Longitudinally Coupled Resonator Filter Busbar Layout for EM Isolation
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Solution Overview
Problem
Undesirable electromagnetic field coupling occurs between the hot-side busbars of adjacent IDT electrodes in longitudinally coupled resonator acoustic wave filters, degrading attenuation characteristics.
Innovation Solution
Incorporating projecting portions on the ground-side busbars of adjacent IDT electrodes to redirect electromagnetic fields away from hot-side busbars, thereby reducing electromagnetic field coupling and enhancing attenuation characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the hot-side busbar of one IDT electrode and the hot-side busbar of the other IDT electrode are aligned with each other in the propagation direction, then the device structure is simplified, but electromagnetic field coupling occurs between the hot-side busbars, degrading attenuation characteristics
Solution Approach 1:
A ground-side busbar is introduced as an intermediary element between the hot-side busbars of adjacent IDT electrodes. This ground-side busbar acts as a shield that redirects electromagnetic fields away from the hot-side busbars, preventing direct coupling between them while maintaining the aligned structure. The ground-side busbar serves as a mediator that resolves the conflict between structural simplicity and electromagnetic isolation.
2Reliability
If the ground-side busbar of one IDT electrode and the hot-side busbar of the other IDT electrode are aligned with each other, then electromagnetic field coupling is reduced, but the device structure becomes more complex
Solution Approach 1:
The ground-side busbars of adjacent IDT electrodes are merged into a continuous structure that serves multiple functions: it provides electromagnetic shielding between hot-side busbars, maintains structural alignment, and simplifies the overall device architecture. By combining the ground-side busbar functions, the patent reduces the number of separate components while achieving electromagnetic isolation.
3Reliability
If projecting portions are added to the ground-side busbar extending beyond the interdigitated region, then electromagnetic field coupling between hot-side busbars is suppressed, but manufacturing complexity increases
Solution Approach 1:
The projecting portions extend the ground-side busbar in the propagation direction (second direction) beyond the interdigitated region, utilizing the spatial dimension to create effective electromagnetic shielding. This dimensional extension allows the ground-side busbar to intercept and redirect electromagnetic fields before they can couple between hot-side busbars, achieving isolation without requiring additional components or complex three-dimensional structures.
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 implementation of projecting portions effectively suppresses electromagnetic field coupling, leading to improved attenuation characteristics in longitudinally coupled resonator acoustic wave filters.
Implementation Method 1
undesirable electromagnetic field coupling occurs between the hot-side busbar of one IDT electrode and the hot-side busbar of the other IDT electrode
Data Source
AI summary
A longitudinally coupled resonator acoustic wave filter includes first and second IDT electrodes on a piezoelectric substrate. A direction in which electrode fingers of the IDT electrodes extend is a first direction, a direction perpendicular or substantially perpendicular to the first direction is a second direction, a ground-side busbar of the first IDT electrode and a hot-side busbar of the second IDT electrode face each other in the second direction, and the longitudinally coupled resonator acoustic wave filter includes a projecting portion, connected to the ground-side busbar of the first IDT electrode, that extends in the second direction toward the second IDT electrode beyond an interdigitated region of the first IDT electrode.