WO2007145440A2

WO2007145440A2 - Method for controlling screen brightness and apparatus for flat-panel display thereof

Info

Publication number: WO2007145440A2
Application number: PCT/KR2007/002700
Authority: WO
Inventors: Seong Hwan Kim
Original assignee: Lg Electronics Inc.
Priority date: 2006-06-12
Filing date: 2007-06-04
Publication date: 2007-12-21
Also published as: KR20070118366A; WO2007145440A3; KR100875420B1

Abstract

A method of adjusting brightness and flat panel display implementing the same are disclosed. The present invention includes adjusting the brightness into a predetermined step value according to a user input, deciding whether the adjusted predetermined step value is below a step value of a reference value, if the adjusted predetermined step value is below the step value of the reference value, finding a difference between the step value of the reference value and the step value of the adjusted brightness, and varying a contrast step value of the screen. Accordingly, error of wavy noise is removed in a brightness adjusting process, whereby an LCD provides a clearer image. And, a variable range of brightness can be maintained at a related art level while wavy noise is prevented.

Description

METHOD FOR CONTROLLING SCREEN BRIGHTNESS AND APPARATUS FOR FLAT-PANEL DISPLAY THEREOF

TECHNICAL FIELD The present invention relates to a flat panel display, and more particularly, to a method of adjusting brightness and flat panel display implementing the same. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for preventing screen noise in adjusting the brightness.

BACKGROUND ART

Generally, a flat panel display has features of lightweight, slim shape, low power consumption, and the like and expanding its applied fields. To keep up with the expansion, the flat panel displays are used for office automation devices, audio/video devices, etc.

For representative examples of the flat panel displays, there are LCD (liquid crystal display) , PDP (plasma display panel) , OLED (organic light emitting diode) , etc.

LCD, which is one of the above-explained flat panel displays, displays a specific color on a screen in a manner of adjusting optical transmissivity of light beam according to a video signal applied to a plurality of control switches arranged in a matrix configuration. Yet, since the LCD is non-self-luminescent device, it needs a light source such as a backlight unit.

So, a halogen cathode fluorescent lamp (HCFL) , a cold cathode fluorescent lamp (CCFL) , or the like is used as a light source for the backlight unit.

In the light sources, the CCFL is a light source tube using cold emission and facilitates low thermal radiation, high luminance, long durability, full color, etc. The CCKL can be classified into a light-guide type, a direct projection type, a reflector type, and the like. In correspondence to a request of LCD, a proper type light source tube is adopted.

As another light source, there exists an internal electrode florescent lamp (IEFL) having electrodes provided within a discharge tube or an external electrode fluorescent lamp (EEFL) having electrodes provided outside a discharge tube. These fluorescent lamps are driven by high voltage AC waveforms.

DISCLOSURE OF THE INVENTION TECHNICAL PROBLEM

However, in the related art LCD monitor and control method thereof, if brightness keeps being lowered, wavy noise is unexpectedly generated from an LCD panel. For instance, if a user adjusts brightness below a specific value in the course of using a TV or an LCD monitor of a computer, wavy noise shown in FIG. 1 is generated. In particular, the wavy noise means a phenomenon that a black bar appears on a screen downwardly if brightness is set to Mark' . For instance, in an LCD monitor employing the CCFL as a backlight, the wavy noise problem may get worse .

TECHNICAL SOLUTION

Accordingly, the present invention is directed to a method of adjusting brightness and flat panel display implementing the same that substantially obviate one or more of the problems due to limitations and disadvantages of the related art.

An object of the present invention is to provide a method of adjusting brightness and flat panel display implementing the same, by which errors of wavy noise can be removed.

Another object of the present invention is to provide a method of adjusting brightness and flat panel display implementing the same, by which a variable range of brightness can be maintained at a related art level despite preventing wavy noise. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims thereof as well as the appended drawings .

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a method of adjusting brightness in a flat panel display, in which the brightness of a screen is adjusted by controlling a backlight lamp, according to the present invention includes the steps of adjusting the brightness into a predetermined step value according to a user input, deciding whether the adjusted predetermined step value is below a step value of a reference value, if the adjusted predetermined step value is below the step value of the reference value, finding a difference between the step value of the reference value and the step value of the adjusted brightness, and varying a contrast step value of the screen.

Preferably, the method further includes the step of if the adjusted predetermined step value is not below the step value of the reference value, adjusting a quantity of a current supplied to the backlight lamp according to the adjusted step value of the reference value.

More preferably, the quantity of the current is adjusted by PWM variation. Preferably, the backlight lamp includes a cold cathode fluorescent lamp (CCFL) .

Preferably, the flat panel display includes an LCD panel having its brightness adjusted by the backlight lamp.

Preferably, the step value of the reference value lies within a range between 70-80% of a maximum brightness step value.

Preferably, the contrast step value of the screen is varied within a range between 65~90% of a maximum step value. Preferably, the contrast step value of the screen is varied in proportion to a predetermined ratio according to the difference between the step value of the reference value and the step value of the adjusted brightness.

To further achieve these and other advantages and in accordance with the purpose of the present invention, a flat panel display having a backlight lamp for adjusting brightness includes a user input unit adjusting the brightness into a predetermined step value according to a user input, a deciding unit deciding whether the adjusted predetermined step value is below a step value of a reference value, and a control unit, if the adjusted predetermined step value is below the step value of the reference value, finding a difference between the step value of the reference value and the step value of the adjusted brightness, the control unit varying a contrast step value of the screen to be proportion to a predetermined ratio according to the found difference.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

ADVANTAGEOUS EFFECTS

The present invention provides the following effects or advantages.

First of all, error of wavy noise is removed in a brightness adjusting process, whereby an LCD provides a clearer image.

Secondly, a variable range of brightness can be maintained at a related art level while wavy noise is prevented. For instance, horizontal noise generated in PWM variable system can be improved while a variable range of brightness and a color quality are maintained as good as those of the related art. DESCRIPTION OF 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 diagram of screen noise on an LCD monitor according to a related art;

FIG. 2 is a block diagram of a flat panel display according to the present invention;

FIG. 3A is a graph of a variation of a dimming frequency dependent on a current of a lamp; FIG. 3B is a graph of another variation of a dimming frequency dependent on a current of a lamp;

FIG. 3C is a graph of a further variation of a dimming frequency dependent on a current of a lamp;

FIG. 4 is a diagram of a progress of a brightness adjusting mode varying per section in an LCD monitor according to the present invention; and

FIG. 5 is a flowchart of a method of adjusting brightness in a flat panel display according to the present invention. BEST MODE

MODE FOR INVENTION

Reference will now be made in detail to a method of adjusting brightness and flat panel display implementing the same according to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings .

An embodiment for preventing screen noise such as wavy noise and the like in an LCD according to the present invention is explained with reference to FIGs. 2 to 4 as follows .

Referring to FIG. 2, a video apparatus 200 according to the present invention includes a user input unit 201, a control unit 202, a PWM controller 203, an inverter 204, an LCD panel 205, a first lamp unit 206, a second lamp unit 107, a video data receiving unit 208, a video processor 209, and a contrast controller 210.

And, the video apparatus 200 shown in FIG. 2 includes an LCD monitor according to the present invention. Moreover, the video apparatus 200 can be a television, a computer, a laptop, an electronic scheduler, or the like, which includes the LCD monitor.

The user input unit 201 receives a command signal for a brightness adjustment, a contrast adjustment or the like from a user and then transfers the received command signal to the control unit 202.

And, the user input unit 201 includes a remote controller, a local key button attached to the video apparatus 200, a local key button attached to the LCD monitor or the like.

The control unit 202 overall controls functions of the respective elements including the PWM controller 203, the video processor 209, the contrast controller 210, and the like, which are provided within the video apparatus 200. The PWM controller 203 varies a dimming frequency under the control of the control unit 202. And, the inverter 204 supplies a different current to the first and second lamp units 206 and 207 according to the dimming frequency varied by the PWM controller 203. PWM (pulse width modulation) is one of pulse modulation schemes and performs modulation by varying a width of pulse according to a size of a modulation signal. If an amplitude of a signal wave is large, a width of a pulse is widened. If an amplitude of a signal wave is small, a width of a pulse is narrowed. Yet, a position or amplitude of the pulse does not vary.

The current supplied to the lamp unit 206 or 207 can be named a backlight current.

According to a quantity of the current supplied to the lamp unit 206 or 207, brightness of an image displayed on the LCD panel is adjusted.

The lamp 206 or 207 generally includes ac cold cathode fluorescent lamp (CCFL) .

Meanwhile, the video data receiving unit 208 plays a role in receiving video data transmitted from a broadcasting station or an external device.

The video processor 209 is responsible for a function of signal-processing the video data, which is received via the video data receiving unit 208, to become outputtable via a screen.

Yet, in some cases of the video data signal-processed by the video processor 209, a contrast value of the screen is adjusted by the contrast controller 210.

Besides, the meaning of ^Λhaving high brightness' corresponds to ^overall brightness is raised' . And, the contrast means a difference between dark and bright sides.

The present invention is explained in detail as follows .

First of all, in case that a user of the video apparatus 200 lowers a brightness value via the user input unit 201 or the like, the inverter 204 reduces a quantity of the current supplied to the lamp units 207 and 207.

If the quantity of the current supplied to the lamp units 207 and 207 is reduced below a predetermined value, an effect such as constructive interference and destructive interference is generated from the influence of a variable frequency. Eventually, the wavy noise, as shown in FIG. 1, is generated on the LCD panel 205.

According to experimental observation, if brightness is adjusted up to a maximum value (100%) , a correlation between a dimming frequency and a lamp current, as shown in FIG. 3A, takes place to avoid generating the wavy noise.

If brightness is adjusted to a relatively high value (75%) , a correlation between a dimming frequency and a lamp current, as shown in FIG. 3B, takes place to ignore the wavy noise.

If brightness is reduced to a considerable range (50%), a correlation between a dimming frequency and a lamp current, as shown in FIG. 3C, takes place to generate the interference considerably.

In particular, the severe wavy noise, as shown in FIG. 1, is generated to interrupt a user to view a screen.

So, the present invention is characterized in adjusting brightness in two ways according to a brightness step, which is different from the related, art.

In a brightness adjusting mode, if a level of brightness, as shown in FIG. 4, lies in a range between

75-100%, the operations of the PWM controller 203 and the inverter 204 vary a quantity of the backlight current supplied to the lamp units 206 and 207 to adjust the brightness.

On the other hand, if a level of brightness, as shown in FIG. 4, lies in a range between 0-75%, a quantity of the backlight current supplied to the lamp units 206 and 207 is maintained at a predetermined level and a contrast value is just varied by controlling the contrast controller 210.

Yet, a predetermined value of the quantity of the backlight current supplied to the lamp units 206 and 207 can be designed to be equal to that applied to the lamp units 206 and 207 in case of the 75% brightness.

For example of varying the contrast value, it is able to design a contrast adjusting mode to be varied by 1-step each time the brightness adjusting mode is varied by 2~3 steps . In particular, if a result of deciding a step value of a reference value is below the step value of the reference value, a difference value between the step value of the reference value and the step value of the adjusted brightness is found. A contrast step value of the screen is then varied according to the found difference value. In this case, the step value of the reference value is set to a range between 70-80% of the maximum brightness step value and the contrast step value of the screen is set to be varied within a range between 65-90% of a maximum step value. If the present invention is implemented in the above- explained manner, since the brightness is continuously varied, it is advantageous for a user to almost feel no difference from the case of varying the backlight current only.

Moreover, the wavy noise or the horizontal noise, which is the constant problem in the brightness adjustment of the LCD monitor, can be substantially eliminated.

Meanwhile, although the above description deals with the detailed numerical values obtained from tests, the corresponding ranges and the like can slightly vary according to the CLD panel characteristic difference between manufacturers, the difference of clock signals

(CLK) of the video apparatus, the inverter IC difference, and the like.

Yet, as the technical background of the present invention is to configure a combination of the PWM adjustment and the contrast adjustment in adjusting brightness or luminance, it is intended that the present invention covers the simple variations of numerical values of this invention that come within the scope of the appended claims and their equivalents.

FIG. 5 is a flowchart of a method of adjusting brightness in a flat panel display according to the present invention, in which a video apparatus including an LCD monitor is controlled to prevent screen noise.

An embodiment of preventing screen noise such as wavy noise and the like in an LCD monitor according to the present invention is explained in time sequence as follows. Yet, as explained in the foregoing description of FIGs. 2 to 4, the operations of the video apparatus and the LCD monitor are fully explained and their details will be omitted in the following description.

Referring to FIG. 5, a brightness adjusting mode is executed in a video apparatus including an LCD monitor (S501) .

In this case, the video apparatus can be a television, a computer, a laptop, an electronic scheduler, or the like, which includes the LCD monitor. After execution of the brightness adjusting mode, brightness is adjusted to a predetermined step value (not shown in the drawing) .

It is then decided whether a current (named a backlight current) to be supplied to a lamp of the LCD monitor is below a prescribed value (S502).

Alternatively, the deciding step S502 can be carried out using the adjusted step value. This is because a quantity of the current supplied to the lamp is varied according to the brightness adjustment step value. As a result of the deciding step S502, if the current to be supplied to the lamp of the LCD monitor is not below the prescribed value, the current supplied to the lamp is adjusted to adjust brightness (S503) .

As a result of the deciding step S502, if the current to be supplied to the lamp of the LCD monitor is below the prescribed value, the current amounting to the prescribed value is fixed to be supplied to the lamp only (S504) .

Finally, by adjusting a contrast step number in proportion to a step number for adjusting the brightness, the brightness is adjusted (S505) .

For instance, in case of the configuration shown in FIG. 4, if the step number of adjusting the brightness corresponds to 3, the contrast step number can be designed to be adjusted by 1.

INDUSTRIAL APPLICABILITY

Accordingly, error of wavy noise is removed in a brightness adjusting process, whereby an LCD provides a clearer image. And, a variable range of brightness can be maintained at a related art level while wavy noise is prevented.

While the present invention has been described and illustrated herein with reference to the preferred embodiments thereof, it will be apparent to those skilled in the art that various modifications and variations can be made therein without departing from the spirit and scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention that come within the scope of the appended claims and their equivalents.

Claims

WHAT IS CLAIMED IS:

1. A method of adjusting brightness in a flat panel display, in which the brightness of a screen is adjusted by controlling a backlight lamp, the method comprising the steps of: adjusting the brightness into a predetermined step value according to a user input; deciding whether the adjusted predetermined step value is below a step value of a reference value; if the adjusted predetermined step value is below the step value of the reference value, finding a difference between the step value of the reference value and the step value of the adjusted brightness; and varying a contrast step value of the screen.

2. The method of claim 1, further comprising the step of if the adjusted predetermined step value is not below the step value of the reference value, adjusting a quantity of a current supplied to the backlight lamp according to the adjusted step value of the reference value.

3. The method of claim 2, wherein the quantity of the current is adjusted by PWM variation.

4. The method of claim 1, wherein the backlight lamp comprises a cold cathode fluorescent lamp (CCFL) .

5. The method of claim 1, wherein the flat panel display comprises an LCD panel having its brightness adjusted by the backlight lamp.

6. The method of claim 1, wherein the step value of the reference value lies within a range between 70-80% of a maximum brightness step value.

7. The method of claim 1, wherein the contrast step value of the screen is varied within a range between 65-90% of a maximum step value.

8. The method of claim 1, wherein the contrast step value of the screen is varied in proportion to a predetermined ratio according to the difference between the step value of the reference value and the step value of the adjusted brightness.

9. A flat panel display having a backlight lamp for adjusting brightness, the flat panel display comprising: a user input unit adjusting the brightness into a predetermined step value according to a user input; a deciding unit deciding whether the adjusted predetermined step value is below a step value of a reference value; and a control unit, if the adjusted predetermined step value is below the step value of the reference value, finding a difference between the step value of the reference value and the step value of the adjusted brightness, the control unit varying a contrast step value of the screen to be proportion to a predetermined ratio according to the found difference.

10. The flat panel display of claim 9, wherein the control unit, if the adjusted predetermined step value is not below the step value of the reference value, adjusts a quantity of a current supplied to the backlight lamp according to the adjusted step value of the reference value.

11. The flat panel display of claim 10, wherein the quantity of the current is adjusted by PWM variation.

12. The flat panel display of claim 9, wherein the backlight lamp comprises a cold cathode fluorescent lamp

(CCFL) .

13. The flat panel display of claim 9, wherein the flat panel display comprises an LCD panel having its brightness adjusted by the backlight lamp.

14. The flat panel display of claim 9, wherein the step value of the reference value lies within a range between 70-80% of a maximum brightness step value.

15. The flat panel display of claim 9, wherein the contrast step value of the screen is varied within a range between 65-90% of a maximum step value.

16. The flat panel display of claim 9, wherein the contrast step value of the screen is varied in proportion to the predetermined ratio according to the difference between the step value of the reference value and the step value of the adjusted brightness.