SAW Duplexer Filter Layout for Steeper Shoulder Characteristics
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Solution Overview
Problem
Surface acoustic wave filters in duplexers for mobile communication devices require steeper shoulder characteristics near the passband and attenuation poles at frequencies higher than the passband to effectively separate transmission and reception signals, while maintaining adequate out-of-band attenuation.
Innovation Solution
A surface acoustic wave device comprising a first and second surface acoustic wave filter, where the second filter has a passband at higher frequencies, with an additional surface acoustic wave resonator connected in parallel to the series-arm resonator, featuring an IDT electrode with a smaller electrode-finger pitch to create a local attenuation pole without deteriorating the pass characteristics of the second filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional ladder filter structure is used, then power durability is improved, but shoulder characteristics near the passband become insufficiently steep
Solution Approach 1:
The filter is divided into multiple resonator units (series-arm resonators and parallel-arm resonators) that can be independently designed and optimized. Each resonator contributes specifically to either power handling or frequency selectivity, allowing the overall filter to achieve both steep shoulder characteristics and high power durability simultaneously.
Solution Approach 2:
Different resonators are assigned different functions: series-arm resonators are optimized for power durability while parallel-arm resonators are optimized for creating steep attenuation poles. This local specialization allows each component to excel at its specific task, resolving the contradiction between overall power durability and local frequency selectivity.
2Manufacturing precision
If capacitance is added in parallel with ladder filter resonators, then shoulder characteristics are improved, but out-of-band attenuation deteriorates
Solution Approach 1:
Parallel-arm resonators serve as intermediary elements that provide the necessary capacitance effect for steep shoulder characteristics while being designed with specific resonance frequencies to maintain out-of-band attenuation. Instead of adding simple capacitance that degrades attenuation, the patent uses specially designed resonators that mediate between the two requirements.
Solution Approach 2:
The resonance frequencies of parallel-arm resonators are specifically set to be higher than the passband frequencies, creating attenuation poles at desired locations. By changing the frequency parameters of these resonators, the patent achieves steep shoulder characteristics while preserving out-of-band attenuation through proper frequency positioning.
3Reliability
If attenuation poles are positioned at higher frequencies, then frequency separation between transmission and reception bands is improved, but filter complexity increases
Solution Approach 1:
The parallel-arm resonators serve multiple functions simultaneously: they provide capacitance for steep shoulder characteristics, create attenuation poles for frequency separation, and maintain out-of-band attenuation. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in filter complexity while achieving improved signal separation.
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 solution achieves steeper shoulder characteristics and improved out-of-band attenuation, minimizing interference with nearby communication standards, while maintaining effective signal separation and reducing insertion losses.
Implementation Method 1
surface acoustic wave device includes a first surface acoustic wave filter and a second surface acoustic wave filter... The series-arm surface acoustic wave resonator includes an IDT electrode... The parallel-arm surface acoustic wave resonator includes an IDT electrode
Implementation Method 2
The additional surface acoustic wave resonator... has a resonance frequency which is higher than the frequency range of the passband of the second surface acoustic wave filter
Data Source
AI summary
A surface acoustic wave device includes a first surface acoustic wave filter forming a ladder filter circuit; and a second surface acoustic wave filter having a passband at a frequency range higher than that of the first surface acoustic wave filter. The first surface acoustic wave filter includes a series-arm surface acoustic wave resonator, a parallel-arm surface acoustic wave resonator and an additional surface acoustic wave resonator. The series-arm surface acoustic wave resonator is on a series arm of the ladder filter circuit and includes an IDT electrode. The parallel-arm surface acoustic wave resonator is on a parallel arm of the ladder filter circuit and includes an IDT electrode. The additional surface acoustic wave resonator includes an IDT electrode, is connected in parallel with the series-arm surface acoustic wave resonator, and has a resonance frequency higher than the frequency range of the passband of the second surface acoustic wave filter.