Acoustic Wave Filter Ground Wiring for Out-of-Band Attenuation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing acoustic wave filter devices with balance-unbalance conversion functions, such as surface and boundary acoustic wave filter devices, face insufficient out-of-band attenuation, which limits their performance and size reduction potential.
Innovation Solution
A longitudinally coupled resonator-type acoustic wave filter unit with at least three IDTs is connected between unbalanced and balanced terminals, featuring specific ground wiring configurations, including branched wiring parts that sandwich the IDT area, enhancing out-of-band attenuation and reducing device size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional ground wiring is used in acoustic wave filter devices, then the device structure is simple, but the out-of-band attenuation is insufficient
Solution Approach 1:
The ground wiring is divided into multiple separate ground wiring patterns (first ground wiring pattern, second ground wiring pattern, third ground wiring pattern) instead of using a single conventional ground wiring structure. Each pattern serves specific functional purposes: the first provides ground connection for the unbalanced terminal, the second connects balanced terminals to ground, and the third forms shielding walls. This segmentation enables independent optimization of each ground wiring pattern's function, thereby achieving sufficient out-of-band attenuation while maintaining structural simplicity.
2Volume of stationary object
If the number of parts is reduced by using integrated ground wiring, then device size decreases, but out-of-band attenuation performance deteriorates
Solution Approach 1:
Multiple ground wiring patterns are integrated onto a single piezoelectric substrate, merging the functions of separate ground connections and shielding structures into one unified device architecture. The first, second, and third ground wiring patterns are all formed on the same substrate and work cooperatively to achieve both compact size and sufficient out-of-band attenuation, eliminating the need for additional separate components.
3Ease of manufacture
If conventional electrode configuration is used, then manufacturing is simple, but loss in the filter device is high
Solution Approach 1:
Different ground wiring patterns are strategically positioned in specific local areas of the piezoelectric substrate to optimize performance. The third ground wiring pattern is specifically located between IDT electrodes to form shielding walls that reduce energy loss, while the first and second patterns provide ground connections in their respective areas. This localized optimization of ground wiring positions reduces filter device loss while maintaining ease of manufacture through standard fabrication processes.
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 proposed configuration significantly increases out-of-band attenuation and reduces loss in acoustic wave filter devices, improving differential characteristics between balanced terminals and allowing for further size reduction.
Implementation Method 1
at least three IDTs and reflectors arranged in this order along the acoustic wave propagation direction on a piezoelectric substrate
Implementation Method 2
a longitudinally coupled resonator-type acoustic wave filter unit having at least three IDTs and having reflectors arranged on either side of the area in which the IDTs are arranged
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
There is provided an acoustic wave filter device having a balance-unbalance conversion function capable of increasing the amount of out-of-band attenuation. An acoustic wave filter device (1) configured in such a manner that a 5-IDT-type longitudinally coupled resonator-type acoustic wave filter unit (12) including IDTs (21 to 25) such that the IDTs (21, 24, and 25) are connected between an unbalanced terminal (3) and first and second balanced terminals (4 and 5), and the IDTs (22 and 23) are connected to the first and second balanced terminals (4 and 5), respectively, is formed between the unbalanced terminal (3) and the first and second balanced terminals (4 and 5), second ground wiring (18) that connects the end portions of the unbalanced-side IDT (21, 23, and 25) on the side connected to the ground potential to a ground terminal (6) is separated from first ground wiring (17), the second ground wiring (18) has first and second branched wiring parts (18a and 18b), and the first and second branched wiring parts (18a and 18b) are provided so as to sandwich an area in which the IDTs (21 to 25) are provided.