JP2001235720A - Liquid crystal display - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a liquid crystal display device having a built-in discharge lamp scanning and lighting device for improving the moving image display performance of liquid crystal, and increasing the cost and brightness of the backlight. SOLUTION: A plurality (N) of discharge lamp lighting inverters having a switch for turning on / off an output are provided, and a plurality (M) of discharge lamps are provided on a secondary side of an output transformer of each inverter. Each lamp is provided with a switch element in series, and the discharge lamp is sequentially lit by sequentially turning on / off the switch by a lighting control signal generation circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-dimensional illumination device for illuminating with a plurality of discharge lamps such as a liquid crystal backlight, and more particularly to a liquid crystal display device incorporating a discharge lamp scanning and lighting device for scanning lighting.

[0002]

2. Description of the Related Art As a flat panel display device, a liquid crystal display device has been widely used as various monitors and TV display devices, taking advantage of its small size and light weight.

However, the conventional liquid crystal display device has no particular problem in displaying a still image because the liquid crystal is a holding type display device and the response characteristic of the liquid crystal is relatively slow. A trailing phenomenon occurs and the image quality is inferior to that of a CRT.

Recently, as a monitor of a personal computer, in addition to a TV, a moving image is often displayed on a liquid crystal display device, and the image quality of the moving image is becoming a problem.

Conventionally, the response speed of the liquid crystal has been continuously improved.
It is very difficult to realize a response speed of 1.7 ms, which is one digit faster than a frame period of 1/60 second, as a response speed sufficient to display a V-type moving image. Most of the current liquid crystal response speeds are several times the frame period, and for fast-moving images, large image quality degradation occurs.

For example, Japanese Patent Application Laid-Open No. H11-202286 discloses a proposal for effectively improving the responsiveness of the liquid crystal by improving the backlight and improving the moving image display performance.

The configuration described in Japanese Patent Application Laid-Open No. 11-202286 divides a backlight of a liquid crystal into a plurality of N regions in a scanning direction and provides a certain time delay with respect to a writing operation of a corresponding liquid crystal display. The corresponding divided areas of the backlight are made to emit light in sequence, and do not emit light during the time when the liquid crystal just after writing does not respond sufficiently, and emit light immediately before writing in the next frame where the response is relatively stable. By doing so, the video performance has been improved. FIG. 7 shows a configuration in which the backlight is divided into N = 4 areas. In FIG. 8, reference numeral 1 denotes a lighting control signal generation circuit including a frequency dividing counter 2 and a shift register 3. 4
-1 to 4-4 are inverters, and 5-1 to 5-4 are discharge lamps connected to the inverters 4-1 to 4-4.

The writing timing of the liquid crystal display panel, the response of the liquid crystal and the lighting timing of the discharge lamp in such a configuration will be described with reference to FIG. FIG. 8 is a diagram showing the most preferable writing timing and response of the liquid crystal and the timing of lighting the lamp. Discharge lamps (5-1 to
5-4), there are four blocks (B1 to B4) of the corresponding four liquid crystal display panels arranged in the vertical direction, and the image signal is written to the liquid crystal corresponding to the blocks B1 to B4 at the period T of the vertical synchronization signal. It is. Normally, signal writing of liquid crystal is line-sequential, so that the writing timing differs between the upper end and the lower end even in a block. For example, block B1
The liquid crystals in the upper and lower lines of the portion have the responses shown by the response characteristics B1-U and B1-L of the LCD, respectively. The lighting timing of the discharge lamp 5-1 corresponding to the block B1 is turned on with a delay of a predetermined time Td from the writing start timing of the block B1, as indicated by the lamp 5-1 in the figure, and immediately before the writing timing of the next frame. Turn off the light. The lighting time is Tw and the duty is about 1 /
It becomes 4. However, as can be seen from the figure, although the response of the liquid crystal is good at the upper end of the block B1, the discharge lamp is turned on at the lower end in a state where the liquid crystal has not yet responded sufficiently, and the luminance difference in the vertical direction within the block is increased. Is generated. This corresponds to the other blocks B2 to B4 and the lamps 5-2 to 5-4.
The same applies to the relationship described above, and vertical luminance unevenness occurs on the screen of the liquid crystal display panel. To improve this, the number of divided blocks, that is, the number of discharge lamps may be increased. However, the cost and duty are reduced to 1 / block number (discharge lamp number), so that the brightness is greatly reduced.

As described above, since the current response speed of the liquid crystal is not sufficient with respect to the frame period, the backlight lighting time according to this method is a short time immediately before writing in the liquid crystal display unit, and the number of divisions of the backlight is small. N needs to be considerably increased. In addition, the number of the inverters, which are the backlight lighting devices, is required as many as the number of the backlights, and the problem of cost and the backlight lighting in the frame time is one of the divided areas. When the number of divisions of the backlight area is N, the brightness is 1 /
N, and there is a problem that as the number of divisions N is increased to improve the moving image performance, the image becomes darker.

[0010]

As described above, in the conventional liquid crystal display device, the liquid crystal is a holding type display device, and the response of the liquid crystal is slow, so that the moving image display performance is significantly inferior to that of a CRT or the like. In order to improve this, in a system in which the backlight is simply divided and turned on, it is necessary to increase the number of divisions N in order to improve the moving image display performance, which causes problems such as an increase in cost and a decrease in brightness. There is.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has a discharge lamp scanning and lighting device that improves the moving image display performance of the liquid crystal and reduces the cost and brightness of the backlight. It is an object to provide a display device.

[0012]

According to a first aspect of the present invention, a discharge lamp scanning and lighting device for a liquid crystal display device includes a plurality of (M) inverters connected to a plurality of (N) inverters corresponding to the liquid crystal display unit. And a total of M * N discharge lamps, and an inverter SW and an electronic SW connected in series to the discharge lamp in synchronization with the writing timing of the liquid crystal display unit.
Control, the corresponding area of the discharge lamp is lit, and the discharge lamp is scanned and lit.

Further, in the discharge lamp scanning and lighting device of the liquid crystal display device according to the second configuration of the present invention, the discharge lighting of the discharge lamp is illuminated by delaying the scanning and lighting timing of the discharge lamp by a predetermined time with respect to the writing timing of the liquid crystal display unit. The light is turned off immediately before the frame write timing.

Further, in the discharge lamp scanning and lighting device of the liquid crystal display device according to the third configuration of the present invention, the N discharge lamps which are temporally overlapped are sequentially shifted to turn on / off the liquid crystal display device. .

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the present invention will be described with reference to the drawings. Embodiment 1 FIG. 1 is a configuration diagram showing a discharge lamp scanning and lighting device in a liquid crystal display device according to Embodiment 1 of the present invention.
This discharge lamp scanning and lighting device illuminates the liquid crystal panel of the liquid crystal display unit, but omits the liquid crystal display unit provided with this liquid crystal panel. The liquid crystal display device includes two (N = 2) inverters 3A and 3B having switches SA and SB for turning on / off a high voltage output, and four inverters connected in parallel to the secondary side of the output transformer T1 of the inverter 3A. (M = 4) discharge lamps L41 to L44, switch elements SW51 to SW54 connected in series to the discharge lamps L41 to L44, and four switches connected in parallel to the secondary side of the output transformer T2 of the inverter 3B. (M = 4) discharge lamps L45 to L48, a vertical synchronizing signal Vd and a horizontal synchronizing signal Hd are input, and switches SA and SB and switch elements SW55 to SW58 are turned on.
And a lighting control signal generating circuit 6 for generating a lighting control signal for turning on / off. The discharge lamps L41 to L
The discharge lamp device 4 comprising 48 constitutes a so-called backlight in a liquid crystal display panel.

In the first embodiment of the present invention, switch elements SW51 to SW58 connected in series to discharge lamps L41 to L48 and switches SA and SB for controlling the high voltage output of inverters 3A and 3B are provided. Switches SA and SB and switch elements SW51 to SW58
By controlling ON / OFF of the switch by the lighting control signal generating circuit 6 in combination with the above, lighting of the discharge lamp can be controlled stably.

The operation of the liquid crystal display will be described in detail with reference to FIG. The switch SA of the inverter 3A and the switch SB of the inverter 3B output a pulse signal (ON / O) intermittently turning off the output of the inverter shown in SA and SB in FIG.
FF signal). Eight pulse signals are generated by the lighting control signal generation circuit 6 in a horizontal scanning period (1 V cycle) of one frame on the display screen of the liquid crystal display panel. This pulse signal is input to inverters 3A and 3B and generates a high-frequency output signal shown in the inverter output of FIG. Further, a rectangular wave lighting control signal is applied to the switch elements SW51 to SW54 connected to the discharge lamps L41 to L44 at timings indicated by S51 to S54 in the drawing.
Switch element SW5 connected to discharge lamps L45 to L48
Lighting control signals in the form of rectangular waves are applied to SW5 to SW58 at timings indicated by S55 to S58 in the drawing. These lighting control signals are related to the inverter output as shown in the figure.
That is, the ON period of each single lighting control signal is two consecutive.
There is a relationship corresponding to the inverter output period. Also,
Looking at each of these lighting control signals, a lighting control signal signal S
In the middle of the ON period 51, the lighting control signal S55 becomes N
In the O state, the lighting control signal S52 is turned on in the middle of the ON period of the lighting control signal S55, and at the same time, the lighting control signal S51 is turned off. Hereinafter, the lighting control signals S53 to S58 are turned on / off by the same timing.
Perform the operation. The pulse signal to each of the switches SA and SB and the lighting control signal (ON / OFF signal) to the switch elements SW51 to SW58 are a vertical synchronization signal Vd composed of a simple and well-known logic circuit such as a counter and a shift register. And a horizontal control signal Hd.

When such lighting control signals S51 to S58 are applied to the switch elements SW51 to SW58, the discharge lamps 41 to 48 are turned on / off at the timing of the waveforms shown by the lamps 41 to 48 in FIG. That is, during a period in which the inverter output is intermittently OFF (shown as a gap in the figure), all the discharge lamps are in the OFF state, and only the discharge lamps to which the lighting control signal is applied to the switch elements are lit. Generally, as shown in FIG. 3, when a voltage equal to or higher than the lighting voltage Vd is applied between the terminals of the discharge lamp, the discharge lamp starts to discharge and the discharge current increases to emit light. The inverter output is applied to the discharge lamps connected to the same inverter at the same time, but the discharge lamp connected to the switch element to which the lighting control signal (ON signal) is applied is first out of the four switch elements connected to the same inverter. When the discharge current Is reaches the lighting voltage Vd and the discharge current Is increases and the light is emitted, the voltage between the terminals of the discharge lamp, that is, the inverter output, decreases as shown in the figure, and the other discharge lamps connected to the same inverter do not reach the lighting voltage and do not light. When the inverter output is output in this way, the lighting control signal (ON) of the four switches connected to the same inverter is output.
Only the discharge lamp connected to the switch element to which the signal (signal) is applied stably emits light. Looking at the discharge lamps L41 to L44 connected to the inverter 3A and the discharge lamps 45 to 48 connected to the inverter 3B, only one lamp is turned on at a certain moment, and the output capacity of each inverter is equivalent to one discharge lamp. Will be good.

Second Embodiment A second embodiment will be described with reference to FIG. The pulse signal applied to the switch elements SA and SB of the inverter according to the first embodiment is applied to a horizontal scanning period (1 V cycle) of one frame on the display screen of the liquid crystal display panel as shown in FIG.
Are composed of four pulse signals whose phases are shifted from each other by a half wavelength. The inverters 3A and 3B receiving the pulse signals SA and SB generate high-frequency output signals indicated by inverter outputs A and B, respectively. Switch elements SW51 to SW51 connected to discharge lamps L41 to L48
SW58 has inverter outputs A and B with respect to S51 to S51 in the figure.
At the timing shown in S58, a lighting control signal having a rectangular wave shape (the same as in the first embodiment) is applied. The mutual timing at which these lighting control signals are applied, that is, the ON / OFF operation, is the same as in the first embodiment, but the pulse width of the lighting control signal is set to be equal to the output period of each inverter output A and B. This is different from the first embodiment. Each switch S
A, the pulse signal to SB and switch element SW51
The lighting control signal (ON / OFF signal) to SW58
Is generated by a lighting control signal generating circuit 6 which receives a vertical synchronizing signal Vd and a horizontal synchronizing signal Hd which are composed of simple and well-known logic circuits such as a counter and a shift register. When the lighting control signals S51 to S58 as shown in FIG. 4 are applied to the switch elements SW51 to SW58,
The discharge lamps 41 to 48 are turned on / off at the timing of the waveforms shown by the lamps 41 to 48 in FIG. In this case, the lighting of each discharge lamp is continuous unlike the case of FIG.
This is convenient when it is necessary to turn off the output of the inverter for a long time to turn off the lamp.

In the embodiment according to the present invention, as shown in FIG. 5, eight discharge lamps (L41 to L48) are arranged in the vertical direction, and eight blocks (B1 to B) of the corresponding liquid crystal display panel are provided.
8) There are blocks B1 to B8 in the period T of the vertical synchronization signal.
And the same operation is performed, but the number of blocks of the liquid crystal panel becomes eight, and the time difference between the write timings of the upper and lower lines in the block is smaller than that of the conventional case where there are four blocks as shown in FIG. For example, when focusing on the top block B1, the response of the liquid crystal in the upper line and the lower line is the response characteristic B1 of the LCD.
-U and B2-U. As shown by the lamp 41 in the figure, the discharge lamp 41 corresponding to the block B1 is turned on with a delay of time Td from the write start timing of the block B1, and is turned off immediately before the write timing of the next frame. The lighting time is Tw and the duty is about 1/4. Block B as can be seen from FIG.
Although the response at the lower end is not perfect compared to the upper end of 1,
As a result, the discharge lamp is turned on in a considerably better response state as compared with the conventional case, and the luminance unevenness in the vertical direction of the screen is greatly reduced. Further, since the brightness depends on the duty, it is the same as that of the first embodiment shown in FIG. In addition, by synchronizing with the timing of starting writing of the block and delaying the timing to the optimal timing of the response characteristic of the liquid crystal, blurring of a moving image can be particularly improved.

Embodiment 3 In the embodiment of FIG. 1, the case where the number N of inverters is 2 is shown. However, when the number of blocks is increased by setting N to 2 or more, the same duty, that is, brightness is changed. The difference in the response of the liquid crystal between the upper end and the lower end in the block can be reduced, and the luminance unevenness on the screen can be greatly improved.

Embodiment 4 FIG. 6 is a block diagram showing Embodiment 4 of the present invention. In this embodiment, an impedance element 61 is inserted in parallel with each of the switch elements SW51 to SW58 shown in the first embodiment of FIG. With this configuration, each of the switch elements SW51 to SW58 applied at the start of the discharge
Can be reduced.

[0023]

According to the liquid crystal display device of the first configuration of the present invention, a switch for controlling the output of the plurality of discharge lamps connected to the plurality of inverters and a switch element for controlling the lighting of the discharge lamps are provided. The display performance, in particular, the luminance unevenness in the vertical direction of the screen can be greatly improved by stably scanning and lighting the discharge lamp using.

According to the liquid crystal display device of the second configuration of the present invention, the scanning lighting of the discharge lamp is synchronized with the writing timing of the liquid crystal display panel, and the scanning lighting timing of the corresponding discharge lamp is delayed for a predetermined time. In particular, blurring of moving images can be significantly improved.

According to the liquid crystal display device of the third configuration of the present invention, the discharge lamps are lit by scanning while the adjacent discharge lamps partially overlap with each other in time, so that the display performance, particularly in the vertical direction of the screen, is improved. Luminance unevenness and blurring of a moving image can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing Embodiment 1 of the present invention.

FIG. 2 is a timing chart showing an operation of the first embodiment of the present invention.

FIG. 3 is a lighting characteristic diagram showing VI characteristics of the discharge lamp used in the first embodiment of the present invention.

FIG. 4 is a timing chart showing the operation of the second embodiment of the present invention.

FIG. 5 is a timing chart showing a response of a liquid crystal and a lighting operation of a discharge lamp according to the first embodiment of the present invention.

FIG. 6 is a configuration diagram showing a third embodiment of the present invention.

FIG. 7 is a configuration diagram showing a backlight portion in a conventional liquid crystal display device.

FIG. 8 is a timing chart showing a response of a liquid crystal and a lighting operation of a discharge lamp in a conventional liquid crystal display device.

[Explanation of symbols]

1 lighting control signal generation circuit, SA, SB switch, 3
A, 3B inverter, L41-L48 discharge lamp,
SW51 to SW58 Switch elements.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Akimasa Yuki 2-3-2 Marunouchi, Chiyoda-ku, Tokyo F-term (reference) 2H093 NA41 NC22 NC27 NC42 NC49 ND47 ND60 5C006 AB05 AF63 AF69 AF71 BF03 BF27 BF49 EA01 FA16 FA25 FA34 FA51 5C080 AA10 BB05 DD05 DD27 DD30 EE28 EE32 JJ02 JJ04 JJ05 KK02 KK43

Claims (3)

[Claims] A liquid crystal display having a liquid crystal display panel;
In a liquid crystal display device having a discharge lamp and a discharge lamp scan lighting section for illuminating the liquid crystal panel, the discharge lamp scan lighting section includes a plurality of inverters each having a switch for turning on / off an output, and an output transformer of each inverter. A plurality of discharge lamps provided on the secondary side, switch elements connected in series to the discharge lamps, and a lighting control signal for sequentially lighting the discharge lamps by sequentially turning on / off the switch elements. A liquid crystal display device comprising a lighting control signal generating circuit that generates the light. 2. The method according to claim 1, wherein the ON / OFF of the switch is set so that the scanning lighting of the discharge lamp is synchronized with the writing timing of the liquid crystal display panel and the scanning lighting timing of the corresponding discharge lamp is delayed for a predetermined time. The liquid crystal display device according to claim 1. 3. The switching device according to claim 1, wherein the discharge lamps adjacent to each other partially overlap with each other in time so as to perform scanning lighting.
3. The liquid crystal display device according to claim 1, wherein N / OFF is set.