JPS59193426A - Driving method of optical modulating element - Google Patents

Abstract

PURPOSE:To obtain a driving method having a high speed responsiveness of a large-sized optical modulating element having a picture element of a high density by applying a prescribed voltage between a scanning electrode group and a signal electrode group which are selected, and both electrode groups which are not selected. CONSTITUTION:Alternating voltage which becomes V and -V at a phase (time) t1 and at a phase t2, respectively is applied to a selected scanning electrode 12 (s) of a bistable liquid crystal cell 11 containing a ferroelectric liquid crystal, and an electric signal of an electrode 12 (n) except said electrode is ''0''. On the other hand, an electric signal applied to a selected signal electrode 13 (s) is V, and voltage of -V is applied to an unselected signal electrode 13 (n). Threshold voltages of the first and the second stable states of the liquid crystal cell 11 are denoted as Vth1 and Vth2, respectively, and the voltage V is set to a desired value for satisfying (V<Vth1<2V), and (-V>-Vth2>-2V). Accordingly, an electric signal applied to the scanning electrode 12 is apt to cause a reversible variation of the first stable state (bright) and the second stable state (dark), therefore, a driving having a high speed responsiveness is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for driving an optical modulation element such as a liquid crystal element, and more particularly to a time-division driving method for a liquid crystal element used in an optical modulation element such as a display element or an optical shuck array.

Conventionally, liquid crystal display elements display images or information by configuring a group of scanning electrodes and a group of signal electrodes in a matrix, filling a liquid crystal compound between the electrodes, and forming a large number of pixels.
well known.

The driving method for Jin's display elements is time-division driving, in which an address signal is selectively applied periodically to a group of scanning electrodes, and a predetermined information signal is selectively applied in parallel to a group of signal electrodes in synchronization with the address signal. However, this display element and its driving method had major and fatal drawbacks as described below.

That is, it is difficult to increase the i bulk density or increase the screen size. Among conventional liquid crystals, most of them are practically used as display elements because they have a relatively high response speed and low power consumption, for example, M, 5ch.
Written by dt and W, Hθlf rich ” Appli
ed Physics Letters ″V
o, 18. No. 4 (1971, 2, 15), p.
, 127~12B Voltage-DePenc
Lent 0ptical Activity
of a TwisteaNematic Liq
vid Crystal” TN (twis
This type of liquid crystal has positive dielectric anisotropy in the absence of an electric field and forms an FF4 structure (helical structure) in which the molecules of the cnematic liquid crystal are twisted in the thickness direction of the liquid crystal layer. However, a structure is formed in which the liquid crystal molecules are arranged in parallel on both electrode surfaces. On the other hand, when an electric field is applied, nematic liquid crystals with positive dielectric anisotropy are aligned in the direction of the electric field, resulting in optical modulation.

When a display element is constructed with a matrix electrode structure using this type of liquid crystal, the area where both the scanning electrode and the signal electrode are selected (selected point) has a threshold value greater than or equal to the threshold required to align the liquid crystal molecules perpendicular to the electrode surface. A voltage is applied to the region where neither the scanning electrode nor the signal electrode is selected (unselected point), and therefore the liquid crystal molecules maintain a stable alignment parallel to the electrode plane. By arranging linear polarizers above and below such a liquid crystal cell in a cross-Nicol relationship with each other, light does not pass through selected points, but light passes through non-selected points, making it possible to use it as an image element. becomes.

However, when a matrix electrode structure is configured, there is a limited number of areas where scan electrodes are selected and signal electrodes are not selected, or areas where scan electrodes are not selected and signal electrodes are selected (so-called 6 half-selected points). The difference between the voltage applied to the selected point and the voltage applied to the half-selected point is sufficiently large, and the voltage threshold required to align the liquid crystal molecules perpendicular to the electric field is set to an intermediate voltage value. If so, the display element will operate normally, but if the number of scanning lines (N) is increased, an effective electric field will be generated at each selected point while scanning the entire screen (one frame). Once upon a time (
duty ratio) or 1. For this reason, the effective voltage difference between selected points and non-selected points when repeat scanning is performed becomes smaller as the number of scanning lines increases9, resulting in a decrease in image contrast and Talk is an unavoidable drawback. This phenomenon is caused by liquid crystals that do not have bistability (the stable state is when the liquid crystal molecules are aligned horizontally with respect to the electrode surface, and they are aligned vertically only while an electric field is effectively applied). This is an essentially unavoidable problem that arises when driving (i.e., repeated scanning) using the temporal accumulation effect. In order to improve this point, voltage averaging methods, dual frequency driving methods, multiple matrix methods, etc. have already been proposed, but all of these methods are insufficient, and as the screen size and density of display elements increases, Currently, the number of scanning lines has reached a plateau because the number of scanning lines cannot be increased sufficiently.

On the other hand, looking at the field of printers, laser beam blinking is a means of obtaining hard copies using electrical signals as input, and is effective in terms of both pixel density and speed. (LBP) is also excellent in current quantity. However, LBP has the following disadvantages: 1. The device used as a printer is large; 2. High-speed driving parts such as polygon scanners generate abrasion noise, and strict mechanical precision is required. In order to overcome these drawbacks, a liquid crystal shutter array has been proposed as an element that converts electrical signals into optical signals. However, when providing pixel signals using a liquid crystal shack array, for example, in order to write pixel signals at a rate of 10 dOt/rm within a length of 200 mm, it is necessary to have 4000 signal generators. figure,
In order to provide independent signals to each, it was originally necessary to wire lead wires to send signals to all of the signal generating parts, which was difficult to manufacture.

Therefore, an attempt has been made to time-divide and provide pixel signals for 1 (line) of I L using signal generators divided into several lines.

By doing so, it is possible to use a common electrode for applying a signal to a plurality of signal generating sections, and the amount of wiring can be substantially reduced. However, in this case, if the number of lines (N) is increased using a liquid crystal that does not have bistability, as is usually done, the signal ON times become substantially equal, and the signals obtained on the photoreceptor are There are disadvantages in that the amount of light decreases and crosstalk problems occur.

SUMMARY OF THE INVENTION An object of the present invention is to provide a novel optical modulation element, particularly a method for driving a liquid crystal element, which solves all the problems of conventional liquid crystal display elements or liquid crystal optical shutters as described above.

Another object of the present invention is to provide a liquid crystal element having high-speed response.
The objective is to provide a driving method.

Another object of the present invention is to provide a method for driving a liquid crystal device having a high density of pixels.

A further object of the present invention is to provide a method for driving a liquid crystal element that does not generate crosstalk.

Furthermore, another object of the present invention is to provide a novel method for driving a liquid crystal device using a liquid crystal that is bistable with respect to an electric field, particularly a chiral smectic C-phase or H-phase liquid crystal that has ferroelectricity. In particular, another object of the present invention is to provide a novel driving method suitable for a liquid crystal device having a high density of pixels and a large surface area.

That is, the object of the present invention is to provide an optical modulation material (for example, liquid crystal) having a scanning electrode group and a signal electrode group, and having bistable properties with respect to an electric field between the scanning electrode group and the signal chamber. In a method for driving an optical modulation element such as a liquid crystal element having a structure in which the bistable liquid crystal is A voltage is applied to align the liquid crystal in one stable state (one optically stable state), and the bistable liquid crystal is brought into a second stable state between the scanning electrode and the unselected signal electrode of the signal electrode group. (the other optically stable state), and at the same time, the threshold voltage -vth2 (second An optical device 7 that applies a voltage set to a value between Vthl (which refers to the threshold voltage in a stable state) and Vthl (which refers to a threshold voltage in a first stable state)
This is achieved by the driving method of the tuner.

In a preferred embodiment of the present invention, the scanning electrode groups are sequentially selected based on the scanning signal and the scanning electrode group is sequentially selected based on the scanning signal. An electrical signal having phases t1 and t2 with different voltages is applied to the selected scanning electrode of the liquid crystal element facing the lz pole group and selected based on a predetermined information signal, and a predetermined 1n signal is applied to the signal electrode group. There is,
By applying electrical signals with different Ih pressures depending on whether the information signal is present or not, the phase 1. In (12), the liquid crystal element can be driven by applying an electric field in the opposite direction to the liquid crystal. A specific example thereof is shown in FIG. 1, and details will be explained later.

The optical modulation material used in the driving method of the present invention has a bistable state consisting of a first optically stable state and a second optically stable state with respect to an electric field, and in particular has a bistable state with respect to an electric field as described above. A liquid crystal with bistability is used.

As a liquid crystal exhibiting bistability that can be used in the PIA m method of the present invention, a chiral smectic liquid crystal having ferroelectricity is most preferable, and chiral smectic C phase (Bmc or H phase (Sm)) is most preferable. (*) liquid crystal is suitable.For this ferroelectric liquid crystal, please refer to LE J
OURNAL DE PHMS ENGINEERING QUKTJKTTER
8” 36 (L-69) 1975, “Fe
rroelectricLiquid, Crystal
Il]J; ”Applied Physi
cs Letters”56 (11)19130
"Submicro 5econd B15table
eElectrooptic Switching
In Liquid Crystal θ''; 1 Solid State Physics'' 16 (141) 1981 ``Liquid Crystals'', etc., and the present invention can use the ferroelectric liquid crystals disclosed in these publications.

FIG. 2 schematically depicts an example of a ferroelectric liquid crystal cell. 21 and 21' are engineering n203. SnO2 and IT
A substrate (glass plate) coated with a transparent electrode such as O (ndium-tin oxide), etc.
A liquid crystal of an SmC* phase or an SmH* phase, in which the liquid crystal layer 22 is oriented perpendicular to the glass surface, is used.

A thick line 23 represents a liquid crystal molecule, and this liquid crystal molecule 23 has a dipole moment (P,) 24 in the direction perpendicular to the molecule on the substrates 21 and 21'. When a voltage higher than a certain threshold is applied between the electrodes, the helical structure of the liquid crystal molecules 23 is broken and the alignment direction of the liquid crystal molecules 23 can be changed so that all dipole moments (P,) 24 are oriented in the direction of the electric field. can. The liquid crystal molecules 23 have an elongated shape and exhibit refractive index anisotropy in the long axis direction and short axis direction. Therefore, for example, if crossed Nicol polarizers are placed above and below the glass surface, the voltage application polarity can be changed. It is easily understood that the liquid crystal optical modulation element has optical characteristics that change depending on the amount of the liquid crystal. Furthermore, when the thickness of the liquid crystal cell is made sufficiently thin (for example, 1μ),
As shown in FIG. 6, even when no electric field is applied, the helical structure of the liquid crystal molecules unwinds, and the dipole moment) P or P' assumes either an upward (64) or downward (34) state.

When an electric field E or E' with a different polarity above a certain threshold value is applied to such a cell as shown in FIG. ', and the liquid crystal molecules change direction accordingly, either in the first stable state 33 or in the second stable state 3.
6' is tilted or oriented in one direction.

There are two advantages to using such a ferroelectric liquid crystal as an optical modulation element. Firstly, the response speed is extremely fast, and secondly, the alignment of liquid crystal molecules has bistability. To explain the second point with reference to FIG. 3, for example, when the electric field E is applied, the liquid crystal molecules are oriented in a first stable state 33, and this state remains stable even when the electric field is turned off.

Moreover, when an electric field E' in the opposite direction is applied, the liquid crystal molecules are aligned to the second stable state 33' and the orientation of the molecules is changed.
Yay! 7 It remains in this state even if the electric field is turned off. or,
As long as the applied electric field E does not exceed a certain threshold value, each orientation state is maintained. In order to effectively realize such fast response speed and bistability, it is preferable for the cell to be as thin as possible, and generally from 0.5μ to
21]μ, especially 1μ to 5μ is suitable. A liquid crystal-electro-optical device having a matrix electrode structure using this type of ferroelectric liquid crystal has been proposed, for example, by Clark and Ragaval in US Pat. No. 4,567,924.

A preferred example of the driving method of the present invention is shown in FIG.

Figure 1 fA+-(a) I-t, cell 11 having a matrix electrode structure with a ferroelectric liquid crystal compound sandwiched between them.
FIG. 12 is a scanning electrode group υ, and 13 is a signal 1E electrode group. Figure 1 (Al-(1)) and (Al-(c)
) indicate the electrical signals given to the selected scanning electrode 12(S) and the electrical signals given to the other scanning electrodes (unselected scanning electrodes) 12(n), respectively, and FIG.
庺-(dJ and (A)-(e) represent the electric signal applied to the selected signal electrode 13 (n) and the electric signal applied to the unselected signal electrode 13 (n), respectively. -(b) to (e) The horizontal axis represents time and the vertical axis represents voltage. For example, when displaying a moving image, the scanning electrode group 12 is selected sequentially and periodically. .Now, if we let v thl be the primary voltage required to maintain the first stable state of a liquid crystal cell with bistability, and −v th2 be the value ν and value voltage needed to provide the second stable state. , the electric signal given to the selected scanning electrode 12t8) becomes -V at phase (time) t, and -V at phase (time) t2, as shown in FIGS. 1(A)-(b). This is an alternating voltage.Also, other scanning electrodes 12
(n) is in a grounded state as shown in FIG. A)
-V as shown in (d), and the electric signal given to the unselected signal electrode 13(n) is as shown in Fig. 1(A)-
As shown in (θ) (-V. In the above, the voltage value V is V<vthl<2V t-V>-Vth2>
It is set to a desired value that satisfies -2V. FIG. 1B shows a voltage waveform applied to each pixel when such an electric signal is used. (B)-(a in Figure 1(B))
), (B)-(b), (B)-(C1 and (II-(C1
) correspond to pixels A, B, C, and D in FIG. 1(A), respectively. That is, as is clear from FIG. 1 (Bl), a voltage of 2V exceeding the threshold value Vth is applied to the pixel A on the selected scanning line at phase t2. At B, a voltage -2■ exceeding the threshold value -vth 2 is applied.Therefore, depending on whether a signal electrode is selected on the selected scanning electrode line,
If selected, the liquid crystal molecules are aligned to the first stable state, and if not selected, the liquid crystal molecules are aligned to the second stable state.

In any case, it has nothing to do with the previous history of each pixel.

On the other hand, on unselected scanning lines as shown in pixels C and D, the voltages applied to all pixels C and D are +V or -V, neither of which exceeds the same voltage. Therefore,
The liquid crystal molecules in each pixel C and D maintain the orientation corresponding to the signal state when scanned last time without changing the orientation state. That is, when a scanning electrode is selected, the signal for one line is loaded, and -
The signal state can be maintained until the frame ends and is selected next time. Therefore, even if the number of scanning electrodes increases, the actual duty ratio does not change, and contrast reduction and crosstalk do not occur at all. At this time, the value of ζ;L pressure value V and the value of phase (t, +t2) - 2 depend on the liquid crystal material used and the thickness of the cell, but usually 0.1 μθθC ~ 3 volts ~ 70 volts 2mF
It is used in the range of 3ec. What is essentially different from conventionally known driving methods is that in the method of the present invention, the electrical signal applied to the selected scanning electrode is in a first stable state (a "bright" state when converted into an optical signal). The point here is that it facilitates a change from a second stable state (which is assumed to be a "dark" state when converted to an optical signal) or vice versa. For this purpose, the signals applied to the selected scanning electrodes alternate from 10 to 1. In addition, the voltage applied to the signal electrode is determined to specify the bright or dark state.
The voltages are of opposite polarity.

In order for the driving method of the present invention to be effectively achieved, the electrical signal applied to the scanning electrode or the signal electrode is not necessarily a simple rectangular wave signal as explained in FIGS. 1(b) to (e). It is obvious that this does not have to be the case. For example, it is also possible to drive with a sine wave or a triangular wave.

Further, FIG. 4 shows another specific example of the driving method of the present invention. Figures 4(a), (b), (C) and (d) show the signals of the selected scanning electrodes, the signals of the unselected scanning poles (1 and 1), and the signals of the selected scanning poles (with information), respectively. ) represents an information signal, signal, and an unselected − (information − no) information signal.That is, as shown in FIG. Even if the voltage (2) is applied and the voltage -V is applied to the signal electrode with no information only during the phase (time) tl, the same driving form as shown in FIG. 1 is obtained as a result.

E4'-S 5121 shows a further modified example of the example shown in FIG. Figure 5 (a) T fb)
l (C) and (a) show the signal of the selected scanning electrode (Fig. 5(a)), the signal of the unselected scanning electrode (Fig. 5(b)), and the signal of the selected scanning electrode (Fig. 5(b)), respectively. 5(C)) and an unselected (no information) information signal (FIG. 5(a)). On this occasion,
Based on the invention - in order to be driven correctly, the 51st
In the driving method shown in λ'1, it is necessary to satisfy the following relationship.

FIG. 6 shows a schematic diagram of a matrix electrode structure when applied to a liquid crystal-optical shield.

At this time, 41 is a pixel, and the electrodes on both sides of this portion are made of transparent material. 42 is a scanning electrode group, 4
3 represents a signal electrode group.

When forming an element using these materials, in order to maintain the salinity state such that the liquid crystal compound becomes an S:C phase or an SmH* phase, the element may be placed in a copper block with a heater embedded as necessary. etc. can be supported.

The method of the present invention can be widely applied to the field of optical shutters and displays such as liquid crystal-optical shutters and liquid crystal televisions.

[Brief explanation of the drawing]

FIG. 1+A++(a) is a plan view schematically showing a liquid crystal element used in the overtime method of the present invention. Figure 1 fA) -%
(b) is an explanatory diagram showing signals of selected scanning electrodes. FIG. 1(A) (%-tc) is an explanatory diagram showing signals of unselected scanning electrodes. Figure 1 (A) 4 (C
1) is an explanatory diagram showing information signals of selected signal electrodes. FIG. 1 is an explanatory diagram showing the information signal of signal 1 which is not selected. Figure 1 FB)-ww
(a) is a waveform diagram of the voltage applied to the liquid crystal of pixel A. FIG. 1(B)-+(b) is a waveform diagram of the voltage applied to the liquid crystal of pixel B. Figure 1 CB) −+ (c)
is a waveform diagram of the voltage applied to the liquid crystal of pixel C. FIG. 1 FB1% (d) is a waveform diagram of the voltage applied to the liquid crystal of each pixel. 2(r) FIG. 2 is a perspective view schematically showing a liquid crystal element using a chiral smect phase liquid crystal. FIG. 3 is a perspective view schematically showing a liquid crystal element used in the present invention. FIG. 4 fa) is an explanatory diagram showing signals of selected scanning electrodes in another specific example. FIG. 4(b) is an explanatory diagram showing signals of unselected scan electrodes in another specific example. FIG. 4(e) is an explanatory diagram showing information signals of selected signal electrodes in another specific example. FIG. 4(d) is an explanatory diagram showing information signals of unselected signal electrodes in another specific example. Fifth
Figure (a) is an explanatory diagram showing signals of selected scanning electrodes in another specific example. FIG. 5(b) is an explanatory diagram showing signals of unselected scanning electrodes in another specific example. FIG. 5 (cl is an explanatory diagram showing the information signal of the selected signal electrode in another specific example. FIG. 5(d) is an explanatory diagram showing the information signal of the unselected signal electrode in another specific example. FIG. 6 is a plan view of a liquid crystal shutter using the driving method of the present invention. 11...Liquid crystal element 12...Scanning electrode group 12 (selected Scanning electrode 12 (nl...scanning electrode not selected 13...
Signal electrode group 13(s)...selected signal electrode 13 (nl...unselected signal electrode 36...first
Liquid crystal 66' oriented in a second stable state...Liquid crystal 34 oriented in a second stable state...Upward dipole moment P 34'...F direction dipole moment P'Patent applicant
Canon Co., Ltd. 3 ■ 21 Bow 4 Item 5 No. 0 (C) (b) (d) Procedural Amendment (Voluntary) April 51, 1982 Commissioner of the Patent Office Kazuo Sugi 1 Display of the case Showa 1958 Patent Application No. 68659 2 Name of the invention Driving method for optical modulation element 3 Relationship with the person who makes the correction 1 Patent applicant Location Tokyo lit Nijin I11-ku Chokuko 3-30-2 Name (+0
0) Canon Co., Ltd. Representative Ryu Nagaku 3rd Department 4th Agent Residence Li] 146 East! ,, L Mercenary F11 Ward Shimomaruko 3-30-2 Canon Co., Ltd. 4 (Telephone 75B-21
11) 5. Specification subject to correction 6, Contents of correction (1) "Optical modulation" on page 5, line 6 of the specification is corrected to "optical modulation." (2) rlOdotJ on the bottom line of page 7 above is 1-20
Correct it to dotJ. (3) On page 16, line 18 of the same page, after “at pixel B”, “
Insert "in the phase tl."

Claims (8)

[Claims] (1) In a method for driving an optical modulation element having a structure including a set electrode group and a signal electrode group, and an optical modulation material having bistable property against an electric field is arranged between the scanning electrode group and the signal electrode group. , applying a voltage to orient the bistable optical modulation material to a first stable state between a selected scan electrode of the scan electrode group and a selected signal electrode of the signal electrode group; A voltage is applied between the scan electrode and the unselected signal electrode of the signal electrode group to orient the bistable optical modulation material to the second stable state, and a voltage is applied between the unselected scan electrode of the scan electrode group and the Threshold voltage of the optical modulation material having bistability between the signal electrode group -
vth2 (referring to the threshold voltage of the second stable state) and vth,
1. A method for driving an optical modulation element, characterized by applying a voltage set to a value between (referring to a threshold voltage in a first stable state). (2) Applying electrical signals having different voltage phases to selected scanning electrodes of the scanning electrode group, and applying electrical signals having different voltages to the selected signal electrodes and unselected signal electrodes of the signal electrode group. A method for driving an optical modulation element according to claim 1. (3) Applying electrical signals having different voltage polarities and phases to selected scanning electrodes of the scanning electrode group, and applying electrical signals having different voltage polarities to the selected signal electrodes and unselected signal electrodes of the signal electrode group. A method for driving an optical modulation element according to claim 1, which provides a signal. (4) The method for driving an optical modulation element according to claim 1, wherein the optical modulation substance having bistability is a ferroelectric liquid crystal. (5) The method for driving an optical modulation element according to claim 4, wherein the ferroelectric liquid crystal is a liquid crystal having a chiral smectoid phase. (6) Claim 5, wherein the liquid crystal having a chiral smectoid phase is a liquid crystal having a C phase or an H phase.
Driving method of the optical modulation element described in 2. (7) The method for driving an optical modulation element according to claim 5, wherein the liquid crystal having a chiral smectic phase is a liquid crystal phase that does not form a helical structure. (8) The method for driving an optical modulation element according to claim 6, wherein the chiral smect liquid crystal having the C phase or H phase is a liquid crystal phase that does not form a helical structure.