JP2008071672A - Illuminating device, and display unit equipped therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an illuminating device capable eliminating occurrence of intereference fringe and waving noise on a display panel, and to provided a display unit equipped therewith. <P>SOLUTION: The illuminating device is provided with a plurality of light sources for lighting a plurality of display regions demarcating a screen of a display panel in a predetermined direction, capable of adjusting luminance of the display screen in the display panel by dimming to control these plurality of light sources in a predetermined period in a PWM dimming mode. Further, the device has an on/off phase control unit generating a plurality of PWM dimming signals with different phases, and the plurality of the PWM dimming signals generated by the on/off phase control unit are used being irregularly distributed to the plurality of light sources. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a lighting device for a display device having excellent image display quality.

  In recent years, liquid crystal display devices have been widely used as display units for home appliances such as computers and televisions. In general, a liquid crystal display device having a transmissive liquid crystal display panel is provided with an illumination device so that the screen is sufficiently bright for an observer.

  In this illuminating device, a fluorescent tube such as a cold cathode tube is widely used as a light source. As a dimming method for these fluorescent tubes, a PWM (Pulse Wide Modulation) method has been conventionally employed. The PWM dimming method is a dimming method that provides a period during which the fluorescent tube is lit and a period during which the fluorescent tube is not lit within a short period called a PWM period. With this method, the amount of light can be adjusted by changing the time ratio (duty rate) between the lighting period and the extinguishing period in the PWM cycle.

  Conventionally, in an illuminating device including a plurality of fluorescent tubes, all the fluorescent tubes are controlled to blink at the same phase in the same PWM cycle by the PWM dimming method. That is, all the fluorescent tubes were turned on at the same time and turned off at the same time. However, when this PWM cycle is close to a multiple of the cycle of the vertical sync signal, which is the cycle of writing video data to the liquid crystal display panel, horizontal stripe noise appears on the screen and flows in the vertical direction, so-called waving noise May occur.

  The occurrence of such waving noise impairs the display quality of the liquid crystal display panel, and conventionally, the PWM cycle has been set so that waving noise does not occur. In addition, the following patent document 1 is mentioned as a prior art document relevant to this invention.

JP 2002-354823 A

  Since this waving noise is caused by interference between the PWM period and the period of the vertical synchronization signal, the generated symptom also changes when the period of the vertical synchronization signal changes or when the duty ratio changes. In other words, when it is used at a specific vertical synchronizing signal cycle, no waving noise occurs, but it may occur when the vertical synchronizing signal cycle is changed. Also, when the user adjusts the brightness, the duty ratio changes, so that waving noise may occur at a certain brightness.

  In the case of using different vertical sync signal periods, the display panel can be adapted to both NTSC and PAL signals for television broadcast display, and the user can select and use the signal method. There are some cases.

  Conventionally, in order to support both the NTSC system signal and the PAL system signal described above, a configuration in which the PWM period is set between the setting suitable for the NTSC system and the setting suitable for the PAL system has been used. It has been. However, with this configuration, waving noise can be made inconspicuous when used by any method, but it is difficult to eliminate it completely.

  Therefore, the problem to be solved by the present invention is to provide an illuminating device that suppresses occurrence of interference fringes and waving noise on a display panel, and a display device including the same.

  In order to solve the above-described problems, an illumination device according to the present invention includes a plurality of light sources that respectively illuminate a plurality of display areas obtained by dividing a screen of a display panel in a predetermined direction. A lighting device capable of adjusting the brightness of a display screen in the display panel by controlling blinking at a constant cycle, and includes a blinking phase control unit that generates a plurality of PWM dimming signals having different phases, and the blinking The gist of the invention is that a plurality of PWM dimming signals generated by the phase control unit are randomly distributed to the plurality of light sources.

  In this case, the plurality of light sources may be divided into a plurality of sets each having adjacent light sources as a set, and the blinking control for the light sources in each set may be the same. The plurality of PWM dimming signals having different phases may be different from each other by an equal angle.

  And it is good to comprise as a display apparatus provided with such an illuminating device.

  According to the illuminating device having the above configuration, the flashing phase control unit that generates a plurality of PWM dimming signals having different phases is provided, and the plurality of PWM dimming signals generated by the flashing phase control unit are provided for a plurality of light sources. Therefore, the light source flickering pattern is less likely to have periodicity. Therefore, even if it is the period of any vertical synchronizing signal of the display panel or adjusted to any brightness, the interference with them is suppressed. As a result, generation of interference fringes on the display panel and generation of waving noise due to vertical movement of the interference fringes can be prevented.

  In this case, if the plurality of light sources are divided into a plurality of sets each having adjacent light sources as a set, and the flashing control for the light sources in each set is the same, an electric circuit used for driving the flashing of the light sources Etc. can be simplified.

  Further, if the plurality of PWM dimming signals having different phases are different from each other by the same angle, the configuration of an electric circuit or the like used for the blinking drive of the light source can be simplified.

  If the lighting device having such a configuration is incorporated into a display device used for a television or the like, even if the period of the vertical synchronization signal is changed from an NTSC signal to a PAL signal, for example, Even if the brightness is adjusted to change the duty factor, the generation of interference fringes on the display panel and the occurrence of waving noise due to the vertical movement of the interference fringes can be prevented.

  Embodiments of a lighting device according to the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of a display device including an illumination device according to the present invention.

  The liquid crystal display panel 1 provided in the illustrated display device 30 is provided with an array substrate 2 made of a glass substrate and a counter substrate 3 facing each other at a predetermined interval via liquid crystal. A common electrode (not shown) is formed on the entire surface of the counter substrate 3.

  The array substrate 2 is provided so that a plurality of pixel signal lines S extending in the vertical direction and arranged in parallel and the scanning lines G extending in the horizontal direction and arranged in parallel intersect each other. ing. In addition, pixel electrodes 4 are respectively formed in the pixel regions partitioned in a matrix by these two wirings. A thin film transistor 5 as a switching element is disposed in the vicinity of the intersection of the two wirings.

  The source electrode of the thin film transistor 5 is connected to the pixel signal line S, and the gate electrode of the thin film transistor 5 is connected to the scanning line G. The drain electrode is connected to the auxiliary capacitor 6 and the pixel electrode 4 facing the liquid crystal 7.

  The pixel signal line S is connected to the source driver 8 and the pixel signal line driving circuit 10, and the scanning line G is connected to the gate driver 12 and the scanning line driving circuit 14. The pixel signal line driving circuit 10 and the scanning line driving circuit 14 are connected to the control circuit 16 and controlled. A display signal of the display screen is supplied to the source driver 8 by the control circuit 16, and a scanning signal is supplied to the gate driver 12 according to the scanning direction 17 by the control circuit 16.

  The video signal is controlled as follows. An external data signal composed of an image display signal, a vertical / horizontal synchronization signal, and a power supply voltage is input to the control circuit 16, and a clock signal or scanning line G for taking data into the source driver 8 based on the vertical / horizontal synchronization signal. A clock signal for switching is generated.

  The source driver 8 starts the operation of the shift register simultaneously with the rising edge of the start pulse, and operates according to the clock. Data input simultaneously with the clock is stored in the sampling memory selected by the shift register, and when display data for all one horizontal line is sent, a latch pulse is output from the control circuit 16. When the source driver 8 receives the latch pulse, the hold memory latches the data stored in the sampling memory all at once. The latched data is D / A converted and output to the pixel signal line S, and an on voltage is applied to one of the scanning lines G, so that all the horizontal rows of the thin film transistors 5 are turned on. Thereby, one line of data is displayed. By repeating this operation in the same manner, the scanning line G is scanned in the vertical direction to drive all the lines.

  On the back surface of the array substrate 2, four direct fluorescent lamps 19 a to 19 d are arranged as backlights. The illustrated direct type fluorescent lamps 19a to 19d are driven with a lighting voltage of 800 Vrms to 1500 Vrms and a lighting frequency of 30 kHz to 60 kHz, for example.

  These lamps 19a to 19d change the time ratio (duty rate) of the lighting period and the extinguishing period in the PWM cycle by a PWM dimming method that provides a period of lighting and a period of non-lighting within a short period called a PWM period. The amount of light is adjusted.

  As shown in the figure, the blinking phase control unit 21 generates a plurality of PWM dimming signals 25 having different phases and supplies the PWM dimming signals 25 to the inverter circuit 23. The inverter circuit 23 supplies an alternating voltage of a predetermined frequency to the lamps 19a to 19d based on the PWM dimming signal 25 from the blinking phase control unit 21, and causes the lamps 19a to 19d to blink at a constant cycle.

  FIG. 2 shows four PWM dimming signals 25 </ b> A to 25 </ b> D generated by the blinking phase control unit 21. As illustrated, the PWM dimming signals 25A to 25D are pulse signals whose phases are different from each other by 90 ° in the period T. That is, with respect to the PWM dimming signal 25A, the PWM dimming signal 25B is shifted by 90 °, the PWM dimming signal 25C is 180 °, and the PWM dimming signal 25D is shifted by 270 °. The period T is, for example, 1/200 second. In this case, the duty ratio of the PWM dimming signals 25A to 25D indicated by the solid line is 25%. The broken line indicates a waveform with a duty factor of 50%, and the alternate long and short dash line indicates a waveform with a duty factor of 75%.

  FIG. 3 shows a configuration in which the four PWM dimming signals 25A to 25D shown in FIG. 2 are irregularly distributed to the lamps 19a to 19d shown in FIG. As illustrated, the PWM dimming signal 25A is used for the lamp 19a, the PWM dimming signal 25C is used for the lamp 19b, the PWM dimming signal 25B is used for the lamp 19c, and the PWM dimming signal 25D is used for the lamp 19d. . That is, the lighting start timing is not sequentially turned on in the order of the lamps 19a to 19d, and is irregular in the order of lamp 19a → lamp 19c → lamp 19b → lamp 19d.

  As described above, the lighting start times of the plurality of lamps are irregularly shifted from each other, so that the blinking patterns of the plurality of lamps are less likely to have periodicity. Accordingly, interference with the period of the vertical synchronizing signal of the liquid crystal display panel 1 is suppressed, and generation of interference fringes on the liquid crystal display panel 1 and generation of waving noise due to vertical movement of the interference fringes are prevented.

  FIG. 4 is a modification of FIG. 3 and shows the waveform of the PWM dimming signal used for blinking the five lamps 19a to 19e with one additional lamp 19e. The solid line shows the waveform when the duty ratio is 20%, and the PWM dimming signals used are pulse signals generated so that the phases differ from each other by 72 °. The wavy line indicates the waveform when the duty ratio is 50%.

  As shown in the drawing, the lighting start time is not sequentially turned on in the order of the arrangement of the lamps 19a to 19e as in the case of FIG. 3, but the lamp 19a → the lamp 19d → the lamp 19b → the lamp 19c → The lamp 19e is irregular.

  Next, the display device 40 shown in FIG. 5 will be described. The display device 40 shown in the drawing is different from the display device 30 shown in FIG. 1 in that the number of direct fluorescent lamps used as a backlight is four, which is doubled to eight. Therefore, the same components as those in FIG. 1 are denoted by the same reference numerals, description thereof is omitted, and different points will be mainly described.

  As shown in the drawing, the eight lamps are driven and controlled by being divided into two sets of upper half lamps 19a to 19d and lower half lamps 20a to 20d. Specifically, the blinking phase control unit 21 generates four PWM dimming signals 25A to 25D as shown in FIG. 2 and outputs them to the upper half lamps 19a to 19d and the lower half lamps 20a to 20d. The inverter circuit 23 and 24 are supplied to each inverter circuit. In addition, two lamps are connected to each of the eight inverter circuits 23 and 24 so that a total of 16 lamps are turned on, eight in the upper half and eight in the lower half. , 24 each with 3 lamps connected to each other so that a total of 24 lamps are lit, 12 in the upper half and 12 in the lower half. It may be configured to connect.

  6 uses the four PWM dimming signals 25A to 25D shown in FIG. 2 in an irregular manner to the upper half lamps 19a to 19d and the lower half lamps 20a to 20d shown in FIG. Shows the configuration. As shown, the PWM dimming signal 25A for the lamp 19a and the lamp 20a, the PWM dimming signal 25C for the lamp 19b and the lamp 20b, the PWM dimming signal 25B for the lamp 19c and the lamp 20c, and the lamp 19d and the lamp 20d. For this, a PWM dimming signal 25D is used. In other words, the lighting start time is not sequentially turned on in the order of the eight lamps 19a to 19d and the lamps 20a to 20d, and the lamp 19a and the lamp 20a → the lamp 19c and the lamp 20c → the lamp 19b and Two lamps are turned on at random, such as lamp 20b → lamp 19d and lamp 20d.

  As described above, even when the plurality of lamps are divided into a plurality of groups each having a group of adjacent lamps, and the blinking control for the lamps in each group is the same, the lighting start timing of the lamps in each group is mutually determined. By irregularly shifting, it becomes difficult for the blinking patterns of the plurality of lamps to have periodicity. Thereby, interference with the period of the vertical synchronizing signal of the liquid crystal display panel 1 is suppressed, and generation of interference fringes on the liquid crystal display panel 1 and generation of waving noise due to vertical movement of the interference fringes are prevented.

  Next, a television receiver provided with the above-described display device will be briefly described. FIG. 7 is an exploded perspective view schematically showing an example of the configuration of a television receiver including the display device 30 according to the above-described embodiment. The television receiver 50 includes a tuner 52 that generates a video signal and an audio signal of a predetermined channel based on a received radio wave and an input signal input from the outside, and a video based on the video signal generated by the tuner 52. The display device 30 includes a loudspeaker 54 that emits sound based on the audio signal generated by the tuner 52, and a power supply substrate 53 that supplies power to the tuner 52, the display device 30, and the loudspeaker 54.

  The tuner 52 may be a conventional general terrestrial (analog, digital, or both) tuner, BS tuner, CS tuner, or the like, and the loudspeaker 54 may be a conventional general loudspeaker such as a general speaker. Applied. Further, the display device 30 is applied with the display device according to the above-described embodiment.

  As shown in FIG. 7, the display device 30, the tuner 52, the loudspeaker 54, and the power supply substrate 53 are housed in a housing constituted by the front cabinet 51 a and the back cabinet 51 b, and are further supported by a stand 55. The By incorporating the display device 30 according to the above-described embodiment into the television receiver 50 having such a configuration, even if the vertical synchronization signal is changed from an NTSC signal to a PAL signal, for example, the user can Even if the duty ratio is changed by adjusting the brightness, it is possible to prevent the occurrence of interference fringes on the display panel and the occurrence of waving noise due to the vertical movement of the interference fringes.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to such embodiment at all, Of course, in the range which does not deviate from the summary of this invention, it can implement in a various aspect. For example, in the above-described embodiment, an example in which four, five, and eight direct fluorescent lamps are provided as the backlight has been described. However, six, seven, nine, ten,. Even in the case where the light source is provided, it is possible to make the light source blinking pattern less likely to have periodicity by irregularly shifting the lighting start timing of the lamps. At this time, as shown in FIG. 5, if a plurality of lamps are divided into a plurality of groups each having a pair of adjacent lamps, and the same flashing control is performed for each group of lamps, the flashing drive is performed. It is possible to simplify the configuration of an electric circuit or the like used in the above.

It is the figure which showed schematic structure of the display apparatus which concerns on embodiment of this invention. It is the figure which showed the waveform of four PWM dimming signals used for the drive of the four lamps of FIG. It is the figure which showed the timing of lighting of the four lamps of FIG. It is the figure which showed the lighting timing at the time of adding one lamp to the four lamps of FIG. It is the figure which showed the modification of the display apparatus of FIG. It is the figure which showed the timing of lighting of the eight lamps of FIG. It is the disassembled perspective view which showed typically the structure of the television receiver with which the display apparatus which concerns on embodiment of this invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid crystal display panel 2 Array substrate 3 Opposite substrate 4 Pixel electrode 5 Thin film transistor 6 Auxiliary capacity 7 Liquid crystal 8 Source driver 10 Pixel signal line drive circuit 12 Gate driver 14 Scan line drive circuit 16 Control circuit 17 Scanning direction 19, 20 Direct type fluorescent lamp Lamp 21 Flashing phase control units 23 and 24 Inverter circuits 25A to 25B PWM dimming signals 30 and 40 Display device 50 Television receiver G Scanning line S Pixel signal line

Claims (4)

  The display panel includes a plurality of light sources that respectively illuminate a plurality of display areas obtained by dividing the screen of the display panel in a predetermined direction, and the plurality of light sources are controlled to blink at a constant cycle by a PWM dimming method. A lighting device capable of adjusting the brightness of a screen, comprising: a blinking phase control unit that generates a plurality of PWM dimming signals having different phases; and a plurality of PWM dimming signals generated by the blinking phase control unit A lighting device characterized in that the light source is irregularly distributed and used.   The lighting device according to claim 1, wherein the plurality of light sources are divided into a plurality of sets each including adjacent light sources, and the blinking control for the light sources of each set is the same.   The lighting device according to claim 1, wherein the PWM dimming signals having different phases are different from each other by an equal angle.   A display device comprising the illumination device according to claim 1.

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