PATENT DOCUMENT

Publication Number: US-9635492-B2
Application Number: US-201414450152-A
Country: US
Kind Code: B2

Title: Systems and methods for performing radio-frequency testing on near-field communications circuitry

Abstract:
An electronic device may be provided with near-field communications (NFC) circuitry for communicating with external equipment. Test equipment may perform radio-frequency testing on the NFC circuitry. During manufacture of an electronic device having the NFC circuitry, the test equipment may be placed into electrical contact with antenna feed terminals on the NFC circuitry prior to attaching an antenna to the feed terminals so that a conductive path is formed between the test equipment and an NFC transceiver on the NFC circuitry. Test signals may be conveyed between the test equipment and the NFC transceiver over the conductive path for characterizing the performance of the NFC circuitry. The conductive path may include an antenna impedance modeling circuit formed on a circuit board substrate that models the impedance of the antenna that is to be attached to the NFC circuitry to allow for suitable power transfer during testing.

Claims:
What is claimed is: 
     
       1. A method of using a test system to perform radio-frequency testing on wireless communications circuitry, wherein the wireless communications circuitry comprises near-field communications transceiver circuitry coupled to an antenna feed terminal, the method comprising:
 placing test equipment in the test system into electrical contact with the antenna feed terminal, wherein placing the test equipment into electrical contact with the antenna feed terminal comprises:
 electrically connecting the antenna feed terminal to an antenna impedance modeling circuit; and 
 electrically connecting the test equipment to the antenna impedance modeling circuit; and 
 
 with the test equipment, providing radio-frequency test signals to the near-field communications transceiver circuitry via the antenna feed terminal. 
 
     
     
       2. The method defined in  claim 1 , further comprising:
 with the test equipment, receiving additional radio-frequency test signals from the near-field communications transceiver circuitry via the antenna feed terminal. 
 
     
     
       3. The method defined in  claim 2 , further comprising:
 with the test equipment, generating radio-frequency performance metric data associated with the wireless communications circuitry based on the received additional radio-frequency test signals. 
 
     
     
       4. The method defined in  claim 3 , further comprising:
 with the test equipment, determining whether the wireless communications circuitry passes testing based on the generated radio-frequency performance metric data; and 
 with assembly equipment, connecting an antenna to the antenna feed terminal in response to determining that the wireless communications circuitry passes testing. 
 
     
     
       5. The method defined in  claim 4 , wherein the test equipment has a first impedance and the near-field communications transceiver circuitry has a second impedance that is less than the first impedance. 
     
     
       6. The method defined in  claim 1 , wherein placing the test equipment into electrical contact with the antenna feed terminal comprises:
 electrically connecting the antenna feed terminal to a conductive trace on a printed circuit board; and 
 electrically connecting the test equipment to the conductive trace on the printed circuit board. 
 
     
     
       7. The method defined in  claim 1 , wherein providing the radio-frequency test signals to the near-field communications transceiver circuitry via the antenna feed terminal comprises:
 providing the radio-frequency test signals to the antenna feed terminal via the antenna impedance modeling circuit. 
 
     
     
       8. The method defined in  claim 7 , further comprising:
 with the test equipment, determining whether the wireless communications circuitry passes testing; 
 with the test equipment, providing the wireless communications circuitry to assembly equipment in response to determining that the wireless communications circuitry passes testing; and 
 with the assembly equipment, connecting an antenna to the antenna feed terminal in response to determining that the wireless communications circuitry passes testing, wherein the antenna has an impedance that is modeled by the antenna impedance modeling circuit. 
 
     
     
       9. The method defined in  claim 8 , wherein connecting the antenna to the antenna feed terminal comprises connecting a loop antenna to the antenna feed terminal, wherein the near-field communications transceiver circuitry is configured to receive radio-frequency signals from external circuitry via the loop antenna. 
     
     
       10. A method for using a test system to characterize near-field communications circuitry, wherein the test system comprises radio-frequency test equipment, the method comprising:
 with the radio-frequency test equipment, obtaining an antenna impedance modeling circuit that includes conductive traces on a printed circuit board; 
 electrically connecting the radio-frequency test equipment to the antenna impedance modeling circuit; 
 electrically connecting the near-field communications circuitry to the antenna impedance modeling circuit; and 
 conveying radio-frequency test signals between the radio-frequency test equipment and the near-field communications circuitry over the antenna impedance modeling circuit. 
 
     
     
       11. The method defined in  claim 10 , wherein obtaining the antenna impedance modeling circuit comprises:
 identifying desired antenna parameters; 
 generating a circuit model based on the desired antenna parameters; and 
 patterning the conductive traces onto the printed circuit board based on the generated circuit model. 
 
     
     
       12. The method defined in  claim 10 , wherein the antenna impedance modeling circuit comprises at least one inductive component and at least one capacitive component coupled in parallel between first and second conductive contact pads on the printed circuit board, wherein electrically connecting the radio-frequency test equipment to the antenna impedance modeling circuit comprises electrically connecting the radio-frequency test equipment to the first and second conductive contact pads, and wherein electrically connecting the near-field communications circuitry to the antenna impedance modeling circuit comprises electrically connecting the near-field communications circuitry to the first and second conductive contact pads. 
     
     
       13. The method defined in  claim 10 , wherein the test equipment has a first impedance and wherein obtaining the antenna impedance modeling circuit comprises obtaining an antenna impedance modeling circuit having a second impedance that is less than the first impedance. 
     
     
       14. The method defined in  claim 10 , further comprising:
 with the test equipment, performing pass-fail testing on the near-field communications circuitry based on the radio-frequency test signals; and 
 with assembly equipment, assembling the near-field communications circuitry within an electronic device housing in response to determining that the near-field communications circuitry passes the pass-fail testing. 
 
     
     
       15. A test system for performing radio-frequency test operations on near-field communications circuitry, comprising:
 radio-frequency test equipment, wherein the radio-frequency test equipment has a first impedance and the near-field communications circuitry has a second impedance that is less than the first impedance; and 
 a conductive path connected between the radio-frequency test equipment and the near-field communications circuitry, wherein the radio-frequency test equipment is configured to receive radio-frequency test signals from the near-field communications circuitry over the conductive path. 
 
     
     
       16. The test system defined in  claim 15 , wherein the conductive path further comprises:
 an antenna impedance modeling circuit, wherein the near-field communications circuitry is configured to transmit signals using an antenna having an impedance that is modeled by the antenna impedance modeling circuit. 
 
     
     
       17. The test system defined in  claim 16 , wherein the first impedance is greater than or equal to 50 Ohms and the antenna impedance modeling circuit has an impedance that is less than 50 Ohms. 
     
     
       18. The test system defined in  claim 15 , wherein the conductive path further comprises:
 a first set of radio-frequency contacts; 
 a second set of radio-frequency contacts; and 
 an antenna impedance modeling circuit formed on a printed circuit board, wherein the first set of radio-frequency contacts are coupled between the antenna impedance modeling circuit and the test equipment and wherein the second set of radio-frequency contacts are coupled between at least one antenna feed terminal on the near-field communications circuitry and the antenna impedance modeling circuit. 
 
     
     
       19. The test system defined in  claim 18 , wherein the antenna impedance modeling circuit comprises first and second conductive contact pads on the printed circuit board, wherein the first set of radio-frequency contacts comprises a first radio-frequency contact that contacts the first conductive contact pad and a second radio-frequency contact that contacts the second conductive contact pad, wherein the second set of radio-frequency contacts comprises a third radio-frequency contact that contacts the first conductive contact pad and a fourth radio-frequency contact that contacts the second conductive contact pad, and wherein the radio-frequency test signals comprise radio-frequency signals generated using a near-field communications protocol.

Description:
BACKGROUND 
     This relates generally to wireless communications circuitry, and more particularly, to electronic devices having 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 can also be provided with satellite navigation system receivers and other wireless circuitry such as near-field communications circuitry. Near-field communications schemes involve electromagnetically coupled communications over short distances, typically 20 cm or less. 
     Wireless communications circuitry such as near-field communications circuitry is tested in a test system to ensure adequate radio-frequency performance. In conventional test systems, radio-frequency testing is performed on near-field communications circuitry after the near-field communications circuitry has been connected to a corresponding antenna and disposed within a fully-assembled electronic device. Components within the near-field communications circuitry are tested by swiping the fully-assembled electronic device over a near-field communications reader to determine whether the near-field communications circuitry is functioning properly. When performing testing in this manner using conventional test systems, the electronic device needs to be disassembled to replace the near-field communications circuitry when a failure is detected in the near-field communications circuitry during testing. Disassembling electronic devices to replace the near-field communications circuitry when a failure is detected can be difficult, time consuming, and cost prohibitive. 
     It would therefore be desirable to be able provide improved systems and methods for testing near-field communications circuitry. 
     SUMMARY 
     An electronic device may be provided with wireless communications circuitry. The wireless communications circuitry may include near-field communications (NFC) circuitry for performing near-field communications with external equipment (e.g., using near-field communications schemes that involve electromagnetically coupled communications over short distances of 20 cm or less and/or using a 13.56 MHz near-field communications frequency band). 
     A test system may be used to perform radio-frequency testing on the near-field communications circuitry to determine whether the near-field communications circuitry has adequate radio-frequency performance. The test system may perform test operations such as pass-fail testing on the near-field communications circuitry prior to assembling the near-field communications circuitry within a fully-assembled electronic device (e.g., prior to attaching a loop antenna to antenna feed terminals on the near-field communications circuitry). 
     The test system may include test equipment (e.g., a signal generator and/or signal analyzer) for testing the near-field communications circuitry. The test equipment may be placed into electrical contact with one or more antenna feed terminals on the near-field communications circuitry so that a conductive path is formed between the test equipment and a near-field communications transceiver on the near-field communications circuitry. Radio-frequency test signals (e.g., near-field communications test signals generated using a near-field communications protocol) may be conveyed between the test equipment and the near-field communications transceiver over the conductive path. 
     For example, the conductive path may include conductive traces on a test circuit board (e.g., a test printed circuit board). First radio-frequency contact structures (e.g., radio-frequency probe contacts) may be coupled between the conductive traces on the test circuit board and the test equipment and second radio-frequency contact structures (e.g., radio-frequency pogo pin contacts) may be coupled between the conductive traces on the test circuit board and the antenna feed terminals of the near-field communications circuitry (e.g., so that the first and second radio-frequency contact structures and the conductive traces form a part of the conductive path between the test equipment and the near-field communications transceiver). 
     If desired, the conductive path may include an antenna impedance modeling circuit formed on the circuit board. During testing, the radio-frequency test signals may be conveyed between the test equipment and the near-field communications transceiver in the near-field communications circuitry over the conductive path (e.g., through the radio-frequency contact structures, the conductive traces on the test PCB, the antenna feed terminals on the near-field communications circuitry, and the antenna impedance modeling circuit on the test PCB). 
     The test equipment and/or the near-field communications circuitry may generate performance metric data that characterizes the radio-frequency performance of the near-field communications circuitry based on the radio-frequency test signals. The test equipment may process the performance metric data to determine whether the near-field communications circuitry has sufficient radio-frequency performance. If the test equipment determines that the near-field communications circuitry has sufficient performance, the near-field communications circuitry may be assembled within a fully-assembled electronic device (e.g., a loop antenna may be attached to antenna feed terminals on the near-field communications circuitry, the near-field communications circuitry may be placed within a device housing, etc.). If the test equipment determines that the near-field communications circuitry has insufficient radio-frequency performance, the near-field communications circuitry may be discarded, reworked, repaired, etc. (e.g., without needing to disassemble a fully-assembled electronic device). 
     The test equipment may have a high impedance terminator such as a terminator having an impedance of 50 Ohms or more that loads the near-field communications circuitry during testing. The antenna impedance modeling circuit may model the impedance of the antenna that is to be connected to the near-field communications circuitry during device assembly (e.g., the antenna impedance modeling circuit may include some or all of the conductive traces and other resistive, conductive, and inductive components arranged in a selected manner to exhibit an impedance that models the impedance of an antenna that will be connected to the antenna feed terminals on the near-field communications circuitry if the near-field communications circuitry passes the radio-frequency testing). In this way, the antenna impedance modeling circuit may compensate for the 50 ohm terminator of the test equipment during testing. For example, the antenna impedance modeling circuitry may have an impedance of less than 50 Ohms (e.g., 20 Ohms) that models the impedance of a loop antenna to be mounted to the antenna feeds (e.g., loop antennas having an impedance of less than 50 Ohms). In this way, the antenna impedance modeling circuit may serve as a similar terminating load to the antenna during testing of the near-field communications circuitry even when the antenna has yet to be assembled onto the near-field communications circuitry (e.g., to allow for a maximum signal power transfer during testing). 
     If desired, the antenna impedance modeling circuit may be formed based on a desired design of the antenna to be attached to the near-field communications circuitry. For example, the test system may identify desired antenna parameters (e.g., an impedance of the antenna), may generate a circuit model based on the desired antenna parameters, and may pattern the conductive traces (and other resistive, inductive, and capacitive components) onto the circuit board based on the generated circuit model to form the antenna impedance modeling circuit. 
     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 schematic diagram of an illustrative electronic device with wireless communications circuitry such as near-field communications circuitry for communicating with external near-field communications devices in accordance with an embodiment of the present invention. 
         FIG. 2  is a diagram showing how near-field communications circuitry may be coupled to a corresponding antenna for transmitting and receiving near-field communications signals in accordance with an embodiment of the present invention. 
         FIG. 3  is a diagram of an illustrative test system for testing near-field communications circuitry prior to assembly of the near-field communications circuitry within an electronic device of the type shown in  FIG. 1  in accordance with an embodiment of the present invention. 
         FIG. 4  is a diagram of an illustrative test system for performing radio-frequency tests on near-field communications circuitry prior to assembly of the near-field communications circuitry within a fully-assembled electronic device in accordance with an embodiment of the present invention. 
         FIG. 5  is a diagram showing how radio-frequency test equipment may be electrically connected to antenna feed points on near-field communications circuitry via an antenna impedance modeling circuit for performing radio-frequency testing on the near-field communications circuitry in accordance with an embodiment of the present invention. 
         FIG. 6  is a flow chart of illustrative steps that may be performed by radio-frequency test equipment for performing radio-frequency testing on near-field communications circuitry prior to assembling the near-field communications circuitry within a completed electronic device in accordance with an embodiment of the present invention. 
         FIG. 7  is a flow chart of illustrative steps that may be performed by radio-frequency test equipment for obtaining an antenna impedance matching circuit for performing radio-frequency testing on near-field communications circuitry prior to assembly of the near-field communications circuitry within a fully-assembled electronic device in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may be provided with wireless circuitry. The wireless circuitry may include near-field communications circuitry. For example, a near-field communications transmitter-receiver (“transceiver”) may use a near-field communications antenna to transmit and receive near-field electromagnetic signals at a frequency such as 13.56 MHz. Near-field communications schemes involve near-field electromagnetic coupling between near-field antennas that are separated by a relatively small distance (e.g., 20 cm or less). The near-field communications antennas may be loop antennas. 
     A schematic diagram of an illustrative configuration that may be used for an electronic device such as electronic device  10  is shown in  FIG. 1 . As shown in  FIG. 1 , electronic device  10  may include control circuitry such as storage and processing circuitry  28  and input-output circuitry such as input-output circuitry  44 . 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. Storage and processing circuitry  28 , input-output circuitry  44 , and other device components and circuitry may be formed within electronic device housing  10 . 
     Storage and processing circuitry  28  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  28  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, power management units, audio codec chips, application specific integrated circuits, etc. 
     Storage and processing circuitry  28  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, software for testing the radio-frequency performance of wireless communications circuitry  34  (e.g., a test operating system), etc. To support interactions with external equipment (e.g., a near-field communications reader, radio-frequency test equipment, etc.), storage and processing circuitry  28  may be used in implementing communications protocols. Communications protocols that may be implemented using storage and processing circuitry  28  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, near-field communications protocols, etc. 
     Input-output circuitry  44  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  44  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, 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 near-field communications circuitry  42 . Near-field communications circuitry  42  may handle near-field communications at frequencies such as the near-field communications frequency of 13.56 MHz or other near-field communications frequencies of interest (e.g., a local high frequency (LHF) band for communicating in a near-field domain with external equipment over a range of 20 cm or less). 
     If desired, wireless communications circuitry  34  may include other transceiver circuitry  36  (e.g., non-near-field communications transceiver circuitry) for communicating in other frequency bands (e.g., for performing wireless communications with external equipment in the far-field domain). For example, transceiver circuitry  36  may include satellite navigation system receiver circuitry such as Global Positioning System (GPS) receiver circuitry (e.g., for receiving satellite positioning signals at 1575 MHz), wireless local area network transceiver circuitry for handling 2.4 GHz and 5 GHz bands for WiFi® (IEEE 802.11) communications and/or the 2.4 GHz Bluetooth® communications band, cellular telephone transceiver circuitry 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, or any other desired transceiver circuitry. 
     If desired, communications circuitry  34  may include circuitry for other short-range and long-range wireless links. For example, wireless communications circuitry  34  may include wireless circuitry for receiving radio and television signals, paging circuits, etc. In near-field communications, wireless signals are typically conveyed over distances of less than 20 cm. 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 include antenna structures  40 . Antenna structures  40  may include one or more antennas. Antennas structures  40  may be formed using any suitable antenna types. For example, antenna structures  40  may include antennas with resonating elements that are formed from loop antenna structures (e.g., antenna coil structures), patch antenna structures, 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. If desired, near-field transceiver circuitry  42  and non-near-field transceiver circuitry  36  may be coupled to respective antennas  40  or transceivers  42  and  36  may share one or more antennas  40 . 
     Near-field communications circuitry  42  may be coupled to antenna structures  40 . In one suitable arrangement, near-field communications circuitry  42  communicates using a loop antenna in antennas  40  (sometimes referred to herein as loop antenna  40 ). Near-field communications circuitry  42  (e.g., a near-field communications transceiver) uses antenna structures  40  to communicate with external near-field communications equipment  58  over near-field communications link  64 . External equipment such as external equipment  58  may communicate with near-field communications circuitry  42  via magnetic induction, for example. Equipment  58  may include an antenna such as antenna  41  (e.g., a loop antenna) that is controlled by control circuitry on external equipment  58 . Loop antenna  41  and a loop antenna formed from antenna structures  40  on device  10  may be electromagnetically coupled to support near-field wireless communications when loop antenna  41  and the loop antenna in structures  40  are within an appropriately close distance of each other such as 20 cm or less, as indicated by near-field communications signals  64 . If desired, portions of the loop antenna in structures  40  may be formed from one or more conductive portions of housing  12  (e.g., from one or more portions of peripheral conductive housing structures that surround electronic device  10 ). 
     Device  10  may use near-field communications circuitry  42  and antenna structures  40  (e.g., the near-field communications loop antenna portion of antenna structures  40 ) to communicate with external near-field communications equipment  58  using passive or active communications. In passive communications, device  10  may use near-field communications circuitry  42  and antenna structures  40  to modulate electromagnetic signals  64  from equipment  58 . In active communications, near-field communications circuitry  42  and antenna structures  40  may transmit radio-frequency electromagnetic signals  64  to external equipment  58 . 
     Near-field transceiver circuitry  42  may be coupled to antenna structures  40  by signal paths such as signal path  70 . Signal paths  70  may include transmission lines, portions of conductive housing structures, ground plane structures, traces on printed circuits, or other conductive paths. If desired, components such as impedance matching circuitry, filtering circuitry, balun circuitry, or other circuitry may be formed on path  70 . Path  70  may couple near-field transceiver circuitry  42  to one or more antenna feeds (e.g., antenna feed terminals) on antenna  40 . For example, NFC circuitry  42  may send and receive signals using antenna  40  via corresponding antenna feeds on antenna  40 . Near-field transceiver circuitry  42  may feed antenna  40  using balanced or unbalanced signals. 
       FIG. 2  is an illustrative diagram showing how near-field communications circuitry such as near-field communications circuitry  42  of  FIG. 1  may be coupled to antenna  40  for transmitting and/or receiving near-field communications signals using antenna  40 . As shown in  FIG. 2 , near-field communications circuitry  42  may be coupled to processor  29 . Processor circuitry  29  may include independent processing circuitry that is separate from storage and processing circuitry  28  of  FIG. 1  or processor circuitry  29  may be formed as a portion of storage and processing circuitry  28  of  FIG. 1 . Processor circuitry  29  may send control signals to near-field communications (NFC) circuitry  42  and NFC circuitry  42  may send received data to processor  29 . If desired, processor  29  may run test software or other desired software for operating NFC circuitry  42 . 
     NFC circuitry  42  may include, for example, NFC baseband circuitry, NFC transceiver circuitry, NFC front end circuitry, or any other desired circuitry for transmitting and receiving near-field signals. Baseband circuitry in NFC circuitry  42  may, for example, receive digital data that is to be transmitted from processing circuitry  29  and may convert received signals into digital data that is provided to storage and processing circuitry  29 . Circuitry  42  may include mixer circuitry that converts digital data processed by the baseband processor to an NFC frequency such as 13.56 MHz and that converts received data at an NFC frequency to a baseband frequency. Front end circuitry in NFC circuitry  42  may include filter circuitry, amplifier circuitry, matching circuitry, converter circuitry, multiplexing circuitry, switching circuitry, or any other desired circuitry for forming an interface between the transceiver circuitry and antennas  40 . 
     NFC circuitry  42  may supply transmit signals TX over one or more transmit ports  72  and may receive signals RX via one or more receive ports  74 . If desired, filter circuitry  76  may be coupled to transmit ports  72  to filter out undesired harmonics of transmit signals TX (e.g., signals that may leak onto receive ports  74  and cause undesired interference with receive signals RX). 
     If desired, near-field communications circuitry  42  may be coupled to antenna  40  using a balun such as optional balun circuitry  78 . NFC circuitry  42  may have a differential output (e.g., signals TX output onto ports  72  referenced to each other) or a single-ended output (e.g., signals TX output onto a port  72  referenced to ground). In scenarios where NFC circuitry  42  is provided with a differential output, balun  78  may convert the differential output from circuitry  42  to single-ended signals for feeding the near-field communications antenna formed from antenna structures  40 . In scenarios where NFC circuitry  42  has a differential output, signal path  70  may be referred to as a balanced signal path, whereas in scenarios where NFC circuitry has a single-ended output, signal path  70  may be referred to as an unbalanced signal path. 
     Antenna  40  may be fed via antenna feed terminals  80 . Impedance matching circuitry such as matching circuitry  82  may be interposed on signal path  70  between optional balun circuitry  78  and antenna feed terminals  80 . Matching circuitry  82  may include components such as inductors, resistors, and capacitors and may be used in matching the impedance of antenna  40  to the impedance of transmission line structures coupled to antenna  40 . Matching network components may be provided as discrete components (e.g., surface mount technology components) or may be formed from housing structures, printed circuit board structures, traces on plastic supports, etc. 
     Antenna  40  may be fed using at least one antenna feeds terminal  80  (sometimes referred to herein as antenna feed points, antenna feed pads, feeds, feed points, or feed pads). Antenna feed terminals  80  may include a positive (signal) feed terminal and a negative (ground) feed terminal. In scenarios where path  70  is formed as a balanced signal path, NFC circuitry  42  may be coupled to the positive and ground feed terminals of antenna  40  via signal path  70 , whereas in scenarios where path  70  is formed as an unbalanced signal path, NFC circuitry  42  may be coupled only to the positive feed terminal of antenna  40  via path  70 . 
     If desired, one or more of processor  29 , near-field communications circuitry  42 , filter circuitry  76 , balun circuitry  78 , path  70 , matching circuitry  82 , and antenna feed terminals (antenna feed contact pads)  80  may be formed on a common substrate  84 . Substrate  84  may be, for example, a dielectric substrate, a printed circuit board substrate (e.g., a rigid printed circuit board or flexible printed circuit board such as a flex circuit), a shared integrated circuit structure, or any other desired substrate. In one suitable arrangement, substrate  84  may be a logic board for electronic device  10  on which components  29 ,  42 ,  76 ,  70 ,  78 ,  80 , and  82  are formed (sometimes referred to herein as a main logic board (MLB) or near-field communications board). If desired, components  29 ,  42 ,  70 ,  76 ,  78 ,  80  and  82  (e.g., the wireless communications circuitry associated with sending and receiving near-field communications signals) may be formed on a common substrate with non-near-field communications circuitry  36  ( FIG. 1 ) or may be formed on a separate substrate from non-near-field communications circuitry  36 . Circuit board  84  may sometimes be referred to herein as near-field communications board  84  or more simply as near-field circuitry  84 . 
     Antenna  40  may be formed on a separate substrate from circuitry  84 . For example, antenna  40  may be formed from conductive traces on a rigid or flexible substrate (e.g., an antenna flex circuit) that is separate from circuit board  84 . Antenna  40  may be mounted (connected) to board  84  during assembly of device  10 . For example, antenna  40  may be electrically connected to antenna feed terminals  80  when mounting antenna  40  to board  84 . Antenna  40  may be electrically coupled to feed terminals  80  using a conductive connecting structure such as solder, conductive adhesive, spring-loaded pins, spring structures, welds, or any other desired conductive connection structure. 
     The radio-frequency performance of wireless communications circuitry  34  (e.g., of near-field circuitry  84 ) in device  10  may be characterized by one or more wireless performance metrics. Processor  29  and/or NFC circuitry  42  may generate data associated with wireless performance metrics in response to signals received from external test equipment. If desired, external test equipment may generate performance metric data associated with signals transmitted by NFC circuitry  42 . For example, external test equipment, processor  29 , and/or NFC circuitry  42  may generate performance metric data such as received power, transmitted power, receiver sensitivity, frame error rate, bit error rate, channel quality measurements based on received signal strength indicator (RSSI) information, Load Modulation Amplitude (LMA), any desired combination of these performance metrics, and other information that is reflective of the performance of near-field circuitry  84  in device  10 . Performance metric data may, for example, include performance metric values measured for a given performance metric (e.g., measured error rate values, measured SNR values, measured RSSI values, etc.). 
     One or more radio-frequency test stations may be provided for performing radio-frequency tests (e.g., radio-frequency pass-fail test operations) on near-field communications circuitry in electronic devices such as device  10  (e.g., to ensure adequate radio-frequency performance of the near-field circuitry). Near-field communications circuitry that is being tested using the one or more radio-frequency test stations may sometimes be referred to as a device under test (DUT). The DUT may be, for example, a partially assembled electronic device (e.g., the DUT may include some or all of wireless circuitry  34  prior to completion of manufacturing). It may be desirable to test near-field circuitry  84  within partially assembled electronic devices so that near-field circuitry  84  can be more readily accessed during test operations (e.g., to test the performance of near-field circuitry  84  that has not yet been enclosed within a device housing). 
     In one suitable arrangement that is sometimes described herein as an example, near-field circuitry  84  (e.g., near-field circuit board  84 ) as shown in  FIG. 2  may be tested using one or more radio-frequency test stations. Near-field circuits  84  under test may sometimes be referred to herein as DUTs  84 ′. This example is merely illustrative. If desired, test stations may perform radio-frequency test operations on any desired portion of device  10  (e.g., some or all of wireless communications circuitry  34 , etc.). In general, by performing radio-frequency testing on near-field circuitry  84  (e.g., prior to assembly of circuitry  84  into a fully-assembled device  10 ), disassembly of a fully assembled device to replace or re-work one or more components of near-field circuitry  84  that fails testing may be omitted, thereby reducing the time and resources required to test and assemble the device relative to scenarios where radio-frequency testing is performed on a fully assembled device. 
     In accordance with an embodiment of the present invention, electronic devices  10  may be manufactured (assembled) using a manufacturing system such as manufacturing system  102  as shown in  FIG. 3 . If desired, manufacturing system  102  may manufacture a number of electronic devices  10  simultaneously (e.g., many electronic devices  10  may each be assembled on a respective assembly line in parallel). Manufacturing system  102  may manufacture electronic devices  10  by assembling different components within production devices (e.g., components such as near-field circuitry  84 , antennas  40 , housing  12 , wireless communications circuitry  34 , etc.). Manufacturing system  102  may test the performance of components for use in electronic devices  10  (e.g., by gathering performance metric data from DUTs  84 ′) using one or more test stations  106  (sometimes referred to herein as test systems). 
     In order to test the performance of many DUTs  84 ′ for use in electronic devices  10  simultaneously, manufacturing system  102  may include a number of assembly lines  104  that each convey a respective DUT  84 ′ to test stations  106  in parallel. Test stations  106  may be any suitable test stations for characterizing the performance of DUTs  84 ′. For example, test stations  106  may gather radio-frequency performance metric data associated with DUTs  84 ′ and may process the radio-frequency performance metric data to characterize the radio-frequency performance of DUTs  84 ′. DUTs  84 ′ that have sufficient radio-frequency performance may be labeled as “passing” components, whereas DUTs  84 ′ that have insufficient radio-frequency performance may be labeled as “failing” components. Passing components may be conveyed to assembly equipment  108  via assembly lines  104  for further assembly, whereas failing components may be discarded or reworked. 
     Assembly equipment  108  may further assemble DUTs  84 ′ within a corresponding electronic device  10 . Assembly equipment  108  may, for example, modify circuitry  84 ′, attach circuitry  84 ′ to additional components, combine multiple circuits  84 ′, etc. In one suitable example, assembly equipment  108  may attach components  84 ′ to antenna circuitry such as loop antenna  40  ( FIG. 1 ) and may enclose components  84 ′ within a housing such as housing  12 . If desired, loop antenna  40  may be formed from one or more portions of housing  12 . Devices  10  with assembled components may be further tested by other test stations, if desired. 
     By forming DUTs  84 ′ without a corresponding antenna and performing radio-frequency testing on the DUTs using test stations  106  prior to attachment of the antenna, test stations  106  may perform radio-frequency testing on NFC circuitry  42  without compensating for variations in antenna  40  (e.g., radio-frequency test stations  106  may characterize the performance of NFC circuitry  84  independently from the radio-frequency performance of the corresponding antenna). 
     In some radio-frequency test systems, the performance of non-near-field wireless circuitry such as wireless circuitry  36  ( FIG. 1 ) is characterized by coupling test equipment such as a signal generator and signal analyzer to antenna feed points using a coaxial connector such as a 50 Ohm coaxial connector. The 50 Ohm coaxial connector suitably matches the input impedance of antennas used by the non-near-field wireless circuitry. 
     However, in near-field communications systems (e.g., near-field circuitry  84 ) that communicate using a near-field loop antenna such as loop antenna  40 , the input impedance of the loop antenna may be less than 50 Ohms. For example, loop antennas used for near-field communications may be 20 Ohms, 10 Ohms, or any other desired impedance that is less than 50 Ohms. In order to properly transmit signals using loop antenna  40  (e.g., to form a suitable resonance on antenna  40  without generating undesired reflected signals, etc.), near-field circuitry  84  may be configured to exhibit an impedance that matches the input impedance of loop antenna  40 . For example, the impedance of the near-field circuitry  84  may be less than 50 Ohms (e.g., the near-field circuitry  84  may have an impedance of 20 Ohms in scenarios where the input impedance of antenna  40  is 20 Ohms, etc.). In other words, near-field circuitry  84  may be provided with a terminated (output) impedance load of less than 50 Ohms. 
     When performing radio-frequency testing on near-field circuitry  84 , a 50 Ohm coaxial cable connector may be unsuitable for coupling near-field circuitry  84  to external test equipment during manufacture of device  10  (e.g., prior to attachment of antenna  40  to circuitry  84 ). For example, as near-field circuitry  84  has an output impedance of less than 50 Ohms, near-field circuitry  84  may be unable to generate a suitable resonance (e.g., using radio-frequency signals transmitted by NFC transceiver  42 ) when coupled to the test equipment prior to attachment of antenna  40  to circuitry  84  (e.g., because near-field circuitry  84  is not provided with a terminated impedance load that suitably matches the impedance of NFC circuitry  42  and the other components of circuitry  84 ). It may therefore be desirable to be able to provide improved methods for performing radio-frequency testing on near-field circuitry  84 . 
     If desired, radio-frequency test systems may be provided with antenna impedance modeling circuitry for performing radio-frequency testing on near-field circuitry  84 .  FIG. 4  is an illustrative diagram of a system for performing radio-frequency testing on near-field circuitry such as near-field circuitry  84  of  FIG. 2  using antenna impedance modeling circuitry. As shown in  FIG. 4 , test system  106  (e.g., a test system such as test station  106  of  FIG. 3 ) may include test equipment  110 , computing equipment such as test host  112  and optional verification equipment  114 , and a test fixture such as test fixture  116 . 
     Test host  112  may be formed from computing equipment such as a personal computer, laptop computer, tablet computer, handheld computing device, or any other desired computing equipment. Verification equipment  114  may include computing equipment such as a personal computer, laptop computer, tablet computer, handheld computing device, or any other desired computing equipment. If desired, verification equipment  114  and test host  112  may be formed from shared computing equipment (e.g., one or more shared personal computers, etc.). Test equipment  110  may include equipment for generating radio-frequency test signals to be provided to DUTs  84 ′ and may include equipment for receiving signals from DUT  84 ′ and analyzing the received signals (e.g., equipment  110  may include a signal generator, signal analyzer, spectrum analyzer, vector network analyzer, oscilloscope, display equipment such as a computer monitor or other types of display screens, or any other desired equipment for generating radio-frequency test signals and performing radio-frequency measurements on signals received from DUTs  84 ′). 
     Test equipment  110  may be operated directly or via computer control (e.g., when test equipment  110  receives commands from test host  112 ). When operated directly, a user may control test equipment  110  using a user input/output interface of test equipment  110 . For example, a user may press buttons in a control panel on test equipment  110  while viewing information that is displayed on a display in test equipment  110 . In computer controlled configurations, test host  112  (e.g., software running autonomously or semi-autonomously on test host  112 ) may communicate with tester equipment  110  by sending and receiving control signals and data over path  111 . 
     Test fixture  116  may receive one or more devices under test  84 ′ during radio-frequency testing operations. For example, one or more DUTs  84 ′ may be placed on test fixture  116  or may be otherwise mounted to test fixture  116  during testing. If desired, multiple DUTs  84 ′ may be mounted to optional test tray  118 . Test tray  118  may be inserted into or mounted to test fixture  116  during testing. If desired, test host  112  may be coupled to test fixture  116  via path  121  (e.g., a universal serial bus USB path or any other desired data path). Test host  112  may provide control signals such as test commands to fixture  116  via path  121  and/or may receive test data from test fixture  116  over path  121 . 
     Test fixture  116  may include one or more test circuit boards for coupling test equipment  110  to near-field communications DUTs  84 ′. Test circuit boards on fixture  116  may include printed circuit boards (PCBs) such as test PCB (TPCB)  120  as shown in  FIG. 4 . Test PCB  120  may be formed as a rigid or flexible printed circuit board. One or more antenna impedance modeling circuits  122  may be formed on test PCB  120 . For example, antenna impedance modeling circuit  122  may be formed from conductive traces (e.g., patterned traces) on TPCB  120 , from discrete components (e.g., surface mount components or embedded components) on TPCB  120 , or from a combination of conductive traces and discrete components. Antenna impedance modeling circuit  122  may include a number of inductive, capacitive, and resistive components (elements) for modeling the impedance load of one or more loop antennas  40 . For example, a given antenna impedance modeling circuit  122  may be patterned onto test PCB  120  so that the modeling circuit has a selected impedance that matches the impedance of a given loop antenna  40 . If desired, multiple antenna impedance modeling circuits  122  may be formed on TPCB  120  for testing multiple DUTs  84 ′ in parallel. 
     Each antenna impedance modeling circuit  122  may include corresponding conductive test pads  124 . Test pads  124  may be formed from conductive contacts (e.g., conductive pad traces on TPCB  120 ) corresponding to the feed terminals of the antenna that is modeled by the corresponding impedance modeling circuit  122 . Test equipment  110  may be connected to antenna impedance modeling circuits  122  on test PCB  120  via path  125  and corresponding test equipment contact structures  126 . Test equipment contact structures  124  may include radio-frequency probe structures having radio-frequency probe contacts (e.g., probe tips) or any other desired radio-frequency contact structures (e.g., two or more radio-frequency probe contacts may be coupled between test equipment  110  and each antenna impedance modeling circuit  122  for testing multiple DUTs  84 ′ in parallel). For example, contacts  124  may include signal and ground contacts that are electrically connected between test equipment  110  and test pads  124  (e.g., to corresponding signal and ground test pads on each impedance modeling circuit  122 ). 
     As shown in  FIG. 4 , test fixture  116  may include radio-frequency contact structures  128  that are coupled to test PCB  120 . Contact structures  128  may be electrically connected to test pads  124  in each impedance modeling circuit  122 . Contact structures  128  may electrically connect antenna feed terminals  80  on DUTs  84 ′ to a corresponding antenna impedance modeling circuit  122  during testing. For example, when DUTs  84 ′ are placed on test fixture  116 , contact structures  128  may couple a the test pads of a respective antenna impedance modeling circuit  122  to a corresponding DUT  84 ′ (e.g., contact structures  128  may include first signal and ground conductors that electrically connect signal and ground test pads  124  in a first antenna impedance modeling circuit  122  to corresponding antenna feed terminals  80  on a first DUT  84 ′, may include second signal and ground conductors that electrically connect signal and ground test pads  124  in a second antenna impedance modeling circuit  122  to corresponding antenna feeds  80  on a second DUT  84 ′, etc.). 
     Contact structures  128  may include any desired radio-frequency contact structures. For example, contact structures  128  may include radio-frequency probe contact structures having radio-frequency probe contacts (e.g., probe tips) or other radio-frequency contact structures such as pogo pins or spring contacts for contacting antenna feed terminals  80  on DUTs  84 ′ when DUTs  84 ′ are loaded onto test fixture  116 . By electrically connecting test equipment contacts  126  to test pads  124  and electrically connecting antenna feeds  80  on DUTs  84 ′ to test pads  124  via contact structures  128 , test equipment  110  may provide radio-frequency test signals to and receive radio-frequency test signals from DUTs  84 ′ (e.g., via contacts  126 , path  125 , test pads  124 , and contacts  128 ). In other words, a conductive path may be formed between test equipment  110  and antenna feed terminals  80  on DUTs  84 ′. Antenna impedance modeling circuit  122  may serve as a similar terminating load for DUTs  84 ′ as antennas  40  (e.g., when implemented in the completed device  10 ) and may thereby allow for proper resonance (e.g., a maximum power transfer) using DUT  84 ′ during testing (e.g., regardless of the impedance of path  125  and contact structures  126 ). In this way, test equipment  110  may perform contact radio-frequency testing of NFC circuitry such as near-field DUTs  84 ′ prior to completed assembly of device  10 . 
     Verification equipment  114  may be used to verify the performance of test PCB  120 , antenna modeling circuits  122 , test fixture  116 , contact structures  128  and  126 , and/or test equipment  110  (e.g., to ensure that radio-frequency testing performed using test system  106  is accurate and reliable). If desired, verification equipment  114  may be formed as a part of test host  112  or at a location remote from test station  106 . 
       FIG. 5  is an illustrative diagram that shows how test equipment  110  may interface with a given DUT  84 ′ through a corresponding antenna impedance modeling circuit  122  for performing radio-frequency testing on DUT  84 ′. As shown in  FIG. 5 , antenna impedance modeling circuit may include conductive traces  136 , inductive components  130  (e.g., a first inductor L 1 , a second inductor L 2 , a third inductor L 3 , etc.), capacitive components  132  (e.g., a capacitor C), and resistive components R coupled in parallel between two conductive test pads  124  (e.g., between a first conductive test pad  124 - 1  and a second conductive test pad  124 - 2 ). 
     The example of  FIG. 5  is merely illustrative. If desired, components  130 ,  132 , and  134  may include any desired number of capacitive elements, inductive elements, and resistive elements arranged in any desired manner (e.g., in series and/or in parallel). Test pads  124  may be coupled to traces  136  and elements  130 ,  132 , and  134  at any desired location. If desired, test pad  124 - 1  may be connected to ground  138  (e.g., a ground plane of test PCB  120 ). If desired, components  130 ,  132 , and  134  may have corresponding inductance, capacitance, and resistance values that have tight tolerances such as a tolerance of less than 2% (e.g., the values may have a margin of error of less than 2%) to ensure that measurements made by test system  106  are not dominated by variations in load  122 . 
     Antenna impedance modeling circuit  122  may have a selected impedance provided by the arrangement of components  130 ,  132 ,  134 , and traces  136  on TPCB  120 . For example, modeling circuit  122  may have a selected number of conductive traces, inductive elements, capacitive elements, and/or resistive elements connected in a desired arrangement such that antenna impedance modeling circuit  122  has the same input impedance as the loop antenna  40  that is to be assembled onto that DUT  84 ′ (e.g., modeling circuit  122  may model the input impedance of the antenna to be used on DUT  84 ′, thereby providing DUT  84 ′ with a terminated load that is similar to the terminated load that the device will have when fully assembled). 
     DUT  84 ′ may include antenna feed terminals  80 . For example, DUT  84 ′ may include a first antenna feed terminal  80 - 1  and a second antenna feed terminal  80 - 1  (e.g., feed points  80  may be formed as conductive pads or traces on a corresponding circuit board). When a given DUT  84 ′ is loaded into test fixture  116 , antenna feed terminals  80  on DUT  84 ′ may be coupled to antenna impedance modeling circuit  122  via contact structures  128  (shown as dashed paths  128 - 1  and  128 - 2 ). For example, first contact path  128 - 1  may be coupled between first feed terminal  80 - 1  on DUT  84 ′ and first test pad  124 - 1 , whereas second contact path  128 - 2  may be coupled between second feed terminal  80 - 2  on DUT  84 ′ and second test pad  124 - 2 . Contact paths  128  may maintain an electrical connection between pads  124  and antenna feeds  80  using any desired contact structures. As one example, contacts  128  may be soldered to test pads  124  and may include be held or compressed against antenna feeds  80  using pressure-providing structures such as pogo pins or spring contact structures (e.g., pogo pins in structures  128  may be soldered or welded to test pads  124  and may be held against antenna feeds  80  during testing, thereby allowing modeling circuit  122  to be used for testing many different DUTs  84 ′). 
     In the example of  FIG. 5 , first antenna feed terminal  80 - 1  on DUT  84 ′ may be a ground (negative) antenna feed terminal whereas second antenna feed terminal  80 - 2  may be a signal (positive) antenna feed terminal. Test equipment  110  may include signal generator equipment such as signal generator  140  and signal analysis equipment such as signal analyzer  142 . Signal analysis equipment  142  and signal generator  140  may be coupled to test pads  124  on antenna impedance modeling circuit  122  via paths  125  and contacts  126  (e.g., via a first path  125 - 1 , a second path  125 - 2 , a third path  125 - 3 , a first probe contact  126 - 1 , and a second probe contact  126 - 2 ). Paths  125  may include any desired number of conductive lines (e.g., conductive wires, transmission line structures, etc.). For example, paths  125  may include two coaxial cables each connecting a respective one of analysis equipment  142  and generator  140  to contacts  126 . 
     In the example of  FIG. 6 , a signal port of signal generator  140  may be coupled to test pad  124 - 2  via path  125 - 2  and connector  126 - 2 . If desired, a resistor divider structure  127  may be interposed on path  125 - 2  between generator  140  and connector  126  (e.g., to obstruct an impedance load of signal generator  140 ). If desired, resistor structures  127  may be formed as a conductive trace on test PCB  120  or as a discrete component on test PCB  120 . Test pad  124 - 2  may serve as a signal (positive) test pad that electrically connects signal generator  140  to positive antenna feed terminal  80 - 2  of DUT  84 ′ (e.g., via connector  128 - 2 ). Signal generator  140  may be grounded to test pad  124 - 1  via path  125 - 1  and test pad  124 - 1 . Test pad  124 - 1  may serve as a ground (negative) test pad that couples signal generator  140  to negative antenna feed terminal  80 - 2  of DUT  84 ′ (e.g., via connector  128 - 1 ). Signal generator  140  may generate test signals and may provide the test signals to DUT  84 ′ via paths  125 - 1  and  125 - 2 , contacts  126 - 1  and  126 - 2 , test pads  124 - 1 , and  124 - 2 , antenna impedance modeling circuit  122 , and contacts  128 - 1  and  128 - 2 . DUT  84 ′ may receive the test signals via antenna terminals  80 - 1  and  80 - 2 . The generated test signals may be generated according to a near-field communications protocol. DUT  84 ′ may generate performance metric data based on the received test signals (e.g., performance metric values associated with receiving radio-frequency signals). 
     Signal analysis equipment  142  may be coupled to test pad  124 - 2  via connector  126 - 2  and signal path  125 - 3 . If desired, DUT  84 ′ may generate additional test signals (e.g., in response to receiving test signals from signal generator  140 , in response to receiving control signals from test host  112  of  FIG. 4  or from a user such as a test station operator) and may convey the test signals to signal analysis equipment  142  via radio-frequency contacts  128 - 1  and  128 - 2 , antenna impedance modeling circuit  122 , contact  126 - 2 , and path  125 - 3 . DUT  84 ′ may generate the additional test signals using a near-field communications protocol (e.g., the same NFC protocol with which signal generator  140  generates test signals). If desired, DUT  84 ′ may provide generated performance metric data to test equipment  110  via antenna modeling circuitry  122  or via other conductive paths between DUT  84 ′ and test equipment  110 . Signal analysis equipment  142  may analyze the radio-frequency signals received from DUT  84 ′ and may generate performance metric data associated with the radio-frequency performance of DUT  84 ′. Signal analysis equipment  142  may provide radio-frequency performance metric data (e.g., data generated by analysis equipment  142  and/or DUT  84 ′) to test host  112  for further processing. If desired, DUT  84 ′ may be coupled to test host  112  via other conductive paths and may provide generated performance metric data to test host  112  directly. 
     Signal analysis equipment  142  and signal generator  140  may, for example, have an impedance of 50 Ohms (e.g., BNC connectors or other 50 Ohm radio-frequency connectors may be formed at the interface of equipment  142  and  140  and path  125 ), whereas DUT  84 ′ has an impedance of less than 50 Ohms (e.g., 20 Ohms or less). By coupling antenna feeds  80  on DUT  84 ′ to antenna modeling circuit  122  having a selected impedance that matches the impedance of DUT  84 ′, DUT  84 ′ may be provided with a suitable terminated load at antenna feed terminals  80  and may thereby transmit suitable signals having a maximum power transfer (e.g., a maximum resonance) indicative of normal operation of DUT  84 ′ (e.g., operation of DUT  84 ′ after incorporation into a completed device). Radio-frequency testing may therefore be indicative of the performance of DUT  84 ′ during normal operation of assembled device  10 . 
     If desired, a single device under test may be coupled to different antenna impedance modeling circuits created to model the impedance of different designs for antenna  40  (e.g., to perform radio-frequency testing on the NFC circuitry in the device under test for a wide range of different antenna designs). If desired, multiple DUTs  84 ′ may be tested using the same configuration of antenna impedance modeling circuitry  122  (e.g., so that multiple devices  84 ′ may be tested for a given antenna design in parallel). 
       FIG. 6  is a flow chart of illustrative steps that may be performed by a test system such as test system  106  as shown in  FIGS. 4 and 5  for performing radio-frequency testing on near-field communications circuitry such as DUT  84 ′. The steps of  FIG. 6  may be performed, for example, after forming the near-field communications circuitry as shown in  FIG. 2  onto a circuit board substrate and prior to attaching loop antenna  40  to antenna feed points  80  in the near-field communications circuitry. 
     At step  200 , test system  106  may obtain unassembled components of an electronic device for testing. For example, test system  106  may obtain NFC communications circuitry such as NFC circuitry  84  of  FIG. 2  for testing prior to full assembly of electronic device  10  (e.g., over a corresponding assembly line  104  as shown in  FIG. 3 ). The obtained NFC circuitry under test (DUT)  84 ′ may have an impedance of less than 50 Ohms and/or may be used for sending and receiving radio-frequency NFC signals using a loop antenna (e.g., over a range of 20 cm or less) that has yet to be assembled onto the device under test. 
     At step  202 , DUT  84 ′ may be loaded onto test fixture  116  (as shown in  FIGS. 4 and 5 ). For example, a test station operator may place DUT  84 ′ onto test fixture  116  or DUT  84 ′ may be autonomously placed within test fixture  116 . If desired, multiple DUTs  84 ′ may be tested in parallel by loading the DUTs onto test tray  118  and mounting test tray  118  within test fixture  116 . 
     At step  204 , test system  106  may obtain one or more antenna impedance modeling circuits such as antenna impedance modeling circuit  122  for modeling the impedance of an NFC loop antenna. Impedance modeling circuit  122  may be designed and built to have a selected impedance that matches the antenna impedance of an associated design for loop antennas  40  that are to be attached to DUTs  84 ′ at a later time. If desired, impedance modeling circuit  122  may be formed from conductive traces and circuit components on test PCB  120 . Test PCB  120  may include other impedance modeling circuits  122  for testing multiple DUTs  84 ′ in parallel. 
     At step  206 , test system  106  may place test equipment  110  into electrical contact with loaded DUT  84 ′ via antenna impedance modeling circuit  122  (e.g., as shown in  FIG. 5 ). For example, test equipment contact structures  126  may be placed into electrical contact with test pads  124  on antenna impedance modeling circuit  122 . Test fixture contact structures  128  may be placed into contact with corresponding antenna feeds  80  on DUT  84 ′. In this way, radio-frequency signals may be conveyed between DUT  84 ′ and test equipment  110  through contacts  126 , antenna impedance modeling circuit  122 , and contacts  128 . Performing radio-frequency testing by forming a direct electrical connection using a conductive path (e.g., a path including contacts  126  and  128  and modeling circuit  122 ) may sometimes be referred to herein as performing contact-based radio-frequency testing or wired radio-frequency testing (e.g., as opposed to scenarios in which wireless radio-frequency testing is performed without establishing a conductive path between the test equipment and the NFC circuitry under test). If desired, multiple sets of contacts may be used for coupling multiple DUTs  84 ′ to test equipment  110  via respective antenna impedance modeling circuits  122  (e.g., for performing testing on multiple DUTs  84 ′ in parallel). 
     At step  208 , test system  106  may perform radio-frequency testing on DUT  84 ′ by generating and transmitting radio-frequency test signals to DUT  84 ′ (e.g., test signals generated in a 13.56 MHz near-field communications frequency band and using a near-field communications protocol). If desired, processing circuitry on DUT  84 ′ (e.g., test software running on processor  29  of  FIG. 2 ) may direct DUT  84 ′ to generate radio-frequency test signals (e.g., autonomously, based on instructions received from test host  112 , or in response to receiving test signals from test equipment  110 ). DUT  84 ′ and/or test equipment  110  may gather performance metric information using the test signals to determine whether DUT  84 ′ has sufficient radio-frequency performance. 
     For example, test equipment  110  may perform pass/fail test operations on DUT  84 ′ using the generated performance metric data. DUTs  84 ′ that exhibit satisfactory radio-frequency performance for each tested performance metric may be labeled as “passing” devices. DUTs  84 ′ that exhibit unacceptable radio-frequency performance for one or more radio-frequency performance metrics may be labeled as “failing” devices. If DUT  84 ′ passes the testing (e.g., is labeled a passing device), processing may proceed to step  216  as shown by path  214 . 
     At step  216 , DUT  84 ′ may be further assembled (e.g., using assembly equipment  108  of  FIG. 3 ), tested, and/or provided to users for normal device operation. For example, DUT  84 ′ may be passed to assembly equipment for attaching a loop antenna  40  to antenna feed terminals  80  on DUT  84 ′ (e.g., an antenna  40  having an impedance modeled by obtained impedance modeling circuit  122 ). If desired, DUT  84 ′ may be assembled within a conductive housing such as housing  12 . In some scenarios, portions of housing  12  may form a part of loop antenna  80  that is attached to DUT  84 ′ (e.g., portions of housing  12  may be electrically connected to antenna feed terminals  80 ). If DUT  84 ′ fails testing (e.g., is labeled a failing device), processing may proceed to step  212  as shown by path  210 . At step,  212 , test system  106  may take appropriate actions to handle the failing DUT. For example, the failing DUT may be discarded, calibrated, re-tested, reworked, redesigned, one or more components on board  84 ′ may be replaced, etc. 
       FIG. 7  is a flow chart of illustrative steps that may be performed by test system  106  and/or other testing equipment to obtain an antenna impedance modeling circuit for performing radio-frequency testing on NFC device under test  84 ′ (e.g., so that DUT  84 ′ has a suitable terminated load even though DUT  84 ′ is not connected to a corresponding antenna). The steps of  FIG. 7  may, for example, be performed while processing step  204  of  FIG. 6 . The steps of  FIG. 7  may be performed by test system  106  and/or using other computing equipment (e.g., using one or more computers located remote to test station  106 ). A scenario in which test host  112  and verification equipment  114  of test station  106  perform the steps of  FIG. 7  is described herein as an example. 
     At step  220 , test host  112  may identify desired antenna parameters associated with antenna  40  that is to be connected to DUT  84 ′. For example, test host  112  may receive antenna parameters associated with a selected design of antenna  40  (e.g., the antenna parameters may be provided by designers of antenna  40  or from any other desired source). The antenna parameters may include, for example, antenna impedance, scattering parameters, resonance frequencies, or any other desired electromagnetic parameters associated with antenna  40 . 
     At step  222 , test host  112  may generate an impedance circuit model based on the identified antenna parameters. For example, circuit modeling software running on test host  112  may be used (e.g., by a test station operator or designer of NFC circuitry  84 ′) to generate a circuit model that implements the identified antenna parameters. Test host  112  may determine a number, size, and arrangement of resistive, capacitive, and/or inductive elements for use in the circuit model such that a circuit having those elements operates at the identified antenna parameters. For example, the generated circuit model may model the impedance of the desired antenna  40 . In the example of  FIG. 5 , the generated circuit model may identify four inductors L 1 , L 2 , L 3 , and L 4  coupled in together in series and coupled in parallel with a capacitor C and a resistor R that is expected to have the desired antenna parameters when provided with radio-frequency signals. A radio-frequency performance simulation may be performed on the circuit model to verify that the model accurately exhibits the desired antenna parameters. 
     At step  224 , simulation software running on test host  112  or on other computing equipment may simulate the radio-frequency performance of the generated circuit model. For example, test host  112  may simulate the power transfer of the generated circuit model when provided with radio-frequency signals. Test host  112  may compare the simulated performance of the circuit model with the desired antenna parameters (e.g., as identified at step  220 ). For example, test host  112  may simulate the performance of an antenna modeling circuit having four inductors L 1 , L 2 , L 3 , and L 4  coupled together in series and coupled in parallel with a capacitor C and a resistor R and may compare the simulated performance to the desired antenna parameters (e.g., test host  112  may compare a simulated impedance of the modeling circuit to the desired antenna impedance). 
     If the simulated performance of the generated circuit model insufficiently matches the desired antenna parameters, processing may loop back to step  222  as shown by path  226  to regenerate an additional circuit model (e.g., a circuit model having a different number, size, and arrangement of capacitive, resistive, and/or inductive elements). If the simulated performance of the generated circuit model sufficiently matches the desired antenna parameters, processing may proceed to step  230  as shown by path  228 . 
     At step  230 , layout generation circuitry on test host  112  may generate a layout for test PCB  120  ( FIG. 5 ) that incorporates the generated circuit model. For example, test host  112  may generate an arrangement for conductive traces such as traces  136  on TPCB  120  that connect the inductive, capacitive, and resistive elements of the circuit model so that antenna modeling circuit  122  may be formed on test PCB  120 . Circuit fabrication equipment and/or operators of system  106  may build test PCB  120  having the generated layout (e.g., may pattern conductive traces, resistive, capacitive, and inductive components on a test PCB  120  for use during testing). When implemented onto circuit board  120 , the generated circuit layout may sometimes be referred to herein as antenna modeling circuit  122 . As the placement of conductive traces  136  on test PCB  120  may contribute to the capacitance and inductance of antenna impedance modeling circuit  122 , additional verification operations may be needed to ensure that test PCB  120  suitably matches the desired antenna parameters. 
     At step  232 , verification equipment  114  may perform test PCB verification operations on the antenna modeling circuit patterned onto test PCB  120 . If desired, verification equipment  114  may include radio-frequency test probe equipment, signal generator equipment, and/or signal analyzer equipment for verifying the radio-frequency performance of antenna modeling circuit  122 . For example, verification equipment  114  may measure the impedance, scattering parameters, resonance frequency, or any other desired radio-frequency parameters of the generated antenna impedance modeling circuit. Verification equipment  114  may compare the measured radio-frequency parameters of antenna modeling circuit  122  to the simulated performance of the circuit model implemented by antenna modeling circuit  122  (e.g., may compare the measured impedance of circuit  122  to the simulated impedance of circuit  122  as determined at step  224 ). In this way, verification equipment  114  may verify that the physical implementation of the circuit model has a corresponding radio-frequency performance that matches the simulated performance. 
     If the radio-frequency performance of antenna modeling circuit  122  insufficiently matches the simulated performance of the circuit model implemented by circuit  122 , processing may loop back to step  230  as shown by path  234  to generate an additional layout (e.g., arrangement of conductive traces  136 ) for test PCB  120 . If the radio-frequency performance of antenna modeling circuit  122  sufficiently matches the simulated performance of the circuit model implemented by circuit  122 , the test PCB may be used for performing testing on DUTs  84 ′ (e.g., processing may proceed to step  206  of  FIG. 6 ). In this way, test system  106  may obtain antenna impedance modeling circuits that accurately model the antenna  40  that is to be used with DUT  84 ′ (e.g., so that the NFC circuitry in DUTs  84 ′ is provided with a suitable terminating load). 
     The example of  FIG. 7  is merely illustrative. If desired, the circuit model for antenna impedance modeling circuitry  122 , the simulation software for simulating the performance of the circuit model, the layout generation software for generating test PCB layouts, and/or verification equipment  114  be formed on remote computing equipment located at a different geographical location from test system  106  (e.g., steps  220 - 232  may be performed at test system  106  or at another location remote from test system  106 ). 
     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: 20140801
Publication Date: 20170425
Grant Date: 20170425
Priority Date: 20140801
Inventors: NARASIMHAN SOWMIYA
Assignee: APPLE INC
CPC Classifications: [{"code": "H04B5/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B5/0043", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W4/008", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W24/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W4/80", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W24/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W4/80", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W24/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04B5/48", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B5/48", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B5/73", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B5/73", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 55181488