JP3029892B2 - Matrix type liquid crystal display device and method of driving the liquid crystal display 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 matrix type liquid crystal display device and a method of driving the matrix type liquid crystal display device, and more particularly, to a matrix type antiferroelectric liquid crystal for use in an optical shutter or a character / image display. The present invention relates to a display device and a method for driving the liquid crystal display element.

[0002]

2. Description of the Related Art Conventionally, as a liquid crystal display element, TN
Various types such as (twisted nematic) type and STN (super twisted nematic) type have been studied.

In recent years, a new type of ferroelectric liquid crystal has been attracting attention as having characteristics such as memory characteristics and high-speed response (Japanese Patent Application Laid-Open No. 56-107216).

However, actually, the smectic layer structure is not an ideal book-shelf structure but a chevron structure, so that desired characteristics such as memory properties cannot be obtained.

As a method for solving these problems of the prior art, three stable states are set by an applied voltage level, and when switching between the states, a hysteresis characteristic peculiar to an applied voltage-transmitted light amount characteristic is provided. "Matrix type ferroelectric liquid crystal display device" adapted to apply three pulse voltages including an adjustment voltage, an erase voltage, and a write voltage in relation to the tristable state and the hysteresis characteristic (Japanese Patent Application Laid-Open No. 2-137724). No.) has been proposed. It is stated that the contrast can be greatly improved by giving the signal a simple waveform change in relation to the applied voltage-transmitted light intensity characteristic.

In the method of driving a matrix type liquid crystal display element, a selection voltage waveform having a positive average potential is applied in an odd frame, and a selection voltage waveform having a negative average potential is applied in an even frame. "Driving method of liquid crystal element" applying non-selection voltage waveform of same sign
No. 5119) has been proposed. It is stated that this enables matrix display of liquid crystal display using antiferroelectric liquid crystal.

[0007]

However, the former display device has a so-called three-pulse drive in which the drive control means applies a signal consisting of a one-pulse erase signal and a two-pulse write signal during a scan selection period. For this reason, there is a problem that a selection time for three pulses is required to perform erasing / writing of one scanning line, and a scanning time per frame is long.

In the latter method of driving a liquid crystal element, the specification of the shape and peak value of a driving pulse to be determined from the correspondence between the threshold voltage and the response speed of the liquid crystal cell is specifically described in the specification. Is difficult to implement. Also,
It is necessary to alternately apply a selection waveform having a positive average potential in an odd-numbered frame and a selection waveform having a negative average potential in an even-numbered frame, and exclude other combinations of selection waveforms. There is a problem that the degree of freedom that can be selected is limited.

The inventors of the present invention have conducted intensive studies to solve the problems of the prior art as described above, and as a result of repeating various systematic experiments, the present invention has been accomplished.

An object of the present invention is to provide a matrix type liquid crystal display device which is excellent in writing speed and display ability, and a driving method of the matrix type liquid crystal display device.

The present inventors have focused on the following with respect to the above-mentioned problems of the prior art. That is, first, erasing is possible even when the voltage is other than 0V. That is, erasing can be performed by applying a voltage in a range from a threshold voltage of OFF (light-off) to a threshold voltage of an opposite polarity and an absolute value of ON (light-on).

Next, in the above-mentioned prior art JP-A-2-137724, a plurality of second drive signals are provided with a first light in writing "bright" in order to eliminate a DC component other than a voltage applied in an offset manner. (V ₀ −V ₁ −) as a waveform having a level equal to or higher than the saturation voltage of the change from the stable state to the second stable state.
V ₂ ) and (V ₀ + V ₁ + V ₂ )
In the “dark” writing, the waveforms (V ₀ −V ₁ + V ₂ ) and (V ₀ + V ₁ −V ₂ ) having a level equal to or higher than the saturation voltage of the change from the first stable state to the second stable state , And the average value of the write voltage for each of the light and dark was determined to be V ₀ .

However, for example, if the polarity of the first frame and the second frame is changed to cancel the DC component, the average of the signal voltages needs to match the voltage (V ₀ ) applied in an offset manner. There is no. Therefore, it has been noted that the average of the write voltage pulse and the voltage pulse for compensating the write voltage pulse need not be equal to V ₀ , and can be set arbitrarily.

From the above, the present invention has been achieved by focusing on the existence of a voltage pulse in a voltage range in which erasing is possible and which can compensate for a DC component with respect to a writing pulse.

[0015]

According to a first aspect of the present invention, there is provided a matrix type liquid crystal display device having a pair of substrates sandwiched opposite to each other at a predetermined interval, and arranged in a stripe shape inside one of the substrates. A scanning electrode, a signal electrode formed inside the other of the pair of substrates, and arranged in a direction substantially perpendicular to the scanning electrode so as to face the scanning electrode; and an electrode of the substrate is formed. A matrix comprising: an alignment film disposed on at least one of the paired substrates; a liquid crystal cell made of antiferroelectric liquid crystal sealed between the pair of substrates; and a drive control means for applying a drive signal to the liquid crystal cell. In the liquid crystal display device of the type, a drive signal applied by the drive control means is applied for temporarily erasing a display, and a first pulse set to be equal to or lower than a first threshold voltage and for performing ON (lighting). The first applied The threshold voltage higher than the voltage or OFF,
When the voltage is lower than the first threshold voltage applied to perform (light-off), the effective voltage added to the first pulse is a certain voltage, and the voltage is inverted during another period, A matrix type liquid crystal display device, comprising two pulses consisting of a second pulse set so that the components are completely canceled, wherein the unit of applied pulse is reduced to improve the writing speed and the display capability. .

The driving method of a matrix type liquid crystal display device according to the second aspect of the present invention is directed to a method of driving a matrix type liquid crystal display device, comprising: In a method of driving a matrix-type liquid crystal display device comprising an alignment layer, a liquid-crystal cell in which matrix-type liquid crystal is sealed between the pair of substrates, and drive control means for applying a drive signal to the liquid-crystal cell, display is performed once. The first pulse set to be equal to or lower than the first threshold voltage for erasing and the effective voltage added to the first pulse become a certain voltage, and when the voltage is inverted in another period, the DC component is completely canceled. The second set to be
A driving signal consisting of two pulses consisting of a pulse and a pulse is applied.

[0017]

The mechanism by which the matrix type liquid crystal display device of the present invention exhibits excellent effects is not yet clear, but is considered as follows.

That is, the matrix type liquid crystal display device according to the first aspect of the present invention comprises a pair of substrates sandwiched opposite to each other at a predetermined interval, a scanning electrode disposed in a stripe shape inside one of the substrates, A signal electrode formed inside the other side of the substrate and arranged in a direction substantially perpendicular to the scanning electrode so as to face the scanning electrode; and a signal electrode arranged on at least one of the sides of the substrate on which the electrode is formed. An alignment film provided, a liquid crystal cell made of antiferroelectric liquid crystal sealed between the pair of substrates, and a drive control means for applying a drive signal to the liquid crystal cell are used.

Next, in the present invention, the drive signal applied in the drive control means of the liquid crystal display device is two pulses. That is, a first pulse that is applied to once erase the display and is set to be equal to or lower than the first threshold voltage, a voltage equal to or higher than the first threshold voltage that is applied to perform ON (lighting),
Alternatively, it is a voltage equal to or lower than a first threshold voltage applied to perform OFF (turn off), and an effective voltage added to the first pulse is a certain voltage, and the voltage is inverted in another period. In this case, two pulses including a second pulse set so that the direct current component is completely cancelled.

By applying such a two-pulse voltage, a DC component can be compensated for the writing pulse, and a DC component other than the voltage applied in an offset manner can be eliminated. The writing speed and the display capability can be improved by reducing the unit of the applied pulse. Therefore, a matrix-type liquid crystal display device excellent in writing speed and display capability can be realized by applying two pulses of voltage which could not be realized conventionally.

That is, in order to write an image, it is necessary to perform ON or OFF for each pixel. In a liquid crystal cell using an antiferroelectric liquid crystal, the first
It is necessary to apply a voltage higher than the threshold voltage or a voltage lower than the first threshold voltage to the pixel. In the present invention, a DC component is compensated to zero by applying a pulse of a peak value at which the average with the write voltage is always a certain voltage adjacent to the write voltage and inverting the polarity of each frame,
The number of pulses for performing ON or OFF can be realized with a minimum of two pulses.

[0022]

According to the matrix type liquid crystal display device of the present invention, driving with excellent writing speed and display capability can be performed.

Further, according to the driving method of the matrix type liquid crystal display device of the present invention, the writing of the liquid crystal display device can be performed at high speed, and the display capability is excellent.

[0024]

The present invention will now be described with reference to specific examples.

A specific example of the matrix type liquid crystal display device of the present invention will be described. First, the liquid crystal cell will be described with reference to FIG. The liquid crystal cell 1 is formed on a pair of substrates 2 and 3 sandwiched oppositely at a predetermined interval, a scanning electrode 4 arranged in a stripe on the one substrate 2, and the other substrate 3. The signal electrodes 5 are arranged on the side of the substrates 2 and 3 on which at least one of the electrodes is formed, and the signal electrodes 5 are arranged so as to face the scanning electrodes 4 at substantially right angles to the scanning electrodes. It comprises an alignment film 6 and an antiferroelectric liquid crystal 7 sealed between the pair of substrates.

As the substrates 2 and 3, substrates commonly used for liquid crystal elements, such as various kinds of glass such as soda glass or Pyrex, or plastic plates such as polyethylene terephthalate can be used. The surface of the substrate may be polished or the like to obtain flatness, or may be coated with SiO ₂ or the like to block alkali ions from the glass. The thickness of the substrate is approximately 2 to 0.
05 mm.

On the substrates 2 and 3, a transparent conductive film such as ITO (indium tin oxide) is formed in a stripe shape, and the scanning electrode 4 and the signal electrode 5 are formed. The width of the transparent conductive film is related to the size of the pixel.
μm, and about 5 cm for large displays. Note that an insulating film such as SiO ₂ may be formed to prevent a short circuit between the opposing electrodes.

The alignment film 6 is provided on at least one of the substrates 2 and 3 on which the transparent electrodes are formed, and is formed by applying and depositing a polymer such as polyimide or polyvinyl alcohol. The alignment film 6 is provided with an alignment property with respect to the liquid crystal by rubbing in one direction using a brush or cloth made of nylon or cotton, or performing a so-called rubbing treatment.

Scan electrodes 4 formed on a pair of substrates 2 and 3
An example of a specific arrangement structure of the signal electrodes 5 will be described with reference to FIG. As shown in the figure, the transparent electrodes 4 and 5 face each other, and the striped electrodes are overlapped so as to be orthogonal to each other to form a matrix as a row electrode and a column electrode, respectively. Become.

The substrates 2 and 3 are fixed with an adhesive or the like. Prior to bonding, in order to maintain the cell thickness, a spherical or circular spacer made of a resin such as divinylbenzene or a ceramic such as silica and having a constant diameter is sprayed between the substrates or added to the adhesive. May go. The distance between the substrates (hereinafter, referred to as cell thickness) is set so that the orientation ratio is good and the transmitted light intensity due to birefringence is maximized in order to increase the contrast ratio.
The interval is usually 1 to 6 μm.

When the antiferroelectric liquid crystal is sealed in the cell prepared as described above at a temperature above its transparent transfer, and cooled to room temperature, the liquid crystal molecules are aligned in the rubbing direction when returning from the isotropic liquid state to the liquid crystal state. As a result, the liquid crystal cell 1 is obtained.

As an antiferroelectric liquid crystal, MHPOBC
(1-methylheptyloxycarbonylphenyl) 4'-octyloxybiph
Various antiferroelectric liquid crystals or compositions, including enyl-4-carboxylate, can be used.

Next, a specific example of the drive control means (drive device) of the matrix type liquid crystal display element of the present invention will be described with reference to FIG. In the matrix drive, a row electrode is sequentially selected one by one, and a selection signal is applied to a column electrode each time, display is written to a pixel, and an image is reproduced, that is, scanning is performed. The driving device 9 includes a scanning-side circuit section 91 for scanning the row electrodes, a signal-side circuit section 92 for applying a selection signal to the column electrodes, and receiving image information from the outside and converting the received image information into voltage data to convert both the scanning side and the signal side. An electronic control unit 93 controls the circuit unit, a storage unit 94 for temporarily storing signal data output from the electronic control unit 93, and a power supply circuit 95.

The electronic control unit 93 receives the serial information of the image information transmitted from the navigation or the television receiver, converts the serial information into a digital signal in the case of an analog signal, and converts the analog signal into a digital signal when the number of input pixels is different from the number of panel pixels. For example, data compression or the like is performed. Further, the electronic control unit 93 has a reference clock generation circuit (not shown), and various kinds of clock signals CL1, CL2, CL3, CL
4 is generated to take the timing of each circuit.

The electronic control unit 93 outputs scan data S1 to the scan circuit unit 91. The scan data is output from the electronic control unit 93 to the scan-side circuit unit 91 to select a row electrode on which an image is to be written. The scanning-side data S1 output from the electronic control unit 93 is serial data, which is once transferred to the shift register 911, converted into parallel data, and output to the data latch 912. When the latch clock CL2 is input from the electronic control unit 93, the data latch 912 sends the scan-side data to the voltage selection circuit 913. 5 to 6 voltage selection circuits 913
And five or six types of predetermined voltage levels are applied to the scanning electrodes (row electrodes) of the panel according to the scanning data.

The electronic control unit 93 is connected to the signal side circuit unit 9.
2 to output signal data S2 via the storage unit 94. The signal data S2 is output to select ON or OFF of each column for the row electrode selected for scanning. The ON or OFF information for each pixel is stored on the data bus D
At B, the position of the pixel is output from the electronic control unit 93 to the storage unit 94 via the address bus AB. The storage unit 94 can store information corresponding to several images, and can output the information at high speed as needed. The image information stored in the storage unit 94 is serially output as signal data S2 to the shift register 921, converted into parallel data, output to the data latch 922, and further output to the voltage selection circuit 923 by the latch clock CL4. The signal voltage is applied to the signal electrodes (column electrodes) of the panel. here,
The signal-side voltage selection circuit 923 includes two transmission gates, and two predetermined voltages are selected.

Next, FIG. 4 shows a model of the state of the molecules of the antiferroelectric liquid crystal in the cell when viewed from a direction perpendicular to the substrate surface. When no electric field is applied, the liquid crystal is in an antiferroelectric state, and the orientation of molecules is alternately arranged between adjacent layers (II in the figure). As a result, the dipole directions are antiparallel to each other, and it is considered that spontaneous polarization does not appear outside. Optically, it is in the average direction of molecules whose optical axis is directed right or left, that is, in the rubbing direction. When the cell in such a state is placed under the perpendicular Nicols and the direction of the polarizer or analyzer is aligned with the rubbing direction, the light passes through because the optical axis of the liquid crystal molecules and the optical axis of the polarizer or analyzer match. A dark state is obtained. When an electric field is applied, the liquid crystal molecules turn right (in the figure: III) or left (in the figure: because of the spontaneous polarization and the torque caused by the electric field).
It is unified to the array inclined to I). At this time, the optical axis of the liquid crystal molecule is deviated from the optical axis of the polarizer or analyzer, so that light is transmitted by birefringence, and a bright state is obtained.

A method of obtaining the threshold voltage according to the conventional method will be described with reference to FIG. Conventionally, a method of obtaining a threshold voltage from an optical response by applying a triangular wave voltage has been performed. That is, in FIG. 5, when a triangular wave voltage is applied to the cell and the voltage is increased from 0 volt, the spontaneous polarization, which has been oriented in the opposite direction to the electric field, is reversed to transfer to the ferroelectric state, and the amount of transmitted light Also sharply increases (in the figure: C1). The voltage at which the transmitted light amount changes by 10% from the initial value is conveniently determined as the threshold voltage V ₁ , and the voltage at which the transmitted light amount changes by 90% is determined as the saturation voltage V ₂ for convenience.

When the voltage is decreased from a voltage of V ₂ or more, the change does not show the same change as when the voltage is increased, and a hysteresis curve (FIG.
C2) indicates that the molecules start to be inverted with the threshold voltage V ₃ and gradually darken, and are completely switched to the dark state with the saturation voltage V ₄ . Here, FIGS. 6 to 8 show the measurement results of the optical response due to the application of the triangular wave voltage measured by changing the frequency. The threshold voltage and the saturation voltage have frequency dependence, and particularly, the threshold voltage V ₃ and the saturation voltage V ₄ when the voltage decreases are remarkable. Therefore, in the method based on the application of the triangular wave voltage, only the threshold voltage can be estimated, and the threshold voltage cannot be accurately measured because the drive voltage is determined.

Therefore, in the present invention, the threshold voltage is
Determined by applying the square wave voltage application method. Hereinafter, a specific example of the threshold value determination will be described.

First, a specific example of the determination of the first threshold voltage will be described. The threshold characteristics at the time of ON (lighting) are shown in FIGS.
As shown in FIG. 11, the first rectangular wave on the low voltage side is fixed at 0 V, and the second rectangular waves having various peak values are applied. At this time,
The response time also changes depending on the magnitude of the rectangular wave voltage. When the rectangular wave voltage is lower than the threshold voltage, the transmitted light intensity changes only slightly (FIG. 9). Only when the rectangular wave voltage exceeds the threshold voltage does the transmitted light intensity greatly change (FIG. 10), and the response time decreases as the rectangular wave voltage increases (FIG. 11). This corresponds to the time required to change from the antiferroelectric state to the ferroelectric state.

FIG. 12 shows the relationship between the response speed and the applied voltage.
Shown in Here, the response time is the time required for the transmittance to change by 90% after the application of the voltage, and is represented by τ _ON . τ
Equation (1) can be applied to _ON for the rectangular wave voltage V. It is considered that α represents the magnitude of the response time, and β represents the magnitude of the change in the response time when the voltage is changed.

[0043]

(Equation 1)

Thus, the ON threshold voltage V _c ^ON (first threshold voltage) is determined. The width of the rectangular wave to be applied and the interval between the rectangular waves are sufficiently longer than the ON response time and the OFF (extinguishing) response time, respectively (three times or more).
did.

It is preferable that the first voltage applied for once erasing the display is within the range of not more than the first threshold voltage and not less than the negative value of the second threshold voltage. The second threshold voltage is a positive value, and “negative value of the second threshold voltage” means that the absolute value of the second threshold voltage is equal to the absolute value and the sign is negative.

Here, a specific example of the determination of the second threshold voltage will be described.

The threshold characteristics when is OFF, after applying a first square wave of V _c ^ON or more high voltage is sufficient ON response as shown in FIGS. 13 to 15, followed by a low voltage Second
Apply a square wave. When the second rectangular wave voltage is equal to or higher than the threshold voltage, the transmitted light intensity hardly changes (FIG. 13). Only when the second rectangular wave voltage becomes smaller than the threshold voltage does the transmitted light intensity greatly change (FIG. 14), and the response time decreases as the second rectangular wave voltage decreases (FIG. 15). this is,
This corresponds to the time required to change from the ferroelectric state to the antiferroelectric state. FIG. 16 shows the relationship between the response speed of the antiferroelectric liquid crystal and the applied voltage and the threshold characteristics. Here, the response time is a time required for the transmittance to change by 90%, and is represented by τ _OFF . Equation (2) can be applied to τ _OFF with respect to the rectangular wave voltage V.

[0048]

(Equation 2)

Thus, the OFF threshold voltage V _c ^OFF (second threshold voltage) is determined. The widths of the high-voltage and low-voltage rectangular waves applied for the measurement were sufficiently longer (three times or more) than the respective response times.

When the pixel configuration of the panel is m rows × n columns,
A pulse train of one frame is composed of m pulse groups, one selected pulse group, and subsequent m-1 non-selected pulse groups. 17, when the frame time Tf seconds time necessary for rewriting one screen, the time required to rewrite one line is Tf / m seconds, the time period T ₁ of the from the time t ₀ to t ₂ 1 the row, assuming that rewrites the second row during the period from t ₂ to t _4, t ₂ -t _0,
t ₄ -t ₂ is Tf / m second. One pulse group consists of two pulses (the driving method of the present invention can be called a “two-pulse method”). In addition,
The two-pulse method is based on inverting the polarity every frame.

First, the principle of screen rewriting by the two-pulse method in the period in which the polarity of the frame is + will be described with reference to FIGS.

The selection pulse group includes an erasing pulse for temporarily turning off the pixel and a writing pulse for selecting continuation of erasing or ON of the pixel. If the polarity of that frame is +,
As shown in FIG. 18, the peak value V _r (r: r
ESET) is -V _c ^OFF to + V _c ^ON V _r ^L or V _r ^H (L, ^H: by being set to indicate the high and low voltage), - If you were ON in a polarity-side frame Alternatively, if it has not been turned on, it can be turned off in any case, and once in the erased state. When a write pulse is applied, the peak value V _w (w:
If the write) is set to be equal to or greater than + V _c ^ON V _w ^H becomes the ON state, the peak value V _W of the write pulse is + V _c
If V _w ^L is set below ^{ON, the} erase state is continued.

[0053] When V _w ^H as the write pulse is selected (Fig. 18), the erase pulse selects V _r ^L as peak value, when V _W ^L is selected as the write pulse (FIG. 1
9), V _r ^H is selected as the peak value of the erase pulse.

[0054] In this case, V _w ^H and V _W difference V _w ^H -V _W of ^L
L, and V _r ^H and V _r ^L and the difference V _r ^H -V _r ^L of is set to be the same. When writing ON, a write pulse V _w ^H is applied following the erase pulse V _r ^L , and O
Although V _W ^L subsequent to V _r ^H at the time of writing of FF is applied, the period of rewriting, namely in the period t ₂ from t _0, the pulse effective voltage rewriting ON or OF
It is kept constant regardless of F.

As shown in FIG. 20, the unselected pulse group is
When the row is not rewritten, that is, when another row is selected, it is applied to the row. A pair of non-selected group of pulses a voltage level ^{_{V ns H (ns: non-}} s
select) pulse and a low voltage level V _ns ^L pulse, and the order of the other selected rows is determined by the difference between ON and OFF. One end ON
The erased pixel cannot be erased unless it is set at + Vc ^OFF or less, and the once erased pixel cannot be ^turned on unless it is set at + Vc ^ON or more. Therefore, by setting two voltage levels V _ns ^H and V _ns ^L below both + Vc ^OFF or + Vc ^ON, once rewritten display state by the selection pulse is maintained.

+ Vc ^OFF while other i rows are selected
<V _ns ^H, the effective voltage of the non-selection pulse is at V _ns ^L <+ Vc ^ON, since the consist of a pair of pulses of V _ns ^H and V _ns ^L, constant at all times irrespective of the ON or OFF of the other row Will be kept.

In the period where the polarity of the frame is-, as shown in FIG. 21, the same drive can be performed by reversing the signs when the polarity of the frame is +.

That is, in the drive control means of the first invention, the drive signal applied for writing the display is applied for once erasing the display, and the first pulse set to be equal to or lower than the first threshold voltage. , A voltage higher than the first threshold voltage applied to perform ON, or a voltage lower than the first threshold voltage applied to perform OFF, and
And a second pulse set such that the effective voltage added to the first pulse is a certain voltage and the DC component is completely canceled when the voltage is inverted in another period. is there.

As described above, according to the display device of the present invention and the driving method of the present invention, in a display element using an antiferroelectric liquid crystal having a tristable state, a threshold voltage characteristic in a hysteresis state is skillfully used. By doing so, rewriting can be performed with two pulses, which is the minimum number of pulses, so that high-speed driving is possible. In addition, the polarity is inverted every frame for the purpose of eliminating the superposition of the DC voltage component, and the effective voltage for each of the selection period and the non-selection period is constant irrespective of ON or OFF. The effective voltage is also constant, and the DC components are completely cancelled between adjacent frames, so that deterioration of the display element can be prevented and the life can be extended.

FIG. 22 shows an example of a voltage waveform actually applied to the scanning electrode and the signal electrode for a frame having a positive polarity in order to realize the voltage waveform applied to the liquid crystal. A selected waveform and a non-selected waveform are applied to the scanning electrodes, and an ON waveform and an OFF waveform are applied to the signal electrodes.

The scanning electrode to which the selection signal is applied and the ON state
At the pixel at the intersection of the signal electrodes to which the signal is applied, O
Rewritten to N. At the time of selection, a pulse group of a voltage level V _e (e: erasing) and a subsequent pulse group of V _p (p: pulse) are applied to the scan electrode. At the same time, the voltage level + V _d
(D: data) and a subsequent pulse of −V _d are applied. Here, the net voltage applied to the liquid crystal is the difference between the voltage of the scanning electrode signal and the voltage of the selection electrode signal. Thus, for liquid crystal, firstly, the voltage pulse V _e -V _d is, pulse followed by V _p + V _d is applied. Here, V _e −V _d is V _r ^L , and −Vc ^off to + Vc ^off
It must be set to Vc ^on. Also, V _p + V _d
Is a V _w ^H, it must be set to be equal to or greater than + Vc ^on.

Scan electrode to which selection signal is applied and OF
At the pixel at the intersection of the signal electrodes to which the F signal is applied,
Rewritten to OFF. For the scan electrode, the voltage level V _e (e: erasin
g) followed by a pulse of V _p (p: pulse) followed by a + V _d pulse. Here, the net voltage applied to the liquid crystal is a difference between the voltage of the scanning electrode signal and the voltage of the selection electrode signal. Therefore, for the liquid crystal, a voltage pulse of V _e + V _d is first applied, followed by V _p -V
A voltage pulse of _d is applied. Here, V _e + V _d is V
_r ^H and must be set to -Vc ^OFF or + Vc ^ON . V _p -V _d is a V _w ^L, it must be set to be equal to or less than + Vc ^on.

In the pixel where the non-selection signal is applied to the scanning electrode, even if either the ON signal or the OFF signal is applied to the signal electrode, the display of ON or OFF rewritten before that period is maintained. Is done. When the scanning electrode is not selected, the voltage level V _b (b: ba
se) continues to be applied. In the same column, pixels in other rows are O
If N has been rewritten, the voltage level + V _d (d: data) and the following −V
A pulse of _d is applied. For liquid crystal, first, V _b
Voltage pulse -V _d is, the voltage pulse followed by V _b + V _d is applied. Here, V _b -V _d is V _ns ^L, V _b + V
_d is a V _ns ^H, it must be both set to + Vc ^OFF to + Vc ^on.

In the same column, when pixels in other rows are rewritten to the point OFF, first, V
voltage pulse _b + V _d is the voltage pulse followed by V _b -V _d is applied. Again, V _b + V _d is V _ns ^H , V _b
-V _d is a V _ns ^L, both + Vc ^off to + Vc ^on
Must be set to

[0065] The pulse width Pw is _{V p + V d (= V} w
It is desirable that the response time is sufficiently longer than that in ^H ).

In the matrix type liquid crystal display device of this example, the voltage level of the first voltage pulse which plays the role of the compensation pulse can be set arbitrarily as described above. That is, depending on the characteristics of the liquid crystal cell,
When the OFF response speed is slower than the ON response speed, the voltage level of the first voltage pulse can be set higher to achieve higher speed. Also, when turning on from OFF,
When the ferroelectric state easily transitions directly to the ferroelectric state (ON state) without passing through the antiferroelectric state (OFF state),
By setting the voltage level of the first voltage pulse to be lower, an OFF state can be obtained even with a short pulse width.

As described above, in this specific example, the number of write pulses is set to the minimum of two pulses. In addition, the second pulse is not limited to the role of merely compensating the voltage, but is effectively moved for rewriting. As a result, the speed can be increased as compared with the conventional antiferroelectric liquid crystal element. That is, by using an antiferroelectric liquid crystal and performing a drive characterized in that rewriting is performed with a minimum of two pulses and that the first pulse can be set arbitrarily, a high-speed drive that is not available in a conventional display device is performed. Can be performed. Further, since no DC component is applied, deterioration due to electrochemical reaction or the like does not occur, and a long life can be obtained.

Hereinafter, embodiments of the present invention will be described.

First Embodiment

The liquid crystal cell uses a substrate made of soda glass having a thickness of 1.1 mm, and the surface of the substrate is subjected to a passivation treatment with a coating of SiO in order to block alkali ions from the glass. Further, a transparent conductive film of ITO (indium tin oxide) is formed on the substrate.
120μm width, 20μm gap (140μm pitch)
In the form of stripes.

The number of electrodes is 192 in the horizontal direction as row electrodes on the upper substrate, and 768 in the vertical direction as column electrodes on the lower substrate. In order to prevent a short circuit between the opposing electrodes, an insulating film such as SiO ₂ may be formed.

Further, on the side of the substrate on which the transparent electrode was formed, a commercially available polyimide was applied by a printing method and baked to form an alignment film.

The alignment film was subjected to a rubbing treatment in the longitudinal direction of the substrate by using a brush in which nylon fibers were planted, thereby giving an alignment property to the liquid crystal. A matrix was formed by overlapping a pair of substrates such that the transparent electrodes faced each other and the striped electrodes were orthogonal. In order to make the cell thickness 2.2 μm,
Spherical spacers made of divinylbenzene resin having a diameter of 2.2 μm were sprayed between the substrates and fixed with a thermosetting adhesive.

In order to increase the contrast ratio, the orientation is set to be good and the transmitted light intensity due to birefringence is set to be maximum. In order to enhance the orientation, usually, an alignment film such as polyimide is formed on the substrate, and rubbed with a brush or the like,
Perform a rubbing operation. At this time, it is preferable to optimize the rubbing pressure, the number of times, and the like. The transmitted light intensity Tr is expressed as follows. Tr∝sin ² (πΔn · d / λ) where Δn is the birefringence of the liquid crystal, d is the cell thickness, and λ is the wavelength of light. When λ is considered at 550 nm, which has the highest visibility, Tr becomes the largest when πΔnd · 550 nm. Therefore, the cell thickness d is adjusted according to Δn of the liquid crystal material.

As the antiferroelectric liquid crystal, a composition comprising the following four components was used.

[0076]

(Equation 3)

In the cell prepared as described above, the antiferroelectric liquid crystal is sealed at a temperature above its transparent transition, and when cooled to room temperature, when the liquid crystal state returns to the smectic A phase from the isotropic liquid crystal state, the rubbing direction Then, the liquid crystal molecules were aligned and the orientation was obtained.

The liquid crystal cell was connected to a drive circuit using an interconnector.

The scan data is output to select a row electrode to be scanned. The scan data output from the electronic control unit is serial data, which is once transferred to a shift register, converted to parallel data, and output to a data latch. The data latch sends scan data to the voltage selection circuit when a latch clock is input from the electronic control unit.

The voltage selection circuit is composed of six (or five) transmission gates, and has six predetermined voltage levels, ie, + V _e , + V _p , + V
_{b, -V e, -V p,} -V b ( however, + V _e = -V _e =
0 is possible: at that time, five types of voltage levels) are applied to the scanning electrodes (row electrodes) of the panel according to the scanning data.

The signal data is output for the purpose of selecting ON or non-ON of each column for the row electrode selected for scanning. The ON or non-ON information for each pixel is sent out from the electronic control unit to the storage unit via the data bus, and the position of the pixel is sent out via the address bus. The storage unit can store information corresponding to several images, and can output the information at high speed as needed. The image information stored in the storage unit is serially output as signal data to a shift register, converted into parallel data, output to a data latch, further output to a voltage selection circuit by a latch clock, and applied to a panel signal electrode. You. Here, the signal-side voltage selection circuit is constituted by two transmission gates, and two predetermined voltages + V _d and −V _d are selected.

These + V _e , + V _p , + V _b , -V _e ,
-V _p, the value of -V _b may be given a measure by the following equation.

[0083] selected group of pulses and erase ^{_{(ON) -V c OFF <+}} V e -V d <+ V c ON ··· (3) · erasing ^{_{(OFF) -V c OFF <+}} V e + V d <+ V c ON · ·· (4) · Write (ON) + V _c ^ON <+ V _p + V _d ··· (5) · Write (OFF) + V _c ^ON > + V _p −V _d ··· (6) Unselected pulse group + V _{c ^{OFF <+ V b -V d <}} + V c ON ··· (7) + V c OFF <+ V b + V d <+ V c ON ··· (8) from equation left side of ^{_{(7), V c OFF +}} V d <+ V _b ··· (9) from equation left side of _{(8), V b <V} c ON - V d ··· (10) V c OFF + V d <V c ON - V d ··· (11) V d <(V _c ^ON −V _c ^OFF ) / 2 (12)

[0084] V Since _d is considered better to largely take is stable with respect to variations in the threshold voltage due to the change or unevenness in the threshold voltage due to temperature change, in formula (12) V _d
Is expressed by Expression (13), and the subsequent calculation is performed. ^{_{V d = (V c ON -V}} c OFF) / 2 ··· (13)

[0085] At this time, V _{b ^{is, V b = (V c ON}} + V c OFF) / 2 ··· (14)

From the left side of equation (3), (V _c ^ON −3 V _c ^OFF ) / 2 <V _e (15)

From the right side of equation (4), at this time, V _e is V _e <(V _c ^ON + V _c ^OFF ) / 2 (16)

From equations (10) and (11), (V _c ^ON −3 V _c ^OFF ) / 2 <V _e <(V _c ^ON + V _c ^OFF ) / 2 (17)

From equations (5) and (9), regarding V _p , (V _c ^ON + V _c ^OFF ) / 2 <V _p (18)

From equations (6) and (9), V _p <(3V _c ^ON −V _c ^OFF ) / 2 (19)

From equations (13) and (14), (V _c ^ON + V _c ^OFF ) / 2 <V _p <(3 V _c ^ON −V _c ^OFF ) / 2 (20)

The conditions relating to V _d , V _b , V _e , and V _p are summarized once again as follows. However, the equal sign in equation (9), and indicate a limit, also, since also V _b of formula (14) and requests from the extreme of the formula (9), V _d,
The value obtained by the expression of _Vb is a guide.

[0093] ^{_{V d = (V c ON -V}} c OFF) / 2 ··· (9) V b = (V c ON + V c OFF) / 2 ··· (14) (V c ON -3V c OFF _{) / 2 <V e <(} V c ON + V c OFF) / 2 ··· (17) (V c ON + V c OFF) / 2 <V p <(3V c ON -V c OFF) / 2 ··・ (20)

As a specific example of a scanning waveform, a signal waveform, and a driving form which is a combination thereof, ON, O,
An example in which rewriting is performed in the order of N, OFF, and OFF will be described with reference to FIG.

[0095] In (1 frame) 1 frame, the pulse of the time t ₀ from time t ₁ to a voltage level V _e in first period T ₁ to the scan electrode is applied, followed by the voltage level from the time t ₁ to time t ₂ pulse V _p is applied, further pulses during a voltage level V _b from time T ₂ to time T _m is applied.

[0096] the signal electrodes, first, the pulse voltage level + V _d from time t ₀ to time t ₁ is applied in the period T _1, followed by the voltage level from the time t ₁ to time t ₂ -
Pulse of V _d is applied. Between the period T ₂ to time T _m, i.e. ON pixels other scanning line is selected
Or by OFF + V _d and -V _d or and -V _d +
_Vd pulses are applied one after another.

As a result, the voltage applied to the liquid crystal is
As shown in FIG. 3, during the period T ₁ , the time t ₀ to the time t ₁
Up to the voltage level V _e −V _d , and V _e −
Since _Vd is set as in equation (3), the display written in the previous frame is deleted. Subsequently, at time t
₁ pulse of the voltage level V _p + V _d to the time t ₂ is applied from, for V _p + V _d is set as in equation (5), the ON state. Between the period T ₂ to the period T _n,
Pulse V _b -V _d or V _b + V _d is applied, V _b
Since −V _d or V _b + V _d is set as in Expressions (7) and (8), the ON state is maintained.

(Second Frame) In the second frame, the polarity is inverted to-. The scan electrodes are first pulse voltage level -V _e is applied in the period T ₁ in the second frame, subsequently, applied pulse voltage level -V _p, further between the voltage from time T ₂ to time T _m pulse level -V _b is applied. The signal electrode is first pulsed voltage level -V _d from the time t ₀ to time t ₁ in the period T ₁ is applied, pulse followed by a voltage level from time t ₁ to time t ₂ -V _d is applied . The period T from the period T ₂
Until _m , as in one frame, −V _d and + V _d by ON or OFF of the pixel of the other selected scanning line.
Or + pulse groups of V _d or -V _d is applied one after another.

As a result, in the composite waveform, in the period T ₁ , the pulse of the voltage level −V _e + V _d is applied from the time t ₀ to the time t _1, the display written in the previous frame is erased, and subsequently the time t 1 voltage level from ₁ to time t ₂ -
V _p -V pulse _d becomes applied ON state, the period T
Between ₂ to period T _n -V _b + V _d or -V _b -V
The pulse of _d is applied and the ON state is maintained.

(Third Frame) In the third frame, the polarity is inverted to +. The same pulse group as in one frame is applied to the scanning electrodes. The signal electrode, first pulse voltage level -V _d from the time t ₀ to time t ₁ in the period T ₁ is applied, followed by a pulse of voltage level + V _d from time t ₁ to time t ₂ is applied . Furthermore during the period T ₂ to time T _m, as with one frame or two frames, ON pixels other scanning line is selected or OF
Pulse group of + V _d and -V _d or -V _d and + V _d by F is applied one after another.

[0102] As a result, the composite waveform is displayed that has been written in the previous frame pulse voltage level V _e + V _d from time t ₀ to time t ₁ is applied in the period T ₁ is erased, followed by a time t ₁ voltage level from up to time t ₂ V _p
OFF-state pulse is applied -V _d is sustained, during the period T ₃ to time T _m V _b -V _d or V _b + V _d
And the OFF state is maintained.

(Fourth Frame) In the fourth frame, the polarity is again inverted to-. Pulse groups similar to those in the two frames are applied to the scanning electrodes. The signal electrode, first pulse voltage level + V _d from time t ₀ to time t ₁ in the period T ₁ is applied, followed by a pulse of voltage level -V _d from time t ₁ to time t ₂ is applied . Between the period T ₂ to time T _m, as with one frame or two frames, ON pixels other scanning line is selected or OF
Pulse group of -V _d and + V _d or + V _d and -V _d is applied one after another by F.

[0103] As a result, the composite waveform display that has been written in the previous frame pulse voltage level -V _e -V _d from time t ₀ to time t ₁ is applied in the period T ₁ is erased, followed by time voltage level from t ₁ to time t ₂ -
Pulse V _p + V _d becomes applied ON state, the period T
Between ₂ to period T _m -V _b + V _d or -V _b -V
The pulse of _d is applied and the ON state is maintained.

As described above, according to the display device and the driving method (two-pulse method) of this embodiment, the screen can be rewritten with only two pulses per line. The response speed is calculated by the formula
As shown in equation (1) and equation (2), it relates to the difference between the applied voltage and the threshold voltage, and is almost determined by the liquid crystal material, the orientation, the cell thickness, and the like, and is considered to be a characteristic inherent to the cell.

On the other hand, the maximum voltage that can be applied to the cell is often limited due to restrictions such as the withstand voltage of the transmission gate in the drive circuit. For example, when rewriting from the OFF state to the ON state, if cells having the same characteristics are driven by the same waveform at the maximum voltage, the response time of the liquid crystal is the same, and the required pulse width is considered to be substantially the same. Therefore, it is considered that the time required for rewriting one row is determined by the number of pulses required for rewriting. Whereas the conventional driving method requires three or more pulses per row, the present driving method requires only two pulses. Further, since the voltage of the first pulse can be optimized with respect to the characteristics of the cell, the condition for minimizing the pulse width itself can be determined, and the rewriting time can be reduced to two thirds or less. From another point of view, it became possible to rewrite the number of lines 1.5 times or more in the same time.

Further, according to the driving method of the present invention, the effective value voltage of the erase and write pulses is constant irrespective of ON or OFF of the display in one frame, and the effective value voltage of the holding pulse is also fixed. By inverting the polarity for each frame, the DC component applied to the liquid crystal could be completely canceled. Thereby, the electrochemical deterioration of the liquid crystal was prevented, and the life of the liquid crystal cell was extended. The polarity inversion is not limited to one frame, but may be performed every two frames or more frames as long as the number of positive polarity frames and the number of negative polarity frames are the same.

Second Embodiment

In the driving method of the present invention, V _d ,
V _b , V _e , and V _p are _{calculated according} to equations (9), (14), (17), and (20).
Can be set arbitrarily to some extent within the range shown in FIG. This embodiment differs from the first embodiment in that the voltage V _e to -7V.

As for the optical response, good switching and contrast could be obtained as in the example.

It is to be noted that V _e is normally set at around 0 V as a standard. However, the response time required to turn off the ON state written in the previous frame may be slower than V _p + V _d when V _e ≒ 0 V. In such a case, it is necessary to widen the pulse width so that erasing can be sufficiently performed even when V _e ≒ 0 V. But,
OFF when the V _e is set to a large voltage in the range of formula (17)
It is possible to shorten the response time required to, V _p
+ V _d can be brought close to the speed of response to be driven while the pulse width was kept small.

Conversely, when V _e ≒ 0 V, the switching is not performed from the ferroelectric state to the ferroelectric state of the opposite polarity directly without passing through the antiferroelectric state, so that the OFF state may not be obtained. In such a case, by setting V _e to the negative polarity, the response is delayed, the antiferroelectric state is easily developed, and the switching to the OFF state can be performed.

As described above, by using the driving method of this embodiment, the display can be rewritten with only two pulses, so that the characteristics of the liquid crystal panel can be flexibly adjusted even when the driving circuit is limited. Accordingly, high-speed driving can be maintained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a cross section of a specific example of a matrix type liquid crystal display device of the present invention.

FIG. 2 is an explanatory diagram showing a specific arrangement structure of scanning electrodes and signal electrodes of the matrix type liquid crystal display device of the present invention.

FIG. 3 is a block diagram showing a specific example of a driving unit of the matrix type liquid crystal display device of the present invention.

FIG. 4 is a model diagram of a state of molecules in a cell of an antiferroelectric liquid crystal of a matrix type liquid crystal display device of the present invention when viewed from a direction perpendicular to a substrate surface.

FIG. 5 is a diagram illustrating a relationship between an applied voltage and a relative transmitted light intensity for explaining how to obtain a threshold voltage according to a conventional method.

FIG. 6 is a diagram showing a measurement result of optical response characteristics of a conventional liquid crystal device by applying a triangular wave voltage (frequency: 0.01 Hz).
It is.

FIG. 7 is a diagram (frequency: 0.1 Hz) showing measurement results of optical response characteristics of a conventional liquid crystal device by applying a triangular wave voltage.

FIG. 8 is a diagram (frequency: 1 Hz) showing measurement results of optical response characteristics of a conventional liquid crystal device when a triangular wave voltage is applied.

FIG. 9 is a diagram illustrating a method for determining a first threshold characteristic in a specific example of the present invention, and is a diagram illustrating a relationship with a light transmittance when a second rectangular wave voltage <Vc ^ON .

FIG. 10 is a diagram illustrating a method for determining a first threshold characteristic in a specific example of the present invention, and is a diagram illustrating a relationship with a light transmittance when a second rectangular wave voltage> Vc ^ON .

FIG. 11 is a diagram illustrating a method of determining a first threshold characteristic in a specific example of the present invention, and is a diagram illustrating a relationship with a light transmittance when a second rectangular wave voltage >> Vc ^ON .

FIG. 12 is a diagram illustrating a method for determining a first threshold characteristic in a specific example of the present invention, and is a diagram illustrating a relationship between an applied voltage and a response speed.

FIG. 13 is a diagram for explaining a method of determining a second threshold characteristic in a specific example of the present invention, and is a diagram illustrating a relationship with a light transmittance when a second rectangular wave voltage> Vc ^OFF .

FIG. 14 is a diagram illustrating a method for determining a second threshold characteristic in a specific example of the present invention, and is a diagram illustrating a relationship with a light transmittance when a second rectangular wave voltage <Vc ^OFF .

FIG. 15 is a diagram for explaining a method of determining a second threshold characteristic in a specific example of the present invention, where a second rectangular wave voltage << Vc ^OFF
FIG. 9 is a diagram showing a relationship with light transmittance at the time of FIG.

FIG. 16 is a diagram illustrating a method of determining a second threshold characteristic in a specific example of the present invention, and is a diagram illustrating a relationship between an applied voltage and a response speed.

FIG. 17 is a voltage waveform chart for explaining a method of driving the matrix type liquid crystal display device of the present invention.

FIG. 18 is a diagram for explaining a driving method of the matrix type liquid crystal display device of the present invention, and is a diagram showing a relationship between an applied voltage at ON and a light transmittance.

FIG. 19 is a diagram for explaining a driving method of the matrix type liquid crystal display device of the present invention, and is a diagram showing a relationship between an applied voltage and a light transmittance at an OFF time.

FIG. 20 is a diagram for explaining a driving method of the matrix type liquid crystal display device of the present invention, and is a voltage waveform diagram at the time of ON and at the time of OFF.

FIG. 21 is a diagram for explaining a method of driving the matrix type liquid crystal display device of the present invention, and is an applied voltage waveform diagram for explaining a period in which a frame is negative.

FIG. 22 is a diagram for explaining a method of driving the matrix type liquid crystal display device of the present invention, and is a diagram illustrating an example (when Ve = 0) of a voltage waveform applied to a scanning electrode and a signal electrode.

FIG. 23 is a diagram for explaining the driving of the liquid crystal display device according to the first embodiment of the present invention, and shows a waveform of a voltage applied to the liquid crystal (Ve =
0).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Liquid crystal cell 2 ... Substrate 3 ... Substrate 4 ... Scanning electrode 5 ... Signal electrode 6 ... Alignment film 7 ... Antiferroelectric liquid crystal 9 ... Driving device 91 ··· Scanning circuit section 911 ··· Shift register 912 ··· Data latch 913 ··· Voltage selection circuit 92 ··· Signal side circuit section 921 ··· Shift register 922 ··· Data latch 923 ··· Voltage selection circuit 93 ··· Electronic control unit 94 Storage unit 95 Power supply circuit S1 Scan data S2 Signal data

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G02F 1/133 560 G09G 3/36

Claims (2)

(57) [Claims] 1. A pair of substrates sandwiched opposite to each other at a predetermined interval, scanning electrodes arranged in a stripe shape inside one of the substrates, and a pair of substrates formed inside the other substrate of the pair of substrates. A signal electrode disposed so as to face the scanning electrode at a right angle to the scanning electrode, and an alignment film disposed on at least one of the sides of the substrate on which the electrode is formed; In a matrix type liquid crystal display device comprising a liquid crystal cell made of an antiferroelectric liquid crystal sealed between a pair of substrates, and a drive control means for applying a drive signal to the liquid crystal cell, the drive control means for writing a display. A driving signal applied to the display for temporarily erasing the display, a first pulse set to a first threshold voltage or less, and a voltage equal to or higher than the first threshold voltage applied to turn on the display, or Turn off And the effective voltage added to the first pulse is a certain voltage, and when the voltage is inverted in another period, the DC component is completely A matrix type liquid crystal display device characterized by two pulses comprising a second pulse set so as to cancel each other, wherein the writing pulse unit and the display capability are improved by reducing the unit of applied pulse. 2. An alignment layer is provided on at least one of a pair of substrates in which scanning electrodes are arranged on one substrate and signal electrodes are arranged on the other substrate in a direction crossing each other, and an antiferroelectric substance is provided between the pair of substrates. In a method for driving a matrix type liquid crystal display device comprising a liquid crystal cell in which liquid crystal is sealed and a drive control means for applying a drive signal to the liquid crystal cell, the liquid crystal cell is set at a first threshold voltage or less to temporarily erase the display. It comprises a first pulse and a second pulse set so that the effective voltage added to the first pulse becomes a certain voltage and the DC component is completely canceled when the voltage is inverted in another period. A method for driving a matrix-type liquid crystal display device, comprising applying a drive signal composed of two pulses.