JPH0422493B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal device using ferroelectric liquid crystal that can be applied to a liquid crystal display device or a liquid crystal one-light shutter array device.

[Description of prior art]

Conventionally, liquid crystal display elements are well known in which a scanning electrode group and a signal electrode group are configured in a matrix, and a liquid crystal compound is filled between the electrodes to form a large number of pixels to display images or information. . 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 Rhysics Letter”) 1971, No. 184
“Voltage Dependant Optical” co-authored by M. Schadt and W. Helfrich, published on pages 127-128.
Activity of a Twisted Nematic Liquid Crystal” (“Voltage”)
Dependent Optical Activity of a Twisted
Nematic Liquid Crystal”)
(twistednematic) 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 Clark and Lagerwall in Japanese Patent Application Laid-open No. 107216/1983 and US Patent No.
It has been proposed in the specification of No. 4367924, etc. As a bistable liquid crystal, a ferroelectric liquid crystal having a chiral smectic C phase (SmC ^* ) or H phase (SmH ^* ) is generally used. It has the property of taking either the first optically stable state or the second optically stable state and maintaining that state when no electric field is applied, that is, it has stability and has a response to changes in the electric field. It is expected that it will be widely used in fields such as quick, high-speed, and memory-type display devices.

[Problem that the invention seeks to solve]

However, problems arise when the number of display pixels is extremely large and high-speed driving is required.
That is, the threshold voltage for providing the first stable state in a ferroelectric liquid crystal cell having bistability for a predetermined voltage application time is -Vth ₁ , and the threshold voltage for providing the second stable state is -Vth 1. +Vth ₂ ,
Even if these threshold voltages are not exceeded, if the voltage continues to be applied for a long time, the display state written to the pixel (e.g., white state) will be reversed to another display state (e.g., black state) Sometimes. 1st
The figure represents the threshold characteristics of a bistable ferroelectric liquid crystal cell.

Figure 1 plots the application time dependence of the threshold voltage (Vth) required for switching when DOBAMBC (12 in the figure) and HOBACPC (11 in the figure) are used as ferroelectric liquid crystals.

As is clear from Fig. 1, the threshold value Vth is dependent on the application time, and the shorter the application time, the more
It is understood that the slope is steep. 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 will always be below Vth from the next scanning onwards. 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.

[Means for Solving the Problems] and [Operations] An object of the present invention is to provide a novel method for driving a liquid crystal element that solves the problems in conventional liquid crystal display elements or liquid crystal light shutters as described above. It is in.

Another object of the present invention is to provide a method for driving a liquid crystal element having high-speed response.

Another object of the present invention is to provide a method for driving a liquid crystal device having high density pixels.

The present invention provides a matrix electrode structure in which a pixel is formed at the intersection of a scanning electrode group and a signal electrode group, and a first a liquid crystal cell having a ferroelectric liquid crystal that produces a stable state in response to an electric field of the other polarity and a second stable state in response to an electric field of the other polarity; b. A scan selection signal in which a pulse is set to have a longer pulse width than a subsequent pulse is sequentially applied, and within the application period of the previous pulse, the first pulse is simultaneously applied to the signal electrode group and to the pixels on the scan electrode selected for scan. A bipolar pulse is applied such that a voltage of one polarity is applied that causes a stable state of the pulse, and within the application period of the subsequent pulse, selectively applies to the signal electrode group and the pixel on the scanning electrode. by applying a pulse of opposite polarity to the subsequent pulse so that a voltage of the other polarity that produces the second stable state is applied to the pixel on the scan electrode selected for the scan. Then, apply the next scan selection signal to the scan electrode selected for scan after the application of the scan selection signal to the scan electrode immediately before it is completed, and then apply the next scan selection signal to the scan electrode that has not been selected for scan. to the pixel of
A first feature of the present invention is a liquid crystal device having: a means for applying an alternating voltage that maintains a write state during scan selection; is arranged between a matrix electrode structure forming a pixel, the scanning electrode group and the signal electrode group, and produces a first stable state with respect to an electric field of one polarity, and a second stable state with respect to an electric field of the other polarity. a liquid crystal cell having a ferroelectric liquid crystal that produces a stable state; b sequentially applying a scan selection signal having one polarity pulse and the other polarity pulse to the front and rear scan electrodes, respectively, to the signal electrode group; In synchronization with the previous one polarity,
Applying a voltage signal such that a voltage of one polarity that causes the first stable state is simultaneously applied to the pixels on the scanning electrode selected for scanning, and applying a voltage signal to the signal electrode group with the subsequent pulse of the other polarity. synchronously with the subsequent other polarity pulse such that a voltage of the other polarity that selectively causes the second stable state is applied to the pixels on the scan electrode; applying information pulses of the same polarity or opposite polarity to the group of signal electrodes located before and after the information pulse, and located before the next information pulse for the scan electrode to be scanned next; By applying a pulse having a polarity opposite to the information pulse and having a pulse width smaller than that of the information pulse, writing is performed to the pixel on the scan electrode selected for scanning, and the pixel on the scan electrode selected for scanning is written. For pixels on no scanning electrodes,
A means for applying an alternating voltage that maintains a writing state at the time of scanning selection; Thirdly, the present invention is characterized by: The matrix electrode structure is arranged between the scanning electrode group and the signal electrode group, and produces a first stable state with respect to an electric field of one polarity and a second stable state with respect to an electric field of the other polarity. a liquid crystal cell having a ferroelectric liquid crystal to be generated; b) sequentially applying a scan selection signal having one polarity pulse, voltage O and the other polarity pulse to the scan electrode in the order of a first phase, a second phase and a third phase; and applying to the signal electrode group, in a first phase, a voltage of one polarity that simultaneously brings about the first stable state in the pixels on the scan selected scan electrode. Put the pixel in the erased state,
In a second phase, a voltage is applied to the pixel on the scanning electrode, which has a polarity opposite to the voltage applied in the first phase and maintains the erased state, and in a third phase,
a bipolar pulse synchronized with the period consisting of the first phase and the second phase, such that a voltage of the other polarity that causes the second stable state is selectively applied to pixels on the scanning electrode; By applying an information signal having one polarity or the other polarity pulse synchronized with the three phases, writing is performed to the pixels on the scan electrodes selected for scanning, and to pixels on the scan electrodes not selected for scanning. ,
The present invention is characterized by a liquid crystal device comprising: means for applying an alternating voltage to maintain a written state during scan selection;

Note that the polarities of the voltages applied to the scan electrodes and the signal electrodes are based on the voltages applied to scan electrodes that are not selected for scanning.

In a preferred embodiment of the present invention, a scanning electrode group is sequentially and periodically selected based on a scanning signal, a signal electrode group facing the scanning electrode group and selected based on a predetermined information signal, and a gap between the two electrodes. orienting the liquid crystal to a first stable state by means of a selected scanning electrode of a liquid crystal element having at least a ferroelectric liquid crystal held at a constant temperature and having at least two stable states with respect to an electric field, and an electric signal of a signal electrode. a first phase t ₁ with a voltage that provides an electric field in one direction and a third phase t with a voltage that assists in reorienting said liquid crystal to a second stable state in response to an electrical signal of a signal electrode; ₃
and an electrical signal having a second phase.
At _t2 , the signal electrode group can be driven by applying an electric signal having a voltage polarity opposite to that of the electric signal applied at the first phase _t1 based on predetermined information. can.

〔Example〕

The optical modulation substance used in the driving method 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. . That is, a substance having a bistable state with respect to an electric field, particularly a liquid crystal having such a property, is used.

As ^the 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.
Phase (SmH ^* ) liquid crystal is suitable. This ferroelectric liquid crystal is described in “Le Journal de Physiove Letters”, Volume 36 (L
-69), 1975's "Ferroelectric Liquid Crystals"
Crystals”; “Applied Physics Letters”, Volume 36 (11
Issue) 1980 "Submicron Second Bistable Electro-Optical Switching in Liquid Crystals"
(“Submicro Second Bistable Electrooptie
"Switching in Liquid Crystals");"Solidsubstance"
161411981 "Liquid Crystal", etc., and the ferroelectric liquid crystal disclosed therein can be used in the present invention.

More specifically, examples of ferroelectric liquid crystal compounds used in the method of the present invention include decyloxybenzylidene-P'-amino-2-methylbutylcinnamate (DOBAMBC), hexyloxybenzylidene-P'-amino- 2-chloropropyl cinnamate (HOBACPC) and 4-0-(2-methyl)
-butylresolcylidene-4'-octylaniline (MBRA8) and the like.

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

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

FIG. 2 schematically depicts an example of a ferroelectric liquid crystal cell. 21a and 21b are In ₂ O ₃ , SnO ₂ or
It is a substrate (glass plate) coated with a transparent electrode such as ITO (indium-tein-oxide).
In between, a liquid crystal of SmC ^* phase, which is oriented such that a liquid crystal molecular layer 22 is perpendicular to the glass surface, is sealed.
The thick line 23 represents liquid crystal molecules,
This liquid crystal molecule 23 has a dipole moment (P⊥) 14 in a direction perpendicular to the molecule. When a voltage higher than a certain threshold is applied between the electrodes on the substrates 21a and 21b, the helical structure of the liquid crystal molecules 23 is unraveled, and the alignment direction of the liquid crystal molecules 23 is changed so that all dipole moments (P⊥) 24 are directed in the direction of the electric field. can be changed. The liquid crystal molecules 23 have an elongated shape and exhibit refractive index anisotropy in the long axis direction and the short axis direction. Therefore, for example, polarizers arranged in a crossed nicol position can be placed above and below the glass surface. For example, 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), the helical structure of the liquid crystal molecules will unravel even when no electric field is applied, as shown in Figure 3, and the dipole moment Pa or Pb will be It takes either an upward direction 34a or a downward direction 34b. When an electric field Ea or Eb of different polarity above a certain threshold value is applied to such a cell for a predetermined time as shown in Fig. 3, the dipole moment will change depending on the electric field Ea or Eb.
The liquid crystal molecules are oriented in either the first stable state 33a or the second stable state 33b, depending on the electric field vector.

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 with reference to FIG. 2, for example, when the electric field Ea is applied, the liquid crystal molecules are oriented in the first stable state 33a, but
This state remains stable even when the electric field is turned off. When an electric field Eb in the opposite direction is applied, the liquid crystal molecules are oriented to a second stable state 33b and change their orientation, but they remain in this state even after the electric field is turned off. Further, as long as the applied electric field Ea does not exceed a certain threshold value, each orientation state is maintained. In order to effectively realize such fast response speed and bistability, it is preferable for the cell to be as thin as possible, generally 0.5μ to 20μ, especially
1μ to 5μ is suitable.

Preferred specific examples of the driving method of the present invention will be explained with reference to FIGS. 4 to 7.

FIG. 4 is a schematic diagram of a cell 41 having a matrix electrode structure in which a ferroelectric liquid crystal compound is sandwiched between. 42 is a scanning electrode group, and 43 is a signal electrode group. Now, to simplify the explanation, an example will be shown in which a black and white binary signal is displayed. In FIG. 4, it is assumed that the pixels indicated by diagonal lines correspond to "black" and the others correspond to "white". FIGS. 5a and 5b respectively show a scan selection signal applied to a selected scan electrode and a scan non-selection signal applied to other scan electrodes (unselected scan electrodes),
FIGS. 5c and 5d represent information selection signals applied to selected signal electrodes and information non-selection signals applied to unselected signal electrodes, respectively. These information selection signals and information non-selection signals each represent different voltage waveforms, and have the same polarity at the first phase _t1 . In FIGS. 5a to 5d, the horizontal axis represents time and the vertical axis represents voltage. t ₁ , t ₂ and t ₃ within the write period are the first and second
This shows that it is the third phase. In this example, t ₁ = t ₂
= _t3 . Writing periods are sequentially selected for the scan electrode group 42 .

Now, the threshold voltage at the application time Δt to give the first stable state (this is white) of a liquid crystal cell having bistability is set to -Vth ₁ , and the second stable state (this is black) is set as -Vth 1. ), the electric signal applied to the selected scanning electrode is 2V ₀ at phases (times) t ₁ and t ₂ as shown in Figure _5a. , at phase t ₃ −
The voltage waveform is 2V ₀ . Further, the other scanning electrodes are in a grounded state as shown in FIG. 5b, and receive an electrical signal O. On the other hand, the electrical signal applied to the selected signal electrode is -V at phase _t1 and _-V0 at phases _t2 and _t3 , as shown in FIG. 5c. Also, the electrical signal applied to the unselected signal electrodes is -V ₀ at phase t ₁ as shown in FIG. 5d. In the above, the voltage value V ₀ is V ₀ <Vth ₂ <3V ₀ and −3V ₀ <−Vth ₁ <−V ₀
is set to a desired value that satisfies FIG. 6 shows the voltage waveform applied to each pixel when such an electric signal is applied.

In FIG. 6, a and b are on the selected scanning electrode, respectively, and are pixels to be displayed with "black" and "white", and c and d are pixels on the unselected scanning electrode, respectively. This is the voltage waveform applied to the As is clear from FIG. 6, all or a predetermined portion of the pixels on the selected scanning electrode are initially affected by the voltage −3V ₀ that exceeds the threshold voltage −Vth ₁ in the first phase t ₁ . It can be arranged in one dan white. This is called the erasure phase. Among these pixels, the pixel to be displayed as "black" transitions to the other optically stable state ("black") because a voltage 3V ₀ exceeding the threshold voltage Vth ₂ is applied at the third phase t ₃ . This is defined as the display selection phase. In addition, in the case of a pixel that exists on the same scanning electrode and is to be displayed as "white", the applied voltage at the third phase _t3 is a voltage _V0 that does not exceed the threshold voltage -Vth. It remains stable.

On the other hand, on unselected scan electrodes, the voltages applied to all pixels are ±V or 0, neither of which exceeds the threshold voltage. Therefore, the liquid crystal molecules maintain the orientation corresponding to the display state when scanned last time without changing the orientation state. That is, when a scanning electrode is selected, first in the first phase t ₁ it is aligned to one optically stable state "white", and then in the third phase t ₃ the selected pixel is aligned It is transferred to the other optically stable state (black), one line of signals is written, and that signal state can be maintained until the next frame is selected. .

FIG. 7 shows the drive signals described above in chronological order. S ₁ -S ₅ are scanning signals applied to the scanning electrodes, I ₁ and I ₃ are information signals applied to the signal electrodes, and A and C are applied to pixels A and C shown in Fig. 4. It is a voltage waveform.

Now, the mechanism of switching by an electric field in a ferroelectric liquid crystal in a bistable state is not necessarily clear from a microscopic perspective, but in general, it is switched to a predetermined (first) stable state by a strong electric field for a predetermined period of time. If the electric field is left in a state where no electric field is applied after that, it is possible to maintain that state almost semi-permanently, but if the electric field is so weak that it does not switch for a certain period of time (in the example explained earlier,
(corresponding to voltages below Vth), if an electric field of opposite polarity is applied for a long time, the orientation state will transition again to the opposite (second) stable state, resulting in the correct orientation. Situations may arise where the display or modulation of information is not achievable. The present inventors have discovered that the ease with which transition of the orientation state (a type of crosstalk) occurs due to the application of such a weak electric field for a long time depends on the material of the substrate surface,
Although it has been recognized that it is affected by roughness, liquid crystal material, etc., it has not yet been determined quantitatively.
However, it has been confirmed that when a uniaxial substrate treatment for aligning liquid crystal molecules is performed, such as rubbing or oblique evaporation of SiO, etc., the tendency for the above-mentioned transition to occur tends to increase. ,
It was also confirmed that this tendency was stronger at higher temperatures.

In any case, in order to achieve correct information display and modulation, it is preferable to avoid applying an electric field in a fixed direction for a long time.

Therefore, in the driving method of the present invention, the first phase is
At t ₁ , all the pixels on the scanning electrode are set to "white", and at the third phase t ₃ , the corresponding pixels are rewritten to "black" according to the information, but in this embodiment, The voltage for making it "white" in the first phase _t1 is _-3V0 , and its application time is Δt. On the other hand, the voltage to change to "black" is 3V ₀
, and the application time is Δt. In addition, the voltage applied to each pixel at times other than scanning is at most 1±
V ₀ 1, and the longest time it is continuously applied can be determined by providing the auxiliary phase (auxiliary signal application phase), which is the second phase of applying the auxiliary signal that does not determine the display state of the pixel. 2Δt at a point like 71 shown in Figure 7, crosstalk does not occur at all, and once the scanning of the previous screen is completed, the displayed information is retained semi-permanently, so it has bistability. There is no need for a refresh process as in display elements using ordinary TN liquid crystals. Moreover, in the present invention, since the voltage waveform applied to the pixel when scanning is not selected is 2Δt at maximum, it is possible to set a wide voltage margin during driving without causing an inversion phenomenon.

Example 1 A polyimide film of about 300 Å was formed by spin coating on a pair of glass plates patterned with transparent conductive films (ITO) mutually forming a 500×500 matrix. Each substrate was subjected to a rubbing treatment using a roller with a terrene cloth wrapped around the back surface, and the substrates were bonded together so that the rubbing directions matched to form a cell. The cell spacing at this time is approximately 1.6μ. Desyloxybenzylidene-P'-amino-2-methylbutylcinnamate (DOBAMBC), a ferroelectric liquid crystal, was injected into this cell.
By slowly cooling from the heated molten state, a uniform monodomain state in the SmC ^* state was obtained. cell temperature
When controlling the temperature at 70℃ and performing line-sequential scanning with the settings V ₀ = 10V, t ₁ = t ₂ = t ₃ = Δt = 50 μsec based on the driving method shown in Figure 3, extremely good results were obtained. Image obtained.

A driving example that is a further improvement of the driving example described above is shown in FIGS.
It is shown in FIG.

FIGS. 8a and 8b respectively show a scan selection signal applied to a selected scan electrode and a scan non-selection signal applied to other scan electrodes (unselected scan electrodes). Phases t ₁ and t ₃ correspond to the above-mentioned erasure phase and display selection phase. phase t ₂
is the aforementioned auxiliary phase (auxiliary signal application phase). This is the same as the applied voltage used in the above driving example.
In this driving example, it is possible to further provide an auxiliary phase as the fourth phase _t4 that does not determine the display state of the pixel. The voltage applied to all scanning electrode lines in the fourth phase t ₄ is 0V, and the auxiliary signal applied to the signal electrodes is from ±V ₀ with opposite polarity to the voltage waveform applied in the third phase t ₃ . voltage is applied.

When scanning is not selected, the voltage applied to each pixel is maximum 1±
V ₀ 1, and the longest time that ±V ₀ is continuously applied is at a point 101 as shown in Figure 10 due to the auxiliary signals applied at phases t ₂ and t ₄ .
2Δt, and the number of times this 2Δt occurs is small, and 2Δt alternates, and the weak voltage applied to each pixel when scanning is not selected becomes small, so crosstalk does not occur at all, and scanning of the entire screen is completed once. Since the displayed information is then retained semi-permanently, there is no need for a refresh process, as is the case with display elements using normal TN liquid crystals that do not have bistability.

Further, in the present invention, the above-mentioned phase t ₄ is the above-mentioned phase
It may be before t ₁ .

11 to 13 show another embodiment of the present invention. FIGS. 11a and 11b show scan selection signals applied to selected scan electrodes and scan non-selection signals applied to other scan electrodes (unselected scan electrodes), respectively. Phases t ₁ and t ₃
corresponds to the erase phase and the display selection phase.
Phases t ₂ and t ₄ are phase auxiliaries that apply auxiliary signals that do not determine the display state. The scan selection signal applied to the selected scan electrode is 3V 0 at phase (time) t 1 and 3V ₀ at phase (time) t ₁ as shown in FIG.
The voltage waveform is 0 at _t2 , _-2V0 at phase _t3 , and 0 at phase _t4 . The other scanning electrodes are in a grounded state as shown in FIG. 11b, and have an electrical signal of 0. On the other hand, the information selection signal applied to the selected signal electrode is 0 at phase t 1 and −V ₀ at phase t ₁ as shown in FIG. 11c _.
is +V ₀ at phase t ₃ and −V ₀ at phase t ₄ . Further, the information non-selection signal applied to the unselected signal electrode is 0 at phase t ₁ and +V ₀ at phase t ₂ , as shown in FIG. 11d.
-V ₀ at phase t ₃ and V ₀ at phase t ₄ . Here, each phase is t ₁ =t ₃ , t ₂ =t ₄ , and 1/2t ₁ =t ₂ . In the above, the voltage value V ₀ is set in the same manner as in the driving example described above. FIG. 12 shows the voltage waveform applied to each pixel when such an electric signal is applied.

In FIG. 12, a and b are on the selected scanning electrode, respectively, and correspond to the pixels to display "black" and "white", and c and d are on the unselected scanning electrode, respectively. This is the voltage waveform applied to the pixel. All or a predetermined pixel on the selected scanning electrode is first aligned to one white level at the first phase _t1 , similar to the driving example described above. this house,
A pixel to be displayed as "black" is displayed as black based on the other optically stable state at the third phase _t3 .
Furthermore, in the case of a pixel that exists on the same scanning electrode and is to be displayed as "white," the applied voltage at the third phase _t3 is a voltage _V0 that does not exceed the threshold voltage _Vth1 . remains in the state.

On the other hand, on unselected scanning electrodes,
As in the driving example described above, the voltages applied to all pixels are ±V or 0, and neither exceeds the threshold voltage. Therefore, the liquid crystal molecules maintain the orientation corresponding to the signal state when scanned last time without changing the orientation state. That is, when a scanning electrode is selected, first in the first phase t ₁ it is aligned to one optically stable state "white", and then in the second phase t ₂ the selected pixel is aligned It is transferred to the other optically stable state (black), one line of signals is written, and that signal state can be maintained until the next frame is selected. .

FIG. 13 shows the drive signals described above in chronological order. S ₁ to _{S 5} are electrical signals applied to the scanning electrodes, I ₁ and I ₃ are electrical signals applied to the signal electrodes, and A and C are applied to pixels A and C shown in Fig. 4. It is a voltage waveform.

In this embodiment, the voltage for making it "white" in the first phase _t1 is _-3V0 , and its application time is Δt.
On the other hand, the voltage for rewriting to "black" is 3V ₀ , and the application time is also Δt. In addition, the voltage applied to each pixel at times other than scanning is at most 1±
V ₀ is 1, and the longest time it is continuously applied is 2.5Δt due to the auxiliary signals applied at phases t ₂ and t ₄ , for example, even when the white signal-white signal is continuous. Moreover, since the weak voltage applied to each pixel is small, crosstalk does not occur at all, and once the entire screen has been scanned, the displayed information is retained semi-permanently.

FIGS. 14 to 16 show another example of driving according to the present invention. FIG. 14a shows a scan selection signal applied to a selected scan electrode line, which is 2V ₀ at phase t ₁ , 0 at phase t ₂ , and −2V ₀ at phase t ₃ . FIG. 14b shows a scanning non-selection signal applied to an unselected scanning electrode line, with phases t ₁ ,
It remains 0 between t ₂ and t ₃ . Figure 14c is
An information selection signal applied to a selected signal electrode,
-V ₀ at phase t ₁ and V ₀ at phases t ₂ and t ₃ . Figure 14d shows an information non-selection signal applied to an unselected signal electrode, with a voltage waveform that alternates with -V ₀ at phase t ₁ , V ₀ at phase t ₂ , and -V ₀ at phase t ₃ . ing.

Figure 15a shows the voltage waveform when the aforementioned scan selection signal and information selection signal are applied synchronously to the pixel, and Figure 15b shows the voltage waveform when the scan selection signal and information non-selection signal are applied synchronously to the pixel. It shows the voltage waveform when

Fig. 15c shows the voltage waveform when the aforementioned scanning non-selection signal and information selection signal are applied to the pixel, and Fig. 15d shows the voltage waveform when the scanning non-selection signal and information selection signal are applied to the pixel. It represents the voltage waveform.

FIG. 16 shows the signal voltage described above in time series. In the figure, A is the time series waveform applied to pixel A in FIG. 4, and B is the time series waveform applied to pixel B in FIG. It represents a series waveform.

In this example as well, as can be seen from Fig. 16, the longest time applied to the pixel when scanning is not selected is 2Δt.
It can be done.

According to the present invention, even if a display panel using a ferroelectric liquid crystal element is driven at high speed, the maximum pulse width of the voltage waveform that continues to be applied to the pixels on the scan electrode line to which the scan non-selection signal is applied is Since it is twice or 2.5 times the pulse Δt during writing, it is possible to effectively prevent the phenomenon in which the display state is reversed to another display state during the writing scan of one screen.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the threshold characteristics of a ferroelectric liquid crystal. FIGS. 2 and 3 are perspective views schematically showing a ferroelectric liquid crystal element used in the present invention. FIG. 4 is a plan view of the matrix pixel structure used in the present invention. Figure 5 a~d, Figure 8 a~
d, FIGS. 11 a to d, and FIGS. 14 a to d are explanatory diagrams showing voltage waveforms of signals applied to the electrodes, respectively. FIGS. 6 a to d, FIGS. 9 a to d, FIGS. 12 a to d, and FIGS. 15 a to d are explanatory diagrams showing voltage waveforms of signals applied to pixels, respectively. FIG. 7, FIG. 10, FIG. 13, and FIG. 16 are explanatory diagrams of voltage waveforms representing the aforementioned signals in time series.

Claims (1)

[Scope of Claims] 1a A matrix electrode structure in which pixels are formed at intersections of a scanning electrode group and a signal electrode group, and a matrix electrode structure arranged between the scanning electrode group and the signal electrode group and resisting an electric field of one polarity. a ferroelectric liquid crystal that produces a first stable state in response to an electric field of the other polarity and a second stable state in response to an electric field of the other polarity, and b. , a scan selection signal in which the previous pulse is set to have a longer pulse width than the subsequent pulse is sequentially applied, and within the application period of the previous pulse, the signals are simultaneously applied to the signal electrode group and to the pixels on the scan electrode selected for scanning. Applying a bipolar pulse so that a voltage of one polarity that causes the first stable state is applied, and applying a bipolar pulse to the signal electrode group and to the pixel on the scanning electrode within the application period of the subsequent pulse. on the selected scan electrode by applying a pulse of opposite polarity to the subsequent pulse such that a voltage of the other polarity is applied that selectively produces the second stable state. Then, the next scan selection signal is applied to the selected scan electrode after the application of the scan selection signal to the immediately previous scan electrode is completed, and the next scan selection signal is applied to the scan electrode that has not been selected for scan. In the pixel on the scanning electrode,
A liquid crystal device comprising: means for applying an alternating voltage to maintain a written state during scan selection; 2 a A matrix electrode structure in which a pixel is formed at the intersection of a scanning electrode group and a signal electrode group, and a first stable state with respect to an electric field of one polarity, which is arranged between the scanning electrode group and the signal electrode group. and a ferroelectric liquid crystal that produces a second stable state in response to an electric field of the other polarity, b. Sequentially applying selection signals to the signal electrode group in synchronization with the previous one polarity,
Applying a voltage signal such that a voltage of one polarity that causes the first stable state is simultaneously applied to the pixels on the scanning electrode selected for scanning, and applying a voltage signal to the signal electrode group with the subsequent pulse of the other polarity. synchronously with the subsequent other polarity pulse such that a voltage of the other polarity that selectively causes the second stable state is applied to the pixels on the scan electrode; applying information pulses of the same polarity or opposite polarity to the group of signal electrodes located before and after the information pulse, and located before the next information pulse for the scan electrode to be scanned next; By applying a pulse having a polarity opposite to the information pulse and having a pulse width smaller than that of the information pulse, writing is performed to the pixel on the scan electrode selected for scanning, and the pixel on the scan electrode selected for scanning is written. For pixels on no scanning electrodes,
A liquid crystal device comprising: means for applying an alternating voltage to maintain a written state during scan selection; 3 a A matrix electrode structure in which pixels are formed at intersections of a scanning electrode group and a signal electrode group, and a first stable state with respect to an electric field of one polarity, which is arranged between the scanning electrode group and the signal electrode group. and a ferroelectric liquid crystal that produces a second stable state in response to an electric field of the other polarity, and b. sequentially applying a scan selection signal having a pulse, a voltage O and a pulse of the other polarity to the group of signal electrodes, in a first phase, simultaneously bringing about the first stable state in the pixels on the scan selected scan electrode; applying a polar voltage to put the pixels on the scanning electrode into an erased state;
In a second phase, a voltage is applied to the pixel on the scanning electrode, which has a polarity opposite to the voltage applied in the first phase and maintains the erased state, and in a third phase,
a bipolar pulse synchronized with the period consisting of the first phase and the second phase, such that a voltage of the other polarity that causes the second stable state is selectively applied to pixels on the scanning electrode; By applying an information signal having one polarity or the other polarity pulse synchronized with the three phases, writing is performed to the pixels on the scan electrodes selected for scanning, and to pixels on the scan electrodes not selected for scanning. ,
A liquid crystal device comprising: means for applying an alternating voltage to maintain a written state during scan selection;