PATENT DOCUMENT

Publication Number: US-8730229-B2
Application Number: US-201113247876-A
Country: US
Kind Code: B2

Title: Devices and methods for zero-bias display turn-off using VCOM switch

Abstract:
Methods and devices employing zero-bias display turn-off circuitry, including turn-off logic and switching devices, are provided. In one example, a method may include supplying a common voltage output of ground to a common electrode of a pixel of an electronic display, supplying an activation signal to the pixel to activate the pixel, supplying a data signal of ground to a pixel electrode of the pixel, and removing the activation signal from the pixel while the data signal is being supplied to the pixel to store the data signal in the pixel. When the activation signal is removed, the method may include causing the common voltage output being supplied to the common electrode of the pixel to change to a floating value to prevent a kickback voltage from affecting the data signal stored in the pixel.

Claims:
What is claimed is: 
     
       1. A method comprising:
 supplying a common voltage output of ground to a common electrode of a pixel of an electronic display; 
 supplying an activation signal to the pixel to activate the pixel while the common voltage output of ground is supplied to the common electrode; 
 supplying a data signal of substantially ground to a pixel electrode of the pixel while the common voltage output of ground is supplied to the common electrode; 
 removing the activation signal from the pixel while the data signal is being supplied to the pixel to store the data signal in the pixel; and 
 during the period in which the activation signal is removed, causing the common voltage output being supplied to the common electrode of the pixel to change to a floating value to inhibit a kickback voltage from affecting the data signal stored in the pixel. 
 
     
     
       2. The method of  claim 1 , wherein causing the common voltage output being supplied to the common electrode of the pixel to change to a floating value comprises sending a control signal to a solid-state switching device that causes the common voltage output being supplied to the common electrode of the pixel to change to the floating value. 
     
     
       3. The method of  claim 1 , wherein causing the common voltage output being supplied to the common electrode of the pixel to change to a floating value comprises changing a switch that causes the common voltage output being supplied to the common electrode of the pixel to change to the floating value. 
     
     
       4. The method of  claim 1 , comprising supplying a shutdown command to the electronic display to turn off the display. 
     
     
       5. The method of  claim 1 , wherein removing the activation signal from the pixel and causing the common voltage output being supplied to the common electrode of the pixel to change to a floating value occur at substantially the same time. 
     
     
       6. An electronic display comprising:
 a plurality of pixels, each pixel having a common electrode and a pixel electrode; 
 a common voltage source configured to supply common voltage outputs to the common electrodes of the pixels; 
 a gate driver configured to supply activation signals to the pixels to activate the pixels; 
 a source driver configured to supply data signals to the pixel electrodes when the pixels are activated; and 
 display turn-off circuitry configured to prepare pixels to be placed in an off state when the display is to be turned off, by issuing control signals to change the common voltage outputs being supplied to the common electrodes; 
 wherein, when the display is to be turned off, the common voltage source supplies common voltage outputs of ground to the common electrodes of the pixels, the gate driver supplies activation signals to the pixels while the common voltage outputs of ground are supplied to the common electrodes, the source driver supplies data signals of ground to the pixel electrodes while the common voltage outputs are at ground to store the data signals in the pixel electrodes, the gate driver removes the activation signals from the pixels, and the display turn-off circuitry causes the common electrodes of the pixels to be disconnected from the common voltage source when the gate driver removes the activation signals from the pixels to inhibit a kickback voltage from affecting data stored in the pixels. 
 
     
     
       7. The electronic display of  claim 6 , wherein, when the display is being turned off, the source driver supplies data signals of ground to the pixel electrodes. 
     
     
       8. The electronic display of  claim 6 , wherein, when the display is being turned off, the source driver supplies data signals of vblack to the pixel electrodes. 
     
     
       9. The electronic display of  claim 6 , wherein the display turn-off circuitry is configured to issue control signals to cause one or more solid state devices to switch states to change the common voltage outputs being supplied to the common electrodes. 
     
     
       10. An electronic device comprising:
 an electronic display configured, when the electronic display is to be turned off, to receive a shut-down command and, in response to the shut-down command, cause a plurality of pixel electrodes to store a data signal of ground and cause common voltage outputs being supplied to common electrodes of the pixels to change while the plurality of pixel electrodes store the data signal of ground to inhibit a kickback voltage from affecting the data signals stored in the pixels; and 
 data processing circuitry configured to control the electronic display by determining when the electronic display is to be turned off and issuing the shut-down command. 
 
     
     
       11. The electronic device of  claim 10 , wherein the electronic display comprises display turn-off circuitry configured to prepare pixels to be placed in an off state when the display is being turned off by issuing control signals to change the common voltage outputs being supplied to the common electrodes to inhibit the kickback voltage from affecting the data signals stored in the pixels. 
     
     
       12. The electronic device of  claim 10 , wherein the electronic display comprises display turn-off circuitry configured to receive the shut-down command, cause the plurality of pixel electrodes to store a data signal of ground, and cause common voltage outputs being supplied to the common electrodes of the pixels to change. 
     
     
       13. The electronic device of  claim 10 , wherein the electronic display is configured to cause common voltage outputs being supplied to common electrodes of the pixels to change to a high impedance to inhibit the kickback voltage from affecting the data signals stored in the pixels. 
     
     
       14. The electronic device of  claim 10 , wherein the electronic display comprises one or more solid state devices to change the common voltage outputs being supplied to the common electrodes of the pixels to inhibit the kickback voltage from affecting the data signals stored in the pixels and the shut-down command causes the solid state devices to switch states. 
     
     
       15. An article of manufacture comprising:
 one or more tangible, non-transitory machine-readable media having instructions encoded thereon for execution by a processor, the instructions comprising:
 instructions to determine when to shut down an electronic display; and 
 instructions to cause, when the display is to be shut down, common voltage outputs of ground to be supplied to common electrodes of a plurality of pixels of the electronic display, activation signals to be supplied to the pixels to activate the pixels while the common voltage outputs of ground are supplied to the common electrodes, data signals of ground to be supplied to pixel electrodes of the pixels while the common voltage outputs of ground are supplied to the common electrodes, the activation signals to be removed from the pixels while the data signals are being supplied to the pixels to store the data signals in the pixels, and the common voltage outputs being supplied to the common electrodes of the pixels to change to a floating value to inhibit a kickback voltage from affecting the data signals stored in the pixels when the activation signals are removed. 
 
 
     
     
       16. A method comprising:
 turning off a first line of pixels by:
 supplying a first common voltage output of ground to a first common electrode of the first line of pixels of an electronic display; 
 supplying a first activation signal to a first gate line to activate the first line of pixels while the first common voltage output of ground is supplied to the first common electrode of the first line of pixels; 
 supplying data signals of ground to pixel electrodes of the first line of pixels while the first common voltage output of ground is supplied to the first common electrode of the first line of pixels; 
 removing the first activation signal from the first gate line while the data signals are being supplied to the pixels to store the data signals in the first line of pixels; and 
 during the period in which the first activation signal is removed from the first gate line, causing the first common voltage output being supplied to the first common electrode to change to a floating value to inhibit a kickback voltage from affecting the data signals stored in the first line of pixels; and 
 
 turning off a second line of pixels by:
 supplying a second common voltage output of ground to a second common electrode of the second line of pixels of the electronic display; 
 supplying a second activation signal to a second gate line to activate the second line of pixels while the second common voltage output of ground is supplied to the second common electrode of the second line of pixels; 
 supplying data signals of ground to pixel electrodes of the second line of pixels while the second common voltage output of ground is supplied to the second common electrode of the second line of pixels; 
 removing the second activation signal from the second gate line while the data signals are being supplied to the pixels to store the data signals in the second line of pixels; and 
 during the period in which the second activation signal is removed from the second gate line, causing the second common voltage output being supplied to the second common electrode to change to a floating value to inhibit a kickback voltage from affecting the data signals stored in the second line of pixels. 
 
 
     
     
       17. The method of  claim 16 , wherein turning off the first line of pixels occurs prior to turning off the second line of pixels. 
     
     
       18. The method of  claim 16 , wherein turning off the first line of pixels occurs at substantially the same time as turning off the second line of pixels. 
     
     
       19. The method of  claim 16 , comprising turning off the first line of pixels, the second line of pixels, and all other lines of pixels of the electronic display at substantially the same time. 
     
     
       20. The method of  claim 16 , wherein the first common voltage output and the second common voltage output are supplied by a common voltage source.

Description:
BACKGROUND 
     The present disclosure relates generally to electronic displays and, more particularly, to liquid crystal displays (LCDs) that can be turned off in a manner that largely eliminates a bias voltage on a liquid crystal. 
     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, when an LCD is turned off, the pixel electrodes of all pixels of the LCD may be supplied a minimal voltage. When the TFT gates are deactivated, a kickback voltage may alter the voltage stored in the pixels. The resulting voltage may be different from the supplied minimal 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, 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 turning off an electronic display to prevent a kickback voltage from affecting data stored in pixels when the display is turned off. By way of example, a method for turning off an electronic display may include supplying a Vcom output of ground to a common electrode of a pixel of an electronic display, supplying an activation signal to the pixel to activate the pixel, supplying a data signal of ground to a pixel electrode of the pixel, and removing the activation signal from the pixel while the data signal is being supplied to the pixel to store the data signal in the pixel. When the activation signal is removed, the Vcom output that is supplied to the common electrode of the pixel is changed to prevent a kickback voltage from affecting the data signal stored in the pixel. 
     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) having zero-bias display turn-off circuitry, 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 turn off pixels of an LCD with reduced kickback voltage, in accordance with an embodiment; 
         FIG. 5  is a circuit diagram of a pixel of an LCD, in accordance with an embodiment; 
         FIG. 6  is a timing diagram illustrating a zero-bias turn-off sequence to turn off pixels of an LCD with reduced kickback voltage, in accordance with an embodiment; and 
         FIG. 7  is a flowchart describing a method for turning off a pixel in an LCD with reduced kickback voltage, 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 display shut-down device, method, or combination thereof. Specifically, rather than turning off an electronic display 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 when the display is turned back on, embodiments of the present disclosure may incorporate zero-bias display turn-off circuitry. This display turn-off circuitry is referred to as “zero-bias” because, when the electronic display is turned off, it results in a significantly reduced amount of residual voltage remaining on the pixels of the electronic display (approaching substantially zero). In fact, the amount of residual voltage remaining on the pixels may be so low as to substantially reduce the effect of any image artifacts that might otherwise form. 
     Specifically, to decrease the amount of residual voltage remaining on the pixels, a Vcom output of ground may be supplied to a common electrode of a pixel of an electronic display. An activation signal may be supplied to the pixel to activate the pixel. A data signal of ground may be supplied to the pixel electrode of the pixel and the activation signal may be removed from the pixel while the data signal is being supplied to the pixel to store the data signal in the pixel. When the activation signal is removed, the common electrode of the pixel may be disconnected from the Vcom voltage supply. That is, the common electrode may be “floated” or maintained in a high-Z or high-impedance configuration. It is believed that disconnecting the common electrode from the Vcom voltage supply may prevent a kickback voltage from affecting data stored in the pixel, thereby maintaining the data signal of ground on the pixel electrode. 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 zero-bias display turn-off capabilities will be provided 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 zero-bias display turn-off circuitry  20 , 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 . 
     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 electronic display  18  by determining when the electronic display  18  is to be turned off and by issuing a turn-off or shutdown command. The turn-off or shutdown command is provided to the display  18 , which uses the zero-bias display turn-off circuitry  20  to turn off the display  18  in a way that reduces 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. Various display components, such as turn-off logic and associated switching devices may be located within the electronic display  18 . As will be described further below, the zero-bias display turn-off circuitry  20  may include circuitry for switching on or off the connection between the pixel common electrodes and a voltage source and/or increasing the impedance between the common electrodes and the voltage source. As such, it should be understood that the zero-bias display turn-off circuitry  20  may include, for example, switching devices that change the signal being supplied from the Vcom voltage source to the common electrodes in response to a shut-down command from the processor(s)  12 . More specifically, when the display  18  is to be turned off, the zero-bias display turn-off circuitry  20  may cause the signal supplied to the common electrodes to switch to a high impedance, floating value, or hi-Z output. It should be noted that the terms “high impedance,” “floating value,” and “hi-Z” may be used interchangeably in this disclosure. 
     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 the zero-bias display turn-off circuitry  20 . 
       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 the zero-bias display turn-off circuitry  20 . 
     Among the various components of an electronic display  18  may be a pixel array  100 , as shown in  FIG. 4 .  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 a 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 TFT  108  may be electrically connected to a source line  106  and a gate  116  of each TFT  108  may be electrically connected to a gate line  104 . A drain  118  of each TFT  108  may be electrically connected to a respective pixel electrode  110 . Each 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 TFTs  108 . 
     When activated, a 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 chip, such as 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. 
     During operation, a kickback voltage may occur when an activation signal is removed by the gate driver  124 . That is, when the activation signal is removed, the voltage stored by the pixel electrode  110  may change by an amount substantially equal to the kickback voltage. When the display  18  is turned off, a very low voltage or ground potential may be applied to the pixel electrodes  110 . Doing so may minimize the voltage difference biasing the liquid crystal between the pixel electrodes  110  and the common electrodes  112 . If a kickback voltage occurs as the display  18  is being shut off, the originally applied voltage could change by the kickback voltage amount, leaving a non-zero bias voltage on the pixel electrodes  110 . It is believed that this bias voltage caused by the kickback 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 zero-bias display turn-off circuitry  20  of the display  18  may operate using turn-off logic  130  to inhibit image artifacts from appearing on the display  18 , such as when the display  18  is turned on after previously being turned off. Specifically, the zero-bias display turn-off circuitry  20  may prepare pixels to be placed in an off state when the display  18  is to be turned off by issuing control signals to change the Vcom outputs being supplied to the common electrodes  112 . The turn-off logic  130  controls the operation of switches  132  and  134  using control lines  136  and  138 . It should be appreciated that other switches and control lines may couple to other common electrodes  112  of other lines of pixels in the display  18 , and that the switches  132  and  134  and control lines  136  and  138  are illustrated by way of example. The turn-off logic  130  may include a microcontroller or other processing device that can execute instructions  131 . Further, the instructions  131  may be stored on any suitable article of manufacture that includes one or more tangible, computer-readable media, such as a memory device. 
     The turn-off logic  130  may send control signals to the switches  132  and  134  to control the position of the switches  132  and  134  (i.e., open or closed). In the “closed position” the switches  132  and  134  electrically connect the Vcom source  128  to the common electrodes  112 . Thus, a voltage (e.g., ground) or other signal supplied by the Vcom source  128  may be received by the common electrodes  112  when the switches  132  and  134  are in the “closed position.” Conversely, in the “open position” the switches  132  and  134  electrically disconnect the Vcom source  128  from the common electrodes  112 . Thus, the common electrodes  112  receive a high impedance or floating value input when the switches  132  and  134  are in the “open position.” 
     The switches  132  and  134  may be any type of switching device. For example, the switches  132  and  134  may be any suitable relay, solid state switch (e.g., a transistor), or other solid state device. As should be understood, the turn-off logic  130  may be controlled by signals from the source driver  120 , the gate driver  124 , the processor(s)  12 , or some other device. For example, the turn-off logic  130  may receive a shut-down command from the processor(s)  12  or the source driver  120  to cause the turn-off logic  130  to change the Vcom output to a high impedance or floating value. 
     In the example of  FIG. 4 , the switch  132  may be used to control the Vcom output to one line of pixels (i.e.,  102 A,  102 B,  102 C), while the switch  134  may be used to control the Vcom output to another line of pixels (i.e.,  102 D,  102 E,  102 F). Alternatively, a single switch may be used to control the Vcom output to all pixels  102  in the electronic display  18 . Further, the lines of pixels  102  in the display  18  may be controlled using the switches  132  and  134 . The switches  132  and  134  may switch between the “closed position” and the “open position” consecutively or concurrently. In some embodiments, the zero-bias display turn-off circuitry  20  may not include the switches  132  and  134 . In place of the switches  132  and  134 , the Vcom source  128  itself may provide a high impedance or floating value to the common electrodes  112  of one or more of the lines of pixels  102 . In such a configuration, the turn-off logic  130  may control when the Vcom source  128  provides a high impedance or floating value output. That is, the Vcom source  128  itself may include the capability of providing a high-impedance or floating condition to the common electrodes  112  upon receipt of a command signal. 
     Within the pixel array  100 , each pixel  102  stores data on the pixel electrodes  110  of the pixel. In the illustrated embodiment of  FIG. 5 , the pixel  102  includes the TFT  108  as previously described. The source  114  of the TFT  108  is electrically connected to the source line (D x )  106  and the gate  116  of the TFT  108  is electrically connected to the gate line (G y )  104 . Further, the drain  118  of the TFT  108  is electrically connected to the pixel electrode  110 . The switch  132  is positioned between the Vcom source  128  and the common electrode  112 . As previously described, the switch  132  may be any suitable switching device that may cause the common electrode  112  to receive a high impedance or floating value input on command (e.g., a transistor). In certain embodiments, the pixel  102  may not have the switch  132  coupled between the common electrode  112  and the Vcom source  128 . In such an embodiment, the Vcom source  128  may directly provide a high impedance or floating value output to the common electrode  112 . A liquid crystal capacitance (C LC )  140  may be present between the pixel electrode  110  and the common electrode  112  and a parasitic capacitance (C gd )  142  may be present between the gate  116  and the drain  118  of the TFT  108 . 
     During operation, the switch  132  is controlled to the “closed position” and a Vcom output is supplied by the Vcom source  128 . In addition, a data signal is supplied to the source line (D x )  106  and, therefore, to the source  114  of the TFT  108 . An activation signal is supplied to the gate line (G y )  104  to activate the gate  116  of the TFT  108 . With the TFT  108  activated, the data signal supplied to the source  114  flows through the TFT  108  to the drain  118 . Thus, the data signal is supplied to the pixel electrode  110 . To store the data signal in the pixel electrode  110 , the activation signal is removed from the gate line (G y )  104  while the data signal is still being supplied to the source line (D x )  106 . However, when the activation signal is removed, a portion of the voltage stored by the pixel electrode  110  charges the parasitic capacitance (C gd )  142 , thereby altering the voltage stored by the pixel electrode  110 . The amount of voltage change by the pixel electrode  110  after the activation signal is removed is the “kickback voltage.” It is believed that this effect is facilitated by the connection of the common electrode  112  to the Vcom source  128  (e.g., the Vcom source  128  may provide a supply of charge to the common electrode  112 ). 
     The present embodiment may reduce and/or eliminate image artifacts caused by the kickback voltage remaining on the pixel electrode  110  when the display  18  is turned off by preventing the common electrode  112  from receiving charge from the Vcom source  128 . When the display  18  is to be shut down, a data signal (e.g., ground, vblack, etc.) is supplied to the pixel electrode  110  as described above. It should be noted that the term “vblack” is used to refer to a specific voltage (e.g., the lowest voltage) that the source driver  120  can apply to the pixel electrode  110 , often used to cause the pixel  102  to appear black. The TFT  108  is activated, and then the activation signal is removed while the data signal is still being supplied to the pixel electrode  110 . At substantially the same time that the activation signal is removed, the switch  132  is controlled from the “closed position” to the “open position” to cause a Vcom output with a high impedance or a floating value to be present at the common electrode  112 . This is believed to inhibit a kickback voltage from affecting the voltage across the pixel electrode  110  because the common electrode  112  does not receive charge from the Vcom source  128 . 
     In some examples, the specific timing of the source signal, activation signal, and Vcom signal being supplied to the pixel  102  during shutdown may be controlled.  FIG. 6  illustrates one embodiment of a timing diagram  150  that shows the timing of the signals in the pixel  102  when the display  18  is to be turned off. The signal applied to the gate  116  (i.e., the activation signal) starts in a deactivated state within segment  152 . At a time  154 , the signal applied to the gate  116  transitions to the activated state throughout segment  156 . Then, at a time  158 , the signal applied to the gate  116  transitions to the deactivated state for segment  160 . 
     In the illustrated embodiment, a signal (e.g., ground or a low/minimum voltage) applied to the source  114  of the TFT  108  remains constant throughout the segment  162 . Therefore, the signal applied to the source  114  is the same before the activation signal is supplied and after the activation signal is removed (i.e., before time  154  and after time  158 , respectively). It should be noted that the signal applied to the source  114  does not necessarily need to remain at a constant level as illustrated. Specifically, the signal applied to the source  114  should be applied while the activation signal is present (i.e., while the gate  116  of the TFT  108  is activated) for a time period sufficient to cause the signal to be present on the drain  118  of the TFT  108  and to be stored in the pixel electrode  110 . Further, the signal applied to the source  114  should continue to be applied until the activation signal is removed. As may be appreciated, the signal applied to the source  114  may be any suitable value that will result in a value of approximately zero volts on the pixel electrode  110 . For example, the signal applied to the source  114  may be ground or vblack when the display  18  is to be shut down. 
     The signal present at the drain  118  is illustrated with two segments  164  and  166 . At segment  164 , the signal present at the drain  118  could be set at any level. Then, at time  154  when the activation signal is supplied, the signal present on the drain  118  is set by the signal on the source  114  (i.e., ground or vblack in this embodiment) as shown by segment  166 . The signal present on the drain  118  remains substantially constant throughout segment  166 , even after the activation signal is removed at time  158 . It should be noted that the effects of a kickback voltage are not seen at the signal on the drain  118  when the activation signal is removed at time  158 . Indeed, in the present embodiment, the Vcom output may inhibit a kickback voltage from occurring. 
     The Vcom output that is present at the common electrode  112  is illustrated by the Vcom line segments  168  and  170 . The Vcom output remains at a set value throughout segment  168 . At time  158  when the activation signal is removed, the Vcom output is switched to a hi-Z output  172 . Thus, after time  158 , the Vcom output is a high impedance, floating value, or hi-Z output throughout segment  170 . Therefore, the kickback voltage does not appear on the signal present at the drain  118 . As may be appreciated, the Vcom output present throughout segment  168  may be any suitable value. For example, in certain embodiments, the Vcom output may be ground. 
     As presented, 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. 7  illustrates one embodiment of a method  180  for turning off one or more pixels  102  of the display  18 . At block  182 , data processing circuitry, or other control circuitry, determines when the display  18  is to be turned off. Then, at block  184  display circuitry, such as the Vcom source  128 , supplies a Vcom output of ground to the common electrode  112  of the pixel  102 . As may be appreciated, in some embodiments, the Vcom output supplied to the common electrode  112  is some voltage other than ground. 
     Next, at block  186 , display circuitry, such as the gate driver  124 , supplies an activation signal to the pixel  102  to activate the pixel. The activation signal enables a data signal to travel from the source  114  of the TFT  108  to the drain  118  of the TFT  108 . At block  188 , display circuitry, such as the source driver  120 , supplies a data signal of ground to the pixel electrode  110  of the pixel  102 . In some embodiments, the data signal may be vblack or another suitably low value. Then, at block  190 , display circuitry, such as the gate driver  124 , removes the activation signal from the pixel  102  while the data signal is being supplied to the pixel  102  to store the data signal in the pixel  102 . Thus, the data signal is stored in the pixel electrode  110 . Next, at block  192 , when the activation signal is removed from the pixel  102 , display circuitry, such as turn-off logic  130 , switches the Vcom output being supplied to the common electrode  112  of the pixel  102  to change to a floating value or a high impedance to prevent a kickback voltage from appearing on the pixel electrode  110  of the pixel  102 . Switching the Vcom output being supplied to the common electrode  112  may include sending a control signal to a switching device, or sending a control signal to a solid state device to cause the Vcom output to change to a floating value or high impedence. In some embodiments, the activation signal may be removed and the Vcom output may be supplied to the common electrode  112  at substantially the same time. Although the method  180  is presented in relation to turning off one pixel, similar operations may be implemented for turning off lines of pixels or for turning off a complete display of pixels. In implementing such additional operations, lines of pixels may be turned off separately or concurrently (i.e., substantially the same time). 
     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.

Metadata:
Filing Date: 20110928
Publication Date: 20140520
Grant Date: 20140520
Priority Date: 20110928
Inventors: AL-DAHLE AHMAD
Assignee: APPLE INC
CPC Classifications: [{"code": "G09G2330/027", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3655", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G3/3655", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G2330/027", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 47910780