PATENT DOCUMENT

Publication Number: US-10565923-B2
Application Number: US-201715700971-A
Country: US
Kind Code: B2

Title: Common-mode noise compensation

Abstract:
Electronic devices and methods for compensating for noise in a display that includes sensing a current in a sensing channel of the display. Compensating for the noise also includes sensing an observation current from noise in an observation channel of the display and scaling the observation current to generate a scaled observation current. The scaled observation current is subtracted from the sense current to generate a compensated output. The compensated output is used to drive compensation operations of the display based at least in part on the compensated output to reduce effects of the noise.

Claims:
What is claimed is: 
     
       1. A method comprising:
 sensing a current in a sensing channel of a display; 
 inducing a differential input mismatch in an observation channel of the display to a level above an differential inherent mismatch in the observation channel; 
 sensing an observation current from noise in the observation channel of the display based at least in part on the differential input mismatch; 
 scaling the observation current to generate a scaled observation current; 
 subtracting the scaled observation current from the sensed current to generate a compensated output; and 
 driving compensation operations of the display based at least in part on the compensated output. 
 
     
     
       2. The method of  claim 1 , wherein the sensed channel comprises a channel corresponding to a pixel of the display. 
     
     
       3. The method of  claim 2 , wherein the observation channel comprises a channel corresponding to a nearby pixel of the display near to the pixel. 
     
     
       4. The method of  claim 3  comprising decoupling the observation channel from a current source configured to supply current to the nearby pixel. 
     
     
       5. The method of  claim 1  comprising calibrating the display, wherein calibrating the display comprises calculating a scaling factor used in scaling the observation current. 
     
     
       6. The method of  claim 5 , wherein the scaling factor is based at least in part on a first calibration output of the sensing channel and a second calibration output of the observation channel during calibration of the display performed prior to sensing the current and sensing the observation current. 
     
     
       7. The method of  claim 6 , comprising inducing a differential input mismatch in the observation channel during calibration. 
     
     
       8. The method of  claim 6 , wherein the scaling factor is calculated using: 
       
         
           
             
               
                 
                   SF 
                   ij 
                 
                 = 
                 
                   
                     G 
                     oj 
                   
                   
                     G 
                     si 
                   
                 
               
               , 
             
           
         
         wherein SFij is the scaling factor for the sensing channel i and the observation channel j, Goj is the second calibration output of the observation channel j, and Gsi is the first calibration output of the sensing channel i. 
       
     
     
       9. The method of  claim 5 , wherein calibrating the display comprises determining a sensing channel calibration output and an observation channel calibration output for each channel of a plurality of channels of the display. 
     
     
       10. The method of  claim 1  comprising sensing the current on the sensing channel using only an inherent differential input mismatch in the sensing channel. 
     
     
       11. The method of  claim 1 , wherein sensing the current and sensing the observation current occur substantially simultaneously. 
     
     
       12. A system comprising:
 a display panel; 
 a first channel configured to sense a sensed parameter sent to a first pixel of a display, wherein the first channel is configured to have only an inherent differential input mismatch during sensing of the first channel; 
 a second channel configured to sense an observation parameter sent to a second pixel of a display, wherein the second channel is configured be induced with an induced differential input mismatch during sensing of the second channel, wherein the induced differential input mismatch has more differential input mismatch than a level corresponding to an inherent differential input mismatch for the second channel; 
 scaling circuitry configured to scale the observation parameter; 
 summing circuitry configured to subtract the scaled observation parameter from the sensed parameter to generate a compensated parameter; and 
 compensation circuitry configured to drive compensation operations of the display based at least in part on the compensated parameter. 
 
     
     
       13. The system of  claim 12 , wherein the sensed parameter and the observation parameter comprise current. 
     
     
       14. The system of  claim 12 , wherein the scaling circuitry is configured to scale the observation parameter using a scaling factor that the scaling circuitry is configure to acquire from a lookup table. 
     
     
       15. The system of  claim 14 , wherein the lookup table is populated during a calibration mode that stores a sensed calibration output and an observation calibration output for each a plurality of channels including the first and second channels, wherein the sensed calibration output and the observation calibration outputs are generated using a same level of the sensed parameter. 
     
     
       16. The system of  claim 15 , wherein the sensed calibration output for each of the plurality of channels is generated using only the inherent differential input mismatch, and the observation calibration output for each of the plurality of channels is generated using a calibration induced differential input mismatch. 
     
     
       17. The system of  claim 16 , wherein the calibration induced differential input mismatch and the induced differential input mismatch include a same level of mismatch. 
     
     
       18. The system of  claim 12  comprising a switch configured to decouple a parameter supply from the second pixel during sensing of the first channel. 
     
     
       19. A method comprising
 sensing a current in a sensing channel of a display having an inherent differential input mismatch; 
 inducing an induced differential input mismatch in an observation channel of the display to a level higher than an inherent amount of differential input mismatch for the observation channel; 
 sensing an observation current from noise in the observation channel; 
 scaling the observation current to generate a scaled observation current using a scaling factor based at least in part on a sensing calibration value corresponding to the sensing channel determined during a calibration mode and an observation calibration value corresponding to the observation channel determined during the calibration mode; 
 subtracting the scaled observation current from the current to generate a compensated output; and 
 compensating operation of the display based at least in part on the compensated output.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Non-Provisional application claiming priority to U.S. Provisional Patent Application No. 62/511,812, entitled “Common-Mode Noise Compensation”, filed May 26, 2017, which is herein incorporated by reference. 
    
    
     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 noise compensation of external common-mode noise in pixels that may be resistant to filtering correction. 
     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 include noise filtering as non-uniformity compensation to reduce noise at each pixel of the display. However, filtering pixels may miss external noise and/or error sources, such as capacitively coupled fluctuations in local supply voltage resulting in a common-mode error. Indeed, filtering may generate erroneous correction values that compromise the effectiveness of the non-uniformity compensation. 
     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 common-mode error, when parameters (e.g., current) of one or more pixels are being sensed through a channel (i.e., the sensing channel), one or more nearby pixels is also sensed through its own channel (i.e., the observation channel) while keeping the pixel emission off for the observation channel. Sensed parameter values from the observation channel are scaled according to the relative mismatches of the sensing and observation channels as determined through an initial calibration process. The scaled parameter may be subtracted from the sensed current value in the sensing channel to determine a compensated sensing value. 
    
    
     
       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 of a single-channel current sensing scheme, in accordance with an embodiment; 
         FIG. 8  illustrates a flow diagram of a process for sensing a current using two channels, in accordance with an embodiment; 
         FIG. 9  illustrates a block diagram view of a dual-channel current sensing scheme used in the process of  FIG. 8 , in accordance with an embodiment; 
         FIG. 10  illustrates a flow diagram of a process  150  for sensing a current using two channels each having differential inputs, in accordance with an embodiment; 
         FIG. 11  illustrates a block diagram view of a dual-channel current sensing scheme with differential input channels employing the process of  FIG. 10 , in accordance with an embodiment; 
         FIG. 12  illustrates a flow diagram of a process for calibrating the noise compensation circuitry to determine a scaling factor used in the process of  FIG. 8 or 10 , in accordance with an embodiment; and 
         FIG. 13  is a block diagram view of calibration scheme used in the process of  FIG. 12 , 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 uniformity can be improved by estimating or measuring a parameter (e.g., current) through pixel, such as an organic light emitting diode (LED). Based on the measured parameter, a corresponding correction value may be applied to compensate for any offsets from an intended value. Per-pixel sensing schemes can employ the use of filters and other processing steps to help reduce or eliminate the unwanted effects of pixel leakage, noise, and other error sources. Although the application generally relates to sensing individual pixels, some embodiments may group pixels for sensing and observation such that at least one channel senses more than a single pixel. However, some external noise and error sources, such as capacitively coupled fluctuations in local supply voltage that result in common-mode error, may not be fully removable through the filtering process, resulting in erroneous correction values that compromise the effectiveness of the non-uniformity compensation. Moreover, this common-mode error is amplified by the inherent mismatches of parasitic capacitance values between different sensing channels within a display as a result of imperfect device process variations. 
     To address this common-mode error, when a given pixel current is being sensed through a channel (i.e., the sensing channel), a nearby pixel is also sensed through its own channel (i.e., the observation channel) while keeping the pixel emission off for the observation channel. Sensed parameter (e.g., current) value from the observation channel is scaled according to the relative mismatches of the sensing and observation channels as determined through an initial calibration process. Then, the scaled parameter is subtracted from the sensed current value from the sensing channel to determine a compensated sensing value. 
     The proximity of the nearby pixel, and hence the observation channel, is dependent on the accuracy level to be used in the system and correspondingly determines the spatial correlation to be used to achieve this accuracy level. 
     The differential input mismatch of the observation channel may be adjustable to ensure that the component of the sensed value attributed to noise and error is higher in the observation channel than it is in the sensing channel. Sensing from both the sensing channel and observation channel may occur at the same time to establish high time correlation. Moreover, the observation channel and/or the sensing channel may utilize single-ended and/or differential sensing channels. 
     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. 
     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. 
     Although the following discusses sensing current through an OLED as a pixel, some embodiments may include measuring other parameters suitable for other pixel types. For example, LED voltage may be sensed at LED pixels near each other in the display. 
       FIG. 7  illustrates a block diagram view of a single-channel current sensing scheme  100 . As illustrated, a target pixel current is provided via a current source  102 . The current provided by the current source  102  then is supplied to a current sensing system  104  via a sensing channel  106 . The sensing channel  106  may include a single-ended or a differential channel. The current sensing system  104  then outputs an output  108  that is used to compensate display panel operation. In other words, in the single-channel current sensing scheme  100 , a single channel  106  is used to detect or estimate pixel current directly from a target pixel. Furthermore, the single-channel current sensing scheme  100  may include amplifiers, filters, analog-to-digital converters, digital-to-analog converters, and/or other circuitry used for processing in the single-channel current sensing scheme  100  that have been omitted from  FIG. 7  for clarity. 
     The single-channel current sensing scheme  100  detects at least some issues for the target pixel. But, common-mode noise sources, such as the noise source  110 , may be picked up by the current sensing system  104  and converted into differential input by any inherent mismatches in the sensing channel  106 . This differential input may result in an error in the sensed current and a resultant error in the pixel current compensation of the output  108 . 
     Instead of using a single channel to sense current, two channels may be used.  FIG. 8  illustrates a flow diagram of a process  120  for sensing a current using two channels. In a sensing channel of a display, a current is sensed through the sensing channel from a target current is driven from a current source (block  122 ). An observation channel of the display is used to detect observation current attributable to noise, such as common-mode noise across the observation and sensing channels (block  124 ). In an observation channel, no current is proactively driven through the channel other than noise generated in the system. For example, the observation channel may be decoupled from a current source used to send signals to a corresponding pixel to cause the pixel to display data. The current sensed on the observation channel is scaled based on a scaling factor determined during calibration (block  126 ). In some embodiments, the calibration may be repeated prior to each sensing operation to ensure accuracy of the calculations using the scaling factor. The scaled current is then subtracted from the current found in the sensed channel to determine a compensated output (block  128 ). The compensated output is used to compensate operation of the display (block  130 ). 
       FIG. 9  illustrates a block diagram view of a dual-channel current sensing scheme  140 . As illustrated, a target pixel current is provided via a current source  142 . The current provided by the current source  142  then is supplied to a current sensing system  144  via a sensing channel  146 . For a pixel near the target pixel, a sensing system  148  is used to detect current through an observation channel  150  that receives current from a noise source  152  (e.g., capacitive coupling). In other words, the observation channel is used to observe noise (e.g., common-mode noise) in the observation channel  150  during driving of the sensing channel  146  to determine a magnitude of the noise (e.g., common-mode noise). 
     To ensure that only noise is passed through the observation channel  150 , the observation channel  150  may be decoupled from a corresponding current source  154  via a switch  155 . A sensed observation current  156  is scaled at scaling circuitry  158  and subtracted from a sensed current  160  at summing circuitry  162  to generate a compensated output  164  indicative of current through the sensing channel  146  substantially attributable to the current provided by the current source  142 . The scaling factor may be determined in a calibration of the display panel to determine an output of each channel in response to an aggressor image/injected signal to determine channel properties to determine a common-mode error between channels. 
     Furthermore, the dual-channel current sensing scheme  140  may include amplifiers, filters, analog-to-digital converters, digital-to-analog converters, and/or other circuitry used for processing in the dual-channel current sensing scheme  140  that have been omitted from  FIG. 9  for clarity. 
     Each channel may include differential inputs. In embodiments with differential input channels, a sensing channel may utilize an inherent differential input mismatch while the observation channel may utilize an intentionally induced differential input mismatch to sense a time-correlated common-mode error.  FIG. 10  illustrates a flow diagram of a process  166  for sensing a current using two channels each having differential inputs. In a sensing channel, a target current is driven from a current source using and sensed with an inherent differential input mismatch (block  168 ). An induced differential mismatch is induced in an observation channel (block  170 ). The observation channel with the induced differential mismatch is used to sense an observation current derived from noise, such as common-mode noise across the observation and sensing channels (block  172 ). In the observation channel, no current is proactively driven through the channel other than noise generated in the system. For example, the observation channel may be decoupled from a current source used to send signals to a corresponding pixel to cause the pixel to display data. The observation current sensed on the observation channel is scaled using scaling factor (block  174 ). As discussed below in relation to  FIGS. 12 and 13 , the scaling factor may be determined from a calibration of the display panel. The scaled current sense is subtracted from the sensed channel to determine a compensated output (block  176 ). The compensated output is used to drive compensation operations of the display (block  178 ). 
       FIG. 11  illustrates a block diagram view of a dual-channel current sensing scheme  180  with differential input channels. As illustrated, a target pixel current is provided via a current source  182 . The current provided by the current source  182  then is supplied to a current sensing system  184  via a sensing channel  186 . The sensing channel  186  includes differential inputs with some inherent differential input mismatch  188  inherent in the sensing channel  186 . 
     For another pixel (e.g., a pixel near to the target pixel), a sensing system  190  is used to detect current through an observation channel  192  that receives current from a noise source  194  (e.g., capacitive coupling). The observation channel  192  includes an induced differential input mismatch  196  that is induced to sense a time-correlated common-mode error with the sensing channel  186 . In other words, the observation channel  192  is used to observe noise (e.g., common-mode noise) in the observation channel  192  during driving of the sensing channel  186  to determine a magnitude of the noise (e.g., common-mode noise). 
     To ensure that only noise is passed through the observation channel  192 , the observation channel  192  may be decoupled from a corresponding current source  198  using a switch  200 . The current source  198  is used to supply data to a pixel corresponding to the observation channel  192 . A sensed observation current  202  is scaled at scaling circuitry  204  and subtracted from a sensed current  206  at summing circuitry  208  to generate a compensated output  210  indicative of current through the sensing channel  186  substantially attributable to the current provided by the current source  182 . 
     Furthermore, the dual-channel current sensing scheme  180  may include amplifiers, filters, analog-to-digital converters, digital-to-analog converters, and/or other circuitry used for processing in the dual-channel current sensing scheme  180  that have been omitted from  FIG. 11  for clarity. 
     The scaling factor may be determined in a calibration of the display panel to determine an output of each channel in response to an aggressor image/injected signal to determine channel properties to determine a common-mode error between channels.  FIG. 12  illustrates a flow diagram of a process  220  for calibrating the noise compensation circuitry. For a plurality of channels in a display, inject a channel with a current with an inherent differential input mismatch (block  222 ). The current may be set using an aggressor image and/or injected signal setting a value for the pixel corresponding to the channel. A first output is sensed for the channel based on the current through the channel with the inherent differential input mismatch (block  224 ). 
     The channel is also tested with an induced differential mismatch by inducing a differential mismatch in the channel (block  226 ). While in the induced mismatch state, the current (e.g., using the same aggressor image/injected signal) is passed into the channel (block  228 ). A second output is sensed for the channel based on the current through the channel with the induced mismatch (block  230 ). 
     Once these outputs are obtained for each channel to be calibrated, the outputs are stored in a lookup table used to establish the scaling factors (block  232 ). For instance, the first output of the sensed channel (G si ) is stored for each channel in an inherent differential sensing mode, and the second output of the sensed channel (G oi ) is stored for each channel in an induced differential observing mode. The storage of these values may be stored in a lookup table, such as that shown below in Table 1. 
                     TABLE 1                  Lookup table for calibration outputs                             Channel                                                 1   2   3   4   . . .   n                                                             Inherent   G s1     G s2     G s3     G s4     . . .   G sn             Mismatch           Induced   G o1     G o2     G o3     G o4     . . .   G on             Mismatch                        
These stored outputs may be used to determine a scaling factor using a relationship between outputs of a sensing channel and an observational channel. For example, the scaling factor that is used to scale observation channel sensed currents may be determined using the following Equation 1:
 
                       SF   ij     =       G   oj       G   si         ,           (     Equation   ⁢           ⁢   1     )               
where channel i is the sensing channel, channel j is the observational channel, SF ij  is the scaling factor used to scale an output of the observational channel j when sensing via channel i, G oj  is the output of channel j during induced differential mode calibration, and G si  is the output of channel i during inherent differential mode calibration. As previously discussed, the scaling factor is used to scale the observational channel output before subtracting from the sensing channel output to ensure that the resulting compensated output is substantially attributable to the sensing channel&#39;s effects on the current through channel without inappropriately applying common-mode noise to the compensation.
 
     In some embodiments, calibration measurements may be conducted multiple times to average the results to improve a signal-to-noise ratio of the outputs. 
       FIG. 13  is a block diagram view of calibration scheme  250 . As illustrated, the calibration scheme  250  includes calibrating values for each channel in a sensing channel mode  252  and an observation channel mode  254 . 
     The sensing channel mode  252  generates a current that is sent through a channel of the display panel  256  corresponding to one or more pixels that is sensed through a sensing channel  258  having an inherent (e.g., non-induced) amount of differential input mismatch  260 . The current through the channel  258  having the inherent differential input mismatch  260  is sensed at a current sensing system  262  producing an output (G si )  264  that is stored in memory (e.g., lookup table illustrated in Table 1) for the inherent mismatch value used in scaling factor calculations. 
     During another calibration step before or after sensing channel mode  252  analysis, an observational channel mode  254  is employed. In the observational channel mode  254 , the same current is generated (e.g., using the same image or injected signal). However, the sensing channel  258  is now equipped with an induced differential input mismatch  266 . The amount of mismatch may be an amount of mismatch used in the observational channel operation during dual-channel sensing previously discussed or may differ to tune the scaling factor. The current in the channel  258  with the induced differential input mismatch  266  is sensed using the current sensing system  262  and an output (G oi )  268  is stored in memory (e.g., lookup table illustrated in Table 1) for the induced mismatch in scaling factor calculations. 
     The specific embodiments described above have been shown by way of example, and it should be understood that these embodiments may be susceptible to various modifications and alternative forms. It should be further understood that the claims are not intended to be limited to the particular forms disclosed, but rather to cover all modifications, equivalents, and alternatives falling within the spirit and scope of this disclosure. 
     The techniques presented and claimed herein are referenced and applied to material objects and concrete examples of a practical nature that demonstrably improve the present technical field and, as such, are not abstract, intangible or purely theoretical. Further, if any claims appended to the end of this specification contain one or more elements designated as “means for [perform]ing [a function] . . . ” or “step for [perform]ing [a function] . . . ”, it is intended that such elements are to be interpreted under 35 U.S.C. 112(f). However, for any claims containing elements designated in any other manner, it is intended that such elements are not to be interpreted under 35 U.S.C. 112(f).

Metadata:
Filing Date: 20170911
Publication Date: 20200218
Grant Date: 20200218
Priority Date: 20170526
Inventors: SHEN, Shiping
SHAEFFER, DEREK K.
CAGDASER, BARIS
NHO, HYUNWOO
BRAHMA, KINGSUK
LIN, HUNG SHENG
HWANG, INJAE
RYU, JIE WON
KIM, HYUNSOO
TAN, JUNHUA
ZHANG, RUI
GAO, SHENGKUI
VAHID FAR, Mohammad B
RICHMOND, Jesse A.
CHANG, SUN-IL
Assignee: APPLE INC
CPC Classifications: [{"code": "G09G2320/0219", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0295", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0233", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3233", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2330/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0285", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0693", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3648", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2320/0209", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2330/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/2092", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G3/20", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2330/021", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2330/06", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0693", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3648", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/2092", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G3/3233", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2330/021", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2330/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0693", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/006", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G2320/0219", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0209", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0285", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2330/06", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0233", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/006", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2320/0295", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/20", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 62092324