JPS6256934A - Driving method for liquid crystal matrix panel - Google Patents

Abstract

PURPOSE:To perform a display of high quality on a high-duty single-paper matrix driving basis by making scanning pulses narrower in width in a nonselection period than in a selection period. CONSTITUTION:When the display panel which has ferroelectric liquid crystal charged between substrates is driven, the scanning pulses are made narrower in width in the nonselection period than in the selection period, a reset pulse having wide pulse width is applied at the end of the nonselection period to reset picture elements, which are inverted when the pulses is the latter half of the selection period is an on voltage and do not change in state when an off voltage. Thus, only an effective voltage is raised without inverting liquid crystal molecules to performs an excellent contrast display with high duty.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for driving a liquid crystal matrix panel having a ferroelectric liquid crystal as a liquid crystal layer.

Prior Art In recent years, reports have been made on ferroelectric liquid crystals with fast response speed and memory properties (for example, Hideo Takezoe, Atsuo Fukuda, Sakae Kuze; "Industrial Materials", Vol. 31, No. 10, 22). ).

Hereinafter, one row of conventional ferroelectric liquid crystal panels will be described 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, 6 is a C director of liquid crystal molecules, and 16 is a dipole moment.

Ferroelectric liquid crystals generally have a dipole moment in the direction perpendicular to the long axis of the molecules, and as they become thinner, they come to have spontaneous polarization. FIG. 7 shows a method of representing a ferroelectric liquid crystal using an array of chiral smectic phases exhibiting ferroelectricity. FIG. 7(IL) shows a representation of a ferroelectric liquid crystal in a state where the long axis of the molecules is tilted by +θ degrees with respect to the normal to the molecular layer, and FIG. 7(b) shows a state in which the molecular long axes are tilted by −0 degrees. 7 is the normal to the layer, 8 is the longitudinal direction of the molecule n, 9 is the dipole moment) Ps, 10 is n! The C director -C111 when projected onto the 7-plane is an inclination angle of ±θ degrees with respect to the normal to the long axis of the molecule. The operating principle of the ferroelectric liquid crystal panel having the above structure will be explained below with reference to the drawings.

FIG. 8 shows a principle diagram of a conventional ferroelectric liquid crystal panel display method. 12 is a liquid crystal molecule whose long axis of the molecule is tilted by +θ degree with respect to the layer normal, 13 is a liquid crystal molecule whose molecular axis is tilted by 1θ degree, 14 is a dipole moment in the direction of the front of the page, 16 is a dipole moment in the direction of the back of the page, 16 is the direction of the two polarizing plates. Now, Figure 8 (&) shows the state in which no voltage is applied, Figure 8 (b) shows the case where a positive voltage is applied from the front to the back of the paper, and Figure 8 (0) shows the positive voltage applied from the back to the front of the paper. This is the operating principle when applying .

In this way, two states in which the entire cell is tilted by ±θ degrees depending on the direction of voltage application can be created, and therefore brightness and darkness can be expressed by using birefringence or dichroism due to the electro-optic effect.

The above is the display principle of a ferroelectric liquid crystal panel, but as a matrix drive method, there is a drive method that is slightly modified from the conventional voltage averaging method. FIG. 9 is an example of this, in which the waveform is based on a voltage averaging method with a 3A bias consisting of two fields, and the polarity of the pulse and the on-voltage and off-voltage are reversed for each field. The molecule is inverted at the on-voltage vd, but not at the off-voltage Vd-2·vh. Therefore, the on state is set in the first field, and the off state is set in the second field. (For example, anti-Japan, exit, residence, Kai: Niss I D'86 Digest, 1985, p. 136 (T.

HMU RADMU, M, TMU GtTCHI, IWASMU, M, NIMU: SID '85 Digest (
1985) p. 131) Problems to be Solved by the Invention The threshold voltage of a ferroelectric liquid crystal becomes smaller in absolute value as the applied pulse width becomes longer. Therefore, with a waveform based on the voltage averaging method as described above, during the non-selection period of the scan electrode, depending on the pixel pattern, a pulse with a pulse width twice as long as the pulse voltage applied during the selection period of the scan electrode may be applied. Since a voltage is applied, the bias ratio must be reduced to reduce the voltage value. When the bias ratio is decreased, the ratio of the on voltage to the off voltage is also decreased, so unless the threshold characteristic is steep, display becomes impossible.

Further, the above conventional method is based on the assumption that there is memory due to the effect of the surface of the substrate of the panel, and a display with high contrast cannot be expected with a panel such as a thick cell that has no or weak memory effect.

In view of the above problems, the present invention provides a ferroelectric liquid crystal display panel, regardless of the quality of the threshold characteristics and memory effect of the panel.
The present invention provides a driving method for a liquid crystal matrix panel that allows high-quality display with high-duty simple matrix driving.

Means for Solving the Problems In order to solve the above problems, the method for driving a liquid crystal matrix panel of the present invention uses a ferroelectric liquid crystal with negative dielectric anisotropy between a pair of substrates having electrodes on opposing surfaces. Clamping, ma) IJ
(Liquid crystal matrix forming sock-like picture elements) Driving of a liquid crystal matrix panel according to IJ Fuchsnell's driving method, characterized in that the pulse width of the scanning voltage pulse in the non-selection period is made shorter than the pulse width of the scanning voltage pulse in the selection period. It is the law-giver. Further, the driving method of the present invention is effective when the pulse width of the scanning voltage pulse during the non-selection period is shorter than the response time of the ferroelectric liquid crystal at the pulse voltage value.

Further, the driving method of the present invention is particularly effective when the amplitude of the pulse voltage applied to the picture element during the non-selection period of the scanning electrode is large enough to produce a stabilizing effect on molecular orientation due to the dielectric anisotropy.

The inversion of the ferroelectric liquid crystal molecules occurs due to the interaction between spontaneous polarization and the electric field, but outside of this blade there is a force proportional to the dielectric anisotropy and the effective voltage that causes the ferroelectric property to change. It also acts on liquid crystal molecules.

The authors' experiments have shown that when the dielectric anisotropy of ferroelectric liquid crystal is negative, a force proportional to the effective voltage has the following two effects on the liquid crystal channel.

First, the force that forces molecules to become parallel to the substrate surface increases in proportion to the effective value of the applied voltage.When this force is greater than the force caused by the interaction between Ps and the electric field, the state of the pixel is Retained. In other words, the effect of improving memory performance is produced. The second effect is that the threshold characteristics are improved. It has been confirmed through experiments that due to the above-mentioned force that produces the first effect, as the effective value voltage increases, the threshold voltage increases overall, but the characteristics become steeper. In order to make effective use of the above two effects, the driving method of the present invention applies a pulse voltage with a pulse width shorter than that applied to the picture element during the selection period to the picture element during the non-selection period. The threshold voltage of a dielectric liquid crystal has pulse width dependence.) (The shorter the pulse width, the higher the threshold voltage. In this driving method) Since the pulse width is short, the threshold voltage is high and the pixel does not change even if the voltage is increased. Although the state does not change, only the effective value increases, and the above two effects act strongly, resulting in a high-quality display.

Example Examples are shown below.

The liquid crystal used in this experiment [HJ] was a mixture of ester-based ferroelectric liquid crystals, and its constant electric anisotropy was negative. In addition, the orientation was performed by the conventional rubbing method, and the distance between the substrates was approximately 3.6
It is μm. In general, orientation by rubbing is more effective than orientation by shear stress or temperature gradient.
The characteristic of voltage versus amount of transmitted light is slow, and therefore the bias ratio cannot be made very small using a driving method based on the conventional voltage averaging method.

In fact, with the liquid crystal IJ hook display panel used in this experiment, it was impossible to display at a duty ratio of 1/100 or more even under various conditions using the conventional driving method shown in Figure 9. .

FIG. 6(b) shows the results of measuring the threshold characteristics by applying the waveform shown in FIG. 5(1L) to the panel and changing the effective value. It can be seen that as the effective value increases, the threshold voltage increases and the characteristics become steeper. It has also been confirmed that the memory effect increases as the effective value increases.

FIGS. 1 and 2 show driving waveforms of the first embodiment of the present invention actually applied to a ferroelectric liquid crystal display panel. Figure 1 (
! L) represents the voltage applied to the scanning electrode and the signal electrode, and FIG. 1(b) represents the voltage applied to the panel. In this example, a reset pulse with a wide pulse width is applied to the scanning electrode at the end of the non-selection period to put the picture element in a reset state.
If the pulse in the second half of the selection period is an on voltage, it will be inverted, and if it is an off voltage, the state will not change. Also, since all pulses are alternating current, the liquid crystal does not deteriorate. In FIG. 1(b),
Vo=20 volts, f O=300 p 5eOVc=
30 volts, bias ratio 1/&=, duty ratio 1
/10oO, a display with good contrast was observed. FIG. 2 shows the actual drive waveform and the change in the amount of light transmitted through the picture element.

3 and 4 are diagrams showing drive waveforms in the second implementation column.
One AC pulse is set above the threshold voltage and the first two AC pulses are set below the threshold voltage to turn on the picture element, and when turning off the picture element, the reverse is done. In this practical row as well, a good display was obtained under the same condition as in the first practical row.

Effects of the Invention The liquid crystal matrix panel driving method of the present invention utilizes the fact that the threshold voltage of ferroelectric liquid crystal has pulse width dependence,
By shortening the pulse width and increasing the amplitude of the pulse applied during the non-selection period, υ provides a dynamic property in which only the effective value voltage can be increased without inverting the numerator. As a result, when the dielectric anisotropy of the ferroelectric liquid crystal is negative, the forcing force acting on the liquid crystal molecules becomes stronger in proportion to the effective voltage, the memory effect increases, the threshold characteristics become steeper, and the higher the duty cycle becomes. However, very good contrast display and optical switching are possible.

Figure 6 (IL) is a waveform diagram of voltage applied to the liquid crystal, Figure 6 (b) is a voltage-transmittance characteristic diagram of ferroelectric liquid crystal, and Figure 6 is a graph of the amount of transmitted light. 7(iL) and (b) are schematic diagrams showing the notation of chiral smectic C liquid crystal, and FIGS. 8(a) and (b).
, (C) is a principle diagram showing the display principle of a conventional ferroelectric liquid crystal panel, and FIG. 9 is a waveform diagram showing the conventional voltage driving method.

1...Glass substrate, 2...Transparent electrode,
3... [Alignment film, 4... Ferroelectric liquid crystal layer, 5... C director of liquid crystal molecules 16...
...Dipole moment, 7...Normal of layer, 8
......Long axis direction of molecule n, 9...Dipole moment, 10...C director-111.
...Inclination angle of the long axis of the molecule with respect to the layer normal ±θ degrees, 1
2...Liquid crystal molecule whose long axis of the molecule is tilted by +θ degrees with respect to the layer normal, 13...Liquid crystal molecule whose molecular axis is tilted by -θ degrees, 1
4...Dipole moment in the direction of the surface of the paper, 16.
...Dipole moment toward the back of the paper, 16...
...Direction of the two polarizing plates.

Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure ((L) tb) Figure 2 Figure 3 (Cb) Figure 4 Figure 5 400) s@C Electric L Vo Figure 8 (α)

Claims (6)

[Claims] (1) In the driving method of a liquid crystal matrix panel in which a ferroelectric liquid crystal with negative dielectric anisotropy is sandwiched between a pair of substrates having electrodes on opposing surfaces to form a matrix of picture elements, scanning during a non-selection period is performed. A method for driving a liquid crystal matrix panel, characterized in that the pulse width of a voltage pulse is made shorter than the pulse width of a scanning voltage pulse during a selection period. (2) The method for driving a liquid crystal matrix panel according to claim 1, wherein the pulse width of the scanning voltage pulse during the non-selection period is shorter than the response time of the ferroelectric liquid crystal at the pulse voltage value. . (3) The method for driving a liquid crystal matrix panel according to claim 1, wherein the driving waveform applied to the picture element becomes an alternating current waveform within one selection period of the scanning electrode. (4) Four pulse voltages are applied to the picture element during one selection period of the scanning electrode, the first and second pulses, the third and fourth pulses
The pulses have the same pulse width, the absolute value of the voltage value is the same, but the polarity is opposite, the polarity of the first and third pulses is also opposite, and the voltage value of the first and second pulse is different from that of the third pulse. 2. The method of driving a liquid crystal matrix panel according to claim 1, wherein one of the fourth pulse voltage values is equal to or higher than the threshold voltage, and the other is equal to or lower than the threshold voltage. (5) The first and second pulses are applied in the first scan, and the third and fourth pulses are applied in the second scan. Driving method of liquid crystal matrix panel. (6) The amplitude of the pulse voltage applied to the picture element during the non-selection period of the scanning electrode is made large enough to produce a stabilizing effect on molecular orientation due to the dielectric anisotropy. Driving method of liquid crystal matrix panel described in Section 2.