PATENT DOCUMENT

Publication Number: US-8587335-B2
Application Number: US-201113163242-A
Country: US
Kind Code: B2

Title: Methods for providing proper impedance matching during radio-frequency testing

Abstract:
Wireless electronic devices may include a transceiver, an antenna resonating element coupled to the transceiver via a transmission line path, transceiver and antenna impedance matching circuits, and other circuitry. The transceiver and the impedance matching circuits may be formed on a first substrate. The antenna resonating element may be formed using a second substrate. The antenna resonating element may be decoupled from the first substrate during testing. First and second sets of test points may be formed at first and second locations long the transmission line path. During testing, a test probe may mate with the first set of test points, whereas an impedance adjustment circuit that serves to electrically isolate the antenna impedance matching circuit from the transceiver may mate with the second set of test points. The impedance adjustment circuit need not be used if the antenna impedance matching circuit is decoupled from the transceiver during testing.

Claims:
What is claimed is: 
     
       1. A method of testing device structures under test with test equipment that includes a radio-frequency test probe, wherein the device structures under test include a transmission line path, radio-frequency transceiver circuitry coupled to a first end of the transmission line path, and an antenna resonating element removably coupled to a second end of the transmission line path, the method comprising:
 temporarily coupling the radio-frequency test probe to the transmission line path at a first location along the transmission line path; 
 temporarily coupling an impedance adjustment circuit to the transmission line path at a second location along the transmission line path; and 
 while the radio-frequency test probe and the impedance adjustment circuit are coupled to the transmission line path, gathering radio-frequency test measurements through the radio-frequency test probe. 
 
     
     
       2. The method defined in  claim 1 , wherein temporarily coupling the impedance adjustment circuit to the transmission line path at the second location substantially isolates the radio-frequency test probe from the second end of the transmission line path, and wherein gathering the radio-frequency test measurements comprises gathering radio-frequency test measurement on the radio-frequency transceiver circuitry. 
     
     
       3. The method defined in  claim 2 , wherein the transmission line path includes first and second sets of test points, wherein temporarily coupling the radio-frequency test probe to the transmission line path at the first location comprises attaching the radio-frequency test probe to the first set of test points, and wherein temporarily coupling the impedance adjustment circuit to the transmission line path at the second location comprises attaching the impedance adjustment circuit to the second set of test points. 
     
     
       4. The method defined in  claim 3 , wherein the first set of test points comprise test pads, and wherein temporarily coupling the radio-frequency test probe to the transmission line path at the first location comprises attaching the radio-frequency test probe to the test pads. 
     
     
       5. The method defined in  claim 4 , wherein the second set of test points comprise test pins, and wherein temporarily coupling the impedance adjustment circuit to the transmission line path at the second location comprises attaching the impedance adjustment circuit to the test pins. 
     
     
       6. The method defined in  claim 4 , wherein the second set of test points comprise conductive through holes, wherein the impedance adjustment circuit is coupled to a jumper circuit having jumper pins, and wherein temporarily coupling the impedance adjustment circuit to the transmission line path at the second location comprises inserting the jumper pins in the conductive through holes. 
     
     
       7. The method defined in  claim 1 , wherein temporarily coupling the impedance adjustment circuit to the transmission line path at the second location substantially isolates the radio-frequency test probe from the first end of the transmission line path, and wherein gathering the radio-frequency test measurements comprises gathering radio-frequency test measurement on the antenna resonating element. 
     
     
       8. The method defined in  claim 7 , wherein the transmission line path includes first and second sets of test points, wherein temporarily coupling the radio-frequency test probe to the transmission line path at the first location comprises attaching the radio-frequency test probe to the first set of test points, and wherein temporarily coupling the impedance adjustment circuit to the transmission line path at the second location comprises attaching the impedance adjustment circuit to the second set of test points. 
     
     
       9. The method defined in  claim 8 , wherein the first set of test points comprise test pads, and wherein temporarily coupling the radio-frequency test probe to the transmission line path at the first location comprises attaching the radio-frequency test probe to the test pads. 
     
     
       10. The method defined in  claim 9 , wherein the second set of test points comprise test pins, and wherein temporarily coupling the impedance adjustment circuit to the transmission line path at the second location comprises attaching the impedance adjustment circuit to the test pins. 
     
     
       11. The method defined in  claim 9 , wherein the second set of test points comprise conductive through holes, wherein the impedance adjustment circuit is coupled to a jumper circuit having jumper pins, and wherein temporarily coupling the impedance adjustment circuit to the transmission line path at the second location comprises inserting the jumper pins in the conductive through holes. 
     
     
       12. A method of testing device structures under test with test equipment that includes a radio-frequency test probe, wherein the device structures under test include a transmission line path coupled between a first radio-frequency circuit and a second radio-frequency circuit, the method comprising:
 connecting the radio-frequency test probe to a first set of test points in the transmission line path; 
 connecting a temporary impedance matching circuit to a second set of test points in the transmission line path that is interposed between the first set of test points and the second radio-frequency circuit, wherein the temporary impedance matching circuit electrically isolates the radio-frequency test probe and the second radio-frequency circuit; and 
 while the radio-frequency test probe is connected to the first set of test points, gathering radio-frequency test measurements on the first radio-frequency test circuit through the first set of test points. 
 
     
     
       13. The method defined in  claim 12 , wherein the first radio-frequency circuit comprises a wireless transceiver circuit, and wherein gathering radio-frequency test measurements on the first radio-frequency test circuit through the first set of test points comprises gather radio-frequency test measurement on the wireless transceiver circuit. 
     
     
       14. The method defined in  claim 13 , wherein the second radio-frequency circuit comprises an antenna resonating element, and wherein connecting the temporary impedance matching circuit to the second set of test points comprises connecting the temporary impedance matching circuit to the second set of test points to electrically isolate the radio-frequency test probe from the antenna resonating element. 
     
     
       15. The method defined in  claim 14 , wherein the device structures under test further comprise an antenna impedance matching circuit, and wherein the antenna impedance matching circuit is at least partly interposed between the antenna resonating element and the second set of test points in the transmission line path. 
     
     
       16. The method defined in  claim 12 , wherein the first radio-frequency circuit comprises an antenna resonating element, and wherein gathering radio-frequency test measurements on the first radio-frequency test circuit through the first set of test points comprises gathering radio-frequency test measurement on the antenna resonating element. 
     
     
       17. The method defined in  claim 16 , wherein the second radio-frequency circuit comprises a wireless transceiver circuit, and wherein connecting the temporary impedance matching circuit to the second set of test points comprises connecting the temporary impedance matching circuit to the second set of test points to electrically isolate the radio-frequency test probe from the wireless transceiver circuit. 
     
     
       18. The method defined in  claim 17 , wherein the device structures under test further comprise a transceiver impedance matching circuit, and wherein the transceiver impedance matching circuit is at least partly interposed between the wireless transceiver circuit and the second set of test points in the transmission line path. 
     
     
       19. A method in which device structures under test are tested using a radio-frequency test probe, wherein the device structures under test include a transmission line path, transceiver circuitry coupled to a first end of the transmission line path, an antenna resonating element removably coupled to a second end of the transmission line path through first and second sets of electrical contacts, an impedance matching circuit coupled to the second set of electrical contacts, and wherein the first set of electrical contacts is coupled to the transceiver circuitry through the transmission line path, the method comprising:
 connecting the radio-frequency test probe to the transmission line path while the antenna resonating element is decoupled from the second set of electrical contacts and while the impedance matching circuit is decoupled from the first set of electrical contacts; and 
 gathering radio-frequency test measurements with the radio-frequency test probe while the radio-frequency test probe is coupled to the transmission line path and while the antenna resonating element is removed from the first and second sets of electrical contacts so that the impedance matching circuit is decoupled from the transmission line path. 
 
     
     
       20. The method defined in  claim 19  further comprising:
 coupling the impedance matching circuit to the transmission line path by attaching the antenna resonating element to the first and second sets of electrical contacts. 
 
     
     
       21. The method defined in  claim 19 , wherein connecting the radio-frequency test probe to the transmission line path comprises mating the radio-frequency test probe with the first set of electrical contacts.

Description:
BACKGROUND 
     This relates to testing and, more particularly, to testing of electronic device structures. 
     Electronic devices such as computers, cellular telephones, music players, and other electronic equipment are often provided with wireless communications circuitry. In a typical configuration, the wireless communications circuitry includes a radio-frequency transceiver that is coupled to an antenna through a radio-frequency switch connector. The transceiver, the switch connector, and an impedance matching circuit are formed on a printed circuit board. The antenna is connected to the printed circuit board through an antenna connector or other coupling mechanism (i.e., via a screw or a spring). 
     During normal device operation, the switch connector serves to electrically connect the transceiver to the antenna so that radio-frequency signals can be conveyed between the transceiver and the antenna. During testing, a radio-frequency test probe is mated with the switch connector to perform radio-frequency testing on the transceiver (i.e., by decoupling the antenna from the transceiver). The test probe is connected to a test box such as a vector network analyzer through a coaxial cable. Radio-frequency test signals are conveyed between the vector network analyzer and the transceiver during transceiver testing. 
     To satisfy consumer demand for small form factor wireless devices, manufacturers are continually striving to implement wireless communications components using compact structures. As device size continues to decrease, there may be insufficient space for the placement of the switch connector on the printed circuit board. To test the transceiver in the absence of the switch connector, the transceiver may be accessed via the antenna connector (with the antenna disconnected from the printed circuit board). If, however, the antenna is decoupled from the antenna connector and the impedance matching circuit is connected in series between the transceiver and the antenna connector on the printed circuit board, the test probe connected to the antenna connector will not see a 50 ohm impedance looking into the transceiver. 
     In view of these considerations, it would be desirable to provide improved ways for testing wireless transceiver circuitry. 
     SUMMARY 
     Electronic devices may include wireless transceiver circuitry and antenna circuitry. The wireless transceiver circuitry may include a cellular telephone transceiver, a wireless local area network transceiver, a satellite navigation systems receiver, and other wireless communications circuitry. The antenna circuitry may include at least one antenna resonating element associated with a loop antenna, inverted-F antenna, strip antenna, planar inverted-F antenna, slot antenna, hybrid antenna that includes antenna structures of more than one type, or other suitable antennas. 
     The transceiver circuitry may be mounted on a substrate (e.g., a printed circuit board), whereas the antenna resonating element may be formed as a separate conductive element. The printed circuit board on which the transceiver circuitry is formed may sometimes be referred to as a main logic board. During normal device operation, radio-frequency signals may be conveyed between the transceiver circuitry and the antenna resonating element via a transmission line path (e.g., the transceiver circuitry may be coupled to a first end of the transmission line path, whereas the antenna resonating element may be coupled to a second end of the transmission line path). 
     The antenna resonating element may be coupled to the transceiver circuitry through first and second coupling structures. The first coupling structure may be formed on the printed circuit board, whereas the second coupling structure may be formed on the antenna resonating element. The first and second coupling structures may include conductive pads, radio-frequency connectors, springs, screws, or other coupling mechanisms. 
     Transceiver and antenna impedance matching circuits may be formed on the printed circuit board. In one suitable arrangement, the transceiver and the antenna impedance matching circuits are coupled in the transmission line path between the transceiver and the antenna resonating element. First and second sets of test points (e.g., test points that tap into the transmission line path at first and second locations along the transmission line path between the transceiver impedance matching circuit and the antenna impedance matching circuit) may be formed on the printed circuit board. During transceiver testing, a test probe may be used to mate with the first set of test points so that the test probe sees desired matching looking into the transceiver circuitry, whereas an impedance adjustment circuit (sometimes referred to as a temporary impedance matching circuit or a test impedance matching circuit) may be coupled to the second set of test points so that the test probe sees high impedance looking into the antenna resonating element (e.g., to isolate the antenna resonating element from the test probe). 
     In another suitable arrangement, the antenna matching circuit may be physically and electrically disconnected from the transceiver circuitry during testing. The first coupling structure may include first and second sets of electrical contacts formed on the printed circuit board. The transceiver impedance matching circuit may be connected to the first set of electrical contacts, whereas the antenna impedance matching circuit may be connected to the second set of electrical contacts. When the second coupling structure is removed from the first coupling structure (i.e., when the antenna resonating element is removed from the printed circuit board), the first set of electrical contacts may be electrically coupled to the transceiver circuitry  16  via the transmission line path, whereas the second set of electrical contacts may be electrically isolated from the first set of electrical contacts (e.g., the antenna impedance matching circuit is decoupled from the transceiver circuitry when the antenna resonating element is removed from the first coupling structure). 
     During transceiver testing, a test probe may be used to mate with the first set of electrical contacts. An impedance adjustment circuit need not be used, because the transceiver impedance matching circuit will allow the test probe to see a desired impedance of 50 ohms looking into the transceiver. The antenna impedance matching circuit will not interfere with transceiver testing because it is decoupled from the transceiver circuitry. After testing, the second coupling structure can be mated with the first coupling structure to couple the antenna impedance matching circuit back into the transmission line path. During normal device operation, antenna impedance matching circuit may serve to provide proper matching between the antenna resonating element and the transceiver circuitry. 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 diagram of an illustrative wireless electronic device in accordance with an embodiment of the present invention. 
         FIG. 2  is a diagram showing device structures being tested using an impedance adjustment circuit in accordance with an embodiment of the present invention. 
         FIGS. 3A and 3B  are cross-sectional side views of illustrative device structures under test having a jumper circuit that is coupled to an impedance adjustment circuit and that is configured to tap into a transmission line path between a transceiver and an antenna in accordance with an embodiment of the present invention. 
         FIG. 4  is a diagram of illustrative device structures under test having an antenna impedance matching circuit that is decoupled from transceiver circuitry during testing in accordance with an embodiment of the present invention. 
         FIG. 5A  is a perspective view of an illustrative coupling mechanism through which the transceiver circuitry and the antenna circuitry of  FIG. 4  may be connected in accordance with an embodiment of the present invention. 
         FIG. 5B  is a cross-sectional side view of the coupling mechanism shown in  FIG. 5A  in accordance with an embodiment of the present invention. 
         FIG. 5C  is a bottom view of the device structures under test shown in  FIG. 5B  in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Wireless electronic devices include antenna and transceiver circuitry that support wireless communications. Examples of wireless electronic devices include desktop computers, computer monitors, computer monitors containing embedded computers, wireless computer cards, wireless adapters, televisions, set-top boxes, gaming consoles, routers, and other electronic equipment. Examples of portable wireless electronic devices include laptop computers, tablet computers, handheld computers, cellular telephones, media players, and small devices such as wrist-watch devices, pendant devices, headphone and earpiece devices, and other miniature devices. 
     Devices such as these 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 at 850 MHz, 900 MHz, 1800 MHz, and 1900 MHz (e.g., the main Global System for Mobile Communications or GSM cellular telephone bands). Long-range wireless communications circuitry may also handle the 2100 MHz band. 
     Electronic devices may use short-range wireless communications links to handle communications with nearby equipment. For example, electronic devices may communicate using the WiFi® (IEEE 802.11) bands at 2.4 GHz and 5 GHz and the Bluetooth® band at 2.4 GHz. It is sometimes desirable to receive satellite navigation system signals such as signals from the Global Positioning System (e.g., to receive GPS signals at 1575 MHz). 
       FIG. 1  is a diagram of an exemplary wireless electronic device. As shown in  FIG. 1 , device  10  may have a device housing structure such as housing structure  12  that forms a case for its associated components. Housing  12  may be formed from 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 conductive elements (e.g., a conductive peripheral bezel member). 
     Device  10  may include within its housing at least one antenna having an associated antenna resonating element  18 , radio-frequency (RF) transceiver circuitry  16 , storage and processing circuitry  14 , input-output devices, and other electronic components. Storage and processing circuitry  14  and transceiver circuitry  16  may be mounted on a substrate such as printed circuit board (PCB)  20 . Printed circuit board  20  may be, for example, a rigid printed circuit board formed from fiberglass-filled epoxy (e.g., FR-4) or may be a flexible printed circuit (“flex circuit”) formed from a sheet of polymer such as a polyimide sheet. Printed circuit board  20  may, if desired, be mounted to housing structure  12 . Storage and processing circuitry  14  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  14  may be used to control the operation of device  10 . This processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio codec chips, application specific integrated circuits, etc. 
     Storage and processing circuitry  14  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  14  may be used in implementing communications protocols. Communications protocols that may be implemented using circuitry  14  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. 
     Radio-frequency transceiver circuitry (sometimes referred to as radio circuitry)  16  may include satellite navigation system receiver circuitry for receiving satellite positioning signals at 1575 MHz, wireless local area network (WLAN) circuitry for handling the 2.4 GHz and 5 GHz WiFi® (IEEE 802.11) communications bands and the 2.4 GHz Bluetooth® communications band, cellular telephone circuitry for handling telephone bands such as bands at 850 MHz, 900 MHz, 1800 MHz, 1900 MHz, and 2100 MHz, and other suitable types of transceiver circuitry. 
     Transceiver circuitry  16  may be coupled to antenna element  18  through a transmission line path  22  and coupling circuitry  24  (e.g., conductive coupling elements interposed between antenna element  18  and board  20 ). Coupling circuitry  24  may include radio-frequency connectors, a screw, a spring, or other suitable coupling mechanisms. Transmission line path  22  may include one or more segments of conductive traces formed in PCB  20  (e.g., a microstrip transmission line, a stripline transmission line, an edge coupled microstrip or stripline transmission line, etc.), one or more segments of coaxial cable, or other conduits through which radio-frequency signals can be conveyed between transceiver  16  and antenna element  18 . 
     Antenna element  18  may include antenna resonating element conductive structures. Antenna element  18  may form at least a portion of a loop antenna, inverted-F antenna, strip antenna, planar inverted-F antenna, slot antenna, hybrid antenna that includes antenna structures of more than one type, or other suitable antennas. The conductive structures may, if desired, be formed from portions of housing structure  12 . The conductive structures may also include patterned metal traces formed on a substrate such as a plastic support structure, a rigid printed circuit board, or a flex circuit. 
     Impedance matching circuitry such as transceiver impedance matching circuitry  25  (e.g., transceiver matching circuits, antenna matching circuit, etc.) may be formed on PCB and may be interposed in the transmission line path between transceiver  16  and antenna element  18  (e.g., impedance matching circuitry  25  may be formed in series between transceiver  16  and antenna element  18 ). During normal operation of device  10 , impedance matching circuits  25 - 1  and  25 - 2  may serve to properly match antenna element  18  to transceiver  16  so that radio-frequency signals can be conveyed through transmission line path  22  between antenna element  18  and transceiver  16  with desired power efficiency. 
     The wireless communications circuitry within housing  12  may be tested and calibrated during production of device  10 . The components being tested and calibrated may sometimes be referred to as device structures under test. Device structures under test may include transceiver circuitry  16 , antenna resonating element  18 , and other wireless communications circuitry. These device structures under test need not be attached to one another or completely assembled within housing  12  during testing. 
       FIG. 2  shows one possible arrangement for performing radio-frequency testing on the device structures under test in device  10 . As shown in  FIG. 2 , the transmission line path connecting transceiver  16  to antenna element  18  may include a signal path  26  and a ground path (sometimes referred to as a signal return path)  28 . Impedance matching circuits such as transceiver impedance matching circuit  25 - 1  and antenna impedance matching circuit  25 - 2  may be formed in the transmission line path between transceiver  16  and antenna element  18 . Antenna element  18  may or may not be electrically connected to transceiver  16  during transceiver testing (i.e., antenna element  18  may be removably coupled to PCB  20  via coupling mechanism  24 ). 
     First and second sets of test points may be formed at first and second locations along the transmission line path between impedance matching circuits  25 - 1  and  25 - 2 . The first set of test points may include signal test point  48  and ground test point  50 . The second set of test points may include signal test point  52  and ground test point  54 . Signal test points  48  and  52  may tap into the signal path  26 , whereas ground test points  50  and  54  may tap into ground path  28 . The first and second sets of test points may be formed on PCB  20  as conductive test pads, protruding test pins, conductive through holes, radio-frequency connectors (e.g., mini U.FL connectors), or other suitable types of conductive structures. 
     The device structures under test may be tested using test equipment. As an example, test equipment  30  may include a test unit  38 , a test probe  32  that is connected to test unit  38  through a radio-frequency cable  40 , and an impedance adjustment circuit  42  (sometimes referred to as a test impedance matching circuit). Cable  40  may, for example, be a coaxial cable that includes an inner signal conductor surrounded by a tubular ground shielding layer, where the signal conductor and the ground shielding layer are separated by dielectric insulating material. 
     Test unit  38  may include a signal generator that generates radio-frequency test signals over a range of frequencies. These test signals may be provided to test probe  32  over radio-frequency cable  40 . Test unit  38  may also include a receiver that is capable of measuring wireless performance information on incoming signals (e.g., radio-frequency signals that are received by test probe  32  from transceiver  16  during testing). 
     With one suitable arrangement, test unit  38  may be a vector network analyzer (VNA) and a computer that is coupled to the vector network analyzer for gathering and processing test results. Tester  38  may, for example, be the CMU300 Universal Radio Communication Tester available from Rohde &amp; Schwarz. This is, however, merely illustrative. Test unit  38  may be a radio communications tester of the type that is used to perform radio-frequency signaling tests for a variety of different radio-frequency communications bands and channels (e.g., test unit  38  may be a spectrum analyzer, a power meter, a wireless protocol tester, etc.). 
     Test probe  32  may be used to mate with the first set of test points during transceiver testing. For example, test probe  32  may include signal conductor  34  and ground conductor  36  that is used to make electrical contact with test points  48  and  50 , respectively, while test probe  32  is in the mated state. Signal conductor  34  may be coupled to the inner signal conductor in cable  40 , whereas ground conductor  36  may be coupled to the ground shielding layer in cable  40 . At least one of test probe conductors  34  and  36  (sometimes referred to as test probe pins) may be spring-loaded to provide improved mate-ability during test operations. 
     Impedance adjustment circuit  42  may be temporarily mated with the second set of test points during transceiver testing. For example, impedance adjustment circuit  42  may have a first terminal that can be electrically connected to test point  52  (as indicated by dotted line  62 ) and a second terminal that can be electrically connected to test point  54  (as indicated by dotted line  64 ). Impedance adjustment circuit  42  may be disconnected from the second set of test points during normal operation of device  10 . 
     When circuit  42  is mated with the second set of test points (i.e., by connecting circuit  42  at least partly in parallel with impedance matching circuit  25 - 2 ), impedance adjustment circuit  42  may serve to decouple antenna impedance matching circuit  25 - 2  from transceiver  16  (e.g., test probe  32  will see high impedance looking into the antenna from reference point  71  while impedance adjustment circuit  42  is in the mated state). Providing high impedance using impedance adjustment circuit  42  may serve to direct most of test radio-frequency signals to transceiver  16  during testing. Impedance adjustment circuit  42  may include discrete resistors, capacitors, and inductors mounted on a semiconductor substrate, integrated impedance matching circuits, and other electrical components coupled in any desired series-parallel configuration. 
     When test probe  32  is mated with test points  48  and  50  at the first location along the transmission line path, it may see high impedance looking into the antenna (from reference point  71 ) and a desired  50  ohm impedance looking into the transceiver (from reference point  70 ). If impedance adjustment circuit  42  is not connected to the device structures under test, test probe  32  may not necessarily see high impedance looking into the antenna, which may result in test radio-frequency signals leaking undesirably towards the antenna element. The distance L 1  between impedance matching circuit  25 - 1  and the first set of test points and distance L 2  between the first and second set of test points may be carefully chosen so that test probe  32  sees the desired impedance values looking into the transceiver from reference point  70  and looking into the antenna from reference point  71 . 
     If desired, impedance adjustment circuit  25 - 1  may be configured to provide any suitable impedance matching during transceiver testing (e.g., impedance adjustment circuit  25 - 1  may allow test probe  32  to see less than 50 ohms or greater than 50 ohms impedance looking into the first set of test points). 
     Impedance adjustment circuit  42  may be configured differently depending on whether antenna element  18  is connected to PCB  20  via coupling mechanism  24  during testing. For example, if antenna element  18  is to be connected to PCB  20  using coupling circuitry  24  during testing, impedance adjustment circuit  42  may be formed using a first configuration. If antenna element  18  is to be disconnected from PCB  20  during testing, impedance adjustment circuit  42  may be formed using a second configuration that is different than the first configuration (e.g., circuit  42  may be formed using different capacitance, inductance, and/or resistance values depending on whether antenna element  18  is removed from on-board coupling circuitry  24 ). 
     With one suitable arrangement of the present invention, a jumper (sometimes referred to as a removable coupling circuit) may tap into the transmission line path between transceiver  16  and antenna element  18 . As shown in  FIG. 3A , radio-frequency signals may be conveyed between transceiver  16  and antenna element  18  through signal path  26  formed in at least one conductive trace routing layer in PCB  20 . Ground path  28  may also be formed in at least one conductive trace routing layer in PCB  20 . Transceiver  16  may be coupled to ground through via  72 . In general, signal and ground paths  26  and  28  may include conductive traces formed in different trace routing layers (e.g., to form a microstrip transmission line), conductive traces formed in the same trace routing layer (e.g., to form an edge-coupled microstrip transmission line), signal and ground conductors in a coaxial cable, and/or other conductive structures suitable for conveying radio-frequency signals. 
     Coupling circuitry  24  may include antenna connectors  24 - 1  and  24 - 2  (as an example). Antenna connector  24 - 1  may be surface mounted on PCB  20  and may be connected to signal path  26  and shorted to ground through via  73 . Antenna connector  24 - 2  may be attached to antenna resonating element  18 . In this example, antenna element  18  may be coupled to transceiver  16  by mating antenna connector  24 - 2  with antenna connector  24 - 1 . In other suitable arrangements, antenna element  18  may be coupled to PCB  20  through corresponding conductive pads (e.g., through antenna pad  24 - 1  formed on an upper surface of PCB  20  and antenna pad  24 - 2  formed on a lower surface of antenna resonating element  18 ), springs, screws, or other conductive structures. 
     Impedance matching circuits  25 - 1  and  25 - 2  may be formed in signal path  26  and may have ground terminals coupled to ground  28  through via  75  and  76 , respectively. Probe pin test pads such as probe pin test pads  78  and  80  may be formed on the upper surface of PCB  20  (as an example). Test pad  78  may tap into signal path  26  through via  82 , whereas test pad  80  may be shorted to ground through via  84 . During testing, signal pins  34  and  36  in test probe  32  may be used to make physical contact with corresponding test pads  78  and  80  to performed desired radio-frequency measurements. 
     In the example of  FIG. 3A , first and second jumper pins  90  and  92  may be formed on PCB  20 . First jumper pin  90  may tap into signal path  26  through via  94 , whereas second jumper pin  92  may be connected to ground  28  through via  96 . During testing, a conductive sleeve  98  (sometimes referred to as a removable coupling circuit, a jumper shunt, or a jumper) may be mated with jumper pins  90  and  92  (i.e., jumper pin  90  may be inserted into a first corresponding hole in jumper  98 , whereas jumper pin  92  may be inserted into a second corresponding hole in jumper  98 ). Jumper  98  may be coupled to associated impedance adjustment circuit  42 . When jumper  98  is in the mated state, the first terminal of impedance adjustment circuit  42  may be coupled to signal path  26  through jumper pin  90  and the second terminal of impedance adjustment circuit  42  may be coupled to ground path  28  through jumper pin  92 . Connecting impedance adjustment circuit  42  using this approach ensures that test probe  32  sees a high impedance value looking into the antenna from reference point  71 . Jumper  98  coupled with impedance adjustment circuit  42  may be mated with pins  90  and  92  only during test operations (i.e., jumper  98  may be removed during normal device operation). 
     In another suitable arrangement of the present invention, through holes  104  and  106  may be formed in PCB  20  instead of protruding jumper pins  90  and  92 . As shown in  FIG. 3B , through hole  104  may be a conductive through hole that taps into signal path  26  (as indicated by connection  108 ), whereas through hole  106  may be a conductive through hole that taps into ground path  28  (as indicated by connection  110 ). 
     During transceiver testing, through holes  104  and  106  may be mated with a corresponding removable coupling circuit  98 ′. Circuit  98 ′ (which may also be referred to as a jumper) may include jumper pins  100  and  102  that can be inserted into holes  104  and  106 , respectively. Jumper  98 ′ may be coupled to associated impedance adjustment circuit  42 . When jumper  98 ′ is in the mated state, the first terminal of impedance adjustment circuit  42  may be coupled to signal path  26  through jumper pin  100 , whereas the second terminal of impedance adjustment circuit  42  may be coupled to ground path  28  through jumper pin  102 . Connecting impedance adjustment circuit  42  using this approach ensures that test probe  32  sees a high impedance value looking into the antenna from reference point  71 . Jumper  98 ′ having impedance adjustment circuit  42  may be inserted into PCB  20  only during test operations (i.e., jumper  98 ′ may be removed during normal device operation). 
     The use of impedance adjustment circuit  42  described in connection with  FIGS. 2 ,  3 A, and  3 B is merely illustrative and does not limit the scope of the present invention. If desired, impedance adjustment circuit  42  may be used during antenna testing to isolate transceiver  16  and transceiver impedance matching circuit  25 - 1  from test probe  32 . In such scenarios, impedance adjustment circuit  42  may be connected at a third location along the transmission line path between the first location (i.e., the location associated with test probe  32 ) and impedance matching circuit  25 - 1 . Connecting circuit  42  at the third location may allow test probe  32  to see high impedance looking into the transceiver and a desired 50 ohm impedance looking into the antenna (e.g., antenna matching circuit  25 - 2  may be configured to provide this 50 ohm impedance for test probe  32 ) during antenna testing. Depending on where impedance adjustment circuit  42  is mated along the transmission line path, transceiver testing or antenna testing may be performed (e.g., to provide bidirectional testing capability). 
     Antenna impedance matching circuit  25 - 2  may be decoupled from transceiver  16  during transceiver testing. As shown in  FIG. 4 , impedance matching circuits  25 - 1  and  25 - 2  may be formed on PCB  20 . In the example of  FIG. 4 , coupling mechanism  24  may include first electrical contact  24 -A, second electrical contact  24 -B, third electrical contact  24 -C, and fourth electrical contact  24 -D. Electrical contact  24 -A may be coupled to transceiver  16  through signal path  26 , whereas electrical contact  24 -B may be coupled to transceiver  16  through ground path  28 . 
     When antenna element  18  is decoupled from PCB  20  (i.e., when antenna element  18  is removed from the electrical contacts), electrical contacts  24 -C and  24 -D may be disconnected from transceiver  16 . Transceiver impedance matching circuit  25 - 1  may be coupled in parallel with electrical contacts  24 -A and  24 -B, whereas antenna impedance matching circuit  25 - 2  may be coupled to electrical contacts  24 -C and  24 -D through lines  120  and  122 . 
     During test operations, antenna element  18  may be decoupled from PCB  20 , signal pin  34  of test probe  32  may make electrical contact with electrical contact  24 -A, and ground pin  36  of test probe  32  may mate with electrical contact  24 -B. If desired, test probe  32  may make contact at other locations along the transmission line path during radio-frequency testing. Transceiver impedance matching circuit  25 - 1  may serve to provide a 50 ohm impedance for test probe  32  during transceiver testing. The loading of antenna impedance matching circuit  25 - 2  does not contribute to the impedance seen by test probe  32 , because circuit  25 - 2  is electrically isolated from transceiver  16  during testing. 
     During normal operation, antenna element  18  may be coupled to PCB  20  by mating a first antenna shorting structure  124  with electrical contacts  24 -A and  24 -C (to short contacts  24 -A and  24 -C) and by mating a second antenna shorting structure  126  with electrical contacts  24 -B and  24 -D (to short contacts  24 -B and  24 -D). When antenna element  18  is coupled to PCB  20 , antenna impedance matching circuit  25 - 2  may serve to properly match antenna element  18  to the device structures on PCB  20 . 
       FIG. 5A  is a perspective view of one possible implementation of the coupling mechanism described in connection with  FIG. 4 . As shown in  FIG. 5A , contacts  24 -A,  24 -B,  24 -C, and  24 -D may be conductive pads formed on the surface of PCB  20 . Shorting structures  124  and  126  may be conductive pads formed on a flex circuit associated with antenna element  18  (as an example). While antenna element  18  is decoupled from PCB  20 , antenna pads  24 -A and  24 -C are electrically isolated from each other, and antenna pads  24 -B and  24 -D are electrically isolated from each other. 
       FIG. 5B  is a cross-sectional side view of the device structures under test in  FIG. 5B  when antenna element  18  is mated with the electrical contacts. As shown in FIG.  5 B, antenna shorting pad  124  may be attached to conductive pads  24 -A and  24 -C using solder  130  (whereas antenna shorting pad  126  may be soldered to conductive pads  24 -B and  24 -D). If desired, antenna shorting pad  124  may be attached to pads  24 -A and  24 -C using conductive adhesive, using direct physical contact via applied pressure, or other means of coupling antenna element  18  to transceiver  16 . A conductive trace  27  may be formed on the flex circuit of antenna element  18  to serve as a signal feed for antenna element  18 . 
     Antenna impedance matching circuit  25 - 2  may be mounted on a lower surface of PCB  20 . As shown in  FIG. 5C , antenna impedance matching circuit  25 - 2  may have a first terminal that is coupled to contact  24 -C through conductive path  136  and via  132  (equivalent to connection path  120  in  FIG. 4 ) and a second terminal that is coupled to electrical contact  24 -D through conductive path  136  and via  134  (equivalent to connection path  122  in  FIG. 4 ). If desired, antenna matching circuit  25 - 2  may be formed on the upper surface of PCB  20 . 
     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. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20110617
Publication Date: 20131119
Grant Date: 20131119
Priority Date: 20110617
Inventors: GREGG JUSTIN
NICKEL JOSHUA G.
Assignee: APPLE INC
CPC Classifications: [{"code": "G01R31/2822", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01R31/2822", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 47353191