DETERMINATION OF A DELAY IN SIGNAL TRANSMISSION ALONG A WIRED TRANSMISSION MEDIUM

Abstract

The present invention is entitled “Determination of a delay in signal transmission along a wired transmission medium”. An exemplary system is provided comprising: a signal generator that outputs a signal based on several carrier frequencies; a wired transmission medium used to transmit the signal, wherein the wired transmission medium is configured to be open at one end to generate a reflection of the signal from the wired transmission medium; and a signal analyzer that receives the reflection and determines a transmission time of the signal along the wired transmission medium based on the reflection.The signal analyzer is configured to perform operations that involve searching based on an estimated signal transmission time along the wired transmission medium and on reflections to determine the transmission time. This search is then used to determine which candidate transmission time should be selected from several possible times.

Description

Technical area

[0001] This description describes an exemplary specific implementation of a test system configured to determine a delay in signal transmission along a wired transmission medium. State of the art

[0002] A test system is configured to test the operation of a device. The device being tested by the test system is called a device under test (DUT). The test system may include test instrumentation for sending test signals, such as radio frequency (RF) signals, and data to the DUT over a wired transmission medium, such as a cable, to perform a test. The DUT responds with a response signal. The test system expects such response signals to contain a specific value and / or have a specific timing. If a response signal has an appropriate value and / or timing, the DUT passes the test. If the response signal does not have such a value and / or timing, the DUT cannot pass the test.

[0003] A wired transmission medium, such as a cable, introduces a delay into the test system. For example, the propagation of the test and response signal along the cable takes a certain amount of time. This time, also called time-of-flight (TOF), is an example of the delay introduced by the cable during signal transmission. This delay can negatively impact testing. For example, when testing timing on a DUT, cable-related delays in signal transmission affect the results.

[0004] Ultra-Wideband (UWB) technology measures the time between two devices and converts it into distance. To obtain the most accurate distance, the cable delay between the test system and the DUT should correspond to a reported time / distance. Therefore, it can be important to know the actual cable delay. The same applies to over-the-air (OTA) measurements, where an antenna transmits a test signal to the DUT and the DUT responds. In some cases, the measurement distance between the antenna and the DUT must be compensated for by an additional delay between a test device and the antenna.

[0005] Therefore, techniques have been implemented to determine the signal transmission delay and incorporate this delay into a test process, for example, calibrating a test system based on this delay. Example techniques for determining signal transmission delay include combining a transmission device with a measuring device at different ends of a cable. This measuring device measures a transmission time based on the time it takes the transmission device to transmit the signal. Such techniques may require a specific fixture that must be first assembled and then disassembled, making them labor-intensive, especially when there are a large number of ports to be connected to the DUT. Therefore, implementing such techniques can be challenging for some DUT types in some test environments. Disclosure of the invention

[0006] The present disclosure provides an exemplary system comprising: a signal generator that outputs a signal based on a plurality of carrier frequencies; a wired transmission medium used to transmit the signal, the wired transmission medium configured to be open at one end to generate a reflection of the signal at the wired transmission medium; and a signal analyzer that receives the reflection and, based on the reflection, determines a transmission time of the signal along the wired transmission medium. The signal analyzer is configured to perform operations including performing a search based on an estimated transmission time of the signal along the wired transmission medium and on the reflection to determine the transmission time.The search is used to determine which candidate transmission time should be selected from among several candidate transmission times. The differences between the multiple candidate transmission times correspond to multiples of a step size. The exemplary system may include one or more of the following features (either individually or in combination).

[0007] These operations may include performing a coarse search based on the reflection to determine the estimated transmission time. The coarse search may be performed to determine which candidate transmission time to select from among multiple candidate transmission times for the estimated transmission time. The differences between the multiple candidate transmission times used in the coarse search may correspond to multiples of a first step size. The search based on the estimated transmission time may include a fine search. The step size in the fine search may be a second step size. The first step size may be larger than the second step size. The multiple candidate transmission times used in the coarse search may include a first candidate transmission time, and the multiple candidate transmission times used in the fine search may include a second candidate transmission time.

[0008] The coarse search may be insensitive to the amplitude and phase shift of a signal with the first candidate transmission time. The coarse search may include detecting a maximum correlation based on the following two criteria: (i) the first candidate transmission time and (ii) a sum of a reflection along the wired transmission medium, a reflection at the open end of the wired transmission medium, and noise, where the maximum correlation may correspond to the estimated transmission time. The fine search may be sensitive to the amplitude and phase shift of a signal with the second candidate transmission time. At least two of the plurality of carrier frequencies may be orthogonal to each other.

[0009] The fine search may include determining the transmission time within a predetermined range around the estimated transmission time based on a difference between the following two values: (i) a value based on the reflection and (ii) a value based on the second candidate transmission time. Determining the transmission time may include identifying one of the values ​​based on a second candidate transmission time that minimizes the difference. The predetermined range may be a range of 200 picoseconds or more.

[0010] The reflection-based value can be based on the amplitude and phase of the reflection. The second candidate transmission time-based value can be based on the amplitude and phase of signals with different transmission times. The differences between the transmission times can be in the range of single-digit picoseconds.

[0011] The signal generator and the signal analyzer may be part of a stand-alone hardware device connected to the wired transmission medium. The stand-alone hardware device may be, or include, a test instrument or test system. The test instrument or test system may include one or more processing devices programmed to perform the search. The multiple carrier frequencies may be upconverted based on direct current (DC) signals. The multiple carrier frequencies may include carrier signals that are not upconverted.

[0012] An example method includes the following acts: outputting a signal on a wired transmission medium based on a plurality of carrier frequencies, wherein the wired transmission medium is configured to be open at one end to create a reflection of the signal at the wired transmission medium; and determining a transmission time of the signal along the wired transmission medium based on the reflection. Determining the transmission time includes performing a search based on an estimated transmission time of the signal along the wired transmission medium and the reflection to determine the transmission time. The search is performed to determine which candidate transmission time to select from a plurality of candidate transmission times for the transmission time. The differences between the plurality of candidate transmission times correspond to multiples of a step size.The exemplary method may include one or more of the following features (either individually or in combination).

[0013] Determining the transmission time may include performing a coarse search based on the reflection to determine the estimated transmission time. The coarse search may be performed to determine which candidate transmission time to select from among multiple candidate transmission times for the estimated transmission time. The differences between the multiple candidate transmission times used in the coarse search may correspond to multiples of a first step size. The search based on the estimated transmission time may include a fine search. The step size in the fine search may be a second step size. The first step size may be larger than the second step size. The multiple candidate transmission times used in the coarse search may include a first candidate transmission time, and the multiple candidate transmission times used in the fine search may include a second candidate transmission time.

[0014] The coarse search may be insensitive to the amplitude and phase shift of a signal with the first candidate transmission time. The coarse search may include detecting a maximum correlation based on the following two criteria: (i) the first candidate transmission time and (ii) a sum of a reflection along the wired transmission medium, a reflection at the open end of the wired transmission medium, and noise. The maximum correlation may correspond to the estimated transmission time.

[0015] The fine search may be sensitive to the amplitude and phase shift of a signal with the second candidate transmission time. At least two of the multiple carrier frequencies may be orthogonal to each other.

[0016] The fine search may include determining the transmission time within a predetermined range around the estimated transmission time based on a difference between the following two values: (i) a value based on the reflection and (ii) a value based on the second candidate transmission time. Determining the transmission time may include identifying one of the values ​​based on a second candidate transmission time that minimizes the difference. The predetermined range may be a range of 200 picoseconds or more.

[0017] The reflection-based value may be based on the amplitude and phase of the reflection. The second candidate transmission time-based value may be based on the amplitude and phase of signals with different transmission times. The differences between the transmission times may be in the range of single-digit picoseconds. The multiple carrier frequencies may be upconverted based on direct current (DC) signals. The multiple carrier frequencies may include carrier signals that are not upconverted.

[0018] Two or more of the features described in this description (including the disclosure of the present invention) may be combined in any way to form embodiments not specifically explained in this description.

[0019] At least some of the devices, systems, techniques, and processes described in this specification may be configured or controlled by executing instructions by one or more processing devices stored on one or more non-transitory machine-readable storage media. Examples of non-transitory machine-readable storage media include read-only memory, an optical drive, a disk drive, and random access memory. At least some of the devices, systems, techniques, and processes described in this specification may be configured or controlled using a computer system comprised of one or more processing devices and a memory storing instructions thereon, where the instructions may be executed by the one or more processing devices to perform various control operations.The devices, systems, techniques, and processes described in this specification may be configured, for example, by design, formation, construction, arrangement, placement, programming, operation, activation, deactivation, and / or control.

[0020] The details of one or more detailed embodiments are explained in the accompanying drawings and the following detailed embodiments. Further features and advantages will become apparent from the detailed embodiments and the drawings, as well as from the claims. Short description of the characters Fig. Figure 1 shows a block diagram illustrating an example signal reflection along an open-ended wired transmission medium. Fig. Figure 2 shows a block diagram of components of an exemplary test system that includes an open-ended wired transmission medium. Fig. 3 shows operation blocks included in an exemplary process for determining a delay in signal transmission along an open-ended wired transmission medium. Fig. Figure 4 shows an example of a waveform diagram illustrating exemplary delays in signal transmission along a wired transmission medium determined using various processes.

[0021] Similar reference numerals in different figures indicate similar elements. Detailed embodiments

[0022] Described herein are processes for determining a delay in signal transmission associated with wired transmission media such as cables, as well as example specific implementations of example systems configured to implement these processes. One example process includes connecting a signal transceiver to one end of a cable and forming the other end of the cable as an open end; for example, the open end is not connected to a device under test (DUT). "Cable" in this example may include any attachment device, such as connectors, etc., that connects the cable to the signal transceiver or connects the cable to the DUT, respectively.

[0023] The signal transceiver outputs signals across multiple carrier frequencies to the cable. Each signal output to the cable can be a carrier signal. The example below describes a carrier signal with a selected carrier frequency upconverted using a direct current (DC) signal, where the carrier signal is referred to herein as an upconverted DC signal. However, other types of carrier signals (including signals of different frequencies) generated at different amplitudes and not subjected to DC upconversion can also be used. DC signals are used because they do not introduce additional complexity, such as an extra phase.In some examples, upconversion includes changing the amplitude of the carrier signal by multiplying the carrier signal by a DC signal—essentially amplitude-modulating the carrier signal with the DC signal. In some examples, at least two carrier signals have orthogonally different frequencies.

[0024] The upconverted DC signal transmitted through the cable is reflected back to the signal transceiver from the open end of the cable. The upconverted DC signal transmitted through the cable can also be due to mismatches or anomalies along a cable path. These mismatches or anomalies can include, for example, an impedance mismatch and a structural anomaly in the cable and / or connectors along the cable.

[0025] Examples of these reflections can be found in Fig. 1. More specifically, a signal transceiver 10 in Fig. 1 outputs an upconverted DC signal 11 to a cable 12. The cable has mismatches 16, 17, and an open end 19. Reflections 20, 21, and 22 of the upconverted DC signal occur at mismatches 16, 17, and open end 19, respectively. Although three reflections are shown, in some examples, there may be up to dozens or hundreds of reflections. The signal transceiver 10 receives these reflections and organizes them into vectors / arrays, each element of which is dedicated to a separate, distinct carrier frequency.

[0026] An exemplary process includes performing a coarse search based on reflection to determine an estimated transmission time t T(grob)of the signal on cable 12. In this example, the coarse search determines, based on the correlation with elements in the vector / array, which candidate transmission time from among several candidate transmission times should be selected for the estimated transmission time. The differences between the candidate transmission times correspond to multiples of a predefined step size. In a coarse search example, this predefined step size can be dozens of picoseconds (ps) or hundreds of picoseconds, or more or less. The candidate transmission time with the maximum correlation to the element of the vector / array is called the estimated transmission time t T(grob) of the signal over the entire length of the cable 12, which is determined by the coarse search, and is used in a subsequent search process or fine search process to determine the transmission time t T to be further refined over the entire length of the cable 12.

[0027] A fine search can be performed in an area around the estimated transmission time t T(grob) For example, the range defined in this example by a value "d" can be selected based on the carrier frequency and the cable length. In some cases, examples of d can be 200 ps, ​​300 ps, ​​400 ps, ​​etc., up to 800 ps or more or less, but are not limited to this. In the fine search, an optimization is performed to determine which candidate transmission time from several candidate transmission times that are in the range of t T(grob) - d to t T(grob) + d, for the transmission time t Tof the signal along the cable is to be selected. The candidate transmission time in the fine search differs from the candidate transmission time used in the coarse search, and the differences between the candidate transmission times in the fine search correspond to multiples of a predefined step size. In a fine search phase, the predefined step size can, in some examples, be a few picoseconds (e.g., 10 ps or less) or tens of picoseconds or less (e.g., 100 ps or less), or smaller or larger.

[0028] The optimization performed during a fine search is sensitive to signal phase and phase shift, whereas the correlation performed during a coarse search is not necessarily sensitive. In this example, a shift indicates that the reflections are not in the same phase, which could be due, for example, to different reflection points along the cable. Therefore, a fine search can provide a more accurate determination of the transmission time than a coarse search. In some specific implementations, a fine search can be performed independently of a coarse search by using ranges determined based on test settings and cable characteristics (such as, but not limited to, cable length, cable composition, and cable geometry).

[0029] Fig. 2 shows a block diagram of the configurations of components of an exemplary test system 25 configured to implement an exemplary process described herein.

[0030] The test system 25 includes one or more test instruments 43. The test instrument may be a hardware device that may include one or more processing devices and / or other processing circuits (not shown). The test instrument may be configured (e.g., programmed) to output test signals via a signal transceiver 26 to test a DUT (not shown) connected to a wired transmission medium such as cable 32. Test signals for testing the DUT may be or include instructions, commands, data, parameters, variables, test patterns, and / or any other information used to elicit a response from the DUT. One or more (e.g., all) of the test instruments may be configured to receive responses from the DUT (via the signal transceiver 26) to test signals sent from the test instruments to the DUT.The test instrument can be configured to analyze this response to determine whether the DUT passed the test or failed. For example, the timing of the response can be analyzed, or the data represented by the response can be analyzed, and so on. The test instruments can include, but are not limited to, an RF instrument for testing radio frequency (RF) signals, a digital test instrument for testing digital signals, an analog test instrument that may include pin electronics and / or a parameter measurement unit (PMU), etc.

[0031] The test system 25 also includes a control system 45. The control system may be or include a computer system that includes one or more processing devices 46 (e.g., microprocessors) and a memory 47 for storage. In one example, the control system 45 may be configured to execute instructions (e.g., computer codes) 49 stored in the memory 47 to control the test instrument 43 to perform a test on the DUT, for example, to send a test program to the test instrument for execution and thereby generate test signals, or to send a test signal to the test instrument for processing and / or forwarding to the DUT. The control system 45 may also be configured to execute instructions to control the signal transceiver 26 described below and / or the coarse search process and the fine search process related to Fig. 3, in whole or in part. Dashed lines 44 indicate a wired or wireless connection between the Fig. 2, wherein analog communication, digital communication and / or RF communication can be transmitted between these components via such a wired or wireless connection.

[0032] The signal transceiver 26 includes a signal generator 28 and a signal analyzer 29, or the functionality of each of these components in one, two, or more hardware devices. In some specific implementations, the signal generator 28 is configured to function as a carrier signal generator. And in this function, it is configured to generate and output a delayed test signal used to test delays along a wired transmission medium, such as a cable 32. The shape and timing of the delayed test signal may be determined (e.g., specified, set, and / or controlled) by the control system 45 and / or the one or more test instruments 43. In this example, the delayed test signal is an upconverted DC signal.The following example uses an upconverted DC signal; however, alternating current (AC) signals, composite signals, or other signal types can also be used as delayed test signals.

[0033] The signal generator 28 is configured to generate a plurality of carrier frequencies to produce an upconverted DC signal based on one or more DC signals. The DC signal used to produce the upconverted DC signal may be provided to the signal generator 28 or generated by the signal generator 28. The number of carrier frequencies used and the number of actual frequencies may be determined by the control system 45 and / or by the one or more test instruments 43. The carrier frequency may be in a range of, but is not limited to, 4 gigahertz (GHz) to 12 GHz. Alternatively, in some examples, it may be greater than 12 GHz. In some examples, there may be dozens or hundreds of carrier frequencies represented by the DC signal (e.g.,based on this DC signal), where these carrier frequencies may differ at regular intervals, for example, increasing at regular intervals. In one non-limiting example, the carrier frequency may start at 4 GHz and increase in an increment of 0.1 GHz to 6 GHz. In another non-limiting example, the carrier frequency may start at 5 GHz and increase in an increment of 0.01 GHz to 9 GHz. Any suitable increments and / or frequency ranges may be used, not limited to those listed here.

[0034] The test system 25 further includes a wired transmission medium 32, such as, but not limited to, a cable (e.g., a coaxial cable), a transmission line, and / or any other type of electrical conductor. The following example describes the use of the cable 32 as a wired transmission medium. In this example, the cable may include a fastening device 34, 35 (e.g., a connector) at each respective end 36, 37 of the cable. In some specific embodiments, the processes described herein explain the presence of these fastening devices and the delays caused by these fastening devices.Therefore, in some specific embodiments, reference to a cable and / or a wired transmission medium includes any conductive medium wherein signal transmission occurs via the conductive medium along with attachment devices at ends or along the length of the conductive medium.

[0035] As described above, the cable 32 in the test system 25 is open at one end. For example, one end 35 / 37 of the cable 32 is not connected to a DUT or other device for receiving signals from the cable. However, in some examples, an RF probe (not shown) may be connected to the end 35 of the cable 32. The RF probe may monitor signals on the cable. The cable may include multiple sections. For example, the cable 32, as shown in Fig. 2, may comprise individual cables (such as cables 32a, 32b) that are each connected to one another via a connector 40. The connector 40 may result in an impedance mismatch, causing reflection (see, for example, Fig. 1). The cable 32 may also include one or more anomalies 41, which may be caused by manufacturing defects or damage, which anomalies may lead to impedance mismatches along the cable length and cause reflections (see, for example, Fig. 1).

[0036] The signal generator 28 is configured to generate an up-converted DC signal (e.g., signal 11 from Fig. 1), which is generated based on several different carrier frequencies, to the cable 32. Since several up-converted DC signals are output, several reflections occur on the cable, with one or more reflections being present for each up-converted DC signal, for example. In the example of Fig. 2, upconverted DC signals based on different carrier frequencies are reflected from the open end 35 / 37 of the cable 32, from the anomaly 41, and from the impedance mismatch 40. These reflections are guided back along the cable to the signal transceiver 26. These reflections are out of phase with each other and propagate over different lengths of the cable, as shown in relation to Fig. 1. This is due, at least in part, to the fact that different frequencies are used and the reflections do not occur at the same location along the cable, and that the reflections do not occur at regular or known intervals corresponding to the phase of the upconverted DC signal.

[0037] The signal analyzer 29 is configured to receive and measure reflections of the upconverted DC signal. With reference to Fig. 1 include the measured reflections x(t i ). For example, a signal analyzer measures a value of the reflected signal x at each time t i . In some specific embodiments, the signal analyzer 29 can be configured to have a transmission time t Tof the upconverted DC signal between the open end 37 and the transceiver 26 is determined based on these reflections using the process 50 described below. With reference to Fig. 1 and Fig. 2 is t T a time-of-flight of a signal from the open end 19, 35 / 37 back to the signal transceiver 26, i.e. a time along the entire length of the cable.

[0038] In some specific embodiments, the signal analyzer 29 may include one or more processing devices and / or circuits configured to determine the transmission time t T of the upconverted DC signal along the entire length of the cable based on the reflections using process 50 from Fig. 3. In some specific embodiments, the signal analyzer 29 may be configured to provide its measurement results to the control system 45, wherein the control system 45 may be configured to determine the transmission time t T of the upconverted DC signal along the entire length of the cable based on the reflections using process 50 from Fig. 3. In some specific embodiments, the signal analyzer 29 may be configured to provide its measurement results to the one or more test instruments 43, wherein the test instrument 43 may be configured to determine the transmission time t T of the DC signal along the entire length of the cable based on the reflections using process 50 from Fig. 3. In some specific embodiments, the signal analyzer 29, the test instrument and / or the control system 45 may be configured to cooperate to determine the transmission time t T of the upconverted DC signal along the entire length of the cable based on the reflections using process 50 from Fig. 3 to be determined.

[0039] With reference to Fig. 3, the process 50 includes: configuring (50a) a test system to determine a delay (e.g., time-of-flight, "TOF") in signal transmission along the cable 32. In this example, the configuration process may include disconnecting the DUT or other device from the fixture 35 such that the end 37 of the cable 32 is an open end, while the cable 32 remains connected to the test system 25 via the fixture 34.

[0040] The signal generator 28 sends (50b) a plurality of different upconverted DC signals (or other signals such as carrier signals, AC signals, composite signals, etc. as delayed test signals) to the cable 32 having the open end 37. As described above, the signal generator 28 may be controlled by the control system 45 and / or the test instrument 32 to output an upconverted DC signal. For example, the control system 45 and / or the test instrument 32 may determine one or more DC signal values ​​and select which carrier frequencies are used to generate a plurality of upconverted DC signals based on programming in these components and / or based on user input. For example, in some specific implementations, a plurality of upconverted DC signals may be based on a single DC value and a plurality of different carrier frequencies (e.g.,formed using these values). For example, in some specific implementations, the multiple upconverted DC signals may be based on multiple different DC values ​​and multiple different carrier frequencies (e.g., formed using these values).

[0041] For example, the upconverted DC signal is reflected from the open end 37 of the cable and from individual points along the cable, as shown in relation to Fig. 1. The signal analyzer 29 receives (50c) the reflected signal from the cable 32; that is, the signal analyzer receives the reflection of the upconverted DC signal. The signal analyzer 29 measures (50d) the reflected signal (i.e., the reflection). For example, the signal analyzer 29 measures the amplitude and phase of the reflection "x" as a function of time "t i“, where the subscript “i” in this example corresponds to different maturities.

[0042] In some specific embodiments, the signal analyzer 29 measures (50d) a signal y based on combined reflections. In this example, the signal y is a vector / array that represents a signal y fn at each measurement frequency contains: y = [y f1 , y f2 , ...], where “fn” stands for a frequency. Each element of y (for example, y f1 etc.) is the sum of x(t i ), x(t T ) and noise n. x(t i ) is a vector defined as follows: x(t i ) = [(x(t i ), f1), (x(t i ), f2) ...], where x(t i ) for a measurement result of the reflections from a signal path with the propagation time t i and the frequency f, and where x(t i ) ∈ C K The measurement results of x(t i) the amplitude, frequency, phase and timing (e.g. a reception time) of each x(t i ) x(t T ) is the reflection from the open end 37 of the cable (e.g., the reflection from the entire length of the cable 32), the value of which is sought in y. x(t T ) is a reflection like an element of x(t i ). n is the random noise in the corresponding reflection, where n ∈ C K . In some examples, only the signal y is actually measurable by the signal analyzer 29; its components, namely x(t i ), x(t T ) and noise n, cannot be measured individually by a signal analyzer.

[0043] The process 50 performs (50e) a coarse search process based on y to find x(t T(grob) ), where x(t T(grob)) represents an estimate of the delay in signal transmission along the entire length of the cable 32, which is determined using the coarse search process. For a measured value of y, the coarse search process determines what the best estimate for the value of t T(grob) More specifically, the coarse search process tests in different step sizes or increments using an estimated value of x(t T ) different candidate values ​​of t i to determine which estimate of t T closest to the value of y, where, for example, yx(t T ), as described above and shown below in equation (1). The estimated value of t T , which is fitted closest to the value of y, forms the estimated delay (t T(grob) ) in the signal transmission along the entire length of the cable 32 and can be further refined by means of the fine search process described below.

[0044] More precisely, the signal analyzer receives a reflection of a defined vector y (i.e. the reflected version of the upconverted DC signal / delayed test signal) that represents the signal x with a target propagation time t T and is defined as follows: y=aT⋅x(tT)+∑iai⋅x(ti)+n where: x(t i ) represents a measured value for reflections along the cable, which may occur at different points; x(t T ) represents a reflection from the open end 37 of the cable and its value is to be determined; a i for an amplitude of reflection x(t i ), where a T for an amplitude of reflection x(t T ) from the open end 37 of the cable and where a i ∈ R K and is a real number, and n stands for a vector containing random noise in each corresponding signal reflection, with n ∈ CK .

[0045] Assuming that the amplitude response ||a t || 2 the target running time t T is the maximum value, the coarse search process uses a correlation process of equation (2) to find t* for maximum correlation: argmaxt.‖xH(t*)y‖2

[0046] More precisely, the correlation process of equation (2) selects different candidates for t T , i.e. t*, by selecting different candidates for x(t T ), i.e. x(t*), to identify which of the candidates for x(t T ) has the maximum correlation with the value in the vector y. The differences between the different candidate times used in the correlation process can be multiples of the step size. For example, a candidate for t T, i.e. t*, correspond to a candidate x(t*) that varies along a continuum between two frequencies (e.g. in the range from 4 GHz to 12 GHz) in the step size (“step_size”) of about tens or hundreds of picoseconds (ps) or more or less incrementally, and that is distributed over x(t* + step_size ), x(t* +step_size × 2 ), x(t* +step_size ×3 ) etc. between a start value x(t*) and an end value x(t* + step_size × (n) (wobei n > 3)), where "x" in the superscript means "multiply by". The start value, end value, and step size can be based on the DUT under test, the frequency used for testing, the length of the cable, and / or other factors. The choice of step size can be a compromise between the achieved resolution, which is limited by noise, and the time required for processing. A smaller step size results in a longer processing time. A step size that is too small can be limited by noise and other minor defects that may be filtered out in some specific designs.

[0047] Fig. 4 shows an example curve diagram illustrating an example correlation 56 determined using equation (2) for different values ​​of x(t) 57 over time t*58 (in picoseconds). As shown in the figure, in this example, the maximum correlation occurs at a value of t*55 at approximately 460 ps. In the fine search process 50 performed by the process 50, the value 55 can be used as the estimate obtained by the coarse search process (t T(grob) ) are used. More specifically, in the fine search process 50, as described above, an optimization is performed to determine which candidate transmission time from a plurality of candidate transmission times that are in the range of t T(grob) - d to t T(grob)+ d for which the transmission time along cable 32 is to be selected. In some examples, the differences between the candidate transmission times used in the fine search process may be, but are not limited to, multiples of the step size, ranging from a few picoseconds to tens of picoseconds or more. In a fine search phase, in some examples, an exemplary predefined step size may be, but is not limited to, single-digit picoseconds (e.g., 10 ps or less).

[0048] The correlation of equation (2) is insensitive to the phase shift (i.e., e jθ x(t T )), where θ is the phase of x(t T(grob) ) and a Tstands for the amplitude. Therefore, the correlation of equation (2) can easily reflect a disturbance of a guideway, since the various reflected signals (i.e., reflections) along the cable 32 are not correlated. This means that the maximum correlation value determined by equation (2) is at value 55 ( Fig. 4) can be influenced by an interference pattern that is not present at the target point t* ≠ t T which leads to errors in t T(grob) This means that the maximum correlation due to the interference pattern may occur at a position where the best estimate 55 for t T does not occur. In this example, the fine search (50f) performed by process 50 is sensitive to the phase shift and the amplitude response. This sensitivity provides a better resolution of t Tcompared to the coarse search process and reduces the influence of the interference pattern introduced by reflections on the estimate of t T(grob) .

[0049] The fine search process (50f), also referred to herein as the null space process, uses some of the same names and variables as the coarse search process. Therefore, these names and variables will not be explained here. The fine search process searches a vector a* x(t*) such that the projection of the vector y - a* x(t*) into a vector space St * is minimized. A vector space St comprises a space that runs along the entire length of the cable 32 over the travel time t and has all possible amplitude responses, such as {a m· x(t*)}, where "m" is an integer greater than 1. The following explains how to determine the optimization for performing a fine search.

[0050] All possible amplitude responses for the reflection “x” are called am (with m = 1, 2, ...) are listed, generating the following set of vectors: Xt=[a1⋅x(t)1a2⋅x(t)1…]

[0051] The decomposition of eigenvalues ​​results in the following: XtIIXt=QtΛtQtII where a λ-matrix of eigenvalues ​​is defined as follows: Λ=(λ1λ2…) and where a q-matrix of the eigenvalues ​​is defined as follows: Q=[q1,q2,…]

[0052] The first L (L > 1) largest eigenvalues, each corresponding to an eigenvector, are retained to construct the vector space St; and the remaining eigenvalues ​​are discarded because they are so small that they have little effect on the vector space St. St=span{q1,q2,…qL}

[0053] When listing all possible amplitude responses to construct St, the applied amplitude shift has little effect on St, since any shift only affects the eigenvalues. The eigenvectors and the space St remain unchanged. Therefore, when listing all possible amplitude responses, only the "shape" of the frequency relative to the amplitude is important.

[0054] The optimization shown in equation (3) below is used to vary t* to find the maximum value of this optimization. The value of t* at this maximum value is called t T(50 g), i.e., the delay along the entire length of cable 32. This is done by varying a* x(t*) for different values ​​of t*. Therefore, both a and x(t*) are searched in this fine search process. The value of a*-x(t*) that yields the maximum value of equation (3) corresponds to the value of t (the delay along cable 32) that minimizes the difference between y and a* x(t*). argmaxa.t.1(y−a.⋅x(t*))TStStH(y−a.⋅x(t*))

[0055] The differences between the different times of t* used in equation (3) (candidates for t T) can correspond to multiples of the step size. For example, different times of t* can correspond to the vector a* x(t*), which varies along a continuum between two frequencies (e.g., in the range from 4 GHz to 12 GHz) in the step size (“step_size”) of about tens of picoseconds (ps) or single-digit picoseconds, or more or less incrementally, and which can be propagated over a* x(t* + step_size ), a*·x(t* + step_size × 2 ), a*·x(t* + step_size × 3 ) etc. between a start value a*·x(t*) and a final value a*·x(t* + step_size × (n) (wobei n> 3) ), where “x” in the superscript means “multiply by.” In some examples, the starting value or the final value can be a* x(t T(grob) - d) or a*·x(t T(grob) + d), where t T(grob) - d and t T(Grob)+ d each represents a time determined using the coarse search process 50. In some examples, the start value and end value may be preprogrammed in the test system and not based on a coarse search process (e.g., without performing a coarse search process). The step size may be based on the DUT under test, the frequency used for testing, the cable length, and / or other factors.

[0056] The search performed using optimization equation (3) is sensitive to the amplitude and phase shift of the reflection. To prove this, assume that the signal analyzer 29 receives a signal y containing a target signal a x. If the optimization of equation (3) is performed using random phase or amplitude shift, the target signal is not completely removed after the subtraction of y - a* x(t*), for example, where a* and x in the candidate a* x(t*) are not equal to the actual values ​​of a* and x inherent in y. The remaining signals are not orthogonal to the subspace St, resulting in a lower value generated by equation (3). If the optimization of equation (3) is performed using accurate phase and amplitude shifts x and a*, respectively, the target signal is completely removed after the subtraction of y - a* x(t*).The projection of the remaining signals onto St is minimized, resulting in the maximum value in equation (3).

[0057] Fig. 4 contains exemplary curves showing the optimization 56 obtained with equation (3) over the range of t T(grob) - d and t T(grob) + d for different values ​​of a*·x(t*). As shown in the figure, in this example, the optimized maximum value occurs at a value of 60 of approximately 456.5 ps, which is known as t T (i.e., the delay along the entire length of the cable 32) and which differs from t T(grob) Likewise, the envelope 61 generated by the fine search process is smaller (e.g., of shorter duration) than the envelope 62 generated by the coarse search process due to reduced interference effects.

[0058] With further reference to Fig. 3, in process 50 the value of t Tprovided to the control system 25. The control system can then calibrate the test system (50h) to determine the effects of the runtime t T along the cable 32 during the DUT test.

[0059] All or part of the test systems and processes described in this specification, as well as various modifications thereof, may be configured or controlled, at least in part, by one or more computers, such as the control system 45 and / or the test instrument 43, using one or more computer programs, wherein the one or more computer programs are tangibly embodied in one or more information carriers, for example, one or more non-transitory machine-readable storage media. A computer program may be written in any form of programming language (including a compiled or interpreted language); and it may be provided in any form, including as a stand-alone program or as a module, part, subprogram, or other unit suitable for use in a computing environment.The computer program may be deployed on a single computer or station, or it may be distributed across multiple locations and executed on multiple computers connected via a network.

[0060] Actions related to configuring or controlling the test system and method described herein may be performed by one or more programmable processors executing one or more computer programs to control or perform all or some of the operations described herein. All or part of the test system and method may be configured or controlled by dedicated logic circuitry such as an FPGA (Field Programmable Gate Array) and / or ASIC (Application Specific Integrated Circuit) or an embedded microprocessor located within instrument hardware.

[0061] For example, processors suitable for executing a computer program include both a general-purpose microprocessor and a dedicated microprocessor, as well as any processor or processors of any type of digital computer. Typically, a processor receives instructions and data from a read-only memory area or from a random access memory area, or both. Elements of a computer include one or more processors for executing instructions and one or more storage devices for storing instructions and data. Typically, a computer also includes (or is operatively coupled to receive data from or transfer data to, or both), one or more machine-readable storage media, for example, a mass storage device for storing data, such as a magnetic disk, a magneto-optical disk, or an optical disk.Non-volatile machine-readable storage media suitable for embodying computer program instructions and data include all forms of non-volatile memory areas, which include, by way of example: a semiconductor storage device, such as EPROM (Erasable Programmable Read Only Memory), EEPROM (Electrically Erasable Programmable Read Only Memory), and flash memory device; a magnetic disk, such as an internal hard disk or a removable disk; a magneto-optical disk; and CD-ROM (Compact Disc Read Only Memory) and DVD-ROM (Digital Versatile Disc Read Only Memory).

[0062] In the description and claims provided herein, the adjectives "first," "second," "third," etc., do not indicate priority or order. Instead, these adjectives serve only to distinguish the nouns they modify.

[0063] Any mechanical or electrical connection herein may include a direct physical connection or an indirect connection including an intermediate component.

[0064] Elements of various described specific embodiments may be combined to form other specific embodiments not specifically set forth above. Elements of previously described systems may be omitted without adversely affecting their function or the operation of the system. Furthermore, various individual elements may be combined into one or more individual elements to perform the functions described herein.

[0065] Other specific embodiments not specifically described in this specification are also within the scope of the following claims.

Claims

[1] System that includes: a signal generator that outputs a signal based on a plurality of carrier frequencies; a wired transmission medium used to transmit the signal, the wired transmission medium being configured to be open at one end to produce a reflection of the signal at the wired transmission medium; and a signal analyzer that receives the reflection and determines a transmission time of the signal along the wired transmission medium based on the reflection, wherein the signal analyzer is configured to perform operations comprising: Performing a search based on an estimated transmission time of the signal along the wired transmission medium and on the reflection to determine the transmission time, wherein the search is used to determine which candidate transmission time from a plurality of candidate transmission times should be selected for the transmission time, and wherein the differences between the plurality of candidate transmission times correspond to multiples of a step size. [2] The system of claim 1, wherein the operations further comprise: Performing a coarse search based on the reflection to determine the estimated transmission time, wherein the coarse search is used to determine which candidate transmission time from a plurality of candidate transmission times should be selected for the estimated transmission time, and wherein the differences between the plurality of candidate transmission times used in the coarse search correspond to multiples of a first step size; wherein the search based on the estimated transmission time comprises a fine search, wherein the step size in the fine search is a second step size and the first step size is larger than the second step size; and wherein the plurality of candidate transmission times used in the coarse search comprise a first candidate transmission time, and wherein the plurality of candidate transmission times used in the fine search comprise a second candidate transmission time. [3] The system of claim 2, wherein the coarse search is insensitive to the amplitude and phase shift of a signal having the first candidate transmission time. [4] The system of claim 2, wherein the coarse search comprises detecting a maximum correlation based on the following two criteria: (i) the first candidate transmission time and (ii) the sum of a reflection along the wired transmission medium, a reflection at the open end of the wired transmission medium and noise, the maximum correlation corresponding to the estimated transmission time. [5] The system of claim 2, wherein the fine search is sensitive to the amplitude and phase shift of a signal having the second candidate transmission time; and wherein at least two of the plurality of carrier frequencies are orthogonal to each other. [6] The system of claim 2, wherein the fine search comprises determining the transmission time within a predetermined range around the estimated transmission time based on a difference between the following two values: (i) a value based on the reflection and (ii) a value based on the second candidate transmission time. [7] The system of claim 6, wherein determining the transmission time comprises detecting one of the values ​​based on a second candidate transmission time of the second candidate transmission times that minimizes the difference. [8] The system of claim 7, wherein the reflection-based value is based on the amplitude and phase of the reflection; and wherein the second candidate transmission time-based value is based on the amplitude and phase of signals with different transmission times. [9] The system of claim 8, wherein the differences between the transmission times are in the range of single-digit picoseconds. [10] The system of claim 6, wherein the predetermined range is a range of 200 picoseconds or more. [11] The system of claim 1, wherein the signal generator and the signal analyzer are parts of a stand-alone hardware device connected to the wired transmission medium and comprising a test device including one or more processing devices programmed to perform the search. [12] The system of claim 1, wherein the plurality of carrier frequencies are upconverted based on direct current (DC) signals; or wherein the plurality of carrier frequencies include carrier signals that are not upconverted. [13] Procedure which includes: Outputting a signal on a wired transmission medium based on a plurality of carrier frequencies, wherein the wired transmission medium is configured to be open at one end to generate a reflection of the signal at the wired transmission medium; and Determining a transmission time of the signal along the wired transmission medium based on the reflection, wherein determining the transmission time comprises: Performing a search based on an estimated transmission time of the signal along the wired transmission medium and on the reflection to determine the transmission time, wherein the search is used to determine which candidate transmission time from a plurality of candidate transmission times should be selected for the transmission time, and wherein the differences between the plurality of candidate transmission times correspond to multiples of a step size. [14] The method of claim 13, wherein determining the transmission time comprises: Performing a coarse search based on the reflection to determine the estimated transmission time, wherein the coarse search is used to determine which candidate transmission time from a plurality of candidate transmission times should be selected for the estimated transmission time, and wherein the differences between the plurality of candidate transmission times used in the coarse search correspond to multiples of a first step size; wherein the search based on the estimated transmission time comprises a fine search, wherein the step size in the fine search is a second step size and the first step size is larger than the second step size; and wherein the plurality of candidate transmission times used in the coarse search comprise a first candidate transmission time, and wherein the plurality of candidate transmission times used in the fine search comprise a second candidate transmission time. [15] The method of claim 13, wherein the coarse search is insensitive to the amplitude and phase shift of a signal having the first candidate transmission time. [16] The method of claim 13, wherein the coarse search comprises detecting a maximum correlation based on the following two criteria: (i) the first candidate transmission time and (ii) the sum of a reflection along the wired transmission medium, a reflection at the open end of the wired transmission medium and noise, the maximum correlation corresponding to the estimated transmission time. [17] The method of claim 13, wherein the fine search is sensitive to the amplitude and phase shift of a signal having the second candidate transmission time; and wherein at least two of the plurality of carrier frequencies are orthogonal to each other. [18] The method of claim 13, wherein the fine search comprises determining the transmission time within a predetermined range around the estimated transmission time based on a difference between the following two values: (i) a value based on the reflection and (ii) a value based on the second candidate transmission time. [19] The method of claim 18, wherein determining the transmission time comprises identifying one of the values ​​based on a second candidate transmission time of the second candidate transmission times minimizing the difference. [20] The method of claim 19, wherein the reflection-based value is based on the amplitude and phase of the reflection; and wherein the second candidate transmission time-based value is based on the amplitude and phase of signals with different transmission times. [21] The method of claim 20, wherein the differences between the transmission times are in the range of single-digit picoseconds. [22] The method of claim 18, wherein the predetermined range is a range of 200 picoseconds or more. [23] The method of claim 13, wherein the plurality of carrier frequencies are upconverted based on direct current (DC) signals; or wherein the plurality of carrier frequencies include carrier signals that are not upconverted.

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