GB2436180A

GB2436180A - Dynamic element matching stage for DAC

Info

Publication number: GB2436180A
Application number: GB0701858A
Authority: GB
Inventors: Anthony James Magrath
Original assignee: Wolfson Microelectronics PLC
Current assignee: Cirrus Logic International UK Ltd
Priority date: 2007-01-31
Filing date: 2007-01-31
Publication date: 2007-09-19
Anticipated expiration: 2027-01-31
Also published as: GB2436180B; GB0701858D0; GB2436180A9

Abstract

The backlight unit 400 comprises a reflector 420 having a plurality of grooves or recesses with an inclined inner circumference, and a plurality of light emitting diodes 430 formed at or in the grooves 423. The groove openings and their lower surfaces may be circular or polygonal. Light emitted by LEDs 430 is reflected upwards at the inner circumference of the groove. The backlight unit supplies light to the LCD panel 460. The unit also comprises a heat sink, light diverter 435 and diffuser plate 447.

Description

I

M&C Folio: GBP94961 24361 80

ACKLIGHT UNIT AND LIOIJJD CRYSTAL DISPLAY DEVICE HAVTNG THE

SAME

BACKLIGHT UNIT AND LIQUID CRYSTAL DISPLAY DEVICE HAVING THE

SAME

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a backlight unit and a liquid crystal display (LCD) device, and more particularly, to a backlight unit capable of enhancing a brightness and an LCD device having the same.

2. Description of the Background Art

Generally, a liquid crystal display (LCD) device among flat panel display devices has been widely applied to a notebook, a monitor, a television, a spaceship, an airplane, etc. The LCD device is largely divided into a LCD panel, a driving circuit unit, and a backlight unit.

The driving circuit unit comprises each kind of circuit device, a printed circuit board (PCB), etc., and the backlight unit comprises a light emitting lamp, each kind of sheet, a supporting mold, etc. The backlight unit is an optical source of the LCD device, and has a maximum power consumption among the components of the LCD device.

Therefore, it is an important for the backlight unit to emit bright light with minimum power. Also, light having the same brightness has to be supplied onto a surface of an LCD panel of a certain size by using a linear optical source such as a fluorescent lamp for a uniform brightness.

Recently, a point optical source such as a light emitting diode (LED) is being used to supply light having the same brightness to a surface of the LCD panel of a certain size.

Hereinafter, the conventional backlight unit for an LCD device to which a point optical source such as an LED has been applied will be explained with reference to FIGS. I to 3.

FIG. I is a sectional view schematically showing an LCD device having a backlight unit in accordance with the conventional art.

As shown, the conventional LCD device having a backlight unit comprises an LCD panel 360 on which pixels are arranged in a matrix form, and a backlight unit 300 for supplying light to the LCD panel 360.

Herein, the LCD panel 360 comprises a thin film transistor (TFT) array substrate (not shown), a color filter substrate (not shown) facing the TFT array substrate with a certain gap, and a liquid crystal layer (not shown) interposed between the color filter substrate and the TFT array substrate.

Although not shown, a common electrode and a pixel electrode are respectively formed at the color filter substrate and the TFT array substrate, thereby applying an electric field to the liquid crystal layer.

The backlight unit comprises a lower cover 350, a light emitting diode (LED) supporter 310 formed on an upper surface of the lower cover 350, a plurality of LEDs 330 arranged on an upper surface of the LED supporter 310 for emitting light in horizontal and vertical directions, a light guiding plate 340 arranged above the LED 330 with a certain gap, a diffusion plate 347 arranged on the light guiding plate 340 for effectively diffusing light emitted from the LED 330, and a plurality of optical sheet layers 349 on the diffusion plate 347. A reflector 320 for enhancing an efficiency of light emitted from the LED is formed at a lower portion of the LED 330.

The light guiding plate 340 is provided at an entire surface of the backlight unit so that light emitted from the LED 330 can be uniformly distributed on the entire surface of the backlight unit.

A diverter 335 for a color mixing of light perpendicularly emitted from the LED 330 is formed at a lower surface of the light guiding plate 340 corresponding to each LED 330. Single-color light emitted from the LED 330 in a perpendicular direction is not directly displayed on the LCD panel by the diverter 335.

The LCD panel 360 and the backlight unit 300 are covered by a guide panel 351, and the covered side surfaces of the LCD panel 360 and the backlight unit 300 are supported by a mold frame 345.

An upper edge of the LCD panel 360 is fixed by a top case 370, the top case 370 is coupled to the guide panel 351, and the guide panel 351 is coupled to the mold frame 345.

FIG. 2 is a sectional view showing a structure of a backlight unit in accordance with the conventional art.

As shown, the conventional backlight unit comprises a lower cover 210, a plurality of LEDs 220 arranged on the lower cover 210 with a certain gap therebetween a light guiding plate 230 formed above the LEDs 220 with a certain distance, and a plurality of diverters 235 having a prism structure or formed of a reflective material at positions corresponding to the LEDs 220. The diverter 235 prevents light Perpendicularly emitted from the LED 220 from being directly displayed on the LCD panel, and is used for a color mixing.

In the conventional backlight unit, light emitted from the LED is not utilized to the maximum thereby to cause an inferior brightness. Thus, as shown in FIG. 3, when power is supplied to the conventional LED, approximately 20% of a total optical amount is emitted in a vertical direction 12, and approximately 80% of the total optical amount is emitted in horizontal directions 14 and 16.

As aforementioned, in the conventional backlight unit and the LCD device having the same, light emitted from side surfaces of the LEDs of the backlight unit is not effectively utilized thereby to cause a brightness decrease.

Furthermore light emitted from the side surfaces of the LEDs of the backlight unit influences on even a peripheral region, so that the backlight unit is not smoothly operated.

BRIEF DESCRIPTION OF THE INVENTION

Therefore an object of the present invention is to seek to provide a backlight unit capable of enhancing brightness and being smoothly driven by comprising a reflector having a plurality of grooves of an inclined inner circumference and a plurality of light emitting diodes formed at the grooves, and a liquid crystal display (LCD) device having the same.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a backlight unit for an LCD device, comprising: a reflector having a plurality of grooves at an upper surface thereof; and a plurality of LEDs formed at the grooves.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is also provided an LCD device, comprising: an LCD panel; and a backlight unit for supplying light to the LCD panel, in which the backlight unit comprises a reflector having a plurality of grooves at an upper surface thereof, and a plurality of LEDs formed at the grooves.

The plural grooves formed at the reflector upwardly reflect light emitted from side surfaces of the plural LEDs, thereby enhancing an optical efficiency.

The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.

In the drawings: FIG. 1 is a sectional view schematically showing a liquid crystal display (LCD) device having a backlight unit in accordance with the conventional art; FIG. 2 is a sectional view showing a structure of a backlight unit in accordance with the conventional art; FIG. 3 is a sectional view schematically showing a direction of light emitted from a light emitting device applied to the backlight unit in accordance with the conventional art; FIG. 4 is a sectional view schematically showing an LCD device having a backlight unit according to the present invention; FIG. 5 is a plan view schematically showing a reflector of the backlight unit and light emitting diodes formed at the reflector according to a first embodiment of the present invention; FIG. 6 is a sectional view schematically showing the reflector of the backlight unit and the light emitting diodes formed at the reflector according to a first embodiment of the present invention; FIG. 7 is a plan view schematically showing various arrangements of the light emitting diodes formed at the reflector of the backlight unit according to a first embodiment of the present invention; and FIG. 8 is a plan view schematically showing a reflector of the backlight unit and light emitting diodes formed at the reflector according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

Hereinafter, a backlight unit and a liquid crystal display (LCD) device having the same wilt be explained with reference to FIGS. 4 to 7.

FIG. 4 is a sectional view showing an LCD device having a backlight unit according to the present invention.

As shown, the LCD device according to the present invention comprises an LCD panel 460 on which pixels are arranged in a matrix form, and a backlight unit 400 formed at a lower surface of the LCD panel 460.

Although not shown, the LCD panel 460 comprises a thin film transistor (TFT) array substrate, a color filter substrate facing the TFT array substrate with a certain gap, and a liquid crystal layer interposed between the color filter substrate and the TFT array substrate.

A common electrode and a pixel electrode are respectively formed at the color filter substrate and the TFT array substrate, thereby applying an

electric field to the liquid crystal layer.

If a voltage of a data signal is applied to the pixel electrode under a state that a voltage has been applied to the common electrode, an electric field is formed between the common electrode and the pixel electrode. Also, the liquid crystal of the liquid crystal layer is arranged according to the electric field.

The LCD device displays an image by controlling an optical transmittance according to each pixel by an anisotropy of the liquid crystal molecules.

A switching device such as a thin film transistor is provided at each pixel in order to control a voltage of a data signal applied to the pixel electrode, which is called as an active matrix driving method.

The backlight unit 400 comprises a lower cover 450, a light emitting diode (LED) supporter 410 formed on an upper surface of the lower cover 450, reflectors 420 formed on an upper surface of the LED supporter 410 and having a plurality of grooves of an inclined inner circumference, a plurality of LEDs 430 arranged at the plural grooves for emitting light in horizontal and vertical directions, a light guiding plate 440 arranged above the reflector 420 with a certain gap for uniformly distributing light to an entire surface of the backlight unit, a diffusion plate 447 arranged on the light guiding plate 430 for effectively diffusing light emitted from the LEDs 430, and a plurality of optical sheet layers 449 on the diffusion plate 447.

A diverter 435 for a color mixing of light emitted from the LEDs 430 is formed at a lower surface of the light guiding plate 440 in correspondence to each LED 430. Single-color light emitted from the LED 430 in a perpendicular direction is not directly displayed on the LCD panel by the diverter 435.

A heat sink formed of an aluminum for removing heat generated when the LEDs 430 emit light is attached to a rear surface of the lower cover 450.

The LCD panel 460 and the backlight unit 400 are covered by a guide panel 451, and the covered side surfaces of the LCD panel 460 and the backlight unit 400 are supported by a mold frame 445.

An upper edge of the LCD panel 460 is fixed by a top case 470, the top case 470 is coupled to the guide panel 451, and the guide panel 451 is coupled to the mold frame 445.

Hereinafter, the backlight unit will be explained in more detail with reference to FIGS. 5 to 7.

FIG. 5 is a plan view showing a reflector of the backlight unit and light emitting diodes formed at the reflector according to a first embodiment of the present invention, FIG. 6 is a sectional view showing the reflector of the backlight unit and the light emitting diodes formed at the reflector according to a first embodiment of the present invention, and FIG. 7 is a plane view showing various arrangements of the light emitting diodes formed at the reflector of the backlight unit according to a first embodiment of the present invention.

As shown in FIGS. 5 and 6, the backlight unit comprises a reflector 420 having a plurality of grooves with an inclined inner circumference, and a plurality of light emitting diodes 430 formed at or in the respective grooves.

Each lower surface and each opening of the grooves formed at the reflectors 420 have a polygonal shape or a circular shape. Preferably, the opening or mouth of the groove is larger than the lower surface of the groove.

For instance, the lower surface and the opening of the groove have a polygonal shape such as a triangular shape, a rectangular shape, a hexagonal shape, etc., and a circular shape. An inner circumferential surface of the groove is inclined by an angle of 10_900 from the lower surface of the reflector 420, and the groove has a height less than 40mm.

Direction of light emitted from the LED 430 will be explained as follows.

Light emitted from the LED 430, especially emitted from a side surface of the LED 430 is reflected to the inner circumferential surface of the groove of the reflector 420 thus to be upwardly guided.

Light emitted from a side surface or a frontal surface of the LED 430 is reflected by the diverter 435. Then, the light is reflected to an inner circumferential surface or a lower surface of the reflector 420 thus to be upwardly guided.

Since light emitted from a side surface of the LED 430 is upwardly guided, a frontal brightness of the LCD device is increased.

The LEDs 430 respectively positioned at or in the grooves of the reflector 420 can have various shapes. For instance, as shown in FIG. 7, the LEDs 430 can have a straight shape, a triangular shape, a rectangular shape, a diamond shape, an X shape, or a combination thereof in which each shape is formed in plural. Preferably, the light emitting devices 430 are light emitting diodes (LED), and the LED is a red diode, a green diode, a brown diode, a white diode, etc. The plural grooves formed at the reflector 420 can have various shapes, such as a horizontal/vertical shape or a zigzag shape.

FIG. 8 is a plan view showing a reflector of the backlight unit and light emitting diodes formed at the reflector according to another embodiment of the present invention. FIG. 8 shows a reflector 520 having a plurality of grooves 523 in a zigzag form and a plurality of LEDs 530 formed at the reflector 520. The groove 523 formed at the reflector 520 can have various shapes as well as a square prism. Also, the LEDs 530 arranged at the grooves can have various shapes as well as a cross shape.

In the backlight unit and the LCD device having the same, light emitted from side surfaces of the LEDs 530 is upwardly guided by the reflector 520, and the guided light is reflected through the light guiding plate 430, the diffusion plate 447, and the optical sheet layers 449. Also, light emitted from the LED 530 in a perpendicular direction is guided into a horizontal direction by a diverter (not shown) formed on the reflector 520, and then is reflected through a light guiding plate, a diffusion plate, and a plurality of optical sheet layers (not shown).

Since light emitted from the side surfaces of the LEDs 530 or light emitted from the LEDs 530 in a perpendicular direction is totally reflected, the light is uniformly transmitted to the entire LCD panel.

Furthermore, since light emitted from the side surfaces of the LEDs 530 does not influence on peripheral regions, the backlight unit can be smoothly driven.

Preferably, the light emitting devices are point optical sources, such as light emitting diodes (LEDs). The LED is a red diode, a green diode, a brown diode, a white diode, etc. As aforementioned, in the backlight unit and the LCD device having the same according to the present invention, light emitted from the side surfaces of the LEDs is efficiently utilized thereby to enhance a brightness of the backlight unit.

Furthermore, since light emitted from the side surfaces of the LEDs is collected so as not to impinge on peripheral regions, the backlight unit can be smoothly driven.

As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalents of such metes and bounds are therefore intended to be embraced by the appended claims.

Claims

CLAIMS

1. A backlight unit for a liquid crystal display (LCD) device, comprising: a reflector having a plurality of grooves at an upper surface thereof; and a plurality of light emitting diodes (LEDs) formed at or in the grooves.

2. A backlight unit according to claim 1, wherein the LEDs are point optical sources.

3. A backlight unit according to claim I or claim 2, wherein a lower surface and an opening of the groove have a polygonal shape or a circular shape.

4. A backlight unit according to any preceding claim, wherein an inner circumferential surface of the groove is inclined by an angle of 10-90 from the lower surface of the reflector.

5. A backlight unit according to any preceding claim, wherein the groove has a height less than 40mm.

6. A backlight unit according to any preceding claim, wherein the grooves are arranged inhorizontal and vertical directions.

7. A backlight unit according to any of claims I to 5, wherein the grooves are arranged in a zigzag form.

8. A backlight unit according to any preceding claim, further comprising: a light guiding plate formed above the reflector; and a plurality of diverters formed at a lower surface of the light guiding plate in correspondence to the LEDs.

9. A liquid crystal display (LCD) device, comprising: an LCD panel; a reflector having a plurality of grooves at or in an upper surface thereof; and a plurality of LEDs formed at the grooves for supplying light to the LCD panel.

10. An LCD device according to claim 9, wherein the LEDs are point optical sources.

11. An LCD device according to claim 9 or claim 10, wherein a lower surface and an opening of the groove have a polygonal shape or a circular shape.

12. An LCD device according to any of claims 9 to 11, wherein an inner circumferential surface of the groove is inclined by an angle of 10-90 from the lower surface of the reflector.

13. An LCD device according to any of claims 9 to 12, wherein the grooves have a height less than 40mm.

14. An LCD device according to any of claims 9 to 13, wherein the grooves are arranged in horizontal and vertical directions.

15. An LCD device according to claim 9, wherein the grooves are arranged in a zigzag form.

16. An LCD device according to any of claims 9 to 15, further comprising: a light guiding plate formed above the reflector; and a plurality of diverters formed at a lower surface of the light guiding plate in correspondence to the LEDs.

17. A backlight unit for a liquid crystal display (LCD) device, comprising a reflector having a plurality of grooves in an upper (as viewed) surface thereof, and light emitting diode means mounted in each groove.

18. An LCD device, comprising an LCD panel and a backlight unit according to claim 17.

19. A backlight unit for a liquid crystal display (LCD) device, substantially as hereinbefore described with reference to Figs 4 to 8 of the accompanying drawings.

20. A liquid crystal display (LCD) device, substantially as hereinbefore described with reference to Figs. 4 to 8 of the accompanying drawings.

AMrE! CLAIMS 1. A digital-to-analogue converter, comprising: a plurality of pairs of digital-to-analogue converter elements; and an adder, connected to form an analogue output signal as the sum of the outputs of the pairs of digital-to-analogue converter elements; and further comprising: an element matching circuit, connected to receive a digital input signal, and apply respective inputs to the pairs of digital-to-analogue converter elements, wherein the element matching circuit comprises a dynamic element matching stage associated with each of the pairs of digital-to-analogue converter elements, and wherein each dynamic element matching stage comprises: an input for a respective stage remainder value, the remainder value having a parity determined by a value of a least significant bit thereof; first and second quantizers, for forming a pair of quantizer outputs, a sum of said quantizer outputs being constrained to be equal to the panty of the remainder value; first and second feedback loops, associated with the first and second quantizers respectively, for forming respective first and second loop values and applying said loop values as inputs to the first and second quantizers respectively, and at least one integrator, for producing an output signal based on at least one of the quantizer outputs during time periods when said first and second loop values are substantially equal, wherein, during subsequent time periods when said first and second loop values are substantially equal, said quantizer outputs are controlled based :... on the output signal of the at least one integrator. * S 555.

* * 25
2. A digital-to-analogue converter as claimed in claim 1, wherein the at least one integrator produces an output signal based on the numbers of positive and negative *: quantizer output values during time periods when said first and second loop values are :. substantially equal, and wherein the quantizers are controlled to produce quantizer * outputs having substantially equal numbers of positive and negative values. S.. * 30

3. A digital-to-analogue converter as claimed in claim 2, comprising: a first integrator, for counting a difference between a number of outputs of the first quantizer produced with positive values and a number of outputs of the first quantizer produced with negative values, during time periods when said first and second loop values are substantially equal; and a second integrator, for counting a difference between a number of outputs of the second quantizer produced with positive values and a number of outputs of the second quantizer produced with negative values, during time periods when said first and second loop values are substantially equal.

4. A digital-to-analogue converter as claimed in claim 1, wherein the at least one integrator produces an output signal based on quantizer error values during time periods when said first and second loop values are substantially equal, and wherein, when said first and second loop values are substantially equal, a quantization error Is measured, and the quantizers are controlled to minimize said quantization error.

5. A digital-to-analogue converter as claimed in claim 4, wherein said at least one integrator forms an integrated value of a difference between a quantizer output and a quantizer input for one of said quantizers.

6. A method of operation of a digital-to-analogue converter, wherein the digital-to-analogue converter comprises: a plurality of pairs of digital-to-analogue converter elements; and an adder, connected to form an analogue output signal as the sum of the outputs of the pairs of digital-to-analogue converter elements; an element matching circuit, connected to receive a digital input signal, and apply * respective inputs to the pairs of digital-to-analogue converter elements, wherein the : *** element matching circuit comprises a dynamic element matching stage associated with a...

each of the pairs of digital-to-analogue converter elements, and wherein each dynamic * ,, 25 element matching stage comprises: : an input for a respective stage remainder value, the remainder value having a S..

* parity determined by a value of a least significant bit thereof; * first and second quantizers, for forming a pair of quantizer outputs; * first and second feedback loops, associated with the first and second quantizers S..

* 30 respectively, for forming respective first and second loop values and applying said loop values as inputs to the first and second quantizers respectively, the method comprising, in at least one dynamic element matching stage: producing an output signal based on at least one of the quantizer outputs during time periods when said first and second loop values are substantially equal; and during subsequent time periods when said first and second loop values are substantially equal, controlling said quantizer outputs based on said output signal, (S while a sum of said quantizer outputs is constrained to be equal to the parity of the respective stage remainder value.

7. A method as claimed in claim 6, further comprising, when said first and second loop values are substantially equal, controlling the quantizers to produce quantizer outputs having substantially equal numbers of positive and negative values.

8. A method as claimed in claim 7, further comprising: counting a difference between a number of outputs of the first quantizer produced with positive values and a number of outputs of the first quantizer produced with negative values, during time periods when said first and second loop values are substantially equal; and counting a difference between a number of outputs of the second quantizer produced with positive values and a number of outputs of the second quantizer produced with negative values, during time periods when said first and second loop values are substantially equal.

9. A method as claimed In claim 6, further comprising, when said first and second loop values are substantially equal: measuring a quantization error; accumulating the measured quantization errors; and controlling the quantizers to minimize said accumulated quantization error. a...

 10. A method as claimed in claim 9, wherein the step of measuring the quantization * *,. 25 error comprises forming an integrated value of a difference between a quantizer output and a quantizer input for one of said quantizers. a.. a

11. An audio device, comprising a digital-to-analogue converter as claimed in one of claims 1 to 5. * 30

12. An electronic device, including an audio device, and comprising a digital-to-analogue converter as claimed in one of claims I to 5.