Acoustic Wave Extractor Layout for Lower IMD in Compact Filters
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Solution Overview
Problem
Existing extractors with combined band pass filters (BPF) and band elimination filters (BEF) suffer from intermodulation distortion (IMD) due to the nonlinearity of acoustic wave resonators, leading to signal noise ratio degradation, especially when the elimination band of the BEF overlaps with the pass band of the BPF, and increasing in size when resonators are divided to reduce IMD.
Innovation Solution
The extractor design incorporates a common terminal with a BPF and a BEF, where at least one of the filters includes a combination of serial and parallel arm resonators defined by acoustic wave resonators, with a specific configuration of divided resonators that reduces IMD while maintaining a compact size by optimizing the number and capacitance of divided resonator groups.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an acoustic wave resonator is divided into a plurality of divided resonators to reduce IMD, then the nonlinear effect is decreased and IMD occurrence is reduced, but the area increases and the extractor size increases
Solution Approach 1:
The patent implements nested resonators where smaller resonators are positioned inside or overlapping with larger resonators. Specifically, a third resonator is nested within the area defined by a first resonator, and a fourth resonator is nested within the area defined by a second resonator. This nesting arrangement allows multiple divided resonators to share spatial footprint, reducing the overall extractor area while maintaining the IMD reduction benefits of having multiple resonators
Solution Approach 2:
The patent transitions from a two-dimensional planar arrangement of resonators to a three-dimensional nested configuration. By stacking resonators in overlapping spatial regions and utilizing vertical or layered positioning, the design achieves higher resonator density without proportionally increasing the planar area, effectively adding a spatial dimension to the resonator arrangement
2Volume of stationary object
If a single acoustic wave resonator is used in the BPF and BEF, then the extractor size is small, but intermodulation distortion (IMD) occurs due to nonlinearity
Solution Approach 1:
The patent divides single resonators into multiple segmented resonators with different frequency characteristics. The first and second resonators have a first center frequency for the pass band, while the third and fourth resonators have a second center frequency for the elimination band. This segmentation allows the system to maintain a compact volume while reducing IMD through the distributed nonlinear characteristics of multiple resonators
Solution Approach 2:
The patent assigns different local quality characteristics to different resonators based on their specific frequency roles. The resonators are configured with specific center frequencies and quality factors optimized for their respective functions (pass band versus elimination band), allowing each resonator to operate in its optimal performance region while collectively achieving both size reduction and IMD mitigation
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 significantly reduces or prevents IMD occurrences while minimizing the size of the extractor, maintaining low-loss pass bands and steep transition bands between the BPF and BEF, thereby enhancing signal quality and reducing noise ratios.
Implementation Method 1
one filter of the band pass filter and the band elimination filter includes at least one serial arm resonator and at least one parallel arm resonator that are each defined by an acoustic wave resonator
Data Source
AI summary
An extractor includes a band pass filter and a band elimination filter. One filter of the band pass filter and the band elimination filter includes at least one serial arm resonator and at least one parallel arm resonator that are each defined by an acoustic wave resonator. Any one of the at least one serial arm resonator and the at least one parallel arm resonator includes, among a divided resonator group divided resonator including a plurality of divided resonators coupled in series to each other, a first divided resonator group that is a largest in number of the divided resonators coupled in series and a smallest in capacitance.