JP2005278014A - Device and method for measuring digital error rate and digital data transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable digital error rate measurement in a high-speed digital transmission at a high-speed system level, which has been impossible if it is performed by a conventional method wherein a sending pattern and a received pattern are compared directly, or by the use of a measuring device for exclusive use. <P>SOLUTION: A high frequency attenuation mechanism 3 being switchable is provided in the middle of a transmission line 4, and the standard deviation of random jitters is found by transmitting a pattern wherein 1 and 0 change each cycle. A jitter at a high frequency attenuation time and a jitter at a normal time are found, and from the difference between the both a jitter increase amount is found, and a digital error rate at the high frequency attenuation time is found. A digital error rate at a normal time is calculated from the digital error rate at the high frequency attenuation time, the standard variation, and the jitter increase amount. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  Currently, transmission systems using high-speed serial signals are becoming mainstream in systems that transmit large volumes of digital data. In high-speed serial transmission, the frequency component of the signal extends to a high frequency, so that the signal deteriorates due to various factors. For this reason, it is necessary to measure the code error rate in the system and evaluate the reliability of data transfer.

However, the code error rate measurement of the conventional digital signal transmission is performed by actually flowing data from the data sending unit to the data receiving unit in the system, and detecting the code error by directly comparing the sending pattern and the receiving pattern. The error rate was measured. Alternatively, a method of measuring the code error rate using a dedicated measuring instrument has been taken (for example, Non-Patent Document 1).
Agilent Technologies, “10GbE technology and device characterization”, [online], October 1, 2002, [March 4, 2004 search], Internet <URL: // literature. Agilent. com / litweb / pdf / 5988-6960JA. pdf>

  Conventional code error rate measurement in which data is actually transmitted and the transmission pattern and reception pattern are directly compared, depending on the required transmission quality, an extremely long measurement time is required to detect the error and determine the code error rate There was a problem of becoming.

  In addition, when measuring using a dedicated measuring instrument, the data sending unit and the data receiving unit are those of the measuring instrument, so that it is impossible to measure the code error rate in an actual system, and the measuring instrument itself is expensive. There was a problem that there was.

  The present invention has been made to solve the above-described problems, and provides a means for performing system-level code error rate measurement of high-speed digital electric signal transmission such as backplane transmission at high speed and at low cost. With the goal.

The code error rate measuring apparatus according to the present invention is:
A code error rate measurement apparatus for measuring a code error rate by transmission using a measurement value of received data received via a transmission path as input, and comprising the following elements (1) Fitting the jitter histogram of the waveform of the above pattern with a normal distribution for the measured value of the received data measured by transmitting the transmission data with a pattern that changes between 1 and 0 every cycle without performing high-frequency attenuation in the transmission path The standard deviation calculation unit for obtaining the standard deviation of random jitter (2) From the measured value of the received data measured by transmitting the transmission data of the random pattern without performing high frequency attenuation in the transmission path, the jitter at the normal time is calculated. Calculate
Furthermore, the jitter at the time of high frequency attenuation is calculated from the measured value of the received data measured by transmitting the random pattern transmission data by performing high frequency attenuation in the transmission path,
Furthermore, an increase jitter amount calculation unit that calculates an increase jitter amount by subtracting the normal jitter from the jitter at the time of high frequency attenuation. (3) Measurement was performed by transmitting random pattern transmission data with high frequency attenuation in the transmission path. A code error rate calculation unit for high frequency attenuation that calculates a code error rate at the time of high frequency attenuation from a measured value of received data. (4) The code error rate at the time of high frequency attenuation, the increased jitter amount, and the standard deviation of the random jitter And a normal code error rate calculation unit that calculates a normal code error rate without performing high-frequency attenuation.

  Since the data transmission unit and data reception unit in an actual system are used and the code error rate is measured indirectly from information such as waveforms, a conventional method for directly comparing the transmission pattern and the reception pattern and a dedicated measuring instrument are used. This makes it possible to perform a high-speed system-level code error rate measurement, which was not possible with the measurement used.

  Moreover, since the measuring instrument used in this method is only a waveform measuring instrument, it can be implemented at a very low cost.

Embodiment 1 FIG.
FIG. 1 is a configuration diagram of a digital data transmission system according to the first embodiment.

  In FIG. 1, reference numeral 1 denotes a data transmission unit, which is connected to the data reception unit 2 via a transmission line 4a, a high-frequency attenuation mechanism 3 capable of switching between valid and invalid, and a transmission line 4b. Reference numeral 5 denotes an observation point of the transmission waveform close to the data receiving unit 2, and the waveform can be observed with a measuring instrument such as an oscilloscope.

  Next, the measurement principle of the code error rate will be described.

FIG. 2 is a schematic diagram showing a transmission waveform eye pattern and a jitter histogram. As shown in this figure, the jitter histogram can be approximately modeled as the sum of two normal distributions. (A) is an eye pattern, (b) is a jitter histogram in a normal state in which the high frequency attenuation mechanism is disabled, and (c) is a jitter histogram in a case where the high frequency attenuation mechanism is enabled. It represents an increase. DJ ₀ deterministic jitter in a normal state in Fig, DJ ₊ the deterministic jitter due to the enabled high-frequency damping mechanism increment, T _S is the data from the peak position of the normal distribution of enabling high frequency attenuation mechanism This is the time until the sampling time.

Here, if the bit error rate in a state of enabling high frequency attenuation mechanism and BER _2, the equation to be satisfied T _S

となる。ただし時間の単位はランダムジッタの標準偏差σで正規化している。Ｐ_ｔｄはデータの遷移確率でデータパターンにより決まる。

It becomes. However, the unit of time is normalized by the standard deviation σ of random jitter. P _td is a data transition probability and is determined by a data pattern.

With T _S obtained from Equation from the peak position of the normal distribution in the normal state of disabling the high frequency attenuation mechanism time to the sampling time of 2 from (b)

とかけるから、通常状態での符号誤り率（ＢＥＲ）は

Therefore, the code error rate (BER) in the normal state is

となる。すなわち、高周波減衰機構が有効なときの符号誤り率、高周波減衰機構を有効にしたことによるジッタの増分、ランダムジッタの標準偏差の３つの値から、高周波減衰機構を無効にした通常の状態における符号誤り率を求めることができる。

It becomes. That is, the code in the normal state where the high frequency attenuation mechanism is disabled is calculated from the three values of the code error rate when the high frequency attenuation mechanism is effective, the increment of jitter due to the high frequency attenuation mechanism being enabled, and the standard deviation of the random jitter. The error rate can be obtained.

  Next, a procedure for measuring the code error rate will be described.

  In the configuration diagram of FIG. 1, the high-frequency attenuation mechanism 3 is disabled and the data pattern transmitted from the data transmission unit 1 is a pattern in which 1 and 0 change in each cycle. The waveform at that time is measured at the waveform observation point 5. FIG. 3 is a diagram showing a measurement example of a pattern that changes every cycle. If the data pattern to be transmitted is a pattern in which 1 and 0 change in each cycle, components that depend on the data pattern can be removed from the factors that constitute deterministic jitter. Can be analyzed.

  The jitter histogram of the waveform of the pattern that changes in each cycle 1 and 0 obtained by measurement is fitted with a normal distribution to obtain the standard deviation of random jitter. When a plurality of normal distributions are superimposed, the largest value is adopted. FIG. 4 is a diagram illustrating an analysis example of the jitter histogram of the measurement example of FIG.

  The data pattern sent from the data sending unit 1 is a random pattern. The waveform at that time is measured at the waveform observation point 5 to determine the jitter value. FIG. 5 is a diagram illustrating a measurement example when the high-frequency attenuation mechanism is invalid.

  Next, the high frequency attenuation mechanism 3 is enabled and the data pattern transmitted from the data transmission unit 1 is set as a random pattern. The waveform at that time is measured at the waveform observation point 5, the value of jitter is obtained, and the amount of jitter increased by enabling the high-frequency attenuation mechanism 3 is calculated. FIG. 6 is a diagram illustrating a measurement example when the high-frequency attenuation mechanism is effective. Further, when the high frequency attenuation mechanism 3 is enabled, jitter increases and a code error occurs in a short time, so that the code error rate can be measured in a short time. The code error rate at this time is measured.

  By using the above procedure to calculate the code error rate when the high-frequency attenuation mechanism is enabled, the jitter increment caused by enabling the high-frequency attenuation mechanism, and the standard deviation of random jitter, A code error rate in a normal state in which the attenuation mechanism is invalid can be obtained.

  As described above, in the first embodiment, the data transmission unit and the data reception unit in an actual system are used, and the code error rate is indirectly measured from information such as a waveform. This makes it possible to perform a high-speed system-level code error rate measurement that cannot be performed by a method of directly comparing received patterns or measurement using a dedicated measuring instrument.

  Moreover, since the measuring instrument used in this method is only a waveform measuring instrument, it can be implemented at a very low cost.

Embodiment 2. FIG.
A code error rate measuring apparatus and method for executing the method shown in the first embodiment will be described.

  FIG. 7 is a diagram illustrating a configuration of the code error rate measuring apparatus. The standard deviation calculating unit 71, the increased jitter amount calculating unit 72, the high frequency decay time code error rate calculating unit 73, and the normal time code error rate calculating unit 74 are configured. The normal code error rate calculation unit 74 will be described in detail with reference to FIG.

  FIG. 8 is a diagram showing the overall processing flow of the code error rate measurement method. First, the standard deviation calculation unit 71 performs standard deviation calculation processing (S801). In this processing, the jitter histogram of the waveform of the above pattern is used for the measured value of the received data measured by transmitting the transmission data having a pattern that changes between 1 and 0 for each cycle without performing high-frequency attenuation in the transmission path. Fitting with a normal distribution to obtain the standard deviation of random jitter.

  Next, the increased jitter amount calculation unit 72 performs an increased jitter amount calculation process (S802). In this process, the jitter at the normal time is calculated from the measured value of the received data measured by transmitting the transmission data of the random pattern without performing high frequency attenuation in the transmission path. Then, the jitter at the time of high frequency attenuation is calculated from the measured value of the received data measured by transmitting the transmission data of the random pattern by performing high frequency attenuation in the transmission path. Further, the increased jitter amount is calculated by subtracting the normal jitter from the jitter at the time of high frequency attenuation.

  Next, the high frequency attenuation code error rate calculation unit 73 performs high frequency attenuation code error rate calculation processing (S803). In this process, the code error rate at the time of high frequency attenuation is calculated from the measured value of the received data measured by transmitting the transmission data of the random pattern by performing high frequency attenuation in the transmission path.

  Finally, the normal code error rate calculation unit 74 performs a normal code error rate calculation process (S804). In this processing, the normal code error rate without high frequency attenuation is calculated based on the code error rate at high frequency attenuation, the increased jitter amount, and the standard deviation of random jitter.

  FIG. 9 is a diagram illustrating a configuration of a normal code error rate calculation unit. It has a high frequency attenuation peak position calculation unit 91, a normal time vs. peak interval calculation unit 92, and a code error rate calculation unit 93.

  FIG. 10 is a diagram showing a normal code error rate calculation processing flow. The high frequency attenuation peak position calculation unit 91 performs high frequency attenuation peak position calculation processing (S1001). In this process, according to the normal distribution of the jitter histogram at the time of high-frequency attenuation normalized by the standard deviation of random jitter, the code error rate at the time of high-frequency attenuation and the transition probability of the data determined from the data pattern The peak position of the normal distribution at the time of high frequency attenuation is calculated.

  Next, the normal time vs. peak interval calculation unit 92 performs normal time vs. peak interval calculation processing (S1002). In this process, half of the increased jitter amount is added to the peak position of the normal distribution at the time of high-frequency attenuation to obtain the normal time vs. peak interval, which is the time from the normal distribution peak position to the sampling position.

  Finally, the code error rate calculation unit 93 performs code error rate calculation processing (S1003). In this process, the normal code error rate is calculated from the normal time vs. peak interval and data transition probability according to the normal distribution of the normal jitter histogram with the time unit normalized by the standard deviation of random jitter. .

  By operating in this way, the measurement according to the first embodiment can be automated.

Embodiment 3 FIG.
FIG. 11 is a configuration diagram of a digital transmission system according to the third embodiment. The high-frequency attenuation mechanism shown in FIG. 1 is a removable stub and a mechanism for attaching the stub.

  In FIG. 11, reference numeral 1 denotes a data sending unit which is connected to the data receiving unit 2 through a transmission line 4a, a mechanism 6a for attaching a stub, and a transmission line 4b. The mechanism 6a for attaching the stub is a through hole or the like provided on the substrate, and the stub 7a such as a coaxial cable can be attached by means such as soldering. When a stub is attached in the middle of the transmission line, the attenuation in the high frequency region increases, so that it operates as a high frequency attenuation mechanism. Reference numeral 5 denotes a transmission waveform observation point in the vicinity of the data receiving unit 2, and it is assumed that the waveform can be observed with a measuring instrument such as an oscilloscope.

  The procedure is the same as in the first and second embodiments. Effective / invalid switching of the high-frequency attenuation mechanism is realized by attaching and removing the stub 7.

  As described above, even in the third embodiment, the data transmission unit and the data reception unit in an actual system are used and the code error rate is indirectly measured from information such as a waveform. This makes it possible to perform a high-speed system-level code error rate measurement that cannot be performed by a method of directly comparing received patterns or measurement using a dedicated measuring instrument.

  Moreover, since the measuring instrument used in this method is only a waveform measuring instrument, it can be implemented at a very low cost.

  Furthermore, this method can be applied to existing systems that are not supposed to be applied to this method, as long as the transmission waveform observation point close to the data receiver and a stub can be attached in the middle of the transmission line. be able to.

Embodiment 4 FIG.
FIG. 12 is a configuration diagram of a digital transmission system according to the fourth embodiment. The high-frequency attenuation mechanism shown in FIG. 1 is a removable capacitive element and a mechanism for attaching the capacitive element.

  In FIG. 12, reference numeral 1 denotes a data transmission unit, which is connected to the data receiving unit 2 through a transmission line 4a, a mechanism 6b for attaching a capacitive element, and the transmission line 4b. The mechanism 6b for attaching the capacitive element is a wiring pattern such as a land provided on the substrate. The capacitive element 7b such as a capacitor can be attached by means such as soldering, and the capacitive element 7b is connected via the capacitive element 7b. Connected to the ground plane 8. When a capacitive element is attached in the middle of the transmission line, the attenuation in the high frequency region becomes large, so that it operates as a high frequency attenuation mechanism. Reference numeral 5 denotes a transmission waveform observation point in the vicinity of the data receiving unit 2, and it is assumed that the waveform can be observed with a measuring instrument such as an oscilloscope.

  The procedure is the same as in the first and second embodiments. The effective / invalid switching of the high-frequency attenuation mechanism is realized by attaching and detaching the capacitive element 7b.

  As described above, even in the fourth embodiment, the data transmission unit and the data reception unit in an actual system are used and the code error rate is indirectly measured from information such as a waveform. This makes it possible to perform a high-speed system-level code error rate measurement that cannot be performed by a method of directly comparing received patterns or measurement using a dedicated measuring instrument.

  Moreover, since the measuring instrument used in this method is only a waveform measuring instrument, it can be implemented at a very low cost.

  Furthermore, this method is an existing system that does not assume the application of this method, if the transmission waveform observation point close to the data receiver and a structure that allows the attachment of capacitive elements in the middle of the transmission line, Can be applied.

Embodiment 5 FIG.
FIG. 13 is a configuration diagram of the digital transmission system according to the fifth embodiment. The high-frequency attenuation mechanism shown in FIG. 1 is a detachable inductor and a mechanism for attaching the inductor.

  In FIG. 13, reference numeral 1 denotes a data sending unit, which is connected to the data receiving unit 2 through a transmission line 4a, mechanisms 6c and 6d for attaching an inductor, an inductor 7c, and a transmission line 4b. The mechanisms 6c and 6d for attaching the inductor are wiring patterns such as lands provided on the substrate, and the inductor 7c can be attached by means such as soldering. The inductor 7c is a chip component or a metal wire, and can be replaced with a component that hardly affects the frequency characteristics of the transmission line such as a 0 ohm resistor or a coaxial cable. When an inductor is attached in the middle of the transmission line, the attenuation in the high frequency region becomes large, and therefore it operates as a high frequency attenuation mechanism. Reference numeral 5 denotes a transmission waveform observation point in the vicinity of the data receiving unit 2, and it is assumed that the waveform can be observed with a measuring instrument such as an oscilloscope.

  The procedure is the same as in the first and second embodiments. The effective / invalid switching of the high-frequency attenuation mechanism is realized by replacing the inductor 7c with a component that hardly affects the frequency characteristics of the transmission line such as a 0 ohm resistor or a coaxial cable.

  As described above, even in the fifth embodiment, the data transmission unit and the data reception unit in an actual system are used to indirectly measure the code error rate from information such as a waveform. This makes it possible to perform a high-speed system-level code error rate measurement that cannot be performed by a method of directly comparing received patterns or measurement using a dedicated measuring instrument.

  Moreover, since the measuring instrument used in this method is only a waveform measuring instrument, it can be implemented at a very low cost.

  Furthermore, this method is a structure that allows the observation point of the transmission waveform close to the data receiver and the chip parts in the middle of the transmission line to be replaced with inductors even in existing systems that are not supposed to be applied to this method. If so, it can be applied.

Embodiment 6 FIG.
FIG. 14 is a configuration diagram of a digital transmission system according to the sixth embodiment. The high-frequency attenuation mechanism of FIG. 1 is a transmission line having a variable length.

  In FIG. 14, reference numeral 1 denotes a data transmission unit which is connected to the data receiving unit 2 through a transmission line 4a, a transmission line 7d having a variable length, and a transmission line 4b. The transmission line 7d having a variable length is a coaxial cable, wiring on a substrate, or the like, and the wiring length can be changed by means such as cable replacement or a switch. Since the attenuation in the high frequency region increases as the transmission line becomes longer, it operates as a high frequency attenuation mechanism. Reference numeral 5 denotes a transmission waveform observation point in the vicinity of the data receiving unit 2, and it is assumed that the waveform can be observed with a measuring instrument such as an oscilloscope.

  The procedure is the same as in the first and second embodiments. The effective / invalid switching of the high-frequency attenuation mechanism is realized by changing the length of the transmission line 7d.

  As described above, also in the sixth embodiment, the data transmission unit and the data reception unit in an actual system are used and the code error rate is indirectly measured from information such as a waveform. This makes it possible to perform a high-speed system-level code error rate measurement that cannot be performed by a method of directly comparing received patterns or measurement using a dedicated measuring instrument.

  Moreover, since the measuring instrument used in this method is only a waveform measuring instrument, it can be implemented at a very low cost.

  Furthermore, this method can be applied to existing systems that are not supposed to be applied to this method, if the observation point of the transmission waveform close to the data receiver and the structure that can extend the transmission line in the middle of the transmission line are applicable. can do.

1 is a configuration diagram of a digital data transmission system according to Embodiment 1. FIG. It is a schematic diagram showing the eye pattern and jitter histogram of a transmission waveform. It is a figure which shows the example of a measurement of the pattern which changes for every cycle. It is a figure which shows the analysis example of the jitter histogram of the example of a measurement of FIG. It is a figure which shows the example of a measurement when a high frequency attenuation | damping mechanism is invalid. It is a figure which shows the example of a measurement when a high frequency attenuation | damping mechanism is effective. It is a figure which shows the structure of a code error rate measuring device. It is a figure which shows the whole processing flow of a code error rate measuring method. It is a figure which shows the structure of a normal time code error rate calculation part. It is a figure which shows the normal time code error rate calculation processing flow. 6 is a configuration diagram of a digital transmission system according to Embodiment 3. FIG. FIG. 6 is a configuration diagram of a digital transmission system according to a fourth embodiment. FIG. 10 is a configuration diagram of a digital transmission system according to a fifth embodiment. FIG. 10 is a configuration diagram of a digital transmission system according to a sixth embodiment.

Explanation of symbols

  71 standard deviation calculation unit, 72 increased jitter amount calculation unit, 73 high frequency attenuation code error rate calculation unit, 74 normal time code error rate calculation unit, 91 high frequency attenuation peak position calculation unit, 92 normal time vs. peak interval calculation unit, 93 Code error rate calculation unit.

Claims (9)

A code error rate measuring apparatus for measuring a code error rate by transmission using a measured value of received data received via a transmission path as input, and comprising the following elements: Measuring apparatus (1) A jitter histogram of the waveform of the above pattern for the measured value of the received data measured by transmitting the transmission data having a pattern that changes between 1 and 0 every cycle without performing high-frequency attenuation in the transmission path The standard deviation calculator (2) for obtaining a standard deviation of random jitter by fitting with a normal distribution, from the measured value of the received data measured by transmitting the transmission data of the random pattern without performing high-frequency attenuation in the transmission path, Calculate the normal jitter,
Furthermore, the jitter at the time of high frequency attenuation is calculated from the measured value of the received data measured by transmitting the random pattern transmission data by performing high frequency attenuation in the transmission path,
Furthermore, an increase jitter amount calculation unit that calculates an increase jitter amount by subtracting the normal jitter from the jitter at the time of high frequency attenuation. (3) Measurement was performed by transmitting random pattern transmission data with high frequency attenuation in the transmission path. A code error rate calculation unit for high frequency attenuation that calculates a code error rate at the time of high frequency attenuation from a measured value of received data. (4) The code error rate at the time of high frequency attenuation, the increased jitter amount, and the standard deviation of the random jitter And a normal code error rate calculation unit that calculates a normal code error rate without performing high-frequency attenuation. The code error rate measuring unit (A) according to claim 1, wherein the normal time code error rate calculation unit has the following elements, wherein the unit of time is normalized by a standard deviation of random jitter. According to the normal distribution of the jitter histogram, the high-frequency attenuation peak position calculation unit that calculates the peak position of the normal distribution at high-frequency attenuation based on the code error rate at high-frequency attenuation and the data transition probability determined from the data pattern ( B) Adding a half of the increased jitter amount to the peak position of the normal distribution at the time of high frequency attenuation to obtain the normal time vs. peak interval which is the time from the peak position of the normal distribution to the sampling position at the normal time Peak interval calculation part (C) According to the normal distribution of the jitter histogram at normal time in which the unit of time is normalized by the standard deviation of random jitter Serial and normal-to-peak interval, by a transition probability of the data, bit error rate calculation unit that calculates a bit error rate of normal. A code error rate measuring method by a code error rate measuring apparatus for measuring a code error rate by transmission using a measurement value of received data received via a transmission path as input, and having the following elements: Characteristic Code Error Rate Measurement Method (1) Regarding the measured value of received data measured by transmitting transmission data having a pattern in which 1 and 0 change every cycle without performing high-frequency attenuation in the transmission path, Standard deviation calculation processing to obtain the standard deviation of random jitter by fitting the jitter histogram of the pattern waveform with a normal distribution (2) Reception measured by transmitting random pattern transmission data without high frequency attenuation Calculate the normal jitter from the measured data,
Furthermore, the jitter at the time of high frequency attenuation is calculated from the measured value of the received data measured by transmitting the random pattern transmission data by performing high frequency attenuation in the transmission path,
Furthermore, the jitter at the high frequency attenuation is subtracted from the jitter at the normal time to calculate the increased jitter amount. (3) The transmission data of the random pattern is transmitted by performing high frequency attenuation in the transmission path and measured. High frequency attenuation code error rate calculation processing for calculating a code error rate at high frequency attenuation from the measured value of received data (4) The code error rate at the high frequency attenuation, the increased jitter amount, and the standard deviation of the random jitter Based on the above, a normal code error rate calculation process for calculating a normal code error rate without high frequency attenuation. 4. The code error rate measurement method according to claim 3, wherein the normal code error rate calculation processing includes the following elements: (A) a unit of time normalized by a standard deviation of random jitter at the time of high frequency attenuation; According to the normal distribution of the jitter histogram, the peak position calculation processing at the time of high frequency attenuation that calculates the peak position of the normal distribution at the time of high frequency attenuation based on the code error rate at the time of high frequency attenuation and the transition probability of data determined from the data pattern ( B) Adding a half of the increased jitter amount to the peak position of the normal distribution at the time of high frequency attenuation to obtain the normal time vs. peak interval which is the time from the peak position of the normal distribution to the sampling position at the normal time Peak interval calculation processing (C) According to the normal distribution of the normal jitter histogram with time units normalized by the standard deviation of random jitter Te, wherein the normal-to-peak interval, by a transition probability of the data, the code error rate calculation process for calculating the bit error rate of normal. Digital data transmission system for transmitting digital data by serial signal (1) Transmission line for transmitting by serial signal (2) Data sending part for converting digital data to serial signal and sending it to transmission line (3) Serial from transmission line A data receiver for receiving a signal and converting it into digital data (4) Provided in the middle of the transmission line, can be switched between valid and invalid, and when it is valid, the frequency component of the serial signal being transmitted Among these, a high-frequency attenuation mechanism for attenuating high-frequency components (5) A waveform measurement point formed as a measurement point of the waveform of the serial signal between the transmission line and the data receiving unit.   6. The digital data transmission system according to claim 5, wherein the high-frequency attenuation mechanism is a detachable stub and a mechanism provided in the middle of the transmission line to which the slab can be attached.   6. The digital data transmission system according to claim 5, wherein the high-frequency attenuation mechanism is a detachable capacitive element and a mechanism that is provided in the middle of the transmission line and to which the capacitive element can be attached.   6. The digital data transmission system according to claim 5, wherein the high-frequency attenuation mechanism is a detachable inductor and a mechanism provided in the middle of the transmission line to which the inductor can be attached.   6. The digital data transmission system according to claim 5, wherein the high-frequency attenuation mechanism is a transmission line having a variable length.

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