JP2547977B2 - Liquid crystal device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal device such as a display panel or a shutter array printer using a ferroelectric liquid crystal.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal display element for displaying an image or information by forming scanning electrodes and signal electrodes in a matrix and filling a liquid crystal compound between the electrodes to form a large number of pixels is often used. Are known. The driving method of this display element is a time-division drive in which an address signal is sequentially and selectively applied to the scanning electrode group and a predetermined information signal is selectively applied in parallel to the signal electrode group in synchronization with the address signal. Has been adopted.

[0003] Most of these services have been used, for example, in "Applied Physics Letters"("App
led Physics Letters ") 197
1 year, 18 (4), pages 127-128. Shut (M. Schadt and W. Helfrich (W. He
lfrich) co-authored “Voltage Dependant Optical Activity of a Twisted Nematic Liquid Crystal” (“V
oltage Dependent Optical
Activity of a Twisted Nem
TN (Twisted Nematic) type liquid crystal shown in "Atomic Liquid Crystal").

In recent years, as an improved type of a conventional liquid crystal element,
The use of bistable liquid crystal devices has been
k) and Lagerwall by both JP-A-56-107216, U.S. Pat.
It is proposed in the specification of 369924. As a bistable liquid crystal, a chiral smectic C phase (SmC
^* ) Or a ferroelectric liquid crystal having an H phase (SmH ^* ) is used, and in these states, either the first optically stable state or the second optically stable state is responsive to an applied electric field. It has a property of maintaining its state when an electric field is not applied, that is, bistability, and has a quick response to changes in the electric field, and is widely used in the fields of high-speed and memory type display devices. Is expected.

However, the above-mentioned ferroelectric liquid crystal device has a problem that flicker occurs during multiplexing driving. In particular, in European Patent Publication No. 149899, an AC voltage in which the phase of the scan selection signal is reversed is applied to each writing frame, and white (cross nicols are arranged to be in a bright state) in a certain frame as shown in FIG. ), And a multiplexing driving method for performing selective writing of black (arranged so that the crossed Nicols are in a dark state) in the subsequent frame is disclosed.

According to such a driving method, at the time of black selective writing after white selective writing, white pixels selectively written in the previous frame are half-selected, and an effective voltage smaller than the writing voltage but applied is applied. become. Therefore, in the multiplexing driving method, at the time of selective writing of black, the half-selection voltage is uniformly reduced to 選 択 for the white selected pixel which is the background of the black character.
The optical characteristics of white selected pixels, which are applied every frame period (the reciprocal of one vertical scanning period which is one frame scanning time) and to which a half selection voltage is applied, change every half frame period. . Therefore, in the case of a display that writes black characters on a white background, the number of pixels that have selected white is overwhelmingly greater than the pixels that have selected black, and the white background appears to flicker. In contrast to the above-described display in which black characters are written on a white background, a flicker also occurs in the case of a white character display on a black background. When the normal frame frequency is set to 30 Hz, the above-mentioned half-selection voltage is applied at the half frame frequency of 15 Hz, which is perceived as a flicker by the observer, and significantly impairs the display quality.

(Summary of the Invention) An object of the present invention is to provide a liquid crystal device which can be applied to a display panel which eliminates the conventional problem of display flicker.

That is, according to the present invention, a liquid crystal panel having a matrix electrode having pixels at intersections of scanning electrodes and signal electrodes and a chiral smectic liquid crystal, and causing the scanning electrodes to output a scanning selection signal and a scanning non-selection signal, In a liquid crystal device having a driving means for outputting an information signal to the signal electrode in synchronization with the output of the scanning selection signal, the driving means has a voltage having one polarity in a first phase with reference to the scanning non-selection signal. A first scan selection signal having a voltage signal of the other polarity in the second phase to the odd-numbered scan electrodes, and a voltage signal of the other polarity in the first phase, and one polarity in the second phase Second scan selection signal having a voltage signal of 1
And means for alternately outputting the second scan selection signal to the scan electrodes, thereby executing the first one vertical scan,
In addition, the first scan selection signal is output to the even-numbered scan electrodes, the second scan selection signal is output to the odd-numbered scan electrodes, and the first and second scan selection signals are alternated. , The second vertical scan is executed by the scan electrode, and the pixel on the scan electrode in which the first scan selection signal is applied to the signal electrode is chiral in the first vertical scan. A first information signal having a voltage waveform for producing the first alignment state of the smectic liquid crystal is output, and a signal electrode in the second one vertical scan is applied to the scan electrode to which the second scan selection signal is applied. The pixel is characterized in that the liquid crystal device is provided with a means for outputting a second information signal having a voltage waveform for producing the second alignment state of the chiral smectic liquid crystal.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of drive waveforms used in the present invention. In FIG. 1, the scan selection signal S _2n-1 (n = 1, 2, 3) applied to the odd-numbered scan electrodes in the odd frame F _2M-1 and the even frame F _2M (M = 1, 2, 3, ...) Is shown. ，
...) and the scan selection signal S applied to the even-numbered scan electrodes.
_2n is shown. According to FIG. 1, the scan selection signal S
_2n-1 is an odd frame F _2M-1 and an even frame F _2M (M =
1, 2, 3, ...) In the same phase, the voltage polarities (voltage polarities based on the voltage of the scanning non-selection signal) are opposite to each other, and so is the scanning selection signal S _2n . further,
Scan selection signals S _2n-1 and S applied within one frame period
_2n has voltage waveforms different from each other, and the voltage polarities of the same phase are opposite to each other.

In the scanning drive waveform example of FIG. 1, the screen is simultaneously stopped (for example, a voltage of 0 is applied to all the pixels constituting the screen all at once).
The third phase of the scanning selection signal is set to voltage 0 (the same level as the voltage of the scanning non-selection signal).

According to FIG. 1, the information signal applied to the signal electrode in the odd frame F _2M-1 is a scanning selection signal S.
_{For 2n-1} , a white signal (combined with the scan selection signal S _2n-1) is applied with a voltage 3V ₀ exceeding the threshold voltage of the ferroelectric liquid crystal in the second phase to form a white pixel. ) And a holding signal (the voltage ± V ₀ smaller than the threshold voltage of the ferroelectric liquid crystal is applied to the pixel by combining the scanning selection signal S _2n-1 )
Are selectively applied, and a voltage -3V ₀ that exceeds the threshold voltage of the ferroelectric liquid crystal is applied in the second phase by the black signal (combined with the scanning selection signal S _2n) with respect to the scanning selection signal S _2n . To form a black pixel) and a holding signal (scanning selection signal S
_The voltage ± V ₀ smaller than that of the ferroelectric liquid crystal is applied to the pixel by the combination with _2n ).

In the even-numbered frame F _2M following the writing of the above-mentioned odd-numbered frame F _2M-1 , the information signal applied to the signal electrode includes a black signal similar to that described above with respect to the scanning selection signal S _2n-1 . The holding signal is selectively applied, and the scanning selection signal S
A white signal and a holding signal similar to those described above are selectively applied to _2n .

FIG. 2 is a timing chart when the display state shown in FIG. 7 is written by the drive waveform shown in FIG. In FIG. 7, ○ indicates a white pixel, and ● indicates a black pixel. 2 is a time series waveform of the voltage applied to the intersection of the I ₁ -S ₁ scan electrode S ₁ and the signal electrode I ₁ in FIG.
I ₂ -S ₁ is a time series waveform of the voltage applied to the intersection between the scanning electrode S ₁ and the signal electrode I _2.

FIG. 3 shows another example of drive waveforms used in the present invention. The scan selection signals S _2n-1 and S _2n used in the driving example shown in FIG. 3 have two voltages having opposite polarities with respect to the voltage of the scan non-selection signal, respectively, and the first half voltage pulse The waveform has a width set to twice the width of the reverse polarity voltage pulse in the latter half. Further, as the information signal, the voltage 0 (the same level as the voltage level of the scanning non-selection signal) is set in the first phase, and the scanning non-selection signal voltage is used as a reference in the second and third phases, The alternating voltages have opposite polarities. FIG. 4 shows a time-series waveform when writing is performed on the display example shown in FIG. 7 by the driving example of FIG.

FIGS. 5 and 6 represent another preferred drive waveform example of the present invention. In the drive waveform examples of FIGS. 5 and 6, the voltage levels of the scan selection signal and the information signal are set to two levels, respectively, so that the design of the drive circuit can be simplified.

In the above-described driving example, the amplitude 2 |
The amplitude of the information signal is set to | ± V ₀ | with respect to ± V ₀ |, but in the present invention, the amplitude of the scanning selection signal is set to | Sap
| And the amplitude of the information signal is | Iap |
| / | Sap | ≦ 1 can be set, and preferably | Ia
It is suitable that p | / | Sap | <1 / 1.2.

In the present invention, when the ferroelectric liquid crystal has two threshold voltages V _th1 and −V _th2 (V _th1 , V _th2 > 0), V ₀ <V _th1 between the aforementioned V _0. <3V ₀ , −3V ₀ <−V _th2 <−V ₀

Table 1 below shows that when forming a white selected pixel,
The timing at which the white selection voltage Sw applied to the pixel and the half selection voltage H at that time are applied in the frames F ₁ , F ₂ , F ₃ , F ₄ ...

[0019]

[Table 1]

Table 2 below shows the timing of writing white selected pixels, which is not included in the present invention.

[0021]

[Table 2]

According to the timing of Table 1 according to the present invention, odd-numbered scanning lines S ₁ , S in the even-numbered frames F ₂ , F _4, ...
₃ ... The half selection voltage is applied to the upper pixels (white selected pixels), while at the timing of Table 2 outside the present invention, the pixels (white pixels) on all the scanning lines at the time of even frames F ₂ , F ₄ ... A half selection voltage is applied to the selected pixel). Therefore, as described above, in a driving example outside the present invention, flicker occurs at a half frame frequency. On the other hand, in the present invention, the number of pixels to which the half-selection voltage is applied in one frame period is ２ of that in the driving example shown in Table 2, so that flicker is effectively prevented.

8 and 9 show a driving example of the present invention. That is, in the driving example shown in FIG. 8, the scan selection signal applied to the first, second, fifth, sixth,... 4N-3rd, 4N-2th scan electrodes and the third, fourth, seventh scan electrodes
The scan selection signals applied to the fourth, eighth,..., 4N−1, and 4Nth scan electrodes differ from frame to frame as shown (N = 1, 2, 3,...). In the driving example of FIG. 9,
.. The first, second, third,... 6N-5th, 6N-4th, 6N-3rd scanning electrodes and the fourth, fifth, sixth,. -1
The scan selection signals applied to the 6th and 6Nth scan electrodes differ from frame to frame as shown (N = 1, 2).
…). Here, N is the number of blocks obtained by dividing the scanning line into a plurality of groups. In the driving examples of FIGS. 8 and 9, the number of scanning lines in the block is two and three, respectively, but the present invention is not limited to that number.

FIG. 11 shows a driving device of the ferroelectric liquid crystal panel 111 on which the matrix electrodes used in the present invention are arranged. In the panel 111 of FIG. 11, a scanning line 112 and a data line 113 are wired so as to cross each other, and a ferroelectric liquid crystal is arranged between the scanning line 112 and the data line 113 at the intersection. In FIG. 11, 114 is a scanning circuit, 115 is a scanning side driving circuit, 116 is a signal side driving voltage generating circuit, 117 is a line memory, 118 is a shift register, 119 is a scanning side driving voltage generating power supply, and 110 is a microprocessor. Represents a unit (MPV).

The scanning-side drive voltage generation power supply 119 is provided with voltages V ₁ , V ₂ and V _C. For example, the voltages V ₁ and V ₂ are used as the power supply for the above-described scanning selection signal, and the voltage V _C is not selected for scanning. It can be a power source for signals.

As the liquid crystal having bistability which can be used in the driving method of the present invention, a chiral smectic liquid crystal having ferroelectricity is most preferable, and among them, a chiral smectic C phase (SmC ^* ) or H phase (SmH ^* ). LCD is suitable. For this ferroelectric liquid crystal,
Journal de Physic Letter ”(“ LeJo
urnal de PhysicLetter ") 36
Volume (L-69), 1975, "Ferroelectric Liquid Crystals"("Ferroelevt
ric Liquid Crystals ”);“ Applied Physics Letters ”(“ Applie ”
d Physical letters ") Volume 36 (11
No.), 1980, "Submicron Second By Stable Electro-Optic Switching In Liquid Crystal"("Submicro S
second Bistable Electroopt
ic Switching in Liquid Cr
ystals ");" Solid State Physics 16 (141) 1981.
As described in “Liquid crystal” and the like, the ferroelectric liquid crystal disclosed therein can be used in the present invention.

More specifically, as an example of the ferroelectric liquid crystal compound used in the method of the present invention, decyloxybenzylidene-P'-amino-2-methylbutyl cinnamate (D
OBAMBC), hexyloxybenzylidene-P'-
Amino-2-chloropropylcinnamate (HOBAC
PC) and 4-o- (2-methyl) -butylresorcylidene-4'-octylaniline (MBRA8).

When an element is formed using these materials, the element is maintained as necessary so that the liquid crystal compound is in the SmC ^* phase or the SmH ^* phase. Can be supported.

In the present invention, it is also possible to use ferroelectric liquid crystals represented by chiral smectic F phase, I phase, J phase, G phase and K phase in addition to the above-mentioned SmC ^* and SmH ^* .

FIG. 12 schematically illustrates an example of a ferroelectric liquid crystal cell. 121a and 121b are In ₂ O
₃ , a substrate (glass plate) coated with a transparent electrode such as SnO ₂ or ITO (indium-tein-oxide). In the meantime, SmC ^* phase liquid crystal in which the liquid crystal molecular layer 122 is oriented so as to be perpendicular to the glass surface is sealed. A thick line 123 represents a liquid crystal molecule, and the liquid crystal molecule 123 has a dipole moment (P⊥) 124 in a direction orthogonal to the molecule. Substrates 121a and 12
When a voltage higher than a certain threshold is applied between the electrodes on 1b,
The orientation direction of the liquid crystal molecules 123 can be changed so that the helical structure of the liquid crystal molecules 123 is released and the dipole moment (P⊥) 124 is all directed to the electric field direction. Liquid crystal molecule 1
23 has an elongated shape and exhibits refractive index anisotropy in the major axis direction and the minor axis direction thereof. Therefore, for example, if polarizers arranged in a crossed Nicols positional relationship are placed above and below the glass surface, It is easy to understand that the liquid crystal optical modulator has optical characteristics that change depending on the applied polarity. Furthermore, when the liquid crystal cell is made sufficiently thin (for example, 1 μ),
As shown in FIG. 13, even when no electric field is applied, the helical structure of the liquid crystal molecules is unwound and its dipole moment Pa
Or Pb is upward (134a) or downward (134b)
Take either state. In such a cell, as shown in FIG.
b for a predetermined time, the dipole moment becomes electric field Ea
Or, the liquid crystal molecules are turned to the upward direction 134a or the downward direction 134b with respect to the electric field vector of Eb, and accordingly, the liquid crystal molecules are shifted to the first stable state 133a or the second stable state 133.
b.

There are two advantages of 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. The second point will be described with reference to FIG. 13, for example. When electrification Ea is applied, the liquid crystal molecules are oriented to a first stable state 133a, and this state is stable even after the electrification is turned off. When a reverse electric field Eb is applied, the liquid crystal molecules are oriented in the second stable state 133b to change the orientation of the molecules, but they remain in this state even when the electric field is cut off. Further, unless the applied electric field Ea exceeds a certain threshold value, the respective alignment states are also maintained. In order to effectively realize such a high response speed and bistability, it is preferable that the cell is as thin as possible, and generally, 0.5 μm to 20 μm, particularly 1 μm to 5 μm is suitable.

[0032]

According to the present invention, it is possible to eliminate the occurrence of flicker that occurs during writing by the conventional driving method, and as a result, it is possible to improve the display quality.

[Brief description of drawings]

FIG. 1 is a waveform diagram of drive waveforms used in the present invention.

FIG. 2 is a time-series waveform diagram when the waveform of FIG. 1 is used.

FIG. 3 is a drive waveform chart used as another specific example of the present invention.

FIG. 4 is a time-series waveform diagram when the waveform of FIG. 3 is used.

FIG. 5 is a waveform diagram of drive waveforms used as another specific example of the present invention.

FIG. 6 is a waveform diagram of drive waveforms used as another specific example of the present invention.

FIG. 7 is a plan view showing a display example.

FIG. 8 is a waveform diagram of drive waveforms used in the present invention.

FIG. 9 is a waveform diagram of another drive waveform used in the present invention.

FIG. 10 is a drive waveform diagram outside the present invention.

FIG. 11 is a block diagram of a display panel of the present invention.

FIG. 12 is a perspective view of a chiral smectic liquid crystal element used in the present invention.

FIG. 13 is a perspective view of another chiral smectic liquid crystal element used in the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tadashi Mihara 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Yoshihiro Onitsuka 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Incorporated (56) References JP-A 61-18931 (JP, A) JP-A 61-94026 (JP, A)

Claims (1)

(57) [Claims] 1. A liquid crystal panel having a matrix electrode having pixels at intersections of scanning electrodes and signal electrodes and a chiral smectic liquid crystal, and a scanning selection signal and a scanning non-selection signal which are output to the scanning electrodes. In the liquid crystal device having a driving unit that outputs an information signal to the signal electrode in synchronism with the output of, the driving unit supplies a voltage signal of one polarity to the first phase on the basis of the scanning non-selection signal, and The first scan selection signal having the voltage signal of the other polarity in the second phase is output to the odd-numbered scan electrodes, the voltage signal of the other polarity in the first phase, and the voltage signal of the one polarity in the second phase. Have second
Means for causing the even-numbered scan electrodes to be output and alternately outputting the first and second scan selection signals to the scan electrodes, thereby executing the first one vertical scan, and The first scan selection signal is output to even-numbered scan electrodes, the second scan selection signal is output to odd-numbered scan electrodes, and the first and second scan selection signals are alternately scanned. The signal is output to the electrode, thereby performing the second vertical scanning, and in the first vertical scanning, the pixel on the scan electrode to which the first scan selection signal is applied to the signal electrode is a chiral smectic liquid crystal. Output a first information signal having a voltage waveform for producing a first alignment state of, and a signal electrode in a second vertical scanning,
The pixel on the scan electrode to which the second scan selection signal is applied includes means for outputting a second information signal having a voltage waveform for causing the second alignment state of the chiral smectic liquid crystal. Liquid crystal device.