Acoustic Wave Filter Divided Resonators for Ripple-Free Sharpness
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Solution Overview
Problem
Acoustic wave filters with high sharpness suffer from spurious signals (ripples) outside the pass band due to the periodic structure based on withdrawal electrodes, which deteriorates the attenuation characteristic and bandpass characteristic of multiplexers.
Innovation Solution
The acoustic wave filter includes a divided resonator group with two acoustic wave resonators coupled in series, where the IDT electrodes in each resonator have different withdrawal electrodes with distinct electrode finger structures, reducing spurious signals and improving sharpness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If IDT electrodes include a withdrawal electrode to improve sharpness, then the sharpness at the pass band is improved, but spurious signals appear outside the pass band
Solution Approach 1:
The IDT electrode is segmented into multiple electrode finger groups with different pitches. Specifically, the IDT electrode includes a first electrode finger group with a first pitch and a second electrode finger group with a second pitch different from the first pitch. This segmentation allows different portions of the electrode to operate at different frequencies, enabling the generation of multiple resonant modes that can suppress spurious signals while maintaining sharpness at the pass band.
Solution Approach 2:
Different regions of the IDT electrode are assigned different local properties through the use of electrode finger groups with different pitches. The first electrode finger group has a first pitch optimized for the pass band frequency, while the second electrode finger group has a second pitch optimized for suppressing spurious signals. This local differentiation allows each region to contribute differently to the overall frequency response, achieving both sharpness and spurious signal reduction.
2Measurement precision
If a periodic structure based on withdrawal electrode is provided, then sharpness is improved, but attenuation characteristic deteriorates
Solution Approach 1:
The IDT electrode is divided into electrode finger groups with different pitches to create multiple periodic structures with different periods. This segmentation allows the filter to achieve sharpness through the primary periodic structure while the secondary periodic structure targets specific spurious frequency regions for attenuation, thereby improving overall attenuation characteristic without sacrificing sharpness.
Solution Approach 2:
The pitch parameter of the electrode finger groups is changed to create different periodic structures. By varying the pitch between the first and second electrode finger groups, the patent creates resonant modes at different frequencies that work together to improve sharpness at the pass band while enhancing attenuation at spurious frequency regions, thus improving the attenuation characteristic.
3Measurement precision
If IDT electrode has withdrawal electrode with periodic structure, then sharpness is improved, but bandpass characteristic deteriorates
Solution Approach 1:
The IDT electrode is segmented into multiple electrode finger groups with different pitches to create a multi-mode resonant structure. This segmentation enables the filter to maintain sharpness at the pass band while suppressing spurious signals that would otherwise degrade the bandpass characteristic, thereby improving overall reliability of the bandpass filtering function.
Solution Approach 2:
Different portions of the IDT electrode are given different local characteristics through the use of electrode finger groups with different pitches. The first electrode finger group maintains the primary periodic structure for sharpness, while the second electrode finger group provides additional periodicity for spurious signal suppression, ensuring reliable bandpass characteristic without compromising sharpness.
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 achieves a sufficient degree of sharpness at the pass band, reduces spurious signals, and enhances the low-loss bandpass characteristic of multiplexers, improving power handling capability and reducing intermodulation distortion.
Implementation Method 1
an acoustic wave resonator including an interdigital transducer (IDT) electrode on a substrate with piezoelectricity
Data Source
AI summary
An acoustic wave filter includes a divided resonator group and series arm resonators in a path connecting an input-output terminal and an input-output terminal to each other and parallel arm resonators each between a node in the path described above and the ground. The divided resonator group, the series arm resonators, and the parallel arm resonators each include an acoustic wave resonator including an interdigital transducer electrode on a piezoelectric substrate. The divided resonator group includes divided resonators coupled in series with each other. The IDT electrode included in the divided resonator includes a first withdrawal electrode. The IDT electrode included in the divided resonator includes a second withdrawal electrode different from the first withdrawal electrode with respect to the electrode finger structure.