Patent Publication Number: US-2023146329-A1

Title: Display device and driving method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 17/036,916, filed Sep. 29, 2020, which claims priority to and the benefit of Korean Patent Application No. 10-2020-0023897, filed Feb. 26, 2020, the entire content of both of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field 
     Aspects of some example embodiments of the present disclosure relate to a display device and a driving method thereof. 
     2. Related Art 
     With the development of information technology, display devices, which provide a connecting medium between information and users, have become more important. Accordingly, the use of display devices, such as liquid crystal display devices, organic light-emitting display devices, plasma display devices, and the like, is increasing. 
     A display device may display a moving or video image by consecutively displaying a plurality of frames. Here, each of the frames may include an image display period, during which an image is displayed, and a mask period, during which no image is displayed. 
     It may be necessary to increase or decrease the mask period depending on the circumstances. A change in the mask period (that is, the increment or decrement) cannot be freely determined due to hardware/time constraints. Accordingly, there may be a problem in which a change in luminance is perceived by users depending on the change in the mask period. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background and therefore the information discussed in this Background section does not necessarily constitute prior art. 
     SUMMARY 
     Aspects of some example embodiments of the present disclosure are directed to a display device and a driving method thereof configured to subdivide the variation of a mask period, thereby preventing or reducing instances of a change in luminance that is perceptible to users even when the mask period is changed. 
     Aspects of some example embodiments of the present disclosure include a display device including a first pixel coupled to a first scan line and a data line, a second pixel coupled to a second scan line and the data line, and a scan driver configured to sequentially supply scan signals having a turn-on level to the first scan line and the second scan line during a first period and to simultaneously or concurrently supply scan signals having a turn-on level to the first scan line and the second scan line during a second period after the first period. A mask period may correspond to the difference between the start point of the second period and the start point of the first period in the next frame period, a first frame period and a second frame period may have different mask periods, a third frame period between the first frame period and the second frame period may have the same mask period as the first frame period, and a fourth frame period between the first frame period and the second frame period may have the same mask period as the second frame period. 
     According to some example embodiments, each frame period may include an image display period and the mask period, and the image display period may correspond to the difference between the start point of the first period and the start point of the second period in one frame period. 
     According to some example embodiments, the display device may further include a data driver configured to apply a data voltage corresponding to a mask grayscale to the data line during the second period. 
     According to some example embodiments, the display device may further include a scan start signal generator configured to supply a first scan start pulse, corresponding to the start point of the first period, and a second scan start pulse, corresponding to the start point of the second period, to the scan driver. 
     According to some example embodiments, the interval between the time at which the first scan start pulse is generated and the time at which the second scan start pulse is generated in the first frame period may be different from that in the second frame period, the interval between the time at which the first scan start pulse is generated and the time at which the second scan start pulse is generated in the third frame period may be the same as that in the first frame period, and the interval between the time at which the first scan start pulse is generated and the time at which the second scan start pulse is generated in the fourth frame period may be the same as that in the second frame period. 
     According to some example embodiments, the display device may further include a third pixel coupled to a third scan line and the data line and a fourth pixel coupled to a fourth scan line and the data line. The scan driver may supply a scan signal having a turn-on level to the third scan line during a third period and supply a scan signal having a turn-on level to the fourth scan line during a fourth period, and the first period, the third period, the second period, and the fourth period may be sequentially located in a frame period. 
     According to some example embodiments, the first period may be longer than each of the second period, the third period, and the fourth period. 
     According to some example embodiments, the second period, the third period, and the fourth period may have the same length. 
     According to some example embodiments, the number of scan signals having a turn-on level and output from the scan driver during the second period in the first frame period may be the same as the number of scan signals having a turn-on level and output from the scan driver during the second period in the second frame period. 
     Aspects of some example embodiments of the present disclosure may include a method of driving a display device including a scan driver, a first pixel coupled to a first scan line and a data line, and a second pixel coupled to a second scan line and the data line. The method may include sequentially supplying, by the scan driver, scan signals having a turn-on level to the first scan line and the second scan line during a first period of each frame period, and simultaneously or concurrently supplying, by the scan driver, scan signals having a turn-on level to the first scan line and the second scan line during a second period in each frame period. A mask period may correspond to the difference between the start point of the second period and the start point of the first period in the next frame period, a first frame period and a second frame period may have different mask periods, a third frame period between the first frame period and the second frame period may have the same mask period as the first frame period, and a fourth frame period between the first frame period and the second frame period may have the same mask period as the second frame period. 
     According to some example embodiments, the method may further include applying a data voltage corresponding to a mask grayscale to the data line during the second period. 
     According to some example embodiments, the method may further include supplying a first scan start pulse, corresponding to the start point of the first period, and a second scan start pulse, corresponding to the start point of the second period, to the scan driver. 
     According to some example embodiments, the interval between the time at which the first scan start pulse is generated and the time at which the second scan start pulse is generated in the first frame period may be different from that in the second frame period, the interval between the time at which the first scan start pulse is generated and the time at which the second scan start pulse is generated in the third frame period may be the same as that in the first frame period, and the interval between the time at which the first scan start pulse is generated and the time at which the second scan start pulse is generated in the fourth frame period may be the same as that in the second frame period. 
     According to some example embodiments, the display device may further include a third pixel coupled to a third scan line and the data line and a fourth pixel coupled to a fourth scan line and the data line. The scan driver may supply a scan signal having a turn-on level to the third scan line during a third period and supply a scan signal having a turn-on level to the fourth scan line during a fourth period, and the first period, the third period, the second period, and the fourth period may be sequentially located in a frame period. 
     According to some example embodiments, the first period may be longer than each of the second period, the third period, and the fourth period. 
     According to some example embodiments, the second period, the third period, and the fourth period may have the same length. 
     According to some example embodiments, the number of scan signals having a turn-on level and output from the scan driver during the second period in the first frame period may be the same as the number of scan signals having a turn-on level and output from the scan driver during the second period in the second frame period. 
     Aspects of some example embodiments of the present disclosure may include a display device including a first pixel coupled to a first scan line and a data line, a second pixel coupled to a second scan line and the data line, a scan driver configured to sequentially supply scan signals having a turn-on level to the first scan line and the second scan line in response to a first scan start pulse and to simultaneously or concurrently supply scan signals having a turn-on level to the first scan line and the second scan line in response to a second scan start pulse after the first scan start pulse, a mask duty controller configured to determine second mask periods for at least two consecutive frame periods based on a single first mask period, and a scan start signal generator configured to supply the first scan start pulse and the second scan start pulse in each frame period and to determine the interval between the time at which the first scan start pulse is generated and the time at which the second scan start pulse is generated based on the second mask period corresponding to each frame period. 
     According to some example embodiments, a first frame period and a second frame period may have different mask periods, a third frame period between the first frame period and the second frame period may have the same mask period as the first frame period, a fourth frame period between the first frame period and the second frame period may have the same mask period as the second frame period, the interval between the time at which the first scan start pulse is generated and the time at which the second scan start pulse is generated in the first frame period may be different from that in the second frame period, the interval between the time at which the first scan start pulse is generated and the time at which the second scan start pulse is generated in the third frame period may be the same as that in the first frame period, and the interval between the time at which the first scan start pulse is generated and the time at which the second scan start pulse is generated in the fourth frame period may be the same as that in the second frame period. 
     Aspects of some example embodiments of the present disclosure may include a display device including a plurality of pixels coupled to the same scan line. The plurality of pixels may display a monochromatic image during a first mask period of q horizontal periods and display a moving or video image during a first image display period of r horizontal periods, in each of consecutive first frame periods, each of the first frame periods may be configured with q+r horizontal periods, each of q and r being an integer greater than 0, the plurality of pixels may display a monochromatic image during a second mask period of q+1u horizontal periods and display a moving or video image during a second image display period of s horizontal periods, in each of consecutive second frame periods, each of the second frame periods may be configured with q+1u+s horizontal periods, each of u and s being an integer greater than 0, q+r horizontal periods may be the same as q+1u+s horizontal periods, the plurality of pixels may display a monochromatic image during a third mask period of q horizontal periods and display a moving or video image during a third image display period of r horizontal periods, in at least one third frame period, the plurality of pixels may display a monochromatic image during a fourth mask period of q+1u horizontal periods and display a moving or video image during a fourth image period of s horizontal periods, in at least one fourth frame period, the at least one third frame period and the at least one fourth frame period may be located between the end point of the consecutive first frame periods and the start point of the consecutive second frame periods, and the at least one third frame period and the at least one fourth frame period may be alternated with each other at regular intervals. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagram illustrating a display device according to some example embodiments of the present disclosure. 
         FIG.  2    is a diagram illustrating a pixel according to some example embodiments of the present disclosure. 
         FIG.  3    is a diagram illustrating a method of driving the pixel of  FIG.  2   . 
         FIG.  4    is a diagram illustrating a scan driver according to some example embodiments of the present disclosure. 
         FIG.  5    and  FIG.  6    are diagrams illustrating an image display period and a mask period according to some example embodiments of the present disclosure. 
         FIG.  7    is a diagram illustrating a difference in luminance perceived by a person depending on a display mode in response to the same image. 
         FIG.  8    is a diagram illustrating a change in luminance when a mask period is changed. 
         FIG.  9    and  FIG.  10    are diagrams illustrating the operations of a mask duty controller and a scan start signal generator according to some example embodiments of the present disclosure. 
         FIG.  11    and  FIG.  12    are diagrams illustrating a method of driving a display device according to some example embodiments of the present disclosure. 
         FIG.  13    and  FIG.  14    are diagrams illustrating other operations of a mask duty controller and a scan start signal generator according to some example embodiments of the present disclosure. 
         FIG.  15    is a diagram illustrating a change in actual luminance and a change in perceived luminance when a mask period is changed a related system. 
         FIG.  16    is a diagram illustrating a change in actual luminance and a change in perceived luminance when a mask period is changed according to some example embodiments of the present disclosure. 
         FIG.  17    is a diagram illustrating a display device according to some example embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, aspects of some example embodiments of the present disclosure will be described in more detail with reference to the attached drawings, such that those skilled in the art can implement embodiments according to the present disclosure. Aspects of embodiments according to the present disclosure may be embodied in various different forms without being limited to the following example embodiments. Aspects of embodiments according to the present disclosure may be used by being combined with each other, or may be used individually. 
     Furthermore, in the drawings, portions which are not related to the present disclosure will be omitted to explain the present disclosure more clearly. Reference should be made to the drawings, in which similar reference numerals are used throughout the different drawings to designate similar components. Therefore, reference numerals described in a previous drawing may be used in other drawings. 
     Since the sizes and thicknesses of respective components are arbitrarily indicated in drawings for convenience of description, the present disclosure is not limited by the drawings. The sizes, thicknesses, etc. of components in the drawings may be exaggerated to make the description of a plurality of layers and areas clear. 
       FIG.  1    is a diagram illustrating a display device according to some example embodiments of the present disclosure. 
     The display device  10  according to some example embodiments of the present disclosure may include a timing controller  11 , a data driver  12 , a scan driver  13 , a pixel component  14 , a sensor  15 , a mask duty controller  16 , and a scan start signal generator  17 . 
     The timing controller  11  may receive grayscale values and control signals for each image frame from an external processor. The control signals may include a vertical synchronization signal, a horizontal synchronization signal, a data enable signal, and the like. The vertical synchronization signal may include a plurality of pulses, and the time at which each of the pulses is generated may indicate that the previous frame period ends and the current frame period starts. The interval between adjacent pulses of the vertical synchronization signal may correspond to one frame period. The horizontal synchronization signal may include a plurality of pulses, and the time at which each of the pulses is generated may indicate that the previous horizontal period ends and a new horizontal period starts. The interval between adjacent pulses of the horizontal synchronization signal Hsync may correspond to one horizontal period. According to some example embodiments, one horizontal period may correspond to the minimum interval between the start points of scan signals having a turn-on level. The data enable signal may have an enable level for specific horizontal periods, and may have a disable level in the period excluding the specific horizontal periods. When the data enable signal has an enable level, this may indicate that grayscale values are supplied in the corresponding horizontal periods. The grayscale values may be supplied in units of pixel rows in each of the corresponding horizontal periods. 
     The timing controller  11  may perform rendering on grayscale values so as to correspond to the specifications of the display device  10 . For example, the external processor may supply a red grayscale value, a green grayscale value, and a blue grayscale value for each unit dot. However, when, for example, the pixel component  14  is in a pentile structure, because neighboring unit dots share a pixel, each grayscale value may not correspond to the pixel in a one-to-one manner. In this case, it is necessary to perform rendering on the grayscale values. When each grayscale value corresponds to the pixel in a one-to-one manner, it may be unnecessary to perform rendering on the grayscale values. The grayscale values on which rendering is or is not performed may be supplied to the data driver  12 . Also, the timing controller  11  may supply the data driver  12 , the scan driver  13 , the sensor  15 , and the like with control signals suitable for the specifications thereof in order to display a frame. Also, the timing controller  11  may supply first mask duty information BDY1. 
     The data driver  12  may generate data voltages to be supplied to data lines D 1 , D 2 , D 3 , and Dm using the grayscale values and control signals. For example, the data driver  12  may sample the grayscale values using a clock signal and apply data voltages, corresponding to the grayscale values, to the data lines D 1  to Dm in units of pixel rows. Here, m may be an integer greater than 0. 
     The scan driver  13  may receive clock signals and output enable signals from the timing controller  11 , and may generate scan signals to be supplied to scan lines S 11 , S 21 , S 12 , S 22 , S 1   n  and S 2   n  by receiving a scan start signal from the scan start signal generator  17 . Here, n may be an integer greater than 0. In a first mode, the scan start signal may include at least two scan start pulses STP 1  and STP 2  in one frame period. In a second mode, the scan start signal may include only one scan start pulse STP 1  in one frame period. The example configuration and operation of the scan driver  13  will be described in more detail later with reference to  FIG.  4   . 
     The sensor  15  may supply an initialization voltage to sensing lines  11 ,  12 ,  13  and Ip by receiving a control signal from the timing controller  11 , or may receive a sensing signal. For example, the sensor  15  may supply the initialization voltage to the sensing lines I 1 , I 2 , I 3  and Ip during at least a portion of a display period. For example, the sensor  15  may receive sensing signals through the sensing lines I 1 , I 2 , I 3  and Ip during at least a portion of a sensing period. The sensor  15 , the timing controller  11 , the data driver  12 , or any other controller may calculate the characteristics of each pixel PXij using the received sensing signals. The characteristics of each pixel PXij may be the threshold voltage of a driving transistor, the mobility, or the degree by which a light-emitting diode is degraded. Here, p may be an integer greater than 0. 
     The pixel component  14  includes a plurality of pixels. Each of the pixels PXij may be coupled to a data line, a scan line, and a sensing line corresponding thereto. The example configuration and operation of the pixel PXij will be described in more detail later with reference to  FIG.  2    and  FIG.  3   . 
     The mask duty controller  16  may receive the first mask duty information BDY 1  and supply second mask duty information BDY 2  based on the first mask duty information BDY 1 . The first mask duty information BDY 1  may include information about a first mask period, and the second mask duty information BDY 2  may include information about a second mask period. The mask duty controller  16  may determine second mask periods for at least two consecutive frame periods based on a single first mask period. 
     The scan start signal generator  17  may receive the second mask duty information BDY 2  and supply a scan start signal including a first scan start pulse STP 1  and a second scan start pulse STP 2  based on the second mask duty information BDY 2 . The second scan start pulse STP 2  may be generated in the same frame period as the first scan start pulse STP 1  corresponding thereto. 
     The scan start signal generator  17  may supply the first scan start pulse STP 1  and the second scan start pulse STP 2  in each frame period, and may determine the interval between the time at which the first scan start pulse STP 1  is generated and the time at which the second scan start pulse STP 2  is generated based on the second mask period corresponding to each frame period. 
     The mask duty controller  16  and the scan start signal generator  17  will be described in more detail with reference to  FIG.  9    and  FIG.  10   . 
       FIG.  2    is a diagram illustrating a pixel according to some example embodiments of the present disclosure. 
     Referring to  FIG.  2   , the pixel PXij according to some example embodiments of the present disclosure may include transistors T 1 , T 2  and T 3 , a storage capacitor Cst, and a light-emitting diode LD. 
     The transistors T 1 , T 2  and T 3  may be configured as N-type transistors. According to some example embodiments, the transistors T 1 , T 2  and T 3  may be configured as P-type transistors. According to some example embodiments, the transistors T 1 , T 2  and T 3  may be configured as a combination of N-type transistors and P-type transistors. The P-type transistor commonly indicates a transistor configured such that the amount of applied current increases when the difference between the voltage of a gate electrode and that of a source electrode increases in a negative direction. The N-type transistor commonly indicates a transistor configured such that the amount of applied current increases when the difference between the voltage of a gate electrode and that of a source electrode increases in a positive direction. The transistor may be configured in any of various forms such as a thin-film transistor (TFT), a field effect transistor (FET), a bipolar junction transistor (BJT), and the like. 
     The first transistor T 1  may be configured such that the gate electrode thereof is coupled to a first node N 1 , the first electrode thereof is coupled to a first power source ELVDD, and the second electrode thereof is coupled to a second node N 2 . The first transistor T 1  may be referred to as a driving transistor. 
     The second transistor T 2  may be configured such that the gate electrode thereof is coupled to a data scan line S 1   i , the first electrode thereof is coupled to a data line Dj, and the second electrode thereof is coupled to the first node N 1 . The second transistor T 2  may be referred to as a scanning transistor. 
     The third transistor T 3  may be configured such that the gate electrode thereof is coupled to a sensing scan line S 2   i , the first electrode thereof is coupled to the second node N 2 , and the second electrode thereof is coupled to a sensing line Ik. The third transistor T 3  may be referred to as a sensing transistor. 
     The storage capacitor Cst may be configured such that the first electrode thereof is coupled to the first node N 1  and the second electrode thereof is coupled to the second node N 2 . 
     The light-emitting diode LD may be configured such that the anode thereof is coupled to the second node N 2  and the cathode thereof is coupled to a second power source ELVSS. The light-emitting diode LD may be configured in any of various forms such as an organic light-emitting diode, an inorganic light-emitting diode, a quantum dot diode, a quantum well diode, and the like. Also, the light-emitting diode LD is illustrated as a single light-emitting diode in  FIG.  2   , but embodiments according to the present disclosure are not limited thereto, and according to some example embodiments, the light-emitting diode LD may be configured as a plurality of light-emitting diodes coupled in parallel, in series, or in series and parallel. 
     Generally, the voltage of the first power source ELVDD may be higher than the voltage of the second power source ELVSS. However, the voltage of the second power source ELVSS may be set higher than the voltage of the first power source ELVDD in a special situation in which the light-emitting diode LD is prevented from emitting light (for example, during a portion of a sensing period). 
       FIG.  3    is a diagram illustrating a method of driving the pixel of  FIG.  2   . 
     During a display period, the sensing line Ik may be coupled to an initialization power source VINT. 
     During the display period, data voltages DV(i−1), DVi and DV(i+1) may be sequentially applied to the data line Dj in units of horizontal periods. A scan signal having a turn-on level (a high level) may be applied to the data scan line S 1   i  in the corresponding horizontal period. Also, a scan signal having a turn-on level may also be applied to the sensing scan line S 2   i  by being synchronized with the data scan line S 1   i.  According to some example embodiments, during the display period, the sensing scan line S 2   i  may be in the state in which a scan signal having a turn-on level is always applied thereto. 
     For example, when a scan signal having a turn-on level is applied to the data scan line S 1   i  and the sensing scan line S 2   i,  the second transistor T 2  and the third transistor T 3  may be turned on. Accordingly, a voltage corresponding to the difference between the data voltage DVi and the initialization power VINT may be written to the storage capacitor Cst of the pixel PXij. 
     In the pixel PXij, the amount of driving current flowing in a driving path that couples the first power source ELVDD, the first transistor T 1 , and the second power source ELVSS is determined depending on the difference between the voltage of the gate electrode of the first transistor T 1  and the voltage of the source electrode of the first transistor T 1 . Depending on the amount of the driving current, the light emission luminance of the light-emitting diode LD may be determined. 
     Then, when a scan signal having a turn-off level (a low level) is applied to the data scan line S 1   i  and the sensing scan line S 2   i,  the second transistor T 2  and the third transistor T 3  may be turned off. Accordingly, regardless of a change in the voltage of the data line Dj, the difference between the voltage of the gate electrode of the first transistor T 1  and the voltage of the source electrode of the first transistor T 1  is maintained by the storage capacitor Cst, and the light emission luminance of the light-emitting diode LD may be maintained. 
       FIG.  4    is a diagram illustrating a scan driver according to some example embodiments of the present disclosure. 
     Referring to  FIG.  4   , the scan driver  13  according to some example embodiments of the present disclosure may include a plurality of scan stages ST 1 , ST 2  and ST 3 . 
     Each of the scan stages ST 1 , ST 2  and ST 3  may be coupled to at least some of clock lines CKS. The first scan stage ST 1  may be coupled to a scan start line STVL and a first carry line CR 1 . Each of the other scan stages ST 2  and ST 3  may be coupled to the carry line coupled to the previous scan stage and the carry line coupled to the next scan stage. For example, the second scan stage ST 2  may be coupled to the first carry line CR 1  and a second carry line CR 2 . The third scan stage ST 3  may be coupled to the second carry line CR 2  and a third carry line CR 3 . 
     The scan stages ST 1 , ST 2  and ST 3  may sequentially transmit a carry signal by being coupled in the form of a shift register. When the first scan stage ST 1  receives a first scan start pulse STP 1 , a first output node ON 1  is charged under the control of clock signals, and a first carry signal may be output to the first carry line CR 1 . When the second scan stage ST 2  receives the first carry signal, a second output node ON 2  is charged under the control of clock signals, and a second carry signal may be output to the second carry line CR 2 . When the third scan stage ST 3  receives the second carry signal, a third output node ON 3  is charged under the control of clock signals, and a third carry signal may be output to the third carry line CR 3 . 
     Each of the scan stages may be coupled to at least two buffers. For example, each of the buffers may be configured in the form of a complementary metal-oxide-semiconductor (CMOS), or may be configured as two transistors that are coupled in series. When it receives an output enable signal in the state in which the output node is charged, each of the buffers may output a scan signal having a turn-on level to a scan line corresponding thereto. The voltage level of the output node in the charged state and the voltage level of the output enable signal may be variously configured depending on the configuration of the buffer. 
     For example, a buffer BF 11  may output a scan signal having a turn-on level to a first data scan line S 11  when it receives an output enable signal OE 11  in the state in which the first output node ON 1  is charged. For example, the buffer BF 11  may output a scan signal having a turn-off level to the first data scan line S 11  if it does not receive the output enable signal OE 11  even though the first output node ON 1  is in the charged state. Similarly, a buffer BF 21  may output a scan signal having a turn-on level to a first sensing scan line S 21  when it receives an output enable signal OE 21  in the state in which the first output node ON 1  is charged. For example, the buffer BF 21  may output a scan signal having a turn-off level to the first sensing scan line S 21  if it does not receive the output enable signal OE 21  even though the first output node ON 1  is in the charged state. 
     The above description may be applied to the buffers BF 12 , BF 22 , BF 13  and BF 23  and the output enable signals OE 12 , OE 22 , OE 13  and OE 23  in the same manner, and thus a repeated description will be omitted. 
     Hereinafter, a data scan line is described as the scan line of a corresponding scan stage for the convenience of description. Because the timing of the scan signal having a turn-on level and applied to a sensing scan line may be synchronized with the timing of the scan signal having a turn-on level and applied to a data scan line during a display period (as shown in  FIG.  3   ), a description will not be made unless it is a special case. 
       FIG.  5    and  FIG.  6    are diagrams illustrating an image display period and a mask period according to some example embodiments of the present disclosure. 
     Hereinafter, a frame period, an image display period, and a mask period will be described based on a first scan line S 11 . 
     Referring to  FIG.  5   , three consecutive frame periods FPN, FP(N+1) and FP(N+2) are illustrated. Each of the frame periods may include a front porch period, an active period, and a back porch period. The front porch period may be the period between the time at which the frame period starts and the time at which the active period starts. The active period may be the period in which grayscale values corresponding to the frame are supplied. The back porch period may be the period between the time at which the active period ends and the time at which the frame period ends. A blank period BP may be a period including the consecutive front porch period and back porch period. In the blank period BP, grayscale values for pixels are not supplied. 
     For example, the N-th frame period FPN may include a front porch period, an active period APN, and a back porch period BPPN. The (N+1)-th frame period FP(N+1) may include a front porch period FPP(N+1), an active period AP(N+1), and a back porch period BPP(N+1). The (N+2)-th frame period FP(N+2) may include a front porch period FPP(N+2), an active period AP(N+2), and a back porch period. 
     The front porch period may start from the time at which the pulse of a vertical synchronization signal Vsync is generated. The length of the front porch period may correspond to an integer multiple of 1 horizontal period 1H. Each of the active period and the back porch period may also correspond to an integer multiple of 1 horizontal period 1H. The 1 horizontal period 1H may correspond to the minimum interval between the start points of sequentially supplied scan signals having a turn-on level. 
     In each of the frame periods FPN, FP(N+1) and FP(N+2), a first scan start pulse STP 1  and a second scan start pulse STP 2  may be sequentially applied to a scan start line STVL (in the case of a first mode). 
     Hereinafter, an image display period ODN and a mask period BDN based on the N-th frame period FPN will be described in more detail with reference to  FIG.  5    and  FIG.  6   . 
     When an active period is started, the first scan start pulse STP 1  may be applied to the scan start line STVL. Here, the scan driver  13  may sequentially supply scan signals having a turn-on level to the scan lines S 11 , S 12 , S 13 , S 14  and S 15  of a scan stage unit. For example, the scan driver  13  may sequentially supply scan signals having a turn-on level to the first scan line S 11  and the second scan line S 12  during a first period P 1 . For example, the scan driver  13  may supply a scan signal having a turn-on level to the (i−1)-th scan line S 1 (i−1) during a third period P 3 . Here, the data driver  12  may sequentially apply data voltages DV 1 , DV 2 , DV 3 , DV 4 , DVS, DV 6 , DV(i−2) and DV(i−1) corresponding to the grayscale values of the frame to the data lines Dj. 
     When the second scan start pulse STP 2  is applied to the scan start line STVL, the scan driver  13  may simultaneously or concurrently supply scan signals having a turn-on level to a mask scan group BSG including two or more scan lines S 11 , S 12 , S 13  and S 14 . For example, the scan driver  13  may simultaneously or concurrently supply scan signals having a turn-on level to the first scan line S 11  and the second scan line S 12  during a second period P 2  after the first period P 1 . Here, the data driver  12  may supply data voltages BV corresponding to a mask grayscale to the data lines Dj. For example, the data driver  12  may apply the data voltage BV corresponding to the mask grayscale to the data line Dj. For example, the mask grayscale may be a black grayscale (a grayscale of 0). For example, the mask grayscale may be a low grayscale (e.g., a set or predetermined low grayscale). 
     The scan signals having a turn-on level and output in response to the second scan start pulse STP 2  may not overlap in time with the scan signals having a turn-on level and output in response to the first scan start pulse STP 1 . That is, when scan signals having a turn-on level are simultaneously or concurrently supplied to the mask scan group BSG in response to the second scan start pulse STP 2 , a scan signal having a turn-on level may not be supplied to the i-th scan line S 1   i.  That is, scan signals having a turn-on level are supplied to the scan lines S 11  to S 1 (i−1) at an interval of 1 horizontal period 1H in response to the first scan start pulse STP 1 , and a scan signal having a turn-on level may be supplied to the i-th scan line S 1   i  at least 2 horizontal periods 2H after the scan signal having a turn-on level is supplied to the (i−1)-th scan line S 1 (i−1). Then, before scan signals having a turn-on level are simultaneously or concurrently supplied to the next mask scan group (e.g., the fifth to eighth scan lines), scan signals having a turn-on level may be sequentially supplied to the scan lines S 1 (i+1) and S 1 (i+2) at an interval of 1 horizontal period 1H. For example, the scan driver  13  may supply a scan signal having a turn-on level to the i-th scan line S 1   i  during a fourth period P 4 . 
     In a frame period FPN, the first period P 1 , the third period P 3 , the second period P 2 , and the fourth period P 4  may be sequentially located. The first period P 1  may be longer than each of the second period P 2 , the third period P 3 , and the fourth period P 4 . The second period P 2 , the third period P 3 , and the fourth period P 4  may have the same length. 
     The interval between the time at which the first scan start pulse STP 1  is generated and the time at which the second scan start pulse STP 2  is generated may be defined as the image display period of the corresponding frame period. Alternatively, according to some example embodiments, for the same scan line, the interval between the time at which a scan signal having a turn-on level and corresponding to the first scan start pulse STP 1  is generated and the time at which a scan signal having a turn-on level and corresponding to the second scan start pulse STP 2  is generated may be defined as the image display period of the corresponding frame period. 
     Alternatively, according to some example embodiments, the interval between the time at which the pulse of a horizontal synchronization signal Hsync corresponding to the first scan start pulse STP 1  is generated and the time at which the pulse of a horizontal synchronization signal Hsync corresponding to the second scan start pulse STP 2  is generated may be defined as the image display period of the corresponding frame period. For example, the image display period ODN may correspond to the difference between the start point of the first period P 1  and the start point of the second period P 2  in a frame period FPN. The variously defined image display periods have the same duration, and those who skilled in the art may define the image display period in a different manner. As illustrated in  FIG.  5   , the frame periods FPN, FP(N+1) and FP(N+2) may include the respective image display periods ODN, OD(N+1) and OD(N+2). 
     The interval between the time at which the second scan start pulse STP 2  is generated and the time at which the first scan start pulse STP 1  of the next frame period is generated may be defined as the mask period of the corresponding frame period. Alternatively, according to some example embodiments, for the same scan line, the interval between the time at which a scan signal having a turn-on level and corresponding to the second scan start pulse STP 2  is generated and the time at which a scan signal having a turn-on level and corresponding to the first scan start pulse STP 1  of the next frame period is generated may be defined as the mask period of the corresponding frame period. 
     Alternatively, according to some example embodiments, the interval between the time at which the pulse of a horizontal synchronization signal Hsync corresponding to the second scan start pulse STP 2  is generated and the time at which the pulse of a horizontal synchronization signal Hsync corresponding to the first scan start pulse STP 1  of the next frame period is generated may be defined as the mask period of the corresponding frame period. For example, the mask period BDN may correspond to the difference between the start point of the second period P 2  and the start point of the first period of the next frame period FP(N+1). The variously defined mask periods have the same duration, and those who skilled in the art may define the mask period in a different manner. As illustrated in  FIG.  5   , the frame periods FPN, FP(N+1) and FP(N+2) may include the respective mask periods BDN, BD(N+1). 
     The number of scan lines included in the mask scan group BSG (e.g., four scan lines in the example of  FIG.  5   ) may be a fixed number that is not easily changed due to hardware/time constraints. That is, when the number of scan lines included in the mask scan group BSG is forcibly changed, a problem in which there is not enough time to charge the pixels PXij with data voltages, a problem in which it is difficult for the sensor  15  to have enough sensing time, a problem in which the phase difference of clocks is not secured, and the like may be caused, and which may result in a problem in the display quality of the display device  10 . 
     For example, the number of scan signals having a turn-on level and output from the scan driver  13  during the second period P 2  of the first frame period may be the same as the number of scan signals having a turn-on level and output from the scan driver  13  during the second period P 2  of the second frame period. The second frame period and the first frame period may be consecutive frames. When the third frame period or the fourth frame period is present in between the second frame period and the first frame period, the number of scan signals having a turn-on level and output from the scan driver  13  during the second period P 2  of the third frame period or the fourth frame period may be the same as the number of scan signals having a turn-on level and output from the scan driver  13  during the second period P 2  of the first frame period or the second frame period. 
     Also, the interval between the time at which scan signals having a turn-on level are simultaneously or concurrently supplied to the current mask scan group BSG and the time at which scan signals having a turn-on level are simultaneously or concurrently supplied to the next mask scan group BSG is also not easily changed. For example, when the mask scan group BSG includes four scan lines and when data voltages corresponding to the mask grayscale are written to the pixels PXij during 1 horizontal period 1H, as illustrated in  FIG.  5   , it is desirable for the mask scan groups BSG to have an interval of 5 horizontal periods. Here, for all of the mask scan groups BSG, the same image display period and the same mask period may be maintained. 
       FIG.  7    is a diagram illustrating a difference in luminance perceived by a person depending on a display mode in response to the same image. 
     A first mode MODE 1  is a driving mode in which each frame period includes an image display period and a mask period. As described above, the scan driver  13  may supply the first scan start pulse STP 1  and the second scan start pulse STP 2  in each frame in the first mode MODE 1 . 
     A second mode MODE 2  is a driving mode in which each frame period includes only an image display period. Here, the scan driver  13  may supply only the first scan start pulse STP 1  in each frame. 
     In the graphs of the first mode MODE 1  and the second mode MODE 2 , the horizontal axis represents time, and the vertical axis represents luminance. 
     For example, it is assumed that an arbitrary pixel PXij emits light with a grayscale of A in the N-th frame period FPN, emits light with a grayscale of B, which is lower than the grayscale of A, in the (N+1)-th frame period FP(N+1), and emits light with a grayscale of C, which is lower than the grayscale of B, in the (N+2)-th frame period FP(N+2). In this case, the speed at which the grayscale perceived by a person changes in the first mode MODE 1  may be higher than that in the second mode MODE 2 , as illustrated in  FIG.  7   . 
     That is, when the display device  10  displays a moving or video image in the second mode MODE 2 , a person may recognize the image later than the time at which the image is actually displayed. This is referred to as a Motion Picture Response Time (MPRT), and in order to improve the MPRT, it is desirable to drive the display device in the first mode MODE 1 . 
       FIG.  8    is a diagram illustrating a change in luminance when a mask period is changed. 
     Referring to  FIG.  8   , the case in which the N-th to (N+2)-th frame periods include mask periods BDN, BD(N+1) and BD(N+2), each of which has q horizontal periods, and the (N+3)-th to (N+5)-th frame periods include mask periods BD(N+3), BD(N+4) and BD(N+5), each of which has q+1u horizontal periods, is illustrated. That is, from the (N+3)-th frame period, the length of the mask period BD(N+3) increases. For example, this may be the case in which the display device  10  displays a still or static image and then displays a moving or video image. Also, for example, this may be the case in which the display device  10  displays a moving or video image having a small number of changes and then displays a moving or video image having a large number of changes. Here, q and u are integers, each of which is greater than 0. 
     When it increases or decreases the interval between the time at which the first scan start pulse STP 1  is generated and the time at which the second scan start pulse STP 2  is generated, the scan start signal generator  17  may increase or decrease the same by an integer multiple of a unit (e.g., a set or predetermined unit) u. When the mask scan groups BSG have an interval of 5 horizontal periods as illustrated in  FIG.  5   , the unit u may be an integer multiple of 5 horizontal periods. This results from a hardware constraint or a time constraint of the display device  10 , as described above. 
     When the mask period increases by an integer multiple of the unit u as illustrated in  FIG.  8   , a problem in which a user may perceive an unnecessary change in luminance due to a change in the mask period. 
       FIG.  9    and  FIG.  10    are diagrams illustrating the operations of a mask duty controller and a scan start signal generator according to some example embodiments of the present disclosure. 
     The mask duty controller  16  may receive first mask duty information BDY 1  and supply second mask duty information BDY 2  based on the first mask duty information BDY 1 . The first mask duty information BDY 1  may include information about a first mask period, and the second mask duty information BDY 2  may include information about a second mask period. The mask duty controller  16  may determine second mask periods for at least two consecutive frame periods based on a single first mask period. 
     For example, when the first mask period included in the first mask duty information BDY 1  is q+(½)u horizontal periods for the N-th and (N+1)-th frame periods FPN and FP(N+1), the mask duty controller  16  may determine the mask period BDN of the N-th frame period FPN to be q horizontal periods and determine the mask period BD(N+1) of the (N+1)-th frame period FP(N+1) to be q+1u horizontal periods. That is, because it is impossible for the scan start signal generator  17  to generate the second scan start pulse STP 2  at an interval of q+(½)u horizontal periods, the mask duty controller  16  may supply second mask periods that enable the scan start signal generator  17  to operate. 
     Also, unlike illustrated in  FIG.  9    and  FIG.  10   , the mask duty controller  16  may determine the mask period BDN of the N-th frame period FPN to be q+1u horizontal periods and determine the mask period BD(N+1) of the (N+1)-th frame period FP(N+1) to be q horizontal periods. That is, the mask duty controller  16  may determine the second mask periods such that the average of the second mask periods is the same as the first mask period. 
     The scan start signal generator  17  may receive the second mask duty information BDY 2  and supply a scan start signal including the first scan start pulse STP 1  and the second scan start pulse STP 2  based on the second mask duty information BDY 2 . The second scan start pulse STP 2  may be generated in the same frame period as the first scan start pulse STP 1  corresponding thereto. 
     The scan start signal generator  17  may supply the first scan start pulse STP 1  and the second scan start pulse STP 2  in each frame period, and may determine the interval between the time at which the first scan start pulse STP 1  is generated and the time at which the second scan start pulse STP 2  is generated based on the second mask period corresponding to each frame period. 
     For example, the scan start signal generator  17  may generate the second scan start pulse STP 2  q horizontal periods before the time at which the first scan start pulse STP 1  of the (N+1)-th frame period FP(N+1) is generated. Accordingly, the mask period BDN having a length of q horizontal periods may be realized in the N-th frame period FPN. 
     Also, the scan start signal generator  17  may generate the second scan start pulse STP 2  q+1u horizontal periods before the time at which the first scan start pulse STP 1  of the (N+2)-th frame period FP(N+2) is generated. Accordingly, the mask period BD(N+1) having a length of q+1u horizontal periods may be realized in the (N+1)-th frame period FP(N+1). 
     According to some example embodiments, the user of the display device  10  may perceive the mask period of q+(½)u horizontal periods in each of the N-th and (N+1)-th frame periods FPN and FP(N+1). That is, according to some example embodiments, a virtual mask period of q+(½)u horizontal periods may be implemented using a time-division driving method. That is, the virtual mask period that slightly increases by a fraction multiple of the unit u based on the previous mask period is displayed, whereby instances of the user perceiving an unnecessary or undesired change in luminance may be prevented or reduced. 
       FIG.  11    and  FIG.  12    are diagrams illustrating a method of driving a display device according to some example embodiments of the present disclosure. 
     Referring to  FIG.  11   , the first frame period FRAME 1  having a mask period of q horizontal periods, the third frame period FRAME 3  having a mask period of q horizontal periods, the fourth frame period FRAME 4  having a mask period of q+1u horizontal periods, and the second frame period FRAME 2  having a mask period of q+1u horizontal periods are illustrated. 
     Here, the first frame period FRAME 1  may have an image display period of r horizontal periods. That is, the first frame period FRAME 1  may be configured with q+r horizontal periods. Here, q and r may be integers, each of which is greater than 0. Similarly, the third frame period FRAME 3  may have an image display period of r horizontal periods. That is, the third frame period FRAME 3  may be configured with q+r horizontal periods. 
     Here, the second frame period FRAME 2  may have an image display period of s horizontal periods. That is, the second frame period FRAME 2  may be configured with q+1u+s horizontal periods. Here, u and s may be integers, each of which is greater than 0. Similarly, the fourth frame period FRAME 4  may have an image display period of s horizontal periods. That is, the fourth frame period FRAME 4  may be configured with q+1u+s horizontal periods. Here, q+r horizontal periods may be the same as q+1u+s horizontal periods. That is, the first to fourth frame periods FRAME 1  to FRAME 4  may have the same length. 
     During the image display period of the first to fourth frame periods FRAME 1  to FRAME 4 , pixels may display a moving or video image. During the mask period of the first to fourth frame periods FRAME 1  to FRAME 4 , the pixels may display a monochromatic image (e.g., a black image or a low-grayscale monochromatic image). Here, a description is made based on pixels coupled to the same scan line. The first frame period FRAME 1  and the second frame period FRAME 2  may have different mask periods. The third frame period FRAME 3  between the first frame period FRAME 1  and the second frame period FRAME 2  may have the same mask period as the first frame period FRAME 1 . The fourth frame period FRAME 4  between the first frame period FRAME 1  and the second frame period FRAME 2  may have the same mask period as the second frame period FRAME 2 . 
     According to some example embodiments, two or more first frame periods FRAME 1  may be consecutively arranged, and two or more second frame periods FRAME 2  may be consecutively arranged. The third frame period FRAME 3  and the fourth frame period FRAME 4  may be alternately arranged. The arrangement pattern of the third frame period FRAME 3  and the fourth frame period FRAME 4  may be repeated x times and then arranged between the first frame periods FRAME 1  and the second frame periods FRAME 2 . Here, x is an integer greater than 0. 
     That is, at least one third frame period FRAME 3  and at least one fourth frame period FRAME 4  may be located between the end point of the consecutive first frame periods FRAME 1  and the start point of the consecutive second frame periods FRAME 2 . Here, the at least one third frame period FRAME 3  and the at least one fourth frame period FRAME 4  may be alternated with each other at regular intervals. 
     Because a user sequentially perceives a mask period of q horizontal periods, a mask period of q+(½)u horizontal periods, and a mask period of q+1u horizontal periods over time, the user may not perceive an unnecessary change in luminance. The embodiment of  FIG.  11    may be used when a displayed image is changed from a still or static image to a moving or video image or when a displayed image is changed from a moving or video image having a small number of changes to a moving or video image having a large number of changes. 
     Referring to  FIG.  12   , the first frame period FRAME 1  having a mask period of q+1u horizontal periods, the third frame period FRAME 3  having a mask period of q horizontal periods, the fourth frame period FRAME 4  having a mask period of q+1u horizontal periods, and the second frame period FRAME 2  having a mask period of q horizontal periods are illustrated. 
     That is, the first frame period FRAME 1  and the second frame period FRAME 2  may have different mask periods. The third frame period FRAME 3  between the first frame period FRAME 1  and the second frame period FRAME 2  may have the same mask period as the second frame period FRAME 2 . The fourth frame period FRAME 4  between the first frame period FRAME 1  and the second frame period FRAME 2  may have the same mask period as the first frame period FRAME 1 . 
     According to some example embodiments, two or more first frame periods FRAME 1  may be consecutively arranged, and two or more second frame periods FRAME 2  may be consecutively arranged. The third frame period FRAME 3  and the fourth frame period FRAME 4  may be alternately arranged. The arrangement pattern of the third frame period FRAME 3  and the fourth frame period FRAME 4  may be repeated x times and then arranged between the first frame periods FRAME 1  and the second frame periods FRAME 2 . Here, x is an integer greater than 0. 
     Because a user sequentially perceives a mask period of q+1u horizontal periods, a mask period of q+(½)u horizontal periods, and a mask period of q horizontal periods over time, the user may not perceive an unnecessary change in luminance. The embodiment of  FIG.  12    may be used when a displayed image is changed from a moving or video image to a still or static image or when the displayed image is changed from a moving or video image having a large number of changes to a moving or video image having a small number of changes. 
       FIG.  13    and  FIG.  14    are diagrams illustrating other operations of a mask duty controller and a scan start signal generator according to some example embodiments of the present disclosure. 
     The mask duty controller  16  may receive first mask duty information BDY 1  and supply second mask duty information BDY 2  based on the first mask duty information BDY 1 . The first mask duty information BDY 1  may include information about a first mask period, and the second mask duty information BDY 2  may include information about a second mask period. The mask duty controller  16  may determine second mask periods for at least two consecutive frame periods based on a single first mask period. 
     For example, when the first mask period included in the first mask duty information BDY 1  is q+(⅓)u horizontal periods for the N-th, (N+1)-th and (N+2)-th frame periods FPN, FP(N+1) and FP(N+2), the mask duty controller  16  may determine the mask period BDN of the N-th frame period FPN to be q horizontal periods, determine the mask period BD(N+1) of the (N+1)-th frame period FP(N+1) to be q horizontal periods, and determine the mask period BD(N+2) of the (N+2)-th frame period FP(N+2) to be q+1u horizontal periods. That is, because it is impossible for the scan start signal generator  17  to generate a second scan start pulse STP 2  at an interval of q+(⅓)u horizontal periods, the mask duty controller  16  may provide second mask periods that enable the scan start signal generator  17  to operate. 
     Also, unlike illustrated in  FIG.  13    and  FIG.  14   , the mask duty controller  16  may determine the mask period BDN of the N-th frame period FPN to be q+1u horizontal periods, determine the mask period BD(N+1) of the (N+1)-th frame period FP(N+1) to be q horizontal periods, and determine the mask period BD(N+2) of the (N+2)-th frame period FP(N+2) to be q horizontal periods. That is, the mask duty controller  16  may determine the second mask periods such that the average of the second mask periods is the same as the first mask period. 
     The scan start signal generator  17  may receive the second mask duty information BDY 2  and supply a scan start signal including the first scan start pulse STP 1  and the second scan start pulse STP 2  based on the second mask duty information BDY 2 . The second scan start pulse STP 2  may be generated in the same frame period as the first scan start pulse STP 1  corresponding thereto. 
     The scan start signal generator  17  may supply the first scan start pulse STP 1  and the second scan start pulse STP 2  in each frame period, and may determine the interval between the time at which the first scan start pulse STP 1  is generated and the time at which the second scan start pulse STP 2  is generated based on the second mask period corresponding to each frame period. 
     For example, the scan start signal generator  17  may generate the second scan start pulse STP 2  q horizontal periods before the time at which the first scan start pulse STP 1  of the (N+1)-th frame period FP(N+1) is generated. Accordingly, the mask period BDN having a length of q horizontal periods may be realized in the N-th frame period FPN. 
     Also, the scan start signal generator  17  may generate the second scan start pulse STP 2  q horizontal periods before the time at which the first scan start pulse STP 1  of the (N+2)-th frame period FP(N+2) is generated. Accordingly, the mask period BD(N+1) having a length of q horizontal periods may be realized in the (N+1)-th frame period FP(N+1). 
     Also, the scan start signal generator  17  may generate the second scan start pulse STP 2  q+1u horizontal periods before the time at which the first scan start pulse STP 1  of the (N+3)-th frame period FP(N+3) is generated. Accordingly, the mask period BD(N+2) having a length of q+1u horizontal periods may be realized in the (N+2)-th frame period FP(N+2). 
     According to some example embodiments, the user of the display device  10  may perceive the mask period of q+(⅓)u horizontal periods in each of the N-th, (N+1)-th and (N+2) frame periods FPN, FP(N+1) and FP(N+2). That is, according to some example embodiments, a virtual mask period of q+(⅓)u horizontal periods may be implemented in a time-division driving method. That is, the virtual mask period that slightly increases by a fraction multiple of the unit u based on the previous mask period is displayed, whereby the user may not perceive an unnecessary change in luminance. 
       FIG.  15    is a diagram illustrating a change in the actual luminance and a change in the perceived luminance when a mask period is changed in the conventional art.  FIG.  16    is a diagram illustrating a change in the actual luminance and a change in the perceived luminance when a mask period is changed according to some example embodiments of the present disclosure. 
     Referring to  FIG.  15    and  FIG.  16   , the case in which a mask period is gradually decreased is illustrated. 
     In the case illustrated in  FIG.  15   , a mask period gradually decreases by an integer multiple of a unit u, whereby a user may perceive an unnecessary change in luminance. 
     In the case illustrated in  FIG.  16   , a mask period gradually decreases by a fraction multiple of the unit u, whereby instances of a user perceiving an unnecessary or undesired change in luminance may be prevented or reduced. 
       FIG.  17    is a diagram illustrating a display device according to another embodiment of the present disclosure. 
     Referring to  FIG.  17   , the data driver  12  and the sensor  15  of the display device  10 ′ may be configured as a single component. For example, the data driver  12  and the sensor  15  may be configured as a single integrated chip (IC)  125 . 
     The other components of the display device  10 ′ of  FIG.  17    are the same as those of the display device  10  of  FIG.  1   , and thus a repeated description will be omitted. 
     A display device and a driving method thereof according to the present disclosure subdivide the variation of a mask period, thereby instances of users perceiving changes in luminance may be prevented or reduced, even when the mask period is changed. 
     The drawings and the detailed description of the present disclosure are examples for the present disclosure and are provided for illustrative purpose, rather than limiting the scope of the present disclosure described in the claims. Therefore, it will be appreciated to those skilled in the art that various modifications may be made and other embodiments are available. Accordingly, the scope of the present disclosure should be determined by the spirit and scope of the appended claims and their equivalents.