JPH0648333B2 - Driving method of liquid crystal matrix display panel - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal matrix display panel having a ferroelectric liquid crystal as a liquid crystal layer, a liquid crystal matrix panel capable of gradation control of an amount of transmitted light, and a driving method of an optical shutter element. is there.

2. Description of the Related Art In recent years, a ferroelectric liquid crystal having a fast response speed and a memory property has been reported (for example, Hideo Takezoe, Atsuo Fukuda, Eiichi Kuze; “Industrial Materials”, Volume 31, No. 10, 22). .

An example of a conventional ferroelectric liquid crystal panel will be described below with reference to the drawings. FIG. 6 shows the structure of a conventional smectic liquid crystal panel. In FIG. 6, 1 is a glass substrate, 2 is a transparent electrode made of ITO (indium tin oxide), 4 is a ferroelectric liquid crystal layer, 5 is a C director of liquid crystal molecules, and 6 is a dipole moment.

Ferroelectric liquid crystals generally have a dipole moment in a direction perpendicular to the long axis of the molecule, and when they are made thin, they have spontaneous polarization. The notation method of ferroelectric liquid crystal is shown in FIG. 7 using an example of a chiral smectic phase exhibiting ferroelectricity. 7th
FIG. 7A is a notation of the ferroelectric liquid crystal in which the molecular long axis is tilted by + θ degrees with respect to the normal line 7 of the molecular layer, and FIG. 7B is a notation of the ferroelectric liquid crystal tilted by −θ degrees. 7 is the layer normal, 8 is the long axis direction of the molecule,
9 is the dipole moment 10 is the C director when is projected on the xy plane,
11 is the angle of inclination ± θ with respect to the normal to the long axis of the molecule. The operation principle of the ferroelectric liquid crystal panel having the above structure will be described below with reference to the drawings.

FIG. 8 shows a principle diagram of a display method of a conventional ferroelectric liquid crystal panel. 12 is a liquid crystal molecule whose molecular long axis is tilted by + θ degrees with respect to the layer normal, 13 is a liquid crystal molecule tilted by −θ degrees, 14 is a dipole moment in the front direction of the paper, 15 is a dipole moment in the back direction of the paper, 16 Is the direction of the two polarizing plates. Now, Fig. 8 (a)
Is the state of no voltage applied, Fig. 8 (b) is the operation principle when a positive voltage is applied from the front to the back of the paper, and Fig. 8 (c) is the operation principle when a positive voltage is applied from the back to the front of the paper. is there. In this way, the entire cell is placed in two states inclining by ± θ degrees depending on the direction of voltage application, and therefore birefringence or 2
Brightness can be represented by utilizing chromaticity.

As described above, the ferroelectric liquid crystal can take only two states microscopically. Therefore, in order to obtain a halftone, it is necessary to obtain the halftone in FIG. 8 (b) to FIG. 8 (c), or FIG. 8 (c). It is possible to use a mixed state of two states as shown in Fig. 8 (a), which is obtained during the transition period from Fig. 8 to Fig. 8 (b), or to change the ratio of the appearance time of two states. (Eg Clark, Ragabar, Wall: Eurodisplay '84 Digest 1984, p. 73, [NA Clark, ST Lagerwall a
nd J, Wahl: Eurodisplay'84 Digest (1984) p. 7
3)).

Problems to be Solved by the Invention However, the state in which the two states are mixed is easily affected by the substrate surface, and the controllability is extremely poor. Further, regarding the method of changing the appearance time ratio of the two states, no detailed study has been made on matrix driving suitable for large-scale display.

In view of the above problems, the present invention provides a driving method of a liquid crystal matrix display panel capable of gradation control of light transmission amount in a ferroelectric liquid crystal panel by high duty matrix driving.

Means for Solving the Problems In order to solve the above problems, a driving method of a liquid crystal matrix display panel of the present invention is such that a ferroelectric liquid crystal is sandwiched between a pair of substrates having electrodes on opposite surfaces to form a matrix. In a liquid crystal matrix display panel for forming pixels, the liquid crystal panel is brought into a desired light transmission state, either bright or dark, by a first pulse voltage group applied in a selection period, and the scan electrode is applied to the scan electrode at an appropriate time point in a non-selection period. By applying a second pulse voltage group having a crest value and a pulse width sufficient to bring the liquid crystal panel to a constant state of either light or dark, and resetting the liquid crystal panel to either the light or dark state, The duration of the light transmission state set by the pulse group is limited, and the light transmission state can be gradation-controlled by scanning a plurality of times while changing the timing of outputting the second pulse voltage group. It

The second pulse voltage group is particularly effective when at least one of its peak value and pulse width is greater than or equal to the first pulse voltage group.

Action Two stable light transmission states modulate the light transmission time width in order to produce many gradations. For the sake of simplicity, assuming that the bright or dark state defined within the selection period is sufficiently maintained during the field period, if the number of gray levels is 2 ^N , the field period of N fields is T, T / 2. , T / 4, ...
·, T ^{/ 2} is varied so that ^{N-1, 2 N-1} , 2 of the gradation data of each field, ..., ^{2 0}
It suffices to correspond to the coefficient of. However, with this method, L
In the case of line-sequential scanning of the two scanning electrodes, the minimum selection time is T / (2 ^N-1 · L), and the selection time becomes shorter as N and L become larger. High-speed response is required. The present invention utilizes the property that the ferroelectric liquid crystal has polarity, which is not present in other liquid crystals, and by applying a reset pulse to the scan electrode at an appropriate point in each field while keeping the field period constant,
The driving method is provided so that the selection time does not suddenly decrease even if the number of gradations increases. Assuming that a set of N fields is 1 frame (F), 1 frame time in the case of changing the conventional field period is Becomes In the driving method of the present invention, one field time is Therefore, 1 selection time (When N is large), the one selection time becomes longer in the driving method of the present invention as the number of gradations 2 ^N increases. For example, when displaying a moving image, the frame time is preferably about 16 msec, but the number of scanning lines is 100
With 0 lines and 64 gradations, in the field cycle change method, 1 selection time is calculated from the formula (1). It is difficult to realize in about 0.25 μsec, but one selection time is required in the method of the present invention. Is about 2.7 μsec, which is a sufficiently realizable length.

Examples Examples are shown below.

FIG. 1 shows the timings of the selection pulse and the reset pulse when displaying 8 gradations and the corresponding changes in the amount of transmitted light. Since it has 8 gradations, it consists of 3 fields,
The reset pulse is applied at the end of the field in the first field, at the time of 1/2 of the field in the second field, and at the third field.
In the field, a reset pulse is applied 1/4 from the beginning of the field.

2A and 2B show the scanning voltage and the signal voltage when the selected signal voltage is set to zero potential. Figure 3 shows
The voltage applied to the pulse at this time is selected, non-selected,
The figure shows the reset period and each case of ON and OFF. In either case, the alternating current is applied within one selection period (hereinafter referred to as one stage), and therefore, no direct current component is applied to the liquid crystal, which prevents deterioration of the liquid crystal. Further, with one pulse (pulse width τ second), the threshold voltages V ₊ and V ₋ at which the molecules are inverted are respectively The conditions of are met. Based on this, the duty ratio 1 /
FIG. 4 shows the drive waveform and the amount of transmitted light at that time when 8 gradations are displayed with 8.

The pixel measuring the amount of transmitted light has a brightness of 100 in binary. One pulse is 240 μsec, V ₀ is 25 V, and the bias voltage is ± 7 V. FIG. 5 shows the case where the pulse width of the reset pulse in the first embodiment is doubled. However, the duty ratio is 1/16. In this case as well, since the scanning voltage and the signal voltage are both AC, the voltage applied to the picture element does not include a DC component. As the pulse width becomes longer, the molecules are more likely to be inverted, and therefore reset is applied even if the pulse voltage is low.

As described above, it was confirmed that by applying the reset pulse to the scan electrode during the non-selection period, gradation display can be performed without shortening one selection period. The liquid crystal used in the above examples was a mixture of ester-based ferroelectric liquid crystals and was aligned by rubbing.

The driving method of the liquid crystal matrix display panel of the present invention utilizes the fact that the ferroelectric liquid crystal panel has a polarity, and by applying a reset pulse to the scan electrode at an appropriate point in the field, This is a driving method capable of gradation display by controlling the light transmission time and changing the timing of applying the reset pulse without changing the above. Since only the light and dark binary states are used, it is possible to perform stable control without being affected by the surface of the substrate as in the case of producing a halftone using a mottled state. Further, since the field period is constant, the selection pulse width does not become too short even if the number of gradations increases with high duty, and the requirement for high-speed response of the liquid crystal material is relaxed.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the timing of selection pulses and reset pulses and the amount of transmitted light when displaying 8 gradations, FIG. 2 is a drive waveform diagram in the first embodiment of the present invention, and FIG. FIG. 4 is a waveform diagram of voltage applied to the panel in FIG.
FIG. 2 is a waveform diagram showing the actual drive waveform and the amount of transmitted light when the duty ratio is 1/8 and 8 gradations, and FIG. 5 shows the drive waveform and the amount of transmitted light in the second embodiment of the present invention. FIG. 6 is a waveform diagram, FIG. 6 is a cross-sectional view of a ferroelectric liquid crystal panel, FIG. 7 is a schematic diagram showing notation of a chiral smectic C liquid crystal, and FIG.
The figure shows the principle of display of a conventional ferroelectric liquid crystal panel. 1 ... Glass substrate, 2 ... Transparent electrode, 3 ... Alignment film, 4
…… Ferroelectric liquid crystal layer, 5 …… C director of liquid crystal molecules, 6 …… Dipole moment, 7 …… Layer normal, 8 ……
Longitudinal direction of molecule n, 9 ... dipole moment, 10 ... C
Director, 11 …… Inclination angle of the molecular long axis with respect to the layer normal ± θ degrees, 12 …… Liquid crystal molecule whose molecular long axis is tilted by + θ degrees with respect to the layer normal, 13 …… Liquid crystal molecule tilted by −θ degrees , 14 …… dipole moment in the front direction of paper, 15 …… dipole moment in the back direction of paper, 16 …… direction of two polarizing plates.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroyuki Onishi, 1006 Kadoma, Kadoma City, Osaka Prefecture, Matsushita Electric Industrial Co., Ltd. 56) References JP 62-9324 (JP, A)

Claims (2)

[Claims] 1. In a driving method of a liquid crystal matrix display panel in which a ferroelectric liquid crystal is sandwiched between a pair of substrates having electrodes on opposite surfaces, a liquid crystal matrix display panel driving method is applied in a selection period of one scan. One of the pulse voltage groups is used to bring the liquid crystal panel into either the light transmission state of light or dark, and the liquid crystal panel is placed in the light transmission state of either light or dark at the scanning electrode at an appropriate point in the non-selection period of the one scan. By applying a second pulse voltage group having a sufficient peak value and pulse width to reset the liquid crystal panel to the one light transmitting state, the other of the light transmitting states set by the first pulse voltage group Is a method of driving a liquid crystal matrix display panel for limiting the duration of the light transmission state, wherein one scan is repeated a plurality of times within a predetermined cycle, and the other light transmission state of the plurality of one scans is continued. The timing of issuing the second pulse voltage group is changed so that the time does not become the same in each one scanning, and the light by the first voltage pulse group applied in the selection period in each one scanning is changed. A driving method of a liquid crystal matrix display panel, which performs gradation display by combining transmission states according to gradation display. 2. The timing of outputting the second pulse voltage group in each one of a plurality of scans is approximately 1 cycle, 1/2 cycle, 1/2 ² cycle, ... ² from the start of the scan cycle. And a signal voltage in the selection period in each one scan is changed in correspondence with a coefficient of a power of 2 when grayscale data is represented by a binary system. 2. A method for driving a liquid crystal matrix display panel according to item 1.