Balanced SAW Duplexer Layout for Out-of-Band Attenuation
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Solution Overview
Problem
Existing acoustic wave filter devices struggle to achieve sufficient out-of-band attenuation without deteriorating the balance between signals output from balanced signal terminals, which is crucial for reducing the number of components in cellular phones while maintaining effective frequency band attenuation.
Innovation Solution
The use of a piezoelectric substrate with multiple longitudinally coupled resonator type surface acoustic wave filters, each with a specific configuration of interdigital transducers (IDTs) and phase relationships, allows for increased out-of-band attenuation while maintaining signal balance by varying the number of electrode finger pairs among the filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the number of pairs of electrode fingers of IDTs in all longitudinally coupled resonator type surface acoustic wave filters are made equal, then the balance between signals output from first and second balanced signal terminals is maintained, but the out-of-band attenuation is insufficient
Solution Approach 1:
The patent applies asymmetry by making the number of pairs of electrode fingers of at least one IDT in at least one filter different from the corresponding IDTs in other filters. This asymmetric configuration creates different attenuation characteristics among filters, achieving sufficient out-of-band attenuation while maintaining signal balance through the specific phase relationships and coupling arrangements.
2Object-generated harmful factors
If the number of pairs of electrode fingers of IDTs are varied among filters to increase out-of-band attenuation, then the attenuation performance improves, but the balance between signals output from balanced signal terminals deteriorates
Solution Approach 1:
The patent applies local quality by varying the number of pairs of electrode fingers of IDTs in specific filters rather than uniformly across all filters. This localized modification allows each filter to have optimized attenuation characteristics while the overall system maintains signal balance through the specific configuration of phase relationships and terminal connections.
Solution Approach 2:
The patent applies parameter changes by modifying the number of pairs of electrode fingers of IDTs as a key parameter. This parameter change directly affects the attenuation characteristics of individual filters, and by strategically varying this parameter across different filters while maintaining specific phase relationships, the system achieves both improved out-of-band attenuation and maintained signal balance.
3Object-generated harmful factors
If multiple components are used to achieve effective frequency band attenuation, then the attenuation performance improves, but the number of components increases
Solution Approach 1:
The patent applies merging by integrating multiple filter functions into a single longitudinally coupled resonator type surface acoustic wave filter device. Multiple IDTs are arranged in a longitudinal sequence on a single piezoelectric substrate, combining what would traditionally require separate components into one integrated structure, thereby achieving effective frequency band attenuation without increasing the number of discrete components.
Solution Approach 2:
The patent applies multi-functionality by designing a single filter device that simultaneously achieves multiple functions: out-of-band attenuation, signal balancing, and frequency selection. The longitudinally coupled resonator structure with multiple IDTs performs multiple filtering functions in one device, eliminating the need for separate components for each function.
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 out-of-band attenuation without compromising the balance between signal outputs, leading to a reduced component count and improved electrical characteristics in cellular phone duplexers.
Implementation Method 1
acoustic wave filter device which utilizes surface acoustic waves and boundary acoustic waves
Implementation Method 2
first and second longitudinally coupled resonator type surface acoustic wave filters connected to one another in a piezoelectric substance
Implementation Method 3
longitudinally coupled resonator type surface acoustic wave filters
Data Source
AI summary
An acoustic wave filter device includes first to fourth longitudinally coupled resonator type surface acoustic wave filters that are configured such that the first and second filters are connected to a first balanced signal terminal, the third and fourth filters are connected to a second balanced signal terminal, and a transmission phase of a signal output from the first balanced signal terminal relative to an input signal differs by about 180 degrees with respect to a transmission phase of a signal output from the second balanced signal terminal relative to an input signal. In addition, the number of pairs of electrode fingers of at least one of IDTs of at least one of the first to fourth longitudinally coupled resonator type surface acoustic wave filters is different from the number of pairs of electrode fingers of corresponding IDTs of the remaining first to fourth filters.