PATENT DOCUMENT

Publication Number: US-9876588-B2
Application Number: US-201414477703-A
Country: US
Kind Code: B2

Title: Systems and methods for performing tester-less radio-frequency testing on wireless communications circuitry

Abstract:
Radio-frequency performance of wireless communications circuitry on an electronic device under test (DUT) may be tested without external test equipment such as signal analyzers or signal generators. A first DUT may transmit test signals to a second DUT. External attenuator circuitry interposed between the DUTs may attenuate the test signals to desired power levels. The second DUT may characterize and/or calibrate receiver performance by generating wireless performance metric data based on the attenuated test signals. A single DUT may transmit test signals to itself via corresponding transmit and receive ports coupled together through the attenuator. The DUT may generate performance metric data based on the test signals. The DUT may include feedback receiver circuitry coupled to an output of a transmitter via a feedback path and may characterize and/or calibrate transmit performance using test signals transmitted by the transmitter and received by the feedback receiver.

Claims:
What is claimed is: 
     
       1. A method of using a test system that includes a test host to perform radio-frequency testing on first and second cellular telephones, the method comprising:
 with the test host, sending a test command to the first cellular telephone directing the first cellular telephone to generate radio-frequency test signals; 
 with the first cellular telephone, transmitting the radio-frequency test signals via a radio-frequency transmit port on the first cellular telephone; 
 with the second cellular telephone, receiving the radio-frequency test signals from the first cellular telephone via a radio-frequency receive port on the second cellular telephone; and 
 with the second cellular telephone, generating radio-frequency performance metric data based on the received radio-frequency test signals. 
 
     
     
       2. The method defined in  claim 1 , further comprising:
 with the test host, sending an additional test command to the second cellular telephone directing the second cellular telephone to generate additional radio-frequency test signals; 
 with the second cellular telephone, transmitting the additional radio-frequency test signals via an additional radio-frequency transmit port on the second cellular telephone; and 
 with the first cellular telephone, receiving the additional radio-frequency test signals from the second cellular telephone via an additional radio-frequency receive port on the first cellular telephone. 
 
     
     
       3. The method defined in  claim 2 , further comprising:
 with the first cellular telephone, generating additional radio-frequency performance metric data based on the received additional radio-frequency test signals. 
 
     
     
       4. The method defined in  claim 1 , further comprising:
 with a third cellular telephone, transmitting additional radio-frequency test signals via an additional radio-frequency transmit port on the cellular telephone; 
 with the first cellular telephone, receiving the additional radio-frequency test signals via an additional radio-frequency receive port on the first cellular telephone; and 
 with the first cellular telephone, generating radio-frequency performance metric data based on the additional radio-frequency test signals. 
 
     
     
       5. The method defined in  claim 1 , wherein the test system comprises attenuator circuitry, wherein an input of the attenuator circuitry is coupled to the radio-frequency transmit port on the first cellular telephone and an output of the attenuator circuitry is coupled to the radio-frequency receive port on the second cellular telephone, the method further comprising:
 with the attenuator circuitry, attenuating the radio-frequency test signals transmitted by the first cellular telephone. 
 
     
     
       6. The method defined in  claim 1 , wherein the second cellular telephone comprises low noise amplifier circuitry having a plurality of gain stages coupled between a receiver circuit and the radio-frequency receive port and wherein generating the radio-frequency performance metric data comprises:
 generating the radio-frequency performance metric data while only a selected one of the gain stages in the plurality of gain stages is activated. 
 
     
     
       7. The method defined in  claim 1 , further comprising:
 with the second cellular telephone, determining whether the generated radio-frequency performance metric data falls within a range of acceptable radio-frequency performance metric values; and 
 generating calibration data for the second cellular telephone that calibrates radio-frequency receiver performance in the second cellular telephone in response to determining that the generated radio-frequency performance metric data does not fall within the range of acceptable radio-frequency performance metric values. 
 
     
     
       8. A method of using a test system to perform radio-frequency testing on first and second electronic devices under test, the method comprising:
 with the first electronic device under test, transmitting radio-frequency test signals via a radio-frequency transmit port on the first electronic device under test; 
 with the second electronic device under test, receiving the radio-frequency test signals from the first electronic device under test via a radio-frequency receive port on the second electronic device under test; 
 with the second electronic device under test, generating radio-frequency performance metric data based on the received radio-frequency test signals; 
 with the second electronic device under test, transmitting additional radio-frequency test signals via an additional radio-frequency transmit port on the second electronic device under test; 
 with the first electronic device under test, receiving the additional radio-frequency test signals from the second electronic device under test via an additional radio-frequency receive port on the first electronic device under test; 
 with the first electronic device under test, generating additional radio-frequency performance metric data based on the received additional radio-frequency test signals; 
 with the first electronic device under test, labeling the first electronic device under test as one of passing testing and failing testing based on the generated additional radio-frequency performance metric data; and 
 with the second electronic device under test, labeling the second electronic device under test as one of passing testing and failing testing based on the generated radio-frequency performance metric data. 
 
     
     
       9. The method defined in  claim 8 , further comprising:
 passing the label of the first electronic device under test and the generated additional radio-frequency performance metric data to a test host for additional processing; and 
 passing the label of the second electronic device under test and the generated radio-frequency performance metric data to the test host for additional processing. 
 
     
     
       10. A method of using a test system to perform radio-frequency testing on first and second electronic devices under test, wherein the first and second electronic devices under test both include cellular telephone transceiver circuitry and the test system includes attenuator circuitry with an input and an output, the method comprising:
 with the first electronic device under test, transmitting radio-frequency test signals via a radio-frequency transmit port on the first electronic device under test while the input of the attenuator circuitry is coupled to the radio-frequency transmit port on the first electronic device under test; 
 with the attenuator circuitry, attenuating the radio-frequency test signals transmitted by the first electronic device under test; 
 with the second electronic device under test, receiving the radio-frequency test signals from the attenuator circuitry via a radio-frequency receive port on the second electronic device under test while the output of the attenuator circuitry is coupled to the radio-frequency receive port on the second electronic device under test; and 
 with the second electronic device under test, generating radio-frequency performance metric data based on the received radio-frequency test signals. 
 
     
     
       11. The method defined in  claim 10 , further comprising:
 after generating the radio-frequency performance metric data based on the received radio-frequency test signals, coupling the input of the attenuator circuitry to a radio-frequency transmit port on the second electronic device under test and the output of the attenuator circuitry to a radio-frequency receive port on the first electronic device under test. 
 
     
     
       12. The method defined in  claim 11 , further comprising:
 with the second electronic device under test, transmitting additional radio-frequency test signals via the radio-frequency transmit port on the second electronic device under test; and 
 with the first electronic device under test, receiving the radio-frequency test signals from the attenuator circuitry via the radio-frequency receive port on the first electronic device under test. 
 
     
     
       13. The method defined in  claim 12 , further comprising:
 with the first electronic device under test, generating additional radio-frequency performance metric data based on the received additional radio-frequency test signals. 
 
     
     
       14. The method defined in  claim 13 , further comprising:
 with the first electronic device under test, determining whether the first electronic device under test has satisfactory radio-frequency receiver performance based on the generated additional radio-frequency performance metric data; and 
 with the second electronic device under test, determining whether the second electronic device under test has satisfactory radio-frequency receiver performance based on the generated radio-frequency performance metric data. 
 
     
     
       15. The method defined in  claim 10 , wherein the first electronic devices under test includes a first touch screen, a first accelerometer, a first speaker, and a first microphone and the second electronic device under test includes a second touch screen, a second accelerometer, a second speaker, and a second microphone. 
     
     
       16. The method defined in  claim 15 , wherein the first electronic devices under test includes a first camera, a first proximity sensor, and a first button and the second electronic device under test includes a second camera, a second proximity sensor, and a second button. 
     
     
       17. The method defined in  claim 10 , wherein the input of the attenuator circuitry is coupled to the radio-frequency transmit port on the first electronic device under test by a first radio-frequency cable and the output of the attenuator circuitry is coupled to the radio-frequency receive port on the second electronic device under test by a second radio-frequency cable.

Description:
BACKGROUND 
     This relates generally to wireless communications circuitry, and more particularly, to electronic devices having wireless communications circuitry. 
     Wireless electronic devices such as portable computers and cellular telephones are often provided with wireless communications circuitry. The wireless communications circuitry is operable to transmit and receive wireless radio-frequency signals. The wireless communications circuitry is tested in a test system to ensure adequate radio-frequency performance. A given wireless electronic device having wireless communications circuitry is typically tested at a test station having external radio-frequency test equipment that includes a radio-frequency test signal generator and signal analyzer equipment that is formed separately from the wireless electronic devices under test. 
     During radio-frequency testing, the external test equipment is connected to a wireless electronic device under test. The external radio-frequency test signal generator generates radio-frequency test signals having selected properties and provides the test signals to the wireless electronic device under test. The wireless electronic device under test performs radio-frequency tests using the test signals received from the test signal generator to characterize the downlink (receive) performance of the wireless communications circuitry. The wireless electronic device under test generates radio-frequency test signals and transmits the test signals to the external signal analyzer equipment. The external signal analyzer equipment receives the radio-frequency test signals from the electronic device under test and analyzes the received signals to characterize the uplink (transmit) performance of the wireless communications circuitry. Performing radio-frequency testing on wireless communications circuitry using external test equipment such as test signal generator equipment and signal analyzer equipment can be excessively costly and time consuming, as external radio-frequency test equipment can be expensive and can require excessive time to set up for testing multiple wireless electronic devices under test. 
     It would therefore be desirable to be able to provide improved test systems for testing wireless communications circuitry without using external radio-frequency test equipment. 
     SUMMARY 
     An electronic device may be provided with wireless communications circuitry. The radio-frequency performance of the wireless communications circuitry may be tested using a test system or may be tested during normal device operation without using external radio-frequency test equipment such as signal analyzer equipment or signal generator equipment. Wireless communications circuitry (or an electronic device on which the circuitry is formed) on which radio-frequency testing is being performed may sometimes be referred to herein as an electronic device under test. 
     A first electronic device under test may be used to perform radio-frequency testing on a second electronic device under test. For example, the first electronic device under test may generate and transmit radio-frequency test signals via a radio-frequency transmit port on the first electronic device under test. The transmit port may be coupled to an input of attenuator circuitry via a radio-frequency test cable. An output of the attenuator circuitry may be coupled to a radio-frequency receive port on the second electronic device under test via an additional radio-frequency cable. The attenuator circuitry may be separate from (e.g., external to) the devices under test. The attenuator circuitry may attenuate the radio-frequency test signals transmitted by the first electronic device under test by one or more attenuation levels (e.g., a sequence of attenuation levels). The second electronic device under test may receive the attenuated radio-frequency test signals from the attenuator circuitry via the radio-frequency receive port on the second electronic device under test. The second electronic device under test (e.g., processing circuitry on the second electronic device under test) may generate radio-frequency performance metric data based on the received radio-frequency test signals and may characterize and/or calibrate the radio-frequency performance of receiver circuitry on the second electronic device under test based on the performance metric data. For example, the second electronic device under test may compare the generated performance metric data to desired (target) performance metric values (e.g., a range of acceptable values) and, if the generated performance metric data does not fall within the range of acceptable values, the processing circuitry may generate and store calibration data on storage circuitry on the second electronic device under test for use during subsequent device operations (e.g., during normal device operations by an end user). 
     If desired, the second electronic device under test may perform radio-frequency testing on the first device under test. For example, the second electronic device under test may generate and transmit additional radio-frequency test signals to the attenuator circuitry via an additional radio-frequency transmit port on the second electronic device under test and the attenuator circuitry may pass the attenuated additional radio-frequency test signals to an additional radio-frequency receive port on the first electronic device under test. The first electronic device under test may generate additional radio-frequency performance metric data based on the attenuated additional radio-frequency test signals and may characterize and/or calibrate the radio-frequency performance of receiver circuitry on the first electronic device under test based on the additional performance metric data. In another suitable arrangement, a third electronic device under test may transmit additional radio-frequency test signals via an additional radio-frequency transmit port on the third electronic device under test to the attenuator circuitry and the attenuator circuitry may convey attenuated versions of the additional radio-frequency test signals to the receive port on the first electronic device under test to characterize and/or calibrate the radio-frequency receive performance of the first electronic device under test, In this way, a group of devices under test may generate test signals for testing and calibrating each other without using external signal generator or analyzer equipment. 
     The second electronic device under test may include low noise amplifier circuitry having multiple gain stages coupled between a radio-frequency receiver circuit on the second electronic device under test and the radio-frequency receive port. The second electronic device under test (e.g., processing circuitry on the second electronic device under test) may generate a first set of the radio-frequency performance metric data while only a selected one of the gain stages is activated and may generate a second set of the radio-frequency performance metric data while all of the gain stages is activated, if desired. The first and second sets of performance metric data may be used to characterize and/or calibrate the radio-frequency performance of the low noise amplifier circuitry and/or the receiver circuitry. 
     A single electronic device under test may generate radio-frequency test signals that are transmitted to itself for testing the radio-frequency performance of the electronic device under test without external tester equipment. The attenuator circuitry may be coupled between a radio-frequency transmit port on the electronic device under test and a radio-frequency receive port on the electronic device under test. Transmitter circuitry on the device under test may transmit radio-frequency test signals that are conveyed to the attenuator circuitry via the radio-frequency transmit port. The attenuator circuitry may attenuate the radio-frequency test signals and may convey the attenuated test signals to the receive port of the device under test. Processing circuitry (e.g., baseband processing circuitry) on the electronic device under test may generate radio-frequency performance metric data based on the attenuated radio-frequency test signals to characterize and/or calibrate the radio-frequency receive performance of the device under test. In this way, the electronic device may characterize/calibrate radio-frequency receive performance on itself without using external radio-frequency signal generator or signal analyzer circuitry. 
     An electronic device under test may include baseband processing circuitry, radio-frequency transmitter circuitry, and feedback receiver circuitry coupled to an output of the radio-frequency transmitter circuitry via a conductive feedback path. The radio-frequency transmitter circuitry may transmit radio-frequency test signals and the feedback receiver circuitry may receive the transmitted radio-frequency test signals from the transmitter circuitry via the conductive feedback path. The feedback receiver circuitry may generate and provide test data corresponding to the transmitted radio-frequency test signals to the baseband processing circuitry. For example, the feedback receiver circuitry may convert the transmitted radio-frequency test signals to in-phase and quadrature-phase (I/Q) test data and may provide the I/Q test data to the baseband processing circuitry. The baseband processing circuitry may generate radio-frequency performance metric data based on the test data received from the feedback receiver circuitry. Processing circuitry (e.g., processing circuitry implementing test software) may process the performance metric data to characterize and/or calibrate the radio-frequency transmit performance of the electronic device (e.g., the radio-frequency performance of the transmitter circuitry, power amplifier circuitry coupled to the transmitter circuitry, filtering circuitry coupled to the transmitter circuitry, etc.). 
     If desired, the processing circuitry may load a sequence of test commands onto the baseband processing circuitry that instruct the radio-frequency transmitter circuitry to generate the radio-frequency test signals (e.g., based on information in the sequence of test commands). The processing circuitry may provide control signals to the baseband processing circuitry prior to transmitting the radio-frequency test signals using the radio-frequency transmitter by providing control signals to the baseband processing circuitry that configure the baseband processing circuitry to measure the performance metric data in response to receiving the test data from the feedback receiver circuitry. The feedback receiver circuitry may be formed separately from radio-frequency receiver circuitry that is configured to receive radio-frequency downlink signals from antenna circuitry on the electronic device. In this way, the electronic device may characterize/calibrate radio-frequency transmit performance on itself without using external radio-frequency signal generator or signal analyzer circuitry. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an illustrative electronic device with wireless communications circuitry for communicating with external communications devices in accordance with an embodiment of the present invention. 
         FIG. 2  is a diagram of an illustrative electronic device under test having wireless communications circuitry that shows how radio-frequency transceiver circuitry may be coupled to antennas within the electronic device under test in accordance with an embodiment of the present invention. 
         FIG. 3  is a diagram of an illustrative test system for testing wireless communications circuitry in which a first electronic device under test provides radio-frequency test signals to a second electronic device under test to test and/or calibrate the receive performance of the second electronic device under test without using external radio-frequency tester equipment in accordance with an embodiment of the present invention. 
         FIG. 4  is a flow chart of illustrative steps that may be performed by a radio-frequency test system of the type shown in  FIG. 3  for using multiple devices under test to provide radio-frequency test signals to each other to test and/or calibrate the receive performance of the devices under test without using external signal generator equipment in accordance with an embodiment of the present invention. 
         FIG. 5  is a flow chart of illustrative steps that may be performed by a radio-frequency test system of the type shown in  FIG. 3  for using a first device under test to provide radio-frequency test signals to a second device under test to characterize and/or calibrate the receive performance of the second electronic device under test without using external signal generator equipment in accordance with an embodiment of the present invention. 
         FIG. 6  is a diagram of an illustrative test system for testing wireless communications circuitry on a device under test in which the device under test provides radio-frequency test signals to itself to test the receive performance of the device tinder test without using external signal generator equipment in accordance with an embodiment of the present invention. 
         FIG. 7  is a flow chart of illustrative steps that may be performed by a radio-frequency test system of the type shown in  FIG. 6  for using a single electronic device under test to provide radio-frequency test signals to itself to characterize and/or calibrate the receive performance of the device under test without using external signal generator equipment in accordance with an embodiment of the present invention. 
         FIG. 8  is a diagram of an illustrative electronic device under test having feedback receiver circuitry and processing circuitry for characterizing and/or calibrating the transmit performance of the electronic device under test without using external radio-frequency tester equipment in accordance with an embodiment of the present invention. 
         FIG. 9  is a flow chart of illustrative steps that may be performed by a radio-frequency test system for testing wireless communications circuitry on a device under test of the type shown in  FIG. 8  for characterizing and/or calibrating the transmit performance of the electronic device under test without using external signal analyzer equipment in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices such as device  10  of  FIG. 1  may be provided with wireless communications circuitry. The wireless communications circuitry may be used to support long-range wireless communications such as communications in cellular telephone bands. Examples of long-range (cellular telephone) bands that may be handled by device  10  include the 800 MHz band, the 850 MHz band, the 900 MHz band, the 1800 MHz band, the 1900 MHz band, the 2100 MHz band, the 700 MHz band, and other bands. The long-range bands used by device  10  may include the so-called LTE (Long Term Evolution) bands. The LTE bands are numbered (e.g., 1, 2, 3, etc.) and are sometimes referred to as E-UTRA operating bands. Long-range signals such as signals associated with satellite navigation bands may be received by the wireless communications circuitry of device  10 . For example, device  10  may use wireless circuitry to receive signals in the 1575 MHz band associated with Global Positioning System (GPS) communications. Short-range wireless communications may also be supported by the wireless circuitry of device  10 . For example, device  10  may include wireless circuitry for handling local area network links such as WiFi® links at 2.4 GHz and 5 GHz, Bluetooth® links at 2.4 GHz, etc. 
     As shown in  FIG. 1 , device  10  may include storage and processing circuitry  28 . 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 . This processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, application specific integrated circuits, etc. 
     Storage and processing circuitry  28  may be used to run software on device  10 , such as radio-frequency testing and calibration software, internet, browsing applications, voice-over-internet-protocol (VOIP) telephone call applications, email applications, media playback applications, operating system functions, functions related to communications band selection during radio-frequency transmission and reception operations, etc. To support interactions with external equipment (e.g., a radio-frequency base station, 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, IEEE 802.16 (WiMax) protocols, cellular telephone protocols such as the “2G” Global System for Mobile Communications (GSM) protocol, the “2G” Code Division Multiple Access (CDMA) protocol, the “3G” Universal Mobile Telecommunications System (UMTS) protocol, the “4G” Long Term Evolution (LTE) protocol, MIMO (multiple input multiple output) protocols, antenna diversity protocols, etc. Wireless communications operations such as communications band selection operations may be controlled using software stored and running on device  10  (i.e., stored and running on storage and processing circuitry  28  and/or input-output circuitry  30 ). 
     Input-output circuitry  30  may include input-output devices  32 . Input-output devices  32  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 devices  32  may include user interface devices, data port devices, and other input-output components. For example, input-output devices may include touch screens, displays without touch sensor capabilities, buttons, joysticks, click wheels, scrolling wheels, touch pads, key pads, keyboards, microphones, cameras, buttons, speakers, status indicators, light sources, audio jacks and other audio port components, digital data port devices, light sensors, motion sensors (accelerometers), capacitance sensors, proximity sensors, etc. 
     Input-output circuitry  30  may include wireless, communications circuitry  34  for communicating wirelessly with external equipment. 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, filtering circuitry, passive RF components, one or more antennas, transmission lines, 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 radio-frequency transceiver circuitry  90  for handling various radio-frequency communications bands. For example, circuitry  90  may include transceiver circuitry  36 ,  38 , and  42 . Transceiver circuitry  36  may handle 2.4 GHz and 5 GHz bands for WiFi® (IEEE 802.11) communications and may handle the 2.4 GHz Bluetooth® communications band. Circuitry  34  may use cellular telephone transceiver circuitry  38  for handling wireless communications in cellular telephone bands such as at 850 MHz, 900 MHz, 1800 MHz, 1900 MHz, and 2100 MHz and/or the LTE bands and other bands (as examples). Circuitry  38  may handle voice data and non-voice data traffic. 
     Transceiver circuitry  90  may include global positioning system (GPS) receiver equipment such as GPS receiver circuitry  42  for receiving GPS signals at 1575 MHz or for handling other satellite positioning data such as Global Navigation Satellite System (GLONASS) data. 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 one or more antennas  40 . Antennas  40  may be formed using any suitable antenna types. For example, antennas  40  may include antennas with resonating elements that are formed from loop antenna structures, patch antenna structures, inverted-F antenna structures, slot antenna structures, planar inverted-F antenna structures, helical antenna structures, hybrids of these designs, etc. Different types of antennas may be used for different bands and combinations of bands. For example, one type of antenna may be used in forming a local wireless link antenna and another type of antenna may be used in forming a remote wireless link antenna. 
     As shown in  FIG. 1 , wireless communications circuitry  34  may also include baseband processor  88 . Baseband processor may include memory and processing circuits and may also be considered to form part of storage and processing circuitry  28  of device  10 . Baseband processor  88  may be used to provide data to storage and processing circuitry  28 . Data that is conveyed to circuitry  28  from baseband processor  88  may include raw data (e.g., downlink data received from external communications equipment) and processed data associated with wireless (antenna) performance metrics (sometimes referred to herein as wireless performance metric data or performance metric data). 
     The radio-frequency performance of wireless communications circuitry  34  in device  10  may be characterized by one or more wireless (radio-frequency) performance metrics. Device  10  (e.g., baseband processor  88  or test software running on device  10 ) may generate data associated with wireless performance metrics in response to received (downlink) signals (sometimes referred to herein as downlink performance metric data, receiver performance metric data, or receive performance metric data associated with the receive performance of device  10 ). For example, device  10  may generate receive performance metric data associated with performance metrics such as received power, receiver sensitivity, frame error rate, bit error rate, channel quality measurements based on received signal strength indicator (RSSI) information, adjacent channel leakage ratio (ACLR) information (e.g., ACLR information in one or more downlink frequency channels), channel quality measurements based on received signal code power (RSCP) information, channel quality measurements based on reference symbol received power (RSRP) information, channel quality measurements based on signal-to-interference ratio (SINR) and signal-to-noise ratio (SNR) information, channel quality measurements based on signal quality data such as Ec/Io or Ec/No data, information on whether responses (acknowledgements) are being received from a cellular telephone tower corresponding to requests from the electronic device, information on whether a network access procedure has succeeded, information about how many re-transmissions are being requested over a cellular link between the electronic device and a cellular tower, information on whether a loss of signaling message has been received, information on whether paging signals have been successfully received, any desired combination of these performance metrics, and other information that is reflective of the performance of wireless circuitry  34  in device  10 . Receive performance metric data may, for example, include receive performance metric values measured for a given performance metric (e.g., measured error rate values, measured power level values, measured SNR values, measured RSSI values, etc.). 
     Storage and processing circuitry  28  may obtain radio-frequency performance metric data generated in response to radio-frequency uplink (transmit) test signals that are transmitted by device  10  (sometimes referred to herein as uplink performance metric data or transmit performance metric data associated with the transmit performance of device  10 ). For example, storage and processing circuitry  28  may receive data associated with Error Vector Magnitude (EVM), output power, spectral parameters, Adjacent Channel Leakage Ratio (ACLR), or any other desired performance metric associated with uplink signal transmission by wireless communications circuitry  34 . Transmit performance metric data may be used to characterize the radio-frequency performance of wireless communications circuitry  34  while transmitting signals. Transmit and receive performance metric data associated with wireless communications circuitry  34  may sometimes be referred to collectively as performance metric data. In general, performance metric data may include data associated with any desired performance metric for the transmission or reception of radio-frequency signals by wireless communications circuitry  34 . 
     Device  10  may perform radio-frequency test operations to characterize the radio-frequency performance (e.g., the transmit and/or receive performance) of wireless communications circuitry  34  (e.g., using one or more transmit and/or receive performance metrics). A device  10  having wireless communications circuitry  34  on which radio-frequency tests are being performed may sometimes be referred to herein as device under test (DUT)  10 ′. DUT  10 ′ may, for example, be a fully assembled electronic device that is enclosed within a form factor or device housing or a partially assembled electronic device (e.g., DUT  10 ′ may include some or all of wireless circuitry  34  prior to completion of manufacturing of device  10 ). 
     An illustrative diagram of a DUT  10 ′ having wireless communications circuitry  34  for testing is shown in  FIG. 2 . As shown in  FIG. 2 , wireless communications circuitry  34  on DUT  10 ′ may include transceiver circuitry  90  coupled to one or more antennas  40  by conductive paths such as paths  45 . Paths  45  may include transmission line structures such as coaxial cables, microstrip transmission lines, stripline transmission lines, etc. Filtering circuitry such as filter circuitry  92  may be interposed on paths  45  between antenna  40  and transceiver circuitry  90 . Filtering circuitry  92  may be used to implement frequency-based multiplexing circuits such as diplexers, duplexers, triplexers, or any other desired multiplexing circuits. Filtering circuitry  92  may, for example, filter radio-frequency signals provided to and received from antenna  40  by the corresponding frequency of the signals. In the example of  FIG. 2 , filtering circuitry  92  may isolate radio-frequency transmit (uplink) signals TX and radio-frequency receive (downlink) signals RX conveyed between antenna  40  and transceiver  90 . 
     DUT  10 ′ may include radio-frequency connector structure  94  (e.g., a radio-frequency switch connector or other radio-frequency connector) interposed on path  45  between antenna  40  and transceiver circuitry  90 . Test cables (not shown for the sake of clarity) may be connected to connector structure  94  during testing. When mated with a test cable, antenna structures  40  may be decoupled from filtering circuitry  92 . At the same time, radio-frequency connector  94  may electrically connect filtering circuitry  92  to the test cable (e.g., so that radio-frequency transmit signals TX and receive signals RX are conveyed over the test cable instead of over antenna  40 ). Connector  94  may form a radio-frequency port of transceiver circuitry  90  through which radio-frequency signals are conveyed to and from transceiver circuitry  90 . Test cabling may be connected to port  94  during radio-frequency testing. Port  94  may sometimes be referred to herein as a transmit port when uplink signals are transmitted to port  94  by transceiver circuitry  90 . Port  94  may sometimes be referred to herein as a receive port when radio-frequency signals are received at port  94  over a corresponding test cable. 
     If desired, other radio-frequency circuity such as radio-frequency front end circuitry, impedance matching circuitry, analog-to-digital converter circuitry, digital-to-analog converter circuitry, and/or switching circuitry may be interposed on path  45  between transceiver circuitry  90  and port  94  (as examples). Transceiver circuitry  90  may contain transmitters such as radio-frequency transmitters  96  and receivers such as radio-frequency receivers  98 . Transmitters  96  and receivers  98  may be implemented using one or more integrated circuits (e.g., cellular telephone communications circuits, wireless local area network communications circuits, circuits for Bluetooth® communications, circuits for receiving satellite navigation system signals, power amplifier circuits for Increasing transmitted signal power, low noise amplifier circuits for increasing signal power in received signals, other suitable wireless communications circuits, and combinations of these circuits). Radio-frequency transmitters  96  may provide radio-frequency transmit signals TX to port  94  over paths  45  and radio-frequency receivers  98  may receive radio-frequency receive signals RX from port  94  over paths  45 . 
     If desired, low-noise amplifier (LNA) circuitry such as LNA circuitry  100  may be interposed on paths  45  between filtering circuitry  92  and receivers  98  in transceiver circuitry  90 . Signals that are received via port  94  (e.g., via antenna  40  or associated test cabling) may be amplified by LNA circuitry  100  and LNA circuitry  100  may provide the amplified signals to receiver circuits  98 . If desired, LNA circuitry  100  may include one or more individual low noise amplifiers (sometimes referred to herein as individual LNA gain stages). Power supply circuitry such as power control circuitry  104  may control LNA circuitry  100  using control signals provided to LNA circuitry  100  over path  106 , Power control circuitry  104  may, for example, provide control signals that adjust the gain provided by each Individual amplifier in LNA circuitry  100  (e.g., control signals that adjust a bias voltage supplied to each amplifier in LNA circuitry  100 ). If desired, power control circuitry  104  may provide control signals to LNA circuitry  100  to selectively activate desired gain stages within LNA circuitry  100  (e.g., so that only a selected one of the gain stages in LNA circuitry  100  is active at a given time while the remaining gain stages are disabled or inactive, etc.). In this way, power control circuitry  104  may actively adjust the gain provided by LNA circuitry  100  to signals RX received from port  94 . 
     Signals that are to be transmitted over antennas  40  by transmitter circuits  96  may be amplified using power amplifier circuitry  102 . If desired, power amplifier circuitry  102  (sometimes referred to as a power amplifier circuit or power amplifier) may contain one or more individual power amplifiers (e.g., gain stages) used to handle a different cellular telephone standard or frequency band. During data transmission, power amplifier circuitry  102  may boost the output power of transmitted signals to a sufficiently high level to ensure adequate signal transmission. If desired, power supply circuitry such as power control circuitry  104  may provide control signals to power amplifier circuitry  102  to adjust the gain provided by amplifier circuitry  102  to signals transmitted by transceiver circuitry  90  (e.g., to activate one or more gain stages in circuitry  102 , to adjust bias voltages, etc.). 
     DUT  10 ′ may have any desired number of antennas  40  coupled to any desired number of transmitters  96  and/or receivers  98 . For example, DUT  10 ′ may include one or more antennas  40  coupled to transmitters and receivers in transceiver circuitry  90  via corresponding filtering circuitry, LNA circuitry, and power amplifier circuitry, DUT  10 ′ may include one or more antennas  40  coupled to only a transmitter in transceiver circuitry  90  via corresponding power amplifier circuitry. DUT  10 ′ may include one or more antennas  40  coupled to only a receiver in transceiver circuitry  90  via corresponding LNA circuitry. DUT  10 ′ may include a combination of these arrangements, etc. Each antenna may have a corresponding radio-frequency port and radio-frequency connector  94  that may be tapped into using radio-frequency cabling during testing of DUT  10 ′. 
     Digital data signals that are to be transmitted by wireless communications circuitry  34  may be provided to transceiver circuitry  90  by baseband processor  88  ( FIG. 1 ). During radio-frequency testing operations, radio-frequency test software such as test software  108  may provide test data (e.g., test signals) to be transmitted to transceiver circuitry  90  (e.g., via baseband processor  88  or directly to transceiver  90 ). Transceiver circuitry  90  may receive radio-frequency test signals (e.g., via port  94 ) and may provide the received test signals and/or corresponding test data to test software  108  for processing (e.g., via baseband  88  or directly to software  108 ). Test software  108  may be implemented on baseband processor  88 , on storage and processing circuitry  28 , on dedicated processing circuitry, or on any other desired processing circuitry on DUT  10 ′. Test software  108  may process the received radio-frequency test data and/or the transmitted radio-frequency test data to characterize the radio-frequency performance of DUT  10 ′. Test software  108  may issue control signals to wireless communications circuitry  34  to control the radio-frequency transmission and/or reception using wireless communications circuitry  34  during testing. If desired, test software  108  may be omitted and wireless communications circuitry  34  may be controlled by external computing equipment such as a test host during testing. 
     In some radio-frequency test systems, a given device under test such as DUT  10 ′ may be tested using external radio-frequency test equipment such as radio-frequency signal generator equipment and radio-frequency signal analyzer equipment (e.g., a vector network analyzer). The external test equipment may be coupled to DUT  10 ′ via port  94  and corresponding radio-frequency cabling during testing. The external radio-frequency test signal generator may generate radio-frequency test signals having selected properties (e.g., having selected power levels, frequencies, etc.) and may provide the test signals to the DUT  10 ′ via the corresponding radio-frequency test cable and post  94 . DUT  10 ′ may perform radio-frequency tests using the test signals received from the test signal generator to characterize the receive performance of the wireless communications circuitry. For example, DUT  10 ′ may calibrate and test the gain of LNA circuitry  100  using the received test signals (e.g., because the received test signals are generated by the signal generator at a known predetermined power level that can be compared to the power level of the signals received at receivers  98 ). 
     If desired, DUT  10 ′ may generate radio-frequency test signals and may transmit the test signals to the external signal analyzer equipment via port  94  and the associated radio-frequency cabling. The external signal analyzer equipment may receive the radio-frequency test signals from DUT  10 ′ and may analyze the received signals to characterize the transmit performance of the wireless communications circuitry. However, performing radio-frequency testing on DUT  10 ′ using external test equipment in this manner can be excessively costly and time consuming, as the external test equipment is typically expensive and can require excessive time to set up and maintain. It would therefore be desirable to be able to provide improved test systems for testing wireless communications circuitry without using external radio-frequency test equipment. 
       FIG. 3  is an illustrative diagram showing how radio-frequency test operations may be performed for multiple devices under test such as DUT  10 ′ of  FIG. 2  without using external test equipment (e.g., without using an external signal generator or signal analyzer that is separate from the device under test). As shown in  FIG. 3 , test system  110  may include two devices under test  10 ′ having corresponding wireless communications circuitry  34  (e.g., a first device under test  10 ′- 1  and a second device under test  10 ′- 2 ). Test system  110  may be located in a manufacturing system (e.g., a device assembly system) associated with the manufacture of device  10  and/or wireless communications circuitry  34 , may be located in a test facility for testing wireless communications circuitry  34  that is at a remote location relative to where the circuitry is manufactured, or may be at any other desired location. 
     Test system  110  may include signal attenuation circuitry such as attenuator circuitry  112 . A first radio-frequency cable  114  may be coupled between a transmit port  94 - 1  on first DUT  10 ′- 1  and an input of attenuator circuitry  112 . Transmit port  94 - 1  may be any desired radio-frequency connector port (as shown in  FIG. 2 ) over which one or more transmitters  96  on first DUT  10 ′- 1  transmit radio-frequency signals. A second radio-frequency cable  116  may be coupled between a receive port  94 - 2  on second DUT  10 ′- 2  and an output of attenuator circuitry  112 . Receive port  94 - 2  may be any desired radio-frequency connector port over which one or more receivers  98  on second DUT  10 ′- 2  receives radio-frequency signals. Radio-frequency cables  114  and/or  116  may include, for example, a miniature coaxial cable with a diameter of less than 2 mm (e.g., 0.81 mm, 1.13 mm, 1.32 mm, 1.37 mm, etc.), a standard coaxial cable with a diameter of about 2-5 mm, and/or other types of radio-frequency cabling or radio-frequency transmission line structures. 
     During test operations, first DUT  10 ′- 1  may transmit radio-frequency test signals over transmit port  94 - 1  at selected output power levels (e.g., transmitter circuits  96  and power amplifier circuitry  102  on first DUT  10 ′- 1  may transmit the radio-frequency test signals at desired output power levels). The transmitted radio-frequency test signals may be conveyed to the input of attenuator circuitry  112  via first test cable  114 . Attenuator circuitry  112  may attenuate the radio-frequency test signals received from first DUT  10 ′- 1  by one or more desired attenuation levels (e.g., attenuator circuitry  112  may reduce the power level of the received signals by selected amounts). Attenuator circuitry  112  may convey the attenuated test signals to second DUT  10 ′- 2  via second cable  116 . Second DUT  10 ′- 2  may receive the attenuated test signals via receive port  94 - 2  and may perform radio-frequency test operations using the received attenuated signals. For example, second DUT  10 ′- 2  may use the received signals to test and calibrate the radio-frequency performance of LNA circuitry  100  and/or receiver circuits  98  using the received attenuated test signals (e.g., because the attenuated test signals have known predetermined power levels as determined by first DUT  10 ′- 1  and attenuator  112 ). 
     Attenuator circuitry  112  may include fixed attenuator circuitry (e.g., attenuator circuitry that attenuates signals received over first cable  114  by a fixed predetermined level such as 20 dB) or programmable/adjustable attenuator circuitry (e.g., attenuator circuitry that actively adjusts the attenuation provided to the received signals). For example, attenuator circuitry  112  may be pre-programmed (e.g., by a test system operator, by a test host, by test software, etc.) to provide a sequence of different attenuation levels to the signals received from first DUT  10 ′- 1  so that a sequence of test signals is provided to second DUT  10 ′- 2  at multiple predetermined power levels. If desired, the test signals generated by first DUT  10 ′- 1  may be provided at a sequence of different output power levels and/or attenuator  112  may provide a sequence of different attenuations to the test signals so that the test signals received at port  94 - 2  of second DUT  10 ′- 2  have predetermined power levels. As one example, attenuator  12  and/or DUT  10 ′- 1  may provide test signals to second DUT  10 ′- 2  at a sequence of power levels such as −20 dB, −60 dB, −80 dB, and −100 dB. Second DUT  10 ′- 2  may use the received test signals having selected power levels to test and/or calibrate the radio-frequency performance of LNA circuitry  100  and/or receiver circuitry  98 . For example, second DUT  10 ′- 2  may generate radio-frequency receiver performance metric data using the received test signals and may process the performance metric data to verify satisfactory radio-frequency operation of the corresponding wireless communications circuitry  34 . 
     If desired, attenuator circuitry  112  may include frequency shifting circuitry that adjusts the frequency of test signals received from first DUT  10 ′- 1  prior to providing the test signals to second DUT  10 ′- 2 . If desired, test system  110  may include optional test computing equipment such as test host  118 . Test host  118  may include computing equipment such as a personal computer, laptop computer, handheld or portable computer, or any other desired computing equipment. Test host  118  may provide test commands (e.g., commands for performing desired testing operations) and/or test software (e.g., test software such as test software  108  of  FIG. 2 ) to devices under test  10 ′- 1  and  10 ′- 2  and/or attenuator circuitry  112  over corresponding control paths  120 . If desired, test host  118  may retrieve test data (e.g., performance metric data, test signals, information identifying whether DUTs  10 ′ pass or fail testing, etc.) from DUTs  10 ′ via paths  120 . 
     By using first DUT  10 ′- 1  to generate test signals that are provided to second DUT  10 ′- 2 , test system  110  may test and/or calibrate the receive performance of second DUT  10 ′- 2  without using additional external test equipment such as a radio-frequency signal generator. If desired, after the receive performance of second DUT  10 ′- 2  is characterized, a transmit port  94  on second DUT  10 ′- 2  may be coupled to the input of attenuator  112  via cable  116  and a receive port  94  on first DUT  10 ′- 1  may be coupled to the output of attenuator  112  via cable  114  for performing radio-frequency testing on receiver  98  and/or LNA circuitry  100  in first DUT  10 ′- 1  (e.g., second DUT  10 ′- 2  may generate test signals that are attenuated by attenuator  112  and received at the receive port of first DUT  10 ′- 1 ), In this way, multiple DUTs  10 ′ may generate test signals for each other to characterize and/or calibrate the receive performance of the DUTs, and expensive and time-consuming external test equipment may be omitted. 
       FIG. 4  is a flow chart of illustrative steps that may be performed by test system  110  for performing radio-frequency test operations on receiver circuitry (e.g., receiver circuitry  98  and/or LNA circuitry  100 ) in DUTs  10 ′. 
     At step  122 , test system  110  may perform transmit calibration and/or verification operations on second DUT  10 ′- 2 . For example, external test equipment such as signal analyzer equipment (e.g., vector network analyzer equipment) may be used to calibrate and/or verify satisfactory signal transmission by DUT  10 ′- 2 . In this scenario, second DUT  10 ′- 2  may transmit radio-frequency signals to the signal analyzer equipment at one or more desired power levels and the signal analyzer may compare the actual measured power level of the received radio-frequency signals transmitted by DUT  10 ′- 2  to the desired power levels to determine whether DUT  10 ′- 2  is transmitting signals at the desired power levels. If the transmitted signals differ significantly from the desired power levels, test host  118  may load transmit calibration data (e.g., one or more power level offset values) onto second DUT  10 ′- 2 . DUT  10 ′- 2  may use the power level offset values when transmitting subsequent radio-frequency signals so that the transmitted radio-frequency signals have the desired power levels. When the signal analyzer equipment determines that the signals transmitted by second DUT  10 ′- 2  have power levels that match the desired power levels, the signal analyzer may determine that the transmit power level performance of second DUT  10 ′- 2  is satisfactory (e.g., may verify satisfactory transmit performance of DUT  10 ′- 2 ). By verifying the transmit power levels provided by second DUT  10 ′- 2 , test system  110  may ensure that DUT  10 ′- 2  provides test, signals with accurate power levels to first DUT  10 ′- 1  during testing of the receive performance of first DUT  10 ′- 1 . 
     At step  124 , test system  110  may perform transmit calibration and/or verification operations on first DUT  10 ′- 1 . External signal analyzer equipment may be used to calibrate and verify signal transmission by first DUT  10 ′- 1 . First DUT  10 ′- 1  may transmit radio-frequency signals to the signal analyzer equipment at one or more desired power levels and the signal analyzer may compare the actual power level of the received radio-frequency signals transmitted by first DUT  10 ′- 1  to the desired power levels to determine whether DUT  10 ′- 1  is transmitting signals at the desired power levels. If the transmitted signals differ significantly from the desired power levels, test host  118  may load transmit calibration data (e.g., one or more power level offset values) onto first DUT  10 ′- 1 . DUT  10 ′- 1  may use the power level offset values when transmitting subsequent radio-frequency signals so that the transmitted radio-frequency signals have the desired power levels. When the signal analyzer equipment determines that the signals transmitted by first DUT  10 ′- 1  have power levels that match the desired power levels, the signal analyzer may determine that the transmit power level performance of first DUT  10 ′- 1  is satisfactory (e.g., may verify satisfactory transmit performance of DUT  10 ′- 1 ). By verifying the transmit power levels provided by first DUT  10 ′- 1 , test system  110  may ensure that DUT  10 ′- 1  provides test signals with accurate power levels to second DUT  10 ′- 2  during testing of the receive performance of second DUT  10 ′- 2 . This example is merely illustrative. If desired, step  124  may be performed prior to step  122  or concurrently with (e.g., in parallel or simultaneously with) step  122 . If desired, steps  122  and  124  may be omitted (e.g., in scenarios where it is known or otherwise predetermined that the transmit power levels of signals generated by DUTs  10 ′ are accurate). 
     At step  126 , test system  110  may couple attenuator  112  between first DUT  10 ′- 1  and second DUT  10 ′- 2 . For example, an operator of test system  110  may couple cable  114  between port  94 - 1  on DUT  10 ′- 1  and the input of attenuator  112  and may couple cable  116  between port  94 - 2  on DUT  10 ′- 2  and the output of attenuator  112  or test system  110  may autonomously couple attenuator  112  to DUTs  10 ′- 1  and  10 ′- 2 . 
     At step  128 , test system  110  may perform receiver calibration and/or verification operations on second DUT  10 ′- 2 . Test host  118  and/or test software  108  running on DUT  10 ′- 1  may direct DUT  10 ′- 1  to generate and transmit a sequence of test signals at one or more desired power levels (e.g., using a list mode sequence of test commands loaded onto DUT  10 ′). DUT  10 ′- 1  may transmit the test signals to attenuator  112  via transmit port  94 - 1 . Attenuator  112  may attenuate the test signals with one or more predetermined attenuation levels so that the attenuated test signals have one or more selected power levels. Attenuator  112  may pass the attenuated signals to receive port  94 - 2  on DUT  10 ′- 2 . DUT  10 ′- 2  may use the received attenuated test signals to calibrate and/or verify the radio-frequency receive performance of the wireless communications circuitry on DUT  10 ′- 2 . For example, DUT  10 ′- 2  may measure receiver performance metric data associated with the received test signals and may compare the measured performance metric data to one or more predetermined thresholds (e.g., desired threshold performance metric values, etc.). If the measured performance metric data varies excessively with respect to the predetermined thresholds or the desired performance metric values. DUT  10 ′- 2  may be labeled as failing testing or DUT  10 ′- 2  may generate calibration data (e.g., a number of offset values) to compensate for the discrepancy between the measured performance metric data and the desired performance metric values. If the measured performance metric data is sufficiently similar to the desired performance metric values, DUT  10 ′- 2  may be labeled as passing testing for that performance metric (e.g., test system  110  may determine that DUT  10 ′- 2  passes testing). Test results (e.g., information on whether DUT  10 ′- 2  passes or fails radio-frequency testing for one or more performance metrics) and/or performance metric data generated by DUT  10 ′- 2  may be passed to test host  118  for additional processing, if desired, DUTs  10 ′- 2  that fail testing for one or more performance metrics may, for example, be reworked, redesigned, discarded, flagged, loaded with new software, re-tested, or calibrated. 
     In one example, second DUT  10 ′- 2  may measure the power level of the received attenuated signals and may compare the measured power level to the desired power level (e.g., the selected power level as determined by the output power level generated by DUT  10 ′- 1  and the known attenuation provided by attenuator  112 ). If the difference between the measured power level and the desired power level is greater than a predetermined threshold, DUT  10 ′- 2  may generate calibration data (e.g., one or more amplifier offset values). DUT  10 ′- 2  may use the generated offset values (e.g., LNA circuitry  100  on DUT  10 ′- 2  may provide a gain to received signals corresponding to the generated offset values) for receiving subsequent radio-frequency signals (e.g., so that the subsequently received signals have the desired power level when received by receivers  98  on DUT  10 ′- 2 ). If the difference between the measured power level and the desired power level is below the predetermined threshold, DUT  10 ′- 2  may be labeled as having satisfactory receiver performance (e.g., test system  110  may verify that DUT  10 ′- 2  has adequate receive performance). 
     At step  130 , the input of attenuator circuitry  112  may be coupled to a transmit port  94  on second DUT  10 ′- 2  and the output of attenuator circuitry  112  may be coupled to a receive port  94  on first DUT  10 ′- 1  for performing radio-frequency receiver performance testing on first DUT  10 ′- 1 . 
     At step  132 , test system  110  may perform receiver calibration and/or verification operations on first DUT  10 ′- 1 . Test host  118  and/or test software  108  running on second DUT  10 ′- 2  may direct second DUT  10 ′- 2  to generate and transmit a sequence of test signals at one or more desired output power levels. Second DUT  10 ′- 2  may transmit the test signals to attenuator  112  via a corresponding transmit port  94 . Attenuator  112  may attenuate the test signals using one or more predetermined attenuation levels so that the attenuated test signals have one or more selected power levels. Attenuator  112  may pass the attenuated signals to a corresponding receive port  94  on first DUT  10 ′- 1 . DUT  10 ′- 1  may use the received attenuated test signals to calibrate and/or verify the radio-frequency receive performance of the wireless communications circuitry on DUT  10 ′- 1 . Test results (e.g., information on whether DUT  10 ′- 1  passes or fails radio-frequency testing for one or more performance metrics) and/or performance metric data generated by DUT  10 ′- 1  may be passed to test host  118  for additional processing, if desired. 
     At optional step  134 , verified and/or calibrated DUT  10 ′- 1  and/or DUT  10 ′- 2  (e.g., DUTs for which satisfactory receive performance has been verified) may be used to perform receiver calibration and/or verification operations on additional devices under test. For example, the transmit port of one of DUTs  10 ′- 1  and  10 ′- 2  may be coupled to a receive port on an additional device under test via attenuator  112  for testing the receiver performance of the additional device under test. The example of  FIG. 3  is merely illustrative. If desired, test system  110  may include any desired number of DUTs  10 ′ that are coupled together via attenuator circuitry for testing the receiver performance of the corresponding wireless communications circuitry. As one example, a first DUT  10 ′ may provide test signals to the receive port of a second DUT  10 ′ to test the receiver performance of the second DUT  10 ′, the second DUT  10 ′ may provide test signals to the receive port of a third DUT  10 ′ to test the receiver performance of the third DUT  10 ′, and the third DUT  10 ′ may provide test signals to the receive port of the first DUT  10 ′ to test the receiver performance of the first DUT  10 ′. Any desired number of DUTs  10 ′ may be tested in a closed chain in this manner without the need for external signal generating or signal analyzing equipment. 
       FIG. 5  is a flow chart of illustrative steps that may be performed by test system  110  to perform receiver calibration and verification operations on second device under test  10 ′- 2  using test signals generated by a first device under test  10 ′- 1  without using external test signal analyzer or generator equipment. The steps of  FIG. 5  may, for example, be performed while processing step  128  of  FIG. 4 . 
     At step  140 , test host  118  and/or test software  108  running on DUT  10 ′- 1  may set transmitter circuitry  96  and/or tuning circuitry on DUT  10 ′- 1  to transmit signals using a selected frequency. For example, DUT  10 ′- 1  may select a frequency for transmission at which DUT  10 ′- 2  receives signals (e.g., may select a cellular, Wi-Fi, or Bluetooth transmit frequency that overlaps with a cellular, Wi-Fi, or Bluetooth receive frequency). In general, test signals received at receive port  94 - 2  on DUT  10 ′- 2  need to be at a frequency that is handled by the receiver circuitry on DUT  10 ′- 2  in order for DUT  10 ′- 2  to properly receive the test signals. 
     At step  142 , first DUT  10 ′- 1  may transmit test signals at the selected frequency and at a selected output power level over transmit port  94 - 1 . Cable  114  may convey the transmitted test signal to the input of attenuator circuitry  112 . 
     At step  144 , attenuator circuitry  112  may attenuate the test signals using one or more selected attenuation levels and may provide the attenuated signals to receive port  94 - 2  on second DUT  10 ′- 2 . Attenuator circuitry  112  may provide the attenuated test signals to second DUT  10 ′- 2  at one or more desired power levels (e.g., by adjusting the attenuation provided by circuitry  112 ). For example, attenuator circuitry  112  may provide an attenuation of 20 dB, 30 dB, and 40 dB to the test signals, may provide an attenuation so that the test signals have consecutive power levels of −20, −60, −80, and −100 dB, etc. In general, attenuator circuitry  112  may provide any desired number of attenuation levels having any desired magnitude to the test signals. 
     At step  146 , second DUT  10 ′- 2  may measure performance metric data using the received attenuated test signals. If desired, DUT  10 ′- 2  may gather receiver performance metric data such as system noise values, RSSI values, or power level values of the received attenuated test signals using only a single gain stage (amplifier) in LNA circuitry  100  (e.g., by enabling only a selected one of the amplifiers in LNA circuitry  100 ), using every gain stage in LNA circuitry  100  (e.g., by enabling all of the amplifiers in LNA circuitry  100 ), and/or using any desired combination of the gain stages in LNA circuitry  100  (e.g., in order to fully characterize the performance of LNA circuitry  100 ). If desired, DUT  10 ′- 2  may sequentially measure performance metric data with one LNA in LNA circuitry  100  activated at a time to individually characterize the performance of each LNA in LNA circuitry  100 . 
     At step  148 , second DUT  10 ′- 2  may compare the measured performance metric data to desired performance metric data to characterize the receive performance of wireless communications circuitry  34 . If desired, DUT  10 ′- 2  may generate calibration data to mitigate differences between the measured performance metric data and the desired performance metric data. For example, DUT  10 ′- 2  may determine desired gains to use for one or more of the amplifiers in LNA circuitry  100  for receiving subsequent signals (e.g., may determine which amplifiers in LNA circuitry  100  to activate using power control circuitry  104  and what gain to provide using LNA circuitry  100 ) such that any subsequently measured performance metric data matches the desired performance metric data. If the measured performance metric data suitably matches the desired performance metric data, satisfactory receive performance of DUT  10 ′- 2  may be considered to be verified (e.g., system  110  may determine that DUT  10 ′- 2  passes testing). By ensuring that test signals are received at DUT  10 ′- 2  at predetermined power levels (e.g., using attenuator  112  and/or DUT  10 ′- 1 ), DUT  10 ′- 2  may accurately characterize the receive performance of wireless communications circuitry  34 . 
     The example of  FIG. 5  is merely illustrative. If desired, step  140  may be omitted and attenuator  112  may be used to shift the frequency of the test signals generated by first DUT  10 ′- 1  to a receive frequency used by second DUT  10 ′- 2  (e.g., while processing step  144 ). In this scenario, attenuator circuitry  112  may shift the frequency of the test signals in addition to attenuating the test signals. If desired, the sequence of test signal power levels provided by attenuator circuitry  112  to second DUT  10 ′- 2  may be determined based on attenuation provided by attenuator  112 , power levels generated by first DUT  10 ′- 1 , or a combination of power level generated by first DUT  10 ′- 1  and attenuation provided by attenuator  112 . If desired, attenuation settings (e.g., pre-programmed attenuation levels) may be stored on attenuator circuitry  112  for subsequent testing operations. 
     If desired, antenna diversity schemes may be implemented on wireless communications circuitry  34  in which multiple redundant antennas are used in handling communications for a particular band or bands of interest. In an antenna diversity scheme, storage and processing circuitry  28  may select which antenna  40  to use in real time based on signal strength measurements or other data. In multiple-input-multiple-output (MIMO) schemes, multiple antennas may be used in transmitting and receiving multiple data streams, thereby enhancing data throughput. In devices under test having multiple redundant antennas (e.g., DUTs that implement a MIMO scheme), a single device under test may perform test operations on itself without using external test equipment or additional devices under test to generate test signals. 
     As shown in  FIG. 6 , test system  110  may include a single device under test  10 ′ having corresponding wireless communications circuitry  34  and multiple antennas (e.g., for implementing a MIMO scheme). Device under test  10 ′ may have two antenna ports  94  (e.g., a first antenna port  94 R coupled to a corresponding receiver circuit  98  in transceiver circuitry  90  and a second antenna port  94 T coupled to a corresponding transmitter circuit  96  in transceiver circuitry  90 ). Ports  94 R and  94 T may, for example, couple transceiver circuitry  90  to respective first and second antennas in DUT  10 ′ when not coupled to radio-frequency cabling. 
     Transmit port  94 T may be coupled to the input of attenuator circuitry  112  via radio-frequency cable  114  whereas receive port  94 R may be coupled to the output of attenuator circuitry  112  via radio-frequency cable  116 . During test operations, DUT  10 ′ may transmit radio-frequency test signals at one or more desired output power levels via transmit port  94 T. The transmitted radio-frequency test signals may be conveyed to the input of attenuator circuitry  112  via first test cable  114 . Attenuator circuitry  112  may attenuate the radio-frequency test signals received from transmit port  94 T by one or more desired attenuation levels. Attenuator circuitry  112  may convey the attenuated test signals to receive port  94 R via second cable  116 . DUT  10 ′ may receive the attenuated test signals via receive port  94 R and may perform radio-frequency test operations using the received attenuated signals. For example, DUT  10 ′ may use the received signals to test and calibrate the radio-frequency performance of LNA circuitry  100  and/or receiver circuits  98  using the received attenuated test signals (e.g., because the attenuated test signals have a known predetermined power level as determined by the transmitter circuitry and power amplifier circuitry of DUT  10 ′ and attenuator  112 ). 
       FIG. 7  is a flow chart of illustrative steps that may be performed by test system  110  for performing radio-frequency test operations on receiver circuitry in a device under test  10 ′ using test signals generated by that device under test (e.g., a device under test that implements a MIMO scheme such as DUT  10 ′ as shown in  FIG. 6 ). 
     At step  150 , test system  110  may perform transmit calibration and/or verification operations on DUT  10 ′. For example, external test equipment such as vector network analyzer equipment may be used to calibrate and verily signal transmission (e.g., transmit power levels) of DUT  10 ′. By verifying the transmit power levels of DUT  10 ′, test system  110  may ensure that DUT  10 ′ provides test signals with accurate power levels to receive port  94 R (e.g., for testing the receive performance of DUT  10 ′). If desired, step  150  may be omitted if the transmit performance (e.g., output power levels) of DUT  10 ′ is known to be accurate. 
     At step  152 , test system  110  may couple attenuator  112  between transmit port  94 T on DUT  10 ′ and receive port  94 R on DUT  10 ′. For example, an operator of test system  110  may couple cable  114  between port  94 T on DUT  10 ′ and the input of attenuator  112  and may couple cable  116  between port  94 R on DUT  10 ′ and the output of attenuator  112  or test system  110  may autonomously couple attenuator  112  to DUT  10 ′. 
     At step  154 , test system  110  may perform receiver calibration and/or verification operations on DUT  10 ′. For example, test host  118  and/or test software  108  running on DUT  10 ′ may direct DUT  10 ′ to generate and transmit a sequence of test signals at one or more desired power levels at port  94 T. DUT  10 ′ may transmit the test signals to attenuator  112  via transmit port  94 T and cable  114 . Attenuator  112  may attenuate the test signals with one or more predetermined attenuation levels so that the attenuated test signals have one or more predetermined power levels. Attenuator  112  may pass the attenuated signals to receive port  94 R. DUT  10 ′ may use the received attenuated test signals to calibrate and/or verify the radio-frequency receive performance of the wireless communications circuitry on DUT  10 ′- 2 . The steps of  FIG. 7  may be repeated on multiple devices under test (e.g., in sequence or in parallel) to test and/or calibrate a group of devices under test. In this way, the receiver performance of DUT  10 ′ may be verified and calibrated without using external test signal generators and/or external signal analyzers. 
     If desired, DUT  10 ′ may characterize the transmit performance of wireless communications circuitry  34  without using external signal analyzer or signal generator equipment. For example, DUT  10 ′ may include a feedback path coupled between one or more transmitter circuits and one or more receiver circuits for receiving signals that are transmitted by the transmitter circuits. 
       FIG. 8  is an illustrative circuit diagram showing how DUT  10 ′ may include a feedback path for performing testing of the radio-frequency transmit performance of wireless communications circuitry  34 . As shown in  FIG. 8 , DUT  10 ′ may include an applications processor  162  that runs applications and other software (e.g., operating system software). Digital data signals that are to be transmitted by DUT  10 ′ may be provided to baseband processor  88  by applications processor  162 . If desired, test software  108  may provide test commands to baseband processor  88  over path  164  that instruct baseband processor to generate desired test signals. Baseband processor  88  may modulate the test signals and may provide the test signals to transmitter circuit  96  in transceiver circuitry  96  over path  166 . Transmitter circuitry  96  may up-convert the test signals to a radio-frequency and may pass the radio-frequency test signals to antenna  40  via duplexer circuitry  92  and power amplifier circuitry  102 . Power amplifier circuitry  102  may amplify the test signals and may provide the transmitted signals with a desired gain. Filtering circuitry such as duplexer circuitry  92  may isolate uplink signals provided to antenna  40  from downlink signals received by antenna  40  (e.g., so that the downlink signals are conveyed to receiver circuitry  98  via LNA circuitry  100 ). 
     As shown in  FIG. 8 , radio-frequency coupling circuitry such as radio-frequency coupler  170  may be coupled between antenna  40  and filtering circuitry  92 . Radio-frequency coupler  170  may pass the radio-frequency test signals transmitted from transmitter  96  to feedback receiver  160  in transceiver circuitry  90  via feedback path  172 . Feedback receiver  160  may be a dedicated receiver circuit in transceiver circuitry  90  that only receives signals that are transmitted by transmitter  96  over feedback path  172 . Feedback receiver circuit  160  may down-convert the test signals received over feedback path  172  from transmitter  96  into corresponding in-phase and quadrature phase data (I/Q data or I/Q test data). Feedback receiver  160  may pass the I/Q data associated with the test signals to baseband processor  88 . 
     Test software  108  may provide control signals to baseband processor  88  via path  164  that direct baseband processor  88  to measure transmit performance metric data associated with the test signals (e.g., the I/Q test data) received from feedback receiver  160 . For example, test software  108  may direct baseband processor  88  to measure error vector magnitude (EVM) data, ACLR data, spectrum data, output power level data, or any other desired transmit performance metric data associated with the transmission of the corresponding test signals using transmitter  96  and/or amplifier  102 . Test software  108  may retrieve the performance metric data from baseband processor  88  over path  164  and may process the performance metric data to characterize the radio-frequency transmit performance of wireless communications circuitry  34 . If desired, test software  108  may provide control signals to feedback receiver  174  to control the operation of feedback receiver  174 . 
     If desired, optional test host  118  may be coupled to DUT  10 ′ for loading test software  108  onto DUT  10 ′, for providing test commands to DUT  10 ′, for receiving performance metric data from DUT  10 ′, and/or for receiving information on whether DUT  10 ′ has satisfactory radio-frequency transmit performance from DUT  10 ′. In one suitable arrangement, DUT  10 ′ may perform radio-frequency testing on itself using test software  108  (e.g., without using a test host) during normal operation of DUT  10 ′ (e.g., while DUT  10 ′ is in use by an end user and is no longer being tested or manufactured). In another suitable arrangement, DUT  10 ′ may perform radio-frequency testing using test commands received from test host  118  (e.g., without loading test software  108 ). 
     Transceiver circuitry  90  may, if desired, be formed on a single integrated circuit or on multiple integrated circuits. For example, transmitter  96 , feedback receiver  160 , and receivers  98  may be formed on a single shared integrated circuit (chip). In another suitable arrangement, transmitter  96  and feedback receiver  160  are formed on a single shared integrated circuit whereas receivers  98  are formed on one or more separate integrated circuits. In yet another suitable arrangement, feedback receiver  160  and receivers  98  are formed on a single common integrated circuit whereas transmitter  96  is formed on a separate integrated circuit. In another suitable arrangement, transmitters  96  and receivers  98  are formed on a first Integrated circuit whereas feedback receiver  160  is formed on a second integrated circuit. In yet another suitable arrangement, transmitter  96 , feedback receiver  160 , and receivers  98  are each formed on different respective integrated circuits. If desired, additional transmitters may be formed on transceiver circuitry  90  (e.g., on a shared integrated circuit with circuitry  96 ,  100 , and  98 ). 
       FIG. 9  is a flow chart of illustrative steps that may be performed by test system  110  for testing the radio-frequency transmit performance of DUT  10 ′ having a feedback receiver  160  that receives radio-frequency test signals transmitted by transmitter circuit  96  (shown in  FIG. 8 ). 
     At step  200 , test host  118  or other external computing equipment may load test software  108  onto DUT  10 ′. For example, test software  108  may be loaded onto storage and processing circuitry  28  of  FIG. 1 , onto applications processor  162 , or onto other circuitry on device  10 ′. In another suitable arrangement, testing may be performed without loading test software onto DUT  10 ′ (e.g., test host  118  may control testing on DUT  10 ′ be providing test commands directly to DUT  10 ′ without loading test software  108  onto DUT  10 ′). 
     At step  202 , test software  108  may provide control signals to feedback receiver  160  via path  174  to configure feedback receiver  160  to receive transmit signals over feedback path  172  and to convert the transmit signals Into corresponding I/Q data. 
     At step  204 , test software  108  may provide control signals to baseband processor  88  via path  164  to configure baseband processor  88  to measure transmit performance metric data from I/Q data received from feedback receiver  160 . For example, test software  108  may instruct baseband processor  88  to measure EVM data, power level data, ACLR data, or any other desired transmit performance metric data using the I/Q test data received from feedback receiver  160 . If desired, test software  108  may load performance metric measurement software (e.g., one or more performance metric measurement routines or algorithms) onto baseband processor  88  that is executed when processor  88  receives I/Q data from feedback receiver  160 . 
     At step  206 , test software  108  may load a sequence of test commands onto baseband processor  88 . The sequence of test commands (e.g., a test command data structure or list such as a list mode sequence of test commands) may direct baseband processor  88  to generate a sequence of desired test signals. The sequence of test commands may be used to control transmitter  96  and power amplifier  102  to provide the test signals with, for example, a desired power level, at a desired frequency, with a desired modulation scheme, etc. 
     At step  208 , baseband processor  88  may generate and transmit test signals using the loaded sequence of test commands (e.g., by executing the sequence of test commands). Baseband processor  88  may pass the test commands to transmitter  96 . Transmitter  96  may modulate the test signals and up-convert the test signals to a radio-frequency. Transmitter  96  may transmit the test signals to amplifier  102  and amplifier  102  may amplify the transmitted test signals. 
     At step  210 , feedback receiver  160  may receive the transmitted radio-frequency test signals from the output of power amplifier  102  via coupler  170  and feedback path  172 . Feedback receiver  160  may convert the transmitted radio-frequency test signals into corresponding I/Q data. Feedback receiver  160  may convey the transmitted test signals (e.g., the corresponding I/Q data) to baseband processor  88 . 
     At step  212 , baseband processor  88  may compute performance metric data associated with the test signals received from feedback receiver  160  (e.g., the corresponding I/Q data received from feedback receiver  160 ). For example, baseband processor  88  may compute the performance metric data using the performance measurement software loaded onto processor  88  by test software  108  while processing step  204 . Baseband processor  88  may compute transmit performance metric data (e.g., EVM data, spectrum flatness data, phase error data, ACLR data, modulation data, spectral data, bit error rate data, minimum and maximum power data, RSSI data, etc.) using the test signals and may convey the transmit performance metric data to test software  108  via path  164 . 
     At step  214 , test software  108  may process the received transmit performance metric data to characterize the radio-frequency transmit performance of DUT  10 ′. For example, test software  108  may compare the transmit performance metric data to one or more performance metric threshold values (or ranges of acceptable performance metric values). If the received performance metric data is within a range of acceptable performance metric values, test software  108  may determine that DUT  10 ′ passes testing for that performance metric. If the received performance metric data is outside of a range of acceptable performance metric values, test software  108  may determine that DUT  10 ′ fails testing for that performance metric, may retest DUT  10 ′ for that performance metric, may flag DUT  10 ′ as needing reworking, redesign, re-testing, or scrapping, etc. 
     At optional step  218 , if the lest software determines that one of the computed performance metric values fails outside of the range of acceptable performance metric values, test software  108  may generate calibration data to correct the radio-frequency performance of circuitry  34  that caused the measured performance metric data to fall outside of the range of acceptable performance metric values (e.g., test software  108  may calibrate the transmit performance of DUT  10 ′). For example, if software  108  determines that a measured power level is below a target (desired) power level, software  108  may generate an offset gain value for use by amplifier  102  when amplifying subsequent signals (e.g., so that the amplified signals have the desired power level). 
     By measuring transmit performance metric data using a feedback receiver coupled to the signal transmission path, DUT  10 ′ may characterize the radio-frequency transmit performance and/or calibrate the radio-frequency transmit performance of wireless communications circuitry  34  without using external signal generator or external signal analyzer equipment. By loading test software  108  onto DUT  10 ′ to direct radio-frequency test operations, DUT  10 ′ may perform test and/or calibration operations without interfacing with an external test host (e.g., DUT  10 ′ may perform testing and calibration operations in the field when in use by an end user). If desired, test software  108  may be removed or uninstalled from DUT  10 ′ after performing test and/or calibration operations. 
     If desired, the receive performance of DUT  10 ′ may be tested/calibrated in addition to testing/calibrating the transmit performance of DUT  10 ′ (e.g., DUT  10 ′ may be tested and calibrated in a test system such as that shown in  FIGS. 3 and/or 4  in addition to testing and calibrating DUT  10 ′ in a test system such as that shown in  FIG. 8 ). For example, test system  110  may test and calibrate the transmit performance of a given DUT  10 ′ without using external test equipment (e.g., using the steps of  FIG. 9 ) and may subsequently use that DUT  10 ′ to provide test signals to a second DUT to test the receive performance of the second DUT  10 ′ (e.g., the steps of  FIG. 9  may be performed while processing steps  122 / 124  of  FIG. 4  if desired). 
     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: 20140904
Publication Date: 20180123
Grant Date: 20180123
Priority Date: 20140904
Inventors: YUAN CHAO
EL-HASSAN WASSIM
VENKATARAMAN VISHWANATH
Assignee: APPLE INC
CPC Classifications: [{"code": "H04B17/0085", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B17/21", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B17/16", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B17/19", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B17/19", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B17/0085", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B17/21", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B17/16", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 55438534