JP2008209678A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device in which animation display performance can be improved without increasing the cost. <P>SOLUTION: A discharge lamp scanning lighting device comprises an inverter 10, a transformer 20, discharge lamps LA1 to LA6 connected in parallel to each other, saturable reactors T1 to T6 respectively connected in series between the discharge lamps LA1 to LA6 and the transformer 20, and a lighting signal generation circuit 30 based on vertical synchronization signals inputted. The lighting signal generation circuit 30 controls the currents flowing to the saturable reactors T1 to T6 respectively, thereby reducing the variations in the impedances in the discharge lamps LA1 to LA6. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device, and more particularly to a technique for improving moving image display performance without increasing costs.

  Liquid crystal display devices have been widely used as flat panel display devices for various monitors and TVs, taking advantage of their small size and light weight. However, the conventional liquid crystal display device has no particular problem in displaying a still image due to the fact that the liquid crystal is a hold-type display device and the response characteristic of the liquid crystal is relatively slow. Compared with CRT, blurring and tailing phenomenon occurred and image quality degradation occurred. In particular, since TV mainly displays moving images, moving image quality has been a problem.

  In liquid crystal display devices, the performance of moving images has been continuously improved, and liquid crystal materials and cell structures with fast response speeds have been developed. However, the image quality is still not sufficient for a frame frequency of 1/60 seconds. Deterioration has occurred.

  For example, Patent Document 1 discloses a proposal for improving the moving image display performance by effectively improving the responsiveness of the liquid crystal by using a backlight.

  The configuration described in Patent Document 1 divides (divides) a liquid crystal backlight into a plurality of N regions in the scanning direction, and has a certain time delay with respect to the writing operation of the corresponding liquid crystal display unit. The divided areas of the backlight to emit light are sequentially emitted. With this configuration, the moving image performance is improved by causing the liquid crystal to emit light immediately before writing in the next frame in which the response is relatively stable, instead of emitting light during a time when the liquid crystal is not sufficiently responding immediately after writing. FIG. 7 of Patent Document 1 shows a configuration in which the backlight is divided into N = 4 areas. In FIG. 7, a lighting control signal generation circuit 1 including a frequency dividing counter 2 and a shift register 3 is disclosed. The lighting control signal generation circuit 1 is connected to the discharge lamps 5-1 to 5-4 via inverters 4-1 to 4-4, respectively.

  In Patent Document 2, as shown in FIG. 1, SW is proposed as a means for sequentially turning on the discharge lamp. However, since the voltage when the SW is open is high, it is difficult to realize with an inexpensive device.

  Further, in Patent Document 2, since the cost of the backlight portion accounts for a large proportion of the cost of the entire liquid crystal display device, the number of transformers that perform parallel driving of the discharge lamps and supply current to the semiconductors that switch high voltage and the lamps By reducing the cost, the cost is reduced.

JP-A-11-202286 JP 2001-235720 A

  As described above, in the conventional liquid crystal display device, the liquid crystal is a hold-type display device, and the response of the liquid crystal is not fast enough, so that the moving image blur and the tailing phenomenon occur when displaying the moving image. However, in order to improve this, when a method of simply dividing and lighting the backlight is adopted, the number of inverters, output transformers, and their control circuits are the same as the division number N or one of them. / 2 times is necessary, which raises the problem of an increase in cost.

  On the other hand, in the conventional liquid crystal display device, as described above, in the discharge lamp drive circuit (generally an inverter circuit is used), a plurality of discharge lamps are driven in parallel to reduce the number of semiconductors and transformers. By doing so, the cost is reduced. For example, when all the discharge lamps are driven in parallel by one drive circuit, only one semiconductor circuit and one output transformer are required for the drive circuit. In this method, since each discharge lamp has a variation in impedance, a balance coil is inserted in series with each lamp as an inductance element for balancing the discharge current.

  However, when the discharge lamps are driven in parallel in this way, a switch is inserted in series with each of the lamps in order to divide the plurality of lamps into N and perform sequential lighting control in synchronization with the data write timing to the liquid crystal. Therefore, a high breakdown voltage semiconductor element is required as a switch. This contradicts the fact that the cost is reduced by reducing the number of high voltage semiconductors by parallel driving. That is, practically, it is difficult to sequentially turn on the discharge lamps for improving the moving image quality while driving the plurality of discharge lamps in parallel.

  In addition, if a switch is performed with a simple switch function (without synchronizing timing) without using a switch made of a semiconductor device having a high breakdown voltage as described above, an increase in cost can be avoided, In the case of a CCFL (cold cathode ray tube) generally used as a backlight lamp, the lighting stability is impaired. Therefore, there is a problem that the moving image display performance is deteriorated.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a liquid crystal display device capable of improving moving image display performance without increasing cost.

  A liquid crystal display device according to the present invention includes a liquid crystal panel for displaying an image, a plurality of discharge lamps that respectively illuminate a plurality of blocks that divide the liquid crystal panel, and a drive voltage applied to the plurality of discharge lamps. An inverter, a plurality of inductance elements arranged in series with the plurality of discharge lamps so as to be interposed between the plurality of discharge lamps and the one inverter, and a control for controlling a current flowing through each of the plurality of inductance elements Means.

  The liquid crystal display device according to the present invention can reduce the variation in impedance among the plurality of discharge lamps by controlling the current flowing through each of the plurality of inductance elements using the control means. Accordingly, the moving image display performance can be improved without increasing the cost.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<Embodiment 1>
FIG. 1 is a block diagram showing a configuration of a discharge lamp scanning lighting device built in the liquid crystal display device according to Embodiment 1 of the present invention. This discharge lamp scanning lighting device illuminates a liquid crystal panel provided in a liquid crystal display unit in order to display an image, but the liquid crystal panel and the liquid crystal display unit itself are not directly related to the present invention. In FIG. 1, illustration is omitted. This liquid crystal display panel is divided (divided) into six blocks in the vertical direction of the screen, and illuminated by six discharge lamps controlled in time division (in parallel drive).

  The discharge lamp scanning lighting device of FIG. 1 includes an inverter 10, a transformer 20 as an output transformer, six discharge lamps LA1 to LA6 connected in parallel to each other, and between the discharge lamps LA1 to LA6 and the transformer 20. Each of the saturable reactors T1 to T6 connected in series and a lighting control signal generation circuit 30 that controls the saturable reactors T1 to T6 based on the input vertical synchronizing signal (and horizontal synchronizing signal).

  Since the discharge lamps LA1 to LA6 have impedance variations, the discharge lamps have saturable reactors T1 to T6 interposed between the discharge lamps LA1 to LA6 and the inverter 10 as inductance elements for balancing the discharge current. Each of LA1 to LA6 is arranged in series.

  Hereinafter, for convenience of explanation, the discharge lamps LA1 to LA6 are collectively referred to as a discharge lamp LAn. Further, the saturable reactors T1 to T6 are collectively referred to as a saturable reactor Tn.

  In FIG. 1, one terminal of a transformer 20 is connected to the inverter 10. One terminal of the saturable reactor Tn is connected to the other terminal of the transformer 20. One terminal of the discharge lamp LAn is connected to the other terminal of the saturable reactor Tn. A GND line for supplying a ground potential is connected to the other terminal of the discharge lamp LAn. The discharge lamp LAn constitutes a backlight in the liquid crystal display panel described above.

  As will be described later with reference to FIG. 2, in the saturable reactor Tn, the primary coil L1 and the secondary coil L2 are wound around the core 51 for control, and the primary coil L1 is discharged from the transformer 20. The secondary coil L2 is connected to the lamp LAn, and the secondary coil L2 is connected to and controlled by the lighting control signal generation circuit 30.

  In FIG. 1, the lighting control signal generating circuit 30 controls the inductance of the primary coil L1 connected to the saturable reactor Tn by controlling the current flowing through the secondary coil L2. For example, when the inductance is increased, the voltage applied to the discharge lamp LAn is decreased, so that the lamp current is decreased and the luminance is decreased. Thereby, lighting of discharge lamp LAn can be controlled stably.

  Next, the operation of the saturable reactor Tn will be described in more detail with reference to FIG. As shown in FIG. 2, in the saturable reactor Tn, a primary coil L1 and a secondary coil L2 are wound around a core 51 serving as a magnetic path, and a magnetic bias is applied to the core 51 by a permanent magnet 52. By applying the saturation characteristic of the core 51, an inductance characteristic as shown in the graph of FIG. 3 is obtained. With reference to the inductance characteristics of the saturable reactor Tn shown in FIG. 3, the lighting control signal generation circuit 30 controls the current flowing through the secondary coil L2, thereby primary connecting the transformer 20 and the discharge lamp LAn. The inductance of the side coil L1 can be controlled.

  As shown in FIG. 2, in the saturable reactor Tn, the secondary coil L2 is wound around the core 51 at a higher density than the primary coil L1. Therefore, even if a large voltage is applied to the primary coil L1, the secondary coil L2 can be controlled with a small voltage and a small current. By utilizing this characteristic, it is possible to control the luminance of the discharge lamp LAn to which a large voltage is applied with a small voltage and a small current.

  That is, for the discharge lamp LAn that is desired to be lit, the inductance of the primary coil L1 of the saturable reactor Tn is reduced by passing a current through the secondary coil L2 of the connected saturable reactor Tn. What is necessary is just to increase the electric current which flows into the discharge lamp LAn.

  On the other hand, for the discharge lamp LAn that is desired to be extinguished (or reduced in brightness), the current is not passed through the secondary coil L2 of the saturable reactor Tn connected (or the flowing current is reduced), so that the saturation is achieved. It is only necessary to increase the inductance of the primary coil L1 of the reactor Tn and to cause a current to flow through the discharge lamp LAn (or to reduce the flowing current). This makes it possible to perform sequential lighting (or sequential luminance control).

  FIG. 4 is a block diagram showing a configuration of a liquid crystal display panel illuminated by the discharge lamp scanning lighting device of FIG. As shown in FIG. 4, the liquid crystal display panel is divided into six blocks B1 to B6 in the vertical direction of the screen, and is sequentially scanned from the block B1 on the upper side of the screen to the block B6 on the lower side of the screen. Controlled or driven in parallel. Also, in each block (for example, block B1), there is a time difference in driving between the upper end line B1-U and the lower end line B1-L.

  FIG. 5 is a timing chart showing time-division control (parallel drive) of the discharge lamps LA1 to LA6 respectively corresponding to the blocks B1 to B6 of FIG.

  This writing control is performed by sequentially dividing the period T of the vertical synchronization signal as shown in FIG. 5A into 6 blocks B1 to B6 in order as shown in FIG. 5B.

  FIG. 5C shows the response characteristics of the LCD at the upper end line B1-U and the lower end line B1-L of the block B1, and FIG. 5D shows the discharge lamp LA1 that illuminates the blocks B1-B6, respectively. The write pulses of ~ LA6 are shown.

  The discharge lamp LA1 that illuminates the block B1 is turned on with a delay of time Td from the timing of starting writing to the block B1, and is turned off after a time Tw immediately before the writing timing of the next frame has elapsed. In FIG. 5, since Tw = Td, the duty is ½.

  As shown in FIG. 5C, in the block B1, the response of the lower end line B1-L is not complete compared to the upper end line B1-U at the time when the discharge lamp LA1 starts lighting. However, since the luminance depends on the duty on average, the timing for starting the lighting of the discharge lamp LA1 may be set in consideration of the luminance. Alternatively, when it is desired to improve the blur of the moving image, the timing at which the discharge lamp LA1 is turned on may be delayed to the optimum timing of the liquid crystal response characteristics in synchronization with the write start timing of the block B1.

  As described above, according to the liquid crystal display device according to the present embodiment, the lighting control signal generation circuit 30 as the control means is used to control the current flowing through each of the saturable reactors T1 to T6 as the plurality of inductance elements. As a result, variations in impedance in the discharge lamps LA1 to LA6 are reduced. Accordingly, the moving image display performance can be improved without increasing the cost.

  In the above description, the configuration in which the number N of inverters 10 is set to 1 has been described with reference to FIG. 1. However, the number of inverters 10 is not limited to N = 1. A configuration in which ≧ 2 may be employed, or a configuration in which the number of discharge lamps LAn driven by one inverter 10 is reduced may be employed. That is, any configuration may be used as long as one inverter 10 drives a plurality of discharge lamps LAn. Even in the configuration where N ≧ 2, the lighting control signal generating circuit 30 is used to synchronize sequentially by sequentially shifting the writing timing to the LCD in the vertical direction of the screen between the plurality of inverters 10 using the lighting control signal generation circuit 30. Thus, it is possible to greatly improve the motion blur.

<Embodiment 2>
FIG. 6 is a block diagram showing a configuration of a discharge lamp scanning lighting device built in the liquid crystal display device according to Embodiment 2 of the present invention. FIG. 6 is a circuit diagram in which resistance elements R1 to R6 are interposed in series with the discharge lamps LA1 to LA6 between the discharge lamps LA1 to LA6 and the GND line in FIG. This is fed back to the signal generator 30. In FIG. 6, the same members as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted here.

  Generally, when the temperature changes, the inductances of the saturable reactors T1 to T6 change, so that the current flowing through the discharge lamps LA1 to LA6 also changes.

  In the discharge lamp scanning lighting device of FIG. 6 according to the present embodiment, the current flowing through the discharge lamps LA1 to LA6 is fed back to the lighting control signal generator 30 using the voltage generated in the resistance elements R1 to R6. . Therefore, it is possible to perform control that alleviates this change in current.

  As described above, according to the liquid crystal display device according to the present embodiment, since the current flowing through the discharge lamps LA1 to LA2 is feedback-controlled using the resistance elements R1 to R6, in addition to the effect of the first embodiment, the temperature There is an effect that a stable operation can be performed with respect to the change.

  In the above description, the case where the current flowing through the discharge lamp is feedback controlled using a resistance element has been described. However, the present invention is not limited to the resistance element, and other impedance elements may be used.

1 is a block diagram showing a configuration of a discharge lamp scanning lighting device built in a liquid crystal display device according to Embodiment 1. FIG. 1 is a diagram showing a configuration of a saturable reactor according to Embodiment 1. FIG. 3 is a graph showing inductance characteristics of the saturable reactor according to the first embodiment. FIG. 3 is a block diagram showing a configuration of a liquid crystal display panel illuminated by the discharge lamp scanning lighting device according to Embodiment 1. 3 is a timing chart showing time-division control (parallel drive) of the discharge lamp according to Embodiment 1. FIG. 6 is a block diagram showing a configuration of a discharge lamp scanning lighting device built in a liquid crystal display device according to a second embodiment.

Explanation of symbols

  10 inverter, 20 transformer, 30 lighting control signal generation circuit, 51 core, 52 permanent magnet, B1-B6 block, B1-L bottom line, B1-U top line, L1 primary coil, L2 secondary coil, LA1 ~ LA6 discharge lamp, R1-R6 resistive element, T1-T6 saturable reactor, Td, Tw time.

Claims (3)

A liquid crystal panel for displaying images;
A plurality of discharge lamps that respectively illuminate a plurality of blocks into which the liquid crystal panel is divided;
An inverter for supplying a driving voltage to the plurality of discharge lamps;
A plurality of inductance elements respectively disposed in series with the plurality of discharge lamps so as to be interposed between the plurality of discharge lamps and the one inverter;
A liquid crystal display device comprising: control means for controlling a current flowing through each of the plurality of inductance elements. The liquid crystal display device according to claim 1,
The inductance element is a liquid crystal display device having a saturable reactor. The liquid crystal display device according to claim 1 or 2,
A plurality of resistance elements or impedance elements respectively disposed in series with the plurality of discharge lamps;
A liquid crystal display device in which voltages generated in the plurality of resistance elements or impedance elements are fed back to the control means.

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