| 摘要 |
PURPOSE:To prevent a bulk wave from being affected on a pass frequency band of a filter, by selecting the thickness of a substrate from a frequency constant of a thickness longitudinal oscillation specific to a piezoelectric crystal in use. CONSTITUTION:The relation of A/d fr exits among a frequency constant A of the thickness longitudinal oscillation of a piezoelectric crystal substrate, the primary resonance frequency (fr), and the thickness (d) of the substrate. Through this relation, the thickness (d) of the substrate is adjusted so that the resonance frequency (fr) of the thickness longitudinal oscillation can not affect the pass frequency band of the filter to be manufactured. For example, in designing the filter having 41-48 MHz of the pass frequency band using lithium niobate crystal substrate of 128 deg. rot. Y-cut, X propagation, when the thickness of the substrate is denoted as 300mum, the primary mode of the thickness longitudinal oscillation is around 11.5MHz, the ternary mode is 34.6MHz and the quinary mode is 57.6Mhz. They are not within the pass frequency band of the filter, allowing to prevent the effect of bulk waves. |
