JPS63118130A - Liquid crystal device - Google Patents

Abstract

PURPOSE:To minimize the influence of a nonselection signal upon a nonselection line and to eliminate a flicker on a display screen by providing a means which applies an auxiliary signal, comparing two successive information signals with each other, and determining the auxiliary signal. CONSTITUTION:An information signal applied to a data line IM (Mth data line and M is an integer) is used to determine the voltage of an auxiliary signal applied between write signals Wn and Wn+1 by comparing the (n)th (n: integer) write signal Wn with the (n+1)th write signal Wn+1 following it. Namely, W1W,2<(>B<)>,3n<...>, where the superscript W is a white write signal, B is a black write signal, and K1,2,3...n is the auxiliary signal. Consequently, the mean value of voltages applied to picture elements at the time of nonselection is substantially 0 and a flicker on the display screen is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal device, and particularly to a liquid crystal device using ferroelectric liquid crystal.

(Description of Prior Art) Conventionally, liquid crystal displays display images or information by configuring a scanning electrode group and a signal electrode group in a matrix, and filling a liquid crystal compound between the electrodes to form a large number of pixels. The element is well known. The driving method for this display element is time-division driving, in which an address signal is selectively and periodically applied 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. It has been adopted.

Most of these that were put to practical use were, for example, “Applied Physics Letters” (“Applied Physics Letters”).
Physics Letters”) 1971,
18(4), pp. 127-128, M. Shutt (
M, 5chadt) and W, Heflich (W, He1fr
ich) Co-author of “Voltage Dependent Optical Activity of a Twisted Nematic Liquid Crystal” (Volt
age Dependent 0ptical
Activity of Twisted N
ematic Liquid Crystal”)
TN (twisted nematic
) type liquid crystal.

In recent years, the use of bistable liquid crystal elements as an improved version of conventional liquid crystal elements has been proposed by both C1ark and Lagerwall in Japanese Patent Application Laid-open No. 107216/1982 and U.S. Pat. No. 4,367,924.
It is proposed in the specification etc. As a bistable liquid crystal,
Generally, chiral smectic C phase (SmC*) or H
A ferroelectric liquid crystal having a phase (SmH*) is used, and in these states assumes either a first optically stable state or a second optically stable state in response to an applied electric field, In addition, it has the property of maintaining its state when no electric field is applied, that is, it has stability, and it responds quickly to changes in the electric field, so it is expected to be widely used in fields such as high-speed and memory-type display devices.

(Problem to be solved by the invention) However, when the number of display pixels is extremely large (and high-speed driving is required), a problem arises. The threshold voltage for providing the first stable state in the liquid crystal cell is −Vt.
hl, and the threshold voltage for providing the second stable state is +
V th2, even if these threshold voltages are not exceeded, if the voltage continues to be applied for a long time, the display state written in the pixel (for example, white state) will change to another display state (for example, black state). ) may be reversed. FIG. 7 shows the threshold characteristics of a bistable ferroelectric liquid crystal cell.

Figure 7 is a plot of the application time dependence of the threshold voltage (v th) required for switching when DOBAMBC (72 in the figure) and HOBACPC (71 in the figure) are used as ferroelectric liquid crystals. .

As is clear from FIG. 7, the threshold value vth has application time dependence, and it is understood that the shorter the application time, the steeper the slope. From this, when applied to an element that has an extremely large number of scanning lines and is driven at high speed, for example, even if a certain pixel is switched to the bright state during scanning, the information signal below vth will always be lower than vth from the next scanning. It can be seen that if the voltage continues to be applied, there is a risk that the pixel will turn into a dark state during the completion of scanning one screen.

Therefore, when multiplexing drive is applied to a ferroelectric liquid crystal element, a low voltage with the opposite polarity to that during writing may continue to be applied for a long time to pixels when not selected, and this may cause crosstalk. It was singing.

It is proposed to apply a waveform signal including a write signal and an auxiliary signal to the data line so that an alternating current voltage is applied to the pixel.

The problem of crosstalk could be solved by the above-mentioned method of Sake et al. ) have the same polarity continuously, the same polarity pulse continues to be applied to the pixel for a time of at least 2Δt, and this causes screen flickering that occurs when used as a display panel (the display surface periodically (a phenomenon in which the light becomes brighter or darker).

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a liquid crystal device using a novel driving method that solves the problems with conventional optical modulation elements, particularly liquid crystal display elements or liquid crystal optical shutters, as described above.

[Means for Solving the Problems] and [Operation] The present invention provides a liquid crystal element in which a ferroelectric liquid crystal is arranged between intersecting scanning lines and data lines, a means for sequentially selecting scanning lines, and n. In synchronization with the scan selection signal applied to the scan line, the n-th first write signal W(n
1) and a means for selectively applying a second write signal Wn', and a means for selectively applying a second write signal Wn' to the data line in synchronization with the scan selection signal applied to the n+1th scan line, with the potential of the unselected scan line as a reference. The n+1th first
write signal W n'+1 and a second write signal W. 2+
1 (however, the n-th first write signal Wn' is applied to the n+1-th first write signal W(n1
)゜1 and n-th second write signals Wn2 and n+1
The n-th second write signal W(n1) and the second write signal W(n1) have the same polarity with respect to the potential of the unselected scanning line.
2n and an n+1 first write signal Wn'. , and the second write signal W n
n+1st write signal W n+ 1 with '++
and means for comparing the nth write signal W. and n+1
The liquid crystal device is characterized in that it has means for applying an auxiliary signal during the th write signal W , , .

The "write signal" described in this specification is applied from the data line at a phase that determines the write state of the pixel (determines the pixel to be either white or black) within the address period in which the scanning lines are sequentially addressed. is an information signal that
Further, the "auxiliary signal" refers to a voltage applied from the data line with a phase that does not determine the write state of the pixel within the address period.

Furthermore, the "polarity" of the voltages applied to the scanning lines and data lines described in this specification is based on the potential of unselected scanning lines.

〔Example〕

FIG. 8 is a plan view of a ferroelectric liquid crystal cell 81 used in the present invention. This ferroelectric liquid crystal cell 81 has data lines 83 (1
+, 2+...) and the scanning line 82 (S+, S2,
) are wired to cross each other. Further, 84 is a scanning circuit, 85 is a scanning side drive voltage generation circuit, 86 is a No. 3 side drive voltage generation circuit, 87 is a line memory, and 88 is a shift register.

FIG. 1 shows a first driving example of the present invention.

In the figure, St, Sz, and Ss are scanning lines S, , S,.

It represents the voltage waveform applied to S3, and the scanning line Sl
, St + s, a sequential scan selection signal S is applied. I1 and 12 represent voltage waveforms applied to data lines I and I2, and data lines ! 1 is white - one white, one black, one white...
The information signals . . . , . Also, (rl-8,) is the scanning line S and the data line ■
The voltage waveform applied to the intersection (pixel) with (12
-St) is a voltage waveform applied to the intersection (pixel) of the scanning line S and the data line I2.

In the driving example shown in FIG. 1, in the erase step T, a voltage 3vo exceeding the threshold voltage of the ferroelectric liquid crystal is applied to all or some of the pixels of the ferroelectric liquid crystal cell 61, and the pixel is is reset to a first optical state (eg, "white") based on a first stable state of the image. Subsequently, in writing step T2, scanning lines SL+S2. S3 is a sequential scanning selection signal S.
.

is applied and synchronized with this scanning selection signal S5, data)! By applying information signals to It and Iz, the display shown in FIG. 6 can be obtained.

Data line IM (MUMth data line, M is 1.2,
3. The information signal to be applied to the nth (integer of n
=1.2,3. . . . ) write signal W. and the following n+1th write signal W 11. , the voltage of the auxiliary signal Kn to be applied between the write signal Wn and Wn or 1 is determined. Among the information signals applied to the data lines 11 and I2 in FIG.
, j +, Is, ) 3. , . . . n (subscript W represents a white write signal, B represents a black write signal) is a write signal, and K 1.2.3. ...7 is an auxiliary signal. At this time, the n-th white write signal wnw (+vo) and n+1
The auxiliary signal K is applied between the th white write signal Wn'* and (+Vo). is the nth white write signal W(n1)
and voltage of opposite polarity -■. Then, the nth black write signal w
n'(-vo) and the n+1st black write signal W- and +(
The auxiliary signal Kn applied between the n-th black write signal Wn'' and the n-th black write signal Wn'' is a voltage +V0 of opposite polarity.Furthermore,
The nth is the white write signal Wnw (or black write signal W,
B), the n+1th following is the black write signal W,
, 1 (or white write signal wn'), voltage 0 is applied as the auxiliary signal Kn. Therefore, in the present invention, a period of 2Δt (referred to as 2Tb pulse) in which pulses of the same polarity are continuous does not occur during selection and non-selection immediately after selection, and the voltage applied to the pixel during non-selection is eliminated. The average value of can be made substantially zero. Furthermore, the present invention was able to prevent flickering on the display screen by eliminating the 2Tb pulse described above.

At this moment, the voltage v0 is +3VOl>Ivthl>lv, l
(vth is the threshold voltage of the ferroelectric liquid crystal).

Also, phase 1 in FIG. is a write signal W having a pulse width Δt. The phase t2 corresponds to the phase of applying the auxiliary signal K.
. This corresponds to the phase at which . Auxiliary signal K at this time
It is also preferable to set the application time of n to Δt.

The drive example shown in FIG. 2 uses three types of voltages as auxiliary signals: an AC voltage having three alternating positive and negative polarity pulses of the voltage O1, and an AC voltage with the opposite phase. This is exactly the same as the driving example shown in FIG. Further, in the present invention, instead of being limited to three alternating currents in which positive and negative pulses are alternately applied, an alternating current voltage having an odd number of alternating pulses can be used.

FIG. 3 represents another preferred driving example of the present invention. In the driving example shown in FIG. 3, a voltage of 3.times.3 is uniformly applied to all or some of the pixels on the scanning line selected at phase t1. By applying an erase pulse of signal wn'(vo) and white write signal W. '(+vo) is selectively applied. The following auxiliary signal is applied at phase t3 in a manner similar to that described in FIGS. 1 and 2 above.

FIG. 4 represents another preferred driving example of the present invention. In the drive example shown in FIG. 4, phase 1. Apply a voltage of −3× uniformly to all or part of the pixels on the selected scan line. By applying an erase pulse of , these pixels can uniformly reset their previous written state. phase t
3 corresponds to the write phase, and at this phase t3, the black write signal WnB (VO) and the white write signal Wr1w (
-V. ) is selectively applied, and the phase t2 is the auxiliary signal K.

This corresponds to the phase at which . To this auxiliary signal, l is applied in a manner similar to that described in FIG.

Next, a block diagram of the drive circuit is shown in FIG.

To explain FIG. 5 together with the time chart shown in FIG. 6, at timing t=1, the information of the first line is transferred to the shift register (S/R), and at timing t=2,
The contents of shift register S/R are stored in line memory I. At timing t=3, the information in the blank memory I is transferred to the line memory 11, and at the same time, the line memory and the line memory I! The comparator 51 compares the information of the data and transfers the result to the line memory III.

That line memory! The drive mode processor 52 mixes the information in the line memory III and the information in the line memory III, and the line decoder 53 converts the 1-bit signal into 2-bit signals.
The level converter 54 and the analog switch section 55 produce an output waveform.

At t=3, the contents of the shift register at t=1 are output, and are sequentially output thereafter.

In Figure 5, CK and CK2 are clocks, LAT
H is the latch signal input, IN is the input of information data to the shift register S/R%"001VSS+ and Vs1+2
is the voltage supply source necessary to drive the analog switch, V
, ,V, and V2 are output level voltages.

The optical modulating substance used in the liquid crystal device of the present invention has at least two stable states, and in particular takes either a first optically stable state or a second optically stable state depending on the applied electric field. In other words, a material having a bistable state with respect to an electric field, particularly a liquid crystal having such properties, is used.

As the liquid crystal having bistability that can be used in the driving method of the present invention, chiral smectic liquid crystal having ferroelectricity is most preferable, and among these, chiral smectic liquid crystal
Phase (SmC*) or H-phase (SmH*) liquid crystals are suitable. Regarding this ferroelectric liquid crystal, “Le Journard
``Le Journ''
alde physiove 1etter”)3
Volume 6 (L-69), 1975 “Ferroelectric Liquid Crystals J (rFerroel
electric Liquid Crystals”
):”Applied Physics Letters’°(“A
pplied Physics Letters”)3
Volume 6 (No. 11) 1980 “Submicron Second Bistiple Electro-Optic Switching in Liquid Crystal J (rsubm
icr.

5econd B15table Electro
optic Switching in Liq
uid Crystals”);”Solid State Physics 16 (
141) 1981 r Liquid Crystal", etc., and the ferroelectric liquid crystal disclosed therein can be used in the present invention.

More specifically, examples of S-primarily dielectric liquid crystal compounds used in the method of the present invention include decyloxybenzylidene-P'-
Amino-2-methylbutylcinnamate (DOBAMB)
C), hexyloxybenzylidene-P'-amino-2
-chloropropyl cinnamate (HOBACPC) and 4-8-(2-methyl)-butylresorsilitin-4
'-octylaniline (MBRA8) and the like.

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

In addition to the above-mentioned SmC book and SmH book, the present invention also uses chiral smectic F phase, ■ phase, and J phase.

It is also possible to use a ferroelectric liquid crystal that appears in a G phase.

FIG. 9 schematically depicts an example of a ferroelectric liquid crystal cell. 91a and 91b are In, O,.

SnO, ITO (indium tin oxide)
It is a substrate (glass plate) coated with transparent electrodes such as
In between, SmC* phase liquid crystal in which liquid crystal molecules N92 are oriented perpendicular to the glass surface is sealed. A thick line 93 represents a liquid crystal molecule, and this liquid crystal molecule 93
has a dipole moment (P) 94 in the direction perpendicular to its molecule. When a voltage higher than a certain dark value is applied between the electrodes on the substrates 91a and 91b, the helical structure of the liquid crystal molecules 93 is unraveled, and the liquid crystal molecules 93 are aligned so that all dipole moments (P) 94 are oriented in the direction of the electric field. You can change direction.

The liquid crystal molecules 93 have an elongated shape and exhibit refractive index anisotropy in the major and minor axis directions. Therefore, for example, if polarizers are placed above and below the glass surface in a crossed nicol positional relationship, It is easily understood that the liquid crystal optical modulation element is a liquid crystal optical modulation element whose optical characteristics change depending on the polarity of applied voltage. Furthermore, if the thickness of the liquid crystal cell is made sufficiently thin (for example, 1μ
), as shown in Fig. 10, even when no electric field is applied, the helical structure of the liquid crystal molecules is released, and the dipole moment Pa or pb is either upward (104a) or downward (104b). take a state. When an electric field Ea or Eb of different polarity above a certain threshold value is applied to such a cell for a predetermined period of time as shown in FIG.
04a or downward 104b, and accordingly, the liquid crystal molecules are aligned in either the first stable state 103a or the second stable state 103b.

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 a bistable state. To explain the second point using, for example, FIG.
When the electric field Ea is applied, the liquid crystal molecules enter the first stable state 103
a, and this state is stable even when the electric field is turned off. Also, when applying an electric field Eb in the opposite direction, the liquid crystal molecules
The molecules are oriented in a stable state 103b and change their orientation, but they remain in this state even after the electric field is turned off. Also, give electricity! ! As long as p and Ea do not exceed a certain dark value,
They are still maintained in their respective orientation states. In order to effectively realize such fast response speed and bistability, it is preferable that the cell be as thin as possible, and generally 0.5 μ to 20 μ, particularly 1 μ to 5 μ is suitable.

(Effect of the invention) By comparing the preceding and following information signals and determining the auxiliary signal as described above, the influence of the non-selected signal on the non-selected line can be minimized, and the display screen It is possible to realize an extremely excellent display without flickering.

[Brief explanation of the drawing]

FIG. 1, FIG. 2, FIG. 3, and FIG. 4 are timing charts showing drive waveforms used in the present invention in a time series. FIG. 5 is an explanatory diagram showing the sequence up to the output of the information signal used in the present invention, and FIG. 6 is a timing chart at that time. FIG. 7 is a characteristic diagram showing the application time dependence of the threshold voltage of a ferroelectric liquid crystal. FIG. 8 is a plan view of the matrix electrode structure used in the present invention. 9 and 10 are schematic perspective views of the ferroelectric liquid crystal element used in the present invention.

Claims (8)

[Claims] (1) A liquid crystal element in which a ferroelectric liquid crystal is arranged between intersecting scanning lines and data lines, and means for sequentially selecting scanning lines;
In synchronization with the scan selection signal applied to the nth scan line,
The n-th first write signal W_(n^1) and the second write signal W_(n^2), which have opposite polarities with respect to the potential of the unselected scanning line, are applied to the data line. The means for selectively applying voltage and the scan selection signal applied to the n+1th scanning line are applied to the data line in synchronization with the scanning selection signal applied to the n+1th scanning line. First write signal W_(n^1)_+_
1 and the second write signal W_(n^2)_+_1 (however, the n-th first write signal W_
(n^1) and the n+1th first write signal W_(n^
1)_+_1 and nth second write signal W_(n
^2) and the n+1th second write signal W_(n^2)
___+_1 has the same polarity with respect to the potential of the unselected scanning line), and the n-th first write signal W_(
n^1) and a second write signal W_(n^2), an n+1th first write signal W_(n^1)_+_1 and a second write signal W_
n+1st write signal W with (n^2)_+_1
_n_+_1; and means for applying an auxiliary signal between the n-th write signal W_n and the n+1-th write signal W_n_+_1. (2) The n-th first write signal W_(n^1) and the auxiliary signal have opposite polarities with respect to the potential of an unselected scanning line. liquid crystal device. (3) The n-th second write signal W_(n^2) and the auxiliary signal have opposite polarities with respect to the potential of an unselected scanning line. liquid crystal device. (4) The n-th first write signal W_(n^1), the second write signal W_(n^2) and the auxiliary signal are selected and have opposite polarities with respect to the potential of the non-scanning line. A liquid crystal device according to claim 1, wherein: (5) the auxiliary signal has an odd number of alternating positive and negative pulses based on the potential of an unselected scanning line;
The n-th first write signal W_(n^1) or the n-th second write signal W_(n^2) is the first auxiliary signal with respect to the potential of the unselected scanning line. The liquid crystal device according to claim 1, wherein the pulse has a polarity opposite to that of the pulse. (6) The n-th first write signal W_(n^1) and the n+1-th second write signal W_(n^2)_+_1
2. The liquid crystal device according to claim 1, wherein the auxiliary signal applied between is 0 volts with respect to the potential of the unselected scanning line. (7) The liquid crystal device according to claim 1, wherein the ferromagnetic liquid crystal is a chiral smectic liquid crystal. (8) The liquid crystal device according to claim 7, wherein the thickness of the chiral smectic liquid crystal is set to be sufficiently thin to eliminate the helical structure of the chiral smectic liquid crystal.