JP3545245B2 - Common mode filter - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a filter used in a balanced communication transmission line, and more particularly, to a filter that suppresses a common mode current that causes electromagnetic noise generated in a balanced transmission line.
[0002]
[Prior art]
In a balanced transmission system using two transmission lines, in a signal transmitted between devices, currents in opposite directions flow through two transmission lines, and such a current component is called a differential mode (balanced component). Apart from this, a current component in the same direction may flow through two transmission lines, and a current may flow through a reference ground plane as a return path. This is referred to as a common mode (unbalanced component) current. At high frequencies, this common mode current forms a large current loop, and becomes a source of electromagnetic noise. In addition, the common mode current serves as a drive source, and may generate electromagnetic noise as an antenna when an external cable or the like is connected.
[0003]
Therefore, conventionally, as a method of reducing the common mode current, there are a common mode choke coil and a common mode filter proposed by the present inventors in Japanese Patent Application No. 10-296237.
[0004]
A common mode choke coil is used in a relatively low frequency region of several hundred MHz or less, and has a structure in which two balanced lines are wound around a ring-shaped ferrite or the like. Since the directions of the magnetic fluxes generated by the transmission lines are the same, the impedance becomes high, and the differential mode current has a low impedance because the directions of the magnetic fluxes generated by the two transmission lines cancel each other in opposite directions.
[0005]
The common mode filter proposed by the present inventor is used in a high frequency region of several hundred MHz or more. In a laminated dielectric substrate, a grounding conductor layer is provided on the upper and lower surfaces of a grounding conductor layer. A structure in which a pair of line-shaped conductors are provided as two transmission lines so as to overlap in an axial direction perpendicular to a ground plane formed by the conductor layer, wherein the pair of line-shaped conductors is an upper grounding conductor layer; A conductor portion having a spiral or meandering pattern formed in proximity to and parallel to the conductor portion, and a spiral or meandering pattern circling in the same direction as the pattern formed earlier in proximity to and parallel to the lower grounding conductor layer is formed. And electrically connected conductor portions to each other.
[0006]
With this structure, when a common mode current flows through a pair of linear conductors, a magnetic wall is formed between the pair of linear conductors, so that no capacitance component (capacitor component) is generated between the pair of linear conductors. , Can be regarded as one transmission line. At this time, the lower spiral or meander pattern conductor and the lower ground conductor layer, the upper spiral or meander pattern and the upper ground conductor layer, and the upper or lower spiral or meander pattern A distributed constant capacitance component is generated between the patterns, and when these are combined with an inductor component generated by a spiral or meander pattern, a π-type low-pass filter is formed, and a preset high-frequency common mode current is set. Attenuate components.
[0007]
While the common mode choke coil uses the difference in the inductor component between the common mode and the differential mode, the common mode filter uses the difference in the capacitance component.
[0008]
[Problems to be solved by the invention]
In the common mode filter, the effect of inductor mutual induction is limited because the permeability of a dielectric such as ceramics is 1 even when the transmission line is formed in a spiral shape to concentrate magnetic flux.
[0009]
The present invention has been made in view of the above points, and provides a common mode filter that increases the attenuation of a common mode current and reduces the loss of a differential mode current by giving the effect of inductor mutual induction to the common mode filter. With the goal.
[0010]
Other objects and novel features of the present invention will be clarified in embodiments described later.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a method of forming a pair of upper and lower grounding conductor layers with a dielectric therebetween, and a pair of line-shaped conductors in parallel in the dielectric and between the pair of grounding conductor layers. Each of the pair of linear conductors is provided with a conductor portion in which a pattern is formed close to and parallel to one of the pair of grounding conductor layers, and the other of the pair of grounding conductor layers. What is claimed is: 1. A common mode filter having a configuration in which conductors having a pattern formed in proximity and parallel to each other are electrically connected to each other, wherein a magnetic body that becomes at least a part of a magnetic path of a magnetic flux due to current of said pair of linear conductors Are disposed between the pair of grounding conductor layers.
[0012]
In the common mode filter, the magnetic body may be a continuous structure having at least a magnetic layer disposed between the grounding conductor layer and the dielectric.
[0013]
Each conductor portion of the pair of linear conductors formed in the dielectric has a spiral pattern of one or more turns having the same central axis, and at least a part of the magnetic material extends along the central axis. It may be configured to be arranged.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of a common mode filter according to the present invention will be described with reference to the drawings.
[0015]
FIG. 1 is a perspective view (perspective view) of a common mode filter portion according to a first embodiment of the present invention, and FIG. 2 is a sectional view of the common mode filter portion, showing a common mode filter function portion incorporated in a multilayer circuit board. Is represented. In these figures, reference numerals 1, 2, 3, 4, and 5 denote dielectric substrates, which are stacked to form a laminated circuit board. Reference numerals 6 and 7 denote grounding conductor layers (ground layers to be grounded) in which the upper and lower surfaces of the stacked dielectric substrates are entirely covered with conductors. Reference numerals 8, 9, 10, and 11 are layers in which conductors of a spiral pattern constituting a pair of line-shaped conductors as transmission lines are arranged. Here, the dielectric substrates 1 and 5 have the same thickness, and the dielectric substrates 2 and 4 have the same thickness.
[0016]
This common mode filter has a structure in which a pair of linear conductors LN1 and LN2 serving as two transmission lines are provided between a pair of upper and lower grounding conductor layers 6 and 7 in parallel (to face each other in parallel). ing. One linear conductor LN1 circulates in the same direction around a conductor portion 12 formed on the layer 8 between the dielectric substrates 1 and 2 and a conductor portion 14 formed on the layer 10 between the dielectric substrates 3 and 4 in the same direction. Are electrically connected by the interlayer connection conductor 16 so as to form a spiral pattern. The other linear conductor LN2 circulates in the same direction around a conductor portion 13 formed on the layer 9 between the dielectric substrates 2 and 3 and a conductor portion 15 formed on the layer 11 between the dielectric substrates 4 and 5. Are electrically connected by the interlayer connection conductor 17 so as to form a spiral pattern. The conductor portions 16 and 17 for interlayer connection are formed by providing through holes or cutouts in the dielectric substrates 2, 3 and 4. The conductors 12 and 13 have a pattern formed close to and parallel to the grounding conductor layer 6, and the conductors 14 and 15 have patterns formed close to and parallel to the grounding conductor layer 7. Here, since the grounding conductor layers 6 and 7 are formed on the front and back surfaces (upper and lower surfaces) of the laminated dielectric substrate and are parallel to each other, the grounding conductor layers 6 and 7 and the conductor portions 12, 13, 14, and 15 are formed. Maintain a parallel relationship with each other. The conductor portions viewed from the vertical direction of the ground plane formed by the grounding conductor layers 6 and 7 are arranged so as to overlap with each other and have the same pattern width. In other words, two line-shaped conductors LN1 and LN2 as transmission lines are formed with the same width so as to overlap in the axial direction perpendicular to the grounding conductor layers 6 and 7.
[0017]
Further, between the lower and upper grounding conductor layers 6 and 7, the Ni—Zn-based material applicable to the high-frequency region along the central axis of the spiral of each of the conductor portions 12, 13, 14, and 15 of the spiral pattern. A columnar magnetic body (ferromagnetic body, more precisely) 18 such as ferrite is arranged. As shown in FIG. 2, the magnetic body 18 is buried in a dielectric composed of a laminated dielectric substrate between the grounding conductor layers 6 and 7.
[0018]
In the first embodiment, in a common mode in which currents in the same direction flow through a pair of transmission lines, that is, a pair of linear conductors LN1 and LN2, a magnetic wall is formed between the linear conductors LN1 and LN2. No capacitance component occurs between the line-shaped conductors LN1 and LN2, and it can be regarded as one transmission line. At this time, the distribution is made between the lower spiral conductors 12 and 13 and the lower grounding conductor layer 6, between the upper spiral conductors 14 and 15 and the upper grounding conductor layer 7, and between the upper and lower conductors. A constant capacitance component is generated. By combining these with the spiral pattern of each conductor and the inductance components generated by the conductors 16 and 17 for interlayer connection, a π-type low-pass filter is formed.
[0019]
Furthermore, in this example, the magnetic body 18 is provided to constitute a part of the magnetic path through which the magnetic flux passes, and the magnetic flux generated from each of the conductors 12, 13, 14, 15 in the spiral pattern concentrates on the magnetic body 18. . In the case of a common mode in which currents in the same direction flow through a pair of transmission lines, that is, a pair of linear conductors LN1 and LN2, as shown in FIG. 3, a magnetic flux H1 (solid line) generated by one linear conductor and another magnetic flux H1 (solid line) are generated. Since the directions of the magnetic fluxes H2 (broken lines) generated by the linear conductors are the same, the inductor component for the common mode current is strengthened, the impedance for the common mode current is increased, and the attenuation of the common mode current is increased. Can be.
[0020]
On the other hand, in a differential mode in which currents in opposite directions flow through the pair of linear conductors LN1 and LN2, an electric wall is formed between the pair of linear conductors LN1 and LN2, and a capacitor component is generated between the linear conductors LN1 and LN2. However, the influence of the capacitor component between the ground conductor layers 6 and 7 becomes small, and does not affect the attenuation of the differential mode current. In addition, as shown in FIG. 4, the direction of the magnetic flux H1 (solid line) generated by one linear conductor and the direction of the magnetic flux H2 (dashed line) generated by the other linear conductor are reversed and cancel each other. The inductor component with respect to the current is reduced, and the impedance with respect to the differential mode current is reduced. In this regard, the attenuation of the differential mode current is not affected.
[0021]
According to the first embodiment, the following effects can be obtained.
[0022]
(1) In the laminated dielectric substrate, a pair of linear conductors LN1 and LN2 are provided in parallel between the pair of ground conductor layers 6 and 7, and the pair of linear conductors LN1 and LN2 is a ground conductor. Conductor portions 12 and 13 in which a spiral pattern is formed close to and parallel to layer 6, and a conductor portion in which a spiral pattern circling in the same direction as the previous conductor portion close to and parallel to grounding conductor layer 7 14 and 15 are electrically connected to each other, and a magnetic body 18 is arranged at the center of the spiral pattern. A π-type low-pass filter can be formed for a common mode current. By concentrating the magnetic flux by each conductor, it is possible to exhibit high impedance with respect to the common mode current, and it is possible to further increase the amount of attenuation with respect to the common mode current.
[0023]
(2) The pattern of the conductors 12, 13, 14, 15 constituting the pair of linear conductors LN1, LN2 is a spiral pattern that circulates in the same direction, and is suitable for miniaturization of the product shape.
[0024]
(3) The pattern of the conductors 12, 13, 14, 15 constituting the pair of linear conductors LN1, LN2 is parallel to the grounding conductor layers 6, 7, and each conductor is viewed from the vertical direction of the grounding conductor layer. Overlap and have the same pattern width, so that the input and output impedances when viewed as a π-type low-pass filter can be made uniform.
[0025]
FIG. 5 is a perspective view (perspective view) of a common mode filter according to a second embodiment of the present invention, and FIG. 6 is a sectional view thereof. In the present embodiment, between a dielectric composed of a laminated circuit board in which dielectric substrates 1, 2, 3, 4, and 5 are laminated, and grounding conductor layers (ground layers to be grounded) 6, 7, Magnetic layers 19 and 20 are provided to physically contact the upper and lower end surfaces of the columnar magnetic body 18. Further, the magnetic material walls 21 and 22 are grounded so that the magnetic material layers 19 and 20 are short-circuited (connected) by covering the outer peripheral portions (side surfaces) of the dielectric material not in contact with the linear conductors LN1 and LN2 as a pair of transmission lines. A continuous structure is provided between layers 6 and 7 (each magnetic body forms a closed magnetic circuit).
[0026]
The other configuration is the same as that of the above-described first embodiment, and the same or corresponding portions are denoted by the same reference characters and description thereof will be omitted.
[0027]
In the case of the common mode in which a current in the same direction flows through the pair of linear conductors LN1 and LN2 in the second embodiment, as shown in FIG. 7, the magnetic flux H1 (solid line) generated by one linear conductor and the magnetic flux H1 (solid line) are generated. Since the direction of the magnetic flux H2 (broken line) generated by the other linear conductor becomes the same, the inductor component for the common mode current reinforces and the impedance for the common mode current increases.
[0028]
On the other hand, in a differential mode in which currents in opposite directions flow through a pair of linear conductors LN1 and LN2, a magnetic flux H1 (solid line) generated by one linear conductor and another linear conductor are generated as shown in FIG. Is generated, the directions of the magnetic fluxes H2 (broken lines) are reversed and cancel each other, so that the inductor component with respect to the differential mode current becomes small and the impedance with respect to the differential mode current becomes small. The operation of the pair of linear conductors LN1 and LN2 due to the capacitance component is as described in the first embodiment.
[0029]
In the present embodiment, since the closed loop of the magnetic flux generated from the spiral line-shaped conductor is confined in the magnetic material, the loss of the magnetic flux is small, and the effect of electromagnetic induction is increased. Therefore, it is possible to further increase the impedance with respect to the common mode current and further increase the attenuation.
[0030]
In these embodiments, an electrically insulated dielectric such as a single crystal semiconductor such as Si or a compound semiconductor such as GaAs may be used as the dielectric substrate in addition to the ceramic and the resin-based dielectric. Further, as the magnetic material, Ni-Zn-based ferrite applicable to a high-frequency region, an insulated metal-based magnetic material, or the like (for example, an Fe-Ni-based material) is used.
[0031]
Alternatively, an electrode may be provided on the side wall of the laminated dielectric substrate, and the ends of the conductor portions 12, 13, 14, and 15 may be electrically connected to form a chip-shaped common mode filter.
[0032]
These embodiments can be used as a countermeasure component to be installed in an arbitrary position on the circuit board, a countermeasure component to be installed in an arbitrary position on the circuit board, and a countermeasure component for the balanced transmission cable.
[0033]
Further, instead of forming the grounding conductor film on the front and back surfaces of the dielectric substrate, a pair of upper and lower grounding conductor layers are formed in the dielectric substrate, and a pair of upper and lower grounding conductor layers are formed in parallel between the pair of upper and lower grounding conductor layers. A structure in which a line-shaped conductor is provided may be used.
[0034]
Although the embodiments of the present invention have been described above, it will be obvious to those skilled in the art that the present invention is not limited to the embodiments and various modifications and changes can be made within the scope of the claims.
[0035]
【The invention's effect】
As described above, according to the common mode filter of the present invention, it is possible to attenuate the common mode current serving as an electromagnetic noise source in an arbitrary frequency band, and to minimize the loss of the differential mode current.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a first embodiment of a common mode filter according to the present invention, showing an internal structure thereof in a see-through manner.
FIG. 2 is a cross-sectional view of the first embodiment.
FIG. 3 is an explanatory diagram illustrating a magnetic flux direction in a common mode according to the first embodiment.
FIG. 4 is an explanatory diagram illustrating a magnetic flux direction in a differential mode according to the first embodiment.
FIG. 5 is a perspective view showing a second embodiment of the present invention and showing an internal structure in a see-through manner.
FIG. 6 is a sectional view of the second embodiment.
FIG. 7 is an explanatory diagram illustrating a magnetic flux direction in a common mode according to the second embodiment.
FIG. 8 is an explanatory diagram illustrating a magnetic flux direction in a differential mode according to the second embodiment.
[Explanation of symbols]
1, 2, 3, 4, 5 Dielectric substrates 6, 7 Grounding conductor layers 12, 13, 14, 15 Conductor portions 16, 17 Interlayer connection conductor portions 18 Magnetic body 19, 20 Magnetic body layers 21, 22 Magnetic body Wall LN1, LN2 Line-shaped conductor

Claims (3)

A pair of upper and lower grounding conductor layers are formed with a dielectric interposed therebetween, and a structure is provided in which a pair of linear conductors are provided in parallel in the dielectric and between the pair of grounding conductor layers. Each of the conductors is a conductor portion having a pattern formed in proximity to and parallel to one of the pair of grounding conductor layers, and a conductor portion having a pattern formed in proximity to and parallel to the other of the pair of grounding conductor layers. In a common mode filter having a configuration electrically connected to each other, wherein a magnetic body serving as at least a part of a magnetic path of a magnetic flux due to current of the pair of linear conductors is disposed between the pair of grounding conductor layers. A common mode filter characterized by the following. The common mode filter according to claim 1, wherein the magnetic body is a continuous structure having at least a magnetic body layer disposed between the grounding conductor layer and the dielectric body. Each conductor portion of the pair of linear conductors formed in the dielectric has a spiral pattern of one or more turns having the same central axis, and at least a part of the magnetic material extends along the central axis. The common mode filter according to claim 1, wherein the common mode filter is arranged.

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