Acoustic Wave Filter Parallel Resonator Capacitance Integration
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Solution Overview
Problem
Existing acoustic wave filters, such as ladder-type filters, face challenges in minimizing the difference between resonance and anti-resonance frequencies, which affects their filtering performance and efficiency.
Innovation Solution
The acoustic wave filter incorporates a piezoelectric substrate with a serial arm and parallel resonance portions, where the parallel resonance portions have a capacity element connected in parallel with the resonators, increasing the capacitance to 0.8 times or more of the IDT electrode capacitance, thereby reducing the frequency difference between resonance and anti-resonance frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If capacity portions are connected in parallel with acoustic wave resonators to reduce the difference between resonance and anti-resonance frequencies, then the filtering performance is improved, but the device complexity increases
Solution Approach 1:
The patent combines the resonator and capacity portion into a single integrated resonance portion structure, where the capacity portion is formed as an electrode pattern on the piezoelectric substrate rather than being a separate component. This merging reduces device complexity while maintaining the improved filtering performance achieved by having the capacity portion connected in parallel with the resonator.
Solution Approach 2:
The IDT electrode serves multiple functions: it acts as both the interdigitated transducer for generating acoustic waves and as the capacity portion that reduces the frequency difference between resonance and anti-resonance. This multi-functionality eliminates the need for separate capacity portions, thereby reducing device complexity while achieving better filtering performance.
2Reliability
If the capacitance of the capacity portion is increased to 0.8 times or more of the IDT electrode capacitance to narrow the passband, then the filtering performance is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The patent achieves the required capacitance ratio by adjusting the geometric parameters of the electrode patterns (such as electrode width, length, and spacing) rather than requiring precise control of material properties or complex assembly processes. This approach to parameter optimization reduces manufacturing precision requirements while achieving the target capacitance of 0.8 times or more of the IDT electrode capacitance for narrowed passband filtering performance.
3Reliability
If the difference between resonance and anti-resonance frequencies is reduced to enhance the steepness of the attenuation area, then the filtering performance is improved, but the device area increases
Solution Approach 1:
The patent nests the capacity portion electrodes within or adjacent to the IDT electrode structure, utilizing the same substrate area for multiple functions. The capacity-forming electrodes are integrated into the existing IDT pattern layout, allowing the resonance portion to achieve reduced frequency difference and enhanced attenuation steepness without requiring additional device area.
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 the steepness of the attenuation area and narrows the passband, improving the filter's performance and allowing for a reduction in the size of the filter components.
Implementation Method 1
an acoustic wave filter including a piezoelectric substrate
Implementation Method 2
an IDT electrode on the piezoelectric substrate
Implementation Method 3
a difference between an anti-resonance frequency and a resonance frequency of the first resonance portion is smaller than a difference between an anti-resonance frequency and a resonance frequency of the first resonator
Data Source
AI summary
A SAW filter includes a piezoelectric substrate, a serial arm and a parallel resonance portion. The serial arm includes one or more serial resonance portions. The parallel resonance portion is located on the piezoelectric substrate and configures a ladder-type filter together with the serial arm. The parallel resonance portion includes a parallel resonator and a capacity element. The parallel resonator includes an IDT electrodes on the piezoelectric substrate and a pair of reflectors on the two sides thereof. The capacity element is connected in parallel with the parallel resonator. A capacitance of the capacity element is 0.8 time or more of a capacitance of the IDT electrode in the parallel resonator. A difference between an anti-resonance frequency and a resonance frequency of the first parallel resonance portion is smaller than a difference between an anti-resonance frequency and a resonance frequency of the first parallel resonator.