| 摘要 |
PURPOSE:To make it possible to obtain desired passing-band width easily by using an interval between split electrodes of a multimode resonator and a single resonator as the resonator of the seires arm of a ladder filter. CONSTITUTION:On the surface of piezoelectric ceramic substrate 30, split electrodes 31 and 32 are formed at an interval of (g) and on the reverse surface of substrate 30, common electrode 33 is formed opposing to electrodes 31 and 32 to form multi- mode resonator C1' of an energy sealed-up type making use of thickness transversal vibration of substrate 30. On both sides of substrate 30, electrodes 34 and 35 are provided opposing each other to form single resonator C2' vibrating in single mode. Then, while a gap between split electrodes of resonator C1' is used as the resonator of a series arm connected between terminal electrodes 37 and 40, resonator C2' is used as a resonator connected between terminal electrodes 40 and 42. Consequently, since the slanting symmetric mode vibration of the multi-mode resonator has a resonance frequency and antiresonance frequncy higher than those of the single resonator, desired passing-band width can easily be obtained. |
