SAW Filter Resonator Ordering for Stable Band-Pass Input Impedance
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Solution Overview
Problem
Surface acoustic wave (SAW) filters used in communications equipment face challenges in maintaining constant input impedance over a frequency band, leading to inefficient power coupling and signal reflection, which affects the performance of duplexers and other radio frequency filters.
Innovation Solution
The optimization of SAW filter input impedance is achieved by reordering the resonant frequencies of SAW resonators within the same group, while maintaining the same general filter transmission characteristics, to minimize impedance variation across the pass band, thereby improving impedance matching with the source impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SAW resonators are arranged in conventional order, then the filter structure is simple, but the input impedance varies significantly across the frequency band causing signal reflection
Solution Approach 1:
The patent changes the arrangement order of SAW resonators with identical resonant frequencies within the same group. By permuting the positions of resonators having the same resonant frequency, the input impedance characteristics of the filter are optimized to achieve better impedance matching and reduced signal reflection across the frequency band.
Solution Approach 2:
The patent applies different arrangement strategies to different groups of resonators. Within each group containing resonators with identical resonant frequencies, a specific optimized ordering is applied, while maintaining the overall filter structure. This localized optimization approach improves input impedance stability without requiring complete redesign of the entire filter architecture.
2Loss of energy
If resonator frequencies are reordered to optimize impedance, then signal reflection is reduced, but the design and analysis complexity increases
Solution Approach 1:
The patent optimizes the arrangement of resonators by changing their positional parameters within groups of identical resonant frequencies. This parameter optimization reduces signal reflection and improves power coupling efficiency, while the methodical approach to reordering keeps the design process manageable.
Solution Approach 2:
The patent employs computational methods that automatically determine the optimal resonator arrangement based on desired impedance characteristics. This self-optimizing approach reduces the need for manual trial-and-error design iterations, thereby managing design complexity while achieving optimal impedance matching.
3Use of energy by moving object
If conventional resonator arrangement is used, then manufacturing is straightforward, but power coupling efficiency is poor due to impedance mismatch
Solution Approach 1:
The patent changes the positional parameters of resonators within groups to optimize input impedance and improve power coupling efficiency. The resonators themselves and their basic connections remain unchanged, maintaining manufacturing simplicity while achieving better energy transfer from the source to the filter.
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 approach results in reduced signal reflection and improved transmission efficiency by ensuring a more stable input impedance over the frequency band, enhancing the overall performance of SAW filters in communications devices.
Implementation Method 1
A radio frequency or microwave signal applied to the first IDT 110 via an input terminal IN may generate an acoustic wave on the surface of the substrate 105
Implementation Method 2
the surface acoustic wave will propagate in the left-right direction
Implementation Method 3
A second IDT 120 may convert the acoustic wave back into a radio frequency or microwave signal at an output terminal OUT
Data Source
AI summary
Methods to design band-pass acoustic wave microwave filters are disclosed. A performance metric related to an input impedance of a baseline filter design is calculated, the baseline filter design including a plurality of series surface acoustic wave resonators and a plurality of shunt surface acoustic wave resonators, each surface acoustic wave resonator having a respective resonant frequency. One or more alternative filter designs is established, each alternative filter design derived from the baseline filter design by reordering the resonant frequencies of two or more of the plurality of series surface acoustic wave resonators and/or two or more of the plurality of shunt surface acoustic wave resonators. A respective performance metric related to an input impedance of each alternative filter designs is calculated. A final filter design is selected from among the baseline filter design and the alternative filter designs based on the respective performance metrics.