Patent Publication Number: US-2013234919-A1

Title: Devices and methods for discharging pixels having oxide thin-film transistors

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Non-Provisional patent application of U.S. Provisional Patent Application No. 61/607,275, entitled “Devices and Methods for Discharging Pixels Having Oxide Thin-Film Transistors”, filed Mar. 6, 2012, which is herein incorporated by reference. 
    
    
     BACKGROUND 
     The present disclosure relates generally to electronic displays and, more particularly, to liquid crystal displays (LCDs) that can discharge pixels of the LCD having oxide thin-film transistors (TFTs) before the LCD is turned off to decrease image artifacts from occurring on the LCD. 
     This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
     Electronic displays, such as liquid crystal displays (LCDs), are commonly used in electronic devices such as televisions, computers, and phones. LCDs portray images by modulating the amount of light that passes through a liquid crystal layer within pixels of varying color. For example, by varying a voltage difference between a pixel electrode and a common electrode in a pixel, an electric field may result. The electric field may cause the liquid crystal layer to vary its alignment, which may ultimately result in more or less light being emitted through the pixel where it may be seen. By changing the voltage difference (often referred to as a data signal) supplied to each pixel, images may be produced on the LCD. 
     To store data representing a particular amount of light that is to be passed through pixels, gates of thin-film transistors (TFTs) in the pixels may be activated while the data signal is supplied to the pixels. Conventionally, TFTs may include an active layer that is typically fabricated using silicon-based materials, such as amorphous silicon (a-Si), poly-silicon (poly-Si), or microcrystalline silicon. Such silicon-based materials typically have a scaling limit, meaning that once they are scaled down to a certain size, they generally cannot be reduced any further in size without affecting operation. Accordingly, certain LCDs may be manufactured with oxide TFTs to overcome deficiencies found in TFTs fabricated using silicon-based materials. 
     However, the leakage current of oxide TFTs may be considerably lower than silicon-based materials. For example, the leakage current of oxide TFTs may be approximately 1000 times smaller than the leakage current of silicon-based materials. Since the pixel electrodes of the pixels of the LCD are not discharged before power is removed from the LCD, the remaining voltage on the pixels may be different from a desired low voltage and may cause an electric field that remains in place after the LCD is turned off. This electric field may continue to impact the liquid crystal layer of the pixels of the LCD while the LCD is off. It is believed that this electric field caused by the voltage on the pixel electrodes may result in image artifacts, such as flickering or image sticking, that could appear after the display is turned on again. 
     SUMMARY 
     A summary of certain embodiments disclosed herein is set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of these certain embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, this disclosure may encompass a variety of aspects that may not be set forth below. 
     Embodiments of the present disclosure relate to devices and methods for discharging pixels of an electronic display having oxide thin-film transistors (TFTs) to store a low voltage (e.g., near-zero or zero volts) in the pixels and to reduce image artifacts from occurring after the display is turned on again. By way of example, a method for discharging a pixel of an electronic display to be turned off may include supplying an activation signal to the pixel to activate the pixel. The method may also include supplying a data signal of substantially ground to a pixel electrode of the pixel. The method may include controlling a common electrode voltage of the pixel toward substantially ground. The method may also include removing the activation signal from the pixel after the common electrode voltage reaches substantially ground. 
     Various refinements of the features noted above may be made in relation to various aspects of the present disclosure. Further features may also be incorporated in these various aspects as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to one or more of the illustrated embodiments may be incorporated into any of the above-described aspects of the present disclosure alone or in any combination. The brief summary presented above is intended only to familiarize the reader with certain aspects and contexts of embodiments of the present disclosure without limitation to the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various aspects of this disclosure may be better understood upon reading the following detailed description and upon reference to the drawings in which: 
         FIG. 1  is a schematic block diagram of an electronic device with a liquid crystal display (LCD) that can discharge pixels of the LCD having oxide thin-film transistors (TFTs) before the LCD is turned off to decrease image artifacts from occurring on the LCD when the LCD is later turned back on, in accordance with an embodiment; 
         FIG. 2  is a perspective view of a notebook computer representing an embodiment of the electronic device of  FIG. 1 ; 
         FIG. 3  is a front view of a handheld device representing another embodiment of the electronic device of  FIG. 1 ; 
         FIG. 4  is a circuit diagram illustrating display circuitry used to discharge pixels of an LCD to reduce the occurrence of image artifacts when the LCD is turned back on, in accordance with an embodiment; 
         FIG. 5  is a circuit diagram illustrating circuitry of an electronic device having resistive devices for discharging pixels before an LCD is turned off to decrease the occurrence of image artifacts when the LCD is turned back on, in accordance with an embodiment; 
         FIG. 6  is a circuit diagram illustrating circuitry of an electronic device having switching devices used for discharging pixels before an LCD is turned off to decrease the occurrence of image artifacts when the LCD is turned back on, in accordance with an embodiment; 
         FIG. 7  is a circuit diagram illustrating circuitry of an electronic device having resistive devices and switching devices used for discharging pixels before an LCD is turned off to decrease the occurrence of image artifacts when the LCD is turned back on, in accordance with an embodiment; 
         FIG. 8  is a timing diagram illustrating a standard turn-off sequence of an LCD with oxide TFTs, which may result in the occurrence of image artifacts when the LCD is turned back on, in accordance with an embodiment; 
         FIG. 9  is a timing diagram illustrating a turn-off sequence used for an LCD with oxide TFTs to reduce the occurrence of image artifacts when the LCD is turned back on, in accordance with an embodiment; and 
         FIG. 10  is a flowchart describing a method for discharging a pixel of an LCD to be turned off to reduce image artifacts from occurring when the LCD is turned back on, in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     One or more specific embodiments of the present disclosure will be described below. These described embodiments are only examples of the presently disclosed techniques. Additionally, in an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     When introducing elements of various embodiments of the present disclosure, the articles “a,” “an,” and “the” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. 
     As mentioned above, embodiments of the present disclosure relate to liquid crystal displays (LCDs) and electronic devices incorporating LCDs that employ a pixel discharging device, method, or combination thereof. Specifically, rather than turning off an electronic display that includes oxide thin-film transistors (TFTs) in a conventional manner, which could result in a residual voltage remaining on the pixels of the electronic display—which could in turn cause image artifacts—embodiments of the present disclosure may incorporate hardware, software, or a combination thereof for discharging pixels as part of the power down sequence of the display. 
     Specifically, to decrease the amount of residual voltage remaining on the pixels, an activation signal is applied to the pixels using oxide TFTs. With the activation signal applied, the gates of the TFTs remain open, thereby allowing current flow between the source and drain of the oxide TFTs. The gates of the TFTs are controlled to remain open until the pixels are discharged. After the pixels are discharged, the gates of the TFTs are controlled to close. As a result, it is believed that a residual voltage may be less likely to appear on the liquid crystal after the LCD is turned off and, accordingly, image artifacts may be less likely to occur when the LCD is turned back on. 
     With the foregoing in mind, a general description of suitable electronic devices that may employ electronic displays having capabilities to discharge pixels of an LCD having oxide TFTs is described below. In particular,  FIG. 1  is a block diagram depicting various components that may be present in an electronic device suitable for use with such a display.  FIGS. 2 and 3  respectively illustrate perspective and front views of a suitable electronic device, which may be, as illustrated, a notebook computer or a handheld electronic device. 
     Turning first to  FIG. 1 , an electronic device  10  according to an embodiment of the present disclosure may include, among other things, one or more processor(s)  12 , memory  14 , nonvolatile storage  16 , a display  18  having pixels with oxide TFTs, input structures  22 , an input/output (I/O) interface  24 , network interfaces  26 , and a power source  28 . The various functional blocks shown in  FIG. 1  may include hardware elements (including circuitry), software elements (including computer code stored on a computer-readable medium) or a combination of both hardware and software elements. It should be noted that  FIG. 1  is merely one example of a particular implementation and is intended to illustrate the types of components that may be present in the electronic device  10 . As will be appreciated, when pixels are not discharged before the display  18  is turned off, a bias voltage may remain on the pixels. It is believed that this bias voltage could affect the liquid crystal, creating image artifacts on the display  18  for a long time (e.g., several minutes) after the display  18  is turned back on. As such, embodiments of the present disclosure may be employed to decrease the occurrence of image artifacts. 
     By way of example, the electronic device  10  may represent a block diagram of the notebook computer depicted in  FIG. 2 , the handheld device depicted in  FIG. 3 , or similar devices. It should be noted that the processor(s)  12  and/or other data processing circuitry may be generally referred to herein as “data processing circuitry.” This data processing circuitry may be embodied wholly or in part as software, firmware, hardware, or any combination thereof. Furthermore, the data processing circuitry may be a single contained processing module or may be incorporated wholly or partially within any of the other elements within the electronic device  10 . As presented herein, the data processing circuitry may control the gates of the oxide TFTs of the electronic display  18  to allow the pixels to be discharged before the display  18  is turned off. Discharging the pixels of the display  18  may reduce the occurrence of image artifacts when the display  18  is later turned back on. 
     In the electronic device  10  of  FIG. 1 , the processor(s)  12  and/or other data processing circuitry may be operably coupled with the memory  14  and the nonvolatile memory  16  to execute instructions. Such programs or instructions executed by the processor(s)  12  may be stored in any suitable article of manufacture that includes one or more tangible, computer-readable media at least collectively storing the instructions or routines, such as the memory  14  and the nonvolatile storage  16 . The memory  14  and the nonvolatile storage  16  may include any suitable articles of manufacture for storing data and executable instructions, such as random-access memory, read-only memory, rewritable flash memory, hard drives, and optical discs. Also, programs (e.g., an operating system) encoded on such a computer program product may also include instructions that may be executed by the processor(s)  12 . 
     The display  18  may be a touch-screen liquid crystal display (LCD), for example, which may enable users to interact with a user interface of the electronic device  10 . In some embodiments, the electronic display  18  may be a MultiTouch™ display that can detect multiple touches at once. As will be described further below, the electronic device  10  may include circuitry to control the discharge of pixels of the display  18  by keeping the gates of oxide TFTs activated until the pixels are substantially discharged. 
     The input structures  22  of the electronic device  10  may enable a user to interact with the electronic device  10  (e.g., pressing a button to increase or decrease a volume level). The I/O interface  24  may enable electronic device  10  to interface with various other electronic devices, as may the network interfaces  26 . The network interfaces  26  may include, for example, interfaces for a personal area network (PAN), such as a Bluetooth network, for a local area network (LAN), such as an 802.11x Wi-Fi network, and/or for a wide area network (WAN), such as a 3G or 4G cellular network. The power source  28  of the electronic device  10  may be any suitable source of power, such as a rechargeable lithium polymer (Li-poly) battery and/or an alternating current (AC) power converter. 
     The electronic device  10  may take the form of a computer or other type of electronic device. Such computers may include computers that are generally portable (such as laptop, notebook, and tablet computers) as well as computers that are generally used in one place (such as conventional desktop computers, workstations and/or servers). In certain embodiments, the electronic device  10  in the form of a computer may be a model of a MacBook®, MacBook® Pro, MacBook Air®, iMac®, Mac® mini, or Mac Pro® available from Apple Inc. By way of example, the electronic device  10 , taking the form of a notebook computer  30 , is illustrated in  FIG. 2  in accordance with one embodiment of the present disclosure. The depicted computer  30  may include a housing  32 , a display  18 , input structures  22 , and ports of an I/O interface  24 . In one embodiment, the input structures  22  (such as a keyboard and/or touchpad) may be used to interact with the computer  30 , such as to start, control, or operate a GUI or applications running on computer  30 . For example, a keyboard and/or touchpad may allow a user to navigate a user interface or application interface displayed on the display  18 . Further, the display  18  may include oxide TFTs that are controlled to enable discharge of pixels of the display  18  before the display  18  is powered off. 
       FIG. 3  depicts a front view of a handheld device  34 , which represents one embodiment of the electronic device  10 . The handheld device  34  may represent, for example, a portable phone, a media player, a personal data organizer, a handheld game platform, or any combination of such devices. By way of example, the handheld device  34  may be a model of an iPod® or iPhone® available from Apple Inc. of Cupertino, Calif. In other embodiments, the handheld device  34  may be a tablet-sized embodiment of the electronic device  10 , which may be, for example, a model of an iPad® available from Apple Inc. 
     The handheld device  34  may include an enclosure  36  to protect interior components from physical damage and to shield them from electromagnetic interference. The enclosure  36  may surround the display  18 , which may display indicator icons  38 . The indicator icons  38  may indicate, among other things, a cellular signal strength, Bluetooth connection, and/or battery life. The I/O interfaces  24  may open through the enclosure  36  and may include, for example, a proprietary I/O port from Apple Inc. to connect to external devices. 
     User input structures  40 ,  42 ,  44 , and  46 , in combination with the display  18 , may allow a user to control the handheld device  34 . For example, the input structure  40  may activate or deactivate the handheld device  34 , the input structure  42  may navigate a user interface to a home screen, a user-configurable application screen, and/or activate a voice-recognition feature of the handheld device  34 , the input structures  44  may provide volume control, and the input structure  46  may toggle between vibrate and ring modes. A microphone  48  may obtain a user&#39;s voice for various voice-related features, and a speaker  50  may enable audio playback and/or certain phone capabilities. A headphone input  52  may provide a connection to external speakers and/or headphones. As mentioned above, the display  18  may include oxide TFTs that are controlled to enable pixels of the display  18  to discharge before power is removed from the display  18 . 
     Among the various components of an electronic display  18  may be a pixel array  100 , as shown in  FIG. 4 . As illustrated,  FIG. 4  generally represents a circuit diagram of certain components of the display  18  in accordance with an embodiment. In particular, the pixel array  100  of the display  18  may include a number of unit pixels  102  disposed in a pixel array or matrix. In such an array, each unit pixel  102  may be defined by the intersection of rows and columns, represented by gate lines  104  (also referred to as scanning lines), and source lines  106  (also referred to as data lines), respectively. Although only six unit pixels  102 , referred to individually by the reference numbers  102 A- 102 F, respectively, are shown for purposes of simplicity, it should be understood that in an actual implementation, each source line  106  and gate line  104  may include hundreds or thousands of such unit pixels  102 . Each of the unit pixels  102  may represent one of three subpixels that respectively filters only one color (e.g., red, blue, or green) of light. For purposes of the present disclosure, the terms “pixel,” “subpixel,” and “unit pixel” may be used largely interchangeably. 
     In the presently illustrated embodiment, each unit pixel  102  includes an oxide thin film transistor (TFT)  108  for switching a data signal supplied to a respective pixel electrode  110 . The potential stored on the pixel electrode  110  relative to a potential of a common electrode  112 , which may be shared by other pixels  102 , may generate an electrical field sufficient to alter the arrangement of a liquid crystal layer of the display  18 . In the depicted embodiment of  FIG. 4 , a source  114  of each oxide TFT  108  may be electrically connected to a source line  106  and a gate  116  of each oxide TFT  108  may be electrically connected to a gate line  104 . A drain  118  of each oxide TFT  108  may be electrically connected to a respective pixel electrode  110 . Each oxide TFT  108  may serve as a switching element that may be activated and deactivated (e.g., turned on and off) for a period of time based on the respective presence or absence of a scanning or activation signal on the gate lines  104  that are applied to the gates  116  of the oxide TFTs  108 . 
     When activated, an oxide TFT  108  may store the image signals received via the respective source line  106  as a charge upon its corresponding pixel electrode  110 . As noted above, the image signals stored by the pixel electrode  110  may be used to generate an electrical field between the respective pixel electrode  110  and a common electrode  112 . This electrical field may align the liquid crystal molecules within the liquid crystal layer to modulate light transmission through the pixel  102 . Thus, as the electrical field changes, the amount of light passing through the pixel  102  may increase or decrease. In general, light may pass through the unit pixel  102  at an intensity corresponding to the applied voltage from the source line  106 . 
     The display  18  also may include a source driver integrated circuit (IC)  120 , which may include a processor, microcontroller, or application specific integrated circuit (ASIC), that controls the display pixel array  100  by receiving image data  122  from the processor(s)  12  and sending corresponding image signals to the unit pixels  102  of the pixel array  100 . It should be understood that the source driver  120  may be a chip-on-glass (COG) component on a TFT glass substrate, a component of a display flexible printed circuit (FPC), and/or a component of a printed circuit board (PCB) that is connected to the TFT glass substrate via the display FPC. Further, the source driver  120  may include any suitable article of manufacture having one or more tangible, computer-readable media for storing instructions that may be executed by the source driver  120 . 
     The source driver  120  also may couple to a gate driver integrated circuit (IC)  124  that may activate or deactivate rows of unit pixels  102  via the gate lines  104 . As such, the source driver  120  may provide timing signals  126  to the gate driver  124  to facilitate the activation/deactivation of individual rows (i.e., lines) of pixels  102 . In other embodiments, timing information may be provided to the gate driver  124  in some other manner. The display  18  may include a Vcom source  128  to provide a Vcom output to the common electrodes  112 . In some embodiments, the Vcom source  128  may supply a different Vcom to different common electrodes  112  at different times. In other embodiments, the common electrodes  112  all may be maintained at the same potential (e.g., a ground potential) while the display  18  is on. 
     When pixel electrodes  110  are not discharged before the display  18  is turned off, a bias voltage may remain on the pixel electrodes  110 . It is believed that this bias voltage could affect the liquid crystal, creating image artifacts on the display  18  for a long time (e.g., several minutes) after the display  18  is turned back on. Accordingly, the oxide TFTs  108  are controlled to allow discharge the pixel electrodes  110  during the display  18  turn-off sequence to inhibit image artifacts from appearing on the display  18 , such as when the display  18  is turned on after previously being turned off. As a result of discharging the pixel electrodes  110 , the bias voltage on the pixel electrodes  110  when the display  18  is turned off may be low, or near zero. 
     Oxide TFTs  108  may have considerably lower leakage current than amorphous silicon (a-Si) TFTs as shown in the following table: 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 a-Si TFT 
                 oxide TFT 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Threshold Voltage 
                 &lt;=0 V 
                 &gt;2 V 
               
               
                   
                 Leakage Current 
                 1E−11 &lt; loff &lt; 1E−10 
                 &lt;1E−14 
               
               
                   
                 (loff) where Vgs = 0 
               
               
                   
                 loff where Vgs &lt; 0 
                 &lt;1E−11 
                 &lt;1E−14 
               
               
                   
                   
               
            
           
         
       
     
     As listed in TABLE 1, a-Si TFTs differ from oxide TFTs  108  in multiple ways. For example, the gate threshold voltage of a-Si TFTs may be generally less than or equal to zero, while the gate threshold voltage for oxide TFTs  108  may be generally greater than two volts. Further, the leakage current of the oxide TFTs  108  may be approximately 1000 times smaller than the leakage current of a-Si TFTs. Accordingly, when the gate  116  of an oxide TFT  108  is not activated (e.g., the gate voltage is lower than the gate threshold voltage), very little current may flow between the source  114  and the drain  118  of the oxide TFT  108 . As such, the pixels  102  may be inhibited from discharging through the oxide TFTs  108  when the gates  116  are not activated. Therefore, in certain embodiments, an electronic device  10  using oxide TFTs  108  may be configured to keep the gates  116  of the oxide TFTs  108  activated for a sufficient amount of time to allow the pixels  102  of the display  18  to discharge through the oxide TFTs  108 . 
     There are many ways to configure the circuitry of the electronic device  10  so that pixels  102  of the electronic display  18  may be discharged before gates  116  of the oxide TFTs  108  are deactivated.  FIG. 5  generally represents one embodiment of a circuit diagram  130  of certain components of the electronic device  10  used for discharging pixels prior to deactivating gates  116  of oxide TFTs  108  before the display  18  is turned off to decrease the occurrence of image artifacts when the display  18  is turned back on. In particular, the electronic device  10  includes a power management unit  132 . The power management unit  132  is used to manage the power of the electronic device  10  and may control when power is applied to, or removed from, other components of the electronic device  10 . For example, the power management unit  132  provides a high gate voltage (VGH)  134  and a low gate voltage (VGL)  134  to the gate driver  124 . As will be appreciated, the gate driver  124  may use the VGH  134  to apply an activation voltage to the gate lines  104 , while the gate driver  124  may use the VGL  136  to apply a deactivation voltage to the gate lines  104 . As such, the gate driver  124  may be configured to couple together either the VGH  134  or the VGL  136  to the gate line  104 . 
     A first resistive device  138  (e.g., pull-down resistor) couples the VGH  134  to ground, while a second resistive device  140  (e.g., pull-down resistor) couples the Vcom source  128  to ground. Each of the first and second resistive devices  138  and  140  may be designed with a resistance suitable for discharging the gate  116  and the pixels  102  respectively, as explained in detail below. During normal operation of the electronic device  10 , the first and second resistive devices  138  and  140  may have little effect on the operation of the electronic device  10 . For example, a voltage applied to VGH  134  is also applied to the first resistive device  138  resulting in power dissipation; however, this power dissipation may generally be small (e.g., when the resistance of the first resistive device  138  is large). As another example, a voltage on the Vcom source  128  is also applied to the second resistive device  140  resulting in power dissipation. Again, this power dissipation may generally be small (e.g., when the resistance of the second resistive device  140  is large). 
     During a power off sequence of the electronic device  10 , the power management unit  132  may remove power from the display  18 . For example, the power management unit  132  may cause the connection between the power management unit  132  and each of the VGH  134 , the VGL  136 , and the Vcom source  128  to operate as an open circuit. Further, during the power off sequence, the gate driver  124  may be configured to couple the VGH  134  to the gate line  104 . In addition, the source driver  120  may be configured to couple the source line  106  to ground. Therefore, voltage that remains on the gate  116  may be discharged via the gate line  104 , the VGH  134 , and the pull-down first resistive device  138 . The discharge rate may be based on the resistance of the first resistive device  138  and a charge that may be stored between the gate  116  and the source  114 . As will be appreciated, as long as the voltage applied to the gate line  104  is greater than the threshold voltage of the gate  116 , the oxide TFT  108  will remain activated. 
     In the present embodiment, the pixel  102  may discharge concurrently with the gate  116  (e.g., the activation voltage and the common electrode  112  voltage may be controlled concurrently). Specifically, while the gate  116  remains activated, the charge stored on liquid crystal capacitor (Clc) and the storage capacitor (Cst) may be discharged via the following path: the Vcom source  128  coupled to ground via the second resistive device  140 , the common electrode  112  coupled to the Vcom source  128 , the pixel electrode  110  coupled to the drain  118 , the source  114  coupled to the source line  106 , and the source line  106  coupled to ground. The discharge rate of the pixel  102  may be based on the resistance of the second resistive device  140  and the charge stored on Clc and Cst. After the gate  116  is deactivated, the charge stored in the pixel  102  may still discharge through the same path; however, the discharge rate will be limited to the leakage current of the oxide TFT  108 , resulting in a slow discharge. As such, to completely discharge the pixel  102 , the resistance of the first and second resistive devices  138  and  140  should be selected so that the pixel  102  will completely discharge before the voltage on the gate line  104  drops below the threshold voltage of the oxide TFT  108 . By discharging the pixel  102  during the power off sequence of the display  18 , image artifacts occurring on the display  18  may be reduced or eliminated. 
     The discharge of pixels  102  of the electronic display  18  may be controlled using switching devices within the power management unit  132 . Accordingly,  FIG. 6  generally represents an embodiment of a circuit diagram  142  of the electronic device  10  using switching devices for discharging pixels  102  before the display  18  is turned off to decrease the occurrence of image artifacts when the display  18  is turned back on. The power management unit  132  includes a first control circuitry  144  and a second control circuitry  146 . The first control circuitry  144  is configured to selectively couple the VGH  134  to ground, while the second control circuitry  146  is configured to selectively couple the Vcom source  128  to ground. As illustrated, in the present embodiment, the first control circuitry  144  and the second control circuitry  146  may each include a FET; however, in other embodiments, the first control circuitry  144  and the second control circuitry  146  may include any suitable output producing devices, such as any type of switching device or solid state device. 
     Using the first control circuitry  144  and the second control circuitry  146 , the power management unit  132  may control the timing of the pixel  102  discharge. Specifically, during a power off sequence of the electronic device  10 , the power management unit  132  may remove power from the display  18 . Further, the gate driver  124  may be configured to couple the VGH  134  to the gate line  104 . In addition, the source driver  120  may be configured to couple the source line  106  to ground. Accordingly, a voltage remaining on the gate  116  may be discharged by the power management unit  132  activating the first control circuitry  144  to enable current flow between the VGH  134  and ground. Furthermore, the pixel  102  may be discharged by the power management unit  132  activating the second control circuitry  146  to enable current flow between the Vcom source  128  and ground. 
     As discussed above, to efficiently discharge the pixel  102 , the pixel  102  should be discharged prior to deactivating the gate  116 . Therefore, during the power off sequence, the power management unit  132  may activate the second control circuitry  146  to discharge the pixel  102 . After the pixel  102  is discharged, the power management unit  132  may activate the first control circuitry  144  to discharge any charge remaining on the gate  116 . Using such a sequence, the pixel  102  may be discharged as part of the power down sequence of the display  18  to reduce the occurrence of image artifacts appearing on the display  18  when the display is turned on at a later time. 
     The discharge of pixels  102  of the electronic display  18  may also be controlled by a combination of resistive devices and switching device. Specifically,  FIG. 7  is a circuit diagram  148  illustrating the electronic device  10  having the first and second resistive device  138  and  140  and the first and second control circuitry  144  and  146  for discharging pixels  102  before the display  18  is turned off to decrease the occurrence of image artifacts when the display  18  is turned back on. During a power off sequence, the second resistive device  140  may generally provide a predetermined discharge rate for discharging the pixel  102 . Furthermore, the power management unit  132  may provide additional control to the rate of pixel  102  discharge using the second control circuitry  146 . For example, the power management unit  132  may use the second control circuitry  146  to increase and/or decrease the rate of pixel  102  discharge. In addition, the first resistive device  138  may generally provide a predetermined discharge rate for discharging any charge remaining on the gate  116 . Again, the power management unit  132  may provide additional control to the rate of gate  116  discharge using the first control circuitry  144 . As such, the pixel  102  may be discharged during the turn-off sequence of the display  18 . 
     If the gates  116  of the oxide TFTs  108  are deactivated prior to completely discharging the pixels  102  of the display  18 , the pixels  102  may store a charge for a long period of time (e.g., many minutes).  FIG. 8  illustrates one embodiment of a timing diagram  150  that shows a standard turn-off sequence of the display  18  with oxide TFTs  108 . As illustrated, external power may be applied to the display  18 , as shown by segment  152 . At a time  154 , the external power may be removed from the display  18 , as shown by segment  156 . Pixel data may be supplied to the source line  106 , as shown by segment  158 , until the external power is removed at the time  154 . After the external power is removed, the source line  106  may be grounded (e.g., apply a low voltage, near-zero voltage, black voltage, zero volts, etc.), as shown by segment  160 . 
     A voltage is applied to the gate line  104  to activate the gate  116 , as shown by segment  162 , until the external power is removed at the time  154 . After the time  154 , the voltage applied to the gate line  104  is reduced and/or discharged during segment  164 . At a time  166 , the voltage on the gate line  104  is at the threshold voltage for the oxide TFT  108 , so that after the time  166 , the gate  116  is not activated. During segment  168 , the voltage on the gate line  104  remains at a low voltage, such as zero or ground. A voltage present on the Vcom source  128  is shown by segment  170 . At the time  154 , the voltage present on the Vcom source  128  may begin to discharge toward zero, near-zero, or ground, as shown by segment  172 . 
     As will be appreciated, the voltage present on the Vcom source  128  may be associated with a charge stored in the pixels  102 . In certain embodiments, the voltage present on the Vcom source  128  may discharge at a faster rate between the times  154  and  166 , until the voltage on the gate line  104  passes the threshold voltage. Further, the discharge of the voltage present on the Vcom source  128  may be limited after the time  166  to the leakage current of the oxide TFTs  108 . Accordingly, the voltage present on the Vcom source  128  may indicate that a voltage remains on the pixels  102 . This voltage present on the pixels  102  may remain for a long period of time (e.g., the duration of segment  172 ) and may result in image artifacts occurring when the display  18  is turned back on. The voltage present on the Vcom source  128  may eventually reach ground  174  (or a low voltage, near-zero voltage, black voltage, zero volts, etc.), as shown by segment  176 . It should be noted that a “ground” voltage or a “black” voltage as used herein may be a voltage that produces a dark pixel (e.g., the darkest pixel voltage). 
     In certain embodiments, the pixels  102  may be discharged through the oxide TFTs  108  if a voltage on the gates  116  of the oxide TFTs  108  is maintained above a threshold voltage.  FIG. 9  illustrates one embodiment of a timing diagram  180  that shows a turn-off sequence used for the display  18  having oxide TFTs  108  to reduce the occurrence of image artifacts when the display  18  is turned back on at a later time. As illustrated, external power may be applied to the display  18 , as shown by segment  182 . At a time  184 , the external power may be removed from the display  18 , as shown by segment  186 . Pixel data may be supplied to the source line  106 , as shown by segment  188 , until the external power is removed at the time  184 . After the external power is removed, the source line  106  may be grounded (e.g., apply a low voltage, near-zero voltage, black voltage, zero volts, etc.), as shown by segment  190 . 
     A voltage is applied to the gate line  104  to activate the gate  116 , as shown by segment  192 , until the external power is removed at the time  184 . After the time  184 , the voltage applied to the gate line  104  is reduced and/or discharged during segment  194 . At a time  196 , the voltage on the gate line  104  is at the threshold voltage for the oxide TFT  108 , so that after the time  196 , the gate  116  is not activated. At a time  198 , the voltage on the gate line  104  reaches ground, a low voltage, a near-zero voltage, a black voltage, or zero volts. During segment  200 , the voltage on the gate line  104  remains at the voltage reached at time  198  (e.g., ground). A voltage present on the Vcom source  128  is shown by segment  202 . At the time  184 , the voltage present on the Vcom source  128  may begin to discharge toward zero, near-zero, or ground, as shown by segment  204 . 
     As will be appreciated, the voltage present on the Vcom source  128  may be associated with a charge stored in the pixels  102 . At a time  206 , the voltage present on the Vcom source  128  may reach ground (or a low voltage, near-zero voltage, black voltage, zero volts etc.) where the voltage remains, as shown by segment  208 . As illustrated, the voltage on the Vcom source  128  (e.g., pixel  102  voltage) discharges before time  206 . Accordingly, the pixels  102  discharge before the time  196  where the voltage on the gate line  104  passes the threshold voltage of the gate  116 . As such, there is a time difference  210 , of greater than or equal to zero, between the time  206  and the time  196 . Therefore, the pixels  102  are able to discharge, decreasing the occurrence of image artifacts that may occur when the display is turned on at a later time. 
     As presented above, the display  18  is shut down using a series of operations that may inhibit image artifacts from appearing when the display  18  is subsequently turned back on.  FIG. 10  illustrates one embodiment of a method  212  for discharging a pixel  102  of the display  18  before power is removed from the display  18 . An activation signal is supplied to the pixel  102  to activate the pixel (block  214 ). For example, the activation signal may be supplied to the pixel  102  via the oxide TFT  108 . Further, a data signal of substantially ground (e.g., a low voltage, near-zero voltage, black voltage, zero volts, etc.) is supplied to the pixel electrode  110  of the pixel  102  (block  216 ). The common electrode  112  voltage of the pixel  102  is controlled toward substantially ground (block  218 ). In certain embodiments, the common electrode  112  voltage of the pixel  102  may be controlled from a voltage that is not zero, or not substantially ground. As will be appreciated, the common electrode  112  voltage may be controlled using a resistive device, a solid state device, or another suitable device. Further, the common electrode  112  voltage may be controlled via the power management unit  132 . The activation signal is removed from the pixel  102  after the common electrode  112  voltage of the pixel  102  reaches substantially ground (block  220 ). In certain embodiments, the activation signal may be removed from the pixel  102  using a resistive device, a solid state device, or another suitable device. It should be noted that removing the activation signal may mean decreasing the activation signal below the threshold voltage for the oxide TFT  108 . In some embodiments, the activation signal is controlled toward the threshold voltage at approximately the same time that the common electrode  112  voltage is controlled toward substantially ground. In certain embodiments, the activation signal is controlled to be above the threshold voltage until the common electrode  112  voltage reaches substantially ground. Technical effects of the present disclosure include, among other things, discharging pixels  102  that use oxide TFTs  108  prior to the display  18  and/or the electronic device  10  being turned off. The pixels  102  are discharged before the gate  116  voltage of the oxide TFTs  108  are deactivated. Accordingly, image artifacts, which may result from pixels  102  not being discharged, may be reduced and/or eliminated. 
     The specific embodiments described above have been shown by way of example, and it should be understood that these embodiments may be susceptible to various modifications and alternative forms. It should be further understood that the claims are not intended to be limited to the particular forms disclosed, but rather to cover all modifications, equivalents, and alternatives falling within the spirit and scope of this disclosure.