JPH0643428A - Driving method for ferroelectric liquid crystal panel - Google Patents

Abstract

PURPOSE:To provide the driving method by which an uneven display does not occur, even if the ferroelectric liquid crystal panel is driven for many hours, and as its result, it can be driven without deteriorating its display contrast. CONSTITUTION:As shown in (c) in (A) of the figure, this method is constituted so that in the case a signal applied to a picture element in a selection period is applied continuously by two pulses or more, any pulse of these continuous pulses does not exceed a threshold, and the sum of the voltage product of each pulse exceeds a threshold.

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 liquid crystal layers of ferroelectric liquid crystal and having a matrix of pixels and a liquid crystal optical shutter array.

[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. That it has a memory property, can respond at high speed, and has good multiplex characteristics. Since then, research has been done vigorously.

The switching of the ferroelectric liquid crystal occurs only when a certain pulse wave is applied to the liquid crystal molecules, and the product of the pulse width and the voltage value is a threshold value or more, and the polarity of the applied voltage. The first stable state (O
Either the N state) or the second stable state (OFF state) is selected. FIG. 3 shows an electrode structure of a matrix type liquid crystal panel including the ferroelectric liquid crystal. A selection voltage is sequentially and cyclically applied to the scan electrodes X1 to X4, and a predetermined information signal is applied to the signal electrodes Y1 to Y4 in parallel in synchronization with the scan electrode signals to display liquid crystal molecules of selected pixels. A time-divisional drive that switches according to information is adopted.

Various methods have been proposed as time-division driving methods. FIG. 4 shows a driving method disclosed in JP-A-62-150334, in which (A) shows an ON state and (B) shows a change in voltage waveform and pixel transmittance when the OFF state is set. There is. The signals applied to the scanning 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 positive and negative pulse pairs, and the polarities of the two pulse pairs are opposite to each other.

Further, the signal applied to the signal electrode also has four phases, and it is turned on or off depending on the combination of four pulses of the scanning side voltage applied in one scanning period and the signal side voltage synchronized therewith. Either of the states can be selected. For example, when a signal voltage as shown in (B) of FIG. 4A is applied, the combined voltage waveform applied to the pixel is as shown by the hatched portion 41 of (C) of FIG.
The ON state is set because the sum of the product values of the pulse width and the voltage value of the second phase and the third phase exceeds the threshold voltage, and the product value of the pulse width of the fourth phase and the voltage value is less than or equal to the threshold voltage. And held. In addition, depending on how the signal voltages are combined,
When a signal voltage waveform such as (B) in (B) is applied, the composite voltage waveform applied to the pixel is as shown in (C) in FIG. 4B, and the two pulses in the first half of the selection period. Is less than the threshold voltage, and the value of the product of the pulse width of the fourth phase and the voltage value exceeds the threshold voltage value as shown by the shaded portion 42, so the OFF state is set by the pulse in the fourth phase of the selection period.

[0006]

However, when the liquid crystal panel is driven for a long time by using this driving method, the alignment state of the liquid crystal molecules differs from the initial state depending on the location of the panel, and the display as the whole panel is displayed. This causes unevenness, resulting in a problem that the contrast is lowered. Therefore, it is an object of the present invention to provide a driving method that does not cause a reduction in contrast even after driving for a long time.

[0007]

In order to achieve the above object, the present invention provides a scanning signal of a ferroelectric liquid crystal panel having pixels in a matrix, in which a signal of a selection period is composed of a plurality of pulses in a scanning electrode. In the driving method of the ferroelectric liquid crystal panel for displaying the display data on the pixel by applying a signal based on the display data in synchronism with the scanning signal to the signal electrode in the selection period of the scanning signal. The write signal applied to the pixel by changing the crest value and polarity of the pulse and the crest value and polarity of the pulse of the signal electrode signal is composed of a plurality of pulses of the same polarity whose voltage-time product is less than or equal to a threshold value. Signal of which the sum of the voltage-time products of the pulses is equal to or more than the threshold value, or a pulse whose voltage-time product exceeds the threshold value and has a pulse having a polarity different from that of the pulse before or after the pulse or a period of zero voltage. Characterized in that it in.

[0008]

As a result of various studies, when driving a ferroelectric liquid crystal, when a pulse having a voltage higher than a threshold voltage required for switching is applied, as shown by a shaded portion 41 in FIG. Immediately after that, it was found that continuous application of pulses of the same polarity affects the alignment state of liquid crystal molecules. Therefore, when such driving is performed for a long time, the alignment state changes compared to the initial state. I found that this leads to uneven display on the panel as a whole, resulting in a reduction in contrast. Therefore, when using a write signal consisting of multiple pulses of the same polarity,
If all the pulses are independently set to the threshold value or less and the sum of the voltage-time products of the pulses exceeds the threshold value, the orientation state does not change compared to the initial state.

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 2 is a cell structure diagram of the liquid crystal panel used in this example. The liquid crystal panel used in this embodiment has a pair of glass substrates 22 having a ferroelectric liquid crystal layer 21 having a thickness of about 2 μm.
It is composed of A and 22B. Electrodes 23A and 23B are formed on the opposite surface of the glass substrate, and polymer alignment films 24A and 24B are applied on the electrodes and rubbing-treated. Further, a first polarizing plate 25A is provided outside the one glass substrate so that the polarizing axis of the polarizing plate is 22.5 ° with the rubbing axis, and the first polarizing plate 25A is provided outside the other glass substrate. The second polarizing plate 25B is installed so as to be different from the polarization axis of the plate 25A by 90 °.

FIG. 1 shows the drive voltage waveform of this embodiment. (A) is a scanning side voltage waveform, (B) is a signal side voltage waveform, (C) is a composite voltage waveform applied to the selected pixel, and (D) is a change in transmittance of light passing through the pixel.
The drive waveform in the present invention is composed of four pulses in one selection period. In FIG. 1, the first of the scanning electrode waveforms during the selected period
Phase is + 8V, second phase is -8V, third phase voltage is-
It is 12V, and the voltage value of the fourth phase is + 12V. The voltage waveform on the signal side when the ON state is selected is 0 V for the first and second phases, -4 V for the third phase, and + for the fourth phase.
It 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 is 100
μs.

FIG. 1A shows a case where a voltage for setting the signal electrode to the ON state is applied to the signal electrode during the selection period.
(B) is a case where a voltage for setting the signal electrode to the OFF state is applied during the selection period, and (A),
(B) shows the combined voltage waveform applied to the pixel when a signal voltage in the ON or OFF state is applied to both signal electrodes, and the product of the pulse width and the voltage value of the pulses 11 and 12 in the shaded area is shown. Since the threshold for switching is exceeded, as can be seen from the change in the transmittance of (d), the ON selection waveform is set to the ON state, and the OFF selection waveform is set to the OFF state. At this time, as shown by the hatched portion 11 in FIG. 1C, the same polarity pulse is continuously applied during the scanning period, but neither the third phase nor the second phase exceeds the threshold value. For this reason, this liquid crystal panel was continuously driven for 24 hours, but display unevenness did not occur, and even if it was driven for a long time as shown in Table 1, the display contrast was not lowered as compared with the conventional driving method, which was excellent. I was able to display.

[0012]

[Table 1]

[0013]

As described in the above embodiments, by performing the driving by the driving method of the present invention, the display unevenness does not occur even if the driving is performed for a long time. Therefore, as a result, good driving can be performed without deterioration of contrast even when driving for a long time.

[Brief description of drawings]

FIG. 1 is a diagram showing a signal waveform according to a driving method of the present invention.

FIG. 2 is a configuration diagram of a liquid crystal element used in an example.

FIG. 3 is a layout view of electrodes of a liquid crystal display panel.

FIG. 4 is a diagram showing signal waveforms in a conventional driving method.

[Explanation of symbols]

 21 Ferroelectric Liquid Crystal Layer 22A, 22B Glass Substrate 23A 23B Electrode 24A, 24B Polymer Alignment Film X1 to X4 Scanning Electrodes Y1 to Y4 Signal Electrodes

Claims (1)

[Claims] 1. A ferroelectric liquid crystal panel having pixels in a matrix form, a scanning electrode is sequentially applied with a scanning signal composed of a plurality of pulses in a selection period, and a signal electrode is displayed in synchronization with the scanning signal. In a method of driving a ferroelectric liquid crystal panel, which applies a signal based on data to display display data on the pixel, a crest value and a polarity of a pulse in a selection period of the scanning signal, a crest value of a pulse of a signal electrode signal, and The write signal to be applied to the pixel by changing the polarity is composed of a plurality of pulses of the same polarity whose voltage-time product is less than or equal to a threshold value, and the sum of the voltage-time product of the plurality of pulses being a threshold value or more, A method for driving a ferroelectric liquid crystal panel, characterized in that the pulse is a pulse whose voltage-time product exceeds a threshold value and has a polarity different from that of the pulse before or after the pulse or a pulse having a period of zero voltage. Law.