Acoustic Wave Filter IDT Weighting for Sharper Passband Edges
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Solution Overview
Problem
Existing surface acoustic wave (SAW) filters face challenges in enhancing sharpness at the edges of the pass band while maintaining the pass band width, as the fractional band width of acoustic wave resonators is decreased when attempting to improve sharpness, leading to difficulties in achieving both high-frequency edge and low-frequency edge enhancements.
Innovation Solution
The proposed acoustic wave filter design includes series arm resonators and parallel arm resonators with interdigital transducer (IDT) electrodes featuring withdrawal-weighting floating electrodes, which are strategically positioned to improve sharpness at the edges of the pass band without reducing the pass band width by generating new resonant modes between the resonant and anti-resonant frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If withdrawal-weighted configuration is applied to enhance sharpness at the edge of the pass band, then the sharpness is improved, but the fractional band width of the acoustic wave resonators is decreased
Solution Approach 1:
The IDT electrode is segmented into multiple electrode fingers with different withdrawal weights. By dividing the electrode structure into discrete segments (electrode fingers) and applying different withdrawal weights to different segments, the patent achieves enhanced sharpness while maintaining overall fractional band width through selective weighting rather than uniform withdrawal.
Solution Approach 2:
Different regions of the IDT electrode are assigned different withdrawal weights to create local quality variations. The electrode fingers closer to the center of the IDT have different withdrawal weights compared to those at the edges, allowing localized optimization of sharpness at the pass band edge while preserving the overall bandwidth characteristics.
2Measurement precision
If fractional band width is decreased to improve sharpness at the edge of the pass band, then the sharpness is enhanced, but the pass band width cannot be maintained
Solution Approach 1:
The patent changes the withdrawal weight parameters of different electrode fingers to optimize both sharpness and pass band width. By adjusting the withdrawal weight parameter distribution across the electrode fingers, the patent achieves enhanced edge sharpness while maintaining the pass band width through parameter optimization rather than structural modification.
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 design effectively enhances the sharpness at both the high-frequency and low-frequency edges of the pass band while maintaining the pass band width, improving the filter's frequency selectivity without compromising the fractional band width.
Implementation Method 1
an interdigital transducer (IDT) electrode provided on a substrate having piezoelectricity
Implementation Method 2
The resonant frequency of the at least one series arm resonator is positioned within the pass band of the acoustic wave filter
Data Source
AI summary
An acoustic wave filter includes series arm resonators each including an IDT electrode on a piezoelectric substrate. Resonant frequencies of the series arm resonators are positioned within the pass band of the acoustic wave filter. The IDT electrode includes a pair of comb-shaped electrodes. Each of the comb-shaped electrodes includes electrode fingers and a busbar electrode. The electrode fingers extend in a direction intersecting a propagation direction of acoustic waves and are parallel with each other. One end of an electrode finger and one end of another electrode finger are connected with each other by the busbar electrode. The IDT electrode of the series arm resonator with the lowest anti-resonant frequency includes two or more withdrawal-weighted floating electrodes without any of the electrode fingers of one of the comb-shaped electrodes interposed therebetween.