Facing Elastic Wave Filters With Frequency Spacing for Better Isolation
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Solution Overview
Problem
Elastic wave devices with piezoelectric substrates facing each other across a cavity face challenges in achieving both reduced size and improved isolation characteristics and out-of-band attenuation, as electromagnetic coupling degrades these performance metrics.
Innovation Solution
The configuration involves arranging pairs of filters on each substrate such that the absolute difference in center frequencies between facing filters is maximized, with a connection member providing conductivity and grounding to reduce electromagnetic coupling, and using a thinner substrate for filters with higher center frequencies to prevent bulk wave responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If piezoelectric substrates are arranged to face each other across a small cavity to reduce size, then device compactness is improved, but isolation characteristics are degraded due to electromagnetic coupling
Solution Approach 1:
The patent applies asymmetry by deliberately creating non-uniform frequency spacing between facing filter pairs. Instead of uniform spacing, the frequency differences are designed to be asymmetric and optimized, creating a non-uniform distribution that reduces electromagnetic coupling while maintaining compact form factor. This asymmetric frequency arrangement breaks the symmetry of electromagnetic interaction between facing substrates.
Solution Approach 2:
The patent changes the frequency parameter distribution between filter pairs. By optimizing the frequency differences to be larger than minimum required values and creating specific frequency spacing patterns, the electromagnetic coupling is reduced. This parameter optimization allows compact substrate arrangement while maintaining isolation characteristics through controlled frequency separation.
2Volume of moving object
If piezoelectric substrates are arranged to face each other across a small cavity to reduce size, then device compactness is improved, but out-of-band attenuation is degraded due to electromagnetic coupling
Solution Approach 1:
The asymmetric frequency spacing between facing filter pairs creates non-uniform electromagnetic field distribution, reducing harmful coupling effects. By designing frequency differences that are larger than minimum values and creating optimized spacing patterns, the patent minimizes electromagnetic interaction while maintaining compact device size.
Solution Approach 2:
The patent optimizes frequency parameters and spacing relationships to change the electromagnetic interaction characteristics. By setting frequency differences to specific optimized values and creating non-uniform frequency distributions, harmful electromagnetic coupling is reduced while preserving the compact cavity structure.
3Device complexity
If filters with close center frequencies are placed on facing substrates, then device integration is improved, but out-of-band attenuation is degraded
Solution Approach 1:
The patent changes the frequency parameter distribution by setting frequency differences between facing filters to be larger than minimum required values. This parameter optimization creates sufficient frequency separation to reduce electromagnetic coupling while maintaining high filter integration on facing substrates.
Solution Approach 2:
The patent performs preliminary frequency planning and optimization before physical implementation. By pre-calculating and setting optimal frequency differences and spacing relationships, the design prevents electromagnetic coupling issues before they occur, enabling successful integration of multiple filters on facing substrates.
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 allows for a reduced-size elastic wave device with enhanced isolation characteristics and out-of-band attenuation, while also improving heat dissipation and power handling capabilities.
Implementation Method 1
piezoelectric substrates 112 and 114, on which comb-shaped interdigital transducer (IDT) electrodes 121 and 123, which are for exciting surface acoustic waves
Implementation Method 2
comb-shaped interdigital transducer (IDT) electrodes 121 and 123, which are for exciting surface acoustic waves
Data Source
AI summary
In an elastic wave device, a first piezoelectric substrate and a second piezoelectric substrate are joined to each other with a joining portion so as to face each other across a cavity. A first set of a plurality of filters located on a facing surface of the first piezoelectric substrate and a second set of a plurality of filters located on a facing surface of the second piezoelectric substrate define a plurality of pairs of filters and face each other across the cavity. An absolute value of a difference between center frequencies of a filter of the first set of filters and a filter of the second set of filters in each pair of filters is larger than a minimum value among absolute values of differences between center frequencies of pairs of filters selected from a group including the first set of filters and the second set of filters.