KR20070076819A - Impedance test device of cable - Google Patents

Abstract

The present invention relates to a test apparatus for measuring a characteristic impedance of a cable for transmitting a signal, comprising: a signal generator for generating a test signal, and a reference impedance agent for providing a target standard impedance value as an input of a test signal of the signal generator; It displays the signal output from the reference impedance provider and the signal output from the test target cable by using the test target cable connected to the test signal of the signal generator, the output of the reference impedance providing unit and the output of the test target cable, respectively. It includes a display unit. As a result, it is possible to confirm whether the characteristic impedance of the cable used to connect the external device to the system or the main body corresponds to the required impedance.

Description

Impedance test device for cable characteristics {APPARATUS FOR TESTING CHARACTERISTIC IMPEDANCE OF CABLE}

1 is a block diagram showing a schematic configuration of a device for checking the characteristic impedance of a cable according to the present invention,

FIG. 2 is a circuit diagram of the cable to be inspected in FIG. 1 as characteristic impedance.

3 is a circuit diagram of the PCB signal line of Figure 1 expressed in terms of the standard impedance,

4A to 4B are waveforms showing an example where the characteristic impedance value of the cable to be inspected is the same as the standard impedance value of the PCB signal line,

5A to 5C are waveforms showing an example in which the characteristic impedance value of the cable to be inspected is different from the standard impedance value of the PCB signal line;

6 is another embodiment according to the invention,

7 is an example of measuring the quality of a cable using a conventional TDR equipment.

Explanation of symbols on the main parts of the drawings

110: signal generator 120: test target cable

130: PCB signal line 140: Comparator

150: display unit

The present invention relates to a characteristic impedance inspection apparatus of a cable for measuring the characteristic impedance of a cable for transmitting a signal.

When the characteristic impedance of the cable used to connect the external device to the system or the main body is the same as the input impedance of the external device, the signal can be transmitted in the best state. Therefore, if the impedance is not matched, the signal is reflected and the level of the signal transmitted to the external device is changed. Therefore, the external device may be malfunctioned or the performance may be degraded.

Therefore, in order to select a cable having excellent characteristics, a user has conventionally used a time domain reflectometry (TDR) which measures characteristic impedance from a signal reflected using a high speed pulse signal.

However, while time-domain reflectometer is an expensive device that can accurately measure the characteristics of the cable, it is difficult to purchase from a general user's point of view and can be used only in limited places.

An object of the present invention is to provide a cable characteristic impedance inspection apparatus capable of measuring the characteristic impedance of a cable with a simple configuration.

In order to achieve the above object, the present invention, in the characteristic impedance inspection apparatus of the cable for measuring the characteristic impedance of the cable for transmitting a signal, the signal generator for generating a test signal, and the test signal of the signal generator as input The signal output from the reference impedance provider and the test using the reference impedance providing unit providing the desired standard impedance value and the output of the reference impedance providing unit and the output of the test target cable connected to the test signal of the signal generator as inputs, respectively A display unit for displaying a signal output from the target cable is provided.

The reference impedance providing unit preferably includes a control element capable of varying an impedance according to a desired standard impedance value, or a control element capable of selecting respective desired standard impedance values.

It is preferable to include a delay circuit capable of delaying a signal to the signal generator, the standard impedance providing means, the comparator or the display unit to compensate for the phase difference along the length of the cable to be inspected.

In order to achieve the above object, the present invention, in the characteristic impedance inspection apparatus of the cable for measuring the characteristic impedance of the cable for transmitting a signal, the signal generator for generating a test signal, and the test signal of the signal generator as input A reference impedance providing unit providing a desired standard impedance value, a comparator comparing voltages with an output of the reference impedance providing unit and an output of a test target cable connected to a test signal of the signal generator, respectively, and outputting from the comparator A display unit for displaying the signal is provided.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram showing a schematic configuration of a characteristic impedance inspection apparatus of a cable according to an embodiment of the present invention, the signal generator 110, the cable to be tested 120, the PCB signal line 130, the comparator 140 ) And a display unit 150.

The signal generator 110 generates a test signal and includes an output terminal 112 for supplying a periodic signal to the test target cable 120 and an output terminal 114 for supplying a periodic signal to the PCB signal line 130. It is. Meanwhile, the signal generator 110 may use a separate signal generator, but may also use an output terminal of a clock generator on the PC.

The cable 120 to be tested is output terminal 112 of the signal generator 110 using suitable connectors 122 and 124 according to the type of cable to be tested-for example, HDMI, DVI, USB, 1394, etc. And an input terminal 142 of the comparator 140.

The PCB signal line 130 is connected to the output terminal 114 of the signal generator 110 and the input terminal 144 of the comparator 140 using the characteristic impedance required for the cable to be inspected as a standard impedance. On the other hand, it may include a control element 132 that can vary the target standard impedance according to the characteristic impedance of the cable to be inspected, and also, as many PCB signal lines corresponding to the desired standard impedance can be used. have. And it may include a delay circuit 134 for compensating the phase difference according to the length of the cable to be inspected. That is, the delay circuit 134 compensates the phase difference caused by the change in the cable length due to the fixed length of the PCB signal line.

The comparator 140 is configured as, for example, a differential amplifier, and the output voltage of the test target cable 120 input to the input terminal 142 and the output voltage of the PCB signal line 130 input to the input terminal 144 are desired. It amplifies to a voltage level and supplies a signal to the display unit 150 through output terminals 146 and 148.

The display unit 150 is connected to the output terminal 146 of the comparator 140 through the input terminal 152, is connected to the output terminal 148 of the comparator 140 through the input terminal 154, amplified Display the voltage.

In this case, the comparator 140 and the display unit 150 may use a configuration of a measuring instrument such as an oscilloscope for displaying a signal, and the display unit 150 may not only measure the waveform of the signal but also measure the measurement result. Or it includes a device that can be displayed as an error.

FIG. 2 is a circuit diagram of the cable to be inspected in FIG. 1 in terms of characteristic impedance. As shown in the figure, the characteristic impedance of the cable is Z1 202, and the termination impedance-in the case of FIG. 1, is the input impedance of the input terminal 142 of the comparator 140-R1 (204). The voltage of the periodic signal of the signal generator is transmitted through the input terminal 206 and distributed by the characteristic impedance Z1 202 and the termination impedance R1 204 of the cable to be inspected to the comparator 140 through the output terminal 208. Delivered.

In this case, since the phase difference from the PCB signal line varies depending on the length of the cable 120 to be inspected, a means for compensating the phase difference by the length of the cable is required. In this embodiment, the phase difference is compensated using the delay circuit 134. do. In general, if you know the length of the cable to be tested, you can calculate the time difference to compensate through the equation.

Here, the characteristic impedance Z1 202 of the cable cannot be variable since it is a unique characteristic of the cable itself, but the end impedance R1 204 should be variable or changeable according to the desired standard impedance value.

FIG. 3 is a circuit diagram of the PCB signal line of FIG. 1 expressed as a standard impedance. FIG. As shown in the figure, the standard impedance of the PCB signal line is Z2 302, and the termination impedance-in the case of FIG. 1, is the input impedance of the input terminal 144 of the comparator 140-R2 (304). The voltage of the periodic signal of the signal generator is transmitted through the input terminal 306 and is distributed by the standard impedance Z2 302 and the termination impedance R2 304 of the PCB signal line to the comparator 140 through the output terminal 308. do.

Here, unlike the characteristic impedance Z1 202 of the cable, the standard impedance Z2 302 of the PCB signal line must be variable or changeable according to the characteristic impedance value required for the cable, and the terminal impedance R2 304 also has a desired standard impedance value. It should be variable or changeable according to. However, since the signal transmission of the cable is best transmitted when the desired standard impedance and the end impedance have the same value, the end impedance R2 304 should be set equal to the standard impedance Z2 302 of the PCB signal line.

First, the waveform in the case of excellent cable quality is shown. 4A illustrates an input waveform of the display unit 150 when the characteristic impedance value of the cable to be inspected is the same as the standard impedance value of the PCB signal line. For example, a waveform is obtained when the characteristic impedance Z1 202 of the cable and the standard impedance Z2 302 of the PCB signal line are equal to 50 Ω. Of course, in this case, since impedance matching is required, both the terminal resistors R1 204 and R2 304 are 50?. 4B illustrates a waveform after compensating for the phase of the waveform of FIG. 4A using the delay circuit 134 by the length of the cable 120 to be inspected. As shown in FIG. 4 (b), the waveform level of the characteristic impedance of the cable and the waveform level of the standard impedance of the PCB signal are displayed in the same manner. That is, when the waveform level of the characteristic impedance of the cable displayed on the display unit and the waveform level of the standard impedance of the PCB signal are the same, it indicates that the quality of the cable to be inspected is excellent.

Next, the waveform in the case where there is a deviation in the characteristic impedance of the cable is shown. FIG. 5A illustrates an input waveform of the display unit 150 when the characteristic impedance value of the cable to be inspected differs from the standard impedance value of the PCB signal line. For example, it is a waveform when the characteristic impedance Z1 202 of a cable is 40 ohms, and a deviation from 50 ohms of the standard impedance Z2 302 of a PCB signal line arises. FIG. 5B shows the waveform after the waveform of FIG. 5A is compensated using the delay circuit 134 by the length of the cable 120 to be inspected. As shown in FIG. 5 (b), the waveform level of the characteristic impedance of the cable and the waveform level of the standard impedance of the PCB signal are displayed differently.

In particular, the low voltage of the waveform level of the standard impedance of the PCB signal indicates 0 V, while the low voltage of the waveform level of the characteristic impedance of the cable indicates the negative level. This indicates that the reflection of the signal occurs because the value of the characteristic impedance Z1 202 of the cable and the value of the termination impedance R1 204 do not match.

These waveform levels can be calculated simply. The waveform level of the standard impedance of the PCB signal is calculated using FIG. 3 as follows.

           50

Vout = ───── x Vin = 0.5Vin

         50 + 50

The waveform level of the characteristic impedance of the cable is calculated using FIG. 2 as follows.

           50

Vout = ───── x Vin = 0.56Vin

         40 + 50

FIG. 5 (c) shows the difference between the two signals in FIG. 5 (b). The larger this difference, the more severe the characteristic impedance value of the cable is from the standard impedance value of the PCB signal. In addition, this difference can be converted into a numerical value in the comparator and the display can be used to display the quality of the cable.

6 is another example of an embodiment of the present invention. By connecting the cable under test and another standard cable to be compared together, the cable quality can be determined by the difference in waveform levels between the two cables. Using a standard cable as a comparison target has many of the same parameters that affect the measurement, resulting in more accurate results than using a PCB signal line.

As described above, according to the present invention, since the characteristic impedance of the cable to be inspected is displayed by simply comparing with the target standard impedance, it is possible to determine whether the characteristic impedance of the cable meets the required impedance, It can prevent the malfunction of external equipment due to the deviation.

In addition, according to the present invention, since the price of the high-speed signal transmission cable-HDMI, DVI, IEEE1394 cable-varies depending on the quality and length, it is possible to select and use a cheap and excellent quality cable through the present invention.

Claims (5)

In the characteristic impedance inspection apparatus of the cable for measuring the characteristic impedance of the cable for transmitting a signal, A signal generator for generating a test signal, A reference impedance providing unit for providing a target standard impedance value as an input of a test signal of the signal generator; And a display unit configured to display a signal output from the reference impedance providing unit and a signal output from the test target cable using the output of the reference impedance providing unit and the output of the test target cable connected to the test signal of the signal generator as inputs, respectively. Characteristic impedance test apparatus of the cable, characterized in that. The method of claim 1, And said reference impedance providing unit is a PCB signal line unit having a desired standard impedance value. The method of claim 2, The PCB signal line part is characterized in that it comprises a control element capable of varying the impedance according to the standard impedance value desired or a control element capable of selecting each standard impedance value desired. The method of claim 1, And a delay circuit for compensating the phase difference according to the length of the cable to be inspected to display the display on the display unit. In the characteristic impedance inspection apparatus of the cable for measuring the characteristic impedance of the cable for transmitting a signal, A signal generator for generating a test signal, A reference impedance providing unit for providing a target standard impedance value as an input of a test signal of the signal generator; A comparator for comparing voltages using the output of the reference impedance providing unit and the output of the test target cable connected to the test signal of the signal generator as inputs; And a display unit for displaying a signal output from the comparator.

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