Common mode filter

The present invention relates to a common mode filter and, more particularly, to a common mode filter of a type in which a pair of wires cross each other along the way and a manufacturing method therefor.

A common mode filter is widely used in many electronic devices, such as mobile electronic devices and on-vehicle LANs, as an element for removing common mode noise superimposed on differential signal lines. In recent years, a common mode filter using a surface-mountable drum core supersedes a common mode filter using a toroidal core (see JP 2019-121791A).

In a common mode filter described in JP 2019-121791A, a pair of wires are made to cross each other an even number of times along the way to enhance the symmetry of differential signals in high frequency regions. In recent years, it has been demanded to sufficiently reduce mode conversion characteristics indicating a rate at which a differential signal component is converted into a common mode noise component in high frequency regions. One of the major factors that degrade the mode conversion characteristics is a disturbance in the symmetry of a pair of wires. Thus, by enhancing the symmetry of a pair of wires as in the common mode filter described in JP 2019-121791A, the mode conversion characteristics in high frequency regions can be improved.

Studies conducted by the present inventors reveal that the degradation in the mode conversion characteristics due to disturbance of a pair of wire is more conspicuous in turns closer to the input side of differential signals. Thus, in the configuration of the common mode filter described in JP 2019-121791A, in which a pair of wires are made to cross each other after winding of several turns from the wire end portion, it is difficult to sufficiently improve the mode conversion characteristics in high frequency regions.

It is therefore an object of the present invention to sufficiently improve the mode conversion characteristics in high frequency regions in a common mode filter in which a pair of wires cross each other along the way.

A common mode filter according to the present invention includes: a core having a winding core part, a first flange part provided at one axial end of the winding core part, and a second flange part provided at the other axial end of the winding core part; first and second wires wound in the same direction around the winding core part; first and second terminal electrodes provided on the first flange part and connected respectively with one ends of the first and second wires; and third and fourth terminal electrodes provided on the second flange part and connected respectively with the other ends of the first and second wires. The first and second wires have a first layer winding portion in which the first and second turns thereof counted respectively from one ends are at least partially wound by layer winding in an aligned state, a second layer winding portion in which the first and second turns thereof counted respectively from the other ends are at least partially wound by layer winding in an aligned state, a third layer winding portion in which at least parts of the first and second wires between the third turns thereof counted respectively from the one ends and the third turns thereof counted respectively from the other ends are wound by layer winding in an aligned state, a first crossing portion positioned between the first and third layer winding portions, at which the first and second wires cross each other, and a second crossing portion positioned between the second and third layer winding portions, at which the first and second wires cross each other. The vertical positions of the first and second wires are reversed at least partially between the first and third layer winding portions, and the vertical positions of the first and second wires are reversed at least partially between the second and third layer winding portions.

According to the present invention, the second turns of the pair of wires cross each other, so that mode conversion characteristics in high frequency regions can be improved. In addition, the pair of wires cross each other at both end portions thereof, so that bidirectional mode conversion characteristics can be improved in a configuration in which differential signals are bidirectionally transmitted. Further, the pair of wires are wound by layer winding as a whole, allowing a reduction in the length of the winding core part in the x-direction.

In the present invention, the first flange part may have a first surface covered with connection portions of the first and second terminal electrodes at which one ends of the first and second wires are respectively connected, and the second flange part may have a second surface covered with connection portions of the third and fourth terminal electrodes at which the other ends of the first and second wires are respectively connected, the winding core part may have a winding surface parallel to the first and second surfaces, and first and second crossing portions may be both positioned on the winding surface. With this configuration, the wire length from the first and second terminal electrodes to the first crossing portion and the wire length from the third and fourth terminal electrodes to the second crossing portion are substantially equal to each other, making it possible to reduce the difference in the mode conversion characteristics due to the difference in input direction of differential signals.

In the present invention, the third layer winding portion may have a fourth layer winding portion positioned on the side close to the first layer winding portion and a fifth layer winding portion positioned on the side close to the second layer winding portion, the first and second wires may further have a third crossing portion positioned between the fourth and fifth layer winding portions, at which the first and second wires cross each other, and the vertical positional relationship between the first and second wires in the first and fifth layer winding portions and the vertical positional relationship therebetween in the second and fourth layer winding portions may be reversed. This further enhance the symmetry between the first and second wires. In this case, to further enhance the symmetry between the first and second wires, the difference in the number of turns between the fourth and fifth layer winding portions is preferably one or less.

In the present invention, the third layer winding portion may have a fourth layer winding portion positioned on the side close to the first layer winding portion, a sixth layer winding portion positioned on the side close to the second layer winding portion, and a fifth layer winding portion positioned between the fourth and sixth layer winding portions, the first and second wires may further have a third crossing portion positioned between the fourth and fifth layer winding portions, at which the first and second wires cross each other and a fourth crossing portion positioned between the fifth and sixth layer winding portions, at which the first and second wires cross each other, and the vertical positional relationship between the first and second wires in the first, second, and fifth layer winding portions and the vertical positional relationship therebetween in the fourth and sixth layer winding portions may be reversed. This can further enhance the symmetry between the first and second wires and can reduce a parasitic capacitance component. In this case, to further enhance the symmetry between the first and second wires, it is preferable to make the numbers of turns in the fourth and sixth layer winding portions the same, and it is more preferable to make the numbers of turns in the fourth, fifth, and sixth layer winding portions the same.

Thus, according to the present invention, the mode conversion characteristics in high frequency regions can be improved in a common mode filter in which a pair of wires cross each other along the way.

The above features and advantages of the present invention will be more apparent from the following description of certain preferred embodiments taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic perspective view illustrating the outer appearance of a common mode filter 1 according to a first embodiment of the present invention;

FIG. 2 is a schematic plan view for explaining the winding layout of the first and second wires W 1 and W 2 in a common mode filter 1 ;

FIG. 3 is a schematic developed view for explaining the winding layout of the first and second wires W 1 and W 2 in a common mode filter 1 ;

FIG. 4 is a schematic plan view for explaining the winding layout of the first and second wires W 1 and W 2 in a common mode filter 2 according to a second embodiment of the present invention;

FIG. 5 is a schematic developed view for explaining the winding layout of the first and second wires W 1 and W 2 in the common mode filter 2 according to the second embodiment of the present invention; and

FIG. 6 is a schematic plan view for illustrating the winding layout of the first and second wires W 1 and W 2 in a common mode filter 3 according to a third embodiment of the present invention.

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic perspective view illustrating the outer appearance of a common mode filter 1 according to a first embodiment of the present invention.

As illustrated in FIG. 1 , the common mode filter 1 according to the first embodiment includes a drum core 10 , a plate core 20 , first to fourth terminal electrodes 31 to 34 , and first and second wires W 1 and W 2 . The drum core 10 and plate core 20 are each made of a magnetic material such as an Ni—Zn based ferrite. The first to fourth terminal electrodes 31 to 34 are each a metal fitting made of a good conductor material such as copper. The first to fourth terminal electrodes 31 to 34 may be obtained by directly baking silver paste or the like onto the drum core 10 .

The drum core 10 has a first flange part 11 , a second flange part 12 , and a winding core part 13 disposed between the first and second flange parts 11 and 12 . The winding core part 13 has its axis direction in the x-direction. The first and second flange parts 11 and 12 are disposed at axial both ends of the winding core part 13 and integrally formed with the winding core part 13 . The plate core 20 is bonded to upper surfaces 11 t and 12 t of the respective flange parts 11 and 12 . The upper surfaces 11 t and 12 t of the respective flange parts 11 and 12 constitute the xy plane, and their opposite surfaces are used as mounting surfaces 11 b and 12 b . The first and second terminal electrodes 31 and 32 are each provided on the mounting surface 11 b of the first flange part 11 and an outer surface 11 s thereof, and the third and fourth terminal electrodes 33 and 34 are each provided on the mounting surface 12 b of the second flange part 12 and an outer surface 12 s thereof. The outer surfaces 11 s and 12 s each constitute the yz plane. Fixation of the first to fourth terminals 31 to 34 is made by using an adhesive or the like.

The first and second wires W 1 and W 2 are wound around the winding core part 13 in the same direction. One and the other ends of the first wire W 1 are connected respectively to connection portions 31 a and 33 a of the first and third terminal electrodes 31 and 33 , and one and the other ends of the second wire W 2 are connected respectively to connection portions 32 a and 34 a of the second and fourth terminal electrodes 32 and 34 . The number of turns of the first wire W 1 and the number of turns of the second wires W 2 are the same. The connection portions 31 a and 32 a of the first and second terminal electrodes 31 and 32 are positioned on the mounting surface 11 b , and connection portions 33 a and 34 a of the third and fourth terminal electrodes 33 and 34 are positioned on the mounting surface 12 b.

FIG. 2 is a schematic plan view for explaining the winding layout of the first and second wires W 1 and W 2 . FIG. 3 is a schematic developed view for explaining the winding layout of the first and second wires W 1 and W 2 .

In the present embodiment, the winding core part 13 has a substantially rectangular shape in yz cross section and has four winding surfaces 41 to 44 as illustrated in FIG. 3 . The winding surfaces 41 and 43 constitute the xy plane, and the winding surfaces 42 and 44 constitute the xz plane. The boundary between the winding surfaces 41 and 42 is defined by an edge E 1 , the boundary between the winding surfaces 42 and 43 is defined by an edge E 2 , boundary between the winding surfaces 43 and 44 is defined by an edge E 3 , and the boundary between the winding surfaces 44 and 41 is defined by an edge E 4 .

As illustrated in FIGS. 2 and 3 , the first and second wires W 1 and W 2 have a first layer winding portion L 1 in which the first and second turns thereof counted respectively from the connection portions 31 a and 32 a are wound by layer winding in an aligned state, a second layer winding portion L 2 in which the first and second turns thereof counted respectively from the connection portions 33 a and 34 a are wound by layer winding in an aligned state, and a third layer winding portion L 3 in which parts of the first and second wires W 1 and W 2 between the third turns thereof counted respectively from the connection portions 31 a and 32 a and the third turns thereof counted respectively from the connection portions 33 a and 34 a are wound by layer winding in an aligned state. Thus, the first and second wires W 1 and W 2 are wound by layer winding as a whole, so that even when the numbers of turns of the first and second wires W 1 and W 2 are large, the length of the winding core part 13 in the x-direction can be reduced. Further, the first and second wires W 1 and W 2 have a first crossing portion C 1 positioned between the first and third layer winding portions L 1 and L 3 , at which the first and second wires W 1 and W 2 cross each other and a second crossing portion C 2 positioned between the second and third layer winding portions L 2 and L 3 , at which the first and second wires W 1 and W 2 cross each other. The positional relationship between the first and second wires W 1 and W 2 is reversed before and after the crossing.

The first turns of the first and second wires W 1 and W 2 counted from one ends thereof are each defined by a section starting at the edge E 1 (denoted by the arrow 51 ) and ending at the edge E 1 (denoted by the arrow 52 ). The same applies to the second and subsequent turns. This is because the terminal electrodes 31 and 32 are disposed offset in the negative y-direction and in the positive y-direction, respectively, as viewed from the center axis of the winding core part 13 , so that the first wire W 1 paired with the second wire W 2 does not exist in a section S 2 of the second wire W 2 positioned on the winding surface 41 . Similarly, the first turns of the first and second wires W 1 and W 2 counted from the other ends thereof are each defined by a section starting at the edge E 4 (denoted by the arrow 53 ) and ending at the edge E 4 (denoted by the arrow 54 ). The same applies to the second and subsequent turns. This is because the terminal electrodes 33 and 34 are disposed offset in the negative y-direction and in the positive y-direction, respectively, as viewed from the center axis of the winding core part 13 , so that the first wire W 2 paired with the first wire W 1 does not exist in a section S 1 of the first wire W 1 positioned on the winding surface 41 .

In the first and second layer winding portions L 1 and L 2 , the first and second wires W 1 and W 2 are wound by layer winding in an aligned state with the second wire W 2 positioned in the lower layer and the first wire W 1 positioned in the upper layer. On the other hand, in the third layer winding portion L 3 , the first and second wires W 1 and W 2 are wound by layer winding in an aligned state with the first wire W 1 positioned in the lower layer and the second wire W 2 positioned in the upper layer. Although the number of turns in the third layer winding portion L 3 is 12 in the example of FIG. 2 , it is not particularly limited. To achieve the layer winding of the first and second wires W 1 and W 2 in an aligned state, the wire in the upper layer needs to be wound along the valley line formed by adjacent turns of the wire in the lower layer, so that the number of turns of the wire in the upper layer is smaller by one than the number of turns of the wire in the lower layer. Thus, in the first layer winding portion L 1 , the first turn of the first wire W 1 counted from the connection portion 31 a is exceptionally positioned in the lower layer; in the third layer winding portion L 3 , the third turn of the second wire W 2 counted from the connection portion 32 a is exceptionally positioned in the lower layer; and in the second layer winding portion L 2 , the second turn of the first wire W 1 counted from the connection portion 33 a is exceptionally positioned in the lower layer.

As described above, in the common mode filter 1 according to the present embodiment, the second turns of the first and second wires W 1 and W 2 counted from one ends thereof connected respectively to the terminal electrodes 31 and 32 cross each other, and the second turns of the first and second wires W 1 and W 2 counted from the other ends thereof connected respectively to the terminal electrodes 33 and 34 cross each other. When the first and second wires W 1 and W 2 are made to cross each other, symmetry therebetween before and after the crossing is enhanced to improve the mode conversion characteristics. As described above, deterioration in the mode conversion characteristics due to disturbance of the symmetry is more conspicuous in turns closer to the input side of differential signals; however, in the common mode filter 1 according to the present embodiment, the second turns of the first and second wires W 1 and W 2 cross each other, so that the mode conversion characteristics in high frequency regions are significantly improved. In addition, the crossing portions C 1 and C 2 are positioned at both end portions of the first and second wires W 1 and W 2 , so that it is possible to provide a common mode filter having no directivity and to improve the signal quality of bidirectional differential signals.

Further, the first and second turns of the first and second wires W 1 and W 2 counted from the respective ends thereof are wound by layer winding, so that the length of the winding core part 13 in the x-direction can be reduced as compared to a case where the wires are bifilar wound. In addition, the vertical positional relationship between the first and second wires W 1 and W 2 in the first and second layer winding portions L 1 and L 2 and the vertical positional relationship therebetween in the third layer winding portion L 3 are reversed, thus reducing the difference in length between the first and second wires W 1 and W 2 .

Further, the crossing portions C 1 and C 2 are both positioned on the winding surface 41 . Thus, the length of the first wire W 1 positioned between the first terminal electrode 31 and the first crossing portion C 1 and the length of the second wire W 2 positioned between the fourth terminal electrode 34 and the second crossing portion C 2 are substantially coincide with each other, and the length of the second wire W 2 positioned between the second terminal electrode 32 and the first crossing portion C 1 and the length of the first wire W 1 positioned between the third terminal electrode 33 and the second crossing portion C 2 substantially coincide with each other. As a result, there is little difference between the mode conversion characteristics when the first and second terminal electrodes 31 and 32 are set as an input side and the mode conversion characteristics when the third and fourth terminal electrodes 33 and 34 are set as an input side.

FIG. 4 is a schematic plan view for explaining the winding layout of the first and second wires W 1 and W 2 in a common mode filter 2 according to a second embodiment.

As illustrated in FIG. 4 , the common mode filter 2 according to the second embodiment differs from the common mode filter 1 according to the first embodiment in that the third layer winding portion L 3 is divided into a fourth layer winding portion L 4 and a fifth layer winding portion L 5 and that a third crossing portion C 3 is provided between the fourth and fifth layer winding portions L 4 and L 5 . Other basic configurations are the same as those of the common mode filter 1 according to the first embodiment, so the same reference numerals are given to the same elements, and overlapping description will be omitted.

In the first and fifth layer winding portions L 1 and L 5 , the first and second wires W 1 and W 2 are wound by layer winding in an aligned state with the second wire W 2 positioned in the lower layer and the first wire W 1 positioned in the upper layer, whereas in the second and fourth layer winding portions L 2 and L 4 , the first wire W 1 is positioned in the lower layer and the second wire W 2 is positioned in the upper layer. Although the number of turns in each of the layer winding portions L 4 and L 5 is six in the example of FIG. 4 , it is not particularly limited. In the first layer winding portion L 1 , the first turn of the first wire W 1 counted from the connection portion 31 a is exceptionally positioned in the lower layer; in the fourth layer winding portion L 4 , the third turn of the second wire W 2 counted from the connection portion 32 a is exceptionally positioned in the lower layer; in the fifth layer winding portion L 5 , the ninth turn of the first wire W 1 counted from the connection portion 31 a is exceptionally positioned in the lower layer; and in the second layer winding portion L 2 , the second turn of the second wire W 2 counted from the connection portion 34 a is exceptionally positioned in the lower layer.

Thus, in the common mode filter 2 according to the second embodiment, the third layer winding portion L 3 is divided into the fourth and fifth layer winding portions L 4 and L 5 , and the vertical positions of the first and second wires W 1 and W 2 are revered between the fourth and fifth layer winding portions L 4 and L 5 , allowing the lengths of the first and second wires W 1 and W 2 to substantially coincide with each other. In addition, the first and second wires W 1 and W 2 cross each other between the fourth and fifth layer winding portions L 4 and L 5 , allowing the symmetry between the first and second wires W 1 and W 2 to be further enhanced.

FIG. 5 is a schematic developed view for explaining the winding layout of the first and second wires W 1 and W 2 in the common mode filter 2 according to the second embodiment.

As illustrated in FIG. 5 , in the common mode filter 2 according to the second embodiment, the first to third crossing portions C 1 to C 3 are all positioned on the winding surface 41 . If the first and second wires w 1 and W 2 are made to cross each other an odd number of times, the positional relationship between the first and second wires W 1 and W 2 at one end side and the positional relationship therebetween at the other end side are disadvantageously reversed. However, in the common mode filter 2 according to the present embodiment, the first turns of the first and second wires W 1 and W 2 counted from the other ends are made to cross each other at a crossing portion CE on the winding surface 44 , so that the positional relationship between the first and second wires W 1 and W 2 at one end side and the positional relationship therebetween at the other end side coincide with each other.

As described above, in the common mode filter 2 according to the second embodiment, the symmetry between the first and second wires W 1 and W 2 is further enhanced, allowing the mode conversion characteristics to be further improved. When the total number of turns in the first and second layer winding portions L 4 and L 5 is even, half of the total number of turns is preferably assigned to each of the first and second layer winding portions L 4 and L 5 to make the numbers of turns in the first and second layer winding portions L 4 and L 5 coincide with each other. On the other hand, when the total number of turns in the first and second layer winding portions L 4 and L 5 is odd, the difference in the number of turns between the first and second layer winding portions L 4 and L 5 is preferably set to one to minimize the difference in the number of turns.

FIG. 6 is a schematic plan view for illustrating the winding layout of the first and second wires W 1 and W 2 in a common mode filter 3 according to a third embodiment.

As illustrated in FIG. 6 , the common mode filter 3 according to the third embodiment differs from the common mode filter 2 according to the second embodiment in that the layer winding portion L 3 is divided into fourth to sixth layer winding portions L 4 to L 6 and that a fourth crossing portion C 4 is provided between the fifth and sixth layer winding portions L 5 and L 6 . Other basic configurations are the same as those of the common mode filter 2 according to the second embodiment, so the same reference numerals are given to the same elements, and overlapping description will be omitted.

In the first, second, and fifth layer winding portions L 1 , L 2 , and L 5 , the first and second wires W 1 and W 2 are wound by layer winding in an aligned state with the second wire W 2 positioned in the lower layer and the first wire W 1 positioned in the upper layer. On the other hand, in the fourth and sixth layer winding portions L 4 and L 6 , the first wire W 1 is positioned in the lower layer and the second wire W 2 is positioned in the upper layer. In the example of FIG. 6 , the number of turns in each of the layer winding portions L 4 to L 6 is four, but not limited thereto. However, the number of turns in the fourth layer winding portion L 4 and the number of turns in the sixth layer winding portion L 6 are preferably made to coincide with each other. In the first layer winding portion L 1 , the first turn of the first wire W 1 counted from the connection portion 31 a is exceptionally positioned in the lower layer; in the fourth layer winding portion L 4 , the third turn of the second wire W 2 counted from the connection portion 32 a is exceptionally positioned in the lower layer; in the fifth layer winding portion L 5 , the seventh turn of the first wire W 1 counted from the connection portion 31 a is exceptionally positioned in the lower layer; in the sixth layer winding portion L 6 , the 11th turn of the second wire W 2 counted from the connection portion 32 a is exceptionally positioned in the lower layer; and in the second layer winding portion L 2 , the second turn of the first wire W 1 counted from the connection portion 33 a is exceptionally positioned in the lower layer.

As described above, the common mode filter 3 according to the third embodiment has the five layer winding portions L 1 , L 2 , L 4 to L 6 , wherein the vertical positional relationship between the first and second wires W 1 and W 2 in the layer winding portions L 1 , L 2 and L 5 and the vertical positional relationship therebetween in the layer winding portions L 4 and L 6 are reversed, thus reducing the difference in length between the first and second wires W 1 and W 2 . In addition, the first and second wires W 1 and W 2 cross each other between the fourth and fifth layer winding portions L 4 and L 5 and between the fifth and sixth layer winding portions L 5 and L 6 , allowing the symmetry between the first and second wires W 1 and W 2 to be further enhanced.

Further, in the common mode filter 3 according to the third embodiment, the third layer winding portion L 3 is divided into three, whereby a parasitic capacitance component is reduced. This makes it possible to further improve signal characteristics in high frequency regions.

It is apparent that the present invention is not limited to the above embodiments, but may be modified and changed without departing from the scope and spirit of the invention.