PATENT DOCUMENT

Publication Number: US-10580381-B2
Application Number: US-201715842364-A
Country: US
Kind Code: B2

Title: Digital VCOM compensation for reducing display artifacts

Abstract:
The present disclosure relates to systems and methods of accounting for the kickback voltage in an LCD display. For example, a method may include obtaining, via a processor, a difference between a nominal voltage of a common electrode of a display and a measured voltage of the common electrode. The processor may obtain image data associated with an image to be displayed on the display. The processor may adjust the image data of a pixel of the display based on the difference. The processor may output an image signal indicative of the adjusted image data to a pixel electrode of the pixel.

Claims:
What is claimed is: 
     
       1. An electronic device comprising:
 an electronic display configured to display image content at least in part by controlling light emission from a plurality of display pixels implemented at corresponding pixel locations on the electronic display based at least in part on corresponding image data, wherein the image data corresponding with a display pixel of the plurality of display pixels comprises a gray level indicative of target light emission from the display pixel in the image content and the plurality of display pixels share a common electrode that has a spatially uniform nominal voltage and a spatially nonuniform offset voltage; and 
 image processing circuitry configured to process the image data corresponding with the display pixel before supply to the electronic display at least in part by:
 determining a compensation table that explicitly associates each of a subset of pixel locations on the electronic display with a compensation value to be applied to corresponding image data, wherein the pixel locations in a row of display pixels that are explicitly identified in the compensation table are nonuniformly spaced; 
 determining a target compensation value to be applied to the image data corresponding with the display pixel based at least in part on the compensation table and a pixel location of the display pixel; and 
 applying the target compensation value to the image data corresponding with the display pixel to adjust the gray level before supply to the electronic display to facilitate offsetting the spatially nonuniform offset voltage of the common electrode. 
 
 
     
     
       2. The electronic device of  claim 1 , wherein the electronic display comprises a data driver electrically coupled to the display pixel via a data line, wherein the data driver is configured to supply an analog electrical signal to the display pixel via the data line to charge, discharge, or both the display pixel based at least in part on the gray level indicated in the image data received by the electronic display. 
     
     
       3. The electronic device of  claim 1 , wherein the image processing circuitry comprises conversion circuitry configured to:
 convert the image data from a gray level domain to a voltage domain before application of the target compensation value, wherein the image processing circuitry is configured to apply the target compensation value in the voltage domain; and 
 convert the image data from the voltage domain back to the gray level domain after application of the target compensation value. 
 
     
     
       4. The electronic device of  claim 3 , wherein:
 the gray level domain is a linear domain; and 
 the voltage domain is a non-linear domain. 
 
     
     
       5. The electronic device of  claim 1 , wherein, before the compensation table is used to process the image data corresponding with the image content, the compensation table is calibrated to the electronic display at least in part by:
 displaying, using the electronic display, a calibration image at least in part by controlling light emission from the plurality of display pixels based on corresponding calibration image data, wherein the calibration image data corresponding with the display pixel of the plurality of display pixels comprises a calibration gray level indicative of target light emission from the display pixel in the calibration image; 
 determining a nominal voltage of the common electrode that is expected to result in the target light emission from the display pixel in the calibration image when the pixel electrode of the display pixel is written based on the calibration gray level indicated in the calibration image data; 
 capturing, using a camera, a picture of the calibration image being displayed on the electronic display; 
 estimating an actual voltage of the common electrode used to display the calibration image based at least in part on the picture of the calibration image being displayed on the electronic display; and 
 calibrating the compensation table to be subsequently used by the image processing circuitry to process the image data corresponding with the image content based at least in part on a difference between the nominal voltage of the common electrode and the actual voltage of the common electrode. 
 
     
     
       6. The electronic device of  claim 1 , wherein the compensation table comprises a two dimensional (2D) lookup table. 
     
     
       7. The electronic device of  claim 1 , wherein the compensation table explicitly identifies more pixel locations in a periphery region of the electronic display and fewer pixel locations in a center region of the electronic display. 
     
     
       8. The electronic device of  claim 1 , wherein:
 the electronic display comprises a scan driver electrically coupled to the display pixel via a scan line; and 
 the compensation table explicitly identifies more pixel locations in a first region of the electronic device closer to the scan driver and fewer pixel locations in a second region of the electronic device farther from the scan driver. 
 
     
     
       9. The electronic device of  claim 1 , wherein the electronic device comprises a laptop computer, a notebook computer, a tablet computer, a desktop computer, a workstation computer, a server, a portable phone, a media player, a personal data organizer, or a handheld game platform. 
     
     
       10. Image processing circuitry configured to process image data before supply to an electronic display of an electronic device, wherein the image processing circuitry comprises:
 correction circuitry configured to:
 receive pixel data comprising a gray level indicative of target light emission from a display pixel on the electronic display, wherein the display pixel shares a common electrode that has spatially nonuniform offset voltages with another display pixel on the electronic display; 
 determine a target correction value to be applied to the pixel data based at least in part on a correction table and a pixel location of the display pixel on the electronic display; and 
 process the pixel data at least in part by applying the target correction value to the pixel data such that the gray level is adjusted to facilitate offsetting the spatially nonuniform offset voltages of the common electrode of the electronic display; and 
 
 memory configured to store the correction table, wherein the correction table explicitly associates each of a subset of pixel locations on the electronic display with a corresponding correction value such that the pixel locations in a line of display pixels that are explicitly identified in the correction table are nonuniformly distributed. 
 
     
     
       11. The image processing circuitry of  claim 10 , wherein the correction circuitry is configured to:
 convert the pixel data from a gray level domain to a voltage domain; 
 apply the target correction value to the pixel data in the voltage domain; and 
 convert the pixel data from the voltage domain back to the gray level domain. 
 
     
     
       12. The image processing circuitry of  claim 10 , wherein the correction table explicitly identifies more pixel locations in a periphery region of the electronic display and fewer pixel locations in a central region of the electronic display. 
     
     
       13. The image processing circuitry of  claim 10 , wherein the correction table explicitly identifies more pixel locations in first region of the electronic display and fewer pixel locations in a second region of the electronic display, wherein the first region is closer to a scan driver of the electronic display than the second region. 
     
     
       14. The image processing circuitry of  claim 10 , wherein, before the correction table is used to process the pixel data, the correction table is calibrated to the electronic display at least in part by:
 displaying, using the electronic display, a calibration image at least in part by controlling light emission from the display pixel based on calibration image data, wherein the calibration image data corresponding with the display pixel comprises a calibration gray level indicative of target light emission from the display pixel in the calibration image; 
 determining a nominal voltage of the common electrode that is expected to result in the target light emission from the display pixel in the calibration image when the display pixel is written based on the calibration gray level indicated in the calibration image data; 
 capturing, using a camera, a picture of the calibration image being displayed on the electronic display; 
 estimating an actual voltage of the common electrode used to display the calibration image based at least in part on the picture of the calibration image being displayed on the electronic display; and 
 calibrating the correction table to be subsequently used by the image processing circuitry to process the pixel data based at least in part on a difference between the nominal voltage of the common electrode and the actual voltage of the common electrode. 
 
     
     
       15. A method for calibrating image processing circuitry to be used to process image data before supply to an electronic display of an electronic device comprising:
 displaying, using the electronic display, an image frame at least in part by controlling light emission from display pixels based at least in part on corresponding image data, wherein a plurality of the display pixels share a common electrode and the image data corresponding with a display pixel comprises a gray level indicative of target light emission of the display pixel; 
 determining a nominal voltage of the common electrode that is expected to result in the target light emission from the display pixel when a pixel electrode of the display pixel is written based on the gray level indicated in the image data; 
 capturing, using a camera, a picture of the image frame being displayed on the electronic display; 
 estimating an actual voltage of the common electrode used to display the image frame based at least in part on the picture of the image frame being displayed on the electronic display; and 
 calibrating a compensation table to be used by the image processing circuitry to process subsequent image data based at least in part on a difference between the nominal voltage of the common electrode and the actual voltage of the common electrode, wherein the compensation table explicitly associates each of a subset of pixel locations that are nonuniformly spaced in a line of display pixels with one or more compensation values to be applied to corresponding image data. 
 
     
     
       16. The method of  claim 15 , wherein calibrating the compensation table comprises calibrating the compensation table to explicitly identify more pixel locations in a periphery region of the electronic display and fewer pixel locations in a central region of the electronic display. 
     
     
       17. The method of  claim 15 , wherein the compensation table comprises a two dimensional (2D) lookup table. 
     
     
       18. The method of  claim 15 , wherein calibrating the compensation table comprises calibrating the compensation table to explicitly identify more pixel locations in a first region of the electronic display and fewer pixel location in a second region of the electronic display, wherein the first region is closer to a scan driver of the electronic display than the second region. 
     
     
       19. The method of  claim 15 , wherein calibrating the compensation table comprises:
 determining a compensation value to be applied to the subsequent image data corresponding with a pixel location of the display pixel based at least in part on the difference between the nominal voltage of the common electrode and the actual voltage of the common electrode; and 
 explicitly associating the compensation value with the pixel location of the display pixel. 
 
     
     
       20. The method of  claim 15 , wherein:
 the subsequent image data comprises red image data, blue image data, and green image data; and 
 the one or more compensation values associated with an explicitly identified pixel location in the compensation table comprise a red component compensation value to be applied to the red image data, a blue component compensation value to be applied to the blue image data, and a green component compensation value to be applied to the green image data.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and benefit from U.S. Provisional Application No. 62/507,604, filed May 17, 2017, entitled “Digital VCOM Compensation for Reducing Display Artifacts,” the contents of which is incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     The present disclosure relates generally to electronic devices and, more particularly, to reducing display artifacts, such as flicker, in displays of the electronic devices. 
     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. 
     Liquid crystal displays (LCDs) are commonly used as screens or displays for a wide variety of electronic devices, including consumer electronics such as televisions, computers, and handheld devices (e.g., cellular telephones, audio and video players, gaming systems, and so forth). Such devices typically provide a flat display in a relatively thin package that is suitable for use in a variety of electronic goods. 
     LCD panels include a backlight and an array of pixels. The pixels contain liquid crystal material that can modulate the amount of light that passes from the backlight through the pixels. By causing different pixels to emit different amounts of light, the pixels may collectively display images on the display. Modulating the amount of light that passes through each pixel involves controlling electric fields applied to the liquid crystal material of each pixel. In particular, each pixel may have a pixel electrode that stores a data voltage. Groups of pixels may share a common electrode that provides a common voltage (VCOM) voltage. The voltage difference between the data voltage on the pixel electrode and the common voltage on the common electrode creates an electric field in each pixel. The electric field causes the liquid crystal material to modulate the amount of light. Indeed, the liquid crystal molecules in the liquid crystal material rotate in a way that causes a particular amount of light to pass through the pixel; this rotation depends on the magnitude of the electric field. That is, what matters is the magnitude of the voltage difference—in fact, a positive voltage difference or a negative voltage difference of the same magnitude will generally cause the liquid crystal material to emit the same amount of light through the pixel. Thus, controlling the magnitude of the voltage difference between the pixel electrode and the common electrode controls the amount of light that passes through each pixel. 
     Yet the common voltage could differ from an expected voltage level under certain conditions. For example, the act of programming the pixels could cause a voltage known as a “kickback” voltage to change the common voltage from what would otherwise be expected. If the common voltage is different than expected, the voltage difference between the data voltage supplied to the pixel electrode and the common voltage on the common electrode could be different than expected. This could cause pixels to emit an incorrect amount of light and therefore produce a less desirable image. Moreover, to prevent long-term image artifacts, the polarity of the voltage difference may be selected to alternate from time to time, while keeping the same magnitude (e.g., if the common voltage is 0 V, and the desired magnitude of the voltage difference between the data voltage and the common voltage is 1 V, the data voltage may be supplied as 1 V at one time and −1 V at another time). But when the common voltage is different than expected, changing the polarity by changing the data voltage will produce different magnitudes of voltage differences at different times—and therefore cause different amounts of light to be emitted by the pixels at different times, even when the pixels should be emitting the same amount of light. When the magnitudes cause enough differences in the light to become visible to the human eye, this may appear as flickering artifacts on the display. 
     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. 
     The present disclosure relates to systems and methods of accounting for a kickback voltage on a common electrode of an LCD display by digitally adjusting the data signal before the data signal is applied to pixels of the display. Thus, a desired electric field between the common electrode and the pixel electrode of the pixel may be generated across the liquid crystal material of the LCD display, which may improve the quality of images produced on the LCD display. In particular, the data signal that will cause a charge to be stored on the pixel electrode may be digitally adjusted to account for a difference between the desired VCOM voltage and a measured VCOM voltage. This may cause the magnitude of the difference between the pixel electrode and the common electrode to result in the desired electric field across the liquid crystal material, and therefore to generate the desired amount of light at the pixel. 
     In some embodiments, a camera may be used to measure a difference between a desired common electrode voltage and a measured common electrode voltage. For example, images of the LCD display may be captured via a camera. The images may be processed to determine light emitted by pixels on the display. For instance, the light emitted by the pixels may be used to determine magnitudes of the VCOM voltage at different parts of the display. The magnitude of the VCOM voltage may be compared to a reference voltage to generate a nonuniform VCOM map of the LCD display. The display may use the nonuniform VCOM map and adjust the pixel electrode voltage to account for the nonuniform VCOM due to the kickback voltages. 
     In an embodiment, a display includes a common electrode, a unit pixel having a pixel electrode and a transistor that switches to store a voltage between the pixel electrode and the common electrode. The display includes a processor operatively coupled to a memory. The processor may obtain a difference between a desired common electrode voltage and a measured common electrode voltage. The processor may receive a desired voltage to be output to the pixel electrode. The processor may output a compensation signal having a voltage based on the difference. 
    
    
     
       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 that may benefit from the inclusion of one or more matched capacitor devices, 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 hand-held device representing another embodiment of the electronic device of  FIG. 1 ; 
         FIG. 4  is a front view of another hand-held device representing another embodiment of the electronic device of  FIG. 1 ; 
         FIG. 5  is a front view of a desktop computer representing another embodiment of the electronic device of  FIG. 1 ; 
         FIG. 6  is a front view and side view of a wearable electronic device representing another embodiment of the electronic device of  FIG. 1 ; 
         FIG. 7  is a schematic diagram of display components of an electronic display, in accordance with an embodiment; 
         FIG. 8  is a circuit diagram of a pixel from the display components of  FIG. 7 , in accordance with an embodiment; 
         FIG. 9  is a circuit diagram of an equivalent circuit of the pixel of  FIG. 8 , in accordance with an embodiment; 
         FIG. 10  is a measurement of a nonuniform VCOM on the electronic display, in accordance with an embodiment; 
         FIG. 11  is a graph of voltage with respect to gray level of a VCOM and the pixel, in accordance with an embodiment; 
         FIG. 12  is another graph of voltage with respect to gray level of a VCOM and the pixel, in accordance with an embodiment; 
         FIG. 13  is a process flow diagram of a process to manufacture the electronic display of the device of  FIG. 1  to compensate for the nonuniform VCOM, in accordance with an embodiment; 
         FIG. 14  is a flow diagram of a VCOM correction that may be performed in the process of  FIG. 13 , in accordance with an embodiment; 
         FIG. 15  is a schematic diagram of a grid of a lookup table that may be stored in the memory of the electronic device of  FIG. 1 , in accordance with an embodiment; and 
         FIG. 16  is a flow diagram of a process performed by the processor of the electronic device of  FIG. 1  to output a voltage to the pixel that generates the desired electric field, in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
     One or more specific embodiments will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are 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. 
     With these features in mind, a general description of suitable electronic devices that may account for nonuniformities in a VCOM voltage on a common electrode of the display. With the foregoing in mind, a general description of suitable electronic devices that may employ a device having matched capacitors in its circuitry will be provided below. With the foregoing in mind, a general description of suitable electronic devices that may employ a device having low-noise capacitor structures in its circuitry will be provided below. 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 , a network interface  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 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 , the handheld device depicted in  FIG. 4 , the desktop computer depicted in  FIG. 5 , the wearable electronic device depicted in  FIG. 6 , or similar devices. It should be noted that the processor(s)  12  and other related items in  FIG. 1  may be generally referred to herein as “data processing circuitry.” Such 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 . 
     In the electronic device  10  of  FIG. 1 , the processor(s)  12  may be operably coupled with the memory  14  and the nonvolatile storage  16  to perform various algorithms. 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. In addition, 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  to enable the electronic device  10  to provide various functionalities. 
     In certain embodiments, the display  18  may be a liquid crystal display (LCD), which may allow users to view images generated on the electronic device  10 . In some embodiments, the display  18  may include a touch screen, which may allow users to interact with a user interface of the electronic device  10 . Furthermore, it should be appreciated that, in some embodiments, the display  18  may include one or more organic light emitting diode (OLED) displays, or some combination of LCD panels and OLED panels. 
     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 interface  26 . The network interface  26  may include, for example, one or more interfaces for a personal area network (PAN), such as a Bluetooth network, for a local area network (LAN) or wireless local area network (WLAN), such as an 802.11x Wi-Fi network, and/or for a wide area network (WAN), such as a 3rd generation (3G) cellular network, 4th generation (4G) cellular network, long term evolution (LTE) cellular network, or long term evolution license assisted access (LTE-LAA) cellular network. The network interface  26  may also include one or more interfaces for, for example, broadband fixed wireless access networks (WiMAX), mobile broadband Wireless networks (mobile WiMAX), asynchronous digital subscriber lines (e.g., ADSL, VDSL), digital video broadcasting-terrestrial (DVB-T) and its extension DVB Handheld (DVB-H), ultra-Wideband (UWB), alternating current (AC) power lines, and so forth. Network interfaces  26  such as the one described above may benefit from the use of tuning circuitry, impedance matching circuitry and/or noise filtering circuits that may include low-noise capacitor structures devices such as the ones described herein. As further illustrated, the electronic device  10  may include a power source  28 . The power source  28  may include any suitable source of power, such as a rechargeable lithium polymer (Li-poly) battery and/or an alternating current (AC) power converter. 
     In certain embodiments, the electronic device  10  may take the form of a computer, a portable electronic device, a wearable electronic device, 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  10 A, is illustrated in  FIG. 2  in accordance with one embodiment of the present disclosure. The depicted computer  10 A may include a housing or enclosure  36 , 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  10 A, such as to start, control, or operate a GUI or applications running on computer  10 A. For example, a keyboard and/or touchpad may allow a user to navigate a user interface or application interface displayed on display  18 . 
       FIG. 3  depicts a front view of a handheld device  10 B, which represents one embodiment of the electronic device  10 . The handheld device  10 B 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  10 B may be a model of an iPod® or iPhone® available from Apple Inc. of Cupertino, Calif. The handheld device  10 B 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 . The I/O interfaces  24  may open through the enclosure  36  and may include, for example, an I/O port for a hard wired connection for charging and/or content manipulation using a standard connector and protocol, such as the Lightning connector provided by Apple Inc., a universal service bus (USB), or other similar connector and protocol. 
     User input structures  22 , in combination with the display  18 , may allow a user to control the handheld device  10 B. For example, the input structures  22  may activate or deactivate the handheld device  10 B, navigate user interface to a home screen, a user-configurable application screen, and/or activate a voice-recognition feature of the handheld device  10 B. Other input structures  22  may provide volume control, or may toggle between vibrate and ring modes. The input structures  22  may also include a microphone may obtain a user&#39;s voice for various voice-related features, and a speaker may enable audio playback and/or certain phone capabilities. The input structures  22  may also include a headphone input may provide a connection to external speakers and/or headphones. 
       FIG. 4  depicts a front view of another handheld device  10 C, which represents another embodiment of the electronic device  10 . The handheld device  10 C may represent, for example, a tablet computer, or one of various portable computing devices. By way of example, the handheld device  10 C 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. of Cupertino, Calif. 
     Turning to  FIG. 5 , a computer  10 D may represent another embodiment of the electronic device  10  of  FIG. 1 . The computer  10 D may be any computer, such as a desktop computer, a server, or a notebook computer, but may also be a standalone media player or video gaming machine. By way of example, the computer  10 D may be an iMac®, a MacBook®, or other similar device by Apple Inc. It should be noted that the computer  10 D may also represent a personal computer (PC) by another manufacturer. A similar enclosure  36  may be provided to protect and enclose internal components of the computer  10 D such as the display  18 . In certain embodiments, a user of the computer  10 D may interact with the computer  10 D using various peripheral input devices, such as the keyboard  22 A or mouse  22 B (e.g., input structures  22 ), which may connect to the computer  10 D. 
     Similarly,  FIG. 6  depicts a wearable electronic device  10 E representing another embodiment of the electronic device  10  of  FIG. 1  that may be configured to operate using the techniques described herein. By way of example, the wearable electronic device  10 E, which may include a wristband  43 , may be an Apple Watch® by Apple, Inc. However, in other embodiments, the wearable electronic device  10 E may include any wearable electronic device such as, for example, a wearable exercise monitoring device (e.g., pedometer, accelerometer, heart rate monitor), or other device by another manufacturer. The display  18  of the wearable electronic device  10 E may include a touch screen display  18  (e.g., LCD, OLED display, active-matrix organic light emitting diode (AMOLED) display, and so forth), as well as input structures  22 , which may allow users to interact with a user interface of the wearable electronic device  10 E. 
     Turning now to  FIG. 7 , which generally represents a circuit diagram of certain components of the display  18  in accordance with some embodiments. In particular, the pixel array  44  of the display  18  may include a number of unit pixels  46  disposed in a pixel array or matrix. In such an array, each unit pixel  46  may be defined by the intersection of rows and columns, represented by gate lines  48  (also referred to as scanning lines), and data lines  50 , respectively. Although only 6 unit pixels  46  are shown for purposes of simplicity, it should be understood that in an actual implementation, each data line  50  and gate line  48  may include hundreds or thousands of such unit pixels  46 . Each of the unit pixels  46  may represent one of three subpixels that respectively filters only one color (e.g., red, blue, or green) of light through, for example, a color filter. The terms “pixel,” “subpixel,” and “unit pixel” may be used largely interchangeably to refer to each individual picture element of the electronic display  18 . However, the term “pixel” also sometimes refers to a collection of subpixels that can collectively display any suitable color (e.g., a pixel may be formed from a red subpixel, a green subpixel, and a blue subpixel; collectively, the pixel may be able to display any suitable color that can be formed by mixing red, green, and blue light). 
     As shown in  FIG. 7 , each unit pixel  46  may include a thin film transistor (TFT)  52  for switching a data signal stored on a respective pixel electrode  54 . The potential stored on the pixel electrode  54  relative to a potential of a common electrode  56  (e.g., creating a liquid crystal capacitance C ST ), which may be shared by other pixels  46 , may generate an electrical field sufficient to alter the arrangement of liquid crystal molecules of each unit pixel  46 . In the illustrated embodiment of  FIG. 7 , a source  58  of each TFT  52  may be electrically connected to a data line  50  and a gate  60  of each TFT  52  may be electrically connected to a gate line  48 . A drain  62  of each TFT  52  may be electrically connected to a respective pixel electrode  54 . Each TFT  52  may serve as a switching element that may be activated and deactivated (e.g., turned “ON” and turned “OFF”) for a predetermined period of time based on the respective presence or absence of a scanning signal on the gate lines  48  that are applied to the gates  60  of the TFTs  52 . 
     When activated, a TFT  52  may store the image signals received via the respective data line  50  as a charge upon the corresponding pixel electrode  54 . As noted above, the image signals stored by the pixel electrode  54  may be used to generate an electrical field between the respective pixel electrode  54  and a common electrode  56 . This electrical field may align the liquid crystal molecules to modulate light transmission through the pixel  46 . Furthermore, it should be appreciated that each unit pixel  46  may also include a storage capacitor, or circuitry that may be modeled as a capacitor, which may be used to sustain the pixel electrode voltage (e.g., V pixel ) during the time in which the TFTs  52  may be switch to the “OFF” state. 
     In certain embodiments, the display  18  also may include a source driver integrated circuit (IC)  64 , which may include a chip, such as a processor or application specific integrated circuit (ASIC) that controls the display pixel array  44  by receiving image data  66  from the processor(s)  12 , and sending corresponding image signals to the unit pixels  46  of the pixel array  44 . The source driver  64  may also provide timing signals to the gate drivers  68  and  70  to facilitate the activation/deactivation of individual rows of pixels  46 . In other embodiments, timing information may be provided to the gate drivers  68  and  70  in some other manner. The display  18  may include a common voltage (VCOM) source  72  to provide a common voltage (VCOM) voltage to the common electrodes  56  of each of the pixels  46 . 
       FIG. 8  shows a more detailed circuit diagram of one of the unit pixels  46  described with respect to  FIG. 7 . The unit pixel  46  includes the TFT  52  having a gate  60  electrically coupled to the gate line  48  of the gate driver  68 . Further, the TFT  52  may include a source  58  electrically coupled to the source driver  64  via the data line  50 . To display a color with a certain amount of light, the processor  12  may transmit, via the source driver  64 , the image signal having a certain charge associated with the desired color on the data line  50 . As mentioned above, the gate  60  of the TFT  52  may receive a gate signal that causes the TFT to close to form a conductive path from the data line  50  to the pixel electrode  54  such that the pixel electrode  54  may store the charge received via the data line  50 . Due to a voltage of the pixel of the pixel electrode  54  and a voltage of the common electrode  56  as well as the physical geometry of the pixel electrode  54  with respect to the common electrode  56 , an electrical field may be present between the common electrode  56  and the pixel electrode. The electric field may cause liquid crystal material in the electric field to modulate an amount of light depending on the magnitude of the electric field across the liquid crystal material. As such, the source driver  64  may be used in conjunction with the gate drivers  68  and  70  to control the light generated by the pixel  46 . 
     To control the gate  60  of the TFT  52 , the gate line  48  may change between a relatively high voltage (e.g., 10V to 20V) and a relatively low voltage (e.g., 0V to −15V). Owing to the change in the voltage and the physical geometry of the gate line  48  and the common electrode  56 , there may be a capacitance  80  that causes a kickback voltage  82  (V KB ), thereby creating nonuniformities in the VCOM voltage. 
     This may be more apparent in  FIG. 9 , which represents a circuit diagram of an equivalent circuit of the pixel  46 . As seen in  FIG. 9 , the pixel  46  includes the TFT  52  electrically coupled to the data line  50  as well as the gate  60  electrically coupled to the gate line  48 . The VCOM voltage with respect to the pixel electrode  54  across the storage capacitance  78  may be altered due to the kickback voltage. That is, the voltage between the common electrode  56  and the pixel electrode  54  may either be reduced or increased, depending on a polarity of a voltage of the pixel electrode  54 , from the kickback voltage (V KB ). This altered voltage difference (VCOM−V KB ) alters the electric field across the liquid crystal material of the pixel  46 , thereby causing output of the display  18  to be different than the desired output. 
     In some LCD displays that use a column inversion scheme, the LCD display  18  may alternate the pixel electrode  54  voltages between a positive polarity and a negative polarity to cause the electric field to reduce or eliminate buildup of ions in the liquid crystal molecules of the LCD display. That is, the pixel electrode  54  may receive a positive charge that causes the electric field to be in a first direction in a first frame and receive a negative charge that causes the electric field to be in a second direction in a second frame where the electrical field has approximately the same magnitude in each frame (e.g., to produce the same gray level). However, due to the kickback voltage, the common electrode may have a voltage different than the expected voltage, thereby causing an offset in the magnitude of the electric field between the first frame and the second frame. For example, the first frame may have a voltage between the common electrode  56  and the pixel electrode  54  of +0.8V and the second frame may have a voltage between the common electrode  56  and the pixel electrode  54  of −0.7V, the offset being 100 mV. Because the magnitude of the electric field is different between the first frame and the second frame, the difference may cause a flicker to occur in the display  18 , thereby reducing the quality in images displayed on the display  18 . For the foregoing reasons, it is desirable to adjust the voltage of the image signals based on the nonuniformities in the VCOM to cause the electric field to be consistent with the desired electric field. 
     Different pixels  46  in the display  18  may have different kickback voltages caused by the gate line  48  due to process variation.  FIG. 10  shows a VCOM nonuniformity map  86  of variations of VCOM across the display  18 . The VCOM nonuniformity map  86  may be obtained by observing changes in light emission in various areas of the display  18  (e.g., during the manufacture of the display  18  or after the display  18  is in commercial use, such as when the electronic device  10  that houses the display  18  is being serviced). For example, a video camera may be used to capture video images of the display  18  over time to map where on the display  18  signs of flicker are more discernible. To obtain the measurements of the nonuniform VCOM, the video camera may record the display  18 . The display  18  may display a pattern that is particularly well-suited to display flicker (e.g., a flicker-identification gray scale pattern) during the recording. Multiple image frames may be recorded. Light emitted from the image frames at various locations across the display  18  may be compared to a nominal value, and a difference between the light emitted at each location on the display  18  may correspond to the variation that would arise between some nominal VCOM voltage and the actual VCOM voltage. In this way, an estimated measurement of the actual VCOM voltage that would produce the levels of flicker or distortion may be used to produce the VCOM nonuniformity map  86 . 
     As seen in the VCOM nonuniformity map  86  shown in  FIG. 10 , due to a resistance-capacitance (RC) delay, there may be a faster variation rate along edges of the display  18 , where the gate drivers  68  and  70  are located, than toward the center of the display  18 . The VCOM nonuniformity map  86  of  FIG. 10  is broken into regions  88 ,  90 ,  92 ,  94 ,  96 ,  98 ,  100 ,  102 ,  104 , and  106  that correspond to a different magnitude of difference between the desired (nominal) VCOM and the actual VCOM that is on the display  18  at the different regions. The regions shown in  FIG. 10  should be understood to be provided by way of example; any suitable number of regions may be used. 
     In the example of  FIG. 10 , regions  88  and  106  may be located closer to the gate drivers  68  and  70  of  FIG. 7  than the regions  92 ,  98 , and  102  towards the center of the display  18 . Additionally or alternatively, there may be VCOM differences, as represented by regions  94  and  100 , due to process variation in manufacturing the display  18 . A scale  108  shows the difference between the measured VCOM of various regions  110  from the VCOM nonuniformity map  86  and the nominal VCOM voltage (e.g., a spatially uniform nominal VCOM voltage). As an example, the nonuniform VCOM of the VCOM nonuniformity map  86  has regions  110  with a variance  112  in the measured VCOM of approximately 160 mV. While a particular example of the variance  112  is shown in  FIG. 10 , any suitable nonuniform VCOM may be present in the display  18 . This nonuniform VCOM may cause the flicker that may be visible depending on the image displayed. Because the flicker may reduce the quality of the display  18 , it is desirable to correct for the nonuniformity of the VCOM voltages. 
       FIG. 11  is a graph  118  of voltage, shown on the y-axis  120 , with respect to gray level, shown on the x-axis  122 , of the unit pixel  46 . The graph  118  shows a pixel electrode  54  voltage profile  124  of various positive voltages and negative voltages of the pixel electrode  54  to obtain certain gray levels on the unit pixel  46 . The graph  118  includes a nominal VCOM voltage line  126  indicating the desired voltage to be output on the VCOM to obtain the desired image. The graph  118  includes the actual VCOM voltage line  128  that is measured using the process described with respect to  FIG. 10 . The kickback voltage may cause the difference  130  between the actual VCOM voltage line  128  and the nominal VCOM voltage line  126 . Further, the difference  130  may cause a first voltage potential  132  while the pixel electrode  54  stores a positive voltage and a second voltage potential  134  while the pixel electrode  54  stores the negative voltage, thereby causing flicker on the display. To compensate for the difference (i.e., offset)  130 , in some embodiments, the actual VCOM voltage line  128  may be controlled. That is, the actual VCOM voltage line  128  may be reduced to the desired nominal VCOM voltage line  126 . However, reducing the actual VCOM voltage line  128  may increase the complexity of the display  18  due to the VCOM operating as a common electrode  56  across the display  18 . Because the common electrode  56  may receive a common voltage across the display, some embodiments described below may adjust the charge stored on the pixel electrode  54  to compensate for the difference  130 . 
     To address the flicker of the display  18  due to the kickback voltage without adjusting the voltage applied to the common electrode  56 , the processor  12  may send, via the source driver  64 , an image signal having a charge to be stored on the pixel electrode  54  that is adjusted based on the difference  130 .  FIG. 12  is a graph  140  of voltage, shown on the y-axis  142 , and gray level, shown on the x-axis  144 , of the unit pixel  46 . In the illustrated embodiment, the display  18  implements a compensation scheme that provides an image signal from the source driver  64  having a charge to be stored on the pixel electrode  54  that is adjusted based on the difference  130 . The graph  140  shows a pixel electrode  54  voltage profile  146  of the positive voltages and negative voltages of the pixel electrode  54  to obtain certain gray levels on the unit pixel  46 . Further, the graph  140  includes the actual VCOM voltage line  148  from the measurements described with respect to  FIG. 10 . To adjust the magnitude of the electric field to output the desired amount of light from the pixel, the processor(s)  12 , which may include any suitable pixel pipeline processing, may output an adjusted image signal that adjusts the charge to be stored by the pixel electrode  54  based on the difference  130 . Further, by adjusting the image signal by an amount based on the difference  130 , the pixel electrode  54  voltage profile  146  may be adjusted a corresponding amount that causes the positive voltage potential  152  and the negative voltage potential  154  to be approximately equal, thereby reducing or eliminating flicker in the display  18 . 
       FIG. 13  is a block diagram of image processing circuitry  170  (e.g., pixel processing pipeline circuitry) that prepares image data to be sent to the display  18 . The image processing circuitry  170  adjusts the image data before the image data is used in the electronic display by changing the image data to correct for spatially nonuniform offset voltages in the VCOM due to kickback voltages. The image processing circuitry  170  may be disposed in a pixel pipeline of part of the display. 
     The image processing circuitry  170  includes white point correction (WPC) circuitry  172  that adjusts the data to be programmed into the pixel to account for changes in the white point. That is, WPC circuitry  172  adjusts the pixel data to define the correct white color of the image. The image processing circuitry  170  may include panel response correction (PRC) circuitry  174  where the response of the panel is corrected. The image processing circuitry  170  may include dimensional (e.g., 1D or 2D) VCOM correction circuitry  176 . Further, a look up table may be stored (e.g., locally) in the VCOM correction circuitry  176  that maps pixels to VCOM voltage differences. In operation, the image processing circuitry  170  may send the adjusted image signal, via the source driver  64  of the display  18 , to the pixel electrode  54  such that the adjusted image signal has a voltage adjustment that matches the VCOM voltage difference  130 . The image processing circuitry  170  may then perform dithering, such as mirage dithering, via dithering circuitry  178  on the adjusted image signal after performing the VCOM voltage correction. 
       FIG. 14  is a flow diagram of the 2D VCOM correction process  180  that may be performed to correct for the spatially nonuniform offset voltage of the VCOM. During a manufacturing process, measurements of a difference between a desired common electrode voltage and a measured common electrode voltage at one or more locations on the display (block  182 ). For example, image frames may be captured and processed as described above with respect to  FIG. 10 . From the obtained measurements, the 2D VCOM distribution of differences (e.g., distribution of voltages) between the desired common electrode and the measured common electrode voltage may be stored in a lookup table in the VCOM correction circuitry  176  that associates locations on the display  18  with the differences (block  184 ). After the manufacturing process is completed, the VCOM correction circuitry  176  may perform the 2D VCOM adjustments (block  186 ) during operation of the display  18 , as described above with respect to  FIG. 13 . In some embodiments, there may be a look up table that is applied to all colors. In other embodiments, a look up table may be created associated with each color. 
     The lookup table may include one or more locations  188 ,  190 ,  192 , and  194  at crossing points of a grid  196 . Each of the locations  188 ,  190 ,  192 , and  194  may be associated with a respective difference between the desired common electrode voltage and the measured common electrode voltage at the respective location. During operation, the processor  12  may obtain the difference associated with the pixel  46  at the location and a desired voltage to be output to the pixel electrode  54 . The processor  12  may output the image signal to cause a charge on the pixel electrode  54  that is adjusted based on the difference, thereby generating the desired electric field associated with the particular image data. Further, the processor  12  may perform any suitable interpolation, such as bilinear interpolation, (block  186 ) between the locations  188 ,  190 ,  192 , and  194  stored in the lookup table to obtain an approximate VCOM voltage difference at location  198  between the locations  188 ,  190 ,  192 , and  194  while limiting the size of the lookup table. 
       FIG. 15  is a schematic diagram of an example of a grid  208  of a lookup table that may be stored in the memory  14 . The lookup table may include VCOM differences at locations of each of the crossing points of the grid  208 . The more locations used, the finer granularity of the grid  208  and the larger the look up table. Because the variance in VCOM differences may be greater along edges (e.g., a periphery) of the panel due to being located closer in proximity to the gate drivers  68  and  70 , the lookup table may include a finer granularity of locations along a first edge  210  and a second edge  212 , as compared to granularity of a center  214  of the grid  208 . While a 2D VCOM grid is described as an example, in other embodiments, a zero dimension or a one dimension grid may also be used. 
       FIG. 16  is a schematic diagram of the VCOM correction circuitry  176  that causes the pixel  46  of the display  18  to generate the desired electric field. The process VCOM correction circuitry  176  may receive the image data  222  from the PRC circuitry  174 , as well as obtain the polarity  224  of the pixel  46  (e.g., from the PRC circuitry  174  or other image processing circuitry). The VCOM correction circuitry  176  may include conversion circuitry to convert the image data  222  and the polarity  224  from a gray level domain, in which the image data  222  and the polarity are represented on a scale of gray level, into a voltage domain, in which the image data  222  and the polarity  224  are represented as a voltage  226 . In the illustrated embodiment, the gray level to voltage conversion is performed via a lookup table. Further, the VCOM correction circuitry  176  may obtain the coordinates  228  and polarity of the pixel  46 . The VCOM correction circuitry  176  may determine anchor points  230  based on the coordinates  228 . The anchor points  230  may refer to vertical anchor points and horizontal anchor points in closest proximity to the coordinates  228  that have coordinates stored in the lookup table associated with a respective VCOM voltage difference. For example, the VCOM correction circuitry  176  may determine the locations  188 ,  190 ,  192 , and  194  having the closest proximity to the coordinates  228  of the pixel  46 . The VCOM correction circuitry  176  may perform interpolation  232  to provide a voltage adjustment  234  corresponding to the approximate VCOM voltage difference from the desired VCOM voltage at the pixel  46 . The processor  12  may adjust the voltage  226  based on the approximate VCOM voltage difference such that the voltage  236  takes into account the nonuniformities of the VCOM due to kickback voltages. The image processing circuitry  170  may then convert the voltage  236  back into the gray level domain to perform dithering after the voltage  236  has been adjusted by the image processing circuitry  170  to correct for the spatially nonuniform offset voltage of the VCOM. The gray level domain values may then be converted to the voltage domain upon output from the dithering circuitry  178 . 
     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. 
     The techniques presented and claimed herein are referenced and applied to material objects and concrete examples of a practical nature that demonstrably improve the present technical field and, as such, are not abstract, intangible or purely theoretical. Further, if any claims appended to the end of this specification contain one or more elements designated as “means for [perform]ing [a function] . . . ” or “step for [perform]ing [a function] . . . ”, it is intended that such elements are to be interpreted under 35 U.S.C. 112(f). However, for any claims containing elements designated in any other manner, it is intended that such elements are not to be interpreted under 35 U.S.C. 112(f).

Metadata:
Filing Date: 20171214
Publication Date: 20200303
Grant Date: 20200303
Priority Date: 20170517
Inventors: ZHANG, SHENG
WANG, CHAOHAO
SACCHETTO, PAOLO
HOU, YUNHUI
Assignee: APPLE INC
CPC Classifications: [{"code": "G09G3/3696", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G2300/0426", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3655", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2320/0223", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0219", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3696", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G2360/145", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3648", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2320/029", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/02", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3655", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2320/0247", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3696", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G2320/02", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3655", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2300/0426", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0219", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/029", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0247", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2360/145", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3648", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2320/0223", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 64269700