JP2012064777A - Noise filter, cable with noise filter, and printed wiring board with noise filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a noise filter capable of suppressing influence on signal transmission of a differential mode at high frequency, and removing common mode noise; a cable with the noise filter; and a printed wiring board with the noise filter.SOLUTION: A cable 1 has a pair of conductors 2A and 2B, dielectrics 3A and 3B for covering the peripheries of the conductors 2A and 2B, and a cable sheath 4 combining the conductors 2A and 2B into one cable shape. The conductors 2A and 2B form a differential transmission line 2 for transmitting signals of opposite phases to each other. On the cable sheath 4, a noise filter 5 is provided so as to surround a fixed range in a longitudinal direction of the cable sheath 4. The noise filter 5 has a cylindrical composite magnetic body 6 made by magnetic body powder and binder, and a cylindrical and sheet-shaped shield conductor 7 pasted on an inner peripheral surface of the composite magnetic body 6.

Description

  The present invention relates to a noise filter that suppresses conductive noise propagating through a substrate wiring and cable for performing differential signal transmission using a magnetic material, a cable with a noise filter having the noise filter, and a printed wiring with a noise filter. Related to the board.

  In general, noise that adversely affects the operation of the apparatus has a problem of disturbing the outside and a problem of causing trouble due to noise from the outside. Noise from the outside is broadly classified into radiation noise that propagates through space and conduction noise that propagates through conductors such as cables and board wiring. In addition, the radiation noise is coupled with a signal wiring or power supply system in the apparatus, and becomes a conduction noise transmitted through the conductor of the signal line or power supply system.

  For such conduction noise, a frequency separation type filter that suppresses noise conduction in a specific frequency region by combining a resistor R, an inductor L, a capacitor C, and the like is used. In recent years, a so-called noise suppression sheet or noise absorbing sheet that suppresses high-frequency noise by simply processing a magnetic material into a sheet and sticking it to a substrate or a cable is used (for example, Patent Document 1). reference).

  In recent years, a differential transmission method is often used as a method for performing high-speed signal transmission. This differential transmission system is a system that uses two conductors, transmits signals of opposite phases to each other, and determines the signal level by taking the difference on the receiving side. This differential transmission system is advantageous for high-speed switching because a large amplitude difference can be obtained by making a difference even if the amplitude per conductor is small.

  Moreover, since external noise is normally coupled to two conductors in the same phase, there is an advantage that the external noise can be canceled out by taking a difference. Such a difference in phase / in-phase propagation is called differential mode / common mode propagation, and there is a common mode choke coil as a mode separation type filter using the difference in propagation mode (for example, Patent Document 2). reference).

International Publication No. 2004/045265 Pamphlet JP-A-7-29755

  Conventionally, the frequency band of the noise is often higher than the frequency band of the signal, and when the frequency of the signal and the frequency of the noise are different as described above, the conventional frequency separation type as described above is used. The filter works effectively. However, with the recent increase in speed of devices, the frequency band of signals has increased, and the frequency band of signals has overlapped with the frequency band of noise. For this reason, the conventional frequency separation type filter has a problem in that not only noise but also signal transmission is hindered.

  In addition, a mode separation type filter such as a common mode choke coil does not affect a normal mode signal in principle. However, a common mode choke coil that actually exists has a problem in that transmission of a high-frequency normal mode signal is also hindered.

  The present invention has been made to solve the above-described problems, and a noise filter and a noise that can remove common mode noise while suppressing the influence on differential mode signal transmission at a high frequency. It aims at obtaining the cable with a filter, and the printed wiring board with a noise filter.

  The noise filter according to the present invention is provided in a differential transmission line including a pair of signal transmission conductors for transmitting signals having opposite phases to each other, and is orthogonal to the signal transmission direction of the pair of signal transmission conductors. A shield conductor provided in the vicinity of the pair of signal transmission conductors so as to overlap the pair of signal transmission conductors in a direction, and shielding a magnetic field generated by a current flowing through the pair of signal transmission conductors; Provided on the opposite side of the pair of signal transmission conductors and having a magnetic body that interacts with a magnetic field generated by a current flowing through the shield conductor and inhibits a current flow through the shield conductor It is.

  A cable with a noise filter according to the present invention includes a pair of signal transmission conductors forming a differential transmission line for transmitting signals having opposite phases to each other, a cable sheath that combines the pair of signal transmission conductors into one, and Provided to surround the pair of signal transmission conductors, provided to surround the shield conductor for blocking the magnetic field generated by the current flowing through the pair of signal transmission conductors, and the pair of signal transmission conductors And a magnetic body that interacts with a magnetic field generated by a current flowing through the shield conductor and inhibits a current flow through the shield conductor.

  The printed wiring board with a noise filter according to the present invention includes a substrate provided with a pair of signal transmission conductors forming a differential transmission line for transmitting signals of opposite phases to each other, and signal transmission of the pair of signal transmission conductors. A shield conductor that is provided in the vicinity of the pair of signal transmission conductors so as to overlap the pair of signal transmission conductors in a direction perpendicular to the direction, and that shields a magnetic field generated by a current flowing through the pair of signal transmission conductors; Provided on the opposite side of the pair of signal transmission conductors in the shield conductor and provided with a magnetic body that interacts with a magnetic field generated by the current flowing through the shield conductor and inhibits the current flow in the shield conductor It is.

  According to the noise filter of the present invention, the shield conductor is provided in the vicinity of the pair of signal transmission conductors so as to overlap the pair of signal transmission conductors in a direction orthogonal to the signal transmission direction of the pair of signal transmission conductors, and magnetically Since the body is provided on the opposite side of the pair of signal transmission conductors in the shield conductor, there is no interaction with the magnetic body for the magnetic field of the differential signal, and the return current for the common mode noise is the shield conductor. The magnetic field generated by trying to flow on the outer surface of the magnetic field interacts with the magnetic material, and the flow of return current is obstructed, thereby suppressing the influence on differential mode signal transmission at high frequency, Mode noise can be removed.

  According to the cable with the noise filter of the present invention, the shield conductor is provided so as to surround the pair of signal transmission conductors, and the magnetic body is disposed on the opposite side of the pair of signal transmission conductors in the shield conductor. Since it is provided so as to surround the periphery of the transmission conductor, there is no interaction with the magnetic material for the magnetic field of the differential signal, and the return current of the common mode noise tends to flow on the outer surface of the shield conductor. The interaction between the magnetic field generated by the magnetic field and the magnetic material causes the return current flow to be inhibited, thereby suppressing the effect on differential mode signal transmission at high frequencies and eliminating common mode noise. it can.

  According to the printed wiring board with a noise filter of the present invention, the shield conductor is adjacent to the pair of signal transmission conductors so as to overlap the pair of signal transmission conductors in a direction orthogonal to the signal transmission direction of the pair of signal transmission conductors. Since the magnetic body is provided on the opposite side of the shielded conductor for the pair of signal transmission conductors, there is no interaction with the magnetic body for the magnetic field of the differential signal, and the return for the common mode noise. The interaction between the magnetic field generated by the current trying to flow on the outer surface of the shield conductor and the magnetic material causes the return current flow to be blocked, thereby affecting the differential mode signal transmission at high frequencies. It is possible to suppress common mode noise.

It is a perspective view which shows the cable with a noise filter by Embodiment 1 of this invention. It is a perspective view which shows the other example of the cable with a noise filter by Embodiment 1 of this invention. It is a block diagram which shows typically the to-be-measured object in the case of the measurement of a signal transmission characteristic. It is a graph which shows the measurement result by the network analyzer about the passage characteristic of the common mode signal and differential mode signal of the to-be-measured object of FIG. It is a perspective view which shows the other example of the cable with a noise filter by Embodiment 1 of this invention. It is a block diagram which shows the noise filter for cables by Embodiment 1 of this invention. It is a perspective view which shows the printed wiring board with a noise filter by Embodiment 2 of this invention. It is a perspective view which shows the printed wiring board with a noise filter by Embodiment 3 of this invention. It is a block diagram which shows the printed wiring board of FIG. It is a perspective view which shows the printed wiring board with a noise filter by Embodiment 4 of this invention. It is a block diagram which shows the printed wiring board of FIG. It is a perspective view which shows the printed wiring board with a noise filter by Embodiment 5 of this invention. It is a block diagram which shows the printed wiring board of FIG.

Embodiment 1 FIG.
1 is a perspective view showing a cable with a noise filter according to Embodiment 1 of the present invention.
In FIG. 1, a cable 1 includes a pair of conductors (signal transmission conductors) 2A, 2B, dielectrics 3A, 3B covering the outer periphery of each of the conductors 2A, 2B, and conductors 2A, 2B. It has a cable sheath 4 that is bundled into a cable shape. The conductors 2A and 2B form a differential transmission line 2 for transmitting signals having opposite phases to each other.

  The cable outer cover 4 is provided with a noise filter 5 so as to surround a certain range in the longitudinal direction. The noise filter 5 includes a cylindrical composite magnetic body (magnetic body) 6 made of magnetic powder and a binder, and a cylindrical and sheet-shaped shield conductor 7 attached to the inner peripheral surface of the composite magnetic body 6. And have.

  Reference numeral 8 in FIG. 1 denotes a ground as another conductor that can serve as a transmission path for the return current of common mode noise. The shield conductor 7 is disposed at a distance from the ground 8, has no connection with the ground 8, and is not electrically connected to the ground 8.

  Here, FIG. 1 shows a structure in which the shield conductor 7 has no connection with the ground 8. However, as shown in FIG. 2, the shield conductor 7 is connected to the ground 8 only at one point of the shield conductor 7 through the conductor 9. May be. In FIG. 2, the shield conductor 7 is connected to the ground 8 at one end portion, but the connection location is not limited to the end portion. If the shield conductor 7 is not connected to the ground 8 at both ends, the shield conductor 7 may be connected to the ground 8 at two or more points (one end portion and one or more intermediate portions or two or more intermediate portions).

  Next, the operation will be described. The two conductors 2A and 2B of the cable 1 form a pair, and differential transmission is performed by carrying signals of opposite phases to each other. Such a transmission mode is called differential mode (or normal mode) transmission, and signals are transmitted by only two conductors 2A and 2B with the other conductor as a return path.

  Further, the cable 1 may generate noise that is conducted by being influenced by radiation noise or the like from the outside. Such noise is transmitted to the conductors 2A and 2B in the cable 1 in the same phase. Such a transmission mode is called common mode transmission, and is generally transmitted as a return path through a conductor (ground 8) existing around the cable 1, such as the ground or an apparatus housing.

  The composite magnetic body 6 has a property of acting on a nearby high-frequency current with a magnetic field generated by the current, and absorbing the high-frequency current by converting it into heat by magnetic loss. Due to such properties, the composite magnetic body 6 functions as an absorption low-pass filter that allows low-frequency current to pass and absorbs high-frequency current. Note that the composite magnetic body 6 is processed into a sheet shape, and the same material as a known magnetic body material used as a noise suppression sheet or a noise absorbing sheet used by being attached to a substrate or a cable is used. it can.

  Next, a configuration when there is no shield conductor 7 will be described. As described above, the composite magnetic body 6 functions as a frequency separation type filter that passes low frequencies and absorbs high frequencies, and thus has an effect of suppressing conduction of noise that is generally high frequency. However, due to the recent increase in communication speed, the signal transmitted through the cable 1 has a high frequency, and in this case, the signal transmission is also hindered.

  On the other hand, in the configuration in which the shield conductor 7 is provided inside the composite magnetic body 6, the shield conductor 7 acts like a shield surrounding the cable 1, and a magnetic field generated by a differential signal flowing through the two conductors 2A and 2B. Is confined inside the shield conductor 7. As a result, the differential signal passes through without being influenced by the composite magnetic body 6.

  Further, the magnetic field of common mode noise flowing through the conductors 2A and 2B is also confined inside the shield conductor 7. At this time, the return current of the common mode noise flows through the inner surface of the shield conductor 7, and the shield conductor 7 does not have a connection with the ground 8. Therefore, the return current flows around the outer surface of the shield conductor 7, and the magnetic field generated thereby is generated. It acts on the composite magnetic body 6. Then, the return current is absorbed by the composite magnetic body 6, and the return current on the inner surface of the shield conductor 7 can no longer flow, and as a result, propagation of common mode noise is suppressed.

  Next, the measurement result of the signal transmission characteristic of the cable using the noise filter 5 of the first embodiment will be described. FIG. 3 is a configuration diagram schematically showing an object to be measured when measuring signal transmission characteristics. The object to be measured shown in FIG. 3 is obtained by wrapping a commercially available noise suppression sheet around the surface of a Twinnax cable (a cable for differential transmission in which two conductors are bundled together) with a cable shield (shield conductor). . The cable length is 10 cm, and BUSTERID (registered trademark) -R4N is used as the noise suppression sheet.

  FIG. 4 is a graph showing a measurement result by a network analyzer regarding the pass characteristics of the common mode signal and the differential mode signal of the DUT of FIG. As shown in FIG. 4A, it can be seen that the common mode signal has the same suppression effect as when the cable shield is not used, even if the cable shield is used unless the cable shield is grounded at both ends. . Further, as shown in FIG. 4B, for the differential mode signal, the passing amount is greatly attenuated in the band of 1 GHz or more in the configuration not using the cable shield, but in the configuration using the cable shield, It can be seen that the loss of the passage amount is improved regardless of the ground contact state.

  Therefore, according to the first embodiment as described above, the shield conductor 7 is provided so as to surround the conductors 2A and 2B, and the composite magnetic body 6 is disposed on the shield conductor 7 on the opposite side of the conductors 2A and 2B. It is provided so as to surround the conductors 2A and 2B. With this configuration, there is no interaction with the composite magnetic body 6 for the magnetic field of the differential signal, and the magnetic field generated by the return current of the common mode noise flowing through the outer surface of the shield conductor 7 and the composite magnetic body. 6 interacts with the flow of the return current. As a result, it is possible to eliminate the common mode noise while suppressing the influence on the differential mode signal transmission at a high frequency.

  In the first embodiment, as shown in FIG. 5, not only the first shield conductor 7A inside the composite magnetic body 6 but also the outside of the composite magnetic body 6 is a cylindrical and sheet-like second. You may make it affix the shield conductor 7B.

  In the first embodiment, the shield conductor 7 may be not only a sheet shape without a gap but also a braided shape (mesh shape) in which thin conductor wires are knitted.

  Furthermore, in the first embodiment, the composite magnetic body 6 composed of the magnetic powder and the binder is used, but a ferrite core may be used instead of the composite magnetic body 6.

  Further, as shown in FIG. 6A, the composite magnetic body is formed into a strip (or sheet) to form a magnetic sheet 12, and the strip (or sheet) shield conductor 7 is provided only on one surface of the magnetic sheet 12. The noise filter 11 may be configured by pasting. In addition, as shown in FIG. 6B, the noise filter 11 may be configured by attaching band-shaped (or sheet-shaped) shield conductors 13 </ b> A and 13 </ b> B to both surfaces of the magnetic sheet 12. In these cases, the noise filter 11 may be wound so that the shield conductor 13 or the shield conductor 13A is on the inner side and the outer surface of the cable sheath is covered.

Embodiment 2. FIG.
In the first embodiment, the cable with the noise filter has been described. On the other hand, Embodiment 2 demonstrates the printed wiring board with a noise filter. FIG. 7 is a perspective view showing a printed wiring board with a noise filter according to Embodiment 2 of the present invention. 7A is a perspective view showing the printed wiring board 21, and FIG. 7B is a configuration showing the state where the printed wiring board 21 is viewed in the direction of arrow A in FIG. 7A. FIG.

  In FIG. 7, the printed wiring board 21 has a dielectric substrate 22 and printed wiring (not shown) formed on the dielectric substrate 22. In addition, a pair of conductors (signal transmission conductors) 23A and 23B are provided on the surface of the dielectric substrate 22. The conductors 23A and 23B are arranged in parallel with a space therebetween. The conductors 23A and 23B form a differential transmission line 23 for transmitting signals with opposite phases.

  On the surface (upper surface) of the dielectric substrate 22, an insulating material 24, a shield conductor 25, and a composite magnetic body 26 are laminated so as to cover a part of the conductors 23A and 23B. The shape of the insulating material 24 is a sheet shape (or plate shape). The insulating material 24 prevents a short circuit between the shield conductor 25 and the conductors 23A and 23B. The shape of the shield conductor 25 is a sheet shape (or plate shape). The composite magnetic body 26 is composed of a magnetic powder and a binder. The shape of the composite magnetic body 26 is a sheet (or plate). The insulating material 24, the shield conductor 25, and the composite magnetic body 26 constitute a sheet-like noise filter 27 having a three-layer structure.

  Here, a ground (not shown) through which the return current of the common mode noise flows is present inside the printed wiring board 21 or around the printed wiring board 21, but the shield conductor 25 is electrically non-conductive with the ground. Connected.

  Next, the operation of the second embodiment will be described. Two conductors 23A and 23B form a pair, and carry differential transmission by carrying signals of opposite phases to each other. Such a transmission mode is called differential mode (or normal mode) transmission, and signal transmission is possible using only the two conductors 23A and 23B with the other conductor as a return path.

  In addition, the conductors 23A and 23B may generate noise that is conducted under the influence of radiation noise or the like from the outside. Such noise is transmitted to the conductors 23A and 23B in the same phase. Such a transmission mode is called common mode transmission, and is transmitted as a return path through a conductor existing in the periphery, such as a ground layer inside the dielectric substrate 22, a device housing, and the ground.

  The composite magnetic body 26 is composed of a magnetic powder and a binder, and acts on a magnetic field generated by the current with respect to a high-frequency current in the vicinity, and has a property of absorbing the high-frequency current by converting it into heat due to magnetic loss, It works as an absorption-type low-pass filter that passes low-frequency current and absorbs high-frequency current. Such a composite magnetic body 26 is processed into a sheet shape and uses a magnetic material equivalent to a magnetic material used as a known noise suppression sheet or noise absorbing sheet used by being attached to a substrate or a cable. Can do.

  Next, a configuration when the shield conductor 25 is not provided will be described. As described above, the composite magnetic body 26 functions as a frequency separation type filter that passes low frequencies and absorbs high frequencies, and thus has an effect of suppressing conduction of noise that is generally high frequency. However, due to the recent increase in communication speed, the signal transmitted through the differential transmission line 23 also has a high frequency. In this case, signal transmission is also hindered.

  Here, when the shield conductor 25 is provided between the composite magnetic body 26 and the conductors 23A and 23B, the shield conductor 25 functions as a shield covering the conductors 23A and 23B, and is caused by a differential signal flowing through the conductors 23A and 23B. The generated magnetic field does not act on the composite magnetic body 26, and the differential signal passes as it is.

  Further, the magnetic field of the common mode noise flowing through the conductors 23A and 23B is also confined below the shield conductor 25. At this time, the return current of the common mode noise flows through the lower surface of the shield conductor 25. A return current flows around the upper surface of the magnetic field, and a magnetic field generated thereby acts on the composite magnetic body 26. Then, the return current is absorbed by the composite magnetic body 26, and the return current on the lower surface of the shield conductor 25 can no longer flow, and as a result, propagation of common mode noise is suppressed.

  According to the second embodiment as described above, the shield conductor 25 is provided in the vicinity of the conductors 23A and 23B so as to overlap the conductors 23A and 23B in the direction orthogonal to the signal transmission direction of the conductors 23A and 23B, and the composite magnetic body 26 is provided on the shield conductor 25 on the opposite side of the conductors 23A and 23B. With this configuration, there is no interaction with the composite magnetic body 26 for the magnetic field of the differential signal, and the magnetic field generated by the return current of the common mode noise flowing through the outer surface of the shield conductor 25 and the composite magnetic body. As a result of the interaction with H. 26 and the flow of the return current being inhibited, the influence on the differential mode signal transmission at a high frequency can be suppressed and common mode noise can be eliminated.

  In the second embodiment, the conductors 23A and 23B in FIG. 7 are provided on the surface of the dielectric substrate 22. However, the conductors 23A and 23B may be provided in the dielectric substrate 22 (inner layer). In the second embodiment, there may be other wiring around the conductors 23A and 23B. Further, in the second embodiment, the shield conductor 25 is not connected to the ground. However, if the conductors 23A and 23B are not connected to the ground at both ends in the signal transmission direction (longitudinal direction), one or more shield conductors 25 are provided. It may be connected to the ground at a point.

  In the second embodiment, the lower surface of the insulating material 24 and the surface of the dielectric substrate 22 are in contact with each other. However, if the insulating material 24 is configured to maintain the insulation between the conductors 23A and 23B and the shield conductor 25, A hollow region may be formed between the lower surface of the insulating material 24 and the surface of the dielectric substrate 22.

  Furthermore, in the second embodiment, the insulating material 24, the shield conductor 25, and the composite magnetic body 26 constitute a sheet-like noise filter 27 having a three-layer structure. However, the present invention is not limited to this example, and the first magnetic shield conductor is provided on one of the upper and lower surfaces of the composite magnetic body, and the second shield conductor is provided on the other surface. A noise filter may be formed.

Embodiment 3 FIG.
In the second embodiment, the printed wiring board in which the conductors 23A and 23B are provided on the surface of the dielectric substrate 22 has been described. In contrast, in the third embodiment, a printed wiring board in which 33A and 33B are provided inside (inner layer) the dielectric substrate 32 will be described.

  FIG. 8 is a perspective view showing a printed wiring board with a noise filter according to Embodiment 3 of the present invention. FIG. 9 is a configuration diagram showing the printed wiring board 31 of FIG. 9A shows a state in which the printed wiring board 31 is viewed in the direction of arrow B in FIG. 8, and FIG. 9B shows the printed wiring board 31 in the direction of arrow C in FIG. Shows the state of viewing.

  8 and 9, the printed wiring board 31 has a dielectric substrate 32 and printed wiring (not shown) formed on the dielectric substrate 32. Inside the dielectric substrate 32 (inner layer), a pair of conductors (signal transmission conductors) 33A and 33B and a shield conductor 34 are provided. The conductors 33A and 33B are arranged in parallel with an interval between each other. The conductors 33A and 33B form a differential transmission line 33 for transmitting signals having opposite phases to each other.

  The shape of the shield conductor 34 is cylindrical and has a square cross section. The shield conductor 34 is disposed so as to surround a certain range in the signal transmission direction (longitudinal direction) of the conductors 33A and 33B. A sheet-shaped (or plate-shaped) composite magnetic body 35 is provided on the upper surface of the dielectric substrate 32. The composite magnetic body 35 is disposed so as to overlap the shield conductor 34 in the thickness direction of the dielectric substrate 32. The shield conductor 34 and the composite magnetic body 35 constitute a noise filter 36.

  Here, a ground (not shown) through which the return current of the common mode noise flows is present inside or around the dielectric substrate 32, but the shield conductor 34 is not electrically connected to the ground. Connected.

  Next, the operation will be described. Operation of propagation of differential mode signals transmitted through conductors 33A and 33B and common mode noise, and operation of composite magnetic body 35 acting as an absorption-type low-pass filter that passes low-frequency current and absorbs high-frequency current These are the same as in the second embodiment. Here, the difference from Embodiment 2 will be mainly described.

  First, the configuration when the shield conductor 34 is not provided will be described. As described above, since the composite magnetic body 35 is a frequency separation type filter that absorbs high frequencies, if the signals transmitted through the conductors 33A and 33B become high speed, the transmission of signals is also hindered.

  Next, the configuration when the shield conductor 34 is used will be described. The shield conductor 34 acts like a shield covering the conductors 33A and 33B, and the magnetic field generated by the differential signal flowing through the conductors 33A and 33B does not act on the composite magnetic body 35, and the differential signal passes through as it is.

  The common mode noise magnetic field flowing through the conductors 33A and 33B is also confined inside the shield conductor 34. At this time, the return current of the common mode noise flows through the inner surface of the shield conductor 34. A return current flows around the outer surface of the magnetic field, and a magnetic field generated thereby acts on the composite magnetic body 35. Then, the return current is absorbed by the composite magnetic body 35, and the return current on the inner surface of the shield conductor 34 also does not flow, and as a result, propagation of common mode noise is suppressed.

  According to the third embodiment as described above, even when the cylindrical shield conductor 34 is provided inside the dielectric substrate 32, the same effects as those of the second embodiment can be obtained.

  In the third embodiment, the shield conductor 34 is not connected to the ground. However, the shield conductor 34 is not connected to the ground at both ends in the longitudinal direction of the conductors 33A and 33B. You may connect.

Embodiment 4 FIG.
In the third embodiment, the printed wiring board using the cylindrical shield conductor 34 has been described. On the other hand, in the fourth embodiment, a printed wiring board using a plate-like (layer-like) shield conductor 44 will be described.

  FIG. 10 is a perspective view showing a printed wiring board with a noise filter according to Embodiment 4 of the present invention. FIG. 11 is a configuration diagram showing the printed wiring board 41 of FIG. 11A shows a state in which the printed wiring board 41 is viewed in the direction of arrow D in FIG. 10, and FIG. 11B shows the printed wiring board 41 in the direction of arrow E in FIG. Shows the state of viewing.

  10 and 11, the printed wiring board 41 has a dielectric substrate 42 and printed wiring (not shown) formed on the dielectric substrate 42. Inside the dielectric substrate 42 (inner layer), a pair of conductors (signal transmission conductors) 43A and 43B and a shield conductor 44 are provided. The conductors 43A and 43B are arranged in parallel with a space therebetween. The conductors 43A and 43B form a differential transmission line 43 for transmitting signals with opposite phases.

  The shape of the shield conductor 44 is a plate (or layer). The shield conductor 44 is disposed in the vicinity of the conductors 43A and 43B so as to overlap the conductors 43A and 43B in a direction orthogonal to the signal transmission direction of the conductors 43A and 43B. A sheet-shaped (or plate-shaped) composite magnetic body 45 is provided on the upper surface of the dielectric substrate 42. The composite magnetic body 45 is disposed so as to overlap the shield conductor 44 in the thickness direction of the dielectric substrate 42. The shield conductor 44 and the composite magnetic body 45 constitute a noise filter 46.

  Here, a ground (not shown) through which a return current of common mode noise flows is present inside or around the dielectric substrate 42, but the shield conductor 44 is not electrically connected to the ground. Connected.

  Next, the operation will be described. Operation of propagation of differential mode signals and common mode noise transmitted through conductors 43A and 43B, and operation of composite magnetic body 45 acting as an absorption-type low-pass filter that passes low-frequency current and absorbs high-frequency current These are the same as in the second embodiment. Here, the difference from Embodiment 2 will be mainly described.

  First, the configuration when the shield conductor 44 is not provided will be described. Since the composite magnetic body 45 is a frequency separation type filter that absorbs a high frequency as in the second and third embodiments, if the signal transmitted through the conductors 43A and 43B becomes high speed, the transmission of the signal is also hindered. End up.

  Next, the configuration when the shield conductor 44 is used will be described. The shield conductor 44 functions to block the magnetic field generated by the current flowing through the conductors 43A and 43B, and the magnetic field generated by the differential signal flowing through the conductors 43A and 43B hardly acts on the composite magnetic body 45, and the differential signal is It passes almost as it is.

  Further, the magnetic field of the common mode noise flowing through the conductors 43A and 43B is also concentrated between the conductor 43A and 43B, and at this time, the return current of the common mode noise flows through the lower surface of the shield conductor 44, and further, the shield conductor A return current flows around the upper surface of 44, and a magnetic field generated thereby acts on the composite magnetic body 45. Then, the return current is absorbed by the composite magnetic body 45, and the return current on the lower surface of the shield conductor 44 can no longer flow, and as a result, propagation of common mode noise is suppressed.

  According to the fourth embodiment as described above, even if the plate-like shield conductor 44 is provided inside the dielectric substrate 42, the same effect as in the second embodiment can be obtained.

  In the fourth embodiment, the shield conductor 44 and the composite magnetic body 45 are provided only above the conductors 43A and 43B. However, the present invention is not limited to this example, and a shield conductor and a composite magnetic body may be provided below the conductors 43A and 43B.

  In the fourth embodiment, the shield conductor 44 is not connected to the ground. However, if the conductors 43A and 43B are not connected to the ground at both ends in the longitudinal direction, the shield conductor 44 is connected to the ground at one or more points. May be.

Embodiment 5 FIG.
In the third embodiment, the printed wiring board provided with the shield conductor 34 having a cylindrical shape and a rectangular cross section has been described. On the other hand, in the fifth embodiment, a printed wiring board provided with a pair of plate-like shield conductors 53A and 53B and a plurality of vias 55 will be described.

  12 is a perspective view showing a printed wiring board with a noise filter according to a fifth embodiment of the present invention. FIG. 13 is a configuration diagram showing the printed wiring board 51 of FIG. 13A shows a state in which the printed wiring board 51 is viewed in the direction of arrow F in FIG. 12, and FIG. 13B shows the printed wiring board 51 in the direction of arrow G in FIG. Shows the state of viewing.

  12 and 13, the printed wiring board 51 includes a dielectric substrate 52 and printed wiring (not shown) formed on the dielectric substrate 52. Inside the dielectric substrate 52 (inner layer), a pair of conductors (signal transmission conductors) 53A and 53B, a pair of shield conductors 54A and 54B, and a plurality of vias 55 are provided. The conductors 53A and 53B are arranged in parallel with a space between each other. The conductors 53A and 53B form a differential transmission line 53 for transmitting signals having opposite phases to each other.

  The shield conductors 54A and 54B have a plate shape. The shield conductors 54A and 54B are arranged in the vicinity of a certain range in the signal transmission direction (longitudinal direction) of the conductors 53A and 53B so as to overlap the conductors 53A and 53B in a direction orthogonal to the signal transmission direction of the conductors 53A and 53B. ing. Further, the shield conductors 54A and 54B are arranged to face each other with a space therebetween so as to sandwich the conductors 53A and 53B.

  The plurality of vias 55 are, for example, a cylindrical conductor, a through hole, or the like. Further, the plurality of vias 55 are arranged at intervals in the longitudinal direction of the conductors 53A and 53B on both sides of the conductors 53A and 53B. The plurality of vias 55 electrically connect the shield conductors 54A and 54B.

  A sheet-shaped (or plate-shaped) composite magnetic body 56 is attached to the upper surface of the dielectric substrate 52. The composite magnetic body 56 is disposed so as to overlap the shield conductor 54 </ b> A in the thickness direction of the dielectric substrate 52. The shield conductors 54 </ b> A and 54 </ b> B, the plurality of vias 55, and the composite magnetic body 56 constitute a noise filter 57.

  Here, a ground (not shown) through which a return current of common mode noise flows is present inside or around the dielectric substrate 52, but the shield conductors 54A and 54B and the plurality of vias 55 are present. Is electrically disconnected from the ground.

  Next, the operation will be described. Operation of propagation of differential mode signals and common mode noise transmitted through the conductors 53A and 53B, and operation of the composite magnetic body 56 acting as an absorption low-pass filter that passes low frequency current and absorbs high frequency current These are the same as in the second embodiment. Here, the difference from Embodiment 2 will be mainly described.

  First, a configuration when the shield conductors 54A and 54B and the plurality of vias 55 are not provided will be described. Since the composite magnetic body 56 is a frequency separation type filter that absorbs high frequencies, as in the second and third embodiments, if the signal transmitted through the conductors 53A and 53B becomes high speed, the signal transmission is also hindered. End up.

  Next, the configuration when the shield conductors 54A and 54B and the plurality of vias 55 are used will be described. The shield conductors 54A and 54B block the magnetic field generated by the current flowing through the conductors 53A and 53B, and the magnetic field generated by the differential signal flowing through the conductors 53A and 53B hardly acts on the composite magnetic body 56. Pass as it is.

  The common mode noise magnetic field flowing through the conductors 53A and 53B is also concentrated between the shield conductors 54A and 54B. At this time, the return current of the common mode noise flows through the lower surface of the shield conductor 54A. A return current flows around the upper surface of 54 A, and a magnetic field generated thereby acts on the composite magnetic body 56. Then, the return current is absorbed by the composite magnetic body 56 and the return current on the lower surface of the shield conductor 54A can no longer flow, and as a result, propagation of common mode noise is suppressed.

  According to the fifth embodiment as described above, the same effects as those of the second embodiment can be obtained even in the configuration using the pair of shield conductors 54A and 54B and the plurality of vias 55.

  In the fifth embodiment, the configuration in which the composite magnetic body 56 is provided only on the upper surface of the dielectric substrate 52 has been described. However, the present invention is not limited to this example, and a composite magnetic material may be provided on both the upper and lower surfaces of the dielectric substrate.

  In the fifth embodiment, the shield conductors 54A and 54B and the plurality of vias 55 are not connected to the ground. However, if the conductors 53A and 53B are not connected to the ground at both ends in the longitudinal direction, It may be connected to the ground at a point or a plurality of points.

  Furthermore, in Embodiments 3 to 5, a plate-like or sheet-like second shield conductor may be provided on the upper surface of the composite magnetic bodies 35, 45, and 56.

  1 cable, 2 differential transmission line, 2A, 2B conductor (signal transmission conductor), 3A, 3B dielectric, 4 cable sheath, 5 noise filter, 6 composite magnetic material, 7 shield conductor, 7A first shield conductor, 7B Second shield conductor, 8 ground, 11 noise filter, 12 magnetic sheet, 13A, 13B shield conductor, 21 printed wiring board, 22 dielectric substrate, 23 differential transmission line, 23A, 23B conductor (signal transmission conductor) ), 24 Insulating material, 25 Shield conductor, 26 Composite magnetic body, 27 Noise filter, 31 Printed wiring board, 32 Dielectric substrate, 33 Differential transmission line, 33A, 33B Conductor (signal transmission conductor), 34 Shield conductor, 35 composite magnetic material, 36 noise filter, 41 printed wiring board, 42 dielectric substrate, 43 differential transmission line Path, 43A, 43B conductor (signal transmission conductor), 44 shield conductor, 45 composite magnetic body, 46 noise filter, 51 printed wiring board, 52 dielectric substrate, 53A, 53B conductor (signal transmission conductor), 53 differential Transmission line, 54A, 54B Shield conductor, 55 via, 56 composite magnetic material, 57 noise filter.

Claims (19)

A noise filter provided in a differential transmission line composed of a pair of signal transmission conductors for transmitting signals having opposite phases to each other,
The pair of signal transmission conductors is provided in the vicinity of the pair of signal transmission conductors so as to overlap with the pair of signal transmission conductors in a direction orthogonal to the signal transmission direction, and the current flowing through the pair of signal transmission conductors A shield conductor that blocks the generated magnetic field;
A magnetic body provided on the opposite side of the pair of signal transmission conductors in the shield conductor, interacting with a magnetic field generated by a current flowing through the shield conductor, and inhibiting the current flowing through the shield conductor; A characteristic noise filter. The pair of signal transmission conductors are provided in a cable,
The shape of the shield conductor and the magnetic body is cylindrical,
The noise filter according to claim 1, wherein the shield conductor and the magnetic body are disposed so as to cover an outer surface of the cable. The pair of signal transmission conductors are provided in a cable,
The shape of the shield conductor and the magnetic body is a band shape,
The noise filter according to claim 1, wherein the shield conductor and the magnetic body are wound around the outer surface of the cable so as to cover the outer surface of the cable. The pair of signal transmission conductors are provided on the surface of the substrate,
The shape of the shield conductor and the magnetic body is a plate or a sheet,
The noise filter according to claim 1, wherein the shield conductor and the magnetic body are laminated on a surface of the substrate via an insulator. The pair of signal transmission conductors are provided inside the substrate,
The shield conductor is provided inside the substrate so as to surround the pair of signal transmission conductors,
The noise filter according to claim 1, wherein the magnetic body is provided on a surface of the substrate. The second shield conductor provided on the opposite side of the first shield conductor as the shield conductor in the magnetic body, further comprising: a first shield conductor according to any one of claims 1 to 5; Noise filter. 7. The shield conductor is in an electrically non-connected state with another conductor that can serve as a transmission path for a return current of common mode noise generated in the pair of signal transmission conductors. The noise filter according to any one of the above. The said shield conductor is electrically connected at one place with the other conductor which can become a transmission path of the return current of the common mode noise which arises in the said pair of signal transmission conductors. The noise filter according to any one of 6 to 6. The shield conductor may be one end or the other end in the signal transmission direction of the pair of signal transmission conductors in the shield conductor and one or more of the intermediate portions, or the pair of signal transmissions in the shield conductor. It is electrically connected to other conductors that can serve as a transmission path for the return current of the common mode noise generated in the pair of signal transmission conductors at two or more places in the middle of the signal transmission direction of the conductors. The noise filter according to any one of claims 1 to 6. A pair of signal transmission conductors forming a differential transmission line for transmitting signals of opposite phases to each other;
A cable sheath that combines the pair of signal transmission conductors into one;
A shield conductor that is provided so as to surround the pair of signal transmission conductors, and that blocks a magnetic field generated by a current flowing through the pair of signal transmission conductors;
A magnetic body provided to surround the pair of signal transmission conductors and interacting with a magnetic field generated by a current flowing through the shield conductor to inhibit the current flowing through the shield conductor. Cable with noise filter. The shape of the shield conductor and the magnetic body is cylindrical,
The cable with a noise filter according to claim 10, wherein the shield conductor and the magnetic body are arranged so as to cover an outer surface of the cable skin. The shape of the shield conductor and the magnetic body is a band shape,
The cable with a noise filter according to claim 10, wherein the shield conductor and the magnetic body are wound around an outer surface of the cable outer cover so as to cover an outer surface of the cable outer cover. The second shield conductor provided on the opposite side of the first shield conductor as the shield conductor in the magnetic body, further comprising: a first shield conductor according to any one of claims 10 to 12. Cable with noise filter. A substrate provided with a pair of signal transmission conductors forming a differential transmission line for transmitting signals having opposite phases to each other;
The pair of signal transmission conductors is provided in the vicinity of the pair of signal transmission conductors so as to overlap with the pair of signal transmission conductors in a direction orthogonal to the signal transmission direction, and the current flowing through the pair of signal transmission conductors A shield conductor that blocks the generated magnetic field;
A magnetic body provided on the opposite side of the pair of signal transmission conductors in the shield conductor, interacting with a magnetic field generated by a current flowing through the shield conductor, and inhibiting the current flowing through the shield conductor; Characteristic printed wiring board with noise filter. The pair of signal transmission conductors are provided on the surface of the substrate,
The shape of the shield conductor and the magnetic body is a plate or a sheet,
The printed wiring board with a noise filter according to claim 14, wherein the shield conductor and the magnetic body are laminated on a surface of the substrate via an insulator. The pair of signal transmission conductors and the shield conductor are provided inside the substrate,
The printed circuit board with a noise filter according to claim 14, wherein the magnetic body is provided in the vicinity of the shield conductor on the surface of the substrate. The printed wiring board with a noise filter according to claim 16, wherein the shield conductor is provided inside the substrate so as to surround the pair of signal transmission conductors. The shield conductors are a pair of shield conductors arranged opposite to each other inside the substrate so as to sandwich the pair of signal transmission conductors,
The printed wiring board with a noise filter according to claim 16, wherein the pair of shield conductors are electrically connected to each other through a plurality of vias. The second shield conductor provided on the opposite side of the first shield conductor as the shield conductor in the magnetic body is further provided. Printed wiring board with noise filter.

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