JP5851937B2 - Decoupling circuit - Google Patents

Description

  The present invention relates to a decoupling circuit used for a lightning surge overvoltage tolerance test, and more particularly, to a communication device in a communication state when a lightning surge overvoltage is applied to a communication device for VDSL (Very High Speed Digital Subscriber Line). The present invention relates to a decoupling circuit used in an overvoltage tolerance test circuit for evaluating a tolerance characteristic against overvoltage.

  Due to the widespread use of the Internet accompanying network broadbandization, for example, in metal communication lines, ICT devices as communication devices for VDSL are used almost always connected as compared to conventional audio transmission signals.

  With the widespread use of always-on communication, reliability against lightning surge overvoltage of ICT equipment for VDSL (hereinafter abbreviated as “ICT equipment”) is required. In these ICT devices, as the communication speed is increased and the bandwidth is increased, the electronic devices to be used are driven at a low voltage and are mounted with high density, so that the proof strength against lightning surge overvoltage tends to decrease. In addition to this, constant connection communication has become widespread, and the probability that an overvoltage has entered due to lightning is considered to be a cause of an increase in temporary communication abnormalities.

  In order to improve the above, it is necessary to evaluate proof strength characteristics against lightning surge overvoltage of ICT equipment. For ICT equipment lightning surge tests, as described in the test conditions of the International Telecommunication Union Telecommunication Standardization Sector Recommendation on Overvoltage Strength Test (hereinafter referred to as ITU-T K.44), ICT It is necessary to carry out the equipment in the operating state.

  However, when conducting a lightning surge overvoltage tolerance test, a decoupling circuit is required to protect the communication equipment, that is, the opposite device from the applied overvoltage. ITU-T K.44 also provides a decoupling circuit. It is stipulated that it is used in principle.

  The implementation of the lightning surge test in the above operating state and the basic use of the decoupling circuit are disclosed in Non-Patent Document 1. Non-Patent Document 2 discloses a guideline aimed at reducing the failure of ICT equipment caused by lightning in the communication equipment manufacturer industry of the Information and Communication Network Industries Association. The decoupling circuit is disclosed in Patent Document 1.

JP 2009-128304 A

ITU-T K.44, “Resistibility tests for telecommunication equipment exposed to overvoltages and overcurrents-Basic Recommendation” 04/2008, p. 10, “7.3 Test conditions”, 1), 3), p. 26, “A.2.4 “A.5.1 General” in “Equipment conditions and states”, p. 29-32, “A.5 Powering, coupling, decoupling and terminations” Information and Communication Network Industries Association, “Guidelines for Protection of Communication Equipment against Lightning Overvoltage”, CES-Q007-1, January 31, 2008, p. 20, 6th line from the bottom, “Decoupling Circuit 1: 500Ω × 2” p 21, "Power feed 1 + Decoupling circuit 1" in the drawing "(1) Between communication line and ground (communication line vertical / common)"

  The decoupling circuit disclosed in Patent Document 1 is designed to transmit a high-speed digital communication signal such as a VDSL ICT device in a lightning surge overvoltage tolerance test. This decoupling circuit is composed of circuit elements including only a 20 mH common mode choke coil. In this common mode choke coil, an air core coil is employed in order to avoid magnetic saturation of the magnetic core, and a balanced cable having a double twisted wire is used as the winding wire. As a result, the winding wire has a good balance and has a seamless winding structure, so that a good transmission line characteristic can be obtained by removing the influence of the reflection of the high-speed digital communication signal. .

  On the other hand, the lightning surge waveform used for the lightning surge overvoltage tolerance test is 10/700 us (expressed as wavefront length / wavetail length, the unit is us), and the frequency spectrum is about DC to several tens of kHz. In the lightning surge overvoltage tolerance test, most of the lightning surge overvoltage applied is applied to the device under test. However, since the common mode impedance generated by the common mode choke coil of the decoupling circuit is a low impedance of several tens of ohms at the maximum in the low frequency range of DC to several hundred Hz, a part of the lightning surge overvoltage is present in the opposing device. Leaks. It is desirable that the leaked lightning surge overvoltage is as low as possible so as not to adversely affect the opposing device.

  As a measure for evaluating the magnitude of the leaking voltage or current, for example, a shunt ratio is used. When the opposing device side and the device under test side of the decoupling circuit are each terminated with a resistor simulating a common mode impedance of 150Ω, the ratio of the voltage or current generated in the former and the latter is expressed in units of dB. In this case, when the shunt ratio is represented by Adv in the case of voltage or Adi in the case of current, the following values are obtained.

Adv = 20 × log ₁₀ (counter device side voltage / device under test side voltage) (dB)
Adi = 20 × log ₁₀ (opposite device side current / device under test side current) (dB)

  In Patent Document 1 (second embodiment), the shunt characteristics of a decoupling circuit configured by a two-divided common mode choke coil are obtained only at Adv = −5.2 dB and Adi = −6.2 dB. . For this reason, in the lightning surge overvoltage tolerance test, the lightning surge overvoltage applied to the device under test, which is the target to which lightning surge overvoltage is applied, has approximately half the decoupling circuit because the shunt characteristics of the decoupling circuit are not sufficient. It can leak to the opposite device side. Since the leaked lightning surge overvoltage is applied to the opposite device that should not be applied originally, it may affect the quality of the VDSL communication signal between the device under test and the opposite device.

  Since the common mode impedance characteristic of the decoupling circuit is several tens of Ω in the frequency range from direct current to several hundred Hz, only the resistance of the common mode choke coil can be obtained. As a result, the frequency spectrum component of the lightning surge overvoltage corresponding to the low common mode impedance region between DC and several hundred Hz leaks without receiving sufficient attenuation from the decoupling circuit to the opposing device side. Adversely affect other ICT devices. For example, if the leaked voltage is about 500 to 700 V, for example, the VDSL communication signal is cut off when the gas arrester installed after the connection connector of the metal communication line of the ICT device operates. For this reason, the transmission characteristics are deteriorated, that is, the payload speed is deteriorated.

  Non-Patent Document 2 discloses a method for increasing the common mode impedance of a decoupling circuit. That is, a common mode impedance of 250Ω can be obtained by inserting a resistor of 500Ω per line in series on both sides of the metal communication line. However, this method can suppress the frequency spectrum component of the lightning surge overvoltage corresponding to the low common mode impedance region from DC to several hundred Hz to some extent, but the transmission mode of the VDSL communication signal is the normal mode. As a result, a resistance of 1 kΩ is added to the communication line, and as a result, a large transmission loss may occur. As a result, the payload speed is degraded. Further, the lightning surge overvoltage tolerance test in Non-Patent Document 2 does not assume a lightning surge overvoltage tolerance test in the communication state of the ICT device, but discloses a test method only when the power supply of the communication device is turned on. Has been.

  The present invention has been made in the above situation, and its object is to provide a device under test without causing an increase in transmission loss or a deterioration in payload speed in a lightning surge overvoltage tolerance test of a VDSL ICT device in a communication state. Another object of the present invention is to provide a decoupling circuit capable of suppressing leakage of a lightning surge overvoltage applied to the counter device to an opposing device.

In order to solve the above problems, the present invention is installed so as to be connectable via a metal communication line between a device under test, which is an ICT device for VDSL, which is an object of a lightning surge overvoltage tolerance test, A decoupling circuit configured to be able to transmit a VDSL signal via the metal communication line, comprising: a common mode choke coil composed of an air-core coil; and a capacitor connected in series to the common mode choke coil. The common mode choke coil is divided into a plurality of pieces and connected in series, and the capacitor has a dielectric strength with respect to a test voltage in a common mode and a normal mode impedance capable of satisfactorily transmitting the VDSL signal, The ICT device is a VDSL modem, and the capacitor suppresses mutual interference between the VDSL line and the ISDN line. In the passing frequency band of the filter, having a magnitude electrostatic capacity caused the normal mode impedance of one-tenth of the normal-mode impedance of the common mode choke coil.

In order to solve the above problems, the present invention is installed so as to be connectable via a metal communication line between a device under test, which is an ICT device for VDSL, which is an object of a lightning surge overvoltage tolerance test, A decoupling circuit configured to be able to transmit a VDSL signal via the metal communication line, comprising: a common mode choke coil composed of an air-core coil; and a capacitor connected in series to the common mode choke coil. The common mode choke coil is divided into a plurality of pieces and connected in series, and the capacitor has a common mode test voltage applied to the device under test, and a part of the current passes through the decoupling circuit. Thus, when leaking to the ICT device, the common mode impedance in the low frequency range from DC to several hundred Hz is the ICT device. 10 times more than the common mode impedance between the ground greatly Ru is set.

In order to solve the above problems, the present invention is installed so as to be connectable via a metal communication line between a device under test, which is an ICT device for VDSL, which is an object of a lightning surge overvoltage tolerance test, A decoupling circuit configured to be able to transmit a VDSL signal via the metal communication line, comprising: a common mode choke coil composed of an air-core coil; and a capacitor connected in series to the common mode choke coil. The common mode choke coil is divided into a plurality of pieces and connected in series, and the capacitor has a common mode test voltage applied to the device under test, and a part of the current passes through the decoupling circuit. In order to cancel the delay caused by the inductance of the common mode choke coil when leaking to the ICT equipment, Serial common mode choke coil of the plurality of wires fraction capacitor Ru is connected in series.

In order to solve the above problems, the present invention is installed so as to be connectable via a metal communication line between a device under test, which is an ICT device for VDSL, which is an object of a lightning surge overvoltage tolerance test, A decoupling circuit configured to be able to transmit a VDSL signal through the metal communication line, a common mode choke coil configured by an air-core coil, a capacitor connected in series to the common mode choke coil, e Bei a first terminal of the test apparatus, and a second terminal of the counter device side, the common mode choke coil is divided into a plurality connected in series, the capacitor winding of the common mode choke coil Connected between the first wire and the first terminal, or between the wire at the end of winding of the common mode choke coil and the second terminal. Ru is.

It is a block diagram which shows the structural example of the test system containing the decoupling circuit in embodiment of this invention. FIG. 2 is a circuit diagram illustrating a configuration example of a decoupling circuit in FIG. 1. It is a figure which shows an example of the common mode impedance characteristic of the decoupling circuit of this embodiment. It is a figure which shows an example of the frequency spectrum of the voltage level in the shunt characteristic of the decoupling circuit of embodiment. It is a figure for demonstrating the experimental result of the shunt characteristic of the decoupling circuit of embodiment. It is a figure for demonstrating the experimental result of the shunt characteristic of a general decoupling circuit. It is a circuit diagram which shows the structural example of the decoupling circuit in a modification.

  Hereinafter, an embodiment of a test system including the decoupling circuit of the present invention will be described. In the test system according to the embodiment, the ICT equipment to be subjected to the lightning surge overvoltage tolerance test will be described using, for example, a VDSL modem sold by Nippon Telegraph and Telephone Corporation. In this case, in order to reduce mutual interference between the VDSL line and the ISDN line, transmission power in a frequency band of 640 kHz or less is suppressed. In VDSL, since there are two communication ports, one pair, that is, two metal communication lines are used.

(Configuration of lightning surge test system)
FIG. 1 is a block diagram illustrating a configuration example of a lightning surge test system including a decoupling circuit according to an embodiment of the present invention.

  This lightning surge test system includes a lightning surge generator 1, a decoupling circuit 5 connected between the opposite device 3 and the device under test 4, a lightning surge generator 1, a device under test 4 and a decoupling circuit. And coupling circuits 2 a and 2 b connected to application points T 1 and T 2 between 5. In this embodiment, a case where a high-speed digital transmission type VDSL modem using a metal subscriber line is used as the opposite device 3 and the device under test 4 is illustrated.

  The lightning surge generator 1 generates a lightning surge voltage as a test voltage of several hundred volts to several tens of kV, and applies the lightning surge voltage to the application points T1 and T2 via the coupling circuits 2a and 2b. ing. The earth port 11 of the lightning surge generator 1 is connected to the earth 10 and maintains a zero potential.

  The ground port 42 of the device under test 4 is connected to the ground 10 and maintains a zero potential. The communication ports 41 a and 41 b of the device under test 4 are connected to the devices under test side 51 a and 51 b of the decoupling circuit 5.

  The opposing device side terminals 53 a and 53 b of the decoupling circuit 5 are connected to the communication ports 31 a and 31 b of the opposing device 3. In addition, the opposing apparatus 3 of this embodiment is made to float in potential without being connected to the earth 10.

(Configuration example of the decoupling circuit 5)
Next, a configuration example of the decoupling circuit 5 will be described with reference to FIG. FIG. 2 is a circuit diagram showing a configuration example of the decoupling circuit 5.

  The decoupling circuit 5 is provided between the low frequency spectrum suppressor 54 provided between the terminals 51a and 51b and the terminals 52a and 52b, and between the terminals 52a and 52b and the terminals 53a and 53b. The choke coil 55 is provided.

  The low frequency spectrum suppressor 54 is constituted by two capacitors C1 and C2. One end of the capacitor C1 is connected to the terminal 51a, and the other end is connected to the terminal 52a. One end of the capacitor C2 is connected to the terminal 51b, and the other end is connected to the terminal 52b. With the configuration of the low frequency spectrum suppressor 54, the low frequency component of the lightning surge overvoltage frequency spectrum is prevented from leaking to the opposing device 3.

  The choke coil 55 is constituted by air core coils L11 to L14 that are divided into two parts D1 and D2 for each of the wires W1 and W2, and can suppress the inflow of lightning surge overcurrent. Note that the start of winding of the air-core coils L11 and L13 is represented by a symbol S in FIG. Moreover, each air-core coil L11-L14 is accommodated in the housing | casing which consists of insulator resin.

  The choke coil 55 is a common mode choke coil that causes the air-core coils L11 to L14 to operate in the common mode.

  In FIG. 2, one end of the air core coil L11 is connected to the terminal 52a, and the other end is connected to one end of the air core coil L13. The other end of the air-core coil L13 is connected to the wire W1. One end of the air core coil L12 is connected to the terminal 52b, and the other end is connected to one end of the air core coil L14. The other end of the air-core coil L14 is connected to the wire W2.

  With the configuration of the decoupling circuit 5, for example, a VDSL communication signal is transmitted between the opposing device 3 and the device under test 4 without being blocked by the decoupling circuit 5.

  Here, the reason why the air-core coils L11 to L14 are divided into two parts is to increase the resonance frequency of the common mode impedance by reducing the capacitance between the windings. By dividing the air-core coils L11 to L14 into two, the resonance frequency can be increased to, for example, 100 kHz or more.

  Here, the inductance value of the air-core coil used in the decoupling circuit 5 is shown as 20 mH in the surge immunity test standard IEC61000-4-5 in the electromagnetic compatibility of the International Electrotechnical Commission.

  In order to obtain the above-described desired inductance of 20 mH, when a coil is divided into multiple bobbins without being divided, the resonance frequency of resonance caused by the capacitance between the windings is about 50 kHz. On the other hand, for example, when the coil is divided into two, the capacitance of the two divided coils is connected in series, so the capacitance of the entire coil is ½. Therefore, the resonance frequency is doubled to about 100 kHz. Similarly to this, when the coil is divided into, for example, four parts, a resonance frequency of 200 kHz can be obtained.

  For example, in order to prevent a component having a high frequency spectrum of a 10/700 us lightning surge waveform from leaking from the device under test 4 side to the counter device 3 side, it is desirable that the resonance frequency of the coil is high. However, if the number of divisions of the coil is increased, the length of the coil becomes longer, and therefore the number of divisions is determined based on the balance between the resonance frequency and the length.

(Capacitance of capacitors C1 and C2)
Next, the capacitances of the capacitors C1 and C2 will be examined. Depending on the capacitance of the capacitor, if an appropriate value of capacitance is used, it is possible to give a large attenuation to the frequency spectrum component corresponding to the low frequency range of direct current to several hundred Hz of lightning surge overvoltage. There is sex.

  First, in order to satisfactorily transmit the VDSL communication signal between the device under test 4 and the opposite device 3, the normal mode impedance of the capacitor in the low frequency spectrum suppressor 54 at 640 kHz is the normal mode impedance of the decoupling circuit 5. It is preferable not to affect the above.

  In the decoupling circuit 5, the normal mode impedance at 640 kHz is 110Ω. In this case, if the normal mode impedance of the capacitor is set to 1/10 of the normal mode impedance of the decoupling circuit 5, the normal mode impedance of the capacitor is 11Ω.

  In order to set the normal mode impedance of the capacitor to 11Ω at 640 kHz, the capacitance of the capacitor is about 22 nF. Note that 22 nF is a value per metal communication line.

  Here, since the lightning surge overvoltage is applied to the two metal communication lines in the common mode, two capacitors with a capacitance of 22 nF are connected in parallel. As a result, the combined capacitance is 44 nF.

  Next, when the shunt ratio is obtained with the capacitance of the capacitor being 44 nF, Adv = −14.7 dB and Adi = −14.7 dB. In this case, when the charging voltage of the lightning surge generator 1 is 1 kV, the voltage leaking to the opposing device 3 side is about 150 V, which is a relatively high voltage value. For this reason, the normal mode impedance is made larger than 11Ω, and the trade-off with the shunt ratio is taken into consideration. That is, when the capacitance of the capacitor is 10 nF per line, the normal mode impedance is about 25Ω, but the shunt ratio Adv = −17.4 dB, Adi = −17.5 dB, and the voltage and current shunt The ratio is expected to improve slightly below 3 dB.

  The reason why the capacitance of the capacitor is determined to be 10 nF per line is that, as will be described later, when a special high-voltage ceramic capacitor that is not handled as a general-purpose product is selected, it is commercially available as a catalog standard product. Therefore, there is an advantage that procurement becomes easy.

  From such a viewpoint, in the embodiment, the capacitance of the capacitor per line is set to 10 nF, for example. Since the decoupling circuit 5 is connected to a pair of metal communication lines, in the common mode, the circuit configuration is such that two 10 nF capacitors C1 and C2 are connected in parallel. The capacitance is 20 nF.

  Next, the ratings of the capacitors C1 and C2 are examined.

  The maximum value of the common mode test voltage in the lightning surge overvoltage tolerance test is 13 kV. The output voltage fluctuation of the lightning surge generator 1 is ± 15%. From this viewpoint, the maximum voltage is required to be 15 kV. In this application, for example, a ceramic capacitor having a characteristic that is not easily damaged even when a voltage higher than the withstand voltage is applied is preferable.

  Generally, ceramic capacitors with a maximum withstand voltage of 15 kV are commercially available with a maximum of 5.6 nF, but there are no ceramic capacitors with 10 nF. For this reason, it is possible to achieve a desired capacitance of 10 nF per wire by connecting two 5 nF capacitors in parallel.

  A 10 nF capacitor per wire configured by connecting two 5 nF ceramic capacitors having a rated voltage of 15 kV in parallel has a frequency spectrum component of 0 to 3 kHz of lightning surge overvoltage at a maximum common mode test voltage of 13 kV in a lightning surge overvoltage tolerance test. It is possible to apply to a circuit element for suppressing leakage through the decoupling circuit to the opposite device 3 side.

  Here, transmission characteristics between the VDSL modem on the device under test 4 side and the VDSL modem on the opposite device 3 side will be described. When the transmission characteristics were evaluated by the payload speed, the payload speed was 91 Mbps downstream and 25 Mbps upstream. On the other hand, a similar payload speed is obtained in the case of the conventional decoupling circuit. From this point of view, it can be seen that there is no difference in transmission speed regardless of the presence or absence of the low frequency spectrum suppressor 54. Therefore, the normal mode impedance characteristic of the low frequency spectrum suppressor 54 is considered reasonable.

  With the configuration of the decoupling circuit 5 described above, the lightning surge overvoltage generated by the lightning surge generator 1 is applied to the application points T1 and T2 via the two coupling circuits 2a and 2b. In this case, the decoupling circuit 5 prevents an overvoltage from flowing into the communication ports 31a and 31b of the opposite apparatus 3 that is a communication device of an ICT device that is not a test target.

  Next, the common mode impedance characteristics of the decoupling circuit 5 will be described with reference to FIG. 3 in comparison with a conventional decoupling circuit. In the following description, the conventional decoupling circuit is the decoupling circuit of the second embodiment described in Patent Document 1.

  FIG. 3 is a diagram for explaining an example of the common mode impedance characteristic of the decoupling circuit 5. In FIG. 3, the horizontal axis represents the frequency (Hz) expressed in logarithm, and the vertical axis represents the common mode impedance (Ω) expressed in logarithm.

  According to the common mode impedance characteristic p in the conventional decoupling circuit, the impedance is several tens of Ω in the frequency range from DC to several hundred Hz. When the frequency becomes higher than that frequency, the common mode impedance increases linearly with respect to the frequency at a rate of 20 dB / decade. Parallel resonance occurs near 100 kHz, and the maximum common mode impedance is about 350 kΩ.

  The parallel resonance frequency is determined by the inductance of the common mode choke coil and the capacitance between the windings. In the frequency region higher than the parallel resonance frequency, the inductance changes to the characteristics of the capacitor, so that the common mode impedance decreases linearly with respect to the frequency at a rate of −20 dB / decade.

  On the other hand, the common mode impedance characteristic c of the spectrum suppressor 54 in the decoupling circuit 5 is indicated by a dotted line in FIG. The characteristics of the common mode impedance of the capacitors C1 and C2 having a combined capacitance of 20 nF for two wires are exemplified with the capacitance per wire being 10 nF.

  According to the impedance characteristic c, the common mode impedance decreases linearly with respect to the frequency at a rate of −20 dB / decade. For example, in the case of 640 kHz, the impedance is about 12Ω. This value corresponds to the value of the common mode impedance at several tens of Hz or less in the conventional decoupling circuit.

  Further, in the impedance characteristic a of the decoupling circuit 5, as shown in FIG. 3, the common mode impedance has characteristics similar to those of a capacitor up to around 2 kHz, and series resonance occurs at about 8 kHz, so that the common mode impedance is It becomes about 11Ω. The series resonance frequency is determined by the capacitances of the capacitors C1 and C2 and the inductance of the common mode choke coil 55. When the frequency is higher than the series resonance frequency, the same characteristic as the impedance characteristic p is exhibited from around 30 kHz.

  From the above, it can be seen that the decoupling circuit 5 has a common mode impedance of 4 kΩ or more larger than that of the conventional decoupling circuit from DC to around 2 kHz.

  Next, the influence of the shunt characteristics given when the common mode impedance of the decoupling circuit 5 decreases near the series resonance point will be described with reference to FIG. 4 in comparison with the conventional decoupling circuit.

  FIG. 4 is a diagram illustrating an example of a frequency spectrum of a voltage level in the shunt characteristics of the decoupling circuit. In FIG. 4, the horizontal axis indicates the frequency (kHz), and the vertical axis indicates the voltage level (V) of the amplitude of the frequency spectrum expressed logarithmically.

  According to FIG. 4, with respect to the voltage level on the device under test 4 side, the voltage level characteristic p1 in the conventional decoupling circuit and the voltage level characteristic a2 in the decoupling circuit 5 show substantially similar characteristics.

  On the other hand, at the voltage level on the counter device 3 side, the voltage level characteristic a1 in the decoupling circuit 5 is much lower than the voltage level characteristic p2 in the conventional decoupling circuit at about 0 to 3 kHz. This indicates that the shunt characteristics of the decoupling circuit 5 are much improved over the conventional one.

  On the other hand, when the frequency is about 5.5 kHz, the solid line indicating the voltage level characteristic a1 and the broken line indicating the voltage level characteristic p2 intersect. Until 12.5 kHz, the voltage level indicated in the voltage level characteristic a1 is higher than that of the voltage level characteristic p2, and when the frequency is higher than that, it is indicated in each voltage level characteristic a1 and p2. The voltage levels are approximately the same.

  In FIG. 4, the voltage level of the voltage level characteristic a1 is not improved at 5.5 kHz to 12.5 kHz. This is presumably because the common mode impedance drops to a V shape near the series resonance point.

  FIG. 5 is a diagram for explaining the experimental results of the shunt characteristics of the decoupling circuit 5. In FIG. 5, the horizontal axis represents time (ms), the left vertical axis represents the voltage generated with respect to the 150Ω resistor, and the right vertical axis represents the current flowing through the 150Ω resistor. V1 represents the voltage on the opposite device 3 side, I1 represents the current on the opposite device 3 side, V2 represents the voltage on the device under test 4 side, and I2 represents the current on the device under test 4 side.

  FIG. 5 shows the results when the lightning surge waveform is a 10/700 us waveform and the charging voltage is 1 kV. The device under test 4 side and the counter device 3 side are each terminated with a 150Ω resistor that simulates the common mode impedance between the device under test 4 and the counter device 3 and the ground 10.

  From FIG. 5, the voltage shunt ratio Adv = −17.6 dB and the current shunt ratio Adi = −15.7 dB were obtained. This experimental result and the above-described calculation results, that is, Adv = −17.4 dB and Adi = −17.5 dB were found to be a maximum difference of 1.8 dB, and it was found that both were almost the same.

  Further, as described above, the shunt characteristics of the conventional decoupling circuit are Adv = −5.2 dB and Adi = −6.2 dB. Therefore, in the case of the decoupling circuit 5, compared to the conventional decoupling circuit. It was found that a great improvement of about 10 to 12 dB was achieved.

  Further, from FIG. 5, it was found that the voltage and current delay generated in the counter device 3 hardly occurred with respect to the voltage and current generated in the device under test 4.

  Next, for reference, an experimental result of a shunt characteristic of a general decoupling circuit will be described with reference to FIG. V3 is a voltage on the opposite device 3 side, I3 is a current on the opposite device 3 side, V4 is a voltage on the device under test 4 side, and I4 is a current on the device under test 4 side.

  FIG. 6 shows an example in which a four-divided air-core coil is used and the charging voltage of the lightning surge generator is 4 kV.

  In this case, it was found that the voltage and current on the counter device 3 side and the voltage and current on the device under test 4 side were delayed by about 300 us. This is because, in this general decoupling circuit, since it is composed only of a common mode choke coil, a phase delay is caused by its 20 mH inductance.

  However, in the decoupling circuit 5 of this embodiment, the low frequency spectrum suppressor 54 includes capacitors C1 and C1 of 10 nF per wire and two wires, and is connected in series with the common mode choke coil 55. It is comprised so that. With this configuration of the low frequency spectrum suppressor 54, the leading phase characteristic of the capacitor can be obtained, and the delayed phase of the common mode choke coil can be canceled.

  When capacitors are not connected in series, the delay amount should be large regardless of whether a four-divided air core coil or a two-divided air core coil is used. Nevertheless, the decoupling circuit 5 of the present embodiment can almost eliminate the delay.

  As described above, the decoupling circuit 5 passes through the decoupling circuit 5 to the opposite device 3 when performing the lightning surge overvoltage tolerance test in the communication state of the VDSL modem that is the device under test 4 and the opposite device 3. Significant improvement in the shunt characteristics for suppressing leakage overvoltage can be realized.

  In the lightning surge overvoltage tolerance test of a VDSL ICT device in communication state, the decoupling circuit 5 detects that the lightning surge overvoltage applied to the device under test 4 does not cause an increase in transmission loss or a deterioration in payload speed. 3 can be prevented from leaking.

  Next, a modification of this embodiment will be described.

  For example, the decoupling circuit 5 shown in FIG. 2 has the common mode choke coil 55 composed of the air core coils L11 to L14 divided into two parts. You may make it have. FIG. 7 shows a decoupling circuit 5A having a common mode choke coil composed of four air-core coils.

  The decoupling circuit 5A shown in FIG. 7 has eight air-core coils L11 to L18, and is different from that of FIG. 2 in that it is divided into four like D1 to D4.

  In the decoupling circuit 5 shown in FIG. 2, the capacitors C1 and C2 are provided between the winding start wire of the common mode choke coil and the terminals 51a and 51b. May be provided between the wire at the end of winding and the terminals 53a and 53b.

  Alternatively, the case where there are two communication ports of the device under test 4 has been described as an example. However, for example, when the number of communication ports is four, the decoupling circuit of the above-described embodiment and the modification can be applied. In this case, the common mode choke coil uses four wires.

  For example, a VDSL modem has been described as the opposing device 3 and the device under test 4. However, the present invention is not limited to this and can be applied to other communication devices such as IT devices.

1 Lightning surge generator 2a, 2b Coupling circuit 3 Opposing device 4 Device under test 5, 5A Decoupling circuit 54 Low frequency spectrum suppressor 55 Common mode choke coil L11-L14 Air core coil C1-C2 Capacitor W1-W2 Wire

Claims (4)

Connected between the device under test, which is an ICT device for VDSL, which is the subject of lightning surge overvoltage tolerance test, and the opposing device via a metal communication line, and VDSL signals can be transmitted via the metal communication line A decoupling circuit configured as follows:
A common mode choke coil composed of air-core coils;
A capacitor connected in series to the common mode choke coil,
The common mode choke coil is divided into a plurality and connected in series ;
The capacitor has a dielectric strength with respect to a test voltage in a common mode and a normal mode impedance capable of satisfactorily transmitting the VDSL signal.
The ICT device is a VDSL modem;
The capacitor generates a static mode impedance that is one tenth of the normal mode impedance of the common mode choke coil within a pass frequency band of a filter that suppresses mutual interference between the VDSL line and the ISDN line. A decoupling circuit having a capacitance . Connected between the device under test, which is an ICT device for VDSL, which is the subject of lightning surge overvoltage tolerance test, and the opposing device via a metal communication line, and VDSL signals can be transmitted via the metal communication line A decoupling circuit configured as follows:
A common mode choke coil composed of air-core coils;
A capacitor connected in series to the common mode choke coil;
With
The common mode choke coil is divided into a plurality and connected in series;
The capacitor is
When a common mode test voltage and a part of the current applied to the device under test leak to the ICT equipment via the decoupling circuit, a low frequency range from DC to several hundred Hz common mode impedance at is, the ICT decoupling you characterized in that large set 10 times more than the common mode impedance between the earth of the equipment. Connected between the device under test, which is an ICT device for VDSL, which is the subject of lightning surge overvoltage tolerance test, and the opposing device via a metal communication line, and VDSL signals can be transmitted via the metal communication line A decoupling circuit configured as follows:
A common mode choke coil composed of air-core coils;
A capacitor connected in series to the common mode choke coil;
With
The common mode choke coil is divided into a plurality and connected in series;
The capacitor is
A delay caused by the inductance of the common mode choke coil when a part of the test voltage and current applied to the device under test leaks to the ICT device through the decoupling circuit. Cancel to, the common mode choke decoupling multiple wires portion of the capacitor to the coil is you characterized by being connected in series. Connected between the device under test, which is an ICT device for VDSL, which is the subject of lightning surge overvoltage tolerance test, and the opposing device via a metal communication line, and VDSL signals can be transmitted via the metal communication line A decoupling circuit configured as follows:
A common mode choke coil composed of air-core coils;
A capacitor connected in series to the common mode choke coil;
A first terminal on the device under test side;
A second terminal on the opposite device side;
Bei to give a,
The common mode choke coil is divided into a plurality and connected in series;
The capacitor is connected between the winding start wire of the common mode choke coil and the first terminal, or between the winding end wire of the common mode choke coil and the second terminal. decoupling it characterized in that there.

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