PATENT DOCUMENT

Publication Number: US-9046365-B2
Application Number: US-201113283438-A
Country: US
Kind Code: B2

Title: Electronic devices with magnetic field compensating conductive traces

Abstract:
Electronic devices may be provided with compasses for detecting the Earth&#39;s magnetic field. Electronic devices may be provided with electronic components that generate interfering magnetic fields for the compass. Electronic components may be coupled between a power supply line and a power return line on a printed circuit. The power return line may be configured to generate a compensating magnetic field to counteract the interfering magnetic fields. The power return line may be formed parallel to the power supply line. The power supply line may have multiple branches equidistant from the compass. The power return line may have a portion closer to the compass than the power supply line and the electronic component. The power return line may have multiple branches, may be provided with resistors on each branch and may include a portion of a circular loop the runs around the compass on the printed circuit board.

Claims:
What is claimed is: 
     
       1. A portable electronic device, comprising:
 a printed circuit board; 
 a compass mounted on the printed circuit board; 
 at least one conductive power line on the printed circuit board that generates an interfering magnetic field for the compass; and 
 at least one conductive return line on the printed circuit board that generates a compensating magnetic field that compensates for the interfering magnetic field for the compass. 
 
     
     
       2. The portable electronic device defined in  claim 1  wherein the printed circuit board comprises opposing first and second sides, wherein the at least one conductive power line and the at least one conductive return line are formed on the first side, and wherein at least a portion of the at least one conductive return line is parallel to the at least one conductive power line. 
     
     
       3. The portable electronic device defined in  claim 2 , further comprising an electronic component coupled to the at least one conductive power line and the at least one conductive return line. 
     
     
       4. The portable electronic device defined in  claim 1  wherein the printed circuit board comprises opposing first and second sides, wherein the at least one conductive power line is formed on the first side, wherein at least a portion of the at least one conductive return line is formed on the second side parallel to the at least one conductive power line. 
     
     
       5. The portable electronic device defined in  claim 4 , further comprising an electronic component configured to receive power from the at least one conductive power line and the at least one conductive return line. 
     
     
       6. The portable electronic device defined in  claim 5 , further comprising at least one conductive via in the printed circuit board that extends from the first side to the second side, wherein the at least one conductive via electrically couples the electronic component to the at least one conductive return line on the second side. 
     
     
       7. The portable electronic device defined in  claim 6 , further comprising a conductive ground plane on the second side that is coupled to the at least a portion of the at least one conductive return line on the second side. 
     
     
       8. The portable electronic device defined in  claim 1  wherein the at least one conductive power line has a minimum distance from the compass and a maximum distance from the at least one conductive return line, and wherein the maximum distance is smaller than the minimum distance. 
     
     
       9. A portable electronic device, comprising:
 a printed circuit board; 
 a compass mounted on the printed circuit board; and 
 first and second conductive power lines mounted on the printed circuit board on opposing sides of the compass, wherein the first and second conductive power lines are separated from the compass by a common minimum lateral distance. 
 
     
     
       10. The portable electronic device defined in  claim 9 , further comprising power supply circuitry, wherein the first and second conductive power lines comprise first and second branches of a common conductive power path that is coupled to the power supply circuitry. 
     
     
       11. The portable electronic device defined in  claim 10 , further comprising a conductive ground plane, wherein the printed circuit board comprises opposing first and second sides, wherein the conductive ground plane is formed on the second side, and wherein the conductive power path is formed on the first side. 
     
     
       12. The portable electronic device defined in  claim 9  wherein the printed circuit board comprises opposing first and second sides, wherein the first and second conductive power lines are formed on the first side, wherein the first conductive power line is separated from the compass by the common minimum distance, and wherein the second conductive power line is separated from the compass by the common minimum distance, the electronic device further comprising:
 a first conductive return line parallel to the first conductive supply line; and 
 a second conductive return line parallel to the second conductive supply line, wherein the first and second conductive return lines are formed on the second side. 
 
     
     
       13. A portable electronic device, comprising:
 a printed circuit board; 
 a compass mounted on the printed circuit board; 
 an electronic component on the printed circuit board; 
 power supply circuitry on the printed circuit board; 
 a first conductive line on the printed circuit board that extends along a path between the power supply circuitry and the electronic component; and 
 a second conductive line on the printed circuit board that is coupled between the power supply circuitry and the electronic component, wherein power is distributed from the power supply circuitry to the electronic component using the first and second conductive lines, wherein the electronic component generates an interfering magnetic field for the compass during operation of the electronic component, and wherein at least a portion of the second conductive line deviates away from the path towards the compass so that the second conductive line generates a compensating magnetic field that compensates for the interfering magnetic field. 
 
     
     
       14. The portable electronic device defined in  claim 13  wherein the second conductive line comprises a first portion that is parallel to the first conductive line, a second portion that is perpendicular to the first conductive line, and at least one portion that is formed at an acute angle with respect to the first conductive line. 
     
     
       15. The portable electronic device defined in  claim 13  wherein the compass is mounted on a surface of the printed circuit board, wherein the second conductive line is formed on the surface, and wherein the portion of the second conductive line comprises a portion of a circular loop that runs around the compass on the surface of the printed circuit board. 
     
     
       16. The portable electronic device defined in  claim 13  wherein the portion of the second conductive line comprises a branch of the second conductive line having a resistor, wherein the second conductive line comprises an additional branch coupled to the branch, wherein the additional branch has an additional resistor, and wherein at least a portion of the additional branch is parallel to the first conductive line. 
     
     
       17. The portable electronic device defined in  claim 16  wherein the compass is mounted on a surface of the printed circuit board, wherein the second conductive line is formed on the surface of the printed circuit board, and wherein the branch of the second conductive line comprises a portion of a circular loop that runs around the compass on the surface of the printed circuit board. 
     
     
       18. The portable electronic device defined in  claim 13 , further comprising power supply circuitry having a positive terminal coupled to the first conductive line. 
     
     
       19. The portable electronic device defined in  claim 18  wherein the electronic component comprises a camera having a lens, at least one fixed magnet, and a wire coil, wherein an electric current that flows through the wire coil and the first conductive line generates the interfering magnetic field, and wherein the power supply circuitry is configured to change the electric current to move the lens. 
     
     
       20. The portable electronic device defined in  claim 13  wherein the electronic component comprises a light source, wherein an electric current that flows through the first conductive line and the second conductive line generates the interfering magnetic field and the compensating magnetic field respectively, and wherein the power supply circuitry is configured to control the electric current to operate the light source. 
     
     
       21. A portable electronic device comprising
 a printed circuit board having at least one layer with opposing first and second sides; 
 a compass mounted on the first side of the layer; and 
 a conductive ground plane on the second side of the layer having a recess under the compass.

Description:
BACKGROUND 
     This relates generally to electronic devices and, more particularly, to electronic devices with compasses. 
     Electronic devices such as portable computers are often provided with compasses and other electronic components. For example, a Global Positioning System (GPS) device or cellular telephone may have a compass for orienting maps displayed to a user on an associated device display. 
     Other electronic components in an electronic device with a compass often generate magnetic fields when the other electronic components are turned on and off or during operation of the other electronic components. For example, electric current is often supplied to an electronic component when the electronic component is operated. The electric current flowing through a power supply line that provides the electric current to the electronic component (or flowing through the electronic component itself) often generates magnetic fields. These magnetic fields can interfere with the proper operation of the compass. 
     In the presence of interfering magnetic fields from other components in the electronic device, a compass may provide compass data that is in error by as much as several angular degrees. Errors of this type may be exaggerated when a compass is in close proximity to an electronic component that produces an interfering magnetic field. It is therefore difficult to provide accurate compass data, particularly in compact electronic devices in which compasses must be placed in close proximity to other electronic components or power supply lines that deliver electric current to the electronic components. 
     It would therefore be desirable to be able to provide electronic devices with improved compasses. 
     SUMMARY 
     Electronic devices may be provided with compasses and other electronic components. A compass may include a magnetic sensor such as a magnetometer for sensing the Earth&#39;s magnetic field. Magnetometer data may be gathered and processed by compass interface circuitry or other control or processing circuitry associated with the electronic device. Magnetometers may be implemented using anisotropic magnetoresistance (AMR) sensors. 
     An electronic device may be configured to simultaneously operate the compass and one or more other electronic components such as cameras, auto-focus lenses, flashlights, camera flashes, displays, proximity sensors, display backlights, central processing units, GPS circuitry, accelerometers, gyroscopes, headphones, speakers, and vibrators. For example, processing circuitry may be used to run software on the electronic device such as search applications that display continuous image frames on a display with location information (obtained using the compass) overlaid on the display. 
     In this type of application, a camera, camera light, camera auto-focus mechanism, control circuitry and other components may be operated in combination with the compass. Electronic component and power supply traces associated with these components may generate interfering magnetic fields that interfere with compass sensing of the Earth&#39;s magnetic field. 
     Conductive lines such as power return lines on a printed circuit board may be formed near other conductive lines such as power supply lines or near the compass. Conductive lines such as power supply lines and power return lines may be formed from conductive metal traces on the printed circuit board. 
     A power return line may generate a compensating magnetic field in the vicinity of the compass that substantially cancels the interfering magnetic field generated by the power supply line or by the electronic component. A compensating magnetic field may, for example, have a substantially equal magnitude and opposite direction to an interfering magnetic field. Because magnetic field strength is a function of distance from the magnetic field source, power return lines may be routed closer to the compass than the magnetic field generating electronic component. 
     Power return lines may be formed parallel to power supply traces on a common layer of a printed circuit board with the compass or on another layer of the printed circuit board. Power return lines may be formed along otherwise unorthodox paths in order to route the power return lines near the compass. For example, a power return line that has an available optimally short route to a ground conductor may be routed along a path to the ground conductor that is longer than the optimally short path. 
     Power return lines may form a portion of a circular loop that runs around a compass on a surface of a printed circuit board. Power return lines may include one or more branches each having resistors that control the amount of current that flows through each branch. If desired, power supply lines may include multiple branches on opposing sides of the compass on the printed circuit board in order to generate compensating magnetic fields. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective front view of an illustrative electronic device having a compass in accordance with an embodiment of the present invention. 
         FIG. 2  is a diagram of illustrative circuitry and components for an electronic device having a compass in accordance with an embodiment of the present invention. 
         FIG. 3  is a perspective rear view of an illustrative electronic device having a compass, a camera having a conductive lines that generate compensating magnetic fields in accordance with an embodiment of the present invention. 
         FIG. 4  is a cross-sectional top view of an illustrative camera having an auto-focus mechanism that generates interfering magnetic fields in accordance with an embodiment of the present invention. 
         FIG. 5  is a cross-sectional side view of an illustrative camera having an auto-focus mechanism that generates interfering magnetic fields in accordance with an embodiment of the present invention. 
         FIG. 6  is a diagram of an illustrative electronic device having a compass with a power line and a notched ground plane in accordance with an embodiment of the present invention. 
         FIG. 7  is a perspective view of a portion of an illustrative printed circuit having a compass and a power supply line with a corresponding power return trace in accordance with an embodiment of the present invention. 
         FIG. 8  is a perspective view of a portion of an illustrative printed circuit having a compass and multiple power supply lines with multiple corresponding power return traces in accordance with an embodiment of the present invention. 
         FIG. 9  is a perspective view of a portion of an illustrative printed circuit having a compass and a power supply line with a corresponding power return trace in accordance with an embodiment of the present invention. 
         FIG. 10  is a diagram of an illustrative electronic device having a compass, an electronic component, a power supply line for the electronic component and a corresponding power return trace near the power supply line in accordance with an embodiment of the present invention. 
         FIG. 11  is a perspective view of a portion of an illustrative printed circuit having a compass and a multiple power supply lines on opposing sides of the compass in accordance with an embodiment of the present invention. 
         FIG. 12  is a perspective view of a portion of an illustrative printed circuit having a compass and a multiple power supply lines with corresponding power return traces on opposing sides of the compass in accordance with an embodiment of the present invention. 
         FIG. 13  is a diagram of an illustrative electronic device having a compass, an electronic component, and multiple branches of a common power supply path for the electronic component in accordance with an embodiment of the present invention. 
         FIG. 14  is a diagram of an illustrative electronic device having a compass, an electronic component with a power supply line, and a power return trace formed with a portion deviates away from the power supply line toward the compass in accordance with an embodiment of the present invention. 
         FIG. 15  is a diagram of an illustrative electronic device having a compass, an electronic component with a power supply line, and a power return trace that carries electric current around the compass in accordance with an embodiment of the present invention. 
         FIG. 16  is a diagram of an illustrative electronic device having a compass, an electronic component with a power supply line, and a power return trace with multiple branches with resistors in accordance with an embodiment of the present invention. 
         FIG. 17  is a diagram of an illustrative electronic device having a compass, an electronic component with a power supply line, and a power return trace a branche with a resistor that carries electric current around the compass in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may be provided with compasses and other electronic components. The compass may include a magnetic sensor such as a magnetometer and compass interface circuitry. The compass interface circuitry may be configured to convert raw magnetometer data into directional compass data (also called compass data). An electronic device may be provided other electronic components and power supply lines that carry electric current to the other electronic components that generate interfering magnetic fields that interfere with the compass. 
     An electronic device may be provided with power return traces that carry return current from the other electronic components. Power return traces may be formed on a common printed circuit board with power supply lines and the compass. Power return traces may be formed on a common surface of the printed circuit board with the compass or on an opposing surface of the printed circuit board. 
     Power return traces may be configured to generate compensating magnetic fields that nearly or completely cancel the interfering magnetic fields in the vicinity of the compass. 
     Other electronic components may include cameras, speakers, auto-focus lens mechanisms, camera flashes, Light Emitting Diodes (LEDs), processing circuitry such as central processing units, memory or other integrated circuits, Global Positioning System (GPS) circuitry, display circuitry, light-emitting display circuitry, display backlights, headphones, batteries, vibrators, actuators or other components. 
     Other electronic components may have corresponding power lines (e.g., wires, conductive traces on a printed circuit board, etc.) that supply power to the electronic components. Power return traces may be routed near power supply lines, near the compass, around the compass or may be otherwise routed to generate suitable compensating magnetic fields. Power return traces and power supply lines may be provided with variable or fixed strength resistors for adjusting an electric current in the power supply line and the power return trace to generate nearly equal and opposite interfering and compensating magnetic fields in the vicinity of the compass. 
     An illustrative electronic device of the type that may be provided with one or more magnetic field compensating power return traces is shown in  FIG. 1 . Electronic device  10  of  FIG. 1  may be a cellular telephone, media player, computer, handheld device, portable computer, tablet computer, Global Positioning System device, camera, gaming device, or other electronic equipment. 
     As shown in  FIG. 1 , device  10  may have a housing such as housing  12 . Housing  12  maybe formed from plastic, metal, carbon fiber composite material, other composites, glass, ceramics, other materials, or combinations of these materials. Housing  12  may be formed using a unibody construction in which housing  12  is substantially formed from a single structure (e.g., machined or cast metal, plastic, etc.) or may be formed from multiple pieces of material. 
     For example, housing  12  may include front and rear planar housing structures. The front planar housing structure may be a display cover layer for a display such as display  14 . The display cover layer may be formed from glass and may sometimes be referred to as cover glass or display cover glass. The display cover layer may also be formed from other transparent materials such as plastic. 
     Device  10  may have input-output devices such as input-output ports, speakers, microphones, displays, status indicator lights, touch screens, buttons, proximity sensors, wireless circuitry, accelerometers, ambient light sensors, touch pads, and other devices for accepting input from a user or the surrounding environment of device  10  and/or for providing output to a user of device  10 . 
     As shown in the illustrative configuration of  FIG. 1 , device  10  may, as an example, have one or more buttons  16  which may be used to gather user input. Buttons  16  may be based on dome switches or other switch circuitry. Buttons  16  may include button members that form push buttons (e.g., momentary buttons), slider switches, rocker switches, etc. Additional buttons such as buttons  16 , additional data ports such as port  26 , and additional input-output components such as speaker  18  may be provided in device  10  if desired. The example of  FIG. 1  is merely illustrative. 
     Device  10  may have a flexible or rigid display such as display  14 . Display  14  may be formed from multiple layers of material. These layers may include a touch sensor layer such as a layer on which a pattern of indium tin oxide (ITO) electrodes or other suitable transparent electrodes have been deposited to form a capacitive touch sensor array. These layers may also include a layer that contains an array of display pixels. The touch sensor layer and the display layer may be formed using flexible sheets of polymer or other substrates having thicknesses of 10 microns to 0.5 mm or other suitable thicknesses (as an example). 
     The display pixel array may be, for example, an organic light-emitting diode (OLED) array. Other types of flexible display pixel arrays may also be formed (e.g., electronic ink displays, etc.). This is, however, merely illustrative. Display  14  may be formed using any suitable display technology such as liquid crystal display (LCD) technology or other display technology. 
     In addition to functional display layers (i.e., the display array and the optional touch sensor array), display  14  may include one or more structural layers. For example, display  14  may be covered with a flexible or rigid cover layer and/or may be mounted on a support structure (e.g., a rigid support 
     In configurations for display  14  in which the flexible layers are covered by a rigid cover glass layer or other rigid cover layer, the rigid layer may be provided with one or more openings and the electronic components may be mounted under the openings. For example, a rigid cover layer may have openings such as a circular openings for button  16  and a speaker port opening such as speaker port opening  18  (e.g., for an ear speaker for a user). Device  10  may also have other openings (e.g., openings in display  14  and/or housing  12  for accommodating volume buttons, ringer buttons, sleep buttons, and other buttons, openings for an audio jack, data port connectors, removable media slots, etc.). 
     As shown in  FIG. 1 , device  10  may be provided with one or more internal magnetic sensitive devices such as compass  20 . Compass  20  may include a magnetic sensor such as a magnetometer (e.g., an anisotropic magnetoresistance (AMR) sensor or other magnetometer) and compass interface circuitry. Compass interface circuitry may be configured to provide compass data to other circuitry. Compass interface circuitry or other control circuitry in device  10  may be configured to store compass calibration data, may be configured to turn compass  20  on and off, may be configured to access information on the operational status of other electronic components, may be configured to apply corrections to compass data based on operational status information (also called status data, operational status data, etc.) associated with other electronic components, may be configured to combine these functions or to perform any other compass related functions for device  10 . 
     Device  10  may include other internal electronic components such as component  22 . Component  22  may receive electric power along an associated power supply path such as conductive line  24  (sometimes referred to herein as a power supply line, power supply trace, or conductive power line). Conductive line  24  may be configured to supply electric power to component  22  from power supply circuitry (sometimes called a power management unit (PMU)). Component  22  may be a camera, a speaker, an auto-focus lens mechanism, a camera flash, a Light Emitting Diode (LEDs), processing circuitry such as central processing units, memory or other integrated circuits, Global Positioning System (GPS) circuitry, display circuitry, a battery, a vibrator, an actuator or other component. Conductive line  24  may be a single wire, a twisted pair of wires, a conductive trace on a printed circuit board, etc. 
     Component  22  may be electrically coupled to an associated power return line (sometimes called a power return trace, return line, conductive line, or return trace) such as conductive line  25 . Component  22  may be configured to receive power (i.e., electric power) from power supply line  24  and power return line  25 . Conductive line  25  may be configured to conduct electric current away from component (e.g., to a ground contact, ground plane etc.). Conductive line  25  may be a single wire, a twisted pair of wires, a conductive trace on a printed circuit board, etc. 
     As shown in  FIG. 2 , compass  20  may include a magnetic sensor such as magnetometer  30  and compass interface circuitry such as compass interface circuitry  32 . Compass interface circuitry  32  may be configured to collect raw magnetometer data and provide compass data to other control circuitry such as storage and processing circuitry  40  of device  10 . Storage and processing circuitry  40  may be configured to deliver compass data from compass  20  to other software applications running on circuitry  40 . 
     Storage and processing circuitry  40  may be configured to further process compass data (e.g., to apply an interference correction offset to the compass data to correct for magnetic interference from components such as components  22  and conductive lines such as conductive line  24  that do not have power return traces for generating compensating magnetic fields). As shown in  FIG. 2 , components  22  may include one or more cameras (e.g., a front-facing camera, a rear-facing camera, etc.), one or more light sources (e.g., a camera flash, an LED camera light, a flashlight, etc.) or other components. 
     Device  10  may include control circuitry such as storage and processing circuitry  40 . Storage and processing circuitry  40  may include storage such as hard disk drive storage, non-volatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. 
     Processing circuitry in storage and processing circuitry  40  and other control circuits such as control circuits in compass  20  may be used to control the operation of device  10 . This processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio codec chips, application specific integrated circuits, etc. 
     Storage and processing circuitry  40  may be used to run software on device  10 , such as internet browsing applications, map applications, voice-over-internet-protocol (VoIP) telephone call applications, email applications, media playback applications, operating system functions, camera functions, camera based applications, light source functions, display functions, GPS operations, etc. 
     Some applications may use combined data from compass  20  and a positioning sensor such as intertial measurement unit (IMU)  44 . Intertial measurement unit  44  may include one or more accelerometers, one or more gyroscopes, GPS circuitry, etc. for determining the location and position of device  10 . Storage and processing circuitry  40  may be configured to operate IMU  44  in combination with antenna  20  to provide position and location information to applications running on device  10 . Compass  20  may be formed separately from IMU  44  or may be formed as an integral part of IMU  44 . In one preferred embodiment that is sometimes discussed herein as an example, compass  20  may be formed as a single integrated circuit attached to a main logic board (e.g., a printed circuit board) using a ball grid array. 
     Storage and processing circuitry  40  may be used to operate power supply circuitry such as power management unit (PMU)  38  to supply electrical power to components  22  such as camera  34  and light source  36 . Storage and processing circuitry  40  may be used to operate input/output components such as input/output components  42  and to process and store data input to device  10  using input/output components  42 . 
     Input/output components  42  may include buttons or speakers such as button  16  and speaker  18  of  FIG. 1 . Input/output components  42  may include touch-sensitive portions of display  14 , may include a keyboard, wireless circuitry such as wireless local area network transceiver circuitry and cellular telephone network transceiver circuitry, and other components for receiving input and supplying output. Components  22  may be internal to device  10  or may have portions that are visible on a portion of an exterior surface of device  10 . 
     Control circuitry such as storage and processing circuitry  40  may include circuitry for interfacing with the resources of compass  20  (e.g., control circuitry of compass interface circuitry  32  may be considered to form part of storage and processing circuitry  40 ). For example, control circuitry  40  may be configured to run a compass interface software application that interfaces with magnetometer  30 . 
     As shown in  FIG. 3 , camera  34  and light source  36  may be visible on a rear surface of device  10 . Camera  34  may be used in combination with light source  36  when capturing images with device  10 . Storage and processing circuitry  40  may be configured to continuously display images received by camera  34  on display  14  while displaying integrated location information based on compass data continuously captured by compass  20  on a portion of display  14 . Operations of this type in which a component such as camera  34  is operated while compass  20  collects compass data may be improved using compass power return traces such as power return traces  25  that are configured to generate compensating magnetic fields that compensate for interfering magnetic fields generated by components such as camera  34  and power supply lines such as power supply lines  24 . 
     Components such as camera  34  and light source  36  may have associated power supply lines such as conductive lines  24  for delivering power from PMU  38 . In the example of  FIG. 3 , light source  36  has a distance  50  from compass  20  while power supply line  24  associated with light source  36  has a minimum distance  52  from compass  20 . Magnetic interference from components such as light source  36  and associated power supply lines depends on distances such as distances  50  and  52  respectively, from compass  20 . A smaller distance  50  between compass  20  and light source  36  produces larger magnetic interference with compass  20  when light source  36  is operated. A smaller distance  50  between compass  20  and light source  36  produces larger magnetic interference with compass  20  when light source  36  is operated. 
     Because magnetic interference depends on distances such as distances  50  and  52 , power return traces such as power return traces  25  may be configured to have distances from compass  20  that optimally compensate for magnetic interference from components such as camera  34  and light source  36 . As shown in  FIG. 3 , device  10  may be provided with power return traces such as power return trace  25 P that is paired with a power supply line  24  and power return trace  25 L that is longer than an associated power supply line  24 . Power return trace  25 P and power return trace  25 L may, if desired form branches of a common power return path. 
     Power return trace  25 L may be routed nearer to compass  20  than an associated power supply line  24 . Power return trace  25 L may be configured to compensate for an interfering magnetic field that is generated by both power supply line  24  and a component  22  (e.g., camera  34  or light source  36 ). Power return trace  25 L may have portions formed between compass  20  and an associated power supply line  24 . Power return trace  25 L may have portions that form at least part of a loop around compass  20 . Power return trace  25 L may have portions formed on a side of compass  20  that is opposite to the side on which an associated power supply line  24  is formed. 
     Paired power return traces such as power return trace  25 P may run parallel to a corresponding power supply line  24  at a distance that is smaller than the distance between the power supply line and compass  20 . Power return traces  25  (e.g., traces  25 L and  25 P) and power supply lines  24  may each be provided with resistors or other discrete components for controlling current in respective power return traces  25  an power supply lines  24 . 
     Magnetic interference may depend on individual component configuration and operation. Components such as camera  34  may include magnets, wire coils or other elements that generate interfering magnetic fields during component operation. As shown in  FIG. 4 , camera  34  may include an array of imaging pixels such image pixel array  76  for capturing image light. Camera  34  may include a lens such as lens  70  that focuses image light onto image pixel array  76 . 
     Camera  34  may include an electronic focusing system for moving lens  70  into an optimal focus position. The focusing system of camera  34  may be an auto-focusing system in which storage and processing circuitry  40  (see  FIG. 2 ) uses image data captured by camera  34  to determine a best focus position for lens  70 . The focusing system of camera  34  may include one or more magnets such as fixed magnets  72  and a coil of conductive wire such as coil  74 . 
     Coil  74  may include any number of turns (e.g., one turn, two turns, more than two turns, more than 5 turns, more than 10 turns, 10 to 500 turns, more than 20 turns, more than 40 turns, 50-60 turns, more than 50 turns, less than 60 turns, less than 100 turns or less than 500 turns) of wire wrapped around lens  70 . Wire coil  74  may be coupled to a power supply line such as power supply line  24 . 
     Electric current may be supplied along power supply line  24  from a power management unit (e.g., PMU  38  of  FIG. 1 ). Electric current may flow from power supply line  24 , through turns of wire associated with coil  74  to a ground line such as power return trace  25 . Power return trace  25  may electrically couple coil  74  to a ground plane or other ground conductor in a layer of a printed circuit board or otherwise positioned in device  10 . Power return trace  25  may run alongside power supply line  24  or may divert from power supply line  24  to route return current near compass  20 . During normal operation of camera  34 , lens  70  may be moved to improve the focus of image light on image sensor array  76 . Changing magnetic fields generated by changing current flowing through coil  74  may interact with fixed magnets  72  and cause lens  70  to move. 
     Lens  70  may be coupled to one or more elastomeric attachment members such as springs  79 , as shown in  FIG. 5 . Springs  79  may be configured to provide a natural position (sometimes referred to as a default position) for lens  70  with respect to image pixel array  76  within camera  34 . Springs  79  may be configured so that the default position of lens  70  with respect to image pixel array  76  is an infinity focus position (i.e., a position in which the lens is a distance from the image pixel array that is equal to the focal length of camera  34 ). 
     Forces on lens  70  generated by interactions between the magnetic field generated by the current flow in coil  74  and fixed magnets  72  may cause lens  70  to move closer to, or further from, image pixel array  76  as indicated by arrows  80 . Moving lens  70  closer to, or further from, image pixel array  76  by changing the current flowing through coil  74  may change the distance from camera  34  at which objects appear in focus at image pixel array  76 . Springs  79  may be configured to provide resistance to motion of lens  70 . 
     A constant current through coil  74  may therefore be needed to hold lens  70  in a position that is different from the default position determined by springs  79 . Changing the current through coil  74  move lens  70  to a new position relative to image pixel array  76 . A relatively larger current through coil  74  may move lens  70  a relatively larger distance from image pixel array  76  than its default position. A relatively larger current may also produce a relatively larger magnetic field that may interfere with the operation of compass  20 . Providing device  10  with one or more power return lines such as traces  25  may provide a return current that automatically rises and falls with the current delivered to, for example, camera  34  in order to compensate for the interfering magnetic field generated by camera  34 . 
     If desired, as shown in  FIG. 6 , device  10  may include a ground plane such as ground plane  204 . Electrical power may supplied to a component such as component  206  from power supply circuitry such as power supply  208  using a power line such as power line  210 . In some configurations, current flowing in a ground plane such as ground plane  204  can generate additional interfering magnetic fields. A recess such as notch  202  may be provided in ground plane  204  under compass  200 . A cutout in a ground plane such as notch  202  may reduce the amount of return current flowing through ground plane  204  in the vicinity of compass  20 . 
     As shown in  FIG. 7 , compass  20  of device  10  may be mounted to a top surface such as surface  92  of a printed circuit board (PCB) such as printed circuit board  90 . Printed circuit board  90  may include one or more layers formed from dielectrics such as fiberglass-filled epoxy (e.g., as a rigid layer in a PCB stack) and polyimide (e.g., as a flexible layer in a PCB stack), FR- 2  (phenolic cotton paper), FR- 3  (cotton paper and epoxy), FR- 4  (woven glass and epoxy), FR- 5  (woven glass and epoxy), FR- 6  (matte glass and polyester), G- 10  (woven glass and epoxy), CEM- 1  (cotton paper and epoxy), CEM- 2  (cotton paper and epoxy), CEM- 3  (woven glass and epoxy), CEM- 4  (woven glass and epoxy), CEM- 5  (woven glass and polyester), paper impregnated with phenolic resin, polystyrene, polyimide, polytetrafluoroethylene (PTFE), plastic, other polymers, ceramics, or other suitable dielectrics. 
     Printed circuit board  90  may include one or more layers of prepreg (i.e., pre-impregnated layers of fiber and resin) and one or more layers of copper or other conductive materials 
     Power supply trace  24  may be a patterned conductive trace (e.g., a metal trace) on surface  92  of PCB  90 . Power supply trace  24  may form a portion of a positive power supply line to a component such as camera  24  or light source  36  of  FIG. 2 . A power return line such as power return trace  25  may be formed on an opposing bottom surface such as surface  94  of PCB  90 . Power return trace  25  may be a patterned conductive trace (e.g., a metal trace) that runs along bottom surface  94  of PCB  90  under power supply trace  24 . In this way, current flowing through power supply trace  24  that generates an interfering magnetic field such as interfering magnetic field MI for compass  20  may be compensated by an equal (magnitude) and opposite (direction) compensating magnetic field such as magnetic field MC generated by current flowing in an opposite direction in power return trace  25 . 
     In order to isolate compass  20  from interfering magnetic fields and to reduce the effect of the distance between power supply trace  24  and power return trace  25  on the interfering and compensating magnetic fields MI and MC, power supply trace  24  and power return trace  25  may be formed at a lateral distance  96  from compass  20 . Lateral distance  96  may be significantly larger than distance  98  between power supply trace  24  and power return trace  25 . As an example, distance  98  may be equal to the thickness of PCB (e.g., 10 microns to 0.5 mm or other suitable PCB thicknesses) while distance  96  may be as much as a several millimeters or more (e.g., more than 1 cm, more than 2 cm, more than 3 cm, 1 cm to 3 cm, 5 mm to 2 cm, 2 cm to 4 cm, etc.). 
     If desired, PCB  90  may include additional PCB layers such as substrate layer  101  under power return trace  25  attached to surface  94  (e.g., power return trace  25  may be formed between two layers of PCB  90 ). PCB  90  may include interior patterned conductive traces that form signal lines that convey signals within PCB  90  and/or from PCB  90  to other components such as components  22  (see  FIG. 2 ). 
     The example of  FIG. 7  in which a single power supply trace  24  has a single corresponding power return trace  25  on surface  94  of PCB  90  is merely illustrative. If desired, multiple power supply traces  24  may be matched by multiple power return traces  25  as shown in  FIG. 8 . As shown in  FIG. 8 , multiple power supply traces  24  for a component such as camera  34  on surface  92  of PCB  90  may be routed around a magnetic sensitive component such as compass  20  on surface  92  (e.g., traces  24  may follow a path on surface  92  that is at predetermined minimum distance from compass  20 ). PCB  90  may be provided with power return traces  25  on bottom surface  94  of PCB  90  that carry return current from, for example, camera  34 . Conductive paths from top surface  92  through to bottom surface  94  of PCB  90  may be formed from vias such as vias  104 . Vias  104  may couple camera  34  to power return traces  25 . 
     Power return traces  25  may follow a path on surface  94  of PCB  90  that mimics that path of power supply traces  24  on surface  92  so that power return traces  25  are formed under power supply traces  24  in order to generate compensating magnetic fields to compensate for interfering magnetic fields generated by power supply lines  24  (and camera  34 ). Power return traces  25  may be formed under power supply lines  24  in the vicinity of compass  20 . Power return traces  25  may include ground contacts such as ground contacts  102  that couple power return traces  25  to a ground plane such as ground plane  100  under PCB  90 . Ground plane  100  may be formed in a region of PCB  90  that is at a predetermined minimum distance from compass  20  (e.g., more than 3 cm, more than 5 cm, 3 to 5 cm, less than 5 cm, more than 2 cm, etc.). 
     If desired, PCB  90  may include additional PCB layers such as substrate layer  101  under ground plane  100  attached to surface  94  (e.g., ground plane  100  may be formed between two layers of PCB  90 ). 
     Providing PCB  90  with a power supply trace on a top surface and a corresponding power return trace on a bottom surface is merely illustrative. If desired, power return trace  25  may be formed on top surface  92  of PCB  90  as shown in  FIG. 9 . As shown in  FIG. 9 , compass  20  and a power supply line such as power supply line  24  of device  10  may be mounted to a top surface such as surface  92  of a PCB  90 . A power return line such as power return trace  25  may run parallel to power supply line  24  on top surface  92  of PCB  90 . Power return trace  25  may be implemented using a patterned conductive trace on top surface  92  of PCB  90  that runs alongside (and parallel to) power supply trace  24 . In this way, current flowing through power supply trace  24  that generates an interfering magnetic field such as interfering magnetic field MI for compass  20  may be compensated by an equal (magnitude) and opposite (direction) compensating magnetic field such as magnetic field MC generated by current flowing in an opposite direction in power return trace  25 . 
     In order to isolate compass  20  from interfering magnetic fields and to reduce the effect of the distance between power supply trace  24  and power return trace  25  on the interfering and compensating magnetic fields MI and MC, power supply trace  24  may be configured to have a minimum distance  106  from compass  20 . Lateral distance  106  may be significantly larger than a maximum distance  108  between power supply trace  24  and power return trace  25 . As an example, distance  108  may be as small as a few microns (e.g., 10 microns-20 microns, 10 microns to 50 microns, 10 microns to 100 microns, 50 microns to 0.2 mm, 50 microns to 0.5 mm, or other suitable distance) while distance  106  may be as much as a several millimeters or more (e.g., more than 1 cm, more than 2 cm, more than 3 cm, 1 cm to 3 cm, 5 mm to 2 cm, 2 cm to 4 cm, etc.). 
     In general, as shown in  FIG. 10 , a power supply line such as power supply line  24  that supplies electric current from circuitry such as power supply unit  38  to a component such as component  22  may have an associated power return trace such as power return trace  25  that runs along the length of power supply line  24 . Power return trace  25  may run alongside power supply trace  24  at a distance such that a maximum distance between power supply trace  24  and power return trace  25  such as distance  108  is smaller than a minimum distance such as distance  106  between power supply trace  24  and a magnetic-sensitive component such as compass  20 . 
     Power supply traces  24  may be coupled to a positive power supply terminal such as terminal  115  of a power source as power management unit  38 . Power return trace  25  may electrically couple component  22  to a ground power supply terminal such as terminal  117  or may couple component  22  to a ground conductor through a ground contact such as contact  119 . 
     As shown in  FIG. 11 , a compensating magnetic field that compensates for an interfering magnetic field generated by a power supply line such as power supply line  24 - 2  may be generated by an additional power supply line such as power supply line  24 - 1  on an opposing side of compass  20 . Dual power supply lines  24 - 1  and  24 - 2  may be formed on surface  92  of PCB  90  on opposing sides of a magnetic sensor such as compass  20 . 
     PCB  90  may be configured to include a power supply line  24  that is formed on surface  92  of PCB  90  having a minimum lateral distance  116  compass  20  (e.g., power supply line  24 - 2  at a distance  116  from edge  118 ) and an associated second power supply line  24  formed at a same (common) minimum lateral distance  116  from compass  20  (e.g., power supply line  24 - 1  at a distance  116  from edge  120 ). A current flowing in power supply line  24 - 2  may generate an interfering magnetic field for compass  20 . An equal or substantially equal current flowing in power supply line  24 - 1  may generate an (equal-magnitude, opposite-direction) compensating magnetic field for compass  20 . 
     Power supply traces  24  may be implemented using patterned conductive traces on surface  92  of PCB  90 . Power supply traces  24  may form portions of a positive power supply line to one or more components  22  such as camera  34  or light source  36  of  FIG. 2 . Power supply traces  24 - 1  and  24 - 2  of  FIG. 11  may be power supply traces for a single component  22  (e.g., branches of common power supply path  24 ) or may be power supply traces for more than one component  22 . 
     If desired, return current from a component  22  that is supplied by power supply lines  24 - 1  and  24 - 2  may flow through a ground plane such as ground plane  114  on bottom surface  94  of PCB  90 . If desired, PCB  90  may include additional PCB layers such as substrate layer  101  under ground plane  114 . 
     Providing PCB  90  with return current from a component  22  that is supplied by power supply lines  24 - 1  and  24 - 2  ground plane  114  is merely illustrative. If desired, power supply traces  24 - 1  and  24 - 2  that are formed on opposing sides of compass  20  on surface  90  may each have associated power return traces  25 - 1  and  25 - 2  for providing enhanced magnetic field compensation for compass  20  as shown in  FIG. 12 . 
     As shown in  FIG. 12 , power return traces such as traces  25 - 1  and  25 - 2  may be formed on an opposing bottom side (e.g., side  94 ) of PCB  90  under associated power supply lines  24 - 1  and  24 - 2 . Compass  20  of device  10  may be mounted to a top surface such as surface  92  of a PCB  90 . Power supply traces  24  may be implemented using patterned conductive trace on surface  92  of PCB  90 . Power supply lines  24 - 1  and  24 - 2  may be formed at a common lateral distance  116  from compass  20 . Each of power supply lines  24 - 1  and  24 - 2  may have an associated power return line such as power return traces  25 - 1  and  25 - 2  formed on an opposing bottom surface such as surface  94  of PCB  90 . Power return traces  25 - 1  and  25 - 2  may be implemented using patterned conductive traces that run along bottom surface  94  of PCB  90  under corresponding power supply traces  24 - 1  and  24 - 2  and parallel to corresponding power supply traces  24 - 1  and  24 - 2  respectively. 
     In this way, current flowing through each power supply trace  24  that generates an interfering magnetic field such as interfering magnetic fields MI- 1  and MI- 2  for compass  20  may be compensated by a substantially equal (magnitude) and opposite (direction) compensating magnetic field such as magnetic fields MC- 1  and MC- 2  generated by current flowing in an opposite direction in power return traces  25 . In this way, current flowing through a ground plane such as ground plane  114  of  FIG. 11  may be avoided in the vicinity of compass  20 . 
     In order to isolate compass  20  from interfering magnetic fields and to reduce the effect of the distance between power supply traces  24 - 1  and  24 - 2  and associated power return traces  25 - 1  and  25 - 2 , respectively, on interfering and compensating magnetic fields MI- 1 , MI- 2 , MC- 1  and MC- 2 , power supply traces  24  and power return traces  25  may be formed at a lateral distance  116  from compass  20 . Lateral distance  116  may be significantly larger than distance  98  between power supply traces  24 - 1  and  24 - 2  and corresponding power return traces  25 - 1  and  25 - 2  respectively. As an example, distance  98  may be equal to the thickness of PCB  90  (e.g., 10 microns to 0.5 mm or other suitable PCB thicknesses) while distance  116  may be as much as a several millimeters or more (e.g., more than 1 cm, more than 2 cm, more than 3 cm, 1 cm to 3 cm, 5 mm to 2 cm, 2 cm to 4 cm, etc.). 
     In general, as shown in  FIG. 13 , power may be supplied from power supply circuitry such as power management unit  38  to component  22  along a conductive power supply path such as power supply path  24  that has multiple branches such as branches  24 - 1  and  24 - 2  that run along on opposing sides of a magnetic sensor such as compass  20 . 
     Electric current flowing through power supply line  24  may be split so that substantially half of the current runs through branch  24 - 1  and substantially half of the current runs through branch  24 - 2 . Power return traces such as return traces  25  may run under power supply path  24  including portions under branch  24 - 1  and portions under branch  24 - 2  as shown in  FIG. 12 . Power supply trace  24  may be coupled to a positive power supply terminal such as terminal  115  of a power source as power management unit  38 . 
     As described above in connection with  FIGS. 4 and 5 , some components  22  may generate interfering magnetic fields in addition to interfering magnetic fields generated by power supply lines that supply electric current to the component. For example, component  22  may include a camera such as camera  34  having a wire coil with multiple turns of wire for a lens focusing mechanism. Electric current flowing through multiple turns of a wire coil may generate magnetic fields. For this reason, power return traces such as power return traces  25  may be configured to run closer to magnetic sensors such as compass  20  than power supply lines  25  to compensate for interfering magnetic fields from both power supply lines  24  and components  22  as shown in  FIGS. 14 ,  15 ,  16 , and  17 . 
     As shown in  FIG. 14 , a power supply line such as power supply line  24  that supplies electric current from circuitry such as power supply unit  38  to a component such as component  22  may have an associated power return trace such as power return trace  25  that runs away from component  22  toward compass  20 . Power return trace  25  may include multiple portions. Power return trace  25  may include a portion such as portion  134  that runs parallel to power supply line  24 , a portion such as portion  130  that runs perpendicular to power supply line  24  and portions such as portions  132  and  133  that run at angles (e.g., acute angles or obtuse angles) with respect to power supply line  24 . Power supply trace  24  and power return trace  25  may be implemented using patterned conductive traces on a surface of PCB  90 . 
     Power return trace  25  may be configured to follow a non-linear path on a surface of PCB  90 . As shown in  FIG. 14 , power return trace  25  may deviate from a power supply path defined by a power supply line such as power supply line  24  that extends along the path between power supply circuitry  38  and electronic component  22 . The deviation of power return trace  25  may extend toward compass  20 . 
     Some portions (e.g., portion  132 ) of power return trace  25  may be shorter than other portions (e.g., portion  133 ) of return trace  25 . Return trace  25  may be configured to pass at a minimum distance such as minimum distance  136  from compass  20 . Minimum distance  136  may be significantly smaller than a minimum distance such as minimum distance  106  between power supply trace  24  and compass  20 . 
     For example, minimum distance  136  may be less than 1 cm, less than 2 cm, less than 3 cm, less than 50 mm, or other distance while minimum distance  106  may be more than 1 cm, more than 2 cm, more than 3 cm, more than 4 cm, 1 cm-4 cm, etc. Because magnetic field strength depends on distance from the magnetic field generating source, providing PCB  90  with a power return trace  25  having a minimum distance  136  that is smaller than the distance (e.g., distance  106 ) from power supply line  24  may help generate compensating magnetic fields that compensate for interfering magnetic fields from both power supply lines such as power supply lines  24  and electronic components such as components  22 . This is because interfering magnetic fields at compass  20  generated by both power supply line  24  and electronic component  22  may be larger than interfering magnetic fields from only one of power supply line  24  and component  22 . 
     The closer proximity of power return trace  25  to compass  20  results in an increased magnetic field strength at compass  20  from power return trace  25  than from power supply trace  24  even if the current flowing in both is the same. Providing PCB  90  with a power return trace such as power return trace  25  that deviates away from a path defined by power supply path  24  toward compass  20  as shown in  FIG. 14  may help generate compensating magnetic fields that compensate for interfering magnetic fields from both power supply lines such as power supply lines  24  and electronic components such as components  22 . 
     Power supply traces  24  may be coupled to a positive power supply terminal such as terminal  115  of a power source as power management unit  38 . Portion  134  of power return trace  25  may electrically couple component  22  to a ground power supply terminal such as terminal  117  or may couple component  22  to a ground conductor through a ground contact such as contact  119 . 
     If desired, power return trace  25  may include a portion that runs around a magnetic sensor such as compass  20  as shown in  FIG. 15 . As shown in  FIG. 15 , a power supply line such as power supply line  24  that supplies electric current from circuitry such as power supply unit  38  to a component such as component  22  may have an associated power return trace such as power return trace  25  that runs at least partially around compass  20 . Power supply trace  24  and power return trace  25  may be implemented using patterned conductive traces on one or more surfaces of PCB  90 . 
     Power return trace  25  may include multiple portions. Power return trace  25  may include portions such as portions  134  that run parallel to power supply line  24 , portions such as portions  130  that run perpendicular to power supply line  24  and portions such as portions  140  that form a portion of a loop that runs around compass  20  (e.g., on a surface of PCB  90 ). Perpendicular portions  130  may be configured to couple portion  140  to portions  134  of power return trace  25 . 
     Electric current that flows through portions  140  that form a portion of a circular loop around compass  20  may generate compensating magnetic fields parallel to the z-axis shown in  FIG. 15 . Compensating magnetic fields parallel to the z-axis may help counter interfering magnetic fields generated by power supply line  24  and/or component  22 . 
     Portions  140  that form a portion of a circular loop around compass  20  may run around compass  20  at a constant distance such as distance  142  from the center of compass  20  (e.g., the radius of partial conductive loop  140  may be equal to distance  142  or loop  140  may be a rectilinear loop around compass  20  at a constant distance from compass  20 ). 
     Because magnetic field strength depends on distance from the magnetic field generating source, the strength of a compensating magnetic field at compass  20  due to portion  140  may be determined by the size of distance  142  (e.g., a larger radius  142  results in a smaller compensating magnetic field). Portion  140  of power return trace  25  may be configured to have radius  142  that results in a compensating magnetic field at compass  20  that is substantially opposite to an interfering magnetic field generated by power supply line  24  and component  22 . 
     As shown in  FIG. 16 , a power supply line such as power supply line  24  that supplies electric current from circuitry such as power supply unit  38  to a component such as component  22  may have an associated power return trace such as power return trace  25  that includes a portion that runs parallel to power supply line  24  and a branch that runs in the direction of compass  20 . 
     Power return trace  25  may include a branch such as branch  25 P that carries return current from component  22  along a path that runs parallel to power supply line  24 . Branch  25 P may be coupled to an additional branch  25 C of power return trace  25 . Branch  25 C may be a compensating magnetic field branch for generating compensating magnetic fields that compensate for interfering magnetic fields for compass  20  generated by component  22 . Branch  25 P may be configured to generate compensating magnetic fields that compensate for interfering magnetic fields generated by current flowing in power supply line  24 . 
     Power return trace  25  may include a portion such as portion  134  that runs perpendicular to power supply line  24  and portions such as portions  132  and  133  that run at angles (e.g., acute angles or obtuse angles) to power supply line  24 . Branches  25 P and  25 C may be implemented using patterned conductive traces on a surface of PCB  90 . 
     Some portions (e.g., portion  132 ) of power return trace  25 C may be shorter than other portions (e.g., portion  133 ) of return trace  25 C. Return trace  25 C may be configured to pass at a minimum distance such as minimum distance  136  from compass  20 . Minimum distance  136  may be significantly smaller than a minimum distance such as minimum distance  106  between power supply trace  24  and compass  20 . 
     Branch  25 C of power return trace  25  may deviate away from a path defined by power supply path  24  toward compass  20 . 
     Power return trace  25 D may run alongside power supply trace  24  so that a power return trace  25 D and power supply trace  24  have a minimum distance such as distance  108  that is smaller than a distance such as distance  106  from power supply line  24  to a magnetic sensitive component such as compass  20 . 
     Because magnetic field strength depends on distance from the magnetic field generating source, providing PCB  90  with a power return trace  25 C having a minimum distance  136  that is smaller than the distance (e.g., distance  106 ) from power supply line  24  may help generate compensating magnetic fields that compensate for interfering magnetic fields electronic components such as components  22 . This is because interfering magnetic fields at compass  20  generated by electronic component  22  may be larger than a compensating magnetic field generated by return trace  25 C at the same distance. 
     The closer proximity of power return trace  25 C to compass  20  may result in a magnetic field strength at compass  20  from power return trace  25 C relative to a magnetic field strength from power supply trace  24  at compass  20  even if the current flowing in both is the same. 
     Current flowing through a branch such as branch  25 P of power return trace  25  that runs alongside (and parallel to) power supply trace  24  may generate a compensating magnetic field that is substantially equal in magnitude and opposite in direction at compass  20  to an interfering magnetic field generated by current flowing in associated power supply line  24 . In this way, branches  25 C and  25 D of power return trace  25  may help reduce or eliminate magnetic interference for compass  20  from power supply line  25  and component  22 . 
     As shown in  FIG. 16 , branches  25 C and  25 P of power return trace  25  may be provided with resistors such as resistors  150  and  152  respectively. Resistors  150  and  152  may have a predetermined or variable resistance. Resistors  150  and  152  may control the relative amount of electric current that flows through branches  25 C and  25 P of power return trace  25 . Providing branches  25 C and  25 P of power return trace  25  with resistors  150  and  152  respectively may help generate compensating magnetic fields generated by branches  25 C and  25 P that better compensate for interfering magnetic fields generated by power supply line  24  and component  22  by allowing different respective current levels in branches  25 C and  25 P. 
     If desired, branch  25 C of power return trace  25  may include a portion such as portion  140  that runs around a magnetic sensor such as compass  20  as shown in  FIG. 17 . 
     As shown in the examples of  FIGS. 16 , and  17 , power supply traces  24  may be coupled to a positive power supply terminal such as terminal  115  of a power source as power management unit  38 . Branch  25 C may be coupled to branch  25 P of power return trace  25 . Branches  25 P and  25 C may electrically couple component  22  to a ground power supply terminal such as terminal  117  or may couple component  22  to a ground conductor through a ground contact such as contact  119 . 
     Portions  140  of branch  25 C of power supply line  25  that form a portion of a circular loop around compass  20  may be implemented as patterned conductive traces on PCB  90  that run around compass  20  on a surface of PCB  90  at a constant distance such as distance  142  from the center of compass  20  (e.g., the radius of partial conductive loop  140  may be equal to distance  142 ). 
     A compensating magnetic field at compass  20  due to portion  140  may be enhanced using a partial loop such as portion  140  at a predetermined constant distance  142  from compass  20 . Portions  140 ,  132 ,  133 , and  134  of branch  25 C may combine with branch  25 P (parallel to power supply trace  24 ) of power return trace  25  to generate a compensating magnetic field at compass  20  that is substantially opposite to an interfering magnetic field generated by power supply line  24  and one or more components such as component  22 . 
     The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention.

Metadata:
Filing Date: 20111027
Publication Date: 20150602
Grant Date: 20150602
Priority Date: 20111027
Inventors: WADE JEREMY L.
ENG MICHAEL
GARRONE RYAN J.
BROWN MARK
Assignee: APPLE INC
CPC Classifications: [{"code": "G01C17/28", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01C17/28", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01C17/28", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01C21/00", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 48170917