Balanced lattice filter device

1. A filter device including a lattice-type filter circuit having a resonator, wherein the lattice-type filter circuit comprises:

first and second balanced signal terminals on the input side to be connected to an external balance circuit;

first and second balanced signal terminals on the output side to be connected to an external balance circuit;

a first resonator being connected to a series arm provided between the first balanced signal terminal on the input side and the first balanced signal terminal on the output side;

a second resonator being connected to a series arm provided between the second balanced signal terminal on the input side and the second balanced signal terminal on the output side;

only a first resonant circuit consisting of impedance elements, being connected to a lattice arm provided between the first balanced signal terminal on the output side and the second balanced signal terminal on the input side; and

only a second resonant circuit consisting of impedance elements, being connected to a lattice arm provided between the second balanced signal terminal on the output side and the first balanced signal terminal on the input side,

wherein the impedance elements of the first and second resonant circuits consist of inductance and capacitance elements, and

wherein the resonant frequencies of the first and second resonant circuits are substantially equal to the antiresonant frequencies of the first and second resonators.

2. The filter device according to claim 1 , wherein each of the first resonant circuit and the second resonant circuit is a series resonant circuit.

3. The filter device according to claim 1 , wherein each of the first resonant circuit and the second resonant circuit is a parallel resonant circuit.

4. The filter device according to claim 1 , wherein at least one impedance element is connected in series with at least one resonator out of the first resonator and the second resonator.

5. The filter device according to claim 1 , wherein at least one impedance element is connected in parallel with at least one resonator out of the first resonator and the second resonator.

6. The filter device according to claim 1 , wherein a plurality of numbers of the lattice-type filter circuits are connected.

7. The filter device according to claim 1 , wherein the first and the second resonators have virtually equal frequency characteristics.

8. The filter device according to claims 1 , wherein the first and the second resonant circuits have virtually equal frequency characteristics.

9. A filter device including a lattice-type filter circuit having a resonator, wherein the lattice-type filter circuit comprises:

a first and a second balanced signal terminal on the input side to be connected to an external balance circuit;

a first and a second balanced signal terminal on the output side to be connected to an external balance circuit;

only a first resonant circuit consisting of impedance elements, being connected to a series arm provided between the first balanced signal terminal on the input side and the first balanced signal terminal on the output side;

only a second resonant circuit consisting of impedance elements, being connected to a series arm provided between the second balanced signal terminal on the input side and the second balanced signal terminal on the output side;

a first resonator being connected to a lattice arm provided between the first balanced signal terminal on the output side and the second balanced signal terminal on the input side; and

a second resonator being connected to a lattice arm provided between the second balanced signal terminal on the output side and the first balanced signal terminal on the input side,

wherein the impedance elements of the first and second resonant circuits consist of inductance and capacitance elements, and

wherein the resonant frequencies of the first and second resonant circuits are substantially equal to the antiresonant frequencies of the first and second resonators.

10. The filter device according to claim 9 , wherein each of the first resonant circuit and the second resonant circuit is a series resonant circuit.

11. The filter device according to claim 9 , wherein each of the first resonant circuit and the second resonant circuit is a parallel resonant circuit.

12. The filter device according to claim 9 , wherein at least one impedance element is connected in series with at least one resonator out of the first resonator and the second resonator.

13. The filter device according to claim 9 , wherein at least one impedance element is connected in parallel with at least one resonator out of the first resonator and the second resonator.

14. The filter device according to claim 9 , wherein a plurality of numbers of the lattice-type filter circuits are connected.

15. The filter device according to claim 9 , wherein the first and the second resonators have virtually equal frequency characteristics.

16. The filter device according to claims 9 , wherein the first and the second resonant circuits have virtually equal frequency characteristics.

17. A filter device including a lattice-type filter circuit having a resonator,

wherein the lattice-type filter circuit comprises:

a first and a second balanced signal terminal on the input side to be connected to an external balance circuit;

a first and a second balanced signal terminal on the output side to be connected to an external balance circuit;

a first resonator being connected to a series arm provided between the first balanced signal terminal on the input side and the first balanced signal terminal on the output side;

a second resonator being connected to a series arm provided between the second balanced signal terminal on the input side and the second balanced signal terminal on the output side;

a first resonant circuit including impedance elements, being connected to a lattice arm provided between the first balanced signal terminal on the output side and the second balanced signal terminal on the input side; and

a second resonant circuit including impedance elements, being connected to a lattice arm provided between the second balanced signal terminal on the output side and the first balanced signal terminal on the input side,

wherein the impedance elements of the first and second resonant circuits consist of inductance and capacitance elements, and

wherein the resonant frequencies of the first and the second resonant circuits are substantially equal to the resonant frequencies of the first and the second resonators.

18. A filter device including a lattice-type filter circuit having a resonator,

wherein the lattice-type filter circuit comprises:

a first and a second balanced signal terminal on the input side to be connected to an external balance circuit;

a first and a second balanced signal terminal on the output side to be connected to an external balance circuit;

a first resonant circuit including impedance elements, being connected to a series arm provided between the first balanced signal terminal on the input side and the first balanced signal terminal on the output side;

a second resonant circuit including impedance elements, being connected to a series arm provided between the second balanced signal terminal on the input side and the second balanced signal terminal on the output side;

a first resonator being connected to a lattice arm provided between the first balanced signal terminal on the output side and the second balanced signal terminal on the input side; and

a second resonator being connected to a lattice arm provided between the second balanced signal terminal on the output side and the first balanced signal terminal on the input side,

wherein the impedance elements of the first and second resonant circuits consist of inductance and capacitance elements, and

wherein the resonant frequencies of the first and the second resonant circuits are substantially equal to the resonant frequencies of the first and the second resonators.