Longitudinally Coupled SAW Filter Pitch Layout for Lower Insertion Loss
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Solution Overview
Problem
Conventional longitudinally coupled resonator-type surface acoustic wave filters face challenges in reducing insertion loss and improving reflection characteristics due to the presence of primary pitch areas, which limit their ability to maintain periodic continuity and suppress bulk wave radiation effectively.
Innovation Solution
The design eliminates primary pitch areas in interdigital transducers by varying the pitch between electrode fingers throughout the IDT, ensuring that no IDT has a constant primary pitch area, allowing for more flexible control of pitch to maintain periodic continuity and reduce bulk wave radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a primary pitch area is used in IDT to maintain structural simplicity, then manufacturing is easier, but periodic continuity cannot be maintained and bulk wave radiation is not sufficiently suppressed
Solution Approach 1:
The patent applies local quality by making the pitch between electrode fingers non-uniform only in specific regions (near the ends of IDT) while maintaining uniform pitch in other regions. This localized variation suppresses bulk wave radiation at critical areas without requiring complete redesign of the entire IDT structure, thus balancing manufacturing ease with performance improvement
Solution Approach 2:
The patent changes the pitch parameter between electrode fingers in specific regions of the IDT. By varying the pitch in the secondary pitch area while maintaining a primary pitch area, the patent achieves better suppression of bulk wave radiation and improved periodic continuity, directly reducing insertion loss
2Ease of manufacture
If pitch is varied only in end portions of IDT, then manufacturing is simplified, but periodic continuity cannot be maintained throughout the structure
Solution Approach 1:
The patent segments the IDT structure into distinct pitch areas: a primary pitch area with uniform pitch and secondary pitch areas with varied pitch at the ends. This segmentation allows each region to serve its specific function while maintaining overall structural coherence and periodic continuity throughout the entire IDT
3Device complexity
If conventional pitch design is used, then device complexity is reduced, but bulk wave radiation cannot be sufficiently suppressed
Solution Approach 1:
The patent applies local quality by making the pitch between electrode fingers non-uniform only in specific regions (near the ends of IDT) while maintaining uniform pitch in other regions. This localized variation suppresses bulk wave radiation at critical areas without requiring complete redesign of the entire IDT structure, thus balancing manufacturing ease with performance improvement
Solution Approach 2:
The patent changes the pitch parameter between electrode fingers in specific regions of the IDT. By varying the pitch in the secondary pitch area while maintaining a primary pitch area, the patent achieves better suppression of bulk wave radiation and improved periodic continuity, directly reducing insertion loss
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 reduces insertion loss and enhances reflection characteristics, enabling better filter performance by allowing for more effective suppression of bulk wave radiation and improved signal balance.
Implementation Method 1
Surface acoustic wave (SAW) filters employ a surface acoustic wave which is generated due to a piezoelectric effect
Data Source
AI summary
Disclosed is a surface acoustic wave filter comprising two or more IDTs arranged in a propagation direction of the surface acoustic wave, wherein said two or more IDTs include at least one pair of IDTs arranged adjacent to each other in order to be acoustically coupled to each other, and have different numbers of paired electrode fingers, and a pitch between each neighboring two of almost all of the electrode fingers included in one of the pair of IDTs which has the smaller number of paired electrode fingers is made different from one to another in order that the IDTs should include no primary pitch area.