JP2004140665A - Instrument and method for measuring delay difference between transmission lines - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a delay difference measuring method for a differential line which enables delay difference measurement of high precision needed for high-frequency signal transmission. <P>SOLUTION: A signal generator 1 generates and supplies the two positive and negative output signals of high frequency with a case wherein the differential transmission line 2 to be measured is actually used to one terminal of the differential transmission line to be measured. Phase shifters 3 and 4 are able to vary the phase of a cable output signal inputted from the other terminal of the transmission line to be measured individually positively and negatively. A code error detector 6 detects code errors of the output signals from the phase shifters. When the phase shifters vary the phases of the cable output signals both positively and negatively, the delay difference of the differential transmission line to be measured is found according to phase variation quantities in both the positive and negative directions when the code error detector detects a code error resulting in a great increase in code error rate. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a measurement of a delay in a transmission line, and more particularly to a measurement apparatus and a measurement method of a delay difference between transmission lines suitable for measuring a transmission line having a large loss or a highly accurate delay required for high-frequency signal transmission.
[0002]
[Prior art]
2. Description of the Related Art A differential transmission cable is known as one of media that can transmit high-speed electric signals. As shown in FIG. 4, an example of the cross section of the differential transmission cable is such that a drain wire extends along a pair of differential signal lines whose core is surrounded by an insulator and whose outer periphery is further surrounded by a skin layer. It is shielded.
[0003]
Conventionally, a method of measuring a propagation delay time difference between differential signal lines in a differential transmission cable generally measures a propagation delay time of each differential signal line and obtains the difference. As a specific technique, a TDR (Time Domain Reflectmeter) method is known. The TDR method is a method in which a test pulse is applied from the other end of a transmission line under test whose far end is open, and the time at which the voltage at the measurement point reaches 25% and 75% of the amplitude value of the test pulse (the round-trip propagation delay time) ) Is measured, and a time obtained by dividing the time difference by 2 is obtained as a propagation delay time.
[0004]
However, such a TDR method assumes an ideal case where there is no signal attenuation in the transmission line, but in reality, attenuation occurs in the transmission line, so that the waveform of the test pulse becomes dull. The round-trip propagation delay time is not equal to twice the propagation delay time to the open end, and a measurement error occurs.
[0005]
Therefore, the correspondence between the attenuation value of the transmission line and the measurement error is obtained and stored in the data table in advance as correction data, and the arithmetic circuit stores the attenuation value obtained by the simulation and the data for correction of the measurement error in the data table. , And a measurement error for correction is subtracted from a propagation delay time obtained by actual measurement, thereby obtaining a propagation delay time with a smaller error (for example, see Patent Document 1).
[0006]
[Patent Document 1]
JP-A-10-38938 (pages 3-4, FIGS. 1 and 2)
[0007]
[Problems to be solved by the invention]
However, when the propagation delay time difference between the differential transmission lines used for high-speed signal transmission of several GHz or more is measured and the line length is adjusted, the accuracy of the propagation delay difference between the differential lines is several tens pS or more. Accuracy is required. However, in the above-described prior art, a test pulse signal is used, and the transmission line under test is also tested in a state different from the connection state actually used. When measured, there is a problem that the simulation accuracy and the measurement accuracy cannot satisfy the required propagation delay difference between the differential lines.
[0008]
A main object of the present invention is to provide a differential line delay difference measuring method that enables highly accurate delay difference measurement particularly required for high-frequency signal transmission.
[0009]
[Means for Solving the Problems]
The apparatus for measuring a delay difference between transmission lines of the present invention generates two positive and negative output signals of the same high frequency as the case where the differential transmission line to be measured (2 in FIG. 1) is actually used, and outputs the differential transmission line to be measured. A signal generator (1 in FIG. 1) that supplies the signal to one terminal of the transmission line and a phase variable device (FIG. 1) that can separately change the phase of the cable output signal input from the other terminal of the transmission line to be measured. 3 and 4) and a code error detector (6 in FIG. 1) for detecting a code error of an output signal from the phase variable device, wherein the phase of the cable output signal is changed in both positive and negative directions in the phase variable device. In this case, the delay difference of the differential transmission line to be measured is determined based on the amount of phase change in both the positive and negative directions when the code error detector detects a code error that causes a remarkable increase in the code error rate.
[0010]
In the present invention, two output signals of the same high frequency as the case where the differential transmission line to be measured is actually used are supplied to one terminal of the differential transmission line to be measured. Then, the phase of the cable output signal input from the other terminal of the transmission line to be measured to the phase variable device is changed positively or negatively, and a code error of the output signal from the phase variable device is detected. At this time, when the phase of the cable output signal is changed in both the positive and negative directions, the measured error is determined based on the amount of phase change in both the positive and negative directions when the code error detector detects a code error that significantly increases the code error rate. Find the delay difference of the dynamic transmission line.
[0011]
As described above, the present invention uses the actually used high-frequency signal and also tests the transmission line under test in the actually used connection state, so that the high-precision differential line required for high-frequency signal transmission is used. Measurement of the propagation delay difference between the two.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
[0013]
[Description of configuration]
FIG. 1 is a block diagram showing an embodiment of a transmission line delay difference measuring apparatus according to the present invention. In FIG. 1, two positive and negative outputs of a signal generator 1 are respectively connected to two terminals at one end (left end) of a differential transmission line 2 to be measured. One terminal of the other end (right end) of the transmission line 2 to be measured is connected to the positive input of the waveform equalizer / regenerator 5 via the phase changer 3 and the other end of the transmission line 2 to be measured is connected to the other end. Is connected to the negative input of the waveform equalizer / regenerator 5 via the phase variable unit 4. The output of the waveform equalizer / regenerator 5 is connected to the input of a code error detector 6.
[0014]
The signal generator 1 generates an output signal 101 of a high frequency of several GHz or more as in the case where the differential transmission line 2 to be measured is actually used. The cross section of the differential transmission line 2 to be measured is as shown in FIG. 7, and a high-speed electric signal of several GHz or more can be transmitted. Since both ends are connected to the signal generator 1 and the phase changers 3 and 4, an actual use state is realized.
[0015]
The phase variable units 3 and 4 are affected by loss and delay when the output signal 101 from the signal generator 1 passes through the differential transmission line 2 to be measured, and the cable output signal whose waveform has deteriorated so that it cannot be measured. For 102, the phases of the positive input and the negative input are adjusted. The adjustment of the phase is performed by operating a dial provided in the phase changers 3 and 4 or controlling the voltage supplied to the phase changers 3 and 4. When the phase is adjusted, as will be described later, the bit error rate detected by the bit error detector 6 changes. Therefore, the delay time difference of the differential transmission line 2 to be measured is obtained by using this.
[0016]
The waveform equalizer / reproducer 5 shapes and reproduces the waveform of the phase variable device output 103 from the phase variable devices 3 and 4. This is because it is difficult to detect a code error in the code error detector 6 without changing the waveform of the phase variable device output 103. Therefore, by shaping and reproducing the waveform of the phase variable device output 103, the code error can be detected without any trouble. It was made possible.
[0017]
The code error detector 6 detects a code error of the output 104 of the waveform equalizer / reproducer. The detection of a code error is performed while changing the positive / negative phase difference between the phase changers 3 and 4 (the positive / negative phase difference is hereinafter referred to as “differential phase difference”). As shown in FIG. 3, the code error rate of the waveform equalizer / regenerator output 104 changes depending on the phase difference between the phase changers 3 and 4. Therefore, a characteristic point of the bit error rate is obtained, and a delay difference of the measured differential transmission line 2 is calculated based on the result.
[0018]
[Description of operation]
Hereinafter, the operation of this embodiment will be described with reference to FIGS. 2, 3, and 5. FIG. The differential transmission line 2 to be measured is connected to the signal generator 1 and the phase changers 3 and 4 as shown in FIG. 1, and the waveform reproduction equalizer 5 and the code error detector 6 are also attached as shown in FIG. Can be
[0019]
The signal generator 1 generates an output signal 101 of a high frequency of several GHz or more, and the output signal 101 is input to the differential transmission line 2 to be measured without deterioration. When the output signal 101 passes through the differential transmission line 2 to be measured, the waveform is significantly deteriorated so as to be unmeasurable due to the effects of transmission line loss and delay. The cable output signal 102 is adjusted by the phase changers 3 and 4, and a phase changer signal 103 is obtained.
[0020]
The phase variable device output 103 is equalized and reproduced by the waveform equalizer / reproducer 5, and becomes a waveform equalizer / reproducer signal 104. The waveform equalizer / reproducer signal 104 is input to the code error detector 6, where the bit error rate is determined.
[0021]
Here, the differential phase difference of the phase variable device output 103 at the input terminal of the waveform equalizer / regenerator 5 is the sum of the delay difference of the measured differential transmission line 2 and the phase difference of the phase variable devices 3 and 4 (hereinafter, referred to as the phase difference). , "Delay between differentials"), as shown in FIG. 2, the amount of jitter of the waveform equalizer / reproducer output signal 104 changes depending on the amount of the differential delay.
[0022]
FIG. 2A shows the waveform of the waveform equalizer / reproducer output signal 104 when the differential delay is 0, and no jitter is observed. FIG. 2B shows the waveform of the waveform equalizer / reproducer output signal 104 when the delay between the differentials is medium. The jitter is conspicuous, but the width of the eye pattern is wider than the width of the jitter. Code identification is still possible. However, as shown in FIG. 2C, if the delay between differentials becomes large and the width of the jitter becomes wider than the width of the eye pattern, the code cannot be identified, and the code error detector Detects a code error.
[0023]
FIG. 3 shows that the phase variable devices 3 and 4 are adjusted to change the differential delay at the input terminal of the waveform equalizer 5, and the code error of the output of the waveform equalizer 5 is detected by the code error detection circuit 6. 7 shows a bit error rate curve in which the bit error rates obtained by the detection and obtained are plotted. Referring to FIG. 3, it can be seen that the code error rate has rapidly increased at points B and C from a state such as point A where there is no code error.
[0024]
Next, a method for obtaining the differential delay difference of the measured differential transmission line 2 will be specifically described with reference to FIG.
[0025]
Now, let X be the delay difference of the measured differential transmission line 2, and let S be the cycle of the test signal. In this case, the differential delay difference of the cable output signal 102 is X as shown in FIG. When the phase difference between the phase changers 3 and 4 is adjusted to 0, as shown in FIG. 5 (2), the differential delay of the phase changer output 103 becomes the difference between the cable output signal 102 in FIG. It becomes X which is the same as the dynamic delay difference. The delay between the differentials of the variable device output 103 at this time is shown as point A in FIG. In this state, no jitter is seen in the waveform of the waveform equalizer / regenerator output signal 104 as shown in FIG.
[0026]
From this state, for example, the phase of the phase variable device 3 is changed in the positive direction. Then, as shown in FIG. 2B, jitter appears in the waveform of the waveform equalizer / reproducer output signal 104, and the width of the jitter increases as the phase of the phase variable device 3 advances in the positive direction. Then, finally, as shown in FIG. 2C, the width of the jitter becomes wider than the width of the eye pattern and the code cannot be identified, and the code error detector 6 detects the code error. I do.
[0027]
Then, once a code error is detected, the code error rate suddenly increases due to exceeding a correct / false threshold. At this point, the point at which the bit error rate has rapidly deteriorated is shown as point B in FIG. The amount of phase change of the phase variable device 3 from FIG. 5 (2) at this time is shown as Y in FIG. 5 (3).
[0028]
Next, the phase of the phase variable device 3 is changed in the negative direction. Then, the state of FIG. 2C is reached via the state of FIG. At this point, the point at which the bit error rate has rapidly deteriorated is shown as point C in FIG. In addition, the amount of phase change of the phase variable device 3 from FIG. 5 (2) at this time is shown as Z in FIG. 5 (3).
[0029]
It is apparent from FIG. 5 that there is a relationship of Y = S + X and Z = SY between S, X, Y and Z described above. From these two equations, X = (YZ) / 2, and the delay difference X of the measured differential transmission line 2 can be obtained by measuring Y (point B) and Z (point C). In FIG. 3, since the center between the points B and C is shown as the point D, the difference E between the points D and A is obtained, and as a result, the delay difference X of the differential transmission line 2 to be measured is shown in FIG. It can be understood that E is indicated by E in FIG.
[0030]
【The invention's effect】
As described above, the present invention uses the actually used high-frequency signal, and also tests the transmission line under test in the actually used connection state. There is an effect that the propagation delay difference between the traffic lines can be measured.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a transmission line delay difference measuring apparatus according to the present invention; FIG. 2 is a diagram showing jitter generation of a waveform equalizer / regenerator output signal when a differential delay is changed in the present invention; FIG. 3 is a diagram showing the appearance; FIG. 3 is a diagram in which the bit error rate based on the bit error detection in the present invention is plotted against the differential delay; FIG. 4 is a cross-sectional view showing an example of a general differential transmission cable; A phase transition diagram of a differential signal when a delay difference between differential transmission lines to be measured is obtained in the present invention.
REFERENCE SIGNS LIST 1 signal generator 2 differential transmission line to be measured 3 phase variable device 4 phase variable device 5 waveform equalizer / reproducer 6 code error detector

Claims (3)

A signal generator that generates two positive and negative output signals of the same high frequency as the case where the measured differential transmission line is actually used and supplies the output signal to one terminal of the measured differential transmission line;
A phase variable device that can change the phase of the cable output signal input from the other terminal of the transmission line to be measured separately for positive and negative;
Including a code error detector that detects a code error of an output signal from the phase variable device,
When the phase of the cable output signal is changed in both the positive and negative directions in the phase variable device, based on the amount of phase change in both the positive and negative directions when the code error detector detects a code error that significantly increases the code error rate. A delay difference between the differential transmission lines to be measured. The delay between transmission lines according to claim 1, wherein a waveform equalizer for equalizing and reproducing the output signal from the phase variable device is inserted between the phase variable device and the code error detector. Difference measuring device. Supplying two output signals of the same high frequency as the case where the differential transmission line to be measured is actually used to one terminal of the differential transmission line to be measured;
A procedure for separately changing the phase of the cable output signal input to the phase variable device from the other terminal of the transmission line to be measured, positively and negatively,
A step of detecting a code error of an output signal from the phase variable device,
When the phase of the cable output signal is changed in both the positive and negative directions, the measured error is determined based on the amount of phase change in both the positive and negative directions when the code error detector detects a code error that causes a significant increase in the bit error rate. Obtaining a delay difference between dynamic transmission lines.

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