the signal electrode during the selection period, and b indicates a case where an OFF-state voltage is applied to the signal electrode during the selection period. Both a and b show a composite voltage waveform applied to a pixel when a signal voltage in the ON or OFF state is applied to the signal electrode. Regardless of whether the signal electrode ON or OFF is applied during the non-selection period, a pause period in which the voltage value is always 0 is formed during the non-selection period. When this liquid crystal panel was continuously driven for 24 hours, the alignment state of the liquid crystal molecules in the liquid crystal layer of the liquid crystal panel did not change as compared with the alignment state at the initial stage of driving, and the length as shown in Table 1 was the same as in Example 1. We were able to obtain stable display contrast over time.

[0016]

As described in the above embodiments, according to the driving method of the present invention, no matter whether the ON or OFF signal voltage is applied during the non-selection period, the signal voltage applied to the pixel is Since the rest period with the voltage value of 0 V is always provided, the alignment state of the liquid crystal molecules in the liquid crystal layer of the liquid crystal panel does not change from the alignment state at the initial stage of driving, and is stable even when driving for a long time. It can be displayed in contrast.

[Brief description of drawings]

FIG. 1 is a diagram showing drive signal waveforms in a first embodiment.

FIG. 2 is a diagram showing drive signal waveforms in a second embodiment.

FIG. 3 is a diagram showing drive signal waveforms in a third embodiment.

FIG. 4 is a panel electrode layout diagram of a liquid crystal display.

FIG. 5 is a diagram showing drive signal waveforms in a conventional drive method.

[Explanation of symbols]

 X1 to X4 scanning electrodes Y1 to Y4 signal electrodes a, b display pixels

Claims (2)

[Claims] 1. A ferroelectric liquid crystal in which ferroelectric liquid crystal is sandwiched between a pair of substrates each having a scanning electrode and a signal electrode on opposite surfaces, and pixels are formed in a matrix form in a time-divisional drive. A method of driving a liquid crystal liquid crystal panel, wherein a period in which a voltage applied to each pixel is zero is provided in a non-selection period of each pixel. 2. Synchronizing with the signal applied to the signal electrode, two or more consecutive pulses of the same polarity whose voltage value is equal to the voltage value of the signal are continuously applied to the scanning electrode, and the The method for driving a ferroelectric liquid crystal panel according to claim 1, wherein a period in which the voltage applied to the pixel is zero is provided in the selection period.