Backlight module and liquid crystal display device using same

A backlight module includes a number of laser units, a number of diffraction units, and a number of diverging units. Each laser unit includes three colored lasers arranged in a first straight line. The three lasers respectively emit red, green, and blue light. Each of the diffraction units includes three diffraction elements. The three diffraction elements are configured to diffract the light along the first straight line. Each of the diverging units is substantially an elongated semi-cylinder, and the longitudinal direction is along the first straight line. The diverging units diffract the three colors of light along a direction which is perpendicular to the direction of the first straight line.

FIELD

The present disclosure is related to backlighting.

BACKGROUND

In a liquid crystal display device, cold cathode fluorescent tubes are generally used as a light source of a backlight module. The color reproduction range of a backlight module using cold cathode fluorescent tubes is only 70%˜85% of the color reproduction range of a cathode ray tube (CRT). It is difficult to reproduce the high quality image for the liquid crystal display device. Therefore, various light sources have been studied to produce a wide reproduction color range. The backlight module using multiple colors (i.e., red, green, blue) light emitting diodes (LEDs) can increase the color reproduction range to 100%. But the lifetimes of different color LEDs are different from each other, it will result in the non-uniform color distribution of a backlight module after a period of use. A light source should have a stable wavelength and light intensity to improve the color reproduction range and non-uniform color distribution.

DETAILED DESCRIPTION

A backlight module to enhance the wide color reproduction range and a liquid crystal display device using the backlight module as a light source is described. The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawing in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean “at least one.”

The backlight module includes a number of laser units, a number of diffraction units, and a number of diverging units. Each of the laser units includes a first laser light source emitting a red light, a second laser light source emitting a green light and a third laser light source emitting a blue light. The first laser light source, the second laser light source, and the third laser light source are arranged along a straight line in a first direction. Each of the diffraction units includes three diffraction elements. The first diffraction element corresponds to the first laser light source and is used to diffract the red light from a point light source to a linear light source with a linear optical field distribution. The second diffraction element corresponds to the second laser light source and is used to diffract the green light from a point light source to a linear light source with a linear optical distribution. The third diffraction element corresponds to the third laser light source and is used to diffract the blue light from a point light source to a linear light source with a linear optical distribution. Each of the diverging units corresponds to a diffraction unit and is substantially an elongated semi-cylinder in shape to match the liner optical field distribution. The longitudinal direction of the diverging unit is along the first direction. The diverging unit is used to diverge the diffracted laser light along a second direction which is perpendicular to the first direction.

According to another aspect of the present disclosure, a liquid crystal display device is provided. The liquid crystal display device includes a backlight module and a liquid crystal display panel. The backlight module includes a number of laser units, a number of diffraction units, and a number of diverging units. Each of the laser units includes a first laser light source emitting a red light, a second laser light source emitting a green light and a third laser light source emitting a blue light. The first laser light source, the second laser light source, and the third laser light source are arranged along a straight line in a first direction. Each of the diffraction units includes three diffraction elements. The first diffraction element corresponds to the first laser light source and is used to diffract the red light from a point light source to a linear optical distribution. The second diffraction element corresponds to the second laser and is used to diffract the green light from a point light source to a linear light source with a linear optical distribution. The third diffraction element corresponds to the third laser and is used to diffract the blue light from a point light source to a linear light source with a linear optical distribution. Each of the diverging units corresponds to a diffraction unit and is substantially an elongated semi-cylinder in shape to match the linear optical field distribution. The longitudinal direction of the diverging unit is along the first direction. The diverging unit is used to diverge the diffracted laser light along a second direction which is perpendicular to the first direction. The liquid crystal display panel receives the light emitted from said diverging units, and said first laser, said second laser, and said third laser are controlled to sequentially turn on or turn off in order. This field sequential method is used to reduce the power consumption and heat generated.

The backlight module according to the present disclosure has a wide color reproduction range and a uniform luminance. In addition, the liquid crystal display device of the present disclosure using the backlight module of present disclosure has a color reproduction range wider than that of the conventional liquid crystal display device. Further, the liquid crystal display device uses a field sequential method to cyclically turn on or turn off the laser light. The power consumption and heat of the liquid crystal display device will be then greatly reduced.

FIGS. 1 and 2respectively show a sectional view and plan view of a first embodiment of a backlight module100. The backlight module100includes a plurality of laser units10, a plurality of diffraction units20, a plurality of reflection units30, a bottom reflection sheet40, a plurality of diverging units50, and a diffusion plate60.FIG. 2shows three laser units10, three diffraction units20, three reflection units30, and three diverging units50, divided into three sets. In addition, the laser unit10, the diffraction unit20, the reflection unit30, and the diverging unit50of each set are arranged in a particular order.

Each laser unit10includes a first laser light source12, a second laser light source14, and a third laser light source16. The first laser light source12emits a collimated red light. The second laser light source14emits a collimated green light. The third laser light source16emits a collimated blue light. The first laser light source12, the second laser light source14, and the third laser light source16are arranged in a straight line along the first direction X, where the first direction X is perpendicular to the surface of the paper on whichFIG. 1is drawn and parallel to the drawing inFIG. 2.

The diffraction unit20is positioned on the light path of a laser unit10. Each diffraction unit20includes a first diffraction element22, a second diffraction element24, and a third diffraction element26. The first diffraction element22corresponding to the first laser light source12diffracts the light emitted by the first laser light source12from a point laser light source to a linear laser light source with a linear optical field distribution; that is, the light is diverged to form a linear laser light source along the first direction X after passing through the first diffraction element22. The second diffraction element24corresponding to the second laser light source14diffracts the light emitted by the second laser light source14from a point laser light source to a linear laser light source with a linear optical field distribution; that is, the light is diverged to form a linear laser light source along the first direction X after passing through the second diffraction element24. The third diffraction element26corresponding to the third laser light source16diffracts the light emitted by the third laser light source16from a point light source to a linear laser light source with a linear optical field distribution; that is, the light is diverged to form a linear laser light source along the first direction X after passing through the third diffraction element26.

The reflection unit30corresponding to a diffraction unit20is located at the side of the diffraction unit20far away from the laser unit10. The reflection unit30reflects the light from a diffraction unit20and laser unit10to a diverging unit50. The reflection unit30can be a reflective mirror or other reflecting element. In other embodiments, the light from a linear laser light source can not be reflected by the reflection unit30. The linear laser light source can be coupled to a diverging unit50after passing through the diffraction unit20.

The reflection sheet40includes a bottom surface42and a reflection surface44. The bottom surface42and the reflection surface44are located on opposite sides of the reflection sheet40. The laser unit10, the diffraction element20, and the reflection unit30are located at the same side of the bottom surface42. The reflection sheet40has a plurality of elongated openings45. The longitudinal direction of each of the elongated openings45is parallel to the first direction X. The reflection unit30faces the elongated openings45.

The diverging unit50can be used as a secondary lens. The diverging unit50corresponding to an elongated opening45is substantially an elongated semi-cylinder to match the linear optical field distribution. The longitudinal direction of the diverging unit50is parallel to the first direction X and the diverging unit50is configured to diverge the diffracted light along a second direction Y which is perpendicular to the first direction X. In present embodiment, the cross-section of the diverging unit50is substantially a semicircle as shown inFIG. 1. The diverging unit50includes an incident surface52and a light output surface54. The incident surface52is a flat surface and the light output surface54is a convex surface. The diverging unit50is carried on the reflection surface44and covers the elongated opening45. Specifically, a part of the incident surface52is in direct contact with the reflection surface44.

The diffusion plate60is positioned above the plurality of diverging units50, and opposite to the reflection surface44and the light output surface54. The light passing through the diffusion plate60becomes a uniform and planar; that is, the diffusion plate60can scatter the light output from the plurality of diverging units50to simulate a uniform and planar light source.

During operation of the backlight module, the collimated light is emitted from the laser unit10(collimated red, green, and blue light), and then passes through the diffraction element20to form a linear laser light source along the first direction X; the linear laser light is then reflected by the reflection unit30and passes through the elongated opening45of the reflection sheet40. The linear laser light thereafter strikes the diverging unit50as incident light from the incident surface52to form a planar light source by diverging the linear light source via the diverging unit50along the second direction Y, wherein the second direction Y is perpendicular to the first direction X. The light emitted from the light output surface54of the diverging unit50has a planar optical distribution. After the planar light passes through the diffusion plate60, the planar light distribution becomes more uniform, that is, the divergent laser light from the diverging unit50has become a uniform and planar light source.

In the present embodiment, the backlight module100uses the diffraction unit20and the diverging unit50to change the light of the laser unit10from a point laser light source to a planar laser light source, so a lesser light source can be applied to the LCD of each unit display area to reduce cost and generated heat. Meanwhile, the backlight module using red, green, and blue laser light provides a wider color reproduction range and a greater clarity and vividness to the display.

FIG. 3shows a liquid crystal display device900in accordance with a first embodiment of the present disclosure. The liquid crystal display device900using the already-described backlight module includes a backlight module100and a liquid crystal display panel900. The backlight module100will not be described again in detail.

The liquid crystal display panel900is located above the diffusion plate60, that is, the liquid crystal display panel900is positioned at a side of diffusion plate60away from the diverging unit50which provides a backlight source for the liquid crystal display panel900. The liquid crystal display panel900includes an array substrate70, a liquid crystal layer90, and a counter substrate80in that order following the diffusion plate60. The liquid crystal layer90is sandwiched between the array substrate70and the counter substrate80.

The array substrate70includes a first transparent substrate72, a plurality of switches (not shown) disposed on the first transparent substrate72, and a plurality of transparent pixel electrodes74. The pixel electrodes74are connected with the plurality of switches. The plurality of switches and the plurality of pixel electrodes74are disposed on the side of the first transparent substrate72facing the liquid crystal layer90. The plurality of switches and the plurality of pixel electrodes74are separately arranged in an array. In the present embodiment, each one of the plurality of switches is formed as a low-temperature poly-crystal silicon (LTPS) thin film transistor (TFT) with a quick response time. The plurality of switches can turn on or turn off quickly. Each one of the plurality of pixel electrodes74is made of indium tin oxide (ITO) or other transparent conductive materials.

The counter substrate80includes a second transparent substrate82and a common electrode84disposed on the second transparent substrate82. The common electrode84is directly formed on the side of the second transparent substrate82toward the liquid crystal layer90. The common electrode84is made of ITO or other transparent conductive materials. The common electrode84is transparent.

The liquid crystal layer90is disposed between the plurality of pixel electrodes74and the plurality of the common electrodes84. The common electrode84is coupled to a reference voltage. The plurality of switches can be turned on or off individually. The voltage level required to turn-on the plurality of switches decides the bias voltage value of the corresponding pixel electrode74. The degree of rotation of the liquid crystal, which is dependent on the voltage difference between the pixel electrode74and the common electrode84, controls the light transmission rate of the pixel area corresponding to the pixel electrode74.

FIG. 4shows a plan view of the liquid crystal display device panel900with a plurality of pixel areas210. Each pixel area210corresponds to a diverging unit50. Light emitted from the laser unit10, diffracted by the diffraction unit20, diverged by the diverging unit50, and diffused by the diffusion plate60, provides a planar backlight light source for a corresponding pixel area210. Each pixel area210includes a plurality of pixels212. Each pixel212corresponds to a pixel electrode74and a switch connected to the pixel electrode74. In addition, each pixel212controls the light transmission rate according to the voltage difference between a corresponding pixel electrode74and the common electrode84, and the grayscale level of the light from pixel212is thus controlled.

During the operation of liquid crystal display device, the first laser light source12, the second laser light source14, and the third laser light source16can be sequentially turned on or turned off according to an alternating control cycle; that is, the laser unit10sequentially alternates in cycles to provide red, green, and blue backlight for a pixel area210. At the same time, all of the pixels212within the same pixel area210pass through the same color light.

Although imperceptible to the human eye, the red, green, and blue light sequentially emitted from the laser unit10individually passes through the pixel212based on the grayscale light predetermined by the pixel212, so that, to the human eye, each pixel212shows a particular color, that is, each pixel212is individually used as a display pixel.

Specifically, the plurality of laser units10are connected to a control system300, for example as shown inFIG. 5. The control system turns on and turns off sequentially and cyclically the first laser light source12, the second laser light source14, and the third laser light source16. When the first laser light source12is turned on and emits red light, and both of the second laser light source14and the third laser light source16are off, all of the pixels212within a pixel area210are turned on, and the red light passes through all of the pixels212. The transmission rate of the red light for each of the pixels within the pixel region210is controlled by a switch301. Similarly, when the second laser light source14is turned on and both of the first laser light source12and the third laser light source16are off, all of the pixels212within a pixel area210are turned on so that the green light passes through all of the pixels212. The transmission rate of the green light for each of the pixels within the pixel region210is then controlled by a switch302. When the third laser light source16is turned on, and both of the first laser light source12and the second laser light source14are off, all of the pixels212within a pixel area210are turned on to make the blue laser light pass through. But the transmission rate of the blue light for each of the pixels within the pixel region210is also controlled by a switch303. Therefore, each pixel of the pixel area210corresponding to a diverging unit50and a laser unit10can sequentially display red, green, and blue color with a predetermined grayscale light level to show a specific color.

In the example ofFIG. 5, the switches301,302, and303pass a frame of selected red (R), green (G), or blue (B) video to conventional matrix de-multiplexing circuitry304that provides a respective transmission value (Tx,y) of voltage to each pixel electrode74. This matrix de-multiplexing circuitry304can be the kind typically found in a black- and white LCD display. For example, the matrix de-multiplexing circuitry samples and holds a new value (Tx,y) of the voltage for each successive frame of red (R), green (G), or blue (B) video.

In the example ofFIG. 5, the control system300operates in response to a clock generator305producing a periodic clock signal at three times the usual color video frame rate. A shift counter306divides the periodic clock signal by three to produce three non-overlapping three-phase clock signals φ1, φ2, φ3, each at the usual frame rate. The first phase clock signal φ1 enables the first switch301and the red lasers307for de-multiplexing and display of a red frame. The second phase clock signal φ2 enables the second switch302and the green lasers308for de-multiplexing and display of a green frame. The third phase clock signal φ3 enables the third switch303for de-multiplexing and display of a blue frame. Therefore the sequential display of the red frame followed by the green frame followed by the blue frame displays a composite color picture similar to that of a conventional color video frame.

The shift counter306includes a first delay flip-flop311, a second delay flip-flop312, a third delay flip-flop313, and an AND gate314providing feedback from the Q bar outputs of the first and second delay flip-flops311,312to the D input of the first delay flip flop311. The control system300includes an additional inverter315and AND gates317,318,319responsive to the periodic clock signal from the clock generator305for ensuring that for each red, green, or blue frame, the video data is first transmitted to the pixel electrodes74, then there is a first duration of time for the LCD to respond to the new voltages on the pixel electrodes (when the signal from the clock305is a logic low and the lasers are turned off), and then the lasers of the respective frame color are turned on for a second duration of time (when the signal from the clock305is a logic high). At the end of the frame, the lasers are turned off, and the shift counter306is incremented to begin control of a next red, green, or blue video frame.

A control sequence of the control system300is shown inFIG. 6. In a first box401, respective red signals are switched onto the LCD pixel electrodes. Then, in box402, the control system waits a first duration of time for the LCD to respond to the red signals. Then, in box403, the red lasers are turned on. Then, in box404, red light is emitted from the LCD pixels for a second duration of time. Then, in box405, the red lasers are turned off. Next, in box406, respective green signals are switched onto the LCD pixel electrodes. Then, in box407, the control system waits the first duration of time for the LCD to respond to the green signals. Then, in box408, the green lasers are turned on. Then, in box409, green light is emitted from the LCD pixels for the second duration of time to display a green video frame. Then, in box410, the green lasers are turned off. Next, in box411, respective blue signals are switched onto the LCD pixel electrodes. Then, in box412, the control system waits the first duration of time for the LCD to respond to the blue signals. Then, in box413, the blue lasers are turned on. Then, in box414, blue light is emitted from the LCD pixels for the second duration of time to display a blue video frame. Then, in box415, the blue lasers are turned off. Then control returns to box401to repeat another cycle of the control sequence.

Preferably, the plurality of laser units10can alternately and sequentially turn on the first laser light source12, the second laser light source14, and a third laser light source16in that same order for each cycle. The plurality of the laser units10can each have a different order of turning on in the alternating cycle. For example, one laser unit10can first turn on the first laser light source12, and then open the second laser light source14, and finally open the third laser light source16. Another laser unit10can first turn on the third laser light source16, and then turn on the second laser light source14, and finally turn on the first laser light source12.

In the present embodiment, the backlight module100of the liquid crystal display device900can turn on the first laser light source12, a second laser light source14, and the third laser light source16according to the alternating sequence of each cycle. The red laser light, the green laser light, and the blue laser light are sequentially, alternately, and cyclically passed through each pixel212in accordance with a predetermined order of the grayscale light levels to display specific colors. Thus, the liquid crystal display panel900of the liquid crystal display device900does not require color filters. Since the red, green, and blue laser light are sequentially turned on and passed through each pixel212, the pixel212does not need to be divided into three dedicated sub-pixels for each pixel; thus, the number of switches for the array substrate70can be reduced to one third of that for a conventional array substrate and can greatly improve the aperture ratio of the liquid crystal display panel.

In other embodiments, as the liquid crystal display device operates, the control system is also able to make a laser unit10emit a single color or composite light according to the display requirement, so that a pixel area210can be used as a display pixel. For example, the first laser light source12and the second laser light source14can be turned on at the same time, and the third laser light source16can be turned off. The red light emitted from the first laser light source12and the green light emitted from the second laser light source14are mixed to provide a color of light for a pixel area210. All of the pixels212within the pixel area210, to the human eye, shown yellow. Therefore, each pixel area210can be used as a display area, especially for a large-size liquid crystal display device. The size of each pixel within a pixel area can be increased to reduce the number of individual pixels in the pixel area, this can also reduce the number of the switches corresponding to the pixels.