Patent Publication Number: US-11386852-B2

Title: Display device performing multi-frequency driving

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2019-0090795, filed on Jul. 26, 2019 in the Korean Intellectual Property Office (KIPO), the entire content of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     1. Field 
     Example embodiments of the present disclosure relate to a display device, and more particularly to a display device that performs multi-frequency driving (MFD). 
     2. Description of the Related Art 
     Reduction of power consumption is desirable in a display device employed in a portable device, such as a smartphone, a tablet computer, etc. Recently, in order to reduce the power consumption of the display device, a low frequency driving technique (which drives or refreshes a display panel at a frequency lower than an input frame frequency of input image data) has been developed. 
     However, in a related art display device to which the low frequency driving technique is applied, when a still image is not displayed in an entire region of a display panel, or when the still image is displayed only in a partial region (e.g., a portion) of the display panel, the entire region of the display panel is driven at a driving frequency substantially the same as the input frame frequency. Thus, in this case, the low frequency driving may not be performed, and the power consumption may not be reduced. 
     SUMMARY 
     An aspect according to some example embodiments is directed toward a display device capable of reducing power consumption by performing multi-frequency driving (MFD) that drives partial panel regions at different driving frequencies and preventing or substantially preventing a frequency change (e.g., a frequency difference) between the partial panel regions from being perceived (e.g., by the user). 
     According to example embodiments, a display device includes a display panel including a first partial panel region and a second partial panel region, and a panel driver to drive the display panel. The panel driver is to further determine a first driving frequency for the first partial panel region and a second driving frequency for the second partial panel region. When the first driving frequency and the second driving frequency are different from each other, the panel driver is to further set a boundary portion including a boundary between the first partial panel region and the second partial panel region, and to determine a third driving frequency for the boundary portion to be between the first driving frequency and the second driving frequency. 
     In example embodiments, the third driving frequency may gradually decrease in a direction from one of the first and second partial panel regions driven at a higher one of the first and second driving frequencies to the other one of the first and second partial panel regions driven at a lower one of the first and second driving frequencies. 
     In example embodiments, the third driving frequency may gradually decrease per scan line. 
     In example embodiments, the third driving frequency may gradually decrease per N scan lines, where N is an integer greater than 0, for example, equal to or greater than 1. 
     In example embodiments, a boundary reference frequency may be determined to be gradually decreased in a direction from one of the first and second partial panel regions driven at a higher one of the first and second driving frequencies to the other one of the first and second partial panel regions driven at a lower one of the first and second driving frequencies, a line random frequency may be determined randomly with respect to each of a plurality of scan lines included in the boundary portion, and the third driving frequency may be determined as a sum of the boundary reference frequency and the line random frequency. 
     In example embodiments, the display device may be a foldable display device, and the boundary between the first partial panel region and the second partial panel region may correspond to a folding line of the foldable display device. 
     In example embodiments, when a moving image is displayed in a portion of the display panel, and a still image is displayed in another portion of the display panel, the first partial panel region may be set as the portion of the display panel in which the moving image is displayed, the second partial panel region may be set as the other portion of the display panel in which the still image is displayed, and the boundary between the first partial panel region and the second partial panel region may be dynamically changed. 
     In example embodiments, a portion of one of the first and second partial panel regions driven at a lower one of the first and second driving frequencies may be set as the boundary portion. 
     In example embodiments, a number of scan lines included in the boundary portion may be set by (e.g., according to) a boundary portion size parameter. 
     In example embodiments, the third driving frequency for the boundary portion may be set by (e.g., according to) a boundary portion frequency parameter. 
     In example embodiments, the panel driver may include a still image detector to receive input image data at an input frame frequency, to divide the input image data into first partial image data for the first partial panel region and second partial image data for the second partial panel region, and to determine whether each of the first and second partial image data represent a still image. 
     In example embodiments, the still image detector may include a representative value memory to store a representative value of the first partial image data in a previous frame and a representative value of the second partial image data in the previous frame, and a still image detecting block to calculate a representative value of the first partial image data in a current frame and a representative value of the second partial image data in the current frame, to determine whether the first partial image data represent the still image by comparing the calculated representative value of the first partial image data and the representative value of the first partial image data stored in the representative value memory, and to determine whether the second partial image data represent the still image by comparing the calculated representative value of the second partial image data and the representative value of the second partial image data stored in the representative value memory. 
     In example embodiments, the panel driver may further include a driving frequency decider to determine the first driving frequency for the first partial panel region according to whether the first partial image data represent the still image, and to determine the second driving frequency for the second partial panel region according to whether the second partial image data represent the still image. 
     In example embodiments, the driving frequency decider may include a flicker lookup table to store flicker values corresponding to a plurality of gray levels of image data, and a driving frequency deciding block to set the first driving frequency at the input frame frequency when the first partial image data do not represent the still image, to decide a first flicker value corresponding to a gray level of the first partial image data by utilizing the flicker lookup table when the first partial image data represent the still image, to set the first driving frequency at a driving frequency corresponding to the first flicker value when the first partial image data represent the still image, to set the second driving frequency at the input frame frequency when the second partial image data do not represent the still image, to decide a second flicker value corresponding to a gray level of the second partial image data by utilizing the flicker lookup table when the second partial image data represent the still image, and to set the second driving frequency at a driving frequency corresponding to the second flicker value when the second partial image data represent the still image. 
     In example embodiments, the panel driver may further include a boundary portion setter to compare the first driving frequency and the second driving frequency, to set a portion of one of the first and second partial panel regions driven at a lower one of the first and second driving frequencies as the boundary portion, and to determine the third driving frequency for the boundary portion to be between the first driving frequency and the second driving frequency, a data output unit to output the first partial image data and the second partial image data except for boundary image data for the boundary portion at the first driving frequency and the second driving frequency, respectively, and to output the boundary image data for the boundary portion at the third driving frequency, and a data driver to provide data signals to the display panel based on the first partial image data, the second partial image data and the boundary image data output from the data output unit. 
     In example embodiments, the panel driver may include a scan driver to provide scan signals to the first partial panel region at the first driving frequency, to provide the scan signals to the second partial panel region at the second driving frequency, and to provide the scan signals to the boundary portion at the third driving frequency. 
     In example embodiments, the scan driver may include a plurality of stages to generate scan signals at an input frame frequency for a plurality of scan lines included in the display panel, and a plurality of logic gates respectively connected to the plurality of stages, and to selectively output the scan signals generated by the plurality of stages in response to a scan output masking signal, respectively, such that the scan signals are provided to the first partial panel region, the second partial panel region and the boundary portion at the first driving frequency, the second driving frequency and the third driving frequency, respectively. 
     In example embodiments, each of the first and second partial panel regions may include a plurality of pixels, and each of the plurality of pixels may include a driving transistor to generate a driving current, a switching transistor to transfer a data signal to a source of the driving transistor, a compensating transistor diode-connected with the driving transistor, a storage capacitor to store the data signal transferred through the switching transistor and the diode-connected driving transistor, a first initializing transistor to provide an initialization voltage to the storage capacitor and a gate electrode of the driving transistor, a first emission controlling transistor to connect a line of a power supply voltage to a source electrode of the driving transistor, a second emission controlling transistor to connect a drain electrode of the driving transistor to an organic light emitting diode, a second initializing transistor to provide the initialization voltage to the organic light emitting diode, and the organic light emitting diode to emit light based on the driving current. At least one transistor selected from the driving transistor, the switching transistor, the compensating transistor, the first initializing transistor, the first emission controlling transistor, the second emission controlling transistor and the second initializing transistor may be implemented with a PMOS transistor, and at least one transistor selected from a remaining one of the driving transistor, the switching transistor, the compensating transistor, the first initializing transistor, the first emission controlling transistor, the second emission controlling transistor and the second initializing transistor may be implemented with an NMOS transistor. 
     According to example embodiments, a display device includes a display panel including a plurality of partial panel regions, and a panel driver to drive the display panel. The panel driver is to further determine a plurality of driving frequencies for the plurality of partial panel regions, respectively. When the driving frequencies for two adjacent partial panel regions of the plurality of partial panel regions are different from each other, the panel driver is to further set a boundary portion including a boundary between the two adjacent partial panel regions, and to determine a driving frequency for the boundary portion to be between the driving frequencies for the two adjacent partial panel regions. 
     In example embodiments, the driving frequency for the boundary portion may gradually decrease in a direction from one of the two adjacent partial panel regions at a relatively higher driving frequency to the other one of the two adjacent partial panel regions at a relatively lower driving frequency. 
     As described above, in a case where a first driving frequency for a first partial panel region and a second driving frequency for a second partial panel region are different from each other, a display device according to example embodiments may determine a third driving frequency for a boundary portion including a boundary between the first partial panel region and the second partial panel region to be between the first driving frequency and the second driving frequency. Accordingly, even when the first and second partial panel regions are driven at the different driving frequencies, a frequency change between the first and second partial panel regions may not be perceived (e.g., by the user). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Illustrative, non-limiting example embodiments will be more clearly understood from the following detailed description in conjunction with the accompanying drawings. 
         FIG. 1  is a block diagram illustrating a display device according to example embodiments. 
         FIG. 2A  is a diagram illustrating an example where a display device of  FIG. 1  is an in-folding display device, and  FIG. 2B  is a diagram illustrating an example where a display device of  FIG. 1  is an out-folding display device. 
         FIG. 3  is a diagram illustrating an example where a first partial panel region is set as a portion of a display panel in which a moving image is displayed and a second partial panel region is set as another portion of the display panel in which a still image is displayed. 
         FIG. 4  is a circuit diagram illustrating an example of a pixel included in a display device according to example embodiments. 
         FIG. 5  is a block diagram illustrating an example of a still image detector included in a display device according to example embodiments. 
         FIG. 6  is a block diagram illustrating an example of a driving frequency decider included in a display device according to example embodiments. 
         FIG. 7  is a diagram for describing an example where a boundary portion setter included in a display device sets a boundary portion according to example embodiments. 
         FIG. 8  is a diagram for describing an example where a data output unit included in a display device outputs first partial image data, second partial image data and boundary image data at different driving frequencies according to example embodiments. 
         FIG. 9  is a block diagram illustrating an example of a scan driver included in a display device according to example embodiments. 
         FIG. 10  is a timing diagram for describing an example of an operation of a scan driver included in a display device according to example embodiments. 
         FIG. 11  is a flowchart illustrating a method of operating a display device according to example embodiments. 
         FIG. 12  is a diagram for describing an example where a driving frequency for a boundary portion gradually decreases per scan line according to a method of  FIG. 11 . 
         FIG. 13  is a flowchart illustrating a method of operating a display device according to example embodiments. 
         FIG. 14  is a diagram for describing an example where a driving frequency for a boundary portion gradually decreases per one or more scan lines according to a method of  FIG. 13 . 
         FIGS. 15A and 15B  are first and second parts of a flowchart illustrating a method of operating a display device according to example embodiments. 
         FIG. 16  is a diagram for describing an example where a driving frequency for a boundary portion is determined based on a boundary reference frequency and a line random frequency according to the method of  FIGS. 15A and 15B . 
         FIG. 17  is a block diagram illustrating a display device according to example embodiments. 
         FIG. 18  is a diagram for describing an example where a boundary portion setter included in a display device sets a boundary portion according to example embodiments. 
         FIG. 19  is a block diagram illustrating an electronic device including a display device according to example embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the present disclosure will be explained in more detail with reference to the accompanying drawings. 
       FIG. 1  is a block diagram illustrating a display device according to example embodiments,  FIG. 2A  is a diagram illustrating an example where a display device of  FIG. 1  is an in-folding display device,  FIG. 2B  is a diagram illustrating an example where a display device of  FIG. 1  is an out-folding display device,  FIG. 3  is a diagram illustrating an example where a first partial panel region is set as a portion of a display panel in which a moving image is displayed and a second partial panel region is set as another portion of the display panel in which a still image is displayed,  FIG. 4  is a circuit diagram illustrating an example of a pixel included in a display device according to example embodiments,  FIG. 5  is a block diagram illustrating an example of a still image detector included in a display device according to example embodiments,  FIG. 6  is a block diagram illustrating an example of a driving frequency decider included in a display device according to example embodiments,  FIG. 7  is a diagram for describing an example where a boundary portion setter included in a display device sets a boundary portion according to example embodiments, and  FIG. 8  is a diagram for describing an example where a data output unit included in a display device outputs first partial image data, second partial image data and boundary image data at different driving frequencies according to example embodiments. 
     Referring to  FIG. 1 , a display device  100  according to example embodiments may include a display panel  110 , and a panel driver  190  that drives the display panel  110 . In some example embodiments, the panel driver  190  may include a data driver  120  that provides data signals DS to the display panel  110 , a scan driver  130  that provides scan signals SS to the display panel  110 , and a controller  140  that controls an operation of the display device  100 . 
     The display panel  110  may include a first partial panel region (e.g., a first portion of the display panel) PPR 1  and a second partial panel region (e.g., a second portion of the display panel) PPR 2 . For example, the display panel  110  may be divided into the first partial panel region PPR 1  and the second partial panel region PPR 2  such that each of the first and second partial panel regions PPR 1  and PPR 2  includes two or more scan lines, and/or two or more pixel rows connected to the two or more scan lines. 
     In some example embodiments, a boundary PPRB between the first partial panel region PPR 1  and the second partial panel region PPR 2  may have a fixed position within the display panel  110 . For example, the display device  100  may be a foldable display device, and the boundary PPRB between the first partial panel region PPR 1  and the second partial panel region PPR 2  may correspond to a folding line of the foldable display device. 
     In an example, as illustrated in  FIG. 2A , the display device  100  may be an in-folding display device  100   a  including an in-folding display panel  110   a  that is folded such that the first and second partial panel regions PPR 1   a  and PPR 2   a  face each other, and the boundary PPRB between the first and second partial panel regions PPR 1   a  and PPR 2   a  may have a fixed position corresponding to a folding line FL at which the in-folding display panel  110   a  is folded. In another example, as illustrated in  FIG. 2B , the display device  100  may be an out-folding display device  100   b  including an out-folding display panel  110   b  that is folded such that one of the first and second partial panel regions PPR 1   b  and PPR 2   b  is located at a front side (e.g., facing the viewer) and the other one of the first and second partial panel regions PPR 1   b  and PPR 2   b  is located at a back side (e.g., facing away from the viewer), and the boundary PPRB between the first and second partial panel regions PPR 1   b  and PPR 2   b  may have a fixed position corresponding to a folding line FL at which the out-folding display panel  110   b  is folded. Although  FIGS. 2A and 2B  illustrate examples where the display device  100  may be the foldable display devices  100   a  and  100   b , in some example embodiments, the display device  100  may be any suitable flexible display device, such as a curved display device, a bended (e.g., bendable) display device, a rollable display device, a stretchable display device, etc. In other example embodiments, the display device  100  may be a flat (e.g., rigid) display device. 
     In other example embodiments, the boundary PPRB between the first partial panel region PPR 1  and the second partial panel region PPR 2  may be dynamically changed. That is, the location of the boundary PPRB between the first partial panel region PPR 1  and the second partial panel region PPR 2  may change according to time. For example, as illustrated in  FIG. 3 , in a case where a moving image is displayed in a portion of the display panel  110   c , and a still image is displayed in another portion of the display panel  110   c , the first partial panel region PPR 1   c  may be set as the portion of the display panel in which the moving image is displayed, the second partial panel region PPR 2   c  may be set as the other portion of the display panel in which the still image is displayed, and thus the boundary PPRB between the first partial panel region PPR 1   c  and the second partial panel region PPR 2   c  may be set as a boundary between the moving image and the still image. In this case, when the boundary between the moving image and the still image is changed, the boundary PPRB between the first partial panel region PPR 1   c  and the second partial panel region PPR 2   c  also may be changed. 
     The display panel  110  may include a plurality of data lines, a plurality of scan lines, and a plurality of pixels PX connected to the plurality of data lines and the plurality of scan lines. Furthermore, each of the first partial panel region PPR 1  and the second partial panel region PPR 2  may include a plurality of pixels PX. In some example embodiments, each pixel PX may include at least one capacitor, at least two transistors and an organic light emitting diode (OLED), and the display panel  110  may be an OLED display panel. Further, in some example embodiments, each pixel PX may be a hybrid oxide polycrystalline (HOP) pixel suitable for low frequency driving capable of reducing power consumption. In the HOP pixel, at least one first transistor may be implemented with a low-temperature polycrystalline silicon (LTPS) p-type metal-oxide-semiconductor (PMOS) transistor, and at least one second transistor may be implemented with an oxide n-type metal-oxide-semiconductor (NMOS) transistor. 
     For example, as illustrated in  FIG. 4 , each pixel PX may include a driving transistor T 1  that generates a driving current, a switching transistor T 2  that transfers the data signal DS from the data driver  120  to a source (i.e., source electrode) of the driving transistor T 1  in response to a first scan signal SSP from the scan driver  130 , a compensating transistor T 3  that diode-connects (e.g., that is diode-connected with) the driving transistor T 1  in response to a second scan signal SSN from the scan driver  130 , a storage capacitor CST that stores the data signal DS transferred through the switching transistor T 2  and the diode-connected driving transistor T 1 , a first initializing transistor T 4  that provides an initialization voltage VINIT to the storage capacitor CST and a gate (i.e., gate electrode) of the driving transistor T 1  in response to a first initialization signal SI from the scan driver  130 , a first emission controlling transistor T 5  that connects a line of a high power supply voltage ELVDD to the source of the driving transistor T 1  in response to an emission control signal SEM from an emission driver, a second emission controlling transistor T 6  that connects a drain (i.e., drain electrode) of the driving transistor T 1  to an organic light emitting diode EL in response to the emission control signal SEM from the emission driver, a second initializing transistor (or a bypass transistor) T 7  that provides the initialization voltage VINIT to the organic light emitting diode EL in response to a second initialization signal (or a bypass signal) SB from the scan driver  130 , and the organic light emitting diode EL that emits light based on the driving current from the line of the high power supply voltage ELVDD to a line of a low power supply voltage ELVSS. 
     At least first one of the driving transistor T 1 , the switching transistor T 2 , the compensating transistor T 3 , the first initializing transistor T 4 , the first emission controlling transistor T 5 , the second emission controlling transistor T 6  and the second initializing transistor T 7  may be implemented with a PMOS transistor, and at least second one of the driving transistor T 1 , the switching transistor T 2 , the compensating transistor T 3 , the first initializing transistor T 4 , the first emission controlling transistor T 5 , the second emission controlling transistor T 6  and the second initializing transistor T 7  may be implemented with an NMOS transistor. That is, at least one transistor selected from the driving transistor T 1 , the switching transistor T 2 , the compensating transistor T 3 , the first initializing transistor T 4 , the first emission controlling transistor T 5 , the second emission controlling transistor T 6  and the second initializing transistor T 7  may be implemented with a PMOS transistor, and at least one transistor selected from the remaining ones of these transistors may be implemented with an NMOS transistor. For example, as illustrated in  FIG. 4 , the compensating transistor T 3 , the first initializing transistor T 4  and the second initializing transistor T 7  may be implemented with the NMOS transistors, and other transistors T 1 , T 2 , T 5  and T 6  may be implemented with the PMOS transistors. In this case, the second scan signal SSN applied to the compensating transistor T 3 , the first initialization signal SI applied to the first initializing transistor T 4  and the second initialization signal SB applied to the second initializing transistor T 7  may be active-high signals suitable for the NMOS transistor. In this case, because the transistors T 3  and T 4  directly connected to the storage capacitor CST and the transistor T 7  directly connected to the organic light emitting diode EL are implemented with the NMOS transistors, leakage currents from the storage capacitor CST and/or a parasitic capacitor of the organic light emitting diode EL may be reduced, and thus the pixel PX may be suitable for the low frequency driving. Although  FIG. 4  illustrates an example where the compensating transistor T 3 , the first initializing transistor T 4  and the second initializing transistor T 7  are implemented with the NMOS transistors, a configuration of each pixel PX according to example embodiments is not limited to the example of  FIG. 4 . In other example embodiments, the display panel  110  may be a liquid crystal display (LCD) panel, and/or the like. 
     The data driver  120  may generate the data signals DS based on output image data ODAT and a data control signal DCTRL received from the controller  140 , and may provide the data signals DS to the plurality of pixels PX through the plurality of data lines. In some example embodiments, the data control signal DCTRL may include, but not be limited to, an output data enable signal, a horizontal start signal and a load signal. In some example embodiments, the data driver  120  and the controller  140  may be implemented with a single integrated circuit, and the integrated circuit may be referred to as a timing controller embedded data driver (TED). In other example embodiments, the data driver  120  and the controller  140  may be implemented with separate integrated circuits. 
     The scan driver  130  may provide the scan signals SS to the plurality of pixels PX through the plurality of scan lines based on a scan control signal SCTRL received from the controller  140 . In some example embodiments, the scan driver  130  may provide the scan signals SS to the plurality of pixels PX sequentially on a row-by-row basis. Further, in some example embodiments, the scan control signal SCTRL may include, but not be limited to, a scan start signal FLM, a scan clock signal SCLK and a scan output masking signal SSOM. In some example embodiments, the scan driver  130  may be integrated with or formed in a peripheral portion of the display panel  110 . In other example embodiments, the scan driver  130  may be implemented with one or more integrated circuits. 
     The controller (e.g., a timing controller (TCON))  140  may receive input image data IDAT and a control signal CTRL from an external host (e.g., a graphic processing unit (GPU) or a graphic card). In some example embodiments, the control signal CTRL may include, but not be limited to, a vertical synchronization signal, a horizontal synchronization signal, an input data enable signal, a master clock signal, etc. The controller  140  may generate the data control signal DCTRL, the scan control signal SCTRL and the output image data ODAT based on the control signal CTRL and the input image data IDAT. The controller  140  may control an operation of the data driver  120  by providing the output image data ODAT and the data control signal DCTRL to the data driver  120 , and may control an operation of the scan driver  130  by providing the scan control signal SCTRL to the scan driver  130 . 
     The panel driver  190  of the display device  100  according to example embodiments may perform multi-frequency driving (MFD) that drives the first partial panel region PPR 1  and the second partial panel region PPR 2  of the display panel  110  at different first and second driving frequencies DF 1  and DF 2  respectively. In a case where the first and second driving frequencies DF 1  and DF 2  for the first and second partial panel regions PPR 1  and PPR 2  are different from each other, the panel driver  190  may set a boundary portion including the boundary PPRB between the first and second partial panel regions PPR 1  and PPR 2 , and may determine a third driving frequency DF 3  for the boundary portion to be between the first driving frequency DF 1  and the second driving frequency DF 2 . To perform these operations, in some example embodiments, the panel driver  190  may include a still image detector  150 , a driving frequency decider  160 , a boundary portion setter  170  and a data output unit  180 . In some example embodiments, as illustrated in  FIG. 1 , the still image detector  150 , the driving frequency decider  160 , the boundary portion setter  170  and the data output unit  180  may be included in the controller  140 . However, locations of the still image detector  150 , the driving frequency decider  160 , the boundary portion setter  170  and the data output unit  180  may not be limited to be inside the controller  140 . 
     The still image detector  150  may receive the input image data IDAT at the input frame frequency IFF, may divide the input image data IDAT into first partial image data PDAT 1  for the first partial panel region PPR 1  and second partial image data PDAT 2  for the second partial panel region PPR 2 , and may determine whether each of the first and second partial image data PDAT 1  and PDAT 2  represent a still image. In some example embodiments, the still image detector  150  may determine whether the first partial image data PDAT 1  represent the still image by comparing the first partial image data PDAT 1  in a previous frame with the first partial image data PDAT 1  in a current frame, and may determine whether the second partial image data PDAT 2  represent the still image by comparing the second partial image data PDAT 2  in the previous frame with the second partial image data PDAT 2  in the current frame. 
     For example, as illustrated in  FIG. 5 , the still image detector  150  may include a representative value memory  152  and a still image detecting block  154 . The representative value memory  152  may store a representative value of the first partial image data PDAT 1  in a previous frame and a representative value of the second partial image data PDAT 2  in the previous frame. The still image detecting block  154  may calculate a representative value of the first partial image data PDAT 1  in a current frame and a representative value of the second partial image data PDAT 2  in the current frame, may determine whether the first partial image data PDAT 1  represent the still image by comparing the calculated representative value of the first partial image data PDAT 1  and the representative value of the first partial image data PDAT 1  stored in the representative value memory  152 , and may determine whether the second partial image data PDAT 2  represent the still image by comparing the calculated representative value of the second partial image data PDAT 2  and the representative value of the second partial image data PDAT 2  stored in the representative value memory  152 . The still image detecting block  154  may output the first partial image data PDAT 1  and the second partial image data PDAT 2  to the driving frequency decider  160 , and may further output a first still image determination signal SSIF 1  representing whether the first partial image data PDAT 1  represent the still image and a second still image determination signal SSIF 2  representing whether the second partial image data PDAT 2  represent the still image. The still image detecting block  154  may store the calculated representative value of the first partial image data PDAT 1  and the calculated representative value of the second partial image data PDAT 2  in the current frame in the representative value memory  152  to be utilized in the next frame. 
     The driving frequency decider  160  may determine the first driving frequency DF 1  for the first partial panel region PPR 1  according to whether the first partial image data PDAT 1  represent the still image, and may determine the second driving frequency DF 2  for the second partial panel region PPR 2  according to whether the second partial image data PDAT 2  represent the still image. That is, the driving frequency decider  160  may set the first driving frequency DF 1  for the first partial panel region PPR 1  according to whether the first partial image data PDAT 1  represent the still image, and may set the second driving frequency DF 2  for the second partial panel region PPR 2  according to whether the second partial image data PDAT 2  represent the still image. In some example embodiments, the driving frequency decider  160  may determine the first driving frequency DF 1  for the first partial panel region PPR 1  as the input frame frequency IFF when the first partial image data PDAT 1  do not represent the still image (and/or represent a moving image), and may determine the first driving frequency DF 1  for the first partial panel region PPR 1  as a frequency lower than the input frame frequency IFF when the first partial image data PDAT 1  represent the still image. Further, the driving frequency decider  160  may determine the second driving frequency DF 2  for the second partial panel region PPR 2  as the input frame frequency IFF when the second partial image data PDAT 2  do not represent the still image (and/or represent the moving image), and may determine the second driving frequency DF 2  for the second partial panel region PPR 2  as a frequency lower than the input frame frequency IFF when the second partial image data PDAT 2  represent the still image. Further, in a case where each of the first and second partial image data PDAT 1  and PDAT 2  represent the still image, the driving frequency decider  160  may determine a flicker value according to a gray level (and/or luminance) of each of the first and second partial image data PDAT 1  and PDAT 2 , and may determine the first and second driving frequencies DF 1  and DF 2  according to the flicker values. 
     For example, as illustrated in  FIG. 6 , the driving frequency decider  160  may include a flicker lookup table (LUT)  162  and a driving frequency deciding block  164 . The flicker lookup table  162  may store flicker values corresponding to respective gray levels of image data. Here, the flicker value may represent a level of the flicker perceived by a user. The driving frequency deciding block  164  may determine (e.g., set) the first driving frequency DF 1  as the input frame frequency IFF in response to the first still image determination signal SSIF 1  representing that the first partial image data PDAT 1  do not represent the still image. In response to the first still image determination signal SSIF 1  representing that the first partial image data PDAT 1  represent the still image, the driving frequency deciding block  164  may decide a first flicker value corresponding to a gray level of the first partial image data PDAT 1  by utilizing the flicker lookup table  162 , and may determine the first driving frequency DF 1  as a driving frequency corresponding to the first flicker value. According to example embodiments, deciding the flicker value and determining the driving frequency may be performed on a pixel-by-pixel basis, a segment-by-segment basis, and/or a partial panel region-by-partial panel region basis. For example, the first partial image data PDAT 1  may be divided into a plurality of segments, flicker values for the respective segments may be decided, driving frequencies for the respective segments may be determined, and the first driving frequency DF 1  may be determined as the maximum one of the determined driving frequencies. That is, the first driving frequency DF 1  may be set at the highest determined driving frequency from among the determined driving frequencies of the plurality of segments of the first partial image date PDAT 1 . Further, the driving frequency deciding block  164  may determine the second driving frequency DF 2  as the input frame frequency IFF in response to the second still image determination signal SSIF 2  representing that the second partial image data PDAT 2  do not represent the still image. In response to the second still image determination signal SSIF 2  representing that the second partial image data PDAT 2  represent the still image, the driving frequency deciding block  164  may decide a second flicker value corresponding to a gray level of the second partial image data PDAT 2  by utilizing the flicker lookup table  162 , and may determine the second driving frequency DF 2  as a driving frequency corresponding to the second flicker value. The driving frequency deciding block  164  may output the first partial image data PDAT 1  and the second partial image data PDAT 2 , and may further output a first driving frequency signal SDF 1  representing the first driving frequency DF 1  for the first partial panel region PPR 1  and a second driving frequency signal SDF 2  representing the second driving frequency DF 2  for the second partial panel region PPR 2 . 
     The boundary portion setter  170  may compare the first driving frequency DF 1  represented by the first driving frequency signal SDF 1  and the second driving frequency DF 2  represented by the second driving frequency signal SDF 2 , may set a boundary portion including the boundary PPRB between the first partial panel region PPR 1  and the second partial panel region PPR 2  when the first driving frequency DF 1  and the second driving frequency DF 2  are different from each other, and may determine the third driving frequency DF 3  for the boundary portion to be between the first driving frequency DF 1  and the second driving frequency DF 2 . In some example embodiments, the boundary portion setter  170  may set a portion of one of the first and second partial panel regions PPR 1  and PPR 2  driven at a lower one of the first and second driving frequencies DF 1  and DF 2  as the boundary portion. 
     For example, as illustrated in  FIG. 7 , in a case where the first partial panel region PPR 1  includes 1st through 1280th scan lines SL 1 , SL 2 , SL 1280  (and/or 1280 pixel rows connected to the 1st through 1280th scan lines SL 1 , SL 2 , SL 1280 ), the second partial panel region PPR 2  includes 1281st through 2560th scan lines SL 1281 , . . . , SL 1290 , SL 1291 , SL 1292 , SL 2560  (and/or 1280 pixel rows connected to the 1281st through 2560th scan lines SL 1281 , SL 1290 , SL 1291 , SL 1292 , SL 2560 ), the first driving frequency DF 1  for the first partial panel region PPR 1  is about 120 Hz, and the second driving frequency DF 2  for the second partial panel region PPR 2  is about 15 Hz, the boundary portion setter  170  may set a portion of the second partial panel region PPR 2  driven at the relatively lower second driving frequency DF 2 , for example, the 1281st through 1290th scan lines SL 1281 , SL 1290  (and/or 10 pixel rows connected to the 1281st through 1290th scan lines SL 1281 , SL 1290 ) as the boundary portion BP. The boundary portion setter  170  may determine the third driving frequency DF 3  for the boundary portion BP to be higher than about 15 Hz and lower than about 120 Hz. Although  FIG. 7  illustrates an example where the boundary portion BP includes 10 scan lines SL 1281 , SL 1290 , a size of the boundary portion BP, and/or the number of scan lines included in the boundary portion BP may not be limited to the example of  FIG. 7 . In some example embodiments, the size of the boundary portion BP, and/or the number of scan lines included in the boundary portion BP may be set or updated by a boundary portion parameter PBP. For example, the controller  140  may store, as the boundary portion parameter PBP, a boundary portion size parameter, and the number of scan lines included in the boundary portion BP may be set by the boundary portion size parameter. 
     In some example embodiments, the boundary portion setter  170  may determine the third driving frequency DF 3  for the boundary portion BP such that the third driving frequency DF 3  may gradually decrease in a direction from one of the first and second partial panel regions PPR 1  and PPR 2  driven at a higher one of the first and second driving frequencies DF 1  and DF 2  to the other one of the first and second partial panel regions PPR 1  and PPR 2  driven at a lower one of the first and second driving frequencies DF 1  and DF 2 . Here, the term “gradually decrease” refers to that the third driving frequency includes one or more values between the values of the first driving frequency and second driving frequency, and is applied in the boundary portion BP in a generally descending order from a location adjacent to one of the first and second partial panel regions PPR 1  and PPR 2  with a higher one of the first and second driving frequencies DF 1  and DF 2  to a location adjacent to the other one of the first and second partial panel regions PPR 1  and PPR 2  driven at a lower one of the first and second driving frequencies DF 1  and DF 2 . In the example of  FIG. 7 , the third driving frequency DF 3  for the boundary portion BP may gradually decrease from the 1281st scan line SL 1281  close (e.g., closer) to the first partial panel region PPR 1  driven at the relatively higher first driving frequency DF 1  to the 1290th scan line SL 1290  close (e.g., closer) to the second partial panel region PPR 2  driven at the relatively lower second driving frequency DF 2 . In an example, the third driving frequency DF 3  for the boundary portion BP may gradually decrease per scan line. In another example, the third driving frequency DF 3  for the boundary portion BP may gradually decrease per N scan lines, where N is an integer greater than 0 (e.g., equal to or greater than 1). In other example embodiments, the third driving frequency DF 3  for the boundary portion BP may roughly (e.g., generally) decrease from the first partial panel region PPR 1  driven at the relatively higher first driving frequency DF 1  to the second partial panel region PPR 2  driven at the relatively lower second driving frequency DF 2 . However, the third driving frequency DF 3  for two directly adjacent scan lines included in the boundary portion BP may suitably increase or decrease. Further, in some example embodiments, the third driving frequency DF 3  for the boundary portion BP may be determined based on the boundary portion parameter PBP. For example, the controller  140  may store, as the boundary portion parameter PBP, a boundary portion frequency parameter including a frequency interval parameter, a frequency change amount parameter, etc., and the third driving frequency DF 3  may be determined or set based on the boundary portion frequency parameter. 
     As the output image data ODAT provided to the data driver  120 , the data output unit  180  may output the first partial image data PDAT 1  and the second partial image data PDAT 2  except for boundary image data BDAT for the boundary portion BP at the first driving frequency DF 1  and the second driving frequency DF 2 , respectively, and may output the boundary image data BDAT for the boundary portion BP at the third driving frequency DF 3 . Thus, the first partial panel region PPR 1  except for the boundary portion BP may be driven at the first driving frequency DF 1 , the second partial panel region PPR 2  except for the boundary portion BP may be driven at the second driving frequency DF 2 , and the boundary portion BP may be driven at the third driving frequency DF 3 . 
     For example, as illustrated in  FIGS. 7 and 8 , in a case where the input image data DAT are received at the input frame frequency IFF of about 120 Hz, the first driving frequency DF 1  for the first partial panel region PPR 1  is determined as about 120 Hz, and the second driving frequency DF 2  for the second partial panel region PPR 2  is determined as about 15 Hz, the boundary portion setter  170  may set a portion of the second partial panel region PPR 2 , for example, the 1281st through 1290th scan lines SL 1281 , . . . , SL 1290  as the boundary portion BP, and may determine the third driving frequency DF 3  for the boundary portion BP to be higher than about 15 Hz and lower than about 120 Hz. Further, in an example, the boundary portion setter  170  may set the third driving frequency DF 3 - 1  for a first portion (e.g., the 1281st through 1285th scan lines) of the boundary portion BP as about 60 Hz, and may set the third driving frequency DF 3 - 2  fora second portion (e.g., the 1286th through 1290th scan lines) of the boundary portion BP as about 30 Hz. In this case, the controller  140  may receive, as the input image data IDAT, 120 frame data FDAT in about 1 second at the input frame frequency IFF of about 120 Hz, and the data output unit  180  of the controller  140  may output the first partial image data PDAT 1  120 times and the second partial image data PDAT 2  15 times in about 1 second such that the first and second partial image data PDAT 1  and PDAT 2  except for boundary image data BDAT may be output at the first and second driving frequencies DF 1  and DF 2  of about 120 Hz and about 15 Hz. Thus, during eight frames, the data output unit  180  may output the first partial image data PDAT 1  eight times, and may output the second partial image data PDAT 2  once. Further, the data output unit  180  may output first boundary image data BDAT 1  for the first portion of the boundary portion BP 60 times in about 1 second such that the first boundary image data BDAT 1  may be output at the third driving frequency DF 3 - 1  of about 60 Hz, and may output second boundary image data BDAT 2  for the second portion of the boundary portion BP 30 times in about 1 second such that the second boundary image data BDAT 2  may be output at the third driving frequency DF 3 - 2  of about 30 Hz. Thus, during eight frames, the data output unit  180  may output the first boundary image data BDAT 1  four times, and may output the second boundary image data BDAT 2  twice. 
     The data driver  120  may receive the first partial image data PDAT 1 , the second partial image data PDAT 2  and the boundary image data BDAT at the first driving frequency DF 1 , the second driving frequency DF 2  and the third driving frequency DF 3 , respectively, and may provide the data signals DS to the display panel  110  based on the first partial image data PDAT 1 , the second partial image data PDAT 2  and the boundary image data BDAT. Because the first partial image data PDAT 1 , the second partial image data PDAT 2  and the boundary image data BDAT are received at the first driving frequency DF 1 , the second driving frequency DF 2  and the third driving frequency DF 3 , respectively, the data driver  120  may provide the data signals DS to the first partial panel region PPR 1  at the first driving frequency DF 1 , may provide the data signals DS to the second partial panel region PPR 2  at the second driving frequency DF 2 , and may provide the data signals DS to the boundary portion BP at the third driving frequency DF 3 . Further, the scan driver  130  may provide the scan signals SS to the first partial panel region PPR 1  at the first driving frequency DF 1 , may provide the scan signals SS to the second partial panel region PPR 2  at the second driving frequency DF 2 , and may provide the scan signals SS to the boundary portion BP at the third driving frequency DF 3 . Accordingly, the first partial panel region PPR 1  may be driven at the first driving frequency DF 1 , the second partial panel region PPR 2  may be driven at the second driving frequency DF 2 , and the boundary portion BP may be driven at the third driving frequency DF 3  between the first driving frequency DF 1  and the second driving frequency DF 2 . 
     In a related art case where the first and second partial panel regions PPR 1  and PPR 2  are driven at the different first and second driving frequencies DF 1  and DF 2 , and no boundary portion BP is set, a frequency change at the boundary PPRB between the first and second partial panel region PPR 1  and PPR 2  may be perceived by a user. However, in the display device  100  according to example embodiments, when the first and second driving frequencies DF 1  and DF 2  for the first and second partial panel regions PPR 1  and PPR 2  are different from each other, the third driving frequency DF 3  for the boundary portion BP may be determined to be between the first driving frequency DF 1  and the second driving frequency DF 2 . Accordingly, even when the first and second partial panel regions PPR 1  and PPR 2  are driven at the different first and second driving frequencies DF 1  and DF 2 , the frequency change at the boundary PPRB between the first and second partial panel regions PPR 1  and PPR 2  may not be perceived by the user. 
       FIG. 9  is a block diagram illustrating an example of a scan driver included in a display device according to example embodiments, and  FIG. 10  is a timing diagram for describing an example of an operation of a scan driver included in a display device according to example embodiments. 
     Referring to  FIGS. 1, 7, 8, 9 and 10 , a scan driver  130  included in a display device  100  according to example embodiments may provide scan signals SS to a first partial panel region PPR 1  at a first driving frequency DF 1 , may provide the scan signals SS to a second partial panel region PPR 2  at a second driving frequency DF 2 , and may provide the scan signals SS to the boundary portion BP at a third driving frequency DF 3 . To perform these operations, the scan driver  130  may include a plurality of stages  131 ,  132 ,  133 ,  134 , . . . , and a plurality of logic gates  136 ,  137 ,  138 ,  139 , . . . respectively connected to the plurality of stages  131 ,  132 ,  133 ,  134 , . . . . 
     The plurality of stages  131 ,  132 ,  133 ,  134 , . . . may generate a plurality of intermediate scan signals ISS 1  through ISS 2560  respectively corresponding to a plurality of scan lines SL 1  through SL 2560 , included in a display panel  110  at an input frame frequency IFF based on a scan start signal FLM and a scan clock signal SCLK. 
     The plurality of logic gates  136 ,  137 ,  138 ,  139 , . . . may selectively output, as a plurality of scan signals SS 1  through SS 2560 , the plurality of intermediate scan signals ISS 1  through ISS 2560  generated by the plurality of stages  131 ,  132 ,  133 ,  134 , . . . in response to a scan output masking signal SSOM, respectively. That is, the plurality of logic gates  136 ,  137 ,  138 ,  139 , . . . may selectively output a plurality of scan signals SS 1  through SS 2560 , in response to a scan output masking signal SSOM and the plurality of intermediate scan signals ISS 1  through ISS 2560  generated by the plurality of stages  131 ,  132 ,  133 ,  134 , . . . respectively. In some example embodiments, as illustrated in  FIG. 9 , the plurality of logic gates  136 ,  137 ,  138 ,  139 , . . . may be, but not be limited to, a plurality of OR gates that perform OR operations on the plurality of intermediate scan signals ISS 1  through ISS 2560  and the scan output masking signal SSOM. For example, each logic gate (e.g.,  136 ) may output a corresponding scan signal (e.g., SS 1 ) having a low level when both of a corresponding intermediate scan signal (e.g., ISS 1 ) and the scan output masking signal SSOM have the low level. 
     For example, as illustrated in  FIGS. 7, 8 and 10 , in a case where the first driving frequency DF 1  for the first partial panel region PPR 1  is determined to be substantially the same as the input frame frequency IFF of about 120 Hz, the second driving frequency DF 2  for the second partial panel region PPR 2  is determined as about 15 Hz, the third driving frequency DF 3 - 1  for a first portion (e.g., 1281st through 1285th scan lines) of the boundary portion BP is set as about 60 Hz, and the third driving frequency DF 3 - 2  for a second portion (e.g., 1286th through 1290th scan lines) of the boundary portion BP is set as about 30 Hz, the plurality of stages  131 ,  132 ,  133 ,  134 , . . . may generate the plurality of intermediate scan signals ISS 1  through ISS 2560  at the input frame frequency IFF of about 120 Hz, 1st through 1280th logic gates may output 1st through 1280th scan signals SS 1  through SS 1280  at the first driving frequency DF 1  of about 120 Hz in response to the scan output masking signal SSOM, 1281st through 1285th logic gates may output 1281st through 1285th scan signals SS 1281 , . . . at the third driving frequency DF 3 - 1  of about 60 Hz with respect to the first portion of the boundary portion BP in response to the scan output masking signal SSOM, 1286th through 1290th logic gates may output 1286th through 1290th scan signals . . . , SS 1290  at the third driving frequency DF 3 - 2  of about 30 Hz with respect to the second portion of the boundary portion BP in response to the scan output masking signal SSOM, and 1291st through 2560th logic gates may output 1291st through 2560th scan signals SS 1291  through SS 2560  at the second driving frequency DF 2  of about 15 Hz in response to the scan output masking signal SSOM. Accordingly, the first partial panel region PPR 1  may be driven at the first driving frequency DF 1 , the second partial panel region PPR 2  may be driven at the second driving frequency DF 2 , and the boundary portion BP may be driven at the third driving frequency DF 3 - 1  and DF 3 - 2  between the first driving frequency DF 1  and the second driving frequency DF 2 . 
       FIG. 11  is a flowchart illustrating a method of operating a display device according to example embodiments, and  FIG. 12  is a diagram for describing an example where a driving frequency for a boundary portion gradually decreases per scan line according to a method of  FIG. 11 . 
     Referring to  FIGS. 1 and 11 , a display device  100  according to example embodiments may receive input image data IDAT at an input frame frequency IFF (S 210 ). A still image detector  150  may divide the input image data IDAT into first partial image data PDAT 1  for a first partial panel region PPR 1  and second partial image data PDAT 2  for a second partial panel region PPR 2  (S 220 ), and may determine whether each of the first partial image data PDAT 1  and the second partial image data PDAT 2  represent a still image (S 230 ). 
     A driving frequency decider  160  may determine a first driving frequency DF 1  for the first partial panel region PPR 1  according to whether the first partial image data PDAT 1  represent the still image, and may determine a second driving frequency DF 2  for the second partial panel region PPR 2  according to whether the second partial image data PDAT 2  represent the still image (S 240 ). For example, the driving frequency decider  160  may determine the first driving frequency DF 1  for the first partial panel region PPR 1  as the input frame frequency IFF when the first partial image data PDAT 1  do not represent the still image (and/or represent a moving image), and may determine the first driving frequency DF 1  for the first partial panel region PPR 1  as a frequency lower than the input frame frequency IFF when the first partial image data PDAT 1  represent the still image. Further, the driving frequency decider  160  may determine the second driving frequency DF 2  for the second partial panel region PPR 2  as the input frame frequency IFF when the second partial image data PDAT 2  do not represent the still image (and/or represent the moving image), and may determine the second driving frequency DF 2  for the second partial panel region PPR 2  as a frequency lower than the input frame frequency IFF when the second partial image data PDAT 2  represent the still image. 
     A boundary portion setter  170  may compare the first driving frequency DF 1  and the second driving frequency DF 2  (S 250 ). When the first driving frequency DF 1  and the second driving frequency DF 2  are substantially the same (S 250 : YES), a boundary portion may not be set, the first partial panel region PPR 1  may be driven at the first driving frequency DF 1 , and the second partial panel region PPR 2  may be driven at the second driving frequency DF 2  (S 290 ). That is, in this case, the first partial panel region PPR 1  may be driven at the first driving frequency DF 1 , and the second partial panel region PPR 2  may be driven at the second driving frequency DF 2  (S 290 ), where the first and second driving frequencies DF 1  and DF 2  are substantially the same. 
     When the first driving frequency DF 1  and the second driving frequency DF 2  are different from each other (S 250 : NO), the boundary portion setter  170  may set a boundary portion including a boundary PPRB between the first partial panel region PPR 1  and the second partial panel region PPR 2  (S 260 ), and may determine a third driving frequency DF 3  for the boundary portion to be between the first driving frequency DF 1  and the second driving frequency DF 2  (S 270 ). In some example embodiments, as illustrated in  FIG. 12 , the boundary portion setter  170  may determine the third driving frequency DF 3  for the boundary portion such that the third driving frequency DF 3  may gradually decrease per scan line in a direction from one of the first and second partial panel regions PPR 1  and PPR 2  driven at a higher one of the first and second driving frequencies DF 1  and DF 2  to the other one of the first and second partial panel regions PPR 1  and PPR 2  driven at a lower one of the first and second driving frequencies DF 1  and DF 2 . 
     For example, as illustrated in  FIG. 12 , in a case where the moving image is displayed in the first partial panel region PPR 1  including 1st through 1280th scan lines SL 1  through SL 1280 , and the still image is displayed in the second partial panel region PPR 2  including 1281st through 2560th scan lines SL 1281  through SL 2560 , the first driving frequency DF 1  for the first partial panel region PPR 1  may be determined to be substantially the same as the input frame frequency IFF of about 120 Hz, and the second driving frequency DF 2  for the second partial panel region PPR 2  may be determined as about 1 Hz (which is lower than the input frame frequency IFF). The boundary portion setter  170  may set a portion of the second partial panel region PPR 2  driven at the relatively lower second driving frequency DF 2 , for example, the 1281st through 1290th scan lines SL 1281 , . . . , SL 1290  as the boundary portion BP. Further, the boundary portion setter  170  may determine the third driving frequency DF 3  for the boundary portion BP such that the third driving frequency DF 3  may gradually decrease per scan line from the 1281st scan line SL 1281  close (e.g., closer) to the first partial panel region PPR 1  driven at the relatively higher first driving frequency DF 1  to the 1290th scan line SL 1290  close (e.g., closer) to the second partial panel region PPR 2  driven at the relatively lower second driving frequency DF 2 . For example, the boundary portion setter  170  may set the third driving frequency DF 3  for the 1281st scan line SL 1281  as about 60 Hz, may set the third driving frequency DF 3  for the 1282nd scan line SL 1282  as about 40 Hz, may set the third driving frequency DF 3  for the 1283rd scan line SL 1283  as about 30 Hz, may set the third driving frequency DF 3  for the 1284th scan line SL 1284  as about 24 Hz, may set the third driving frequency DF 3  for the 1285th scan line SL 1285  as about 20 Hz, may set the third driving frequency DF 3  for the 1286th scan line SL 1286  as about 15 Hz, may set the third driving frequency DF 3  for the 1287th scan line SL 1287  as about 12 Hz, may set the third driving frequency DF 3  for the 1288th scan line SL 1288  as about 6 Hz, may set the third driving frequency DF 3  for the 1289th scan line SL 1289  as about 3 Hz, and may set the third driving frequency DF 3  for the 1290th scan line SL 1290  as about 2 Hz. 
     A panel driver  190  may drive the first partial panel region PPR 1  at the first driving frequency DF 1 , may drive the second partial panel region PPR 2  at the second driving frequency DF 2 , and may drive the boundary portion BP at the third driving frequency DF 3  that gradually decreases per scan line in a direction from the first partial panel region PPR 1  driven at the relatively higher first driving frequency DF 1  to the second partial panel region PPR 2  driven at the relatively lower second driving frequency DF 2  (S 290 ). Accordingly, even when the first and second partial panel regions PPR 1  and PPR 2  are driven at the different first and second driving frequencies DF 1  and DF 2 , a frequency change between the first and second partial panel region PPR 1  and PPR 2  may not be perceived (e.g., by the user). 
       FIG. 13  is a flowchart illustrating a method of operating a display device according to example embodiments, and  FIG. 14  is a diagram for describing an example where a driving frequency for a boundary portion gradually decreases per one or more scan lines according to the method of  FIG. 13 . 
     The method of  FIG. 13  may be substantially the same as the method of  FIG. 11 , except that a third driving frequency DF 3  for a boundary portion may gradually decrease per N scan lines (S 275 ), where N is an integer greater than 0 (e.g., equal to or greater than 1). In the method of  FIG. 13 , a boundary portion setter  170  may determine the third driving frequency DF 3  for the boundary portion such that the third driving frequency DF 3  may gradually decrease per the N scan lines in a direction from one of the first and second partial panel regions PPR 1  and PPR 2  driven at a higher one of the first and second driving frequencies DF 1  and DF 2  to the other one of the first and second partial panel regions PPR 1  and PPR 2  driven at a lower one of the first and second driving frequencies DF 1  and DF 2  (S 275 ). 
     For example, as illustrated in  FIG. 14 , in a case where the moving image is displayed in the first partial panel region PPR 1  including 1st through 1280th scan lines SL 1  through SL 1280 , and the still image is displayed in the second partial panel region PPR 2  including 1281st through 2560th scan lines SL 1281  through SL 2560 , the first driving frequency DF 1  for the first partial panel region PPR 1  may be determined to be substantially the same as an input frame frequency IFF of about 120 Hz, and the second driving frequency DF 2  for the second partial panel region PPR 2  may be determined as about 1 Hz (which is lower than the input frame frequency IFF). The boundary portion setter  170  may set a portion of the second partial panel region PPR 2  driven at the relatively lower second driving frequency DF 2 , for example, the 1281st through 1290th scan lines SL 1281 , . . . , SL 1290  as the boundary portion BP. Further, the boundary portion setter  170  may determine the third driving frequency DF 3  for the boundary portion BP such that the third driving frequency DF 3  may gradually decrease per one or more scan lines from the 1281st scan line SL 1281  (close to the first partial panel region PPR 1  driven at the relatively higher first driving frequency DF 1 ) to the 1290th scan line SL 1290  (close to the second partial panel region PPR 2  driven at the relatively lower second driving frequency DF 2 ). For example, the boundary portion setter  170  may set the third driving frequency DF 3  for the 1281st through 1284th scan lines SL 1281  through SL 1284  as about 60 Hz, may set the third driving frequency DF 3  for the 1285th through 1287th scan lines SL 1285  through SL 1287  as about 30 Hz, may set the third driving frequency DF 3  for the 1288th and 1289th scan line SL 1288  and SL 1289  as about 10 Hz, and may set the third driving frequency DF 3  for the 1290th scan line SL 1290  as about 5 Hz. 
     A panel driver  190  may drive the first partial panel region PPR 1  at the first driving frequency DF 1 , may drive the second partial panel region PPR 2  at the second driving frequency DF 2 , and may drive the boundary portion BP at the third driving frequency DF 3  that gradually decreases per one or more scan lines in a direction from the first partial panel region PPR 1  driven at the relatively higher first driving frequency DF 1  to the second partial panel region PPR 2  driven at the relatively lower second driving frequency DF 2  (S 290 ). Accordingly, even when the first and second partial panel regions PPR 1  and PPR 2  are driven at the different first and second driving frequencies DF 1  and DF 2 , a frequency change between the first and second partial panel region PPR 1  and PPR 2  may not be perceived (e.g., by the user). 
       FIGS. 15A and 15B  are first and second parts of a flowchart (e.g.,  FIGS. 15A and 15B  together forms a complete flowchart) illustrating a method of operating a display device according to example embodiments, and  FIG. 16  is a diagram for describing an example where a driving frequency for a boundary portion is determined based on a boundary reference frequency and a line random frequency according to the method of  FIGS. 15A and 15B . 
     The method of  FIGS. 15A and 15B  may be substantially the same as the method of  FIG. 11 , except that, with respect to a boundary portion, a boundary reference frequency may be determined (S 280 ), a line random frequency may be determined (S 282 ), and a third driving frequency DF 3  may be determined based on the boundary reference frequency and the line random frequency (S 284 ). In the method of  FIGS. 15A and 15B , a boundary portion setter  170  may determine the boundary reference frequency that gradually decreases in a direction from one of the first and second partial panel regions PPR 1  and PPR 2  driven at a higher one of the first and second driving frequencies DF 1  and DF 2  to the other one of the first and second partial panel regions PPR 1  and PPR 2  driven at a lower one of the first and second driving frequencies DF 1  and DF 2  (S 280 ), may randomly determine the line random frequency with respect to each of a plurality of scan lines included in the boundary portion (S 282 ), and may determine the third driving frequency DF 3  as a sum of the boundary reference frequency and the line random frequency (S 284 ). 
     For example, as illustrated in  FIG. 16 , in a case where the moving image is displayed in the first partial panel region PPR 1  including 1st through 1280th scan lines SL 1  through SL 1280 , and the still image is displayed in the second partial panel region PPR 2  including 1281st through 2560th scan lines SL 1281  through SL 2560 , the first driving frequency DF 1  for the first partial panel region PPR 1  may be determined to be substantially the same as an input frame frequency IFF of about 120 Hz, and the second driving frequency DF 2  for the second partial panel region PPR 2  may be determined as about 1 Hz (which is lower than the input frame frequency IFF). The boundary portion setter  170  may set a portion of the second partial panel region PPR 2  driven at the relatively lower second driving frequency DF 2 , for example, the 1281st through 1290th scan lines SL 1281 , . . . , SL 1290  as the boundary portion BP. Further, the boundary portion setter  170  may determine the boundary reference frequency BRF that gradually decreases per scan line as about 60 Hz, about 40 Hz, about 30 Hz, about 24 Hz, about 20 Hz, about 15 Hz, about 12 Hz, about 6 Hz, about 3 Hz and about 2 Hz with respect to the 1281st through 1290th scan lines SL 1281 , . . . , SL 1290 , may randomly determine the line random frequency LRF as about 0 Hz, about −10 Hz, about +10 Hz, about −9 Hz, about +4 Hz, about −9 Hz, about +3 Hz, about −4 Hz, about +1 Hz and about 0 Hz with respect to the 1281st through 1290th scan lines SL 1281 , . . . , SL 1290 , and thus may determine the third driving frequency DF 3  as about 60 Hz, about 30 Hz, about 40 Hz, about 15 Hz, about 24 Hz, about 6 Hz, about 15 Hz, about 2 Hz, about 4 Hz and about 2 Hz with respect to the 1281st through 1290th scan lines SL 1281 , . . . , SL 1290 . Accordingly, in the example of  FIG. 16 , the third driving frequency DF 3  for the boundary portion BP may roughly (e.g., generally) decrease from the first partial panel region PPR 1  driven at the relatively higher first driving frequency DF 1  to the second partial panel region PPR 2  driven at the relatively lower second driving frequency DF 2 . However, the third driving frequency DF 3  for two directly adjacent scan lines included in the boundary portion BP may increase or decrease. 
     A panel driver  190  may drive the first partial panel region PPR 1  at the first driving frequency DF 1 , may drive the second partial panel region PPR 2  at the second driving frequency DF 2 , and may drive the boundary portion BP at the third driving frequency DF 3  that roughly (e.g., generally) decreases in a direction from the first partial panel region PPR 1  driven at the relatively higher first driving frequency DF 1  to the second partial panel region PPR 2  driven at the relatively lower second driving frequency DF 2  (S 290 ). Accordingly, even when the first and second partial panel regions PPR 1  and PPR 2  are driven at the different first and second driving frequencies DF 1  and DF 2 , a frequency change between the first and second partial panel region PPR 1  and PPR 2  may not be perceived (e.g., by the user). 
       FIG. 17  is a block diagram illustrating a display device according to example embodiments, and  FIG. 18  is a diagram for describing an example where a boundary portion setter included in a display device sets a boundary portion according to example embodiments. 
     Referring to  FIG. 17 , a display device  300  according to example embodiments may include a display panel  310 , and a panel driver  390  that drives the display panel  310 . In some example embodiments, the panel driver  390  may include a data driver  320 , a scan driver  330 , and a controller  340 . Further, in some example embodiments, the controller  340  may include a still image detector  350 , a driving frequency decider  360 , a boundary portion setter  370  and a data output unit  380 . The display device  300  of  FIG. 17  may have a similar operation and a similar configuration to a display device  100  of  FIG. 1 , except that the display panel  310  may include three or more partial panel regions PPR 1 , PPR 2 , PPR 3  and PPR 4 , and the boundary portion setter  370  may set at least one boundary portion including a boundary PPRB 1 , PPRB 2  and/or PPRB 3  between adjacent two panel regions of the three or more partial panel regions PPR 1 , PPR 2 , PPR 3  and PPR 4 . 
     For example, as illustrated in  FIG. 18 , in a case where a moving image is displayed in a first portion of the display panel  310 , a still image is displayed in a second portion of the display panel  310 , a moving image is displayed in a third portion of the display panel  310 , and a still image is displayed in a fourth portion of the display panel  310 , the panel driver  390  may set the first portion of the display panel  310  in which the moving image is displayed as a first partial panel region PPR 1 , may set the second portion of the display panel  310  in which the still image is displayed as a second partial panel region PPR 2 , may set the third portion of the display panel  310  in which the moving image is displayed as a third partial panel region PPR 3 , and may set the fourth portion of the display panel  310  in which the still image is displayed as a fourth partial panel region PPR 4 . In some example embodiments, the number and positions of the partial panel regions PPR 1 , PPR 2 , PPR 3  and PPR 4  of the display panel  310  set by the panel driver  390  may be dynamically changed according to the number and positions of the moving images and the still images. 
     The driving frequency decider  360  may respectively determine first through fourth driving frequencies DF 1 , DF 2 , DF 3  and DF 4  for the first through fourth partial panel regions PPR 1 , PPR 2 , PPR 3  and PPR 4 . For example, the driving frequency decider  360  may determine the first driving frequency DF 1  for the first partial panel region PPR 1  in which the moving image is displayed to be substantially the same as an input frame frequency IFF, may determine the second driving frequency DF 2  for the second partial panel region PPR 2  in which the still image is displayed to be lower than the input frame frequency IFF, may determine the third driving frequency DF 3  for the third partial panel region PPR 3  in which the moving image is displayed to be substantially the same as the input frame frequency IFF, and may determine the fourth driving frequency DF 4  for the fourth partial panel region PPR 4  in which the still image is displayed to be lower than the input frame frequency IFF. 
     When the driving frequencies for two adjacent partial panel regions of the first through fourth partial panel regions PPR 1 , PPR 2 , PPR 3  and PPR 4  are different from each other, the boundary portion setter  370  may set a boundary portion BP 1 , BP 2  and BP 3  including a boundary PPRB 1 , PPRB 2  and PPRB 3  between the two adjacent partial panel regions of the first through fourth partial panel regions PPR 1 , PPR 2 , PPR 3  and PPR 4 , and may set a driving frequency for the boundary portion BP 1 , BP 2  and BP 3  to be between the driving frequencies for the two adjacent partial panel regions of the first through fourth partial panel regions PPR 1 , PPR 2 , PPR 3  and PPR 4 . 
     For example, as illustrated in  FIG. 18 , the boundary portion setter  370  may set a portion of the second partial panel region PPR 2  as a first boundary portion BP 1  between the first and second partial panel regions PPR 1  and PPR 2 , may set another portion of the second partial panel region PPR 2  as a second boundary portion BP 2  between the second and third partial panel regions PPR 2  and PPR 3 , and may set a portion of the fourth partial panel region PPR 4  as a third boundary portion BP 3  between the third and fourth partial panel regions PPR 3  and PPR 4 . Further, the boundary portion setter  370  may set a fifth driving frequency DF 5  for the first boundary portion BP 1  to be higher than the second driving frequency DF 2  for the second partial panel region PPR 2  and lower than the first driving frequency DF 1  for the first partial panel region PPR 1 , may set a sixth driving frequency DF 6  for the second boundary portion BP 2  to be higher than the second driving frequency DF 2  for the second partial panel region PPR 2  and lower than the third driving frequency DF 3  for the third partial panel region PPR 3 , and may set a seventh driving frequency DF 6  for the third boundary portion BP 3  to be higher than the fourth driving frequency DF 4  for the fourth partial panel region PPR 4  and lower than the third driving frequency DF 3  for the third partial panel region PPR 3 . In some example embodiments, the boundary portion setter  370  may set the fifth driving frequency DF 5  for the first boundary portion BP 1  to gradually decrease in a direction from the first partial panel region PPR 1  to the second partial panel region PPR 2 , may set the sixth driving frequency DF 6  for the second boundary portion BP 2  to gradually decrease in a direction from the third partial panel region PPR 3  to the second partial panel region PPR 2 , and may set the seventh driving frequency DF 6  for the third boundary portion BP 3  to gradually decrease in a direction from the third partial panel region PPR 3  to the fourth partial panel region PPR 4 . Accordingly, even when the two adjacent partial panel regions of the first through fourth partial panel regions PPR 1 , PPR 2 , PPR 3  and PPR 4  are driven at the different driving frequencies, a frequency change between the adjacent two partial panel regions of the first through fourth partial panel regions PPR 1 , PPR 2 , PPR 3  and PPR 4  may not be perceived (e.g., by the user). 
       FIG. 19  is an electronic device including a display device according to example embodiments. 
     Referring to  FIG. 19 , an electronic device  1100  may include a processor  1110 , a memory device  1120 , a storage device  1130 , an input/output (I/O) device  1140 , a power supply  1150 , and a display device  1160 . The electronic device  1100  may further include a plurality of ports for communicating with a video card, a sound card, a memory card, a universal serial bus (USB) device, other electric devices, etc. 
     The processor  1110  may perform various suitable computing functions or tasks. The processor  1110  may be an application processor (AP), a micro processor, a central processing unit (CPU), etc. The processor  1110  may be coupled to other components via an address bus, a control bus, a data bus, etc. Further, in some example embodiments, the processor  1110  may be further coupled to an extended bus (such as a peripheral component interconnection (PCI) bus). 
     The memory device  1120  may store data for operations of the electronic device  1100 . For example, the memory device  1120  may include at least one non-volatile memory device such as an erasable programmable read-only memory (EPROM) device, an electrically erasable programmable read-only memory (EEPROM) device, a flash memory device, a phase change random access memory (PRAM) device, a resistance random access memory (RRAM) device, a nano floating gate memory (NFGM) device, a polymer random access memory (PoRAM) device, a magnetic random access memory (MRAM) device, a ferroelectric random access memory (FRAM) device, etc., and/or at least one volatile memory device such as a dynamic random access memory (DRAM) device, a static random access memory (SRAM) device, a mobile dynamic random access memory (mobile DRAM) device, etc. 
     The storage device  1130  may be a solid state drive (SSD) device, a hard disk drive (HDD) device, a CD-ROM device, etc. The I/O device  1140  may be an input device such as a keyboard, a keypad, a mouse, a touch screen, etc., and/or an output device such as a printer, a speaker, etc. The power supply  1150  may supply power for operations of the electronic device  1100 . The display device  1160  may be coupled to other components through the buses or other communication links. 
     In a case where a first driving frequency for a first partial panel region and a second driving frequency for a second partial panel region are different from each other, the display device  1160  according to example embodiments may determine a third driving frequency for a boundary portion including a boundary between the first partial panel region and the second partial panel region to be between the first driving frequency and the second driving frequency. Accordingly, even when the first and second partial panel regions are driven at the different driving frequencies, a frequency change between the first and second partial panel regions may not be perceived (e.g., by the user). 
     The subject matter of the present disclosure may be applied to any suitable display device  1160 , and any suitable electronic device  1100  including the display device  1160 . For example, the subject matter of the present disclosure may be applied to a mobile phone, a smart phone, a wearable electronic device, a tablet computer, a television (TV), a digital TV, a 3D TV, a personal computer (PC), a home appliance, a laptop computer, a personal digital assistant (PDA), a portable multimedia player (PMP), a digital camera, a music player, a portable game console, a navigation device, etc. 
     Expressions such as “at least one of” or “at least one selected from” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. Further, the use of “may” when describing embodiments of the present invention refers to “one or more embodiments of the present invention.” Also, the term “exemplary” is intended to refer to an example or illustration. It will be understood that when an element or layer is referred to as being “on”, “connected to”, “coupled to”, or “adjacent to” another element or layer, it can be directly on, connected to, coupled to, or adjacent to the other element or layer, or one or more intervening elements or layers may be present. In contrast, when an element or layer is referred to as being “directly on,” “directly connected to”, “directly coupled to”, or “immediately adjacent to” another element or layer, there are no intervening elements or layers present. 
     As used herein, the term “substantially,” “about,” and similar terms are used as terms of approximation and not as terms of degree, and are intended to account for the inherent deviations in measured or calculated values that would be recognized by those of ordinary skill in the art. Moreover, any numerical range recited herein is intended to include all sub-ranges of the same numerical precision subsumed within the recited range. For example, a range of “1.0 to 10.0” is intended to include all subranges between (and including) the recited minimum value of 1.0 and the recited maximum value of 10.0, that is, having a minimum value equal to or greater than 1.0 and a maximum value equal to or less than 10.0, such as, for example, 2.4 to 7.6. Any maximum numerical limitation recited herein is intended to include all lower numerical limitations subsumed therein and any minimum numerical limitation recited in this specification is intended to include all higher numerical limitations subsumed therein. Accordingly, Applicant reserves the right to amend this specification, including the claims, to expressly recite any sub-range subsumed within the ranges expressly recited herein. All such ranges are intended to be inherently described in this specification such that amending to expressly recite any such subranges would comply with the requirements of 35 U.S.C. § 112, first paragraph, or 35 U.S.C. § 112(a), and 35 U.S.C. § 132(a). 
     The display device and/or any other relevant devices or components according to embodiments of the present invention described herein may be implemented utilizing any suitable hardware, firmware (e.g. an application-specific integrated circuit), software, or a combination of software, firmware, and hardware. For example, the various components of the display device may be formed on one integrated circuit (IC) chip or on separate IC chips. Further, the various components of the display device may be implemented on a flexible printed circuit film, a tape carrier package (TCP), a printed circuit board (PCB), or formed on one substrate. Further, the various components of the display device may be a process or thread, running on one or more processors, in one or more computing devices, executing computer program instructions and interacting with other system components for performing the various functionalities described herein. The computer program instructions are stored in a memory which may be implemented in a computing device using a standard memory device, such as, for example, a random access memory (RAM). The computer program instructions may also be stored in other non-transitory computer readable media such as, for example, a CD-ROM, flash drive, or the like. Also, a person of skill in the art should recognize that the functionality of various computing devices may be combined or integrated into a single computing device, or the functionality of a particular computing device may be distributed across one or more other computing devices without departing from the scope of the exemplary embodiments of the present invention. 
     The foregoing is illustrative of example embodiments and is not to be construed as limiting thereof. Although a few example embodiments have been described, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from the novel teachings and advantages of the present disclosure. Accordingly, all such modifications are intended to be included within the scope of the present disclosure as defined in the claims, and equivalents thereof. Therefore, it is to be understood that the foregoing is illustrative of various example embodiments and is not to be construed as limited to the specific example embodiments disclosed, and that modifications to the disclosed example embodiments, as well as other example embodiments, are intended to be included within the scope of the appended claims, and equivalents thereof.