Patent Publication Number: US-8542257-B2

Title: Method of driving a light source, apparatus for performing the method and display apparatus having the apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 2009-6047, filed on Jan. 23, 2009 in the Korean Intellectual Property Office (KIPO), the entire content of which are incorporated by reference herein. 
     BACKGROUND 
     1. Field of the Invention 
     The present disclosure relates to display devices, and, more particularly, to a method of driving a light source, an apparatus for performing the method, and a display apparatus having the apparatus. 
     2. Discussion of the Related Art 
     Typically, liquid crystal display (LCD) devices, among the various types of flat panel display devices, have thinner thickness, lighter weight, lower driving voltage and lower power consumption, etc., as compared to other types of display devices, such as cathode ray tube (CRT) devices, plasma display panel (PDP) devices, and the like. As a result, LCD devices are being widely employed for various electronic devices such as monitors, laptop computers, cellular phones, large-size televisions, etc. An LCD device includes an LCD panel that displays an image using the light transmittance of liquid crystal molecules, and a backlight assembly that is disposed below the LCD panel to provide the LCD panel with light. 
     The LCD panel typically includes an array substrate, a color filter substrate and a liquid crystal layer. The array substrate includes a plurality of pixel electrodes and a plurality of thin-film transistors (TFTs) electrically connected to the pixel electrodes. The color filter substrate faces the array substrate and has a common electrode and a plurality of color filters. The liquid crystal layer is interposed between the array substrate and the color filter substrate. 
     The backlight assembly may employ a plurality of cold cathode fluorescent lamps (CCFLs) as a light source. However, recently the backlight assembly has employed a plurality of light-emitting diodes (LEDs) having low power consumption and high color reproducibility. 
     Further, an LCD device has been developed that is capable of reducing power consumption by converting image data of red, green and blue image data into red, green, blue and white image data. 
     SUMMARY 
     Exemplary embodiments of the present invention provide a method of driving a light source capable of enhancing power efficiency. 
     Exemplary embodiments of the present invention also provide a light source apparatus for performing the above-mentioned method. 
     Exemplary embodiments of the present invention further also provide a display apparatus having the above-mentioned light source apparatus. 
     According to an exemplary embodiment of the present invention, there is provided a method of driving a light source. In the method, primary image data of a red color, a green color and a blue color is converted into first image data including at least white image data. Luminance data of the first image data is obtained. Sensing data is obtained based upon an external illuminance. A light source module providing a display panel with light is driven based upon the luminance data and the sensing data. 
     In an exemplary embodiment of the present invention, in driving the light source module, driving data may be obtained by multiplying the luminance data by the sensing data. Then, a driving signal having a pulse width may be generated based upon the driving data to provide the light source module with the driving signal having a pulse width. 
     In an exemplary embodiment of the present invention, in obtaining the driving data, a least significant bit of the driving data may be removed to obtain the amplitude of the driving data from the luminance data and the sensing data. 
     In an exemplary embodiment of the present invention, in obtaining the driving data, the driving data may be determined in accordance with an external input signal. 
     In an exemplary embodiment of the present invention, in determining the driving data, driving data of a minimum level may be maintained when the external input signal is no higher than driving data of the minimum level. 
     In an exemplary embodiment of the present invention, in obtaining the sensing data, at least one illuminance signal may be obtained by measuring an illuminance of an external environment. Then, illuminance data may be obtained by converting the illuminance signal from analog form to digital form. Then, a representative value of the illuminance data may be selected. Then, the sensing data corresponding to the representative value of the illuminance data may be obtained. 
     According to an exemplary embodiment of the present invention, a light source apparatus includes a light source module, a luminance determiner, an illuminance sensor and a light source driver. The light source module provides a display panel with light. The luminance determiner obtains luminance data of first image data including at least white image data that is converted from image data of a red color, a green color and a blue color. The illuminance sensor obtains sensing data based upon an external illuminance. The light source driver drives the light source module based upon the luminance data and the sensing data. 
     In an exemplary embodiment of the present invention, the light source driver may include a calculating unit and a pulse width generating unit. The calculating unit may obtain driving data by multiplying the luminance data by the sensing data. The pulse width generating unit may generate a driving signal having a pulse width based upon the driving data to provide the light source module with the driving signal having a pulse width. 
     In an exemplary embodiment of the present invention, the calculating unit may remove a least significant bit of the driving data in order to obtain the amplitude of the driving data from the luminance data and the sensing data. 
     In an exemplary embodiment of the present invention, the light source driver may further include a user adjusting unit determining the driving data in accordance with an external input signal. 
     In an exemplary embodiment of the present invention, the light source driver may further include a minimum level maintenance unit which maintains driving data of a minimum level when the external input signal is no higher than driving data of the minimum level. 
     In an exemplary embodiment of the present invention, the light source driver may further include a user adjusting unit determining the driving data in accordance with an external input signal. 
     In an exemplary embodiment of the present invention, the light source driver may further include a minimum level maintenance unit which maintains driving data of a minimum level when the external input signal is no higher than driving data of the minimum level. 
     In an exemplary embodiment of the present invention, the illuminance sensor may include a sensing unit, an analog-to-digital converter (ADC), a selection unit and a mapping unit. The sensing unit may obtain a plurality of illuminance signals by measuring an illuminance of an external environment. The ADC may convert the illuminance signal having analog value into illuminance data having digital value. The selection unit may select a representative value of the illuminance data. The mapping unit may output sensing data corresponding to the representative value of the illuminance data to the light source driver. 
     In an exemplary embodiment of the present invention, the illuminance sensor may further include a filtering unit removing a noise component of the illuminance data to provide the selection unit with the illuminance data in which a noise component is removed. 
     According to an exemplary embodiment of the present invention, a display apparatus includes a display panel, a panel driver and a light source apparatus. The display panel includes at least a white pixel. The panel driver may convert primary image data of a red color, a green color and a blue color into first image data including at least white image data to drive the display panel. The light source apparatus includes a light source module, a luminance determiner, an illuminance sensor and a light source driver. The light source module provides the display panel with light. The luminance determiner obtains luminance data of the first image data. The illuminance sensor obtains sensing data based upon an external illuminance. The light source driver drives the light source module based upon the luminance data and the sensing data. 
     In an exemplary embodiment of the present invention, the light source driver may include a calculating unit and a pulse width generating unit. The calculating unit may obtain driving data by multiplying the luminance data by the sensing data. The pulse width generating unit may generate a driving signal having a pulse width based upon the driving data to provide the light source module with the driving signal having a pulse width. The calculating unit may remove a least significant bit of the driving data to obtain the amplitude of the driving data from the luminance data and the sensing data. The illuminance sensor may include a sensing unit, an ADC, a selection unit and a mapping unit. The sensing unit may obtain a plurality of illuminance signals by measuring an illuminance of an external environment. The ADC may convert the illuminance signal having analog value into illuminance data having digital value. The selection unit may select a representative value of the illuminance data. The mapping unit may output sensing data corresponding to the representative value of the illuminance data to the light source driver. 
     In an exemplary embodiment of the present invention, the sensing unit may include at least one illuminance sensor mounted on the display panel. 
     According to exemplary embodiments of the present invention, primary image data of red, green and blue is converted into first image data including at least white image data to display the first image data on a display panel and a driving signal of a light source module providing the display panel with light, so that the luminance of a display apparatus may be increased and the power consumption of the display apparatus may be reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings, in which: 
         FIG. 1  is a block diagram illustrating a display apparatus according to an exemplary embodiment of the present invention; 
         FIG. 2  is a block diagram illustrating the illuminance sensor of  FIG. 1 ; 
         FIG. 3  is a graph showing one example of the lookup table (LUT) of  FIG. 2 ; 
         FIG. 4  is a block diagram illustrating the light source driver of  FIG. 1 ; and 
         FIG. 5  is a flowchart showing a method of driving a light source according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     The present invention is described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the present invention are shown. The present invention may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. In the drawings, the sizes and relative sizes of layers and regions may be exaggerated for clarity. 
     It will be understood that when an element or layer is referred to as being “on,” “connected to” or “coupled to” another element or layer, it can be directly on, connected or coupled to the other element or layer or intervening elements or layers may be present. Like numerals refer to like elements throughout. 
     Referring now to  FIG. 1 , the display apparatus includes a display panel  100 , a panel driver  170  and a light source apparatus  200 . 
     The display panel  100  includes a plurality of data lines DL, a plurality of gate lines GL crossing the data lines DL, and a plurality of pixels electrically connected to the data lines DL and the gate lines GL. The pixels each include at least one white pixel. That is, each of the pixels includes a unit pixel including a red pixel P R , a green pixel P G , a blue pixel P B  and a white pixel P w . Each of the red, green, blue and white pixels includes a switching element (not shown) connected to a gate line GL and a data line DL, and a liquid crystal capacitor (not shown) and a storage capacitor (not shown) that are connected to the switching element. 
     The panel driver  170  includes a timing controller  110 , a data converter  120 , a data driver  140  and a gate driver  150 . 
     The timing controller  110  receives a control signal CS from an external device (not shown). The control signal CS may include a vertical synchronizing signal (Vsync), a horizontal synchronizing signal (Hsync), and a data enable signal (DE). The vertical synchronizing signal (Vsync) represents a time required for displaying one frame. The horizontal synchronizing signal (Hsync) represents the time required for displaying one line of the frame. The data enable signal (DE) represents a time required for supplying the pixel with data. 
     The timing controller  110  generates a timing control signal TS which controls a driving timing of the display panel  100  by using the control signal CS. The timing control signal TS may include a clock signal, a horizontal start signal and a vertical start signal. The vertical start signal is provided to the gate driver  150  so as to sequentially activate a plurality of gate lines of the panel driver  170 . 
     The data converter  120  converts primary image data of red, green and blue image data received from an external device (not shown) in correspondence with the red, green, blue and white image pixels P R , P G , P B  and P W  of the display panel  100 . That is, the data converter  120  converts the primary image data of a red color, a green color and a blue color that are received from an external device into first image data including at least white image data. In an exemplary embodiment, the data converter  120  converts the primary image data into the first image data including red, green, blue and white image data. The data converter  120  provides the data driver  140  and the light source driving apparatus  200  with the first image data. 
     The data driver  140  provides the data line DL with a data voltage by using a data control signal received from the timing controller  110  and the first image data received from the data converter  120 . That is, the data driver  140  converts the first image data into an analog data voltage, and outputs the analog data voltage to the data line DL. 
     The gate driver  150  drives the gate line GL by using a gate control signal received from the timing controller  110 . In an exemplary embodiment the gate driver  150  sequentially provides the gate lines GL with a gate signal to activate the gate line GL. 
     The light source driving apparatus  200  includes a light source module  210  and a light source module driver  270 . 
     The light source module  210  includes at least one light source. The light source module  210  is divided into I×J (‘I’ and ‘J’ are natural numbers) light-emitting blocks B. The light-emitting block B are individually driven, which corresponds to an image displayed on the display panel  100 , in accordance with a local dimming method. Each of the light-emitting blocks B includes a plurality of white light sources. Alternatively, each of the light-emitting blocks B may include a plurality of red light sources, a plurality of green light sources and a plurality of blue light sources. The at least one light source is an LED. 
     The light source module driver  270  includes a luminance determiner  220 , an illuminance sensor  230  and a light source driver  250 . 
     The luminance determiner  220  obtains luminance data LD from the first image data provided from the data converter  120 . The luminance data LD is output by a frame of an image. The luminance determiner  220  provides the light source driver  250  with the luminance data LD. 
     The light source module driver  270  obtains sensing data SD based upon illuminance signals corresponding to an illuminance of an external environment which is measured by a sensor unit  231  adjacent to the display panel  100 . The illuminance sensor  230  provides the light source driver  250  with the sensing data SD. A detailed description of the illuminance sensor  230  will be described more fully hereinafter with reference to  FIGS. 2 and 3 . 
     The light source driver  250  drives the light source module  210  based upon the luminance data LD provided from the luminance determiner  220  and the sensing data SD provided from the illuminance sensor  230 . A detailed description of the light source driver  250  will be described more fully hereinafter with reference to  FIG. 4 . 
       FIG. 2  is a block diagram illustrating an illuminance sensor  230  of  FIG. 1 .  FIG. 3  is a graph showing one example of an LUT  239  of  FIG. 2 . 
     Referring to  FIGS. 2 and 3 , the illuminance sensor  230  includes a sensing unit  231 , an analog to digital converter  233  (hereinafter ADC refers to the analog to digital converter), a selection unit  235  and a mapping unit  237 . In the exemplary embodiment the illuminance sensor  230  further includes a filtering unit  234 . 
     The sensing unit  231  measures an illuminance of an external environment to obtain illuminance signals, and outputs the illuminance signals to the ADC  233 . The sensing unit  231  includes at least one illuminance sensor that is mounted on the display panel  100  of the display apparatus (see  FIG. 1 ). The sensing unit  231  may further include a temperature compensation sensor. In an exemplary embodiment, the illuminance sensor  230  is mounted on the display panel  100  of the display apparatus. However, the position of an illuminance sensor  230  is not limited thereto. That is, the illuminance sensor may be disposed at various positions at which an illuminance of an external environment can be measured in a display apparatus. 
     The ADC  233  obtains illuminance data by converting the illuminance signals into digital illuminance data. The illuminance sensor  230  further includes a filtering unit  234  which removes a noise component from the illuminance data. 
     The selection unit  235  selects a representative value of illuminance data that is output from the filtering unit  234 . When the filtering unit  234  is omitted from the illuminance sensor  230 , the selection unit  235  selects the representative value of the illuminance data that is output from the ADC  233 . In an exemplary embodiment, the representative value can be one of the illuminance data. In an exemplary embodiment, the representative value can be an average value of the illuminance data. 
     The mapping unit  237  provides the light source driver  250  with sensing data SD corresponding to the representative value of the illuminance data. The mapping unit  237  includes an LUT  239  in which illuminance data and information of sensing data corresponding to the illuminance data are stored. As shown in  FIG. 3 , the sensing data, which corresponds to the illuminance data that is stored in the LUT  239 , has a hysteretic characteristic. 
     Referring to  FIG. 3 , the x-axis represents illuminance data ID, and the y-axis represents sensing data SD corresponding to the illuminance data ID. In an exemplary embodiment, the illuminance data ID is 10-bit data and the sensing data SD is 8-bit data. In  FIG. 3 , I 0 , I 1 , I 2 , I 3 , I 4 , I 5 , I 6 , I 7  and I 8  are illuminance data ID when illuminance data ID are increased, and D 0 , D 1 , D 2 , D 3 , D 4 , D 5 , D 6 , D 7  and D 8  are illuminance data when the illuminance data ID is decreased. 
     In  FIG. 3 , an increasing line ‘h 1 ’ in a stepped shape in accordance with I 0  to I 8  shows sensing data SD corresponding to I 0  to I 8  when illuminance data ID are increased, and a decreasing line ‘h 2 ’ in a stepped shape in accordance with D 0  to D 8  shows sensing data SD corresponding to D 0  to D 8  when illuminance data ID is decreased. As shown in  FIG. 3 , the LUT  239  has a portion of increased illuminance data ID and a portion of decreased illuminance data ID overlapped with each other at a boundary of the sensing data SD. That is for maintaining a current state at a predetermined area so as to prevent flicker from being generated when an external illuminance is finely varied. For example, overlapping of increased illuminance data and decreased illuminance data is shown by the arrow head and tail of a particular D/I pairing (e.g., arrow head D 2  and tail I 2 ) at a boundary (e.g., level SD 2 ). 
       FIG. 4  is a block diagram illustrating a light source driver  250  of  FIG. 1 . The light source driver  250  includes a calculating unit  252  and a pulse width generating unit  258 . 
     The calculating unit  252  multiplies the luminance data LD provided from the luminance determiner  220  by the sensing data SD provided from the illuminance sensor  230  and outputs driving data DD. The calculating unit  252  removes a least significant bit of the driving data, so that the amplitude of the luminance data LD may be substantially equal to that of the sensing data. The calculating unit  252  provides the pulse width generating unit  258  with the driving data DD. 
     The pulse width generating unit  258  generates a driving signal GS having a pulse width based upon driving data DD provided from the calculating part  252 . The pulse width generating part  258  provides the light source module  210  with the generated driving signal GS to drive the light source module  210 . 
     The light source driver  250  further includes a user adjusting unit  254  between the calculating unit  252  and the pulse width generating unit  258 . 
     In an exemplary embodiment the user adjusting unit  254  preferentially determines the driving data DD in accordance with an input signal UI provided from an external device. For example, the user adjusting unit  254  may be connected to an external keyboard to output the driving data DD for adjusting the luminance of a display apparatus in accordance with the input signal UI that is input in accordance with an operation of the user. 
     The light source driver further includes a minimum level maintenance unit  256  disposed between the user adjusting unit  254  and the pulse width generating unit  258 . 
     The minimum level maintenance unit  256  maintains driving data DD of a minimum level when the input signal UI is no higher than driving data of the minimum level. Thus, the minimum level maintenance unit  256  provides a minimum luminance needed for displaying of the display apparatus. 
     The display apparatus in accordance with an exemplary embodiment of the present invention includes a display panel  100  having a unit pixel on which a red pixel P R , a green pixel P G , a blue pixel P B  and a white pixel P W  are formed. The display apparatus converts primary image data of red, green and blue data that is provided from an external device so as to display an image, and provides the converted image data to the display panel  100 . The above technology will be referred to as PenTile® technology, where PenTile is a registered trademark of Clairvoyante. 
     In the PenTile® technology, a plurality of white pixels P W  is further included in a display apparatus, so that a luminance can be obtained by about 200% in comparison with a conventional display apparatus which only uses red, green and blue pixels P R , P G  and P B . Thus, when PenTile® technology is employed in the display apparatus to be adjusted so as to obtain the luminance of about 100%, so that the power consumption of a light source providing the display panel  100  with light can be reduced by about 50% so that power consumption can be enhanced. 
     Moreover, the PenTile® technology can be employed in the display apparatus and luminance thereof additionally adjusted in accordance with an external illuminance, so that the power consumption of the display apparatus can be even more reduced. 
       FIG. 5  is a flowchart showing a method of driving a light source according to an exemplary embodiment of the present invention. 
     Referring to  FIGS. 1 to 5 , the data converter  120  converts primary image data of a red color, a green color and a blue color into first image data including at least white image data (step S 100 ). The luminance determiner  220  obtains luminance data LD from the first image data that are provided from the data converter  120  (step S 300 ). The luminance data LD may be outputted by one frame. The luminance data LD that is output from the luminance determiner  220  is provided to the light source driver  250 . 
     A plurality of illuminance signals corresponding to an exterior environment, which is measured by the sensor part  231  adjacent to the display panel  100 , is obtained as sensing data SD by the illuminance sensor  230  (step S 500 ). The sensing data SD that is output from the illuminance sensor  230  is provided to the light source driver  250 . 
     In step  5500 , the sensor part  231  measures an external illuminance to output illuminance signals (step S 510 ). The sensor part  231  includes at least one illuminance sensor that is mounted on the display panel  100 . The sensor part  231  may further include a temperature compensation sensor. In an exemplary embodiment, the illuminance sensor is mounted on the display panel  100  of the display apparatus. However, the position of the illuminance sensor is not limited to the exemplary embodiment. That is, a disposed position of the illuminance sensor can be placed at any position where an external illuminance of the display apparatus is measured. 
     The illuminance signals are digitally converted by the ADC  233  so that digital illuminance data is output (step S 530 ). Moreover, filtering the digitally converted illuminance data through a filter unit  234  may be further included in step S 530 . 
     A representative value of the illuminance data that is output from the ADC  233  is selected by the selection part  235  (step S 550 ). In an exemplary embodiment, the representative value of the illuminance data can be one of the illuminance data. In an exemplary embodiment, the representative value of the illuminance data can be an average value of the illuminance data. 
     Sensing data SD corresponding to the representative value of the illuminance data is output from the mapping unit  237  to be provided to the light source driver  250  (step S 570 ). The mapping unit  237  includes an LUT  239  in which illuminance data and information of sensing data corresponding to the illuminance data are stored. As shown in  FIG. 3 , the sensing data, which corresponds to the illuminance data that is stored in the LUT  239 , has a hysteretic characteristic. To prevent flicker from being generated when an external illuminance is finely varied, the LUT  239  has a portion of increased illuminance data ID and a portion of decreased illuminance data ID that are overlapped with each other at a boundary of the sensing data SD. 
     The light source driver  250  drives the light source module  210  which provides the display panel with light, based upon the luminance data LD provided from the luminance determiner  220  and the sensing data SD provided from the illuminance sensor  230  (step S 700 ). 
     In step S 700 , the luminance data LD provided from the luminance determiner  220  and the sensing data SD provided from the illuminance sensor  230  are multiplied by the calculating unit  252  to be output as driving data (step S 710 ). A least significant bit of the driving data is removed, so that the amplitude of the luminance data LD is substantially equal to that of the sensing data SD. In step  5710 , preferentially determining the driving data may be further performed in accordance with an input of an external device (not shown). For example, the luminance of the display apparatus may be adjusted in accordance with an input of a user through an external keypad connected to the user adjusting unit  254 . Moreover, when an external input corresponding to no higher than driving data of a minimum level is applied to the user adjusting unit  254 , maintaining driving data of the minimum level may further be performed. For example, a minimum luminance required for driving the display apparatus may be maintained by the minimum level maintenance unit  256 . 
     Driving data provided from the calculating unit  252  is converted as a driving signal having a pulse width by the pulse width generating unit  258  (step S 730 ). The pulse width generating unit  258  provides the light source module  210  with the converted driving signal, so that the light source module  210  is driven. 
     As described above, since PenTile® technology which obtains the luminance of about 200% in comparison with a conventional display apparatus is employed in the display apparatus of the present invention, the luminance of the display apparatus can be additionally adjusted so that the power consumption of the display apparatus can be enhanced. 
     As described above, according to the embodiments of the present invention, a unit pixel of red, green, blue and white pixels P R , P G , P B  and P W  is used in a display apparatus, so that the luminance of the display can be increased by about 200% in comparison with a conventional display apparatus. Moreover, the luminance of the display apparatus can be further adjusted in accordance with a variation of an external illuminance, so that the luminance of the display apparatus can be increased. Furthermore, the power consumption of the display apparatus can be reduced. 
     Although exemplary embodiments of the present invention have been described, those skilled in the art will readily appreciate that many modifications are possible and are intended to be included within the scope of the present invention as defined in the following claims.