Time domain, frequency domain and statistical domain combined jitter measurement method in digital oscilloscope

Abstract

The invention discloses a time domain, frequency domain and statistical domain combined jitter measurement method in a digital oscilloscope, which comprises the following steps of: firstly, acquiring a long string of continuous signals by the digital oscilloscope, forwarding sampling data to an upper computer, and then finding out each jump moment of a signal to be measured; a software phase-locked loop is used for recovering a reference edge moment according to the jump moment of the signal to be measured, then the jump moment of the signal to be measured and the reference jump moment are subtracted to obtain a group of time interval error sequences, and finally, jitter is analyzed and processed from a plurality of information domains on the basis of the sequences. And obtaining total jitter, deterministic jitter, random jitter, periodic jitter, data correlation jitter, intersymbol interference and duty ratio distortion.

Description

Technical Field

[0001] The present invention belongs to the technical field of digital oscilloscopes, and more specifically, relates to a jitter measurement method combining time domain, frequency domain and statistical domain in a digital oscilloscope. Background Art

[0002] As an instrument for electronic measurement and signal analysis, the digital oscilloscope is a representative of modern test instruments and the most widely used and most used general test instrument in the field of electronic information. From industrial production, teaching and scientific research to national defense construction and equipment development, digital oscilloscopes are indispensable. As electronic signals become more and more complex, the functions of digital oscilloscopes are also more diversified. Jitter analysis, as an important function of high-end digital oscilloscopes, can measure and analyze the jitter in the signal, thereby evaluating the performance and stability of the system.

[0003] Jitter is one of the main reasons that affect data transmission in high-speed serial links. Only by analyzing jitter efficiently and accurately, tracing its source, and then taking measures to reduce the impact of jitter, can the impact of different modules on the transmission signal in high-speed serial links be described by different jitter components, thereby playing a role in diagnosis and debugging. Different jitter components and their time domain / frequency domain / statistical domain characteristics provide information for studying the jitter components contained in the jitter process and their size.

[0004] The current jitter standard describes the jitter phenomenon according to the jitter component analysis method, and proposes primary jitter analysis and secondary jitter analysis. The purpose of primary jitter analysis is to examine the bit error performance of the system to determine whether the system has met the bit error rate requirements or complies with certain specifications; the secondary analysis technology separates each jitter component from the total jitter to examine the system characteristics and diagnose possible problems in the system. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a jitter measurement method combining time domain, frequency domain and statistical domain in a digital oscilloscope, analyze the jitter from multiple information domains, obtain the results of each jitter component, and realize the separation of jitter components.

[0006] To achieve the above-mentioned object of the invention, the present invention provides a jitter measurement method combining time domain, frequency domain and statistical domain in a digital oscilloscope, characterized in that it comprises the following steps:

[0007] (1) Collecting the signal to be tested through the acquisition system of the digital oscilloscope to obtain continuous sampling data including multiple edges of the signal to be tested;

[0008] (2) The FPGA of the digital oscilloscope forwards the sampled data to the host computer, and then performs amplitude histogram statistics on the sampled data to obtain the high level and low level of the signal to be tested;

[0009] (3) Calculate the hysteresis range and crossover level based on the high level and low level of the signal to be measured;

[0010] (4) Traverse all sampling points, find the sampling moments corresponding to the crossover level, which are the transition moments of the signal to be measured, and then store these transition moments in an array;

[0011] (5) Use the software phase-locked loop in the host computer to recover the reference jump time of the reference signal, and then subtract it from the corresponding jump time in the array to obtain a set of time interval error sequences;

[0012] (6) Analyze the time interval error sequence in the time domain, frequency domain, and statistical domain to obtain the jitter measurement value.

[0013] The object of the invention of the present invention is achieved in this way:

[0014] The present invention discloses a jitter measurement method combining time domain, frequency domain and statistical domain in a digital oscilloscope. Firstly, the digital oscilloscope collects a long series of continuous signals and forwards the sampled data to a host computer. Then, each jump moment of the signal to be measured is found. Then, a software phase-locked loop is used to restore the reference edge moment according to the jump moment of the signal to be measured. Then, the jump moment of the signal to be measured is subtracted from the reference jump moment to obtain a group of time interval error sequences. Finally, based on the sequence, the jitter is analyzed and processed from multiple information domains to obtain the size of the overall jitter, deterministic jitter, random jitter, periodic jitter, data correlation jitter, inter-symbol interference and duty cycle distortion.

[0015] At the same time, the jitter measurement method combining time domain, frequency domain and statistical domain in the digital oscilloscope of the present invention also has the following beneficial effects:

[0016] (1) The clock recovery in the present invention adopts a software phase-locked loop with flexible and configurable parameters, and uses the signal jump time as input, which greatly reduces the amount of data required for the phase-locked loop calculation process, reduces the storage burden and calculation pressure of the digital oscilloscope system, and improves the analysis efficiency.

[0017] (2) The present invention analyzes jitter from three information domains: time domain, frequency domain, and statistical domain, thereby avoiding the problem of inaccurate and incomplete analysis in a single information domain, realizing primary and secondary analysis of jitter, and achieving the purpose of comprehensive jitter analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a flow chart of the jitter measurement method combining the time domain, frequency domain and statistical domain in the digital oscilloscope of the present invention;

[0019] Figure 2 It is the collected signal samples and statistical histogram;

[0020] Figure 3 It is a schematic diagram of signal edge detection;

[0021] Figure 4 It is the basic structure of software phase-locked loop;

[0022] Figure 5 It is the statistical histogram of jitter;

[0023] Figure 6 is the bit error rate cumulative distribution function of jitter;

[0024] Figure 7 is the bathtub curve;

[0025] Figure 8 is the Q factor curve;

[0026] Fig. 9 is the amplitude spectrum of jitter; DETAILED DESCRIPTION

[0027] The specific implementation of the present invention is described below in conjunction with the accompanying drawings so that those skilled in the art can better understand the present invention. It should be noted that in the following description, when the detailed description of known functions and designs may dilute the main content of the present invention, these descriptions will be omitted here.

[0028] Example

[0029] In this embodiment, if Figure 1 As shown, the jitter measurement method combining time domain, frequency domain and statistical domain in the digital oscilloscope of the present invention comprises the following steps:

[0030] (1) Collecting the signal to be tested through the acquisition system of the digital oscilloscope to obtain continuous sampling data containing at least 100 edges of the signal to be tested;

[0031] The signal to be tested is a clock signal or a data signal. If it is a data signal, it must have a repeating data pattern.

[0032] (2) The FPGA of the digital oscilloscope forwards the sampled data to the host computer, and then performs amplitude histogram statistics on the sampled data. Generally speaking, the clock signal or non-return-to-zero code data signal has two peaks, such as Figure 2 As shown, we can obtain the high level and low level of the signal to be tested;

[0033] (3) Calculate the hysteresis range and crossover level based on the high level and low level of the signal to be measured;

[0034] The hysteresis range and crossing level are calculated as:

[0035]

[0036]

[0037] Among them, V top and V base Respectively represent the high and low level values ​​of the signal to be measured, V crossing Indicates the crossover level, V hystersis_high 、V hystersis_low Respectively represent the upper and lower limits of the hysteresis range.

[0038] (4) Traverse all sampling points, find the sampling moments corresponding to the crossover level, which are the transition moments of the signal to be measured, and then store these transition moments in an array;

[0039] In this embodiment, the specific method for obtaining each transition moment of the signal to be tested is:

[0040] (4.1) Traverse all sampling points and find all continuous sampling point segments that cross the hysteresis range, which are regarded as valid signal edges. If there is a sampling point whose level value is equal to the crossover level value in these segments, the sampling moment corresponding to the sampling point is the signal jump moment, otherwise, go to step (4.2);

[0041] (4.2) Find the two sampling points above and below the crossing level of the effective signal edge, and perform linear interpolation. The number of the actual sampling point is S i , i=1,2,…;…

[0042] Calculate the signal transition time T(E n ):

[0043]

[0044] V(E n )=V crossing

[0045] T s =T(S i+1 )-T(S i )

[0046] Among them, V(S i ) represents the sampling point S i The level value, T(S i ) represents the sampling point S i The corresponding sampling time, V(E n ) represents the trip point E n The level value, T(E n ) represents the trip point E n The jump time, n = 1, 2, ... represents the jump point number, T s is the sampling time interval between two adjacent sampling points.

[0047] In this embodiment, since the signal to be measured is collected by the ADC, the sampled data is the voltage value of a discrete point, so there may be no actual sampling point at the crossover level. Figure 3 As shown in the figure, the black dots S1, S2, ... are the actual sampling points, and the white dots E1, E2, ... are the points where the crossover level intersects with the signal edge, that is, the points at the time of signal jump. 14 and S 15 , S 30 and S 31 ) to perform linear interpolation and obtain the time information T(E1) and T(E2) of E1 and E2.

[0048] (5) Use the software phase-locked loop in the host computer to recover the reference jump time of the reference signal, and then subtract it from the corresponding jump time in the array to obtain a set of time interval error sequences; in this embodiment, the structure of the software phase-locked loop is as follows: Figure 4 As shown;

[0049] In this embodiment, the specific method for obtaining each reference jump time is:

[0050] (5.1), let each reference jump time be T(E' n ), n=1,2,…, let T(E′1)=T(E1);

[0051] (5.2) The transition time of the signal to be tested is T(E n ) and the reference transition time T(E' n ) are the input and output of the software phase-locked loop, and T(E n ) and T(E' n ) is used as the input of the phase detector in the software phase-locked loop, and the output of the phase detector is low-pass filtered through the loop filter;

[0052] The filtering result is compared with the reference jump time T(E' n ) and the duration of one symbol of the signal to be tested, the next reference transition time T(E' n+1 );

[0053] (5.3), the reference jump time T(E' n+1 ) is fed back to the input terminal and the jump time T(E n+1 ) and then make a difference, and repeat the above operation for the difference value to get the next reference jump time T(E' n+2 ), and so on, to obtain a reference transition moment that is consistent with the number of transition moments of the signal to be measured.

[0054] (6) Analyze the time interval error sequence in the time domain, frequency domain, and statistical domain to obtain the jitter measurement value;

[0055] (6.1), let the time interval error sequence obtained in step (5) be T;

[0056] (6.2), make a statistical histogram of the time interval error sequence T, such as Figure 5 As shown;

[0057] (6.3), integrating the statistical histogram from both sides to the middle, we get Figure 6 The distance between the two points where the straight line parallel to the horizontal axis and the curve intersects the bit error rate cumulative distribution function shown is the size of the overall jitter under a specific bit error rate. Since the number of time interval error samples required for statistical domain processing is very large, it takes a lot of time to obtain it directly, so the extrapolation method is used. The solid line is the actual sample data, and the dotted line is the extrapolated sample data;

[0058] (6.4), move the left and right branches of the bit error rate integral graph to the opposite sides respectively, and we get Figure 7 The bathtub curve shown;

[0059] (6.5), the bathtub curve is converted into a Q-factor curve with a linear tail through the Q function, such as Figure 8 As shown;

[0060] (6.6) Perform a linear fit on the tail of the Q factor curve to obtain a fitting straight line, and then calculate the deterministic jitter DJ and random jitter RJ based on the intercept and slope of the fitting straight line, and further obtain the total jitter TJ;

[0061] The calculation method of deterministic jitter DJ is:

[0062] DJ=μ L +μ R

[0063] Among them, μ L and μ R They are the intercepts of the two straight lines fitted at the tail of the Q factor curve;

[0064] The calculation method of random jitter RJ is:

[0065]

[0066] Among them, slope1 and slope2 are the slopes of the two straight lines fitted at the tail of the Q factor curve;

[0067] The total jitter TJ is calculated as:

[0068] TJ=DJ+14×RJ

[0069] (6.7) Determine the type of the signal to be tested. If the signal to be tested is a data signal, proceed to step (6.8); if the signal to be tested is a clock signal, proceed to step (6.9);

[0070] (6.8) If the signal to be measured is a data signal, the time interval error sequence T is averaged in the time domain according to the pattern length, and then the time interval error sequences before and after the average are subtracted to remove the random jitter and periodic jitter that are not related to the data pattern, and a set of time interval error sequences containing only data-related jitter is obtained. Among them, the time interval error sequence corresponding to the rising edge is recorded as The time interval error sequence corresponding to the falling edge is recorded as

[0071] Then, data correlation jitter DDJ, inter-symbol interference ISI, and duty cycle distortion DCD are obtained according to these three time interval error sequences;

[0072] The calculation method of data dependency jitter DDJ is:

[0073]

[0074] The calculation method of inter-symbol interference ISI is:

[0075]

[0076] The duty cycle distortion is calculated as:

[0077]

[0078] Among them, max(x) means taking the maximum value in sequence x, min(x) means taking the minimum value in sequence x, max[a,b] means taking the larger value of a and b; mean(x) means calculating the mean of sequence x.

[0079] Finally, the time interval error sequence T is subtracted from the time interval error sequence Get a set of time interval error sequences that do not contain data correlation jitter Then proceed to step (6.4);

[0080] (6.4), perform fast Fourier transform on the time interval error sequence and obtain the amplitude spectrum of the time interval error, such as Fig. 9 As shown;

[0081] A decision threshold is set, and the amplitude above the decision threshold is recorded as periodic jitter, otherwise it is recorded as random jitter;

[0082] Finally, the periodic jitter and random jitter are respectively subjected to inverse Fourier transform to obtain the time interval error sequence T containing only the periodic jitter. PJ and the time error interval sequence T containing only random jitter RJ , and express periodic jitter and random jitter in peak-to-peak and RMS values ​​respectively.

[0083] The calculation method of periodic jitter PJ is:

[0084] PJ=max(T PJ )-min(T PJ )

[0085] Among them, max(T PJ )、min(T PJ ) are the time interval error sequences T containing only periodic jitter. PJ The maximum and minimum values ​​of ;

[0086] The calculation method of random jitter RJ is:

[0087] RJ=RMS(T RJ )

[0088] Among them, RMS(T RJ ) represents the time interval error sequence T containing only random jitter. RJ The root mean square value of .

[0089] Although the above describes the illustrative specific embodiments of the present invention to facilitate those skilled in the art to understand the present invention, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations using the concept of the present invention are protected.

Claims

1. A jitter measurement method combining time domain, frequency domain and statistical domain in a digital oscilloscope, characterized in that: The following steps are involved: (1) Collecting the signal to be tested through the acquisition system of the digital oscilloscope to obtain continuous sampling data including multiple edges of the signal to be tested; (2) The FPGA of the digital oscilloscope forwards the sampled data to the host computer, and then performs amplitude histogram statistics on the sampled data to obtain the high level and low level of the signal to be tested; (3) Calculate the hysteresis range and crossover level based on the high level and low level of the signal to be measured; (4) Traverse all sampling points, find the sampling moments corresponding to the crossover level, which are the transition moments of the signal to be measured, and then store these transition moments in an array; (5) Use the software phase-locked loop in the host computer to recover the reference jump time of the reference signal, and then subtract it from the corresponding jump time in the array to obtain a set of time interval error sequences; (6) Analyze the time interval error sequence in the time domain, frequency domain, and statistical domain to obtain the jitter measurement value.

2. The jitter measurement method combining time domain, frequency domain and statistical domain in a digital oscilloscope according to claim 1, characterized in that: The signal to be tested is a clock signal or a data signal. If it is a data signal, it must have a repeated data pattern.

3. The jitter measurement method combining time domain, frequency domain and statistical domain in a digital oscilloscope according to claim 1, characterized in that: The calculation method of the hysteresis range and the crossover level is: Among them, V top and V base Respectively represent the high and low level values ​​of the signal to be measured, V crossing Indicates the crossover level, V hystersis_high 、V hystersis_low Respectively represent the upper and lower limits of the hysteresis range.

4. The jitter measurement method combining time domain, frequency domain and statistical domain in a digital oscilloscope according to claim 1, characterized in that: The method for obtaining each transition moment of the signal to be tested in step (4) is: (4.1) Traverse all sampling points and find all continuous sampling point segments that cross the hysteresis range, which are regarded as valid signal edges. If there is a sampling point whose level value is equal to the crossover level value in these segments, the sampling moment corresponding to the sampling point is the signal jump moment, otherwise, go to step (4.2); (4.2) Find two sampling points above and below the intersection of the effective signal edge and perform linear interpolation. The number of the sampling point after linear interpolation is S. i , i=1,2,…; Calculate the signal transition time T(E n ): V(E n )=V crossing T s =T(S i+1 )-T(S i ) Among them, V(S i ) represents the sampling point S i The level value, T(S i ) represents the sampling point S i The corresponding sampling time, V(E n ) represents the trip point E n The level value, T(E n ) represents the trip point E n The jump time, n = 1, 2, ... represents the jump point number, T s is the sampling time interval between two adjacent sampling points.

5. The jitter measurement method combining time domain, frequency domain and statistical domain in a digital oscilloscope according to claim 1, characterized in that: The method for obtaining each reference jump time in step (5) is: (5.1), let each reference jump time be T(E' n ), n=1,2,..., let T(E'1)=T(E1); (5.2) The transition time of the signal to be tested is T(E n ) and the reference jump time T(E' n ) are the input and output of the software phase-locked loop, and T(E n ) and T(E' n ) is used as the input of the phase detector in the software phase-locked loop, and the output of the phase detector is low-pass filtered through the loop filter; The filtering result is compared with the reference jump time T(E' n ) and the duration of one symbol of the signal to be tested, the next reference transition time T(E' n+1 ); (5.3), the reference jump time T(E' n+1 ) is fed back to the input terminal and the transition time T(E n+1 ) and then make a difference, repeat the above operation with the difference value to get the next reference jump time T(E' n+2 ), and so on, to obtain a reference transition moment that is consistent with the number of transition moments of the signal to be measured.

6. The jitter measurement method combining time domain, frequency domain and statistical domain in a digital oscilloscope according to claim 1, characterized in that: The method for obtaining the jitter measurement value in step (6) is: (6.1), let the time interval error sequence obtained in step (5) be T; (6.2) Make a statistical histogram of the time interval error sequence T; (6.3) Integrate the statistical histogram from both sides to the middle to obtain the bit error rate integral graph; (6.4), move the left and right branches of the bit error rate integral graph to the opposite sides respectively, and obtain the bathtub curve; (6.5), convert the bathtub curve into a Q-factor curve with a linear tail through the Q function; (6.6) Perform a linear fit on the tail of the Q factor curve to obtain a fitting straight line, and then calculate the deterministic jitter DJ and random jitter RJ based on the intercept and slope of the fitting straight line, and further obtain the total jitter TJ; (6.7) Determine the type of the signal to be tested. If the signal to be tested is a data signal, proceed to step (6.8); if the signal to be tested is a clock signal, proceed to step (6.9); (6.8) If the signal to be measured is a data signal, the time interval error sequence T is averaged in the time domain according to the pattern length, and then the time interval error sequences before and after the average are subtracted to remove the random jitter and periodic jitter that are not related to the data pattern, and a set of time interval error sequences containing only data-related jitter is obtained. Among them, the time interval error sequence corresponding to the rising edge is recorded as The time interval error sequence corresponding to the falling edge is recorded as Then, data correlation jitter DDJ, inter-symbol interference ISI, and duty cycle distortion DCD are obtained according to these three time interval error sequences; Finally, the time interval error sequence T is subtracted from the time interval error sequence Get a set of time interval error sequences that do not contain data correlation jitter Then proceed to step (6.4); (6.4) Perform fast Fourier transform on the time interval error sequence to obtain the amplitude spectrum of the time interval error; A decision threshold is set, and the amplitude above the decision threshold is recorded as periodic jitter, otherwise it is recorded as random jitter; Finally, the periodic jitter and random jitter are respectively subjected to inverse Fourier transform to obtain the time interval error sequence T containing only the periodic jitter. PJ and the time error interval sequence T containing only random jitter RJ , and the periodic jitter and random jitter are expressed as peak-to-peak value and RMS value respectively.

7. The jitter measurement method combining time domain, frequency domain and statistical domain in a digital oscilloscope according to claim 6, characterized in that: The calculation method of the deterministic jitter DJ is: DJ=μ L +m R Among them, μ L and μ R They are the intercepts of the two straight lines fitted at the tail of the Q factor curve; The calculation method of the random jitter RJ is: Among them, slope1 and slope2 are the slopes of the two straight lines fitted at the tail of the Q factor curve; The total jitter TJ is calculated as: TJ=DJ+14×RJ The calculation method of the periodic jitter PJ is: PJ=max(T PJ )-min(T PJ ) Among them, max(T PJ )、min(T PJ ) are the time interval error sequences T containing periodic jitter respectively. PJ The maximum and minimum values ​​of ; The calculation method of the data dependency jitter DDJ is: in, are the time interval error sequences containing data correlation jitter The maximum and minimum values ​​of ; The calculation method of the inter-symbol interference ISI is: in, and They are The time interval error sequence corresponding to the rising and falling edges, max(x) means taking the maximum value in the sequence x, min(x) means taking the minimum value in the sequence x, and max[a,b] means taking the larger value of a and b; The calculation method of the duty cycle distortion is: Here, mean(x) means calculating the mean of the sequence x.

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