PATENT DOCUMENT

Publication Number: US-10825385-B2
Application Number: US-201715701056-A
Country: US
Kind Code: B2

Title: Active sensing and compensation for display panel hysteresis

Abstract:
An apparatus receives current image frame data and data relating to at least one previous image frame for an electronic display. One or more parameters related to hysteresis of transistors in the electronic display are sensed. A correlation device, such as a look-up table, receives the sensed parameter or parameters and the data relating to one or more image frames, and uses this information, at least in part, to output an appropriate compensation signal for the current image frame data. The compensated current image frame data may then be supplied to the electronic display to reduce or eliminate the effects of hysteresis on the displayed image.

Claims:
What is claimed is: 
     
       1. A method of operating an electronic display, the method comprising:
 sensing a parameter related to hysteresis of transistors in the electronic display; 
 obtaining information related to at least one previous image frame displayed on the electronic display; and 
 compensating, based at least on the parameter and the information, a new image frame to reduce effects of hysteresis of the transistors on the new image frame to be displayed on the electronic display. 
 
     
     
       2. The method as set forth in  claim 1 , wherein sensing the parameter comprises sensing a supply current delivered from the respective transistors to their respective organic light emitting diodes. 
     
     
       3. The method as set forth in  claim 1 , wherein sensing the parameter comprises sensing a temperature of the electronic display. 
     
     
       4. The method as set forth in  claim 3 , wherein obtaining information comprises storing a look up table that correlates data from the at least one previous image frame to a change in threshold voltage for each of the respective transistors for a plurality of temperatures. 
     
     
       5. The method as set forth in  claim 4 , wherein the data comprises previous frame pixel voltage and wherein the change in threshold voltage comprises a corrected change in threshold voltage. 
     
     
       6. The method as set forth in  claim 1 , wherein sensing the parameter comprises sensing a threshold voltage of the respective transistors. 
     
     
       7. The method as set forth in  claim 1 , wherein obtaining information comprises storing information related to at least one previous image frame displayed on the electronic display. 
     
     
       8. The method as set forth in  claim 7 , wherein storing information comprises storing a look up table that correlates data from the at least one previous image frame to a change in threshold voltage for each of the respective transistors. 
     
     
       9. The method as set forth in  claim 8 , wherein the data comprises previous frame pixel voltages and wherein the change in threshold voltage comprises a corrected change in threshold voltage. 
     
     
       10. The method as set forth in  claim 1 , wherein obtaining information comprises storing information related to a plurality of previous image frames displayed on the electronic display. 
     
     
       11. The method as set forth in  claim 10 , wherein storing information comprises storing a look up table that correlates data from the plurality of previous image frames to a change in threshold voltage for each of the respective transistors. 
     
     
       12. The method as set forth in  claim 11 , wherein the data comprises respective pixel voltages of the plurality of previous image frames and wherein the change in threshold voltage comprises a corrected change in threshold voltage. 
     
     
       13. The method as set forth in  claim 11 , wherein the data comprises a moving average of respective pixel voltages of the plurality of previous image frames and wherein the change in threshold voltage comprises a corrected threshold voltage. 
     
     
       14. An apparatus for operating an electronic display, the apparatus comprising:
 means for sensing a parameter related to hysteresis of transistors in the electronic display; 
 means for obtaining information related to at least one previous image frame displayed on the electronic display; and 
 means for compensating, based at least on the parameter and the information, a new image frame to reduce effects of hysteresis of the transistors on the new image frame to be displayed on the electronic display. 
 
     
     
       15. The apparatus as set forth in  claim 14 , wherein means for sensing the parameter comprises means for sensing a supply current delivered from the respective transistors to their respective organic light emitting diodes. 
     
     
       16. The apparatus as set forth in  claim 14 , wherein means for sensing the parameter comprises means for sensing a temperature of the electronic display. 
     
     
       17. The apparatus as set forth in  claim 16 , wherein means for obtaining information comprises means for storing a look up table that correlates data from the at least one previous image frame to a change in threshold voltage for each of the respective transistors for a plurality of temperatures. 
     
     
       18. The apparatus as set forth in  claim 17 , wherein the data comprises previous frame pixel voltage and wherein the change in threshold voltage comprises a corrected change in threshold voltage. 
     
     
       19. The apparatus as set forth in  claim 14 , wherein means for sensing the parameter comprises means for sensing a threshold voltage of the respective transistors. 
     
     
       20. The apparatus as set forth in  claim 14 , wherein means for obtaining information comprises means for storing information related to at least one previous image frame displayed on the electronic display. 
     
     
       21. The apparatus as set forth in  claim 20 , wherein means for storing information comprises means for storing a look up table that correlates data from the at least one previous image frame to a change in threshold voltage for each of the respective transistors. 
     
     
       22. The apparatus as set forth in  claim 21 , wherein the data comprises previous frame pixel voltages and wherein the change in threshold voltage comprises a corrected change in threshold voltage. 
     
     
       23. The apparatus as set forth in  claim 14 , wherein means for obtaining information comprises means for storing information related to a plurality of previous image frames displayed on the electronic display. 
     
     
       24. The apparatus as set forth in  claim 23 , wherein means for storing information comprises means for storing a look up table that correlates data from the plurality of previous image frames to a change in threshold voltage for each of the respective transistors. 
     
     
       25. The apparatus as set forth in  claim 24 , wherein the data comprises respective pixel voltages of the plurality of previous image frames and wherein the change in threshold voltage comprises a corrected change in threshold voltage. 
     
     
       26. The apparatus as set forth in  claim 24 , wherein the data comprises a moving average of respective pixel voltages of the plurality of previous image frames and wherein the change in threshold voltage comprises a corrected threshold voltage.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and benefit from U.S. Provisional Application No. 62/397,835, filed Sep. 21, 2016, entitled “Active Sensing and Compensation for Display Panel Hysteresis,” the contents of which is incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     The present disclosure relates generally to electronic displays and, more particularly, to techniques to compensate for certain anomalies, such as hysteresis, in electronic displays. 
     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. 
     Many electronic devices include an electronic display that displays visual representations based on received image data. More specifically, the image data may include a voltage that indicates desired luminance (e.g., brightness) of a display pixel. For example, in an organic light emitting diode (OLED) display, the image data may be input to and amplified by one or more amplifiers. The amplified image data may then be supplied the gate of a switching device (e.g., a thin film transistor) in a display pixel. Based on magnitude of the supplied voltage, the switching device may control magnitude of supply current flowing into a light emitting component (e.g., OLED) of the display pixel. 
     The display pixel may then emit light based on magnitude of the supply current flowing through the light emitting component. For example, as magnitude of the supply current increases, the luminance (e.g., brightness and/or grayscale value) of the display pixel may increase. On the other hand, as magnitude of the supply current decreases, the luminance of the display pixel may decrease. In other words, any change in magnitude of the supply current may cause a change in luminance of a display pixel. 
     For example, in active matrix organic light emitting diode (AMOLED) displays, a matrix of thin film transistors (TFTs), typically formed on an amorphous or polycrystalline polysubstrate, are used to supply the image data to the OLEDs. Such AMOLED displays have become quite popular because of their high brightness, deep black level, and wide viewing angle capabilities. Moreover, such TFTs are often advantageous because they provide high uniformity in large areas. Unfortunately, however, the TFTs exhibit some degree of hysteresis in switching between positive and negative voltages. This hysteresis can affect the threshold voltage of the transistors, and thus, the magnitude of the current being provided to the OLEDS. As a result, the luminance provided by the OLEDS may be inaccurate in that it does not match the image data being supplied to the TFTs. This phenomenon can lead to a residual image, sometimes referred to as image sticking, where the previously displayed image remains somewhat apparent in the subsequently displayed image. Moreover, the phenomenon can lead to other undesirable image artifacts such as mura artifacts, flicker, etc. 
     In addition to the above potential issues, various environmental conditions can also adversely affect the image quality of an AMOLED display. For example, changes in temperature, humidity, and even ambient light, can lead to changes in the threshold voltage of the TFTs and, thus, adversely affect the luminance of the OLEDs. 
     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 generally relates to electronic displays that display image frames to facilitate visually presenting information. Generally an electronic display displays an image frame by controlling luminance of its display pixels based at least in part on image data indicating desired luminance of the display pixels. For example, to facilitate displaying an image frame, an organic light emitting diode (OLED) may display may receive image data, amplify the image data using one or more amplifiers, and supply amplified image data to display pixels. When activated, display pixels may apply the amplified image data to the gate of a switching device (e.g., thin-film transistor) to control magnitude of the supply current flowing through a light emitting component (e.g., OLED). In this manner, since the luminance of OLED display pixels is based on supply current flowing through their light emitting components, the image frame may be displayed based at least in part on corresponding image data. 
     With this background in mind, and to address some of the issues mentioned above, the present techniques provide a method of operating an electronic display to compensate a new or current frame image to reduce or eliminate the effects of hysteresis exhibited by the TFTs used to drive the pixels. The method may generally include sensing one or more parameters related to hysteresis of TFTs in the electronic display, and such parameters may include, for example, threshold voltage, supply current, temperature, etc. Information related to one or more previous image frames may be obtained. Utilizing the sensed parameter or parameters along with the previous image frame information, a new image frame may be compensated to reduce or eliminate the effects of hysteresis on the new image frame to be displayed on the electronic display. 
    
    
     
       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 including an electronic display, 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  illustrates a schematic diagram of an organic light emitting diode (OLED) electronic display in accordance with at least one embodiment; 
         FIG. 8  is a graph illustrating transfer characteristics of TFTs demonstrating hysteresis at two different temperatures; 
         FIG. 9  illustrates a schematic diagram of an example of a pixel circuit in sensing mode in accordance with at least one embodiment; 
         FIG. 10  illustrates an example of hysteresis effects of image data relative sensed current; 
         FIG. 11  is a graph illustrating the effect of gate voltage of a previous frame relative to sensed current; 
         FIG. 12  illustrates a block diagram of an example of a hysteresis sensing and compensation circuit in accordance with the present techniques; 
         FIG. 13  illustrates a block diagram of another example of a hysteresis sensing and compensation circuit in accordance with the present techniques; 
         FIG. 14  illustrates a block diagram of yet another example of a hysteresis sensing and compensation circuit in accordance with the present techniques; 
         FIG. 15  is a graph illustrating pixel luminance over several frames with various sensing time options; 
         FIG. 16  is a graph illustrating pixel luminance over several frames with an example of multiple senses per frame; 
         FIG. 17  illustrates a block diagram of a sensing scheme with hysteresis correction using one or more line buffers to store content of one or more previous frames for the correction of content history dependent threshold voltage hysteresis in accordance with the present techniques; 
         FIG. 18  illustrates a block diagram illustrating a portion of  FIG. 17  in greater detail; 
         FIG. 19  is a graph illustrating change in threshold voltage versus change is sensed current; 
         FIG. 20  illustrates an example of threshold hysteresis effects that may be dependent upon frame duration; 
         FIG. 21  illustrates a portion of  FIG. 17  in greater detail where previous frame duration may be incorporated into the hysteresis correction scheme; 
         FIG. 22  illustrates a portion of  FIG. 17  in greater detail where multiple line buffers are provided for the content of multiple previous frames; 
         FIG. 23  illustrates a portion of  FIG. 17  in greater detail where the hysteresis compensation scheme utilizes a moving average of the content of previous frames; and 
         FIG. 24  illustrates a portion of  FIG. 17  in greater detail where the compensation scheme uses temperature information. 
     
    
    
     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. 
     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 electronic displays used to display visual representations as image frames. Thus, electronic displays are often included in various electronic devices to facilitate visually presenting information to users. In fact, different electronic devices may utilize different types of electronics displays. For example, some electronic devices may utilize a liquid crystal (LCD) display while other electronic devices utilize organic light emitting diode (OLED) display, such as active matrix organic light emitting diode (AMOLED) displays and passive matrix organic light emitting diode (PMOLED) displays, and still other electronic devices may utilize micro light emitting diode (μLED) displays. 
     However, operation between different types of electronic displays may vary. For example, an LCD display may display an image frame by controlling luminance (e.g., brightness and/or grayscale value) of LCD display pixels based on orientation of liquid crystals. More specifically, in an LCD display pixel, a voltage based on received image data may be applied to a pixel electrode, thereby generating an electric field that orients the liquid crystals. In some embodiments, to reduce likelihood of polarizing the LCD display pixel, polarity of the voltage applied to the pixel electrode may be positive for some image frames and negative for other image frames. 
     On the other hand, an OLED display may display an image frame by controlling luminance (e.g., brightness and/or grayscale value) of OLED display pixels based on magnitude of supply current flowing through a light emitting component (e.g., OLED) of the display pixels. More specifically, a voltage based on received image data may be applied to the gate of a switching device (e.g., thin-film transistor) in an OLED display pixel to control magnitude of supply current flowing to its light emitting component. In some embodiments, since luminance of the OLED display pixel is controlled by magnitude of supply current, polarity of the voltage applied to the switching device may remain the same for each image frame. 
     Although differences exist, some operational principles of different types of electronic displays may be similar. For example, as described above, the LCD display and the OLED display may both display image frames by controlling luminance of their display pixels. Additionally, the LCD display and the OLED display may both control luminance of their display pixels based on received image data, which may indicate desired luminance of display pixels based on magnitude of its voltage. Furthermore, in some embodiments, the LCD display and the OLED display may both amplify the image data and use the amplified image data to control operation in their display pixels. In other words, although the present disclosure is described in regard to OLED displays, one of ordinary skill in the art should be able to adapt the techniques described herein to other types of suitable electronic displays. 
     As described above, an OLED display may display image frames by controlling luminance of its display pixels. In some embodiments, an OLED display pixel may include a self-emissive light emitting component that emits light based at least in part on magnitude of current supplied to a storage capacitor. For example, as magnitude of the supply current increases, the luminance of the display pixel may also increase. On the other hand, as magnitude of the supply current decreases, the luminance of the display pixel may also decrease. 
     Additionally, the OLED display may control magnitude of the supply current to the display pixel using a switching device (e.g., a thin-film transistor). In some embodiments, the OLED display may receive image data indicating desired luminance of the display pixel, amplify the image data, and apply the amplified image data to a gate of the switching device. In such embodiments, voltage of the amplified image data may control width of the switching device channel available to conduct supply current to the light emitting component. For example, as magnitude of the amplified image data increases, the magnitude of the supply current may increase. On the other hand, as magnitude of the amplified image data decreases, the magnitude of the supply current may decrease. In this manner, the OLED display may adjust luminance of the display pixels based at least in part on received image data. 
     However, the luminance of OLED display pixels may also be affected by other factors, such as noise introduced in the image data, the amplified image data, and/or the supply current. When drastic enough, the luminance variations caused by introduced noise may be perceivable as visual artifacts or muras. Such noise may be caused by various environmental factors, such as temperature and humidity, as well as by various operating parameters within the electronic display itself, such as the hysteresis behavior of the thin-film transistors (TFTs) in the pixel circuits and by image data from previous frames, as well as the refresh rate of the display. 
     To address some of these concerns, the present techniques may sense one or more parameters from the display, such as luminance, current, voltage, or other measurable pixel properties, which may be used as feedback in either real time or as triggered by device usage. Such feedback may be used in a map or look-up table to compensate for factors that may adversely affect pixel luminance, such as hysteresis, refresh rate, temperature, previous image data, etc. Indeed, as described in further detail below, such displays may be used in a variety of electronic devices, and various techniques may be used to provide compensation for such displays. 
     With the foregoing in mind, a general description of suitable electronic devices that may employ an electronic display 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 , network interfaces  26 , a transceiver  28 , and a power source  29 . 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/or other data processing circuitry 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  and/or other data processing circuitry 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. 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  to enable the electronic device  10  to provide various functionalities. 
     In certain embodiments, the display  18  may be an active-matrix organic light emitting diode (AMOLED) display, 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 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) 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 3 rd  generation (3G) cellular network, 4 th  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 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. 
     In certain embodiments, to allow the electronic device  10  to communicate over the aforementioned wireless networks (e.g., Wi-Fi, WiMAX, mobile WiMAX, 4G, LTE, and so forth), the electronic device  10  may include a transceiver  28 . The transceiver  28  may include any circuitry the may be useful in both wirelessly receiving and wirelessly transmitting signals (e.g., data signals). Indeed, in some embodiments, as will be further appreciated, the transceiver  28  may include a transmitter and a receiver combined into a single unit, or, in other embodiments, the transceiver  28  may include a transmitter separate from the receiver. For example, the transceiver  28  may transmit and receive OFDM signals (e.g., OFDM data symbols) to support data communication in wireless applications such as, for example, PAN networks (e.g., Bluetooth), WLAN networks (e.g., 802.11x Wi-Fi), WAN networks (e.g., 3G, 4G, and LTE and LTE-LAA cellular networks), WiMAX networks, mobile WiMAX networks, ADSL and VDSL networks, DVB-T and DVB-H networks, UWB networks, and so forth. As further illustrated, the electronic device  10  may include a power source  29 . The power source  29  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. 
     As described above, the computing device  10  may include an electronic display  18  to facilitate presenting visual representations to one or more users. Accordingly, the electronic display  18  may be any one of various suitable types. For example, in some embodiments, the electronic display  18  may be an LCD display while, in other embodiments, the display may be an OLED display, such as an AMOLED display or a PMOLED display. Although operation may vary, some operational principles of different types of electronic displays  18  may be similar. For example, electronic displays  18  may generally display image frames by controlling luminance of their display pixels based on received image data. 
     To help illustrate, one embodiment of an OLED display  18  is described in  FIG. 7 . As depicted, the OLED display  18  includes a display panel  50 , a source driver  52 , a gate driver  54 , and a power supply  29 . Additionally, the display panel  50  may include multiple display pixels  56  arranged as an array or matrix defining multiple rows and columns. For example, the depicted embodiment includes a six display pixels  56 . It should be appreciated that although only six display pixels  56  are depicted, in an actual implementation the display panel  50  may include hundreds or even thousands of display pixels  56 . 
     As described above, an electronic display  18  may display image frames by controlling luminance of its display pixels  56  based at least in part on received image data. To facilitate displaying an image frame, a timing controller may determine and transmit timing data on line  58  to the gate driver  54  based at least in part on the image data. For example, in the depicted embodiment, the timing controller may be included in the source driver  52 . Accordingly, in such embodiments, the source driver  52  may receive image data that indicates desired luminance of one or more display pixels  56  for displaying the image frame, analyze the image data to determine the timing data based at least in part on what display pixels  56  the image data corresponds to, and transmit the timing data to the gate driver  54 . Based at least in part on the timing data, the gate driver  54  may then transmit gate activation signals to activate a row of display pixels  56  via gate lines  60 . 
     When activated, luminance of a display pixel  56  may be adjusted by amplified image data received via data lines  62 . In some embodiments, the source driver  52  may generate the amplified image data by receiving the image data and amplifying voltage of the image data. The source driver  52  may then supply the amplified image data to the activated pixels. Thus, as depicted, each display pixel  56  may be located at an intersection of a gate line  60  (e.g., scan line) and a data line  62  (e.g., source line). Based on received amplified image data, the display pixel  56  may adjust its luminance using electrical power supplied from the power supply  29  via power supply lines  64 . 
     As depicted, each display pixel  56  includes a circuit switching thin-film transistor (TFT)  66 , a storage capacitor  68 , an OLED  70 , and a driving TFT  72 . To facilitate adjusting luminance, the driving TFT  72  and the circuit switching TFT  66  may each serve as a switching device that is controllably turned on and off by voltage applied to its gate. In the depicted embodiment, the gate of the circuit switching TFT  66  is electrically coupled to a gate line  60 . Accordingly, when a gate activation signal received from its gate line  60  is above its threshold voltage, the circuit switching TFT  66  may turn on, thereby activating the display pixel  56  and charging the storage capacitor  68  with amplified image data received at its data line  62 . 
     Additionally, in the depicted embodiment, the gate of the driving TFT  72  is electrically coupled to the storage capacitor  68 . As such, voltage of the storage capacitor  68  may control operation of the driving TFT  72 . More specifically, in some embodiments, the driving TFT  72  may be operated in an active region to control magnitude of supply current flowing from the power supply line  64  through the OLED  70 . In other words, as gate voltage (e.g., storage capacitor  68  voltage) increases above its threshold voltage, the driving TFT  72  may increase the amount of its channel available to conduct electrical power, thereby increasing supply current flowing to the OLED  70 . On the other hand, as the gate voltage decreases while still being above its threshold voltage, the driving TFT  72  may decrease amount of its channel available to conduct electrical power, thereby decreasing supply current flowing to the OLED  70 . In this manner, the OLED display  18  may control luminance of the display pixel  56 . The OLED display  18  may similarly control luminance of other display pixels  56  to display an image frame. 
     As described above, image data may include a voltage indicating desired luminance of one or more display pixels  56 . Accordingly, operation of the one or more display pixels  56  to control luminance should be based at least in part on the image data. In the OLED display  18 , a driving TFT  72  may facilitate controlling luminance of a display pixel  56  by controlling magnitude of supply current flowing into its OLED  70 . Additionally, the magnitude of supply current flowing into the OLED  70  may be controlled based at least in part on voltage supplied by a data line  60 , which is used to charge the storage capacitor  68 . However, since image data may be received from an image source, magnitude of the image data may be relatively small. Accordingly, to facilitate controlling magnitude of supply current, the source driver  52  may include one or more amplifiers (e.g., buffers) that amplify the image data to generate amplified image data with a voltage sufficient to control operation of the driving TFTs  72  in their active regions. 
     As mentioned above, the TFTs  72  typically exhibit hysteresis behavior that can affect the supply current to the OLEDs  70  and, thus, affect the luminence of the OLEDs  70 . An example of such hysteresis behavior is illustrated in  FIG. 8 . The first set of curves  80  and  82  represent a transfer characteristic of a TFT  72  at a first temperature, such as room temperature. As can be seen, the threshold voltage of the TFT  72  in the forward voltage sweep direction illustrated by the curve  80  is lower than the threshold voltage of the TFT  72  in the reverse voltage sweep direction illustrated by the curve  82 . As a result, at a given temperature, the threshold voltage and the current through the TFT  72  can differ depending upon the direction of the voltage sweep across the TFT  72 . Furthermore, the second set of curves  84  and  86  illustrate the transfer characteristic of the TFT  72  at a second temperature higher than the first temperature. As can be seen, the threshold voltage of the TFT  72  in the forward voltage sweep direction illustrated by the curve  84  is lower than the threshold voltage of the TFT  72  in the reverse voltage sweep direction illustrated by the curve  86 . Further, the threshold voltage of the TFT  72  in either voltage sweep direction at the higher temperature is lower than the threshold voltage of the TFT  72  at the lower temperature. Hence, the temperature of the TFT  72  can also affect the threshold voltage and, thus, the supply current through the TFT  72 . As a result, both the hysteresis behavior of the TFT  72  and its operating temperature can affect the luminance produced by the OLEDs  70 . 
     The threshold voltage of the TFTs  72  may be sensed to determine any variation in threshold voltage, due to hysteresis, temperature, aging, etc. For example,  FIG. 9  illustrates a display pixel  56  on a portion of the display panel  50  in sensing mode. In the sensing mode, the sensor current from the TFT  72  is delivered to the source driver IC  52  via the data line  62 . The source driver IC  52  includes a digital-to-analog converter  90  and an analog front end and analog to digital converter  92  that facilitate communication between the source driver IC  52  and the host  94 . As further illustrated in  FIG. 10 , it can be seen that the data delivered to the TFT  72  and the OLED  70  during an emission mode of the display pixel  56  and affect the level of current sensed during the sensing mode. Specifically,  FIG. 10  illustrates that a high level of frame data in a previous frame results in lower sensed current because of different data history. Indeed,  FIG. 11  illustrates this phenomenon in another manner. When a TFT  72  experiences different starting gate voltages Vg, it exhibits different output currents Io due to the hysteresis phenomenon and due to the different starting gate voltages Vg, as illustrated by the curve  98 . 
     One example of a hysteresis sensing and compensation circuit  100  for addressing one or more of these issues is illustrated in  FIG. 12 . The circuit  100  may be embodied on the source driver IC  52  for instance. To compensate for hysteresis, temperature, aging, or other factors that may affect the luminance of the OLEDs  70  of the display  18 , the circuit  100  receives image data from one or more previous image frames  102 . This previous image frame data  102  is delivered to a digital signal processor (DSP)  104  and a map  106 , which may be embodied in a lookup table (LUT) and/or correction algorithm, for example. The circuit  100  also includes a sensing feedback circuit  108  that may sense one or more parameters from the panel  50  and deliver the sensed parameters to the DSP  104  for a correlation with the previous image frame data  102 . For example, such sensed feedback may include luminance levels of the OLEDs  70 , supply current from the TFTs  72  to the respective OLEDs  70 , threshold voltage levels of the TFTs  72 , or any other measurable pixel properties. Further, the feedback may be in real time or it could be triggered by device usage, such as turning the display panel  50  on or off, periodic sampling, etc. This feedback may be delivered to the DSP  104  where it is correlated with the previous image frame data  102  and delivered to the map  106 . The map  106  may include, for example, a map of gate voltage VG versus change in threshold voltage V th  (ΔV th ), V G V ·ΔV G , V th V ·ΔV th , or V th V ·ΔV G . Once the proper amount of compensation is selected from the map  106  based on the previous image frame data  102  and the information from the DSP  104 , the compensation information is delivered to a summer  110  where it is combined with the current image frame data  112 . The compensated current image frame data is delivered to a data driver  114  for delivery to the panel  50 . Hence, the compensated current image frame data received by the panel  50  should reduce or eliminate the effects of hysteresis, threshold voltage, supply current, etc., that might affect the luminance of the OLEDs  70  in the panel  50  to provide for a more consistent and accurate image to be displayed by the panel  50 . 
     Another embodiment of a hysteresis sensing and compensation circuit  100 A is illustrated in  FIG. 13 . The circuit  100 A includes the items from the circuit  100 , but adds an additional map  116  to provide “fine tuning” of the compensation signal delivered to the summer  110  to compensate the current image frame data  112 . In this embodiment, the map  116  receives the current image frame data  112  along with the least significant bits (LSB) of the compensation information from the map  106 . Here, the map  116  may include, for example, change in threshold voltage versus change in supply current (ΔV th V ·ΔI o ) or change in gate voltage versus in change in supply current (ΔV G V ·ΔI o ), and it may deliver change in supply current (ΔI o ) data to a summer  118  so that such information may be subtracted from the sensing feedback prior to delivery to the DSP  104 . As a result, the most significant bits (MSB) from the map  106  may be delivered to the summer  110  to compensate the current image frame data  112  prior to delivery to the data driver  114  and the panel  50 . 
     It has also been found that, at least under certain circumstances, not only can the immediately previous image frame data  102  adversely affect the display of the next frame of image data, but two or more previous frames of image data  102  can also affect the display of the current image frame. Accordingly, as illustrated in  FIG. 14 , an alternative embodiment of the hysteresis compensation and sensing circuit  100 B is illustrated. Here, in addition to the items discussed above with respect to  FIG. 12 , the circuit  100 B includes an accumulator  120  that accumulates data from two or more previous image frames. This accumulated previous image frame data is then delivered to the DSP  104  and the map  106  so that it may be taken into account prior to delivery of the compensation information to the summer  110 . Specific example are described below with references to  FIGS. 22 and 23 . 
     It should also be noted that because the luminance of the OLEDs  70  can vary from the beginning of the frame to the end of the frame, the time during which the sensing feedback circuit  108  senses parameters, such as luminance, from the panel  50  may affect the overall manner in which the hysteresis sensing and compensation circuits  100  operate. For example, as illustrated in  FIGS. 15 and 16 , the luminance of an OLED  70  may be slightly higher at the beginning of a frame, as the data essentially decays until the beginning of the next frame, as illustrated by the luminance curves  130  during a sample five frame period. Hence, the sensor feedback circuit  108  may sense at the beginning of a frame to obtain the transient peak, may sense during the middle of a frame for optimization, or may sense throughout the entire frame to obtain the average luminance. Alternatively, as illustrated in  FIG. 16 , the sensing feedback circuit  108  may sense multiple times during a frame to capture a time constant of the decay, for example. 
     A more specific implementation of a hysteresis sensing and correction circuit  100 C is illustrated in  FIG. 17 . In this embodiment, one or more line buffers  140  is used to store one or more frames of previous image frame data  102 . As illustrated, for each sensed line of image data, the previously sensed line is stored instead via the one or more line buffers  140 . One or more sensed parameters from the pixels  56  from the display panel  50  is delivered to a threshold voltage look-up table (Vth LUT) and correction algorithm  142  via the AFE and ADC  92 . The Vth LUT and correction algorithm  142  utilize the information from the previous frame or frames stored in the one or more line buffers  140  in conjunction with the sensed parameters to deliver compensation information to a threshold voltage Vth compensation circuit  144 . The current image frame data  112  is adjusted via a gamma circuit  146  and delivered to the Vth compensation circuit  144 , where the current image frame data  112  is further adjusted based on the compensation information from the Vth LUT and correction algorithm  142 . The compensated current image frame data is then delivered to the pixels  56  of the display panel  50  via a DAC  90 . 
     A portion of the hysteresis sensing and correction circuit  100 C is illustrated in greater detail in  FIG. 18 . Here, the lookup table (LUT)  148  of the V th  LUT and correction algorithm  142  includes a table  150  that relates previous frame pixel voltage to corrected ΔV th . Hence, based upon the previous frame pixel voltage received from the one or more line buffers  140 , the corrected ΔV th  is delivered to a summer  152  along with certain sensed parameters  154 , such as I o v ·I o  relative to the ΔV th  sensed. The information from the summer  152  is delivered to the V th  compensation circuit  144  for further processing as described above. Indeed,  FIG. 19  illustrates a ΔV th v . ΔI o  for two examples of curves  160  and  162  depicting V th V . I o . 
     It should also be noted that, at least in some circumstances, the duration of the frame emission period may also affect the V th  of the TFTs  72  as illustrated in  FIG. 20 . To address this concern, the hysteresis sensing and compensation circuit  100 C illustrated in  FIG. 21  includes information related to the duration or one or more previous frames to be used in the compensation of the current image frame data  112 . As illustrated in  FIG. 21 , the LUT  148  includes tables  150 A of frame pixel voltages versus corrected ΔV th  for various frame durations. Hence, this information may be processed as described with respect to  FIGS. 17 and 18  above to compensate the current image frame data  112 . 
     As previously mentioned, the V th  of the TFTs  72  and, thus, the supply current (Is) delivered to the OLEDs  70  may be affected not just by the immediately previous image frame data, but also by multiple frames of previous image frame data  102 . Accordingly, the LUT  148  may include multiple tables  150 B as illustrated in  FIG. 22 . Specifically, the tables  150 B may include the pixel voltage from two or more previous frames relative to corrected ΔV th  which may be used to compensate the current image frame data  112  as described previously. Moreover, another way of taking into account multiple frame history is by use of a moving average filtering method. As illustrated in  FIG. 23 , the hysteresis sensing and compensation circuit  100 C may include a moving average filter  170  that averages the contents of multiple previous frames that are stored in the line buffers  140 . The LUT  148  may include one or more tables  150 C that relate the average pixel voltage provided by the moving average filter  170  to an appropriate corrected ΔV th  which may be provided by the LUT  148  to the remaining portions of the circuit  100 C to be processed as described above to compensate the current image frame data  112 . 
     As also mentioned previously, the temperature of the TFTs  72  can impact their hysteresis behavior. Accordingly, as illustrated in  FIG. 24 , the hysteresis sensing and compensation circuit  100 C may obtain temperature information  172 , using any appropriate temperature sensing device on the panel  50 , for example. The LUT  148  may include one or more tables  150 D that relate previous frame pixel voltage to corrected ΔV th  for various temperatures. The LUT  148  can thus select the most appropriate ΔV th  to be delivered for processing as described above to compensate the current image frame data  112 . 
     It should be appreciated that while many of the techniques have been described separately above to ensure clarity, many of these techniques can be combined and used with one another to provide the most appropriate compensation information to be used to correct or compensate current image frame data  112  for any of these parameters that may affect the V th  of the TFTs  72  and or the I o  of the OLEDs  70 . 
     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: 20170911
Publication Date: 20201103
Grant Date: 20201103
Priority Date: 20160921
Inventors: WANG, CHAOHAO
YEH, CHIH-WEI
LIN, CHIN-WEI
LIN, HUNG SHENG
NHO, HYUNWOO
HWANG, INJAE
RYU, JIE WON
TAN, JUNHUA
SACCHETTO, PAOLO
ZHANG, RUI
GAO, SHENGKUI
CHANG, SUN-IL
YAO, WEI H.
TANG, HOWARD H.
Assignee: APPLE INC
CPC Classifications: [{"code": "G09G2320/043", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0693", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0295", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2310/0262", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2300/0861", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3275", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2310/0262", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/043", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3233", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G2340/16", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2330/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0693", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2360/18", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0257", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3233", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G2330/02", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0295", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2300/0861", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0233", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/043", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0295", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2340/16", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2330/02", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3275", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/3233", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G2300/0861", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0693", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0233", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2310/0262", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2330/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2360/18", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0257", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 61620528