Abstract:
A display device capable of accurately sensing object presence at lower power consumption is presented, as well as a method of driving the display device. The display device includes a sensing circuit that detects the presence of an object by sensing radiation, and a radiation source array that provides radiation to the sensing circuit. First signals are provided to the scan lines of the sensing circuit, sequentially activating the sensors during a frame period. Second signals are provided to a radiation source array to selectively activate different portions of the radiation source array. The first and second signals are synchronized in their timing such that the portion of the radiation source array that supplies radiation to the activated sensors are turned on.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application relies for priority upon Korean Patent Application No. 2009-110465 filed on Nov. 16, 2009, the content of which is herein incorporated by reference in its entirety. 
       FIELD OF INVENTION 
       [0002]    The present invention refers generally to a display device and more particularly to an object-sensing (e.g., touch-sensing) display device. 
       BACKGROUND 
       [0003]    An object-sensing device is a device capable of sensing the presence of an object, and sometimes determines the location of the object on the device. Incorporation of object-sensing capability into display devices is becoming increasingly desirable, as it allows the display device itself to also be used as a user input device, eliminating the need for cumbersome components such as keyboards, keypads, and mouse. Using an object-sensing display device, a user can, for example, touch images of buttons on the display to make a selection or type a word. Object-sensing display devices can be useful for applications such as automatic telling machines (ATMs), mobile/cellular phones, and personal digital assistants (PDAs). 
         [0004]    As the object-sensing capability requires extra components, adding the object-sensing capability usually results in higher power consumption for the display device. Both from a practical standpoint and an environmental standpoint, object-sensing display apparatuses that can operate at reduced power consumption are desirable. 
       SUMMARY 
       [0005]    In one aspect, the invention is a method for driving a display device that is capable of sensing object presence (e.g., a touch). The method entails providing first signals to a sensing circuit that detects a presence of an object by sensing radiation, wherein the sensing circuit includes scan lines for receiving the first signals. Second signals are provided to a radiation source array that provides radiation to the sensing circuit, wherein the second signals selectively activate radiation sources in the radiation source array. The timings of the first and second signals are synchronized so that radiation is provided to a portion of the sensing circuit receiving the first signals. 
         [0006]    In another aspect, the invention is a method for driving a display device that is capable of object detection. An array of infrared radiation sources are divided into a plurality of groups. The plurality of groups is activated sequentially one at a time. 
         [0007]    In yet another aspect, the invention is a display device that includes a sensor array and a radiation source array coupled to each other. The sensor array includes sensing circuits, wherein each of the sensing circuits includes a scan line and a sensing transistor that outputs a detection signal when an object is detected and the scan line is receiving a first signal, and wherein the sensing circuits are sequentially activated by a series of first signals. The radiation source array emits radiation that is used by the sensing transistor to detect the object, and the radiation sources in the radiation source array are activated by second signals that are synchronized with the first signals. 
         [0008]    In yet another aspect, the invention is a display device that includes a sensor array and a radiation source array coupled to each other. The sensor array includes sensing circuits, wherein each of the sensing circuits includes a scan line and a sensing transistor that outputs a detection signal when an object is detected and the scan line is receiving a first signal, and wherein the sensing circuits are sequentially activated by a series of first signals. The radiation source array emits radiation that is used by the sensing transistor to detect the object, and the radiation sources in the radiation source array are activated by second signals that are synchronized with the first signals. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a sectional view showing an exemplary embodiment of a display apparatus having a light source and a radiation source. 
           [0010]      FIG. 2  is an enlarged view of a portion B of  FIG. 1 . 
           [0011]      FIG. 3  is a block diagram of the display apparatus of  FIG. 1 . 
           [0012]      FIG. 4  is a plan view of one embodiment of the backlight unit. 
           [0013]      FIG. 5  is a plan view of another embodiment of the backlight unit. 
           [0014]      FIG. 6  is a timing diagram showing the synchronization between the scan signals to a sensing circuit and activation of radiation sources. 
           [0015]      FIG. 7  is a timing diagram showing the turn-on duration of radiation sources when a driving current is increased. 
           [0016]      FIG. 8  is a plan view showing a backlight unit according to another exemplary embodiment of the present invention. 
           [0017]      FIG. 9A  is a timing diagram showing the synchronization between the scan signals to a sensing circuit and activation of sub-groups of radiation sources. 
           [0018]      FIG. 9B  is a timing diagram showing sub-PWM signals applied to the sub-groups of  FIG. 8 . 
           [0019]      FIG. 10A  is a timing diagram showing the synchronization between the scan signals to a sensing circuit and activation of sub-groups of radiation sources according to another embodiment of the invention. 
           [0020]      FIG. 10B  is a timing diagram showing sun-PWM signals applied to the sub-groups according to another embodiment of the present invention. 
           [0021]      FIG. 11  is a sectional view of a display apparatus according to another embodiment of the present invention. 
           [0022]      FIG. 12  is a plan view showing the backlight unit of  FIG. 11 . 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Generally, one way for a display device to detect the presence of an object is by using sensing circuits that have scan lines laid across the display panel. When an object touches or otherwise activates a point on the display panel, the scan line(s) that is closest to that point will indicate the presence and location of the object by generating a signal. The signal on the scan line(s) may be generated, for example, by receiving radiation that is reflected by the object. In that case, radiation sources are often incorporated into the display device to provide the radiation that can be reflected by the object and sensed by the sensing circuit. Typically, the radiation sources are turned on continuously to make sure the object will be detected whenever it is present. 
         [0024]    The invention reduces power consumption dramatically while allowing the object detection to be performed at high accuracy by taking advantage of the fact that the scan lines that detect the radiation reflected by an object may not all be turned on continuously. For example, the scan lines are frequently “scanned” sequentially from one end of the panel to the other. The scanning frequency is high relative to the typical duration that an object is present (e.g., duration of a human touch) so that even though not all the scan lines are turned on continuously, there is no concern for a touch or an object presence being missed. The invention reduces power consumption by dividing the radiation sources into multiple groups and selectively turning on certain groups of radiation sources as needed, instead of keeping all the radiation sources turned on continuously. For example, the radiation sources near the scan lines that are activated may be turned on because an object is sensed by an activated scan line, while others remain turned off. This way, any “wasting” of power from turning on the radiation sources that are not near activated scan lines may be eliminated. The structure of the display device with this power-efficient object-sensing capability and the method of detection will now be described. 
         [0025]    A “light source,” as used herein, emits visible light. A “radiation source” emits radiation that is used for object detection, wherein the radiation may be visible (e.g., white light), invisible (e.g., infrared), or a combination of the two. 
         [0026]      FIG. 1  is a sectional view of a display apparatus according to one embodiment of the present invention. As shown, a display apparatus  300  includes a display panel  100  and a backlight unit  200  illuminating the display panel  100 . The display panel  100  includes a lower substrate  110 , an upper substrate  120  facing the lower substrate  110 , and a liquid crystal layer  125  interposed between the upper and lower substrates  120  and  110 . 
         [0027]    The backlight unit  200  includes a circuit substrate  201  provided below the display panel  100 , a plurality of light sources  210  (see  FIG. 1 ) mounted on the circuit substrate  201  to output a white light L 1 , and a plurality of radiation sources  220  (see  FIG. 1 ) mounted on the circuit substrate  201  to output an infrared ray L 2 . In the embodiment of  FIG. 1 , the light source  210  and radiation source  220  are arranged in an alternating manner—at least one radiation source  220  may be provided between adjacent light sources  210 . The light sources  210  and radiation sources  220  may include a light emitting diode. As will be explained in more detail below, the light sources  210  are useful for image display and the radiation sources  220  are useful for object detection. 
         [0028]      FIG. 2  is an enlarged view of a portion B of  FIG. 1 . As shown in  FIG. 2 , the lower substrate  110  includes a first base substrate  111  and a plurality of pixels arranged on the first base substrate  111 . Each pixel includes one of red, green, and blue color pixels R, G, and B, and a pixel electrode  115  provided on the one color pixel. Each pixel may further include a thin film transistor in addition to the color pixels R,G, and B and the pixel electrode  115 . The structure of each pixel will be described in detail with reference to  FIG. 3 . 
         [0029]    A black matrix  112  is arranged between the red, green, and blue color pixels R, G, and B. The red, green, and blue color pixels R, G, and B are covered by an organic insulating layer  114 . The pixel electrode  115  is provided on the organic insulating layer  114 . 
         [0030]    The upper substrate  120  includes a second base substrate  121  facing the first base substrate  111  and a plurality of sensors SN (see  FIG. 3 ) provided on a bottom surface of the second base substrate  121  facing the lower substrate  110 . Each sensor SN includes a sensing device (hereinafter, refer to as a sensing transistor ST 1 ). For example, the sensing transistor ST 1  may include an amorphous silicon transistor. The upper substrate  120  further includes an insulating layer  122  that covers the sensors SN and a common electrode  123  provided on the insulating layer  122  to face the pixel electrode  115 . A liquid crystal capacitor Clc is formed by the pixel electrode  115 , the common electrode  123 , and the liquid crystal layer  125 . 
         [0031]    Although  FIG. 2  shows that the red, green, and blue color pixels R,G, and B are provided in the lower substrate  110 , the color pixels R,G, and B may be provided in the upper substrate  120  in some embodiments. 
         [0032]    As shown, the white light L 1  output from the light sources  210  is supplied to the display panel  100 , and the supplied white light L 1  passes through the liquid crystal layer  125 . Light transmittance of the liquid crystal layer  125  is controlled by an electric field formed between the pixel electrode  115  and the common electrode  123 . The display panel  100  controls the transmittance of the white light L 1  by the liquid crystal layer  125 , thereby displaying an image having desired gray scales. 
         [0033]    The infrared ray L 2  emitted from the radiation sources  220  is supplied to the display panel  100 , and the supplied infrared ray L 2  passes through the display panel  100 . Since the infrared ray L 2  is not visible to a user, the infrared ray L 2  does not affect the image displayed on the display panel  100  as perceived by the user. A portion of the infrared ray L 2  emitted from the radiation sources  220  is reflected by the layers in the display panel  100 . The portion of the infrared ray L 2  that is not reflected may pass through the display panel  100  and get radiated outside of the display panel  100 . If an object  10  (for example, a finger of a user) is on the display panel  100 , the infrared ray L 2  reflects off the object  10 . 
         [0034]    The infrared ray L 2  that has been reflected by the object  10  may be sensed through the sensing transistor ST 1 . In other words, if the reflected infrared ray L 2  is supplied to the sensing transistor ST 1 , the sensing transistor ST 1  outputs a signal that indicates an amount of the reflected infrared ray L 2 . The sensing transistor ST 1  may include an amorphous silicon layer. The display apparatus  300  determines the location of an object on its surface by using the signal generated from the touch. 
         [0035]    When the sensing transistor ST 1  is provided on the upper substrate  120 , the distance between the object  10  and the sensing transistor ST 1  is shorter than it would be if the sensing transistor ST 1  were provided on the lower substrate  110 . Accordingly, the sensitivity of the sensing transistor ST 1  may be improved, and the touch point may be accurately detected. It may be desirable to form the sensing transistor ST 1  to overlap the black matrix  112 , thereby avoiding decreasing the aperture ratio of the display panel  100 . 
         [0036]    Although the sensors (including the sensing transistor ST 1 ) are embedded in the display panel  100  in the embodiment of  FIG. 2 , a touch panel (not shown) including the sensors may be provided at an upper portion of the display panel  100  in other embodiments. Alternatively, the sensing transistor ST 1  may be provided on the lower substrate  110  in some embodiments. 
         [0037]      FIG. 3  is a block diagram showing the display apparatus of  FIG. 1 . As shown, the display apparatus  300  includes a timing controller  130 , a data driver  150 , a gate driver  140 , a read-out circuit  170 , a sensor driver  160 , and the display panel  100 . 
         [0038]    The timing controller  130  receives a plurality of image signals RGB and a plurality of control signals CS from a device outside the display apparatus  300 . The timing controller  130  converts the data format of the image signals RGB to make them suitable for interface requirements with the data driver  150 , and provides the converted image signals R′G′B′ to the data driver  150 . In addition, the timing controller  130  provides data control signals (e.g., an output starting signal TP, a horizontal starting signal STH, etc.) to the data driver  150 . The timing controller  130  provides gate control signals (e.g., a vertical starting signal STV 1 , a vertical clock signal CK 1 , and a vertical clock bar signal CKB 1 ) to the gate driver  140 . 
         [0039]    The gate driver  140  sequentially outputs gate signals G 1  to Gn in response to the gate control signals (the vertical starting signal STV 1 , the vertical clock signal CK 1 , and the vertical clock bar signal CKB 1 ) from the timing controller  130 . 
         [0040]    The data driver  150  converts the image signals R′G′B′ into data voltages D 1  to Dm in response to the data control signals (the output starting signal TP and the horizontal starting signal STH) from the timing controller  130  and outputs the data voltages D 1  to Dm. The data voltages D 1  to Dm are applied to the display panel  100 . 
         [0041]    The display panel  100  includes a plurality of pixels PX and a plurality of sensors SN. The pixels PX and the sensors SN are embedded in the display panel  100 . In some embodiments, the pixels PX are provided in the lower substrate  110 , and the sensors SN are provided in the upper substrate  120 . 
       Structure of an Exemplary Pixel PX 
       [0042]    The lower substrate  110  (shown in  FIG. 2 ) includes a plurality of gate lines GL and a plurality of data lines DL crossing the gate lines GL to form the pixels PX. Each pixel PX includes a thin film transistor PT, the liquid crystal capacitor Clc, and a storage capacitor Cst. The thin film transistor PT includes a gate electrode connected with a gate line corresponding thereto from among the gate lines GL, a source electrode connected with a data line corresponding thereto from among the data lines DL, and a drain electrode connected with the liquid crystal capacitor Clc and the storage capacitor Cst. 
         [0043]    The gate lines GL are connected with the gate driver  140 , and the data lines DL are connected with the data driver  150 . The gate lines GL receive the gate signals G 1  to Gn from the gate driver  140 , and the data lines DL receive the data voltages D 1  to Dm from the data driver  150 . The thin film transistor PT is turned on in response to a gate signal supplied to the corresponding gate line, and the liquid crystal capacitor Clc is charged with a data voltage that has been supplied to the corresponding data line through the thin film transistor PT. Accordingly, each pixel PX may display an image corresponding to the data voltage. 
       Structure of an Exemplary Sensor 
       [0044]    The upper substrate  120  includes a plurality of scan lines SL, a plurality of read-out lines RL crossing the scan lines SL, and the sensors SN. Each sensor SN includes the sensing transistor ST 1 , a switching transistor ST 2 , and a capacitor Cs. The switching transistor ST 2  includes a first electrode connected with a scan line corresponding thereto from among the scan lines SL, a second electrode connected with a read-out line corresponding thereto from among the read-out lines RL, and a third electrode connected with the capacitor Cs and the sensing transistor ST 1   
         [0045]    The capacitor Cs has a first electrode connected with the third terminal of the switching transistor ST 2  and a second electrode receiving a ground voltage. The sensing transistor ST 1  includes a first terminal connected with the third terminal of the switching transistor ST 2 , a second terminal receiving a bias voltage, and a third terminal that is also connected with the second electrode of the capacitor Cs and ground. 
         [0046]    The sensing transistor ST 1  senses the infrared ray L 2  reflected from the object  10  and outputs a signal corresponding to the amount of the reflected infrared ray L 2 . The amount of charge on the capacitor Cs changes according to the signal output from the sensing transistor ST 1 . In other words, as the amount of the reflected infrared ray L 2  increases, the amount of charge on the capacitor Cs also increases. 
         [0047]    The scan lines SL are connected with the sensor driver  160  to sequentially receive a plurality of scan signals S 1  to Sn, respectively. The sensor driver  160  receives sensor control signals STV 2 , CK 2 , and CKB 2  from the timing controller  130  to output the scan signals S 1  to Sn. The sensor control signals STV 2 , CK 2 , and CKB 2  may be synchronized with the gate control signals (the vertical starting signal STV 1 , the vertical clock signal CK 1 , and the vertical clock bar signal CKB 1 ). 
         [0048]    Each read-out line RL is connected with the read-out circuit  170  to supply the charged voltage of the sensor SN corresponding to each read-out line RL to the read-out circuit  170 . 
         [0049]    When the switching transistor ST 2  is turned on in response to a scan signal corresponding thereto, the sensor SN supplies a charged voltage from the capacitor Cs to the read-out line RL corresponding to the sensor SN. When an object  10  is sensed, the sensing transistor closes, allowing the charge to come out of the capacitor Cs. This drop in the charge on the capacitor Cs is detected when the switching transistor ST 2  is turned on, indicating the presence of an object  10 . 
         [0050]    Accordingly, the read-out circuit  170  supplies a voltage received from the sensor SN to the timing controller  130 . The timing controller  130  may create two-dimensional coordinates of a point touched by the object  10  based on a time at which the scan signal is generated and the read-out voltage. 
         [0051]      FIG. 4  is a plan view of a backlight unit. As shown, the backlight unit  200  includes the circuit substrate  201 , the light sources  210  mounted on the circuit substrate  201  to output white light L 1  (shown in  FIG. 2 ), and the radiation sources  220  mounted on the circuit substrate  201  to output the infrared ray L 2  (shown in  FIG. 2 ). The light sources  210  are arranged in a matrix, and the radiation sources  220  are arranged in a matrix at positions different from those of the light sources  210 . The arrangement of the radiation sources  220  are not limited thereto, but may vary according to a total number of the radiation sources  220 . 
         [0052]    In the embodiment of  FIG. 4 , the number of the radiation sources  220  provided in the backlight unit  200  is approximately equal to the number of the light sources  210 . In this particular embodiment, a first interval P 1  between two first light sources  210  adjacent to each other in a row direction D 2  is set to about 27 mm, and a second interval P 2  between two first light sources  210  adjacent to each other in a first direction D 1  is set to about 27 mm. A third interval P 3  between two radiation sources  220  adjacent to each other in the row direction D 2  is set to about 27 mm, and a fourth interval P 4  between two radiation sources  220  adjacent to each other in the first direction D 1  is set to about 27 mm. If the number of the radiation sources  220  is reduced, the third and fourth intervals P 3  and P 4  may increase. 
         [0053]      FIG. 5  is a plan view showing a backlight unit according to another exemplary embodiment of the invention. As shown, a backlight unit  205  includes about twice as many radiation sources  220  as light sources  210  in this embodiment. The first interval P 1  between two light sources  210  adjacent to each other in the row direction D 2  is set to about 27 mm, and the second interval P 2  between two first light sources  210  adjacent to each other in the first direction D 1  is set to about 27 mm. A fifth interval P 5  between two radiation sources  220  adjacent to each other in the row direction D 2  is set to about 20 mm, and a sixth interval P 6  between two radiation sources  220  adjacent to each other in the first direction D 1  is set to about 19 mm. 
         [0054]    In both embodiments of  FIGS. 4 and 5 , since the radiation sources  220  are not used for image display, they are disposed primarily on the inner region of the circuit substrate  201  unlike the light sources  210 , which are distributed evenly across the backlight unit  200 . A distance d 1  between a first edge SS 1  of the circuit substrate  201  and the light sources  210  closest to the first edge SS 1  is set to a value of about 10 mm to about 13 mm, and a distance d 2  between the first edge SS 1  and the radiation sources  220  closest to the first edge SS 1  is set to about 30 mm. The first edge SS 1  may be a short side of a rectangular substrate. In addition, distances between a second edge SS 2  parallel to the first edge SS 1  and the light sources  210  and radiation sources  220  are set similarly to the distances d 1  and d 2  between the first edge SS 1  and the light sources  210  and radiation sources  220 , respectively. 
         [0055]    A distance d 3  between a third edge LS 1  of the circuit substrate  210  and the light sources  210  closest to the third edge LS 1  is set to about 13 mm, and a distance d 4  between the third edge LS 1  and the radiation sources  220  closest to the third edge LS 1  is set to about 27 mm. The third edge LS 1  may be a long side of a rectangular substrate. In addition, distances between a fourth edge LS 2  parallel to the third edge LS 1  and the light and radiation sources  210  and  220  are set similarly to the distances d 3  and d 4  between the third edge LS 1  and the light and radiation sources  210  and  220 . 
         [0056]    Meanwhile, the backlight unit  200  and  205  is classified into p groups (hereinafter, referred to as a first group G 1  to a sixth group G 6 ) arranged in the first direction D 1 . The first direction D 1  is also the direction in which the scan lines SL of the sensors are arranged (see  FIG. 3 ). “p” is a natural number greater than or equal to 2, and each of the first to sixth groups G 1  to G 6  includes the radiation sources  220 . The first to sixth groups G 1  to G 6  may include the same number of the radiation sources  220 . According to an exemplary embodiment of the present invention, each of the first to sixth groups G 1  to G 6  may include  192  radiation sources  220 . Although the first to sixth groups G 1  to G 6  are shown in  FIG. 4 , the invention is not limited to any specific number of groups. 
         [0057]    The first to sixth groups G 1  to G 6  may be turned on for different durations from each other. The turn-on durations of the first to sixth groups G 1  to G 6  will be described in detail with reference to  FIGS. 5 to 6 . 
         [0058]      FIG. 6  is a timing diagram showing turn-on time of the first to sixth groups shown in  FIG. 4  and how the scan signals to the sensor are synchronized with pulse width modulation (PWM) signals to radiation sources  220 . 
         [0059]    Referring to  FIG. 6 , the first to sixth groups receives a first PWM signal PS 1  to a sixth PWM signal PS 6 , respectively. The first to sixth PWM signals PS 1  to PS 6  are sequentially generated during one frame period FR 1 . For example, a high duration of each of the first to sixth PWM signals PS 1  to PS 6  is defined as a first time period A 1 . 
         [0060]    The display panel  100  may include k scan lines SL (see  FIG. 3 ) corresponding to each of the first to sixth groups G 1  to G 6 . In other words, the display panel  100  includes n scan lines in total (n=pk). If the n scan lines are divided by 6 corresponding to the first to sixth groups G 1  to G 6 , k (n/6) scan lines may correspond to each of the first to sixth groups G 1  to G 6 . The first time period A 1  may be defined as a value obtained by dividing the one frame period FR 1 , which is defined as a unit for image display in the display panel  100 , by the number of the groups (p=6). When the display panel  100  is driven at a frequency of 60 Hz, the frame period FR 1  is set to about 16.3 ms. In this case, the first time period A 1  may be set to about 2.7 ms. 
         [0061]    The 6 k scan signals S 1  to S k , S k+1  to S 2k , . . . , and S 5k+1  to S 6k  are sequentially applied to 6 k (6 k=n) scan lines provided in the display panel  100 . Each of the 6 k scan signals S 1  to S k , S k+1  to S 2k , . . . , and S 5+1  to S 6k  is generated at a high state for one horizontal scanning period (1 H period). In this case, the high duration of each of the scan signals S 1  to S k  may be defined as turn-on duration of each scan line SL. 
         [0062]    The k scan signals S 1  to S k , S k+1  to S 2k , . . . , or S 5k+1  to S 6k  are sequentially applied to the k scan lines corresponding to each of the first to sixth groups G 1  to G 6  during the first time period A 1 . For example, k scan signals S 1  to S k  are sequentially applied to k scan lines corresponding to the first group G 1  during the first time period A 1 . 
         [0063]    Each of the first to sixth groups G 1  to G 6  may be turned on for the first time period A 1  in which the scan signals S 1  to S k , S k+1  to S 2k , . . . , or S 5k+1  to S 6k  are applied to the scan lines corresponding to each of the first to sixth groups G 1  to G 6 . In other words, the radiation sources  220  included in the first group G 1  may be consecutively turned on from a rising edge of a first scan signal S 1 , which is applied to a first scan line from among the k scan lines in the first group G 1 , to the falling edge of a last scan signal S k  which is applied to a last scan line among the k scan lines in the first group G 1 . When the first time period A 1  elapses after the first group G 1  is turned on, the first group G 1  is turned off and the second group G 2  is turned on during the next first time period A 1 . This procedure is repeated so that the first to sixth groups G 1  to G 6  may be turned on at different times. As shown in  FIG. 6 , the first to sixth groups G 1  to G 6  may be sequentially turned on in the first direction D 1 . In this case, the turn-on durations of the first to sixth groups G 1  to G 6  do not overlap with each other. 
         [0064]    When the turn-on duration of each of the first to sixth groups G 1  to G 6  is reduced to the first period A 1 , power consumption in the backlight unit  200  may be reduced to about ⅙ as compared with power consumption when the first to sixth groups G 1  to G 6  are turned on throughout the one frame period FR 1 . 
         [0065]    The length of the turn-on duration of each of the first to sixth groups G 1  to G 6  may be adjusted according to the characteristics of the sensing transistor ST 1  (shown in  FIG. 3 ) provided in the each sensor SN. Since the time (charge time) required to charge the sense signal of the sensing transistor ST 2  and the capacitor Cs (shown in  FIG. 3 ) corresponds to several micro-seconds, even if the turn-on duration of each of the first to sixth groups G 1  to G 6  is reduced to about 2.7 ms, the sensors SN may normally sense the infrared ray L 2 . 
         [0066]    In the embodiment of  FIG. 6 , by dividing the radiation sources  220  into 6 groups (p=6) and turning on the six blocks sequentially throughout one frame period FR 1 , power consumption can be lowered to about ⅙ of what it would have been if all the radiation sources were continually turned on. 
         [0067]      FIG. 7  is a timing diagram showing the turn-on duration of the first to sixth groups when a driving current supplied to the radiation sources of  FIG. 4  is increased. 
         [0068]    Referring to  FIG. 7 , if a driving current supplied to the radiation sources  220  included in each of the first to sixth groups G 1  to G 6  is increased, the high duration of each of the first to sixth PWM signals PS 1  to PS 6  may become shorter than the first time period A 1  (where A 1 =FR 1 /p). 
         [0069]    For example, if the driving current supplied to the radiation sources  220  when the high duration of each of the first to sixth PWM signals PS 1  to PS 6  is set to the first period A 1  as shown in  FIG. 6  were 50 mA, increasing the driving current supplied to the radiation sources  220  to 80 mA allows each of the first to sixth PWM signals PS 1  to PS 6  to have the high duration of a second time period A 2  shorter than the first time period A 1  without lowering the intensity on the infrared ray L 2 . According to one exemplary embodiment of the present invention, the second time period A 2  may be about 1.6 ms. Even if the turn-on duration is reduced as described above, the first to sixth groups G 1  to G 6  may output the infrared ray L 2  having a same intensity as the intensity of the infrared ray L 2  output from the backlight unit  200  corresponding to the exemplary embodiment of  FIG. 6 . 
         [0070]    Alternatively, when the turn-on duration of each of the first to sixth groups G 1  to G 6  is set to the first period A 1  as shown in  FIG. 6 , and the driving current applied to the radiation sources  220  is increased to 80 mA from 50 mA, fewer radiation sources  220  may be included in the backlight unit  200  without sacrificing the accuracy of the object-sensing capability. 
         [0071]    Although the backlight unit  200  corresponding to the embodiment of  FIG. 6  includes  432  light sources  210  and  1152  radiation sources  220 , the number of the radiation sources  200  included in the backlight unit  200  may be reduced when the driving current applied to the radiation sources  220  is increased or a duty ratio of the first to sixth groups G 1  to G 6  is increased. 
         [0072]    To reduce the number of the radiation sources  220  included in the backlight unit  200 , if the duty ratio of each of the first to sixth groups G 1  to G 6  is increased, the turn-on durations of each of the first to sixth groups G 1  to G 6  may partially overlap with each other. Alternatively, if the amplitude of the current supplied to the radiation sources  220  is decreased to below 50 mA, each group may have to stay turned on for longer than the first duration A 1 , causing the turn-on durations of each of the groups G 1  to G 6  to overlap. 
         [0073]      FIG. 8  is a plan view showing a backlight unit according to another embodiment of the invention. As shown, a backlight unit  250  is partitioned into the first to sixth groups G 1  to G 6  in the first direction D 1 . Each of the first to sixth groups G 1  to G 6  includes m (m is a natural number greater than or equal to 2) sub-groups (e.g., SG 1  to SG 8 , SG 9  to SG 16 , . . . , or SG 41  to SG 48 ) partitioned in the second direction D 2 . Each of the sub-groups SG 1  to SG 8 , SG 9  to SG 16 , . . . , and SG 41  to SG 48  includes the radiation sources  220 . Each of the first to sixth groups G 1  to G 6  includes a same number of the radiation sources  220 , and even each of the sub-groups SG 1  to SG 8 , SG 9  to SG 16  . . . , and SG 41  to SG 48  includes a same number of the radiation sources  220 . According to an embodiment of the present invention, each of the sub-groups SG 1  to SG 8 , SG 9  to SG 16 , . . . , and SG 41  to SG 48  may include  24  radiation sources  220 . Although  FIG. 4  shows 6 groups G 1  to G 6  and  48  sub-groups SG 1  to SG 8 , SG 9  to SG 16  . . . , and SG 41  to SG 48 , the present invention is not limited to any specific number of sub-groups. 
         [0074]    The first to sixth groups G 1  to G 6  are sequentially turned on in the first direction D 1 , and the sub-groups SG 1  to SG 8 , SG 9  to SG 16 , . . . , and SG 41  to SG 48  included in each of the first to sixth groups G 1  to G 6  are sequentially turned on in the second direction D 2 . The turn-on duration of each of the sub-groups SG 1  to SG 8 , SG 9  to SG 16 , . . . , and SG 41  to SG 48  will be described in detail with reference to  FIG. 9 . 
         [0075]      FIG. 9A  is a timing diagram showing scan signals applied to scan lines SL corresponding to each of the first to sixth groups shown in  FIG. 8 , and  FIG. 9B  is a timing diagram showing sub-PWM signals applied to the sub-groups of  FIG. 8 . As shown, the display panel  100  includes k scan lines in each of the first to sixth groups G 1  to G 6 . Accordingly, 6 k scan signals S 1  to S k , S k+1  to S 2k , . . . , and S 5k+1  to S 6k  k are sequentially applied to 6 k (6 k=n) scan lines provided in the display panel  100 . Each of the 6 k scan signals S 1  to S k , S k+1  to S 2k , . . . , and S 5k+1  to S 6k  is generated at a high state for one horizontal scanning period (1 H period). 
         [0076]    The time required to sequentially apply k scan signals S 1  to S k , S k+1  to S 2k , . . . , or S 5k+1  to S 6k  to the k scan lines corresponding to each of the first to sixth groups G 1  to G 6  may be defined as the first time period A 1 . 
         [0077]    The first to sixth groups G 1  to G 6  are sequentially turned on in the first direction D 1  for each frame period FR 1  or FR 2 . In addition, the sub-groups SG 1  to SG 48  included in each of the first to sixth groups G 1  to G 6  are sequentially turned on in the second direction D 2 . 
         [0078]    As shown in  FIG. 9B , the k sub-groups SG 1  to SG  48  included in each of the first to sixth groups G 1  to G 6  sequentially receive k sub-PWM signals PS 1 - 1  to PS 6 - k . In particular, the k sub-PWM signals PS 1 - 1  to PS 6 - k  are sequentially generated at a high state for the first time period A 1 . In an exemplary embodiment of the present invention, a first sub-PWM signal PS 1 - 1  to an eight sub-PWM signal PS 1 - k  respectively applied to a first sub-group SG 1  to an eight sub-group SG 8  are simultaneously generated at a high state for a third time period A 3  within a first frame FR 1 . 
         [0079]    A first sub-group SG 1  to an eighth sub-group SG 8  included in the first group G 1  are simultaneously turned on for the third time period A 3  in the first frame period FR 1  in response to the first to eight sub-PWM signal PS 1 - 1  to PS 1 - k  to ensure that the capacitor Cs will get sufficient charging time. (A 3 =FR 1 /pm) The first to eighth sub-groups SG 1  to SG 8  of the first group G 1  are turned on for the third time period A 3  shorter than the first time period A 1 . According to an exemplary embodiment of the present invention, even if the third time period A 3  may be set as a duration from the rising edge of a first scan signal S 1  to a time point in which about 0.3 ms has elapsed from the rising time point, the third time period A 3  may be adjusted within a time duration shorter than or equal to the first time period A 1 . 
         [0080]    The sub-groups SG 9  to SG 48  included in each of the second to sixth groups G 2  to G 6  are sequentially turned on for each frame period FR 1  or FR 2 . Particularly, the sub-blocks SG 9  to SG 48  included in each of the second to sixth groups G 2  to G 6  are sequentially turned on in each group unit for a duration ranging from the rising edge of a first scan signal applied to a first scan line of a previous group to the falling edge of a last scan signal applied to a last scan line of the previous group. 
         [0081]    In detail, a ninth sub-group SG 9  from among the sub-groups SG 9  to SG 16  of the second group G 2  is turned on for a fourth time period A 4  from the rising edge of the first scan signal S 1  applied to the first scan line from among the scan lines corresponding to the previous group (i.e., the first group B 1 ). This is to precharge the capacitor Cs by the switching transistor ST 2  for a short time. Next, a tenth sub-group SG 10  to a sixteenth sub-group SB 16  are sequentially turned on in each group unit for the fourth time period A 4  until the falling time point of the last scan signal S k  applied to the last scan line from among the scan lines corresponding to the first group B 1 . 
         [0082]    The fourth time period A 4  may be set to a value obtained by dividing the first time period A 1  by m. According to one exemplary embodiment of the present invention, since the first time period A 1  is set to 2.7 ms and m is 8, the fourth time period A 4  may be set to about 0.3 ms. 
         [0083]    The forty-first sub-group SG 41  from among the sub-groups SG 41  to SG 48  of the sixth group G 6  is turned on for the fourth time period A 4  from the rising edge of the first scan signal S 4k+1  applied to the first scan line from among the scan lines corresponding to a previous group (i.e., the fifth group G 5 ). Thereafter, a forty-second sub-group SG 42  to a forty-eighth sub-group SG 48  are sequentially turned on in each group unit for the fourth time period A 4  until the falling edge of the last scan signal S 5K  applied to the last scan line from among the scan lines corresponding to the fifth group G 5 . 
         [0084]    Similarly, the ninth to forty-eighth sub-groups SG 9  to SG 48  of the second to sixth groups G 2  to G 6  can be sequentially turned on for the first frame period FR 1 . 
         [0085]    When the turn-on duration of each of the first to forty-eighth sub-groups SG 1  to SG 48  is reduced to the third time period A 3  or the fourth time period A 4 , power consumption may be reduced to about ⅛ as compared with power consumption when each of the first to forty-eighth sub-groups SG 1  to SG 48  is continuously turned on throughout one frame period FR 1 . 
         [0086]    Meanwhile, the first sub-group SG 1  of the first group G 1  is turned on for the fourth period A 4  from the rising edge of the first scan signal S 5k+1  applied to the first scan line from among the scan lines corresponding to the last group (i.e., the sixth group G 6 ) of a previous frame period (the first frame period FR 1 ) in a second frame period FR 2 . Next, the second to eighth sub-groups SG 2  to SG 8  are sequentially turned on in each group unit for the fourth time period A 4  until the falling edge of the last scan signal S 6k  applied to the last scan line from among the scan lines corresponding to the sixth group G 6 . 
         [0087]    In other words, after the display apparatus  300  has been powered on, the first to eighth sub-groups SG 1  to SG 8  of the first group G 1  are simultaneously turned on only in the first frame period FR 1 , and sequentially turned on in the next frame period FR 2 . 
         [0088]      FIG. 10A  is a timing diagram showing the turn-on duration of sub-groups according to another embodiment of the present invention, and  FIG. 10B  is a timing diagram showing PWM signals applied to the sub-groups according to another embodiment of the present invention. As shown, after the display apparatus  300  has been powered on, the first to eighth sub-groups SG 1  to SG 8  of the first group G 1  may remain turned off in the first frame period FR 1 . Thereafter, from the second frame period FR 2 , the first to eighth sub-groups SG 1  to SG 8  of the first group G 1  may be turned on in synchronization with the scan signals to the scan lines corresponding to the last group B 6  of the previous frame. 
         [0089]    Although not shown, before the first frame period FR 1  starts and after the display apparatus  300  has been powered on, the first to eighth sub-groups SG 1  to SG 8  of the first group G 1  may be sequentially turned on for the first time period A 1 . 
         [0090]      FIG. 11  is a sectional view showing a display apparatus according to another embodiment of the present invention. Since the liquid crystal display panel  100  of  FIG. 11  has substantially the same structure as that of the liquid crystal display panel  100  of  FIG. 1 , details of the liquid crystal display panel  100  of  FIG. 11  will be omitted.  FIG. 12  is a plan view showing a backlight unit shown in  FIG. 11 . 
         [0091]    Referring to  FIGS. 11 and 12 , a display apparatus  500  according to another exemplary embodiment of the present invention includes an edge-type backlight unit  400 . The edge-type backlight unit  400  includes a light guide plate  430 , a first LED bar  401  and a second LED bar  402 . The first and second LED bars  401  and  402  are provided at two opposite sides  431  and  432  of the light guide plate  430 , respectively. 
         [0092]    The light guide plate  430  is provided below the display panel  100 , and the first and second LED bars  401  and  402  are provided at both lateral sides  431  and  432  of the light guide plate  430  facing each other. A plurality of first light sources  411  and a plurality of first radiation sources  421  are mounted on the first LED bar  401 , and a plurality of second light sources  412  and a plurality of second radiation sources  422  are mounted on the second LED bar  402 . The first and second light sources  411  and  412  include W-LEDs to output white light, and the first and second radiation sources  421  and  422  include IR-LEDs to output infrared ray for object detection. 
         [0093]    At least one first radiation source  421  may be interposed between two adjacent first light sources  411  on the first LED bar  401 , and at least one second radiation source  422  may be interposed between two adjacent second light sources  412  on the second LED bar  402 . 
         [0094]    According to an exemplary embodiment of the present invention, the first and second radiation sources  421  and  422  may be classified into p groups (the first to sixth groups G 1  to G 6 ) arranged along the first direction D 1  in which p is a natural number greater than or equal to 2, and each of the first to sixth groups G 1  to G 6  includes a same number of the first and second radiation sources  421  and  422 . 
         [0095]    The first to sixth groups G 1  to G 6  are turned on at different times even in the edge-type backlight unit  400 . Accordingly, the turn-on durations of the first to sixth groups G 1  to G 6  do not overlap. 
         [0096]    The first to sixth groups G 1  to G 6  are sequentially turned on in the first direction D 1 . According to an embodiment of the present invention, the first and second radiation sources  421  and  422  of the first to sixth groups G 1  to G 6  are turned on from the rising edge of the first scan signal applied to the first scan line to the falling edge of the last scan signal applied to the last scan line. The first to sixth groups G 1  to G 6  are turned on according to a similar method as in the embodiment of  FIGS. 6 and 7 . 
         [0097]    Therefore, the radiation source driving scheme according to the present invention can reduce power consumption. 
         [0098]    Although the foregoing invention has been described in some detail by way of illustration and examples for purposes of clarity and understanding, it will be apparent that modifications and alternative embodiments of the invention are contemplated which do not depart from the spirit and scope of the invention as defined by the foregoing teachings and appended claims.