JPS61243430A - Driving method for ferroelectric liquid crystal element - Google Patents

Abstract

PURPOSE:To shorten a write time by clamping an optical modulating element with scanning signal lines and information signal lines and constituting a matrix picture element structure, selecting plural scanning signal lines at the same time, and writing an information signal. CONSTITUTION:A ferroelectric material which has the 1st and the 2nd optically stable states is made into liquid crystal as the optical modulating element. This optical modulating element is clamped with scanning signal lines S11-S15 and S21-S25 and information signal lines I1-I10 to constitute the matrix picture element structure. Further, two groups of scanning signal lines S11-S15 and S21-S25 are driven in two directions at the same time to make a selection in each group. Then, the scanning lines S11 and S21 are selected at the same time to write information by the information signal lines I1-I10. Thus the optical modulating element which has a fast response speed is used and scanning signals are selected and written at the same time, so the write speed is increased while picture elements are prevented from being applied with a reverse bias.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for driving a liquid crystal display element, and particularly to a method for driving a matrix of a ferroelectric liquid crystal element.

[Prior art] Conventionally used display methods such as the FN method using nematic liquid crystals utilize the dielectric anisotropy of nematic liquid crystal molecules to control the direction of the molecules when an electric field is applied. , it does not matter whether the electric field is positive or negative; it is driven by the effective value.
I was able to However, when using ferroelectric liquid crystals, which have recently attracted attention, the electric field PS of spontaneous polarization in the phase that exhibits ferroelectricity (for example, chiral smectin C phase)
With respect to the product of E and the applied electric field, the response speed responds in the relationship of τ η/Ps·E (η: viscosity), so the sign of the electric field is an important issue. This is because the direction of the spontaneous polarization vector, that is, the direction of the director of the molecule, is controlled by the positive or negative polarity of the applied electric field. Therefore, when driving with a matrix electrode configuration, in a simple driving method, as shown in Fig. 7. As shown in FIG. 2, an electric field (2) having a polarity opposite to that of the write signal (2) may be applied when not selected. This depends on the liquid crystal material used, but in many cases there is no DC-like threshold characteristic, and even if the voltage is lower than the write voltage, if the application time exceeds a certain limit, inversion will occur again.

[Problems to be Solved by the Invention] In order to avoid this phenomenon, conventional driving methods have been developed that prevent reverse bias from being applied by adding various auxiliary signals between write signals. However, this increases the time it takes to write one pixel, which becomes an even more inconvenient problem when displaying on a large screen.The purpose of the present invention is to eliminate these drawbacks. It is an object of the present invention to provide a method for driving a ferroelectric liquid crystal element that prevents the application of a reverse bias for a long period of time and enables an increase in writing speed.

[Means for Solving the Problems] In the present invention, means for solving the above problems include a driving method for driving a ferroelectric liquid crystal element with a matrix circuit configuration of scanning signal lines and information signal lines. A method for driving a ferroelectric liquid crystal device, which is characterized in that a plurality of scanning signal lines are selected at the same time and an information signal is written.More specifically, an auxiliary signal is added to the information signal, and the auxiliary signal , the voltage compensation for all the pixels selected in one simultaneous selection is performed, and the scanning signal waveforms of the plurality of scanning signal lines selected at the same time are different voltage waveforms, and This is a driving method that includes varying information signal waveforms by combining pixel patterns on a plurality of scanning signal lines.

The ferroelectric substance used in the present invention includes a substance that takes either a first optically stable state or a second optically stable state depending on an applied electric field, that is, a bistable state with respect to an electric field; In particular, liquid crystals having such properties are used.

As the ferroelectric liquid crystal having bistability that can be used in the present invention, chiral smectic liquid crystal having ferroelectricity is most preferable, and among these, chiral smectic C phase (SmG) and H phase (SmHo) liquid crystals are most preferable. This ferroelectric liquid crystal is suitable for “LE JOU Physique Rutile” (LE JOU
RNAL DE PHYSIOUELETTERS”
) In 1975, ``Ferroelectric Liquid Crystals J (
rFerroelectric Liquid Cry
stals J) ; “Applied Physics Letters” (APPLIEOPHYSIC: S
``Submicro Second Bistiple Electro-Optic Switching in Liquid Crystals'' published in Issue 3B(11) in 1980.
B15table ElectroopticSwi
tching in Liquid Crystals
J) ; “Solid State Physics” 1981, 1B (14
1), and the ferroelectric liquid crystals disclosed therein can be used in the present invention.

More specifically, examples of ferroelectric liquid crystal compounds used in the method of the present invention include decyloxybenzylidene-P'-7
Minnow 2-methylbutyl cinnamate (DOBAMBC)
), hexyloxybenzylidene-p-amino-
2-Chloropropyl cinnamate (HOBAC: PC
) and 4-o-(2-methyl)-butylresolsiliten-4'-octylaniline (MBRA 8).

When constructing an element using these materials, in order to maintain the temperature at which the liquid crystal compound becomes the SIlc" phase or the SmH" phase, the element may be placed in a copper block with a heater embedded, etc., as necessary. can be supported.

FIG. 8 schematically depicts an example of a ferroelectric liquid crystal cell. 1 and 1' are. In203. Sn02 and IT
It is a substrate (glass plate) coated with a transparent electrode such as O (Indium-Tin-Oxide), between which is sealed an SmC'' phase liquid crystal oriented so that the liquid crystal molecular layer 2 is perpendicular to the glass surface. A thick line 3 represents a liquid crystal molecule, and this liquid crystal molecule 3 is
Dipole moment (P↓)4 in the direction perpendicular to the molecule
have. When a voltage higher than a certain threshold is applied between the constant electrodes on the substrates l and 1', the helical structure of the liquid crystal molecules 3 is unraveled, and the liquid crystal molecules 3 are turned so that all of the dipole moments CP and 4 are directed in the direction of the electric field. The orientation direction can be changed. The liquid crystal molecules 3 have a long and thin shape and exhibit refractive index anisotropy in the long axis direction and the short axis direction.
It is easily understood that if polarizers are placed above and below the surface in a crossed nicol positional relationship, a liquid crystal optical modulation element whose optical characteristics change depending on the polarity of applied voltage can be obtained. Furthermore, when the thickness of the liquid crystal cell is made sufficiently thin (for example, IJ
As shown in Fig. 9, the helical structure of the liquid crystal molecules unwinds (non-helical structure) even when no electric field is applied, and its dipole moment P or P' points upward (4a
) or downward (4b). When an electric field E or E' with a different polarity above a certain threshold value is applied to such a cell for a predetermined period of time as shown in FIG. or downward (4b), and accordingly the liquid crystal molecules are aligned in either the first alignment state 5 or the second alignment state 5'.

The advantage of using such a ferroelectric liquid crystal as an optical modulation element is that the response speed is extremely fast and the orientation of the liquid crystal molecules has a bistable state. When the electric field is applied, the liquid crystal molecules are aligned in the first alignment state 5, and this state is stable even when the electric field is turned off. Furthermore, when an electric field E' in the opposite direction is applied, the liquid crystal molecules are aligned to the second alignment state 5' and the orientation of the molecules is changed, but they remain in this state even after the electric field is turned off. Also,
As long as the electric field E does not exceed a certain threshold value, each orientation state is still 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, the thickness is 0.5
IJL ~ 5 pots are suitable, especially IJL ~ 5 pots. A liquid crystal-electro-optical device having a matrix electrode structure using ferroelectric liquid crystals of this kind has been proposed, for example, by Clark and Ragabal in US Pat. No. 43B7924.

[Function] If a plurality of scanning signal lines are selected at the same time, the writing time is shortened and the information signal has a margin.

1 and 2 are diagrams for explaining the present invention in detail. As an example, assuming a matrix cell of IOX 10, FIG. 1 is a circuit configuration diagram thereof, and FIG. 2 is a diagram for explaining the present invention in detail. It is a pixel configuration diagram. In FIG. 1, the scanning signal lines implementing the present invention are divided into two groups (S11 to S15 and 321 to 525) to be driven alternately from different directions, and can be driven from two directions simultaneously. , one tree from each group, that is, two trees can be selected at the same time. Of course, the principle of the present invention is
The selection is not limited to books, and a desired plurality of books can be selected according to the number of divided groups.

Next, in FIG. 2, if we consider eight pixels surrounded by dotted line A-A' as an example, they correspond to scanning signal lines Sl+ and S21, and these two can be selected at the same time. Therefore, the scanning signal line S11. S21 is selected at the same time, and from the information signal line 11 [black-white], from ■2 [mountain-black], from I3 [white-white], from I4 [black-black]
It would be sufficient if the data could be written, and the writing time saved by selecting 2 water volume would be used to make some improvements to the information signal side. is possible.

[Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 3 is an explanatory diagram of driving waveforms showing an example of a method for driving a ferroelectric liquid crystal element according to the present invention, and FIG.
shows each voltage waveform applied to the scanning signal line and the information signal line, FIG. 3(a) shows the voltage waveform applied to each pixel, and FIG. 3(c) shows the voltage waveform applied to each pixel on the matrix panel. The contents of each pixel are shown below. Note that the writing method is a writing method after erasing the entire surface, and a signal for refreshing the entire surface to "white" is input at the beginning of each signal. Each pixel in FIG. 3(c) is the eight pixels illustrated in FIG. 2, and when these are driven by the scanning signal line and information signal line illustrated in FIG.
, C, D), and a signal line S2 that scans the lower pixels (E, F, G, H).
1 is simultaneously selected, and the information signal line II +I2 *
Writing is performed from I3+Ia.

Here, it is assumed that each pixel inverts its state by applying a pulse of pulse width ΔT and pulse voltage Vth and can be written to, and when 2V<Vth<3V, the data is transferred to two simultaneously selected signal lines Sll and S21. As input voltage waveforms, the upper stage signal line S I + D is 2V.
-IV-OV and AT pulse width 3ΔT that descends in two steps
A voltage of 0 V is applied to the lower signal line S 21 d.
-IV-2V,! :A linearly symmetrical voltage waveform that rises in steps is applied.

When a pulse voltage with a waveform as shown in FIG. 3(A) is applied to the information signal line ll-I4, the voltage waveform applied to each pixel becomes as shown in FIG. 3(B). For example, since a voltage of 3V exceeding Vth is applied to pixel A for the first 67 hours, the state is reversed and "black" is written. On the other hand, since the waveform of the pixel E on the same information signal line Il is symmetrical to that of the pixel A from the scanning signal line S21, a voltage exceeding VLh is not applied to the pixel E, and no inversion of the state occurs. Similarly, pixels B and F on the information signal line 2 are input with an information type symmetrical to the information signal line II.
In this case, contrary to the case of pixels A and E, the upper row B
remains "white", and the lower F is reversed to "black". Pixels C and G with zero information input are both "white", and pixels I and H are both "black".

FIG. 4 is an explanatory diagram showing an example of drive waveforms when the present invention is implemented in the line erase/line write method, and FIG. 4(a) shows each voltage waveform applied to the signal line; Figure (b) shows the voltage waveform applied to each pixel. The illustration of each pixel is the same as in Fig. 3, and the pulse application and writing principles are also almost the same, but since it is a line drive method, a clear signal (-3V) is input on the scanning signal line side just before the scanning signal. It has become so.

5 and 6 are explanatory diagrams showing another example of driving waveforms according to the method of driving a ferroelectric liquid crystal element according to the present invention. This is applied to driving. These are based on the same principle as FIGS. 3 and 4, but in FIGS. 5 and 6, the temporal pattern of the scanning signals of the two selected scanning signal lines S11 and S21 is It is. However, since the waveforms are symmetrical, the multiplicity of the selected scanning signal line is set to 2.
It has the advantage of being easier to increase than books. Of course, it goes without saying that the more the degree of multiplicity is increased, the shorter the writing time will be.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide a method for driving a ferroelectric liquid crystal element that can increase writing speed while preventing reverse bias from being applied to pixels.

[Brief explanation of the drawing]

Fig. 1 is a circuit configuration diagram explaining the present invention in detail, Fig. 2 is a configuration diagram of a matrix cell, Figs. The figure is an explanatory diagram of drive waveforms in a conventional example, and FIGS. 8 and 9 are explanatory diagrams of a ferroelectric liquid crystal element. 1...Substrate, 3...Liquid crystal molecules, Sn...Scanning signal line, ■1...Information signal line.

Claims (4)

[Claims] (1) A driving method for driving a ferroelectric liquid crystal element using a matrix circuit configuration of scanning signal lines and information signal lines, which is characterized in that a plurality of scanning signal lines are simultaneously selected and information signals are written therein. Driving method of liquid crystal element (2) An auxiliary signal is added to the information signal, and the auxiliary signal compensates for all voltages of pixels selected in one simultaneous selection. How to drive a ferroelectric liquid crystal element. (3) The method for driving a ferroelectric liquid crystal element according to claim 1 or 2, wherein the scanning signal waveforms of the plurality of scanning signal lines selected at the same time are different voltage waveforms. . (4) According to any one of claims 1 to 3, the information signal waveform is made different by a combination of pixel patterns on a plurality of simultaneously selected scanning signal lines. ferroelectric liquid crystal device driving method.