Acoustic Wave Filter Resonator Layout for Wide Bandwidth and Steep Attenuation
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Solution Overview
Problem
Acoustic wave filters designed for multiband operations face challenges in achieving a wide pass band and steep attenuation characteristics, particularly in meeting the demands of LTE Band 41 and WLAN bands, as existing configurations struggle to increase pass band and stop band widths while maintaining steep transition regions.
Innovation Solution
The acoustic wave filter device incorporates a combination of series-arm and parallel-arm resonators, with specific resonant and anti-resonant frequency relationships and effective electromechanical coupling coefficients, along with dielectric layers and capacitors, to enhance pass band and stop band widths and steepness of the transition region between them.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the effective electromechanical coupling coefficient of one parallel-arm resonator is made comparatively low to achieve steep attenuation characteristics, then the attenuation characteristics become steep, but the width of the pass band and the width of the stop band near the pass band cannot be increased
Solution Approach 1:
The filter is divided into multiple parallel-arm resonators (first, second, third, and fourth parallel-arm resonators) with different effective electromechanical coupling coefficients. By segmenting the resonators and assigning different coupling coefficients to different positions, the patent achieves both steep attenuation characteristics and wider pass band width simultaneously, resolving the contradiction between attenuation steepness and bandwidth.
Solution Approach 2:
Different parallel-arm resonators are assigned different effective electromechanical coupling coefficients based on their positional requirements. The first and second parallel-arm resonators have lower coupling coefficients for steep attenuation, while the third and fourth have higher coupling coefficients for wider bandwidth. This local differentiation of properties allows simultaneous achievement of steep attenuation and wide bandwidth.
2Length of stationary object
If the effective electromechanical coupling coefficient is increased to achieve a wider pass band, then the pass band width increases, but the attenuation characteristics become less steep
Solution Approach 1:
The parallel-arm resonators are segmented into different groups with different coupling coefficients. Those requiring steep attenuation (first and second parallel-arm resonators) have lower coupling coefficients, while those requiring wide bandwidth (third and fourth parallel-arm resonators) have higher coupling coefficients. This segmentation allows both requirements to be satisfied simultaneously.
Solution Approach 2:
The effective electromechanical coupling coefficient is locally optimized for each parallel-arm resonator based on its functional requirement. Lower coupling coefficients are applied where steep attenuation is needed, and higher coupling coefficients are applied where wide bandwidth is needed, resolving the contradiction between bandwidth and attenuation steepness.
3Adaptability or versatility
If a filter device is designed to meet both wide band width and steep attenuation characteristics, then the filter can handle multiband operations, but the device complexity increases
Solution Approach 1:
The filter uses multiple parallel-arm resonators with different effective electromechanical coupling coefficients to achieve multiband operation. By segmenting the resonators and assigning different coupling coefficients, the patent enables wide bandwidth and steep attenuation characteristics simultaneously, providing multiband capability without excessive complexity.
Solution Approach 2:
Different parallel-arm resonators are assigned different effective electromechanical coupling coefficients based on their positional requirements for multiband operation. This local differentiation allows the filter to achieve complex multiband characteristics using a relatively simple ladder structure, resolving the contradiction between versatility and complexity.
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 wider pass band and stop band on the lower side of the pass band with improved steepness of the transition region, while also providing lower insertion loss and miniaturization, and maintains performance under varying temperature conditions.
Implementation Method 1
an acoustic wave resonator including a piezoelectric body and interdigital transducer (IDT) electrodes
Implementation Method 2
The resonant frequency of the second parallel-arm resonator is the highest of all the parallel-arm resonators of the acoustic wave filter device. The anti-resonant point of a parallel-arm resonator determines the bandpass characteristics in the pass band of a filter, and the resonant point determines the attenuation characteristics on the lower side of the pass band of the filter.
Data Source
AI summary
An acoustic wave filter includes a series-arm resonator, a first parallel-arm resonator, and a second parallel-arm resonator. The series-arm resonator is disposed on a path connecting first and second input/output terminals. The first parallel-arm resonator is disposed on a path that connects ground with a node, which is located on a path connecting the series-arm resonator with the first input/output terminal. The second parallel-arm resonator is disposed on a path that connects ground with a node, which is located on a path connecting the series-arm resonator with the second input/output terminal. The parallel-arm resonator has a resonant frequency lower than the resonant frequency of the second parallel-arm resonator. The first parallel-arm resonator has an anti-resonant frequency higher than the anti-resonant frequency of the second parallel-arm resonator. The second parallel-arm resonator has the highest resonant frequency of all the parallel-arm resonators.