Ladder Filter Resonator Layout for Steeper Duplexer Isolation
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Solution Overview
Problem
Ladder filters face challenges in achieving good steepness and sufficient out-of-band attenuation without deteriorating electric power handling capability, particularly in duplexer applications where high isolation characteristics are required.
Innovation Solution
The design incorporates a ladder filter with series-arm resonators and a parallel-arm resonator, where the electrode finger center-to-center distance between the IDT electrode and reflector is less than 0.5λ, and the anti-resonant frequency of at least one series-arm resonator is higher than the others, ensuring increased steepness and out-of-band attenuation without compromising electric power handling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the electrode finger center-to-center distance between IDT electrode and reflector is reduced to less than 0.5λ, then steepness and out-of-band attenuation are improved, but electric power handling capability deteriorates
Solution Approach 1:
The patent applies local quality by setting different electrode finger center-to-center distances for different series-arm resonators. Specifically, at least one series-arm resonator has an electrode finger center-to-center distance of less than 0.5λ to achieve high steepness and out-of-band attenuation, while other series-arm resonators have distances of 0.5λ or more to maintain electric power handling capability. This localized differentiation allows each resonator to optimize for its specific functional requirement within the overall filter system.
2Manufacturing precision
If a capacitor is connected in parallel with a series-arm resonator to improve steepness, then higher frequency steepness is improved, but anti-resonant frequency decreases and electric power handling capability deteriorates
Solution Approach 1:
The patent applies parameter changes by modifying the electrode finger center-to-center distance parameter of the IDT electrode relative to the reflector, rather than adding external components like capacitors. By controlling this geometric parameter to be less than 0.5λ in at least one series-arm resonator, the patent achieves the desired steepness improvement while avoiding the side effect of anti-resonant frequency reduction that would occur with parallel capacitor connections.
3Stability of the object's composition
If the electrode finger pitch of reflector is increased to reduce ripple in pass band, then ripple is reduced, but out-of-band attenuation near pass band deteriorates
Solution Approach 1:
The patent applies local quality by differentiating the electrode finger center-to-center distance parameter across different series-arm resonators. By setting at least one resonator with distance less than 0.5λ, the patent simultaneously achieves both ripple reduction and high out-of-band attenuation near the pass band, resolving the contradiction that would arise from uniformly increasing reflector pitch across all resonators.
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 enhances steepness and out-of-band attenuation while maintaining good electric power handling capability, thereby improving isolation characteristics in duplexers and elastic wave filter devices.
Implementation Method 1
an electrode finger pitch of the IDT electrode is different from an electrode finger pitch of each of the reflectors
Implementation Method 2
An anti-resonant frequency of the at least one of the series-arm resonators is higher than an anti-resonant frequency of at least another one of the plurality of series-arm resonators
Data Source
AI summary
A ladder filter includes series-arm resonators each including an IDT electrode and a reflector, and a parallel-arm resonator. In at least one of the series-arm resonators, where a wavelength that is determined by an electrode finger pitch of the IDT electrode is λ, an electrode finger center-to-center distance between an electrode finger located closest to the reflector among electrode fingers of the IDT electrode and an electrode finger located closest to the IDT electrode among electrode fingers of the reflector is less than about 0.5λ, and an anti-resonant frequency of the at least one of the series-arm resonators is higher than an anti-resonant frequency of at least another one of the series-arm resonators.