Determining delays in transmission of signals along wired transmission medium

Abstract

The invention relates to determining a delay in a signal transmission along a wired transmission medium. An exemplary system is provided that includes a signal generator that outputs a signal based on a plurality of carrier frequencies; the wired transmission medium is used for carrying signals, and the wired transmission medium is configured to be open at the tail end so as to generate reflection of the signals on the wired transmission medium; and a signal analyzer that receives the reflections and determines a transmission time of the signal along the wired transmission medium based on the reflections. The signal analyzer is configured to perform operations including performing a search to determine a transmission time based on an estimated transmission time and a reflection of the signal along the wired transmission medium. The search is used to determine which of a plurality of candidate transmission times to select for the transmission time.

Description

Technical Field

[0001] This specification describes example implementations of a test system configured to determine delays in signal transmission along a wired transmission medium. Background Art

[0002] The test system is configured to test the operation of the device. The device tested by the test system is called a device under test (DUT). The test system may include a test instrument for sending test signals (such as radio frequency (RF) signals) and data to the DUT through a wired transmission medium (such as a cable) for testing. The DUT responds with a response signal. The test system expects these response signals to contain specific values ​​and / or have specific timings. If the response signal has the appropriate value and / or timing, the DUT passes the test. If the response signal does not have those values ​​and / or timing, the DUT may not pass the test.

[0003] Wired transmission media, such as cables, introduce delays into the test system. For example, it takes time for the test signal and the response signal to propagate along the cable. This time is also called time of flight (TOF) and is an example of the delay introduced by the cable during signal transmission. This delay may have an adverse effect on the test. For example, when testing the timing on the DUT, the delay in the signal transmission associated with the cable will affect the results.

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

[0005] Therefore, techniques have been implemented to determine the delay in signal transmission and incorporate this delay into the test process, such as calibrating the test system based on the delay. An exemplary technique for determining the delay in signal transmission includes combining transmission and measurement equipment at different ends of the cable. The measurement equipment measures the transmission time based on the time it takes the transmission equipment to transmit the signal. Techniques such as these may require specialized equipment that must be installed and then disassembled, which makes them labor-intensive, especially when there are a large number of ports to be connected to the DUT. Therefore, for some types of DUTs, in some test environments, implementing techniques such as these may be challenging. Summary of the invention

[0006] The present disclosure provides an exemplary system, which includes: a signal generator that outputs a signal based on multiple carrier frequencies; a wired transmission medium that is used to carry the signal, wherein the wired transmission medium is configured to be open-ended to generate reflections of the signal on the wired transmission medium; and a signal analyzer that receives the reflections and determines the transmission time of the signal along the wired transmission medium based on the reflections. The signal analyzer is configured to perform an operation that includes performing a search based on the estimated transmission time and reflection of the signal along the wired transmission medium to determine the transmission time. The search is used to determine which candidate transmission time of multiple candidate transmission times is selected for the transmission time. The multiple candidate transmission times vary by multiples of the step size. The exemplary system may include one or more of the following features (alone or in combination).

[0007] The operations may include performing a coarse search based on the reflections to determine an estimated transmission time. The coarse search may be performed to determine which candidate transmission time of a plurality of candidate transmission times to select for the estimated transmission time. The plurality of candidate transmission times used in the coarse search may vary by a multiple 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 greater than the second step size. The plurality of candidate transmission times used in the coarse search may include a first candidate transmission time, and the plurality of 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 offset of the signal having the first candidate transmission time. The coarse search may include identifying a maximum correlation based on (i) the first candidate transmission time and (ii) the sum of reflections along the wired transmission medium, reflections at the open end of the wired transmission medium, and noise, the maximum correlation may correspond to the estimated transmission time. The fine search may be sensitive to the amplitude and phase offset of the signal having the second candidate transmission time. At least two of the plurality of carrier frequencies may be orthogonal.

[0009] The refined search may include determining a transmission time within a predetermined range of the estimated transmission time based on a difference between: (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 ​​of the second candidate transmission time that minimizes the difference in the second candidate transmission time. The predetermined range may be in the range of 200 picoseconds or greater.

[0010] 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 a signal having a different transmission time. The different transmission times may vary in single-digit picoseconds.

[0011] The signal generator and the signal analyzer may be part of a single hardware device connected to a wired transmission medium. The single hardware device may be or include a tester or a test system. The tester or the test system may include one or more processing devices programmed to perform the search. Multiple carrier frequencies may be up-converted based on a direct current (DC) signal. Multiple carrier frequencies may include carrier signals that have not undergone up-conversion.

[0012] An exemplary method includes the following operations: outputting a signal on a wired transmission medium based on multiple carrier frequencies, wherein the wired transmission medium is configured to be open-ended to produce reflections of the signal on the wired transmission medium; and determining a transmission time of the signal along the wired transmission medium based on the reflections. Determining the transmission time includes performing a search to determine the transmission time based on an estimated transmission time of the signal along the wired transmission medium and the reflections. The search is performed to determine which candidate transmission time of a plurality of candidate transmission times is selected for the transmission time. The plurality of candidate transmission times vary by a multiple of a step size. The exemplary method may include one or more of the following features (alone or in combination).

[0013] Determining the transmission time may include performing a coarse search based on the reflections to determine the estimated transmission time. The coarse search may be performed to determine which candidate transmission time of the plurality of candidate transmission times is selected for the estimated transmission time. The plurality of candidate transmission times used in the coarse search may vary by a multiple 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 greater than the second step size. The plurality of candidate transmission times used in the coarse search may include a first candidate transmission time, and the plurality of 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 offset of the signal having the first candidate transmission time. The coarse search may include identifying a maximum correlation based on (i) the first candidate transmission time and (ii) the sum of reflections along the wired transmission medium, reflections 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 amplitude and phase offsets of the signal having the second candidate transmission time.At least two of the plurality of carrier frequencies may be orthogonal.

[0016] The refined search may include determining a transmission time within a predetermined range of the estimated transmission time based on a difference between: (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 ​​of the second candidate transmission time that minimizes the difference in the second candidate transmission time. The predetermined range may be in the range of 200 picoseconds or greater.

[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 the signal with different transmission times. The different transmission times may vary by single-digit picoseconds. Multiple carrier frequencies may be up-converted based on a direct current (DC) signal. The multiple carrier frequencies may include a carrier signal that has not undergone up-conversion.

[0018] Any two or more of the features described in this specification (including this summary) may be combined to form implementations not specifically described in this specification.

[0019] At least a portion of the devices, systems, techniques, and processes described in this specification may be configured or controlled by executing instructions stored on one or more non-transitory machine-readable storage media on one or more processing devices. Examples of non-transitory machine-readable storage media include read-only memory, optical disk drives, memory disk drives, and random access memory. At least a portion of the devices, systems, techniques, and processes described in this specification may be configured or controlled using a computing system consisting of one or more processing devices and a memory storing instructions, which may be executed by 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, construction, composition, arrangement, placement, programming, operation, activation, deactivation, and / or control.

[0020] The details of one or more implementations are set forth in the accompanying drawings and the detailed description that follows. Other features and advantages will be apparent from the detailed description and drawings, and from the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a block diagram illustrating exemplary signal reflections along a wired transmission medium having an open end.

[0022] Figure 2 is a block diagram of components of an exemplary test system including a wired transmission medium having an open end.

[0023] Figure 3 are operational blocks included in an exemplary process for determining delay in signal transmission along a wired transmission medium having an open end.

[0024] Figure 4 are examples of graphs illustrating exemplary delays in signal transmission along a wired transmission medium determined using different procedures.

[0025] Like reference numbers in different drawings indicate similar elements. DETAILED DESCRIPTION

[0026] Described herein are exemplary implementations of processes for determining delays in signal transmission associated with a wired transmission medium, such as a cable, and exemplary systems configured to implement the processes. The exemplary processes include connecting a signal transceiver to one end of the cable and leaving the other end of the cable open-ended; e.g., not connected to a device under test (DUT). The "cable" in this example may include any fixture that connects the cable to the signal transceiver and to the DUT, such as a connector or the like.

[0027] The signal transceiver outputs the signal to the cable via a plurality of carrier frequencies. Each signal output to the cable may be a carrier signal. The examples given below describe a carrier signal having a selected carrier frequency that is up-converted using a DC signal, which is referred to herein as a DC up-converted signal. However, other types of carrier signals may also be used, including signals of different frequencies that are generated to have different amplitudes without undergoing DC up-conversion. DC signals are used because they do not introduce additional complexity, such as additional phases. In some examples, up-conversion includes changing the amplitude of a carrier signal by multiplying the carrier signal by a DC signal, essentially amplitude modulating the carrier signal using a DC signal. In some examples, at least two carrier signals have different frequencies that are orthogonal.

[0028] The DC up-converted signal transmitted through the cable is reflected from the open end of the cable back to the signal transceiver. The DC up-converted signal transmitted through the cable may also be reflected from mismatches or anomalies along the cable path. These mismatches or anomalies may include, for example, impedance mismatches, structural anomalies in the cable and / or connectors along the cable.

[0029] Examples of these reflections are Figure 1 More specifically, Figure 1 In FIG. 1 , a signal transceiver 10 outputs a DC up-converted signal 11 to a cable 12. The cable has mismatches 16, 17 and an open end 19. Reflections 20, 21 and 22 of the DC up-converted signal occur at the mismatches 16, 17 and the open end 19, respectively. Although three reflections are shown, there may be dozens or hundreds in some examples. The signal transceiver 10 receives these reflections and organizes them into a vector / array, each element of which is for a separate different carrier frequency.

[0030] The exemplary process includes performing a rough search based on the reflections to determine an estimated travel time t of the signal on the cable 12. T(粗略)In this example, the coarse search determines which of the multiple candidate transmission times to select for estimating the transmission time based on correlation with elements in the vector / array. The candidate transmission times vary by multiples of a predefined step size, which in the example of a coarse search may be tens or hundreds of picoseconds (ps) or more or less. The candidate transmission time with the highest correlation with the elements of the vector / array is deemed to be the estimated transmission time t of the signal over the entire length of the cable 12 as determined by the coarse search. T(粗略) , and is used in subsequent or fine search operations to further refine the transmission time t across the entire length of the cable 12 T .

[0031] The estimated transmission time t T(粗略) A fine search is performed within a range of t. For example, the range defined by the value "d" in this example may be selected based on the carrier frequency and the cable length. In some cases, examples of d may be, but are not limited to, 200 ps, ​​300 ps, ​​400 ps, ​​etc. up to 800 ps or more or less. The fine search performs an optimization to determine the range of t T(粗略) -d to t T(粗略) Which candidate transmission time among a plurality of candidate transmission times within the range of +d is selected for the transmission time t of the signal along the cable T The candidate transmission times in the fine search are different from those used in the coarse search and vary by multiples of the predefined step size. In the fine search phase, in some examples, the predefined step size may be a few picoseconds (such as 10 ps or less), or tens of picoseconds or less (such as 100 ps or less), or smaller or larger.

[0032] The optimization performed in the fine search is sensitive to the signal phase and the offset of the signal phase, while the correlation performed in the coarse search is not necessarily so. In this example, the offset indicates that the phase of the reflections is not the same, which may be due to, for example, different reflection points along the cable. Therefore, the fine search can enable a more accurate determination of the transmission time than the coarse search. In some specific implementations, the fine search can be performed independently of the coarse search by using a range determined based on the test setup and the properties of the cable (such as, but not limited to, the cable length, the composition of the cable, and the geometry of the cable).

[0033] Figure 2 is a block diagram illustrating a configuration of components of an example test system 25 configured to implement the example processes described herein.

[0034] 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 a test signal via the signal transceiver 26 to test a DUT (not shown) connected to a wired transmission medium (such as a cable 32). The test signal for testing the DUT may be or include instructions, commands, data, parameters, variables, test modes, and / or any other information designed to elicit a response from the DUT. One or more (e.g., all) test instruments may be configured to receive a response from the DUT (via the signal transceiver 26) to a test signal sent from the test instrument to the DUT. The test instrument may be configured to analyze the response to determine whether the DUT has passed or failed the test. For example, the timing of the response may be analyzed, the data represented by the response may be analyzed, and the like. The test instrument may include, but is 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), and the like.

[0035] The test system 25 also includes a control system 45. The control system can be or include a computing 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 can be configured to execute instructions (e.g., computer code) 49 stored in the memory 47 to control the test instrument 43 to perform tests on the DUT, for example, to send a test program to the test instrument to execute to generate a test signal, or to send a test signal to the test instrument to process and / or forward to the DUT. The control system 45 can also be configured to execute instructions to control the signal transceiver 26 described below and / or to perform operations with respect to Figure 3 The rough search process and the fine search process are all or part of the above. The dotted line 44 indicates Figure 2 The wired or wireless connections between the components depicted in the drawings, and analog communications, digital communications, and / or RF communications between these components can be transmitted via these wired or wireless connections.

[0036] The signal transceiver 26 includes the functions of a signal generator 28 and a signal analyzer 29 or each of these components in one, two or more hardware devices. In some embodiments, the signal generator 28 is configured to function as a carrier signal generator, and in this capacity is configured to generate and output a delay test signal that is used to test the delay along a wired transmission medium (such as cable 32). The form and timing of the delay test signal can be determined by (e.g., indicated, set and / or controlled by) the control system 45 and / or one or more test instruments 43. In this example, the delay test signal is a DC up-converted signal. A DC up-converted signal is used in the following examples; however, an alternating current (AC) signal, a composite signal, or other types of signals may also be used as the delay test signal.

[0037] The signal generator 28 is configured to generate a plurality of carrier frequencies to generate a DC up-converted signal based on one or more DC signals. The DC signal for generating the DC up-converted signal may be provided to the signal generator 28 or generated by the signal generator 28. The number of carrier frequencies used and the actual frequency may be determined by the control system 45 and / or by one or more test instruments 43. The carrier frequency may be in a range such as, but not limited to, 4 gigahertz (GHz) to 12 GHz, or in some examples, greater than 12 GHz. In some examples, there may be tens or hundreds of carrier frequencies up-converted by a DC signal (e.g., based on the DC signal), and these carrier frequencies may differ by regular intervals, such as increasing by regular intervals. In a non-limiting example, the carrier frequency may start from 4 GHz and increase by 0.1 GHz to 6 GHz. In another non-limiting example, the carrier frequency may start from 5 GHz and increase by 0.01 GHz to 9 GHz. Any appropriate increment and / or frequency range may be used; not just those listed here.

[0038] The test system 25 also 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 a cable 32 as a wired transmission medium. In this example, the cable may include fixtures 34, 35, such as connectors, located at each corresponding end 36, 37 of the cable. In some implementations, the processes described herein account for the presence of these fixtures and the delays caused by these fixtures. Therefore, in some implementations, references to cables and / or wired transmission media include any conductive medium through which a signal is transmitted together with a fixture at the end or along the length of the conductive medium.

[0039] As previously described, in the test system 25, the cable 32 is open ended. For example, one end 35 / 37 of the cable 32 is not connected to the DUT or other device to receive a signal from the cable. However, in some examples, an RF probe (not shown) can be connected to the end 35 of the cable 32. The RF probe can monitor the signal on the cable. The cable can include multiple sections. For example, Figure 2 As shown, the cable 32 may include individual cables, such as cables 32a, 32b, connected via a connector 40. The connector 40 may cause impedance mismatches, thereby causing reflections (see, e.g., Figure 1 The cable 32 may also include one or more anomalies 41, which may be caused by manufacturing defects or damage, which result in impedance mismatches along the length of the cable and may cause reflections (see, e.g. Figure 1 ).

[0040] The signal generator 28 is configured to output a DC up-converted signal (such as Figure 1 Signal 11). Since multiple DC up-converted signals are output, the result is that multiple reflections appear on the cable, for example, there is one or more reflections for each DC up-converted signal. Figure 2 In the example of FIG. 1 , DC up-converted signals based on various carrier frequencies are reflected from the open ends 35 / 37 of the cable 32, from the anomaly 41, and from the impedance mismatch 40. These reflections are directed along the cable back to the signal transceiver 26. These reflections are out of phase with each other and travel along different lengths of the cable, such as relative to Figure 1 This is due, at least in part, to the use of different frequencies, the reflections not occurring at the same locations along the cable, and the reflections not occurring at regular or known intervals corresponding to the phase of the DC up-converted signal.

[0041] The signal analyzer 29 is configured to receive the reflection of the DC up-converted signal and measure the reflection. Figure 1 , the measured reflection includes x(t i ). For example, the signal analyzer measures the reflected signal x at each time t i In some implementations, signal analyzer 29 can be configured to determine the transmission time t of the DC up-converted signal between open end 37 and transceiver 26 based on these reflections using process 50 described below. T . refer to Figure 1 and Figure 2 , t T is the flight time of the signal from the open end 19, 35 / 37 back to the signal transceiver 26, ie the time along the entire length of the cable.

[0042] In some implementations, the signal analyzer 29 may include one or more processing devices and / or circuits configured to use Figure 3 The process 50 determines the transmission time t of the DC up-converted signal along the entire length of the cable based on reflection. T In some implementations, the signal analyzer 29 can be configured to provide its measurements to the control system 45, and the control system 45 can be configured to use Figure 3 The process 50 determines the transmission time t of the DC up-converted signal along the entire length of the cable based on reflection. T In some implementations, the signal analyzer 29 can be configured to provide its measurements to one or more test instruments 43, and the test instruments 43 can be configured to use Figure 3 The process 50 determines the transmission time t of the DC signal along the entire length of the cable based on reflection. T In some implementations, the signal analyzer 29, the test instrument, and / or the control system 45 may be configured to operate in coordination to use Figure 3 The process 50 determines the transmission time t of the DC up-converted signal along the entire length of the cable based on reflection. T .

[0043] refer to Figure 3 , process 50 includes configuring (50a) the test system to determine the delay (e.g., time of flight "TOF") in the transmission of a signal along cable 32. In this example, the configuration operation may include disconnecting the DUT or other device from fixture 35, leaving end 37 of cable 32 open-ended, while still maintaining cable 32 connected to test system 25 via fixture 34.

[0044] The signal generator 28 sends (50b) a plurality of different DC up-converted 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 can be controlled by the control system 45 and / or the test instrument 32 to output the DC up-converted signals. For example, the control system 45 and / or the test instrument 32 can determine one or more DC signal values ​​and select which carrier frequencies to use to generate the plurality of DC up-converted signals based on programming and / or user input in these components. For example, in some specific implementations, the plurality of DC up-converted signals can 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 plurality of DC up-converted signals can be based on a plurality of different DC values ​​and a plurality of different carrier frequencies (e.g., formed using these values).

[0045] For example, the DC up-converted signal is reflected from the cable open end 37 and from various points along the cable, such as relative to Figure 1The signal analyzer 29 receives (50c) a reflected signal from the cable 32; that is, the signal analyzer receives a reflection of the DC up-converted 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 travel times.

[0046] In some implementations, the signal analyzer 29 measures (50d) a signal y based on the combined reflections. In this example, the signal y is a signal y at each measurement frequency. fn Vector / array of: y = [y f1 ,y f2 ,…], where “fn” is the frequency. Each element of y (e.g., y f1 etc.) is x(t i )、x(t T ) and the noise n. i ) is a vector defined as follows: x(t i )=[(x(t i ),f 1 ),(x(t i ),f 2 )…], where x(t i ) is from a process with travel time t i and the reflection of the signal path of frequency f, and where x(t i )∈C K . x(t i ) can include each x(t i )’s amplitude, frequency, phase, and timing (e.g., reception time). T ) is the reflection from the open end 37 of the cable (e.g., the reflection from the entire length of the cable 32), whose value is searched in y. T ) is similar to x(t i ) is the reflection of the element. n is the random noise in the corresponding reflection, where n∈C K In some examples, only signal y is actually measurable by the signal analyzer 29; its component, namely x(t i )、x(t T ) and noise n cannot be measured individually by a signal analyzer.

[0047] Process 50 performs (50e) a coarse search process based on y to determine x(t T(粗略) ), where x(t T(粗略)) is an estimate of the delay in signal transmission along the entire length of cable 32 obtained using the coarse search process. For the measured value of y, the coarse search process determines t T(粗略) More specifically, the coarse search process uses the estimated x(t T ) value to test t i different candidate values ​​of t in order to determine T Which estimate of most closely matches the value of y, for example, where y contains x(t T ), as described above and shown below in equation (1). The t that most closely matches the y value T The estimated value of constitutes the estimated delay (t T(粗略) ), which can be further refined using the fine search process described below.

[0048] In more detail, the signal analyzer receives a reflection defining a vector y (ie, a reflected version of the DC up-converted signal / delayed test signal) comprising a plurality of signals with a target travel time t T The signal x is defined as follows:

[0049]

[0050] in:

[0051] x(t i ) is a measure of reflections along the cable, which may occur at different points,

[0052] x(t T ) is the reflection from the open end 37 of the cable and its value is to be determined,

[0053] a i is the reflection x(t i ), where a T is the reflection x(t T ), where a i ∈R K and is a real number, and

[0054] n is a vector containing random noise in each corresponding signal reflection, where n∈C K .

[0055] By assuming that the target travel time t T The amplitude response of ∥a t ∥ 2 The coarse search process uses the correlation process of formula (2) to find the t for maximum correlation. * :

[0056]

[0057] More specifically, the correlation process of formula (2) is achieved by choosing x(t T ), that is, x(t * ), to select t T Different candidates, namely t * , in order to identify x(t T ) has the greatest correlation with the value in vector y. The different candidate times used in the correlation process can vary by multiples of the step size. For example, t T The candidate, t * , may correspond to x(t(t)) being varied incrementally along a continuum between two frequencies (e.g., in the range of 4 GHz to 12 GHz) with a step size (“step_size”) of, for example, tens or hundreds of picoseconds (ps) or more or less. * ), which passes through x(t *+step_size )、x(t *+step_sizex2 )、x(t *+step_sizex3 ) and so on between x(t * )’s starting and ending values ​​x(t *+step_sizex(n) (where n>3)), where the "x" in the superscript means "multiplied". The starting value, ending value, and step size can be based on the DUT to be tested, the frequency used for testing, the length of the cable, and / or other factors. Selecting the step size can be a trade-off between the resolution obtained (limited by noise) and the time required for processing. Smaller step sizes will result in more processing time. Step sizes that are too small may be limited by noise and other minor impairments, which may be filtered out in some implementations.

[0058] Figure 4 An exemplary graph is shown which shows the relationship between x(t) 57 and time t * Example correlation 56 obtained using equation (2) for different values ​​of t 58 (in picoseconds). As shown, in this example, the maximum correlation occurs at about 460 ps t * In the fine search process 50 performed by process 50, value 55 can be used as the estimated value (t T(粗略) ). More specifically, as described above, the fine search process 50 performs an optimization to determine the optimal T(粗略) -d to t T(粗略)Which candidate transmission time among a plurality of candidate transmission times within a range of +d is selected for the transmission time along the cable 32. In some examples, the candidate transmission times used in the fine search process can vary in multiples of a few picoseconds or tens of picoseconds or more, but is not limited thereto. In the fine search stage, in some examples, an exemplary predefined step size can be, but is not limited to, single-digit picoseconds, such as 10ps or less.

[0059] The correlation of formula (2) to the phase shift (i.e., e jθ x(t T )) is not sensitive, where θ is x(t T(粗略) ) and a T is the amplitude. Therefore, the correlation of formula (2) may be prone to reflection travel path interference because the different reflected signals (ie, reflections) along the cable 32 are uncorrelated. This means that the value 55 determined by formula (2) is ( Figure 4 ) may be affected by the maximum correlation value not being at the target point: t * ≠t T The influence of the interference pattern at T(粗略) That is, the maximum correlation due to the interference pattern may occur when it is not t T The best estimate 55 of t is located at the location of t. In this example, the fine search (50f) performed by process 50 is sensitive to phase offset and amplitude response. This sensitivity can provide better t relative to the coarse search process. T resolution and reduce the interference pattern introduced by reflections on t T(粗略) The impact of the estimated value.

[0060] The fine search process (50f), also referred to herein as the null space process, uses some of the same nomenclature and variables as the coarse search process. Therefore, these nomenclature and variables are not explained here. The fine search process searches for the vector a*·x(t * ), so that the vector ya * ·x(t * ) to vector space The projection of is minimized. The vector space S t The space comprising the entire length of the cable 32 spanning the travel time t and having 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 refined search.

[0061] Listing all possible amplitude responses of reflection "x" as am, where m = 1, 2, ..., yields the following set of vectors:

[0062] X t=[a 1 , x(t), a 2 x(t), ...]

[0063] The eigenvalue decomposition is produced as follows:

[0064]

[0065] The eigenvalue λ matrix is ​​defined as follows:

[0066]

[0067] And the eigenvalue q matrix is ​​defined as follows:

[0068] Q=[q 1 ,q 2 ,…]

[0069] Retain the first L (L>1) largest eigenvalues ​​corresponding to the eigenvector to construct the vector space S t , and discard the remaining eigenvalues ​​because they are so small that they have no effect on the vector space S t Almost no impact.

[0070] S t = span {q 1 ,q 2 , ...q L}

[0071] When all possible amplitude responses are listed to construct S t When the amplitude offset is used, S t will have little effect, since any offset will act only on the eigenvalues. Eigenvectors and the space S t will remain the same. Therefore, when listing all possible magnitude responses, only the "shape" of frequency relative to magnitude is important.

[0072] The optimization shown in the following formula (3) is used to change t * To identify the optimal maximum value. * The value (50g) is determined as t T That is, the delay along the entire length of the cable 32. This is achieved by measuring the delay for t * Different values ​​of a * ·x(t * ). Therefore, in this fine search process, the search for a and x(t * ) Both. The maximum value of a in formula (3) is * ·x(t * ) value corresponds to the value that makes y and a * ·x(t *) is the value of t (the delay along cable 32) that minimizes the difference between them.

[0073]

[0074] The t used in formula (3) * Different time (t T The candidate) can be changed by multiples of the step size. For example, t * The different times may correspond to a varying in increments of, for example, tens of picoseconds (ps), single-digit picoseconds, or more or less along a continuum between two frequencies (e.g., in the range of 4 GHz to 12 GHz). * ·x(t * ), which passes through a * ·x(t *+step_size ), a * ·x(t *+step_sizex2 ), a * ·x(t *+step_sizex3 ) etc. between a * ·x(t * )'s starting and ending values ​​a * ·x(t *+step_sizex(n)(其中n>3) ), where the superscript "x" means "multiplied by". In some examples, the starting value and the ending value may be a * ·x(t T(粗略) -d) and a * ·x(t T(粗略) +d), where t T(粗略) -d and t T(粗略) +d is the time determined using the coarse search process 50. In some examples, the start value and the end value may be pre-programmed into the test system and may not be based on the coarse search process (e.g., without performing the coarse search process). The step size may be based on the DUT to be tested, the frequency used for testing, the length of the cable, and / or other factors.

[0075] The search performed using the optimization formula (3) is sensitive to the amplitude and phase offset of the reflection. To demonstrate this, assume that the signal analyzer 29 receives a signal y containing the target signal a x. When the optimization of formula (3) is performed using random phase or amplitude offsets, the target signal is * ·x(t * ) will not be completely removed after subtraction, for example, candidate a * ·x(t * ) * and x is not equal to a inherent in y * and the actual value of x. The remaining signals will not be related to the subspace S tquadrature, resulting in a lower value produced by equation (3). When using precise phase and amplitude offsets x and a respectively * When performing the optimization of formula (3), the target signal is * ·x(t * ) will be completely removed after subtraction. The remaining signal to S t The projection of will be minimized, resulting in the maximum value in formula (3).

[0076] Figure 4 Contains information showing the * ·x(t * ) using formula (3) across t T(粗略) -d and t T(粗略) +d is an exemplary curve of the optimization 56 obtained. As shown, in this example, the maximum value of the optimization occurs at a value 60 of about 456.5 ps, which is determined as t T , i.e., the delay along the entire length of the cable 32, and which is different from t T(粗略) Likewise, since interference effects are reduced, the envelope 61 generated using the fine search process is smaller, eg, shorter in duration, than the envelope 62 generated using the coarse search process.

[0077] Return to reference Figure 3 , process 50 can be t T The value is provided to the control system 25. The control system can then calibrate (50h) the test system to account for and / or eliminate the travel time t along the cable 32 during the DUT test. T impact.

[0078] All or part of the test systems and processes described in this specification, and various modifications thereof, may be configured or controlled, at least in part, by one or more computers, such as control system 45 and / or test instrument 43, using one or more computer programs tangibly embodied in one or more information carriers, such as in one or more non-transitory machine-readable storage media. Computer programs may be written in any form of programming language, including compiled or interpreted languages, and may be deployed in any form, including as stand-alone programs or as modules, parts, subroutines, or other units suitable for use in a computing environment. Computer programs may be deployed to execute on a single computer or at a single site or on multiple computers distributed across multiple locations and interconnected by a network.

[0079] The actions associated with configuring or controlling the test systems and methods 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 systems and methods may be configured or controlled by dedicated logic circuits (such as FPGAs (field programmable gate arrays) and / or ASICs (application specific integrated circuits)) or embedded microprocessors localized to instrument hardware.

[0080] Processors suitable for computer program execution include (for example) both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Typically, the processor will receive instructions and data from a read-only storage area or a random access storage area or both. The elements of a computer include one or more processors for executing instructions and one or more storage area devices for storing instructions and data. Typically, a computer will also include (or be operatively coupled to receive data from it or transfer data to it or both) one or more machine-readable storage media, such as a mass storage device for storing data, such as a magnetic disk, magneto-optical disk, or optical disk. Non-transitory machine-readable storage media suitable for embodying computer program instructions and data include all forms of non-volatile storage areas, including (by way of example) semiconductor storage area devices, such as EPROM (erasable programmable read-only memory), EEPROM (electrically erasable programmable read-only memory), and flash storage area devices; magnetic disks, such as internal hard disks or removable disks; magneto-optical disks; and CD-ROM (compact disk read-only memory) and DVD-ROM (digital versatile disk read-only memory).

[0081] In the description and claims provided herein, the adjectives "first", "second", "third", etc. do not specify priority or order. Instead, these adjectives are used only to distinguish the nouns they modify.

[0082] Any mechanical or electrical connections herein may include a direct physical connection or an indirect connection involving intermediate components.

[0083] The elements of the different implementations described may be combined together to form other implementations not specifically described above. Elements may be omitted from a previously described system without generally adversely affecting its operation or the operation of the system. In addition, individual elements may be combined into one or more single elements to perform the functions described in this specification.

[0084] Other implementations not specifically described in this specification are also within the scope of the following claims.

Claims

1. A system, comprising: a signal generator that outputs a signal based on a plurality of carrier frequencies; a wired transmission medium, the wired transmission medium being used to carry the signal, the wired transmission medium being configured to be open-ended so as to generate reflection of the signal on the wired transmission medium; and a signal analyzer that receives the reflection and determines a transmission time of a signal along the wired transmission medium based on the reflection, the signal analyzer being configured to perform operations comprising: A search is performed to determine the transmission time based on an estimated transmission time of the signal along the wired transmission medium and the reflections, the search being used to determine which candidate transmission time of a plurality of candidate transmission times to select for the transmission time, the plurality of candidate transmission times varying by a multiple of a step size.

2. The system of claim 1, wherein the operations further comprise: performing a coarse search based on the reflections to determine the estimated transmission time, the coarse search being used to determine which of a plurality of candidate transmission times to select for the estimated transmission time, the plurality of candidate transmission times used in the coarse search varying by a multiple of a first step size; wherein the search based on the estimated transmission time comprises a refined search, the step size in the refined search is a second step size, and the first step size is greater than the second step size; and The multiple candidate transmission times used in the coarse search include a first candidate transmission time, and the multiple candidate transmission times used in the fine search include a second candidate transmission time.

3. The system of claim 2, wherein the coarse search is insensitive to amplitude and phase offsets of a signal having the first candidate transmission time.

4. A system according to claim 2, wherein the coarse search includes identifying a maximum correlation based on: (i) the first candidate transmission time and (ii) the sum of reflections along the wired transmission medium, reflections at an 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 amplitude and phase offset of a signal having the second candidate transmission time; and Wherein at least two carrier frequencies among the plurality of carrier frequencies are orthogonal.

6. The system of claim 2, wherein the refined search comprises determining the transmission time within a predetermined range of the estimated transmission time based on a difference between: (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 identifying one of the values ​​of the second candidate transmission time that is based on one of the second candidate transmission times that minimizes the difference.

8. The system of claim 7, wherein the value based on the reflection is based on a magnitude and a phase of the reflection; and Wherein the value based on the second candidate transmission time is based on the amplitude and phase of signals having different transmission times.

9. The system of claim 8, wherein the different transmission times vary by single-digit picoseconds.

10. The system of claim 6, wherein the predetermined range is within 200 picoseconds or greater.

11. The system of claim 1 , wherein the signal generator and the signal analyzer are part of a single hardware device connected to the wired transmission medium, the single hardware device comprising a tester including one or more processing devices programmed to perform the search.

12. The system of claim 1, wherein the plurality of carrier frequencies are up-converted based on a direct current (DC) signal; or The plurality of carrier frequencies include carrier signals that have not undergone up-conversion.

13. A method comprising: outputting signals based on a plurality of carrier frequencies on a wired transmission medium, the wired transmission medium being configured to be open-ended to generate reflections of the signals on the wired transmission medium; as well as Determining a transmission time of a signal along the wired transmission medium based on the reflection, wherein determining the transmission time comprises: A search is performed to determine the transmission time based on an estimated transmission time of the signal along the wired transmission medium and the reflections, the search being used to determine which candidate transmission time of a plurality of candidate transmission times to select for the transmission time, the plurality of candidate transmission times varying by a multiple of a step size.

14. The method of claim 13, wherein determining the transmission time comprises: performing a coarse search based on the reflections to determine the estimated transmission time, the coarse search being used to determine which of a plurality of candidate transmission times to select for the estimated transmission time, the plurality of candidate transmission times used in the coarse search varying by a multiple of a first step size; wherein the search based on the estimated transmission time comprises a refined search, the step size in the refined search is a second step size, and the first step size is greater than the second step size; and The multiple candidate transmission times used in the coarse search include a first candidate transmission time, and the multiple candidate transmission times used in the fine search include a second candidate transmission time.

15. The method of claim 13, wherein the coarse search is insensitive to amplitude and phase offsets of a signal having the first candidate transmission time.

16. A method according to claim 13, wherein the coarse search includes identifying a maximum correlation based on: (i) the first candidate transmission time and (ii) the sum of reflections along the wired transmission medium, reflections at an 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 amplitude and phase offset of a signal having the second candidate transmission time; and Wherein at least two carrier frequencies among the plurality of carrier frequencies are orthogonal.

18. The method of claim 13, wherein the refined search comprises determining the transmission time within a predetermined range of the estimated transmission time based on a difference between: (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 ​​of the second candidate transmission time that is based on one of the second candidate transmission times that minimizes the difference.

20. The method of claim 19, wherein the value based on the reflection is based on a magnitude and a phase of the reflection; and Wherein the value based on the second candidate transmission time is based on the amplitude and phase of signals having different transmission times.

21. The method of claim 20, wherein the different transmission times vary by single-digit picoseconds.

22. The method of claim 18, wherein the predetermined range is within 200 picoseconds or greater.

23. The method of claim 13, wherein the plurality of carrier frequencies are up-converted based on a direct current (DC) signal; or Wherein the plurality of carrier frequencies include carrier signals that have not undergone up-conversion.

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