Patent Publication Number: US-9406254-B2

Title: Display device and driving method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     Korean Patent Application No. 10-2013-0106531, filed on Sep. 5, 2013, and entitled “Display Device and Driving Method Thereof,” is incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Field 
     One or more embodiments described herein relate to a display device and a driving method. 
     2. Description of the Related Art 
     Display devices remain a focus of system designers as information technology continues to develop. Examples of flat panel display devices include liquid crystal display devices (LCDs), organic light emitting display devices (OLEDs), and plasma display panels (PDPs). 
     SUMMARY 
     In accordance with one embodiment, a display device includes a timing controller to output a first control value including information on low gray scale values, a second control value including information on high gray scale values, and a third control value including information on subfields, corresponding to input data; and a data driver to control the gray scale value of a pixel in a plurality of subfields in one frame based on the first, second and third control values, wherein the pixel is driven in an analog manner when the gray scale value corresponds to a voltage or is driven in a digital manner when the gray scale value corresponds to an emission time during a predetermined subfield among the plurality of subfields. 
     The pixel may be driven in the digital manner during subfields other than the predetermined subfield in the one frame. The pixel may be set to a non-emission state in an i-th subfield other than the predetermined subfield and maintains the non-emission state after the i-th subfield, wherein i is a natural number. 
     Each of the plurality of subfields may be set to a same time. Each of the plurality of subfields may be set to implement j gray scale value(s) when the pixel is driven in the digital manner, wherein j is a natural number. The pixel may be driven in the analog manner when the predetermined subfield implements 0 to j−1 gray scale values. 
     The timing controller may generate the first control value based on lower bits of the data, may generate the second control value based on upper bits of the data, and may generate the third control value which is increased in the order of “0”, “1”, “2”, . . . , corresponding to the order of the subfields. The data driver may include, in each channel, a controller to control the gray scale value corresponding to the first, second, and third control values. 
     The controller may include an operator to increase the third control value by 1 when the first control value is 0, and maintain the third control value as a previous number when the first control value is a number different from 0; a comparator to output a signal corresponding to the analog driving when the third control value is 0, and output a signal corresponding to the digital driving when the third control value is different from 0; and an output to generate a first data signal when the gray scale value indicated by the first control value corresponds to an analog driving signal, and to generate a second data signal when the gray scale value of the second control value corresponds to a digital driving signal. 
     The comparator may output the second data signal corresponding to the non-emission state of the pixel when the third control value is greater than the second control value, and output the second data signal corresponding to the emission state of the pixel when the third control value is not greater than the second control value. 
     In accordance with another embodiment, a method of driving a display device includes generating a first control value including information on low gray scale values of data, a second control value including information on high gray scale values of the data, and a third control value including subfield information; and controlling the gray scale value of a pixel in a plurality of subfields in one frame based on the first, second and third control values, wherein the pixel is driven in an analog manner when the gray scale value corresponds to a voltage or in a digital manner when the gray scale value corresponds to an emission time during a predetermined subfield among the plurality of subfields. 
     The pixel may be driven in the digital manner for subfields different from the predetermined subfield. The pixel may be set to a non-emission state in an i-th subfield other than the predetermined subfield and maintains the non-emission state after the i-th subfield, wherein i is a natural number. 
     Each of the plurality of subfields may be set to a same time. Each of the plurality of subfields may be set to implement j gray scale value(s) when the pixel is driven in the digital manner, wherein j is a natural number. The pixel may be driven in the analog manner during the predetermined subfield implements 0 to j−1 gray scale values. 
     The first control value may be generated based on lower bits of the data, the second control value may be generated based on upper bits of the data, and the third control value may be increased in the order of “0”, “1”, “2”, . . . , corresponding to the order of the subfields. 
     Controlling the gray scale value may include increasing the third control value by 1 when the first control value is 0, and maintaining the third control value as a previous value when the first control value is different from 0; determining whether the third control value is 0; driving the pixel in the analog manner during the predetermined subfield, when the third control value is 0; determining whether the third control value is greater than the second control value when the third control value is not 0; and allowing the pixel not to emit light during a corresponding subfield, when the third control value is greater than the second control value, and allowing the pixel to emits light when the third control value is not greater than the second control value. 
     In accordance with another embodiment, a display device includes a controller to generate a first control signal when a first number of bits of input data lie in a first range of gray scale values and a second control signal when the first number of bits lie in a second range of gray scale values; and a data driver to drive a pixel in a first manner based on the first control signal and to drive the pixel in a second manner based on the second control signal in a predetermined subfield of a frame. 
     The first manner may correspond to analog driving; the second manner may correspond to digital driving; and the predetermined subfield may be a first subfield of the frame. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features will become apparent to those of ordinary skill in the art by describing in detail exemplary embodiments with reference to the attached drawings in which: 
         FIG. 1  illustrates an embodiment of a display device; 
         FIG. 2  illustrates an example of a frame that may drive the display device; 
         FIG. 3  illustrates an embodiment of gray scale values that may be displayed during a frame period in  FIG. 2 ; 
         FIG. 4  illustrates an embodiment of a method for driving a display device; and 
         FIG. 5  illustrates an embodiment of a controller in a data driver of the display device. 
     
    
    
     DETAILED DESCRIPTION 
     Example embodiments are described more fully hereinafter with reference to the accompanying drawings; however, they may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey exemplary implementations to those skilled in the art. 
     In the drawing figures, the dimensions of layers and regions may be exaggerated for clarity of illustration. Also, when a first element is described as being coupled to a second element, the first element may be not only directly coupled to the second element but may also be indirectly coupled to the second element via a third element. Further, some of the elements that are not essential to the complete understanding of the invention are omitted for clarity. 
       FIG. 1  illustrates an embodiment of a display device which includes a scan driver  110 , a data driver  120 , a pixel unit  130  configured to include pixels  140 , and a timing controller  150 . The scan driver  110  supplies a scan signal to scan lines S 1  to Sn. For example, the scan driver  110  progressively supplies the scan signal to the scan lines S 1  to Sn every plural subfields included in one frame. 
     The timing controller  150  receives data (Data) and a synchronization signal from an external source. The timing controller  150  controls the scan driver  110  and the data driver  120  based on the synchronization signal. Also, the timing controller  150  generates a control signal CS using the Data and supplies the generated control signal CS to the data driver  120 . The control signal CS includes a first control value including information on low gray scale values, a second control value including information on high gray scale values, and a third control value including information on one or more subfields in a frame for driving the display device. 
     The data driver  120  supplies a data signal to data lines D 1  to Dm, corresponding to the scan signal during a subfield period. In one embodiment, the data driver  120  supplies a first data signal corresponding to analog driving and a second data signal corresponding to digital driving, corresponding to the first, second, and third control values during a specific or predetermined subfield period in one frame. The data driver  120  supplies the second data signal corresponding to digital driving during the other subfields except the specific or predetermined subfield. To this end, the data driver  120  may include a controller configured to output information on the gray scale value of a subfield corresponding to the first, second and third control values. 
     The first data signal is set to a specific voltage in a predetermined voltage range corresponding to a gray scale value to be expressed. For example, the first data signal may be set to a specific voltage so that low gray scale values (e.g., gray scale values from s 1 to 63) can be implemented. 
     The second data signal is set to a voltage corresponding to emission or non-emission of pixel  140 . The pixel  140  receiving the second data signal corresponding to the emission is set to an emission state during a corresponding subfield period. The pixel  140  receiving the second data signal corresponding to non-emission is set to a non-emission state during a corresponding subfield period. 
     The pixel unit  130  includes pixels  140  disposed in matrix form. Each pixel  140  receives the first or second data signal. When the pixel  140  receives the first data signal, the pixel  140  generates light with a luminance corresponding to the voltage of the first data signal during a specific subfield period. The pixel  140  receives the second data signal set to the emission or non-emission state during a corresponding subfield period. In the present embodiment, the pixel  140  may be implemented in various forms, e.g., pixel  140  may be configured to include an organic light emitting diode and a plurality of transistors. 
       FIG. 2  illustrates an example of a frame for driving a display device. The display may be the one illustrated in  FIG. 1  or may be a different display device. In this example, the frame includes four subfields SF 1  to SF 4 . A different number of subfields may be included in a frame in other embodiments. 
     Referring to  FIG. 2 , the frame  1 F is divided into first to fourth subfields SF 1  to SF 4 . The first subfield SF 1  is driven in a digital manner or an analog manner, and the second to fourth subfields SF 2  to SF 4  are driven in the digital manner. In one embodiment, the first to fourth subfields SF 1  to SF 4  are set to have the same duration. Thus, when the first to fourth subfields SF 1  to SF 4  are driven in a digital manner, each of the first to fourth subfields SF 1  to SF 4  implements the same gray scale value. For example, each of the first to fourth subfields SF 1  to SF 4  may implement 64 gray possible scale values corresponding to emission of the pixel  140 . If the subfields SF 1  to SF 4  implement the same gray scale value, it is possible to reduce false contour noise caused by an emission time difference. 
     The pixel  140  is set to continuously emit light during the second to fourth subfields SF 2  to SF 4  when driven in the digital manner. For example, when the pixel  140  is set to the non-emission state in the second subfield SF 2 , the pixel  140  is also set to the non-emission state in the third and fourth subfield periods SF 3  and SF 4 . Put differently, when pixel  140  is set to the non-emission state in a previous subfield corresponding to subfields SF 2  to SF 4  driven in the digital manner, the pixel  140  is also set to the non-emission state in a current subfield period that is not the first subfield SF 1 . 
     The first subfield SF 1  is driven in the analog or digital manner. For example, when driven in the analog manner, the first subfield SF 1  implements a gray scale value (e.g., gray scale value of 63 or less) lower than that (e.g., gray scale value of 64) to be expressed when driven in the digital manner. Thus, the pixels  140  receiving the first data signal supplied during the first subfield SF 1  generate light with a luminance corresponding to the voltage of the first data signal (e.g., implementation of gray scale values of 0 to 63). 
     Pixels  140  which receive the second data signal supplied during the first subfield SF 1  emit light corresponding to the second data signal. The pixels  140  receiving the second data signal may implement a gray scale value (e.g., gray scale value of 64) higher than that (e.g., gray scale value of 63) to be implemented with the first data signal. 
     As described above, in the present embodiment, low gray scale values are implemented in the analog manner during the first subfield SF 1 . As a result, it is possible to minimize the number of subfields SF 1  in the frame  1 F. This may improve gray scale value expression power. For example, in other display devices, about four subfields are additionally provided to implement low gray scales. Consequently, the supply time (every subfield) of a scan signal contributing to luminance is increased. Therefore, the number of gray scales to be expressed is limited. 
     However, in the present embodiment, pixel  140  is driven in the analog or digital manner during the first subfield SF 1 . Hence, it is possible to minimize false contour noise. In other words, as shown in  FIG. 3 , a gray scale value of 63 or less (in analog driving) and gray scale value of 64 or more (in digital driving) are expressed during the first subfield SF 1 . False contour noise caused by an emission time difference is not generated when driven in this way. 
     Specifically, if one of 63 possible gray scale values are implemented in the first subfield SF 1  and a gray scale value of 64 or more is implemented in the second subfield SF 2 , false contour noise is generated by an emission time difference. However, in the present embodiment, when one of 63 possible gray scale values of the input data is implemented and when gray scale values of the input data in a high range (e.g., gray scale values of 64 or more) are implemented, a gray scale value (e.g., 63+0=63) in this low range is expressed a gray scale value (e.g., 0+64=64) are expressed according to the movement of time. Thus, false contour noise is not generated. 
       FIG. 4  illustrates operations in an embodiment of a method for driving a display device. The display device may be the one in  FIG. 1  or another display device. 
     Referring to  FIG. 4 , the timing controller  140  generates first, second, and third control values corresponding to input data (operation S 200 ). The first control value (information on low gray scale values) includes information on gray scale values to be expressed in the analog manner in the first subfield SF 1 . The second control value (information on high gray scale values) includes information on other gray scale values except the gray scale value in the first control value. The third control value includes information on a subfield to be currently expressed. 
     For example, in a case where input data has 8 bits (i.e., 256 gray possible scale values), the lower 6 bits include information on 63 possible gray scale values. The upper 2 bits include information on 64 or more gray scale values. Thus, in the case where the input data has a value of “00111111”, the first control value is set to a gray scale value of 63 and the second control value is set to 0. The third control value is increased in the order of 0 (SF 1 ), 1 (SF 2 ), 2 (SF 3 ) and 3 (SF 4 ), corresponding to the four subfields of  FIG. 2 . 
     The control values generated in operation S 200  are supplied to the data driver  200 . The data driver  120  receiving the control values decides whether the first control value is “0” (operation S 202 ). If it is decided that the first control value is “0” in operation S 202 , the third control value is increased by “1” (operation S 204 ). 
     If the first control value is not “0” in operation S 202 , the data driver  120  decides whether the third control value is “0” (operation S 206 ). Similarly, after the third control value is increased by “1” in operation S 204 , the data driver  120  decides whether the third control value is “0” (operation S 206 ). 
     If the third control value is “0” in operation S 206 , a specific pixel is driven in the analog manner corresponding to the information on low gray scale values included in the first control value during the first subfield SF 1  (operation S 208 ). In other words, the data driver  120  generates a first data signal corresponding to the first control value. The first data signal is supplied to a specific pixel. Then, the specific pixel implements a predetermined gray scale value while controlling a current value corresponding to the first data signal during the first subfield SF 1 . 
     If the third control value is not “0” in operation S 206 , the data driver  120  decides whether the third control value is greater than the second control value (operation S 210 ). If the third control value is greater than the second control value, the specific pixel is set to a non-emission state during the corresponding subfield period (operation S 212 ). If the third control value is not greater than the second control value in operation S 210 , the specific pixel is set to an emission state during the corresponding subfield period (operation S 214 ). 
     As described above, in the present embodiment, the data driver  120  drives the pixels  140  in an analog or digital manner during the first subfield SF 1  using the control values supplied from the timing controller  150 . The data driver  120  expresses gray scale values while controlling the emission and non-emission of the pixels  140  during the second to fourth subfields SF 2  to SF 4  using the control values. 
     In one embodiment, the gray scale values may be implemented as shown in Table 1, which corresponds to the flowchart of  FIG. 4 . 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 First 
                 Second 
                 Third 
                   
                   
                   
                   
               
               
                   
                 control 
                 control 
                 control 
                   
                   
                   
                   
               
               
                 Data 
                 value 
                 value 
                 value 
                 SF1 
                 SF2 
                 SF3 
                 SF4 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 00 111111   
                 63 
                 0 
                 0→1→ 
                 Analog 
                 Non- 
                 Non- 
                 Non- 
               
               
                 (63) 
                   
                   
                 2→3 
                 (63) 
                 emission 
                 emission 
                 emission 
               
               
                 01 000000   
                 0 
                 1 
                 0→1→ 
                 Emission 
                 Non- 
                 Non- 
                 Non- 
               
               
                 
                   (64) 
                 
                   
                   
                 2→3 
                 (64) 
                 emission 
                 emission 
                 emission 
               
               
                 01 000001   
                 1 
                 1 
                 0→1→ 
                 Analog 
                 Emission 
                 Non- 
                 Non- 
               
               
                 
                   (65) 
                 
                   
                   
                 2→3 
                 (1) 
                 (64) 
                 emission 
                 emission 
               
               
                 10 001111   
                 15 
                 2 
                 0→1→ 
                 Analog 
                 Emission 
                 Emission 
                 Non- 
               
               
                 
                   (143) 
                 
                   
                   
                 2→3 
                 (15) 
                 (64) 
                 (64) 
                 emission 
               
               
                 11 000000   
                 0 
                 3 
                 0→1→ 
                 Emission 
                 Emission 
                 Emission 
                 Non- 
               
               
                 
                   (192) 
                 
                   
                   
                 2→3 
                 (64) 
                 (64) 
                 (64) 
                 emission 
               
               
                   
               
            
           
         
       
     
     In Table 1, (63), (64), etc., corresponds to gray scale values. In one embodiment, pixels  140  implement gray scale values while being driven in an analog or digital manner during the first subfield SF 1 . For example, in a case where the first control value of a specific pixel  140  is not “0” during the first subfield SF 1  (i.e., has gray scale values in the range of 1 to 63), the specific pixel  140  generates light of a corresponding gray scale value corresponding to the first data signal. The first control value of a specific pixel  140  is set to “0” when the gray scale value in the first subfield SF 1  is “0.’ 
     For example, consider the case where Data has a value of 143 corresponding to a binary string of bits of 10 001111 . The first six bits of Data (which have been underlined for emphasis) is a non-zero value, i.e., 15. The first control value, therefore, will have the value of 15. On the other hand, when the value of Data is 1192 corresponding to a binary string of bits of 11 000000 , the first six bits of Data is a zero value, i.e., 0. Thus, the first control value will have a value of 0. The first control value, therefore, is used to designate the value of a first number of bits in Data, which bits define a predetermined range of gray scale values, e.g., 0 to 63 in this example embodiment. 
     In a case where the second control value of the specific pixel  140  has a value of “1” or more, the specific pixel  140  is driven in the digital manner. For example, when a specific pixel  140  implements gray scale values corresponding to Data of “01000000,” “10000000,” and “11000000,” the second control value is set to the emission state corresponding to the second data signal during the first subfield SF 1 . 
       FIG. 5  illustrates an embodiment of the controller in the data driver. In this embodiment, the controller is positioned in each channel of the data driver to output information of the gray scale value of a subfield. 
     Referring to  FIGS. 4 and 5 , the controller includes an operation unit  122 , a comparison unit  124 , and an output unit  126 . The operation unit  122  receives first, second, and third control values from the timing controller  150  (operation S 200 ). Subsequently, the operation unit  122  increases the third control value by “1” when the first control value is “0”, and maintains the third control value as it is when the first control value is not “0” (operations S 202  and S 204 ). 
     The comparison unit  124  receives the third control value from the operation unit  122  and receives the second control value from the timing controller  150 . The comparison unit  124  outputs a signal corresponding to an analog driving when the third control value is “0” (operations S 206  and S 208 ). In this case, the output unit  126  generates a first data signal corresponding to the first control value and supplies the generated first data signal to a corresponding pixel  140 . 
     In a case where the third control value is not “0,” the comparison unit  124  compares the third and second control values. For example, the comparison unit  124  outputs a signal corresponding to a non-emission state when the third control value is greater than the second control value. Otherwise, the comparison unit  124  outputs a signal corresponding to an emission state (operations S 210 , S 212 , and S 214 ). In this case, the output unit  126  generates a second control signal corresponding to the emission or non-emission state and supplies the generated second data signal to the corresponding pixel  140 . 
     In one or more of the aforementioned embodiments, pixels are driven in subfield SF 1  based on the first control value or the second control value. In other embodiments, the pixel may be driven in a subfield different from the first subfield based on these control values. Also, pixels have been indicated to be driven in analog or digital (emission state) manner, or not driven at all (non-emission) based on these values. 
     By way of summation and review, a flat panel display device is driven in an analog or digital manner. When driven in the analog manner, a predetermined voltage is charged in a pixel and the luminance of the pixel is controlled to correspond to the charged voltage, thereby implementing a gray scale value. However, when driven in the analog manner, it is difficult to implement a uniform gray scale value due to variations of the threshold voltages and mobilities of the transistors in each pixel. 
     When driven in the digital manner, a voltage corresponding to an emission or non-emission state is charged in the pixel. The emission time of the pixel is controlled corresponding to the charged voltage, thereby implementing a gray scale value. Also, when driven in the digital manner, the voltage corresponding to the emission or non-emission state is supplied to the pixel. Hence, it is possible to implement a uniform gray scale value regardless of differences in the characteristics of the transistors in the pixels. However, when driven in the digital manner, the display quality may be lowered due to false contour noise caused by an emission time difference. 
     In the display device and the driving method thereof according to the aforementioned embodiments, pixels are driven in the analog or digital manner during a specific subfield period in each frame. For example, during the specific subfield period, a first pixel can implement 63 gray scale values in the analog manner, and a second pixel can implement 64 gray scale values in a digital manner. In this case, false contour noise is not generated by the emission time difference, and it is therefore possible to improve display quality. 
     Further, low gray scale values are implemented in the analog manner during a specific subfield period. Hence, it is possible to minimize the number of subfields included in the each frame. 
     The methods and processes described herein may be performed by code or instructions to be executed by a computer, processor, or controller. Because the algorithms that form the basis of the methods are described in detail, the code or instructions for implementing the operations of the method embodiments may transform the computer, processor, or controller into a special-purpose processor for performing the methods described herein. 
     Also, another embodiment may include a computer-readable medium, e.g., a non-transitory computer-readable medium, for storing the code or instructions described above. The computer-readable medium may be a volatile or non-volatile memory or other storage device, which may be removably or fixedly coupled to the computer, processor, or controller which is to execute the code or instructions for performing the method embodiments described herein. 
     Example embodiments have been disclosed herein, and although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. In some instances, as would be apparent to one of ordinary skill in the art as of the filing of the present application, features, characteristics, and/or elements described in connection with a particular embodiment may be used singly or in combination with features, characteristics, and/or elements described in connection with other embodiments unless otherwise specifically indicated. Accordingly, it will be understood by those of skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present invention as set forth in the following claims.