JP2004191675A - Illumination device, liquid crystal display device and driving method thereof - Google Patents

Abstract

Provided is a liquid crystal display device capable of suppressing an increase in cost and reducing an afterimage at the time of displaying a moving image to improve display quality (particularly, display quality of a moving image), an illumination device used therefor, and a driving method of the illumination device. I do.
In a liquid crystal panel having a plurality of display elements, when display elements having the same scanning timing are used as a display element group, the display elements are provided in a group of display elements for each display element group. A plurality of fluorescent tubes 13 each having an external electrode 52 for forming an electric field for forming and exciting an internal plasma are provided for each display element group. An inverter drive circuit 14 for generating electric power for forming the electric field is provided. A high withstand voltage switching circuit 15 for controlling the light emission of each fluorescent tube 13 by connecting and disconnecting power supply from the inverter drive circuit 14 to each electrode 52 is provided.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a liquid crystal display device suitable for displaying moving images, an illumination device used for the same, and a method for driving the liquid crystal display device.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a liquid crystal display device that can be made thinner has been used as a display device such as a desktop word processor or a notebook PC (personal computer). In recent years, a desktop word processor or a notebook PC has been able to display a movie or a moving image of a television with the improvement of its processing capability.
[0003]
However, in the conventional liquid crystal display device, when displaying a moving image, due to the characteristics of the liquid crystal, sufficient responsiveness cannot be obtained, resulting in a blurred image such as an afterimage such as a trail or blurring of the image. Degradation is a problem.
[0004]
Therefore, for example, JP-A-1-082019 (publication date: March 28, 1989), JP-A-11-202285 (publication date: July 30, 1999), and JP-A-11-202286 (publication date) On July 30, 1999), the illumination unit has a plurality of light emitting regions in the scanning direction, and the plurality of light emitting regions emit light sequentially in synchronization with a vertical synchronization signal of the liquid crystal display device. That is, it is described that good display quality can be obtained by forming each light-emitting body to be turned on immediately after scanning of the display unit and turned off after a predetermined time.
[0005]
In the illumination unit, a cold cathode tube or the like arranged in parallel to a scanning line in a scanning direction is arranged in a backlight unit on a back surface of a display unit, and each illuminates a liquid crystal corresponding to a predetermined number of scanning lines. It has such a configuration.
[0006]
[Problems to be solved by the invention]
However, when an image is displayed using the above-described illumination unit, there are the following problems.
[0007]
That is, in order to improve the display quality by suppressing the after-image or the like at the time of displaying a moving image with the above configuration, it is necessary to illuminate each light emitting region with a sufficiently short time width. This is because the motion blur of the moving image is caused not only by the response time of the liquid crystal, but also by the display characteristics peculiar to the liquid crystal display that is a hold-type display (Reference: IEICE EID 2001-84; This is because the image quality (Taiichiro Kurita)) can be improved, and the effect of improving the quality of the moving image can be improved by lighting the impulse-like (short time width) illumination light source.
[0008]
However, when a conventional cold cathode tube is used for a shorter time width, the screen luminance (time average luminance) of the liquid crystal display device decreases, resulting in a dark screen, which impairs the display characteristics as a television.
[0009]
In order to secure a sufficient screen brightness that satisfies the comfortable viewing of the monitor on the display screen, it is necessary to increase the brightness of each fluorescent tube or increase the number of fluorescent tubes.
[0010]
In a conventional cold-cathode fluorescent tube, the lamp surface brightness and the life (reliability) are in a trade-off relationship. This is for the following reason. The cold cathode fluorescent tube has an electrode inside, and gas particle ions of a rare gas component excited and discharged by a high electric field collide with the cathode electrode, at which time secondary electrons are emitted from the cathode electrode. Ionizes the rare gas while colliding with the rare gas particles one after another to maintain the plasma gas discharge state. That is, the electrodes present therein are constantly exposed to bombardment of plasma gas particles.
[0011]
The first factor of the life (reliability) factor of the fluorescent tube is the sputtering (metal scattering) of the electrode (metal) present inside. Generally, when the energy to be injected into a light emitting element (input power in the case of a fluorescent tube) is increased, the light emitting energy (luminance or luminous intensity) increases.
[0012]
However, in the cold cathode fluorescent tube, as the power is increased, the plasma discharge becomes stronger, the collision of the plasma gas particles with the electrode is increased, and the reliability is significantly reduced.
[0013]
In the cold cathode fluorescent tube, an increase in the number of fluorescent tubes causes an increase in the number of inverter driving circuits. It is for the following reasons. The cold cathode fluorescent tube has a negative characteristic, and has a ballast capacitor in the inverter drive circuit in order to stabilize the tube current at the time of discharge. When a large number of cold cathode fluorescent lamps are arranged after the ballast condenser, if the distance between the inverter drive circuit output terminal and the fluorescent tube voltage input terminal is different, the individual fluorescent tubes may be affected by the leakage current due to the parasitic capacitance. In this case, the amount of injected current varies, and the luminance of each fluorescent tube varies, so that there is a restriction that wires are connected at the same distance and as short as possible.
[0014]
Therefore, current cold cathode fluorescent tubes generally have a configuration of 1 inverter (1 transformer output) -1 fluorescent tube or 1 inverter (2 transformer output) -2 fluorescent tube. That is, the inverter drive circuit requires the number of fluorescent tubes or half the number of fluorescent tubes.
[0015]
Therefore, in the configuration using the conventional cold cathode fluorescent tubes, when the number of the fluorescent tubes is increased in order to light up in a short time width and secure a sufficient screen luminance, the inverter driving circuit also increases in proportion, and the drastically increases. There is a problem that the cost is increased.
[0016]
The present invention has been made in view of the above problems, and has as its object to reduce the afterimage when displaying a moving image without deteriorating the reliability of the lighting device, suppressing an increase in the cost of the lighting device, and reducing the display quality. It is an object of the present invention to provide a liquid crystal display device capable of improving (particularly, display quality of a moving image), a lighting device used therefor, and a driving method of the lighting device.
[0017]
[Means for Solving the Problems]
In order to solve the above problem, the lighting device of the present invention forms a plurality of fluorescent tubes each having an external electrode for forming an internal plasma and forming an electric field for excitation, and an electric power for forming the electric field. It is characterized by comprising an inverter drive circuit to be generated, and a high breakdown voltage switching element for connecting and disconnecting power supply from the inverter drive circuit to each electrode to control light emission of each fluorescent tube.
[0018]
According to the above configuration, an external electrode fluorescent tube having an electrode outside the fluorescent tube is used as a fluorescent tube constituting the lighting device, and the external electrode fluorescent tube has no electrode inside, so the electrode using plasma gas particles is used. Without being damaged, high reliability can be maintained even when used in a larger power injection state, that is, in a high brightness light emission state, as compared with a conventional cold cathode fluorescent tube having electrodes inside.
[0019]
In addition, the electrode structure of the external electrode fluorescent tube forms capacitive coupling between the metal electrode outside the fluorescent tube, the glass wall (dielectric) of the fluorescent tube, and the virtual electrode on the fluorescent tube inner wall. The drive voltage applied to the external electrode induces accumulated charge in the virtual electrode inside the fluorescent tube through this capacitive coupling, and the rare gas discharge inside the fluorescent tube is caused by the potential difference between both ends of the fluorescent tube formed by this charge. It can be generated to form and excite an internal plasma.
[0020]
The conventional cold cathode fluorescent tube has a state in which the electrodes are exposed to the discharge space, and the actual current flows into the electrodes, so that it is susceptible to fluctuations in the actual current (such as leakage current due to parasitic capacitance). However, since the electrodes are not exposed to the discharge space, the external electrode fluorescent tube does not allow a real current to flow into the electrodes, and discharges due to a potential difference due to charges accumulated in the capacitive coupling portion. That is, the capacitive coupling serves as a so-called buffer (buffer), and the influence of the actual current fluctuation such as in a cold cathode fluorescent tube is reduced.
[0021]
This makes it possible for the external electrode fluorescent tube to drive many (three or more) fluorescent tubes in parallel with one inverter, which is difficult with a conventional cold cathode fluorescent tube having electrodes inside. .
[0022]
Therefore, the external electrode fluorescent tube can reduce the number of inverter drive circuits for driving the fluorescent tubes, for example, to one, even if the number of fluorescent tubes (lamps) is increased, as compared with the related art, and can avoid an increase in the number of inverter drive circuits. . That is, even if the number of fluorescent tubes is increased, the increase in the cost of the inverter driving circuit is reduced, and the increase in the cost of the fluorescent tubes is suppressed.
[0023]
As described above, by using external electrode fluorescent tubes, the fluorescent tubes can be made brighter without loss of reliability, and the number of fluorescent tubes can be increased without increasing the cost of the inverter drive circuit, so that the lamps can be turned on in a short time span. It is possible to configure a lighting device that can secure a sufficient screen luminance even when the lighting device is used, and by using this lighting device, a high-voltage switching element sequentially lights up in conjunction with the display timing of the display pixel of the liquid crystal display element, By turning off the light, a liquid crystal display device with good responsiveness to moving images can be realized.
[0024]
Further, as an external electrode fluorescent tube constituting an illuminating device according to another embodiment of the present invention, a rectangular parallelepiped planar surface-emitting fluorescent discharge lamp in which strip-shaped metal electrodes are arranged on the outer side surface in the longitudinal direction may be used.
[0025]
In the above-described surface-emitting fluorescent discharge lamp, surface light is obtained by performing surface discharge in the short side direction between the external side electrodes sandwiching the surface-emitting fluorescent discharge lamp. Further, a band-shaped external side surface electrode sandwiched between adjacent surface emitting fluorescent discharge lamps is shared between the two. That is, the odd-numbered lower surface electrode and the even-numbered upper surface electrode in the surface-emitting fluorescent discharge lamp are the same. The upper surface indicates an upstream side with respect to the vertical synchronization direction of the liquid crystal display device, and the lower surface indicates a downstream side with respect to the vertical synchronization direction.
[0026]
The advantage of this electrode arrangement is that the number of output terminals in the high breakdown voltage switching element can be reduced. That is, assuming that the odd-numbered upper surface electrodes are A1, A3,..., And the even-numbered upper surface electrodes are B1, B2,. When the second surface-emitting fluorescent discharge lamp is turned on during the discharge between the electrodes, the discharge is performed between the B2 and A3 electrodes.
[0027]
Therefore, the number of drive terminals for sequentially driving and lighting the 2n surface-emitting fluorescent discharge lamps is (n + 1) A terminals and n B terminals, for a total of (2n + 1) terminals.
[0028]
In the case of a fluorescent tube configuration in which external electrodes are arranged at both ends of one fluorescent tube, the number of drive terminals is twice as large as the number of fluorescent tubes, so that 2n fluorescent tubes are sequentially turned on. Has 4n drive terminals.
[0029]
Therefore, as described above, by sharing the strip-shaped electrodes of the even-numbered surface-emitting fluorescent discharge lamps adjacent to the odd-numbered surface-emitting fluorescent discharge lamps, the number of output terminals of the high-voltage switching element for sequential lighting drive is reduced. As a result, the driving circuit of the lighting device can be further reduced in cost.
[0030]
In addition, the above-described elongated cylindrical fluorescent tube causes unevenness in surface luminance of the lighting device due to the linear light source. In order to alleviate the unevenness in surface luminance, an illumination device is configured by a diffusion plate, a plurality of optical sheets, and the like. Light from the illuminated fluorescent tube leaks to a display pixel group other than a display pixel to be displayed in conjunction with reflection and diffusion in the illumination device. It is necessary to provide a partition in the reflector in the lighting device so as to avoid the light leakage (unnecessary irradiation) and irradiate only the display pixels that are linked.
[0031]
As described above, by using the tile-shaped surface-emitting fluorescent discharge lamp in which the strip-shaped metal electrodes are arranged on the side faces in the longitudinal direction, the strip-shaped metal electrodes on the side faces have a role of a light partition plate. Further, since the light source is a surface light source, a diffusion mechanism such as a diffusion plate can be omitted, so that the influence of light leakage can be reduced, and the cost can be reduced by reducing the number of members.
[0032]
By using the external electrode surface-emitting fluorescent discharge lamp having the strip electrodes in the longitudinal direction having the configuration as described above, the number of output terminals of the switching element is reduced by half, and the number of members such as the diffusion plate is further reduced and the cost is reduced. An illumination device with less light leakage can be configured, and by using this illumination device, a high withstand voltage switching element sequentially turns on and off in conjunction with the display timing of the display pixel of the liquid crystal display element. A liquid crystal display device with good moving image response can be realized.
[0033]
In the lighting device, the inverter drive circuit may include a drive control circuit in which the drive power to each electrode of the fluorescent tube is a sine wave or a rectangular wave having phases opposite to each other. With the above configuration, the input voltage to the high-voltage switching circuit at the subsequent stage can be reduced to about 1/2 of the driving voltage of the illumination light source.
[0034]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a liquid crystal display device of the present invention, a lighting device used therefor, and a driving method thereof will be described with reference to the drawings. As shown in FIG. 1, the liquid crystal display device 1 according to the present embodiment is of an active matrix type having a TFT (thin film transistor) of 640 × 480 dots, for example.
[0035]
The liquid crystal panel (display unit) 3 is provided with a liquid crystal layer that modulates a light transmission state according to a source signal and a gate signal based on a video signal (image data) applied while being scanned. As the liquid crystal layer, for example, a thin twisted nematic (TN) liquid crystal layer, an OCB liquid crystal layer, or a ferroelectric liquid crystal layer may be used.
[0036]
The liquid crystal panel 3 is provided with a gate driver 4 for driving a scanning line in the liquid crystal panel 3 by a gate signal and a source driver 5 for driving a pixel data signal line by a source signal. The liquid crystal display device 1 is provided with a liquid crystal panel control circuit 2 to which a video signal is input so as to output a drive signal based on the video signal.
[0037]
A driving signal based on a video signal is supplied from the liquid crystal panel control circuit 2 to the liquid crystal panel 3 via the gate driver 4 and the source driver 5, and the driving signal is applied to the liquid crystal display element. That is, the data signal voltage of the drive signal is applied to the corresponding signal line at the timing when the scan pulse is applied to the corresponding scan line.
[0038]
The lighting device 11 includes a backlight unit 12 that illuminates the display surface of the liquid crystal panel 3. The backlight unit 12 includes n external electrode fluorescent tubes 13 arranged at equal intervals and in parallel with each other along the vertical scanning direction of the liquid crystal panel 3.
[0039]
The illumination device 11 includes an inverter drive circuit (drive control circuit) 14, a high withstand voltage switching circuit (high withstand voltage switching element, and a switching control circuit) as a mechanism for controlling lighting (light emission) of the external electrode fluorescent tubes 13. 15), a shift register 16 and a frequency dividing counter 17.
[0040]
In the illumination device 11, the scanning shift clock is frequency-divided by the counter 17, and the frequency-divided signal is supplied to the inverter driving circuit 14 and the high-voltage switching circuit 15 by the shift register 16 in synchronization with the vertical synchronization signal. The fluorescent tube driving voltage output from the circuit 14 is switched (switched) by the high voltage switching circuit 15 to the driving pair SA1-SB1 → the driving pair SA2-SB2 →... → the driving pair SAn-SBn. The external electrode fluorescent tubes 13 (L1 to Ln) are sequentially turned on one by one at a predetermined cycle, and then sequentially turned off.
[0041]
Here, the relationship between each fluorescent tube 13 as the fluorescent tube of the lighting device 11 and the display element group of the liquid crystal display element will be briefly described. Assuming that the number of the fluorescent tubes 13 is N and the number of scanning lines, that is, the number of pixels in the scanning direction is M, the n-th fluorescent tube 13 has [(n−1) · (M / N) +1] th to [ [n · (M / N)] illuminates the pixel for the scan line. As a specific example, when a display element having a resolution of 640 (horizontal) × 480 (vertical) is illuminated by six fluorescent tubes, one fluorescent tube corresponds to 80 scanning lines.
[0042]
That is, the pixels for the first to 80th scanning lines are illuminated by the first fluorescent tube 13, and the pixels for the 81st to 160th lines are illuminated by the second fluorescent tube 13. Similarly, the last sixth fluorescent tube illuminates pixels corresponding to the 401th to 480th scanning lines.
[0043]
The number of the fluorescent tubes 13 is not particularly limited as long as the number of the fluorescent tubes 13 can be effectively reduced to reduce the display quality such as a trailing phenomenon in a high-speed moving image.
[0044]
The configuration for limiting the pixel area to be illuminated will be described based on the module configuration of an actual liquid crystal display device. FIG. 2 shows a vertical sectional view in the scanning direction. A reflection partition plate 22 is provided to evenly partition between the external electrode fluorescent tubes 13, and a diffusion plate 23, a diffusion sheet 24, a condensing sheet 25 and the like are arranged between the external electrode fluorescent tubes 13 and the liquid crystal panel 3. I have. The illumination area is partitioned at regular intervals by the reflective partition plate 22 and mounted so as to match a predetermined display area.
[0045]
Here, the liquid crystal display elements having the same scanning timing are referred to as a display element group. That is, in this example, one display element group includes 640 liquid crystal display elements corresponding to one scanning line. The display element groups are grouped into display element groups in the order of earlier scanning time and at least one display element group belongs to one group. That is, in this example, one display element group is configured for each of 640 × 80 liquid crystal display elements corresponding to 80 adjacent scanning lines in the order of earlier scanning timing.
[0046]
Next, the relationship between the image display and the lighting timing of the lighting device 11 will be briefly described. FIG. 3 schematically shows the vertical synchronization signal received by the drive circuit system (shift register 16 in FIG. 1) of the lighting device 11 and the timing of the lighting state of the first to sixth external electrode fluorescent tubes 13. As shown in FIG. 3, each fluorescent tube 13 is sequentially turned on and off in synchronization with the vertical synchronization signal.
[0047]
Assuming that the light-on time is ta, the light-off time is tb, and one frame time is f, there is a relationship of ta + tb = f. td represents the phase shift amount of the light-off timing (light-up timing). In the case of n fluorescent tubes, the relationship is td = f / n. In the case of the present embodiment, td = f / n. 6. From the relationship shown in FIG. 4, the shorter the lighting time ta, the better the moving image response performance. In experiments, 1/6 duty lighting (ta = f / 6) has lower display quality such as tailing in high-speed moving image display than 1/4 duty lighting (ta = f / 4). It was confirmed that it was reduced.
[0048]
In this experiment, in order to compensate for the illumination light amount becoming 2/3 with the lighting time going from f / 4 to f / 6, individual fluorescent lamps were utilized by utilizing the high reliability of the external electrode fluorescent tubes. The tube 13 was used with the brightness increased 1.5 times (the drive voltage was increased). Regarding power consumption, the instantaneous power is high due to the increase in instantaneous luminance, but the lighting time is short, and the integrated time average power amount is 1/4 duty lighting and 6%. There is no difference from 1 / duty lighting, and the power consumption does not change.
[0049]
Here, the external electrode fluorescent tube used in the embodiment of the present invention will be described in more detail. FIGS. 5A and 5C are simplified structural drawings of the external electrode fluorescent tube 13 used in the present invention. 5 (b) and 5 (d) show, for comparison, simple structural drawings of a cold cathode fluorescent tube conventionally used as a liquid crystal backlight.
[0050]
The conventional cold cathode fluorescent tube has an electrode 53 inside the fluorescent tube, and is connected to an external power supply line via a harness cable 54. On the other hand, the external electrode fluorescent tube 13 has no electrode inside the fluorescent tube. In the external electrode fluorescent tube 13 used in the present invention, the metal electrodes 52 were formed in close contact with the outer tube walls at both ends of the fluorescent tube in a ring shape. As the electrode material, it is preferable to use a metal having a low resistance, such as Ag, Cu and Al.
[0051]
In the present embodiment, an Ag electrode that can be easily formed by processing is used. The discharge gas composition and the gas pressure inside the fluorescent tube were set to Ar (5%) / Ne (95%) and 8 kPa as in the conventional cold cathode fluorescent tube. Considering use in sequential lighting in a short time width, a phosphor having as short as possible afterglow characteristics and uniform afterglow characteristics of three wavelengths of red, green and blue was selected.
[0052]
Since the external electrode fluorescent tube 13 used in the lighting device of the present invention does not include the internal electrode 53 like a conventional cold cathode fluorescent tube, it does not suffer any electrode damage (sputtering of the metal electrode) by the discharge gas.
[0053]
In a conventional cold cathode fluorescent tube, a harness cable is passed through the end of the glass tube to energize the internal electrodes, and the harness and the glass wall are welded (sealed). Slow leak (small gas leak) from the seal portion occurs due to stress due to thermal expansion, and there is a decrease in reliability due to a change in gas composition.
[0054]
However, since the external electrode fluorescent tube 13 according to the lighting device of the present invention has no penetrating portion of such a metal wire, the reliability is further improved. In the present embodiment, by utilizing this high reliability, a liquid crystal display device which is lit at 1.5 times the luminance and has a satisfactory moving image response in high-speed moving image display and has sufficient screen luminance is realized.
[0055]
Here, the driving of the external electrode fluorescent tube 13 used in the embodiment of the present invention will be described in more detail. As shown in FIG. 5, the external electrode fluorescent tube has a metal electrode on the outside of the fluorescent tube wall, and during discharge through the glass tube (dielectric), a virtual electrode is formed on the inner wall of the glass by accumulated charges. Thus, a capacitive coupling, that is, a structure in which a capacitor is worn (added) to the fluorescent tube itself is formed.
[0056]
As described above, this capacitive coupling enables multiple inverters to be lit in parallel with one inverter. However, a voltage higher than that of a normal cold cathode fluorescent tube is required due to the voltage distribution of the capacitor. Therefore, in the single-sided single voltage drive, the withstand voltage of the switching circuit is severe.
[0057]
Therefore, in driving the external electrode fluorescent tube 13, a voltage applied to the high voltage switching circuit 15 is applied to each of the electrodes 52 on both sides thereof by sine waves or rectangular waves having phases opposite to each other. The driving method is such that the voltage is half of the above.
[0058]
According to this driving method, the relationship between the vertical synchronization signal and the fluorescent tube lighting timing schematically shown in FIG. 3 described above is as shown in FIG. 6 when represented by a driving voltage waveform applied to the fluorescent tube.
[0059]
The sine wave of the opposite phase is output from the inverter driving circuit 14 to the high voltage switching circuit 15A located on the left side of the fluorescent tube 13 and the high voltage switching circuit 15B located on the right side of the fluorescent tube 13 and sent from the shift register 16. Each high voltage switching circuit 15 controls the output timing of the tube driving waveform based on the shift clock / synchronous frequency-divided signal, and simultaneously transmits the positive potential driving waveform to the first left electrode of the external electrode fluorescent tube 13, and simultaneously outputs the right potential driving waveform to the right. Negative potential drive waveforms are transmitted to the electrodes, and a pair of drive waveforms having opposite phases are sequentially transmitted to the electrodes at both ends of the second, third,... At predetermined timing to sequentially turn on / off the external electrode fluorescent tubes 13. .
[0060]
Next, a second embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 7, the external electrode fluorescent tube used in the present embodiment has a rectangular parallelepiped shape in which strip-shaped metal electrodes 62 are arranged on the outer side surface in the longitudinal direction, and is referred to as a planar type surface-emitting fluorescent discharge lamp. Things.
[0061]
In the above-mentioned surface-emitting fluorescent discharge lamp, surface light emission is obtained by performing surface discharge in the short side direction between the upper electrode 62 and the lower electrode 62. Using the flat surface-emitting discharge lamp shown in FIG. 7, tiles are juxtaposed and juxtaposed as shown in FIG. 8, and odd-numbered and even-numbered strip-shaped metal electrodes 62 adjacent to each other are shared. That is, the first lower surface electrode and the second upper surface electrode are the same band-shaped metal electrode B1, and the second lower surface electrode and the third upper surface electrode are the same band-shaped metal electrode A2. Similarly, the odd-numbered lower surface electrode and the even-numbered upper surface electrode, and the even-numbered lower surface electrode and the next odd-numbered upper surface electrode are made identical.
[0062]
Further, the odd-numbered upper-side electrodes (even-numbered lower-side electrodes) are connected to the high-voltage switching circuit 15A, which is a drive circuit terminal on one side (the left side in FIG. 8), and the even-numbered upper-side electrodes ( The odd-numbered lower surface electrodes are connected so as to be connected to the high-voltage switching circuit 15B which is the drive circuit terminal on the other side (the right side in FIG. 8).
[0063]
As shown in FIG. 9, if the odd-numbered upper surface electrodes are A1, A3,..., And the even-numbered upper surface electrodes are B1, B2,. When the second surface-emitting fluorescent discharge lamp is lit by discharging between the electrodes A1 and B2, the discharge is performed between the electrodes B2 and A3.
[0064]
A driving method of sequentially lighting the fluorescent tubes at the timing of FIG. 3 using the flat surface-emitting fluorescent discharge lamp provided with the electrode arrangement will be described with reference to FIG.
[0065]
The sine wave of the opposite phase is output from the inverter driving circuit 14 to the high voltage switching circuit 15A located on the left side of the fluorescent tube 13 and the high voltage switching circuit 15B located on the right side of the fluorescent tube 13 and sent from the shift register 16. The high withstand voltage switching circuit controls the output timing of the tube driving waveform based on the shift clock / synchronous frequency-divided signal, and the positive potential is applied to the upper surface electrode (A1) of the first (L1) upper surface electrode (A1) of the flat surface fluorescent lamp 91. When the driving waveform is transmitted, a driving waveform having the same potential and opposite phase is simultaneously applied to the lower surface electrode (B2). At the timing when the second (L2) is turned on in sequence at the timing of FIG. 3, drive waveforms having the same potential and opposite phase are applied to the B2 electrode and the A3 electrode, respectively, and at the timing when the third (L3) is turned on, the A3 electrode is A drive waveform having the same potential and opposite phase is applied to each of the B4 electrodes.
[0066]
In this manner, by applying a pair of drive waveforms having opposite phases to the upper surface electrode and the lower surface electrode of the planar surface emitting fluorescent discharge lamp 91 at the lighting timing of FIG. Are sequentially turned on and off.
[0067]
According to this electrode configuration, the number of drive terminals for sequentially driving 2n planar surface-emitting fluorescent discharge lamps is (n + 1) terminals A and n terminals B, for a total of (2n + 1) terminals. On the other hand, in the case of a fluorescent tube configuration in which external electrodes are arranged at both ends of one fluorescent tube, the number of drive terminals is twice as large as the number of fluorescent tubes, so that 2n fluorescent tubes are sequentially turned on. Therefore, the number of driving terminals is 4n.
[0068]
Therefore, with the electrode configuration shown in the present embodiment, it is possible to reduce the number of output terminals of the high breakdown voltage switching circuit 15 for sequential lighting drive by half, and to further reduce the cost of the drive circuit system of the lighting device. Was.
[0069]
The relationship between the surface-emitting fluorescent discharge lamp, which is a fluorescent tube of the illumination device, and the display element group of the liquid crystal display element is the same as that described in the first embodiment, and a description thereof will be omitted.
[0070]
Here, a module configuration of a liquid crystal display device using the lighting device described in this embodiment mode will be described below. FIG. 10 shows a vertical sectional view in the scanning direction. The band-shaped electrodes 92 are evenly arranged between the planar surface-emitting fluorescent discharge lamps 91, and the diffusion sheet 24, the condensing sheet 25, and the like are arranged between the surface-emitting fluorescent discharge lamp 91 and the liquid crystal panel 3. Have been.
[0071]
The strip-shaped electrode 92 not only supplies electricity to the flat surface-emitting fluorescent discharge lamp 91 but also functions as a reflection partition plate, and divides the illumination area at equal intervals to limit the display area. Further, since the flat surface-emitting fluorescent discharge lamp 91 is a surface light source, a diffusion plate is not required.
[0072]
【The invention's effect】
As described above, by using an external electrode fluorescent tube having no electrode inside as a fluorescent tube constituting the lighting device of the present invention, that is, using an external electrode fluorescent tube having an electrode outside the fluorescent tube, the fluorescent tube can be used without loss of reliability. It is possible to configure an illuminating device capable of securing sufficient screen luminance even when the brightness is increased and the lighting is performed in a short time width. Using this illuminating device, in conjunction with the display timing of the display pixels of the liquid crystal display element, By turning on and off, there is an effect that a liquid crystal display device with good moving image responsiveness can be realized.
[0073]
Further, only one inverter drive circuit for driving the external electrode fluorescent tubes constituting the lighting device of the present invention is possible, and an increase in the number of inverter drive circuits can be suppressed. That is, even if the number of fluorescent tubes is increased, an increase in the cost of the inverter driving circuit can be avoided, and the increase in the cost of the fluorescent tubes is suppressed.
[0074]
Therefore, by increasing the number of fluorescent tubes without increasing the cost of the inverter driving circuit, it is possible to configure a lighting device that can secure sufficient screen luminance even when the lighting device is turned on in a short time width. By sequentially turning on and off the light in conjunction with the display timing of the display pixel of the display element, there is an effect that a liquid crystal display device with good responsiveness to moving images can be realized at low cost.
[0075]
In addition, as an external electrode fluorescent tube constituting an illumination device according to another embodiment of the present invention, a rectangular parallelepiped flat surface-emitting fluorescent discharge lamp in which strip-shaped metal electrodes are arranged on the outer side surface in the longitudinal direction is used, and a diffusion plate or the like is used. Therefore, the effect of light leakage can be reduced, and the effect of reducing costs by reducing the number of members can be achieved.
[0076]
In addition, by using a common strip-shaped electrode between adjacent planar surface-emitting fluorescent discharge lamps, that is, by using the same electrode, the number of output terminals of the high breakdown voltage switching element can be reduced by half. And turning on and off sequentially in synchronization with the display timing of the display pixels of the liquid crystal display element, it is possible to realize a liquid crystal display device having good moving image responsiveness at low cost.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration example of a liquid crystal display device and an illumination device used therein according to the present invention.
FIG. 2 is a cross-sectional view illustrating a configuration example of the liquid crystal display device.
FIG. 3 is a timing chart showing timing between a vertical synchronization signal and a fluorescent tube lighting state in the liquid crystal display device.
FIG. 4 is a schematic diagram illustrating response characteristics of a liquid crystal and a moving image response performance depending on a fluorescent tube lighting state in a general liquid crystal display device.
5 (a) and 5 (c) are structural diagrams of an external electrode fluorescent tube used in one embodiment of the present invention, and FIGS. 5 (b) and 5 (d) It is a structural diagram of the conventional cold cathode tube.
FIG. 6 is a timing chart showing timings of an output waveform from an inverter drive circuit and a vertical synchronization signal and an output drive waveform from a high withstand voltage switching circuit in the liquid crystal display device of the present invention.
FIGS. 7A and 7B show a planar surface-emitting fluorescent discharge lamp used in another configuration example of the liquid crystal display device and the lighting device used in the present invention, wherein FIG. 7A is a front view, and FIG. It is AA 'arrow sectional drawing.
FIG. 8 is a configuration diagram showing an arrangement of a plurality of flat surface-emitting fluorescent discharge lamps and side electrodes shared by the adjacent discharge lamps.
FIG. 9 is a block diagram showing another configuration example of the liquid crystal display device according to the present invention and a lighting device used therefor.
FIG. 10 is a sectional view of the liquid crystal display device.
[Explanation of symbols]
1 liquid crystal display device 2 liquid crystal panel control circuit
3 LCD panel 4 Gate driver
5 Source driver 11 Lighting device
12 Backlight part 13 External electrode fluorescent tube
14 Inverter drive circuit 15 High breakdown voltage switching circuit
16 shift register 17 counter
21 Reflector 22 Reflector
23 Diffusion plate 24 Diffusion sheet
25 Condensing sheet
51 Fluorescent tube wall 52 External electrode
53 Internal electrode 54 Harness cable
91 Planar surface emitting fluorescent discharge lamp 92 Side electrode

Claims (8)

A plurality of fluorescent tubes each having an external electrode for forming an internal plasma and forming an electric field for excitation,
An inverter drive circuit that generates electric power for forming the electric field;
A lighting device comprising: a high withstand voltage switching element for connecting and disconnecting power supply from an inverter drive circuit to each electrode to control light emission of each fluorescent tube. 2. The lighting device according to claim 1, wherein the inverter drive circuit includes a drive control circuit that sets a drive power to each electrode of the fluorescent tube to a sine wave or a rectangular wave having opposite phases. The lighting device according to claim 1, wherein the high withstand voltage switching circuit includes a switching control circuit that sequentially turns on and off the fluorescent tubes. Each of the fluorescent tubes is a planar surface-emitting discharge lamp having an electrode on a long side surface, and adjacent side electrodes between the adjacently arranged discharge lamps are shared by the discharge lamps adjacent to each other. The lighting device according to claim 1, wherein: In the drive electrode group of the fluorescent tube, odd-numbered electrodes are connected to one high-voltage switching element, and even-numbered electrodes are connected to the other high-voltage switching element. 5. The lighting device according to claim 4, wherein driving waveforms having phases opposite to each other are applied to control the lighting of the fluorescent tubes. The lighting device according to claim 4, wherein each of the fluorescent tubes is sequentially turned on and off. A plurality of display elements for forming a display screen by modulating light based on image data applied while being scanned, and an illumination unit that illuminates the display element with the light are provided.
The lighting unit is the lighting device according to any one of claims 1 to 6,
When display elements having the same scanning timing are used as display element groups, the display elements are grouped into display element groups for each of the display element groups, and at least one fluorescent tube is provided for each of the display element groups. And
A liquid crystal comprising a control circuit for sequentially turning on and off the fluorescent tubes at the same cycle as one frame time of a screen and at different timings for each of the display element groups. Display device. A method for driving a liquid crystal display device that forms a display screen by illuminating a plurality of display elements that modulate illuminated light based on image data applied while being scanned,
When the same display element of the scanning time is a display element group, each of the display elements is divided into display element groups for each of the display element groups, and sequentially emits light to each of the display element groups,
A method for driving a liquid crystal display device, characterized in that timings of irradiating light for each of the display element groups are set to be different from each other and have overlapping portions.

Images