Balanced Acoustic Wave Filter Ground Layout for Signal Balance
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Solution Overview
Problem
Existing balanced acoustic wave filter devices have insufficient signal balance levels and attenuation characteristics outside the pass band, particularly on the higher frequency side, due to inadequate grounding arrangements on piezoelectric substrates.
Innovation Solution
The proposed balanced acoustic wave filter device features a specific arrangement of ground terminals and IDTs on a piezoelectric substrate, with a first ground terminal positioned closer to the unbalance terminal and a third ground terminal arranged in a point-symmetric relationship relative to the first ground terminal, enhancing the grounding influence among IDTs connected to balance terminals, thereby improving signal balance and attenuation characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If ground-side ends of IDTs are connected in common to one ground terminal, then device size is reduced, but signal balance level and attenuation characteristic outside the pass band deteriorate
Solution Approach 1:
The patent divides the grounding system into multiple separate ground terminals (first ground terminal connected to second and third IDTs, second ground terminal connected to fourth and fifth IDTs) rather than using a single common ground terminal. This segmentation allows independent optimization of ground connections for different IDT groups, improving signal balance and attenuation characteristics while maintaining compact device size.
2Volume of stationary object
If ground-side ends of IDTs are connected in common to one ground terminal, then device size is reduced, but attenuation characteristic outside the pass band deteriorates
Solution Approach 1:
The patent segments the grounding system into multiple ground terminals to prevent harmful interactions between signals from different IDTs. By providing separate ground paths (first ground terminal for second and third IDTs, second ground terminal for fourth and fifth IDTs), the design reduces unwanted coupling and improves attenuation characteristics in frequency bands outside the pass band.
3Reliability
If multiple ground terminals are used, then signal balance level and attenuation characteristic improve, but device complexity increases
Solution Approach 1:
The patent combines multiple IDTs that require the same ground connection to shared ground terminals. Specifically, the second and third IDTs share the first ground terminal, while the fourth and fifth IDTs share the second ground terminal. This merging approach reduces the total number of ground terminals needed compared to providing individual ground terminals for each IDT, thereby simplifying the grounding arrangement while still improving signal balance and attenuation characteristics.
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 effectively increases signal balance levels and improves attenuation characteristics outside the pass band on higher frequency sides, reducing differences in attenuation between balance terminals and enhancing overall filter performance.
Implementation Method 1
a piezoelectric substrate, a first longitudinally-coupled acoustic wave filter element disposed on the piezoelectric substrate
Data Source
AI summary
In an acoustic wave filter device, first and second acoustic wave filter elements are connected in parallel to an unbalance terminal. Of first to third IDTs, the second and third IDTs are connected to a first balance terminal. Of fourth to sixth IDTs, the fifth and sixth IDTs are connected to a second balance terminal. The first ground terminal is arranged at a position close to the side of the unbalance terminal and shifted to the side of the first acoustic wave filter element. The third ground terminal is arranged in a point-symmetric relationship relative to the first ground terminal with respect to a middle point between the first and second acoustic wave filter elements.