PATENT DOCUMENT

Publication Number: US-8437715-B2
Application Number: US-69330310-A
Country: US
Kind Code: B2

Title: Multi-carrier-based testing

Abstract:
A device under test (DUT) may be connected to test equipment. The test equipment may include a multi-carrier signal generator and a host computer. The signal generator may provide a multi-carrier test signal that is fed to input-output devices of the DUT. The DUT may tune to a given radio channel on the test signal. The DUT may output an audio signal to the host computer to test for audio quality. Once desired measurements have been taken, the DUT may scan up or down to the next available radio channel on the test signal. The signal generator may not need to be reconfigured between scans, because the test signal contains multiple radio channels. The host computer may run a test program that directs a test program running on the DUT to perform the required tasks during testing.

Claims:
What is claimed is: 
     
       1. A test system for testing of a device under test that has a radio tuner and that has an audio jack having first, second, and third contacts that are respectively coupled to a ground line, a left audio line, and a right audio line, the test system comprising:
 a host computer that is configured to send test commands to the device under test via the second and third contacts of the audio jack; and 
 a multi-carrier frequency modulation (FM) signal generator that is coupled to the device under test via the first contact of the audio jack, wherein the FM signal generator is configured to provide a multi-carrier test signal to the device under test, wherein the multi-carrier test signal contains at least first test signals in a first radio channel and second test signals in a second radio channel, and wherein the first and second test signals are simultaneously transmitted from the signal generator to the device under test. 
 
     
     
       2. The test system defined in  claim 1 , wherein the host computer comprises storage and processing circuitry that generates the test commands to the device under test during radio tuner testing. 
     
     
       3. The test system defined in  claim 1 , wherein the host computer is configured to send the test commands to the device under test while the device under test is tuned to the first radio channel and wherein the test commands direct the device under test to scan upwards in frequency to detect the second radio channel that is at a higher frequency than the first radio channel. 
     
     
       4. The test system defined in  claim 3 , wherein the host computer is configured to direct the device under test to tune to the second radio channel, wherein the host computer is configured to receive an audio output signal from the device under test while the device under test is tuned to the second radio channel, and wherein the host computer is configured to analyze audio quality for the audio output signal. 
     
     
       5. The test system defined in  claim 1 , wherein the host computer is configured to send the test commands to the device under test while the device under test is tuned to the first radio channel and wherein the test commands direct the device under test to perform an automatic frequency scan to locate the second radio channel. 
     
     
       6. The test system defined in  claim 5 , wherein the test command directs the device under test to tune the radio tuner from the first radio channel to the second radio channel. 
     
     
       7. A method of testing a portable electronic device that has a frequency modulation (FM) radio tuner using a multi-carrier frequency modulation (FM) signal generator and a host computer, the method comprising:
 with the multi-carrier signal generator, providing a multi-carrier frequency modulation (FM) radio test signal to the portable electronic device, wherein the multi-carrier signal contains at least first, second, and third FM radio channels, wherein the first and second FM radio channels generate intermodulation products in the third FM radio channel; 
 receiving a corresponding audio output signal at the host computer from the portable electronic device; and 
 with the host computer, directing the portable electronic device to adjust the radio tuner so that the radio tuner tunes to a given one of the at least first, second, and third FM radio channels. 
 
     
     
       8. The method defined in  claim 7  further comprising:
 with the host computer, analyzing audio quality for the audio output signal while the radio tuner of the portable electronic device is tuned to the given one of the at least first, second, and third radio channels. 
 
     
     
       9. The method defined in  claim 8 , wherein analyzing the audio quality of the audio output signal comprises measuring a selected one of: a frequency response, a signal-to-noise ratio, a maximum output level, a total harmonic distortion plus noise level, and a crosstalk level. 
     
     
       10. A method of using test equipment to test a portable electronic device having a frequency modulation (FM) radio tuner with scan capabilities, comprising:
 with a multi-carrier signal generator in the test equipment, providing audio test signals to the FM radio tuner in the portable electronic device simultaneously over first and second radio channels; 
 with a host computer in the test equipment, receiving audio output from the portable electronic device that corresponds to the audio test signals that have been received by the portable electronic device using the FM radio tuner while the FM radio tuner is tuned to the first radio channel; 
 with the host computer, performing audio quality analysis operations on the received audio output to ascertain how well the FM radio tuner is receiving the audio test signals over the first FM radio channel while the second FM radio channel is being simultaneously provided to the FM radio tuner; and 
 with the host computer, directing the portable electronic device to adjust the FM radio tuner to tune to a given one of the first and second radio channels. 
 
     
     
       11. The method defined in  claim 10 , wherein performing the audio quality analysis operations comprises measuring a signal-to-noise-ratio that is associated with the received audio output. 
     
     
       12. The method defined in  claim 10  wherein the portable electronic device has automatic FM radio channel tuning capabilities,
 wherein directing the portable electronic device to use the FM radio tuner to tune to the given one of the first and second radio channels comprises directly the portable electronic device to automatically scan for an available FM radio channel while the first and second radio channels are being simultaneously provided to the FM radio tuner. 
 
     
     
       13. The method defied in  claim 12  wherein the audio test signals include signals at multiple audio frequencies and wherein performing the audio quality analysis operations comprises making audio frequency response measurements on the received audio output. 
     
     
       14. The method defined in  claim 12  wherein providing the audio test signals to the FM radio tuner in the portable electronic device simultaneously over the first and second radio channels comprises providing the audio test signals to the FM radio tuner in the portable electronic device simultaneously over first and second FM radio channels in a frequency band ranging from 76 MHz to 108 MHz. 
     
     
       15. The method defined in  claim 10 , wherein providing the audio test signals to the FM radio tuner in the portable electronic device simultaneously over the first and second radio channels comprises providing the audio test signals to the FM radio tuner in the portable electronic device simultaneously over first and second FM radio channels in a frequency band ranging from 76 MHz to 108 MHz. 
     
     
       16. The method defined in  claim 10 , wherein performing the audio quality analysis operations comprises making a maximum output measurement on the received audio output. 
     
     
       17. The method defined in  claim 10 , wherein performing the audio quality analysis operations comprises making a crosstalk measurement on the received audio output. 
     
     
       18. The method defined in  claim 10 , wherein performing the audio quality analysis operations comprises making a total harmonic distortion plus noise level measurement on the received audio output.

Description:
BACKGROUND 
     This invention relates to electronic devices, and more particularly, to testing electronic devices with wireless communications capabilities. 
     Wireless electronic devices may include radio-frequency tuners. For example, a wireless electronic device may have a frequency modulation (FM) radio tuner. An FM radio tuner allows an electronic device to selectively receive FM radio signals at specified radio frequencies. FM signals are radio-frequency signals that are generated by varying the frequencies of carrier waves depending on the strength of input signals that are to be transmitted. 
     FM radio stations broadcast audio material on respective FM radio channels. FM radio channels typically lie at frequencies ranging from 76 MHz to 108 MHz. Numerous FM radio stations broadcast material simultaneously. For example, a first radio channel at 94.9 MHz may broadcast a first set of FM radio signals while a second radio channel at 101.5 MHz simultaneously broadcasts a second set of FM radio signals. 
     During manufacturing, wireless electronic devices are typically tested for their ability to receive radio-frequency signals. For example, a device with an FM tuner can be tested to evaluate how well the device receives FM radio signals from various FM radio channels. A single-carrier (single channel) FM signal generator is commonly used to test this type of device. The single-carrier FM signal generator generates a test signal for a single radio channel at a time. In testing a wireless electronic device, the device is connected to the single-carrier FM signal generator and a host computer. To test performance at different portions of the FM band, the FM channel of the test signal can be varied while tuning the FM tuner in the device accordingly. While this type of arrangement is helpful in testing basic FM performance, it is unable to accurately simulate real-world conditions in which multiple channels are being broadcast simultaneously. Moreover, because a single-carrier signal generator can only generate one radio channel per test iteration, the signal generator must be reconfigured between each test run to test multiple radio channels. 
     The additional time required to set up the test equipment for each test channel can be significant when performing tests for a large number of radio channels. 
     It would therefore be desirable to be able to provide improved methods for testing wireless electronic devices for their ability to receive audio signals at various radio channels. 
     SUMMARY 
     A wireless electronic device with a radio tuner may be tested. When tested, the device may sometimes be referred to as a device under test (DUT). 
     A DUT may include storage and processing circuitry and input-output devices. A test operating system (OS) may be installed on the storage and processing circuitry. The test operating system or a test application that runs on a regular operating system may be used to run test code (i.e., a test program). The input-output devices of the DUT may include audio devices such as audio interface equipment (e.g., a female audio jack), a connector such as a 30-pin connector, and wireless communications circuitry. 
     The DUT may be connected to test equipment during radio testing. The test equipment may include a multi-carrier frequency modulation (FM) signal generator or other multi-channel radio transmitter and a host computer. The host computer may be used to control the signal generator and the DUT. The FM signal generator may be used to generate a multi-carrier test signal containing FM signals for multiple radio channels. FM signals, which are radio-frequency signals generated by varying the frequencies of a carrier wave depending on the strength of input signals to be transmitted, can be received by FM tuner circuitry in the wireless communications circuits of the DUT. Because radio performance can be tested in the presence of multiple test channels, real-world conditions in which multiple channels are present simultaneously may be accurately simulated. The ability of the device to perform functions such as channel scanning can also be tested. 
     Digital and analog radio may be conveyed using FM transmission schemes. The test equipment may therefore broadcast analog FM channels, digital FM channels, or combinations of analog and digital FM channels. 
     The test signals that are produced by the test equipment may contain multi-frequency audio test tones (e.g., test audio signals at multiple audio frequencies ranging from 50 Hz to 15 KHz). These test audio signals may be transmitted at various FM radio channels in the FM frequency band ranging from 76 MHz to 108 MHz. 
     The FM signal generator may contain a digital signal processor (DSP) and a digital-to-analog converter (DAC). The digital signal processor may generate the multi-carrier test signal in digital form. The digital output of the digital signal processor may be converted to an analog signal by the digital-to-analog converter. 
     The host computer may include storage and processing circuitry and an analog-to-digital converter (ADC). The storage and processing circuitry of the host computer may run a test program (code) that communicates with the test program of the DUT. The test code of the DUT and the host computer may communicate by sending information back and forth through a 30-pin connector or other input-output data port on the DUT. The test program of the host computer may send test commands to the test program of the DUT to direct the DUT to perform tasks during testing. 
     The DUT may have a three-contact female connector (e.g., an audio jack) with three electrical contacts such as first, second, and third contacts. There may be a corresponding three-contact male connector (e.g., audio plug) with three corresponding contacts. Connectors with fewer or more contacts may also be used. The audio plug may mate with the audio jack, so that the corresponding contacts form electrical connections in the mated state. A test signal cable carrying the multi-channel test signals that have been generated by the FM signal generator may be coupled to the audio plug. The corresponding audio jack may be connected to the wireless communications circuitry in the DUT. 
     The wireless communications circuitry may include a radio receiver having a radio tuner. During normal operation, FM signals may be received using an FM antenna coupled to the audio jack (e.g., using an FM antenna formed from a ground line in a headset). During testing, the radio receiver may use the audio jack to receive the multi-carrier test signals that are fed through the test signal path from the FM signal generator. 
     The radio tuner may be used to tune to a desired radio channel to produce a received audio signal. The received audio signal may then be fed to audio circuitry in the device. The audio circuitry may include an audio codec chip. The audio codec may decode audio signals by converting audio signals between digital and analog waveforms. The audio circuitry may include left and right amplifiers that output the received audio signals in analog form to contacts in the audio jack or contacts in other suitable input-output connectors. 
     Left and right contacts in the audio jack may be connected to left and right audio lines, respectively. The left and right audio lines may form an output signal path. The audio plug may have one portion that mates with the audio jack. The audio plug may have another portion connected to the host computer. Connected in this way, the host computer may be coupled to the output signal path and may obtain the audio signals that have been received by the FM tuner in the device. The received audio signals may be fed over the output signal path to an analog-to-digital converter in the host computer. The analog-to-digital converter can convert the received audio signals into a digital data stream for testing. 
     The digital data received by the host computer may be tested for audio quality. For example, signal-to-noise ratios (SNR), maximum output levels, frequency responses, crosstalk, and other characteristics of the received audio signals may be measured. 
     Once a desired amount of measurement data has been acquired for a given DUT at a given radio channel, the host device may direct the DUT to tune to a new radio channel (e.g., by scanning up/down until a next available radio channel is detected). The FM signal generator need not always be reprogrammed to provide a new radio channel between scans, because the FM signal generator provides a multi-carrier test signal that contains multiple radio channels. The multi-carrier test signal may be used to accurately simulate real-world radio-frequency signal environments that contain multiple simultaneously active channels and may therefore allow designers to test channel selectivity in the DUT. 
     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 schematic view of an illustrative test system that includes a device under test connected to test equipment in accordance with an embodiment of the present invention. 
         FIG. 2  is a schematic view of an illustrative test system showing detailed wiring that connects a device under test to test equipment in accordance with an embodiment of the present invention. 
         FIG. 3  is a graph of an illustrative multi-frequency test tone before upconversion to higher frequencies in accordance with an embodiment of the present invention. 
         FIG. 4  is a graph of an illustrative multi-carrier test signal that is generated by a multi-carrier frequency modulation (FM) signal generator and that contains multi-frequency test tones of the type shown in connection with  FIG. 3  at multiple FM radio channels in accordance with an embodiment of the present invention. 
         FIG. 5  is a graph of an illustrative measured audio signal that is measured by a host computer in accordance with an embodiment of the present invention. 
         FIG. 6  is a flow chart of illustrative steps involved in testing a device under test with test equipment in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     This relates generally to wireless communications, and more particularly, to testing electronic devices that have wireless communications capabilities such as portable electronic devices that contain radio tuners. 
     Portable electronic devices such as handheld media players, mobile telephones, laptop computers, and other devices often radio tuners and other wireless communications circuitry. Radio tuners allow devices to tune to desired radio channels. Radio stations broadcast songs and other audio content in the form of radio-frequency (RF) signals. To test the ability of wireless electronic devices to tune to different radio channels, the audio quality of audio signals that are received by the devices can be measured as the devices are tuned to receive wireless signals from different radio channels. 
     An illustrative test system that may be used to test the radio tuning capabilities of a wireless electronic device is shown in  FIG. 1 . Test system  10  may include test equipment such as test equipment  12 . Equipment  12  may be connected to a device under test (DUT) such as DUT  28 . DUT  28  may be any suitable type of wireless electronic device. For example, DUT  28  may be a portable media player with radio tuner circuitry, a portable computer with radio tuner circuitry, a cellular telephone with radio tuner circuitry, or other equipment that has the ability to receive radio signals. 
     Test equipment  12  may contain a signal generator such as multi-carrier frequency modulation (FM) signal generator  14 . Equipment  12  may also generate amplitude modulation (AM) test signals or radio signals using other modulation techniques. Test scenarios involving FM signals are sometimes described herein as an example. 
     FM signal generator  14  may generate FM radio-frequency test signals. FM signals are radio-frequency signals that are generated by varying the frequency of a radio-frequency carrier signal depending on the strength of input signals that are to be transmitted. Analog and digital data can be carried over an FM carrier. 
     FM signal generator  14  may include digital signal processing circuitry such as digital signal processor (DSP)  16  and a digital-to-analog converter (DAC) such as digital-to-analog converter  18 . Digital signal processor  16  and converter  18  may be used to produce a multi-carrier test signal. The multi-carrier test signal contains multiple FM radio channels. In contrast to single-carrier test signals (test signals for only one radio channel) that are used in conventional test processes, multi-carrier test signals may more accurately resemble real-world radio-frequency signals, because in practice, wireless signals almost always have multi-channel characteristics. 
     If desired, signal generator  14  may generate amplitude modulation (AM) signals (e.g., signals that are generated by varying the amplitudes of a carrier wave depending on the strength of input signals to be transmitted), HD Radio® signals, signals in pure digital form, hybrid digital-analog signals containing both digital and analog signals in respective radio channels, or other suitable radio test signals. Multi-carrier test signals generated for digital radio may be FM signals or AM signals. 
     Test equipment  12  may also include a host computer such as host computer  20 . Host computer  20  may have storage and processing circuitry such as storage and processing circuitry  22  and an analog-to-digital converter (ADC) such as analog-to-digital converter  26 . Storage and processing circuitry  22  may run a test program such as test program  24 . Test program  24  may generate test commands that control test system  10 . The test commands may be conveyed over control path  46 . Analog-to-digital converter  26  may have an input terminal connected to a signal path such as output signal path  44 . Output signal path  44  may carry analog audio signals (e.g., the same type of audio signals that are routed to headphones during normal use of DUT  28 ). Analog-to-digital converter  26  may convert the analog audio signals into digital data. The digital data that is converted by analog-to-digital converter  26  may then be fed to storage and processing circuitry  22  for further analysis (e.g., measurement or testing at the host computer). 
     Device under test (DUT)  28  may be connected to test equipment  12  using paths such as paths  42 ,  44 , and  46 . DUT  28  may include storage and processing circuitry such as storage and processing circuitry  30  and input-output (I/O) devices such as input-output devices  36 . Storage and processing circuitry  30  may run a test operating system (OS) such as test operating system  32  or may be a standalone application (as examples). A test program such as test program  34  may be installed on DUT  28 . Test program  34  may be part of test operating system  32 . Test program  34  of DUT  28  may communicate with test program  24  of host computer  20  by sending information over control path  46 . Test program  24  may, for example, send test commands to test program  34  directing DUT  28  to set initial settings, to adjust output power settings, to tune to a desired radio channel, to scan up or down to the next available channel, etc. 
     Test operating system  32  and test program  34  may only be used during device testing, if desired. For example, a device under test may have read-only memory (ROM) circuitry that is flashed (reprogrammed) with test operating system  32  for production testing purposes. If a device is deemed satisfactory after testing, the device may then be flashed with another operating system suitable for operating a device for sale to potential users. A final product (i.e., the device for sale) may not need to be flashed if test program  34  is hidden from the users (e.g., not accessible to users). 
     In another suitable arrangement, a test application may be installed on storage and processing circuitry  32  on DUT  28  during production testing. The test application may communicate with test program  24  that runs on host computer  20 . The test application may communicate with test program  24  to control DUT  28  during testing. The test application may be deleted after a device has been tested. If desired, the test application may not need to be deleted if the test application is not accessible to users. 
     Test program  24  running on host computer  20  need not be used if test program  34  on DUT  28  can autonomously direct DUT  28  to perform desired test procedures. Test program  34  may therefore be able to direct DUT  28  to initialize with proper settings, to adjust volume settings, to tune and scan to desired radio channels, and to output received audio signals, without receiving instructions from host computer  20 . 
     Input-output devices  36  in DUT  28  may contain audio devices such as audio devices  38 , connectors such as connector  40 , and wireless communications circuitry such as wireless communications circuitry  52 . Audio devices  38  may include audio interface equipment having one or more input-output female connectors (e.g., audio jacks) for external headphones (as an example). Connector  40  may contain a 30-pin data port connector (as an example). Wireless communications circuitry  52  may include circuitry that receives radio-frequency signals (e.g., an FM tuner). 
     Input-output devices  36  may be coupled to test signal path  42 . Input-output devices  36  may have an output terminal coupled to output signal path  44 . DUT  28  may output audio signals it receives during testing onto output signal path  44 . Output signal path  44  may be coupled to host computer  20 . In general, DUT  28  may output received audio signals using either audio devices  38  (e.g., through an audio jack) or connector  40  (e.g., through two or more pins in a 30-pin connector). 
       FIG. 2  shows one suitable type of arrangement that may be used to connect DUT  28  to test equipment  12 . Audio devices  38  may include a female connector such as three-contact audio jack  47 . Audio jack  47  may have first, second, and third electrical contacts. The first, second, and third contacts may be connected to a ground (G) line, left (L) audio line  58 , and right (R) audio line  60 , respectively. 
     The three-contact audio jack  47  may mate with a corresponding male connector such as three-contact audio plug  49 . Audio plug  49  may have three corresponding electrical contacts that form electrical connections with the respective contacts of audio jack  47  in the mated state. 
     Doted line  48  may represent an interface at which audio jack  47  connects with audio plug  49 . Components shown to the left of dotted line  48  are components internal to DUT  28  (e.g., coupled to the contacts of audio jack  47 ). 
     Components shown to the right of line  48  are components external to DUT  28  (e.g., coupled to the contacts of audio plug  49 ). 
     As shown in  FIG. 2 , wireless communications circuitry  52  may include a radio receiver such as radio receiver  54 . Radio receiver  54  may include a radio tuner such as radio tuner  56 . Radio receiver  54  may receive radio-frequency signals. Radio tuner  56  may tune the radio receiver to a specified frequency to selectively receive radio-frequency signals from a desired radio channel. Radio tuner  56  may, for example, be an FM radio tuner that can tune to desired FM radio channels. 
     Audio devices  38  may further include audio codec (coder-decoder) circuitry such as audio codec  39 . Audio codec  39  may include a digital-to-analog converter and an analog-to-digital converter. Audio codec  39  may be capable of converting audio signals from an analog waveform to a digital data stream or from a digital data stream to an analog waveform. Audio codec  39  may be useful for processing digital radio broadcasts. For example, FM signal generator  14  may output a multi-carrier test signal. Radio receiver  54  may receive the multi-carrier test signal. Radio tuner  56  may tune the radio receiver to only receive radio-frequency signals from a given radio channel (e.g., by filtering out wireless signals at other frequencies). Signals on this channel may be sent to audio codec  39  so that codec  39  can produce an analog signal to supply to audio jack  47 . 
     As an example, consider a scenario in which generator  14  produces a multi-carrier test signal that includes test channels at 80 MHz, 85.7 MHz, 93.1 MHz, and 101.9 MHz (i.e., corresponding to four FM radio channels). FM radio tuner  56  may be used to tune the radio station at 93.1 MHz. Test signals at other frequencies may be filtered out by tuner  56 . The received 93.1 MHz channel may contain audible test tones (e.g., test tones in a frequency range from 50 Hz to 15 KHz). Audio signals generated in this way may be referred to as received audio signals. 
     During test, the received audio signal may be fed to audio devices  38  through path  62 . Audio devices  38  may include amplifiers such as left amplifier  50 -L and right amplifier  50 -R. Amplifiers  50 -L and  50 -R may have output terminals connected to left and right audio lines  58  and  60 , respectively. Lines  58  and  60  may be connected to the second the third contacts of audio jack  47 . Lines  58  and  60  may form output signal path  44 . Amplifiers  50 -L and  50 -R may drive audio output signals onto output signal path  44 . 
     Output signal path  44  may be fed to audio jack  47 . Audio jack  47  may be mated with corresponding audio plug  49 . In the mated state, output signal path  44  may run through the audio plug cable to connect to host computer  20  (see, e.g.,  FIG. 2 ). Output signal path  44  may conduct audio output signals. The audio output signals may be fed to analog-to-digital converter  26 . Analog-to-digital converter  26  may convert the audio output signals to digital data that can then be measured and analyzed by host computer  20 . To summarize the signal flow, a test signal may originate at FM signal generator  14 . The test signal is fed through the audio interface (e.g., a connection between audio plug  49  and audio jack  47 ) to the radio receiver. The radio receiver tunes to a particular one of the test channels in the test signal and provides a received audio signal. The received audio signal is output by audio devices  38  as an audio output signal. The audio output signal is then fed through the audio interface to host computer  20  for final testing. 
     A multi-frequency audio test tone such as multi-frequency test tone  64  of  FIG. 3  may be generated by digital signal processor  16 . In its un-modulated form (e.g., prior to frequency mixing or upconversion), multi-frequency test tone  64  may have non-zero signal magnitude in the audible frequency range from 50 Hz to 15 KHz, as shown in  FIG. 3 . Multi-frequency test tone  64  may have signal magnitude peaks at multiple frequencies. For example, multi-frequency test tone  64  may have five peaks at audio frequencies f A , f B , f C , f D , and f E , respectively. Frequencies f A -f E  may be spaced equally apart or may be spaced at varying intervals from one another, if desired. The signal magnitude of multi-frequency test tone  64  may be negligible (e.g., close to zero) outside the audible frequency range. 
     Digital signal processor  16  may then generate a test signal based on multi-frequency test tone  64 . The test signal may have multi-frequency test tones  64  on multiple radio-frequency (radio) channels. For example, the test signal may have multi-frequency test tones  64  at four different radio-frequency carrier frequencies f 1 , f 2 , f 3 , and f 4 , as shown in  FIG. 4 . The four different frequencies f 1 -f 4  may correspond to four different radio channels. The test signal may be an FM radio-frequency signal. FM signals are typically broadcast at a frequency band ranging from 76 MHz to 108 MHz. The four frequencies f 1 -f 4  may therefore be located within this frequency range. 
     The differences between the frequencies may be unique to reduce undesired intermodulation interferences. For example, consider a scenario in which f 1 , f 2 , f 3 , and f 4  are at 77 MHz, 87 MHz, 97 MHz, and 107 MHz, respectively. In the scenario above, the four radio channels at f 1 -f 4  are evenly spaced apart (e.g., the difference between each successive frequency is equal to 10 MHz). Equal or unequal spacing may be used. Fewer than four test channels or more than four test channels may also be used. 
     A pair of radio-frequency carriers may produce undesired interference signals that are referred to as 3 rd  order intermodulation (IM3) products. In the first scenario, test tones at f 1  and f 2  may create a first 3 rd  order intermodulation product at 97 MHz (e.g., two times f 2  subtracted by f 1 ; (2*87)−77=97). Test tones at f 2  and f 3  may also create a second 3 rd  order intermodulation product at 77 MHz (e.g., two times f 2  subtracted by f 3 ; (2*87)−97=77) and a third 3 rd  order intermodulation product at 107 MHz (e.g., two times f 3  subtracted by f 2 ; (2*97)−87=107). Additionally, test tones at f 3  and f 4  may also create a fourth 3 rd  order intermodulation product at 87 MHz (e.g., two times f 3  subtracted by f 4 ; (2*97)−107=87). 
     Note that the first, second, third, and fourth 3 rd  order intermodulation products coincide with f 3 , f 4 , f 1 , and f 2 , respectively. These 3 rd  order intermodulation products may therefore serve as undesired interference signals, because the intermodulation products fall directly on the radio channels of interest. 
     It may therefore be desirable to space the radio channels at unique frequency intervals (e.g., the difference between each successive frequency should be distinct from one another). Consider another scenario in which f 1 , f 2 , f 3 , and f 4  are at 77 MHz, 83 MHz, 93 MHz, and 101 MHz, respectively. In this scenario, the first and second radio channels are spaced 6 MHz apart, the second and third radio channels are spaced 10 MHz apart, and the third and fourth radio channels are spaced 8 MHz apart. Note that the spacing between each successive radio channel is unique. 
     In this example, test tones at f 1  and f 2  may create a first 3 rd  order intermodulation product at 89 MHz (e.g., two times f 2  subtracted by f 1 ; (2*83)−77=89). Test tones at f 2  and f 3  may also create a second 3 rd  order intermodulation product at 73 MHz (e.g., two times f 2  subtracted by f 3 ; (2*83)−93=73) and a third 3 rd  order intermodulation product at 103 MHz (e.g., two times f 3  subtracted by f 2 ; (2*93)−83=103). Test tones at f 3  and f 4  may also create a fourth 3 rd  order intermodulation product at 85 MHz (e.g., two times f 3  subtracted by f 4 ; (2*93)−101=85). 
     In this scenario, the first, second, third, and fourth 3 rd  order intermodulation products in the second scenario do not coincide with any of the four radio channels in the second scenario. It may thus be desirable to configure radio channels in a multi-carrier test signal (e.g., analog or digital) in this way. The test signal shown in  FIG. 4  is merely illustrative. Any number of radio channels may be generated. For example, a test signal may contain two, three, five, or more than five radio channels. Regardless of the number of radio channels that are provided on the multi-carrier test signal, it may be helpful to configure the radio channels such that intermodulation products do not interfere directly with any one of the radio channels. 
       FIG. 5  shows an illustrative frequency response of an audio output signal that is measured by host computer  20 . Host computer  20  may measure the signal amplitude of the received audio signal at frequencies f A -f E  corresponding to the peaks of the original multi-frequency test tone generated by FM signal generator  14 . Symbol “+” in  FIG. 5  may indicate a measured audio signal amplitude provided on left audio line  58 . Symbol “∘” in  FIG. 5  may indicate a measured audio signal amplitude provided on right audio line  60 . The measured signal amplitude may differ slightly between the left and right audio lines. In addition to measuring frequency response, performance metrics such as signal-to-noise radio, audio channel crosstalk, and/or radio channel crosstalk (interference) can also be measured. 
     Illustrative steps involved in testing DUT  28  are shown in  FIG. 6 . At step  66 , DUT  28  may be connected to test equipment  12  (e.g., multi-carrier FM signal generator  14  and host computer  20 ). Once DUT  28  is connected to test equipment  12 , DUT  28  may be powered on (step  68 ). 
     At step  70 , host computer  20  may direct DUT  28  to run test program  34  (e.g., an operating system function, a test application, or other suitable test code). Running test program  34  may initialize DUT  28  by adjusting settings to set the output power (e.g., volume) of DUT  28  to a maximum level, to enable a radio data system (RDS) feature on DUT  28 , etc. The volume may, for example, be set to an output level of −20.1 dBV (i.e., decibel representation of a voltage level with respect to one volt). Enabling RDS functionality may allow DUT  28  to extract relevant information in association with each radio channel (e.g., information such as radio channel frequency, radio channel name, etc.). 
     At step  72 , DUT  28  may be tuned to a given radio channel for testing (e.g., DUT  28  may be tuned to a specified frequency by scanning up/down until a next available radio channel is detected or may be directly tuned to a specified frequency). After tuning to the given radio channel, host computer  20  may analyze the audio output signal broadcast by the given channel. For example, host computer  20  may measure a signal-to-noise ratio (SNR), a maximum output level, a frequency responses of the type described in connection with  FIG. 5 , a total harmonic distortion plus noise (THDN), crosstalk, etc. 
     SNR may refer to a ratio of a desired signal strength to peripheral noise amplitude. Maximum output level may refer the actual volume outputted by the device under test. For example, the device may be configured to output audio signals with an output level of −20.1 dBV, but the device may only actually only output audio signals with an output level of −23.7 dBV. THDN may refer to a ratio of a desired signal strength to peripheral noise amplitude in combination with all spurious harmonic signals (e.g., interference signals located at integer multiples of the frequency at which the desired signal is located). Crosstalk may refer an undesired effect in which signals traveling on the left audio line may induce transient disturbances for signals traveling on the right audio line. For example, in quantifying crosstalk, signal isolation between the left and right audio lines may be measured in terms of decibels. Because there are one or more radio channels present in the test signal in addition to the channel to which DUT  28  is currently tuned, real-world conditions are accurately replicated. 
     Measured results may be stored on host computer  20  for processing. After the measurements have been taken for the given radio channel, processing may loop back to step  72  to scan up or down for the next available radio channel, as indicated by path  76 . In contrast to traditional test processes that require additional setup time necessary to reconfigure single-carrier test signals to a new radio channel per test iteration, it may not be necessary to reconfigure FM signal generator  14  during testing, because the test signal that multi-carrier FM signal generator  14  generates contains multiple radio channels. 
     It is important to note that host computer  20  may not explicitly specify what radio frequency DUT  28  tunes to next. DUT  28  may rely on radio tuner  56  to scan up/down and to detect a next available radio channel. An advantage of testing DUT  28  in this way is that the ability of DUT  28  to scan for arbitrary radio channels can be tested. 
     For example, consider a scenario in which a multi-carrier test signal contains first, second, third, and fourth radio channels. DUT  28  may be initialing tuned to the first radio channel. Measurements may be taken when DUT  28  is tuned to the first radio channel. Thereafter, DUT  28  may be directed by host computer  20  to scan for the next available radio channel. DUT  28  may detect the second radio channel and may tune to the second radio channel. Measurements may be taken when DUT  28  is tuned to the second radio channel. DUT  28  may again be directed by host computer  20  to scan for the next available radio channel. DUT  28  may detect the fourth radio channel and may tune to the fourth radio channel. Measurements may be taken when DUT  28  is tuned to the fourth radio channel. Host computer  20  may be able to discover that DUT  28  failed to detect the third radio channel. A DUT may fail to detect any one or any number of radio channels. This failure to detect a certain number of radio channels during scanning may be discovered by the host computer and may present useful information during production testing. 
     Also, channel selectivity of the DUT can be tested, because the DUT is essentially tuning to a specific radio channel while filtering out the other radio channels in the multi-carrier test signal. There may inevitably be interference signals such as intermodulation products located nearby each radio channel, so the ability of the DUT to attenuate these nearby noise sources may be of interest to test engineers as well. 
     For example, a test signal may be broadcast by FM signal generator containing a first radio channel at 81 MHz, a second radio channel at 91 MHz, and a third radio channel at 103 MHz. A device may use an FM radio tuner to tune to the third radio channel. There may be a pass-band filter centered at 103 MHz that strives to attenuate signals at other frequencies. There may be a 3 rd  order intermodulation (IM3) product created by the first and second radio channels located at 101 MHz (e.g., two times 91 MHz subtracted by 81 MHz; (2*91)−81=101). The IM3 product is located only two megahertz away from the third radio channel. The pass-band filter may or may not be able to sufficiently attenuate the IM3 product. The ability of the pass-band filter to attenuate undesired signals such as the IM3 product may be referred to as channel selectivity. 
     Multiple DUTs  28  may be simultaneously connected to a common multi-carrier FM signal generator. Each DUT may run its own tests separately (e.g., testing does not need to be performed in a lock-step fashion) and may feed the results to a shared host computer. For example, consider a scenario in which first and second DUTs are being tested. The first DUT may be tuned to a first radio channel while the second DUT is tuned to a second radio channel that is different from the first radio channel. The second DUT may finish testing all desired radio channels before the first DUT and may be replaced by a third DUT that is to be tested. 
     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: 20100125
Publication Date: 20130507
Grant Date: 20130507
Priority Date: 20100125
Inventors: FLICKINGER JASON A.
GREGG JUSTIN
Assignee: APPLE INC
CPC Classifications: [{"code": "H04B17/0085", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B17/0085", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 44309322