JP2003140110A - Liquid crystal display device and its drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve luminous efficiency and also to reduce power consumption without lowering luminance, to widen the dynamic range of a back light sharply and to prolong the life of a cold cathode fluorescent lamp. SOLUTION: In this liquid crystal display device, a back light which illuminates a liquid crystal panel is constituted of a plurality of cold cathode fluorescent lamps 4 and the array of a plurality of light emitting diodes 5 which is arranged in an adjacent relation to these cold cathode fluorescent lamps 4 and the back light is driven by combining these fluorescent lamps 4 and these light emitting diodes 5 in accordance with the luminance of a picture.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a display device having a novel light source structure to control the driving mode according to the image signal, the ambient temperature or the light amount of the light source to display the luminance during operation. The present invention relates to a liquid crystal display device provided with a backlight that responds to changes in signal brightness at high speed to improve image quality, and a drive circuit thereof.

[0002]

2. Description of the Related Art Liquid crystal display devices are widely used as display means for monitors for various information terminals such as personal computers and mobile phones, or for television receivers. This type of liquid crystal display device visualizes an electronic image formed on a liquid crystal panel by illuminating it. Some small information devices use ambient light as a light source for this visualization,
In order to observe a good image regardless of the ambient light conditions or on a relatively large screen, the liquid crystal panel is equipped with an illumination light source, and the electronic image formed on the liquid crystal panel is illuminated by this illumination light source. Many are configured to illuminate.

Some small-sized liquid crystal display devices have a so-called front light installed as a light source on the front surface of the liquid crystal panel or in the vicinity thereof. However, in a notebook computer, a computer monitor, a television receiver, etc. An illumination light source called a backlight installed on the back is adopted.

There are roughly two types of backlights, one of which is a side edge type backlight used for a notebook computer or a computer monitor in which the depth of equipment is limited, and the other one requires high brightness. For a relatively large computer monitor or television receiver, a direct type backlight is installed just below the back surface of the liquid crystal panel.

FIG. 29 is a schematic diagram for explaining one constitutional example of a side edge type backlight using a cold cathode fluorescent lamp as a light source. FIG. 29A is a perspective view for explaining the whole constitution, and FIG. It is a perspective view which shows the mechanism created. This backlight includes a light guide plate 8 formed of a transparent material such as an acrylic plate, a reflection plate 9, a light diffusion plate (hereinafter, simply referred to as a diffusion plate) 10, and a cooling plate installed along at least one side of the light guide plate 8. It is composed of a cathode fluorescent lamp (CFL) 4 and a lamp reflection sheet 11 for effectively utilizing the emitted light of the cold cathode fluorescent lamp. Although the lower surface of the light guide plate 8 (on the side of the reflection sheet 11) or the upper surface of the reflection plate 9 (on the side of the light guide plate 8) has dot-like reflective printing, it is not shown.

A reflection sheet 9 is installed on the lower side of the light guide plate 8 (opposite the liquid crystal panel: the back surface), and a diffusion sheet 10 is installed on the upper side (the liquid crystal panel side: the upper surface) of the cold cathode fluorescent lamp driven by an alternating current. The light from 4 is incident on the light guide plate 8. Light guide plate 8
The incident light propagates through the inside of the light guide plate 8 and is emitted from the diffusion sheet 10 on the upper surface as illumination light L _P indicated by an arrow toward the liquid crystal panel (not shown).

Reference numeral 12 is a reflection print (or a reflection tape) for returning the light propagating through the light guide plate 8 back into the light guide plate 8. The backlight constitutes a surface light source that illuminates the liquid crystal panel from the back side. The backlight of this configuration is mainly used in many portable information devices which are lightweight and small in size.

FIG. 30 is a schematic sectional view for explaining another example of the structure of a side edge type backlight having a cold cathode fluorescent lamp as a light source. The same reference numerals as those in FIG. 29 correspond to the same functional parts. In this configuration example, two opposite sides (2
A cold cathode fluorescent lamp 4 is arranged on each of the two long side edges. A reflection plate 9 is provided on the lower surface side of the light guide plate 8, and dot printing 9'of a fluorescent substance or the like is provided on the upper surface of the reflection plate 9. Other configurations are the same as those in FIG. 29 described above.

The backlight constitutes a surface light source for illuminating the liquid crystal panel from the back side as in the case of FIG. The backlight having this configuration is also used in a portable information device like the one shown in FIG. 29, but is also used in a display monitor or the like which requires higher screen brightness.

FIG. 36 is a schematic sectional view for explaining one constitutional example of a direct type backlight using a cold cathode fluorescent lamp as a light source. The direct type backlight does not usually have the light guide plate as described above, but means a plurality of light sources arranged in parallel to the main surface (display surface and back surface) of the liquid crystal panel. The direct type backlight is one in which a plurality of cold cathode fluorescent lamps 4 are installed in parallel on the inner bottom portion of a frame 1 which is a backlight housing, and it is preferable to efficiently use the light of each cold cathode fluorescent lamp 4. A reflection plate 7 of a mountain shape or the like is provided. A diffusion plate 2 is provided on the liquid crystal panel side (not shown).

On the lower surface of the diffusion plate 2, a light shielding layer 3 having light shielding dots 3A for adjusting the brightness of the light of the cold cathode fluorescent lamp 4 therebelow is formed. Conventional examples of this type of direct type backlight are disclosed in, for example, JP-A Nos. 11-242219 and 11-8437.
It is disclosed in Japanese Patent Publication No. 7 and the like.

By the way, in an early backlight, the cold cathode fluorescent lamp, which is the main light source, was kept on during operation. In recent years, the "blink" that automatically determines the light source of this backlight according to the brightness of the image displayed on the liquid crystal panel and controls the light emission amount of the light source, especially the cold cathode fluorescent lamp, in real time to the brightness according to the characteristics of the image・ A lighting system called "light control" or "active light control (AI)" technology has been proposed (for example, "Liquid Crystal AI Technology" website of Matsushita Electric Industrial Co., Ltd., "Monthly FPD Intelligence"). 2000.3
"Required characteristics of LCD TVs and challenges in making pictures (liquid crystal AI technology)").

Further, a temperature sensor is provided in the vicinity of the backlight, and when the temperature in the vicinity of the backlight is low, the duty of the intermittent driving of the cold cathode fluorescent lamp is increased, and when it is high, the duty is decreased to raise the brightness at low temperature. It has been proposed that the cold cathode fluorescent lamp be prolonged by suppressing the decrease in brightness at room temperature (for example, Japanese Patent Laid-Open No. 9-288262).

[0014]

Although the liquid crystal AI technology is used to control the brightness of the backlight, the cold cathode fluorescent lamp has a slow response and dimming control is difficult to follow in real time. In addition, since the brightness of the cold cathode fluorescent lamp is controlled to be high in the image of a bright or high-luminance scene, when the image is stopped in a bright scene or when the image of a bright scene lasts for a long time, Power consumption increases.

Further, as the temperature of the backlight and its vicinity rises, the luminous efficiency of the cold cathode fluorescent lamp deteriorates, the brightness gradually decreases, and the life of the cold cathode fluorescent lamp shortens.

A method of providing a temperature sensor in the vicinity of a backlight using a cold cathode fluorescent lamp and increasing the duty of the cold cathode fluorescent lamp that is intermittently driven when the temperature is low and decreasing the duty when the temperature is high is known. Although the life of the cold cathode fluorescent lamp can be extended, it is difficult to achieve compatibility with the liquid crystal AI technology described above.

In view of the above problems of the prior art, an object of the present invention is to provide a liquid crystal display device capable of controlling the light amount of a backlight according to the brightness of a displayed video signal in real time and capable of high speed response control. It is to provide the driving circuit.

Another object of the present invention is to improve the luminous efficiency of the cold cathode fluorescent lamp which constitutes the light source of the backlight, reduce the power consumption without lowering the brightness, and significantly widen the dynamic range to reduce the cold. An object of the present invention is to provide a liquid crystal display device provided with a backlight capable of extending the life of a cathode fluorescent lamp and a driving circuit thereof.

Further, the inventor of the present application makes the backlight intermittently light up (or intermittently blinks) in synchronization with a synchronization signal (vertical synchronization signal: Vsync) for vertical synchronization (frame synchronization) of the video signal. ), A new problem that occurs when a so-called blink light control that controls lighting is adopted. That is, in the blink light control, the transient response time of the rise of the brightness when the cold cathode fluorescent lamp is turned on (lighted) and the transient response time of the fall of the brightness when turned off (light off) are long.

Therefore, due to the overlap of the transient response period of the liquid crystal transmittance of the liquid crystal panel and the transient response period of the rise or fall of the cold cathode fluorescent lamp, there is light emission with low brightness once and then light emission with high brightness occurs. . Therefore, when the moving image is displayed on the liquid crystal panel, the outline of the moving image may be observed in double.
This means that as long as the cold cathode fluorescent lamp is used for the backlight, the overlapping area of the transient response time during lighting and extinguishing of the cold cathode fluorescent lamp will increase the area in which double contours are observed on the screen. It is a fundamental problem that it will end.

As a reference related to the blink light control, "SIDDIGEST" (3
5.2 pp990-993) "Super TFT-
LCD for Moving Picture Im
age with theBlink Backlig
ht System ”.

In addition, JP-A-11-109921 and JP-A-2
000-293142. JP-A-11-10992
In No. 1, it is intended to improve the moving image display performance by separately providing a period for applying a grayscale voltage according to a video signal to the liquid crystal panel and a period for applying a black grayscale voltage. However, in this method, the longer the period in which the black gradation voltage is applied, the lower the screen brightness. In a hold type display device such as a thin film transistor (TFT) type liquid crystal display device, the moving image display performance is not improved unless the period of 1/2 or more of one frame is black, but the black display period is 1/2 of one frame. In this case, the display period of the video signal is halved, so that the luminance is halved.

In Japanese Patent Laid-Open No. 2000-293142, display data is written to pixels in 2/3 of one frame period, the backlight is kept in the off state, and then in the remaining 1/3 period of one frame period. The back light is turned on to display the written display data. However, for this purpose, it is necessary to write display data at high speed, and there is a problem that high luminance cannot be obtained because the lighting period of the cold cathode fluorescent lamp is 1/3 of one frame.

Therefore, still another object of the present invention is to shorten the period in which the transient response periods of rising or falling of the cold cathode fluorescent lamp are overlapped with each other, thereby avoiding the occurrence of double contours in moving image display, and to provide a high quality image. An object is to provide a liquid crystal display device capable of displaying and a driving circuit thereof.

[0025]

In order to achieve the above objects, the present invention provides a cold cathode fluorescent lamp and a white or R, G, B as a light source of a backlight constituting a liquid crystal display device.
The light emitting diode arrays are used together or only the light emitting diode arrays are used, and the current value of the cold cathode fluorescent lamp is kept low to control the brightness with the light emitting diode arrays. With this configuration, it is possible to realize a video expression with a wide dynamic range and a high-speed responsiveness of the brightness of a display video without increasing power consumption.

Further, in order to achieve the above-mentioned objects, the present invention comprises a backlight comprising a cold cathode fluorescent lamp and a light emitting diode array arranged in parallel, and a video signal displayed as a driving circuit of the backlight. The cold cathode fluorescent lamp blinks in synchronism with the vertical synchronization signal of and the lighting control of the light emitting diode array is performed at the timing of correcting the brightness at the time of rising of the cold cathode fluorescent lamp and the brightness at the time of falling of the cold cathode fluorescent lamp. . Hereinafter, a typical configuration of the present invention will be described.

(1) A liquid crystal display device having a backlight on the back surface of a liquid crystal panel, wherein the backlight is
The liquid crystal panel may include a plurality of cold cathode fluorescent lamps arranged in parallel directly below the liquid crystal panel, and a plurality of light emitting diode arrays arranged adjacent to the cold cathode fluorescent lamps.

(2) The light emitting diode array is provided between the plurality of cold cathode fluorescent lamps.

(3) A liquid crystal display device having a backlight on the back surface of a liquid crystal panel, wherein the backlight is
It has a plurality of light emitting diode arrays arranged directly below the liquid crystal panel.

(4) A liquid crystal display device having a backlight on the back surface of the liquid crystal panel and provided with a drive circuit for controlling the brightness of the backlight according to the brightness of a video signal displayed on the liquid crystal panel. And the backlight is
Image quality of a video signal displayed on the liquid crystal panel, which has a plurality of cold cathode fluorescent lamps arranged in parallel directly below the liquid crystal panel and a plurality of light emitting diode arrays arranged adjacent to the cold cathode fluorescent lamps. An image quality control circuit for controlling the brightness of the video signal, a brightness detection circuit for detecting the brightness of the video signal, and a dimming signal for the backlight based on the brightness detection signal of the video signal detected by the brightness detection circuit. And a light emitting diode drive circuit that controls the light emission brightness of the light emitting diode according to the dimming signal.

In (5) and (4), a temperature sensor for detecting the temperature near the cold cathode fluorescent lamp and a light quantity sensor for detecting the brightness of the cold cathode fluorescent lamp are provided, and the temperature sensor and the light quantity sensor are provided. Is added to the dimming signal.

(6) A liquid crystal display device having a backlight on the back surface of the liquid crystal panel and provided with a drive circuit for controlling the brightness of the backlight according to the brightness of a video signal displayed on the liquid crystal panel. And the backlight is
An image quality control circuit having a plurality of light emitting diode arrays arranged directly below the liquid crystal panel, for controlling the image quality of a video signal displayed on the liquid crystal panel, and a brightness detection circuit for detecting the brightness of the video signal. A control / arithmetic circuit that generates a dimming signal of the backlight based on a brightness detection signal of a video signal detected by the brightness detection circuit; and light emission that controls the light emission brightness of the light emitting diode by the dimming signal. And a diode drive circuit.

(7) A liquid crystal display device having a backlight on the back surface of the liquid crystal panel and provided with a drive circuit for controlling the brightness of the backlight according to the brightness of a video signal displayed on the liquid crystal panel. And the backlight is
An image quality control circuit that has a plurality of cold cathode fluorescent lamps and a plurality of light emitting diode arrays that are alternately arranged immediately below the liquid crystal panel and that controls the image quality of a video signal displayed on the liquid crystal panel; and a brightness of the video signal. Brightness detection circuit for detecting brightness, a control / arithmetic circuit for generating a dimming signal of the backlight based on the brightness detection signal of the video signal detected by the brightness detection circuit, and A light emitting diode drive circuit for controlling the light emission brightness of the light emitting diode, wherein the light emitting diode drive circuit controls the brightness of the plurality of light emitting diode arrays in two directions, that is, the row direction and the column direction of the liquid crystal panel. It is characterized by having a diode driver.

(8) A liquid crystal display device having a backlight on the back surface of the liquid crystal panel and provided with a drive circuit for controlling the brightness of the backlight according to the brightness of a video signal displayed on the liquid crystal panel. And the backlight is
An image quality control circuit having a plurality of light emitting diode arrays arranged directly below the liquid crystal panel, for controlling the image quality of a video signal displayed on the liquid crystal panel, and a brightness detection circuit for detecting the brightness of the video signal. A control / arithmetic circuit that generates a dimming signal of the backlight based on a brightness detection signal of a video signal detected by the brightness detection circuit; and light emission that controls the light emission brightness of the light emitting diode by the dimming signal. A diode driving circuit, wherein the light emitting diode driving circuit includes a light emitting diode driver for controlling the light emission brightness of the plurality of light emitting diode arrays in two directions, that is, a row direction and a column direction of the liquid crystal panel. To do.

(9) A liquid crystal panel, a backlight for illuminating the liquid crystal panel, a video signal drive circuit for displaying a video signal on the liquid crystal panel based on a vertical synchronizing signal and a horizontal synchronizing signal, and A liquid crystal display device having a backlight drive circuit for driving a backlight,
The backlight comprises a cold cathode fluorescent lamp and a light emitting diode array arranged in parallel, and the backlight driving circuit blinks the cold cathode fluorescent lamp in synchronization with the vertical synchronizing signal. And a light emitting diode drive circuit for controlling the light emission of the light emitting diode array at a timing for correcting the brightness at the time of rising of the cold cathode fluorescent lamp and the brightness at the time of falling of the cold cathode fluorescent lamp.

In (10) and (9), the light emitting diode drive circuit is provided with a timing generating circuit for controlling blinking of the light emitting diode array based on the vertical synchronizing signal and a timing signal generated by the timing generating circuit. A light emitting diode current reference value generating circuit for generating a plurality of current reference values to be applied to the light emitting diode array based on the light emitting diode array; and a light emitting diode for applying the current reference value to the light emitting diode array in synchronization with a timing signal from the timing generating circuit. And a current reference value switching circuit.

In (11), (9) or (10), a plurality of the cold cathode fluorescent lamps and a plurality of the light emitting diode arrays are arranged side by side immediately below the liquid crystal panel.

In (12), (9) or (10), a light guide plate is provided directly below the liquid crystal panel, and the cold cathode fluorescent lamp and the light emitting diode array are arranged on at least two sides of the light guide plate. It is characterized by

In any one of (13) and (9) to (12), the light emitting diode is turned on when the cold cathode fluorescent lamp is started.

In any one of (14), (9) to (12), the light emitting diode is turned on at the start of lighting of the cold cathode fluorescent lamp.

In any one of (15) and (9) to (12), the cold cathode fluorescent lamp turns on the light emitting diode when the temperature is low.

It is needless to say that the present invention is not limited to the above-mentioned constitution and the constitution of the embodiments described later, and various modifications can be made without departing from the technical idea of the present invention.

[0043]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a liquid crystal display device and a driving circuit thereof according to the present invention will be described below in detail with reference to the drawings of the embodiments. 1A and 1B are schematic views illustrating an embodiment of a direct type backlight that constitutes a liquid crystal display device of the present invention, FIG. 1A is a cross-sectional view, and FIG. 1B is a plan view seen from the liquid crystal panel side.

In the direct type backlight of this embodiment, a plurality of cold cathode fluorescent lamps 4 and a plurality of light emitting diodes 5 which are arranged in parallel are installed at the bottom inside the case frame 1.
Here, a plurality of white light emitting diodes 5 are arranged as an array in three rows between three cold cathode fluorescent lamps 4. The light emitting diode 5 can be made substantially white by combining R, G, and B light emitting diodes. In the following, the diode array may be simply described as a diode or an LED.

The light emitting diodes 5 are mounted on a circuit board 6 installed on the outer wall of the bottom of the case frame 1, so that each light emitting diode 5 projects inward from the bottom of the case frame 1 through an opening formed in the bottom of the case frame 1. It is located in. As in FIG. 36, the diffusion plate 2 and the light shielding layer 3 are installed on the upper part of the case frame 1. A light-shielding dot 3A is formed in a portion of the light-shielding layer 3 that faces a region directly above the cold cathode fluorescent lamp 4. In this embodiment, the reflector as shown in FIG. 36 is not particularly provided, and the function of the reflector may be provided by forming the inner wall of the case frame 1 as a mirror surface. Needless to say, a reflector may be installed.

In this embodiment, the emission light L _LED of the light emitting diode array 5 is connected to the liquid crystal panel from between the cold cathode fluorescent lamps 4 as shown by the inverted C-shaped line spreading upward in FIG. Light emitted from the cold cathode fluorescent lamp 4 through the diffusion plate 4 toward the liquid crystal panel (not shown) and illuminated.

The cold cathode fluorescent lamp 4 and the light emitting diode array 5 are drive-controlled by a drive circuit described later, and the light quantity control of the backlight according to the brightness of the video signal displayed on the liquid crystal panel is controlled in real time at high speed. It is possible to realize an image representation with a wide dynamic range and a high-speed response of the brightness of a display image without increasing power consumption.

2A and 2B are schematic views for explaining another embodiment of the direct type backlight which constitutes the liquid crystal display device of the present invention. FIG. 2A is a sectional view and FIG. 2B is a plan view seen from the liquid crystal panel side. It is a figure. The direct type backlight of this embodiment has the structure shown in FIG.
This is the same as the first embodiment except that the light emitting diode array in 1 is installed on the inner surface of the side wall of the case frame 1.
In this case, a mountain-shaped reflector 7 shown by a dotted line in the drawing may be provided on the inner surface of the bottom of the case frame 1.

The emitted light L _LED of the light emitting diode array 5 is emitted from the side wall of the case frame 1 in the direction of the liquid crystal panel, as shown by the inverted C-shaped line in FIG. The emitted light is emitted to the liquid crystal panel side (not shown) through the diffusion plate 4 to illuminate it. In this embodiment, in particular, it is possible to correct the shortage of the amount of light in the peripheral portion of the liquid crystal panel, and it is possible to obtain a more uniform illumination light distribution in the entire display area of the liquid crystal panel.

The cold cathode fluorescent lamp 4 and the light emitting diode array 5 are drive-controlled by a drive circuit described later, and the light quantity control of the backlight according to the brightness of the video signal displayed on the liquid crystal panel is controlled in real time at high speed. It is possible to realize an image representation with a wide dynamic range and a high-speed response of the brightness of a display image without increasing power consumption.

3A and 3B are schematic views for explaining another embodiment of the direct type backlight which constitutes the liquid crystal display device of the present invention. FIG. 3A is a sectional view and FIG. 3B is a plane viewed from the liquid crystal panel side. It is a figure. The direct type backlight of this embodiment has the structure shown in FIG.
2 is a combination of the light emitting diode array in FIG. 2 and the light emitting diode array in FIG. Also in this case, as in the first embodiment shown in FIG. 1, no reflector is provided, and the inner wall of the case frame 1 may be mirror-finished to have the function of the reflector. Needless to say, a reflector may be installed.

Light emitted from the light emitting diode array 5 is shown in FIG.
As shown by the line of inverted C shape in (a), the light is emitted from the bottom and side walls of the case frame 1 toward the liquid crystal panel, and the light emitted from the cold cathode fluorescent lamp 4 is passed through the diffusion plate 4 to the liquid crystal panel side not shown. And illuminates it. According to the present embodiment, an effect obtained by combining the effects of the above-described one embodiment of FIG. 1 and the other embodiment of FIG. 2 is achieved.

The cold cathode fluorescent lamp 4 and the light emitting diode array 5 are drive-controlled by a drive circuit described later, and the light quantity control of the backlight according to the brightness of the video signal displayed on the liquid crystal panel is response-controlled in real time. It is possible to realize an image representation with a wide dynamic range and a high-speed response of the brightness of a display image without increasing power consumption.

4A and 4B are schematic diagrams for explaining another embodiment of the direct type backlight which constitutes the liquid crystal display device of the present invention. FIG. 4A is a sectional view and FIG. 4B is a plan view seen from the liquid crystal panel side. It is a figure. In the direct type backlight of this embodiment, only the diode array 5 is installed on the bottom of the case frame 1.

The drive circuit formed on the circuit board 6 is controlled in two systems so that the brightness of the diode array 5 can be controlled from both the row (column) direction and the column (row) direction of the liquid crystal panel. I am doing it.

Therefore, in the backlight of this embodiment,
It is possible to selectively control the diodes corresponding to only the vicinity of the image having the brightness equal to or higher than the threshold value on the display screen to further increase the brightness near the image. For example, when a bright window is displayed on the computer screen, the area of the window is illuminated brighter than the other areas.

With this configuration, the light amount control of the backlight according to the partial brightness of the video signal displayed on the liquid crystal panel is also controlled in real time at high speed, and the image expression in a wide dynamic range and the brightness of the displayed video at high speed are achieved. Responsiveness can be realized without increasing power consumption.

The number of cold cathode fluorescent lamps or light emitting diodes installed in each of the above embodiments is adjusted depending on the size of the liquid crystal panel, the light emitting characteristics of the cold cathode fluorescent lamps and the light emitting diodes, and the like. Further, the arrangement of the light emitting diodes is not limited to the square arrangement in the column direction and the row direction, but may be a staggered arrangement, an arrangement corresponding to the aspect ratio of the liquid crystal panel, or the like.

FIG. 5 is a schematic sectional view for explaining an embodiment of the side edge type backlight which constitutes the liquid crystal display device of the present invention. The overall structure is similar to that shown in FIG. 30, except that the cold cathode fluorescent lamp 4 is disposed on one of the two opposite sides of the light guide plate 8 and the light emitting diode array 5 is disposed on the other side. The light emitting diodes 5 are mounted on the substrate 6 and arranged in an array. FIG. 5A shows a reflection printing 9'of a fluorescent film or the like provided on the upper surface of the reflecting plate 9, and FIG. 5B shows a reflection printing 9'of the fluorescent film or the like provided on the lower surface of the light guide plate 8. It is a thing.

FIG. 6 is a block diagram showing an embodiment of a drive circuit of the liquid crystal display device of the present invention. The liquid crystal display is provided with a drive circuit for detecting the characteristics of the video signal and controlling the light emitting diode array of the backlight. It is a block diagram of an apparatus. In FIG. 6, this liquid crystal display device includes a liquid crystal panel (LCD panel) 14 having a direct type backlight having a cold cathode fluorescent lamp 4 and a light emitting diode array 5. One cold cathode fluorescent lamp 4 and one light emitting diode 5 are schematically shown in the figure.

The liquid crystal panel 14 is a panel controller 17
The cold cathode fluorescent lamp 4 is AC-driven by the inverter circuit 13 having an LCD driver (column) 15 and an LCD driver (row) 16 driven by. A video signal (image signal, display signal) is supplied from the image quality control circuit 18 to the panel controller 17. The image quality control circuit 18 includes a contrast control circuit 18A, a DC level control circuit 18B, and a digital γ correction circuit 18C.

On the other hand, the cold cathode fluorescent lamp 4 is supplied with a low power drive current from an inverter circuit (hereinafter, also simply referred to as an inverter) 13. The light emitting diode array 5 includes a light emitting diode drive circuit (LED drive circuit) 21.
A dimming signal is supplied through. The light emitting diode drive circuit 21 is connected to the control / arithmetic circuit 20 that generates a dimming signal according to the image quality of the video signal. The control / arithmetic circuit 20 has an image quality control amount calculation circuit 20A and a backlight brightness control circuit 20B. Further, this liquid crystal display device has a video signal brightness detection circuit 19.
The brightness detection circuit 19 has an APL detection circuit 19A, a MAX detection circuit 19B, and a MIN detection circuit 19C.

The APL detection circuit 19A receives a video signal input from an external circuit (a signal source such as a computer main body), detects the average luminance level thereof, and the MAX detection circuit 19A.
The B and MIN detection circuits 19C detect the maximum luminance value and the minimum luminance value of the video signal, respectively. The average brightness level and the maximum brightness value and the minimum brightness value detected by the brightness detection circuit 19 are input to the backlight brightness control circuit 20B, and the image quality control amount is calculated.

The image quality control amount calculated by the image quality control amount calculation circuit 20A of the control / arithmetic circuit 20 is given to the backlight brightness control circuit 20B, which generates an optimum dimming signal to pass through the light emitting diode drive circuit 21 to the light emitting diode. Applied to the array 5. In response to this dimming signal, the light emitting diode array 5 is dimmed at high speed.

The image quality control amount calculated by the image quality control amount calculation circuit 20A of the control / arithmetic circuit 20 is the image quality control circuit 1
8 contrast control circuit 18A and DC level control circuit 18B. Contrast control circuit 18A and D
The C level control circuit 18B controls the contrast and DC level of the video signal to optimal values according to the input image quality control amount.

The cold cathode fluorescent lamp 4 has an inverter circuit 13
Thus, AC driving is performed with a low current that has a margin such that an average luminance level of the video signal can be obtained regardless of the change in the luminance of the video signal. The light emitting diode array 5 is controlled so as to increase the amount of light mainly during a video scene of a video signal of high brightness. That is, when the brightness (luminance) of the video scene of the video signal is large, it is dealt with by increasing the light quantity of the light emitting diode array 5 which is DC-driven or pulse-driven.

Therefore, according to the present embodiment, it is possible to reduce the circuit scale of the inverter circuit which is the driving power source of the cold cathode fluorescent lamp which requires the AC drive, so that the heat generation amount is reduced, and as a result, the cold cathode due to the temperature rise is increased. Deterioration of the fluorescent lamp is suppressed and a long life can be achieved.

As with the conventional liquid crystal AI technique described above, in addition to the driving method of increasing or decreasing the light emission brightness of the light emitting diode array according to the brightness of the video scene, when the video signal exceeds a certain threshold value. By further increasing the emission brightness of the light emitting diode, it is possible to provide the same peak intensity characteristic as that of the cathode ray tube.

Further, in order to supplement the limit of color reproducibility of the color filter of the liquid crystal panel, the light emitting diode array is a combination of R, G, and B, and the light emitting diodes of each color are individually controlled to increase the monochromatic brightness and color. It is possible to improve reproducibility and realize high-quality display.

FIG. 7 is a block diagram showing another embodiment of the drive circuit of the liquid crystal display device of the present invention. The liquid crystal has a drive circuit for detecting the characteristics of the video signal and controlling the light emitting diode array of the backlight. It is a block diagram of a display device.
In FIG. 7, this liquid crystal display device includes a temperature sensor 23 and an optical sensor 2 in a cold cathode fluorescent lamp 4 which constitutes a backlight.
4 is provided.

The temperature sensor 23 and the optical sensor 24 detect the temperature and the light emission amount of the cold cathode fluorescent lamp, and when the control by the liquid crystal AI technique described above is off, the light emission efficiency of the cold cathode fluorescent lamp 4 is increased due to the high temperature. The decrease is prevented by decreasing the brightness of the cold cathode fluorescent lamp, and the decrease in brightness of the cold cathode fluorescent lamp is increased by the white or R, G, B light emitting diode array. is there. The backlight of this embodiment is not limited to the direct type.

In FIG. 7, reference numeral 25 is a temperature detection control circuit, 26 is a light amount detection control circuit, 27 is a detected temperature data holding circuit, and 28 is a detected light amount data holding circuit. Reference numeral 180 is an image quality control circuit (static), 181 is an image quality control circuit (dynamic), 200 is an image quality control amount calculation / backlight brightness control circuit, and 220 is a dimming signal generation circuit (static). SW1 to SW6 are changeover switches, and the same symbols as those in FIG. 6 correspond to the same functional portions.

The drive circuit of the present embodiment suppresses the temperature rise of the backlight BL by the control system for performing the image quality control and the backlight brightness control, the dynamic control using the liquid crystal AI technology, and the temperature sensor and the optical sensor. The control system for performing static control can be set by switching between two systems.

When the dynamic control / static control switching signal input is in static control, the switches SW1 to SW6 are in the illustrated state. At this time, the control signal of the temperature detection control circuit 25 based on the detection output of the temperature sensor 23 is applied to the inverter circuit 13 from the switch SW3, and the control signal of the light amount detection control circuit 26 based on the detection output of the photosensor 24 switches the switch SW5. It is added to the output of the dimming signal of the switch SW2, and is given to the LED drive circuit 21.

The switch SW1 applies the image quality control signal from the image quality control circuit (static) 180 to the panel controller 17, and the switch SW2 applies the light control signal from the light control signal generation circuit (static) 220 to the LED drive circuit 21. By this control, the decrease in brightness due to the low temperature of the cold cathode fluorescent lamp 4 is compensated by increasing the brightness of the white or R, G, B light emitting diode 5, and when the temperature of the cold cathode fluorescent lamp 4 is high, The current supplied to the cold cathode fluorescent lamp 4 is reduced to prevent the efficiency from being lowered due to the high temperature. Then, the luminance of the cold cathode fluorescent lamp 4 is reduced to compensate the luminance by improving the luminance of the light emitting diode 5.

When the dynamic control / static control switching signal input is dynamic control, the switches SW1 to SW6 are switched from the illustrated state. The detection signals of the temperature sensor 23 and the optical sensor 24 are held as a dimming control signal in the detected temperature data holding circuit 27 and the detected light amount data holding circuit 28, respectively.

When the dynamic control / static control switching signal is dynamic control, the image quality control circuit (dynamic) 181 operates in the same manner as the image quality control circuit 18 of FIG. 6 and the brightness detection circuit (dynamic).
190 performs the same operation as the brightness detection circuit 19 of the video signal of FIG. 6, and performs image quality control calculation / backlight brightness control circuit 20.
0 performs the same operation as the control / arithmetic circuit 20 of FIG. 6, and after the dimming signal from the image quality control calculation / backlight brightness control circuit 200 and the dimming signal of the detected light amount holding circuit 28 are added, LED driving is performed. A dimming signal is supplied to the light emitting diode array 5 by the circuit 21.

The dynamic control / static control switching signal is required to increase / decrease the backlight light amount according to the video signal, as in the video signal from a personal computer or the video setting mode for movie reproduction called cinema mode. If there is no light, or if the backlight light amount is not increased or decreased in accordance with the video signal, the image quality is high, and the condition that the liquid crystal AI is applied, such as the display of a video signal taken by a TV broadcast or a video camera. In the case of the video signal of, even if the liquid crystal AI is turned off by the user in the screen setting menu, the dynamic control / static control switching signal is switched to the static control, and the video signal taken by TV broadcasting or a video camera is displayed. To
If the liquid crystal AI is turned on under the condition that the liquid crystal AI is applied, the dynamic control / static control switching signal is switched to the dynamic control.

Next, the temperature characteristics of the temperature sensor, the optical sensor, and the cold cathode fluorescent lamp shown in FIG. 7 will be described. FIG. 8 is a circuit diagram illustrating a configuration example near the temperature sensor in FIG. 7. In this temperature sensor 23, a thermistor is used as the temperature sensor element T. In the figure, DA is a difference amplifier, which compares the terminal voltage of the temperature sensor element T with respect to the reference voltage V _{ref and} outputs the control voltage V as the difference output.
Output _TC .

FIG. 9 is a circuit diagram for explaining a configuration example near the photosensor in FIG. In this optical sensor 24, CdS is used as the optical sensor element P. In the figure, DA is a difference amplifier, which compares the terminal voltage of the photosensor element P with the reference voltage V _ref and outputs the control voltage V _PC as the difference output.

FIG. 10 is an explanatory diagram of the relationship between the temperature in the vicinity of the cold cathode fluorescent lamp and its brightness, with the horizontal axis representing the ambient temperature (° C).
Is shown by taking the relative luminance (%) on the vertical axis. Room temperature T in the figure
The relative luminance at _R (around 25 °) is shown as 100%.
As is clear from this relationship diagram, the cold cathode fluorescent lamp is
It has a characteristic that the relative brightness decreases at room temperature or lower, and the relative brightness decreases if it exceeds about 40 °, that is, the brightness decreases at high temperature.

According to the above embodiment, the life of the cold cathode fluorescent lamp which could not be realized by the backlight using only the cold cathode fluorescent lamp can be extended and the dynamic range is remarkably widened as compared with the cold cathode fluorescent lamp only. be able to. As a result, it becomes possible to control the backlight having a high-speed response characteristic and realize a high quality liquid crystal display device.

FIG. 11 is a block diagram showing a third embodiment of the drive circuit of the liquid crystal display device of the present invention. The control / arithmetic circuit 20 in one embodiment (FIG. 6) of the drive circuit realizes the peak luminance characteristic. Control / arithmetic circuit 20 with additional functions
It is a block diagram explaining. In the figure, the same reference numerals as those in the drawings of the above-mentioned embodiments correspond to the same functional parts, and 20A1 is L
ED driver column / row determination circuit, 20A2 is a comparator. Similar to the control / arithmetic circuit 20 of FIG. 6, this circuit generates an image quality control signal to the image quality control circuit 18 and a dimming signal to the LED drive circuit 21 according to the signal from the brightness detection circuit 19.

In addition, the backlight brightness control circuit 20B
Comparing the brightness signal, which is the output of
0A2, when the brightness is larger than the peak luminance reference amount, the LED driver column / row determination circuit 20A
1 is supplied with an in-screen position signal having brightness. LE
The D driver column / row determination circuit 20A1 determines which LED or LED group of the light emitting diode (LED) array is to be further brightened from the region where the brightness exists, and the LED driver (column) and the LED driver ( Row) to the LED driver column / row decision signal.

FIG. 12 is a diagram for explaining a method of realizing peak luminance by an LED column / low signal by using a part of an LED array and a part of an LED driver (column) and an LED driver (row). LED in the circled area in the figure
The circuit provided in the vicinity is an LED, two current limiting resistors,
FET is arranged. In the present embodiment, the dimming signal is supplied from the anode side of the LED, and the current flows to the ground via the two current limiting resistors. LED
The current supply capacity of the drive circuit determines the number of circuits that supply the dimming signal.

The LED driver (column) and the LED driver (row) have the function of supplying the LED array with the dimming signal from the LED drive circuit 21 shown in FIG.
FE placed near the LED by column / row signal
It has a function of turning on / off T. When dimming an LED at a normal brightness other than the peak brightness, the FET arranged near the LED is in an off state. That is, the FET control switches provided in the LED driver (column) and the LED driver (row) are turned off.

The FET on / off switch of the LED driver (column) designated by the LED column / low signal is turned on, and the FET on / off of the LED driver (low) is turned on.
When the off switch is turned on, the source of the FET provided near the LED is connected to the ground, the gate of the FET becomes the FET on voltage, the FET is turned on, and the LE is turned on.
One of the two current limiting resistors that were connected to the current path of D and the FET are now connected in parallel, and the current path of the LED is grounded via the drain-source of the FET through one resistance. Is changed to. Therefore, the current flowing through the LED is limited by one current limiting resistance and the ON resistance of the FET. If the ON resistance of the FET and the resistance connected in parallel to the FET are set to desired values, L of the desired location is reduced.
A larger amount of current can be passed through the ED as compared with an LED in which the FET is off.

FIG. 13 is a block diagram showing another embodiment of the drive circuit of the liquid crystal display device of the present invention. The same reference numerals as those in the above-described embodiments correspond to the same functional parts. Normally, the image quality control and the backlight control of the liquid crystal AI technology are performed as in the embodiment described with reference to FIG. 6. However, when the same image signal continues for several frames, the temperature sensor 23 and the optical sensor 24 are controlled by two. Switch S so that two control systems are connected
Select W1 to SW6.

When the temperature of the cold cathode fluorescent lamp 4 rises too much, its brightness is lowered and the brightness corresponding to the lowered brightness of the cold cathode fluorescent lamp 4 is compensated by increasing the brightness of the light emitting diode 5. Further, when the temperature of the cold cathode fluorescent lamp 4 is low, the brightness of the light emitting diode 5 is increased to suppress the fluctuation of the screen brightness due to the change of temperature and realize the high image quality.

FIG. 14 is a block diagram showing another embodiment of the drive circuit of the liquid crystal display device of the present invention. The same reference numerals as those in the above-described embodiments correspond to the same functional parts. In this embodiment, only the light emitting diode 5 is used as the light source of the backlight, and the configuration of one embodiment of the drive circuit described in FIG. 6 is used by using the other embodiment of the backlight described in FIG. Is used.

The present embodiment is constructed by excluding the cold cathode fluorescent lamp and the inverter circuit which is the power source thereof in FIG. 6, and the main operation of the circuit is the same as in FIG. The brightness of the backlight BL is controlled by controlling the light emitting diode 5 by the dimming signal created by the control / arithmetic circuit 20.
In the present embodiment, since the cold cathode fluorescent lamp is not used as the light source, the dynamic range is wide and the brightness control can be performed at high speed by following the brightness of the video signal.

FIG. 15 is a block diagram showing another embodiment of the drive circuit of the liquid crystal display device of the present invention. The same reference numerals as those in the above-described embodiments correspond to the same functional parts. In this embodiment, a combination of the cold cathode fluorescent lamp 4 and the light emitting diode 5 described with reference to FIG. 3 is used as the light source of the backlight BL, and the circuit configuration shown in FIG. 6 is used as the driving circuit thereof. is there.

Then, the light emitting diode 5 is controlled so as to be controlled in two directions of the column and the row of the LCD panel.
An ED driver (column) 21A and an LED driver (row) 21B are provided. The image quality control amount calculation circuit 20A of the control / arithmetic circuit 20 has the configuration shown in FIG. 11, and increases the brightness of the light emitting diode in the area corresponding to the high brightness part of the displayed scene to increase the speed of the scene. It is possible to follow changes in brightness.

FIG. 16 is a block diagram showing another embodiment of the drive circuit of the liquid crystal display device of the present invention. The same reference numerals as those in the above-described embodiments correspond to the same functional parts. In this embodiment, only the light emitting diode 5 is used as the light source of the backlight BL, and the circuit configuration shown in FIG. 15 is used as the driving circuit thereof.

Then, as in FIG. 15, the light emitting diode 5 is
LED driver (column) 21A and LED so that the LCD panel is controlled in two directions, column and row.
A driver (low) 21B is provided. The image quality control amount calculation circuit 20A of the control / arithmetic circuit 20 has the configuration shown in FIG. 11, and increases the brightness of the light emitting diode in the area corresponding to the high brightness part of the displayed scene to increase the speed of the scene. It is possible to follow changes in brightness.

According to each of the embodiments described above, the light quantity control of the backlight is controlled at high speed in accordance with the brightness of the video signal, the luminous efficiency of the cold cathode fluorescent lamp is improved, the power consumption is reduced, and the light is emitted. By controlling the light emission of the diode, the dynamic range of the backlight can be expanded to widen the dynamic range as a whole, and the life of the cold cathode fluorescent lamp can be extended.

Next, a liquid crystal display device capable of displaying a high-quality image by shortening the period in which the transient response periods of rising or falling of the cold cathode fluorescent lamp overlap to avoid the occurrence of double contours in moving image display. And an embodiment of the drive circuit thereof will be described.

FIG. 17 is a drive waveform diagram when the liquid crystal panel is illuminated by the blink light control using only the cold cathode fluorescent lamp as the backlight, and the case where the previous frame changes from the black state to the white state Indicates. In the figure, reference numeral F is one frame period, 101 is a vertical synchronizing signal (Vsync), 103 is the transmittance of the liquid crystal panel (cell) at the top of the screen during black → white display, and 104 is the liquid crystal panel at the center of the screen. The (cell) transmittance, 105 is the (cell) transmittance of the liquid crystal panel at the lower end of the screen, and 106 is the brightness of the cold cathode fluorescent lamp.

The hatched portion indicated by reference numeral 109 is black →
The brightness of the liquid crystal panel at the top of the screen in the transient response state at the time of white change, the shaded portion indicated by 110 is the brightness of the liquid crystal panel in the center of the screen in the same transient response state, and the shaded portion indicated by 111 is the liquid crystal in the transient response state at the bottom of the screen. The change in the brightness of the panel is shown.

At the upper and lower edges of the screen, the period during which the backlight is turned off overlaps with the transient response period of the liquid crystal panel (liquid crystal cell). Therefore, a period during which the backlight is turned on after a blank period is generated after low-luminance light emission once occurs. In addition, since the transmittance of the liquid crystal panel (liquid crystal cell) is in a steady state, when the image of a white vertical bar or the like moves, its contour is double observed. In order to avoid this, a backlight is constructed by using a cold cathode fluorescent lamp and a light emitting diode array together as described below, and the following method is newly adopted as a driving method thereof.

FIG. 18 is a drive waveform diagram for explaining an example of a blink light control using a backlight in which a cold cathode fluorescent lamp and a light emitting diode array are used in combination. Similar to FIG. 17, reference numeral F indicates 1 frame period, 1
01 is a vertical synchronization signal (Vsync), 103 is the transmittance of the liquid crystal panel (cell) at the top of the screen during black → white display, 10
4 is the transmittance of the liquid crystal panel (cell) at the center of the screen,
105 is the transmittance of the liquid crystal panel at the lower end of the screen, 106 is the brightness of the cold cathode fluorescent lamp, 107 is the brightness of the light emitting diode, and 108 is each change in the combined brightness of the cold cathode fluorescent lamp and the light emitting diode.

18, since the transient response time of the cold cathode fluorescent lamp is long in one frame period (vertical writing period) F as described with reference to FIG. 17, the transmittance of the liquid crystal panel (of the cell) is equal to that of the screen. The curves 103, 104 and 105 at the upper end, the center and the lower end are as shown in the figure. On the other hand, the brightness of the cold cathode fluorescent lamp that turns on / off (lights on / off) has a long transient response of rising and falling at the time of on / off, as shown by the curve 106 in the figure, and the transmissivity of the liquid crystal cell is transient. The response period overlaps with the transient response period of the rise and fall of the cold cathode fluorescent lamp. In this state, the double observation of the contour in the moving image display described with reference to FIG. 17 occurs.

In this embodiment, as shown by the curve 107, the light emitting diode is turned on at the beginning timing and the falling timing of the brightness 106 of the cold cathode fluorescent lamp, and as shown by the curve 108, as a whole. The luminance response characteristics of the backlight are approximated to a rectangular shape. This reduces the occurrence of the double contour described above.

FIG. 19 is a drive waveform diagram for explaining another example of the blink light control using the backlight in which the cold cathode fluorescent lamp and the light emitting diode array are used in combination. In the figure, the same reference numerals as those in FIGS. 17 and 18 correspond to the waveforms having the same functions.

In this embodiment, the backlight is lit at the upper end of the screen and the center of the screen during the transient response period of the liquid crystal panel (liquid crystal cell). Since white is displayed following the transient response, the double contour does not occur because the high brightness state is continuous. Also, since the backlight is off during the response period at the bottom of the screen, double contours do not occur here either.

FIG. 20 is a block diagram for explaining the schematic structure of a drive circuit for a backlight in which a cold cathode fluorescent lamp and a light emitting diode are arranged in parallel. The cold cathode fluorescent lamp 4 gives an on / off signal generated by a timing generation circuit 112 based on a vertical synchronizing signal (Vsync) 101 to an inverter 13, and the inverter 13 controls lighting and extinguishing. On the other hand, the light emitting diode 5 is an LE controlled by the ON / OFF signal generated by the timing generation circuit 112.
It is driven by the D drive circuit 21. This LED drive circuit 21
The drive by means of FIG. 18 is finely controlled by the current as shown by the waveform 107 in FIG.

FIG. 21 is a block diagram for explaining a configuration example of the LED drive circuit in FIG. Light emitting diode 5
Since the luminance of the light emitting diode is substantially proportional to the current flowing through the light emitting diode, the luminance of the light emitting diode 107 in FIG.
In order to realize the brightness shown by the curve, the circuit configuration shown in the figure is adopted. That is, the LED drive circuit 21 is composed of the LED current reference value generation circuit 113, the LED current reference value switching circuit 114, and the LED drive stage circuit 115.

The LED current reference value generation circuit 113 is provided with n light emitting diode current reference values (denoted as LED current reference value in FIG. 21, the same applies in the following description). N LED current reference values BS of the LED current reference value generation circuit 113
The outputs of 1, BS2, BS3, ... BSn are connected to the LED current reference value switching circuit 114. The LED current reference value switching circuit 114 is a timing generation circuit 112.
The n-th LED current reference values BS1, BS2, BS3, ...

The LED current reference value switching circuit 114 determines which n LED current reference values BS1, BS2, BS3 according to the timing signal from the timing generation circuit 112.
.... Also has an allocation function of controlling which of BSn is supplied to the LED drive stage circuit 115. A description of this allocation function will be given later.

FIG. 22 is a block diagram illustrating an ON / OFF control signal generation circuit for the cold cathode fluorescent lamp in FIG. 23 and 24 are timing diagrams for generating an on / off control signal in the circuit configuration of FIG.

In FIG. 22, reference numeral 116 is a first counter, and reference numeral 117 is a second counter. The first counter 116 counts the horizontal synchronizing signal 102 and uses the vertical synchronizing signal (Vsync) 101 as a reset signal.
The second counter 117 counts the horizontal synchronizing signal and uses the carry signal SC of the first counter 116 as a reset signal.

The on / off control signal generating operation of the cold cathode fluorescent lamp of FIG. 22 will be described with reference to FIGS. 23 and 24.
The first counter 116 is a lighting start timing generation circuit for the cold cathode fluorescent lamp, and is a cold cathode fluorescent lamp (CFL).
The lighting start signal SC of No. 4 is generated as a carry signal at a desired timing (at the start of rising of the CFL waveform 106 in FIG. 18). The second counter 117 generates a blinking control signal EC for the cold cathode fluorescent lamp (CFL) 4 based on the lighting start signal SC.

That is, the first counter 116 counts the horizontal synchronizing signal (Hsync), and the lighting start signal SC is used as a carry signal at the desired timing (the rising start point of the CFL waveform 106 in FIG. 18).
To the counter 117 (see FIG. 23). The second counter 117 counts the horizontal synchronizing signal (Hsync) using the inputted lighting start signal SC as a reset signal, and counts a desired period (from the rising start time of the CFL waveform 106 to the falling start time of the waveform 106 in FIG. 18). period)
The blinking control signal EC is set to high (on) (see FIG. 24).

The structure of the counter is not limited to the illustrated counter, and it is also possible to use one system of counter and combination circuit to generate the lighting start signal point SC and the extinction control signal EC.

FIG. 25 is a block diagram for explaining a configuration example of an LED current reference value generating circuit which constitutes the LED drive circuit in FIG. 20, and FIG. 26 is a drive signal generation timing diagram of the circuit configuration of FIG. 25 and 26, reference numeral 118 is a third counter, and reference numeral 119 is a fourth counter. The third counter 118 outputs a horizontal synchronizing signal (H
sync) 102 is counted, and the desired timing (the rising start point of the CFL waveform 106 in FIG. 18,
That is, the LED lighting start signal SL is output to the fourth counter 119 at the time point when the first current of the LED is selected) and reset by the vertical synchronization signal (Vsync) 101.

The fourth counter 119 has a horizontal synchronizing signal (H
sync) 102 is counted, and the LED lighting start signal S
Using L as a reset signal, the output is set to high for a desired period (period in which each selected current flows), and the LED current reference value selection signal BS1 is generated. In addition, the fourth counter 11
9 also outputs a reset signal BSR of the LED reference current value selection shift register described later.

FIG. 27 is a block diagram for explaining an example of the circuit configuration of the LED current reference value generating circuit which constitutes the LED drive circuit in FIG. 20 in the latter stage of FIG. 25, and FIG. 28 is a timing diagram of the circuit configuration of FIG. 27 and 28, reference numeral 120 is a fifth counter, and reference numeral 121 is a shift register. The fifth counter 120 counts the horizontal synchronization signal (Hsync) 102 and generates a clock signal SRC for the shift register 121.

The shift register 121 is reset by the LED reference current value selection shift register reset signal BSR from the fourth counter 119 described in FIG. By inputting the LED current reference value BS1 to the data input DATA of this shift register 121, the LE is applied to its output.
D current reference values BS2, BS3, ... BSn are sequentially output. This LED current reference value BS1, BS2, BS
.. BSn is applied to the LED current reference value switching circuit 114 of FIG. The CFL waveform in FIG.
When the brightness of L is sufficiently high and the LED current is 0, the current reference value is 0.

FIG. 31 is a schematic diagram for explaining the structure of another embodiment of a side edge type backlight using a cold cathode fluorescent lamp and a light emitting diode array. In this backlight, the cold cathode fluorescent lamp 4 is installed along one of the opposite sides (here, the long side) of the light guide plate 8 and white or R, G, or B is provided along the other opposite long sides. A light emitting diode array (LED) 5 is installed.

In this structural example, the light from the cold cathode fluorescent lamp 4 and the light from the light emitting diode 5 respectively propagate in the light guide plate 8 in the direction of the arrow in the figure, and form a surface light source similar to that shown in FIG. . The shortage of the light quantity of the cold cathode fluorescent lamp 4 is complemented by the light emitted from the light emitting diode array 5, the cold cathode fluorescent lamp 4 or the light emitting diode 5 is switched and used depending on the surrounding light / dark state, or both of them are simultaneously turned on to increase the brightness. It is possible to display brightness.

FIG. 32 is a schematic diagram for explaining the structure of another embodiment of a side edge type backlight using a cold cathode fluorescent lamp and a light emitting diode array. In this backlight, cold cathode fluorescent lamps 4 are installed on each of two opposite sides (here, the long side) of the light guide plate 8, and each side (here, the short side) adjacent to the two sides is installed. A white or R, G, B light emitting diode array 5 is installed along.

In this structure, two cold cathode fluorescent lamps 4 are used.
And the light from the two light emitting diode arrays 5 respectively propagate in the light guide plate 8 in the direction of the arrow in the figure, and form a surface light source similar to that of FIG. The insufficient light quantity of the cold cathode fluorescent lamp 4 is further complemented by the light emitted from the light emitting diode array 5, the cold cathode fluorescent lamp 4 or the light emitting diode 5 is switched and used depending on the surrounding light / dark state, or both are selected simultaneously or simultaneously. The display is turned on to enable higher brightness display.

FIG. 33 is a schematic diagram for explaining another example of the structure of a side edge type backlight using a cold cathode fluorescent lamp and a light emitting diode array. In this backlight, a cold cathode fluorescent lamp 4 is installed on one of two adjacent sides (long side and short side) of a light guide plate 8, and a white or R, G, B light emitting diode array 5 is provided along the other side. The cold cathode fluorescent lamp and the light emitting diode array are installed such that they are opposed to each other on each of the parallel long side and the parallel short side. A large number of light emitting diode arrays can be installed on the long side.

Even with this configuration, the two cold cathode fluorescent lamps 4 are
And the light from the two light emitting diode arrays 5 respectively propagate in the light guide plate 8 in the direction of the arrow in the figure, and form a surface light source similar to that of FIG. The insufficient light quantity of the cold cathode fluorescent lamp 4 is further complemented by the light emitted from the light emitting diode array 5, the cold cathode fluorescent lamp 4 or the light emitting diode 5 is switched and used depending on the surrounding light / dark state, or both are selected simultaneously or simultaneously. The display is turned on to enable higher brightness display.

FIG. 34 is a schematic view for explaining the structure of another embodiment of the side edge type backlight using the cold cathode fluorescent lamp and the light emitting diode array. The cold cathode fluorescent lamp 4 and the light emitting diode array in FIG. 5 are installed on opposite short sides of the light guide plate 8, respectively, and other configurations and effects are the same as those in FIG.

FIG. 35 is a schematic diagram for explaining the configuration of another embodiment of the side edge type backlight using the cold cathode fluorescent lamp and the light emitting diode array. The cold cathode fluorescent lamp 4 and the light emitting diode array in FIG. 5 are installed on the opposing short side and long side of the light guide plate 8, respectively, and other configurations and effects are the same as those in FIG.

FIG. 37 is a block diagram of another embodiment of the liquid crystal display device having a drive circuit for detecting the characteristics of the video signal and controlling the backlight. In FIG. 37, this liquid crystal display device is a liquid crystal panel (in the figure, written as an LCD panel).
14 includes a side edge type backlight having a light guide plate 8 and two cold cathode fluorescent lamps 4.

The liquid crystal panel 14 is a panel controller 17
It has an LCD driver (column) 15 and an LCD driver (row) 16 which are liquid crystal panel drive circuits driven by. This backlight is AC-driven by the inverter circuit 13. The panel controller 17 includes an image quality control circuit 18
Supplies a video signal (also referred to as an image signal or a display signal). The image quality control circuit 18 includes a contrast control circuit 18A, a DC level control circuit 18B, and a digital γ.
The correction circuit 18C is provided.

On the other hand, a control / arithmetic circuit 20 for generating a dimming signal according to the image quality of the video signal is connected to the inverter circuit 13. The control / arithmetic circuit 20 has an image quality control amount calculation circuit 20A and a backlight brightness control circuit 20B. Further, this liquid crystal display device has a video signal brightness detection circuit 19. The brightness detection circuit 19 includes an APL detection circuit 19A, a MAX detection circuit 19B, and a MIN.
It has a detection circuit 19C.

The APL detection circuit 19A detects the average luminance level of a video signal input from an external circuit (a signal source such as the computer main body), and the MAX detection circuit 19B and the MIN detection circuit 19C detect the maximum luminance value of the video signal, respectively. Detect the minimum brightness value. The average brightness level and the maximum brightness value and the minimum brightness value detected by the brightness detection circuit 19 are input to the backlight brightness control circuit 20B, and the image quality control amount is calculated.

The image quality control amount calculated by the image quality control amount calculation circuit 20A of the control / arithmetic circuit 20 is given to the backlight brightness control circuit 20B to generate an optimum dimming signal and supply driving power to the backlight. It is applied to the inverter circuit 13. The dimming signal causes the inverter circuit 13 to control the drive voltage or current supplied to the cold cathode fluorescent lamp 4.

The image quality control amount calculated by the image quality control amount calculation circuit 20A of the control / arithmetic circuit 20 is the image quality control circuit 1
8 contrast control circuit 18A and DC level control circuit 18B. Contrast control circuit 18A and D
The C level control circuit 18B controls the contrast and DC level of the video signal to optimal values according to the input image quality control amount.

As described above, by using the backlight in which the cold cathode fluorescent lamp and the light emitting diode are arranged in parallel, the transient response period of the transmittance of the liquid crystal panel and the transient response period of rising or falling of the cold cathode fluorescent lamp overlap. The period can be shortened. As a result, the area in which the contour is double observed on the screen at the time of displaying a moving image is narrowed, and a moving image with high image quality can be obtained.

[0134]

As described above, according to the present invention,
It enables real-time control of the light quantity of the backlight according to the brightness of the displayed video signal, which enables high-speed response control, improves the luminous efficiency of the cold cathode fluorescent lamp, and reduces power consumption without lowering the brightness. By using light emitting diode, the dynamic range can be significantly widened.
It is possible to provide a liquid crystal display device provided with a backlight that can extend the life of a cold cathode fluorescent lamp and a drive circuit thereof.

Further, the occurrence of double contours in displaying a moving image is reduced, and a high quality moving image display can be obtained.

[0136]

[Brief description of drawings]

FIG. 1 is a schematic diagram illustrating an example of a direct type backlight that constitutes a liquid crystal display device of the present invention.

FIG. 2 is a schematic diagram illustrating another embodiment of a direct type backlight that constitutes the liquid crystal display device of the present invention.

FIG. 3 is a schematic view for explaining another embodiment of the direct type backlight which constitutes the liquid crystal display device of the present invention.

FIG. 4 is a schematic view for explaining another embodiment of the direct type backlight which constitutes the liquid crystal display device of the present invention.

FIG. 5 is a schematic cross-sectional view illustrating an example of a side edge type backlight that constitutes the liquid crystal display device of the present invention.

FIG. 6 is a block diagram showing an embodiment of a drive circuit of the liquid crystal display device of the present invention.

FIG. 7 is a block diagram showing another embodiment of the drive circuit of the liquid crystal display device of the present invention.

FIG. 8 is a circuit diagram illustrating a configuration example near a temperature sensor in FIG.

9 is a circuit diagram illustrating a configuration example in the vicinity of the optical sensor in FIG.

FIG. 10 is an explanatory diagram of a relationship between a temperature in the vicinity of a cold cathode fluorescent lamp and its brightness.

FIG. 11 is a block diagram showing another embodiment of the drive circuit of the liquid crystal display device of the present invention.

FIG. 12 is a diagram illustrating a method of realizing peak luminance by an LED column / low signal by using a part of an LED array and an LED driver (column) and a part of an LED driver (row).

FIG. 13 is a block diagram showing another embodiment of the drive circuit of the liquid crystal display device of the present invention.

FIG. 14 is a block diagram showing another embodiment of the drive circuit of the liquid crystal display device of the present invention.

FIG. 15 is a block diagram showing another embodiment of the drive circuit of the liquid crystal display device of the present invention.

FIG. 16 is a block diagram showing another embodiment of the drive circuit of the liquid crystal display device of the present invention.

FIG. 17 is a drive waveform diagram when a liquid crystal panel is illuminated by blink light control using only a cold cathode fluorescent lamp as a backlight.

FIG. 18 is a drive waveform diagram for explaining an example of a blink light control using a backlight that uses both a cold cathode fluorescent lamp and a light emitting diode array.

FIG. 19 is a drive waveform diagram for explaining another example of blink light control using a backlight in which a cold cathode fluorescent lamp and a light emitting diode array are used in combination.

FIG. 20 is a block diagram illustrating a schematic configuration of a driving circuit of a backlight in which a cold cathode fluorescent lamp and a light emitting diode are arranged in parallel.

21 is a block diagram illustrating a configuration example of an LED drive circuit in FIG. 20. FIG.

22 is a block diagram illustrating an ON / OFF control signal generation circuit of the cold cathode fluorescent lamp in FIG.

FIG. 23 is a timing diagram of generating an on / off control signal in the circuit configuration of FIG. 22.

FIG. 24 is a timing diagram for generating an on / off control signal in the circuit configuration of FIG. 22.

FIG. 25 is a diagram showing L constituting the LED drive circuit in FIG. 20;
FIG. 3 is a block diagram illustrating a configuration example of an ED current reference value generation circuit.

FIG. 26 is a timing diagram of generation of drive signals of the circuit configuration of FIG. 25.

FIG. 27 is a diagram showing L constituting the LED drive circuit in FIG. 20.
FIG. 26 is a block diagram illustrating a circuit configuration example of the latter stage of FIG. 25 of the ED current reference value generation circuit.

28 is a timing diagram of the circuit configuration of FIG. 27.

FIG. 29 is a schematic diagram illustrating a configuration example of a side edge type backlight using a cold cathode fluorescent lamp as a light source.

FIG. 30 is a schematic cross-sectional view illustrating another configuration example of a side edge type backlight having a cold cathode fluorescent lamp as a light source.

FIG. 31 is a schematic diagram illustrating the configuration of another embodiment of a side edge type backlight using a cold cathode fluorescent lamp and a light emitting diode array.

FIG. 32 is a schematic diagram illustrating the configuration of another embodiment of a side edge type backlight using a cold cathode fluorescent lamp and a light emitting diode array.

FIG. 33 is a schematic diagram illustrating the configuration of another embodiment of a side edge type backlight using a cold cathode fluorescent lamp and a light emitting diode array.

FIG. 34 is a schematic view illustrating the configuration of another embodiment of the side edge type backlight using a cold cathode fluorescent lamp and a light emitting diode array.

FIG. 35 is a schematic diagram illustrating the configuration of another embodiment of the side edge type backlight using a cold cathode fluorescent lamp and a light emitting diode array.

FIG. 36 is a schematic cross-sectional view illustrating one configuration example of a direct type backlight using a cold cathode fluorescent lamp as a light source.

FIG. 37 is a block diagram of a liquid crystal display device including a drive circuit that detects characteristics of a video signal and controls a backlight.

[Explanation of symbols]

1 ... Case frame, 2 ... Diffusion plate, 3 ...
..Light-shielding layer, 3A .... Light-shielding dot, 4 .... Cold cathode fluorescent lamp (CFL), 5 ... Light-emitting diode (LED), 6 ... Circuit board, 7 ... Chevron-shaped reflector, 9 ..., reflector, 9 '...
... Light guide plate, 10 ... Diffuser, 11 ... Lamp reflection sheet, 12 ... Reflective printing (or reflective tape), 13 ... Inverter circuit, 14 ... Liquid crystal Panel (LCD panel), 15 ... LCD driver (column), 16 ... LCD driver (low),
17 ... Panel controller, 18 ... Image quality control circuit, 18A ... Contrast control circuit, 18B
.... DC level control circuit, 18C ... Digital .gamma. Correction circuit, 19 ... Brightness detection circuit, 19A ...
.... APL detection circuit, 19B ... MAX detection circuit
19C ... ・ MIN detection circuit, 20 ... Control / calculation circuit, 20A ... Image quality control amount calculation circuit, 20B
... Backlight brightness control circuit, 21 ... Light emitting diode drive circuit (LED drive circuit), 23 ... Temperature sensor, 24 ... Optical sensor, 25 ... Temperature detection control circuit, 26 ... Light quantity detection control circuit, 27, 2
8 ... Retaining circuit, 29 ... Retaining circuit, 30 ...
・ ・ Same frame judgment circuit, 101 ・ ・ ・ ・ ・ ・ Vertical sync signal, 102 ・ ・ ・ ・ Horizontal sync signal, 103 ・ ・ ・ ・ Transmittance of the liquid crystal panel at the top of the screen, 104 ... Transmittance, 105 ... Transmittance of liquid crystal panel at the bottom of the screen, 106 ..., CFL backlight brightness, 107 ... LED backlight brightness, 108
.... Brightness of CFL + LED backlight, 109 ...
... Brightness of liquid crystal panel at the time of black → white change at the top of the screen, 1
10 ...- Brightness of the liquid crystal panel when the black in the center of the screen changes to white, 111 ...- Brightness of the liquid crystal panel when the black at the bottom of the screen changes to white, 112 ...
.... LED current reference value generation circuit, 114 ... L
ED current reference value switching circuit, 115 ... LED driving stage circuit, 116 ... First counter, 117 ...
-Second counter, 118 ... Third counter, 1
19 ... 4th counter, 120 ... 5th counter, 121 ... Shift register, 180 ...
Image quality control circuit (static), 181, ... Image quality control circuit (dynamic), 190 ... Brightness detection circuit (dynamic), 200 ... Image quality control amount calculation / backlight brightness control circuit, 220 .... Dimming signal generation circuit (static).

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[Procedure amendment]

[Submission date] January 21, 2002 (2002.1.2
1)

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0114

[Correction method] Change

[Correction content]

[0114] The configuration of the counter is not limited to the illustrated counter may be configured to generate a lighting start signal SC and flashing control signal EC by one system counters and combinational circuit.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0123

[Correction method] Change

[Correction content]

FIG. 33 shows another side edge type backlight using a cold cathode fluorescent lamp and a light emitting diode array.
It is a schematic diagram explaining the structure of an Example . In this backlight, a cold cathode fluorescent lamp 4 is installed on one of two adjacent sides (long side and short side) of a light guide plate 8, and a white or R, G, B light emitting diode array 5 is provided along the other side. The cold cathode fluorescent lamp and the light emitting diode array are installed such that they are opposed to each other on each of the parallel long side and the parallel short side. A large number of light emitting diode arrays can be installed on the long side.

Continued front page    (72) Inventor Junichi SQUARE             Hitachi, Ltd. 3300 Hayano, Mobara-shi, Chiba             Factory Display Group F term (reference) 2H091 FA42Z FA45Z GA11 LA01                 2H093 NC42 NC44 NC54 NC56 NC57                       NC59                 5F041 AA09 BB10 FF11 FF16

Claims (15)

[Claims] 1. A liquid crystal display device having a backlight on the back surface of a liquid crystal panel, wherein the backlight has a cold cathode fluorescent lamp and a light emitting diode array arranged adjacent to the cold cathode fluorescent lamp. Characteristic liquid crystal display device. 2. The liquid crystal display device according to claim 1, wherein a plurality of the cold cathode fluorescent lamps are provided, and the light emitting diode array is provided between the plurality of cold cathode fluorescent lamps. 3. A liquid crystal display device having a backlight on the back surface of a liquid crystal panel, wherein the backlight has a plurality of light emitting diode arrays arranged immediately below the liquid crystal panel. apparatus. 4. A backlight is provided on the back surface of the liquid crystal panel,
A liquid crystal display device comprising a driving circuit for controlling the brightness of the backlight according to the brightness of a video signal displayed on the liquid crystal panel, wherein the backlight is a cold cathode fluorescent lamp and a light emitting diode array. An image quality control circuit for controlling the image quality of a video signal displayed on the liquid crystal panel, a brightness detection circuit for detecting the brightness of the video signal, and a brightness of the video signal detected by the brightness detection circuit. Liquid crystal display comprising: a control / arithmetic circuit that generates a dimming signal of the backlight based on a brightness detection signal; and a light emitting diode drive circuit that controls the brightness of the light emitting diode by the dimming signal. Device drive circuit. 5. A temperature sensor for detecting a temperature and a light amount sensor for detecting the brightness of the cold cathode fluorescent lamp are provided, and the detection outputs of the temperature sensor and the light amount sensor are added to the dimming signal. The drive circuit for the liquid crystal display device according to claim 4. 6. A backlight is provided on the back surface of the liquid crystal panel,
A liquid crystal display device comprising a drive circuit for controlling the brightness of the backlight according to the brightness of a video signal displayed on the liquid crystal panel, wherein the backlight is a plurality of liquid crystal display devices arranged directly below the liquid crystal panel. And an image quality control circuit for controlling the image quality of the video signal displayed on the liquid crystal panel, a brightness detection circuit for detecting the brightness of the video signal, and the brightness detection circuit. A control / arithmetic circuit that generates a dimming signal of the backlight based on a brightness detection signal of a video signal, and a light emitting diode drive circuit that controls the brightness of the light emitting diode by the dimming signal. The drive circuit of the liquid crystal display device. 7. A backlight is provided on the back surface of the liquid crystal panel,
A liquid crystal display device comprising a drive circuit for controlling the brightness of the backlight according to the brightness of a video signal displayed on the liquid crystal panel, wherein the backlights are alternately arranged immediately below the liquid crystal panel. A plurality of cold cathode fluorescent lamps and a plurality of light emitting diode arrays, and an image quality control circuit for controlling the image quality of the video signal displayed on the liquid crystal panel, and a brightness detection circuit for detecting the brightness of the video signal. A control / arithmetic circuit that generates a dimming signal of the backlight based on a brightness detection signal of a video signal detected by the brightness detection circuit; and a light emitting diode that controls the brightness of the light emitting diode by the dimming signal. A driving circuit, and the luminance of the plurality of light emitting diode arrays is supplied to the light emitting diode driving circuit in two directions of a row direction and a column direction of the liquid crystal panel. Driving circuit of the liquid crystal display device characterized by having a light emitting diode driver for respective control. 8. A backlight is provided on the back surface of the liquid crystal panel,
A liquid crystal display device comprising a drive circuit for controlling the brightness of the backlight according to the brightness of a video signal displayed on the liquid crystal panel, wherein the backlight is a plurality of liquid crystal display devices arranged directly below the liquid crystal panel. And an image quality control circuit for controlling the image quality of the video signal displayed on the liquid crystal panel, a brightness detection circuit for detecting the brightness of the video signal, and the brightness detection circuit. A light emitting diode drive circuit that controls the brightness of the light emitting diode based on the dimming signal and a control / arithmetic circuit that generates a dimming signal of the backlight based on a brightness detection signal of a video signal; The diode driving circuit includes a light emitting diode driver for controlling the brightness of the plurality of light emitting diode arrays in two directions, that is, a row direction and a column direction of the liquid crystal panel. Driving circuit of the liquid crystal display device characterized by having a driver. 9. A liquid crystal panel, a backlight for illuminating the liquid crystal panel, a video signal drive circuit for displaying a video signal on the liquid crystal panel based on a synchronization signal, and a backlight drive for driving the backlight. A liquid crystal display device having a circuit, wherein the backlight includes a cold cathode fluorescent lamp and a light emitting diode array, and the backlight driving circuit synchronizes with a vertical synchronization signal to generate the cold cathode fluorescent lamp. And a cold cathode fluorescent lamp driving circuit for blinking, and the light emitting diode driving circuit for controlling lighting of the light emitting diode array at a timing to correct the brightness at the rising when the cold cathode fluorescent lamp is lit and at the falling when the cold cathode fluorescent lamp is extinguished. A liquid crystal display device characterized by the above. 10. The light emitting diode drive circuit provides a timing generation circuit for controlling blinking of the light emitting diode array based on a vertical synchronizing signal, and a timing generation circuit based on a timing signal generated by the timing generation circuit to the light emitting diode array. A light emitting diode current reference value generating circuit for generating a plurality of current reference values, and a light emitting diode current reference value switching circuit for applying the current reference value to the light emitting diode array in synchronization with a timing signal from the timing generating circuit. The liquid crystal display device according to claim 9, wherein 11. The liquid crystal display device according to claim 9, wherein a plurality of the cold cathode fluorescent lamps and a plurality of the light emitting diode arrays are arranged side by side immediately below the liquid crystal panel. 12. A light guide plate is provided directly below the liquid crystal panel,
11. The liquid crystal display device according to claim 9, wherein the cold cathode fluorescent lamp and the light emitting diode array are arranged on at least two sides of the light guide plate. 13. The light emitting diode is turned on when the cold cathode fluorescent lamp is started.
13. The liquid crystal display device according to any one of 12. 14. The liquid crystal display device according to claim 9, wherein the light emitting diode is turned on when the lighting of the cold cathode fluorescent lamp is started. 15. The light emitting diode is turned on when the cold cathode fluorescent lamp is at a low temperature.
13. The liquid crystal display device according to any one of 12.