JP2000214827A - Color liquid crystal display device in field sequential drive system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To significantly reduce power consumed by a backlight by selecting a pixel having maximum permeability for each color in one field period for constituting one image, controlling the gradation of the backlight by setting a brightness signal for this picture element to 100%, and correcting permeability of each pixel of a liquid crystal. SOLUTION: A selecting/correcting circuit 14 for field maximum brightness comprises a calculating portion and I/O and reads a maximum brightness signal (0-255 gradations) of each color from an image memory 12. A pixel, having maximum permeability is selected in relation to each color in a single field period for constituting one image, and gradation of the back light is controlled by setting a brightness signal for this pixel to 100%. This gradation control output is outputted to a three-color RGB backlight control circuit 16. Following such gradation control of the backlight, permeability of each pixel of a liquid crystal is corrected, corresponding to the control in order to provide a prescribed brightness and is written in an image memory 15.

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, and more particularly to a field sequential driving type color liquid crystal display device for displaying a color image without using a color filter.

[0002]

2. Description of the Related Art As a color liquid crystal display device which does not require a color filter, there is a field sequential driving method. This is because the backlight is controlled within one field period of one image to sequentially change the illumination light among three colors (the three primary colors red (R), green (G), and blue (B)). Let me
A control circuit for controlling a liquid crystal panel to write an image signal of a corresponding light to a pixel while synchronizing with a light emission timing of each color illumination light. Background Art Conventionally, there are backlights using a fluorescent tube system, an LED system, and an electroluminescence element. As a backlight control method, three colors are set so that the illumination is turned on for a predetermined time in the order of red (R) → green (G) → blue (B) → red (R) within one field period. In this method, the gradation is controlled sequentially for each color, and the gradation of each color is controlled in synchronization with the lighting of the backlight by controlling the transmittance of the liquid crystal for each pixel.
JP-A-9-325317, JP-A-9-325317
17419, JP-A-5-504416, and JP-A-61-281492.

A color liquid crystal display device using this method is:
Currently, a prototype has been announced and is under development for practical use. Further, as a color display device using the field sequential driving method, a projection type using a DMD (Digital Micromirror Device) is already commercially available from several companies.

The feature of this method is that one pixel can display the three primary colors of red, green and blue without using a color filter, so that it is one-third that of a liquid crystal display device using a color filter.
The same resolution can be obtained with the number of pixels. Further, since no color filter is used, the transmittance of the backlight is increased three times or more.

[0005] Therefore, as compared with the method using a color filter, a color filter is not required, the number of liquid crystal driving circuits is reduced to one third, and a manufacturing technique similar to a monochrome display liquid crystal display panel is three times as high. A color liquid crystal display device can be manufactured inexpensively, for example, because it is easy to manufacture because resolution is obtained.

[0006]

As a backlight which has been conventionally announced for a field sequential driving system, a backlight using a fluorescent tube system, an LED system, and an electroluminescent device have been announced. A backlight control method is a method of sequentially switching the three primary colors of red, green, and blue in time series, and a method of controlling the transmittance of the liquid crystal for each pixel is used for gradation control of each color. . In this backlight control method, for example, even when only the green screen is displayed on the entire liquid crystal panel, the red and blue backlights are lit in time series like green, and all the power required for lighting is wasted. Was. Alternatively, when the entire screen is displayed in halftone, the red, green, and blue backlights are always lit at a constant output of 100% even if the components of each color are 30%, which is necessary for lighting. Power was wasted. In particular, in portable color liquid crystal display devices, the challenge is to reduce the weight of the battery by reducing the power consumption of the liquid crystal, which accounts for about half of the power consumption, and to reduce the power consumption by the backlight. Is important.

Accordingly, an object of the present invention is to provide a field-sequential driving type color liquid crystal display device for displaying a color image without using a color filter, and the power consumption by the backlight is significantly reduced as compared with the conventional device. To provide a color liquid crystal display device having a field sequential drive method.

[0008]

As a result of intensive studies, the inventor of the present application has selected a pixel having the maximum transmittance for each color in one field period constituting one image, and the luminance signal for the pixel is set to 100. %, By controlling the gradation of the backlight and correcting the transmittance of each pixel of the liquid crystal, it is possible to eliminate the power consumption caused by the unnecessary lighting of the backlight, thereby reducing the power consumption by the backlight. The present inventors have completed the present invention by recognizing that it can be significantly reduced.

That is, the present invention comprises a liquid crystal panel having a plurality of pixels, and a plurality of three-color backlights for irradiating the pixels, and the three-color backlights are sequentially switched in time series to illuminate the pixels. In the field sequential driving type color liquid crystal display device which displays a color image on the liquid crystal panel by performing the above operation, a pixel having a maximum transmittance for each color within one field period constituting one image is selected. Provided is a field sequential driving type color liquid crystal display device, wherein gradation of the backlight is controlled by setting a luminance signal for a pixel to 100%, and transmittance of a liquid crystal of each pixel is corrected.

[0010]

FIG. 1 shows the basic structure of a color liquid crystal display device according to the present invention. In FIG.
1 is a liquid crystal panel, 2 is a pixel arrangement area of the liquid crystal panel 1, 3
Is a backlight for color display arranged on the back surface of the liquid crystal panel 1. The red LED 4, the green LED 5, and the blue LED 6, which emit alternately three primary colors, are arranged in a predetermined order in one field period. → Green LED → Blue LED → Red L
ED... Are respectively turned on in the order of the backlight driving units. Reference numeral 7 denotes a transmission / diffusion plate which is disposed between the liquid crystal panel 1 and the backlight 3 and serves to make the light of the backlight 3 a uniform surface light source. The basic configuration is the same as that of the conventional device.

FIG. 2 is a block diagram of the signal processing, which includes a signal processing circuit 11, image memories 12 and 15, a timing generator 13, a field maximum luminance selection and correction circuit 14, which is a feature of the present invention, and a backlight control circuit. 1
6, a liquid crystal panel drive circuit 17 is provided. These circuits constitute an integrated control circuit as a whole, and control the operations of the liquid crystal panel 1 and the backlight 3.

That is, as shown in FIG. 3 (a timing chart of a conventional apparatus which does not include the field maximum luminance selection correction circuit 14 which will be described later in detail), one image constituting one image is formed.
During the field period, the backlight 3 is controlled to sequentially change the illumination light between the three colors, and the liquid crystal panel 1 is controlled to write the video signal of the corresponding color to the pixel while synchronizing with the emission timing of the illumination light of each color. Let Specifically, the signal processing circuit 11 separates a color video signal input from the outside into each of red, green, and blue. The image memory 12 records each color video signal for one field.

The intra-frame maximum luminance selection and correction circuit 14, which is a feature of the present invention, comprises an operation unit and I / O shown in FIG. 4, selects the maximum luminance of each color pixel in one field, and sets the backlight lighting time. And the transmittance of the liquid crystal is corrected (this will be described in more detail later). Further, the timing generator 13 writes and reads data from and to the image memories 12 and 15, controls the liquid crystal panel driving circuit 17, switches the emission color of the backlight 1 via the backlight control circuit 16, and controls the liquid crystal panel driving circuit 17. Control and generate respective timing signals. The backlight control circuit 16 controls the operation of the backlight 3, and switches the emission color in the order of red, green, and blue at high speed within one field period of the input video signal. At this time, a video signal corresponding to the emission color of the backlight 3 is transmitted to the image memory 1 within the emission time of each color.
5, and is written to the liquid crystal panel 1 via the liquid crystal panel drive circuit 17. With the above procedure, red, green, and blue images are sequentially displayed on the liquid crystal panel 1 within one field period, and are recognized as full-color images by human eyes.

Next, the operation will be described with reference to the timing chart of FIG. From the liquid crystal panel driving circuit of FIG. 2 to the scanning electrodes 18 and the signal electrodes 19 of the active matrix type monochrome liquid crystal panel, the data to all the pixels within the pixel drawing time allocated within one third of one field period. Write. Next, the first color of the backlight 3 is turned on via the backlight control circuit 16. Next, similarly, the second color and the third color are turned on, and the three colors are sequentially displayed within one field period.

In the conventional method, as shown in the timing chart of FIG. 3, the backlight lighting time is fixed to a preset value.
As shown in (1), the backlight lighting time is set to a necessary minimum, and control is performed so that the transmittance of the liquid crystal corresponding to the pixel displaying the maximum luminance in one field is maximized. That is, when attention is paid to red, in a plurality of pixels constituting one color image, the luminance signal for the pixel having the maximum red transmittance is set to 100%, and the gradation of the backlight is controlled. For example, when the transmittance of a pixel having the maximum red transmittance in the image is 50%,
Since the gradation of the backlight is controlled with the luminance signal giving 50% as 100%, the lighting time of the red backlight is 50% of the conventional pixel drawing time. Similarly, when a certain color image does not use red at all (for example, in the case of one color of green), the transmittance of a pixel having the maximum red transmittance in the image is 0%. Backlight does not light. On the other hand, since the gradation of the backlight is controlled in this way, the transmittance of the liquid crystal is corrected correspondingly to provide a predetermined luminance. That is, in the conventional control method, it is assumed that the backlight is always turned on for 100% of the lighting time. Therefore, when the lighting time of the backlight is shortened according to the present invention, the transmittance of the liquid crystal is increased accordingly. Otherwise, a predetermined luminance cannot be obtained. Such backlight gradation control and correction of the transmittance of each pixel are performed by the field maximum luminance selection correction circuit 14.

The field maximum luminance selection correction circuit 14
As shown in FIG. 4, a maximum luminance signal (0 to 255 gradations) of each color is read from the image memory 12 by an arithmetic unit and an I / O, and the gradation control output (5 bits, The gradation (0 to 15) and the gradation (0 to 255) after all pixel correction are written in the image memory 15.

YR = (INT (Max (R (1,1),... R (n, m))) + 1) / 16 + 1 R ′ (1,1) = INT (R (1,1) * 16 / YR R '(1,2) = INT (R (1,2) * 16 / YR R' (n, m) = INT (R (n, m) * 16 / YR

Here, R (1,1)... R (n, m) is the luminance (0 to 2) of the red pixel of the original read out from the image memory 12.
55 gradations), and YR represents the maximum luminance of the red pixel of the original image as 1
This is a value converted into 6 gradations, and is connected to the control circuit of the red backlight through 5-bit I / O. Also, R '(1,1)
R ′ (n, m) is the luminance (0 to 255 gradations) of the red pixel after correction, and is written to the image memory 15. Green,
For blue, the same processing is sequentially performed.

In this embodiment, the illuminance of the backlight is set to LE.
Controlled by D lighting time, but fixed lighting time, LED
The amount of light may be adjusted by a current or a voltage applied to the light source, or a combination of both may be used. In addition, as the illumination, a fluorescent tube or an electroluminescent element having extremely little afterglow may be used.

In this embodiment, the field maximum luminance selection correction circuit is realized by a combination of a personal computer and an I / O. However, it is known to those skilled in the art that the field maximum luminance selection correction circuit can be made as a custom IC. it is obvious.

[0021]

As described above, according to the present invention,
By controlling the illuminance of the backlight to the minimum required, a very power-saving color liquid crystal display device can be manufactured. When general full-color moving image display is performed in 16 steps of backlight gradation control and 256 steps of liquid crystal gradation control, in the conventional method, the maximum luminance in one field is 60 times the liquid crystal transmittance of 256 gradations. % To 80% in many cases, and the power saving effect of the backlight according to the present invention is expected to be about 30%.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a liquid crystal display according to an embodiment of the present invention.

FIG. 2 is a control block diagram of the liquid crystal display device shown in FIG.

FIG. 3 is a timing chart illustrating an operation of a liquid crystal display device according to a conventional method.

FIG. 4 is an explanatory diagram of a calculation unit of the frame maximum luminance selection correction circuit.

FIG. 5 is a timing chart illustrating the operation of the liquid crystal display device according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 TFT liquid crystal panel 2 Liquid crystal panel pixel area 3 LED 3 color backlight 4 Red LED 5 Green LED 6 Blue LED 11 Signal processing circuit 12 Image memory 13 Timing generator 14 Field maximum luminance selection correction circuit 15 Image memory 16 Backlight control circuit 17 Liquid crystal panel drive circuit 18 TFT liquid crystal panel scanning electrode driver 19 TFT liquid crystal panel signal electrode driver 20 TFT

Continued on the front page F-term (reference) 2H093 NA16 NA65 NA80 NC13 NC14 NC34 NC43 NC50 NC90 ND06 ND07 ND17 ND39 ND48 ND54 NE06 NF05 NH15 5C006 AA01 AA15 AA16 AA17 AA22 AF03 AF44 AF46 AF51 AF52 AF69 BB16 FA05 EB29 BF16 BB05 CC03 DD04 DD25 DD26 EE28 EE30 FF11 GG08 JJ02 JJ04 JJ05 5G435 AA00 BB12 BB15 CC12 EE26 EE30 GG23 GG26 GG27

Claims (2)

[Claims] 1. A liquid crystal panel having a plurality of pixels, and a plurality of three-color backlights for irradiating the pixels, wherein the three-color backlights are sequentially switched in time series and illuminated. In the field sequential driving type color liquid crystal display device for displaying a color image on the liquid crystal panel, a pixel having a maximum transmittance for each color in one field period constituting one image is selected, and a luminance signal for the pixel is selected. , The gradation of the backlight is controlled, and the transmittance of each pixel of the liquid crystal is corrected. 2. The apparatus according to claim 1, wherein the gradation control of the backlight is performed by controlling a lighting time and / or illuminance of the backlight.