JPS6256936A - Driving method for liquid crystal matrix display panel - Google Patents

Abstract

PURPOSE:To perform gradational control on the quantity of transmitted light without varying a field period light by applying a reset pulse which has a sufficient crest value and pulse width to a ferroelectric liquid crystal panel in a desired light transmission state during a nonselection period. CONSTITUTION:The liquid crystal panel is placed in the desired light transmission state with the 1st pulse voltage group applied in a selection period and the 2nd pulse voltage group which has the sufficient crest value and pulse width is applied to scanning electrodes in a nonselection period to reset the panel to a constant light or dark state. The reset pulse is applied at the end of the 1st field, the 1/2 time point of the 2nd field, and the 1/4 time point of the 3rd field to make a display having eight gradations. Therefore, the gradational control on the quantity of transmitted light is performed without varying the field period.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a liquid crystal matrix display panel having a ferroelectric liquid crystal as a liquid crystal layer, and relates to a liquid crystal matrix panel capable of controlling the gradation of transmitted light and a method for driving a light shutter element. be.

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). ).

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 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 how to describe ferroelectric liquid crystal using an example of a chiral smectic phase exhibiting ferroelectricity. 7th
FIG. 7(a) shows a representation of a ferroelectric liquid crystal in a state in which the long axis of the molecules is tilted by ±θ degrees with respect to the normal 7 of the molecular layer, and FIG. 7(b) shows a state in which the molecular long axes are tilted by −θ degrees. 7 is the normal to the layer, 8 is the long axis direction n of the molecule, 9 is the dipole moment Pi, 10 is the C director when n is projected onto the xy plane, 1) is the normal to the long axis of the molecule The tilt angle is ±θ degrees. 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 degrees 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 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 (+1) shows the state in which no voltage is applied, Fig. 8 (b) shows the case where a positive voltage is applied from the front to the back of the paper, and Fig. 8 (C1 shows the case where a positive voltage is applied from the back to the front of the paper). This is the operating principle when voltage is applied.In this way, depending on the direction of voltage application, the entire cell assumes two states tilted by ±θ degrees. Therefore, if birefringence or dichroism due to the electro-optic effect is used, brightness and darkness can be changed. can be expressed.

As mentioned above, ferroelectric liquid crystals can take only two states when viewed microscopically, so in order to produce halftones, it is necessary to change the state from Figure 8 (bl to Figure 8 (C1) or from Figure 8 (C) to Figure 8 (bl
Methods are being considered, such as using a mixed state of two states as shown in Figure 8(a) obtained during the transition period, or changing the ratio of the appearance times of the two states (for example, Clark, , Wall Neurodisplay 84 Digest 1984, p. 73 (N, A,
C1ark, S., T., Lagerwal.
Land J, Wahl: Eurodisp.
lay' 84 Digest (1984) l)
, 73) ).

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

In view of the above-mentioned problems, the present invention provides a method for driving a liquid crystal matrix display panel in which the gradation of light transmission can be controlled in a ferroelectric liquid crystal panel by high-duty matrix driving.

Means for Solving the Problems In order to solve the above-mentioned problems, the method for driving a liquid crystal matrix display panel of the present invention involves sandwiching a ferroelectric liquid crystal between a pair of substrates having electrodes on opposing surfaces. In a liquid crystal matrix display panel forming a pixel, the liquid crystal panel is brought into a desired light transmitting state, either bright or dark, by a first group of pulse voltages applied during a selection period, and applied to a scanning electrode at an appropriate time within a non-selection period. By applying a second pulse voltage group with sufficient peak value and pulse width to bring the liquid crystal panel into a constant state of either brightness or darkness, the liquid crystal panel is reset to a constant state of either brightness or darkness. The light transmission state can be controlled fija IN by limiting the m1 time of the light transmission state set by the pulse group and performing multiple scans by changing the timing of outputting the second pulse voltage group.

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

By using two stable light transmission states, the light transmission time width is modulated to produce many gradations. For simplicity, assuming that the brightness and darkness determined within the selection period are sufficiently maintained during the field period, if the number of gradations is 2N, the feel period of N fields is T, T/ 2. T/4.
... T / 2 M-1, and each field has gradation data of 21-1.2.
．． However, in this method, when L scanning electrodes are scanned line-sequentially, the minimum selection time is T/(2'-・L), and N and L are large (the selection time becomes short, and a ferroelectric liquid crystal that does not respond to an effective value requires high-speed response of the liquid crystal.The present invention is applicable to other liquid crystals in which the ferroelectric liquid crystal has polarity). A driving method that takes advantage of the fact that the field period remains constant and applies a reset pulse to the scanning electrode at an appropriate point in each field, so that the selection time does not suddenly shorten even when the number of gradations increases. If a set of N fields is one frame (F), the time for one frame when changing the conventional field period is F.
=Σ(%) ”-' T = (2-(!4) '-') T (
1) In the driving method of the present invention, the time for one field is as follows, and the time for one selection is (when N is large).As the number of gradations increases to 28, the time for one selection becomes becomes longer. For example, when displaying a moving image, the frame time is preferably about 16m5ec, but with 1000 scanning lines and 64 gradations, in the field period variation method, the time for one selection is −T from equation (1).
F/(2(!4)')(2'-L)
(2'・L)16X10-'/22'-1000 = 0.25xlO-'', which is difficult to realize at about 0.25 μsec, but with the method of the present invention, the time for one selection is F 16 Xl0-'' N- L 6 x 1000 1) 2.7 x 10-h, which is approximately 2.7 μsec, which is a sufficiently achievable length.

Example □ Examples are shown below.

FIG. 1 shows the timing of the selection pulse and reset pulse when displaying 8 gradations, and the corresponding change in the amount of transmitted light. Since it has 8 gradations, it consists of 3 fields.
The reset pulse is applied to the first field at the end of the field, to the second field at the 172nd point in the field, and to the third field at the 1/4 point from the beginning of the field.

Figure 2 +8), (b) represents the scanning voltage and signal voltage when the selected signal voltage is set to zero potential.

FIG. 3 shows the voltages applied to the panel at this time for each of the selection, non-selection, reset periods, and on and off states. In either case, alternating current is applied within one selection period (hereinafter referred to as l stage), and therefore no direct current component is applied to the liquid crystal, thereby preventing deterioration of the liquid crystal.

Moreover, the dark value voltages V, V- at which the molecule is reversed with 1 pulse (pulse width τ seconds) are VO>V+>(1-)V, respectively. .

Vo>V-<　(1-)V.

The conditions are met. Based on this, the duty ratio is 1
FIG. 4 shows the driving waveform and the amount of transmitted light when displaying 8 gradations in 78.

The pixel measuring the amount of transmitted light has a brightness of 100 in binary. One pulse is 240μsec, V.

is 25 volts, and the bias voltage is ±7 volts.

FIG. 5 shows a case where the pulse width of the reset pulse of the first embodiment is doubled. However, the duty ratio is 1716. As the pulse width becomes longer, the molecules tend to reverse, so the pulse voltage is low (but reset is applied).

As described above, it was confirmed that gradation display can be achieved without shortening one selection period by applying the 7) pulse to the scanning electrode during the non-selection period.

It was done. Note that the liquid crystal used in the above examples was a mixture of ester-based ferroelectric liquid crystals, and was oriented by pinning.

Effects of the Invention The method for driving a liquid crystal matrix display panel of the present invention takes advantage of the fact that a ferroelectric liquid crystal panel has polarity and applies a reset pulse to the scanning electrode at an appropriate point in the field, thereby adjusting the field period. This is a driving method that allows gradation display by controlling the light transmission time and changing the timing of applying the reset pulses in a plurality of fields without changing the image quality. Since only the binary states of light and dark are used, stable control is possible without being affected by the substrate surface, unlike when using a mottled state to create halftones. In addition, since the field period is constant, the selection pulse width does not become too short even when the number of gradations increases with a high duty cycle, which alleviates the requirement for high-speed response of the liquid crystal material.

[Brief explanation of the drawing]

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 Example 1 of the present invention, and FIG.
The figure is a waveform diagram of the voltage applied to the panel in the case of Figure 2, Figure 4 is a waveform diagram showing the actual drive waveform and amount of transmitted light in the case of 8 gray levels with a duty ratio of 1/8 in Figure 2. 5 is a waveform diagram showing the drive waveform and amount of transmitted light in Example 2 of the present invention, FIG. 6 is a cross-sectional view of a ferroelectric liquid crystal panel, FIG. 7 is a diagram showing the notation of chiral smectic C liquid crystal, and FIG. FIG. 8 is a thickness diagram of the display of a conventional ferroelectric liquid crystal panel. l...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-1)1.
...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, 15.
...Dipole moment toward the back of the paper, 16...
...Direction of the two polarizing plates. Name of agent Patent attorney Toshio Nakao (1 person) Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 7 Figure 8

Claims (2)

[Claims] (1) In a driving method for a liquid crystal matrix display panel in which a ferroelectric liquid crystal is sandwiched between a pair of substrates having electrodes on opposing surfaces to form a matrix of pixels, the first voltage applied during the selection period of one scan is A group of pulse voltages is used to bring the liquid crystal panel into a desired light transmitting state, either bright or dark, and at an appropriate time during the non-selection period of the scan, a peak value sufficient to bring the liquid crystal panel into a constant bright or dark state is applied to the scanning electrode. By applying a second pulse voltage group having a pulse width of and resetting the liquid crystal panel to the state, the duration of the light transmitting state set by the first pulse voltage group is limited, and the scanning is changed to A method for driving a liquid crystal matrix display panel, characterized in that the timing of outputting the second pulse voltage group is changed and repeated multiple times. (2) Driving the liquid crystal matrix display panel according to claim 1, wherein at least one of the peak value or the pulse width of the first pulse voltage group is greater than or equal to the first pulse voltage group. Law.