| 摘要 |
PURPOSE:To improve the symmetry of attenuation characteristics by improving the attenuation degree of a high-frequency side by decreasing the antiresonance frequency of the series arm of a ladder type filter by connecting a capacitor between the input terminal and output terminal of the series arm. CONSTITUTION:On piezoelectric substrate 1, at least one couple of multiple-mode resonator 2 and single-mode resonator 3 are formed and used as the series arm and parallel arm of a ladder type filter respectively. Then, capacitor C is connected between terminal electrode 5 connecting with split electrode 2a at the input side of the multiple-mode resonator and terminal electrode 7 connecting with split electrode 2b at the output side of multiple-mode resonator 2 by way of one electrode of single- mode resonator 3. Therefore, the antiresonance frequency of the series arm forming a high-frequency side pole decreases, and consequently the attenuation degree of the high-frequency side improve, improving the symmetry of attenuation characteristics. |
