Abstract:
A display device and a method of driving the display, wherein the volume of background music is controlled depending upon the color or brightness of display images, and the power consumption is reduced. The display device includes a display unit with a plurality of pixels, a signal controller, and a volume controller. The display unit displays images by selectively activating pixels from among the plurality of pixels in accordance with input video signals and input image control signals. The signal controller reads the input video signals to generate on-pixel signals having information about the ratio of a number of the active pixels compared to a total number of pixels in the plurality of pixels per each frame. The volume controller determines a range from among predetermined ratio ranges corresponding to the ratio of the number of active pixels to define a plurality of volume levels, and determine the volume level corresponding to the on-pixel signal to control the volume according to the ratio corresponding to the determined volume level.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Korean Patent Application No. 10-2009-0050024, filed Jun. 5, 2009, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The described technology relates generally to a display device and a driving method thereof, and more particularly, to an organic light emitting diode (OLED) display and a method of driving the same. 
     2. Description of the Related Art 
     A display device has a display area including a plurality of pixels arranged on a substrate in the form of a matrix and scan and data lines connected to the respective pixels. Data signals are selectively applied to the pixels to display desired images. The display devices are classified into passive and active matrix types, depending upon the method of driving the pixels. Because of display resolution, contrast and response time, the current trend is towards using the active matrix type display device where respective unit pixels selectively turn on or off. 
     The display device is used as a display unit for a personal computer, a portable phone, a PDA, and other mobile information devices, or as a monitor for various kinds of information systems. A liquid crystal panel-based LCD, an organic light emitting diode (OLED) display, a plasma panel-based PDP, etc., are well known. Various kinds of emissive display devices, which are lighter in weight and volume than CRTs, have been recently developed, and particularly, the OLED display has come to the forefront as it provides increases in emissive efficiency, luminance, and viewing angle, and has a short response time. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the described technology and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
     SUMMARY OF THE INVENTION 
     Aspects of the present invention provide a display device and a driving method thereof having advantages of controlling the volume of background music depending upon the color or brightness of display images, and reducing the power consumption. 
     Aspects of the present invention provide a display device including a display unit having a plurality of pixels, a signal controller, and a volume controller. The display unit displays images by selectively activating pixels from among the plurality of pixels in accordance with input video signals and input image control signals. The signal controller reads the input video signals to generate on-pixel signals having information about a ratio of a number of the active pixels compared to a total number of pixels in the plurality of pixels per each frame. The volume controller determines a range from among predetermined ratio ranges corresponding to the ratio of the number of active pixels to define a plurality of volume levels, and determining the volume level corresponding to the on-pixel signal to control the volume according to the ratio corresponding to the detected volume level. The volume controller maintains a constant volume until the ratio of the active pixels reaches a predetermined reference value. The volume controller reduces the volume level-by-level based on the maintained volume until the ratio of the active pixels reaches the predetermined reference value. 
     In a method of driving a display device according to an exemplary embodiment, a plurality of pixels are selectively activated in accordance with input video signals and input image control signals so as to display images. The input video signals are read so as to generate on-pixel signals having information about the ratio of the number of active pixels to the total number of pixels in the plurality of pixels per each frame. The ratio of the number of active pixels is determined to correspond to a range from among predetermined ratio ranges to define a plurality of volume levels, the volume level corresponding to the on-pixel signal is determined, and the volume is controlled according to the ratio corresponding to the detected volume level. The volume is maintained constant until the ratio of the active pixels reaches a predetermined reference value. With the volume controlling, the volume is reduced level-by-level based on the maintained volume until the ratio of the active pixels reaches the predetermined reference value. 
     According to aspects of the present invention, the volume of background music is controlled according to the color or brightness of the display images so that the power consumption can be reduced. 
     Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a block diagram of a display device according to an exemplary embodiment; 
         FIG. 2  is an equivalent circuit diagram of the pixel PX shown in  FIG. 1 ; and 
         FIG. 3  is a flowchart illustrating a method of driving a display device according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. 
     Herein, when a first element is described as being connected to a second element, the first element may be directly connected to the second element or may be electrically connected or indirectly connected to the second element via a third element. 
       FIG. 1  is a block diagram of a display device according to an exemplary embodiment, and  FIG. 2  is an equivalent circuit diagram of the pixel PX shown in  FIG. 1 . Referring to  FIG. 1 , a display device according to an exemplary embodiment includes a display unit  100 , a scan driver  200 , a data driver  300 , a signal controller  400 , a volume controller  500 , and a sound output unit  600 . From the viewpoint of an equivalent circuit, the display unit  100  includes a plurality of signal lines S 1  to Sn and D 1  to Dm, and a plurality of pixels PX connected to those signal lines and arranged roughly in the form of a matrix. The signal lines S 1  to Sn and D 1  to Dm include a plurality of scan lines S 1  to Sn for transmitting scan signals, and a plurality of data lines D 1  to Dm for transmitting data voltages. The scan lines S 1  to Sn extend roughly in the pixel row direction and are substantially parallel to each other, and the data lines D 1  to Dm extend roughly in the pixel column direction and are substantially parallel to each other. Referring to  FIG. 2 , the pixel PXij, which is representative of the pixel PX illustrated in  FIG. 1 , is connected to the i-th (i=1, 2, . . . , n) scan line Si and the j-th (j=1, 2, . . . , m) data line Dj, and includes an organic light emitting element OLED, a driving transistor M 1 , a capacitor Cst, a switching transistor M 2 , and an emission control transistor M 3 . 
     The driving transistor M 1  has a control terminal, an input terminal, and an output terminal. The control terminal of the driving transistor M 1  is connected to the switching transistor M 2 , the input terminal of the driving transistor M 1  is connected to the driving voltage VDD, and the output terminal of the driving transistor M 1  is connected to the organic light emitting element OLED. The driving transistor M 1  outflows an electric current IOLED, which has a varied amperage corresponding to the voltage difference between the control and output terminals. 
     The switching transistor M 2  has a control terminal, an input terminal, and an output terminal. The control terminal of the switching transistor M 2  is connected to the scan line Si, the input terminal of the switching transistor M 2  is connected to the data line Dj, and the output terminal of the switching transistor M 2  is connected to the driving transistor M 1 . The switching transistor M 2  transmits a data signal, that is, a data voltage applied to the data line Dj, to the control terminal of the driving transistor M 1  in response to the scan signal applied to the scan line Si. 
     The capacitor Cst is connected between the control and input terminals of the driving transistor M 1 . The capacitor Cst stores the data voltage applied to the control terminal of the driving transistor M 1 , and stores it even after the switching transistor M 2  turns off. 
     The organic light emitting element OLED may be an organic light emitting diode (OLED), and has an anode connected to the output terminal of the driving transistor M 1  and a cathode connected to a common voltage VSS. The organic light emitting element OLED emits light that is varied in intensity, depending upon the electric current IOLED supplied from the driving transistor M 1 . 
     The organic light emitting elements OLED may emit light of one of the primary colors red, green, and blue, and the desired color may be expressed by a spatial or temporal sum of the three primary colors. Some of the organic light emitting elements OLED may emit light of a white color so as to heighten the luminance. Alternatively, the organic light emitting elements OLED of each of the respective pixels PX of the display unit  100  may emit light of a white color, and in this case, some of the pixels PX may further include a color filter (not shown) for converting the white-colored light from the organic light emitting elements OLED into any one of the primary colors. 
     The driving transistor M 1  and the switching transistor M 2  are each a p-channel field effect transistor (FET). In this case, the control terminal, the input terminal, and the output terminal correspond to the gate, the source, and the drain, respectively. However, at least one of the switching transistor M 2  and the driving transistor M 1  may be an n-channel field effect transistor. Furthermore, the transistors M 1  and M 2 , the capacitor Cst, and the organic light emitting element OLED may be changed in interconnection. The pixel PXij shown in  FIG. 2  illustrates a pixel of a display device, and another pixel having a different structure with at least two transistors or at least one capacitor may be used instead. 
     Referring to  FIG. 1  again, the scan driver  200  is connected to the scan lines S 1  to Sn of the display unit  100 , and sequentially applies scan signals to the scan lines S 1  to Sn in accordance with the scan control signals CONT 1 . The scan signals include a gate-on voltage Von (not shown) for turning on the switching transistor M 2 , and a gate-off voltage Voff (not shown) for turning off the switching transistor M 2 . If the switching transistor M 2  is a p-channel field effect transistor, the gate-on voltage Von and the gate-off voltage Voff are low and high voltages, respectively. 
     The data driver  300  is connected to the data lines D 1  to Dm of the display unit  100 , and converts the data signals DR, DG, and DB that are input from the signal controller  400  into data voltages in accordance with the data control signals CONT 2  so as to apply them to the data lines D 1  to Dm. 
     The signal controller  400  receives input signals IS, horizontal synchronization signals Hsync, vertical synchronization signals Vsync, and main clock signals MCLK from the outside, and generates image data signals DR, DG, and DB, scan control signals CONT 1 , data control signals CONT 2 , and sound control signals CONT 3 . The scan control signals CONT 1  include a scan start signal STV, and at least one clock signal for controlling the output cycle of the gate-on voltage Von. The scan control signals CONT 1  may further include an output enable signal OE for defining the duration of the gate-on voltage Von. The data control signals CONT 2  include horizontal synchronization start signals STH for starting the transmission of image data signals DR, DG, and DB, which correspond to a row of pixels PX, to the data driver  300 , and load signals LOAD for applying data voltages to the data lines D 1  to Dm. The volume control signals CONT 3  include on-pixel signals (OPS) containing information about the number of active pixels for one frame. The on-pixel signal (OPS) represents a percent ratio of the number of active pixels compared to the total number of pixels in the display unit  100 . For example, if the total number of pixels in the display unit  100  is 100, the on-pixel signal (OPS) is generated at 10% when the number of active pixels for one frame is 10. 
     The volume controller  500 , which controls the audio output of the display device as an audio controller, determines the ratio of the number of active pixels PX to the total number of pixels volume level-by-level, and detects the volume level corresponding to the on-pixel signals (OPS). The volume controller  500  controls the volume such that it is reduced by the ratio corresponding to the volume level corresponding to the on-pixel signal (OPS). According to the present exemplary embodiment, the volume controller  500  determines which of four volume levels corresponds to the ratio of the number of active pixels to the total number of pixels PX. That is, a first volume level demarcates the ratio of the number of active pixels to the total number of pixels PX in a range from 60% to less than 70%. A second volume level demarcates the ratio of the number of active pixels PX to the total number of pixels PX in a range from 70% to less than 80%. A third volume level demarcates the ratio of the number of active pixels PX to the total number of pixels PX in a range from 80% to less than 90%, and a fourth volume level demarcates the ratio of the number of active pixels PX to the total number of pixels PX in a range from 90% to 100%. However, aspects of the present invention are not limited thereto, and the ratio range of the number of active pixels may be varied so that the number of volume levels may increase or decrease. The volume controller  500  reduces the volume by a predetermined ratio as the volume level goes up, based on the reference volume. According to an exemplary embodiment, the volume is reduced by 10% at the first volume level, by 15% at the second volume level, by 20% at the third volume level, and by 30% at the fourth volume level. Furthermore, the volume is maintained to be constant when the ratio of the number of active pixels to the total number of pixels is in a range from 0% to 60%, and this volume is defined as a reference volume. However, it is understood that aspects of the present invention are not limited thereto, and the range of the reference volume may be varied in accordance with the ranges for the volume levels for the percent ratio of the active pixels PX. Furthermore, the volume control ratio per respective level may increase or decrease in accordance with the power consumption. 
     The sound output unit  600  controls the volume of the sound in accordance with the outputs of the volume controller  500  and outputs the volume-controlled sound. 
       FIG. 3  is a flowchart illustrating a method of driving a display device according to an exemplary embodiment. 
     Referring to  FIG. 3 , the signal controller  400  detects the number of active pixels PX per each frame from the input signals IS, and computes the ratio of the number of active pixels PX to the number of all of the pixels PX with a first operation S 1 . The computed ratio is output as the on-pixel signal (OPS). Thereafter, the volume controller  500  detects the level corresponding to the ratio computed at the first operation S 1 . Specifically, the volume controller  500  determines whether the ratio computed at the first operation S 1  is in the range of 60% to less than 70% with a second operation S 2 . When it is determined that the ratio computed at the first level S 1  is in that range, the volume controller  500  controls the volume such that the output volume is reduced by 10% of the reference volume with a third operation S 3 . When the ratio computed at the first operation S 1  is not in that range, a fourth operation S 4  is executed. In the operation S 4 , the volume controller  500  determines whether the ratio computed at the first operation S 1  is in the range of 70% to less than 80%. When it is determined that the ratio computed at the first operation S 1  is in that range, the volume controller  500  controls the volume such that the output volume is reduced by 15% of the reference volume with a fifth operation S 5 . When the ratio computed at the first operation S 1  is not in that range, a sixth operation S 6  is executed. In the operation S 6 , the volume controller  500  determines whether the ratio computed at the first operation S 1  is in the range of 80% to less than 90%. When it is determined that the ratio computed at the first operation S 1  is in that range, the volume controller  500  controls the volume such that the output volume is reduced by 20% of the reference volume, with a seventh operation S 7 . When the ratio computed at the first operation S 1  is not in that range, an eighth operation S 8  is executed. In the operation S 8 , the volume controller  500  determines whether the ratio computed at the first operation S 1  is in the range of 90% to 100%. When it is determined that the ratio computed at the first operation S 1  is in that range, the volume controller  500  controls the volume such that the output volume is reduced by 30% of the reference volume, with a ninth operation S 9 . 
     According to the exemplary embodiment described above, with a display device and a driving method thereof, when the ratio of the active pixels computed per-frame from the image signal increases, the volume is reduced level-by-level so that power consumption can be decreased. 
     Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of whic is defined in the claims and their equivalents.