System and method for compensating for power loss due to radio frequency (RF) signal probe mismatch in conductive signal testing

Abstract

A system and method for compensating for power loss due to RF signal probe mismatch in a radio frequency (RF) data signal transceiver device under test (DUT) conductive RF signal test is provided. Isolation of power loss due to mismatch between the RF signal probe and RF DUT connection is achieved with an RF vector signal transceiver providing an RF test signal at multiple test frequencies and compensating for the power loss based on a predetermined loss of the RF signal path.

Description

BACKGROUND

[0001] The present invention relates to compensating for power loss due to RF signal probe mismatch in conducted signal testing of radio frequency (RF) data signal transceivers, and in particular to compensating for such power loss during conducted signal testing.

[0002] Many electronic devices today utilize wireless signal technology for both connectivity and communication purposes. Because wireless devices transmit and receive electromagnetic energy, and because two or more wireless devices have the potential to interfere with each other's operation due to their signal frequencies and power spectral densities, these devices and their wireless signal technology must adhere to various wireless signal technology standard specifications.

[0003] In designing such wireless devices, engineers need to take extra care to ensure that such devices will comply with or exceed each of the specifications in the standards based on the wireless signal technology included in the device. Furthermore, when these devices are subsequently mass manufactured, these devices are tested to ensure that manufacturing defects will not result in improper operation, including the devices' adherence to the specifications based on the included wireless signal technology standards.

[0004] Testing of such wireless devices typically involves testing of the receiving and transmitting subsystems of the device under test (DUT). A test system will send a prescribed sequence of test data packet signals to the DUT, using different frequencies, power levels, and / or signal modulation techniques, for example, to determine whether the DUT receiving subsystem is working properly. Similarly, the DUT will transmit test data packet signals at a variety of frequencies, power levels, and / or modulation techniques, to be received and processed by the test system, to determine whether the DUT transmitting subsystem is operating normally.

[0005] For testing of these devices after they have been manufactured and assembled, current wireless device test systems typically employ a test system having various subsystems for providing test signals to each device under test (DUT) and analyzing signals received from each DUT. Some systems, often referred to as "testers," include at least one or more test signal sources (e.g., in the form of a vector signal generator or "VSG") for providing source signals to be transmitted to the DUT, and one or more receivers (e.g., in the form of a vector signal analyzer or "VSA") for analyzing signals produced by the DUT. The test signal generation by the VSG and the signal analysis performed by the VSA are generally programmable (e.g., through the use of an internal programmable controller or an external programmable controller, such as a personal computer) to allow each to be used to test a variety of devices to adhere to a variety of wireless signal technology standards having different frequency ranges, bandwidths, and signal modulation characteristics.

[0006] The test environment can include one or both of two general forms of RF signal delivery: (1) conducted or wired, and / or (2) radiated or wireless. In the former case (typically implemented as a coaxial cable having a signal conductor surrounded by a ground conductor that acts as a shield against external electromagnetic interference), one important characteristic is the signal path loss through the conductive signal path. Another is the signal reflection and power loss due to the mismatch between the impedance of the conductive signal path and the impedance of the conductive signal connector of the DUT caused by the RF signal probe connected to the DUT. While the actual techniques for determining the signal path loss and / or probe mismatch are simple, they require interruption and reconfiguration of the RF signal connection as part of the test operation, e.g., before and / or during each test sequence. This results in longer test times and increased test costs due to this time delay and potential repair or rework of the signal connection. SUMMARY

[0007] Systems and methods for compensating for power loss due to RF signal probe mismatch in conductive RF signal testing of radio frequency (RF) data signal transceiver devices under test (DUTs). Providing the RF test signal with the RF vector signal transceiver at a plurality of test frequencies enables isolation of the power loss due to the mismatch between the RF signal probe and the RF DUT connection and compensation for the power loss based on a predetermined loss of the RF signal path.

[0008] According to an example embodiment, a system for compensating for power loss of a radio frequency (RF) signal probe used in electrically-conductive RF signal testing of a device under test (DUT) includes: an RF vector signal transceiver that responds to one or more transceiver control signals by generating one or more outgoing RF signals and time-domain processing one or more incoming RF signals; an RF signal probe that respectively transmits and receives the one or more outgoing RF signals and the one or more incoming RF signals to and from the DUT; an electrically-conductive RF signal path that is respectively connected to and between the RF vector signal transceiver and the RF signal probe via first and second signal path ends to transmit the one or more outgoing RF signals and the one or more incoming RF signals; one or more processors coupled to communicate with the RF vector signal transceiver; and one or more memory devices coupled to the one or more processors and including non-transitory computer-readable media containing a plurality of computer-readable instructions. The plurality of computer-readable instructions, when executed by the one or more processors, cause the one or more processors to provide the one or more transceiver control signals so that: the one or more outgoing RF signals include a plurality of mutually different RF signal frequencies having an iteration of a single frequency tone; the one or more incoming RF signals include a plurality of reflected RF signals from the RF signal probe and related to at least a portion of the one or more outgoing RF signals; and the time-domain processing one or more incoming RF signals includes: calculating a plurality of measured signal magnitudes of the plurality of reflected RF signals, and calculating a plurality of net signal magnitudes of the plurality of reflected RF signals reduced by a corresponding one of a plurality of predetermined path losses of the electrically-conductive RF signal path corresponding to the plurality of mutually different RF signal frequencies.

[0009] According to further exemplary embodiments, a method for compensating for power loss of a radio frequency (RF) signal probe used in electrically-conductive RF signal testing of a device under test (DUT) includes: responding to one or more transceiver control signals using an RF vector signal transceiver by generating one or more outgoing RF signals and time-domain processing one or more incoming RF signals; communicating the one or more outgoing RF signals and the one or more incoming RF signals to and from the DUT, respectively, via the RF signal probe; communicating the one or more outgoing RF signals and the one or more incoming RF signals via an electrically-conductive RF signal path connected to the RF vector signal transceiver and the RF signal probe and between the RF vector signal transceiver and the RF signal probe via first and second signal path ends, respectively; and communicating with the RF vector signal transceiver by accessing and executing a plurality of computer-readable instructions. Execution of the computer-readable instructions causes providing the one or more transceiver control signals such that: the one or more outgoing RF signals include a plurality of mutually different RF signal frequencies having iterations of a single frequency tone; the one or more incoming RF signals include a plurality of reflected RF signals from the RF signal probe and related to at least a portion of the one or more outgoing RF signals; and the time-domain processing one or more incoming RF signals includes calculating a plurality of measured signal amplitudes of the plurality of reflected RF signals and calculating a plurality of net signal amplitudes of the plurality of reflected RF signals reduced by a corresponding one of a plurality of predetermined path losses of the electrically-conductive RF signal path corresponding to the plurality of mutually different RF signal frequencies. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 A common test environment for electrically-conductive RF signal testing is depicted.

[0011] Figure 2 A test environment for electrically-conductive RF signal testing according to exemplary embodiments is depicted.

[0012] Figure 3 Design and use of a signal data filter according to exemplary embodiments is depicted.

[0013] Figure 4 Comparison of empirical test data using conventional OSL techniques and techniques according to exemplary embodiments is depicted.

[0014] Figure 5 A test environment for electrically-conductive RF signal testing according to exemplary embodiments is depicted.

[0015] Figure 6 Comparison of empirical test data using a conventional RF power meter and an SMA coaxial connector as an RF probe according to exemplary embodiments is depicted.

[0016] Figure 7 The time relationship between the corresponding incident and reflected RF signals is depicted. DETAILED DESCRIPTION

[0017] The following DETAILED DESCRIPTION is of exemplary implementations of the present invention that are presently protected by the annexed claims. Such description is intended to be illustrative of the present invention and is not intended to be limiting. Such implementations are described in detail to enable one of ordinary skill in the art to make and use the subject invention, and it is understood that other implementations can be practiced with some variations without departing from the spirit or scope of the present subject invention.

[0018] Throughout this disclosure, where a specific number of circuit elements is recited, it is understood that the recited number can be a single or a plural number unless specifically indicated to the contrary or context clearly dictates otherwise. For example, the term "circuit" can include a single component or a plurality of components that are active and / or passive and are connected or otherwise coupled together (e.g., into one or more integrated circuit chips) to provide the described function. Additionally, the term "signal" can refer to one or more currents, one or more voltages, or a data signal. In the drawings, like or related elements will have like or related numbering reference designators. Also, while the present invention has been discussed using discrete electronic circuits (preferably in the form of one or more integrated circuit chips), alternatively, the functions of any portion of such circuits can be implemented using one or more appropriately programmed processors, depending on the signal frequencies or data rates to be processed. Further, with respect to the illustrations of functional blocks of the schematic diagrams showing various implementations, the functional blocks do not necessarily represent a partitioning of hardware circuits.

[0019] Reference Figure 1 A common test environment 10a for electrically conductive RF signal testing includes a tester 12 (e.g., a VSG and VSA combination, or a vector transceiver) and an electrically conductive RF test signal path 14 to connect to a DUT 16. The signal path 14 can include one or more RF cables and fixtures 15a connected to the tester 12 via an RF connector 15b and to the DUT 16 via another RF connector 15c. To accurately test the DUT 16, the RF signal loss of the signal path 14 must be determined to enable accurate measurement of the signal received by the DUT 16 and from the DUT. There are three techniques that are currently dominant for doing this.

[0020] A method includes using an RF signal source (e.g., tester 12) connected via RF signal path 14 to a power meter (not shown) in place of DUT 16 to measure the absolute power difference between the power received by the power meter and the known signal power from the source. However, this requires a high precision measurement difference between the source and the power meter, and reconfiguring the DUT test arrangement to connect the signal source and the power meter via signal path 14.

[0021] A second method includes using a two-port vector network analyzer (VNA, not shown) in place of tester 12, where both ports measure the insertion loss (commonly referred to in S- parameter terms as S21) in a more direct way at each connection 15b, 15c to RF signal path 14. Thus, this requires more expensive test equipment, e.g., a VNA, and reconfiguring the DUT test arrangement to connect to the VNA.

[0022] A third method includes using tester 12 at one connection 15b to RF signal path 14, and using an open connection (OPEN) with the proper characteristic impedance (e.g., 50 ohm resistance) of the RF system being tested, a short connection (SHORT), and a load connection (LOAD) at the other connection 15c each time to enable the measurement of the return loss of each terminal connection (OPEN, SHORT, and LOAD). All three measurement results can then be used to calculate the path loss. This has the effect of effectively using a standard DUT test device as a simulated vector network analyzer (VNA) to measure return loss (S-parameter S11). Modern VSA / VSG systems can also perform such measurements if they support simultaneous VSG / VSA operation and perform the appropriate processing of the transmitted and received signals. While this method can enable the DUT test arrangement to be maintained, it still requires a dedicated connector designed for the OPEN, SHORT, and LOAD measurements and three operations to switch between these three dedicated connectors. (This is commonly referred to as the OSL method).

[0023] The disadvantages of these approaches can be avoided using the presently disclosed exemplary embodiments of systems and methods. As discussed in greater detail below, a vector transceiver (e.g., tester 12) is connected to the input 15b of the RF signal path 14 and an OPEN connection is made at the output 15c. Advantages include maintaining the DUT test arrangement and avoiding the need for additional or different test equipment, thereby saving operating time and cost. Moreover, while a dedicated OPEN connector can be helpful, it should not be necessary as it can simply be replaced with an un-terminated output connection 15c of the RF signal path 14 and thereby used as an OPEN. In most automated test arrangements, an RF signal probe can be used at the end of a cable that, when un-terminated (e.g., not connected to a load such as a DUT), can act as an OPEN connection.

[0024] Reference is made to Figure 2 A test environment 10b for conductive RF signal testing in accordance with exemplary embodiments includes a tester 12 (e.g., a vector signal transceiver) and a conductive RF test signal path 14 including one or more RF cables and fixtures 15a connected to the tester 12 via an input RF connector 15b and an output RF connector 15c. However, when the test path is lossy, the output RF connector 15c can remain un-terminated to provide an OPEN connection 15cc.

[0025] As an optional initial procedure, information about the test hardware configuration being used can be established or otherwise determined. For example, such information can include details about the RF signal path 14, such as the number of interconnecting cables, the length of each cable, how many connectors are in place, etc. As noted above, rather than connecting the output connector 15c to the DUT 16, an RF OPEN connector is connected or the output connector 15c is left unconnected (i.e., un-terminated).

[0026] The range of RF test signal frequencies to be measured (e.g., with a corresponding frequency margin) can be selected or defined based on expected or anticipated DUT operation. The vector signal transceiver tester can be programmed or otherwise controlled to provide (e.g., generate and transmit) a single DC tone for each of the RF test signal frequencies at baseband frequencies with its transmitter and to enable its receiver to capture a corresponding return signal for each of the RF test signal frequencies. The captured I / Q signal samples can be averaged over the capture time to compute a single complex number. Repeating these steps of transmitting an incident signal and capturing a reflected signal over some or all of the defined frequency range can enable computation of an array of complex numbers, each of which corresponds to a respective one of the defined frequencies. Such an array of complex numbers can be processed in accordance with known principles to compute the path loss for each frequency to be measured.

[0027] refer to Figure 3 The process 20 may include the following steps: by processing 22 the returned signal data 21 to extract time or distance information 23 (discussed in more detail below) for designing a filter 24, the characteristics 25 of which can be used to filter the returned signal data 21 26. The filtered returned signal data 27 can be averaged to calculate 28 the absolute path loss 29 at the frequency being tested. Such a process 20 can be constructed or applied from the perspective of the distance domain or the frequency domain to be effectively used for the same purpose, for example, by processing, filtering, and averaging measurement signal data in a manner corresponding to (e.g., the distance traveled by the incident and / or reflected signal pulses) or (e.g., the frequency of the incident and / or reflected signal).

[0028] refer to Figure 4 Linear graphs of empirical test results of path loss measured using conventional OSL methods and methods according to exemplary embodiments discussed above in the frequency range from below 1 GHz to above 5 GHz represent how the more advantageous techniques discussed herein produce test results that closely track the test results of conventional OSL techniques.

[0029] As described above, conventional path loss measurement and compensation techniques fail to account for, let alone compensate for, the additional signal loss at the RF probe connected to the DUT, effectively assuming a perfect match between the RF probe and the RF connector on the DUT. However, successful connection of the RF probe to the DUT relies primarily on mechanical manipulation and is controlled by applying appropriate physical forces. Therefore, shortly after multiple connections have been formed and removed, the associated changes in surface wear and forces lead to degradation in the match between the RF probe and the DUT connector. This results in further power losses in the signal path that cannot be detected or compensated solely by path loss measurements as described above. Such additional power losses caused by RF probe connector mismatch can lead to a higher DUT retest rate, which in turn requires additional instances of DUT connections and can result in reduced manufacturing yield.

[0030] refer to Figure 5A test environment 40, according to an exemplary embodiment, for detecting and enabling compensation for RF probe mismatch during conductive RF signal testing, includes a tester 42 (e.g., a VSG / VSA combination or vector signal transceiver) and a conductive RF test signal path 44 to enable connection to a DUT 16. The signal path 44 may include one or more RF cables and mounting brackets 45a connected to the tester 42 via an RF connector 45b and to the DUT 16 via an RF probe assembly 45c. Connection to the DUT 16 is completed via an input RF probe connector 45cb, an RF probe 45ca, and an output RF probe connector 45cc, which in turn connects to an RF connector 17 of the DUT 16.

[0031] As discussed in more detail below, according to an exemplary embodiment, compensation for power loss due to RF probe mismatch in conductive RF signal testing can be provided by measuring the returned signal to estimate the reflected signal caused by RF probe mismatch and interpreting this reflection as additional signal path power loss. Advantages include maintaining the DUT test configuration, as any additional power loss can be measured by keeping the DUT in its intended test configuration. Because DUT control actions are unnecessary, full control can be maintained by the tester. Compensation for such additional power loss can be provided after each DUT is inserted into the test configuration, thereby increasing the accuracy of DUT RF testing.

[0032] This process can be performed by first connecting the DUT to the RF probe. This can be done before, after, or simultaneously with defining the specific frequency at which the measurement will be performed. The vector transceiver tester transmits a single DC tone at the baseband signal frequency, and any resulting reflections from such incident signal transmission can be captured by the tester's receiver. The average of the captured I / Q samples over time can be calculated to provide a single complex number. Such incident signal transmission, reflected signal capture, and averaging calculation can be iterated over a defined frequency range. Finally, the calculated complex number can be processed to determine the reflected signal caused by RF probe mismatch.

[0033] This processing of the calculated complex number can be performed in conjunction with the RF signal path loss data previously determined using the conventional OSL method discussed above to determine the reflected signal caused by RF probe mismatch. This will allow the removal of RF signal path effects from the original test configuration, where any remaining loss is attributed to and compensated for by the reflected signal caused by RF probe mismatch. Alternatively, this processing can be performed in conjunction with the RF signal path loss data determined using the techniques discussed above, in which an OPEN (e.g., unterminated) RF signal path termination is used with a vector transceiver tester to extract the reflected signal from the RF probe caused by mismatch issues. If the reflected signal exceeds or otherwise crosses a predetermined threshold, the test can be aborted to allow for correction or other resolution of such problems. Otherwise, compensation for the increased power loss can be applied by the tester while the DUT RF test continues.

[0034] refer to Figure 6 A linear graph of empirical test results for path loss due to RF probe reflection measured in a frequency range from below 1 GHz to close to 6 GHz using conventional power meter methods and methods according to exemplary embodiments discussed above illustrates how the more advantageous techniques discussed herein closely produce test results that closely track the test results of conventional power meter techniques.

[0035] refer to Figure 7 As described above, these operations can be performed from the perspective of the time domain or the distance domain. As depicted herein, and as will be readily understood by those skilled in the art, the interrelationship between the processing in the time domain and the distance domain is more readily understood given the fact that the reflected signal pulse will be captured by the receiver of the tester after a time delay ΔT, which is known to relate to the distance the reflected signal pulse must travel after the transmission of the incident signal pulse.

[0036] Various other modifications and alternatives to the structure and operation of the present invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. While the invention has been described in conjunction with specific preferred embodiments, it should be understood that the invention protected by the claims should not be unduly limited to such specific embodiments. It is intended that the following claims define the scope of the invention and thereby should cover the structures and methods within the scope of these claims and their equivalents.

Claims

1. An apparatus comprising a system for compensating for power loss of an RF signal probe used in conductive RF signal testing of a device under test (DUT), the apparatus comprising: An RF vector signal transceiver that responds to one or more transceiver control signals by generating one or more outgoing RF signals and processing one or more incoming RF signals in the time domain. RF signal probes, wherein the RF signal probes transmit one or more outgoing RF signals and one or more incoming RF signals to and from the RF connector of the DUT, respectively; A conductive RF signal path, which is connected to the RF vector signal transceiver and the RF signal probe via first and second signal path terminals respectively, and between the RF vector signal transceiver and the RF signal probe, to transmit the one or more outgoing RF signals and the one or more incoming RF signals; One or more processors, the one or more processors being coupled to communicate with the RF vector signal transceiver; and One or more memory devices coupled to one or more processors and including a non-transitory computer-readable medium containing a plurality of computer-readable instructions, which, when executed by the one or more processors, cause the one or more processors to provide the one or more transceiver control signals, such that... The one or more emitted RF signals include multiple mutually distinct RF signal frequencies that are iterative and have a single frequency tone. The one or more incoming RF signals include a plurality of reflected RF signals from the RF signal probe and associated with at least a portion of the one or more outgoing RF signals, and The time-domain processing of one or more incoming RF signals includes Calculate the amplitude of multiple measured signals of the multiple reflected RF signals, and Multiple net signal amplitudes of the multiple reflected RF signals are calculated by reducing the corresponding predetermined path loss of the conductive RF signal path corresponding to the multiple mutually different RF signal frequencies from the multiple reflected RF signals.

2. A method for compensating for power loss of an RF signal probe used in conductive RF signal testing of a device under test (DUT), the method comprising: An RF vector signal transceiver responds to one or more transceiver control signals by generating one or more outgoing RF signals and processing one or more incoming RF signals in the time domain. One or more outgoing RF signals and one or more incoming RF signals are transmitted to and from the RF connector of the DUT via RF signal probes, respectively; The one or more outgoing RF signals and the one or more incoming RF signals are transmitted via conductive RF signal paths, the conductive RF signal paths being connected to the RF vector signal transceiver and the RF signal probe respectively via first and second signal path ends, and between the RF vector signal transceiver and the RF signal probe; and Communicating with the RF vector signal transceiver by accessing and executing multiple computer-readable instructions to provide the one or more transceiver control signals, such that... The one or more emitted RF signals include multiple mutually distinct RF signal frequencies that are iterative and have a single frequency tone. The one or more incoming RF signals include a plurality of reflected RF signals from the RF signal probe and associated with at least a portion of the one or more outgoing RF signals, and The time-domain processing of one or more incoming RF signals includes Calculate the amplitude of multiple measured signals of the multiple reflected RF signals, and Multiple net signal amplitudes of the multiple reflected RF signals are calculated by reducing the corresponding predetermined path loss of the conductive RF signal path corresponding to the multiple mutually different RF signal frequencies from the multiple reflected RF signals.

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