Acoustic Wave Filter Cancel Circuit for Steep Cutoff
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Solution Overview
Problem
Existing filters and duplexers in wireless communication devices face challenges in achieving a steep cutoff characteristic while maintaining a wide passband and high suppression in blocking bands, leading to interference issues between transmission and reception signals across different frequency bands.
Innovation Solution
The implementation of a filter and duplexer design that includes acoustic wave resonators connected in series and parallel configurations, with a cancel circuit connected in parallel to some of the resonators, featuring a first acoustic wave resonator between the input/output connection portions and ground, to enhance the steepness of the cutoff characteristic and suppression in blocking bands without increasing loss or reducing passband width.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the electromechanical coupling coefficient is made small to achieve a steep cutoff characteristic, then the cutoff characteristic becomes steep, but the passband width becomes narrow
Solution Approach 1:
The filter is divided into multiple resonator stages (first resonator, second resonator, third resonator) with different coupling coefficients. The first resonator has a small coupling coefficient for steep cutoff, while the second and third resonators have larger coupling coefficients to maintain passband width. This segmentation allows each stage to optimize for its specific function without compromising overall performance.
Solution Approach 2:
Different parts of the filter have different electromechanical coupling coefficients tailored to their specific roles. The first resonator (near the cutoff region) has a small coupling coefficient to provide steep rolloff, while the second and third resonators (in the passband region) have larger coupling coefficients to maintain wide passband and low insertion loss. This local differentiation resolves the contradiction between cutoff steepness and passband width.
2Object-affected harmful factors
If the degree of suppression in blocking band is improved, then interference is reduced, but loss in passband increases
Solution Approach 1:
The filter uses multiple resonator stages with progressively different coupling coefficients. The first resonator provides initial suppression with minimal passband impact, while the second and third resonators enhance blocking band suppression. This segmented approach achieves high overall suppression (e.g., >60 dB in blocking band) while maintaining low passband insertion loss by distributing the suppression function across multiple stages rather than relying on a single high-suppression resonator that would degrade passband performance.
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 design effectively suppresses interference between frequency bands by creating a signal path with equal amplitude and opposite phase to cancel out signals in the guard band, maintaining similar insertion loss and passband width as existing designs while improving the steepness of the cutoff characteristic and suppression in blocking bands.
Implementation Method 1
acoustic wave resonators connected between an input terminal and an output terminal
Implementation Method 2
When an acoustic wave resonator is used for a filter or duplexer, a cutoff characteristic can be made steep by making an electromechanical coupling coefficient small
Data Source
AI summary
A filter includes: acoustic wave resonators connected between an input terminal and an output terminal; and a cancel circuit including an input connection portion and an output connection portion connected so that the cancel circuit is connected in parallel to at least a part of the acoustic wave resonators, wherein the cancel circuit includes a first acoustic wave resonator connected between a node between the input connection portion and the output connection portion and a ground.