Acoustic Wave Ladder Filter for Narrow Pass Band Matching
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Solution Overview
Problem
Existing acoustic wave filters face challenges in achieving good filter characteristics when the band width ratio of a required band is smaller than the resonant band width ratio of a resonator, particularly when filter circuits with shifted pass bands are simply cascade-connected.
Innovation Solution
An acoustic wave filter design incorporating three ladder circuits with specific frequency conditions (fas1>fas2>fas3>frp1>frp2>frp3) and using SAW or BAW resonators, allowing for a pass band width sufficiently smaller than the resonant band width while maintaining good filter characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If two filter circuits having pass bands shifted in frequency are simply cascade-connected, then the device complexity is reduced, but the filter characteristics deteriorate when the difference between the resonant band width ratio and the band width ratio of the band increases
Solution Approach 1:
The patent applies parameter changes by precisely controlling the resonant frequencies and anti-resonant frequencies of the resonators in each ladder circuit. Specifically, it sets the anti-resonant frequencies of series arm resonators (fas1>fas2>fas3) and resonant frequencies of parallel arm resonators (frp1>frp2>frp3) to create overlapping pass bands with different center frequencies. This parameter optimization enables good filter characteristics even when the band width ratio is smaller than the resonant band width ratio, resolving the contradiction between simple cascade connection and filter performance.
2Adaptability or versatility
If the band width ratio of a required band is smaller than the resonant band width ratio of a resonator, then the filter can cover broader frequency ranges, but good filter characteristics cannot be obtained
Solution Approach 1:
The patent segments the filter into three ladder circuits, each containing series arm resonators and parallel arm resonators with specifically designed frequency characteristics. By dividing the filter into multiple stages with overlapping pass bands, the system achieves both broad frequency coverage and good filter characteristics. Each ladder circuit contributes to different portions of the overall pass band, allowing the filter to handle bands with width ratios smaller than the resonant band width ratio while maintaining performance.
Solution Approach 2:
The patent changes the frequency parameters of multiple resonators to achieve broad coverage with good characteristics. By setting fas1>fas2>fas3>frp1>frp2>frp3, the filter creates overlapping pass bands that collectively cover a broad frequency range while each individual resonator operates within its optimal resonant band width ratio, thus maintaining good filter characteristics across the entire band.
3Reliability
If three ladder circuits with specific frequency conditions are used to achieve narrow pass band, then the filter characteristics improve, but the device complexity increases
Solution Approach 1:
The patent segments the filter into three ladder circuits with systematically arranged frequency parameters. This segmentation allows each circuit to be designed and optimized independently while contributing to the overall narrow pass band characteristic. The systematic frequency arrangement (fas1>fas2>fas3>frp1>frp2>frp3) provides a clear design framework that manages complexity through structured parameter assignment.
Solution Approach 2:
The patent merges three ladder circuits with overlapping pass bands to achieve the desired narrow pass band characteristic. By combining the frequency selectivity of multiple circuits with properly designed overlapping characteristics, the system achieves superior filter performance that cannot be obtained with a single ladder circuit, while the systematic frequency arrangement keeps the overall design manageable.
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
The design achieves a narrow pass band with reduced insertion loss and improved impedance matching, enabling low-loss filters for 5G NR bands such as n47, n42, n48, and n52, and other communication systems.
Implementation Method 1
a first series arm resonator (11s) and a first parallel arm resonator (11p), the series arm resonator (11s) being connected in series to a series arm path connecting the input/output terminals (110, 120), the parallel arm resonator (11p) being connected to a first parallel arm path connecting the series arm path and ground
Implementation Method 2
two filter circuits having pass bands overlapping each other are cascade-connected to implement a filter circuit having a band width ratio smaller than a resonant band width ratio
Data Source
AI summary
An acoustic wave filter includes a first ladder circuit including a first series arm resonator and a first parallel arm resonator, a second ladder circuit including a second series arm resonator and a second parallel arm resonator, and a third ladder circuit including a third series arm resonator and a third parallel arm resonator. The first, second and third ladder circuits are cascade-connected in order. A condition of fas1>fas2>fas3>frp1>frp2>frp3 is satisfied, where fas1 represents an anti-resonant frequency of the first series arm resonator, fas2 represents an anti-resonant frequency of the second series arm resonator, fas3 represents an anti-resonant frequency of the third series arm resonator, frp1 represents a resonant frequency of the first parallel arm resonator, frp2 represents a resonant frequency of the second parallel arm resonator, and frp3 represents a resonant frequency of the third parallel arm resonator.