Composite Acoustic Filter Layout for Higher Out-Band Attenuation
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Solution Overview
Problem
Existing composite filter devices, particularly those with acoustic wave resonators, face challenges in achieving sufficient out-band attenuation in band pass filters.
Innovation Solution
The composite filter device incorporates a piezoelectric substrate with a band pass filter featuring a longitudinally coupled resonator-type acoustic wave filter, a second filter with an inductor, and a reference potential wiring line with a substantially annular portion surrounding the resonator, where parallel wiring portions and the reference potential connection portion overlap, ensuring currents flow in the same direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional band pass filter configurations are used, then device simplicity is maintained, but out-band attenuation is insufficient
Solution Approach 1:
The patent combines a longitudinally coupled resonator-type acoustic wave filter with an inductor to form an integrated band pass filter structure. The inductor is positioned to overlap with the acoustic wave filter in plan view, merging electromagnetic and acoustic filtering functions into a single compact device that achieves superior out-band attenuation without proportionally increasing complexity
Solution Approach 2:
The patent utilizes the vertical dimension by positioning the inductor above or below the acoustic wave filter in a stacked configuration. This three-dimensional arrangement allows the filtering functions to overlap in space, achieving enhanced out-band attenuation while maintaining a compact footprint and avoiding planar layout conflicts
2Reliability
If out-band attenuation is increased through additional filtering elements, then frequency selectivity is improved, but insertion loss increases
Solution Approach 1:
The patent optimizes the inductance value and geometric parameters of the inductor to achieve the desired out-band attenuation while minimizing insertion loss. By carefully controlling the inductor's dimensions, position, and electrical characteristics, the filter achieves superior frequency selectivity without excessive energy loss in the pass band
Solution Approach 2:
The patent uses the acoustic wave filter structure itself as a template for positioning the inductor, with the inductor overlapping the acoustic wave filter in a configured manner. This copying approach ensures optimal coupling and interaction between the two filtering mechanisms, achieving enhanced out-band attenuation while maintaining low insertion loss through geometric optimization
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 enhances electromagnetic coupling, resulting in increased out-band attenuation of the band pass filter, particularly in the vicinity of the pass band and beyond, without significant insertion loss.
Implementation Method 1
a piezoelectric substrate, a first filter that is a band pass filter and includes a longitudinally coupled resonator-type acoustic wave filter provided on the piezoelectric substrate
Implementation Method 2
This configuration enhances electromagnetic coupling, resulting in increased out-band attenuation of the band pass filter
Data Source
AI summary
A composite filter device includes a piezoelectric substrate, a first filter that is a band pass filter and includes a longitudinally coupled resonator-type acoustic wave filter on the piezoelectric substrate, a second filter that includes at least one resonator and an inductor connected to a reference potential, and a reference potential wiring line on the piezoelectric substrate and connected to the reference potential, that has a substantially annular portion having an annular shape including a gap, and that surrounds, in the substantially annular portion, the longitudinally coupled resonator-type acoustic wave filter. The substantially annular portion of the reference potential wiring line includes first and second end portions facing each other across the gap, and a reference potential connection portion extending with the first end portion as a starting point and that connects the longitudinally coupled resonator-type acoustic wave filter to the reference potential.