PATENT DOCUMENT

Publication Number: US-8736538-B2
Application Number: US-201213479066-A
Country: US
Kind Code: B2

Title: Devices and methods for reducing a voltage difference between VCOMs of a display

Abstract:
Methods and devices for reducing a voltage difference between common voltage layers (VCOMs) of a display are provided. In one example, a method may include supplying an activation signal to a row of pixels of the display to activate the row of pixels. The method may also partially removing the activation signal from the row of pixels at a predetermined rate. The method may include detecting a voltage difference between a first VCOM of a first set of pixels of the display and a second VCOM of a second set of pixels of the display after the activation signal has been partially removed. The method may also include controlling removal of the activation signal from the row of pixels based at least partially on the detected voltage difference.

Claims:
What is claimed is: 
     
       1. A method for reducing a voltage difference between common voltage layers (VCOMs) of a display to improve image quality of the display, comprising:
 supplying an activation signal to a row of pixels of the display to activate the row of pixels; 
 partially removing the activation signal from the row of pixels at a predetermined rate; 
 detecting a first voltage difference between a first VCOM of a first set of pixels of the display and a second VCOM of a second set of pixels of the display after the activation signal has been partially removed; and 
 controlling removal of the activation signal from the row of pixels based at least partially on the detected first voltage difference. 
 
     
     
       2. The method of  claim 1 , wherein controlling the removal of the activation signal from the row of pixels comprises changing a rate that the activation signal is removed. 
     
     
       3. The method of  claim 1 , wherein controlling the removal of the activation signal from the row of pixels comprises determining a rate that the activation signal is to be removed. 
     
     
       4. The method of  claim 1 , wherein controlling the removal of the activation signal from the row of pixels comprises retrieving a rate that the activation signal is to be removed from a mapping table that correlates voltage differences with rates that the activation signal is to be removed. 
     
     
       5. The method of  claim 1 , wherein controlling the removal of the activation signal from the row of pixels comprising controlling application of a second activation signal to a second row of pixels. 
     
     
       6. The method of  claim 5 , wherein the second activation signal is supplied while the activation signal is being removed. 
     
     
       7. The method of  claim 1 , wherein the row of pixels comprises a first subset of the first set of pixels and a second subset of the second set of pixels. 
     
     
       8. The method of  claim 1 , wherein detecting the voltage difference between the first VCOM of the first set of pixels and the second VCOM of the second set of pixels comprises detecting the voltage difference using a differential amplifier. 
     
     
       9. The method of  claim 1 , wherein detecting the voltage difference between the first VCOM of the first set of pixels and the second VCOM of the second set of pixels comprises receiving the voltage difference from a voltage sensing device. 
     
     
       10. The method of  claim 1 , comprising detecting a second voltage difference between the first VCOM and the second VCOM after the activation signal has been partially removed. 
     
     
       11. The method of  claim 10 , comprising controlling removal of the activation signal from the row of pixels based at least partially on the detected second voltage difference. 
     
     
       12. An electronic display comprising:
 a first set of pixels having a first common voltage device (VCOM); 
 a second set of pixels having a second VCOM; 
 a gate driver configured to supply an activation signal to the first set of pixels and the second set of pixels concurrently; 
 a voltage sensing device configured to detect a first voltage difference between the first VCOM and the second VCOM; and 
 a control device configured to control features associated with supplying the activation signal, removing the activation signal, or some combination thereof, wherein the control of the activation signal is based at least partially on the first voltage difference detected by the voltage sensing device. 
 
     
     
       13. The electronic display of  claim 12 , comprising a first row of pixels having the first set of pixels and the second set of pixels. 
     
     
       14. The electronic display of  claim 12 , comprising a third set of pixels having a third VCOM and a fourth set of pixels having a fourth VCOM. 
     
     
       15. The electronic display of  claim 14 , wherein the first VCOM and the third VCOM are each approximately a first size, and the second VCOM and the fourth VCOM are each approximately a second size. 
     
     
       16. The electronic display of  claim 14 , wherein the voltage sensing device is configured to detect a second voltage difference between the third VCOM and the fourth VCOM. 
     
     
       17. The electronic display of  claim 16 , wherein the first voltage difference and the second voltage difference are approximately the same. 
     
     
       18. The electronic display of  claim 14 , wherein the first VCOM is coupled to the third VCOM and the second VCOM is coupled to the fourth VCOM. 
     
     
       19. An electronic device comprising:
 a housing; 
 a processor disposed within the housing; 
 one or more input structures configured to transmit input signals to the processor; and 
 an electronic display coupled to the housing and configured to supply an activation signal to a row of pixels having a first portion coupled to a first common voltage device (VCOM) and a second portion coupled to a second VCOM, partially remove the activation signal from the row of pixels at a predetermined rate, detect a voltage difference between the first VCOM and the second VCOM after the activation signal has been partially removed, and control removal of the activation signal from the row of pixels based at least partially on the detected voltage difference. 
 
     
     
       20. The electronic device of  claim 19 , wherein the electronic display comprises a sensing device configured to detect the voltage difference between the first VCOM and the second VCOM.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Non-Provisional Patent Application of U.S. Provisional Patent Application No. 61/612,068, entitled “Devices and Methods for Reducing a Voltage Difference Between VCOMS of a Display”, filed Mar. 16, 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 reduce a voltage difference between common voltage layers (VCOMs) of an LCD to improve image quality of the LCDs. 
     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. When the TFT gates are deactivated, a kickback voltage may alter the voltage stored in the pixels. In certain configurations, the LCD may include a segmented VCOM such that a portion of the pixels of the LCD use a first VCOM and a portion of the pixels of the LCD use a second VCOM. In such a configuration, the kickback voltage for the pixels using the first VCOM may be different than the kickback voltage for the pixels using the second VCOM. Accordingly, the kickback voltage difference between the pixels may result in undesirable image quality (e.g., pixels using the first VCOM may display an image differently than pixels using the second VCOM). 
     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 reducing a voltage difference between common voltage layers (VCOMs) of a display to improve image quality of the display. By way of example, a method for reducing a voltage different between VCOMs of a display may include supplying an activation signal to a row of pixels of the display to activate the row of pixels. The method may also include partially removing the activation signal from the row of pixels at a predetermined rate. The method may include detecting a voltage difference between a first VCOM of a first set of pixels of the display and a second VCOM of a second set of pixels of the display after the activation signal has been partially removed. The method may also include controlling removal of the activation signal from the row of pixels based at least partially on the detected voltage difference. 
     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 reduce a voltage difference between common voltage layers (VCOMs) of the LCD to improve image quality of the LCD, 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 reduce a voltage difference between VCOMs of an LCD to improve image quality of the LCD, in accordance with an embodiment; 
         FIG. 5  is a circuit diagram illustrating circuitry of an electronic device for controlling a voltage difference between VCOMs of an LCD to improve image quality of the LCD, in accordance with an embodiment; 
         FIG. 6  is a circuit diagram illustrating circuitry of an electronic device for controlling a voltage difference between sets of VCOMs of an LCD to improve image quality of the LCD, in accordance with an embodiment; 
         FIG. 7  is a circuit diagram illustrating circuitry of an electronic device having multiple voltage sensing devices for sensing voltage differences between VCOMs of an LCD, in accordance with an embodiment; 
         FIG. 8  is a timing diagram illustrating a reduction of a voltage difference between VCOMs of an LCD by controlling a rate that an activation signal is removed from pixels to improve image quality of the LCD, in accordance with an embodiment; 
         FIG. 9  is a timing diagram illustrating a reduction of a voltage difference between VCOMs of an LCD by controlling a time that an activation signal is applied to pixels to improve image quality of the LCD, in accordance with an embodiment; and 
         FIG. 10  is a flowchart describing a method for reducing a voltage difference between VCOMs of an LCD by controlling removal of an activation signal from pixels of the LCD to improve image quality of the LCD, 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 device, method, or combination thereof for controlling removal of a pixel activation signal to decrease a voltage difference between different common voltage layers (VCOMs) of the LCD. Specifically, rather than allowing the activation signal to be supplied and/or removed with default characteristics, which could result in undesirable image quality (e.g., color variations between different portions of the LCD), embodiments of the present disclosure may incorporate hardware, software, or a combination thereof for controlling the application and/or removal of the activation signal to reduce a voltage difference between VCOMs of the LCD. 
     Specifically, to reduce a voltage difference between VCOMs of the LCD, an activation signal is applied to a row of pixels. With the activation signal applied, the gates of the TFTs remain open, thereby allowing current flow between the source and drain of the TFTs. The gates of the TFTs are partially closed at a predetermined rate to limit current flow between the source and drain of the TFTs. After the gates of the TFTs are partially closed, the voltage difference between VCOMs of the LCD is detected. The gates of the TFTs are controlled to completely close at a certain rate and/or time to decrease the voltage difference between VCOMs of the LCD. As a result, it is believed that the voltage difference of the VCOMs may be reduced and, accordingly, image quality between portions of the LCD using different VCOMs may be improved. 
     With the foregoing in mind, a general description of suitable electronic devices that may employ electronic displays having capabilities to control removal of activation signals to reduce voltage difference between VCOMs 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 , 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 there is a voltage difference between VCOMs of the display  18 , image quality of the display  18  may be distorted. For example, portions of the display  18  using one VCOM may produce different colors than portions of the display  18  using a different VCOM. As such, embodiments of the present disclosure may be employed to increase image quality. 
     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 TFTs of the electronic display  18  to reduce a voltage difference between VCOMs of the display  18 . 
     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 gates of the TFTs of the display  18 . 
     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 TFTs that are controlled to reduce voltage differences of VCOMs of the display  18 . 
       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 TFTs that are controlled to reduce voltage difference of VCOMs of 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 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 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. 
     There are many ways to configure the circuitry of the electronic device  10  so that gates  116  used to activate pixels  102  of the electronic display  18  may be controlled to decrease a voltage difference between VCOMs of the display  18 .  FIG. 5  generally represents one embodiment of a circuit diagram of components of the electronic device  10  for controlling a voltage difference between VCOMs of the display  18  to improve image quality of the display  18 . In particular, the electronic device  10  includes a VCOM_A  130  and a VCOM_B  132 . As illustrated, the VCOM_A  130  and the VCOM_B  132  each have multiple pixels  102  coupled thereon. Specifically, the common electrodes  112  of the illustrated pixels  102  are electrically coupled to either VCOM_A  130  or VCOM_B  132 . Although four pixels  102  are illustrated as being electrically coupled to VCOM_A  130  and six pixels  102  are illustrated as being electrically coupled to VCOM_B  132 , any suitable number of pixels  102  may be electrically coupled to VCOM_A  130  and to VCOM_B  132 . 
     The electronic device  10  of the present embodiment includes a power management unit (PMU)  134 . The PMU  134  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 PMU  134  provides a high gate voltage (VGH)  136  to the gate driver  124 . In the present embodiment, the PMU  134  provides a low gate voltage (VGL)  138  to a gate control device  140 . The gate control device  140  receives a voltage difference  142  and uses the voltage difference  142  to produce a controlled VGL  144  that is provided 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 controlled VGL  144  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 controlled VGL  144  to the gate lines  104 . 
     A voltage sensing device  146  is used to determine the voltage difference  142  between a first input  148  and a second input  150 . In the present embodiment, the first input  148  is electrically coupled to the VCOM_A  130  and the second input  150  is electrically coupled to the VCOM_B  132 . Accordingly, the voltage sensing device  146  detects the voltage difference  142  between the VCOM_A  130  and the VCOM_B  132 . The voltage sensing device  146  may be any suitable voltage sensing device, such as an electronic amplifier (e.g., operational amplifier, differential amplifier, etc.). 
     As illustrated, the VCOM_A  130  and the VCOM_B  132  may not physically be the same size. Accordingly, the voltage difference  142  between the VCOM_A  130  and the VCOM_B  132  may result from resistive differences between the VCOM_A  130  and the VCOM_B  132 . For example, when one of the gate lines  104  is deactivated, voltages stored on pixels  102  may change due to kickback voltage. As will be appreciated, the kickback voltage may not be the same for the VCOM_A  130  and the VCOM_B  132  due to their resistive differences. Therefore, the voltage sensing device  146  may detect the voltage difference  142 . 
     To reduce the voltage difference  142 , the voltage sensing device  146  provides the voltage difference  142  to the gate control device  140 . The gate control device  140  may use the voltage difference  142  to modify the VGL  138  and provide the controlled VGL  144  to the gate driver  124 . Specifically, after the gate control device  140  receives the VGL  138  indicating that the gates  116  should be deactivated, the gate control device  140  may modify the VGL  138  based at least partially on the voltage difference  142  to produce the controlled VGL  144 . For example, the gate control device  140  may modify the rate that the activation voltage on the gate lines  104  transitions to the deactivation voltage. By modifying the rate that the gate lines  104  transition from the activation voltage to the deactivation voltage, the voltage difference  142  between the VCOM_A  130  and the VCOM_B  132  may be reduced. As will be appreciated, the gate control device  140  may use a mapping table to determine a rate that the gate lines  104  should transition to the deactivation voltage for a particular voltage difference  142 . For example, the mapping table may include multiple voltage differences and rates of deactivation that correspond to each voltage difference. 
     The display  18  may have any number of VCOMs and the VCOMs may vary in size.  FIG. 6  generally represents a diagram of circuitry of the electronic device  10  for controlling a voltage difference between sets of VCOMs of the display  18  to improve image quality of the display  18 . Specifically, in the present embodiment, the display  18  includes the VCOM_A  130 , the VCOM_B  132 , a VCOM_C  152 , and a VCOM_D  154 . As illustrated, each of the VCOM_A  130 , the VCOM_B  132 , the VCOM_C  152 , and the VCOM_D  154  generally have a length  156 . Further, the VCOM_A  130  has a width  158 , the VCOM_B  132  has a width  160 , the VCOM_C  152  has a width  162 , and the VCOM_D  154  has a width  164 . In certain embodiments, the width  158  and the width  162  may generally be the same. In addition, the width  160  and the width  164  may generally be the same. Accordingly, the input  148  may be coupled to the VCOM_A  130  and the VCOM_C  152  (e.g., because they are generally the same size and will generally have similar resistive qualities), while the input  150  may be coupled to the VCOM_B  132  and the VCOM_D  154  (because they are generally the same size and will generally have similar resistive qualities). Therefore, in the present embodiment a single voltage sensing device may be used. 
     The display  18  may have more than one voltage sensing device (e.g., when there are more than two sizes of VCOMs). Accordingly,  FIG. 7  illustrates one embodiment of circuitry of the electronic device  10  having multiple voltage sensing devices for sensing voltage differences between VCOMs of the display  18 . In the present embodiment, the gate control device  140  is configured to receive the VGH  136  and the VGL  138 . As such, the gate control device  140  provides a controlled VGH  166  and the controlled VGL  144  to the gate driver  124 . Thus, the gate control device  140  may control the rates and/or timing of the activation and deactivation voltages that are applied to the gates  116  via the gate lines  104 , as explained in detail below in relation to  FIG. 9 . 
     Further, the gate control device  140  receives a second voltage difference  168  from a second voltage sensing device  170 . As illustrated, the voltage sensing device  146  receives inputs  148  and  150 , which are electrically coupled to the VCOM_A  130  and the VCOM_B  132 , respectively. The second voltage sensing device  170  receives inputs  172  and  174 , which are electrically coupled to the VCOM_B  132  and the VCOM_C  152 , respectively. Accordingly, the gate control device  140  may receive the voltage difference  142  (e.g., the voltage difference between the VCOM_A  130  and the VCOM_B  132 ) and the voltage difference  170  (e.g., the voltage difference between the VCOM_B  132  and the VCOM_C  152 ). Although the gate control device  140  does not receive a voltage difference between the VCOM_A  130  and the VCOM_C  152 , the gate control device  140  may determine such a voltage difference. The gate control device  140  may use a mapping table where each row includes two voltage differences (e.g., for two voltage sensing devices) that together correspond to a rate of deactivation for the two voltage differences. 
     As illustrated, the VCOM_A  130  and the VCOM_B  132  may each have a length  176 , while the VCOM_C  152  has a length  178 . Further, the VCOM_A  130 , the VCOM_B  132 , and the VCOM_C  152  may have widths  180 ,  182 , and  184 , respectively. Accordingly, the VCOM_A  130 , the VCOM_B  132 , and the VCOM_C  152  may each be a different size and therefore may have different resistive characteristics. As such, two voltage sensing devices  146  and  170  may be used to detect the voltage differences between the VCOMs. As will be appreciated, in embodiments with a greater number if different sizes of VCOMs, the number of voltage sensing devices may increase. It should be noted that each gate line  104  may include a subset of pixels  102  from each VCOM. For example, one gate line  104  includes a subset  186  from the VCOM_A  130 , a subset  188  from the VCOM_B  132 , and a subset  190  from the VCOM_C  152 . 
     In certain embodiments, the rate that an activation signal is removed from pixels  102  is controlled to decrease the voltage difference between VCOMs.  FIG. 8  illustrates one embodiment of a timing diagram  192  that shows a reduction of the voltage difference  142  between VCOMs of the display  18  by controlling a rate that a voltage on a gate line  104  (e.g., GATE_A) is removed from pixels  102  to improve image quality of the display  18 . As illustrated by segment  194 , the gate line  104  may start in a logic low (deactivated) state. At a time  195 , the gate line  104  may transition to a logic high (activated) state where it remains through segment  196 . At a time  198 , the gate line  104  may begin to transition toward the logic low state at a fixed rate, during segment  200 . The fixed rate of transition may be a predetermined rate configured to be applied for a fixed period of time (e.g., until a time  202 ). At the time  202 , the transition rate toward the logic low state may become variable (e.g., actively controlled) and may be based on the voltage difference  142 , in order to decrease the voltage difference  142  between the VCOM_A  130  and the VCOM_B  132 , as shown by segment  204 . After the gate line  104  reaches the logic low state, the gate line  104  remains in the logic low state, as shown by segment  206 . 
     In the present embodiment, a voltage is applied to the VCOM_A  130  during segment  208 . At a time  210 , a kickback voltage alters the voltage of the VCOM_A  130 , as shown by segment  212 . As illustrated, the voltage of the VCOM_A  130  may change by a voltage  214 . The voltage of the VCOM_A  130  then begins to return to the voltage applied during segment  208 , as shown by segments  216  and  218 . Segment  216  corresponds to the rate that the gate line  104  is deactivated during segment  200 , while segment  218  corresponds to the rate that the gate line  104  is deactivated during segment  204 . At a time  220 , the voltage of the VCOM_A  130  may vary from the voltage applied during segment  208  by a voltage  222 . During segment  224 , the voltage of the VCOM_A  130  may be approximately the same as the voltage applied during segment  208 . 
     A voltage is applied to the VCOM_B  132  during segment  226 . At the time  210 , a kickback voltage alters the voltage of the VCOM_B  132 , as shown by segment  228 . As illustrated, the voltage of the VCOM_B  132  may change by a voltage  230 . The voltage of the VCOM_B  132  then begins to return to the voltage applied during segment  226 , as shown by segments  232  and  234 . Segment  232  corresponds to the rate that the gate line  104  is deactivated during segment  200 , while segment  234  corresponds to the rate that the gate line  104  is deactivated during segment  204 . At the time  220 , the voltage of the VCOM_B  132  may vary from the voltage applied during segment  226  by a voltage  236 . During segment  238 , the voltage of the VCOM_B  132  may be approximately the same as the voltage applied during segment  226 . 
     In certain embodiments, the voltage applied to the VCOM_A  130  and the VCOM_B  132  may be approximately the same and, therefore, the voltage difference  142  between the VCOM_A  130  and the VCOM_B  132  during segments  208  and  226  may be approximately zero. Furthermore, the voltage difference  142  between the VCOM_A  130  and the VCOM_B  132  at the time  212  may be approximately the difference between the voltage  214  and the voltage  230 . As previously described, such a voltage difference  142  may decrease the quality of an image on the display  18 . Accordingly, the display  18  uses this voltage difference  142  to control the rate that the activation signal is removed from the pixels  102  (e.g., via the gate line  104 ) to decrease the voltage difference  142 . Specifically, during segment  204  of the gate line  104 , the display  18  uses the voltage difference  142  between the VCOM_A  130  and the VCOM_B  132  to change the rate that the activation signal is removed from the pixels  102 . For example, the voltage difference  142  is reduced from its value at time  210  to a voltage difference  142  of the difference between the voltage  222  and the voltage  236  at the time  220 . Further, during segments  224  and  238  the voltage difference  142  may be reduced to approximately zero. 
     In some embodiments, the time that an activation signal is applied to pixels  102  is controlled to decrease the voltage difference between VCOMs.  FIG. 9  illustrates one embodiment of a timing diagram  240  that shows a reduction of the voltage difference  142  between VCOMs of the display  18  by controlling a time that a voltage on a second gate line  104  (e.g., GATE_B) is applied to pixels  102  to improve image quality of the display  18 . As illustrated by segment  244 , the first gate line  104  (e.g., GATE_A) may start in a logic low (deactivated) state. At a time  245 , the first gate line  104  may transition to a logic high (activated) state where it remains through segment  246 . At a time  248 , the gate line  104  may transition toward the logic low state at a fixed rate, during segment  250 . After the first gate line  104  reaches the logic low state, the first gate line  104  remains in the logic low state, as shown by segment  252 . 
     As illustrated by segment  254 , the second gate line  104  (e.g., GATE_B) may start in a logic low (deactivated) state. At the time  248 , the second gate line  104  may transition toward a logic high (activated) state at a fixed rate, as shown by segment  256 . The fixed rate of transition may be a predetermined rate configured to be applied for a fixed period of time (e.g., until a time  258 ). At the time  258 , the transition rate toward the logic high state may become variable (e.g., actively controlled) and may be based on the voltage difference  142 , in order to decrease the voltage difference  142  between the VCOM_A  130  and the VCOM_B  132 , as shown by segment  260 . After the second gate line  104  reaches the logic high state, the second gate line  104  remains in the logic high state, as shown by segment  262 . 
     In the present embodiment, a voltage is applied to the VCOM_A  130  during segment  264 . At the time  258 , a kickback voltage alters the voltage of the VCOM_A  130 , as shown by segment  266 . As illustrated, the voltage of the VCOM_A  130  may change by a voltage  268 . The voltage of the VCOM_A  130  then returns to the voltage applied during segment  264 , as shown by segment  270 . Segment  270  corresponds to the rate that the second gate line  104  is activated during segment  260 . During segment  262 , the voltage of the VCOM_A  130  may be approximately the same as the voltage applied during segment  264 . 
     A voltage is applied to the VCOM_B  132  during segment  274 . At the time  258 , a kickback voltage alters the voltage of the VCOM_B  132 , as shown by segment  276 . As illustrated, the voltage of the VCOM_B  132  may change by a voltage  278 . The voltage of the VCOM_B  132  then returns to the voltage applied during segment  274 , as shown by segment  280 . Segment  280  corresponds to the rate that the second gate line  104  is activated during segment  260 . During segment  282 , the voltage of the VCOM_B  132  may be approximately the same as the voltage applied during segment  274 . 
     In certain embodiments, the voltage applied to the VCOM_A  130  and the VCOM_B  132  may be approximately the same and, therefore, the voltage difference  142  between the VCOM_A  130  and the VCOM_B  132  during segments  264  and  274  may be approximately zero. Furthermore, the voltage difference  142  between the VCOM_A  130  and the VCOM_B  132  at the time  258  may be approximately the difference between the voltage  268  and the voltage  278 . As previously described, such a voltage difference  142  may decrease the quality of an image on the display  18 . Accordingly, the display  18  uses this voltage difference  142  to control the rate and/or timing that the activation signal is applied to the pixels  102  (e.g., via the second gate line  104 ) to decrease the voltage difference  142 . Specifically, during segment  260  of the second gate line  104 , the display  18  uses the voltage difference  142  between the VCOM_A  130  and the VCOM_B  132  to change the rate that the activation signal is applied to the pixels  102 . For example, the voltage difference  142  is reduced from its value at time  258  to a voltage difference  142  of approximately zero during segments  272  and  282 . 
     As presented above, the display  18  may use a series of operations for reducing the voltage difference  142  to improve image quality of the display  18 .  FIG. 10  illustrates one embodiment of a method  284  for reducing the voltage difference  142  between VCOMs of the display  18  by controlling removal of an activation signal from pixels  102  of the display  18 . An activation signal is supplied to a row of pixels  102  of the display  18  to activate the pixels (block  286 ). For example, the activation signal may be supplied to the pixels  102  via the first gate line  104  (e.g., GATE_A). Further, the activation signal is partially removed from the row of pixels  102  at a predetermined rate (block  288 ). In certain embodiments, the predetermined rate may be a fixed rate for a fixed period of time. The predetermined rate may be any suitable rate, such as a rate that will result in a minimal voltage difference  142  between VCOMs. A first voltage difference  142  is detected between a first VCOM (e.g., VCOM_A  130 ) of a first set of pixels  102  of the display  18  and a second VCOM (e.g., VCOM_B  132 ) of a second set of pixels  102  of the display  18 , after the activation signal has been partially removed (block  290 ). The first voltage difference  142  may be detected using the voltage sensing device  146 , such as a differential amplifier. Removal of the activation signal from the row of pixels  102  is controlled and may be based at least partially on the detected voltage difference  142  (block  292 ). In certain embodiments, the controlled removal of the activation signal may include changing a rate that the activation signal is removed. The controlled removal of the activation signal may also include determining a rate that the activation signal is to be removed. In some embodiments, controlling removal of the activation signal may include retrieving a rate that the activation signal is to be removed from a mapping table that correlates voltage differences  142  with rates that the activation signal is to be removed. 
     Controlling removal of the activation signal may also include controlling application of a second activation signal (e.g., via the second gate line  104 ) to a second row of pixels  102 . In certain embodiments, the application of the second activation signal may occur while the activation signal is being removed. To control removal of the activation signal, a second voltage difference  142  between the first VCOM and the second VCOM may be detected. The controlled removal of the activation signal may be based at least partially on the second voltage difference  142 . Further, the voltage difference  142  may regularly be detected, and the removal of the activation signal may be based at least partially on each detected voltage difference  142  (e.g., the voltage difference  142  may provide active feedback to the activation signal driving circuitry). Accordingly, reduced image quality, which may result from a voltage difference  142  between the VCOMs, may be improved by minimizing the voltage difference  142  between the VCOMs. 
     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: 20120523
Publication Date: 20140527
Grant Date: 20140527
Priority Date: 20120316
Inventors: AL-DAHLE AHMAD
Assignee: APPLE INC
CPC Classifications: [{"code": "G09G3/3611", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G3/3611", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G3/3696", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2310/08", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0204", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0204", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2310/08", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3696", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 49157168