Acoustic Wave Filter Electrode Layout for Pass-Band Ripple Reduction
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Solution Overview
Problem
Existing acoustic wave filters with longitudinally coupled resonators experience ripples in the pass band due to significant differences in the number of electrode fingers between resonators.
Innovation Solution
The acoustic wave filter design includes a plurality of longitudinally coupled resonators, where each resonator has three IDT electrodes with specific configurations of wide and narrow pitch electrode finger groups. The number of electrode fingers in these groups is adjusted to fall within specific percentage ranges relative to each other, reducing ripple occurrence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the numbers of electrode fingers largely differ between the one longitudinally coupled resonator and the other longitudinally coupled resonator, then the acoustic wave filter can be designed with different resonator configurations, but ripples occur in the pass band
Solution Approach 1:
The patent applies parameter changes by carefully controlling the number of electrode fingers in the IDT electrodes of longitudinally coupled resonators. Specifically, it sets the number of electrode fingers of IDT electrodes in different resonators to differ by a controlled amount (1-11 fingers), which prevents excessive parameter divergence while maintaining design flexibility. This controlled parameter adjustment eliminates ripples in the pass band by ensuring proper impedance matching and wave propagation characteristics across coupled resonators.
2Reliability
If the numbers of electrode fingers are controlled to reduce ripples, then the pass band quality improves, but the device complexity increases due to precise finger count requirements
Solution Approach 1:
The patent establishes specific parameter ranges for electrode finger counts (differing by 1-11 fingers between resonators) to optimize pass band quality. This approach balances reliability improvement with manageable complexity by providing clear design guidelines rather than requiring excessive precision.
Solution Approach 2:
The patent applies partial action by controlling only the critical parameter of electrode finger count difference within specific ranges, rather than optimizing all possible geometric and electrical parameters. This focused approach achieves sufficient pass band quality while avoiding the complexity of comprehensive optimization.
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 or prevents ripples in the pass band of the acoustic wave filter, improving its frequency response characteristics.
Implementation Method 1
each of the first longitudinally coupled resonator and the second longitudinally coupled resonator includes three IDT electrodes that include a plurality of electrode fingers extending in a first direction along a main surface of a substrate
Data Source
AI summary
An acoustic wave filter includes a first longitudinally coupled resonator including first and second IDT electrodes, and a second longitudinally coupled resonator including third and fourth IDT electrodes. Each IDT electrode includes a wide pitch electrode finger group and a narrow pitch electrode finger group. A number of electrode fingers in the wide pitch electrode finger group of the first IDT electrode is smaller than that in the wide pitch electrode finger group of the second IDT electrode by a percentage equal to or more than about 4.2% and equal to or less than about 23.5%. A number of the electrode fingers in the wide pitch electrode finger group of the IDT electrode third is smaller than that in the wide pitch electrode finger group of the fourth IDT electrode by a percentage equal to or more than about 9.5% and equal to or less than about 52.4%.