Acoustic Wave Filter IDT Apodization for Lower Insertion Loss
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Solution Overview
Problem
Existing surface and boundary acoustic wave filter devices face issues with transverse mode spurious responses and insertion loss, particularly when size reduction occurs, leading to increased spurious responses due to the trapping effect as a waveguide.
Innovation Solution
A longitudinally coupled resonator acoustic wave filter device is designed with narrow pitch electrode finger portions and apodization weights assigned to vary electrode finger overlap widths, maximizing overlap at ends adjacent to narrow pitch portions and minimizing in the middle, effectively reducing insertion loss and suppressing ripples within the pass band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the overlap width of each IDT is reduced to reduce the size, then the device size is reduced, but a transverse mode spurious response is likely to occur
Solution Approach 1:
The patent applies local quality by differentiating the electrode finger interval across different regions of the IDT. Specifically, narrow pitch electrode finger portions are positioned at ends adjacent to adjacent IDTs, while other portions have wider spacing. This localized variation in electrode geometry allows the device to maintain compact size while suppressing transverse mode spurious responses through strategic placement of narrow pitch regions where they most effectively confine the acoustic wave.
2Object-generated harmful factors
If apodization weights are assigned to reduce transverse mode spurious response, then the spurious response is reduced, but insertion loss increases
Solution Approach 1:
The patent employs parameter changes by systematically varying the electrode finger overlap width across different regions of the IDT according to apodization weight principles. By controlling the overlap width parameter - making it larger at ends adjacent to narrow pitch portions and smaller in middle portions - the invention optimizes both the suppression of transverse mode spurious responses and the minimization of insertion loss through careful parameter optimization.
3Volume of moving object
If narrow pitch electrode finger portions are introduced to reduce device size, then the device size is reduced, but a spurious response due to transverse mode tends to be relatively large in boundary acoustic wave devices
Solution Approach 1:
The patent resolves this contradiction by applying local quality through strategic placement of narrow pitch electrode finger portions only at specific locations - namely, at ends of IDTs that are adjacent to other IDTs. This localized application of narrow pitch regions provides effective transverse mode confinement where most needed, while wider spacing in other portions maintains lower insertion loss, thus achieving both size reduction and spurious response suppression.
Solution Approach 2:
The invention uses parameter changes by systematically varying the electrode finger interval parameter across different regions of the IDT. By introducing narrow pitch portions (smaller interval) at strategic locations and maintaining wider spacing elsewhere, the patent optimizes the balance between device size reduction and suppression of transverse mode spurious responses in boundary acoustic wave devices.
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 solution significantly reduces transverse mode spurious responses and insertion loss, improving the filter's performance by minimizing ripple and insertion loss within the pass band, making it suitable for both surface and boundary acoustic wave applications.
Implementation Method 1
an acoustic wave filter device includes a piezoelectric body
Implementation Method 2
a longitudinally coupled resonator acoustic wave filter device that utilizes a boundary acoustic wave or a surface acoustic wave
Implementation Method 3
various boundary acoustic wave filter devices that utilize a boundary acoustic wave have also been developed
Implementation Method 4
in a longitudinally coupled resonator surface acoustic wave filter device that utilizes an inter-IDT resonance mode
Data Source
AI summary
A longitudinally coupled resonator acoustic wave filter device that utilizes an inter-IDT resonance mode with a reduced insertion loss has a structure in which apodization weights are assigned in first to third IDTs having narrow pitch electrode finger portions in portions other than the narrow pitch electrode finger portions, such that the electrode finger overlap width sequentially varies in an acoustic wave propagating direction in which an acoustic wave propagates, and portions of the IDTs located at ends adjacent to the narrow pitch electrode finger portions have a maximum electrode finger overlap width.