JP2006003255A - Jitter measuring method and jitter measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To grasp accurately pattern-dependent jitter. <P>SOLUTION: Waveform information of a data signal wherein noise jitter is suppressed by averaging data signals to be measured is generated by time-series data at fixed intervals shorter than the period of a clock signal having a frequency corresponding to a bit rate (S1), and a wide-band clock reproduction processing is performed to the waveform information (S2), and a clock signal including the pattern-dependent jitter is reproduced. Then, the reproduced clock signal is subjected to phase detection to thereby determine phase variation of each bit position (S3), and the phase variation is subjected to filter processing in a jitter measuring band specified beforehand by the bit rate of the data signal to the phase variation, to thereby determine the pattern-dependent jitter in each bit (S4). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a technique for measuring pattern-dependent jitter generated depending on a data signal pattern among jitter components included in a data signal.

In a data transmission system, when the phase fluctuation (jitter) of the data signal increases, the data signal cannot be transmitted normally.
For this reason, it is necessary to measure in advance the jitter characteristics of the data transmission system and the devices constituting them.

  As one method for measuring the jitter of a data signal, as shown in FIG. 7, the data signal is input to a waveform observing apparatus to display its eye pattern, and the rising and falling edges of the displayed eye pattern are displayed. There is a method of grasping the jitter amount of the data signal from the width W of the crossing portion.

  A method for obtaining the jitter by observing the eye pattern of the data signal in this way is described in, for example, the following Patent Document 1.

JP-A-5-145582

  However, in the method of measuring jitter based on the eye pattern width W displayed on the waveform observation apparatus as described above, it is impossible to grasp pattern-dependent jitter generated depending on the pattern of the data signal.

  That is, the jitter does not depend on the pattern of the data signal to be transmitted, and has random noise or periodic noise generated due to noise of the device itself or external noise (hereinafter referred to as noise jitter). And pattern-dependent jitter generated due to the pattern of the data signal to be transmitted.

  Pattern-dependent jitter is a device that has a waveform distortion, a data signal duty cycle distortion, and a transmitted signal frequency that are caused by the inability to pass a DC component when the data transmission passband to be measured is high (several GHz). This jitter is caused by waveform distortion caused by insufficient frequency characteristics.

  This pattern-dependent jitter does not pose a major problem when the data signal is highly random like a pseudo-random pattern, but it is always the head of a data signal sequence actually used for data transmission, such as an SDH frame or SONET frame. In the case of a data signal having a specific pattern that is not scrambled at a position, a large pattern-dependent jitter occurs at the frame interval (for example, 125 μs interval).

  In addition, the frequency of the jitter generated at this frame interval falls within the frequency band defined by the jitter measurement of the SDH frame and SONET frame, so that it cannot be distinguished from the noise jitter component.

  In addition, in the measurement of jitter depending on the pattern of the data signal as described above, it is necessary to be able to grasp the relationship between the position of the data and the jitter, but in the observation of the eye pattern as described above, the accuracy of the relationship is accurate. It is also difficult to grasp.

  Therefore, it has been strongly desired to realize a jitter measuring apparatus and a jitter measuring method that can accurately grasp pattern-dependent jitter.

  An object of the present invention is to solve this problem and provide a jitter measuring method and a jitter measuring apparatus capable of accurately grasping pattern-dependent jitter.

In order to achieve the above object, a jitter measurement method according to claim 1 of the present invention comprises:
Generating waveform information of a signal in which a noisy jitter component independent of the pattern of the data signal is suppressed from the data signal to be measured from time-series data with a constant interval (S1);
Regenerating a clock signal including pattern dependent jitter from the generated waveform information (S2);
Detecting a phase fluctuation component of the regenerated clock signal (S3);
Performing a predetermined band limiting process on the detected phase fluctuation component and extracting the pattern-dependent jitter component (S4).

The jitter measuring apparatus according to claim 2 of the present invention is
A waveform data string generation unit (21) for generating waveform information of a signal in which a noisy jitter component independent of a data signal pattern is suppressed from a data signal to be measured as time-series data with a constant interval;
A clock recovery means (22) for recovering a clock signal including pattern-dependent jitter from the waveform information generated by the waveform data string generator;
Phase detection means (23) for detecting a phase fluctuation component of the clock signal reproduced by the clock reproduction means;
A band limiting unit (24) for performing a predetermined band limiting process on the output signal of the phase detection unit and extracting the pattern-dependent jitter component;
An evaluation calculation unit (25) for performing an evaluation calculation on the pattern-dependent jitter component extracted by the band limiting unit.

The jitter measuring apparatus according to claim 3 of the present invention is the jitter measuring apparatus according to claim 2,
The waveform data string generator is
The reference timing is the timing at which the level of the reference clock signal changes in a predetermined direction upon receiving the data signal to be measured and a reference clock signal having a frequency corresponding to the bit rate of the data signal to be measured and including no jitter. A time difference detecting means (21a) for obtaining a time difference of the level transition timing of the measured data signal with respect to the reference timing for a plurality of pattern periods of the measured data signal;
An average value calculating means (21c) for respectively obtaining an average value of the time differences for each level transition timing within the pattern period of the data signal under measurement based on the time difference obtained by the time difference detecting means;
Generates waveform information of a signal having a level transition with an average value of the time difference obtained by the average value calculation means with respect to each reference timing in the same pattern as the data signal to be measured as time-series data at regular intervals. Data string generation means (21d).

The jitter measuring apparatus according to claim 4 of the present invention is the jitter measuring apparatus according to claim 2,
The waveform data string generator is
The waveform information of the data signal to be measured is acquired for a plurality of pattern periods, averaged, and waveform information of the signal in which the noise jitter component is suppressed is generated.

  As described above, the jitter measuring method and apparatus according to the present invention generates waveform information of a signal in which a noise-dependent jitter component independent of a pattern is suppressed from a data signal to be measured using time-series data with a constant interval, and the generated waveform information Reproduce a clock signal containing jitter that depends on the pattern from the signal, detect the phase fluctuation component of the recovered clock signal, perform a predetermined band limiting process on the detected phase fluctuation component, and detect the pattern-dependent jitter component is doing.

  For this reason, it is possible to accurately measure the pattern-dependent jitter that has been subjected to the band limiting process defined by the jitter measurement such as SDH / SONET, which is impossible with the conventional eye pattern observation. .

First, the principle of the jitter measurement method of the present invention will be described.
As described above, the jitter component of the data signal includes pattern-dependent jitter that occurs depending on the pattern and noise-related jitter that does not depend on the pattern. Both jitters cause the level transition timing ( That is, the phase) varies.

  In order to extract a pattern-dependent jitter component from this phase variation, it is necessary to suppress the noise-related jitter component as much as possible.

  Here, at each level transition timing, the amount of phase fluctuation due to noise jitter can be suppressed to almost zero if averaged over a certain amount of time, so the level transition timing of the data signal under measurement or the measurement target By averaging the entire waveform of the data signal for a plurality of pattern periods, phase fluctuations due to the effects of noise jitter can be substantially eliminated.

  Since the phase fluctuation of the data signal in which the influence of the noise jitter is suppressed in this way is a component depending on the pattern of the data signal, the phase fluctuation component is extracted, and the phase fluctuation component is extracted from the extracted phase fluctuation component. The pattern-dependent jitter can be obtained quantitatively by performing filtering with a filter having a predetermined band limiting characteristic.

  In order to perform this filtering process, the sampling period of the signal to be processed needs to be constant. However, the data signal to be measured is generally in NRZ format, and level transition does not occur during a period in which the same code continues. Therefore, the phase fluctuation amount of each bit cannot be obtained within a period in which the same code continues, and the sampling period of data applied to the filter changes depending on the data code, and thus the filtering process cannot be performed correctly.

  Therefore, in the present invention, as shown in the flowchart of FIG. 1, the waveform information of the data signal obtained by averaging the measured data signal and suppressing the noise jitter is represented by the frequency corresponding to the bit rate of the data signal. A time-series data having a constant interval shorter than the cycle of the clock signal is generated (S1), and a wide-band clock recovery process (S2) is performed on the waveform information to recover a clock signal including pattern-dependent jitter.

  Then, the recovered clock signal is phase-detected to determine the phase fluctuation amount at each bit position (S3), and the phase fluctuation amount is subjected to filter processing in a jitter measurement band preliminarily defined by the bit rate of the data signal. As a result, a pattern-dependent jitter for each bit is obtained (S4), an evaluation operation is performed on the jitter, and the result is output (S5).

  According to the above method, the phase fluctuation amount for each bit of the data signal can be obtained, and the pattern dependent jitter of the data signal to be measured can be accurately measured by the filtering process.

FIG. 2 shows the configuration of the jitter measuring apparatus 20 of the present invention based on the above method.
The jitter measuring device 20 is generated based on a reference clock signal CK having a predetermined frequency output from a measurement target, a frame synchronization signal S, and a reference clock signal CK, and a predetermined frame number N is used to form one frame. This is for receiving the pattern-measured data signal Dr in the NRZ format and measuring the pattern-dependent jitter of the measured data signal Dr.

  Here, the entire N-bit data string constituting one frame is described as the measured data signal Dr. For example, an N-bit header portion in an SDH / SONET frame having a bit rate of about 2.5 Gbps or about 10 Gbps. Only the measured data signal Dr may be used.

  Further, assuming that the reference clock signal CK does not include jitter, the data signal Dr to be measured will be described as an electrical signal.

  The measured data signal Dr is input to the waveform data string generator 21 together with the reference clock signal CK and the frame synchronization signal S.

  As shown in FIG. 3, the waveform data string generation unit 21 includes a time difference detection unit 21a, a memory 21b, an average value calculation unit 21c, and a data string generation unit 21d.

The time difference detecting means 21a receives the frame synchronization signal S, the reference clock signal CK and the data signal Dr to be measured shown in FIGS. 4A, 4B and 4C, and the level of the reference clock signal CK is in a predetermined direction ( for example the timing of transitions in the rising direction) as a reference timing t _r, the time difference T (i) between the reference timing t _r and level transition timing t _i of the rising and falling of the measured data signal Dr, a predetermined resolution ΔT A plurality of pattern periods are obtained and stored in the memory 21b.

Here, each time the rising (or falling) timing of the reference clock signal CK as a reference timing t _r, and the level transition timings t _i of the measured data signal Dr, the reference timing respectively corresponding to the level transition timing it is assumed to determine the difference as the time difference T (i) with, there is one in one frame of the reference clock signal CK (e.g., first) rising (or falling) timing as the reference timing t _r, the one the difference may be determined as the time difference T (i) between each level transition timings t _i of the reference timing t _r and the measured data signal Dr.

  The resolution ΔT is set to be significantly shorter than the period of the reference clock signal CK. For example, if the bit rate of the data signal to be measured Dr is 10 Gbps, the cycle of the reference clock signal CK is 100 ps (picoseconds), while the resolution ΔT is a value of 0.1 ps to 1 ps, for example.

  However, since it is not realistic to measure the time difference with a clock having a frequency of 1000 to 10000 GHz corresponding to the resolution ΔT, the frame synchronization signal S is used as a trigger signal, and the data signal Dr to be measured and the reference clock signal CK are set to an offset time ΔT. The waveform information is obtained with a resolution ΔT, and a plurality of time differences between the obtained rise timing (reference timing) of the reference clock signal waveform and each level transition timing of the measured data signal waveform are obtained. Are obtained and stored in the memory 21b.

  The average value calculation means 21c averages the time difference values stored in the memory 21b for each level transition timing in the pattern period.

  For example, when an N-bit data signal to be measured is level-shifted P times within one pattern period and a time difference corresponding to m pattern periods is obtained, the time difference T1 (1) to T1 (P) of the level transition timing of each pattern period , T2 (1) to T2 (P),..., Tm (1) to Tm (P) average values (hereinafter referred to as time difference average values) Ta1 to TaP are respectively calculated by the following calculations.

Ta1 = {T1 (1) + T2 (1) + ...... + Tm (1)} / m
Ta2 = {T1 (2) + T2 (2) + ...... + Tm (2)} / m
…………
TaP = {T1 (P) + T2 (P) + ...... + Tm (P)} / m

These time difference average values Ta1 to TaP are output to the data string generation means 21d.
As shown in FIG. 5, the data string generation means 21d has the same pattern as the pattern of the data signal to be measured specified in advance, and the time difference average value for each reference timing _tr (or the one reference timing described above). A data string x (k) whose level is changed between Ta1 and TaP is generated at intervals of ΔT.

  This waveform data is a data string that switches from a value 0 to a value 1 or from a value 1 to a value 0 with a level transition timing as a boundary.

  In this way, the phase fluctuation due to noise jitter is suppressed, and the waveform data string x (k) having only the phase fluctuation due to pattern dependent jitter is output to the clock recovery means 22.

  The clock recovery means 22 performs a broadband clock recovery process on the waveform data string output from the waveform data string generator 21 to recover the clock signal CKj including pattern-dependent jitter.

  For example, as shown in FIG. 6, the clock recovery means 22 delays the waveform data string x (k) by ½ period of the reference clock signal CK by the delay unit 22a, and the delayed waveform data string x (k). 'And the original waveform data string x (k) are input to an exclusive OR (EX-OR) circuit 22b, and converted into data of 1 when the two do not match and 0 when they match.

  By this process, for example, 1-bit data in the NRZ format is converted into 1 and 0 data, that is, a signal having a frequency equal to the frequency of the clock signal.

  The output y (k) of the exclusive OR circuit 22b is input to the filter 22c. The filter 22c performs a filtering process on the signal y (k) so that the center frequency is the clock frequency and the pass bandwidth is, for example, about four times the jitter measurement band. For example, if the clock frequency is 10 GHz and the upper limit of the jitter measurement band is 80 MHz, a band limiting process of 10 GHz ± 320 MHz is performed.

  The signal y (k) ′ output from the filter 22 c in a substantially sine wave shape is shaped into a rectangular wave clock signal CKj by the waveform shaping circuit 22 d and outputted to the phase detection means 23.

  Note that the clock recovery means 22 is not limited to the method of filtering the data signal by doubling the data as described above, but may be configured by a PLL circuit that feedback-controls the frequency and phase of the VCO so as to match the phase of the data signal. Good.

  The phase detection unit 23 detects the phase fluctuation of the clock signal CKj output from the clock recovery unit 22.

  In this detection, a time difference j (1) to j (N) between each timing of rising (or falling) of the clock signal CKj for one pattern period and a reference timing corresponding to the bit rate of the measured data signal Dr. Is detected.

  The band limiting unit 24 performs band limiting processing defined by the bit rate on the time difference data j (1) to j (N) obtained by the phase detection unit 23, and extracts the jitter component J.

  This bandwidth limiting means 24 is, for example, ITU-TO. In the case of SDH / SONET with a bit rate of about 2.5 Gbps, 5 kHz to 20 MHz, 12 kHz to 20 MHz, Any band limiting process of 1 MHz to 20 MHz is performed. Further, when the bit rate is about 10 Gbps, any one of the band limiting processes of 20 kHz to 80 MHz, 50 kHz to 80 MHz, and 4 MHz to 80 MHz is performed.

  The time difference data input to the band limiting unit 24 is obtained at regular intervals for each clock cycle, and since there is no omission, the above-mentioned specified band limiting process can be performed correctly, and accurate jitter is detected. be able to.

  Note that the high-speed processing of the clock recovery processing by the clock recovery means 22, the phase fluctuation detection processing by the phase detection means 23, and the band limitation processing by the band limitation means 24 described above is an arithmetic processing (ΔT interval data string x (k) Software processing).

  The pattern-dependent jitter obtained by this band limiting process can be evaluated in the jitter measurement band defined by SDH / SONET or the like.

  The evaluation calculation unit 25 calculates, for example, the magnitude (pp value) or effective value (rms) from the negative peak value to the positive peak value of the jitter signal sequence J output from the band limiting unit 24. This is output as a pattern-dependent jitter measurement result Jdp to a display unit, printer, or external device (not shown).

  The measurement result may be output after being converted into a unit of UI (unit interval) in addition to the phase difference expressed in units of time as described above.

  As described above, in the jitter measuring apparatus 20 and the measuring method according to the embodiment, the waveform information of the data signal in which the noise jitter component is suppressed by the averaging process on the data signal to be measured is generated, and the wideband clock reproduction is performed on the waveform. Processing and phase detection processing of the recovered clock signal to obtain phase change data for all bits in the pattern period of the data signal to be measured, and a prescribed band limiting process for the phase change information Is used to measure pattern-dependent jitter.

  For this reason, it is possible to accurately measure only pattern-dependent jitter, which was impossible with conventional eye pattern observation.

  Further, since the pattern-dependent jitter subjected to the band limitation process can be obtained for all the bit positions in the pattern period of the data signal to be measured, the relationship between the bit position and the pattern-dependent jitter can be easily grasped.

  In order to generate the waveform of the data signal in which the noise jitter is suppressed, the waveform data string generation unit 21 according to the embodiment, for example, rises of the reference clock signal CK without jitter and each level transition timing of the data signal to be measured. Is obtained by averaging the data for a plurality of pattern periods and artificially generating a data signal sequence whose level transition is caused by the averaged time difference. By generating the waveform information of the signal for a plurality of pattern periods and performing an averaging process including the entire waveform, that is, including the time axis and the amplitude axis, a waveform of the data signal with suppressed noise jitter is generated, This may be output to the clock recovery means 22.

  Of the constituent elements of the waveform data string generation unit 21 described above, at least the time difference detection means 21a, the memory 21b, and the average value calculation means 21c can be configured using the sampling and calculation functions of an existing digital sampling oscilloscope. It is.

  In addition, when the waveform of a data signal with suppressed noise jitter is generated by averaging the entire waveform information as described above, the data averaging can be simplified by using the waveform averaging mode of the digital sampling oscilloscope. Can be obtained.

  In the above description, the case where the input signal is an electrical signal has been described. However, in the case of an optical signal, it may be converted into an electrical signal by a photoelectric converter and input as described above. A device that performs equivalent time sampling with respect to an optical signal with a high-speed optical sampling pulse has been realized. By using such an optical-compatible digital sampling oscilloscope, the jitter measuring apparatus can be easily configured.

The flowchart which shows the procedure of the jitter measuring method of this invention The figure which shows the structure of embodiment of this invention The figure which shows the structural example of the principal part of embodiment. The figure for demonstrating the operation | movement of the principal part of embodiment. The figure for demonstrating the operation | movement of the principal part of embodiment. The figure which shows the structural example of the principal part of embodiment. Diagram for explaining a conventional jitter measurement method

Explanation of symbols

  DESCRIPTION OF SYMBOLS 20 ... Jitter measuring device, 21 ... Waveform data sequence generation part, 21a ... Time difference detection means, 21b ... Memory, 21c ... Average value calculation means, 21d ... Data sequence generation means, 22 ... Clock reproduction means , 23... Phase detection means, 24... Band limiting means, 25.

Claims (4)

Generating waveform information of a signal in which a noisy jitter component independent of the pattern of the data signal is suppressed from the data signal to be measured from time-series data with a constant interval (S1);
Regenerating a clock signal including pattern dependent jitter from the generated waveform information (S2);
Detecting a phase fluctuation component of the regenerated clock signal (S3);
A jitter measurement method comprising: performing a predetermined band limiting process on the detected phase fluctuation component and extracting the pattern-dependent jitter component (S4). A waveform data string generation unit (21) for generating waveform information of a signal in which a noisy jitter component independent of a data signal pattern is suppressed from a data signal to be measured as time-series data with a constant interval;
A clock recovery means (22) for recovering a clock signal including pattern-dependent jitter from the waveform information generated by the waveform data string generator;
Phase detection means (23) for detecting a phase fluctuation component of the clock signal reproduced by the clock reproduction means;
A band limiting unit (24) for performing a predetermined band limiting process on the output signal of the phase detection unit and extracting the pattern-dependent jitter component;
A jitter measurement apparatus comprising: an evaluation calculation unit (25) that performs an evaluation calculation on the pattern-dependent jitter component extracted by the band limiting unit. The waveform data string generator is
The reference timing is the timing at which the level of the reference clock signal changes in a predetermined direction upon receiving the data signal to be measured and a reference clock signal having a frequency corresponding to the bit rate of the data signal to be measured and including no jitter. A time difference detecting means (21a) for obtaining a time difference of the level transition timing of the measured data signal with respect to the reference timing for a plurality of pattern periods of the measured data signal;
An average value calculating means (21c) for respectively obtaining an average value of the time differences for each level transition timing within the pattern period of the data signal under measurement based on the time difference obtained by the time difference detecting means;
Generates waveform information of a signal having a level transition with an average value of the time difference obtained by the average value calculation means with respect to each reference timing in the same pattern as the data signal to be measured as time-series data at regular intervals. 3. The jitter measuring apparatus according to claim 2, further comprising a data string generating means (21d). The waveform data string generator is
3. The jitter measuring apparatus according to claim 2, wherein the waveform information of the data signal under measurement is acquired for a plurality of pattern periods and averaged to generate waveform information of the signal in which the noise jitter component is suppressed.

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