Surface Acoustic Wave Filter Apodized Weighting Optimization
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Solution Overview
Problem
Conventional surface acoustic wave filters experience high loss in transmission characteristics, particularly at resonance frequency, due to large apodized weighting factors in interdigital transducer electrodes, which affect the Q factor and introduce spurious modes.
Innovation Solution
A surface acoustic wave filter design incorporating a piezoelectric substrate made of lithium niobate with series and parallel resonators, where the apodized weighting factor of the first interdigital transducer electrode is smaller than that of the second, optimizing the Q factor at resonance and anti-resonance frequencies to reduce loss and spurious modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large apodized weighting factor is used in the interdigital transducer electrode, then the Q factor at anti-resonance frequency is improved, but the loss at resonance frequency increases
Solution Approach 1:
The filter is divided into multiple resonators (first series resonator, second series resonator, and parallel resonator) with different apodized weighting factors. The first series resonator uses a larger apodized weighting factor to achieve high Q factor at anti-resonance frequency, while the second series resonator uses a smaller apodized weighting factor to reduce loss at resonance frequency. This segmentation allows each resonator to be optimized for different frequency characteristics, resolving the contradiction between Q factor improvement and loss reduction.
2Reliability
If a large apodized weighting factor is used in the interdigital transducer electrode, then the Q factor is improved, but spurious modes are introduced
Solution Approach 1:
Different regions of the filter (different resonators) are assigned different apodized weighting factors according to their specific functional requirements. The first series resonator located at positions where high Q factor is critical uses a larger apodized weighting factor, while the second series resonator uses a smaller apodized weighting factor to suppress spurious modes. This local optimization approach allows each resonator to contribute differently to the overall filter performance, achieving high Q factor while minimizing spurious modes.
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 design achieves reduced loss and spurious suppression by optimizing the apodized weighting factors and metallization ratios, enhancing the Q factor and bandwidth of the surface acoustic wave filter, particularly at resonance and anti-resonance frequencies.
Implementation Method 1
a piezoelectric substrate including lithium niobate
Implementation Method 2
interdigital transducer electrode provided on the piezoelectric substrate
Implementation Method 3
series resonator including a first interdigital transducer electrode provided on the piezoelectric substrate, and a parallel resonator including a second interdigital transducer electrode
Data Source
AI summary
A surface acoustic wave filter includes a piezoelectric substrate including lithium niobate, a series resonator including a first interdigital transducer electrode provided on the piezoelectric substrate, and a parallel resonator including a second interdigital transducer electrode provided on the piezoelectric substrate and being electrically connected to the series resonator. An apodized weighting factor of the first interdigital transducer electrode is smaller than an apodized weighting factor of the second interdigital transducer electrode. This surface acoustic wave filter has a small loss.