JP2633225B2 - 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 phase 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 a scanning electrode group and a signal electrode group in a matrix, filling a liquid crystal compound between the electrodes to form a large number of pixels, and the like. well known. As a driving method of this display element, time division driving 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 by synchronizing the address signal with the signal electrode group. 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
Ifrich) co-authored “Voltage Dependent Optical Activity of a Twisted Nematic Liquid Crystal” (“V
older 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.
369924 and the like. As a bistable liquid crystal, a chiral smectic C phase (SmC
^* ) Or a ferroelectric liquid crystal having an H phase (SmH ^* ). In these states, the liquid crystal takes one of the first optically stable states in response to an applied electric field, and the electric field is applied. It has the property of maintaining its state when not performed, that is, has bistability, has a quick response to a change in electric field, and is expected to be widely used in fields such as high-speed and storage-type display devices.

However, the above-described ferroelectric liquid crystal measures have 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 a white selected pixel to which a half-selection voltage is applied every frame period (the reciprocal of one vertical scanning period that is one frame scanning time) 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.

According to the present invention, first, a liquid crystal panel having a matrix electrode and a chiral smectic liquid crystal constituted by a scanning electrode and a signal electrode, and a scanning selection signal and a scanning non-selection signal are output to the scanning electrode, and the scanning is performed. In a liquid crystal device having a driving unit that outputs an information signal to the signal electrode in synchronization with the output of the line selection signal, the driving unit includes:
Means for outputting a first scan selection signal for each odd-numbered scan electrode block among scan electrode blocks formed of two or more adjacent scan electrodes, thereby executing a first vertical scan; and A second scan selection signal formed with a waveform different from the waveform of the first scan selection signal is output for each even-numbered scan electrode block among the scan electrode blocks, whereby the second vertical A liquid crystal device comprising means for executing scanning, secondly, a liquid crystal panel having a matrix electrode and a chiral smectic liquid crystal formed by a scanning electrode and a signal electrode, and a scanning selection signal applied to the scanning electrode. And a driving means for outputting a scanning non-selection signal and outputting an information signal to the signal electrode in synchronization with the output of the scanning line selection signal. The means includes, based on a scan non-selection signal, a first scan selection signal having a first polarity voltage signal in a first phase and a second polarity voltage signal in a second phase. Means for outputting an odd-numbered scan electrode block among scan electrode blocks formed by matching scan electrodes, thereby executing a first vertical scan, and a first phase based on a scan non-selection signal. A voltage signal of the other polarity, and a second scan selection signal having a voltage signal of one polarity in the second phase, for each of the even-numbered scan electrode blocks among the scan electrode blocks,
This is a liquid crystal device comprising means for executing the second one vertical scan.

[0009]

FIG. 1 shows an example of a driving waveform used as a reference example of the present invention. FIG. 1 shows a scan selection signal S _2n-1 (n = ₂ ) applied to odd-numbered scan electrodes in odd _- numbered frames F _2M-1 and even _- numbered frames F _2M (M = 1, 2, 3,...).
, 1, 2, 3,...) And the scan selection signal S _2n applied to the even-numbered scan electrodes. According to FIG. 1, the scan selection signal S _2n-1 includes an odd frame F _2M-1 and an even frame F _2M.
(M = 1, 2, 3,...) At the same phase (polarity with reference to the voltage of the scanning non-selection signal) are opposite to each other, and the scanning selection signal S _2n is also the same. Further, the scanning selection signal S applied within one frame period
_2n-1 and S _2n have different voltage waveforms from each other,
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.
The combination of the white signal (scanning selection signal S _2n-1 for _2n-1, 2-th voltage 3V ₀ exceeding a threshold voltage of the ferroelectric liquid crystal phase is applied to form a white pixel ) And a holding signal (a 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 )
Is selectively applied, and a voltage -3V ₀ exceeding the threshold voltage of the ferroelectric liquid crystal in the second phase due to the black signal (combined with the scanning selection signal S _2n) is applied to the scanning selection signal S _2n . And a holding signal (a voltage ± V ₀ smaller than the ferroelectric liquid crystal is applied to the pixel by combining the scanning selection signal S _2n with the pixel).

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 a voltage applied to an intersection of the I ₁ -S ₁ scan electrode S ₁ and the signal electrode I ₂ 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 a driving waveform used as a reference example of 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.
When the information signal is set to voltage 0 (the same level as the voltage level of the scanning non-selection signal) in the first phase, and when 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 show examples of driving waveforms used as reference examples of the present invention. 5 and 6, the voltage levels of the scanning selection signal and the information signal are 2
Since the level is set, 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, preferably | Iap |
/|Sap|<1/1.2 is suitable.

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 the white selected pixel outside the present invention.

[0021]

[Table 2]

At the timings in Table 1 according to the present invention, the odd-numbered scanning lines S ₁ , S _{4 at the} even frames F ₂ , F ₄ .
₃ ... while half-select voltage to the pixel (white selection pixels) above is applied, the present invention outside of the even frame F ₂ in the timing in Table 2, F ₄ ... entire scan line when the pixel (the white 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.

FIGS. 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 shown in 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 this 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 a chiral smectic C phase (SmC ^* ) or H phase (SmH ^* ) is preferred. Liquid crystals are suitable. This ferroelectric liquid crystal is described in "Le Journal de Physic Letter"("Le Jo
urnal de Physic Letter ”) 3
6 (L-69), 1975, "Ferroelectric Liquid Crystals"("Ferroelec
tric Liquid Crystals ");" Applied Physics Letters "(" Appli Physics Letters ").
Ed Physics Letters ") 36 volumes (1
No. 1), 1980, "Submicron Second Bistable Electrooptic Switching Switching"
In Liquid Crystal "(" Submicro
Second Bistable Electroloop
tic Switching in Liquid C
rystals ");" Solid State Physics 16 (141) 198
1 "Liquid crystal" and the like, and in the present invention, the ferroelectric liquid crystal disclosed therein can be used.

More specifically, as an example of the ferroelectric liquid crystal compound used in the method of the present invention, decyloxybenzylidene-P'-amino-2-methylbutylcinnamate (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 bold line 123 represents a liquid crystal molecule, and the liquid crystal molecule 123 has a dipole moment (P⊥) 124 in a direction perpendicular 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
Reference numeral 23 has an elongated shape and exhibits refractive index anisotropy in the major axis direction and the minor axis direction. Therefore, for example, if polarizers arranged in a crossed Nicols positional relationship above and below the glass surface, the It is easily understood that the liquid crystal optical deflector changes its optical characteristics depending on the applied polarity. Further, when the thickness of the liquid crystal cell is made sufficiently thin (for example, 1 μm),
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 of the states. 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. First, the response speed is extremely fast, and second, the orientation of the 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. Further, when an electric field Eb in the opposite direction is applied, the liquid crystal molecules are oriented to the second stable state 133b and change the direction of the molecules, but remain in this state even after the electric field is turned off. As long as the applied electric field Ea does not exceed a certain threshold value, each orientation state is 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 the drawings]

FIG. 1 is a waveform diagram of a driving waveform used as a reference example of the present invention.

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

FIG. 3 is a driving waveform diagram used as another reference 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 a driving waveform used as another reference diagram of the present invention.

FIG. 6 is a waveform diagram of a driving waveform used as another reference diagram of the present invention.

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

FIG. 8 is a waveform diagram of a driving waveform 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.

 ──────────────────────────────────────────────────続 き Continuing on 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 Inside the corporation

Claims (2)

(57) [Claims] 1. A liquid crystal panel having a matrix electrode and a chiral smectic liquid crystal constituted by a scanning electrode and a signal electrode, a scanning selection signal and a scanning non-selection signal being output to the scanning electrode, and an output of the scanning line selection signal. In a liquid crystal device having a driving unit that outputs an information signal to the signal electrode in synchronization with the driving unit, the driving unit may output a first scan selection signal from a scan electrode block including two or more adjacent scan electrodes. Means for outputting for each odd-numbered scanning electrode block, thereby executing the first vertical scanning, and a second scanning selection signal formed with a waveform different from the waveform of the first scanning selection signal. A means for outputting an even-numbered scan electrode block among the scan electrode blocks, thereby executing a second one vertical scan. Crystal devices. 2. A liquid crystal panel having a matrix electrode and a chiral smectic liquid crystal constituted by a scanning electrode and a signal electrode, and a scanning selection signal and a scanning non-selection signal are output to the scanning electrode. In a liquid crystal device having a driving unit for outputting an information signal to the signal electrode in synchronization with the driving unit, the driving unit applies a one-polarity voltage signal to a first phase based on a scanning non-selection signal, and a second A first scan selection signal having a voltage signal of the other polarity at the phase of is output for each odd-numbered scan electrode block among the scan electrode blocks composed of two or more adjacent scan electrodes. Means for executing one vertical scan, and a voltage signal of the other polarity in the first phase and a voltage signal of one polarity in the second phase with reference to the scan non-selection signal A second scanning selection signal among the scan electrode block,
A liquid crystal device comprising: means for outputting for each even-numbered scan electrode block, thereby executing a second vertical scan.