Elastic Wave Filter Layout for Suppressing Transverse Mode Ripples
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Solution Overview
Problem
Existing elastic wave filter devices struggle to reliably suppress transverse mode ripples, as simply varying the width of acoustic velocity areas between serial and parallel arm resonators is insufficient.
Innovation Solution
The elastic wave filter device configures serial and parallel arm resonators with differing widths of low acoustic velocity areas, where the width of the low acoustic velocity area in at least one resonator is smaller than in others, effectively suppressing transverse mode ripples by utilizing a piston mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the width of low acoustic velocity areas is set to be different between serial and parallel arm resonators, then transverse mode ripples are suppressed, but the device complexity increases due to multiple different width specifications
Solution Approach 1:
The patent applies local quality by creating different width specifications for low acoustic velocity areas in specific positions within the resonator structure. The first and second low acoustic velocity areas have a first width, while the third and fourth low acoustic velocity areas have a second width that is different from the first width. This localized differentiation suppresses transverse mode ripples by creating asymmetric acoustic velocity distributions in specific regions of the serial and parallel arm resonators, thereby improving filter characteristics without requiring complete redesign of the entire device.
2Volume of moving object
If the intersecting width of parallel arm resonator is made larger to suppress spurious response, then miniaturization is realized, but transverse mode harmonics increase
Solution Approach 1:
The patent applies parameter changes by systematically varying the widths of low acoustic velocity areas across different resonator arms. Specifically, the first and second low acoustic velocity areas have a first width, while the third and fourth low acoustic velocity areas have a second width different from the first. This parameter differentiation allows the device to achieve miniaturization through optimized intersecting widths while simultaneously suppressing transverse mode harmonics by creating controlled acoustic velocity variations that disrupt the formation of spurious responses.
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 effectively suppresses transverse mode ripples within the pass band, improving the filter's performance by reducing ripples generated near the resonant and anti-resonant frequencies.
Implementation Method 1
a variety of filter devices including serial and parallel arm resonators configured of surface acoustic wave resonators have been proposed
Implementation Method 2
an acoustic velocity in an electrode finger leading end-side portion is lower than an acoustic velocity in an electrode finger intersecting portion
Implementation Method 3
a piston mode is formed by using the above structure so that ripples due to transverse modes can be suppressed
Data Source
Figure 1(a)~1(b)
Figure 2
Figure 3(a)~3(b)
AI summary
Provided is an elastic wave filter device in which transverse mode ripples can be effectively suppressed. An elastic wave filer device (1) includes serial and parallel arms and also includes a plurality of elastic wave resonators. Each elastic wave resonator includes an IDT electrode. In the case where a direction in which electrode fingers (23 and 24) extend is taken as a width direction of the IDT electrode, the IDT electrode is so configured as to have a central area at a center in the width direction, a low acoustic velocity area at an outer side portion of the central area, and a high velocity area at a further outer side portion thereof. A width (W1A) of the low acoustic velocity area of at least one elastic wave resonator differs from a width (W1B) of the low acoustic velocity area of the other elastic wave resonators.