JPH0677324U - Electromagnetic protection filter device for terminal equipment - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an electromagnetic protection filter device for a terminal device in which the optimum attenuation characteristics can be selectively switched according to the impedance of the transmission line and the terminal device and the frequency and type of common mode noise. [Structure] A plurality of common mode choke coils L1 to L4 having different center frequencies, a common mode choke coil selection switch 12 which makes the plurality of common mode choke coils L1 to L4 selectable, and a plurality of capacitors Cb1 having different capacities. The common mode choke coil selection switch 12 and the capacitor selection switch 11 are used for the common mode. The choke coils L1 to L4 and the capacitor Cb1 to
Cb4, Ce1 to Ce4 can be independently or serially connected in any combination to form a filter circuit, and each terminal 8, between the transmission line terminal and the terminal device,
It is characterized in that the filter circuit is inserted using 9, 13, and 14.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 This plan is a terminal that is inserted between the terminal of the transmission line of the telecommunication line equipment and the terminal equipment to remove common mode noise of high frequency current mixed in the transmission line and prevent the occurrence of high frequency interference in the terminal equipment. Electromagnetic protection filter device for equipment.

[0002]

[Prior art]

 Twisted pair / quad cables, loaded cables, unloaded cables, etc. are used as the local cables that have low multiplexing and a large number of logarithms among the transmission lines of telecommunication line facilities. Since these cables have insufficient electric shielding effect against external electromagnetic fields, they act as a kind of antenna, and the high-frequency currents of these external electromagnetic fields induced by electromagnetic induction are mixed in relatively easily.

The high-frequency current mixed in the cable is demodulated in the terminal device as a terminal station and superposed on the original demodulated signal, or so-called sneak is generated in an electronic circuit built in the terminal device, and It caused a malfunction. The noise component of the high frequency current is roughly classified into normal mode noise (positive phase noise) and common mode noise (common mode noise).

Normal mode noise is a noise component that appears at different potentials between paired transmission lines, and its removal is relatively difficult. On the other hand, common-mode noise is a noise component that appears in equal potential between paired transmission lines, that is, in-phase, and can be relatively easily removed by canceling out these in-phase components.

Therefore, conventionally, as a method of reducing the common mode noise mixed in the transmission line, a common mode choke coil and a capacitor are used to measure the noise level of each transmission line, the frequency band of the noise, the type of the noise, the transmission line A method has been adopted in which the transmission lines are paired or the transmission line termination and the terminal device are connected in series or in parallel, depending on the impedance of the terminal device.

That is, these elements are made to function as a band elimination filter (band elimination filter) having a required amount of attenuation in a frequency band in which the common mode noise has a level of a certain value or more, and a constant frequency band is obtained. This is a method of removing common mode noise having a width.

Here, the common-mode choke coil is a common-mode component applied to both poles by winding the start and end of the windings of both poles of the transmission line forming a pair with a ferrite core in the same direction. It is a type of choke coil that has the effect of canceling each other out by the back electromotive force. In addition, as a device for reducing common mode noise mixed in a transmission line, there has been a noise filter selection device in which a plurality of common mode choke coils are selectively inserted between the end of the transmission line and a terminal device.

A conventional noise filter selection device will be described with reference to the drawings. 6 is an external perspective view of a conventional noise filter selection device, FIG. 7 is the same circuit configuration diagram, and FIG. 8 is the same attenuation characteristic diagram. In the figure, A is a noise filter selection device, and 1 is a device case which is a shield case made of a conductor.

Reference numeral 2 is a four-core transmission line side modular jack attached to the device casing 1 so as to be connected to the end of the transmission line, 3a to 3d are 4-circuit interlocking type filter selection switches, and 4 is a terminal device. 4 cores attached to the device casing 1 so as to be connected to the terminal device side modular jack 5 is electrically connected to the device casing 1 for grounding, and is an earth terminal, and 6a to 6d are for 4 circuits. It is a built-in common mode choke coil.

In the circuit configuration diagram of FIG. 7, the transmission signal containing the common mode noise from the transmission line side modular jack 2 is fed to the common mode choke filters 6a to 6d having different center frequencies by the filter selection switches 3a to 3d. It is connected so that it can be sequentially passed or bypassed, and after common mode noise is removed, it is output to the modular jack 4 on the terminal equipment side.

In this way, by passing through the common mode filters 6a to 6d having different center frequencies, the attenuation amount of a certain value or more is continuously ensured in a certain frequency band. Further, since the filter selection switches 3a to 3d can be independently switched, it is possible to pass the transmission signal to the plurality of common mode choke filters 6a to 6d. Here, the transmission signal is collectively switched by interlocking four circuits.

FIG. 8 shows an attenuation characteristic diagram of a conventional noise filter selection device. The measurement was performed in an impedance of 50Ω system. This measurement result shows that an attenuation amount of 30 dB is obtained in the frequency band of 65 kHz to 40 MHz and an attenuation amount of 40 dB is obtained in the frequency band of 200 kHz to 3.5 MHz. The maximum attenuation was 58 dB (at 800 kHz).

[0013]

[Problems to be solved by the device]

 However, in these conventional methods and devices, only the common mode choke coil which is an inductance or the capacitor which is a capacitance is connected in series or in parallel to the transmission line, and therefore sufficient capacitance for constructing an LC resonance circuit is provided. Alternatively, the inductance could not be obtained. Therefore, a band elimination filter based on LC resonance cannot obtain a sufficient amount of attenuation and has a drawback that a high common mode noise removing effect cannot be obtained.

Furthermore, in the conventional method, the connection method of the common mode choke coil or the capacitor and various constants are appropriately selected for each terminal device to be connected, and the best element is measured while measuring the common mode noise step by step. This required a lot of work to choose, and this work was very complicated.

Since the common mode choke coil and the capacitor are temporarily connected to the transmission line by a method such as temporary attachment by soldering, insertion into the connector portion, or gripping and grasping the transmission line with a crocodile clip, etc. Contact failure frequently occurred, reliability was poor, and the common mode noise removal effect could not be measured accurately. Further, in the conventional noise filter selection device, since the center frequencies of the plurality of built-in common mode choke coils are close to each other, the applicable frequency band is narrow (500 kHz to 10 MHz in the conventional example). Had.

Therefore, the medium-wave broadcast wave (0.5 to 1.6 MHz) and the short-wave amateur radio wave (mainly 3.5, 7 and 14 MHz band) in the frequency band to which the noise filter selection device can be applied. Can be removed, but various electromagnetic induced noises at frequencies lower than these, short-wave / ultra-high-frequency amateur radio waves using higher frequencies (mainly 21,28,50MHz band) and illegal high-power citizens The effect of removing common mode noise against high frequency interference caused by radio (CB) waves (27 MHz band), commercial radio waves (40 MHz band), etc. was insufficient.

Furthermore, since the arrival of these amateur radio waves and the like is sporadic, it is difficult to measure the common mode noise removal effect and a great deal of time is spent on adjustment work. Here, the present invention is intended to provide an electromagnetic protection filter device for a terminal device, in which the optimum attenuation characteristics can be selectively switched according to the impedance of the transmission line and the terminal device and the frequency and type of common mode noise.

[0018]

[Means for Solving the Problems] The solution of the above problems is achieved by adopting the novel characteristic construction means enumerated below by the present invention. That is, the first feature of the present invention is that a plurality of common mode choke coils having different center frequencies, a common mode choke coil selection switch that makes the plurality of common mode choke coils selectable, and a plurality of capacitors having different capacities are provided. The common mode choke coil and the capacitors can be connected independently or in any combination in series and parallel by the common mode choke coil selection switch and the capacitor selection switch. An electromagnetic protection filter device for terminal equipment, in which the filter circuit is configured as, and the filter circuit is inserted between the transmission line end and the terminal equipment by using respective terminals.

A second feature of the present invention is for a terminal device in which a plurality of common mode choke coils and a plurality of capacitors according to the first feature are connected to each other by a connection sequence changeover switch so that the connection sequence can be changed freely. It is an electromagnetic protection filter device.

A third feature of the present invention is an electromagnetic protection filter device for a terminal device, wherein the filter circuit according to the first or second feature is integrally mounted in a small metal device casing.

A fourth characteristic of the present invention is that the terminals in the first, second or third characteristic are electromagnetic devices for terminal equipment in which various easily connectable / detachable connecting means such as modular jacks and screw terminals are used. It is a protective filter device.

[0022]

[Action]

 Since the present proposal adopts the above-mentioned configuration means, the type and constant of the filter can be freely selected according to the type of common mode noise and the frequency band. Furthermore, it is possible to easily make an electrical connection between the end of the transmission line and the terminal equipment.

[0023]

【Example】

 An embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is an external perspective view of an electromagnetic protection filter device for terminal equipment according to the present embodiment, FIG. 2 is a circuit configuration diagram of the same, FIG. 3 (a) is a common mode choke coil, (b) is a balanced capacitor, and (c). Is a grounding capacitor, (d) is a resonance type filter in which a grounding capacitor is connected in parallel to the transmission line side of the common mode choke coil, and (e) is a resonance type filter in which a grounding capacitor is connected in parallel to the terminal equipment side of the common mode choke coil. Fig. 4 shows the attenuation characteristic diagram of the same / common mode choke coil, and Fig. 5 shows the attenuation characteristic diagram of the resonant filter in which a grounding capacitor is connected in parallel to the transmission line side of the same / common mode choke coil. Is.

In the figure, B is an electromagnetic protection filter device for terminal equipment, Cb and Cb1 to Cb4 are balanced capacitors, Ce and Ce1 to Ce4 are ground capacitors, CP is a bypass line, and L and L1 to L4 are common mode chokes. A coil, LP is a bypass wire, 7 is a device casing which is a shield case made of a conductor, and 8 is a two-core transmission line side modular jack attached to the device casing 7.

Reference numeral 9 is a transmission line side terminal, 10 is a connection order changeover switch, 11 is a capacitor selection switch, 12 is a common mode choke coil selection switch, and 13 is a two-core terminal device side modular device attached to the device casing 7. A jack, 14 is a terminal device side terminal, and 15 is a ground terminal which is electrically connected to the apparatus casing 7 and grounded.

In FIG. 2, a transmission line terminal (not shown) is connected to either the transmission line side modular jack 8 or the transmission line side terminal 9 that are connected in parallel, and is connected to the terminal 10 a of the connection order changeover switch 10. There is. Similarly, a terminal device (not shown) is connected to either the terminal device side modular jack 13 or the terminal device side terminal 14 which are connected in parallel, and is connected to the terminal 10d of the connection order changeover switch 10.

The connection order changeover switch 10 is capable of freely changing the connection order of the common mode choke coils L1 to L4 and the capacitors Cb1 to Cb4 and Ce1 to Ce4. The terminal 10b of the connection order switch 10 is connected to the terminal 11a of the capacitor selection switch 11.

The capacitor selection switch 11 selectively passes any of the balanced capacitors Cb1 to Cb4, the grounded capacitors Ce1 to Ce4, and the bypass line CP. The balance capacitors Cb1 to Cb4 are connected in parallel to a pair of transmission lines. The grounding capacitors Ce1 to Ce4 ground the paired transmission lines via capacitors of the same capacity. The bypass line CP serves to bypass the capacitors Cb1 to Cb4 and Ce1 to Ce4 when they are not needed.

The terminal 11 b of the capacitor selection switch 11 is connected to the terminal 12 a of the common mode choke coil selection switch 12. The common mode choke coil selection switch 12 selectively passes any of the common mode choke coils L1 to L4 and the bypass line LP. The common mode choke coils L1 to L4 are connected in series with the transmission line. The bypass line LP plays a role of bypassing the common mode choke coils L1 to L4 when they are unnecessary.

In this embodiment, the capacitors Cb1 to Cb4 and Ce1 to Ce4 have capacitances of 1 μF, 0.1 μF, 0.01 μF, 0.001 μF, 1 μF, 0.1 μF, 0. 01 μF and 0.001 μF, and the attenuation characteristics of the common mode choke coils L1 to L4 are 30 Hz to 300 kHz (40 dB loss), 300 Hz to 600 kHz (40 dB loss), 200 kHz to 3 MHz (40 dB loss), 6 MHz to 40 MHz ( 30 dB loss).

The terminal 12b of the common mode choke coil selection switch 12 is again connected to the terminal 10c of the connection order changeover switch 10. Further, the earth terminal 15 is grounded at a single point to the device casing 7 which is a ground electrode and a conductor of the ground capacitors Ce1 to Ce4 and is connected to the ground.

Next, the specification of the present embodiment is such a specific embodiment, and its operation will be described in detail. When common mode noise due to high frequency current is mixed in the terminal equipment, the electromagnetic protection filter device B for terminal equipment of the present embodiment is inserted between the end of the transmission line and the terminal equipment. Specifically, the modular plug that is the terminal end of the transmission line is disconnected from the modular jack of the terminal device, and connected to the transmission line side modular jack 8 and the terminal device side modular jack 13 of the electromagnetic protection filter device B for the terminal device, respectively.

When the transmission line terminal or the terminal device does not employ a modular plug / jack, the transmission line side terminals connected in parallel to the transmission line side modular jack 8 and the terminal device side modular jack 13 respectively. 9 or the terminal 14 on the terminal device side.

Next, the capacitor selection switch 11 and the common mode choke coil selection switch 12 are respectively operated to select a filter configuration that minimizes common mode noise and a combination of constant values. If necessary, the connection order changeover switch 10 is also operated to select the connection order of the filter that minimizes the common mode noise.

Here, the circuit configuration of each filter shown in FIGS. 3A to 3E will be described in detail. In FIG. 3A, a common mode choke coil L is inserted in series between the transmission line terminal and the terminal device, and acts as a large inductance component with respect to the common mode noise in the frequency band peculiar to the common mode noise filter L. Block the passage of.

In FIG. 3 (b), a balancing capacitor Cb is connected between the paired transmission lines to keep the transmission lines electrically unbalanced at the frequency of the common mode noise electrically balanced. In FIG. 3 (c), the common mode noise is grounded and removed by inserting a grounding capacitor Ce, which has a low impedance in the frequency band of the common mode noise, between each pair of the transmission line and the ground.

In FIG. 3D, a grounding capacitor Ce is connected in parallel to the transmission line side of the common mode choke coil L to form an LC resonance type filter, and the common mode impedance of the transmission line is the common mode impedance of the terminal device. Effective when higher. Common mode noise mixed from the transmission line side is absorbed in the frequency band where the grounding capacitor Ce has a low impedance, so compared with the case of FIG. 3A in which only the common mode choke coil L is connected in series. And higher attenuation is obtained over a wider band.

In FIG. 3E, a grounding capacitor Ce is connected in parallel to the terminal device side of the common mode choke coil L to form an LC resonance type filter, and the common mode impedance of the terminal device is the common mode impedance of the transmission line. When it is higher than that, the connection method is effective, and the same effect as in FIG.

As shown in FIGS. 3D and 3E, a common mode choke coil L having an inherent center frequency is combined with the capacitors Cb and Ce to forcibly change the resonance frequency. In the present embodiment, the maximum capacitance of the capacitors Cb and Ce is 1 μF, the minimum capacitance is 0.001 μF, and the ratio is 1000 times, so that a very wide band elimination filter can be constructed.

(Measurement Results) FIGS. 4 to 5 show attenuation characteristic diagrams of the electromagnetic protection filter device B for terminal equipment of this embodiment. Fig. 4 shows the attenuation characteristic diagram of the common mode choke filter, and Fig. 5 shows the attenuation characteristic diagram of the resonance type filter in which the ground filter is connected to the transmission line side of the common mode choke filter. The measurement was carried out in an impedance of 50Ω system.

In FIG. 4, an attenuation amount of 30 dB in the frequency band of 10 Hz to 35 MHz, an attenuation amount of 40 dB in the frequency band of 40 Hz to 3.5 MHz, and an attenuation amount of 30 dB in the frequency band of 10 Hz to 70 MHz in FIG. However, it is shown that the attenuation amount of 40 dB is obtained in the frequency band of 40 Hz to 50 MHz.

Therefore, the attenuation characteristic is significantly improved as compared with the case of using the conventional noise filter selection device shown in FIG. In addition, the maximum attenuation is 104 dB (at 3.5 kHz) in the case of FIG. 4, and 103 dB (at 3.5 kHz) in the case of FIG. 5, which is extremely low compared to the case of using the conventional noise filter selection device A. It was possible to obtain a high attenuation rate.

In order to sufficiently attenuate the common mode noise, the filter is required to have an attenuation amount of 30 to 40 dB or more, but if various filters selectable in the present invention are used, a wide band of 30 to 60 MHz can be obtained. It is possible to obtain an attenuation amount of 40 to 100 dB over the width. In particular, by covering the frequency band of 100 Hz to 1 MHz, which is a frequency band with a large amount of common mode noise at all times, most of the common mode noise that enters the terminal device can be removed.

In the present embodiment, the electromagnetic protection filter device B for terminal equipment for one line has been described in detail, but it goes without saying that it can be applied to more lines. At this time, a filter may be configured with a pair of transmission lines as a unit, or the filters may be collectively switched for all transmission lines.

[0045]

[Effect of device]

 Thus, according to the present invention, the common mode choke coil and the capacitor can be selectively combined and connected, and various filters can be configured, so that the common mode noise rejection capability is high over a wide band.

Since the values of the common mode choke coil and the capacitor are freely selectable by the common mode choke coil selection switch and the capacitor selection switch, respectively, the maximum removal effect is achieved according to the frequency band of the common mode noise. can do.

Similarly, the connection changeover switch, the common mode choke coil selection switch, and the capacitor selection switch allow various preset filters to be selected, so that the impedance of the transmission line and the terminal device and the transmission line can be changed. It is possible to easily select the filter that exhibits the best removal effect according to the condition. Since the circuit configuration does not become so complicated compared to the conventional noise filter selection device, it can be manufactured in a small size, light weight, and at low cost, is easy to handle, and has portability.

Further, by measuring the resonance frequency of the filter in advance, it is possible to quickly select a filter that matches the frequency band of common mode noise, or conversely, measure the frequency band of common mode noise. Is. Furthermore, the connection between the end of the transmission line and the terminal equipment is made possible by using a detachable modular jack, etc., so that attachment / detachment and adjustment work are easy and workability is greatly improved.

[Brief description of drawings]

FIG. 1 is an external perspective view of an electromagnetic protection filter device for terminal equipment showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing the same as above.

FIG. 3A is a common mode choke coil, and FIG.
Is a balanced capacitor, (c) is a grounded capacitor, (d) is a resonance type filter in which a grounded capacitor is connected in parallel to the transmission line side of the common mode choke coil, and (e) is a grounded capacitor on the terminal device side of the common mode choke coil. FIG. 3 is a circuit configuration diagram of resonance filters connected in parallel.

FIG. 4 is the same as the above, and is an attenuation characteristic diagram when a common mode choke coil is used as a filter.

FIG. 5 is an attenuation characteristic diagram when a resonance type filter in which a grounding capacitor is connected to the transmission line side of a common mode choke coil is used as a filter.

FIG. 6 is an external perspective view of a conventional noise filter selection device.

FIG. 7 is a circuit diagram showing the same as above.

FIG. 8 is the same as the above-mentioned attenuation characteristic diagram.

[Explanation of symbols]

 A: Noise filter selection device B: Electromagnetic protection filter device for terminal equipment Cb, Cb1 to Cb4 ... Balanced capacitors Ce, Ce1 to Ce4 ... Grounding capacitors L, L1 to L4 ... Common mode choke coil 1 ... Device housing 2 ... Transmission line Side modular jacks 3a to 3d ... Filter selection switch 4 ... Terminal equipment side modular jack 5 ... Ground terminal 6a to 6d ... Common mode choke coil 7 ... Device housing 8 ... Transmission line side modular jack 9 ... Transmission line side terminal 10 ... Connection Order changeover switch 11 ... Capacitor selection switch 12 ... Common mode choke coil selection switch 13 ... Terminal equipment side modular jack 14 ... Terminal equipment side terminal 15 ... Ground terminal

Claims (4)

[Scope of utility model registration request] 1. A plurality of common mode choke coils having different center frequencies, a common mode choke coil selection switch that makes the plurality of common mode choke coils selectable, a plurality of capacitors having different capacities, and a plurality of the capacitors. The common mode choke coil selection switch and the capacitor selection switch constitute a filter circuit in which the common mode choke coil and the capacitor can be connected individually or in any combination in series and parallel. At the same time, the electromagnetic protection filter device for terminal equipment is characterized in that the filter circuit is inserted between the terminal of the transmission line and the terminal equipment by using respective terminals. 2. The electromagnetic protection filter device for a terminal device according to claim 1, wherein the plurality of common mode choke coils and the plurality of capacitors are connected to each other so that the connection order can be freely changed by a connection order changeover switch. 3. The electromagnetic protection filter device for terminal equipment according to claim 2 or 3, wherein the filter circuit is integrally mounted in a small metallic device casing. 4. Each terminal is a modular jack,
The electromagnetic protection filter device for terminal equipment according to claim 2, 3 or 4, wherein various types of connection means such as screw terminals that are easily removable are used.