PATENT DOCUMENT

Publication Number: US-8903326-B2
Application Number: US-201113018348-A
Country: US
Kind Code: B2

Title: Simultaneous downlink testing for multiple devices in radio-frequency test systems

Abstract:
A test station may include a test host, a signal generator, and a test chamber. Multiple devices under test (DUTs) may be placed in the test chamber during production testing. Radio-frequency signals may be conveyed from the signal generator to the multiple DUTs using a conducted arrangement through a radio-frequency signal splitter circuit or using a radiated arrangement through an antenna in the test chamber. The signal generator may broadcast initialization downlink signals. The multiple DUTs may synchronize with the initialing downlink signals. The signal generator may broadcast test downlink signals at a target output power level. The multiple DUTs may receive the test downlink signals and compute a corresponding downlink transmission performance level based on the received downlink signals. A given DUT is marked as a passing DUT if the downlink performance level is satisfactory. A given DUT may be retested if the downlink performance level fails design criteria.

Claims:
What is claimed is: 
     
       1. A method of testing devices under test with a test station, wherein the test station includes a signal generator and a test chamber in which the devices under test are tested, the method comprising:
 with the signal generator, broadcasting radio-frequency test signals to each of the devices under test in the test chamber in parallel; 
 with the test station, gathering performance metric data from each of the devices under test, wherein the performance metric data of each device under test is indicative of radio-frequency performance of that device under test in receiving the broadcast radio-frequency test signals; 
 obtaining respective path loss values associated with each of the devices under test in the test chamber; 
 selecting a minimum path loss value from the respective path loss values associated with each of the devices under test in the test chamber; and 
 computing a target output power level based on the minimum path loss value. 
 
     
     
       2. The method defined in  claim 1 , wherein the test station further comprises a test host, the method further comprising:
 with the test host, directing each of the devices under test to compute the performance metric data. 
 
     
     
       3. The method defined in  claim 1 , wherein the test station further comprises a test host, the method further comprising:
 with the test host, directing each of the devices under test to compute the performance metric data, wherein the performance metric data is a symbol error rate, a frame error rate, a bit error rate, or a packet error rate. 
 
     
     
       4. The method defined in  claim 1 , further comprising:
 loading each device under test with a test operating system, wherein the test operating system configures each device under test to compute the performance metric data by analyzing the radio-frequency test signals broadcast from the signal generator. 
 
     
     
       5. The method defined in  claim 1 , further comprising:
 loading each device under test with a test operating system, wherein the test operating system configures each device under test to compute the performance metric data by analyzing the radio-frequency test signals broadcast from the signal generator and wherein the performance metric data is a symbol error rate, a frame error rate, a bit error rate, or a packet error rate. 
 
     
     
       6. The method defined in  claim 1 , further comprising:
 directing the signal generator to broadcast radio-frequency initialization signals at a given output power level. 
 
     
     
       7. The method defined in  claim 6 , further comprising:
 directing each of the devices under test to synchronize with the initialization signals broadcast from the signal generator. 
 
     
     
       8. The method defined in  claim 7 , wherein broadcasting the radio-frequency test signals to each of the devices under test in the test chamber in parallel comprises:
 broadcasting the radio-frequency test signals to each of the devices under test in the test chamber at the target output power level, wherein the target output power level is less than the given output power. 
 
     
     
       9. The method defined in  claim 8 , further comprising:
 in response to gathering the performance metric data from each of the devices under test, determining whether each of the devices under test satisfies design criteria. 
 
     
     
       10. The method defined in  claim 9 , further comprising:
 in response to determining that a given device under test satisfies design criteria, marking the given device under test as a passing device under test. 
 
     
     
       11. The method defined in  claim 10 , further comprising:
 in response to determining that a given device under test fails to satisfy design criteria, retesting the given device under test. 
 
     
     
       12. The method defined in  claim 11 , wherein retesting the given device under test comprises:
 retesting the given device under test at a new location in the test chamber. 
 
     
     
       13. The method defined in  claim 11 , wherein retesting the given device under test comprises:
 retesting the given device under test while the signal generator broadcasts the radio-frequency test signal at an output power level that is higher than the target output power level. 
 
     
     
       14. A radio-frequency test station for testing devices under test, wherein the radio-frequency test station comprises a signal generator and a test chamber in which the devices under test are tested, and wherein the radio-frequency test station is configured to perform the steps of  claim 1 .

Description:
This application claims the benefit of provisional patent application No. 61/413,959, filed Nov. 15, 2010, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to testing wireless electronic devices and more particularly, to testing multiple wireless electronic devices placed in a test chamber. 
     Wireless electronic devices typically include transceiver circuitry, antenna circuitry, and other radio-frequency circuitry that provide wireless communications capabilities. During testing, wireless electronic devices under test (DUTs) can exhibit different performance levels. For example, each wireless DUT in a group of DUTs can exhibit its own output power level, gain, frequency response, efficiency, linearity, dynamic range, etc. 
     The performance of a wireless DUT can be measured using a radio-frequency (RF) test station. An RF test station typically includes a test host, a tester (e.g., a signal generator), and a test chamber. The signal generator is connected to the test host. Arranged in this way, the test host configures the signal generator to transmit radio-frequency signals during test operations. 
     In conventional radio-frequency test arrangements, a wireless DUT is placed into the test chamber. The DUT is connected to the test host using a control cable. The test host directs the signal generator to broadcast downlink signals at a predetermined output power level to the DUT over a wireless path or a wired path. The test host directs the DUT to synchronize with the downlink signals broadcast from the signal generator. 
     The DUT receives the downlink signals. The received downlink signals exhibit a power level that is substantially less than the predetermined output power level (e.g., the power level of the received downlink signals may be 20 dB less than the predetermined output power level). The DUT analyzes the received downlink signals and determines whether the received downlink signals satisfy performance criteria. For example, the DUT can compute a bit error rate based on the received downlink signals. If the bit error rate is less than a predetermined threshold, the DUT is marked as a passing DUT. If the bit error rate is greater than the predetermined threshold, the DUT is marked as a failing DUT. 
     After the DUT has been marked as a passing DUT or a failing DUT, the DUT is disconnected from the test host (i.e., by unplugging the control cable from the DUT) and is removed from the test chamber. To test additional DUTs, an additional DUT is connected to the test host (i.e., by plugging the control cable into a corresponding mating connector in the additional DUT) and is placed into the test chamber for downlink testing. 
     Wireless testing using this conventional approach may be inefficient, because the process of connecting a DUT to the test host, placing the DUT in the test chamber, testing the DUT, removing the DUT from the test chamber, and disconnecting the DUT from the test host one DUT at a time is time-consuming. 
     It would therefore be desirable to be able to provide improved ways of performing downlink testing. 
     SUMMARY 
     Test stations in a radio-frequency test system can be used to perform wireless testing on wireless devices under test (DUTs). Each test station may include a test host, a signal generator, and a test chamber. During wireless testing, more than one DUT may be placed within the test chamber. 
     In one suitable test arrangement, the tester may be coupled to the multiple DUTs in the test chamber through a radio-frequency signal splitter circuit. In particular, the DUTs may include transceiver circuits that are electrically connected to the coupling circuit through radio-frequency cables. Testing the DUTs using this conducted test setup bypasses over-the-air transmission. 
     In another suitable test arrangement, radio-frequency signals may be conveyed between the signal generator and the multiple DUTS through a test antenna that is placed within the test chamber. The antenna may transmit and receive radio-frequency signals to and from the multiple DUTs in the test chamber. Testing the DUTs using this radiated test setup takes into account the effect of over-the-air transmission. 
     Whether the multiple DUTs are tested using the conducted arrangement or the radiated arrangement, downlink sensitivity testing may be performed on the multiple DUTs within a test chamber. Downlink sensitivity (or receive signal power sensitivity) may be defined as the minimum receive signal power level for which the received radio-frequency signals exhibit performance levels (e.g., link performance data) that satisfy design criteria. 
     During downlink testing, the test host may direct the signal generator to broadcast initialization radio-frequency signals. The test host may direct each of the multiple DUTs to synchronize with the initializing signals in parallel. After each of the DUTs has been synchronized, the test host may direct the signal generator to broadcast test radio-frequency signals at a target output power level. The target output power level may be computed based on path loss values associated with each of the multiple DUTs in the test chamber and a target sensitivity level (e.g., a sensitivity level selected so that at least 99% of DUTs will satisfy performance criteria and be marked as passing DUTs during production testing). 
     The DUTs may receive the test downlink signals. The DUTs may analyze the received test downlink signals and compute a communications link performance level based on the received test signals. For example, the DUTs may each calculate a symbol error rate, frame error rate, bit error rate, packet error rate, and other performance metrics based on the received test signals. If a given DUT exhibits a calculated performance level that satisfies design criteria, the given DUT will be marked as a passing DUT. If a given DUT exhibits a calculated performance level that is unsatisfactory, the given DUT may be retested using other test configurations (e.g., the given DUT may be retested based on a new target output power level, may be retested in a different location in the test chamber, may be retested in another test station, etc.). 
     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 device under test with radio-frequency circuitry in accordance with an embodiment of the present invention. 
         FIG. 2  is a diagram of illustrative test stations each connected to computing equipment and each including a test host, a signal generator, a radio-frequency signal splitter, and a test chamber in accordance with an embodiment of the present invention. 
         FIG. 3  is a diagram of illustrative test stations each connected to computing equipment and each including a test host, a signal generator, a test chamber, and an antenna in the test chamber in accordance with an embodiment of the present invention. 
         FIG. 4  is a plot illustrating a statistical distribution of receive signal power sensitivity for wireless devices under test in accordance with an embodiment of the present invention. 
         FIG. 5  is a flow chart of illustrative steps involved in performing simultaneous downlink sensitivity testing for multiple devices under test that are placed within a test chamber 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, or 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 (GPS). Electronic devices may therefore be provided with circuitry for receiving satellite navigation signals such as GPS signals at 1575 MHz. 
     In testing environments, the wireless electronic devices are sometimes referred to as devices under test (DUTs).  FIG. 1  shows an example of a test device such as DUT  10 . DUT  10  may be a portable electronic device, a cellular telephone, a computer, a multimedia device, or other electronic equipment. DUT  10  may have a device housing such as housing  2  that forms a case for its associated components. 
     DUT  10  may have storage and processing circuitry such as storage and processing circuitry  4 . Storage and processing circuitry  4  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  4  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, application specific integrated circuits, etc. 
     Circuitry  4  may interact with a transceiver circuit such as transceiver circuit  6 . Transceiver circuit  6  may include an analog-to-digital converter (ADC), a digital-to-analog converter (DAC), a digital down-converter (DDC), and a digital up-converter (DUC). 
     In a scenario in which DUT  10  is transmitting, circuitry  4  may provide digital data (e.g., baseband signals) to the DUC. The DUC may convert or modulate the baseband digital signals to an intermediate frequency (IF). The IF digital signals may be fed to the DAC to convert the IF digital signals to IF analog signals. The IF analog signals may then be fed to an RF front end such as RF front end  8 . 
     When DUT  10  is receiving wireless signals, RF front end  8  may provide incoming IF analog signals to the ADC. The ADC may convert the incoming IF analog signals to incoming IF digital signals. The incoming IF digital signals may then be fed to the DDC. The DDC may convert the incoming IF digital signals to incoming baseband digital signals. The incoming baseband digital signals may then be provided to circuitry  4  for further processing. Transceiver circuit  6  may either up-convert baseband signals to IF signals or down-convert IF signals to baseband signals. Transceiver block  6  may therefore sometimes be referred to as an IF stage. 
     RF front end  8  may include circuitry that couples transceiver block  6  to one or more antenna such as antenna  9 . RF front end  8  may include circuitry such as matching circuits, band-pass filters, mixers, low noise amplifier circuitry, power amplifier circuitry, etc. Circuitry  4 , transceiver block  6 , RF front end  8 , and antenna  9  may be housed within housing  2 . 
     In the scenario in which DUT  10  is transmitting, RF front end  8  may up-convert the IF analog signals from transceiver block  6  to RF analog signals (e.g., the RF signals typically have higher frequencies than the IF signals). The RF analog signals may be fed to antenna  9  for broadcast. If desired, more than one antenna may be used in DUT  10 . 
     In the scenario in which DUT  10  is receiving wireless signals, antenna  9  may receive incoming RF analog signals from a broadcasting device such as a base transceiver station, network access point, etc. The incoming RF analog signals may be fed to RF front end  8 . RF front end  8  may down-convert the incoming RF analog signals to IF analog signals. The IF analog signals may then be fed to transceiver circuit  6  for further data processing. 
     Examples of cellular telephone standards that may be supported by the wireless circuitry of device  10  include: the Global System for Mobile Communications (GSM) “2G” cellular telephone standard, the Evolution-Data Optimized (EVDO) cellular telephone standard, the “3G” Universal Mobile Telecommunications System (UMTS) cellular telephone standard, the “3G” Code Division Multiple Access 2000 (CDMA 2000) cellular telephone standard, and the “4G” Long Term Evolution (LTE) cellular telephone standard. Other cellular telephone standards may be used if desired. These cellular telephone standards are merely illustrative. 
     During testing, many wireless devices (e.g., hundreds, thousands, or more of DUTs  10 ) may be tested in a test system such as test system  11  of  FIG. 2 . Test system  11  may include test accessories, computers, network equipment, tester control boxes, cabling, test chambers, test antennas within the test chambers, and other test equipment for transmitting and receiving radio-frequency test signals and gathering test results. Test system  11  may include multiple test stations such as test stations  13 . There may, for example, be 80 test stations  13  at a given test site. Test system  11  may include any desired number of test stations to achieve desired test throughput. 
     Each test station  13  may include a test host such as test host  26 , a signal generator such as signal generator  22 , and a test chamber such as test chamber  32 . Test host  26  may, for example, be a personal computer or other types of computing equipment. 
     Signal generator  22  may be a radio communications tester of the type that is sometimes referred to as a call box or a base station emulator. Signal generator  22  may, for example, be the CMU300 Universal Radio Communication Tester available from Rohde &amp; Schwarz. Signal generator  22  may be used to emulate the behavior of a base transceiver station during a telephone call with a wireless device under test (as an example). If desired, signal generator  22  may be configured to emulate the behavior of a network access point to test the ability of transceiver  6  to support the WiFi® communications protocol, the Bluetooth® communications protocol, or other communications standards. 
     Signal generator  22  may be operated directly or via computer control (e.g., when signal generator  22  receives commands from test host  26 ). When operated directly, a user may control signal generator  22  by supplying commands directly to the signal generator using the user input interface of signal generator  22 . For example, a user may press buttons in a control panel on the signal generator while viewing information that is displayed on a display in generator  22 . In computer controlled configurations, a test host such as computer  26  (e.g., software running autonomously or semi-autonomously on the computer) may communicate with signal generator  22  (e.g., by sending and receiving data over a wired path  27  or a wireless path between the computer and the signal generator). 
     During testing, more than one DUT  10  may be placed within test chamber  32 . Test chamber  32  may have a cubic structure (six planar walls), a rectangular prism-like structure (six rectangular walls), a pyramid structure (four triangular walls with a rectangular base), or other suitable structures. 
     Multiple DUTs  10  may be attached to a test structure such as test structure (test tray)  58  within test chamber  32 . Test tray  58  may serve to secure DUTs  10  in desired locations within test chamber  32 . 
     DUTs  10  may be coupled to test host  26  through wired path  28  (e.g., data signals may be conveyed between test host  26  and a respective DUT over data path  28 ). Connected in this way, test host  26  may send commands over bus  28  to configure DUTs  10  to perform desired operations during testing. Test host  26  and DUTs  10  may be interconnected using a Universal Serial Bus (USB) cable, a Universal Asynchronous Receiver/Transmitter (UART) cable, or other types of cabling (e.g., bus  28  may be a USB-based connection, a UART-based connection, or other types of connections). 
     In one suitable arrangement, DUTs  10  may be coupled to signal generator  22  through a radio-frequency signal splitter such as RF signal splitter  50 . As shown in  FIG. 2 , splitter  50  may have a given port  100  that is connected to signal generator  22  through radio-frequency cable  24  (e.g., a coaxial cable). Splitter  50  may include additional ports each of which is coupled to respective DUTs  10 . 
     For example, circuit  50  may have a first port  102  that is electrically coupled to a first DUT using RF cable  54 - 1 , a second port  104  that is electrically coupled to a second DUT using RF cable  54 - 2 , a third port  106  that is electrically coupled to a third DUT using RF cable  54 - 3 , and a fourth port  108  that is electrically coupled to a fourth DUT using RF cable  54 - 4 . Cable  54 - 1  may be directly connected to transceiver  6  of first DUT  10  (e.g., cable  54 - 1  may have an RF connector that mates with corresponding RF connector  56  in first DUT  10 ). Cable  54 - 2  may be directly connected to transceiver  6  of second DUT  10  (e.g., cable  54 - 2  may have an RF connector that mates with corresponding RF connector  56  in second DUT  10 ). Cable  54 - 3  may be directly connected to transceiver  6  of third DUT  10  (e.g., cable  54 - 3  may have an RF connector that mates with corresponding RF connector  56  in third DUT  10 ). Cable  54 - 4  may be directly connected to transceiver  6  of fourth DUT  10  (e.g., cable  54 - 4  may have an RF connector that mates with corresponding RF connector  56  in fourth DUT  10 ). 
     Testing DUTs  10  using this type of arrangement may be referred to as conducted testing, because directly tapping into transceivers  6  bypasses over-the-air (radiated) transmission (e.g., antennas  9  of DUTs  10  are not in use during conducted testing). Cables  54 - 1 ,  54 - 2 ,  54 - 3 , and  54 - 4  may be, for example, miniature coaxial cables with diameters that are less than 2 mm (e.g., 0.81 mm, 1.13 mm, 1.32 mm, 1.37 mm, etc.), whereas cable  24  may be, for example, a cable with a diameter of about 2-5 mm (as an example). 
     As shown in  FIG. 2 , power attenuators may be coupled between splitter  50  and DUTs  10 . For example, attenuator  52 - 1  may be interposed in the signal path connecting port  102  to first DUT  10  (e.g., radio-frequency signals may be conveyed from port  102  to first DUT  10  through attenuator  52 - 1  over cable  54 - 1 ). Attenuator  52 - 2  may be interposed in the signal path connecting port  104  to second DUT  10  (e.g., radio-frequency signals may be conveyed from port  104  to second DUT  10  through attenuator  52 - 2  over cable  54 - 2 ). Attenuator  52 - 3  may be interposed in the signal path connecting port  106  to third DUT  10  (e.g., radio-frequency signals may be conveyed from port  106  to third DUT  10  through attenuator  52 - 3  over cable  54 - 3 ). Attenuator  52 - 4  may be interposed in the signal path connecting port  108  to fourth DUT  10  (e.g., radio-frequency signals may be conveyed from port  108  to fourth DUT  10  through attenuator  52 - 4  over cable  54 - 4 ). 
     The attenuators (i.e., attenuators  52 - 1 ,  52 - 2 ,  52 - 3 , and  52 - 4 ) may serve to provide impedance matching (e.g., to provide an impedance of 50 ohms, 75 ohms, 100 ohms, or other impedance values) and to reduce signal leakage among DUTs  10 . For example, consider a scenario in which first DUT  10  receives a first set of RF signals. The first set of received signals may have a power level of −100 dBm (as an example). A portion of the first set of RF signals may be reflected back towards port  102  of splitter  50 . These reflected signals may leak undesirably into ports  104 ,  106 , and  108  of splitter  50 . The attenuators may attenuate these reflected leakage signals by 40 dB (as an example) so that the reflected leakage signals do not interfere with test signals transmitted by signal generator  22 . In this example, the reflected leakage signals received by second, third, and fourth DUTs  10  may have power levels that are less than −140 dBm (−100 minus 40). Attenuating the reflected leakage signals using this approach may minimize signal interference among the multiple DUTs. 
     Radio-frequency signals may be transmitted in a downlink direction (as indicated by arrow  29 ) from signal generator  22  to DUTs  10  through splitter circuit  50 . During downlink signal transmission, test host  26  may direct signal generator  22  to generate RF test signals at its output port  25 . Splitter  50  may receive the test signals generated by signal generator  22  through port  100 . Splitter  50  may split the received signals into multiple reduced-power versions of the received signals. The reduced-power versions of the received signals may be routed to respective ports  102 ,  104 ,  106 , and  108 . Configured using this arrangement, DUTs  10  may each receive reduced-power versions of the test signals generated by signal generator  22 . 
     Radio-frequency signals transmitted from signal generator  22  to a given DUT  10  and radio-frequency signals transmitted from signal generator  22  to a different DUT  10  may experience different path loss values. Path loss is defined as the attenuation in power as radio-frequency signals propagate through a particular medium/channel. 
     Sources of path loss that may exist between signal generator  22  and a given DUT  10  include first cable path loss (e.g., path loss associated with cable  24 ), splitter path loss (e.g., power reduction introduced when splitter  50  is used to split radio-frequency signals into multiple reduced-power versions), attenuator path loss (e.g., power attenuation provided by attenuators  52 - 1 ,  52 - 2 ,  52 - 3 , and  52 - 4 ), and second cable path loss (e.g., path loss associated with cables  54 - 1 ,  54 - 2 ,  54 - 3 , or  54 - 4 ). Sources of path loss offset that exist from one downlink signal path to another may include variations in each attenuator (e.g., process, voltage, and temperature variations that may affect the operation of attenuators  52 - 1 ,  52 - 2 ,  52 - 3 , and  52 - 4 ), variations in RF cable path loss (e.g., path loss associated with RF cables  54 - 1 ,  54 - 2 ,  54 - 3 , and  54 - 3 ), and other sources of variation. 
     For example, a first set of RF signals transmitted from signal generator  22  to first DUT  10  may experience a path loss of 10.3 dB, whereas a second set of RF signals transmitted from signal generator  22  to second DUT  10  may experience a path loss of 9.8 dB (as an example). The path loss associated with each DUT  10  for the test setup of  FIG. 2  may be characterized prior to production testing. 
     The test setup of  FIG. 2  is merely illustrative. More than four DUTs  10  or less than four DUTs  10  may be mounted on tray  58  during test operations. Splitter  50  may include a sufficient number of ports to accommodate the desired number of DUTs  10 . For example, consider a scenario in which eight DUTs  10  are attached to tray  58  in test chamber  32 . Circuit  50  may therefore include port  100  that is coupled to signal generator  22  and eight additional ports that are coupled to respective DUTs  10  (as an example). 
     Test tray  58  may or may not be placed within test chamber  32 . If test chamber  32  is used, test chamber  32  may serve to isolate DUTs  10  that are placed within test chamber  32  from external sources of radiation, interference, and noise so that DUTs  10  are being tested in a controlled environment. 
       FIG. 3  shows another suitable arrangement of test stations  13 . As shown in  FIG. 3 , test station  13  may be configured to perform over-the-air (OTA) testing (sometimes referred to as radiated testing). In the test setup of  FIG. 3 , signal generator  22  is connected to a test antenna such as antenna  62  through RF cable  60 . Antenna  62  may be a microstrip antenna such as a microstrip patch antenna, a horn antenna, or other types of antennas. 
     Antenna  62  may be placed within a test chamber such as test chamber  64 . Test chamber  64  may, for example, be a pyramidal-shaped transverse electromagnetic (TEM) cell. TEM cell  64  may be used to perform electromagnetic compatibility (EMC) radiated tests without interference from ambient electromagnetic environment. Multiple DUTs  10  may be placed within test chamber  64  during wireless testing. 
     During downlink signal transmission, signal generator  22  may generate radio-frequency test signals. Antenna  62  may wirelessly transmit the test signals to DUTs  10  in TEM cell  64  (as an example). Antennas  9  in DUTs  10  may receive the radiated test signals. 
     Radio-frequency signals transmitted over-the-air from signal generator  22  to a given DUT  10  and radio-frequency signals transmitted over-the-air from signal generator  22  to a different DUT  10  may experience different path loss values. Sources of path loss that exist between signal generator  22  and a given DUT  10  in the wireless test setup of  FIG. 3  may include RF cable path loss (e.g., path loss associated with cable  60 ), antenna path loss (e.g., path loss associated with antenna  62 ), and over-the-air (OTA) path loss (e.g., e.g., path loss associated with the propagation of radio-frequency signals as they propagate through air). Sources of path loss offset that exist from one downlink signal path to another may include variations in OTA path loss, variations in the location of the different DUTs in test chamber  64 , and other sources of variation. 
     For example, a first set of RF signals transmitted from signal generator  22  to first DUT  10  may experience a path loss of 40.3 dB, whereas a second set of RF signals transmitted from signal generator  22  to second DUT  10  may experience a path loss of 39.8 dB (as an example). The path loss associated with each DUT  10  for the test setup of  FIG. 3  may be characterized prior to production testing. 
     As shown in  FIGS. 2 and 3 , each test station  13  may be connected to computing equipment  36  through line  38 . Computing equipment  36  may include storage equipment on which a database  40  is stored. Test measurements obtained during test operations may be stored in database  40 . 
     During production testing, pass/fail criteria may be applied to each DUT based on a DUT&#39;s ability to receive radio-frequency signals. The ability of DUT  10  to receive radio-frequency signals may be quantified by a receive signal sensitivity level (or downlink sensitivity). Downlink sensitivity may be defined as the minimum receive signal power level for which the received radio-frequency signals exhibit performance levels that satisfy design criteria. 
     For example, consider a scenario in which a maximum acceptable bit error rate is specified to be equal to two percent. A given DUT may receive RF signals. If the power level of the received RF signals is equal to −99 dBm, the bit error rate may be equal to 1.9%. If the power level of the received RF signals is equal to −100 dBm, the bit error rate may be equal to 2.0%. If the power level of the received RF signals is equal −101 dBm, the bit error rate may be equal to 2.1%. In this example, the downlink sensitivity of the given DUT is equal to −100 dBm, because RF signals with power levels that are less than −100 dBm result in unacceptable bit error rates for the given DUT. Testing the receive signal sensitivity of electronic devices during production testing may sometimes be referred to as performing downlink sensitivity testing. 
       FIG. 4  is a frequency distribution plot showing a statistical distribution of DUT downlink sensitivity. Sensitivity characteristic curve  70  may be obtained by testing hundreds or thousands of DUTs  10  and measuring their sensitivity levels. Curve  70  may have a peak DUT count that corresponds to sensitivity level S′. Sensitivity level S′ may correspond to the median, mean (average), or mode of an entire set of measured downlink sensitivity values (e.g., sensitivity S′ is the most frequently occurring receive signal sensitivity level). 
     As shown in  FIG. 4 , curve  70  may have a substantially Gaussian profile. A majority of DUTs  10  may exhibit sensitivity levels that are within one standard deviation (e.g., one sigma) of sensitivity level S′. Approximately 68% of DUTs  10  may exhibit sensitivity levels that are within one standard deviation of sensitivity level S′. Approximately 95% of DUTs  10  may exhibit sensitivity levels that are within two standard deviations of sensitivity level S′. 
     It may be desirable to test the ability of production DUTs to receive RF signals at a low power level corresponding to a target sensitivity level S TARG  (e.g., a sensitivity level that is at least two standard deviations greater than S′). For example, sensitivity level S′ may be equal to −112 dBm, whereas target sensitivity level S TARG  may be equal to −110 dBm. 
     During production testing, a given DUT may, for example, receive RF signals having a power level of −110 dBm. If the given DUT receives the RF signals and the received RF signals exhibit acceptable error rate performance, the given DUT has a sensitivity level that is lower than −110 dBm and will be marked as a passing DUT. If the given DUT receives the RF signals and the received RF signals exhibit unacceptable error rate performance, the given DUT has a sensitivity level that is greater than −110 dBm and will be marked as a failing DUT. A suitable S TARG  may be selected so that 99.5% of DUTs will satisfy performance criteria and be marked as passing DUTs during production testing (as an example). 
       FIG. 5  shows illustrative steps involved in downlink sensitivity testing. At step  72 , pre-characterized path loss for each DUT  10  in the test chamber (e.g., test chamber  32  of  FIG. 2  or test chamber  64  of  FIG. 3 ) may be obtained. Path loss may be characterized using conventional path loss characterization techniques prior to step  72 . 
     At step  74 , test host  26  may direct signal generator  22  to broadcast RF initialization signals at a desired output power level (e.g., at a maximum output power level). The initialization test signals may be grouped into frames for protocol-compliant transmission (e.g., the downlink RF test signals may be organized into groups of digital signals that are transmitted by DUT  10  when DUT  10  is used to transmit protocol-compliant data). For example, each frame may include control information such as a frame header and a frame trailer and may include user data (sometimes referred to as payload). The frame header may include information such as a preamble, start frame delimiter, source and destination address, and other control information, whereas the frame trailer may include information such as cyclic redundancy check bits and other sequencing information (as an example). 
     For example, signal generator  22  may be configured to emulate the behavior of a base transceiver station during a telephone call with a wireless device under test and to transmit data frames over a GSM-compliant link. As another example, signal generator  22  may be configured to emulate the behavior of a network access point and to transmit data packets over a WiFi-compliant link. 
     At step  76 , test host  26  may direct DUTs  10  in the test chamber to synchronize with the initialization signals broadcast from signal generator  22  (e.g., to synchronize signal generator  22  to the Global System for Mobile Communications (GSM) time division multiple access (TDMA) timing  26 -multiframe structure). DUTs  10  are synchronized when they transmit uplink signals with frame headers and trailers that are respectively aligned with the frame headers and trailers of the downlink initialization signals broadcast from signal generator  22 . 
     At step  78 , test host  26  may determine a desired downlink path loss based on the pre-characterized path loss values. For example, consider a scenario in which the path loss associated with a first DUT in a test chamber is equal to 10 dB, the path loss associated with a second DUT in the test chamber is equal to 10.5 dB, the path loss associated with the third DUT in the test chamber is equal to 9 dB, and the path loss associated with a fourth DUT in the test chamber is equal to 10.1 dB. Test host  26  may select the least amount of path loss as the desired downlink path loss (e.g., test host  26  may select 9 dB path loss associated with the third DUT as the desired downlink path loss for downlink sensitivity testing). Selecting the least amount of path loss in this way ensures testing DUTs in a worst case scenario. If desired, test host  26  may compute the desired downlink path loss by calculating an average path loss value based on the different path loss values associated with each of the four DUTs. 
     At step  80 , test host  26  may direct signal generator  22  to broadcast downlink test signals at a target output power level by taking into account the desired downlink path loss and target test sensitivity level S TARG . The target output power level may be calculated by adding the magnitude of the desired path loss value (i.e., the path loss value selected during step  78 ) to target sensitivity level S TARG . For example, if S TARG  is equal to −110 dBm and the desired path loss value is equal to 9 dB, the target output power level will be equal to −101 dBm (−110 plus 9). 
     At step  82 , each DUT  10  may calculate desired transmission performance metric data (or communications link performance metrics) that is indicative of radio-frequency performance of that device under test in receiving the broadcast radio-frequency test signals. Test host  26  may direct each of the multiple DUTs to compute the link performance metric data. If desired, each of the DUTs may be loaded with a test operating system. The test operating system may configure each DUT to automatically compute the performance metric data in response to receiving the test radio-frequency signals broadcast from signal generator  22 . 
     For example, each DUT  10  may receive the test signals broadcast from signal generator  22  and may calculate a symbol error rate (SER), received signal strength indicator (RSSI), and other performance metrics based on the received test signals. These performance values may be retrieved from DUTs  10  by test host  26  over line  28  and may be stored in database  40 . 
     At step  84 , pass/fail criteria may be applied to each DUT  10 . If a given DUT exhibits performance levels that fail to satisfy design criteria (e.g., the given DUT exhibits a SER that is greater than a predetermined threshold of 10%), the given DUT may be retested (step  86 ). 
     During retest procedures, test host  26  may direct signal generator  22  to broadcast downlink signals at a target output power level that takes into account the downlink path loss associated with the given DUT (if not equal to the desired downlink path loss selected during step  78 ) and test the receive capabilities of the given DUT using this new target output power level. For example, if S TARG  is equal to −110 dBm and the path loss associated with the given failing DUT is equal to 10.2 dB, the new target output power level that is used to retest the failing DUT will be equal to −99.8 dBm (−110 plus 10.2). 
     If desired, retest procedures may involve retesting the failing DUT by configuring the failing DUT to measure standard protocol performance metrics such as frame error rate (FER), bit error rate (BER), packet error rate (PER), or other performance parameters. If desired, retest procedures may involve retesting the failing DUT in different positions in the test chamber, in another test station  13 , etc. If the retested DUT fails to satisfy performance criteria a second time, the DUT may be permanently marked as a failing DUT. If the retested DUT performs satisfactorily during retest operations, the DUT may be marked as a passing DUT. 
     At step  88 , if a given DUT exhibits performance levels that satisfy design criteria (e.g., the given DUT exhibits a SER that is less than the predetermined threshold of 10%), the given DUT will be marked as a passing DUT. If there are additional DUTs to be tested, processing may loop back to step  72  to test another set of DUTs, as indicated by path  90 . 
     The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention.

Metadata:
Filing Date: 20110131
Publication Date: 20141202
Grant Date: 20141202
Priority Date: 20101115
Inventors: GREGG JUSTIN
SYED ADIL
VENKATARAMAN VISHWANATH
Assignee: APPLE INC
CPC Classifications: [{"code": "H04W24/06", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04L43/0882", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L43/50", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L43/0882", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L12/2697", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W24/06", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04L43/50", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 46048196