Acoustic Wave Filter Tuning With Magnetic Coupling for Lower-Band Attenuation
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Solution Overview
Problem
Conventional acoustic wave filter devices experience deterioration in lower side pass band attenuation when the attenuation pole is shifted higher in frequency, leading to inadequate filtering performance in multiband operations.
Innovation Solution
The acoustic wave filter device incorporates a series-arm resonant circuit and a parallel-arm resonant circuit with a switching element, allowing for magnetic coupling between transmission lines to create an additional attenuation pole, thereby improving attenuation on the lower side of the pass band by shifting the resonant frequency of the parallel-arm resonant circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the attenuation pole is shifted higher in frequency by switching the switching element, then the filter can operate in different frequency bands, but the attenuation on the lower side of the pass band deteriorates
Solution Approach 1:
The filter is divided into multiple resonant circuits (first series-arm resonant circuit, second series-arm resonant circuit, first parallel-arm resonant circuit, second parallel-arm resonant circuit) that can be independently controlled. By segmenting the filter into controllable sections with switching elements, different resonance modes can be activated to achieve both frequency adaptability and maintain attenuation performance.
Solution Approach 2:
The filter employs dynamic switching elements that can change the circuit configuration in real-time. By switching between different resonant circuit configurations, the filter dynamically adjusts its characteristics to maintain optimal attenuation across different operating bands, resolving the contradiction between frequency adaptability and attenuation performance.
2Reliability
If additional components are added to improve attenuation, then the filtering performance improves, but the device size increases
Solution Approach 1:
Each resonant circuit is designed to serve multiple functions: the series-arm resonant circuits provide both passband transmission and attenuation pole formation, while the parallel-arm resonant circuits provide both impedance matching and attenuation enhancement. This multi-functionality allows the filter to achieve superior filtering performance without requiring additional dedicated components, thus avoiding area increase.
Solution Approach 2:
The patent merges the functions of multiple resonant circuits into a unified filter structure where the series-arm and parallel-arm resonant circuits work together. By combining these circuits with shared components and integrated layout, the filter achieves enhanced attenuation performance without a proportional increase in device area.
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 enhances the attenuation on the lower side of the pass band without increasing the filter device's size, maintaining effective filtering performance across multiband operations.
Implementation Method 1
The first transmission line and the second transmission line are in magnetic coupling with each other
Implementation Method 2
bulk acoustic wave (BAW) resonator
Data Source
AI summary
An acoustic wave filter device includes a first resonant circuit, a second resonant circuit, a first interconnect line, and a second interconnect line. The second resonant circuit includes a second parallel-arm resonator, and a frequency-tuning circuit that allows tuning of the resonant frequency of the second parallel-arm resonator. The frequency-tuning circuit includes a capacitor, and a switching element connected in parallel with the capacitor. The first interconnect line is an interconnect line connected to the portion of the series-arm resonator located adjacent to the first input/output terminal. The second interconnect line is an interconnect line connecting the parallel-arm resonator with the switching element, or an interconnect line connecting the parallel-arm resonator with the capacitor. A first transmission line formed by the first interconnect line, and a second transmission line formed by the second interconnect line are magnetically coupled with each other.