Ladder Elastic Wave Filter Resonator Layout for Steeper High-Side Roll-Off
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Solution Overview
Problem
Conventional ladder-type elastic wave filters face difficulties in securing steepness of passing characteristics at frequency regions higher than their passband, which affects the performance of antenna duplexers.
Innovation Solution
The proposed ladder-type elastic wave filter configuration includes series resonators and parallel resonators connected in a ladder form, with a second parallel resonator having a resonance frequency higher than the series resonators but lower than their antiresonance frequencies, forming an attenuation pole in a lower frequency region than the series resonators, thereby enhancing the steepness of passing characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional ladder-type elastic wave filter configuration is used, then the filter structure is simple, but the steepness of passing characteristic at frequency region higher than passband cannot be secured
Solution Approach 1:
The filter is divided into multiple resonator stages (series resonators and parallel resonators) with specific resonance frequency relationships. Each resonator group contributes to forming attenuation poles at different frequency regions, enabling the steep passing characteristic through segmented frequency control rather than a single complex structure
Solution Approach 2:
The invention changes the resonance frequency parameters of the parallel resonators relative to the series resonators. Specifically, the second parallel resonator is designed with resonance frequency higher than the series resonator but lower than its antiresonance frequency, creating an attenuation pole in a specific frequency region that enhances the steepness of the passing characteristic
2Manufacturing precision
If the passing characteristic steepness is improved by adding more resonators, then the frequency selectivity is enhanced, but the heat generation and power consumption increase
Solution Approach 1:
Instead of adding multiple resonators across all frequency regions, the invention applies partial action by strategically placing only the necessary resonators (specifically the second parallel resonator with controlled frequency) to achieve the required attenuation pole positioning. This partial configuration achieves the frequency selectivity goal while minimizing the number of resonators and associated energy losses
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 improves the steepness of passing characteristics in the frequency region higher than the passband, reducing heat generation and power consumption, and enhancing the electric power resistance of the filter.
Implementation Method 1
a second parallel resonator connected in parallel to the first parallel resonator. The second parallel resonator has a resonance frequency higher than the resonance frequency of the series resonator and lower than the antiresonance frequency of the series resonator
Data Source
AI summary
A ladder-type elastic wave filter includes an input terminal, an output terminal, and a ground terminal, a first series resonator and a second series resonator connected in series between the input terminal and the output terminal, and a first parallel resonator having a first terminal electrically connected to the series connection between the first series resonator and the second series resonator and a second terminal electrically connected to the ground terminal. A resonance frequency of the first parallel resonator is higher than a resonance frequency of both of the first series resonator and the second series resonator and lower than an antiresonance frequency of both of the first series resonator and the second series resonator.