PATENT DOCUMENT

Publication Number: US-8626101-B2
Application Number: US-201113212990-A
Country: US
Kind Code: B2

Title: Wireless electronic device with antenna cycling

Abstract:
A wireless electronic device may contain multiple antennas. Control circuitry in the wireless electronic device may adjust antenna switching circuitry so that the device repeatedly cycles through use of each of the antennas. In a device with first and second antennas, the device may repeatedly toggle between the first and second antennas. During each toggling cycle time period, the first antenna may transmit for a fraction of the time period and the second antenna may transmit for a fraction of the time period. The wireless device may control the average power emitted by each antenna by adjusting the fractions of time assigned to each antenna. By performing antenna toggling, the average transmit power produced by each antenna may be reduced while maintaining the average transmit power produced by the device at a desired level.

Claims:
What is claimed is: 
     
       1. A wireless electronic device, comprising:
 at least first and second antennas; 
 at least one radio-frequency transmitter; 
 switching circuitry coupled between the transmitter and the first and second antennas, wherein the switching circuitry is configured to route radio-frequency signals from the radio-frequency transmitter to a selected one of the first and second antennas; 
 control circuitry configured to repeatedly toggle the switching circuitry between a first configuration in which the radio-frequency signals are transmitted through the first antenna for a first fraction of a toggling cycle time period and a second configuration in which the radio-frequency signals are transmitted through the second antenna for a second fraction of the toggling cycle time period; and 
 an accelerometer that generates orientation data, wherein the control circuitry is further configured to adjust the first and second fractions based at least partly on orientation data from the accelerometer. 
 
     
     
       2. The wireless electronic device defined in  claim 1  further comprising at least one sensor, wherein the control circuitry is further configured to adjust the first and second fractions based at least partly on data from the sensor. 
     
     
       3. The wireless electronic device defined in  claim 2  wherein the sensor comprises a proximity sensor. 
     
     
       4. The wireless electronic device defined in  claim 2  further comprising a housing having first and second opposing ends, wherein the first antenna is located at the first end and the second antenna is located at the second end. 
     
     
       5. The wireless electronic device defined in  claim 1  further comprising a housing having first and second opposing ends, wherein the first antenna is located at the first end and the second antenna is located at the second end. 
     
     
       6. A method of operating a wireless electronic device having first and second antennas, a radio-frequency transmitter, control circuitry, and switching circuitry that selectively routes radio-frequency signals from the transmitter to the first and second antennas in response to signals from the control circuitry, comprising:
 repeatedly toggling the switching circuitry between a first configuration in which the radio-frequency signals are transmitted through the first antenna for a first fraction of a toggling cycle time period and a second configuration in which the radio-frequency signals are transmitted through the second antenna for a second fraction of the toggling cycle time period; and 
 with the control circuitry, adjusting the first and second fractions based at least partly on antenna efficiencies of the first and second antennas. 
 
     
     
       7. The method defined in  claim 6  wherein repeatedly toggling the switching circuitry comprises applying control signals to the switching circuitry from the control circuitry. 
     
     
       8. The method defined in  claim 7  wherein the wireless electronic device includes at least one sensor, the method further comprising:
 with the control circuitry, adjusting the first and second fractions based at least partly on data from the at least one sensor. 
 
     
     
       9. The method defined in  claim 8  wherein the at least one sensor comprises a proximity sensor and wherein adjusting the first and second fractions comprises adjusting the first and second fractions based at least partly on proximity sensor data from the proximity sensor. 
     
     
       10. The method defined in  claim 8  wherein the at least one sensor comprises an accelerometer and wherein adjusting the first and second fractions comprises adjusting the first and second fractions based at least partly on data from the accelerometer. 
     
     
       11. The method defined in  claim 10  wherein the wireless electronic device has a housing with first and second opposing ends, wherein the first antenna is located at the first end and the second antenna is located at the second end, and wherein repeatedly toggling the switching circuitry comprises repeatedly toggling the switching circuitry between the first configuration so that the radio-frequency signals are transmitted through the first antenna at the first end and the second configuration so that the radio-frequency signals are transmitted through the second antenna at the second end. 
     
     
       12. The method defined in  claim 6  wherein the wireless electronic device has a housing with first and second opposing ends, wherein the first antenna is located at the first end and the second antenna is located at the second end, and wherein repeatedly toggling the switching circuitry comprises repeatedly toggling the switching circuitry between the first configuration so that the radio-frequency signals are transmitted through the first antenna at the first end and the second configuration so that the radio-frequency signals are transmitted through the second antenna at the second end. 
     
     
       13. A method of transmitting radio-frequency signals with a wireless electronic device having at least first and second antennas, comprising:
 during each of a plurality of repeating cycles each of which has an associated cycle time period, transmitting radio-frequency signals for a first fraction of the cycle time period using the first antenna and transmitting radio-frequency signals for a second fraction of the cycle time period using the second antenna; 
 determining whether the first antenna is closer to an external object than a second antenna; and 
 in response to determining that the first antenna is closer to the external object than the second antenna, reducing the first fraction of the cycle time period and increasing the second fraction of the cycle time period. 
 
     
     
       14. The method defined in  claim 13  further comprising:
 while transmitting the radio-frequency signals using the first and second antennas, adjusting the first and second fractions of the cycle time period based on data from a sensor within the wireless electronic device. 
 
     
     
       15. The method defined in  claim 14  wherein the sensor comprises a proximity sensor and wherein adjusting the first and second fractions comprises adjusting the first and second fractions based on data from the proximity sensor. 
     
     
       16. The method defined in  claim 14  wherein the sensor comprises an accelerometer and wherein adjusting the first and second fractions comprises adjusting the first and second fractions based on data from the accelerometer. 
     
     
       17. The method defined in  claim 13  wherein the wireless electronic device comprises transmitter circuitry and switching circuitry that routes radio-frequency signals from the transmitter circuitry to the first and second antennas and wherein transmitting the radio-frequency signals for the first fraction of the cycle time period using the first antenna and transmitting the radio-frequency signals for the second fraction of the cycle time period using the second antenna comprises controlling the switching circuitry. 
     
     
       18. The method defined in  claim 13  wherein the wireless electronic device has a housing with first and second opposing ends, wherein the first antenna is located at the first end and the second antenna is located at the second end, wherein transmitting the radio-frequency signals with the first antenna comprises transmitting the radio-frequency signals with the first antenna at the first end, and wherein transmitting the radio-frequency signals with the second antenna comprises transmitting the radio-frequency signals with the second antenna at the second end. 
     
     
       19. The method defined in  claim 13  wherein the radio-frequency signals are transmitted with an average power, the method further comprising:
 adjusting the first and second fractions while maintaining the average power of the radio-frequency signals. 
 
     
     
       20. The method defined in  claim 13  further comprising:
 adjusting the first and second fractions based on signal strength of wireless signals received from a base station.

Description:
BACKGROUND 
     This invention relates generally to electronic devices, and more particularly, to wireless electronic devices that have two or more antennas. 
     Electronic devices such as handheld electronic devices and other portable electronic devices are becoming increasingly popular. Examples of handheld devices include handheld computers, cellular telephones, media players, and hybrid devices that include the functionality of multiple devices of this type. Popular portable electronic devices that are somewhat larger than traditional handheld electronic devices include laptop computers and tablet computers. 
     Due in part to their mobile nature, portable electronic devices are often provided with wireless communications capabilities. For example, portable electronic devices may use long-range wireless communications to communicate with wireless base stations and may use short-range wireless communications links such as links for supporting the Wi-Fi® (IEEE 802.11) bands at 2.4 GHz and 5.0 GHz and the Bluetooth® band at 2.4 GHz. 
     To satisfy consumer demand for small form factor wireless devices, manufacturers are continually striving to reduce the size of components that are used in these devices while providing enhanced functionality. It is generally impractical to completely shield a user of a portable device from transmitted radio-frequency signals. For example, conventional cellular telephone handsets generally emit signals in the vicinity of a user&#39;s head during telephone calls. Government regulations limit radio-frequency signal powers. In particular, so-called specific absorption rate (SAR) standards are in place that impose maximum energy absorption limits on handset manufacturers. At the same time, wireless carriers require that the handsets that are used in their networks be capable of producing certain minimum radio-frequency power levels so as to ensure satisfactory operation of the handsets. 
     The manufacturers of portable wireless electronic devices therefore face challenges in producing devices with adequate wireless performance that are compliant with applicable government regulations. 
     It would therefore be desirable to be able to provide electronic devices with improved wireless communications capabilities. 
     SUMMARY 
     A wireless electronic device may be subject to maximum energy absorption limits that restrict the maximum wireless transmit powers of the device. The wireless electronic device may have two or more antennas. The wireless electronic device may perform periodic antenna switching operations to provide increased energy absorption safety margins and increased performance. 
     For example, in a wireless device with a first antenna at one end of the device and a second antenna at an opposing end of the device, the device may repeatedly cycle between a first configuration in which a first antenna is active and a second configuration in which a second antenna is active. During each time period in this switching cycle, the first antenna may be active for a first fraction of the time period and the second antenna may be active for a second fraction of the time period. By toggling between antennas in this way, the amount of power emitted for each antenna may be reduced to help provide additional safety margin while satisfying performance criteria. 
     By adjusting the fractions of time that the first and second antennas are active for each cycle time period while toggling between the first and second antennas, the wireless device may control the time-averaged power emitted by each antenna and distribute radio-frequency power more evenly in space. The antenna toggling process may therefore reduce the concentration of wireless emissions produced by each antenna while maintaining a desired overall emitted power level. 
     Further features of the present 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 view of an illustrative electronic device with antenna toggling capabilities in accordance with an embodiment of the present invention. 
         FIG. 2  is a schematic diagram of an illustrative portable electronic device in accordance with an embodiment of the present invention. 
         FIG. 3  is a diagram of an illustrative scenario in which radio-frequency transmissions may be toggled between a first and second antenna in accordance with an embodiment of the present invention. 
         FIG. 4  is a diagram of an illustrative antenna toggling scheme that may be used in the scenario of  FIG. 3  in accordance with an embodiment of the present invention. 
         FIG. 5  is a diagram of an illustrative scenario in which a first antenna may be assigned a smaller fraction of a toggling cycle time period than a second antenna in accordance with an embodiment of the present invention. 
         FIG. 6  is a diagram of an illustrative antenna toggling scheme that may be used in the scenario of  FIG. 5  in accordance with an embodiment of the present invention. 
         FIG. 7  is a diagram illustrating how a wireless device that performs antenna toggling may accommodate desired transmit power levels while providing increased energy emission safety margins in accordance with an embodiment of the present invention. 
         FIG. 8  is a diagram showing how control circuitry in an electronic device may be used to periodically adjust switching circuitry in the device to toggle between use of first and second antennas in accordance with an embodiment of the present invention. 
         FIG. 9  is a flow chart of illustrative steps that may be performed to compute fractions of time that each antenna is to be active in accordance with an embodiment of the present invention. 
         FIG. 10  is a flow chart of illustrative steps that may be performed to toggle between first and second antenna when transmitting data in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention relates generally to wireless communications, and more particularly, to wireless electronic devices that perform antenna toggling when transmitting radio-frequency signals. 
     The wireless electronic devices may be portable electronic devices such as laptop computers or small portable computers of the type that are sometimes referred to as ultraportables. Portable electronic devices may include tablet computing devices (e.g., a portable computer that includes a touch-screen display). Portable electronic devices may also be somewhat smaller devices. Examples of smaller portable electronic devices include wrist-watch devices, pendant devices, headphone and earpiece devices, and other wearable and miniature devices. With one suitable arrangement, the portable electronic devices may be handheld electronic devices. 
     The wireless electronic devices may be, for example, cellular telephones, media players with wireless communications capabilities, handheld computers (also sometimes called personal digital assistants), remote controllers, global positioning system (GPS) devices, tablet computers, and handheld gaming devices. The wireless electronic devices may also be hybrid devices that combine the functionality of multiple conventional devices. Examples of hybrid portable electronic devices include a cellular telephone that includes media player functionality, a gaming device that includes a wireless communications capability, a cellular telephone that includes game and email functions, and a portable device that receives email, supports mobile telephone calls, has music player functionality and supports web browsing. These are merely illustrative examples. 
     An illustrative portable electronic device in accordance with an embodiment of the present invention is shown in  FIG. 1 . Device  10  of  FIG. 1  may be, for example, a portable electronic device. 
     Device  10  may have housing  12 . Antennas for handling wireless communications may be housed within housing  12  (as an example). 
     Housing  12 , which is sometimes referred to as a case, may be formed of any suitable materials including, plastic, glass, ceramics, metal, or other suitable materials, or a combination of these materials. In some situations, housing  12  or portions of housing  12  may be formed from a dielectric or other low-conductivity material, so that the operation of conductive antenna elements that are located in proximity to housing  12  is not disrupted. Housing  12  or portions of housing  12  may also be formed from conductive materials such as metal. An illustrative housing material that may be used is anodized aluminum. Aluminum is relatively light in weight and, when anodized, has an attractive insulating and scratch-resistant surface. If desired, other metals can be used for the housing of device  10 , such as stainless steel, magnesium, titanium, alloys of these metals and other metals, etc. In scenarios in which housing  12  is formed from metal elements, one or more of the metal elements may be used as part of the antennas in device  10 . For example, metal portions of housing  12  may be shorted to an internal ground plane in device  10  to create a larger ground plane element for that device  10 . To facilitate electrical contact between an anodized aluminum housing and other metal components in device  10 , portions of the anodized surface layer of the anodized aluminum housing may be selectively removed during the manufacturing process (e.g., by laser etching). 
     Housing  12  may have a bezel  14 . The bezel  14  may be formed from a conductive material and may serve to hold a display or other device with a planar surface in place on device  10 . As shown in  FIG. 1 , for example, bezel  14  may be used to hold display  16  in place by attaching display  16  to housing  12 . 
     Display  16  may be a liquid crystal diode (LCD) display, an organic light emitting diode (OLED) display, or any other suitable display. The outermost surface of display  16  may be formed from one or more plastic or glass layers. If desired, touch screen functionality may be integrated into display  16  or may be provided using a separate touch pad device. An advantage of integrating a touch screen into display  16  to make display  16  touch sensitive is that this type of arrangement can save space and reduce visual clutter. 
     Display screen  16  (e.g., a touch screen) is merely one example of an input-output device that may be used with electronic device  10 . If desired, electronic device  10  may have other input-output devices. For example, electronic device  10  may have user input control devices such as button  19 , and input-output components such as port  20  and one or more input-output jacks (e.g., for audio and/or video). Button  19  may be, for example, a menu button. Port  20  may contain a 30-pin data connector (as an example). Openings  24  and  22  may, if desired, form microphone and speaker ports. In the example of  FIG. 1 , display screen  16  is shown as being mounted on the front face of portable electronic device  10 , but display screen  16  may, if desired, be mounted on the rear face of portable electronic device  10 , on a side of device  10 , on a flip-up portion of device  10  that is attached to a main body portion of device  10  by a hinge (for example), or using any other suitable mounting arrangement. 
     If desired, device  10  may include sensors such as proximity sensors, accelerometers, or other sensors. The sensors may be built into housing  12  or formed in other locations in device  10 . For example, display  16  may be a touch screen display that detects when a head of a user is in contact with the touch screen display (e.g., when the user is making a phone call). Device  10  may include capacitive proximity sensors, light source based proximity sensors, touch sensors, radio-frequency based proximity sensors, or any other desirable proximity sensor. Device  10  may use the sensors to identify the positioning of device  10  relative to nearby objects. For example, device  10  may use the proximity sensor to identify that device  10  is near an object such as a head or a hand of a user. Device  10  may use multiple sensors to provide more accurate information about the positioning of the device. As an example, device  10  may use a first proximity sensor to identify that the device is held near a head of a user, may use a second proximity sensor to identify that the device is being held by a hand, and may use an accelerometer to identify that the device is being held at an angle. 
     A user of electronic device  10  may supply input commands using user input interface devices such as button  19  and touch screen  16 . Suitable user input interface devices for electronic device  10  include buttons (e.g., alphanumeric keys, power on-off, power-on, power-off, and other specialized buttons, etc.), a touch pad, pointing stick, or other cursor control device, a microphone for supplying voice commands, or any other suitable interface for controlling device  10 . Although shown schematically as being formed on the top face of electronic device  10  in the example of  FIG. 1 , buttons such as button  19  and other user input interface devices may generally be formed on any suitable portion of electronic device  10 . For example, a button such as button  19  or other user interface control may be formed on the side of electronic device  10 . Buttons and other user interface controls can also be located on the top face, rear face, or other portion of device  10 . If desired, device  10  can be controlled remotely (e.g., using an infrared remote control, a radio-frequency remote control such as a Bluetooth remote control, etc.). 
     Electronic device  10  may have ports such as port  20 . Port  20 , which may sometimes be referred to as a dock connector, 30-pin data port connector, input-output port, or bus connector, may be used as an input-output port (e.g., when connecting device  10  to a mating dock connected to a computer or other electronic device). Device  10  may also have audio and video jacks that allow device  10  to interface with external components. Typical ports include power jacks to recharge a battery within device  10  or to operate device  10  from a direct current (DC) power supply, data ports to exchange data with external components such as a personal computer or peripheral, audio-visual jacks to drive headphones, a monitor, or other external audio-video equipment, a subscriber identity module (SIM) card port to authorize cellular telephone service, a memory card slot, etc. The functions of some or all of these devices and the internal circuitry of electronic device  10  can be controlled using input interface devices such as touch screen display  16 . 
     Components such as display  16  and other user input interface devices may cover most of the available surface area on the front face of device  10  (as shown in the example of  FIG. 1 ) or may occupy only a small portion of the front face of device  10 . Because electronic components such as display  16  often contain large amounts of metal (e.g., as radio-frequency shielding), the location of these components relative to the antenna elements in device  10  should generally be taken into consideration. Suitably chosen locations for the antenna elements and electronic components of the device will allow the antennas of electronic device  10  to function properly without being disrupted by the electronic components. 
     Examples of locations in which antenna structures may be located in device  10  include region  18  (e.g., a first antenna) and region  21  (e.g., a second antenna). These are merely illustrative examples. Any suitable portion of device  10  may be used to house antenna structures for device  10  if desired. 
     A schematic diagram of an embodiment of an illustrative portable wireless electronic device such as a portable electronic device is shown in  FIG. 2 . Portable device  10  may be a mobile telephone, a mobile telephone with media player capabilities, a handheld computer, a laptop computer, a tablet computer, an ultraportable computer, a combination of such devices, or any other suitable portable electronic device. 
     As shown in  FIG. 2 , device  10  may include control circuitry  35  such as processing circuitry  36  and storage  34 . 
     Storage  34  may include one or more different types of storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory), volatile memory (e.g., battery-based static or dynamic random-access-memory), etc. 
     Processing circuitry  36  may be used in control circuitry  35  to control the operation of device  10 . For example, processing circuitry  36  and storage  34  of control circuitry  35  may be used in adjusting switching circuitry for controlling which antenna in device  10  is being used as a currently active antenna and may be used in implementing other control functions. 
     Processing circuitry  36  may be based on a processor such as a microprocessor and other suitable integrated circuits. With one suitable arrangement, processing circuitry  36  and storage  34  are used to run software on device  10 , such as internet browsing applications, voice-over-internet-protocol (VOIP) telephone call applications, email applications, media playback applications, operating system functions, etc. Processing circuitry  36  and storage  34  may be used in implementing suitable communications protocols. Communications protocols that may be implemented using processing circuitry  36  and storage  34  include internet protocols, wireless local area network protocols (e.g., IEEE 802.11 protocols—sometimes referred to as Wi-Fi®), protocols for other short-range wireless communications links such as the Bluetooth® protocol, protocols for handling 3G data services such as UMTS, cellular telephone communications protocols, protocols for handling 4G data services such as LTE, etc. 
     Input-output devices  38  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Display screen  16 , button  19 , microphone port  24 , speaker port  22 , and dock connector port  20  are examples of input-output devices  38 . 
     Input-output devices  38  can include user input-output devices  40  such as buttons, touch screens, joysticks, click wheels, scrolling wheels, touch pads, key pads, keyboards, microphones, cameras, etc. A user can control the operation of device  10  by supplying commands through user input devices  40 . Display and audio devices  42  may include liquid-crystal display (LCD) screens or other screens, light-emitting diodes (LEDs), and other components that present visual information and status data. Display and audio devices  42  may also include audio equipment such as speakers and other devices for creating sound. Display and audio devices  42  may contain audio-video interface equipment such as jacks and other connectors for external headphones and monitors. 
     Wireless communications devices  44  may include communications circuitry such as radio-frequency (RF) transceiver circuitry formed from one or more integrated circuits, power amplifier circuitry (e.g., power amplifier circuitry that is controlled by control signals from processing circuitry  36  to minimize power consumption), passive RF components, antennas, and other circuitry for handling RF wireless signals. Wireless signals can also be sent using light (e.g., using infrared communications). 
     Sensing circuitry  45  may include proximity sensors such as capacitive proximity sensors, touch sensors, light-emitting photosensors, inductive proximity sensors, touch screen sensors, radio-frequency antenna-based proximity sensors, and other desirable proximity sensors. Sensing circuitry  45  may also include accelerometers and other sensing circuitry. 
     Wireless network  49  may include any suitable network equipment, such as cellular telephone base stations, cellular towers, wireless data networks, computers associated with wireless networks, etc. For example, wireless network  49  may include network management equipment that monitors the wireless signal strength of the wireless handsets (cellular telephones, handheld computing devices, etc.) that are in communication with network  49 . 
     To improve the overall performance of the network and to ensure that interference between handsets is minimized, the network management equipment may send power adjustment commands (sometimes referred to as transmit power control commands) to each handset. The transmit power control settings that are provided to the handsets direct handsets with weak signals to increase their transmit powers, so that their signals will be properly received by the network. At the same time, the transmit power control settings may instruct handsets whose signals are being received clearly at high power to reduce their transmit power control settings. This reduces interference between handsets and allows the network to maximize its use of available wireless bandwidth. 
     The antenna structures and wireless communications devices of device  10  may support communications over any suitable wireless communications bands. For example, wireless communications devices  44  may be used to cover communications frequency bands such as cellular telephone voice and data bands at 850 MHz, 900 MHz, 1800 MHz, 1900 MHz, and the communications band data at 2170 MHz band (commonly referred to as a UMTS or Universal Mobile Telecommunications System band), the Wi-Fi® (IEEE 802.11) bands at 2.4 GHz and 5.0 GHz (also sometimes referred to as wireless local area network or WLAN bands), the Bluetooth® band at 2.4 GHz, and the global positioning system (GPS) band at 1550 MHz. If desired, wireless communications devices  44  may also be used to cover the Long Term Evolution (LTE) uplink and downlink communications frequency bands. 
     Device  10  can cover these communications bands and/or other suitable communications bands with proper configuration of the antenna structures in wireless communications circuitry  44 . Any suitable antenna structures may be used in device  10 . For example, device  10  may have multiple antennas. The antennas in device  10  may each be used to cover a single communications band or each antenna may cover multiple communications bands. If desired, one or more antennas may cover a single band while one or more additional antennas are each used to cover multiple bands. These are merely illustrative arrangements. Any suitable antenna structures may be used in device  10  if desired. 
     A wireless device such as device  10  may be operated in scenarios in which restrictions are imposed on the radio-frequency power emitted by the device. Device  10  that communicates with a cellular base station may be required to meet specific absorption rate (SAR) requirements (e.g., due to government regulations). The SAR requirements may impose limits on the amount of power that is emitted from device  10  and absorbed by a nearby object. For example, government regulations may require that less than 2 Watts per Kilogram is absorbed from device  10  by a nearby object. 
     As an example, device  10  may communicate with a base station that directs the device to increase or decrease transmit power levels (e.g., to maintain acceptable levels of radio-frequency signals received at the base station). In this scenario, the base station may identify that radio-frequency signals received from the device are relatively poor (e.g., because the device is too far away from the base station or because there are interfering radio-frequency signals from other devices). The base station may direct device  10  to increase transmit powers so that signal quality at the base station is improved. However, increased transmit power levels may emit concentrations of radio-frequency power that exceed acceptable levels. Device  10  may be unable to comply with the instructions from the base station (e.g., because of government regulations) and wireless communications between the device and the base station may be disrupted (e.g., because wireless transmissions produced by device  10  may have insufficient power to reach the base station). 
     To increase radio-frequency transmit power levels and reduce the concentration of radiated energy from the device, device  10  may perform antenna toggling.  FIG. 3  shows an illustrative scenario in which a device  10  located near an object  202  may perform antenna toggling. As shown in  FIG. 3 , device  10  may have a first antenna ANT 1  and a second antenna ANT 2 . Device  10  may be subject to energy absorption limits such as specific absorption ratio (SAR) requirements that limit the amount of power that is allowed to be absorbed by any given portion of object  202 . As an example, SAR requirements may limit the maximum amount of radio-frequency power absorbed by any given portion of object  202  from device  10  to 1.6 Watts per kilogram. 
     Device  10  may toggle between antennas ANT 1  and ANT 2  by repeatedly cycling between antennas ANT 1  and ANT 2  (e.g., using switching circuitry). Region  208  of object  202  may absorb most of the radio-frequency signals transmitted by antenna ANT 1  and region  210  of object  202  may absorb most of the radio-frequency signals transmitted by antenna ANT 2 . By toggling between antennas ANT 1  and ANT 2 , the average power absorbed by object  202  from device  10  may be distributed over an increased area (e.g., the combined area of regions  208  and  210 ). Therefore the average power absorbed by any given region of object  202  may be reduced. 
     In the scenario of  FIG. 3 , the energy emitted into portion  208  by antenna ANT 1  may be substantially equal to the energy emitted into portion  210  by antenna ANT 2  (e.g., because the distance between portion  208  and antenna ANT 1  may be the same as the distance between portion  210  and antenna ANT 2 ). To minimize the power absorbed by portion  208  and portion  210 , it may be desirable for device  10  to toggle equally between antennas ANT 1  and ANT 2 . 
     Antenna toggling may be performed based on repeating cycles. As shown in  FIG. 4 , device  10  may divide radio-frequency transmissions into toggling cycle time periods  212  that each correspond to a transmission time t. As an example, time t may correspond to the time required to transmit a given number of data packets. Each toggling cycle time period  212  may be partitioned into a first fraction (portion) transmitted by antenna ANT 1  and a second fraction transmitted by antenna ANT 2  (e.g., antenna ANT 1  may transmit during time t 1  of each toggling cycle time period, antenna ANT 2  may transmit during time t 2  of each toggling cycle time period, and time t may be the sum of times t 1  and t 2 ). 
     The proportions of times t 1  and t 2  relative to toggling cycle time period t may be selected to maximize a radio-frequency transmission power of device  10  while ensuring sufficient energy absorption safety margins (e.g., ensuring that SAR levels remain below a maximum allowable SAR level specified by government regulations). Times t 1  and t 2  may be selected based on antenna characteristics (e.g., antenna efficiency), the positioning of device  10  relative to objects such as objects  202  that are subject to specific absorption rate requirements, or the strength of signals received at each antenna from a base station (as examples). In a scenario such as  FIG. 3  in which the time-averaged power emitted by antennas ANT 1  and ANT 2  are equally absorbed by object  202 , times t 1  and t 2  may be assigned the same value (e.g., to equally partition radio-frequency signals between antennas ANT 1  and ANT 2 ). 
     Antenna toggling may be adjusted based on the position of device  10  relative to object  202 .  FIG. 5  shows an illustrative example of a device  10  positioned relative to object  202  such that radio-frequency transmissions from antenna ANT 1  have a greater effect on object  202  than radio-frequency transmissions from antenna ANT 2  (e.g., because antenna ANT 2  may be further away from object  202  than antenna ANT 1 ). In the example of  FIG. 5 , radio-frequency signals  256  from antenna ANT 2  may be mostly absorbed by object portion  260  and radio-frequency signals  254  from antenna ANT 1  may be mostly absorbed by object portion  258 . 
     To decrease the amount of radio-frequency power absorbed by object  202 , device  10  may increase the fraction of each toggling cycle time period that is assigned to antenna ANT 2  and decrease the fraction of each toggling cycle time period that is assigned to antenna ANT 1  (e.g., because object  202  absorbs less of the radio-frequency signals from antenna ANT 2  than the radio-frequency signals from antenna ANT 1 ). In this way, the safety of device  10  may be improved while maintaining transmission power levels of the device. 
       FIG. 6  shows how antenna toggling may be performed by wireless device  10  in a scenario such as  FIG. 5 . As shown in  FIG. 6 , each toggling cycle time period of a radio-frequency transmission may be partitioned into a first fraction (portion) transmitted by antenna ANT 1  over time t 3  and a second fraction transmitted by antenna ANT 2  over time t 4 . In the example of  FIG. 6 , the proportion of each toggling cycle time period assigned to antenna ANT 1  may be smaller than the proportion of each toggling cycle time period assigned to antenna ANT 2  (e.g., t 3  may be less than t 4 ). In this way, the average power transmitted by each antenna may be reduced (e.g., because each antenna transmits for only a fraction of each toggling cycle time period) while maintaining the average power transmitted by device  10 . 
     The examples of  FIGS. 3-6  showing antenna toggling between two antennas are merely illustrative. If desired, radio-frequency transmissions may be partitioned between any suitable number of antennas. For example, a wireless device  10  with three antennas may partition radio-frequency transmissions between the three antennas to provide improved performance and to reduce radio-frequency emissions of each antenna. 
     The positioning of device  10  relative to object  202  in  FIGS. 3 and 5  are merely illustrative. Device  10  may be located in many different positions (e.g., next to the head of a user, on a user&#39;s lap, in a user&#39;s pocket, in a user&#39;s hand, etc.). For each scenario, device  10  may adjust the fractions of each toggling cycle time period assigned to each antenna to maximize performance and ensure sufficient energy absorption safety margins. 
     By reducing the average power transmitted by each antenna using antenna toggling, device  10  may provide increased performance and energy absorption safety margins.  FIG. 7  is an illustrative diagram showing how antenna toggling may decrease maximum measured SAR values for various required transmit powers. The maximum measured SAR values may correspond to the maximum power absorbed by any portion of object  202  for a given required transmit power and a given position of device  10  (e.g., the device position of  FIG. 3  or  FIG. 5 ). The required transmit power may be provided by a cellular base station (e.g., provided by transmit power control commands that are sent from the cellular base station to device  10 ). 
     In the example of  FIG. 7 , line  312  may correspond to maximum measured SAR values for a conventional wireless device (e.g., a device that does not perform antenna toggling). As shown by line  312 , the maximum measured SAR values may be proportional to the required transmit power (e.g., a minimum transmit power required to communicate with a cellular base station). At transmit power TX 1 , the maximum measured SAR value for the conventional device may reach a maximum allowed SAR value (e.g., a maximum allowed SAR value determined by government regulations). At transmit powers greater than TX 1 , SAR values measured from the conventional device may exceed the maximum allowed value. To avoid violating government regulations, the conventional device may be unable to increase transmit power levels beyond TX 1 . 
     A device that does not perform antenna toggling may be unable to comply with commands from a cellular base station to increase transmit powers beyond TX 1  (e.g., transmit power control commands). As an example, a cellular base station may instruct the conventional wireless device to increase transmit power to a value greater than TX 1  when the cellular base station receives a relatively weak transmitted signal from the conventional device (e.g., when the device is too far away from the cellular base station). If the wireless device is unable to increase transmit power beyond TX 1 , communication with the cellular base station may be undesirably disrupted. 
     A wireless device  10  that performs antenna toggling may produce maximum measured SAR values that correspond to line  314 . As shown by line  314 , the maximum measured SAR values for device  10  may be less than the maximum measured values for a conventional device for any given required transmit power. For example, measured SAR values for device  10  at transmit power TX 1  may have a maximum value V 1 . V 1  may be less than the maximum allowed SAR value and provide improved margins of safety (e.g., a device  10  that produces maximum measured SAR values of V 1  at a transmit power of TX 1  may provide improved safety margins over a conventional device that produces the maximum allowed SAR value at transmit power TX 1 ). 
     By performing antenna toggling, device  10  may provide improved wireless performance. As shown in  FIG. 7 , device  10  may be able to provide transmit powers that are greater than TX 1  while maintaining acceptable energy absorption safety margins. At a required transmit power of TX 2 , device  10  may produce a maximum measured SAR value of V 2  that is less than the maximum allowed SAR value (as an example). A conventional wireless device would be unable to increase transmit powers to TX 2 , because the convention device would produce unacceptable SAR values (e.g., because V 3  exceeds the maximum allowed SAR value). By performing antenna toggling, device  10  may be able to increase transmit power levels to TX 3  while maintaining acceptable energy absorption safety margins. 
       FIG. 8  is a diagram showing how control circuitry  35  may be used in controlling switching circuitry to toggle between first and second antennas in device  10 . If desired, more than two antennas may be used in device  10  and control circuitry  35  may direct the switching circuitry to sequence through the use of each of these antennas. The example of  FIG. 8  in which device  10  has a pair of antennas and in which control circuitry  35  is used to toggle repeatedly back and forth between the two antennas is merely illustrative. 
     As shown in  FIG. 8 , device  10  may include radio-frequency transceiver circuitry such as transceiver circuitry  100 . Transceiver circuitry  100  may include one or more transmitters such as transmitter  102  (e.g., one or more cellular telephone transmitters or transmitters associated with other radio access technologies). Transceiver circuitry  100  may also include one or more radio-frequency receiver circuits such as receiver  104  (e.g., for receiving cellular telephone signals or other wireless traffic). Control circuitry  35  may provide data that is to be wirelessly transmitted to transceiver circuitry  100  via path  114 . During signal reception operations, received data may be provided to control circuitry  35  from transceiver circuitry  100  via path  114 . 
     During operation, transmitted signals from transmitter  102  may be conveyed to antennas  44 A and  44 B (e.g., antennas ANT 1  and ANT 2  of  FIG. 3 ) via front-end circuitry  106 . Front-end circuitry  106  may also be used to convey radio-frequency signals from antennas  44 A and  44 B to receiver  104  during signal reception operations. 
     Front-end circuitry  106  may include filter circuitry such as duplexers and diplexers, impedance matching circuitry, switches such as switch  108 , and other radio-frequency circuitry for coupling transceiver circuitry  100  to antennas  44 A and  44 B. 
     Switching circuitry  108  may be controlled by control signals provided by control circuitry  35  over path  110 . The control signals may be generated by a processing circuit in control circuitry  35  (e.g., a baseband processor or a microprocessor). During operation of device  10 , the control signals on path  110  may direct switch  108  to alternate between first and second states. In the first state, antenna  44 A is switched into use and is coupled to transceiver circuitry  100  (via path  112 ). In the first state, antenna  44 B is isolated from transceiver circuitry  100  and therefore is not used in transmitting or receiving signals. In the second state, antenna  44 B is switched into use in place of antenna  44 A. In the second state, signals can be transmitted through antenna  44 B using transmitter  102  and signals can be received from antenna  44 B using receiver  104 . 
     To help balance the power that is transmitted through a given antenna, control circuitry  35  may toggle antennas  44 A and  44 B. For example, control circuitry  35  may issue control signals on path  110  so that switching circuitry  108  alternates between its first configuration in which antenna  44 A is switched into use and its second configuration in which antenna  44 B is switched into use. By periodically cycling between antennas  44 A and  44 B in this way, neither antenna is used exclusively and the time-averaged power emitted from each antenna is reduced. This may help device  10  comply with regulatory limits on emitted radio-frequency power (e.g., SAR requirements). 
     Any suitable partitioning scheme may be used to control the fraction of time that each antenna is active. With one suitable arrangement, control circuitry  35  may be configured to switch the first antenna into use for a first fraction of a time period and may be configured to switch the second antenna into use for a second fraction of a time period. The sum of the first and second fractions of the time period may be equal to the length of the time period, so that either the first or second antenna (but not both) is active at any point in time. As described in connection with  FIG. 6 , for example, control circuitry  35  may toggle between use of the first and second antennas with a period t. During each period t, antenna  44 A may be active for subperiod t 3  (i.e., the fraction of time that antenna  44 A is active is t 3 /t). Antenna  44 B may be active for subperiod t 4  within each period (i.e., the fraction of time that antenna  44 B is active is t 4 /t). Because t 3 +t 4  is equal to t, at least one of the two antennas will be used at any point in time. 
     In configurations of device  10  in which accelerometers, proximity sensors, or other sources of proximity information, orientation information, etc. are available, device  10  may control the relative amount of time that each antenna is active in real time. For example, if control circuitry  35  receives information from sensors  45  indicating that antenna  44 A is closer to an external object than antenna  44 B (or is otherwise likely to emit more signal power into the external object than antenna  44 B), control circuitry  35  may increase time period t 4  and can decrease time period t 3  by a corresponding amount. The period t may be maintained at a constant value (as an example), but the fraction of time that antenna  44 A is used may be decreased while the fraction of time that antenna  44 B is used may be increased. During operation, device  10  may therefore continually adjust the duty cycle (fraction of time in which each antenna is active) for each antenna to help distribute the localized emission of radio-frequency signal power in a way that ensures regulatory compliance. 
     Device  10  may continually update the optimum values of t 3  and t 4  in real time based on sensor data. As shown in  FIG. 9 , control circuitry  35  may, at step  116 , receive sensor data from sensors  45  (e.g., accelerometer data indicating the position of device  10  and therefore a probable position relative to an external object, proximity sensor data indicating the position of device  10  relative to an external object, etc.). Based on the sensor data and other data (e.g., information on the relative efficiencies of each antenna, information on the spatial radiation-emission properties of each antenna, etc.), control circuitry  35  may, at step  118 , update the values of t 3  and t 4 . As shown by line  120 , the operations of steps  116  and  118  may be performed continually in real time, so that device  10  is continually provided with updated information on an optimal allocation between use of antenna  44 A and antenna  44 B. 
     Steps involved in transmitting signals from device  10  based on the settings produced during the operations of  FIG. 9  or based on default (e.g., fixed) settings are shown in  FIG. 10 . During the operations of  FIG. 10 , device  10  may toggle back and forth repeatedly between antennas  44 A and  44 B, so that neither antenna is used continuously. In this way, emitted radio-frequency signals are effectively spread across both antennas and an enlarged portion of device  10 . If, for example, antenna  44 A is located at one end of device  10  whereas antenna  44 B is located at another end of device  10 , toggling between the two antennas will tend to spread the radiated power from device  10  across both ends of device  10 , rather than concentrating this power at only one end of device  10 . 
     Transmitter  102  may be used in transmitting signals for both antenna  44 A and antenna  44 B. Switching circuitry  108  may be toggled between its first and second configurations. During the operations of step  122 , control circuitry  35  may place switching circuitry  108  in its first configuration, so that transmitted radio-frequency signals from transmitter  102  are transmitted through first antenna  44 A. During the operations of step  124 , control circuitry  35  may place switching circuitry  108  in its second configuration, so that transmitted radio-frequency signals from transmitter  102  are transmitted through second antenna  44 B. The operations of steps  122  and  124  may each be performed once per toggling cycle time period (i.e., step  122  is performed once and step  124  is performed once per each of the complete toggling cycles indicated by line  124 ). 
     Each loop (cycle) through the steps  122  and  124  therefore corresponds to a separate toggling cycle time period t (i.e., the period of a complete toggling cycle that involves use of each antenna for its respective fraction of time is equal to t). The duration that the first antenna is used (step  122 ) is time t 3  and the fraction of time that the first antenna is used during the toggling cycle time period is t 3 /t. The duration that the second antenna is used (step  124 ) is time t 4  and the fraction of time that the second antenna is used during the toggling cycle time period is t 4 /t. 
     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: 20110818
Publication Date: 20140107
Grant Date: 20140107
Priority Date: 20110818
Inventors: STALLMAN MICHAEL J.
LUM NICHOLAS W.
Assignee: APPLE INC
CPC Classifications: [{"code": "H04B1/3838", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B1/3838", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B7/0814", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q21/28", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04B7/0814", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01Q21/28", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 47712982