Common mode filter

1. A common mode filter, comprising:

a drum core that includes a winding core portion and a pair of flange portions provided at both ends of the winding core portion; and

first and second wires that are wound around the winding core portion so as to form a plurality turns of pair-wire,

the first and second wires including:

one or a plurality of sparsely-wound portions in which adjacent turns of the pair-wire are spaced from each other; and

one or a plurality of closely-wound portions in which adjacent turns of the pair-wire are in close contact with each other,

wherein the one or the plurality of sparsely-wound portions include a first sparsely-wound portion,

wherein the one or the plurality of closely-wound portions include first and second closely-wound portions, and

wherein the first sparsely-wound portion is arranged between the first and second closely-wound portions.

2. The common mode filter as claimed in claim 1 , wherein the first and second wires are wound in order that a relationship between a number of each of the pair-wires counted from one of the pair of flange portions and arrangement of the one or plurality of sparsely-wound portions, and a relationship between a number of each of the pair-wires counted from an other flange portion and arrangement of the one or plurality of sparsely-wound portions are substantially the same with each other.

3. The common mode filter as claimed in claim 1 , wherein the first and second wires are wound by layer winding in which the second wire is wound as a first layer, and the first wire is wound as a second layer, and

wherein the first and second wires are wound in order that a relationship between a number of each of the pair-wires counted from one of the pair of flange portions and a position at which the first wire falls to the first layer at an end of the first closely-wound portion, and a relationship between a number of each of the pair-wires counted from an other flange portion and a position at which the first wire falls to the first layer at an end of the second closely-wound portion are substantially the same with each other.

4. The common mode filter as claimed in claim 1 , wherein the first and second wires are wound by bifilar winding, and

wherein the first and second wires cross each other within the first sparsely-wound portion.

5. The common mode filter as claimed in claim 1 , wherein the first and second wires are wound by layer winding.

6. The common mode filter as claimed in claim 1 , wherein the first and second wires are wound by bifilar winding.

7. A common mode filter, comprising:

a drum core that includes a winding core portion and a pair of flange portions provided at both ends of the winding core portion; and

first and second wires that are wound around the winding core portion so as to form a plurality turns of pair-wire,

the first and second wires including:

one or a plurality of sparsely-wound portions in which adjacent turns of the pair-wire are spaced from each other; and

one or a plurality of closely-wound portions in which adjacent turns of the pair-wire are in close contact with each other,

wherein the first and second wires are wound in order that a relationship between a number of each of the pair-wires counted from one of the pair of flange portions and arrangement of the one or plurality of sparsely-wound portions, and a relationship between a number of each of the pair-wires counted from an other flange portion and arrangement of the one or plurality of sparsely-wound portions are substantially the same with each other,

wherein the one or the plurality of sparsely-wound portions include a first sparsely-wound portion,

wherein the one or the plurality of closely-wound portions include first and second closely-wound portions, and

wherein the first sparsely-wound portion is arranged between the first and second closely-wound portions,

wherein the first and second wires are wound by bifilar winding, and

wherein the first and second wires cross each other within the first sparsely-wound portion.

8. A common mode filter, comprising:

a winding core portion; and

a pair of wires including first and second wires that are wound around the winding core portion, wherein the pair of wires is wound around the winding core portion in N turns including i−2 th turn, i−1 th turn, i th turn, i+1 th turn, and i+2 th turn where i is more than two and less than N−1,

wherein the i−1 th turn and the i th turn are wound so as to be spaced from each other,

wherein the i th turn and the i+1 th turn are wound so as to be spaced from each other,

wherein the i−1 th turn and the i−2 th turn are wound so as to be in close contact with each other, and

wherein the i+1 th turn and the i+2 th turn are wound so as to be in close contact with each other.

9. The common mode filter as claimed in claim 8 , wherein the i is (N+1)/2 if the N is an odd number, and the i is N/2 or (N/2)−1 if the N is an even number.

10. The common mode filter as claimed in claim 8 , wherein the first and second wires are wound by bifilar winding.

11. The common mode filter as claimed in claim 10 , wherein the first and second wires cross each other within an area from the i−1 th turn to the i+1 th turn.

12. A common mode filter, comprising;

a winding core portion; and

first and second wires that are wound around the winding core portion, each of the first and second wires including at least i th turn, i+1 th turn, and i+2 th turn,

wherein the i th turn of the first wire and the i th turn of the second wire are wound in a first pitch,

wherein the i th turn of the second wire and the i+1 th turn of the first wire are wound in a second pitch,

wherein the i+1 th turn of the first wire and the i+1 th turn of the second wire are wound in a third pitch,

wherein the i+1 th turn of the second wire and the i+2 th turn of the first wire are wound in a fourth pitch,

wherein the i+2 th turn of the first wire and the i+2 th turn of the second wire are wound in a fifth pitch,

wherein the second pitch is wider than each of the first, third, fourth, and fifth pitches,

wherein each of the first and second wires further includes i−1 th turn,

wherein the i−1 th turn of the first wire and the i− th turn of the second wire are wound in a sixth pitch,

wherein the i−1 th turn of the second wire and the i th turn of the first wire are wound in a seventh pitch,

wherein each of the second and seventh pitches is wider than each of the first, third, fourth, fifth, and sixth pitches,

wherein each of the first and second wires further includes i−2 th turn,

wherein the i−2 th turn of the first wire and the i−2 th turn of the second wire are wound in an eighth pitch,

wherein the i−2 th turn of the second wire and the i−1 th turn of the first wire are wound in a ninth pitch, and

wherein each of the second and seventh pitches is wider than each of the first, third, fourth, fifth, sixth, eighth, and ninth pitches.