Balanced Acoustic Wave Filter Layout for Out-of-Passband Attenuation
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Solution Overview
Problem
The existing surface acoustic wave filter devices with multiple filters on a single piezoelectric substrate suffer from reduced out-of-passband attenuation due to asymmetry in the electrode and line pattern, which is exacerbated by the need for common electrical connections that increase line length and reduce symmetry.
Innovation Solution
The acoustic wave filter device incorporates a longitudinally-coupled resonator type filter with balanced-to-unbalanced transforming function, featuring a common connection line and ground line arrangement that ensures equal distances between connection points and balanced terminals, enhancing the symmetry of the line pattern and improving out-of-passband attenuation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If multiple surface acoustic wave filters are formed on a single piezoelectric substrate, then the number of parts is reduced and device miniaturization is achieved, but the out-of-passband attenuation is reduced due to asymmetry in electrode and line pattern
Solution Approach 1:
The patent applies asymmetry principle by intentionally designing the line pattern configuration to achieve symmetry in electrical characteristics. The ground line is positioned such that the distance from the first balanced terminal to the ground line equals the distance from the second balanced terminal to the ground line, creating symmetrical electrical characteristics despite the physical asymmetry of having multiple filters on a single substrate. This resolves the contradiction by transforming the asymmetrical layout into symmetrical electrical performance.
Solution Approach 2:
The patent implements equipotentiality by connecting both balanced terminals to the ground potential through lines of equal length and characteristic impedance. The ground line is configured to provide equal electrical path length from each balanced terminal to ground, ensuring that both terminals experience identical electrical conditions. This equipotential configuration eliminates the asymmetry-induced degradation of out-of-passband attenuation while maintaining the compact multi-filter structure.
2Device complexity
If common electrical connections are used to connect multiple filters, then the number of connections is reduced, but the line length increases and symmetry is reduced
Solution Approach 1:
The patent applies segmentation by dividing the ground connection into separate dedicated ground lines for each balanced terminal, rather than using a single common ground connection. Each ground line is independently configured to have equal length and impedance characteristics. This segmentation approach maintains symmetry for each filter connection while avoiding the asymmetry that would result from a shared common ground line, thus preserving out-of-passband attenuation performance.
Solution Approach 2:
The patent implements local quality by providing customized ground line configurations for each balanced terminal based on their specific positions and requirements. Each ground line is locally optimized to have equal electrical characteristics relative to its associated balanced terminal, rather than using a uniform common ground structure. This local optimization ensures that each filter connection maintains symmetrical electrical characteristics, preserving attenuation performance while accommodating the multi-filter layout.
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 reduces the size of the device while significantly enhancing out-of-passband attenuation characteristics, achieving improved filter performance without increasing device size.
Implementation Method 1
a piezoelectric substrate (2) and a plurality of acoustic wave filters (3, 4) disposed on the piezoelectric substrate (2)
Implementation Method 2
first IDT (21a) having a first end connected to an unbalanced terminal (5) and a second end connected to a ground potential, a second IDT (21b) having a first end connected to a ground potential and a second end connected to a first balanced terminal (6), and a third IDT (21c) having a first end connected to a ground potential and a second end connected to a second balanced terminal (7)
Data Source
AI summary
An acoustic wave filter device includes a plurality of acoustic wave filters disposed on the same piezoelectric substrate, and achieves enlargement of out-of-passband attenuation without a large increase in its size. For at least the first acoustic wave filter, ends of second IDTs and of third IDTs connected to first and second balanced terminals, the ends being connected to a ground potential, are connected to a common connection line, the common connection line is connected to a ground terminal by a ground line, and a distance between a connection point, at which the ground line is connected to the common connection line, and the first balanced terminal, and a distance between the connection point and the second balanced terminal, is the same or substantially the same.