Patent ID: 7880566
Filing Date: 2011-02-01
Classification: H03H

Abstract:
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.