Elastic Wave Ladder Filter Topology With Fewer Inductors
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Solution Overview
Problem
Existing π-type elastic wave ladder filters require an increased number of stages to achieve high attenuation characteristics, leading to larger size and higher costs when multiple stop bands are needed, as they necessitate a greater number of inductors.
Innovation Solution
The elastic wave filter configuration includes series arm resonators connected in series with an inductor in parallel, and parallel arm resonators arranged between series arm resonators, allowing for improved attenuation characteristics with fewer inductors by forming LC filters with attenuation poles within stop bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the number of stages in a π-type elastic wave ladder filter is increased to achieve multiple stop bands or high attenuation characteristics, then the attenuation characteristics are improved, but the size and cost of the filter are significantly increased due to the increased number of inductors
Solution Approach 1:
The patent combines multiple series arm resonators (at least two) into a single parallel connection with one inductor, rather than using separate inductors for each resonator. This merging approach maintains the attenuation characteristics while reducing the total number of inductors required in the filter circuit
Solution Approach 2:
The single inductor in the patent serves multiple functions by being connected in parallel with multiple series arm resonators simultaneously, allowing one inductor to provide the filtering function for multiple resonator stages rather than requiring dedicated inductors for each stage
2Adaptability or versatility
If the number of stages in a π-type elastic wave ladder filter is increased to achieve multiple stop bands, then the stop band coverage is improved, but the size of the filter is increased
Solution Approach 1:
The patent merges multiple resonator-inductor stages into a configuration where one inductor serves multiple resonators, thereby reducing the overall filter size while maintaining multiple stop bands through the resonant frequencies of different series arm 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 reduces the size and cost of the filter while enhancing attenuation characteristics by creating broader bandwidth and higher attenuation stop bands with fewer inductors, maintaining or improving performance compared to traditional π-type filters.
Implementation Method 1
the two or more series arm resonators, with which the inductor is connected in parallel, include a first series arm resonator and a second series arm resonator that has a resonant frequency equal to or higher than an anti-resonant frequency of the first series arm resonator. Furthermore, resonant points of the parallel arm resonators form two attenuation regions in the passband of the elastic wave filter and the first inductor forms, with equivalent circuits of the first and second series arm resonators, an LC filter having two attenuation poles arranged in said two attenuation regions.
Data Source
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AI summary
An elastic wave filter having satisfactory filter characteristics is provided. An elastic wave filter (1) includes: a plurality of series arm resonators (S1 and S2), an inductor (13a), and a plurality of parallel arm resonators (P1 to P3). The plurality of the series arm resonators (S1 and S2) are connected in series to one another on a series arm (12) connecting an input terminal (10) to an output terminal (11). The inductor (13a) is connected to the series arm (S1 and S2) in such a manner as to be in parallel with two or more of the plurality of the series arm resonators (S1 and S2). The plurality of the parallel arm resonators (P1 to P3) are arranged on parallel arms (16a and 16c) connecting connection nodes (14 and 15) of the inductor (13a) and the series arm (12) to a ground potential, and on an parallel arm (16b) connecting a connection node (17) of the series arm resonators (S1 and S2) adjacent to each other to the ground potential.