JP2001228459A - Driving method for liquid crystal display element and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a driving method which is capable of making display elements provided with liquid crystal indicating a cholesteric phase perform a display at high speed and and also is capable of making them display halftones and in which output levels of drivers are managed to be small. SOLUTION: This method is a driving method driving liquid crystal display elements indicating cholesteric phases capable of maintaining a display in an electric field-OFF state with plural scanning electrodes and plural signal electrodes which are intersected in a state in which they are opposed with each other in a matrix. This driving method includes a reset period Tr making liquid crystal to be in a homeotrophic state, a selection period Ts for selecting the final display state and a sustenance period Te for establishing the state selected in the selection period Ts and periods Ts1, Ts3 when voltage value becomes zero substantially are provided before and after a period Ts2 when selection pulse voltages are applied to the liquid crystal in the selection period Ts.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of driving a liquid crystal display element, and more particularly, to a method of driving a liquid crystal exhibiting a cholesteric phase capable of maintaining a display in an electric field-off state by a plurality of scanning electrodes and a plurality of scanning electrodes intersecting each other. The present invention relates to a method for driving a liquid crystal display element driven by a matrix with signal electrodes and a liquid crystal display device including a liquid crystal display element driven by the driving method.

[0002]

2. Description of the Related Art In recent years, as a medium for reproducing digital information into visible information, attention has been paid to the advantage that a reflection type liquid crystal display device using a liquid crystal exhibiting a cholesteric phase at room temperature can be manufactured with low power consumption and at low cost. Various developments and researches have been conducted. However, it has been found that a display element using this kind of memory liquid crystal has a specific disadvantage that the driving speed is slow.

[0003] As a conventionally known prior art, there is US Pat. No. 5,748,277. Here, the liquid crystal having bistability is driven by a preparation period for bringing the liquid crystal into a homeotropic state, a selection period for bringing the liquid crystal into a focal conic state or a planar state, and an evolution period for fixing the state. The display state of the liquid crystal is selected by controlling the voltage value applied during the selection period to two levels, high and low.

However, in such a driving method,
It has the following problems. That is, only two-tone display of ON and OFF can be realized, and no consideration is given to displaying a halftone. In addition, the type of the driving voltage is the driving IC of the scanning electrode.
In this case, at least seven values are required for the signal electrode drive IC, and at least two values are required for the drive IC for the signal electrodes, which increases the cost of the driver. Further, even after the display state is determined, a pulse voltage for writing is applied with the same voltage value from the signal electrode to each pixel, and image deterioration occurs due to crosstalk.

Accordingly, an object of the present invention is to provide an improved driving method of a liquid crystal display element and a liquid crystal display device which can solve the above problems.

[0006]

In order to achieve the above objects, the driving method according to the first aspect of the present invention provides a reset period for bringing the liquid crystal into a homeotropic state and a selection period for selecting a final display state. And a sustain period for establishing a state selected in the selection period. The selection period includes a period in which the voltage value applied to the liquid crystal is substantially zero before and after the period in which the selection pulse is applied to the liquid crystal. It is characterized by having been provided.

In the first aspect, by driving the liquid crystal during the reset period, the selection period, and the sustain period, a desired display can be realized at a relatively high speed.
Since the voltage value has a period of substantially zero during the selection period,
As a result, the number of output levels of the driving driver can be reduced.

[0008] During the selection period of the predetermined selected scanning electrode, the selection period of the next selected scanning electrode may be started. The reset period, the selection period, and the sustain period may be set to integral multiples of the shortest period among these three periods. The voltage value of the selection pulse may be equal to or less than the voltage value of the reset pulse.

After the scan electrodes are collectively selected and each pixel on each scan electrode is reset, during the period of selection to a predetermined scan electrode, the absolute value of the next scan electrode to be selected is smaller than zero. A large maintenance voltage may be applied. The reset state can be maintained by applying the sustain voltage.

The display state may be selected by modulating the pulse width of the selection pulse applied during the selection period. By modulating the pulse width of the selection pulse, halftone display can be realized.

The driving method according to the second invention is characterized in that the energy of the crosstalk voltage applied to the pixels on the unselected scanning electrodes is smaller than the energy of the voltage applied to the signal electrodes. A driving method according to a third aspect is characterized in that a pulse width of a crosstalk voltage applied to a pixel on a non-selected scanning electrode is smaller than a pulse width of a voltage applied to a signal electrode.

In the second and third aspects of the present invention, since the energy of the crosstalk voltage is small or the pulse width is small, the influence of crosstalk from an adjacent pixel is reduced, and deterioration of an image can be eliminated.

On the other hand, in the liquid crystal display device according to the present invention, a liquid crystal exhibiting a cholesteric phase capable of maintaining a display in an electric field-off state is driven in a matrix by a plurality of scanning electrodes and a plurality of signal electrodes which cross each other in a facing state. In a liquid crystal display device, a liquid crystal display element is driven by the driving method. Further, the output of the scan electrode driver for applying a voltage to the scan electrode is three or less, and the output of the signal electrode driver for applying a voltage to the signal electrode is two or less.

[0014] At least one of the scan electrode driver and the signal electrode driver may be provided with an analog switch connected to a plurality of power supplies having different voltage values. By doing so, the types of output values of the driver itself can be reduced.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a driving method and a liquid crystal display device according to the present invention will be described with reference to the accompanying drawings.

(Liquid crystal display device, see FIGS. 1 to 4)
A liquid crystal display element having a built-in liquid crystal exhibiting a cholesteric phase and constituting a liquid crystal display device will be described.

FIG. 1 shows a reflection type full-color liquid crystal display device using a simple matrix drive system. The liquid crystal display element 100 has a red display layer 111R on the light absorption layer 121, which performs display by switching between red selective reflection and a transparent state.
, And a green display layer 111G for displaying by switching between green selective reflection and a transparent state is laminated thereon, and a blue display layer 111B for displaying by switching between blue selective reflection and a transparent state is further stacked thereon. Are laminated.

Each display layer 111R, 111G, 111B
Has a structure in which a resin columnar structure 115, a liquid crystal 116 and a spacer 117 are sandwiched between transparent substrates 112 on which transparent electrodes 113 and 114 are formed, respectively. Transparent electrode 11
An insulating film 118 and an orientation control film 119 are provided on the 3, 114 as needed. Further, a sealing material 1 for sealing the liquid crystal 116 is provided on an outer peripheral portion (outside the display area) of the substrate 112.
20 are provided.

The transparent electrodes 113 and 114 are driven
C131 and 132 (see FIG. 4), and a predetermined pulse voltage is applied between the transparent electrodes 113 and 114, respectively. In response to the applied voltage, the display is switched between a transparent state in which the liquid crystal 116 transmits visible light and a selective reflection state in which visible light of a specific wavelength is selectively reflected.

The transparent electrodes 113 and 114 provided on each of the display layers 111R, 111G and 111B are composed of a plurality of strip electrodes arranged in parallel at a fine interval, and the directions of the strip electrodes are mutually different. They are opposed so as to be at right angles. Current is sequentially applied to these upper and lower strip electrodes. That is, display is performed by sequentially applying a voltage to each liquid crystal 116 in a matrix. This is referred to as matrix driving, and a portion where the electrodes 113 and 114 intersect constitutes each pixel. By performing such matrix driving sequentially or simultaneously for each display layer, a full-color image is displayed on the liquid crystal display element 100.

More specifically, in a liquid crystal display device in which a liquid crystal exhibiting a cholesteric phase is sandwiched between two substrates, display is performed by switching the state of the liquid crystal between a planar state and a focal conic state. When the liquid crystal is in the planar state, assuming that the helical pitch of the cholesteric liquid crystal is P and the average refractive index of the liquid crystal is n, light of wavelength λ = P · n is selectively reflected. Also,
In the focal conic state, the light is scattered when the selective reflection wavelength of the cholesteric liquid crystal is in the infrared light range, and transmits visible light when the wavelength is shorter than that. Therefore, by setting the selective reflection wavelength in the visible light range and providing the light absorbing layer on the side opposite to the observation side of the element, it is possible to display the selective reflection color in the planar state and display black in the focal conic state. In addition, by setting the selective reflection wavelength in the infrared light range and providing a light absorption layer on the side opposite to the observation side of the element, light in the infrared light range is reflected in the planar state, but the wavelength in the visible light range is reflected. Is transmitted, so that a black display and a white display due to scattering in the focal conic state are possible.

In the liquid crystal display element 100 in which the display layers 111R, 111G, and 111B are stacked, the blue display layer 111B and the green display layer 111G are in a transparent state in which liquid crystals are in a focal conic arrangement, and the red display layer 111R is formed of a liquid crystal. A red display can be performed by setting the array in the selective reflection state. Also, the blue display layer 111B
Is set in a transparent state in which liquid crystals are in a focal conic arrangement, and the green display layer 111G and the red display layer 111R are in a selective reflection state in which liquid crystals are in a planar arrangement, whereby yellow display can be performed. Similarly, red, green, blue, white, cyan, magenta, yellow, and black can be displayed by appropriately selecting the state of each display layer between a transparent state and a selective reflection state. Further, by selecting an intermediate selective reflection state as the state of each of the display layers 111R, 111G, and 111B, an intermediate color can be displayed, and the display layer can be used as a full-color display element.

As the transparent substrate 112, a colorless and transparent glass plate or a transparent resin film can be used.

The transparent electrodes 113 and 114 are made of ITO.
(Indium Tin Oxide) and other transparent electrodes can be used, and metal electrodes such as aluminum and silicon, or amorphous silicon and BSO (Bismuth Silicon Oxid) can be used.
A photoconductive film such as e) can also be used. Further, as for the lowermost transparent electrode 114, a black electrode can be used including the role as a light absorber.

As the insulating film 118, an inorganic film such as silicon oxide or an organic film such as a polyimide resin or an epoxy resin is used so as to function also as a gas barrier layer.
12 to prevent short circuit and improve the reliability of the liquid crystal. In addition, polyimide is a typical example of the orientation control film 119.

The liquid crystal 116 preferably exhibits a cholesteric phase at room temperature. In particular, a chiral nematic liquid crystal obtained by adding a chiral dopant to a nematic liquid crystal is preferable.

The chiral dopant is an additive having a function of twisting the molecules of the nematic liquid crystal when added to the nematic liquid crystal. By adding a chiral dopant to a nematic liquid crystal, a helical structure of liquid crystal molecules having a predetermined twist interval is generated, thereby exhibiting a cholesteric phase.

The chiral nematic liquid crystal has the advantage that the pitch of the helical structure can be changed by changing the amount of the chiral dopant to be added, whereby the selective reflection wavelength of the liquid crystal can be controlled. In addition,
In general, as a term representing the pitch of the helical structure of liquid crystal molecules, a “helical pitch” defined by a distance between molecules when the liquid crystal molecules rotate 360 degrees along the helical structure of the liquid crystal molecules is used.

As a material used for the columnar structure 115, for example, a thermoplastic resin can be used. For this purpose, a material which is softened by heating and solidified by cooling, is desired not to cause a chemical reaction with a liquid crystal material to be used and to have appropriate elasticity.

The columnar structure 115 is formed by printing the above-mentioned substance by using a known printing method and using a pattern so as to form dot columns as shown in FIG. Liquid crystal display element 100
Depending on the size of the pixel and the pixel resolution,
The arrangement pitch and shape (a column, a drum shape, a polygon, etc.) are appropriately selected. The columnar structure 1 is preferentially provided between the electrodes 113.
Arranging 15 is more preferable because the aperture ratio is improved.

The spacer 117 is preferably a particle made of a hard material that does not deform by heating or pressing. For example, finely divided glass fibers, inorganic materials such as ball-shaped silicate glass and alumina powder, or organic synthetic spherical particles such as divinylbenzene-based crosslinked polymers and polystyrene-based crosslinked polymers can be used.

As described above, the hard spacer 117 for maintaining the gap between the two substrates 112 at a predetermined size, and the pair of substrates 112 which are arranged in the display area based on a predetermined arrangement rule and adhere and support the pair of substrates 112. By providing a resin structure 115 mainly composed of a thermoplastic polymer material,
2, the two substrates 112 are firmly supported, there is no uneven arrangement, and the generation of bubbles can be suppressed in a low-temperature environment. Note that the spacer 117 is not always necessary.

Here, a manufacturing example of the liquid crystal display element 100 will be briefly described. First, a plurality of strip-shaped transparent electrodes are formed on two transparent substrates, respectively. The transparent electrode is formed by forming an ITO film on a substrate by a sputtering method or the like and then performing patterning by a photolithography method.

Next, a transparent insulating film or an orientation control film is formed on the transparent electrode forming surface of each substrate. The insulating film and the orientation control film can be formed by a known method such as a sputtering method, a spin coating method, or a roll coating method using an inorganic material such as silicon oxide or an organic material such as a polyimide resin. Note that a rubbing treatment is not usually performed on the alignment control film. Although the function of the alignment control film is not yet clear, it is considered that the presence of the alignment control film can give a certain degree of anchoring effect to the liquid crystal molecules, and the characteristics of the liquid crystal display element change over time. Can be prevented. In addition, a function as a color filter may be provided by adding a dye to these thin films to improve color purity and contrast.

Thus, a columnar structure is formed on the electrode forming surface of one of the substrates provided with the transparent electrode, the insulating film, and the alignment control film. The columnar structure is a printing method in which a paste-like resin material obtained by dissolving a resin in a solvent is extruded with a squeegee through a screen plate or a metal mask and printed on a substrate mounted on a flat plate, a dispenser method or an inkjet method. For example, it can be formed by a method in which a resin material is discharged onto a substrate from the tip of a nozzle, or a transfer method in which a resin material is supplied onto a flat plate or a roller and then transferred to the substrate surface. . It is desirable that the height at the time of forming the columnar structure be larger than the desired thickness of the liquid crystal display layer.

A sealing material is provided on the electrode forming surface of the other substrate by using an ultraviolet curable resin, a thermosetting resin, or the like. The sealant is arranged in a continuous ring at the outer edge of the substrate. The arrangement of the sealing material, like the columnar structure described above, a method of forming a resin by discharging a resin from the tip of a nozzle onto a substrate such as a dispenser method or an inkjet method, a screen plate, a printing method using a metal mask, or the like, After the resin is formed on a flat plate or a roller, the resin may be transferred onto a transparent substrate by a transfer method or the like. Further, spacers are sprayed on the surface of at least one of the substrates by a conventionally known method.

Then, the pair of substrates are overlapped so that the electrode forming surfaces face each other, and heated while pressing from both sides of the pair of substrates. Pressing and heating are performed, for example, as shown in FIG. 25, by placing the substrate 112a on which the columnar structure 115 is formed on the flat plate 150, and stacking the opposing substrate 112b,
The heating can be performed by passing between the roller 151 and the flat plate 150 while applying heat and pressure by the heating / pressing roller 151 from the end. By using such a method, a cell can be manufactured with high accuracy even using a flexible substrate having flexibility such as a film substrate. If the columnar structure is formed of a thermoplastic polymer material, the columnar structure can be softened by heating and solidified by cooling, and the two substrates can be bonded by the columnar structure. When a thermosetting resin material is used as the sealing material, the sealing material may be cured by heating when the substrates are superposed.

In this overlapping step, a liquid crystal material is dropped on one of the substrates, and the liquid crystal material is injected into the liquid crystal element simultaneously with the overlapping of the substrates. In this case, the spacer may be included in the liquid crystal material in advance, and the spacer may be dropped on at least one of the substrates on which the strip-shaped electrode is formed.

The liquid crystal material can be filled in the entire area of the substrate by dropping the liquid crystal material on the edge of the substrate and spreading the liquid crystal material to the other end while overlapping the substrates with a roller. By doing so, it is possible to reduce the entrapment of bubbles generated when the substrates are overlapped with each other in the liquid crystal material.

Thereafter, the substrate is continuously pressed until the substrate temperature falls below the softening temperature of the resin material constituting the columnar structure, and then the pressing is stopped. Further, a photo-curable resin material is used as a sealing material. If so, light irradiation is performed thereafter to cure the sealing material.

In the same procedure, the liquid crystal material is changed to a material having a different selective reflection wavelength, and cells for blue display, green display, and red display are manufactured. The cells thus manufactured are stacked in three layers, these are attached with an adhesive, and a light absorbing layer is further provided as a lowermost layer to obtain a full-color liquid crystal display device.

As shown in FIG. 4, the pixel configuration of the liquid crystal display element 100 includes a plurality of scanning electrodes R1, R2 to R2.
m and signal electrodes C1, C2 to Cn (n and m are natural numbers). The scan electrodes R1, R2 to Rm are connected to the output terminal of the scan drive IC 131, and the signal electrodes C
1, C2 to Cn are connected to output terminals of the signal drive IC 132.

The scanning drive IC 131 includes scanning electrodes R1, R
A selection signal is output to a predetermined one of 2 to Rm to be in a selected state, while a non-selection signal is output to other electrodes to be in a non-selected state. The scan driving IC 131 sequentially switches the scan electrodes R1, R2 to R2 while switching the electrodes at predetermined time intervals.
A selection signal is applied to Rm. On the other hand, the signal drive IC 1
32 simultaneously outputs signals corresponding to the image data to the signal electrodes C1, C2 to Cn in order to rewrite each pixel on the selected scanning electrodes R1, R2 to Rm. For example,
When the scanning electrode Ra is selected (a is a natural number satisfying a ≦ m), the scanning electrode Ra and each of the signal electrodes C1, C2 to Cn
, The pixels LRa-C1 to LRa-Cn at the intersection with are rewritten simultaneously. Thereby, the voltage difference between the scanning electrode and the signal electrode in each pixel becomes the rewriting voltage of the pixel,
Each pixel is rewritten according to the rewriting voltage.

The driving circuits are a central processing unit 135, an LCD controller 136, an image processing unit 137, an image memory 1
38 and drive ICs (drivers) 131 and 132, and the LCD controller 136 drives the drive ICs 131 and 13 based on the image data stored in the image memory 138.
2 is applied, a voltage is sequentially applied between each scanning electrode and the signal electrode of the liquid crystal display element 100, and an image is written on the liquid crystal display element 100. The detailed configuration of the driving ICs 131 and 132 will be described later.

Here, assuming that the first threshold voltage for untwisting the liquid crystal exhibiting the cholesteric phase is Vth1, the voltage Vth1 is applied for a sufficient time and then the voltage is reduced to the second threshold voltage Vth1 smaller than the first threshold voltage Vth1. When the voltage is lowered to the threshold voltage Vth2 or less, a planar state is set. When a voltage of Vth2 or more and Vth1 or less is applied for a sufficient time, a focal conic state is established. These two states are stably maintained even after the voltage application is stopped. By applying a voltage between Vth1 and Vth2, halftone display, that is, gradation display is possible.

When partial rewriting is to be performed, only specific scanning lines may be sequentially selected so as to include a portion to be rewritten. As a result, only necessary parts can be rewritten in a short time.

The rewriting of each pixel can be performed by the above-described method. If an image is already displayed, reset all the pixels to the same display state before rewriting in order to eliminate the influence of the image. Is preferred. The reset may be performed for all pixels at once or for each scan electrode.

When partial rewriting is to be performed, resetting may be performed for each scanning line or may be collectively reset only between specific scanning lines including a portion to be rewritten.

In the liquid crystal display element 100, the element configuration in which the resin columnar structure is included in the liquid crystal display layer has been described. With such a configuration, it is possible to manufacture a light-weight liquid crystal display element having excellent display characteristics using a film substrate, and at the same time, it is easy to increase the size, the driving voltage is relatively small, and various excellent properties such as impact resistance are obtained. It has features and is particularly useful.

However, the memory liquid crystal itself is not necessarily limited to this configuration, and the conventionally known polymer 3
The liquid crystal display layer can be configured as a so-called polymer dispersed liquid crystal composite film in which liquid crystal is dispersed in a three-dimensional network structure or a three-dimensional network structure of a polymer is formed in the liquid crystal. .

(Driving Principle, See FIGS. 5 and 6) First, the driving principle of the driving method according to the present invention will be described. In addition,
Here, a specific example using an AC pulse waveform will be described, but it goes without saying that the driving method according to the present invention is not limited to this waveform. The driving method of this example is roughly divided into reset periods T as shown in FIG.
r, a selection period Ts, a sustain period Te, and a display period Td.

In FIG. 5, the upper part of the drawing shows the driving waveform applied to the liquid crystal (LCD1) of a certain pixel.
The lower part of the figure schematically shows the state of the liquid crystal in each period. As shown in FIG. 5, in this example, the reset period T
r is twice the selection period Ts, and the maintenance period Te is the selection period Ts.
Is set to be three times as long as. Therefore, the selection period Ts
The rewriting of one line is completed in a period that is six times as large as that of the above. When line-sequential driving is performed, a strip-shaped dark portion corresponding to six lines appears to run.

In the reset period Tr, first, a voltage having an absolute value Vr is applied to a pixel on a scanning electrode to be written, whereby the pixel on the scanning electrode is reset to a homeotropic state (FIG. 5). a).

The selection period Ts has three further periods (a pre-selection period Ts1, a selection pulse application period Ts2, and a post-selection period Ts).
s3). In the previous selection period Ts1, the voltage applied to the pixel on the scan electrode to be written is set to zero. At this time, the liquid crystal is slightly twisted (first
Transition state) (see b in FIG. 5). Next, a selection pulse corresponding to an image to be displayed is applied (selection pulse application period Ts2). In the selection pulse application period Ts2, a pixel that finally wants to select the planar state and a pixel that wants to select the focal conic state have the following characteristics.
The shape of the applied pulse is different. Therefore, the case where the planar state is selected and the case where the focal conic state is selected will be described separately after the selection pulse application period Ts2.

When selecting the planar state, a selection pulse having an absolute value Vsel is applied during the selection pulse application period Ts2, and the liquid crystal is again brought into the homeotropic state (see c1 in FIG. 5). Thereafter, when the voltage is reduced to zero in the post-selection period Ts3, the liquid crystal is in a state in which the twist is slightly restored (FIG. 5).
Middle d1). This state is considered to be substantially equal to the previous first transition state.

In the subsequent maintenance period Te, first,
A pulse voltage having an absolute value Ve is applied to a pixel on a scanning electrode to be written. The liquid crystal in which the twist has slightly returned in the previous selection period Ts is untwisted again by the application of the pulse voltage Ve, and is in a homeotropic state (e in FIG. 5).
1).

In the display period Td, the voltage applied to the liquid crystal is set to zero. The liquid crystal in the homeotropic state is brought into a planar state by setting the voltage to zero (f1 in FIG. 5).
reference). In this way, the planar state is selected.

On the other hand, when it is desired to finally select the focal conic state, the voltage applied to the liquid crystal is set to zero during the selection pulse application period Ts2. As a result, a state in which the twist of the liquid crystal is further restored (second transition state) is reached (c in FIG. 5).
2). Then, during the post-selection period Ts3, the voltage applied to the liquid crystal is set to zero as in the case of selecting the planar state. By doing so, it is considered that the liquid crystal is untwisted and the helical pitch is expanded to about twice (third transition state) (see d2 in FIG. 5). This state is considered to be close to a state called a transient planar described in the above-mentioned US Pat. No. 5,748,277.

In the subsequent sustain period Te, as in the case of selecting the planar state, a pulse voltage having an absolute value Ve is applied to the pixels on the scanning line to be written. The liquid crystal whose twist has returned in the previous selection period Ts has the pulse voltage Ve
(4th transition state, see e2 in FIG. 5).

In the display period Td, the voltage applied to the liquid crystal is set to zero as in the case where the planar state is selected.
Even if the voltage of the liquid crystal in the focal conic state becomes zero,
It is fixed in the focal conic state. In this way, the focal conic state is selected (f in FIG. 5).
2).

As described above, the final display state of the liquid crystal can be selected by the selection pulse applied in the middle short period of the selection period Ts, that is, the selection pulse application period Ts2.
Further, by adjusting the pulse width of the selection pulse, specifically, by changing the shape of the pulse applied to the signal electrode according to the image data, it is possible to display a halftone.

As described above, by setting the voltage value applied to the liquid crystal to zero during the pre-selection period Ts1 and the post-selection period Ts3 and setting it to be the idle period, a simple driver configuration as described later can be adopted. It is effective due to cost reduction. Of course, the voltage is not zero, and may be a value close to zero and within a range of a voltage value at which substantially no voltage acts.

FIG. 6 shows a drive voltage waveform applied to the liquid crystal of a certain pixel among a plurality of pixels arranged in a matrix, and scanning electrodes (rows) and signal electrodes (columns) for obtaining this waveform.
An example of the waveform of FIG. In FIG. 6, a row means one line on a scanning electrode, and a column means one line on a signal electrode. The LCD means a liquid crystal layer for one pixel where a row and a column intersect.

As shown in FIG. 6, in the case of matrix driving, a predetermined voltage is applied from the signal electrode as a crosstalk voltage to write data to pixels on other scanning electrodes even after the elapse of the sustain period Te. . A period during which the crosstalk voltage is applied is referred to as a crosstalk period Td '.
Since the crosstalk voltage has a small pulse width and small energy, it hardly affects the state of the liquid crystal.

When the selection of all the scan electrodes is completed and the sustain period Te of the last selected scan electrode ends, all the crosstalk periods Td 'of the other scan electrodes end, and all scan electrodes and signal electrodes are connected. And the display period T
d. This state is continued until the next rewriting.

In FIG. 6, for the sake of simplicity, the reset period Tr, the selection period Ts, the sustain period Te, and the crosstalk period Td 'are all shown with the same length. For the same reason, in FIG. 6, all the signals in the column are drawn as pulses for selecting the planar state.

Hereinafter, a specific example of the matrix driving waveform will be described. In Examples 1 to 4 shown below, rows 1 to 3 mean three scanning electrodes selected in order,
The column means one signal electrode crossing each of the scanning electrodes, and the LCDs 1 to 3 mean liquid crystal layers corresponding to three pixels formed at the intersection of the rows 1 to 3 and the column.

(Example 1 of Matrix Driving) As described above, in the driving method of this embodiment, the reset period,
It has a selection period, a sustain period, and a crosstalk period. Further, the selection period is divided into three, a pre-selection period, a selection pulse application period, and a post-selection period, and the selection pulse is applied to only a part of the selection period.

It is necessary to change the shape of the selection pulse depending on the image data to be displayed on the pixel to be written, and it is necessary to apply a selection pulse having a different shape to the column according to the image data. On the other hand, in the pre-selection period and the post-selection period, since a voltage of zero is always applied to the liquid crystal in the pixel, a fixed combination of pulse waveforms can be used for both the row and the column so as to obtain the voltage of zero. In Example 1 shown in FIG. 7, utilizing this, reset, maintenance, and display are simultaneously performed on pixels on a plurality of scan electrodes.

For example, when the LCD 2 is in the previous selection period, a pulse voltage + V1 having a different phase is applied to the rows 2 and 3, and a voltage of + V1 / 2 is applied to the row 1. At this time, if a pulse voltage + V1 having a phase different from that of the row 3 is applied to the column, the voltage ± VR = ±
V1 reset pulse, LCD2 voltage zero, L
A sustain pulse of voltage ± Ve = ± V1 / 2 is applied to CD1.

When the LCD 2 is in the selection pulse application period, since a data pulse (voltage + V1) of a different shape is applied from the column depending on the image data, a pulse of voltage + V1 / 2 is applied to both row 1 and row 3. LCD
1. A voltage of ± V1 / 2 is applied to the LCD 3. A pulse of voltage + V1 is applied to row 2 and a voltage difference from the data pulse applied to the column (± V1 or zero)
Is applied to the LCD 2 as a selection pulse of the voltage ± Vsel. By changing the shape of the data pulse applied to the column, the pulse width of the selection pulse can be changed.

In the subsequent selection period, the same operation as in the previous selection period is performed. That is, a pulse voltage + V1 having a different phase is applied to rows 2 and 3, and a voltage of + V1 / 2 is applied to row 1. Then, by applying a pulse voltage + V1 having a phase different from that of the row 3 to the column, a reset pulse of a voltage ± VR = ± V1 is applied to the LCD3, a voltage of zero is applied to the LCD2, and a sustain pulse of a voltage ± Ve = ± V1 / 2 is applied to the LCD1. Apply.

During the periods other than the reset period, the selection period, and the sustain period, a waveform having the same phase as the data pulse applied from the signal electrode during the pre-selection period and the post-selection period of the other scan electrodes is applied to each scan electrode. And a pulse of voltage + V1 / 2 is applied during the selection pulse application period of the other scan electrodes. Thus, a crosstalk voltage of ± V1 / 2 is applied to the liquid crystal in this portion with the same pulse width as the selection pulse in accordance with the image data. This crosstalk voltage does not affect the display state of the liquid crystal because the pulse width is narrow.

An image can be displayed by sequentially and repeatedly applying the above-described pulse voltage to each scanning electrode. Selection of each scanning electrode may be performed line-sequentially, or may be performed in an arbitrary order. Further, since the reset pulse, the selection pulse, and the sustain pulse can be applied to an arbitrary scanning electrode, partial rewriting can be performed.

In Example 1, the number of output voltages required for the drive IC is ternary (V1, V1 / 2, GND) on the row side and binary (V1, GND) on the column side.

(Example of Configuration of Drive IC of Example 1) FIG. 8 shows an internal circuit of a scan drive IC that outputs the drive waveforms shown in FIG.
The scan driving IC includes a shift register 300, a latch 30
1, a decoder 302 and a level shifter / high withstand voltage ternary driver 303. In this scan driving IC, the decoder 3
02, the mode switching signal MODE and the polarity inversion signal PC are input, the strobe signal STB is input to the latch 301, and the data signal DATA, the shift clock signal CLK, and the clear signal CLR are input to the shift register 300.

The operation of the scan driving IC will be described below. 2-bit data signal D input to shift register 300
2-bit data is set in the shift register 300 by the ATA and the shift clock signal CLK. Next, the data of the shift register 300 is latched by the latch 301 according to the strobe signal STB. The decoder 302 decodes the 2-bit data signal DATA in response to the latched 2-bit data signal DATA, polarity inversion signal PC, and mode switching signal MODE, and outputs the level shifter /
The high withstand voltage ternary driver 303 is driven. Level shifter /
The high withstand voltage ternary driver 303 includes Vr1, Vr2, GND
An arbitrary voltage value is output among the three values.

Table 1 shown below is a truth table of the scanning drive IC. As shown in Table 1, the 2-bit data signal DA
TA1,2, polarity inversion signal PC, mode switching signal MO
Vr1, Vr2, G by the combination of DE1 and DE2
An arbitrary voltage value among the three values of ND can be output. Vr1
= V1, Vr2 = V1 / 2, high withstand voltage ternary driver 303
, The scanning waveform shown in FIG. 7 can be output.

[0079]

[Table 1]

Next, FIG. 9 shows an internal circuit of the signal drive IC for outputting the drive waveform shown in FIG. The signal driving IC includes a shift register 500, a latch 501, a comparator 50
2, decoder 503, level shifter / high voltage driver 5
04 and a counter 505. In this signal driving IC, the output inhibition signal OE and the polarity inversion signal PC are input to the decoder 503, and the strobe signal ST is input to the latch 501.
B is input, 8-bit data signal DATA, shift clock signal CLK, and clear signal CLR are input to shift register 500, and clock signal CCLK and clear signal CCLR are input to counter 505.

The operation of the signal driving IC will be described. The 8-bit data signal DATA and the shift clock signal CLK input to the shift register 500 set 8-bit data in the shift register 500. Next, the shift register 50 is activated by the strobe signal STB.
The data of 0 is latched by the latch 501. Here, the 8-bit output is counted up from zero by the clock signal CCLK input to the counter 505. The comparator 502 compares the output of the latch 501 with the output of the counter 505, and outputs a high-level signal when the output of the latch 501 is large. Further, when the count-up of the counter 505 proceeds and the output of the latch 501 decreases, a low-level signal is output. Then, a signal for driving the level shifter / high withstand voltage driver 504 is output from the decoder 503 based on the output of the comparator 502, the output inhibition signal OE, and the polarity inversion signal PC.

Table 2 shown below is a truth table of the signal driving IC. As shown in Table 2, two types of voltages, Vc1 and GND, can be output by a combination of the output of the comparator 502, the output inhibition signal OE, and the polarity inversion signal PC. By inputting Vc1 = V1, FIG.
Can be output.

[0083]

[Table 2]

As described above, the cost of the driving IC can be reduced by using a ternary driver on the scanning side and a binary driver on the signal side.

(Example 2 of Matrix Driving) In Example 1 described above,
While the voltage Vsel of the selection pulse applied during the selection period is equal to the voltage Vp of the reset pulse Vp = V1, in Example 2 described here, the voltage Vse of the selection pulse is
1 is set to a voltage V2 (specifically, a value smaller than V1) different from the voltage V1. In Example 2, by making the voltage of the selection pulse smaller than the voltage of the reset pulse, energy loss is reduced and halftone control is facilitated. FIG. 10 shows a driving waveform of Example 2.

For example, when the LCD 2 is in the previous selection period, the row 2 and the row 3 have different phases of the pulse voltage + V
1 and a voltage of + V1 / 2 is applied to row 1.
At this time, a pulse voltage having a phase different from that of row 3 is applied to the column.
When V1 is applied, a reset pulse of voltage ± Vr = ± V1 is applied to LCD3, a voltage of zero is applied to LCD2, and
Is applied with a sustain pulse of voltage ± Ve = ± V1 / 2.

When the LCD 2 is in the selection pulse application period, a data pulse (voltage + V2) having a different shape depending on the image data is applied from the column. Therefore, a pulse of voltage + V2 / 2 is applied to both row 1 and row 3. LCD
1. A voltage of ± V2 / 2 is applied to the LCD 3. A voltage + V2 is applied to the row 2, and the voltage difference (± V2 or zero) from the data pulse applied to the column is equal to the voltage ± V2.
Vsel is applied to the LCD 2 as a selection pulse. By changing the shape of the data pulse applied to the column, the pulse width of the selection pulse can be changed.

In the post-selection period, a pulse is applied to rows 1 to 3 and the column in the same manner as in the pre-selection period.

During the periods other than the reset period, the selection period, and the sustain period, a waveform having the same phase as the data pulse applied from the signal electrode during the pre-selection period and the post-selection period is applied to each scan electrode. Is applied, a pulse of voltage + V2 / 2 is applied. By doing so, a crosstalk voltage of ± V2 / 2 is applied to the liquid crystal in this portion with the same pulse width as the selection pulse according to the image data. This crosstalk voltage does not affect the display state of the liquid crystal because the pulse width is narrow.

An image can be displayed by sequentially and repeatedly applying the above-described pulse voltage to each scanning electrode. Of course, partial rewriting is also possible.

In Example 2, the number of output voltages required for the driving IC is five on the low side (V1, V1 / 2, V2, V2 / V2).
2, GND), 3 values on the column side (V1, V2, GND)
Becomes

(Example of Configuration of Drive IC of Example 2) FIG. 11 shows an internal circuit of a scan drive IC that outputs the drive waveforms shown in FIG. This scan driving IC has a configuration in which a voltage switching circuit is added to the circuit shown in FIG. 8 to enable a ternary driver to output quinary values. That is, the scanning drive IC
Are a shift register 800, a latch 801 and a decoder 8
02, a level shifter / high withstand voltage ternary driver 803 and analog switches 810 and 811. This scan drive I
In C, the mode switching signal MODE and the polarity inversion signal PC are input to the decoder 804, the strobe signal STB is input to the latch 801, and the data signal DATA, the shift clock signal CLK, and the clear signal CLR are input to the shift register 800. You.

The operation of the scanning drive IC will be described below. 2-bit data signal D input to shift register 800
2-bit data is set in the shift register 800 by the ATA and the shift clock signal CLK. Next, the data of the shift register 800 is latched by the latch 801 according to the strobe signal STB. In response to the latched 2-bit data signal DATA, polarity inversion signal PC, and mode switching signal MODE, the decoder 802 decodes the 2-bit data signal DATA, and
The high withstand voltage ternary driver 803 is driven. Level shifter /
The high withstand voltage ternary driver 803 includes Vr1, Vr2, GND
An arbitrary voltage value is output among the three values.

The voltages Vr1 and Vr2 are changed by analog switches 810 and 811 to voltages V1 and V2, V1 / 2 and Vr.
It is switched to 2/2. By performing this switching during the selection period, the voltage of the selection pulse can be set to V2.

Next, FIG. 12 shows the internal circuit of the signal drive IC that outputs the drive waveform shown in FIG. Signal drive IC
Has basically the same configuration as the circuit shown in FIG. 9, and includes a shift register 900, a latch 901, and a comparator 90.
2. Decoder 903, level shifter / high voltage driver 9
04, a counter 905 and an analog switch 914. In this signal driving IC, the output inhibition signal OE and the polarity inversion signal PC are input to the decoder 903,
1, the strobe signal STB is input, the 8-bit data signal DATA, the shift clock signal CLK, and the clear signal CLR are input to the shift register 900, and the clock signal CCLK and the clear signal CCLR are input to the counter 905.
Is input.

The operation of the signal driving IC will be described. The 8-bit data signal DATA and the shift clock signal CLK input to the shift register 900 set 8-bit data in the shift register 900. Next, the strobe signal STB causes the shift register 90
Data of 0 is latched by the latch 901. Here, the 8-bit output is counted up from zero by the clock signal CCLK input to the counter 905. The comparator 902 compares the output of the latch 901 with the output of the counter 905, and outputs a high-level signal when the output of the latch 901 is large. Further, when the count-up of the counter 905 progresses and the output of the latch 901 decreases, a low-level signal is output. Then, a signal for driving the level shifter / high withstand voltage driver 904 is output from the decoder 903 based on the output of the comparator 902, the output inhibition signal OE, and the polarity inversion signal PC.

The voltage Vc1 is switched between the voltages V1 and V2 by the analog switch 914. By performing this switching during the selection period, the voltage of the selection pulse can be set to V2.

As described above, by inserting analog switches capable of selecting voltages supplied from a plurality of power supplies having different voltage values from each other, drivers having ternary and binary outputs can be used as drivers, and cost can be reduced. The rise can be suppressed.

(Example 3 of Matrix Driving) In Examples 1 and 2, reset is performed for each scan electrode to be rewritten. In Example 3 described here, however, all the pixels included in the area to be rewritten are reset. This is a full-surface reset method in which the scan electrodes are reset collectively. FIG. 13 shows the driving waveform. In this method, by providing a voltage switching means in the drive IC, the required number of output voltages becomes a binary value on the row side and a binary value on the column side.

First, the entire screen is reset once. At this time, the voltage value of the reset pulse ± VR output from the drive IC is V1, but the high-voltage input voltage of all the drive ICs may be set to V1 in order to apply the reset pulse to all the screens simultaneously. And
When sequentially scanning each scanning electrode, the high-voltage input voltage of the driving IC is switched to V1 / 2.

When LCD 2 is in the previous selection period, row 1
A pulse voltage + V1 / 2 having the same phase is applied to row 3 and a pulse voltage + V1 / 2 having a different phase is applied only to row 2. At this time, when a pulse voltage + V1 / 2 having the same phase as that of the row 2 is applied to the column, a zero voltage is applied to the LCD 2 and a sustain pulse of a voltage ± Ve = ± V 1/2 is applied to the LCDs 1 and 3.

When the LCD 2 is in the selection pulse application period, a pulse of voltage + V1 / 2 is applied to all of the rows 1, 2 and 3. The voltage difference (± V2 or zero) from the data pulse applied to the column is applied to the LCD 2 as a selection pulse of the voltage ± Vsel. By changing the shape of the data pulse applied to the column, the pulse width of the selection pulse can be changed.

In the post-selection period, a pulse is applied to rows 1 to 3 and the column in the same manner as in the previous selection period.

During a period other than the reset period, the selection period, and the sustain period, a waveform having the same phase as the data pulse applied from the signal electrode during the previous selection period and the subsequent selection period is applied to each scan electrode, and the other scan electrodes are applied. Is applied, a pulse of voltage + V1 / 2 is applied. Thus, a crosstalk voltage of ± V1 / 2 is applied to the liquid crystal in this portion with the same pulse width as the selection pulse in accordance with the image data. This crosstalk voltage does not affect the display state of the liquid crystal because the pulse width is narrow.

An image can be displayed by repeatedly applying the above-described pulse voltage to each scanning electrode sequentially. Of course, partial rewriting is also possible.

In Example 3, the number of output voltages required for the drive IC is three (V1, V1 / 2, GND) on the row side and three (V1, V1 / 2, GND) on the column side. V1 is required only at the time of full reset. Therefore, as described in Example 2, the voltage is switched between the reset period and the period after the voltage by the voltage switching means such as an analog switch and supplied. , GND), binary value on the column side (V1, G
ND), when selected, low-side binary (V1 / 2, GND),
Rewriting is possible with binary values on the column side (V1 / 2, GND). Therefore, the cost of the driver can be further reduced.

(Example 4 of Matrix Driving) FIG. 14 shows, as Example 4, a driving waveform that can take a longer time to return the twist of the liquid crystal. Here, the selection period includes a period in which a pulse of voltage ± V2 / 2 is applied, a period in which a selection pulse of voltage ± V2 is applied, and a period in which a pulse of voltage ± V2 / 2 is applied. I have. The pulse of the voltage ± V2 / 2 has the same voltage and shape as the crosstalk, and the scanning waveform and data waveform applied at this time are the same as those applied during the crosstalk period. By applying such a waveform, the time during which the voltage is zero becomes longer in the selection period, so that the time during which the twist of the liquid crystal returns is longer. In this case, the time for selecting one line can be shorter than the time for returning the twist of the liquid crystal, so that the screen rewriting speed can be increased.

As the driving IC, a circuit similar to the circuit shown in Example 1 (see FIGS. 8 and 9) can be used.

(Other Embodiments) The driving method and the liquid crystal display device according to the present invention are not limited to the above embodiments, but can be variously modified within the scope of the invention.

In particular, the configuration, material, manufacturing method, and configuration of the driving circuit of the liquid crystal display element are arbitrary.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of a liquid crystal display element.

FIG. 2 is a plan view showing a state in which a columnar structure and a sealing material are formed on a film substrate of the liquid crystal display element.

FIG. 3 is an explanatory view showing a manufacturing process of the liquid crystal display element.

FIG. 4 is a block diagram showing a driving circuit of the liquid crystal display element.

FIG. 5 is an explanatory diagram showing the principle of a driving method according to the present invention.

FIG. 6 is a chart showing basic driving waveforms in the driving method according to the present invention.

FIG. 7 is a chart showing driving waveforms in driving example 1.

FIG. 8 is a block diagram showing a circuit of a scan driving IC used in driving example 1.

FIG. 9 is a block diagram showing a circuit of a signal driving IC used in driving example 1;

FIG. 10 is a chart showing a driving waveform in Driving Example 2.

FIG. 11 is a block diagram showing a circuit of a scan driving IC used in driving example 2;

FIG. 12 is a block diagram showing a circuit of a signal driving IC used in driving example 2;

FIG. 13 is a chart showing driving waveforms in driving example 3;

FIG. 14 is a chart showing a driving waveform in Driving Example 4.

[Explanation of symbols]

 100: liquid crystal display element 113, 114: electrode 116: chiral nematic liquid crystal 131: scan drive IC (driver) 132: signal drive IC (driver) 810, 811, 914: analog switch Tr: reset period Ts: selection period Ts1 ... before Selection period Ts2: selection pulse application period Ts3: post-selection period Te: sustain period

Continued on the front page F-term (reference) 2H093 NA14 NA43 NA56 NC22 NC25 NC26 NC27 ND06 ND49 NF09 NF14 5C006 AA15 AA22 AF31 AF42 AF43 BA11 BB08 BB12 BF03 BF04 BF14 BF26 BF46 FA41 FA51 5C080 AA10 BB05 BB05 JJ05 DD03

Claims (11)

[Claims] 1. A method for driving a liquid crystal display element in which a liquid crystal exhibiting a cholesteric phase capable of maintaining a display in an electric field-off state is matrix-driven by a plurality of scanning electrodes and a plurality of signal electrodes crossing each other in a facing state. A reset period for bringing the liquid crystal into a homeotropic state, a selection period for selecting a final display state, and a maintenance period for establishing the state selected in the selection period. A driving method, wherein a period in which a voltage value applied to the liquid crystal is substantially zero is provided before and after the period in which the pulse is applied to the liquid crystal. 2. The driving method according to claim 1, wherein a selection period of a next selected scanning electrode is started during a predetermined selection period of the selected scanning electrode. 3. The driving method according to claim 1, wherein the reset period, the selection period, and the sustain period are integral multiples of the shortest of the three periods. 4. The driving method according to claim 1, wherein the voltage value of the selection pulse is equal to or less than the voltage value of the reset pulse. 5. The method according to claim 1, further comprising: selecting all the scan electrodes and resetting each pixel on each of the scan electrodes; 5. The driving method according to claim 1, wherein a large sustaining voltage is applied. 6. A display state is selected by modulating a pulse width of a selection pulse applied during the selection period. The driving method described. 7. A method for driving a liquid crystal display element in which a liquid crystal exhibiting a cholesteric phase capable of maintaining a display in an electric field off state is matrix-driven by a plurality of scanning electrodes and a plurality of signal electrodes crossing each other in a facing state. A driving method, wherein energy of a crosstalk voltage applied to a pixel on a non-selected scanning electrode is smaller than energy of a voltage applied to a signal electrode. 8. A method for driving a liquid crystal display element in which a liquid crystal exhibiting a cholesteric phase capable of maintaining a display in an electric field-off state is matrix-driven by a plurality of scanning electrodes and a plurality of signal electrodes crossing each other in a facing state. A driving method, wherein a pulse width of a crosstalk voltage applied to a pixel on a non-selected scanning electrode is smaller than a pulse width of a voltage applied to a signal electrode. 9. A liquid crystal display element driven by the driving method according to claim 1, claim 2, claim 3, claim 3, claim 4, claim 5, claim 6, claim 7, or claim 8. A liquid crystal display device characterized by the above-mentioned. 10. A liquid crystal display device in which a liquid crystal exhibiting a cholesteric phase capable of maintaining a display in an electric field-off state is driven in a matrix by a plurality of scanning electrodes and a plurality of signal electrodes crossing each other in an opposed state, wherein the scanning is performed. A liquid crystal display device comprising: a scan electrode driver for applying a voltage to an electrode; and an output of a signal electrode driver for applying a voltage to the signal electrode having a ternary value or less. 11. An analog switch connected to a plurality of power supplies having different voltage values from each other in at least one of the scan electrode driver and the signal electrode driver. Liquid crystal display device.