Acoustic Wave Filter Layout for Low-Loss Sharp High-Frequency Cutoff
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Solution Overview
Problem
Existing acoustic wave filter devices face challenges in reducing size while maintaining low loss within the pass band and sharpness on the high-frequency side, as simply downsizing can lead to increased loss and deteriorated sharpness.
Innovation Solution
The acoustic wave filter device incorporates a series-arm resonant circuit with a first and second parallel-arm resonator, where the second parallel-arm resonator has a higher resonant frequency and anti-resonant frequency than the first, and excludes a reflector to minimize loss and maintain sharpness, while the first resonator includes a reflector to enhance Q values at anti-resonant and resonant frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the size of the acoustic wave filter device is reduced, then the device becomes more compact, but the loss within the pass band increases and the sharpness on the high-frequency side deteriorates
Solution Approach 1:
The filter device is divided into multiple resonators with different frequency characteristics (first resonator with lower resonant frequency, second resonator with higher resonant frequency). Each resonator is configured to provide specific attenuation at different frequency ranges, allowing the overall filter to maintain sharp attenuation characteristics and low loss even when downsized.
Solution Approach 2:
Different regions of the filter (different resonators) are given different local characteristics - the first resonator targets lower frequency attenuation while the second resonator targets higher frequency attenuation. This localized frequency-specific optimization allows the compact filter to maintain sharpness across the entire pass band without requiring uniform size increase.
2Volume of moving object
If the size of the acoustic wave filter device is reduced, then the device becomes more compact, but the sharpness on the high-frequency side of the pass band deteriorates
Solution Approach 1:
The filter is segmented into resonators with staggered resonant frequencies, where the second resonator (with higher resonant frequency) specifically addresses the high-frequency attenuation requirement. This segmentation allows the high-frequency sharpness to be maintained independently of the overall device size.
Solution Approach 2:
The resonant frequencies of the resonators are specifically designed with different values (second resonator has higher resonant frequency than first resonator). By changing the frequency parameters of individual resonators, the filter achieves sharp high-frequency attenuation without requiring proportional increases in physical dimensions.
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 allows for a reduced size of the acoustic wave filter device with minimized loss within the pass band and preserved sharpness on the high-frequency side, achieving improved filter characteristics.
Implementation Method 1
The second parallel-arm resonator includes an IDT electrode that excites an acoustic wave
Implementation Method 2
a resonant frequency of the second parallel-arm resonator is higher than a resonant frequency of the first parallel-arm resonator
Implementation Method 3
The first parallel-arm resonator includes an IDT electrode that excites an acoustic wave, and a reflector that reflects the acoustic wave excited by the IDT electrode
Data Source
AI summary
A filter includes a series-arm resonator connected to a path connecting input/output terminals, and first and second parallel-arm resonators connected between the same node on the path and ground. A resonant frequency of the second parallel-arm resonator is higher than a resonant frequency of the first parallel-arm resonator, and an anti-resonant frequency of the second parallel-arm resonator is higher than an anti-resonant frequency of the first parallel-arm resonator. The second parallel-arm resonator includes an IDT electrode that excites an acoustic wave, and does not include a reflector.