JPH07318905A - Liquid crystal device and its driving method - Google Patents

Abstract

PURPOSE:To obtain a desired halftone regardless of positions of pixels by improving an electric field modulation method in display of the halftone with a liquid crystal display device. CONSTITUTION:This liquid crystal device is provided with a light control layer holding a liquid crystal material 3 between a pair of transparent electrodes 2 and a heating means 20 for executing addressing by heating the regions corresponding to the respective pixels set in this light control layer. The external driving voltage to be applied by a liquid crystal driving circuit 30 between the transparent electrodes 2 is modulated by a memory 31 for correcting the effective voltage in such a manner that the effective electric fields to be impressed to the respective pixels during the addressing are kept constant at every halftone to be displayed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal device for displaying and recording information by utilizing two kinds of properties of liquid crystal, a transparent state and a white turbid state, and a driving method thereof. The present invention relates to an improvement in an electric field modulation method in which the strength of an electric field is changed to give a halftone to liquid crystal.

[0002]

2. Description of the Related Art Conventionally, smectic A is provided between a pair of electrodes.
A thermoelectric effect was used as a method for selecting the display state of each pixel set in the dimming layer, that is, for addressing a liquid crystal device having a dimming layer holding a liquid crystal material having a phase. Simple matrix method,
There are a method using a simple matrix using dynamic confusion, a method using laser heating using a thermoelectric effect, and the like. In particular, the addressing method (laser addressing method) by laser heating utilizing the thermoelectric effect can limit the heating area to a small area, and since a shadow mask is unnecessary, the pixel occupancy can be increased, which is high in liquid crystal devices. It is suitable as a method for providing pixel density and large capacity display capability.

Most of the liquid crystal display devices that have been put into practical use at present use nematic liquid crystal as a liquid crystal material. Since a liquid crystal display device using a nematic liquid crystal has no memory property, it is necessary to continuously perform addressing or time-division driving in order to maintain a display state. On the other hand, since the laser address type liquid crystal display device described above has a memory property, it is sufficient to write once in one frame, and the writing speed becomes a design parameter. Therefore, there is an advantage that flicker does not occur and there is no need to manage the brightness and contrast. Further, in a liquid crystal display device which has a memory property but takes a short time, rewriting must be performed at a cycle within a short time, which limits the total number of pixels constituting the liquid crystal display device. . On the other hand, in a liquid crystal display device having a long-time memory property, the number of pixels is determined only by its size and resolution. That is, in the laser address liquid crystal display device that heats by irradiating the laser light described above, the number of pixels is determined by the resolution of the lens that constitutes the projection optical system, so the limit is at least 100 million pixels,
It is possible to display large maps and engineering drawings in detail.

In the above-described laser addressing smectic liquid crystal display device, as a method of giving a halftone to the density of each pixel, an intensity modulation method of giving a halftone to a pixel by changing the laser intensity and applying between electrodes are applied. There are two types of paper, the gray scale in laser-addre method, which is an electric field modulation method in which the intensity of the electric field is changed to give a halftone to the pixel.
ssed smectic storange display "(R. Dalay, A.
J. Hughes and DG McDonnell, Display, July 1988, pp. 137-140). Hereinafter, the intensity modulation method and the electric field modulation method will be described.

FIG. 5 is a graph schematically showing the transmittance of a smectic liquid crystal showing a thermoelectric effect at each temperature.
(A) is a randomly aligned smectic A phase, (b) is a randomly aligned nematic phase, (c) is a homeotropically aligned smectic A phase, (d) is a homeotropically aligned nematic phase, and (v) is a liquid phase Respectively,
(F) and (g) indicate the transient period. That is, when the randomly oriented smectic A phase (a) state is heated, it becomes a randomly oriented nematic phase (b) state, and when it is further heated, it becomes a liquid phase (e) state. Next, when cooling is performed from the liquid phase (e) in a state where a voltage is applied between the electrodes, a nematic phase (d) state of homeotropic alignment is obtained, and when further cooling is performed, a smectic A phase (c) of homeotropic alignment is formed. It becomes a state. The transparent state (C) is maintained even when the voltage application is stopped in the homeotropically aligned smectic A phase (C) state. Further, when cooling is performed from the liquid phase (e) in a state where no voltage is applied, the random alignment nematic phase (b) is obtained, and when further cooling is performed, the random alignment smectic A phase (b) is obtained.

FIG. 6 is a schematic view showing the addressing of pixels by a laser beam by using a sectional view of a liquid crystal display device. The liquid crystal material 3 is held by the transparent electrode 2 supported by the transparent substrate 1. Figure 6
In (a), the liquid crystal material 3 has been subjected to homeotropic alignment treatment (state C in FIG. 5) and is entirely transparent in the smectic phase. When the address for one pixel is performed by the laser beam, the region corresponding to one pixel is heated by absorbing the laser beam, and passes through the homeotropically aligned nematic phase 4 (two states in FIG. 5) (see FIG. 6 (b)), a region that becomes the isotropic liquid phase 5 (e-state in FIG. 5) appears (FIG. 6 (c)).

This region passes through a randomly oriented nematic phase 6 (b state in FIG. 5) during the cooling process (FIG. 6 (d)),
It becomes a region showing the smectic phase 7 (random state in FIG. 5) of random orientation (FIG. 6 (e)), and becomes a cloudy state. This cloudy region is permanent unless it reaches a temperature (for example, a temperature 2 K lower than the C (SN transformation) in FIG. 5) in which a phase transition may occur in the liquid crystal material exhibiting transparent homeotopic alignment. Stored in. Therefore, it is possible to display an image or the like by utilizing whether each pixel of the liquid crystal display device is transparent or cloudy.

In order to erase the image, it is sufficient to apply a high frequency between the transparent electrodes or to heat the image area and then cool it while applying an alternating current of a low frequency. The image area is homeotropically oriented. After passing through the nematic phase (dual state in FIG. 5), it becomes a homeotropically aligned smectic phase (state C in FIG. 5) and becomes transparent again.

The intensity modulation method is a method that changes the intensity of the laser light during addressing with the laser light in FIG. 6 to change the transmittance and enable display of a halftone. FIG. 7 schematically shows the relationship between the energy density given by laser light and the transmittance at a certain environmental temperature with a characteristic curve (solid line). At this time, no AC voltage is applied between the transparent electrodes. The relationship between the energy density and the transmittance is that (A) the area where the energy-density does not reach the amount necessary for the phase transition and the transparent state is maintained, and (B) the transmittance depends on the given energy density. It can be divided into three regions, that is, a region that continuously changes and a region (C) where the entire liquid crystal layer becomes cloudy because the energy density exceeds the amount required for the phase transition of the entire liquid crystal layer. In the region (B), the transmittance continuously changes in accordance with the energy density given by the laser light, so by changing the energy density in this region, it is possible to form a pixel having an arbitrary transmittance. Become.

On the other hand, in the electric field modulation method, the transmissivity is changed by changing the applied voltage applied between the transparent electrodes at the time of addressing by the laser light in FIG. This is a possible method. FIG. 8 schematically shows the relationship between the applied voltage and the transmittance. At this time, the intensity of the laser light is constant, and the energy density thereof is the value in the region (C) of FIG. As for the relationship between the applied voltage and the transmittance, (D) the applied voltage does not reach the threshold voltage required for alignment, and thus the state becomes cloudy.
Three regions: (E) a region where the transmittance changes continuously according to the applied voltage, and (F) the entire liquid crystal layer is kept transparent because the applied voltage exceeds the saturation voltage required for alignment. Can be divided into In the region (E), the transmittance continuously changes according to the applied voltage. Therefore, by changing the applied voltage between the transparent electrodes in this region, it is possible to form a pixel having an arbitrary transmittance.

[0011]

The intensity modulation method and the electric field modulation method described above are effective as methods for giving a halftone to a liquid crystal display device. However, since the intensity modulation method is a method of controlling the local temperature of the liquid crystal material very precisely, it has a problem that it is difficult to obtain a constant image density because it has a high dependency on the environmental temperature. For example, when the environmental temperature is higher than the environmental temperature at which the characteristic curve (solid line) of FIG. 7 is obtained, the heating energy density required for the phase transition is small,
The characteristic curve showing the relationship between the energy density and the transmittance is shifted to the left and becomes like a dotted line. Therefore, the transmittance for the same energy density is lowered, and it becomes impossible to represent an image in a high density portion. On the contrary, if the environmental temperature is as shown in FIG.
When the characteristic curve (solid line) of is lower than the environmental temperature that can be obtained, the heating energy density required for the phase transition becomes large, so the characteristic curve showing the relationship between energy density and transmittance shifts to the right and is indicated by the alternate long and short dash line. become that way. Therefore, contrary to the above, it becomes impossible to represent an image of a low density portion.

Further, in the electric field modulation method, it is necessary to apply an electric field corresponding to the image density to the area corresponding to the pixel portion. However, in the case of a liquid crystal display device having a large display unit,
Due to the voltage drop of the transparent electrode, the electric field generated between the electrodes in the area corresponding to the pixel portion varies depending on the pixel position, and even if the same applied voltage is applied to the transparent electrode, the halftone density differs at the pixel position. There was a problem that it would end up. Since the transparent electrode used in the liquid crystal display device has a larger electric resistance than the metal electrode, the voltage applied to the liquid crystal is lowered in the liquid crystal at a position distant from the liquid crystal drive circuit, and the characteristic curve of FIG. 8 shifts to the right. It becomes like a dashed line.
Further, at a position close to the liquid crystal drive circuit, the voltage applied to the liquid crystal increases and the characteristic curve shifts to the left and becomes a dotted line. In particular, when a resin film such as PET is used as the electrode substrate, the voltage drop becomes large and the image density unevenness becomes remarkable.

The present invention has been made in view of the above circumstances, and in the halftone display of a liquid crystal display device, the electric field modulation method can be improved to obtain a desired halftone regardless of the position of the pixel. An object of the present invention is to provide a liquid crystal display device and a driving method thereof.

[0014]

In order to achieve the above object, the invention of claim 1 provides a light control layer in which a liquid crystal material is held between a pair of electrodes, and each pixel set in the light control layer. In a liquid crystal device provided with a heating means for heating an area corresponding to the area for addressing, an effective electric field applied to each pixel during the addressing is constant for each halftone to be displayed. It is characterized in that it has a correction means for modulating the external drive voltage applied between the two. That is, the voltage is corrected by an electric field modulation method with respect to an external drive voltage applied between the electrodes so that a desired halftone density can be easily obtained.

According to a second aspect of the present invention, a light control layer holding a liquid crystal material is provided between a pair of electrodes, and an area corresponding to each pixel set in the light control layer is heated to perform addressing. In the method of driving a liquid crystal device, in which an effective electric field is applied to each pixel during addressing to perform display, after heating the liquid crystal material from ambient temperature to a phase transition temperature or higher, It is characterized in that the external drive voltage is modulated and applied between the electrodes so that the effective electric field applied to the pixel is constant for each halftone to be displayed.

[0016]

According to the present invention, after heating the liquid crystal material from the ambient temperature to the phase transition temperature or higher by the heating means, the voltage applied between the electrodes is adjusted by the correcting means for modulating the external drive voltage, The effective electric field applied to each pixel during addressing is made constant for each halftone to be displayed. Therefore, a desired halftone can be obtained regardless of the position of the pixel in the light control layer.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. The liquid crystal display device corresponds to a liquid crystal cell 10 including a light control layer that holds a liquid crystal material 3 having a smectic A phase between a pair of transparent substrates 1 and each pixel set in the light control layer. Heating means 20 for heating an area with laser light for addressing
And a drive circuit 30 for applying an external drive voltage between the transparent substrates 1 and an effective voltage correction memory 31 for correcting the external drive voltage. The transparent substrate 1 is ITO
The transparent electrode 2 made of a film is formed of a PTE film on which a metal electrode 11 is formed along one side on the transparent electrode 2 at one end of each substrate. An alternating voltage is applied from the liquid crystal drive circuit 30 between the metal electrodes 11.

In the heating means 20, the laser beam emitted from the semiconductor laser light source 22 which emits light in response to the signal from the LD drive circuit 21 is collimated by a collimator 23 and then collimated into a parallel beam. And the light is focused on the liquid crystal cell 10 in a spot state by the fθ focusing optical system 26, and the region corresponding to each pixel is sequentially scanned by the laser light so that the liquid crystal material 3 is heated from the ambient temperature to the phase transition temperature or higher. It is designed to be heated to addressing. Further, the energy density of the laser light is set to a constant value set in the range of the C region of FIG. 7, and if the heating temperature by the laser is set sufficiently higher than the phase transition temperature of the liquid crystal (for example, 20 degrees Celsius or more), it depends on the environment. Can be reduced.

The liquid crystal drive circuit 30 is configured to adjust the applied voltage applied between the electrodes of the liquid crystal cell 10 in accordance with the density of the image signal and change the effective electric field to enable halftone display. (Electric field modulation method). Then, the applied voltage is modulated based on the voltage correction data previously input to the effective voltage correction memory 31 in accordance with the position signal indicating the laser focus position on the liquid crystal cell 10, and this modulation is performed. The liquid crystal cell 10 is driven by a voltage.

Therefore, according to the above configuration, if an effective electric field is applied to the transparent electrode 2 by the voltage applied from the liquid crystal drive circuit 30 during the addressing, the addressed area (corresponding to a pixel) becomes the effective electric field. According to the transmittance, the display can be performed. At this time, the applied voltage according to the image density applied from the liquid crystal drive circuit 30 to the transparent electrode 2 is modulated based on the voltage correction data previously input to the effective voltage correction memory 31 according to the position signal. Therefore, an effective electric field is generated between the electrodes so that the transmittance corresponds to the desired concentration. As a result, the liquid crystal cell 1
In a region corresponding to each pixel of 0, a desired halftone can be obtained regardless of the position of the pixel.

Next, an example of an image display device using the liquid crystal display device of the present invention will be described with reference to the block diagram of FIG. The image display device includes a liquid crystal cell 10
0, a lamp 101 serving as a light source of the liquid crystal cell 100, a screen 102 for displaying light from the lamp 101 through the liquid crystal cell 10, a laser emitting device 103 for emitting laser light, and a pixel portion on the liquid crystal cell 101 for scanning laser light. XY galvanometer 104, image processing device 105 for outputting an image signal, circuit interface 1
An image memory 107 to which an image signal from the image processing device 105 is input via 06, a circuit interface 1
An address generation circuit 108 to which an image signal from the image processing device 105 is input via 06, an LD drive circuit 109 for driving the laser emission device 103, and an XY mirror position by an XY galvanometer 104 are controlled. A scanning circuit 110, a liquid crystal drive circuit 111 that receives an image signal from the image memory 107 and applies an applied voltage to the liquid crystal cell 100, an effective voltage correction memory 112 for correcting the applied voltage, an address generation circuit 108, and a scanning circuit 110. The CPU 114 controls the liquid crystal drive circuit 111 via the bus 113.

The scanning circuit 110 generates a position designation signal for designating the position of the XY mirror. This position designation signal is used as a scanning signal in the address generation circuit 108.
To the image memory 10 by the address generation circuit 108.
7 is converted into an address signal indicating the pixel position, and laser light is emitted from the laser emission device 103 at the timing of heating all regions corresponding to each pixel of the liquid crystal cell 100, and the condensed laser light is the position designation. The liquid crystal cell 10 is scanned by an XY mirror controlled by a signal, and regions corresponding to the respective pixels are sequentially heated.

On the other hand, the scanning signal from the scanning circuit 110 is converted into a position signal indicating the laser focusing position on the liquid crystal cell 10 via the address generating circuit 108. Upon receiving this position signal, the effective voltage correction memory 112
An applied voltage corresponding to the density of the image signal from the image memory 107 is applied from the liquid crystal drive circuit 111 between the electrodes of the liquid crystal cell 10 based on the voltage correction data corresponding to each pixel area which is input in advance. . Therefore, for example, in the case of an image signal of density 1, the applied voltage for displaying density 1 is applied by the liquid crystal drive circuit 111, but the applied voltage is adjusted by the effective voltage correction memory 112 according to the pixel position. The density of 1 can be displayed on the screen 102 regardless of whether the central pixel area or the peripheral pixel area of the liquid crystal cell 100 has a constant effective electric field in the pixel area for the same density.

Next, a method of creating voltage correction data corresponding to each pixel area in the effective voltage correction memory 112 will be described. As a first example, after the image display device shown in FIG. 3 is created, the effective voltage correction memory 11 is
Measure the display density of the halftone image that is actually displayed when the image signal of the same density is input without modulating the applied voltage by 2 and correct the voltage of each pixel area based on this measurement value. Create data for use. As shown in FIG. 4A, the display surface of the liquid crystal cell 100 is divided into (n squared) correction unit regions (regions O to W) (nine regions in the example in the drawing), and each correction unit region is divided. In each of the correction unit areas, images having light densities are displayed in the upper areas O to Q, images having normal density in the middle areas R to T, and lower areas U in the middle areas R to T.
An image with a high density is displayed in ~ W. First, in the image processing apparatus 105, three types of different densities (density 0.3, density 0.8, density 1.2) are used as shown in FIG.
(Saturation density)) image (line diagram) is created and output as a plotter control signal. In the liquid crystal drive circuit 111,
As described above, the position signal indicating the laser focus position on the liquid crystal cell 100 is received, and the density becomes 0.3, 0.8, and 0.9 corresponding to the image signal from the image memory 107. A driving voltage is applied between the electrodes, and an electric field is applied to a region corresponding to each pixel. In this way, the image displayed in the state in which the applied voltage is not modulated by the effective voltage correction memory 112 is the correction unit area (area S) at the center of the middle stage where the image with the density of 0.8 should be displayed on the screen. An image with a density of 0.9 was displayed. In addition, it is measured whether the densities displayed in the regions R and T are halftone densities that are proportional to the densities displayed in the regions O and Q and the densities displayed in the regions U and W.

Next, in the same manner as described above, when a display was performed with a driving voltage such that the density was 0.8 on the entire surface, the image of the correction unit area (area S) at the center of the middle part had a density of 0.9, and The concentration gradually became 0.8 from the center to the peripheral portion. An image with a density of 0.8 in a peripheral area was measured with a densitometer, and the voltage required to achieve a density of 0.8 was converted from the relationship between the applied voltage and the transmittance (density) in FIG. there were. Furthermore, an image with a density of 0.9 in the correction unit area in the central portion was measured with a densitometer, and
From the relationship between the applied voltage and the transmittance (concentration), the voltage required for setting the concentration to 0.9 was 19V.
That is, it can be seen that the applied voltage is lowered by 1 V in the central portion due to the voltage drop of the transparent electrode as compared with the peripheral portion.

Next, a driving voltage 2 which gives a density of 0.8 on the entire surface
Display is performed at 0 V, the image distribution of the display is measured by an image sensor, and a 16-bit density data table representing the density of each correction unit area is created. Similarly, drive voltage 2V
A 16-bit density data table is created every 0 to 30 V up to 30 V corresponding to the saturation density, and the relationship between the drive voltage and the transmittance (density) in each correction unit area is obtained.
Further, the relationship between the driving voltage and the transmittance (density) in each correction unit area is compared with the standard relationship between the driving voltage and the transmittance (density) in FIG. 8, and the necessary voltage correction is approximated by a linear expression. And used as voltage correction data in the area corresponding to each pixel. And
The voltage correction data for each pixel is printed in the effective voltage correction memory 112 including a ROM. When the liquid crystal cell 100 is driven using the voltage correction data created in this way, as shown in FIG. 4B, the density of the correction unit area in the central portion does not become dark, and An image with a desired density can be displayed regardless of the position. Also,
Since the voltage correction data is obtained individually after the image display device is created, even if there are individual differences in the liquid crystal cell due to the thickness of the transparent electrode in the liquid crystal cell 100 or the film deposition state, the influence on the display due to these is corrected. be able to.

Next, another example of the method of creating the voltage correction data corresponding to each pixel area will be described. As a second example, voltage correction data for each pixel region is created by numerical calculation from the configuration of the liquid crystal display device. That is, from the resistance value of the transparent electrode (ITO) of the liquid crystal cell, an electric field model corresponding to the liquid crystal cell is created by using the finite element method, and it is estimated which part has what electric field with respect to the applied voltage. The voltage correction data in the area corresponding to each pixel is obtained based on the applied voltage distribution. That is, the voltage correction data is obtained by using the result of the numerical calculation of the finite element method so that the effective electric field applied to the pixel becomes constant for each halftone displayed. According to this, since the correction data can be obtained regardless of the measurement after the liquid crystal cell is completed,
The manufacturing process can be shortened.

[0028]

According to the present invention, in a liquid crystal device, an external driving voltage applied between electrodes is modulated so that an effective electric field applied to a pixel is constant for each halftone to be displayed. Since it is configured, it is possible to eliminate the influence of the voltage drop of the electrode and obtain a desired halftone regardless of the position of the pixel in the light control layer.

[Brief description of drawings]

FIG. 1 is a structural explanatory view of a liquid crystal device according to an example.

2 is a plan view of a liquid crystal cell portion of the liquid crystal device shown in FIG.

FIG. 3 is a block diagram of an image display device using the liquid crystal device of FIG.

FIGS. 4A and 4B are plan explanatory views of a liquid crystal cell portion for explaining generation of voltage correction data.

FIG. 5 is a diagram showing a relationship between temperature, phase change, and transmittance in liquid crystal.

6A to 6E are schematic diagrams showing the principle of thermal recording on liquid crystal.

FIG. 7 is a schematic diagram showing the principle of an intensity modulation method in liquid crystal.

FIG. 8 is a schematic diagram showing the principle of the electric field modulation method in liquid crystal.

[Explanation of symbols]

1 ... Transparent substrate, 2 ... Transparent electrode, 3 ... Liquid crystal material,
10 ... Liquid crystal cell, 11 ... Metal electrode, 20 ... Heating means, 21 ... LD drive circuit, 30 ... Liquid crystal drive circuit,
31 ... Effective voltage correction memory

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location G09G 3/36

Claims (2)

[Claims] 1. A dimming layer holding a liquid crystal material between a pair of electrodes, and heating means for heating an area corresponding to each pixel set in the dimming layer to perform addressing. The liquid crystal device further comprises a correction unit that modulates an external drive voltage applied between the electrodes so that an effective electric field applied to each pixel during the addressing becomes constant for each halftone to be displayed. LCD device. 2. A dimming layer holding a liquid crystal material is provided between a pair of electrodes, and an area corresponding to each pixel set in the dimming layer is heated to perform addressing, and at the same time during addressing, In a method of driving a liquid crystal device which applies an effective electric field to pixels to perform display, after heating the liquid crystal material from an ambient temperature to a phase transition temperature or higher, an effective electric field applied to each pixel during the addressing is A method for driving a liquid crystal device, wherein an external drive voltage is modulated and applied between the electrodes so that it becomes constant for each halftone to be displayed.