Acoustic Wave Filter Ground Segmentation for Spurious Response Control
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Solution Overview
Problem
Existing acoustic wave filters with longitudinally coupled resonators face challenges in achieving sufficient attenuation on the higher frequency side of the pass band due to spurious responses generated by the resonant mode, which degrades bandpass characteristics and isolation in multiplexers.
Innovation Solution
The acoustic wave filter design includes a substrate with piezoelectricity, separated ground terminals for IDT electrodes, and a configuration of comb-shaped electrodes to increase inductance and reduce parasitic capacitance, shifting the attenuation pole to a lower frequency side and improving insertion loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a longitudinally coupled resonator with commonly connected ground terminals is used, then the ground is strengthened, but spurious responses occur on the higher frequency side causing insufficient attenuation
Solution Approach 1:
The ground terminals are segmented into two separate groups: a first ground terminal connected to even-numbered IDT electrodes and a second ground terminal connected to odd-numbered IDT electrodes. This segmentation prevents the formation of spurious responses while maintaining ground strength through distributed grounding points.
Solution Approach 2:
Different IDT electrodes are connected to different ground terminals based on their position (even vs odd numbering). This local differentiation in grounding configuration optimizes the electrical characteristics at each location, eliminating spurious responses in specific frequency regions while maintaining overall ground effectiveness.
2Object-generated harmful factors
If the attenuation pole is positioned on the higher frequency side, then out-of-band attenuation is improved, but insertion loss in the pass band increases
Solution Approach 1:
The grounding configuration parameters are optimized by connecting specific IDT electrodes to different ground terminals, which changes the electrical characteristics and shifts the attenuation pole position to achieve both low insertion loss and high out-of-band attenuation.
3Object-generated harmful factors
If multiple ground terminals are used to reduce spurious responses, then attenuation is improved, but device complexity increases
Solution Approach 1:
The ground system is segmented into two terminals with a regular alternating connection pattern to IDT electrodes. This segmentation achieves effective spurious response attenuation while maintaining relatively simple device structure through the systematic even-odd connection scheme.
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 attenuation on the high-frequency side of the pass band, reduces insertion loss, and prevents degradation of bandpass characteristics in multiplexers, thereby improving the overall performance of acoustic wave filters and multiplexers.
Implementation Method 1
a substrate having piezoelectricity
Data Source
AI summary
An acoustic wave filter includes a substrate having piezoelectricity, input/output terminals on the substrate, ground terminals on the substrate and separated from each other, and a longitudinally coupled resonator on the substrate and arranged on a path connecting the input/output terminals, in which each of IDT electrodes included in the longitudinally coupled resonator includes a pair of comb-shaped electrodes each of which is provided with a plurality of electrode fingers and a busbar electrode, the other of the pair of the comb-shaped electrodes included in the IDT electrode arranged at a position closest to the input/output terminal is connected to the ground terminal on the substrate, and the other of the pair of comb-shaped electrodes included in each of all the IDT electrodes other than the IDT electrode is connected to the ground terminal on the substrate.