Acoustic Wave Filter Apodization for Transverse Mode Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Surface and boundary acoustic wave filter devices face issues with high transverse mode spurious responses due to large confinement effects, which lead to increased insertion loss and ripple within the pass band, especially when size reduction occurs.
Innovation Solution
A longitudinally coupled resonator acoustic wave filter device is designed with narrow pitch electrode finger portions and apodization weights assigned to vary electrode finger overlap widths, maximizing overlap at ends adjacent to narrow pitch portions and minimizing in the middle, creating a waisted-drum shape to reduce insertion loss and suppress transverse mode ripples.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If apodization weights are assigned in IDTs to reduce transverse mode spurious response, then transverse mode suppression is improved, but insertion loss increases
Solution Approach 1:
The patent applies different electrode finger overlap widths at different locations within the IDT. Specifically, the overlap width is varied along the acoustic wave propagating direction, with different overlap widths in different regions. This local variation in overlap width allows suppression of transverse modes in certain regions while maintaining good signal transmission in other regions, thus reducing insertion loss. The key is that each local region has optimized quality characteristics suited to its function.
Solution Approach 2:
The IDT is divided into multiple sections along the acoustic wave propagating direction, with each section having a specific electrode finger overlap width. This segmentation allows different portions of the IDT to perform different functions: some portions focus on transverse mode suppression while others focus on signal transmission. By segmenting the IDT and optimizing each segment independently, the patent achieves both transverse mode suppression and low insertion loss.
2Area of stationary object
If the overlap width of each IDT is reduced to reduce filter size, then device area is reduced, but transverse mode spurious response increases
Solution Approach 1:
The patent employs different electrode finger overlap widths at different locations within the IDT structure. By making the overlap width a variable parameter that changes along the acoustic wave propagating direction, the patent can suppress transverse modes in specific regions without requiring uniform reduction of overlap width across the entire IDT. This local optimization allows size reduction while maintaining transverse mode suppression performance.
Solution Approach 2:
The patent changes the electrode finger overlap width parameter along the acoustic wave propagating direction. Instead of using a constant overlap width, the overlap width is varied as a function of position. This parameter change allows the filter to achieve size reduction while maintaining effective transverse mode suppression, as the overlap width is optimized at each location rather than uniformly reduced.
3Device complexity
If narrow pitch electrode finger portions are used in IDTs for inter-IDT resonance mode, then device complexity is reduced, but transverse mode spurious response increases due to large confinement effect
Solution Approach 1:
The patent combines narrow pitch electrode finger portions with position-dependent overlap widths. The narrow pitch portions provide simple inter-IDT resonance mode operation, while the varied overlap widths at different locations suppress transverse modes. This local quality variation in overlap width compensates for the increased confinement effect caused by narrow pitch, achieving transverse mode suppression without increasing device complexity.
Solution Approach 2:
The patent changes the electrode finger overlap width parameter along the acoustic wave propagating direction to suppress transverse modes in narrow pitch configurations. By making the overlap width a position-dependent parameter rather than a constant, the patent can mitigate the transverse mode issues inherent in narrow pitch designs while maintaining the simplicity of the inter-IDT resonance mode operation.
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
The solution effectively reduces insertion loss and suppresses transverse mode ripples within the pass band, enhancing the filter's performance and power withstanding capability.
Implementation Method 1
an electrode structure schematically shown in FIG. 9 is formed on a piezoelectric substrate 502
Implementation Method 2
a longitudinally coupled resonator acoustic wave filter device that utilizes a boundary acoustic wave or a surface acoustic wave
Implementation Method 3
various boundary acoustic wave filter devices that utilize a boundary acoustic wave have also been developed
Implementation Method 4
in a longitudinally coupled resonator surface acoustic wave filter device that utilizes an inter-IDT resonance mode
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A longitudinally coupled resonator acoustic wave filter device that utilizes an inter-IDT resonance mode with a further low loss is provided. In a longitudinally coupled resonator acoustic wave filter device (100) that utilizes an inter-IDT resonance mode, the apodization weights are assigned in first to third IDTs (111 to 113) having narrow pitch electrode finger portions (111A, 111B, 112A and 113A), but other than the narrow pitch electrode finger portions, in such a manner that the electrode finger overlap width sequentially varies in an acoustic wave propagating direction in which an acoustic wave propagates and portions of the IDTs, located at ends adjacent to the narrow pitch electrode finger portions (111A, 111B, 112A and 113A), have a maximum electrode finger overlap width.