Boundary Acoustic Wave Filter Layout for Lower Spurious Response
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Solution Overview
Problem
Boundary acoustic wave filter devices face challenges in reducing insertion loss while minimizing spurious responses in frequency bands higher than the pass band, as existing designs often result in increased spurious responses due to narrow pitch electrode finger portions.
Innovation Solution
The design incorporates a longitudinally coupled resonator boundary acoustic wave filter device with SH-type boundary acoustic waves, featuring narrow pitch electrode finger portions with varying pitches and polarities across IDTs, connected to unbalanced and balanced terminals to reduce spurious responses by shifting the frequency band of excited Stoneley waves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If narrow pitch electrode finger portions are provided in IDTs to reduce insertion loss in pass band, then insertion loss is reduced, but spurious response increases in frequency band higher than pass band
Solution Approach 1:
The patent applies local quality by providing narrow pitch electrode finger portions only at specific locations where IDTs are adjacent to each other, rather than uniformly across all IDTs. This localized modification reduces insertion loss at the coupling regions while limiting the generation of spurious responses. The electrode finger pitch is varied locally at boundary regions between IDTs, creating different electrical characteristics in different parts of the filter structure.
Solution Approach 2:
The patent introduces asymmetry by making the electrode finger pitch of narrow pitch portions different from the standard pitch used in other regions. Specifically, the narrow pitch portions have a smaller pitch value than the standard electrode finger pitch, creating an asymmetric structure that optimizes coupling efficiency while controlling spurious response characteristics in the high frequency band.
2Ease of manufacture
If uniform electrode finger pitch is used across all IDTs, then manufacturing is simplified, but insertion loss increases in pass band
Solution Approach 1:
The patent maintains ease of manufacture by using a uniform standard electrode finger pitch for the majority of IDT regions, which simplifies the fabrication process. The narrow pitch portions are introduced only locally at specific coupling regions between adjacent IDTs, allowing most of the structure to be manufactured with standard processes while achieving improved performance at critical locations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively reduces undesirable spurious responses in higher frequency bands, enhancing the filter's performance and suitability for applications where such responses are undesirable, while maintaining reduced insertion loss within the pass band.
Implementation Method 1
a piezoelectric body, a dielectric body laminated on the piezoelectric body, and an electrode structure arranged at a boundary between the piezoelectric body and the dielectric body, wherein the boundary acoustic wave filter device utilizes an SH-type boundary acoustic wave that propagates along the boundary
Implementation Method 2
the electrode finger pitch of a portion of electrode fingers of one IDT, located at an end adjacent to the other IDT, is less than the electrode finger pitch of a portion of electrode fingers of the one IDT, adjacent to that portion, whereby a narrow pitch electrode finger portion is provided
Data Source
AI summary
A boundary acoustic wave filter device includes an electrode structure provided at a boundary between a piezoelectric body and a dielectric body laminated on the piezoelectric body and utilizes an SH-type boundary acoustic wave that propagates along the boundary. In the boundary acoustic wave filter device, the electrode structure includes a longitudinally coupled resonator boundary acoustic wave filter portion that has a first IDT and second and third IDTs arranged respectively on both sides of the IDT in a direction in which the boundary acoustic wave propagates. At portions at which two IDTs are located adjacent to each other in the direction in which the boundary acoustic wave propagates, narrow pitch electrode finger portions are provided in the IDTs, and the pitch of the electrode fingers of the narrow pitch electrode finger portion is different from the pitch of the electrode fingers of each of the narrow pitch electrode finger portions.