PATENT DOCUMENT

Publication Number: US-10642083-B1
Application Number: US-201816008980-A
Country: US
Kind Code: B1

Title: Predictive temperature compensation

Abstract:
Electronic devices and methods for compensating for temperature-dependent fluctuations in a display include receiving a temperature index may be received from a sensor and/or calculations that indicates a temperature of the system, a pixel, a panel, a grid of a panel, or a combination thereof. The temperature is used to predict a voltage change across an emissive element (V HILO ), such as an organic light emitting diode (OLED). This predicted voltage change is then compensated for before emission.

Claims:
What is claimed is: 
     
       1. A method comprising:
 at a processor, obtaining an indication of a temperature; 
 
       using the processor, predicting a voltage change across an emissive element of a display based at least in part on the indication of the temperature; and
 compensating for the predicted voltage change prior to an emission state of the emissive element, wherein the compensating for the predicted voltage change comprises:
 an injection mode in which a voltage is applied to the emissive element, wherein the voltage is an inverse of the predicted voltage change; and 
 a sensing mode, after the injection mode, in which a return current is sensed, wherein the return current indicates a functionality of the emissive element with temperature compensation using the applied voltage. 
 
 
     
     
       2. The method of  claim 1 , wherein obtaining the indication of the temperature comprises receiving a temperature measurement from a temperature sensor. 
     
     
       3. The method of  claim 1 , wherein obtaining the indication of the temperature comprises receiving a calculated temperature for a pixel, grid of pixels, or a panel of grids of pixels. 
     
     
       4. The method of  claim 3 , wherein the calculated temperature is based at least in part on a measured temperature from a temperature sensor. 
     
     
       5. The method of  claim 4 , wherein the calculated temperature comprises an interpolation based on a condition of an electronic device including the display. 
     
     
       6. The method of  claim 1 , wherein compensating for the predicted voltage change comprises using an enhanced sensing voltage during the sensing mode. 
     
     
       7. The method of  claim 6 , wherein the enhanced sensing voltage comprises a static sensing voltage plus an inversion of the predicted voltage change. 
     
     
       8. The method of  claim 1 , wherein predicting the voltage change comprises:
 deriving empirical data indicative of the voltage change corresponding to temperature changes; 
 storing the empirical data in a lookup table; and 
 looking up the predicted voltage change in the lookup table using the indication of the temperature. 
 
     
     
       9. The method of  claim 8 , wherein deriving empirical data indicative of the voltage change corresponding to temperature changes comprises:
 deriving multiple-pass empirical data for each pixel or grid; and 
 averaging the multiple-pass empirical data to the empirical data to reduce possible noise in deriving the empirical data. 
 
     
     
       10. The method of  claim 1 , wherein predicting the voltage change comprises predicting the voltage change based at least in part on a grayscale level to be emitted by the emissive element. 
     
     
       11. The method of  claim 10 , wherein compensating for the predicted voltage comprises:
 applying a compensation voltage for a first set of grayscale levels; and 
 not applying the compensation voltage for a second set of grayscale levels. 
 
     
     
       12. The method of  claim 1 , wherein predicting the voltage change comprises predicting the voltage change based at least in part on a color of the emissive element. 
     
     
       13. A system comprising:
 a display panel comprising a plurality of pixels each comprising an emissive element; 
 a processor configured to:
 determine a voltage level to be used in an emission state for the emissive element; 
 receive a correlation model that correlates temperature to a voltage shift across a corresponding emissive element; 
 receive an indication of a temperature for the system; 
 predict the voltage shift based at least in part on the indication of the temperature and the correlation model; and 
 compensate the voltage level based on the predicted voltage shift, wherein the compensating the voltage level comprises:
 applying a voltage to the emissive element, wherein the voltage is an inverse of the predicted voltage shift; and 
 sensing, after the voltage is applied to the emissive element, a return current indicating a functionality of the emissive element with temperature compensation using the applied voltage. 
 
 
 
     
     
       14. The system of  claim 13 , wherein the voltage shift is at least partially attributable to parasitic capacitance in the display panel. 
     
     
       15. The system of  claim 13 , comprising a temperature sensor, wherein the processor receives the indication of the temperature from the temperature sensor as a temperature measurement. 
     
     
       16. The system of  claim 15 , wherein the indication of the temperature comprises an overall system temperature for the system, and the correlation model correlates the overall system temperature to a temperature at a respective emissive element. 
     
     
       17. The system of  claim 15 , wherein a pixel of the plurality of pixels comprises sensing circuitry configured to sense the return current. 
     
     
       18. Non-transitory, computer-readable, and tangible medium storing instructions thereon that, when executed, are configured to cause a processor to:
 receive an indication of a temperature of a display panel; 
 receive a grayscale level of an emissive element of the display panel; 
 predict a voltage shift at the emissive element based at least in part on the grayscale level and the indication of the temperature; and 
 compensate for the predicted voltage shift during a sensing phase for the emissive element, wherein compensating for the predicted voltage comprises:
 applying a voltage to the emissive element, wherein the voltage is an inverse of the predicted voltage shift; and 
 sensing, after the voltage is applied to the emissive element, a return current indicating a functionality of the emissive element with temperature compensation using the applied voltage. 
 
 
     
     
       19. The non-transitory, computer-readable, and tangible medium of  claim 18 , wherein the instructions are configured to determine an emission color for the emissive element, and wherein predicting the voltage shift comprises predicting the voltage shift based at least in part on the emission color.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/712,460, filed Sep. 22, 2017, which claims the benefit of U.S. Provisional Application No. 62/511,818, filed on May 26, 2017, the contents of which are herein expressly incorporated by reference for all purposes. 
    
    
     BACKGROUND 
     The present disclosure relates generally to techniques to cancelling noise resultant in a display. More specifically, the present disclosure relates generally to techniques for compensating for artifacts and/or non-uniformity in a display panel based at least in part on display variations due to temperature. 
     This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
     Electronic display panels are used in a plethora of electronic devices. These display panels typically consist of multiple pixels that emit light. These pixels may be formed using self-emissive units (e.g., light emitting diode) or pixels that utilize units that are backlit (e.g., liquid crystal diode). These displays may undergo temporal temperature shifts and/or temporal differences across the panel that may cause the display to behave differently than intended, such as artifacts or non-uniform displaying due to temperature changes. 
     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. 
     To address temperature-based display fluctuations, a temperature index may be received from a sensor and/or calculations that indicates a temperature of the system, a pixel, a panel, a grid of a panel, or a combination thereof. The temperature is used to predict a voltage change across an emissive element (V HILO ), such as an organic light emitting diode (OLED). This predicted voltage change is then compensated for before emission. For instance, the pixel voltage (e.g., voltage of a node in the pixel) is pre-adjusted to compensate for the predicted V HILO  change. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various aspects of this disclosure may be better understood upon reading the following detailed description and upon reference to the drawings in which: 
         FIG. 1  is a schematic block diagram of an electronic device including a display, in accordance with an embodiment; 
         FIG. 2  is a perspective view of a notebook computer representing an embodiment of the electronic device of  FIG. 1 , in accordance with an embodiment; 
         FIG. 3  is a front view of a hand-held device representing another embodiment of the electronic device of  FIG. 1 , in accordance with an embodiment; 
         FIG. 4  is a front view of another hand-held device representing another embodiment of the electronic device of  FIG. 1 , in accordance with an embodiment; 
         FIG. 5  is a front view of a desktop computer representing another embodiment of the electronic device of  FIG. 1 , in accordance with an embodiment; 
         FIG. 6  is a front view of a wearable electronic device representing another embodiment of the electronic device of  FIG. 1 , in accordance with an embodiment; 
         FIG. 7  illustrates a block diagram view a circuit diagram of the display of  FIG. 1 , in accordance with an embodiment; 
         FIG. 8  illustrates a block diagram of a sensing period during a progressive scan of a display, in accordance with an embodiment; 
         FIG. 9  illustrates a block diagram view of a simplified pixel in the circuit diagram of  FIG. 9 , in accordance with an embodiment; 
         FIG. 10A  illustrates a graph of a relationship between an OLED current and V HILO  in various temperatures for a red pixel, in accordance with an embodiment; 
         FIG. 10B  illustrates a graph of a relationship between an OLED current and V HILO  in various temperatures for a green pixel, in accordance with an embodiment; 
         FIG. 10CA  illustrates a graph of a relationship between an OLED current and V HILO  in various temperatures for a blue pixel, in accordance with an embodiment; 
         FIG. 11A  illustrates a block diagram view a graph showing a relationship between gray level and V HILO  shift for a red pixel, in accordance with an embodiment; 
         FIG. 11B  illustrates a block diagram view a graph showing a relationship between gray level and V HILO  shift for a green pixel, in accordance with an embodiment; 
         FIG. 11C  illustrates a block diagram view a graph showing a relationship between gray level and V HILO  shift for a blue pixel, in accordance with an embodiment; 
         FIG. 12  illustrates a schematic diagram of pixel control circuitry for an OLED, in accordance with an embodiment; 
         FIG. 13  is timing diagram of ideal operation of the pixel control circuitry of  FIG. 12 , in accordance with an embodiment; 
         FIG. 14  is timing diagram of non-ideal operation of the pixel control circuitry of  FIG. 12 , in accordance with an embodiment; 
         FIG. 15  is a flow chart illustrating a process for compensating for VHILO fluctuations due to temperature, in accordance with an embodiment; 
         FIG. 16  is a block diagram of a system used to perform the process of  FIG. 15 , in accordance with an embodiment; 
         FIG. 17  is a schematic diagram of the pixel control circuitry of  FIG. 12  in an emission phase, in accordance with an embodiment; 
         FIG. 18  is a schematic diagram of the pixel control circuitry of  FIG. 12  in a data write phase, in accordance with an embodiment; 
         FIG. 19  is a schematic diagram of the pixel control circuitry of  FIG. 12  in an sense injection voltage phase, in accordance with an embodiment; and 
         FIG. 20  is a schematic diagram of the pixel control circuitry of  FIG. 12  in a sense phase, in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
     One or more specific embodiments will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     Display panel quality and/or uniformity can be negatively effected by temperature. For example, as the temperature changes a voltage (V HILO ) across the high and low terminals of a light-emissive solid-state device may cause unintended variation of light emission from the light-emissive solid-state device. The light-emissive solid-state device may include an organic light emitting diode (OLED), a light emitting diode (LED), or the like. Herein, the following refers to an OLED, but some embodiments may include any other light-emissive solid-state devices. 
     Specifically, as the temperature changes in a pixel around the OLED, a corresponding driving transistor (e.g., thin-film transistor TFT) fluctuates a voltage/current provided to the OLED. Using a temperature index and a relationship between system temperature and a temperature of the OLED, a V HILO  may be predicted and compensated for even when direct measurement of the OLED temperature is impossible or impractical. 
     With the foregoing in mind and referring first to  FIG. 1 , an electronic device  10  according to an embodiment of the present disclosure may include, among other things, one or more processor(s)  12 , memory  14 , nonvolatile storage  16 , a display  18 , input structures  20 , an input/output (I/O) interface  22 , a power source  24 , and interface(s)  26 . The various functional blocks shown in  FIG. 1  may include hardware elements (e.g., including circuitry), software elements (e.g., including computer code stored on a computer-readable medium) or a combination of both hardware and software elements. It should be noted that  FIG. 1  is merely one example of a particular implementation and is intended to illustrate the types of components that may be present in electronic device  10 . 
     In the electronic device  10  of  FIG. 1 , the processor(s)  12  and/or other data processing circuitry may be operably coupled with the memory  14  and the nonvolatile storage  16  to perform various algorithms. Such programs or instructions, including those for executing the techniques described herein, executed by the processor(s)  12  may be stored in any suitable article of manufacture that includes one or more tangible, computer-readable media at least collectively storing the instructions or routines, such as the memory  14  and the nonvolatile storage  16 . The memory  14  and the nonvolatile storage  16  may include any suitable articles of manufacture for storing data and executable instructions, such as random-access memory, read-only memory, rewritable flash memory, hard drives, and/or optical discs. Also, programs (e.g., an operating system) encoded on such a computer program product may also include instructions that may be executed by the processor(s)  12  to enable the electronic device  10  to provide various functionalities. 
     In certain embodiments, the display  18  may be a liquid crystal display (e.g., LCD), which may allow users to view images generated on the electronic device  10 . In some embodiments, the display  18  may include a touch screen, which may allow users to interact with a user interface of the electronic device  10 . Furthermore, it should be appreciated that, in some embodiments, the display  18  may include one or more light emitting diode (e.g., LED) displays, or some combination of LCD panels and LED panels. 
     The input structures  20  of the electronic device  10  may enable a user to interact with the electronic device  10  (e.g., pressing a button to increase or decrease a volume level, a camera to record video or capture images). The I/O interface  22  may enable the electronic device  10  to interface with various other electronic devices. Additionally or alternatively, the I/O interface  22  may include various types of ports that may be connected to cabling. These ports may include standardized and/or proprietary ports, such as USB, RS232, Apple&#39;s Lightning® connector, as well as one or more ports for a conducted RF link. 
     As further illustrated, the electronic device  10  may include the power source  24 . The power source  24  may include any suitable source of power, such as a rechargeable lithium polymer (e.g., Li-poly) battery and/or an alternating current (e.g., AC) power converter. The power source  24  may be removable, such as a replaceable battery cell. 
     The interface(s)  26  enable the electronic device  10  to connect to one or more network types. The interface(s)  26  may also include, for example, interfaces for a personal area network (e.g., PAN), such as a Bluetooth network, for a local area network (e.g., LAN) or wireless local area network (e.g., WLAN), such as an 802.11 Wi-Fi network or an 802.15.4 network, and/or for a wide area network (e.g., WAN), such as a 3rd generation (e.g., 3G) cellular network, 4th generation (e.g., 4G) cellular network, or long term evolution (e.g., LTE) cellular network. The interface(s)  26  may also include interfaces for, for example, broadband fixed wireless access networks (e.g., WiMAX), mobile broadband Wireless networks (e.g., mobile WiMAX), and so forth. 
     In certain embodiments, the electronic device  10  may include a sensing system  28 , which may include a chip, such as processor or ASIC, that may control various aspects of the display  18 . For instance, the sensing system  28  may use a voltage/current that is to be provided to a pixel of the display  18  to sense the gray level depicted by the pixel. Generally, when the same voltage/current is provided to each pixel of the display  18 , each pixel should depict the same gray level. However, due to various sources of noise or non-uniformity (e.g., temperature response), the same voltage/current being applied to a number of pixels may result in a variety of different gray levels depicted across the number of pixels. As such, the sensing system  28  may sense a threshold voltage of each pixel, a power output by each pixel, an amount of current provided to each pixel and the sensing system  28  may send the threshold voltage to the processor(s)  12  or other circuit component to determine a compensation value for each pixel. The processor(s)  12  may then adjust the data signals provided to each pixel based on the compensation value. Although the sensing system  28  is described as providing the threshold voltage or sensitivity characteristics to another circuit component that may determine a compensation value, it should be noted that, in some embodiments, the sensing system  28  may also perform the determination of the compensation value and the modification of the data provided to a pixel based on the compensation value. 
     The electronic device  10  may also include one or more temperature sensors  29  that enable measurement of a temperature in and/or around the electronic device. A single sensor may be used to find an overall system temperature. Additionally or alternatively, a grid system may be used to track temperatures at various locations within the device using direct measurements from a temperature sensor in at least a portion of the grid locations. Furthermore, in some embodiments, some temperatures about the display may be interpolated from conditions (e.g., camera running, display running, processor usage, etc.). For example, a temperature of portions near a camera of the electronic device  10  may be set as being higher than a measured temperature away from the camera when the camera is operating. 
     By way of example, the electronic device  10  may represent a block diagram of the notebook computer depicted in  FIG. 2 , the handheld device depicted in either of  FIG. 3  or  FIG. 4 , the desktop computer depicted in  FIG. 5 , the wearable electronic device depicted in  FIG. 6 , or similar devices. It should be noted that the processor(s)  12  and/or other data processing circuitry may be generally referred to herein as “data processing circuitry.” Such data processing circuitry may be embodied wholly or in part as software, firmware, hardware, or any combination thereof. Furthermore, the data processing circuitry may be a single contained processing module or may be incorporated wholly or partially within any of the other elements within the electronic device  10 . 
     In certain embodiments, the electronic device  10  may take the form of a computer, a portable electronic device, a wearable electronic device, or other type of electronic device. Such computers may include computers that are generally portable (e.g., such as laptop, notebook, and tablet computers) as well as computers that are generally used in one place (e.g., such as conventional desktop computers, workstations and/or servers). In certain embodiments, the electronic device  10  in the form of a computer may be a model of a MacBook®, MacBook® Pro, MacBook Air®, iMac®, Mac® mini, or Mac Pro® available from Apple Inc. By way of example, the electronic device  10 , taking the form of a notebook computer  30 A, is illustrated in  FIG. 2  in accordance with one embodiment of the present disclosure. The depicted computer  30 A may include a housing or enclosure  32 , a display  18 , input structures  20 , and ports of the I/O interface  22 . In one embodiment, the input structures  20  (e.g., such as a keyboard and/or touchpad) may be used to interact with the computer  30 A, such as to start, control, or operate a GUI or applications running on computer  30 A. For example, a keyboard and/or touchpad may allow a user to navigate a user interface or application interface displayed on display  18 . 
       FIG. 3  depicts a front view of a handheld device  30 B, which represents one embodiment of the electronic device  10 . The handheld device  30 B may represent, for example, a portable phone, a media player, a personal data organizer, a handheld game platform, or any combination of such devices. By way of example, the handheld device  30 B may be a model of an iPod® or iPhone® available from Apple Inc. of Cupertino, Calif. 
     The handheld device  30 B may include an enclosure  32  to protect interior components from physical damage and to shield them from electromagnetic interference. The enclosure  32  may surround the display  18 , which may display indicator icons. The indicator icons may indicate, among other things, a cellular signal strength, Bluetooth connection, and/or battery life. The I/O interfaces  22  may open through the enclosure  32  and may include, for example, an I/O port for a hard-wired connection for charging and/or content manipulation using a connector and protocol, such as the Lightning connector provided by Apple Inc., a universal serial bus (e.g., USB), one or more conducted RF connectors, or other connectors and protocols. 
     The illustrated embodiments of the input structures  20 , in combination with the display  18 , may allow a user to control the handheld device  30 B. For example, a first input structure  20  may activate or deactivate the handheld device  30 B, one of the input structures  20  may navigate user interface to a home screen, a user-configurable application screen, and/or activate a voice-recognition feature of the handheld device  30 B, while other of the input structures  20  may provide volume control, or may toggle between vibrate and ring modes. Additional input structures  20  may also include a microphone that may obtain a user&#39;s voice for various voice-related features, and a speaker to allow for audio playback and/or certain phone capabilities. The input structures  20  may also include a headphone input (not illustrated) to provide a connection to external speakers and/or headphones and/or other output structures. 
       FIG. 4  depicts a front view of another handheld device  30 C, which represents another embodiment of the electronic device  10 . The handheld device  30 C may represent, for example, a tablet computer, or one of various portable computing devices. By way of example, the handheld device  30 C may be a tablet-sized embodiment of the electronic device  10 , which may be, for example, a model of an iPad® available from Apple Inc. of Cupertino, Calif. 
     Turning to  FIG. 5 , a computer  30 D may represent another embodiment of the electronic device  10  of  FIG. 1 . The computer  30 D may be any computer, such as a desktop computer, a server, or a notebook computer, but may also be a standalone media player or video gaming machine. By way of example, the computer  30 D may be an iMac®, a MacBook®, or other similar device by Apple Inc. It should be noted that the computer  30 D may also represent a personal computer (e.g., PC) by another manufacturer. A similar enclosure  32  may be provided to protect and enclose internal components of the computer  30 D such as the display  18 . In certain embodiments, a user of the computer  30 D may interact with the computer  30 D using various peripheral input devices, such as the keyboard  37  or mouse  38 , which may connect to the computer  30 D via an I/O interface  22 . 
     Similarly,  FIG. 6  depicts a wearable electronic device  30 E representing another embodiment of the electronic device  10  of  FIG. 1  that may be configured to operate using the techniques described herein. By way of example, the wearable electronic device  30 E, which may include a wristband  43 , may be an Apple Watch® by Apple, Inc. However, in other embodiments, the wearable electronic device  30 E may include any wearable electronic device such as, for example, a wearable exercise monitoring device (e.g., pedometer, accelerometer, heart rate monitor), or other device by another manufacturer. The display  18  of the wearable electronic device  30 E may include a touch screen (e.g., LCD, an organic light emitting diode display, an active-matrix organic light emitting diode (e.g., AMOLED) display, and so forth), which may allow users to interact with a user interface of the wearable electronic device  30 E. 
     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  28  of  FIG. 1 . Generally, the brightness depicted by each respective pixel in the display  18  is generally controlled by varying an electric field associated with each respective pixel in the display  18 . Keeping this in mind,  FIG. 7  illustrates one embodiment of a circuit diagram of the display  18  that may generate the electrical field that energizes each respective pixel and causes each respective pixel to emit light at an intensity corresponding to an applied voltage. As shown, display  18  may include a self-emissive pixel array  80  having an array of self-emissive pixels  82 . 
     The self-emissive pixel array  80  is shown having a controller  84 , a power driver  86 A, an image driver  86 B, and the array of self-emissive pixels  82 . The self-emissive pixels  82  are driven by the power driver  86 A and image driver  86 B. Each power driver  86 A and image driver  86 B may drive one or more self-emissive pixels  82 . In some embodiments, the power driver  86 A and the image driver  86 B may include multiple channels for independently driving multiple self-emissive pixels  82 . The self-emissive pixels may include any suitable light-emitting elements, such as organic light emitting diodes (OLEDs), micro-light-emitting-diodes (p-LEDs), and the like. 
     The power driver  86 A may be connected to the self-emissive pixels  82  by way of scan lines S 0 , S 1 , . . . S m-1 , and S m  and driving lines D 0 , D 1 , . . . D m-1 , and D m . The self-emissive pixels  82  receive on/off instructions through the scan lines S 0 , S 1 , . . . S m-1 , and S m  and generate driving currents corresponding to data voltages transmitted from the driving lines D 0 , D 1 , . . . D m-1 , and D m . The driving currents are applied to each self-emissive pixel  82  to emit light according to instructions from the image driver  86 B through driving lines M 0 , M 1 , . . . M n-1 , and M n . Both the power driver  86 A and the image driver  86 B transmit voltage signals through respective driving lines to operate each self-emissive 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 self-emissive pixel  82 . 
     The controller  84  may control the color of the self-emissive pixels  82  using image data generated by the processor(s)  12  and stored into the memory  14  or provided directly from the processor(s)  12  to the controller  84 . The sensing system  28  may provide a signal to the controller  84  to adjust the data signals transmitted to the self-emissive pixels  82  such that the self-emissive pixels  82  may depict substantially uniform color and luminance provided the same current input in accordance with the techniques that will be described in detail below. 
     With the foregoing in mind,  FIG. 8  illustrates an embodiment in which the sensing system  28  may incorporate a sensing period during a progressive data scan of the display  18 . In some embodiments, the controller  84  may send data (e.g., gray level voltages or currents) to each self-emissive pixel  82  via the power driver  86 A on a row-by-row basis. That is, the controller  84  may initially cause the power driver  86 A to send data signals to the pixels  82  of the first row of pixels on the display  18 , then the second row of pixels on the display  18 , and so forth. When incorporating a sensing period, the sensing system  28  may cause the controller  84  to pause the transmission of data via the power driver  86 A for a period of time (e.g., 100 microseconds) during the progressive data scan at a particular row of the display (e.g., for row X). The period of time in which the power driver  86 A stops transmitting data corresponds to a sensing period  102 . 
     As shown in  FIG. 8 , the progressive scan  104  is performed between a back porch  106  and a front porch  108  of a frame  110  of data. The progressive scan  104  is interrupted by the sensing period  102  while the power driver  86 A is transmitting data to row X of the display  18 . The sensing period  102  corresponds to a period of time in which a data signal may be transmitted to a respective pixel  82 , and the sensing system  28  may determine certain sensitivity properties associated to the respective pixel  82  based on the pixel&#39;s reaction to the data signal. The sensitivity properties may include, for example, power, luminance, and color values of the respective pixel when driven by the provided data signal. After the sensing period  102  expires, the sensing system  28  may cause the power driver  86 A to resume the progressive scan  104 . As such, the progressive scan  104  may be delayed by a data program delay  112  due to the sensing period  102 . 
     In order to incorporate the sensing period  102  into the progressive scans of the display  18 , pixel driving circuitry may transmit data signals to pixels of each row of the display  18  and may pause its transmission of data signals during any portion of the progressive scan to determine the sensitivity properties of any pixel on any row of the display  18 . Moreover, as sizes of displays decrease and smaller bezel or border regions are available around the display, integrated gate driver circuits may be developed using a similar thin film transistor process as used to produce the transistors of the pixels  82 . In some embodiments, the sensing periods may be between progressive scans of the display. 
       FIG. 9  is a block diagram for a simplified pixel  140  that controls emission of an OLED  142 . As illustrated, the OLED  142  is an active matrix OLED (AMOLED) that uses a storage capacitor  144  that enables data to be written to the storage capacitor  144  to multiple pixel rows and/or columns sequentially. The storage capacitor  144  maintains a line pixel state in the pixel  140 . The pixel  140  also includes a current source  146  that may be representative of one or more TFTs that provide a current to the OLED  142 . 
     The output of the current source  146  depends upon the voltage stored in the storage capacitor  144 . For example, the storage capacitor  144  may equal a gate-source voltage V GS  of a TFT of the current source  146 . However, the voltage in the storage capacitor  144  may change due to parasitic capacitances represented by the capacitor  148 . The amount of parasitic capacitance may change with temperature that causes operation of the current source  146  to vary thereby causing changes in emission of the OLED  142  based at least in part on temperature fluctuations. Temperature may also cause other fluctuations in the pixel current through the OLED  42 , such as fluctuations of operation of the TFTs making up the current source and/or operation of the OLED  46  itself. 
       FIGS. 10A-10C  illustrates graph of V HILO  versus the current I OLED  through the OLED  42  over various temperatures (e.g., 45° C. to 30° C.). However, the change may vary based on a color of the OLED. For example,  FIG. 10A  may represent a change in ratio of V HILO  to I OLED  for a red color OLED,  FIG. 10B  may represent a change in ratio of V HILO  to I OLED  for a green color OLED, and  FIG. 10C  may represent a change in ratio of V HILO  to I OLED  for a blue color OLED. 
     Furthermore, grayscale levels may also affect a change in an amount of shift in V HILO  and its corresponding I OLED .  FIGS. 11A-11C  illustrate such relationships. As with the relationship between V HILO  and I OLED , the relationship between gray level and V HILO  shift may be color-dependent. For example,  FIG. 11A  may represent a relationship between a gray level and a V HILO  shift for a red OLED,  FIG. 11B  may represent a relationship between a gray level and a V HILO  shift for a green OLED, and  FIG. 11C  may represent a relationship between a gray level and a V HILO  shift for a blue OLED. 
       FIG. 12  illustrates a more detailed depiction of an embodiment of a pixel control circuitry. The pixel driving circuitry  170  may include a number of semiconductor devices that may coordinate the transmission of data signals to an OLED  172  of a respective pixel  82 . In some embodiments, the pixel driving circuitry  170  may receive input signals (e.g., an emission signal and/or one or more scan signals). 
     With this in mind, the pixel driving circuitry  170  may include switches  174 ,  178 , and  180  along with transistor  176 . These switches may include any type of suitable circuitry, such as transistors. Transistors (e.g., transistor  176 ) may include N-type and/or P-type transistors. That is, depending of the type of transistors used within the pixel driving circuitry  170 , the waveforms or signals provided to each transistor should be coordinated in a manner to cause the pixel control circuitry. 
     As shown in  FIG. 12 , the transistor  176  and the switches  174 ,  178 , and  180  may be driven by scan and emission signals. Based on these input signals, the pixel driving circuitry  170  may implement a number of pixel driving schemes for a respective pixel. 
     As illustrated in  FIG. 13 , the scan and/or emission signals may cause the pixel control circuitry  170  to be placed in a data write mode  182 . During the data write mode  182 , a voltage V ANODE  at a node  184  in  FIG. 11  between the transistor  176  and the switch  180  is driven to a voltage V DATA  of the data. Returning to  FIG. 12 , in a subsequent emission period  186  (e.g., caused by the emission signal), the V ANODE  becomes a sum of a VSSEL supply voltage (e.g., −3V˜−2.5V), the V HILO . The gate-source voltage V GS  of the transistor  176  (across storage capacitor  188 ) also changes by ΔV GS  during the emission period  186 . This ΔV GS  is determined by V HILO  sensitivity and the V ANODE . The V HILO  sensitivity is a ratio of a parasitic capacitance at the gate of transistor  176  (represented by gate capacitor  190  in  FIG. 11 ) to a sum of capacitances of the storage capacitor  188  and the parasitic capacitance  190 . 
                       Δ   ⁢           ⁢     V   GS       =         V   HILO     ⁢           ⁢   sensitivity   ×   Δ   ⁢           ⁢     V   ANODE       =         C   GATE       (       C   ST     +     C   GATE       )       ×   Δ   ⁢           ⁢     V   ANODE           ,           (     Equation   ⁢           ⁢   1     )               
where C GATE  is the capacitance of parasitic capacitance at the gate and C ST  is the capacitance of the storage capacitor  188 .
 
     Although the pixel sensitivity ratio may be reduced by increasing capacitance of the storage capacitor, size in the pixel control circuitry  170  may be limited due to display size, compactness of pixels (i.e., pixels-per-inch), part costs, and/or other constraints. In other words, the V HILO  sensitivity cannot be reasonably eliminated. Thus, in realistic situations, as previously discussed, V HILO  may shift due to temperature and/or other causes.  FIG. 14  illustrates an embodiment of emission levels in response to a V HILO  shift. The data write period  182  remains unchanged. However, in emission period  192  the V ANODE  is the sum of VSSEL and V HILO  including any shift that has occurred on the V HILO  as voltage of ΔV HILO  due to temperature and/or other changes. Since the ΔV HILO  shifts the V ANODE , the ΔV HILO  also shifts the V GS . Thus, the ΔV HILO  creates a V GS  error ΔV gs  that is attributable to the V HILO  sensitivity and the ΔV HILO  that has been added to the V ANODE . 
                     Δ   ⁢           ⁢     V   gs       =         C   GATE       (       C   ST     +     C   GATE       )       ×   Δ   ⁢           ⁢     V   HILO               (     Equation   ⁢           ⁢   2     )               
In other words, this ΔV gs  error is created by parasitic capacitance on the gate of the transistor  176  in a source-follower-type pixel. In other embodiments, the error may be shifted around to other locations due to other parasitic capacitances.
 
     To address these problems a predictive V HILO  model may be used to mitigate a temperature effect on V HILO .  FIG. 15  illustrates an embodiment of a process  200  for mitigating temperature effect on V HILO  variation. The processor  12  obtains an indication of temperature (block  202 ). The indication of temperature may be a direct measurement of a temperature from a temperature sensor. Additionally or alternatively, the indication of the temperature may include adjustments to a measured temperature as an interpolated or calculated temperature. Furthermore, the temperature may be an overall system temperature and/or may include a grid temperature that logically divides the electronic device into regions or grids that have a common temperature indication. 
     The processor  12  then predicts a change in V HILO  based at least in part on the indication of the temperature (block  204 ). If the indication of temperature corresponds to an overall system temperature, the indication of temperature may be interpolated from a system temperature to a temperature for a pixel or group of pixels based on a location of the pixel or group of pixels relative to heat sources in the electronic device  10 , operating states (e.g., camera running, high processor usage, etc.) of the electronic device, an outside temperature (e.g., received via the interface  26 ), and/or other temperature factors. 
     Using either the received indication directly or an interpolation based on the received indication, the prediction may be performed using a lookup table that has been populated using empirical data reflecting how ΔV HILO  is related to temperature for the pixel in an array of pixels in a display panel, a grid of the panel, an entire panel, and/or a batch of panels. This empirical data may be derived at manufacture of the panels. In some embodiments, the empirical data may be captured multiple times and averaged together to reduce noise in the correlation between ΔV HILO  and temperature. In some embodiments, instead of a lookup table with empirically derived data, the empirical data may be used to derive a transfer function that is formed from a curve fit of one or more empirical data gathering passes. 
     As previously note, in addition to temperature, ΔV HILO  may depend on grayscale levels and/or emission color of the OLED  172 . Thus, the prediction of the ΔV HILO  may also be empirically gathered for color effects and/or grayscale levels. In other words, the predicted ΔV HILO  may be based at least in part on the temperature, the (upcoming) grayscale level of the OLED  172 , the color of the OLED  172 , or any combination thereof. 
     The processor  12  compensates a pixel voltage inside the pixel control circuitry  170  to compensate based at least in part on the predicted ΔV HILO  (block  206 ). Compensation includes offsetting the voltage based on the predicted ΔV HILO  by submitting a voltage having an opposite polarity but similar amplitude on the pixel voltage (e.g., V ANODE ). The compensation may also include compensating for other temperature-dependent (e.g., transistor properties) or temperature-independent factors. Furthermore, since some grayscale levels are more likely to be visible due to human detection factors or properties of the grayscale level and ΔV HILO , in some embodiments, the compensation voltage may be applied for some grayscale level content but not applied for other grayscale level content. 
       FIG. 16  illustrates an embodiment of a compensation system  218  that utilizes a correlation model  220  that correlates various voltage shifts to a temperature. As previously discussed, this correlation model  220  may receive data corresponding to a first stored relationship  222  between temperature and ΔV shift at the OLED  172 . Additionally or alternatively, the correlation model  220  may receive data corresponding to a second stored relationship  224  between temperature and ΔV shift at a TFT (e.g., transistor  176 ). The second stored relationship  224  may also include a temperature index indicating a temperature at the TFT based on direct measurements and/or calculations from a system measurement. 
     The correlation model  220  is used by the processor  12  to convert to predict V HILO  (block  226 ) based on the temperature index and a current ΔV as determined from a sensing control  228  used to determine how to drive voltages for operating a pixel. The sensing control  230  is used to control voltages used during an emission state based on results of a sensing phase. Additionally or alternatively, a transfer function may be used from the temperature index/ΔV. This prediction may be made using a first lookup table that converts ΔV and a temperature index to a predicted ΔV HILO . The predicted ΔV HILO  is then used to determine a V SENSE  level that is used in a sensing state to offset the ΔV HILO  using the processor to access a second lookup table (block  232 ). Additionally or alternatively, a transfer function may be used from ΔV HILO  to determine the V SENSE  compensating for the ΔV HILO . 
       FIG. 17  illustrates an embodiment of an emission mode for the pixel control circuitry  170  in an emission state. In the emission state, an I TFT  current  250  is passed through the OLED  172  to cause emission. To achieve a desired level, the V ANODE  may be set to compensate for the ΔV HILO . To achieve this level, voltage at the ANODE may be set during the sensing phase of the display  18 .  FIGS. 18-20  illustrates compensating the V ANODE  for ΔV HILO  due to temperature and/or other factors.  FIG. 18  illustrates a loading step  260  the C ST    188  using V REF    262  and V DATA    264  via the closed switches  174  and  180 .  FIG. 19  illustrates an injection mode  270  that injects a V SENSE    272  that includes a V SENSE  and a compensation for ΔV HILO . The V SENSE  may be a static voltage level that is sufficiently high to determine whether a return current is as expected to determine health (e.g., age) and/or expected functionality of the corresponding pixel.  FIG. 20  illustrates the return current I TFT    282  through the transistor  176  and closed switches  178  and  180  to sensing circuitry  284 . 
     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: 20180614
Publication Date: 20200505
Grant Date: 20200505
Priority Date: 20170526
Inventors: HWANG, INJAE
ZHANG, RUI
LIN, HUNG SHENG
KIM, HYUNSOO
NHO, HYUNWOO
RICHMOND, Jesse A.
RYU, JIE WON
TAN, JUNHUA
BRAHMA, KINGSUK
GAO, SHENGKUI
SHEN, Shiping
CHANG, SUN-IL
Assignee: APPLE INC
CPC Classifications: [{"code": "G02F1/133382", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G2320/041", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3258", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/3696", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3696", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/041", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3258", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133382", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G3/36", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0295", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3233", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G2320/041", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 70461602