JPH07109457B2 - Liquid crystal device - Google Patents

Description

Description: 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 phase.

[Prior 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 and filling a liquid crystal compound between the electrodes to form a large number of pixels is often used. Are known. As a driving method of this display element, there 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 to the signal electrode group in parallel in synchronization with the address signal. Has been adopted.

Most of these practical applications were, for example, “Applied Physics Letters”.
"Tters") 1971, 18 (4), pages 127-128, co-authored by M. Schadt and W. Helfrich, "Voltage Day Pendant Optical Activity of.""A twisted nematic liquid crystal"("Voltage Dependent Opti
cal Activity of a Twisted Nematic Liquid Crysta
It was a TN (Twisted Nematic) type liquid crystal shown in l ").

In recent years, the use of bi-stable liquid crystal elements as an improved version of conventional liquid crystal elements has been disclosed by both Clark and Lagerwall in JP-A-56-107216 and US Pat. No. 4,367,924. It is proposed in the calligraphy. As the bistable liquid crystal, a ferroelectric liquid crystal having a chiral smectic C phase (SmC ^* ) or an H phase (SmH ^* ) is generally used, and in these states, the first liquid crystal responds to an applied electric field. Of the optical stable state and the second optical stable state, and has the property of maintaining that state when an electric field is not applied, that is, bistability, and has a quick response to changes in the electric field. Therefore, it is widely used in the field of high-speed and memory type display devices and the like.
This ferroelectric liquid crystal element can be driven by the method disclosed in US Pat. No. 4,548,476 or US Pat. No. 4,655,561.

However, the above-mentioned ferroelectric liquid crystal device has a problem that flicker occurs during multiplexing driving. In particular, in European Publication No. 149899, an AC voltage in which the phase of the scan selection signal is reversed for each writing frame is applied, and white (cross nicol is turned into a bright state in a certain frame as shown in FIG. 8). There is disclosed a multiplexing driving method in which selective writing of (arrangement) is performed and black (cross nicol is arranged so as to be in a dark state) is selectively written in a subsequent frame.

In such a driving method, when the black is selectively written after the white is selectively written, the white pixels selectively written in the previous frame are half-selected, and an effective voltage smaller than the writing voltage is applied. Therefore, in this multiplexing driving method, at the time of selective writing of black, the half-selected voltage is uniformly applied to the selected white pixels which are the background of the black characters at a half frame period (one vertical scanning which is one frame scanning time). In the white selected pixel to which the half selection voltage is applied every half frame period, the optical characteristics change every 1/2 frame period. Therefore, in the case of a display in which black characters are written on a white background, the number of pixels for which white is selected is overwhelmingly larger than the number of pixels for which black is selected, and the white background appears to flicker. Further, in contrast to the above-described display in which black characters are written on a white background, flicker is also observed in the case of a black character white display. When the normal frame frequency is set to 30 Hz, the above half-select voltage is applied at a half frame frequency of 15 Hz, so that it is perceived as flicker by an observer, and the display quality is significantly impaired.

[Outline of Invention]

An object of the present invention is to provide a liquid crystal device using a chiral smectic liquid crystal, which eliminates the conventional problem of display flicker.

That is, the present invention is directed to a liquid crystal panel including a matrix electrode composed of a scanning electrode group and a signal electrode group and a chiral smectic liquid crystal, a scanning side driving means to which the scanning electrode group is connected, and a signal side driving to which the signal electrode group is connected. A driving device having means, wherein the scanning side driving means divides the scanning electrode group into a plurality of blocks within one vertical scanning period,
Each block is composed of a plurality of scan electrodes, and one polarity voltage is applied to the plurality of scan electrodes in the block sequentially and alternately for each block based on the voltage applied to the scan non-selection electrodes. Outputting a first scan selection signal and a second scan selection signal having a voltage of the other polarity and having a voltage waveform different from that of the first scan selection signal;
And, in at least two vertical scanning periods, outputting the first scan selection signal and the second scan selection signal to a plurality of scan electrodes in the block, and The signal-side driving means includes the first and second
The liquid crystal device is characterized in that it outputs an information signal composed of an alternating voltage waveform in synchronism with the scan selection signal.

[Detailed Description of Embodiments of the Invention]

FIG. 1 is an example of a reference drive waveform outside the present invention. FIG. 1 shows an odd frame F _2M-1 and an even frame F _2M (M = 1,2,3,
, And the scan selection signal S _2n-1 (n = 1, 2, 3, ...) Applied to the odd-numbered scan electrodes and the scan selection signal S _2n applied to the even-numbered scan electrodes. According to FIG. 1, the scanning selection signal S _2n-1 is determined by the voltage polarity (the voltage of the scanning non-selection signal) in the same phase between the odd frame F _2M-1 and the even frame F _2M (M = 1,2,3, ...). (The voltage polarities based on the above) are opposite to each other, and so are the scan selection signals S _2n . Further, the scan selection signals S _2n-1 and S _2n applied within one frame period have different voltage waveforms, and the voltage polarities of the same phase are opposite to each other.

Further, in the scan drive waveform example of FIG. 1, the phase for suspending the screen all at once (for example, applying the voltage 0 to all the pixels forming the screen at the same time) is provided first, and the scan selection signal The first and third phases are set to voltage 0 (the same level as the voltage of the scanning non-selection signal).

Further, according to FIG. 1, the information signal applied to the signal electrodes in odd-numbered frame F _2M-1, with respect to the scanning selection signal S _2n-1 Synthesis of the white signal (scanning selection signal S _2n-1 As a result, a voltage 3V ₀ that exceeds the threshold voltage of the ferroelectric liquid crystal is applied in the second phase to form a white pixel) and a holding signal (scan selection signal S _2n-1 ) dielectric voltage ± V ₀ is smaller than the threshold voltage of the liquid crystal is applied) and is selectively applied for the scanning selection signal S _2n by synthesizing a black signal (scanning selection signal S _2n, 2 th A voltage lower than the ferroelectric liquid crystal is applied to the pixel by combining the holding signal (scanning selection signal S _2n ) with a voltage −3V ₀ that exceeds the threshold voltage of the ferroelectric liquid crystal applied to form a black pixel. ± V ₀ is applied) and are selectively applied.

Even frame F following writing of odd frame F _2M-1 above
_{At 2M} , as the information signal to be applied to the signal electrode, for the scanning selection signal S _2n-1 , the black signal and the holding signal similar to the above are selectively applied, and for the scanning selection signal S _2n . Is
The white signal and the holding signal similar to those described above are selectively applied.

FIG. 2 shows a timing chart when the display state shown in FIG. 7 is written by the drive waveform shown in FIG. In FIG. 7, circles represent white pixels, and black circles represent black pixels. 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 of the scan electrode S ₁ and the signal electrode I ₂ .

FIG. 3 shows another reference drive waveform example other than the present invention. Scan selection signals S _2n-1 and S used in the driving example shown in FIG.
_2n is a drive waveform in which the first phase of the voltage 0 of the scan selection signal shown in FIG. 1 is _removed , and the scanning time is shorter than that in FIG. Further, the information signal has a form in which the first phase of the voltage 0 in the information signal shown in FIG. 1 is removed similarly to the scanning selection signal, and the first and second information signals shown in FIG. When the scanning non-selection signal voltage is used as a reference in each phase, the alternating voltages have mutually opposite polarities.

FIG. 4 shows another reference drive waveform example other than the present invention. In the drive waveform example of FIG. 4, the relationship between the white signal or the black signal of the information signal and the voltage waveform of the holding signal is a relationship in which the phases are merely shifted, so that it is possible to further reduce the flicker.

Further, in the present invention, the ferroelectric liquid crystal has two threshold voltages V _th1 and −
When it has V _th2 (V _th1 , V _th2 > 0), the relation of V ₀ <V _th1 <3V ₀ , −3V ₀ <−V _th2 <−V ₀ is established with V ₀ described above.

5 and 6 show a driving example of the present invention. That is, in the driving example shown in FIG. 5, the 1st, 2nd, 5th, 6th
4N-3rd, 4N-2nd scan selection signals to be applied to the 2nd scanning electrode and 3rd, 4th, 7th, 8th, ... 4N-1
The scan selection signals applied to the 4th and 4Nth scan electrodes are different for each frame as shown (N = 1, 2, 3, ...).
Further, in the driving example of FIG. 6, the first, second, third, ... 6N-
Scan selection signals applied to the 5th, 6N-4th, 6N-3rd scan electrodes, and 4th, 5th, 6th, ... 6N-2nd, 6N
The scan selection signals applied to the -1st and 6Nth scan electrodes are different for each frame as shown (N = 1, 2,
…). The above N is the number of blocks obtained by dividing the scanning line into a plurality of grapes. In the driving examples of FIGS. 5 and 6, the number of scanning lines in the block is two and three, respectively, but the present invention is not limited to that number.

Further, in the present invention, when the pulse width of the one polarity voltage or the other polarity voltage of the scan selection signal is ΔT, the application period of the voltage of the same level as the voltage applied to the scan non-selection electrode of the scan selection signal is set. It can be set to 2ΔT or more.

FIG. 9 shows a driving device for the ferroelectric liquid crystal panel 111 in which the matrix electrodes used in the present invention are arranged. 9th
In the panel 111 in the figure, the scanning lines 112 and the data lines 113 intersect each other, and the ferroelectric liquid crystal is arranged between the scanning lines 112 and the data lines 113 at the intersections. or,
In FIG. 9, 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 micro processor. It represents a unit (MPU).

The scanning-side drive voltage generating power supply 119 is provided with voltages V ₁ , V ₂ and Vc. For example, the voltages V ₁ and V ₂ are used as the power supply for the scan selection signal and the voltage Vc is used as the power supply for the scan non-selection signal. be able to.

As a liquid crystal having bistability that 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 among them is most preferable.
A liquid phase of phase (SmC ^* ) or H phase (SmH ^* ) is suitable. For this ferroelectric liquid crystal, please refer to "Le Journal de
"Fujitsu Letter"("Le Journal de Physic letter
r ") 36 (L-69), 1975" Ferroelectric Liquid Crystals "(" Ferroelectric Liquid
Crystals ");" Applied Physics Letters "36 (11), 198
"Submicron Second Bistable Electro-Switching In Liquid Crystal"("Submicro Second Bistable Electro
optic Switching in Liquid Crystals ”);“ Solid physics
16 (141) 1981 "Liquid Crystal", US Patent No. 4561726, US Patent No. 4589996, US Patent No. 4592858, US Patent No. 4596667, US Patent No. 4613209, US Patent No. 4639089. Etc., and the ferroelectric liquid crystal disclosed therein can be used in the present invention.

More specifically, examples of the ferroelectric liquid crystal compound used in the method of the present invention include desiloxybenzylidene-P'-amino-2-methylbutylcinnamate (DOBAMBC) and hexyloxybenzylidene-P'-amino-. 2-chloropropyl cinnamate (HOBACPC) and 4-o- (2
-Methyl) -butyl resorcylidene-4'-octylaniline (MBRA8) and the like.

When a device is constructed using these materials, the device is supported by a copper block with a heater embedded, if necessary, in order to keep the liquid crystal compound in a temperature state in which it is in the SmC ^* phase or SmH ^* phase. be able to.

Further, in the present invention, in addition to SmC ^* and SmH ^* described above, it is also possible to use a ferroelectric liquid crystal exhibiting a chiral smectic F phase, I phase, J phase, G phase or K phase.

FIG. 10 is a schematic drawing of an example of a ferroelectric liquid crystal cell. 121a and 121b are substrates (glass plates) coated with transparent electrodes such as In ₂ O ₃ , SnO ₂ and ITO (indium-thein-oxide), between which the liquid crystal molecular layer 122 is perpendicular to the glass surface. Liquid crystal of SmC ^* phase oriented like this is enclosed. 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. Boards 121a and 1
When a voltage above a certain threshold is applied between the electrodes on 21b,
The helical structure of the liquid crystal molecule 123 is unwound, and all the dipole moments (P⊥) 124 are oriented in the direction of the electric field.
The orientation direction of can be changed. The liquid crystal molecules 123 have an elongated shape and exhibit refractive index anisotropy in the major axis direction and the minor axis direction thereof. Therefore, for example, if polarizers arranged in a crossed Nicol positional relationship above and below a glass surface are placed. It is easily understood that the liquid crystal optical modulation element has optical characteristics that change depending on the polarity of voltage application. Furthermore, when the thickness of the liquid crystal cell is made sufficiently thin (for example, 1 μ), the helical structure of the liquid crystal molecules is unraveled and the dipole moment Pa or Pb is It takes either the upward (134a) or downward (134b) state. To such a cell, as shown in FIG. 11, when electric fields Ea or Eb having different polarities equal to or more than a certain threshold value are applied for a predetermined time,
The dipole moment changes direction to upward 134a or downward 134b with respect to the electric field belt of the electric field Ea or Eb, and the liquid crystal molecules are accordingly oriented to either the first stable state 133a or the second stable state 133b. To do.

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. Explaining the second point with reference to FIG. 11, for example, when the electric field Ea is applied, the liquid crystal molecules are aligned in the first stable state 133a, but this state is stable even when the electric field is cut off. In addition, when a reverse electric field Eb is applied, the liquid crystal molecules are in the second stable state 13
It is oriented in 3b and changes its molecular orientation, but it remains 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, generally 0.5 μ to 20 μ, and particularly 1 μ to
5 is suitable.

〔The invention's effect〕

According to the present invention, it is possible to eliminate the occurrence of flickering 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 a reference drive waveform outside the present invention, and FIG. 2 is a time-series waveform diagram when using it. 3 and 4 are waveform diagrams of other reference drive waveforms outside the present invention.
5 and 6 are waveform diagrams of drive waveforms used in the present invention. FIG. 7 is a plan view showing a display example. FIG. 8 is a drive waveform diagram outside the present invention. FIG. 9 is a block diagram of the display panel of the present invention. 10 and 11 are perspective views of the ferroelectric liquid crystal device used in the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-60-235121 (JP, A) JP-A-61-228496 (JP, A) JP-A-61-286819 (JP, A) JP-A-63- 180937 (JP, A)

Claims (7)

[Claims] 1. A liquid crystal panel comprising a matrix electrode composed of a scanning electrode group and a signal electrode group and a chiral smectic liquid crystal, a scanning side driving means connected to the scanning electrode group and a signal side driving means connected to the signal electrode group. Wherein the scanning side driving means divides the scan electrode group into a plurality of blocks within one vertical scanning period, and each block is constituted by a plurality of scan electrodes, and within each block. A plurality of scan electrodes sequentially and alternately for each block, having a first scan selection signal having one polarity voltage and the other polarity voltage with reference to the voltage applied to the scan non-selection electrodes, A second scanning selection signal having a voltage waveform different from that of the first scanning selection signal, and at least 2
Within one vertical scanning period, the first scanning selection signal and the second scanning selection signal are output to the plurality of scanning electrodes in the block, and the signal side driving means is provided. However, the liquid crystal device is configured so as to output the information means having an alternating voltage waveform in synchronization with the first and second scan selection signals. 2. The first scanning selection signal has a first same-level voltage that is the same level as the voltage applied to the one polarity voltage and the scanning non-selection voltage with reference to the scanning non-selection signal, The second scan selection signal has a second same-level voltage that is the same level as the other polarity voltage and the voltage applied to the scan non-selection electrode based on the voltage applied to the scan non-selection electrode. Generates a voltage having a polarity opposite to the one-polarity voltage with reference to the voltage applied to the scanning non-selective electrode, and a voltage that exceeds one threshold voltage of the chiral smectic liquid crystal by a combined voltage with the one-polarity voltage. The first threshold voltage of the chiral smectic liquid crystal is opposite to that of the other polarity voltage based on the first information signal having a voltage or the voltage applied to the scanning non-selection electrode, and the combined voltage of the other polarity voltage and the other polarity voltage. Voltage liquid crystal device of the second information signal a is Claims claim 1 wherein with voltage causing beyond the. 3. The first information signal is a voltage having the same polarity with respect to the one polarity voltage with reference to the voltage applied to the scan non-selection electrodes when the first and second same level voltages are applied. The second information signal is a voltage having the same polarity with respect to the other polarity voltage based on the voltage applied to the scan non-selection electrodes when the first and second same level voltages are applied. The liquid crystal device according to claim 2, further comprising: 4. When the pulse width of the one polarity voltage or the other polarity voltage is ΔT, the application period of the first and second same-level voltages is a period of 2ΔT, and the application period of the 2ΔT is In the period ΔT of the period, the first information signal has a voltage having the same polarity with respect to the one polarity voltage with respect to the voltage applied to the scanning non-selection electrode, and the second information signal Has a voltage having the same polarity with respect to the voltage of the other polarity with respect to the voltage applied to the scan non-selection electrode, and in the other period ΔT of the period of 2ΔT, the first Information signal and second
4. The liquid crystal device according to claim 3, wherein said information signal has the same voltage level as the voltage applied to the scanning non-selection electrodes. 5. When the pulse width of the one polarity voltage or the other polarity voltage is ΔT, the application period of the first and second same level voltages is a period of 2ΔT, and the application period of the 2ΔT is In the period ΔT of the period, the first information signal has a voltage having the same polarity with respect to the one polarity voltage with respect to the voltage applied to the scanning non-selection electrode, and the second information signal Has a voltage at the same level as the voltage applied to the scanning non-selection electrodes,
In the other period ΔT of the 2ΔT period, the first information signal has a voltage of the same level as the voltage applied to the scanning non-selection electrodes, and the second information signal is scanning non-selection. 4. The liquid crystal device according to claim 3, wherein the liquid crystal device has a voltage having the same polarity as the other polarity voltage based on the voltage applied to the electrodes. 6. The liquid crystal device according to claim 1, wherein the film thickness of the chiral smectic liquid crystal is set to be sufficiently thin so as to eliminate the helical structure inherent thereto when no electric field is applied. 7. The liquid crystal device according to claim 1, wherein one vertical scanning period is one frame or one field period.