PATENT DOCUMENT

Publication Number: US-11158253-B1
Application Number: US-201916563500-A
Country: US
Kind Code: B1

Title: Systems and methods for sensing pixel voltages

Abstract:
A display device may include a plurality of pixels configured to display image data on a display. The display device may also include a circuit that measures a first current associated with a light-emitting diode (LED) of a pixel of the plurality of pixels in response to the circuit receiving a first data voltage. The circuit may also measure a second current associated with the LED of the pixel of the plurality of pixels in response to the circuit receiving a second data voltage. The circuit may then determine a voltage associated with the LED based at least in part on the first current and the second current.

Claims:
What is claimed is: 
     
       1. A display device, comprising:
 a plurality of pixels configured to display image data on a display; and 
 a circuit configured to:
 measure a first current associated with a light-emitting diode (LED) of a pixel of the plurality of pixels in response to the circuit receiving a first data voltage via a data line configured to provide a plurality of data voltages that corresponds to the image data to one or more gates of one or more switches; 
 measure a second current associated with the LED of the pixel of the plurality of pixels in response to the circuit receiving a second data voltage via the data line; and 
 determine a voltage at a node of the LED based at least in part on the first current and the second current, wherein the voltage is determined based on the first data voltage, the second data voltage, a reference voltage provided to the circuit via a reference line coupled to the node of the LED and different from the data line, and a threshold voltage of the LED for the voltage when a first current amount associated with the first current substantially matches a second current amount associated with the second current, wherein the threshold voltage corresponds to an operation of the LED. 
 
 
     
     
       2. The display device of  claim 1 , wherein the circuit is configured to determine the voltage at the node of the LED by:
 continuously adjusting the second data voltage until the first current substantially matches the second current; and 
 determining the voltage at the node of the LED based at least in part on the first current substantially matching the second current. 
 
     
     
       3. The display device of  claim 1 , wherein the circuit is configured to measure the first current associated with the LED at least in part by:
 programming the LED based at least in part on the first data voltage; and 
 directing the first current to a sensing circuit configured to detect the first current amount associated with the first current. 
 
     
     
       4. The display device of  claim 3 , wherein the circuit is configured to measure the second current associated with the LED at least in part by:
 programming the LED based at least in part on the second data voltage; and 
 directing the second current to the sensing circuit configured to detect the second current amount associated with the second current. 
 
     
     
       5. The display device of  claim 1 , wherein the first current corresponds to a current conducted via a drive thin-film-transistor of the circuit. 
     
     
       6. The display device of  claim 1 , wherein the second current corresponds to a current conducted via the LED. 
     
     
       7. The display device of  claim 1 , wherein the first current and the second current are measured while the LED is not illuminated. 
     
     
       8. A method, comprising:
 receiving a first current associated with a light-emitting diode (LED) of a pixel of a plurality of pixels in response to circuitry receiving a first data voltage via a data line configured to provide a plurality of data voltages that corresponds to image data to one or more gates of one or more switches; 
 receiving a second current associated with the LED of the pixel of the plurality of pixels in response to the circuitry receiving a second data voltage via the data line; 
 adjusting the second data voltage until the first current is substantially equal to the second current; and 
 determining a voltage at a node of the LED based at least in part on the first current and the second current after the second data voltage has been adjusted until the first current is substantially equal to the second current, wherein the voltage is determined based on the first data voltage, the second data voltage, a reference voltage provided to the circuitry via a reference line coupled to the node of the LED and different from the data line, and a threshold voltage of the LED corresponding to an operation of the LED. 
 
     
     
       9. The method of  claim 8 , wherein receiving the first current comprises:
 closing, via the circuitry, a first switch coupled to the data line configured to provide the first data voltage to a gate of a drive thin-film-transistor (TFT) switch; and 
 opening, via the circuitry, the first switch, thereby causing the first current to be input into a sensing circuit configured to measure an amount of current of the first current. 
 
     
     
       10. The method of  claim 9 , wherein the first current corresponds to a current conducted via the drive TFT switch. 
     
     
       11. The method of  claim 9 , wherein receiving the second current comprises:
 closing, via the circuitry, the first switch in response to the data line receiving the second data voltage; 
 opening, via the circuitry, a second switch in response to the data line receiving the second data voltage; and 
 opening, via the circuitry, the first switch and closing the second switch after a capacitor coupled between the first switch and the second switch is charged to a threshold, thereby causing the second current to be input into the sensing circuit configured to measure an additional amount of current of the second current. 
 
     
     
       12. The method of  claim 11 , wherein the second current corresponds to a current conducted via the LED. 
     
     
       13. The method of  claim 8 , wherein the LED comprises an organic light-emitting diode. 
     
     
       14. The method of  claim 13 , wherein the voltage at the node of the LED is determined according to:
     V   OLED   =V   DATA1   −V   DATA2   −V   REF    
 wherein V OLED  corresponds to the voltage, V DATA1  corresponds to the first data voltage, V DATA2  corresponds to the second data voltage, and V REF  corresponds to the reference voltage provided to the circuitry. 
 
     
     
       15. The method of  claim 8 , wherein determining the voltage at the node of the LED is based at least in part on the first data voltage and the second data voltage. 
     
     
       16. A non-transitory computer-readable medium comprising computer-executable instructions that, when executed, cause a processor to:
 receive a first current associated with a light-emitting diode (LED) of a pixel of a plurality of pixels in response to the pixel receiving a first data voltage via a data line configured to provide a plurality of data voltages that corresponds to image data to one or more gates of one or more switches; 
 receive a second current associated with the LED of the pixel of the plurality of pixels in response to the pixel receiving a second data voltage via the data line; 
 adjust the second data voltage until the first current is substantially equal to the second current; and 
 determine a voltage at a node of the LED based at least in part on the first current and the second current after the second data voltage has been adjusted until the first current is substantially equal to the second current, wherein the voltage is determined based on a reference voltage provided to the pixel via a reference line coupled to the node of the LED and different from the data line and a threshold voltage of the LED corresponding to an operation of the LED. 
 
     
     
       17. The non-transitory computer-readable medium of  claim 16 , wherein the voltage at the node of the LED corresponds to an age of the LED. 
     
     
       18. The non-transitory computer-readable medium of  claim 16 , wherein the first data voltage and the second data voltage correspond to a first grey level and a second grey level, respectively. 
     
     
       19. The non-transitory computer-readable medium of  claim 16 , wherein the computer-executable instructions cause the processor to adjust pixel data provided to a display device based at least in part on the voltage. 
     
     
       20. The non-transitory computer-readable medium of  claim 16 , wherein the LED comprises an organic light-emitting diode.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 62/728,665, entitled “Systems and Methods for Sensing 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 certain embodiments, a sensing system of a display device may use a sensing circuit and a pixel driving circuit to determine or measure a voltage (V OLED ) associated with a light-emitting diode (LED) of the pixel. The voltage (V OLED ) associated with the LED in a pixel may change over time due to aging of the LED. As such, an accurate measurement of the voltage (V OLED ) associated with the LED while the LED receives some current may be useful in compensating image data received by a display, such that the compensated image data may cause a respective LED to more accurately present a desired luminance or gray level, as specified in the originally received image data. Moreover, as different LEDs age over time, the sensing system may use the voltage (V OLED ) at the LED to compensate image data provided to each pixel of the display, thereby enabling the display to present image data more uniformly across various pixels in the display. 
     With the foregoing in mind, the present embodiments described herein may include a sensing system of a display device that may control the operations of a pixel circuit. In some embodiments, the pixel circuit may receive a first data voltage (V DATA1 ) from the sensing system. After sending the first data voltage first data voltage (V DATA1 ) to the pixel circuit, the sensing system may control various switches in the pixel circuit to cause a drive thin-film transistor (TFT) to receive a current (I TFT ). The drive TFT current (I TFT ) may then be routed to a sensing circuit (e.g., active-front-end circuit), instead of a light-emitting diode of the pixel circuit. The sensing circuit may detect or measure the amount of current (I TFT ) conducted through the drive TFT switch. 
     The sensing system may then program the LED with a second data voltage by causing the drive TFT to send current to LED. After programming the LED, the sensing system may direct the current from the LED to the sensing circuit to determine the amount of current conducted through the LED (LEO. After determining the LED current (LEO, the sensing system may adjust the second data voltage until the LED current (LEO is substantially equal (e.g., within 1-10%) to the drive TFT current (I TFT ). Based at least in part on known variables including the first data voltage, the second data voltage, the threshold voltage of the LED, the sensing system may determine the voltage at the LED (WED). This LED voltage (WED) may provide an indication of how the LED of the pixel circuit is aging. That is, the LED current (LEO received by the LED should correspond to an expected voltage level for the LED. As the LED ages, the voltage level at the LED degrades or decreases when the same LED current (LEO is provided to the LED. 
     In some embodiments, the voltage at the LED (VLED) may be sensed by transmitting test image data to the respective pixel circuit. However, this method may cause visual artifacts and a user may notice that the display device is changing its display. To make the sensing of LED voltages (VLED) less noticeable, the present embodiments employ the drive TFT to assist in determining the LED voltage (VLED). That is, the current through the drive TFT may be sensed without sending current to the LED and compared with a current read out from the pixel circuit after programming the respective LED. 
     After determining the LED voltage (VLED), the sensing system or other suitable component may then use the LED voltage (VLED) to determine a compensation factor to apply to pixel data provided to a respective pixel. In other words, image data received by the sensing system that includes pixel data representative of a grey level to be presented by a respective LED may be adjusted based at least in part on the change in voltage, as indicated based at least in part on the sensed LED voltage (VLED) and the corresponding LED current (LEO. The adjusted image data may then be transmitted to the respective pixel circuit to cause the respective LED to present light according to the adjusted image data. By employing the sensing 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 LEDs 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 measuring current through a thin-film-transistor associated with a pixel in the display of the electronic device of  FIG. 1 , in accordance with an embodiment; 
         FIG. 8  is a circuit diagram of an example pixel driving circuit for measuring current through a light-emitting diode (LED) associated with a pixel in the display of the electronic device of  FIG. 1 , in accordance with an embodiment; and 
         FIG. 9  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 a sensed voltage of a light-emitting diode (LED) in a pixel circuit, 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 sensing a voltage of the OLED for a particular current conducted through the OLED. The sensed voltage level may then be used 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. Additional details with regard to the manner in which a sensing system may be used to detect a voltage at the LED of a pixel circuit are detailed below with reference to  FIGS. 1-9 . 
     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 sensing system  30 , which may detect a voltage (V OLED ) at an anode side of an LED while the LED receives a particular current value (LED). In some embodiments, the sensing system  30  and/or the display driver  29  may adjust image data provided to the display  26  based at least in part on a difference between an expected voltage at the LED and the sensed voltage at the LED to compensate for aging effects of the LED over time. As will be described in more detail below, the sensing system  30  may sense the voltage levels 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 sensing 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 sensing 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 sensing 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, 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, scan signals), 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, as shown in  FIG. 7 . Although the following description of the pixel driving circuit  90  is illustrated with the N-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 an emission signal (e.g., EM) is provided to a gate of the respective switch (e.g., switch  98 ), the OLED  92  may receive a current that corresponds to the data stored in the capacitor  94  when a switch  100  is open. As the OLED  92  illuminates in response to receiving the current (I OLED ), a voltage (e.g., V OLED ) 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 . 
     With the foregoing in mind, the sensing system  30  may coordinate the operation of the switches in the pixel driving circuit  90  to sense a current (I TFT ) conducted via a drive thin-film-transistor (TFT) (e.g., switch  102 ), which may be used to drive the OLED  92 . By way of operation, a first data voltage (V DATA1 ) may be received via the data line  96  during a programming stage of the pixel drive circuit  90  and a reference voltage (V REF ) may be received via a reference line  106 . Switches  100  and  104  may be closed during the programming stage to charge the capacitor  94  to a voltage value that corresponds to a difference between the first data voltage (V DATA1 ) and the reference voltage (V REF ). During a read-out phase of operation, the sensing system  30  may close the switches  98  and  100 , while opening the switch  104 . As a result, a drive TFT current (I TFT )  108  may be conducted via the switches  98 ,  102 , and  100  into a sensing circuit  110 . 
     The sensing circuit  110  may include any suitable sensor that measures electrical characteristics (e.g., voltage, current) related to a connected node. In one embodiment, the sensing circuit  110  may include an active-front end (AFE) circuit that detects a voltage level or a current amount. The sensed drive TFT current (I TFT )  108  may be stored in a suitable storage component or the like for further analysis. 
     As illustrated in  FIG. 7 , the OLED  92  remains off during the programming and read-out stages of operation. That is, since the switch  100  is closed during both the programming stage and the read-out stage, the drive TFT current (I TFT )  108  does not conduct through the OLED  92 . As such, the OLED  92  is not illuminated during these stages and thus do not cause the display  26  to depict any image data. In this way, the sensing system  30  may perform these operations during off time when the display  26  is not actively in use. 
     By employing the programming and read-out stages of operation as described above, the drive TFT current (I TFT )  108  can be characterized based at least in part on certain electrical properties of the pixel drive circuit  90 . For example, drive TFT current (I TFT )  108  may be represented as shown below in Equation (1):
 
 I   TFT   =K ( V   DATA1   −V   REF   −V   TH ) 2   (1)
 
where K is a constant, V DATA1  is the first data voltage provided via the data line  96 , V REF  is the reference voltage provided via the reference line  106 , and V TH  is a threshold voltage of the OLED  92 .
 
     With the foregoing in mind,  FIG. 8  illustrates a circuit diagram that depicts the sensing of an OLED current (I OLED ), which may be used to determine an OLED voltage (V OLED ) of the OLED  92  based at least in part on the drive TFT current (I TFT )  108  described above. That is, the sensing system  30  may coordinate the operations of the switches in the pixel driving circuit  90  to cause the OLED current (I OLED ) or the current conducted in the OLED  92  while the OLED  92  is being programmed to be sent to the sensing circuit  110 . In some embodiments, the sensing system  30  may sweep through data voltages until the OLED current (I OLED ) substantially matches the drive TFT current (I TFT )  108  described above. Using the known data voltages provided to pixel driving circuit  90  to cause the OLED current (I OLED ) to substantially match the drive TFT current (I TFT )  108 , the sensing system  30  may determine the OLED voltage (V OLED ) that corresponds to the OLED  92  for a particular current, thereby sensing the OLED voltage (V OLED ). 
     Referring now to  FIG. 8 , the sensing system  30  may initially close switches  98  and  109  and open switch  100  during a programming stage of operation. In addition, the sensing system  30  may send a second data voltage (VDATA 2 ) to the data line  96 , thereby providing a gate signal to the switch  102 . The resulting OLED current (I OLED )  112  may initially be provided to the OLED  92  to program the OLED  92 . 
     During a read-out stage of operation, the sensing system  30  may open the switch  109  and close the switch  100 . As a result, the OLED current (I OLED )  112  may be input into the sensing circuit  110 , which may sense a value or amount of current provided via the OLED current (I OLED )  112 . The OLED current (I OLED )  112  may be characterized according to Equation (2) shown below:
 
 I   OLED   =K ( V   DATA2   −V   OLED   −V   TH ) 2   (2)
 
where V DATA2  corresponds to the second data voltage provided to the pixel driving circuit  90 .
 
     In certain embodiments, the sensing system  30  may adjust the second data voltage provided to the pixel driving circuit  90  until the OLED current (I OLED )  112  substantially matches (e.g., within 1-10%) the drive TFT current (I TFT )  108  stored in the storage component. By setting Equations (1) and (2) equal to each other, as shown in Equation (3), the sensing system  30  may solve for the OLED voltage (V OLED ), as shown in Equation (4).
 
 K ( V   DATA1   −V   REF   −V   TH ) 2   =K ( V   DATA2   −V   OLED   −V   TH ) 2   (3)
 
 V   OLED   =V   DATA1   −V   DATA2   −V   REF   (4)
 
     Keeping the foregoing in mind,  FIG. 9  illustrates a flow chart of a method  120  for determining the OLED voltage (V OLED ) discussed above with reference to  FIGS. 7 and 8 . For the purposes of discussion, the following description of the method  120  will be described as being performed by the sensing system  30 , but it should be noted that any suitable processing device may perform the method  120 . Moreover, although the method  120  is described in a particular order, it should be understood that the method  120  may be performed in any suitable order. 
     Referring now to  FIG. 9 , at block  122 , the sensing system  30  may send a first data voltage (V DATA1 ) to a pixel driving circuit  90  of a particular pixel  82  in the display  26 . The first data voltage (V DATA1 ) may be a test value that is known to the sensing system  30 , used for testing the aging parameter of the OLED  92  during manufacturing, or the like. 
     At block  124 , the sensing system  30  may determine the drive TFT current  108  in the pixel circuit  90  based at least in part on the programming and read-out operations described above with reference to  FIG. 8 . That is, the sensing system  30  may coordinate the operations of the switches  98 ,  100 ,  102 , and  104  to receive the first data voltage (V DATA1 ) at the gate of the switch  102  and the capacitor  94 . The sensing system  30  may then coordinate the operations of the switches  98 ,  100 ,  102 , and  104  to direct the drive TFT current (I TFT ) to the sensing circuit  110  to measure the drive TFT current (I TFT ). 
     After sensing the drive TFT current (I TFT ), the sensing system  30  may, at block  126 , send a second data voltage (V DATA2 ) to the pixel driving circuit  90 . The second data voltage (V DATA2 ) may be different from the first data voltage (V DATA1 ) or the same. In any case, the second data voltage (V DATA2 ) is intended to cause the OLED  92  to receive a current (I OLED ) that substantially matches the drive TFT current (I TFT ) determined at block  124 . 
     As such, at block  128 , the sensing system  30  may determine the OLED current (I OLED ) based at least in part on the programming and read-out operations described above with reference to  FIG. 8 . That is, the sensing system  30  may coordinate the operations of the switches  98 ,  100 ,  102 , and  104  to receive the second data voltage (V DATA2 ) at the gate of the switch  102  and the capacitor  94 . The sensing system  30  may then coordinate the operations of the switches  98 ,  100 ,  102 , and  104  to direct the OLED current (I OLED ) to the sensing circuit  110  to measure the OLED current (I OLED ). 
     At block  130 , the sensing system  30  may determine whether the sensed drive TFT current (I TFT ) substantially matches (e.g., within 1-10%) or equals the sensed OLED current (I OLED ). If the sensed drive TFT current (I TFT ) does not substantially match or equal the sensed OLED current (I OLED ), the sensing system  30  may proceed to block  132  and adjust the second data voltage (V DATA2 ). The sensing system  30  may then return to block  126  and send the adjusted second data voltage (V DATA2 ) to the pixel drive circuit  90 . 
     If, however, the sensed drive TFT current (I TFT ) does substantially match or equal the sensed OLED current (I OLED ), the sensing system  30  may proceed to block  134  and determine the OLED voltage (V OLED ) based at least in part on Equations (3) and (4) provided above. At block  136 , the sensing system  30  may use the OLED voltage (V OLED ) to determine an adjustment to pixel data or image data received by the display driver  29 . That is, as discussed above, the OLED voltage (V OLED ) may represent a degradation or aging of the OLED  92  over time. As the OLED  92  ages, the threshold voltage (V TH ) that corresponds to operating the OLED  92  may shift. To compensate for this shift, the sensing system  30  may determine a difference between an expected voltage at the anode of the OLED  92  for a target current (e.g., I TFT ) and the sensed voltage (e.g., V OLED ) at the anode of the OLED  92  when the OLED  92  receives the target current. Based at least in part on this difference, the sensing system  30 , the display driver  29 , or other suitable component may determine a compensation value (e.g., ΔV) to apply to the pixel data received by the display driver  29 . As a result, the display  26  may present image data that more accurately represents the desired color and luminance values of the input image data. 
     By employing the systems and methods described herein, the sensing system  30  may detect for aging effects to OLEDs without illuminating the OLEDs as compared to other sensing schemes. Since 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, each OLED ages in a different manner. As such, the presently disclosed embodiments may enable the sensing of the OLED voltage to assist the display driver  29  in depicting image data via the display  26  while compensating for the effects of the OLED aging. 
     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: 20211026
Grant Date: 20211026
Priority Date: 20180907
Inventors: HWANG, INJAE
LIN, HUNG SHENG
NHO, HYUNWOO
CHANG, SUN-IL
ZHANG, RUI
VAHID FAR, MOHAMMAD B.
BRAHMA, KINGSUK
RICHMOND, Jesse A.
KIM, HYUNSOO
TAN, JUNHUA
Assignee: APPLE INC
CPC Classifications: [{"code": "G09G2320/045", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/043", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0295", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2300/0842", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2300/0861", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3233", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G2320/0233", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2300/0852", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2300/0861", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3275", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2310/027", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3233", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G2300/0852", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2300/0861", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3275", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/3233", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G2310/027", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 78219013