JP2000182793A - Light source device and liquid crystal display device - Google Patents

Abstract

(57) Abstract: A light source device capable of reducing generation of noise radiated from an inverter applied to a backlight and thereby suppressing deterioration of display operation and image quality, and the light source device The present invention provides a liquid crystal display device equipped with. SOLUTION: In a backlight for irradiating irradiation light from the back side of a transmission type liquid crystal panel for displaying image information,
A plurality of fluorescent tubes, a plurality of inverter circuits provided separately for each of the fluorescent tubes and supplying an AC voltage for driving the fluorescent tubes, and a control for supplying an inverter control signal for controlling the operation of the inverter circuit A signal source, and the inverter control signal is configured to operate the plurality of inverter circuits in mutually opposite phases.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light source device and a liquid crystal display device, and more particularly to the application of the present invention as a backlight of a transmission type liquid crystal display device to suppress the generation of noise and prevent the deterioration of image quality. And a liquid crystal display device equipped with the light source device.

[0002]

2. Description of the Related Art Conventionally, the mainstream of displays has been a cathode ray tube (Cathode Ray Tube; hereinafter abbreviated as CRT), but has disadvantages such as a large size, heavy weight, and large power consumption. . Therefore, the CRT has a problem that it is difficult to mount the CRT on a portable device, and that a large installation space is required even on a desk. On the other hand, although liquid crystal display devices were very expensive at the beginning of development, they had drawbacks such as poor image quality, difficulty in increasing the size, and low brightness. However, with the development of semiconductor technology and the establishment of manufacturing technology in recent years, the above-mentioned problems have been gradually solved, and the merits unique to liquid crystal display devices, such as being thinner and lighter and lowering power consumption, are attracting attention. It has become. In addition, with the rapid development of the information society, as a substitute for personal computer monitors, large displays, and televisions, video cameras, electronic still cameras,
Personal Digital Assistant (PDA: Personal Digital Assistant)
Liquid crystal display devices have been used as display means such as s). In particular, in the case of a liquid crystal display device, which has become very popular as a substitute for a CRT, it is required to have a high luminance characteristic as well as a screen size in comparison with a conventional CRT. In response to such a demand, a configuration is known in which a backlight having a fluorescent tube as an illumination light source is provided on the back side of a transmission type liquid crystal panel to realize high luminance. Further, in order to compensate for a decrease in luminance due to an increase in screen size, a configuration including a plurality of fluorescent tubes used for a backlight is also employed.

[0003] The structure of a backlight portion applied to a transmissive liquid crystal display device will be described below with reference to the drawings. FIG. 5 is a schematic configuration diagram showing the structure of a backlight unit in which two fluorescent tubes are arranged at two positions above and below a liquid crystal panel to perform illumination, and FIG. 6 is a diagram showing the backlight unit shown in FIG. It is XX sectional drawing of. In FIG. 5, reference numeral 10 denotes a panel unit, 20a and 20b denote fluorescent tubes constituting a backlight, 21a and 21b denote harnesses, 30a and 30b denote inverter circuits, and 31a and 31b denote inverter transformers. Although not shown, each inverter circuit 30
a and 30b are connected to a common operation control means for controlling the operation. As shown in FIG. 6, the panel unit 10 is roughly configured by laminating a liquid crystal panel 11, a diffusion sheet 12, a light guide plate 13, and a reflection sheet 14, and is disposed on both end sides of the light guide plate 13. Fluorescent tubes 20a, 20b
Reflecting mirrors 15a and 15b are provided so as to cover.

The functions of these configurations are as follows. The liquid crystal panel 11 includes, for example, two transparent insulating substrates stacked and bonded at a predetermined interval so that a surface on which a transparent electrode for display and an alignment film or the like are stacked faces each other, and a peripheral portion of both substrates. The liquid crystal is sealed and sealed inside the sealing material provided in the above, and a deflecting plate is provided outside both substrates. Desired image information is displayed by controlling the alignment state of the liquid crystal based on a display signal described later. The light guide plate 13 is made of transparent synthetic resin such as acrylic, and is emitted from the fluorescent tubes 20a and 20b.
Irradiation light incident from the side surface is uniformly diffused inside and irradiates the liquid crystal panel 11.

[0005] The diffusion sheet 12 is provided between the liquid crystal panel 11 and the light guide plate 13 and diffuses the irradiation light emitted from the light guide plate 13 and emits it to the liquid crystal panel 11.
The reflection sheet 14 is arranged on the back side of the light guide plate 13 and reflects the irradiation light diffused inside the light guide plate 13 to the liquid crystal panel 11 side. The reflecting mirrors 15a and 15b are reflectors that cover the fluorescent tubes 20a and 20b arranged along the end surfaces of the light guide plate 13 in a U-shape over substantially the entire length thereof, and emit light emitted from the fluorescent tubes 20a and 20b on the inner side. The light is reflected by the reflection surface of (1), is guided to the side surface of the light guide plate 13, and is incident. The fluorescent tubes 20a and 20b are linear light sources such as cold-cathode fluorescent tubes arranged in parallel along both upper and lower end surfaces of the light guide plate 13, and the inverter circuits 30a and 30b are provided by operation control means (not shown). Built-in inverter transformers 31a and 31 based on the inverter control signal of
b to generate an AC voltage for driving the fluorescent tubes 20a and 20b and supply the AC voltage via the harnesses 21a and 21b,
It emits irradiation light having a desired luminance.

[0006]

In the liquid crystal display device as described above, the fluorescent tubes 20a and 20b are AC driven based on an inverter control signal from the operation control means to emit irradiation light having a desired luminance. Irradiates the liquid crystal panel 11 uniformly through the light guide plate 13, but has sufficient capacity to drive and control each of the fluorescent tubes 20a and 20b in order to realize a high brightness display screen. It has a configuration in which inverter circuits 30a and 30b are individually provided. On the other hand, in a configuration in which an AC voltage is generated by an inverter transformer built in the inverter circuit and the fluorescent tube is driven, noise of an AC component is generated from the inverter transformer, the fluorescent tube, the harness, etc. during operation of the inverter circuit. It is known to Therefore, in the above-described configuration in which the plurality of inverter circuits 30a and 30b are individually provided for the plurality of fluorescent tubes 20a and 20b,
a, 20b (ie, inverter circuits 30a, 30b)
Are driven in the same phase, radiated noise waveforms reinforce each other, affecting the operation of the liquid crystal panel 11 and peripheral circuits, and deteriorating display image quality.

That is, as shown in FIGS. 7A and 7B, when the fluorescent tubes 20a and 20b are AC-driven, each of the inverter transformers 31a and 31b receives the harness 21 from each of the inverter transformers 31a and 31b.
The noise waveforms radiated through the a and 21b are combined as shown in FIG. 7 (c) when the driving cycles of the fluorescent tubes 20a and 20b are synchronized.
This greatly affects the operation of peripheral circuits such as the liquid crystal panel 11. Conventionally, as a method for solving such a problem, a configuration in which a metallic shield is applied to the inverter transformers 31a and 31b, which are noise generating sources, to discharge radiated noise to a ground potential, and a method such as a chroma noise. For noise of a specific frequency, a noise filter using a coil, a capacitor, or the like is known. However, in the former, there is a problem that the high-voltage AC component generated in the transformer for the inverter is not completely discharged, and the residual component is radiated as noise and mixed into the power supply line and the signal line of the liquid crystal panel. Even if the AC component is forcibly ground-discharged, if the ground level is unstable, there is a problem that noise is generated due to the fluctuation of the ground level. On the other hand, the latter has a problem that noise in a specific band can be satisfactorily removed, but combined high-frequency noise cannot be completely removed.

Therefore, the present invention reduces the generation of noise radiated from an inverter applied to a backlight,
Accordingly, an object of the present invention is to provide a light source device capable of suppressing a deterioration in display operation, image quality, and the like, and a liquid crystal display device including the light source device.

[0009]

According to a first aspect of the present invention, there is provided a light source device for irradiating irradiation light from a back side of a transmission type display means for displaying image information, wherein a plurality of light sources and each of the light sources are provided. And a plurality of driving means for individually supplying a driving signal for driving the light source, and a control signal source for supplying a control signal for controlling the operation of the driving means, wherein the control signal is The means are set to operate in opposite phases to each other. Claim 2
The light source device according to claim 1 is a light source device according to claim 1,
A first group including a half of the light source and the driving unit, wherein the light source and the driving unit are provided in an even number each;
And a phase of the control signal supplied to each of the second group consisting of the light source and the remaining half of the driving means is set to be mutually inverted.

The liquid crystal display device according to claim 3 is
A liquid crystal panel that displays image information, a plurality of fluorescent tubes that constitute a backlight that illuminates the liquid crystal panel from the back side, and a plurality of inverters that are individually provided for each of the fluorescent tubes and that drive the fluorescent tubes by AC. Circuit, a display drive circuit that generates a display drive pulse corresponding to the image information to be displayed on the liquid crystal panel, and supplies the drive pulse to the liquid crystal panel, and a drive control circuit that supplies a control signal for controlling the operation of the display drive circuit Wherein the plurality of inverter circuits are set to operate in opposite phases to each other, and the operation timing of the plurality of inverter circuits and the operation timing of the display drive circuit are synchronized. Is set to. In the liquid crystal display device according to a fourth aspect, in the liquid crystal display device according to the third aspect, the plurality of inverter circuits receive a signal synchronized with the control signal output from the drive control circuit and perform the display. The operation is controlled so as to be synchronized with the operation timing of the drive circuit.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. First, an embodiment of the light source device according to claim 1 or 2 will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram illustrating a light source device according to the present embodiment. Here, the description of the configuration equivalent to the above-described conventional technology will be simplified. In FIG. 1, 10
Denotes a panel unit (display means), 20a and 20b denote fluorescent tubes (light sources) constituting a backlight, 21a and 21b denote harnesses, 30a and 30b denote inverter circuits (drive means), 3
1a and 31b are inverter transformers, 40 is a signal inverter, and 50 is an inverter control signal. Panel section 10
Has a liquid crystal panel 11, a diffusion sheet 12, a light guide plate 13, a reflection sheet 14, and a reflection mirror 15, similarly to the configuration shown in FIG. The function of each component is the same as that of the prior art, and thus the description is omitted.

The fluorescent tubes 20a and 20b are connected to a harness 21.
a, 21b via inverter circuits 30a, 3b, respectively.
0b, and the inverter circuits 30a, 30b
Generates and supplies an AC voltage for driving each of the fluorescent tubes 20a and 20b by the built-in inverter transformers 31a and 31b. The signal inverter 40 is provided only on one of the signal lines to which the inverter control signal 50 is supplied, on the side of one of the inverter circuits 30a, and is configured to invert the phase of the control signal supplied to the inverter circuit 30b. Have been. The inverter control signal 50 is a control signal supplied from an operation control unit (control signal source) that controls the operation of the inverter circuits 30a and 30b. The inverter circuit applied to the light source device of the present embodiment is configured so that the operation is controlled by an external inverter control signal as described above. This is disclosed in, for example, Japanese Patent Application Laid-Open No. 9-5705. Is disclosed.

Next, the operation of the light source device of this embodiment will be described with reference to the drawings. FIG. 2 is a waveform diagram illustrating a waveform of noise radiated from each unit of the light source device according to the present embodiment. As described in the related art, when the fluorescent lamps 20a, 20 are AC-driven by the inverter circuits 30a, 30b, the inverter transformers 31a, 31
b, the harnesses 21a and 21b, the fluorescent tubes 20a and 20b, etc., generate noise of an AC component. Here, in the present embodiment, the inverter control signal for controlling the operation of the inverter circuits 30a and 30b is output from one of the inverter circuits 3a and 30b.
For 0a, the signal phase is 1 by the signal inverter 40.
The data is supplied after being inverted by 80 °, and supplied to the other inverter circuit 30b without any processing. With such a configuration, the inverter circuit 30
a and the inverter circuit 30b operate at a cycle that is 180 ° inverted from each other.
a, 30b, respectively, and the fluorescent tubes 20a,
The signal waveform of the AC voltage supplied to 20b has a phase of 18
The inverted state is shifted by 0 °.

The inverter transformers 31a, 3a
1b through the harnesses 21a and 21b is generated along with the AC voltage generated and supplied by the inverter circuits 30a and 30b. Therefore, the noise waveform is also shown in FIGS. As shown in b), the phases are mutually inverted. Therefore, the noise radiated from both the inverter circuits 30a and 30b as a whole cancels each other out as shown in FIG. 2C, and the noise around the panel unit 10 and the like due to the mixing of the noise component. It is possible to provide a light source device in which influence on a circuit is suppressed and operation failure, deterioration of image quality, and the like can be prevented. In the present embodiment,
Although an example is shown in which the signal inverter 40 for inverting the signal waveform of the inverter control signal 50 supplied to one of the inverter circuits 30a is applied, the present invention is not limited to this, and the inverter circuits 30a and 30b May have a different configuration as long as they invert each other's operation cycles or invert the signal waveform of the AC voltage generated and supplied by the inverter circuits 30a and 30b by 180 °. Absent. Further, two sets (even number sets) of the fluorescent tube and the inverter circuit are provided and the operation timing is inverted by 180 °. However, the present invention is not limited to this. In short, the number of fluorescent tubes and inverter circuits, so that noise components generated due to the operation of the plurality of inverter circuits cancel each other out,
In addition, another configuration may be used as long as the operation timing is set. According to such a configuration, it is possible to provide a favorable light source device that suppresses the influence of noise while increasing the luminance.

Next, an embodiment of the liquid crystal display device according to claim 3 or 4 will be described with reference to the drawings. FIG.
1 is a schematic configuration diagram illustrating a liquid crystal display device according to the present embodiment. Here, a description of the same configuration as that of the above-described embodiment will be omitted. In FIG. 3, 10 is a panel unit, 20a and 20b are fluorescent tubes constituting a backlight,
21a and 21b are harnesses; 30a and 30b are inverter circuits; 31a and 31b are inverter transformers;
Is a signal inverter, 51 is a synchronization signal, 60 is a signal side drive circuit, 70 is a scan side drive circuit, 80 is a display drive circuit, 90
Is a drive control circuit. Here, the panel unit 10 corresponds to FIG.
However, for convenience of explanation, only the liquid crystal panel 11 and the light guide plate 13 are shown separated from each other, and other configurations are omitted.

The functions of these structures are as follows. As described above, the liquid crystal panel 11 has a structure in which liquid crystal is sealed and sealed between two transparent insulating substrates, a plurality of signal lines and scanning lines are arranged in a matrix on opposing surfaces of each substrate, and a pixel is provided at an intersection thereof. It is formed by forming electrodes (liquid crystal cells). The signal side driving circuit 60 is connected to one end of a plurality of signal lines provided in the liquid crystal panel 11 and outputs a liquid crystal driving pulse corresponding to a gradation level based on gradation data and a control clock included in a display signal. It is generated and applied to each signal line at a predetermined timing, thereby displaying a gradation. The scanning-side driving circuit 70 is connected to one end of a plurality of scanning lines provided on the liquid crystal panel 11, generates a scanning signal, sequentially supplies the scanning signal to each scanning line of the liquid crystal panel 11, and sets a selected state. A voltage is applied to the liquid crystal at each pixel position crossing the line to drive the liquid crystal.

The display driving circuit 80 receives a horizontal synchronizing signal, a vertical synchronizing signal and a display signal from a driving control circuit 90 to be described later, and sends a control signal having a desired timing pattern to the signal side driving circuit 60 and the scanning side driving circuit 70. Is supplied, and a display signal to be displayed on the liquid crystal panel is converted into gradation data and supplied to the signal side driving circuit 60, thereby driving the signal lines while sequentially scanning the scanning lines of the liquid crystal panel 11. A predetermined liquid crystal cell of the liquid crystal panel 11 is driven. The drive control circuit 90 controls the operation of the entire liquid crystal display device. For example, the drive control circuit 90 causes the liquid crystal panel 11 to display an image according to a predetermined operation clock,
Control such as generation of a synchronization signal in the system is executed.
In particular, in the present embodiment, in addition to controlling the display of image information on the liquid crystal panel 11, the inverter circuits 30a, 30b
And outputs an inverter control signal for controlling the operation of. Here, as an inverter control signal output from the drive control circuit 90, a signal synchronized with the display timing (control clock) of the image information by the display drive circuit 80 is extracted (or generated), and is used as a synchronization signal 51. It is supplied to the inverter circuits 30a and 30b. Note that the synchronization signal 51 may be the operation clock itself which is the basis of the control clock, or may be a signal multiplied by an integer.

Next, the operation of the liquid crystal display device of the present embodiment will be described with reference to the drawings. FIG. 4 is a waveform diagram showing signal and noise waveforms in each part of the liquid crystal display device according to the present embodiment. As shown in FIG. 4, the inverter control signal in the present embodiment is a synchronization signal 51 synchronized with an operation clock for timing-controlling the display operation on the liquid crystal panel 11, and based on the synchronization signal 51, the inverter circuit 30a , 30b are controlled. In particular, as described in the above-described embodiment, the synchronization signal whose signal level is inverted is supplied to the inverter circuit 30a and the inverter circuit 30b by the signal inverter 40, so that the inverter circuits 30a and 30b are in opposite phases. As a result, the noises accompanying the generated AC voltage cancel each other out and cancel each other, thereby suppressing the influence of the noise components on the peripheral circuits. On the other hand, with the configuration described above, the liquid crystal panel 1
1 display operation timing and the inverter circuit 30
Since the driving timings of the fluorescent tubes 20a and 20b by the a and 30b are synchronized, the image to be driven for display and the fluorescent tube 2
The effect of suppressing the deterioration of the image quality due to the flickering of the screen and the noise due to the interference of the irradiation light by 0a and 20b is obtained at the same time as the above effect. In the present embodiment, the inverter circuits 30a and 30b and the display drive circuit 80
As a configuration for synchronizing the operation timing with the inverter circuit 3, the synchronization signal 51 is taken out from the drive control circuit 90.
0a and 30b, the present invention is not limited to this.
Other configurations may be used as long as the drive timing of Ob and the display timing of the liquid crystal panel 11 are synchronized.

[0019]

According to the first or second aspect of the present invention, in a light source device for irradiating irradiation light from the rear side of a transmission type display means for displaying image information, a plurality of light sources and each of the light sources are provided. A plurality of driving means provided separately and supplying a driving signal for driving the light source; and a control signal source supplying a control signal for controlling the operation of the driving means. Since the operation is performed in the phase, the noise components generated by the operation of the driving and driving means cancel each other, so that the effect of noise on peripheral circuits such as the display means can be suppressed. In particular, an even number of light sources and driving means are provided, respectively, and the phases of the control signals supplied to each of the first group consisting of half of the light sources and driving means and the second group consisting of the remaining half are mutually inverted. With such a setting, the noise components can be canceled by the same number of noise sources, so that it is possible to provide a light source device in which the operation of peripheral circuits due to noise is suppressed while the luminance is increased. .

Further, the light source device according to claim 3 or 4 is
A liquid crystal panel for displaying image information, a plurality of fluorescent tubes constituting a backlight for illuminating the liquid crystal panel from the back side,
A plurality of inverter circuits that are individually provided for each of the fluorescent tubes and that drive the fluorescent tubes by AC, a display drive circuit that generates a display drive pulse corresponding to image information to be displayed on the liquid crystal panel, and supplies the display drive pulse to the liquid crystal panel; And a drive control circuit for supplying a control signal for controlling the operation of the display drive circuit, a plurality of inverter circuits are set to operate in opposite phases to each other, and Since the operation timing and the operation timing of the display drive circuit are set so as to be synchronized, noises generated accompanying the AC voltage generated by the inverter circuit cancel each other, and the influence of the noise component on the peripheral circuits is suppressed. At the same time, it is said that image flickering due to interference between the image to be displayed and the light emitted by the fluorescent tube and image quality deterioration due to noise are suppressed. Two effects can be obtained at the same time. In particular, a plurality of inverter circuits receive a signal synchronized with a control signal output from the drive control circuit and control the operation so as to be synchronized with the operation timing of the display drive circuit, so that the display drive can be performed with a simple configuration. Therefore, it is possible to provide a liquid crystal display device in which the deterioration of the image quality due to the flickering of the screen and the noise is further reduced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating a light source device according to an embodiment.

FIG. 2 is a waveform diagram showing a waveform of noise radiated from each unit of the light source device according to the embodiment.

FIG. 3 is a schematic configuration diagram illustrating a liquid crystal display device according to the embodiment.

FIG. 4 is a waveform chart showing waveforms of signals and noise in each part of the liquid crystal display device according to the embodiment.

FIG. 5 is a schematic configuration diagram illustrating a structure of a backlight unit.

FIG. 6 is a sectional view taken along line XX of the backlight unit.

FIG. 7 is a waveform diagram showing a waveform of noise radiated from each part of the light source device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Panel part (display means) 11 Liquid crystal panel 12 Diffusion sheet 13 Light guide plate 14 Reflection sheet 15 Reflection mirror 20a, 20b Fluorescent tube (light source) 30a, 30b Inverter circuit (drive means) 40 Signal inverter 50 Inverter control signal (control signal) 51) Synchronous signal 60 Signal side drive circuit 70 Scan side drive circuit 80 Display drive circuit 90 Drive control circuit

Continued on the front page F-term (reference) 2H091 FA42Z GA12 LA16 LA30 2H093 NB25 NC02 NC07 NC42 ND40 NE06 3K072 AA19 CA03 CA16 EB08 FA00 GB01 GC04 5C006 AA01 AA16 AC02 AF51 AF71 BB11 BB29 BF27 BF41 BF01 EB01 DD08 JJ02 JJ04 JJ06

Claims (4)

[Claims] 1. A light source device for irradiating irradiation light from the rear side of a transmission type display means for displaying image information, comprising: a plurality of light sources; and drive signals individually provided for each of the light sources for driving the light sources. And a control signal source for supplying a control signal for controlling the operation of the driving means, wherein the control signal is set to operate the driving means in opposite phases. A light source device. 2. An even number of the light sources and the driving means are provided, respectively, a first group consisting of half of the light sources and the driving means, and a second group consisting of the other half of the light sources and the driving means. The light source device according to claim 1, wherein the phases of the control signals supplied to each of the groups are set so as to be inverted. 3. A liquid crystal panel for displaying image information, a plurality of fluorescent tubes constituting a backlight for illuminating the liquid crystal panel from the back side, and each of the fluorescent tubes is individually provided, and the fluorescent tubes are connected to each other. A plurality of inverter circuits to be driven, a display drive circuit that generates a display drive pulse corresponding to the image information to be displayed on the liquid crystal panel and supplies the display drive pulse to the liquid crystal panel, and a control signal for controlling the operation of the display drive circuit. And a drive control circuit for supplying the plurality of inverter circuits, wherein the plurality of inverter circuits are set to operate in phases opposite to each other, and the operation timing of the plurality of inverter circuits and the operation of the display drive circuit A liquid crystal display device wherein the timing is set to be synchronized. 4. The operation of the plurality of inverter circuits is controlled to receive a signal synchronized with the control signal output from the drive control circuit and synchronize with an operation timing of the display drive circuit. The liquid crystal display device according to claim 3, wherein