JPH0756545B2 - 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 and a method for driving an optical shutter element.

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, 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. FIG. 7 (a) is a notation of the ferroelectric liquid crystal in which the molecular long axis is tilted by + θ degrees with respect to the normal to the molecular layer, and FIG. 7 (b) is a notation of the ferroelectric liquid crystal tilted by −θ degrees. 7 is the layer normal, 8 is the long axis direction n of the molecule, 9 is the dipole moment P _s , 10 is the C director C when n is projected on the xy plane, and 11 is the normal to the long axis of the molecule. The tilt angle is ± θ degrees. 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) shows a state in which no voltage is applied, FIG. 8 (b) shows a case where a positive voltage is applied from the front side to the back side of the paper, and FIG. 8 (c) shows a positive voltage from the back side to the front side of the paper. Is the principle of operation when a voltage is applied. In this way, the entire cell tilted ± θ degrees depending on the voltage application direction.
Light and dark can be represented by taking one of two states and utilizing birefringence or dichroism due to the electro-optic effect.

The above is the display principle of the ferroelectric liquid crystal panel, but as a matrix driving method, there is a driving method in which the conventional voltage averaging method is slightly modified. FIG. 9 shows an example of the waveform, which has two fields and is based on the 1/4 bias voltage averaging method, and the polarity of the pulse and the on-voltage and the off-voltage are reversed for each field. The molecules are inverted at the on-voltage V _d , but are not inverted at the off-voltage V _d −2 · V _h . Therefore, the ON state is set in the first field, and the OFF state is set in the second field. (For example, Harada, Taguchi, Iwasa, Kai: S.I.D.'85 digest, 1985.
Year, page 135 (T.HARADA, M.TAGUCHI, K.IWASA, M.KAI: SID′8
5 Digest (1985) p.131] Problems to be Solved by the Invention The absolute value of the threshold voltage of the ferroelectric liquid crystal becomes smaller as the applied pulse width becomes longer. Therefore, in the waveform according to the voltage averaging method as described above, a time twice as long as the pulse width of the pulse voltage applied in the non-selection period of the scan electrode and, depending on the pixel pattern, in the selection period of the scan electrode. Since a long DC component is applied, the bias ratio must be reduced. When the bias ratio is reduced, the ratio between the on-voltage and the off-voltage is also reduced and the display becomes impossible unless the threshold characteristic is steep.

Further, the above-mentioned conventional method is premised on that there is a memory due to the effect of the substrate surface of the panel, and it is not possible to expect a high-contrast display without a memory effect such as a thick cell or a weak panel.

In view of the above problems, the present invention is a liquid crystal matrix display panel, which can display a ferroelectric liquid crystal display panel with high display quality by simple matrix driving with high duty, regardless of whether the threshold characteristic or memory effect of the panel is good or bad. It provides a driving method.

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 driving method for driving a liquid crystal matrix display panel for forming pixels, a first pulse voltage is applied to a signal electrode forming either one of an on pixel and an off pixel in the first half of a scanning selection period, and in the latter half, A second pulse voltage having a shorter cycle than the first pulse voltage is applied, and the second pulse voltage is applied to the first half and the first pulse voltage is applied to the second half to the signal electrodes forming the other pixel. , A pulse voltage having the same period as the second pulse voltage is applied to the scan electrodes during the non-selection period of scanning, and a pulse voltage having the same period as the first pulse voltage is applied to the scan electrodes during the selection period. It is characterized by doing.

Action The threshold voltage of a ferroelectric liquid crystal panel has pulse width dependence. FIG. 4 is a diagram showing the voltage-transmittance characteristics of the ester-based ferroelectric liquid crystal for three pulse widths, and it can be seen that the longer the pulse width, the lower the threshold voltage. From another point of view, there is a critical pulse width that can invert the molecule for one voltage, and this is considered to be the response speed. FIG. 5 is a diagram showing an example of the voltage corresponding speed of the ferroelectric liquid crystal at 27 ° C. Interaction between spontaneous polarization P _s and electric field P _s · E
The response speed is proportional to 1 / E, but according to our experiments, the response speed does not become faster even if the voltage is increased, according to our experiments. In Fig. 5, the inclination becomes 1 / E or less when it exceeds 25 volts. The numerator is not inverted by the pulse of the voltage V _a and the pulse width τ _a in the region (a) of FIG. 5, but is inverted by the pulse of the voltage V _b and the pulse width τ _{b in} the region (b). The driving method of the present invention utilizes the pulse width dependence of the threshold voltage as described above to bring a pixel into a desired light transmission state. FIG. 1 shows an example of a driving method of a liquid crystal matrix display panel of the present invention. FIG. 1 (a) is a diagram showing the scanning voltage and the signal voltage divided into a selection period and a non-selection period, and FIG. 1 (b) is a diagram showing the voltage applied to the picture element. Paying attention to FIG. 1 (b), in the selection period of the scan electrode, the inversion pulse of the region (b) is added to the latter half of the stage for the ON picture element and the first half for the OFF picture element to realize the desired light transmission state. In the other half stage, the amount of injected charges is neutralized by the non-inversion pulse in the region (a) having the opposite polarity to the pulse, and the deterioration of the liquid crystal due to the electrochemical reaction is prevented. Since the pulse width of the non-inversion pulse can be arbitrarily changed, even if the voltage-response speed characteristic in FIG. 5 changes, it can be dealt with by narrowing the pulse width.

Further, it has been confirmed by experiments that when a burst pulse voltage is applied to a ferroelectric liquid crystal panel, the smaller the direct current component of the burst pulse is, and the closer it is to a perfect alternating current, the more difficult the molecules are to invert. As shown in FIG. 1 (b), an AC pulse is applied to the scanning voltage in the non-selected period and an AC pulse having an amplitude twice or 0 times that of the signal voltage is applied as shown in FIG. 1 (b). Further, the complete AC waveform is applied to the picture element during the non-selection period of the scan electrode, and a high memory property is obtained within the non-selection period.

In addition, when the paraelectric anisotropy of the ferroelectric liquid crystal is negative, the force of the molecules trying to be parallel to the substrate surface increases in proportion to the effective value of the applied voltage, and this force becomes P _s and the electric field. When the force is larger than the interaction force, the state of the picture element is retained.
In the driving method of the present invention, the voltage applied to the picture element during the non-selection period is a perfect AC waveform, so that the inversion of molecules is unlikely to occur, and if the pulse width is shortened, the molecules do not invert even if the voltage is increased, and the effective You can greatly increase the memory by increasing only the value.

Examples Examples are shown below.

The liquid crystal used in this example is a mixture of ester-based ferroelectric liquid crystals, and its paraelectric anisotropy is negative. The alignment is performed by the conventional rubbing method, and the distance between the substrates is about 3.5 μm. In general, when the orientation is performed by rubbing, the voltage − is higher than the orientation by the shear stress or the orientation by the temperature gradient.
The characteristic of the amount of transmitted light becomes slow, and therefore, the bias method cannot be made so small by the driving method based on the conventional voltage averaging method. In fact, in the liquid crystal matrix display panel used in this example, it was impossible to display with a duty ratio of 1/100 or more by the conventional driving method of FIG. 9 even if various conditions were changed. 2 and 3 show examples of drive waveforms of the present invention actually applied to the ferroelectric liquid crystal display panel. 2 (a) and 3 (a) are scan voltages, FIG. 2 (b), and FIG.
FIG. 2 (b) shows the signal voltage, FIG. 2 (c), FIG. 3 (c) show the voltage applied to the panel, and FIG. 2 (d) and FIG. 3 (d) show the amount of transmitted light. At a temperature of 20 to 40 degrees, the pulse width τ _b of the non-selection period is 60 to 100 μsec, the amplitude V _ac is 20 to 25 volts,
The pulse width τ _a of the long pulse (writing pulse) in the first half or the second half of the selection period is 2 to 8 times τ _b , and the voltage is
When V _a is 20 V or more, the duty ratio is 1 /
A very good display quality with a contrast ratio of 10 or more even at 1000 was confirmed in the matrix display panel. Second
As shown in FIGS. 3D and 3D, the change in the amount of transmitted light in the non-selection period is very small, and the molecule does not move in the pulse having the opposite polarity to the write pulse in the selection period. However, there was almost no flicker below 30 Hz. When the pulse amplitude during the non-selection period is set to 15 V or less, the change in the amount of transmitted light during the non-selection period becomes considerably large. Therefore, it is clear that the paraelectric anisotropy enhances the memory property. If the absolute value of the anisotropy becomes large, it is considered that the driving can be performed at a lower voltage than that in this example. Further, in this embodiment, 1/1000 due to the limitation of the drive circuit.
Although the display was confirmed only up to the duty, it is expected from the change in the amount of transmitted light that similar display quality can be obtained even at higher duty.

The driving method of the liquid crystal matrix display panel of the present invention utilizes the fact that the threshold voltage of the ferroelectric liquid crystal display panel has a pulse width dependence, and the pixel width is changed by changing the pulse width applied during the selection period. ON / OFF can be controlled, and the pulse width can be arbitrarily increased without changing the waveform in the non-selection period. Therefore, set the conditions that are not affected by the quality of the panel threshold characteristics and the temperature dependence. It is possible. Also,
The complete AC waveform is added in the non-selection period, and its pulse width can be arbitrarily shortened, so that the state of the picture element does not easily change during the non-selection period. In particular, when the paraelectric anisotropy of the ferroelectric liquid crystal is negative, if the pulse width in the non-selection period is shortened and the amplitude is increased, only the effective value is increased without inverting the molecules and the pulse is increased. The memory performance of can be greatly enhanced. Therefore, high-quality display can be realized even with a high duty of 1/1000 or more. Further, since the drive waveform is made alternating as a whole, deterioration of the liquid crystal due to an electrochemical reaction does not occur.

[Brief description of drawings]

FIGS. 1 (a) and 1 (b) are diagrams showing an embodiment of a driving method of a liquid crystal matrix display panel of the present invention separately for a case where a scanning voltage and a signal voltage are selected and a case where they are not selected, and FIG. ),
(B), (c), (d) and FIGS. 3 (a), (b),
(C) and (d) are examples of actual driving waveforms of the driving method of the present invention and a diagram of transmitted light amount, FIG. 4 is a voltage-transmittance characteristic diagram of a ferroelectric liquid crystal, and FIG. FIGS. 9 (a) and 9 (b), which show the response speed, are driving waveform diagrams of pulses in the conventional ferroelectric liquid crystal matrix display. FIG. 6 is a sectional view of a ferroelectric liquid crystal panel, FIG. 7 (a),
FIG. 8 (b) is a diagram showing the notation of a chiral smectic C liquid crystal, and FIGS. 8 (a), 8 (b), and 8 (c) are principle diagrams of the 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.

Front page continued (72) Inventor Shuko Oba 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. Author Shingo Fujita 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP 61-246721 (JP, A) JP 61-223828 (JP, A)

Claims (3)

[Claims] 1. A method of driving a liquid crystal matrix display panel in which a ferroelectric liquid crystal is sandwiched between a pair of substrates having electrodes on opposite surfaces to form a matrix of pixels, and either one of an on pixel and an off pixel is used. For the signal electrodes to be composed,
The first pulse voltage is applied in the first half of the scanning selection period, the second pulse voltage whose period is shorter than the first pulse voltage is applied in the latter half, and the signal electrode forming the other pixel is described in the first half. A second pulse voltage, the first pulse voltage is applied to the latter half, respectively, and a pulse voltage having the same period as the second pulse voltage is applied to the scan electrodes in the non-selection period of scanning, and in the selection period. A method of driving a liquid crystal matrix display panel, wherein a pulse voltage having the same period as the first pulse voltage is applied to the scan electrodes. 2. The amplitude of the pulse voltage applied to the scan electrodes during the non-selection period of scanning is approximately 1 / the amplitude of the second pulse voltage.
2. The method of driving a liquid crystal matrix display panel according to claim 1, wherein the difference from the second pulse voltage does not include a DC component. 3. The ferroelectric liquid crystal has a negative dielectric anisotropy, and the amplitude of the pulse voltage applied to the scanning electrode during the non-selection period of scanning produces a stabilizing effect of molecular orientation due to the dielectric anisotropy. The method for driving a liquid crystal matrix display panel according to claim 2, wherein the driving method is set to a relatively large value.