US Patent 9083301 Balance filter

A balance filter includes an unbalanced terminal, a first balanced terminal, a second balanced terminal, a ground terminal, an unbalanced-side coupling coil, a balanced-side coupling coil electromagnetically coupled to the unbalanced-side coupling coil, and an unbalanced-side capacitor. The unbalanced-side capacitor, the unbalanced-side coupling coil, and a portion of the balanced-side coupling coil define an LC parallel resonant circuit. A first end of the balanced-side coupling coil is a terminal having the same polarity as that of a first end of the unbalanced-side coupling coil. A second end of the unbalanced-side coupling coil is connected to the first end of the balanced-side coupling coil.