Patent Publication Number: US-10332477-B2

Title: Display device and driving method thereof

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application claims the benefit of priority to Taiwan Patent Application No. 105103811, filed Feb. 4, 2016. The entire content of the above identified application is incorporated herein by reference. 
     Some references, which may include patents, patent applications and various publications, are cited and discussed in the description of this disclosure. The citation and/or discussion of such references is provided merely to clarify the description of the present disclosure and is not an admission that any such reference is “prior art” to the disclosure described herein. All references cited and discussed in this specification are incorporated herein by reference in their entireties and to the same extent as if each reference was individually incorporated by reference. 
     FIELD 
     The present disclosure relates to a display device. Specifically, the present disclosure relates to a display device in which a refresh rate can be switched. 
     BACKGROUND 
     In recent years, as picture quality and resolutions of screens improve, complexity of animations and images processed by a display card also increases. However, during processing of complex animations or images, a display card needs a relatively long time to perform computation, and when a computation time cannot match a refresh rate of a display, a phenomenon of discontinuous frames occurs. To resolve this problem, some display devices can dynamically adjust a refresh rate, so as to reduce the refresh rate when a display card performs complex computation, thereby maintaining smooth frame output. 
     However, under the limit of material characteristics, when a refresh rate is reduced, brightness of a screen is reduced accordingly, causing problems that frames of a display device have uneven brightness and flicker when the refresh rate changes. Therefore, how to maintain stable brightness of a screen during dynamic adjustment of a refresh rate is an research subject in the field. 
     SUMMARY 
     An aspect of the present disclosure is a display device. The display device includes: a display array, including at least one scan line; and a driving circuit, configured to drive the display array. The driving circuit includes: a timing controller, configured to control a refresh rate of the display array at a first frequency or a second frequency, where the first frequency is substantially higher than the second frequency; and a gate driver, configured to switch between supplying an enable voltage signal and supplying a disable voltage signal to the scan line of the display array. When the refresh rate is at the first frequency, there is a first voltage difference between the enable voltage signal and the disable voltage signal, and when the refresh rate is at the second frequency, there is a second voltage difference between the enable voltage signal and the disable voltage signal. The first voltage difference is greater substantially than the second voltage difference. 
     Another aspect of the present disclosure is a driving method of a display device. The display device includes a display array and a driving circuit configured to drive the display array. The driving method includes: detecting a refresh rate of the display array; when the refresh rate of the display array is at a first frequency, switching between supplying an enable voltage signal and supplying a disable voltage signal to the display array, where there is a first voltage difference between the enable voltage signal and the disable voltage signal; and when the refresh rate of the display array is at a second frequency, switching between supplying the enable voltage signal and supplying the disable voltage signal to the display array, where there is a second voltage difference between the enable voltage signal and the disable voltage signal. The first frequency is substantially higher than the second frequency, and the first voltage difference is substantially greater than the second voltage difference. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a display device according to some embodiments of the present disclosure; 
         FIG. 2  is a schematic diagram of a pixel unit according to some embodiments of the present disclosure; 
         FIG. 3  and  FIG. 4  are respectively schematic waveform diagrams of a data voltage signal, a pixel voltage, and a scan voltage signal when the display device is at different refresh rates according to some embodiments of the present disclosure; 
         FIG. 5A  and  FIG. 5B  are schematic waveform diagrams of the scan voltage signal and the pixel voltage according to some embodiments of the present disclosure; and 
         FIG. 6  is a characteristic curve diagram of a refresh rate to a brightness change according to some embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Detailed description is provided below with reference to the embodiments and the companying drawings to further understand the aspects of the present disclosure. However, the provided embodiments are not used to limit the scope of the present disclosure. The description of structures and operations are not used to limit an execution sequence of the operations. Any apparatus having equivalent efficacy produced by using a structure of recombined elements falls within the scope of the present disclosure. In addition, according to standard and common measures in the industry, the drawings are only used for the purpose of assisting description and are not drawn by original sizes, and in fact, sizes of various features can be randomly increased or reduced for ease of description. The same elements are described by using the same symbols in the following description for ease of understanding. 
     The terms used in the entire specification and the claims, unless specifically indicated, usually have common meanings of the terms used in the art and in the disclosed content and special content. Some terms used to describe the present disclosure are discussed below or somewhere else in this specification, so as to provide additional guidance in the description of the present disclosure to a person skilled in the art. 
     In addition, the terms “comprise”, “include”, “have”, “contain” and the like used herein are all non-exclusive words, that is, refer to “include, but is not limited thereto”. Moreover, “and/or” used herein includes any one or any combination of one or more items of related listed items. 
     When elements are “connected” or “coupled” herein, the elements may be “electrically connected” or “electrically coupled”. “Connecting” and “coupling” may both refer to that two or more elements are interoperable or interacting. In addition, although the words “first”, “second”, . . . , are used herein to describe different elements, the words are only used to distinguish elements or operations that are described by using the same technical words. Unless specifically indicated in the context, the words do not specifically specify or imply an order or a sequence, and are not used to limit the present invention. 
     Referring to  FIG. 1 ,  FIG. 1  is a schematic diagram of a display device  100  according to some embodiments of the present disclosure. As shown in  FIG. 1 , the display device  100  includes a display array  120  and a driving circuit  140 . In some embodiments, the display array  120  includes a plurality of data lines DL 1  to DLm, a plurality of scan lines SL 1  to SLn, and multiple pixel units PX that are arranged into an array between the data lines DL 1  to DLm and the scan lines SL 1  to SLn. Each pixel unit PX is respectively electrically connected to the corresponding data lines DL 1  to DLm and the corresponding scan lines SL 1  to SLn. 
     Referring  FIG. 2  in combination,  FIG. 2  is a schematic diagram of the pixel unit PX according to some embodiments of the present disclosure. As shown in  FIG. 2 , the pixel unit PX 11  is electrically connected to the corresponding data line DL 1  and the corresponding scan line SL 1 . Specifically, the pixel unit PX includes a switch SW and a storage capacitor Cst. A first end of the switch SW is electrically connected to the data line DL 1 , and is configured to receive a data voltage Vdata 1 . A second end of the switch SW is electrically connected to a first end of the storage capacitor Cst. A control end of the switch SW is electrically connected to the scan line SL 1 , and is configured to receive a scan voltage signal VSL 1 , so that the switch SW is selectively turned on according to the scan voltage signal VSL 1 . A second end of the storage capacitor Cst is electrically connected to a reference voltage Com. In this way, when the scan voltage signal VSL 1  turns on the switch SW, the data voltage Vdata 1  on the data line DL 1  can charge the storage capacitor Cst. 
     Referring to  FIG. 1  again, as shown in the figure, in some embodiments, the driving circuit  140  is electrically connected to the display array  120 , and is configured to drive the display array  120 . As shown in  FIG. 1 , the driving circuit  140  includes a timing controller  142 , a gate driver  144 , and a control unit  146 . Specifically, the timing controller  142  may dynamically control a refresh rate of the display array  120  by outputting a clock signal CK. For example, the timing controller  142  may control the refresh rate of the display array  120  at 144 hertz (Hz), 60 hertz (Hz), 30 hertz (Hz), and the like. When an image processed by a display card is excessively complex and a relatively long time is needed to perform data computation, the timing controller  142  may control the display array  120  at a relatively low refresh rate (for example, 30 hertz), so as to prevent a phenomenon of delayed or discontinuous frames from occurring. 
     The gate driver  144  is electrically connected to the timing controller  142  and the scan lines SL 1  to SLn. The gate driver  144  receives the clock signal CK from the timing controller  142 , and switches between supplying an enable voltage signal (for example, a high level) and supplying a disable voltage signal (for example, a low level) to the scan lines SL 1  to SLn of the display array  120 . As shown in  FIG. 1 , in some embodiments, the gate driver  144  respectively outputs scan voltage signals VSL 1  to VSLn to the corresponding scan lines SL 1  to SLn. When the scan voltage signal VSL 1  is at a high level and the scan voltage signals VSL 2  to VSLn are at a low level, the gate driver  144  enables the scan line SL 1 . When the scan voltage signal VSL 2  is at a high level and the scan voltage signals VSL 1  and VSL 3  to VSLn are at a low level, the gate driver  144  enables the scan line SL 2 , and the like. In this way, by enabling the scan lines SL 1  to SLn in turn, the gate driver  144  may drive the pixel unit PX in the display array  120  corresponding to the refresh rate of the display array  120 . 
     The control unit  146  is electrically connected to the timing controller  142  and the gate driver  144 . In some embodiments, the timing controller  142  outputs a corresponding frequency detection signal FS to the control unit  146  according to the refresh rate of the display array  120 . In some embodiments, the timing controller  142  may determine the current refresh rate of the display array  120  according to a period of a frame on the display array  120 , to output the frequency detection signal FS. In this way, the control unit  146  may adjust a voltage level of an enable reference voltage VH according to the frequency detection signal FS received from the timing controller  142 . 
     In some embodiments, the control unit  146  may also choose to adjust a voltage level of the enable reference voltage VH or a disable reference voltage VL according to the frequency detection signal FS, or simultaneously adjust the voltage levels of the enable reference voltage VH and the disable reference voltage VL. In this way, the control unit  146  may determine the refresh rate of the display array  120  according to a different frequency detection signal FS, and output the corresponding enable reference voltage VH and the disable reference voltage VL to the gate driver  144 . Accordingly, the gate driver  144  may respectively supply the enable voltage signal and the disable voltage signal to the scan lines SL 1  to SLn of the display array  120  according to the enable reference voltage VH and the disable reference voltage VL. 
     Specifically, in some embodiments, when the refresh rate is relatively high, a voltage difference between the enable voltage signal and the disable voltage signal (that is, a voltage difference between the enable reference voltage VH and the disable reference voltage VL) is relatively large. When the refresh rate is relatively low, the voltage difference between the enable voltage signal and the disable voltage signal (that is, the voltage difference between the enable reference voltage VH and the disable reference voltage VL) is relatively small. For ease of description, in the following paragraphs, a relationship between the refresh rate of the display array  120  and the voltage difference between the enable voltage signal and the disable voltage signal is described in detail with reference to the embodiments and the accompanying drawings. 
     Referring to  FIG. 3  and  FIG. 4 ,  FIG. 3  and  FIG. 4  are respectively schematic waveform diagrams of a data voltage signal, a pixel voltage, and a scan voltage signal when the display device  100  is at different refresh rates according to some embodiments of the present disclosure. For ease of description, the voltage waveforms in  FIG. 3  and  FIG. 4  are described with reference to the display device  100  in the embodiment shown in  FIG. 1  and  FIG. 2 . In some embodiments,  FIG. 3  is a schematic waveform diagram of a data voltage signal, a pixel voltage, and a scan voltage signal when the display device  100  is at a refresh rate of 144 hertz, where 144 frames are included per second.  FIG. 4  is a schematic waveform diagram of a data voltage signal, a pixel voltage, and a scan voltage signal when the display device  100  is at a refresh rate of 30 hertz, where 30 frames are included per second. 
     When the display device  100  is at a refresh rate of 144 hertz, as shown in  FIG. 3 , in each frame, within first timing P 1 , the scan voltage signal VSL 1  is at a high level (that is, the voltage level of the enable reference voltage VH). In this case, the switch SW is turned on, and a data voltage signal Vdata 1  charges a pixel voltage Vpx 11  between two ends of the storage capacitor Cst. In second timing P 2 , the scan voltage signal VSL 1  is switched from a high level (that is, the voltage level of the enable reference voltage VH) to a low level (that is, the voltage level of the disable reference voltage VL). In this case, because of the existence of parasitic capacitance, the pixel voltage Vpx 11  is affected during timing switching to cause a voltage drop, and the part of the voltage drop of the pixel voltage Vpx 11  is a feed through voltage. 
     Next, in third timing P 3 , the pixel unit is in a blanking stage. In this case, the data voltage signal Vdata 1  is kept at a fixed level, so that charging and discharging of the parasitic capacitance are avoided, to reduce a leakage current on the data line DL 1 , thereby reducing power consumption of a panel. In this stage, output of the data voltage signal Vdata 1  does not change a voltage level of the pixel voltage Vpx 11 . In some embodiments, a voltage level of the data voltage signal Vdata 1  in the third timing P 3  has reversed polarity. In some other embodiments, the voltage level of the data voltage signal Vdata 1  in the third timing P 3  may also have non-reversed polarity. Therefore, the embodiment shown in  FIG. 3  is only one of the possible implementation manners of the present disclosure, and is not used to limit the present disclosure. 
     In some embodiments, when the display device  100  is at a refresh rate of 144 hertz, the enable voltage signal (that is, the scan voltage signal VSL 1  at a high level) is approximately 30 volts (V). The disable voltage signal (that is, the scan voltage signal VSL 1  at a low level) is approximately −6 volts (V). 
     When the display device  100  is switched to a refresh rate of 30 hertz, as shown in  FIG. 4 , each frame also includes the first timing P 1 , the second timing P 2 , and the third timing P 3 . As compared with that the display device  100  is at a refresh rate of 144 hertz, a period of the first timing P 1  is the same. In other words, regardless of whether the refresh rate of the display array  120  is at 144 hertz or 30 hertz, an enable (charging) period in which the gate driver  144  supplies the enable voltage signal is the same. In contrast, when the refresh rate is at 30 hertz, a time of the third timing P 3  is relatively long. When the refresh rate is at 144 hertz, the time of the third timing P 3  is relatively short. In other words, the gate driver  144  may adjust a time length during which the data voltage signal Vdata 1  is kept at a fixed level to make the pixel unit PX in a blanking stage. In this way, even if an enable period during which the gate driver  144  supplies the enable voltage signal is the same, the gate driver  144  may still adjust a time period of each frame, thereby implementing that the display array  120  is at different refresh rates. 
     In some embodiments, when the display device  100  is at a refresh rate of 30 hertz, the enable voltage signal (that is, the scan voltage signal VSL 1  at a high level) is approximately 22 volts (V). The disable voltage signal (that is, the scan voltage signal VSL 1  at a low level) is approximately −6 volts (V). 
     In other words, when the refresh rate is relatively high (for example, 144 Hz), the voltage difference between the enable voltage signal and the disable voltage signal is relatively large (for example, 36 V). When the refresh rate is relatively low (for example, 30 Hz), the voltage difference between the enable voltage signal and the disable voltage signal is relatively small (for example, 28 V). Specifically, the driving circuit  140  may output, corresponding to the refresh rate by using the control unit  146 , the enable reference voltage VH having a different voltage level to implement the foregoing operation. 
     Referring to  FIG. 5A  and  FIG. 5B ,  FIG. 5A  and  FIG. 5B  are schematic waveform diagrams of the scan voltage signal VSL 1  and the pixel voltage Vpx 11  according to some embodiments of the present disclosure. As shown in  FIG. 5A , when the scan voltage signal VSL 1  is turned off, regardless of whether the pixel voltage Vpx 11  has a positive polarity or negative polarity, the feed through voltage respectively causes voltage drops Vft 1  and Vft 2 . As shown in the figures, the induced voltage drop Vft 1 , when the pixel voltage Vpx 11  has a positive polarity, is substantially greater than the induced voltage drop Vft 2 , when the pixel voltage Vpx 11  has a negative polarity. Similarly, in  FIG. 5B , the feed through voltage also respectively causes the voltage drops Vft 3  and Vft 4  in the pixel voltage Vpx 11 . As shown in the figures, the induced voltage drop Vft 3 , when the pixel voltage Vpx 11  has a positive polarity, is substantially greater than the induced voltage drop Vft 4 , when the pixel voltage Vpx 11  has a negative polarity. 
     Furthermore, the voltage drops Vft 1  to Vft 4  caused by the feed through voltage are directly proportional to a voltage difference between a high level and a low level of the scan voltage signal VSL 1 . Therefore, in a case in which the induced voltage drops Vft 1  and Vft 3 , when the pixel voltage Vpx 11  has a positive polarity, are respectively substantially greater than the induced voltage drops Vft 2  and Vft 4 , when the pixel voltage Vpx 11  has a negative polarity. When the voltage difference between the high level and the low level of the scan voltage signal VSL 1  is larger, a cross voltage between positive polarity and negative polarity of the pixel voltage Vpx 11  is smaller. 
     In other words, because an enable level of the scan voltage signal VSL 1  in  FIG. 5A  is substantially greater than the enable level of the scan voltage signal VSL 1  in  FIG. 5B , a cross voltage Va between positive polarity and negative polarity of the pixel voltage Vpx 11  in  FIG. 5A  is substantially less than a cross voltage Vb between positive polarity and negative polarity of the pixel voltage Vpx 11  in  FIG. 5B . In this way, the cross voltage between positive polarity and negative polarity of the pixel voltage Vpx 11  may be increased by reducing the voltage difference between the high level and the low level of the scan voltage signal VSL 1 . When the cross voltage between positive polarity and negative polarity of the pixel voltage Vpx 11  is increased, brightness of a pixel PX is increased accordingly. 
     Accordingly, compensation may be performed on brightness of the display array  120  by adjusting the enable level or a disable level of the scan voltage signal VSL 1 , so that brightness of the display array  120  stays consistent at different refresh rates, thereby preventing a case of flickering frames from occurring. Specifically, in some embodiments, when the refresh rate is reduced, brightness of the pixel PX is reduced due to material characteristics. Therefore, when reduction of the refresh rate of the display array  120  is detected, the control unit  146  may synchronously reduce the voltage difference between the high level and the low level of the scan voltage signal VSL 1 . 
     In some embodiments, the control unit  146  may adjust the voltage level of the enable reference voltage VH according to the refresh rate, and maintain the voltage level of the disable reference voltage VL unchanged, so that when the refresh rate is at a first frequency (for example, 144 Hz), the enable voltage signal has a first level (for example, 30 V), and when the refresh rate is at a second frequency, the enable voltage signal has a second level (for example, 25 V) substantially less than the first level. At different refresh rates, the disable voltage signal has a same voltage level (for example, −6 V), but the present disclosure is not limited thereto. 
     For example, in some other embodiments, the control unit  146  may also adjust the voltage level of the disable reference voltage VL according to the refresh rate, and maintain the voltage level of the enable reference voltage VH unchanged, so that when the refresh rate is at the first frequency (for example, 144 Hz), the disable voltage signal has a first level (for example, −6 V), and when the refresh rate is at the second frequency, the disable voltage signal has a second level (for example, −1 V) substantially higher than the first level. At different refresh rates, the enable voltage signal has a same voltage level (for example, 30 V). In other words, in a manner of adjusting one of the enable reference voltage VH and the disable reference voltage VL and maintaining the other unchanged, the control unit  146  may provide the scan voltage signal VSL 1  with a relatively large voltage difference when the refresh rate is relatively high, and may provide the scan voltage signal VSL 1  with a relatively small voltage difference when the refresh rate is relatively high, so as to perform compensation on the brightness of the display array  120 . 
     For the voltage level and the refresh rate in the foregoing embodiments, quantities and values of the voltage level and the refresh rate are only exemplary, and are not used to limit the present disclosure. For example, in some embodiments, the display device  100  may be at three or more different refresh rates, and the timing controller  142  may output corresponding frequency detection signals FS according to different refresh rates, so that the control unit  146  adjusts the voltage levels of the enable reference voltage VH and the disable reference voltage VL respectively corresponding to the different refresh rates. 
     For example, in some embodiments, the timing controller  142  may control the refresh rate of the display array  120  at the first frequency (for example, 144 Hz), the second frequency (for example, 60 Hz) or a third frequency (for example, 30 Hz). When the refresh rate is at the first frequency, there is a first voltage difference between the enable voltage signal and the disable voltage signal, when the refresh rate is at the second frequency, there is a second voltage difference between the enable voltage signal and the disable voltage signal, and when the refresh rate is at the third frequency, there is a third voltage difference between the enable voltage signal and the disable voltage signal. The first voltage difference is substantially greater than the second voltage difference, and the second voltage difference is substantially greater than the third voltage difference. For example, the control unit  146  may maintain the voltage level of the disable reference voltage VL at −6 V, and adjust the voltage level of the enable reference voltage VH to 30 V at the first frequency (for example, 144 Hz), to 26 V at the second frequency (for example, 60 Hz), and to 22 V at the third frequency (for example, 30 Hz), so as to implement the foregoing operation. 
     Referring to  FIG. 6 ,  FIG. 6  is a characteristic curve diagram of a refresh rate to a brightness change according to some embodiments of the present disclosure, wherein a horizontal axis represents the refresh rate, and a vertical axis represents a proportion of the brightness change. In  FIG. 6 , a curve L 1  represents a brightness change of the display array  120  when the enable reference voltage VH is not adjusted according to the refresh rate. A curve L 2  represents the brightness change of the display array  120  when the enable reference voltage VH is correspondingly adjusted according to the refresh rate. As shown in  FIG. 6 , when the enable reference voltage VH is adjusted corresponding to the refresh rate, compensation of brightness from approximately 77% to approximately 95% may be performed. In this way, brightness of the display array  120  stays consistent at different refresh rates, thereby preventing a case of flickering frames from occurring. 
     In conclusion, in the present disclosure, by means of application of certain foregoing embodiments, a voltage difference between a high level and a low level of a scan voltage signal is adjusted corresponding to a refresh rate, so that brightness compensation can be performed on pixels in a display array, so as to improve output quality of display frames. 
     Although the present disclosure is disclosed as above by using the implementation manners, the implementation manners are not used to limit the present disclosure. Any person skilled in the art may make various variations and modifications without departing from the spirit and scope of the present disclosure, and therefore the protection scope of the present disclosure should be as defined by the appended claims.