PATENT DOCUMENT

Publication Number: US-9236663-B2
Application Number: US-201313849428-A
Country: US
Kind Code: B2

Title: Electronic device having adaptive filter circuitry for blocking interference between wireless transceivers

Abstract:
An electronic device may include radio-frequency transceiver circuitry and antenna structures. The radio-frequency transceiver circuitry may transmit signals for the antenna structures that pass through electrical components such as switches. Harmonics of the transmitted signals may be generated as the signals pass through the electrical components. To reduce interference that might otherwise adversely affect sensitive receiver circuitry in the electronic device, adjustable filter circuitry may be interposed between the electrical components and the antenna structures. Control signals may adjust the adjustable circuitry in real time during operation of an electronic device to ensure that transmitted signals can pass through the adjustable filter circuitry while blocking the harmonic signals.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 control circuitry; 
 antenna structures comprising first and second antennas; 
 an electrical component comprising a switch having first, second, third, and fourth ports; 
 radio-frequency transceiver circuitry that is coupled to the antenna structures through the electrical component, wherein the radio-frequency transceiver circuitry includes a transmitter that transmits radio-frequency signals and a receiver; and 
 adjustable filter circuitry interposed between the electrical component and the antenna structures, wherein the first and second ports are coupled to the radio-frequency transceiver circuitry, the third port is coupled to the first antenna through a first portion of the adjustable filter circuitry, the fourth port is coupled to the second antenna through a second portion of the adjustable filter circuitry, and the adjustable filter circuitry is configured by the control circuitry to allow the radio-frequency signals from the transmitter to pass to the antenna structures while blocking interference from harmonics that are produced while the radio-frequency signals from the transmitter circuitry pass through the electrical component. 
 
     
     
       2. The electronic device defined in  claim 1  adjusted by additional control signals from the control circuitry. 
     
     
       3. The electronic device defined in  claim 1  wherein the radio-frequency transceiver circuitry includes a cellular telephone transceiver in which the transmitter is formed and includes a wireless local area network receiver, wherein the adjustable filter circuitry is configured to allow radio-frequency signals from the transmitter in the cellular telephone transceiver to pass and is configured to prevent the harmonics from reaching the wireless local area network receiver. 
     
     
       4. The electronic device defined in  claim 3  wherein the first antenna is configured to transmit the radio-frequency signals from the transmitter in the cellular telephone transceiver. 
     
     
       5. The electronic device defined in  claim 4  wherein the second antenna is configured to receive wireless local area network signals for the wireless local area network receiver. 
     
     
       6. The electronic device defined in  claim 1 , wherein the transmitter is configured to transmit the radio-frequency signals at a frequency of 817 MHz to 823 MHz, the receiver is configured to receive radio-frequency signals in a 2.4 GHz communications band, and the control circuitry configures the adjustable filter circuitry to prevent a third harmonic of the signals at the frequency of 817 MHz to 823 MHz from interfering with reception of the radio-frequency signals in the 2.4 GHz communications band by the receiver. 
     
     
       7. The electronic device defined in  claim 1 , wherein the transmitter is configured to transmit the radio-frequency signals at a frequency of 1900 MHz, the receiver is configured to receive radio-frequency signals in a 5 GHz communications band, and the control circuitry configures the adjustable filter circuitry to prevent a third harmonic of the signals at the frequency of 1900 MHz from interfering with reception of the radio-frequency signals in the 5 GHz communications band by the receiver. 
     
     
       8. The electronic device defined in  claim 1 , wherein the transmitter is configured to transmit the radio-frequency signals at a frequency of 782 MHz, the receiver is configured to receive radio-frequency signals in a Global Positioning System communications band at 1574 MHz, and the control circuitry configures the adjustable filter circuitry to prevent a second harmonic of the signals at the frequency of 782 MHz from interfering with reception of the radio-frequency signals in the Global Positioning System communications band by the receiver. 
     
     
       9. The electronic device defined in  claim 1 , wherein the transmitter is configured to transmit the radio-frequency signals at a frequency of 2.6 to 2.7 GHz, the receiver is configured to receive radio-frequency signals in a 5 GHz communications band, and the control circuitry configures the adjustable filter circuitry to prevent a second harmonic of the signals at the frequency of 2.6 to 2.7 GHz from interfering with reception of the radio-frequency signals in the 5 GHz communications band by the receiver. 
     
     
       10. The electronic device defined in  claim 1 , wherein the adjustable filter circuitry has fifth and sixth ports, a plurality of inductors coupled in series between the first and second ports, and a plurality of adjustable capacitors controlled by control signals from the control circuitry. 
     
     
       11. The electronic device defined in  claim 10  wherein the plurality of adjustable capacitors each has an input that receives the control signals from the control circuitry. 
     
     
       12. The electronic device defined in  claim 10  wherein the inductors and capacitors are configured to form a pi network. 
     
     
       13. The electronic device defined in  claim 1 , wherein the switch comprises a cross bar switch. 
     
     
       14. An electronic device, comprising:
 a cellular telephone transmitter that transmits signals; 
 a receiver; 
 antenna structures comprising first and second antennas that are coupled to the cellular telephone transmitter and the receiver, wherein the cellular telephone transmitter and the receiver are formed within a radio-frequency transceiver; 
 a switch through which the transmitted signals pass, wherein harmonics of the transmitted signals are generated when the transmitted signals pass through the switch; and 
 adjustable low pass filter circuitry between the switch and the antenna structures, wherein the adjustable low pass filter circuitry is configured to allow the transmitted signals to pass from the switch to the antenna structures and is configured to block the harmonics to prevent the harmonics from interfering with the receiver, the switch has first, second, third, and fourth ports, the first and second ports are coupled to the radio-frequency transceiver, the third port is coupled to the first antenna through a first portion of the adjustable low pass filter circuitry, and the fourth port is coupled to the second antenna through a second portion of the adjustable low pass filter circuitry. 
 
     
     
       15. The electronic device defined in  claim 14  wherein the adjustable low pass filter circuitry and the switch form portions of a switch module, the electronic device further comprising control circuitry that supplies control signals to the switch and to the adjustable low pass filter circuitry. 
     
     
       16. The electronic device defined in  claim 14  wherein the adjustable low pass filter circuitry includes a plurality of inductors and a plurality of adjustable capacitors. 
     
     
       17. The electronic device defined in  claim 14  wherein the receiver comprises a wireless local area network receiver and wherein the transmitter is configured to transmit signals at 2.6 to 2.7 GHz while the adjustable low pass filter circuitry is configured to block the harmonics of the signals at 2.6 to 2.7 GHz. 
     
     
       18. The electronic device defined in  claim 14 , wherein the switch comprises a cross bar switch. 
     
     
       19. The electronic device defined in  claim 18 , further comprising control circuitry, wherein the control circuitry is configured to place the cross bar switch in a first configuration in which the first port is coupled to the third port and the second port is coupled to the fourth port, and the control circuitry is configured to place the cross bar switch in a second configuration in which the first port is coupled to the fourth port and the second port is coupled to the third port. 
     
     
       20. An electronic device, comprising:
 control circuitry; 
 antenna structures; 
 an electrical component; 
 radio-frequency transceiver circuitry that is coupled to the antenna structures through the electrical component, wherein the radio-frequency transceiver circuitry includes a transmitter that transmits radio-frequency signals and a receiver; and 
 adjustable filter circuitry interposed between the electrical component and the antenna structures, wherein the adjustable filter circuitry comprises at least one adjustable capacitor circuit, the electrical component comprises a switch having a plurality of ports coupled to the radio-frequency transceiver circuitry, the antenna structures comprise first and second antennas, and the switch comprises a first port coupled to the first antenna through a first portion of the adjustable filter circuitry and a second port coupled to the second antenna through a second portion of the adjustable filter circuitry.

Description:
BACKGROUND 
     This relates generally to electronic devices, and more particularly, to antennas for electronic devices with wireless communications circuitry. 
     Electronic devices such as portable computers and cellular telephones are often provided with wireless communications capabilities. For example, electronic devices may use long-range wireless communications circuitry such as cellular telephone circuitry to communicate using cellular telephone bands. Electronic devices may use short-range wireless communications circuitry such as wireless local area network communications circuitry to handle communications with nearby equipment. Electronic devices may also be provided with satellite navigation system receivers and other wireless circuitry. 
     To satisfy consumer demand for small form factor wireless devices, manufacturers are continually striving to implement wireless communications circuitry such as antenna components using compact structures. At the same time, it may be desirable to support multiple communications bands to support a variety of desired services. Switches may be incorporated into devices for supporting the use of multiple antennas. 
     Switches and other components can exhibit non-linear behaviors. When radio-frequency signals are transmitted through these components, signal harmonics can be produced. These harmonics can cause interference for sensitive receivers. 
     To reduce the impact of harmonic interference, static low pass filters are sometimes coupled to the output of a switch. The low pass filters can help filter out aggressors such as harmonics that are produced by the non-linear behavior of a switch before these aggressors cause interference for victims such as sensitive wireless receivers in other communications bands. This type of low pass filter arrangement may, however, be of little or no use in many operating scenarios. For example, a low pass filter will not be able to protect circuitry such as a wireless local area network receiver at 2.4 GHz from interference at 2.4 GHz without disrupting cellular telephone traffic at frequencies above 2.4 GHz. 
     SUMMARY 
     Electronic devices may include radio-frequency transceiver circuitry and antenna structures. The radio-frequency transceiver circuitry may transmit signals for the antenna structures that pass through electrical components such as switches. For example, the radio-frequency transceiver circuitry may transmit cellular telephone signals through switches. The switches may be antenna signal routing switches that are used in selecting antennas in an electronic device. 
     Harmonics of the transmitted signals may be generated as the signals pass through the electrical components. The harmonics may coincide with the communications frequencies being received by sensitive receiver circuitry. For example, a satellite navigation system receiver or a wireless local area network receiver might be vulnerable to interference from harmonics. 
     To reduce interference that might otherwise adversely affect the sensitive receiver circuitry in an electronic device, adjustable filter circuitry may be interposed between the electrical components and the antenna structures. The adjustable filter circuitry may be based on a pi network formed from series-connected inductors and adjustable capacitors that couple nodes between the inductors to ground. The adjustable capacitors may be placed in multiple different capacitor configurations each characterized by a distinct capacitance value. 
     During operation of an electronic device, control circuitry with knowledge of the currently transmitted signal band may produce control signals for the adjustable filter circuitry. The control signals may be used to place the adjustable circuitry in a configuration that allows the transmitted signals from the cellular telephone transmitter or other transmitter to pass while blocking interference such as harmonics from reaching sensitive circuitry such as satellite navigation system receiver circuitry and wireless local area network receiver circuitry. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device with wireless communications circuitry in accordance with an embodiment of the present invention. 
         FIG. 2  is a schematic diagram of an illustrative electronic device with wireless communications circuitry in accordance with an embodiment of the present invention. 
         FIG. 3  is a diagram of an illustrative antenna system having multiple antenna resonating elements in accordance with an embodiment of the present invention. 
         FIG. 4  is a diagram of an illustrative antenna system based on an antenna resonating element with multiple feeds in accordance with an embodiment of the present invention. 
         FIG. 5  is a diagram of wireless circuitry with adjustable filter circuitry for reducing harmonic interference in accordance with an embodiment of the present invention. 
         FIG. 6  is a graph showing simulated filter performance when an adjustable filter of the type shown in  FIG. 5  has been placed in a first configuration with a relatively low cutoff frequency in accordance with an embodiment of the present invention. 
         FIG. 7  is a graph showing simulated filter performance when an adjustable filter of the type shown in  FIG. 5  has been placed in a second configuration having a cutoff frequency that is greater than the cutoff frequency of  FIG. 6  in accordance with an embodiment of the present invention. 
         FIG. 8  is a graph showing simulated filter performance when an adjustable filter of the type shown in  FIG. 5  has been placed in a third configuration having a cutoff frequency that is greater than the cutoff frequency of  FIG. 7  in accordance with an embodiment of the present invention. 
         FIG. 9  is a table in which aggressor and victim frequencies have been listed for a variety of possible operating scenarios in an electronic device in accordance with an embodiment of the present invention. 
         FIG. 10  is a table in which simulated insertion loss and rejection values have been computed for an adjustable filter of the type shown in  FIG. 5  when operated in scenarios of the type shown in  FIG. 9  in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices such as electronic device  10  of  FIG. 1  may be provided with wireless communications circuitry. The wireless communications circuitry may be used to support wireless communications in multiple wireless communications bands. The wireless communications circuitry may include one or more antennas. 
     The antennas can include loop antennas, inverted-F antennas, strip antennas, planar inverted-F antennas, slot antennas, hybrid antennas that include antenna structures of more than one type, or other suitable antennas. Conductive structures for the antennas may, if desired, be formed from conductive electronic device structures. The conductive electronic device structures may include conductive housing structures. The housing structures may include peripheral structures such as a peripheral conductive member that runs around the periphery of an electronic device. The peripheral conductive member may serve as a bezel for a planar structure such as a display, may serve as sidewall structures for a device housing, and/or may form other housing structures. Gaps in the peripheral conductive member may be associated with the antennas. Antennas may also be formed from metal traces on plastic carriers, metal traces on printed circuit substrates or other dielectric substrates, stamped metal foil, wires, and other conductive structures. 
     Electronic device  10  may be a portable electronic device or other suitable electronic device. For example, electronic device  10  may be a laptop computer, a tablet computer, a somewhat smaller device such as a wrist-watch device, pendant device, headphone device, earpiece device, or other wearable or miniature device, a cellular telephone, or a media player. Device  10  may also be a television, a set-top box, a desktop computer, a computer monitor into which a computer has been integrated, or other suitable electronic equipment. 
     Device  10  may include a housing such as housing  12 . Housing  12 , which may sometimes be referred to as a case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of these materials. In some situations, parts of housing  12  may be formed from dielectric or other low-conductivity material. In other situations, housing  12  or at least some of the structures that make up housing  12  may be formed from metal elements. 
     Device  10  may, if desired, have a display such as display  14 . Display  14  may, for example, be a touch screen that incorporates capacitive touch electrodes. Display  14  may include image pixels formed from light-emitting diodes (LEDs), organic LEDs (OLEDs), plasma cells, electrowetting pixels, electrophoretic pixels, liquid crystal display (LCD) components, or other suitable image pixel structures. A display cover layer such as a layer of clear glass or plastic may cover the surface of display  14 . Buttons such as button  16  may pass through openings in the cover layer. The cover layer may also have other openings such as an opening for speaker port  18 . 
     Housing  12  may include peripheral conductive housing structures such as a metal bezel or band with a rectangular ring shape that runs around the periphery of housing  12 . The peripheral conductive housing structures may form part of an antenna or antennas for device  10 , if desired. 
     If desired, housing  12  may have a conductive rear surface. For example, housing  12  may be formed from a metal such as stainless steel or aluminum. The rear surface of housing  12  may lie in a plane that is parallel to display  14 . In configurations for device  10  in which the rear surface of housing  12  is formed from metal, it may be desirable to form parts of peripheral conductive housing structures for device  10  as integral portions of the housing structures forming the rear surface of housing  12 . For example, a rear housing wall of device  10  may be formed from a planar metal structure and portions of peripheral housing structures on the left and right sides of housing  12  may be formed as vertically extending integral metal portions of the planar metal structure. Housing structures such as these may, if desired, be machined from a block of metal. 
     Display  14  may include conductive structures such as an array of capacitive electrodes, conductive lines for addressing pixel elements, driver circuits, etc. Housing  12  may include internal structures such as metal frame members, a planar housing member (sometimes referred to as a midplate) that spans the walls of housing  12  (i.e., a substantially rectangular sheet formed from one or more parts that is welded or otherwise connected between opposing sides of member  16 ), printed circuit boards, and other internal conductive structures. These conductive structures may be located in the center of housing  12  under display  14  (as an example). 
     In regions  22  and  20  or other portions of device  10 , openings may be formed within the conductive structures of device  10  (e.g., between peripheral conductive housing structures and opposing conductive structures such as a conductive housing midplate or rear housing wall structures, a conductive ground plane associated with a printed circuit board, and conductive electrical components in device  10 ). These openings, which may sometimes be referred to as gaps, may be filled with air, plastic, and other dielectrics. Conductive housing structures and other conductive structures in device  10  may serve as a ground plane for the antennas in device  10 . The openings in regions  20  and  22  may serve as slots in open or closed slot antennas, may serve as a central dielectric region that is surrounded by a conductive path of materials in a loop antenna, may serve as a space that separates an antenna resonating element such as a strip antenna resonating element or an inverted-F antenna resonating element from the ground plane, or may otherwise serve as part of antenna structures formed in regions  20  and  22 . 
     In general, device  10  may include any suitable number of antennas (e.g., one or more, two or more, three or more, four or more, etc.). The antennas in device  10  may be located at opposing first and second ends of an elongated device housing, along one or more edges of a device housing, in the center of a device housing, in other suitable locations, or in one or more of such locations. The arrangement of  FIG. 1  is merely an example. 
     In one illustrative configuration, device  10  may have upper and lower antennas (as an example). An upper antenna may, for example, be formed at the upper end of device  10  in region  22 . A lower antenna may, for example, be formed at the lower end of device  10  in region  20 . The antennas may be used separately to cover identical communications bands, overlapping communications bands, or separate communications bands. The antennas may be used to implement an antenna diversity scheme or a multiple-input-multiple-output (MIMO) antenna scheme. Switching circuitry may be used to switch the antennas in device  10  in and out of use. For example, switching circuitry in device  10  may be used to switch an upper antenna in region  22  in use in place of a lower antenna in region  20  when the performance of the lower antenna is temporarily degraded due to the presence of external objects near lower region  22  or other effects. Scenarios in which both antennas are being used simultaneously may also be supported. 
     Antennas in device  10  may be used to support any communications bands of interest. For example, device  10  may include antenna structures for supporting local area network communications, voice and data cellular telephone communications, global positioning system (GPS) communications or other satellite navigation system communications, Bluetooth® communications, etc. 
     A schematic diagram of an illustrative configuration that may be used for electronic device  10  is shown in  FIG. 2 . As shown in  FIG. 2 , electronic device  10  may include control circuitry such as storage and processing circuitry  24 . Storage and processing circuitry  24  may include storage such as hard disk drive storage, nonvolatile 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  24  may be used to control the operation of device  10 . The processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors such as baseband processor integrated circuit  26 , power management units, audio codec chips, application specific integrated circuits, etc. 
     Storage and processing circuitry  24  may be 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. To support interactions with external equipment, storage and processing circuitry  24  may be used in implementing communications protocols. Communications protocols that may be implemented using storage and processing circuitry  24  include internet protocols, wireless local area network protocols (e.g., IEEE 802.11 protocols—sometimes referred to as WiFi®), protocols for other short-range wireless communications links such as the Bluetooth® protocol, cellular telephone protocols, etc. 
     Circuitry  24  may be configured to implement control algorithms that control the use of antennas in device  10 . For example, circuitry  24  may perform signal quality monitoring operations, sensor monitoring operations, and other data gathering operations and may, in response to the gathered data and information on which communications bands are to be used in device  10 , control which antenna structures within device  10  are being used to receive and process data and/or may adjust one or more switches, tunable elements, or other adjustable circuits in device  10  to adjust antenna performance. As an example, circuitry  24  may control which of two or more antennas is being used to receive incoming radio-frequency signals, may control which of two or more antennas is being used to transmit radio-frequency signals, may control the process of routing incoming data streams over two or more antennas in device  10  in parallel, may place and adjustable filter in an appropriate configuration to help reduce interference while allowing device  10  to transmit and receive signals in one or more desired communications band, etc. 
     In performing these control operations, circuitry (e.g., baseband processor  26  or other control circuitry) may generate control commands on outputs such as output  28 . The control signals that are produced by circuitry  24  may be applied to the control inputs of adjustable components in  FIG. 2  (see, e.g., control input  58  of switch module  50  and control inputs  48  of adjustable filters  46 ). Circuitry  24  may open and close switches, may turn on and off receivers and transmitters, may adjust impedance matching circuits, may configure switches in front-end-module (FEM) radio-frequency circuits that are interposed between radio-frequency transceiver circuitry and antenna structures (e.g., filtering and switching circuits used for impedance matching and signal routing), may adjust switches, tunable circuits, and other adjustable circuit elements that are formed as part of an antenna or that are coupled to an antenna or a signal path associated with an antenna, and may otherwise control and adjust the components of device  10 . 
     Input-output circuitry  30  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. Input-output circuitry  30  may include input-output devices  32 . Input-output devices  32  may include touch screens, buttons, joysticks, click wheels, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, tone generators, vibrators, cameras, sensors, light-emitting diodes and other status indicators, data ports, etc. A user can control the operation of device  10  by supplying commands through input-output devices  32  and may receive status information and other output from device  10  using the output resources of input-output devices  32 . 
     Wireless communications circuitry  34  may include radio-frequency (RF) transceiver circuitry formed from one or more integrated circuits, power amplifier circuitry, low-noise input amplifiers, passive RF components, one or more antennas, filters, duplexers, and other circuitry for handling RF wireless signals. Wireless signals can also be sent using light (e.g., using infrared communications). 
     Wireless communications circuitry  34  may include satellite navigation system receiver circuitry such as Global Positioning System (GPS) receiver circuitry  40  (e.g., for receiving satellite positioning signals at 1574 MHz) or satellite navigation system receiver circuitry associated with other satellite navigation systems. Wireless local area network transceiver circuitry such as transceiver circuitry  38  may handle 2.4 GHz and 5 GHz bands for WiFi® (IEEE 802.11) communications and may handle the 2.4 GHz Bluetooth® communications band. Circuitry  24  may use cellular telephone transceiver circuitry  36  for handling wireless communications in cellular telephone bands such as bands in frequency ranges of about 700 MHz to about 2700 MHz or bands at higher or lower frequencies. Wireless communications circuitry  34  can include circuitry for other short-range and long-range wireless links if desired. For example, wireless communications circuitry  34  may include wireless circuitry for receiving radio and television signals, paging circuits, etc. Near field communications may also be supported (e.g., at 13.56 MHz). In WiFi® and Bluetooth® links and other short-range wireless links, wireless signals are typically used to convey data over tens or hundreds of feet. In cellular telephone links and other long-range links, wireless signals are typically used to convey data over thousands of feet or miles. 
     Wireless communications circuitry  34  may have antenna structures such as one or more antennas  42 . Antennas structures  42  may be formed using any suitable antenna types. For example, antennas structures  42  may include antennas with resonating elements that are formed from loop antenna structures, patch antenna structures, inverted-F antenna structures, dual arm inverted-F antenna structures, closed and open slot antenna structures, planar inverted-F antenna structures, helical antenna structures, strip antennas, monopoles, dipoles, hybrids of these designs, etc. Different types of antennas may be used for different bands and combinations of bands. For example, one type of antenna may be used in forming a local wireless link antenna and another type of antenna may be used in forming a remote wireless link. Antenna structures in device  10  such as one or more of antennas  42  may be provided with one or more antenna feeds, fixed and/or adjustable components, and optional parasitic antenna resonating elements so that the antenna structures cover desired communications bands. 
     Switching circuitry such as switch module  50  may be used in routing signals between radio-frequency transceiver circuitry in wireless communications circuitry  34  and antenna structures  42 . In the illustrative configuration of  FIG. 2 , switch module  50  includes a switch such as switch  52  that has four ports (ports X, Y, F, and G). Transmission line paths  54  are coupled to two of the ports and transmission line paths  56  are couple to the other two of the ports. Switch  52  may be a crossbar switch that has a first configuration in which switch  52  routes paths  54  to paths  56  so that port X is coupled to port F and so that port Y is coupled to port G and a second configuration in which switch  52  routes paths  54  to paths  56  so that port X is coupled to port G and so that port Y is coupled to port F. Paths  56  may be coupled to different respective antennas  42 , as shown in  FIG. 2 . Control circuitry  24  can control the state of cross-bar switch  52  in switch module  50  to switch a primary antenna into use (i.e., when the switch is in a first state) or to switch a secondary antenna into use when a primary antenna has been blocked (i.e., when the switch is in a second state). Switches with additional settings, switches that are coupled to different feeds of an antenna rather than being coupled to different antennas, switches that are coupled to three or more feeds and/or three or more separate antennas, or other types of switching circuitry may be used in device  10  if desired. The example of  FIG. 2  in which a pair of antennas is coupled to transceiver circuitry  36  via switch module  50  is merely illustrative. 
     Switching circuitry such as switch module  50  may be used in routing signals associated with wireless local area network transceiver circuitry  38 , satellite navigation system transceiver circuitry  40 , and/or other wireless circuitry. 
     Wireless communications circuitry  34  may include impedance matching circuitry such as illustrative impedance matching circuitry  44  of  FIG. 2 . Impedance matching circuitry may be used to help match the impedance between transmission lines  56  and antennas  42 . Each transmission line may include one or more transmission line segments (e.g., segments of coaxial cable transmission line, microstrip transmission line, etc.). Matching circuits  44  may be coupled within transmission line structures  56 . 
     Adjustable filters  46  may be implemented using surface acoustic wave (SAW) devices, bulk acoustic wave (BAW) devices, and/or circuits formed from discrete components such as resistors (e.g., tunable and/or fixed resistors), inductors (e.g., tunable and/or fixed inductors), and capacitors (e.g., tunable and/or fixed capacitors). With one illustrative configuration, which is sometimes described herein as an example, tunable filters  46  may be formed from networks of adjustable capacitors and fixed inductors. This is merely illustrative. Any suitable circuitry may be used in implementing adjustable filter circuitry  46  if desired. 
     Adjustable filter circuitry  46  may be formed as part of switch module  50  and/or as stand-alone filters that are interposed between switch module  50  and antennas  42 . The presence of adjustable filters  46  may help reduce harmonics such as harmonics that may arise when transmitting radio-frequency signals from transceiver circuitry  36  that pass through potentially non-linear electrical components such as switch module  50  (i.e., crossbar switch  52 , which may be formed from transistors or other solid state components). Adjustable filters  46  may be adjusted by storage and processing circuitry  24 . For example, control circuitry  24  can issue control commands on output  28  that are supplied to adjustable filters  46  at inputs  48 . Adjustable filters  46  may form filters such as low pass filters with adjustable cutoff frequencies. Control circuitry  24  may adjust the cutoff frequencies of tunable filters  46  in real time depending on the frequencies of the signals being handled by cellular telephone transceiver circuitry  36 . Control circuitry  24  may, for example, adjust the adjustable filter circuitry to allow signals such as transmitted cellular telephone signals to pass through the adjustable filter circuitry while blocking interfering harmonics. 
     Antenna structures  42  such as the antenna structures that are coupled to the pair of transmission line paths  56  at the output of switch module  50  of  FIG. 2  may be formed from separate respective antenna resonating elements forming respective first and second antennas or may be formed from an antenna resonating element that has multiple ports. Consider, as an example, antenna structures  42  of  FIG. 3 . In this type of arrangement, antenna structures  42  include two antennas  42 - 1  and  42 - 2 . Antenna  42 - 1  is formed from antenna resonating element  42 - 1 ′ and shared antenna ground  42 G. Antenna  42 - 1  may be an inverted-F antenna resonating element having an antenna feed with positive (+) and ground (−) antenna feed terminals) coupled to respective positive and ground lines in transmission line path  56 - 1 . Antenna  42 - 2  is formed from antenna resonating element  42 - 2 ′ and antenna ground  42 G. Antenna resonating element  42 - 2 ′ may be an inverted-F antenna resonating element having a feed with positive (+) and ground (−) antenna feed terminals) coupled to respective positive and ground lines in transmission line path  56 - 2 . Transmission line paths  56 - 1  and  56 - 2  may be used to couple the antenna feeds from antennas  42 - 1  and  42 - 2  to transceiver circuitry  36 . Additional antenna resonating elements may be coupled to transceiver circuitry  36  by additional transmission line paths, if desired. Switching circuitry such as switch module  50 , matching circuitry such as matching circuitry  44  of  FIG. 2 , and adjustable filter circuitry  46  may be interposed in the transmission line paths, as described in connection with  FIG. 2 . 
     In the illustrative configuration of  FIG. 4 , antenna structures  42  include a two-arm inverted-F antenna resonating element having two antenna feeds. Antenna ground  42 G and the antenna resonating element form a two-feed antenna. Feed  42 F 1  is coupled to transceiver  36  by transmission line  56 - 1 . Feed  42 F 2  is coupled to transceiver  36  by transmission line  56 - 2 . Additional antenna feeds may be incorporated into a multi-feed antenna of the type shown in  FIG. 4  if desired. Antenna structures  42  may also be formed that include a combination of separate antenna resonating elements of the type shown in  FIG. 3  and one or more antennas with multiple ports of the type shown in  FIG. 4 . 
       FIG. 5  is a circuit diagram of an illustrative adjustable filter  46  coupled between a radio-frequency transceiver (transceiver  36  with transmitter TX and receiver RX) and antenna  42  (switch module  50 , additional antennas, and additional transceivers for other communications bands are not shown in  FIG. 5  to avoid over-complicating the drawing). 
     As shown in  FIG. 5 , output signals from transmitter TX may be amplified by power amplifier  60 . Incoming signals that are being received by receiver RX may be amplified by low noise amplifier  62 . Duplexer  64  may route signals based on frequency and may be coupled between tunable filter  46  and amplifiers  60  and  62 . 
     Adjustable filter  46  may include components such as inductors, capacitors, and other electrical devices. Adjustable filter  46  may have two ports (port 1 and port 2). The inductors, capacitors, and other electrical devices of adjustable filter  46  may be coupled between ports 1 and 2. 
     As shown in the example of  FIG. 5 , a set of three inductors  66  may be coupled in series between duplexer  64  and antenna  42 . Adjustable capacitors  68  may be coupled between ground  74  and nodes  74  and  76 , respectively. This type of filter topology may sometimes be referred to as a pi network. Filter  46  may, in general, be a T-network (i.e., a network with three poles), a pi network (i.e., a network with five poles), a three pole network, a four pole network, a five pole network, a network with more than five poles, etc. The configuration of  FIG. 5  is merely illustrative. 
     Capacitors  68  may be programmable capacitors that each include a variable capacitor  72  controlled by a respective circuit block  70 . Circuit blocks  70  may include communications circuitry for receiving control commands provided by control circuitry  24  over input path  48 . As an example, each circuit block  70  may have a communications circuit that receives a capacitor setting command from path  48  and that issues corresponding control signals on paths  80  to variable capacitors  72 . Variable capacitors  72  may be configured to exhibit continuously variable or selectable discrete capacitor values. As an example, variable capacitors  72  may have multiplexers or other switches that are controlled based on signals on paths  80 . The switches may be used to switch a desired discrete capacitor into use. 
     With one illustrative configuration, the leftmost inductor  66  in tunable filter  46  has an inductance value of 5 nH, the center inductor  66  in tunable filter  46  has an inductance value of 10 nH, and the rightmost inductor  66  in tunable filter  46  has an inductance value of 5 nH. Capacitors  68  may each have three selectable capacitance values such as a first capacitance of 5 pF, a second capacitance of 1.5 pF, and a third capacitance of 1.0 pF (as examples). Other component values may be used in filter circuitry  46  if desired. This illustrative configuration is merely an example. 
     Capacitors  68  may be configured dynamically based on signals from control circuitry  24 . In a first state, capacitors  68  may be adjusted to exhibit a capacitance of 5 pF each. In a second state, capacitors  68  may be adjusted to exhibit a capacitance of 1.5 pF each. In a third state, capacitors  68  may be adjusted to exhibit a capacitance of 1.0 pF each. The cutoff frequency of filter  46  may vary as a function of the values of capacitors  68 . For example, when capacitors  68  are configured to exhibit a 5 pF capacitance, filter  46  may exhibit S 11  (return loss) and S 21  (insertion loss) characteristics of the type shown in  FIG. 6  (i.e., the cutoff frequency for the filter may be about 1.25 GHz). When capacitors  68  are configured to exhibit a 1.5 pF capacitance, filter  46  may exhibit S 11  and S 21  characteristics of the type shown in  FIG. 7  (i.e., the cutoff frequency for filter  46  may be about 2.5 GHz). When capacitors  68  are configured to exhibit a 1.0 pF capacitance, filter  46  may exhibit S 11  and S 21  characteristics of the type shown in  FIG. 8  (i.e., the cutoff frequency for filter  46  may be about 3.2 GHz). Each of these different settings for adjustable filter circuitry  46  may be used under different operating conditions for wireless circuitry  34 , so that harmonics can be adequately suppressed, while allowing communications signals to pass through filter  46  without excessive attenuation. 
     When filter circuitry  46  is placed in the  FIG. 6  configuration, cellular telephone signals in the range of 0.7 to 1 GHz will be passed through filter circuitry  46  without significant attenuation, as indicated by portion  82  of the S 21  curve in  FIG. 6 . (Note that there are generally no cellular telephone bands at frequencies of about 1-1.7 GHz). Harmonics of the cellular telephone aggressors that fall above about 1.25 GHz will be suppressed due to the presence of filter circuitry  46  (i.e., interference for victims such as a GPS receiver at 1.574 GHz and wireless local area network bands at 2.4 GHz and 5 GHz will be blocked). 
     Consider, as an example, scenario A of  FIG. 9 . In this type of scenario, a cellular telephone signal such as CDMA (code division multiple access) band class 10 at 817 to 823 MHz is being transmitted by transmitter TX. Filter circuitry  46  can be placed in the  FIG. 6  configuration to prevent the third harmonic of this cellular telephone frequency from creating interference for a wireless local area network receiver operating at 2.4 GHz. As another example, consider scenario C of  FIG. 9 . In this type of scenario, a cellular telephone signal such as Long Term Evolution (LTE) band  13  at 782 MHz is being transmitted by transmitter TX, so filter  46  can be placed in the  FIG. 6  configuration to prevent the second harmonic of LTE band  13  from creating interference for Global Positioning System (GPS) or other satellite navigation system receiver operating at about 1.574 GHz. 
     When filter circuitry  46  is placed in the  FIG. 7  configuration, cellular telephone signals in the range of 1.7 to 2.2 GHz will be passed through filter circuitry  46  without significant attenuation (i.e., with minimum insertion loss), as indicated by portion  84  of the S 21  curve in  FIG. 7 . Harmonics of these cellular telephone aggressors that fall above 2.5 GHz will be blocked (i.e., interference for a victim such as a wireless local area network band at 5 GHz will be suppressed) due to the presence of filter circuitry  46 . 
     Consider, as an example, scenario B of  FIG. 9 . In this type of scenario, a cellular telephone signal in a communications band at 1900 MHz such as wideband code division multiple access frequency division duplex 2 (WCDMA FDD2) is being transmitted by transmitter TX, so filter  46  can be placed in the  FIG. 7  configuration to prevent the third harmonic of this cellular telephone frequency from creating interference for a wireless local area network receiver operating at 5 GHz. 
     When filter circuitry  46  is placed in the  FIG. 8  configuration, cellular telephone signals in the range of 2.2 to 2.7 GHz will be passed through filter circuitry  46  without significant attenuation (i.e., with minimum insertion loss), as indicated by portion  86  of the S 21  curve in  FIG. 8 . Harmonics of these cellular telephone aggressors that fall above 3.2 GHz will be blocked (i.e., interference for a victim such as a wireless local area network band at 5 GHz will be suppressed) due to the presence of filter circuitry  46 . 
     Consider, as an example, scenario D of  FIG. 9 . In this type of scenario, a cellular telephone signal in a communications band at 2.6 to 2.7 GHz such as Long Term Evolution (LTE) band  38  is being transmitted by transmitter TX, so filter  46  can be placed in the  FIG. 8  configuration to prevent the second harmonic of this cellular telephone frequency from creating interference for a wireless local area network receiver operating at 5 GHz. As the scenario D example illustrates, harmonic interference can be blocked by adjustable filter circuitry  46  while allowing signals at relatively high cellular telephone signal frequencies to be transmitted. When lower frequency harmonics are to be blocked, the adjustable filter circuitry can be reconfigured accordingly. 
     The table of  FIG. 10  shows simulation results for the use of filter circuitry  46  (e.g., an adjustable low pass filter) under a variety of operating scenarios compared to a static low pass filter (LPF). The performance of filter circuitry  46  at frequencies of less than 1 GHz is shown in row R 1 . The performance of filter circuitry  46  at frequencies of 1.7 to 2.2 GHz is shown in row R 2 . The performance of filter circuitry  46  at frequencies of 2.2 to 2.7 GHz is shown in row R 3 . For comparison, the simulated performance of a static low pass filter (i.e., a static low pass filter interposed between a switch module and antenna structures) is provided in row R 4 . 
     As shown by the entries in column C 1  of the table of  FIG. 10 , the expected passband insertion loss (S 21 ) due to filter  46  is comparable to the expected passband insertion loss of the static low pass filter. 
     As shown by the entries in column C 2  of the table of  FIG. 10 , the passband return loss (S 11 ) is relatively high (as desired) and is comparable to the return loss for the static low pass filter. 
     The entries at row R 1 , column C 3  and at row R 1 , column C 4  correspond to filter  46  in the  FIG. 6  configuration when operating wireless circuitry  34  in scenario C and show how interference at the GPS receiver is reduced by 13 dB while interference at a wireless local area network receiver at 2.4 GHz is reduced by more than 30 dB. 
     The entries in columns C 3  and C 4  of rows R 2  and R 3  correspond to a situation in which the GPS and 2.4 GHz receivers are not receiving harmonic interference (i.e., rejection performance is the same as for the static low pass filter, as shown in row R 4 , columns C 3  and C 4 ). 
     Column C 5  contains entries in which 5 GHz rejection is compared between filter  46  (rows R 1 , R 2 , and R 3 ) with a static low pass filter (row R 4 ). Row R 1 , column C 5  shows how filter  46  exhibits a rejection of more than 40 dB when placed in the  FIG. 6  configuration. Row R 2 , column C 5  shows how filter  46  exhibits a rejection of more than 35 dB when placed in the  FIG. 7  configuration. Row R 3 , column C 5  shows how filter  46  exhibits a rejection of more than 25 dB when placed in the  FIG. 8  configuration. These performance metrics equal or exceed the simulated performance of the static low pass filter (25 dB, as shown in row R 4 , column C 5 ). 
     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: 20130322
Publication Date: 20160112
Grant Date: 20160112
Priority Date: 20130322
Inventors: AKHI FRAIDUN
LIU GE
Assignee: APPLE INC
CPC Classifications: [{"code": "H01Q21/0006", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B1/525", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q21/0006", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B1/525", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B1/525", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 51569518