Acoustic Wave Multiplexer Resonator Layout for Ripple Suppression
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Solution Overview
Problem
The use of existing acoustic wave filters in multiplexers on higher frequency sides can lead to ripple generation near the pass band of lower frequency filters due to inductive impedance, resulting in increased insertion loss.
Innovation Solution
A multiplexer design incorporating a first filter with a first pass band and a second filter with higher frequencies, utilizing a series-arm resonator and a parallel-arm resonator configuration that sets specific anti-resonant frequencies to reduce insertion loss, including a first anti-resonant frequency lower than the second pass band and a second anti-resonant frequency higher than the second pass band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an acoustic wave filter with series-arm resonators is used on a higher frequency side of a multiplexer, then the filter can achieve its designed pass band characteristics, but inductive impedance is generated in frequency bands lower than the first anti-resonant frequency, causing ripple near the pass band of lower frequency filters
Solution Approach 1:
A parallel-arm resonator is introduced as an intermediary element between the series-arm resonators and the ground. This parallel-arm resonator acts as a mediator that absorbs or counteracts the inductive impedance generated by the series-arm resonators in frequency bands below the first anti-resonant frequency, thereby preventing ripple generation in lower frequency filter pass bands while maintaining the higher frequency filter's performance
Solution Approach 2:
The patent strategically positions the third anti-resonant frequency of the parallel-arm resonator to be lower than the lower frequency end of the second pass band. By changing the frequency parameter of the parallel-arm resonator's anti-resonance point, the inductive impedance effect is suppressed in the critical frequency region, eliminating ripple without affecting the main pass band characteristics
2Adaptability or versatility
If multiple filters are connected in common in a multiplexer, then frequency multiplexing is achieved, but insertion loss increases in the pass bands due to impedance interactions between filters
Solution Approach 1:
The patent applies local quality by making each filter have distinct resonator configurations with specifically positioned anti-resonant frequencies. The parallel-arm resonator in each filter provides localized impedance control in specific frequency regions, allowing each filter to maintain low insertion loss in its own pass band while coexisting with other filters in the multiplexer
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 proposed design effectively reduces insertion loss in the pass bands of filters connected in common by minimizing impedance variations and ripple generation, enhancing filter performance.
Implementation Method 1
acoustic wave resonators each including a first series-arm resonator on a series arm path
Implementation Method 2
A resonator including the first series-arm resonator and the second series-arm resonator that are combined together has a first anti-resonant frequency that is lower than the second pass band and a second anti-resonant frequency that is higher than the second pass band
Data Source
AI summary
A multiplexer includes a first filter with a first pass band, and a second filter with a second pass band higher than the first pass band. Acoustic wave resonators included in the second filter include a first series-arm resonator on a series arm path of the second filter, a second series-arm resonator connected in parallel with the first series-arm resonator, and a parallel-arm resonator on a parallel arm path connecting a connection point between the first and second series-arm resonators to the ground. A series-arm resonator including the first and second series-arm resonators has an anti-resonant frequency lower than the second pass band and an anti-resonant frequency higher than the second pass band. The parallel-arm resonator has an anti-resonant frequency lower than a lower frequency end of the second pass band.