SAW Multiplexer Reflector Pitch Layout for Lower Spurious Emissions
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing duplexers with surface acoustic wave resonators face issues with rapid impedance variation at the high-frequency end of the stopband and lack improvement in filter characteristics, particularly at the low-frequency end, leading to increased spurious emissions and degradation in filter performance.
Innovation Solution
A multiplexer design incorporating series and parallel resonators with specific pitch ratios and grating bar configurations, where the stopband of the reflectors includes both passbands of the filters, reducing impedance variation and enhancing filter characteristics by ensuring the stopband encompasses the passbands of both filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the pitch of the reflector is configured to be greater than the pitch of the IDT in the series resonator closest to the common terminal, then the stopband includes the resonant and antiresonant frequencies, but rapid impedance variation occurs at the high-frequency end of the stopband and spurious emissions increase
Solution Approach 1:
The patent applies local quality by configuring different pitch relationships between reflectors and IDTs in different resonators. Specifically, in the series resonator closest to the common terminal, the reflector pitch is made greater than the IDT pitch, while in other series resonators, the reflector pitch is made equal to or less than the IDT pitch. This localized differentiation optimizes the stopband characteristics and reduces spurious emissions in specific frequency regions without compromising overall filter performance.
Solution Approach 2:
The patent utilizes parameter changes by adjusting the pitch ratio between reflectors and IDTs based on the position and function of each resonator. The pitch relationship is changed from greater than (in the first series resonator) to equal to or less than (in other series resonators), thereby controlling the stopband frequency characteristics and reducing impedance variation and spurious emissions across different operating bands.
2Loss of energy
If the stopband is configured to include both passbands of the filters, then signal loss is reduced and transmission characteristics are improved, but the device complexity increases due to specific pitch ratio requirements
Solution Approach 1:
The patent achieves reduced signal loss by carefully controlling the pitch parameters of reflectors relative to IDTs. By setting specific pitch ratios (greater than, equal to, or less than) in different resonators, the stopband is configured to encompass both filter passbands, thereby minimizing energy loss and improving transmission characteristics across the operating frequency range.
Solution Approach 2:
The patent introduces dynamic characteristics by making the pitch relationship between reflectors and IDTs variable depending on the resonator position and function. Rather than using a uniform pitch relationship throughout, the configuration adapts locally to optimize stopband coverage and minimize signal loss in different frequency regions, effectively creating a dynamically optimized structure.
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 reduces signal loss and improves transmission characteristics by ensuring the stopband of the reflectors includes both passbands, thereby minimizing spurious emissions and enhancing the overall performance of the multiplexer.
Implementation Method 1
In the surface acoustic wave resonator, reflectors that reflect the acoustic wave excited by an inter digital transducer (IDT) are located at both sides of the IDT
Implementation Method 2
reflectors that reflect the acoustic wave excited by an inter digital transducer (IDT)
Implementation Method 3
each of the parallel resonators including a pair of comb-shaped electrodes and a pair of reflectors, the pair of comb-shaped electrodes including electrode fingers, the pair of reflectors sandwiching the pair of comb-shaped electrodes therebetween and including grating bars
Data Source
AI summary
A multiplexer includes: a first filter connected between a common terminal and a first terminal; and a second filter connected between the common terminal and a second terminal, a passband of the second filter being higher than a passband of the first filter, the second filter including series resonators connected in series and parallel resonators connected in parallel between the common terminal and the second terminal, each of the parallel resonators including a pair of comb-shaped electrodes including electrode fingers and a pair of reflectors sandwiching the pair of comb-shaped electrodes therebetween and including grating bars, PR1>PD1 where PR1 represents an average pitch of the grating bars of a parallel resonator closest to the common terminal among the parallel resonators and PD1 represents an average pitch of the electrode fingers of the parallel resonator closest to the common terminal.