Patent Publication Number: US-6982684-B2

Title: Brightness compensating low power display device and controller

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a display device, a display controller and a display control method. In particular, the present invention relates to a power saving display device, controller and control method. 
   A display device is shown in which low power consumption is achieved by driving pixels with driving voltages having opposite polarities in groups of every predetermined number of lines so as to reduce the frequency of inverting voltage polarity to be applied to the pixels. 
   However, it has been difficult for the above described display device to display images that maintain certain image quality with respect to uniform brightness over the entire display panel. 
   Therefore, it is a purpose of the present invention to provide a display device, a control device or controller, and a control method which solves the above described problem. This purpose is achieved by a combination of characteristics according to the independent claims of the present invention. In addition, dependent claims define further advantageous specific examples of the present invention. 
   SUMMARY OF THE INVENTION 
   According to a first form of the present invention, a display device including: a display panel having a plurality of pixels arranged in directions of a horizontal scanning and a vertical scanning; a driving voltage control unit or controller unit, for outputting to each of the plurality of pixels, a driving voltage for driving the above described pixel; and a correction unit, for each of the plurality of pixels to be driven by the driving voltage, for correcting a brightness of the pixel depending on a position of the above described pixel in the vertical scanning direction in the display panel, and a control device and a control method for controlling the above described display device are proposed. 
   According to a second form of the present invention, a display device including: a display panel having a plurality of pixels arranged in directions of a horizontal scanning and a vertical scanning; a data conversion unit for generating conversion data by converting data to be displayed for each of the plurality of pixels, depending on a position of the above described pixel in the vertical scanning direction in the display panel; and a driving voltage control unit for supplying each of the plurality of pixels with a driving voltage of a size or amplitude associated with the conversion data, and a control device and a control method for controlling the above described display device are proposed. 
   The above summary of the invention does not enumerate all of the necessary features for the present invention, but some combinations of these features may be also inventive features. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Some of the purposes of the invention having been stated, others will appear as the description proceeds, when taken in connection with the accompanying drawings, in which: 
       FIG. 1  is a functional block diagram of a display device  16 ; 
       FIG. 2  shows an example of a signal outputted by a gate driver  20  and a source driver  30 ; 
       FIG. 3  shows an example of the signal outputted by a gate driver  20  and a source driver  30 , in a first embodiement; 
       FIG. 4  is the functional block diagram of the display device  16  in a second embodiement; and 
       FIG. 5  shows an example of the signal outputted by a gate driver  20  and a source driver  30 , in the second embodiement. 
   

   DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS 
   While the present invention will be described more fully hereinafter with reference to the accompanying drawings, in which a preferred embodiment of the present invention is shown, it is to be understood at the outset of the description which follows that persons of skill in the appropriate arts may modify the invention here described while still achieving the favorable results of this invention. Accordingly, the description which follows is to be understood as being a broad, teaching disclosure directed to persons of skill in the appropriate arts, and not as limiting upon the present invention. 
   The present invention will be described in detail with respect to an embodiment thereof with reference to the accompanying drawings. 
   Referring now more particularly to the accompanying drawings,  FIG. 1  is a functional block diagram of a display device  16 . The display device  16  includes a gate driver  20 , a source driver  30 , a display panel  160  and a control device or controller  180 . The display panel  160  includes pixels  162   a–d  and transistors  164   a–d . The control device  180  is, for example, an LSI for controlling the display panel  160 , and includes a voltage supply unit  182  and a correction unit  184 . The source driver  30  is an example of a driving voltage control unit according to the present invention. 
   The display device  16  outputs a driving voltage of a size or amplitude associated with display data in each of a plurality of pixels, in a different polarity for every two lines in the display panel  160 . In this case, the display device  16  displays each pixel with a brightness which is different depending on whether the above described pixel is arranged at an odd line number or an even line number in the display panel  160 . For example, even if the display device  16  receives an indication for displaying an image of a uniform brightness from a user, it displays, as a result, a striped pattern in which the brightness of the pixel arranged at the even line number and the brightness of the pixel arranged at the odd line number are different from each other. Therefore, the display device  16  may provide a uniform image quality over the entire display panel  160  by correcting the brightness of a certain pixel depending on a position of the above described pixel in a vertical scanning direction in the display panel  160 . 
   The voltage supply unit  182  is supplied power by an external power supply, and supplies a voltage for generating the driving voltage to the gate driver  20  and the source driver  30 . The correction unit  184  receives externally generated clock signal and a control signal (not shown). Then the correction unit  184  converts a cycle of the clock signal in a predetermined method. The correction unit  184  sends the converted clock signal to the gate driver  20  along with the control signal. 
   The pixels  162   a–d  are condensers for changing a light transmitting volume or brightness with an electric charge volume, and are associated and connected with the transistors  164   a–d , respectively, for applying the voltage to the above described condensers. The source driver  30  receives the data to be displayed for each of the pixels  162   a–d  from outside the device, and outputs the appropriate size of driving voltage depending on the above described data. Then the gate driver  20  outputs a selection signal to the transistors  164   a–d  based on an instruction and the clock signal from the correction unit  184 , and applies the driving voltage to each of the pixels  162   a–d , respectively. 
   The source driver  30 , for example, outputs the driving voltage depending on the data to be displayed for each pixel, for each line in the display panel  160  (for example, first the pixel  162   a  and the pixel  162   b , and next the pixel  162   c  and the pixel  162   d ). In this case, the gate driver  20  outputs the selection signal to the transistors for each line in the display panel  160  (for example, first the transistor  164   a  and the transistor  164   b , and next the transistor  164   c  and the transistor  164   d ) via selection signal lines  166   a–c  to apply the driving voltage to the pixel on that line and correct the brightness of the above described pixel. 
     FIG. 2  shows an example of the signal outputted by the gate driver  20  and the source driver  30 . In each graph shown in  FIG. 2 , a horizontal axis represents a time. In each graph shown in  FIG. 2 , a vertical axis denotes the size of the driving voltage by the selection signal from the gate driver  20  and the source driver  30 . If the display device  16  receives the indication for displaying the data of the uniform brightness from outside, it outputs the driving voltage and the selection signal for applying the driving signal to the pixel as will be described below. 
   The source driver  30  outputs the driving voltage of the different polarity for every two lines as a predefined line number in the vertical scanning direction in the display panel  160  (FIG.  3 ( 1 )). For example, the source driver  30  outputs the driving voltage of a positive polarity to the pixels  162   a  and the pixel  162   c , and outputs the driving voltage of a negative polarity to the pixels arranged subsequently in the vertical scanning direction. Then, while the driving voltage is outputted to each pixel, the gate driver  20  outputs the selection signal to the selection signal line corresponding to the position of the above described pixel in the vertical scanning direction (for example, the selection signal line  166   a  with respect to the pixel  162   a ). 
   Then, the brightness of the pixel is affected by the size of the driving voltage at the time when the selection signal falls. Accordingly, in order to ensure that a desired driving voltage is applied to the pixel, the gate driver  20  desirably shifts the selection signal to fall earlier than falling of the driving voltage. For example the gate driver  20  shifts the selection signal on the selection signal line  166   b  to fall earlier than the falling of the driving voltage to the pixel  162   c.    
   On the other hand, the gate driver  20  may also shift a timing of rising of the selection signal by shifting the falling of the selection signal. For example, the gate driver  20  may shift the selection signal on the selection signal line  166   b  to rise earlier than starting of supplying the driving voltage to the pixel  162   c . Thereby, the brightness of the pixel  162   c  is affected by the driving voltage to the pixel  162   a . Here, the pixel  162   c  is affected by the driving voltage of the pixel  162   a  of the same positive polarity as the driving voltage of the above described pixel  162   c . On the other hand, the pixel adjacent to the pixel  162   c  in the vertical scanning direction is affected by the driving voltage of the pixel  162   c  of the polarity which is different from the polarity of the driving voltage to the above described pixel. In this way, overlapping of the selection signal and the driving voltage may be different depending on whether the pixel is arranged at the odd line number or the even line number. As a result, the display device  16  displays each pixel with the brightness which is different depending on whether the pixel is arranged at the odd line number or the even line number in the display panel  160 . 
   Therefore, the correction unit  184  outputs the clock signal whose cycle interval is periodically changed, to the gate driver  20 . Then the gate driver  20  outputs the selection signal having the same width as the cycle interval of this clock signal for each line in a horizontal scanning direction in the display panel, and thereby outputs the selection signal having a width which is different depending on the position in the vertical scanning direction in a predefined line number. For example, in  FIG. 2 , while the gate driver  20  outputs the selection signal having a predetermined width with respect to the odd line number (for example, the transistor  164   a  via the selection signal line  166   a ), the gate driver  20  outputs the selection signal having a width which is larger than the above described width (for example, the signal having a long application time) with respect to the even line number (for example, the transistor  164   c  via the selection signal line  166   b ). That is similar with respect to the third and subsequent lines. 
   The correction unit  184  may output the selection signal having a waveform which is different depending on whether each of the pixels is arranged at the odd line number or the even line number in the display panel  160 , as another example of correction depending on the position in the vertical scanning direction. For example, the correction unit  184  may output the selection signal having a rectangular shape to the pixel at the odd line number, and may output the selection signal having a trapezoidal shape to the pixel at the even line number. In addition, the correction unit  184  may output the selection signal with a frequency which is different depending on an arrangement position for the pixel. 
   In this way, the correction unit  184  may correct the brightness of the pixel depending on its position in the vertical scanning direction in the display panel  160 , for example, based on a setting and the like by a manufacturer or the user. As a result, the display device  16  may correct a bias of the waveform of the driving voltage and the like, and may provide the display of the uniform brightness over the entire display panel  160 . 
     FIG. 3  shows an example of the signal outputted by the gate driver  20  and the source driver  30 , in a first embodiement. Since the functional block diagram of the display device  16  in this embodiement is approximately the same as the functional block diagram of the display device  16  in  FIG. 1 , the description thereof is omitted. Since the respective axes in graphs shown in  FIG. 3  and FIG.  3 ( 1 ) are approximately the same as those in the graphs shown in  FIG. 2  and FIG.  2 ( 1 ), respectively, the description thereof is omitted. If the display device  16  receives the indication for displaying the data of the uniform brightness from outside, it outputs the driving voltage and the selection signal as will be described below. 
   The correction unit  184  outputs the selection signal having the waveform of a height which is different depending whether each of the plurality of pixels is arranged at the odd line number or the even line number in the display panel  160 , thereby corrects the brightness of the above described pixel (FIG.  3 ( 2 )). Specifically, the voltage supply unit  182  supplies the gate driver  20  with a plurality of voltages having sizes which are different from each other. Then the gate driver  20  selects these voltages alternately based on the instruction from the correction unit  184 , to output the selection signal having the waveform of the height which is different depending on the position in the vertical scanning direction in the display panel  160 . For example, in  FIG. 3 , while the gate driver  20  outputs the selection signal having the waveform of a certain height with respect to the transistor  164   a , the gate driver  20  outputs the selection signal having the waveform of a height which is higher than the above described height with respect to the transistor  164   c . That is similar with respect to the third and subsequent lines. In this way, in the first embodiement, the correction unit  184  may correct a deviation of the brightness due to the bias of the signal waveform of the driving voltage, by applying the driving voltage with the selection signal having the waveform of the height which is different depending on the position in the vertical scanning direction in the display panel  160 , and may provide the display of the uniform brightness over the entire display panel  160 . 
     FIG. 4  is a functional block diagram of the display device  16  in a second embodiement. The display device  16  in  FIG. 4  is configured by excluding the correction unit  184  from the display device  16  in  FIG. 1  and further adding a clock generation unit  194  and a data conversion unit  192  to the display device  16  in  FIG. 1 . The data conversion unit  192  receives the data to be displayed for the pixel. Then the data conversion unit  192  generates conversion data by converting the above described data depending on the position of the above described pixel in the vertical scanning direction in the display panel  160 , and sends the conversion data to the source driver  30 . For example, the data conversion unit  192  has a predetermined setting value (for example, 0.7) stored, and multiplies the data to be displayed for the pixel by this setting value to generate the conversion data. Then the source driver  30  supplies the driving voltage of the size associated with this conversion data to each of the pixels  162   a–d . On the other hand, the clock supply unit  194  acquires an externally generated reference clock and generates a predetermined clock signal to output it to the gate driver  20 . Since the remaining configuration is the same as  FIG. 2 , the description thereof is omitted. 
   As shown in  FIG. 4 , in the second embodiement, the display device  16  may convert the size of the driving voltage to be applied to each pixel by converting the data depending on the position in the vertical scanning, and may correct the brightness of the pixel. 
     FIG. 5  shows an example of the signal outputted by the gate driver  20  and the source driver  30 , in the second embodiement. Since the respective axes in graphs shown in  FIG. 5  are approximately the same as those in the graphs shown in  FIG. 2 , the description thereof is omitted. If the display device  16  receives the indication for displaying the data of the uniform brightness, it outputs the driving voltage and the selection signal as will be described below. In  FIG. 5 , if the pixel to be driven is located at the odd line number in the display panel  160 , the data conversion unit  192  executes a conversion of multiplying a data value by the setting value (for example, 0.7) previously stored, to generate the conversion data. On the other hand, the data conversion unit  192  does not execute the conversion with respect to the data of the pixel located at the even line number. The source driver  30 , based on the conversion data received from the data conversion unit  192 , outputs the driving voltage of the different polarity for every two lines as the predefined line number in the display panel  160  (FIG.  5 ( 1 )). In  FIG. 5 , for example, the gate driver  20  outputs the driving voltage of the size of multiplying the driving voltage to the pixel  162   c  by the predetermined setting value (for example, 0.7), to the pixel  162   a . On the other hand, the correction unit  184  outputs the uniform selection signal regardless of the arrangement position for the pixel, by the gate driver  20  (FIG.  5 ( 2 )). 
   In this way, the source driver  30  may compensate the bias of the waveform of the driving voltage by outputting the driving voltage of the size which is different depending the position in the vertical scanning direction in the display panel  160 , and may provide the display of the uniform brightness over the entire display panel  160 . 
   As apparent from this embodiment, if the display device  16  outputs the driving voltage of the different polarity for every predefined line number in the display panel  160 , it may provide the display of the uniform brightness over the entire display panel  160 . That is, the display device  16  may lower a frequency of inverting the polarity of the driving voltage, without degrading the image quality over the entire display panel  160 . Therefore, the display device  16  may reduce electric power consumption due to the low frequency of inverting the polarity of the driving voltage. 
   According to the embodiment described above, display devices, control devices and control methods are realized as will be described in the following respective items. 
   Though the present invention has been described above using the embodiment, a technical range of the present invention is not limited to a range described in the above describe embodiment. Various modifications or improvements may be added to the above described embodiment. It is apparent from the description in the claims that forms added with such modifications or improvements may also be included in the technical range of the present invention. For example, with respect to the above embodiment, the first embodiement and the second embodiement, a form in which all of them are combined and a form in which any two of them are combined are also included in the technical range of the present invention. 
   In the drawings and specifications there has been set forth a preferred embodiment of the invention and, although specific terms are used, the description thus given uses terminology in a generic and descriptive sense only and not for purposes of limitation. While the present invention has been described with respect to the embodiment of the invention, the technical scope of the present invention is not limited to the described embodiment. Various changes and modifications may be made in the described embodiment. As is apparent from the description in the appended Claims, modes of the present invention characterized by such changes and modifications are also included in the technical scope of the invention.