Elastic Wave Filter Layout for Unwanted Mode Cancellation
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Solution Overview
Problem
Existing elastic wave devices with longitudinally coupled resonator elements face issues with unwanted modes due to wave interference, which complicates achieving steepness on the lower frequency side of the pass band and sufficient out-of-band attenuation.
Innovation Solution
Incorporating a different acoustic velocity portion within the ground interconnection between reflectors of longitudinally coupled resonator elastic wave elements, achieved through a gap or a mass addition member, to cancel out unwanted modes and enhance frequency selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the distance between the first and second longitudinally coupled resonator elastic wave filters is shortened to reduce device size, then the device footprint is reduced, but wave interference between the filters increases causing unwanted modes to become more significant
Solution Approach 1:
A ground interconnection is introduced as an intermediary element between the first and second longitudinally coupled resonator elastic wave filters. This ground interconnection acts as a mediator that prevents direct wave interference between the filters while maintaining electrical connectivity, thus reducing unwanted modes without increasing device footprint.
Solution Approach 2:
The ground interconnection is specifically positioned and configured in the region between the reflectors where the filters are adjacent to each other. By localizing the ground interconnection in this specific region, the patent targets the wave interference problem at its source without affecting other parts of the device, enabling compact design while controlling unwanted modes.
2Object-generated harmful factors
If the reflector is designed to prevent generation of unwanted modes, then unwanted modes are suppressed, but steepness on the lower frequency side of the pass band cannot be achieved
Solution Approach 1:
The patent separates the functions of unwanted mode suppression and frequency response shaping into two independent elements: the ground interconnection handles unwanted mode suppression by preventing wave interference, while the reflector design can focus on achieving steep frequency response. This functional segmentation allows both objectives to be optimized independently.
Solution Approach 2:
The ground interconnection serves as an intermediary that specifically targets unwanted mode generation through its positioning between the reflectors. This allows the reflector design to concentrate on achieving steep frequency response without being compromised by unwanted modes, as the ground interconnection handles that aspect separately.
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
Significantly reduces the influence of unwanted modes and achieves steepness on the lower frequency side of the pass band while maintaining high out-of-band attenuation.
Implementation Method 1
there is provided a different acoustic velocity portion in which an acoustic velocity is different from an acoustic velocity in the remaining portion of the above-mentioned section
Implementation Method 2
cancel out unwanted modes
Implementation Method 3
a first longitudinally coupled resonator elastic wave element that is provided on the piezoelectric substrate
Data Source
AI summary
An elastic wave device includes first and second longitudinally coupled resonator elastic wave elements aligned on a piezoelectric substrate. A second reflector of the first longitudinally coupled resonator elastic wave element and a third reflector of the second longitudinally coupled resonator elastic wave element are adjacent to each other in an elastic wave propagation direction. A ground interconnection extends in a direction intersecting with the elastic wave propagation direction and in a region between the second reflector and the third reflector. A gap in one portion of the ground interconnection includes a different acoustic velocity portion where an acoustic velocity is different from an acoustic velocity in another portion of the ground interconnection.