JPH07334129A - Liquid crystal display device and its driving method - Google Patents

Abstract

PURPOSE:To provide a liquid crystal display device displaying a color image by using a liquid crystal display element for displaying a color complied with an applied voltage. CONSTITUTION:A CPU 11 executes a program and writes image data in an image memory 15. A display control circuit 17 reads the image data stored in the image memory 15 and transfers them to a transformation table 19. The transformation table 19 stores a voltage value complied with a displaying color determined based on the relation between the applied voltage of a liquid crystal display element 23 and a displaying color and outputs voltage data complied with the image data. When the image data instruct a color unable to be displayed, the data are converted to voltage data complied with the approximated color capable of display. A D/A converter 21 converts the voltage data to an analog voltage and supplys it to a column driver 33. The column driver 33 drives a liquid crystal display element 23 by using the supplied voltage and displays a proper color.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color liquid crystal display device using a liquid crystal display element for displaying a color corresponding to an applied voltage and a driving method thereof.

[0002]

2. Description of the Related Art Conventionally, a color display device obtains an arbitrary display color by additive color mixture of three primary colors of red, green and blue, and has dots corresponding to the three primary colors of red, green and blue. Then, this color display device displays each arbitrary color by independently controlling the brightness of the red, green, and blue dots corresponding to each primary color. For this reason, television sets, personal computers, etc. equipped with color display devices are
Three brightness data corresponding to the three primary colors of blue are supplied to the display device, the brightness of the dots of each color is controlled according to the brightness data of these three primary colors, and the desired color is displayed in pixel units.

Similarly, in a color liquid crystal display device, electrodes for forming a plurality of dots are arranged so as to form one pixel from three dots corresponding to color filters of three primary colors (red, green and blue). By independently controlling the intensity of light passing through each of the dots, the display color of one pixel composed of the three dots is driven.

The liquid crystal display device provided with the three primary color filters is used in a television set, a personal computer or the like as a transmissive liquid crystal display device having a strong light source on the back because of its low light transmittance. However, since the color liquid crystal display element has a large light absorption by the color filter, it is not possible to obtain a reflection type color liquid crystal display device which does not require illumination from the back surface.

An electric field control birefringence effect type is known as a liquid crystal display element capable of color display of a plurality of colors without using a color filter. This electric field control birefringence effect type liquid crystal display element is composed of a liquid crystal cell in which a liquid crystal is sealed between a pair of substrates subjected to an alignment treatment, and two polarizing plates arranged so as to sandwich the liquid crystal cell. By changing the molecular alignment of the liquid crystal by applying an electric field, the birefringence effect of the liquid crystal layer is changed, and the change of the birefringence effect changes the spectral distribution of the light passing through the liquid crystal cell to obtain a desired color. It is displayed and color-displayed.

The electric field control birefringence effect type liquid crystal display element can display color without using a color filter, and the display is bright because light is not absorbed by the color filter. Therefore, there is an advantage that a reflective color liquid crystal display device can be realized and the structure of the liquid crystal display element is simple.

[0007]

A liquid crystal display element of the electric field control birefringence effect type has a plurality of desired colors by controlling the voltage applied between electrodes facing each other arranged on the substrates facing each other of the liquid crystal cell. Each dot forms one pixel, and each color has a one-to-one correspondence with each voltage applied between the electrodes forming the one pixel. Therefore, in the three luminance data corresponding to the three primary colors of red, green and blue supplied to the conventional color display device, the electric field control birefringence effect type liquid crystal display element that displays a plurality of colors in one pixel is turned on. I couldn't drive.

Further, in the electric field control birefringence effect type liquid crystal display element, the display color changes along a predetermined locus on the chromaticity diagram according to the applied voltage, and the display color changes according to the applied voltage. Since it is uniquely determined, it is difficult to obtain a predetermined display color according to the supplied luminance data of red, green, and blue.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a liquid crystal display device for displaying a color image using a liquid crystal display element for displaying a color corresponding to an applied voltage and a driving method thereof. And Further, the present invention provides an electric field control birefringence effect type liquid crystal display device capable of displaying a display color designated by red, green and blue luminance data with a simple circuit configuration and a driving method thereof. To aim. Further, the present invention provides a color liquid crystal display device and a driving method thereof for selecting and displaying a color closest to a display color designated by red, green, and blue luminance data from displayable display colors. With the goal.

[0010]

In order to achieve the above object, a liquid crystal display device according to the present invention has a liquid crystal display element that displays a plurality of colors according to an applied voltage and a designated display color of the liquid crystal display element. A color instructing means for instructing, storing a relationship between a display color determined based on a relationship between a voltage applied to the liquid crystal display element and the designated display color and a voltage value corresponding thereto, and instructing by the color instructing means. Converting means for outputting voltage data corresponding to the specified designated display color, and supply means for displaying a predetermined display color by supplying a drive voltage corresponding to the voltage data output by the converting means to the liquid crystal display element. And are provided.

Further, the driving method of the liquid crystal display device according to the present invention comprises a color instructing step for instructing a designated display color, and a conversion step for converting the designated display color instructed by the color instructing step into a corresponding voltage. A driving step of displaying a color image on the liquid crystal display device by supplying the voltage obtained by the converting step to a liquid crystal display device displaying a color corresponding to an applied voltage to drive the liquid crystal display device. To do.

[0012]

According to the present invention, the display color of the liquid crystal display element for displaying the color corresponding to the applied voltage and the conversion means or the conversion step for outputting the voltage data corresponding to the designated color are provided. Various color images can be displayed on the liquid crystal display device.

Further, when a color that cannot be displayed by the liquid crystal display device is designated, the color is converted into a voltage corresponding to a displayable color that is the closest to the color, so that an appropriate color image can be displayed. You can

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a circuit configuration of a birefringence control type liquid crystal display element and a driving circuit thereof according to an embodiment of the present invention.

As shown in the figure, this circuit is a CPU that controls the entire system according to a predetermined program.
11, a program memory 13 for storing an operation program of the CPU 11, for example, an image creation program, and C
An image memory (display memory) 15 into which image data is written by the PU 11, a display control circuit 17 that sequentially reads the image data stored in the image memory 15 under the control of the CPU 11, and image data read by the display control circuit 17. Conversion table 1 for converting voltage to corresponding voltage data
9, a D / A (digital-analog) converter 21 for converting the voltage data output from the conversion table 19 into an analog voltage signal, and an active matrix liquid crystal display element 23 of the birefringence control system.

Active matrix liquid crystal display element 23
Is a liquid crystal display panel 31 on which electrodes and thin film transistors (TFTs) 45 are formed, and an output signal of the D / A converter 21 is sampled, and the data line 49 and the TFT.
The column driver (drain driver) 33 is supplied to the pixel electrode 43 via the line driver 45, and the row driver (gate driver) 35 for turning on / off the TFT 45.
A pair of transparent substrates 41 and 5 that constitute the liquid crystal display panel 31.
A transparent pixel electrode 43 and a source T connected to the pixel electrode 43 are provided on the substrate 41 below 1 (for example, a glass substrate).
The FT 45 and the FT 45 are arranged in a matrix.

As shown in FIG. 1 or FIG. 9, a pair of transparent substrates 41 and 51 (for example,
A transparent pixel electrode 43 is provided on a lower substrate 41 (a glass substrate).
And the TFTs 45 whose sources are connected to the pixel electrodes 43 are arranged in a matrix. Further, a gate line (scanning line) 47 is arranged in the row direction on the lower substrate 41, and the gate line 47 is connected to the gate electrode of the TFT 45 in the corresponding row. Further, a data line (gradation signal line) 49 is laid out in the column direction and connected to the drain of the TFT 45 in the corresponding column. In addition, as shown in FIG. 9, the lower substrate 41 has pixel electrodes 43 and T
An alignment film 60 which has been subjected to a predetermined alignment treatment is provided on the FT 45, and a polarizing plate 53 is provided on the back surface side thereof and a reflecting plate 55 made of metal such as aluminum is provided on the back surface side of the polarizing plate 53. Has been.

On the other hand, each pixel electrode 43 is formed on the upper substrate 51.
A transparent counter electrode 58 is formed so as to face the. Furthermore, on the counter electrode 58 of the upper substrate 51, an alignment film 59 that has been subjected to a predetermined alignment treatment is provided. Upper substrate 5
A retardation plate 52 is provided on the front surface side of 1, and a polarizing plate 54 is provided on the front surface side of the retardation plate 52. The two substrates 41 and 51 are adhered to each other via a frame-shaped sealing material (not shown). For example, a nematic liquid crystal having a positive dielectric anisotropy is formed in a region surrounded by the two substrates 41 and 51 and the sealing material. 56 is twist-oriented by the alignment films 59 and 60 and is enclosed.

The alignment direction of liquid crystal molecules on the surface of the alignment film 59 of the upper substrate 51 of the liquid crystal display panel 31 and the polarizing plate 5
The transmission axis directions of 3 and 54 are set with the orientation direction of liquid crystal molecules on the surface of the orientation film 60 of the lower substrate 41 of the liquid crystal display panel 31 as the azimuth angle of 0 °, and this direction is used as a reference. The alignment direction of the liquid crystal molecules on the upper substrate 51 of the liquid crystal display panel 31 is, for example, counterclockwise when viewed from above, that is, the observation side with respect to the alignment direction of the liquid crystal molecules on the lower substrate 41, that is, the direction of azimuth angle 0 °. Almost 90 °
The liquid crystal molecules are displaced, and the liquid crystal molecules are twist-aligned between the substrates 41 and 51 at a twist angle of approximately 90 °.

Further, the transmission axis of the polarizing plate 54 is in the direction of 30 ° from the observation side, that is, the surface side, with respect to the direction of azimuth angle of 0 °, and the transmission axis of the polarizing plate 53 is observed in the direction of azimuth angle of 0 °. It is in the direction of 50 ° when viewed from the side, and the slow axis of the retardation plate 52 is obliquely displaced from the transmission axis of the upper polarizing plate 54.

The liquid crystal display panel 31 is a reflection type in which light incident from the upper polarizing plate 54 side is reflected by the reflection plate 55 and displayed. The incident light is the upper polarizing plate 54 and the phase difference plate 5.
2, the liquid crystal 56 and the lower polarizing plate 53 in order, and the reflecting plate 5
5, the reflected light is reflected by the lower polarizing plate 53 and the liquid crystal 5.
6, the phase difference plate 52 and the upper polarization plate 54 are sequentially emitted.

The slow axis of the retardation plate 52 is the upper polarizing plate 54.
Of the upper polarizing plate 5 because it is skewed with respect to the transmission axis of
When the linearly polarized light polarized through 4 passes through the retardation plate 52, it becomes elliptically polarized light which is different for each wavelength light due to its birefringence effect. The state is changed and emitted to the lower polarization plate 53, and only the polarized component of each wavelength light in the transmission axis direction of the lower polarization plate 53 is transmitted and reflected by the reflection plate 55.

The reflected light is reflected by the lower polarizing plate 53, the liquid crystal 56,
In the process of sequentially passing through the retardation plate 52 and the upper polarization plate 54, the polarization effect and the birefringence effect are exerted, and the light enters the upper polarization plate 54 again. The light that has entered the upper polarizing plate 54 has only the polarized component in the transmission axis direction thereof transmitted, and is colored according to the wavelength light having the transmitted polarized component. The birefringence effect of the liquid crystal 56 is
The light emitted from the liquid crystal display panel 31 changes to the voltage applied to the liquid crystal 56 because the spectrum distribution of the light emitted changes depending on the voltage applied to the liquid crystal display 6 and the difference in the birefringence effect. Accordingly, it is colored in a plurality of colors.

That is, the liquid crystal display element 23 changes the arrangement of the liquid crystal molecules interposed between the pixel electrode 43 and the counter electrode 58 by applying a voltage between the pixel electrode 43 and the counter electrode 58. It is polarized by the refraction effect and the display color is controlled for each pixel to display a color image.

The image data generated by the CPU 11 and stored in the image memory 15 is composed of, for example, 6-bit data per pixel as shown in FIG. 2, 2 bits being red (R) and 2 bits being green ( G) 2 bits represent the brightness of blue (B), and the composite color (designated display color) of these is the color that is originally desired to be displayed in each pixel.

Under the control of the CPU 11, the display control circuit 17 sequentially reads the image data stored in the image memory 15 one scan line at a time and outputs it to the conversion table 19.
The conversion table 19 stores, for example, as shown in FIG. 3, voltage data corresponding to the image data in each storage area having the image data as an address, and is supplied from the display control circuit 17 under the control of the CPU 11. The voltage data stored in the position addressed by the image data to be read is read and output.

The storage data (voltage data) of the conversion table 19 is set as follows, for example. First, the characteristics of the birefringence control type liquid crystal display element 23 (the characteristics of the change in the display color depending on the applied voltage) are shown in FIG.
Obtained as shown in the GB color space. That is, when a voltage of 0 V to 5 V is applied between the pixel electrode 43 of the liquid crystal display panel 31 and the counter electrode 58, the display of the pixel changes as indicated by the arrow. Next, eight display colors are obtained when eight voltages corresponding to 3-bit voltage data are applied to the liquid crystal.

Next, with respect to each of 64 (2 ² × 2 ² × 2 ² ) colors defined by data of 2 bits for each of RGB and 6 bits in total, the corresponding or the closest approximation is made from among the 8 display colors. The display color is obtained, and the voltage data corresponding to this display color is set in the corresponding storage area. When selecting similar colors, for example, as shown in FIG.
A displayable color with the shortest distance in the color space is selected, and voltage data corresponding to this color is set in the corresponding storage area.

Under the control of the CPU 11, the D / A converter 21 receives the 3-bit voltage data supplied from the conversion table 19, converts it into a voltage signal in the range of 0 to 5 V, and outputs it. The D / A converter 2 is controlled by the CPU 11.
1 outputs a signal of a predetermined level in each horizontal synchronization period. Therefore, the analog video signal output from the D / A converter 21 has a waveform as shown in FIG.

The column driver 33 samples the analog video signal for one line supplied from the D / A converter 21, and outputs the video signal sampled one horizontal scanning period before to the data line 49. The row driver 35
Gate pulses are sequentially applied to the gate line 47 in accordance with the timing signal from the CPU 11. The TFT 45 connected to the gate line 47 to which the gate pulse is applied is turned on, and the voltage (writing voltage) corresponding to the display color is applied from the data line 49 to the pixel electrode 43 connected to the turned on TFT 45.

The row driver 35 turns off the gate pulse immediately before the voltage applied to the data line 49 is switched. Then, the TFT 45 is turned off, and the voltage applied until then is held in the capacitance formed by the pixel electrode 43, the counter electrode 58, and the liquid crystal 56 therebetween. As a result, the alignment state of the liquid crystal molecules is maintained in a desired state during the non-selection period, and a desired display color is maintained.

Next, the operation of the liquid crystal display device and its drive circuit shown in FIG. 1 will be described. The CPU 11 processes the program stored in the program memory 13, and the image memory 1
Image data defining an image to be displayed in 5 is appropriately written. The image data is data indicating the color to be displayed, and C
At the stage of creating a program executed by the PU 11, it is not necessary to have knowledge of the characteristics of the liquid crystal display element to be used, and it is not necessary to consider the characteristics in particular. Therefore, the programmer can create a program considering only the operation of the CPU 11 and the color of the image to be displayed.

The image data written in the image memory 15 by the CPU 11 is read by the display control circuit 17 for each one scanning line in a pixel unit (6 bit unit) and sequentially supplied to the address terminal of the conversion table 19. An address, that is, 3-bit voltage data corresponding to the image data is stored at a position addressed by the image data of the conversion table 19, and the voltage data is read out and stored in the D / A converter 21. Supplied.

The D / A converter 21 converts the 3-bit voltage data sequentially supplied from the conversion table 19 into an analog voltage and outputs it as an analog video signal as shown in FIG. The column driver 33 samples the video signal for one line supplied from the D / A converter 21, and outputs it to the data line 49 in the next horizontal scanning period. The row driver 35 follows the timing signal from the CPU 11
A gate pulse is sequentially applied to the gate line 47 to sequentially select (scan) the pixel electrodes 43, and a voltage corresponding to a display color is applied to the pixel electrodes 43 of the selected row via the data line 49 and the TFT 45. Is applied. As described above, this voltage may be a voltage corresponding to the color originally desired to be displayed, or may be a voltage corresponding to a displayable color approximate to the color originally desired to be displayed.

The row driver 35 turns off the gate pulse, turns off the TFT 45 immediately before the voltage applied to the data line 49 is switched, and turns off the pixel electrode 43 and the counter electrode 5.
The write voltage is held in the capacitance formed by 8 and the liquid crystal 56 between them. Therefore, the alignment state of the liquid crystal molecules is maintained in a desired state during the non-selection period, the desired birefringence is maintained, and the display color is maintained.

By repeating such operations in sequence, an image substantially equal to the image defined by the image data stored in the image memory 15 is displayed on the liquid crystal display element 23.

As described above, according to this embodiment,
When creating the program stored in the program memory 13, it is not necessary to consider the "applied voltage-display color" characteristic of the liquid crystal display element 23, and the display program can be created only by considering the color image to be displayed. , It becomes easy to create a program. Even when the liquid crystal display elements 23 having different characteristics are used, an arbitrary color image can be created without modifying the display program main body simply by changing the storage data of the conversion table 19 according to the characteristics. .

In the above embodiment, the contents of the conversion table 19 are set based on the applied voltage and the display color on the RGB chromaticity diagram, but the conversion is performed based on the locus of the display color on the CIE chromaticity diagram shown in FIG. The contents of the table 19 may be set. Also in this case, for colors that cannot be displayed, the voltage data corresponding to the closest displayable color on the chromaticity diagram is set in the conversion table. Alternatively, as shown in FIG. 8, the chromaticity diagram is radially divided with the white point as a reference, and the colors belonging to each divided area are replaced by the displayable color in the divided area. May be.

In the above embodiment, the table is used as the simplest example of converting the image data into the voltage data.
For example, the applied voltage-display color characteristics shown in FIG. 3 or FIG. 7 may be stored in the form of a function, and the voltage data may be obtained by performing calculation every time image data is supplied.

In the liquid crystal display element in the above-mentioned embodiment, nematic liquid crystal having a positive dielectric anisotropy was twisted and used in the liquid crystal cell. However, the present invention is directed to a vertical molecular alignment (DAP) type using a cell in which liquid crystal molecules are homeotropically aligned, a parallel molecular alignment (homogeneous) type using a cell in which liquid crystal molecules are arranged in a twist-free homogeneous state, and a liquid crystal molecule. A hybrid molecular array (HAN) type cell using a hybrid molecular array cell in which the array is vertical on one substrate surface, parallel on the other substrate surface, and the array continuously changes between both substrates, or The present invention can be applied to various display elements such as a liquid crystal alignment mode type which uses a cell having a liquid crystal layer in which liquid crystal molecules change between splay alignment and bend alignment depending on a voltage. Further, in the above embodiment, the retardation plate was used, but depending on the arrangement of liquid crystal molecules,
It may be removed as appropriate. Further, the present invention is applicable not only to the reflective type but also to a transmissive type liquid crystal display element.

[0041]

As described above, according to the present invention, the designated display color is automatically converted into the voltage, so that an appropriate color image can be displayed on the liquid crystal display element. Also, even if a color that cannot be displayed by the liquid crystal display device is specified, an approximate displayable color is selected and automatically converted to a voltage corresponding to that color, so an appropriate color display image can be obtained. You can When using liquid crystal display elements with different characteristics, simply change the stored data in the conversion table according to the characteristics of the liquid crystal display element.
An arbitrary color image can be displayed without modifying the display program itself.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of image data stored in an image memory shown in FIG.

FIG. 3 is a diagram showing a configuration example of a conversion table shown in FIG.

FIG. 4 is an RGB chromaticity diagram showing an example of a relationship between an applied voltage of a liquid crystal display element and a display color.

FIG. 5 is a diagram illustrating a method of setting voltage data corresponding to a color that cannot be displayed.

FIG. 6 is a diagram showing an example of an output signal of a D / A converter.

FIG. 7 is a CIE chromaticity diagram showing an example of a relationship between a voltage applied to a liquid crystal display element and a display color.

FIG. 8 is a diagram illustrating a method of setting voltage data corresponding to a color that cannot be displayed.

FIG. 9 is a cross-sectional view of a liquid crystal display panel.

[Explanation of symbols]

11 ... CPU, 13 ... Program memory, 15 ... Image memory, 17 ... Display control circuit, 19 ... Conversion table, 21 ... D / A converter, 23 ... Liquid crystal Display element, 31
... liquid crystal display panel, 33 ... column driver, 35 ... row driver, 41 ... substrate, 43 ... pixel electrode, 45 ... thin film transistor (TFT), 47 ... gate line, 49.
..Data lines, 51 ... Substrate, 52 ... Retardation plate, 53
... Polarizing plate, 54 ... Polarizing plate, 55 ... Reflecting plate, 56 ... Liquid crystal, 58 ... Counter electrode, 59 ... Alignment film, 60 ... Alignment film

Claims (10)

[Claims] 1. A liquid crystal display element for displaying a plurality of colors according to an applied voltage, a color designating means for designating a designated display color of the liquid crystal display element, a voltage applied to the liquid crystal display element and the designated display color. And a conversion unit that stores a relationship between a display color determined based on the relationship between the display color and a voltage value corresponding to the display color, and outputs voltage data corresponding to the designated display color designated by the color designating unit; And a supply means for displaying a predetermined display color by supplying a driving voltage corresponding to the voltage data output by the liquid crystal display element to the liquid crystal display element. 2. The converting means outputs voltage data corresponding to a displayable color closest to the designated display color with respect to the designated display color designated by the color designating means. Item 2. The liquid crystal display device according to item 1. 3. The conversion means is a voltage data corresponding to a displayable color which is the shortest distance in the RGB color space of the display color with respect to the designated display color designated by the respective color designating means, or CIE. 3. The liquid crystal display device according to claim 1, wherein voltage data corresponding to a displayable color located at the shortest distance on the chromaticity diagram is output. 4. The conversion means includes digital output means for outputting voltage data as a digital signal, and the supply means includes a digital-analog converter for converting the voltage data output from the conversion means into an analog voltage. The liquid crystal display device according to claim 1, 2 or 3, further comprising: a drive unit that supplies the analog voltage output from the digital-analog converter to the liquid crystal display element as the drive voltage. 5. The color instructing means executes a program memory for storing an image generating program, an image memory for storing color data for instructing a display color, and the image generating program stored in the program memory, 5. An execution means for storing color data defining color display in an image memory, and a means for supplying the color data stored in the image memory to the conversion means, according to any one of claims 1 to 4. 2. The liquid crystal display device according to item 1. 6. A color instructing means for outputting color data for instructing a display color in pixel units, a converting means for converting the color data into a corresponding voltage, and a voltage output by the converting means in accordance with an applied voltage. Driving means for displaying a color image on the liquid crystal display element by supplying and driving the liquid crystal display element for displaying colors,
A liquid crystal display device comprising: 7. A liquid crystal display element for displaying a plurality of colors in accordance with an applied voltage, and a color indicating means for outputting color data for specifying a plurality of colors having different wavelength ranges for displaying a predetermined color, A conversion unit that outputs voltage data corresponding to the color data output from the color instruction unit, and a voltage corresponding to the voltage data output from the conversion unit to the liquid crystal display element by supplying the liquid crystal display element with a voltage corresponding to the voltage data. A liquid crystal display device comprising: a supply unit that displays an image. 8. The liquid crystal display device according to claim 1, wherein the liquid crystal display element performs display by an optical effect by controlling birefringence. 9. A color instructing step for instructing a designated display color; a conversion step for converting the designated display color instructed by the color instructing step into a corresponding voltage; and a voltage obtained by the converting step to be an applied voltage. And a driving step of displaying a color image on the liquid crystal display device by supplying the liquid crystal display device with a corresponding color and driving the liquid crystal display device. 10. The conversion step comprises the step of preparing a table storing the relationship between the voltage applied to the liquid crystal of the liquid crystal display device and the display color, and the designated display color designated by the color designating step, 10. The method of driving a liquid crystal display device according to claim 9, further comprising: a conversion step of converting the voltage into a corresponding voltage by using.