PATENT DOCUMENT

Publication Number: US-10997914-B1
Application Number: US-201916563286-A
Country: US
Kind Code: B1

Title: Systems and methods for compensating pixel voltages

Abstract:
A system may include a display panel that includes number of pixels that display image data on a display. The system may also include a circuit that measures a voltage associated with a light-emitting diode (LED) of a pixel of the number of pixels in response to the LED receiving a current. In addition to the circuit, the system may employ data processing circuitry that may generate a calibrated prediction model based at least in part on the voltage and the current, such that the calibrated prediction model predicts a change in voltage performance of the LED as the LED ages.

Claims:
What is claimed is: 
     
       1. A system comprising:
 a display panel comprising a plurality of pixels configured to display image data; 
 a circuit configured to measure a voltage associated with a light-emitting diode (LED) of a pixel of the plurality of pixels in response to the LED receiving a current; and 
 data processing circuitry configured to:
 receive a prediction model for predicting a change in voltage performance of the LED as the LED ages; and 
 calibrate the prediction model based on a plurality of test currents provided to the LED at a plurality of times, wherein the prediction model is calibrated by:
 acquiring a measured voltage at the LED after each test current of the plurality of test currents is provided to the LED; 
 determining a difference between the measured voltage at the LED after each test current of the plurality of test currents is provided to the LED and an expected voltage associated with each test current at the plurality of times, wherein the expected voltage is retrieved from the prediction model; and 
 updating the prediction model based on the difference. 
 
 
 
     
     
       2. The system of  claim 1 , wherein the data processing circuitry is configured to:
 receive pixel data representative of image data to be depicted on the pixel; and 
 generate adjusted pixel data based at least in part on the calibrated prediction model and the pixel data, wherein the adjusted pixel data is configured to be displayed on the display panel. 
 
     
     
       3. The system of  claim 2 , wherein the data processing circuitry is configured to use a capacitance ratio associated with the pixel to generate the adjusted pixel data based at least in part on the calibrated prediction model, the pixel data, and the capacitance ratio. 
     
     
       4. The system of  claim 3 , wherein the data processing circuitry is configured to generate the adjusted pixel data based at least in part on a product between the capacitance ratio and one or more values provided via the calibrated prediction model. 
     
     
       5. The system of  claim 3 , wherein the capacitance ratio is representative of a capacitance of a pixel driving circuit associated with the pixel. 
     
     
       6. The system of  claim 5 , wherein the capacitance comprises a parasitic capacitance of the pixel driving circuit. 
     
     
       7. The system of  claim 1 , wherein the calibrated prediction model comprises at least three delta voltage values representative of at least three differences between at least three expected measured voltages associated with the LED and at least three input currents provided to the LED. 
     
     
       8. The system of  claim 1 , wherein the display panel and the circuit configured to measure the voltage are disposed as components of an electronic display, and wherein the data processing circuitry is disposed as external to the electronic display. 
     
     
       9. A method, comprising:
 sending a test current to a light-emitting diode (LED) of a pixel circuit; 
 measuring a voltage associated with the LED in response to the LED receiving the test current; 
 determining a difference between the voltage at the LED after the test current is provided to the LED and an expected voltage associated with the test current, wherein the expected voltage is retrieved from a prediction model, 
 wherein the prediction model comprises information indicative of a plurality of relationships between an expected voltage associated with the LED and a target current provided to the LED at a plurality of times; and 
 updating the prediction model based on the difference. 
 
     
     
       10. The method of  claim 9 , wherein each of the plurality of times corresponds to a different age of the LED. 
     
     
       11. The method of  claim 9 , wherein the LED comprises an organic light-emitting diode. 
     
     
       12. The method of  claim 9 , wherein the prediction model is generated based at least in part on testing a second LED that is representative of the LED under a plurality of stress conditions. 
     
     
       13. The method of  claim 12 , wherein the plurality of stress conditions comprises illuminating the LED for one or more amounts of time. 
     
     
       14. The method of  claim 9 , wherein calibrating the prediction model comprises adjusting the expected voltage associated with the LED based at least in part on the voltage measured at the LED. 
     
     
       15. The method of  claim 9 , wherein the prediction model comprises one or more changes in voltage associated with the LED as the LED ages. 
     
     
       16. A non-transitory computer-readable medium comprising computer-executable instructions that, when executed, cause a processor to:
 receive pixel data representative of a grey level for display via a light-emitting diode (LED) of a pixel in an electronic device; 
 receive an indication of an age of the LED; 
 query a prediction model indicative of a change in voltage associated with the pixel data using the pixel data and the age, wherein the prediction model comprises information indicative of a plurality of relationships between an expected voltage associated with the LED and pixel current provided to the LED at a plurality of times; 
 adjust the pixel data based at least in part on the change in voltage, wherein the adjusted pixel data is configured to cause a pixel driving circuit associated with the LED to more uniformly display an image; 
 calibrate the prediction model calibrated by:
 sending a test current to the LED; 
 measuring a pixel voltage at the LED in response to the LED receiving the test current; 
 determining a difference between the pixel voltage at the LED and an expected pixel voltage associated with the test currents, wherein the expected pixel voltage is retrieved from the prediction model; and 
 updating the prediction model based on the difference. 
 
 
     
     
       17. The non-transitory computer-readable medium of  claim 16 , wherein the age of the LED corresponds to an amount of time that the LED is illuminated. 
     
     
       18. The non-transitory computer-readable medium of  claim 16 , wherein the information comprises at least three delta voltage values and at least three current values representative of current provided to the LED to present a grey level. 
     
     
       19. The non-transitory computer-readable medium of  claim 18 , wherein the computer-executable instructions cause the processor to query the prediction model by analyzing the pixel data with respect to a curve that comprise the at least three delta voltage values and the at least three current values.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 62/728,659, entitled “Systems and Methods for Compensating Pixel Voltages,” filed on Sep. 7, 2018, which is incorporated herein by reference in its entirety for all purposes. 
    
    
     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. 
     In certain electronic display devices, light-emitting diodes such as organic light-emitting diodes (OLEDs) or active matrix organic light-emitting diodes (AMOLEDs) may be employed as pixels to depict a range of gray levels for display. However, due to various properties associated with the operation of these pixels within the display device, a particular gray level output by one pixel in a display device may be different from a gray level output by another pixel in the same display device upon receiving the same electrical input. More specifically, aging of circuit components, such as the OLED used to emit light, may cause the electrical properties associated with the corresponding pixel current to change, thereby producing inconsistent or non-uniform colors across the display device. 
     With this in mind, the electrical inputs used to represent image data may be calibrated to account for the aging effects of the OLED by sensing the electrical values that get stored into the corresponding pixel circuit and adjusting the input electrical values accordingly. Since the aging effects of the OLED or other pixel circuit component changes over time, the present disclosure details various systems and methods that may be employed to implement a sensing scheme to sense variations in pixel properties (e.g., current, voltage) and modify a data voltage applied to a respective pixel based at least in part on the sensed variation. The corrected data voltage, when applied to the respective pixel, may compensate for the variations in the pixel properties that may be due to the aging of the pixel circuit component (e.g., LED) to achieve a more uniform image that will be depicted on the display device. 
     In one embodiment, a compensation system of a display device may sense a pixel current applied to a respective pixel during a panel scan for data program. That is, the compensation system may transmit pixel data (e.g., current over a period of time) to a particular pixel to detect a corresponding voltage of the respective OLED in response to the OLED receiving the pixel data. For example, during a panel scan for one row of pixels, the compensation system may send a test data voltage to drive a thin film transistor (TFT) of a respective pixel. After the test data voltage is transmitted to the TFT, the TFT may provide a corresponding current (I OLED ) to the OLED of the pixel circuit. As the OLED illuminates in response to receiving the current (I OLED ), the compensation system may determine a voltage (V OLED ) across the OLED. As the OLED ages, the voltage (V OLED ) may decrease when the same current (I OLED ) is received by the OLED. This decrease in the voltage (V OLED ) may cause the OLED to display a different color than expected for an input image data. Moreover, as different OLEDs in the display device ages differently, each OLED may react differently to the provided current. 
     To reduce the visibility of these non-uniform properties across the display device, the compensation system may employ a prediction model that provides an expected current-voltage (I-V) characteristic curve for an OLED over time. The prediction model may be generated by testing certain display devices under various stress conditions (e.g., different test images, different emission times, different ambient temperatures). However, each individual display device may not experience the same aging effects or may not be used in a manner represented by the testing used to generate the prediction model. Accordingly, in some embodiments, the compensation system may calibrate the prediction model based at least in part on the detected voltage (V OLED ) across the OLED in response to the test current (e.g., I OLED ) provided to the OLED. That is, the compensation system may compare the relationship between the detected voltage (V OLED ) and the test current (I OLED ) to the predicted current-voltage relationship for the display device at the respective time (e.g., period of time of use). Based at least in part on this comparison, the compensation system may calibrate or update the prediction model to more accurately represent the expected voltage behavior with respect to the provided current over time. The calibrated prediction model may now provide a more accurate representation of an error or change in voltage for an input current provided to the OLED. 
     The compensation system may then use the change in voltage provided by the calibrated prediction model to adjust input pixel data provided to a respective pixel circuit. In other words, image data received by the compensation system that includes pixel data representative of a grey level to be presented by a respective OLED may be adjusted based at least in part on the expected change in voltage provided by the calibrated prediction model. The adjusted image data may then be transmitted to the respective pixel circuit to cause the respective OLED to present light according to the adjusted image data. By employing the compensation system described herein for one or more pixels in a display device, the display device may present image data more uniformly across the display as the OLEDs of the device ages. 
     Various refinements of the features noted above may exist in relation to various aspects of the present disclosure. Further features may also be incorporated in these various aspects as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to one or more of the illustrated embodiments may be incorporated into any of the above-described aspects of the present disclosure alone or in any combination. The brief summary presented above is intended only to familiarize the reader with certain aspects and contexts of embodiments of the present disclosure without limitation to the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various aspects of this disclosure may be better understood upon reading the following detailed description and upon reference to the drawings in which: 
         FIG. 1  is a simplified block diagram of components of an electronic device that may depict image data on a display, in accordance with embodiments described herein; 
         FIG. 2  is a perspective view of the electronic device of  FIG. 1  in the form of a notebook computing device, in accordance with embodiments described herein; 
         FIG. 3  is a front view of the electronic device of  FIG. 1  in the form of a desktop computing device, in accordance with embodiments described herein; 
         FIG. 4  is a front view of the electronic device of  FIG. 1  in the form of a handheld portable electronic device, in accordance with embodiments described herein; 
         FIG. 5  is a front view of the electronic device of  FIG. 1  in the form of a tablet computing device, in accordance with embodiments described herein; 
         FIG. 6  is circuit diagram of the display of the electronic device of  FIG. 1 , in accordance with an embodiment; 
         FIG. 7  is a circuit diagram of an example pixel driving circuit for a pixel in the display of the electronic device of  FIG. 1 , in accordance with an embodiment; 
         FIG. 8  is a graph illustrating changes to current-to-voltage relationships of an organic light emitting diode (OLED) in the display of the electronic device of  FIG. 1  over time, in accordance with an embodiment; 
         FIG. 9  is a data flow diagram representative of a process for compensating pixel data for display via the display of the electronic device of  FIG. 1  as the display ages, in accordance with an embodiment; 
         FIG. 10  is a flow chart of a method for calibrating a prediction model of a current-to-voltage changes of the OLED over time in the display of the electronic device of  FIG. 1  as the display ages, in accordance with an embodiment; and 
         FIG. 11  is a flow chart of a method for compensating pixel data for display via the display of the electronic device of  FIG. 1  based at least in part on the calibrated prediction model, in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     One or more specific embodiments of the present disclosure will be described below. These described embodiments are only examples of the presently disclosed techniques. Additionally, in an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but may 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. Furthermore, the phrase A “based at least in part on” B is intended to mean that A is at least partially based at least in part on B. Moreover, the term “or” is intended to be inclusive (e.g., logical OR) and not exclusive (e.g., logical XOR). In other words, the phrase A “or” B is intended to mean A, B, or both A and B. 
     As electronic displays are employed in a variety of electronic devices, such as mobile phones, televisions, tablet computing devices, and the like, manufacturers of the electronic displays continuously seek ways to improve the consistency of colors depicted on the electronic display devices. For example, given variations in manufacturing, various noise sources present within a display device, aging of circuit components in the display device, or various ambient conditions in which each display device operates, different pixels within a display device might emit a different color value or gray level even when provided with the same electrical input. It is desirable, however, for the pixels to uniformly depict the same color or gray level when the pixels programmed to do so to avoid visual display artifacts due to inconsistent color. 
     Organic light-emitting diode (e.g., OLED, AMOLED) display panels provide opportunities to make thin, flexible, high-contrast, and color-rich electronic displays. Generally, OLED display devices are current driven devices and use thin film transistors (TFTs) as current sources to provide certain amount of current to generate a certain level of luminance to a respective pixel electrode. OLED Luminance to current ratio is generally represented as OLED efficiency with units: cd/A (Luminance/Current Density or (cd/m 2 )/(A/m 2 )). Each respective TFT, which provides current to a respective pixel, may be controlled by gate to source voltage (V gs ), which is stored on a capacitor (C st ) electrically coupled to the LED of the pixel. 
     Generally, the application of the gate-to-source voltage V gs  on the capacitor C st  is performed by programming voltage on a corresponding data line to be provided to a respective pixel. However, as the OLED ages, the OLED may respond differently to the current provided to it. As a result, different OLEDs receiving the same amount of current may react differently, thereby providing non-uniformity in luminance or color across the display. 
     With the foregoing in mind, the present disclosure describes a system and method for compensating pixel data provided to a respective pixel circuit to cause the respective OLED to react or depict light (e.g., grey level) more uniformly across the display. More specifically, in some embodiments, a compensation system may calibrate a prediction model that predicts an expected change in voltage across an OLED for one or more input current values based at least in part on a detected voltage across the OLED due to a test current at a particular time. Based at least in part on the difference between the expected change in voltage and the actual change in voltage over the OLED, the compensation system may calibrate the prediction model. The calibrated prediction model may then may employed to adjust pixel data of input image data for a respective pixel circuit, such that the OLED may produce a light that more accurately represents the desired image data. Additional details with regard to the manner in which the compensation system may calibrate the prediction model and adjust the pixel data are detailed below with reference to  FIGS. 1-11 . 
     By way of introduction,  FIG. 1  is a block diagram illustrating an example of an electronic device  10  that may include the sensing system mentioned above. The electronic device  10  may be any suitable electronic device, such as a laptop or desktop computer, a mobile phone, a digital media player, television, or the like. By way of example, the electronic device  10  may be a portable electronic device, such as a model of an iPod® or iPhone®, available from Apple Inc. of Cupertino, Calif. The electronic device  10  may be a desktop or notebook computer, such as a model of a MacBook®, MacBook® Pro, MacBook Air®, iMac®, Mac® Mini, or Mac Pro®, available from Apple Inc. In other embodiments, electronic device  10  may be a model of an electronic device from another manufacturer. 
     As shown in  FIG. 1 , the electronic device  10  may include various components. The functional blocks shown in  FIG. 1  may represent hardware elements (including circuitry), software elements (including code stored on a computer-readable medium) or a combination of both hardware and software elements. In the example of  FIG. 1 , the electronic device  10  includes input/output (I/O) ports  12 , input structures  14 , one or more processors  16 , a memory  18 , nonvolatile storage  20 , network device  22 , power source  24 , display  26  with a display driver  29 , and one or more imaging devices  28 . It should be appreciated, however, that the components illustrated in  FIG. 1  are provided only as an example. Other embodiments of the electronic device  10  may include more or fewer components. To provide one example, some embodiments of the electronic device  10  may not include the imaging device(s)  28 . 
     Before continuing further, it should be noted that the system block diagram of the device  10  shown in  FIG. 1  is intended to be a high-level control diagram depicting various components that may be included in such a device  10 . That is, the connection lines between each individual component shown in  FIG. 1  may not necessarily represent paths or directions through which data flows or is transmitted between various components of the device  10 . Indeed, as discussed below, the depicted processor(s)  16  may, in some embodiments, include multiple processors, such as a main processor (e.g., CPU), and dedicated image and/or video processors. In such embodiments, the processing of image data may be primarily handled by these dedicated processors, thus effectively offloading such tasks from a main processor (CPU). 
     Considering each of the components of  FIG. 1 , the I/O ports  12  may represent ports to connect to a variety of devices, such as a power source, an audio output device, or other electronic devices. The input structures  14  may enable user input to the electronic device, and may include hardware keys, a touch-sensitive element of the display  26 , and/or a microphone. 
     The processor(s)  16  may control the general operation of the device  10 . For instance, the processor(s)  16  may execute an operating system, programs, user and application interfaces, and other functions of the electronic device  10 . The processor(s)  16  may include one or more microprocessors and/or application-specific microprocessors (ASICs), or a combination of such processing components. For example, the processor(s)  16  may include one or more instruction set (e.g., RISC) processors, as well as graphics processors (GPU), video processors, audio processors and/or related chip sets. As may be appreciated, the processor(s)  16  may be coupled to one or more data buses for transferring data and instructions between various components of the device  10 . In certain embodiments, the processor(s)  16  may provide the processing capability to execute an imaging applications on the electronic device  10 , such as Photo Booth®, Aperture®, iPhoto®, Preview®, iMovie®, or Final Cut Pro® available from Apple Inc., or the “Camera” and/or “Photo” applications provided by Apple Inc. and available on some models of the iPhone®, iPod®, and iPad®. 
     The electronic device  10  may include a display driver  29 , which may include a chip, such as processor or ASIC, that may control various aspects of the display  26 . It should be noted that the display driver  29  may be implemented in the CPU, the GPU, image signal processing pipeline, display pipeline, driving silicon, or any suitable processing device that is capable of processing image data in the digital domain before the image data is provided to the pixel circuitry. 
     In certain embodiments, the display driver  29  may include a compensation system  30 , which may adjust image data provided to the display  26  based at least in part on a calibrated prediction model that predicts how LEDs of the display  26  may change in behavior over time. As will be described in more detail below, the compensation system  30  may test the behavior of one or more OLEDs of the display  26  over time to compensate for aging effects of the respective OLEDs. As a result, the image data presented by the display  26  may be depicted more uniformly across the display  26 . 
     A computer-readable medium, such as the memory  18  or the nonvolatile storage  20 , may store the instructions or data to be processed by the processor(s)  16 . The memory  18  may include any suitable memory device, such as random access memory (RAM) or read only memory (ROM). The nonvolatile storage  20  may include flash memory, a hard drive, or any other optical, magnetic, and/or solid-state storage media. The memory  18  and/or the nonvolatile storage  20  may store firmware, data files, image data, software programs and applications, and so forth. 
     The network device  22  may be a network controller or a network interface card (NIC), and may enable network communication over a local area network (LAN) (e.g., Wi-Fi), a personal area network (e.g., Bluetooth), and/or a wide area network (WAN) (e.g., a 3G or 4G data network). The power source  24  of the device  10  may include a Li-ion battery and/or a power supply unit (PSU) to draw power from an electrical outlet or an alternating-current (AC) power supply. 
     The display  26  may display various images generated by device  10 , such as a GUI for an operating system or image data (including still images and video data). The display  26  may be any suitable type of display, such as a liquid crystal display (LCD), plasma display, or an organic light emitting diode (OLED) display, for example. In one embodiment, the display  26  may include self-emissive pixels such as organic light emitting diodes (OLEDs) or micro-light-emitting-diodes (μ-LEDs). 
     Additionally, as mentioned above, the display  26  may include a touch-sensitive element that may represent an input structure  14  of the electronic device  10 . The imaging device(s)  28  of the electronic device  10  may represent a digital camera that may acquire both still images and video. Each imaging device  28  may include a lens and an image sensor capture and convert light into electrical signals. 
     In certain embodiments, the electronic device  10  may include a compensation system  30 , which may include a chip, such as processor or ASIC, that may control various aspects of the display  26 . It should be noted that the compensation system  30  may be implemented in the CPU, the GPU, or any suitable processing device that processes image data in the digital domain before the image data is provided to the pixel circuitry. 
     As mentioned above, the electronic device  10  may take any number of suitable forms. Some examples of these possible forms appear in  FIGS. 2-5 . Turning to  FIG. 2 , a notebook computer  40  may include a housing  42 , the display  26 , the I/O ports  12 , and the input structures  14 . The input structures  14  may include a keyboard and a touchpad mouse that are integrated with the housing  42 . Additionally, the input structure  14  may include various other buttons and/or switches which may be used to interact with the computer  40 , such as to power on or start the computer, to operate a GUI or an application running on the computer  40 , as well as adjust various other aspects relating to operation of the computer  40  (e.g., sound volume, display brightness, etc.). The computer  40  may also include various I/O ports  12  that provide for connectivity to additional devices, as discussed above, such as a FireWire® or USB port, a high definition multimedia interface (HDMI) port, or any other type of port that is suitable for connecting to an external device. Additionally, the computer  40  may include network connectivity (e.g., network device  22 ), memory (e.g., memory  18 ), and storage capabilities (e.g., storage device  20 ), as described above with respect to  FIG. 1 . 
     The notebook computer  40  may include an integrated imaging device  28  (e.g., a camera). In other embodiments, the notebook computer  40  may use an external camera (e.g., an external USB camera or a “webcam”) connected to one or more of the I/O ports  12  instead of or in addition to the integrated imaging device  28 . In certain embodiments, the depicted notebook computer  40  may be a model of a MacBook®, MacBook® Pro, MacBook Air®, or PowerBook® available from Apple Inc. In other embodiments, the computer  40  may be portable tablet computing device, such as a model of an iPad® from Apple Inc. 
       FIG. 3  shows the electronic device  10  in the form of a desktop computer  50 . The desktop computer  50  may include a number of features that may be generally similar to those provided by the notebook computer  40  shown in  FIG. 4 , but may have a generally larger overall form factor. As shown, the desktop computer  50  may be housed in an enclosure  42  that includes the display  26 , as well as various other components discussed above with regard to the block diagram shown in  FIG. 1 . Further, the desktop computer  50  may include an external keyboard and mouse (input structures  14 ) that may be coupled to the computer  50  via one or more I/O ports  12  (e.g., USB) or may communicate with the computer  50  wirelessly (e.g., RF, Bluetooth, etc.). The desktop computer  50  also includes an imaging device  28 , which may be an integrated or external camera, as discussed above. In certain embodiments, the depicted desktop computer  50  may be a model of an iMac®, Mac® mini, or Mac Pro®, available from Apple Inc. 
     The electronic device  10  may also take the form of portable handheld device  60  or  70 , as shown in  FIGS. 4 and 5 . By way of example, the handheld device  60  or  70  may be a model of an iPod® or iPhone® available from Apple Inc. The handheld device  60  or  70  includes an enclosure  42 , which may function to protect the interior components from physical damage and to shield them from electromagnetic interference. The enclosure  42  also includes various user input structures  14  through which a user may interface with the handheld device  60  or  70 . Each input structure  14  may control various device functions when pressed or actuated. As shown in  FIGS. 4 and 5 , the handheld device  60  or  70  may also include various I/O ports  12 . For instance, the depicted I/O ports  12  may include a proprietary connection port for transmitting and receiving data files or for charging a power source  24 . Further, the I/O ports  12  may also be used to output voltage, current, and power to other connected devices. 
     The display  26  may display images generated by the handheld device  60  or  70 . For example, the display  26  may display system indicators that may indicate device power status, signal strength, external device connections, and so forth. The display  26  may also display a GUI  52  that allows a user to interact with the device  60  or  70 , as discussed above with reference to  FIG. 3 . The GUI  52  may include graphical elements, such as the icons, which may correspond to various applications that may be opened or executed upon detecting a user selection of a respective icon. 
     Having provided some context with regard to possible forms that the electronic device  10  may take, the present discussion will now focus on the compensation system  30  of  FIG. 1 . As shown in  FIG. 6 , the display  26  may include a pixel array  80  having an array of one or more pixels  82 . The display  26  may include any suitable circuitry to drive the pixels  82 . In the example of  FIG. 6 , the display  26  includes a controller  84 , a power driver  86 A, an image driver  86 B, and the array of the pixels  82 . The power driver  86 A and image driver  86 B may drive individual luminance of the pixels  82 . In some embodiments, the power driver  86 A and the image driver  86 B may include multiple channels for independent driving of the pixel  82 . Each of the pixels  82  may include any suitable light emitting element, such as a LED, one example of which is an OLED. However, any other suitable type of pixel may also be used. Although the controller  84  is shown in the display  26 , the controller  84  may be located outside of the display  26  in some embodiments. For example, the controller  84  may also be located in the processor  16 . 
     The scan lines S 0 , S 1 , . . . , and Sm and driving lines D 0 , D 1 , . . . , and Dm may connect the power driver  86 A to the pixel  82 . The pixel  82  may receive on/off instructions through the scan lines S 0 , S 1 , . . . , and Sm and may generate programming voltages corresponding to data voltages transmitted from the driving lines D 0 , D 1 , . . . , and Dm. The programming voltages may be transmitted to each of the pixel  82  to emit light according to instructions from the image driver  86 B through driving lines M 0 , M 1 , . . . , and Mn. Both the power driver  86 A and the image driver  86 B may be transmitted voltage signals at programmed voltages through respective driving lines to operate each pixel  82  at a state determined by the controller  84  to emit light. Each driver may supply voltage signals at a duty cycle and/or amplitude sufficient to operate each pixel  82 . 
     The intensities of each of the pixels  82  may be defined by corresponding image data that defines particular gray levels for each of the pixels  82  to emit light. A gray level indicates a value between a minimum and a maximum range, for example, 0 to 255, corresponding to a minimum and maximum range of light emission. Causing the pixels  82  to emit light according to the different gray levels causes an image to appear on the display  26 . In this manner, a first brightness of light (e.g., at a first luminosity and defined by a gray level) may emit from a pixel  82  in response to a first value of the image data and the pixel  82  may emit a second brightness of light (e.g., at a second luminosity) in response to a second value of the image data. Thus, image data may create a perceivable image output through indicating light intensities to apply to individual pixels  82 . 
     The controller  84  may retrieve image data stored in the storage device(s)  20  indicative of light intensities for the colored light outputs for the pixels  82 . In some embodiments, the processor  16  may provide image data directly to the controller  84 . The image data may indicate the pixel light intensity and/or refresh rate data. For example, the controller  84  may receive an indication of the refresh rate of the display  26 , a desired refresh rate of the display  26 , frame and sub-frame period duration, or desired pixel luminance. The controller  84  may control the pixel  82  by using control signals to control elements of the pixel  82 . 
     The pixel  82  may include any suitable controllable element, such as a transistor, one example of which is a metal-oxide-semiconductor field-effect transistor (MOSFET). However, any other suitable type of controllable elements, including thin film transistors (TFTs), p-type and/or n-type MOSFETs, and other transistor types, may also be used. 
     In some embodiments, the pixel  82  may include a number of circuit components to enable the respective LED produce light for a prescribed amount of time or produce a particular gray level. By way of example,  FIG. 7  illustrates a pixel driving circuit  90  that may include a number of semiconductor devices that may coordinate the transmission of data signals to an organic light-emitting diode (LED)  92  of a respective pixel  82 . In one embodiment, the pixel driving circuit  90  may receive input signals (e.g., emission signals  1  and  2 , scan signals  1  and  2 ), which may be coordinated in a manner to cause the pixel driving circuit  90  to display image data and transmit a test data signal used to determine the OLED voltage (V OLED ) (e.g., voltage at Node  3 ) of the OLED  92 . 
     With this in mind, the pixel driving circuit  90  may include, in one embodiment, N-type semiconductor devices and P-type semiconductor devices, as shown in  FIG. 7 . Although the following description of the pixel driving circuit  90  is illustrated with the N-type semiconductor devices and the P-type semiconductor devices, it should be noted that the pixel driving circuit  90  may be designed using any suitable combination of N-type or P-type semiconductor devices. 
     In addition to the semiconductor devices, the pixel driving circuit  90  may include a capacitor  94  that may store data provided via data line  96 . The close proximity between the various circuit components of the pixel driving circuit  90  and the various voltage sources (e.g., VDD, VSS) may also create parasitic capacitance within the pixel driving circuit  90 . The capacitor  94  and the parasitic capacitance of the pixel driving circuit  90  may be combined in a capacitance ratio that represents the total capacitance of the pixel driving circuit  90 . 
     In some embodiments, one or more of the semiconductors (e.g., TFTs) of the pixel driving circuit  90  may produce a current in response to the voltage received via the data line  96 . When the emission signal  1  (e.g., EM1) is provided to a gate of the respective switch, the OLED  92  may receive a current that corresponds to the data stored in the capacitor  94 . As the OLED  92  illuminates in response to receiving the current (I OLED ), a voltage (e.g., V OLED ) at Node  3  may change when the OLED  92  receives the same amount of current over time. This change in voltage is representative of the aging effects of the OLED  92 . 
     To further illustrate the aging effects of the OLED  92 ,  FIG. 8  illustrates a graph  100  of a current-to-voltage relationship of an example OLED. As shown in the graph  100 , curve  102  represents the current I OLED  conducted via the OLED  92  at time T 0  and curve  104  represents the current I OLED  conducted via the OLED  92  at a later time (e.g., T AGED ) after the OLED  92  has been in use and aged. As shown in  FIG. 8 , when the current I OLED  is at current I for time T 0  and time T AGED , the curve  102  indicates that the OLED voltage (V OLED ) is V 1 , and the curve  104  indicates that the OLED voltage (V OLED ) is V 2 . As such, although the OLED  92  receives the same amount of current I 1 , the voltage across the OLED  92  decreases. This change in voltage changes the behavior (e.g., luminance) of the OLED  92 . 
     Keeping this in mind,  FIG. 9  illustrates a data flow diagram  110  for compensating input pixel data for a respective pixel  82  to achieve a more uniform properties across the display  26 . In some embodiments, the data flow diagram  110  may be performed by the processor  16 , the display driver  29 , the compensation system  30 , or other suitable processing component. In addition, it should be noted that the data flow diagram  110  may be implemented in software via data processing circuitry (e.g., image signal processor, data processing pipeline, image data processing pipeline), using hardware components, or a combination of software and hardware components. In some embodiments, the data processing circuitry that performs the operations related to the data flow diagram  110  and other related processes described herein may be performed external to the display  26 . For the purposes of discussion, the following description of the data flow diagram  110  will be described as being performed by the compensation system  30 , but it should be noted that the process should not be limited to be being performed by the compensation system  30 . 
     Referring now to  FIG. 9 , the data flow diagram  110  may involve sending an indication to a voltage sensing component  114  that the current I OLED    112  is provided to the OLED  92 . The current I OLED    112  may represent an amount of current that is provided to the OLED  92 . The current I OLED    112  may be sensed using sensing circuitry or may correspond to a known test current value. 
     After receiving indication that the current I OLED    112  is provided to the OLED  92 , the voltage sensing component  114  may sense or measure a voltage V OLED    116  at an anode of the OLED  92  (e.g., at node  3 ). The voltage V OLED    116  may then be used by a calibration component  118  to calibrate a prediction model for the behavior of the OLED  92  over time. The calibration component  118  may determine whether the voltage V OLED    116  matches an expected voltage for the current I OLED    112 . That is, a prediction model for the voltage V OLED    116  may indicate an expected voltage value to be measured at the Node  3  for the OLED  92  after the display  26  has been in use for a certain amount of time. The prediction model may be generated during the manufacturing phase of the display  26  or under a testing phase of the display  26 . As such, the display  26  and the corresponding pixels  82  may have been aged using stress tests under various pixel data conditions, luminance conditions, and the like. In one example, the prediction model may observe the decrease in the OLED voltage over time, as the respective pixel  82  continuously displayed a particular grey level. 
     Based at least in part on the difference between the expected voltage value of the OLED  92  according to the prediction model and the measured voltage V OLED    116 , the calibration component  118  may determine a correction factor  120  for the voltage V OLED    116 . The correction factor may represent the difference or error between the expected voltage value for the OLED  92  after the OLED  92  has been in use for a certain amount of time according to the prediction model and the measured voltage V OLED    116 . 
     The correction factor  120  may be provided to a prediction model component  122 , which may adjust its prediction model based at least in part on the correction factor  120 . In one embodiment, the prediction model component  122  may include the prediction model for the expected voltages of the OLED at one or more input currents (I OLED ) at various times or ages for the display  26 . The prediction model may be stored as a look-up-table, an algorithm, or the like. The algorithm may correspond to an expected voltage decay curve that represents the measured decay in OLED voltage over time for the input current I OLED , as determined during testing, simulation, or the like. 
     After the prediction model component  122  calibrates the prediction model, the prediction model component  122  may produce one or more delta voltage values  124  that represent a current-to-voltage relationship (e.g., I-V curve) for the OLED  92 . In one embodiment, the prediction model component  122  may produce at least three delta voltage values  124  that represent the change in voltage at the OLED  92  at three different input current values. In this way, the delta voltage values  124  represent a more accurate current-to-voltage relationship between a current I OLED  provided to the OLED  92  and the corresponding voltage V OLED  measured at the anode of the OLED  92 . 
     Using the one or more delta voltage values  124 , a voltage compensator component  126  may adjust input pixel data  128  received by the pixel driving circuit  90 . That is, the voltage compensator component  126  may generate a compensated pixel voltage  130  based at least in part on the pixel data  128  and the expected current-to-voltage relationship between the input current (e.g., pixel data  128 ) and the corresponding voltage applied to the OLED  92 . In one embodiment, the pixel data  128  may represent a current amount provided to the OLED  92  to produce a particular grey level. Using the current-to-voltage relationship determined based at least in part on the one or more delta voltage values  124 , the data voltage compensator component  126  may determine a voltage that should be applied to the OLED  92  to enable the aged OLED  92  to produce the expected amount of light or grey level. The data voltage compensator component  126  may then output the compensated pixel voltage  130  to the pixel driving circuit  90  via the data line  96 , thereby causing the OLED  92  to receive the appropriate current I OLED  to depict the desired grey level indicated in the pixel data  128 . 
     In certain embodiments, the capacitance ratio of the pixel driving circuit  90  may cause the OLED  92  to operate differently. As such, the data voltage compensator component  126  may also receive an expected capacitance ratio  132  of the respective pixel driving circuit  90  and use a product between the expected capacitance ratio  132  and the one or more delta voltage values  124  to determine the current-to-voltage relationship between a current I OLED  provided to the OLED  92  and the corresponding voltage V OLED  measured at the anode of the OLED  92 . By accounting for the capacitance ratio  132  of the pixel driving circuit  90 , the data voltage compensator component  126  may provide a more accurate representation of the current-to-voltage relationship between a current I OLED  provided to the OLED  92  and the corresponding voltage V OLED  measured at the anode of the OLED  92 . 
     With the foregoing in mind,  FIG. 10  illustrates a flow chart of a method  140  for calibrating the prediction model discussed above with reference to  FIG. 9 . For the purposes of discussion, the following description of the method  140  will be described as being performed by the compensation system  30 , but it should be noted that any suitable processing device may perform the method  140 . Moreover, although the method  140  is described in a particular order, it should be understood that the method  140  may be performed in any suitable order. 
     Referring now to  FIG. 10 , at block  142 , the compensation system  30  may send a pixel current (I OLED ) to the OLED  92  of a particular pixel  82  in the display  26 . The pixel current (I OLED ) may be a test value that is known to the compensation system  30 , used for testing the aging parameter of the OLED  92  during manufacturing, used to generate the prediction model described above, or the like. 
     At block  144 , the compensation system  30  may receive a sensed pixel voltage (V OLED ) that may correspond to the voltage at the anode of the OLED  92  (e.g., Node  3 ) while the OLED  92  is receiving the pixel current (I OLED ). In some embodiments, the pixel voltage (V OLED ) may be measured using measurement circuitry, determined based at least in part on other detected electrical properties in the pixel driving circuit, or the like. 
     After receiving the sensed pixel voltage (V OLED ), at block  146 , the compensation system  30  may calibrate a prediction model that characterizes the expected relationship between the pixel current (I OLED ) and the pixel voltage (V OLED ) at various times as the OLED  92  ages. To calibrate the prediction model, in some embodiments, the compensation system  30  may determine an amount of time in which the OLED  92  has been in operation (e.g., time illuminated) and identify a corresponding indication in the prediction model representative of the expected pixel current and voltage relationship at that time. By way of example, the prediction model may be stored in the storage device  20  or the like as a look-up table that includes a collection of current values (I OLED ) a corresponding collection of voltage values (V OLED ) at various times (e.g., OLED aging hours). In another example, the prediction model may be represented by a number of current-voltage (I-V) curves that indicates a relationship between the pixel current values (I OLED ) and the pixel voltage values (V OLED ) at various points in time that correspond to the aging of the OLED  92 . 
     In any case, the compensation system  30  may calibrate the prediction model by determining a difference between the expected pixel voltage for the pixel current (I OLED ) as indicated in the prediction model and the sensed pixel voltage (V OLED ) received at block  144 . In some embodiments, the compensation system  30  may update the values of the prediction model based at least in part on the difference. The values of the prediction model may include delta values (e.g., Δ VOLED ) that represent a change in voltage for pixel data provided to the display  26 . That is, the voltage delta values may indicate how pixel data (e.g., image data) provided to the display  26  should be adjusted to cause the OLED  92  to more accurately depict a desired luminance or color value, as defined in input image data. As a result, the prediction model may more accurately represent the aging effects to the current-voltage relationship at the OLED  92 . 
     After the prediction model is calibrated, the compensation system  30  may use the calibrated prediction model to adjust image data received by the processor  16  or the like to reduce the effects due to the aging of the OLED  92 . With this in mind,  FIG. 11  illustrates a flow chart of a method  150  for adjusting image data to be depicted via the display  26  in accordance with the embodiments described herein. Like the method  140 , the following description of the method  150  will be described as being performed by the compensation system  30 , but it should be noted that any suitable processing device may perform the method  150 . Moreover, although the method  150  is described in a particular order, it should be understood that the method  150  may be performed in any suitable order, including omitting certain operations. 
     Referring now to  FIG. 11 , at block  152 , the compensation system  30  may receive pixel data (e.g., image data) that may correspond to a desired luminance and/or color (e.g., grey level) for the OLED  92 . In one embodiment, the pixel data may include a grey level or luminance for different sub-pixels (e.g., red, green, blue) of the pixel  82 . The pixel data may correspond to a pixel current (I pixel ) that may be provided to the OLED  92  to cause the OLED  92  to depict a luminance or color that corresponds to the pixel data. 
     At block  154 , the compensation system  30  may receive a capacitance ratio of the pixel driving circuit  90 . As mentioned above, the capacitance ratio may represent the capacitance of the pixel driving circuit  90  for the respective pixel  82  that the pixel data is directed towards. The capacitance of the pixel driving circuit  90  may include the capacitors of the circuit itself and any expected parasitic capacitance that is expected to be present in the pixel driving circuit  90 . 
     Based at least in part on the pixel data received at block  152 , the compensation system  30  may, at block  156 , determine an expected change in pixel voltage based at least in part on the calibrated prediction model described above with reference to  FIG. 9 . In some embodiments, the compensation system  30  may use the pixel current (I pixel ) and any suitable indication of the age of the respective OLED  92  as an index to query the calibrated prediction model. The age of the respective OLED  92  may be determined by the compensation system  30  based at least in part on data indicative of an amount of time that the OLED  92  has been illuminated, an amount of time that the electronic device  10  has been in use, or other suitable methods. As such, the compensation system  30  may retrieve one or more voltage delta values that represent how the pixel data should be adjusted to cause the OLED  92  to depict the desired luminance and color value despite the aging of the OLED  92 . 
     In certain embodiments, the calibrated prediction model may provide at least three voltage delta values (e.g., ΔN gs1,2,3 ) for three pixel currents (e.g., I pixel1,2,3 ) that can be plotted, such that the compensation system  30  may determine a curve that describes the voltage adjustments to apply to a variety of pixel currents, as specified by the pixel data. The compensation system  30  may then, at block  158 , use the determined voltage adjustments to adjust the pixel data (e.g., voltage representative of a grey level for the OLED  92 ). That is, the compensation system  30  may increase or decrease the pixel data received at block  152  based at least in part on the expected change in pixel voltage determined via the calibrated prediction model. 
     In some embodiments, the compensation system  30  may multiply the expected change in pixel voltage as provided by the prediction model by the capacitance ratio received at block  154 . In this way, the compensation system  30  may account for the capacitance of the pixel driving circuit  90  when determining the voltage delta values (e.g., Δ gs1,2,3 ) to use to determine the adjusted pixel data. The resulting product of the expected change in pixel voltage as provided by the prediction model and the capacitance ratio received at block  154  may be used to determine the at least three voltage delta values (e.g., Δ gs1,2,3 ) for three pixel currents (e.g., I pixel1,2,3 ) that can be plotted, such that the compensation system  30  may determine a curve that describes the voltage adjustments to apply to a variety of pixel currents, as described above. 
     At block  160 , the compensation system  30  may transmit the adjusted pixel data to the respective pixel driving circuit  90  to cause the respective OLED  92  to depict the desired grey level. As a result, the display  26  may present image data with reduced image artifacts that are caused by pixel current drops due to non-ideal bootstrapping in the pixel driving circuit  90 , parasitic capacitance present in the pixel driving circuit  90 , the aging of the OLED  92 , and the like. 
     By employing the systems and methods described herein, the prediction model for aging effects to OLEDs may be improved to more accurately represent the aging of the actual OLEDs in the respective display devices. That is, the prediction models may generally be created based at least in part on an expected behavior of the OLEDs over time, but each individual OLED and display device may be manufactured using different processes, be composed of different types of material, operated in different manners, be stored in different ambient conditions, and the like. As such, the presently disclosed embodiments may enable the prediction model for a particular display device to more accurately represent the effects of the OLED aging. In addition, in some embodiments, the prediction model may be calibrated at certain times and the calibrated prediction model may be used to adjust pixel data during the operation of the display device. In this way, the pixel voltage (V OLED ) sensing frequency may be reduced, as the prediction model may be relied on to provide an accurate representation of the aging effects of the OLED. 
     Although the foregoing description of the embodiments for improving the uniformity of the display  26  is described with respect to OLED aging, it should be noted that the embodiments presented herein are not limited to being applied to OLEDs. Instead, the presently disclosed embodiments may be applied to any suitable light emitting diode used in an electronic display. 
     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: 20190906
Publication Date: 20210504
Grant Date: 20210504
Priority Date: 20180907
Inventors: HWANG, INJAE
LEE, JIYE
ZHANG, YIFAN
NHO, HYUNWOO
CHANG, SUN-IL
TAN, JUNHUA
RYU, JIE WON
KIM, HYUNSOO
CHOI, MYUNGJOON
SHEN, Shiping
BRAHMA, KINGSUK
RICHMOND, Jesse A.
Assignee: APPLE INC
CPC Classifications: [{"code": "G09G3/3688", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/045", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0295", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0233", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3233", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G3/3233", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G3/3688", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2320/029", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2300/0465", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3258", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2300/0465", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3233", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G3/3688", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2320/029", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3258", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 75689611