Acoustic Wave Filter Shielded Serial Arm Layout

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Solution Overview

Problem

Existing acoustic wave filters, particularly ladder-type filters, face challenges in achieving improved attenuation characteristics outside the passing band due to electromagnetic coupling between serial resonators, and there is a need for enhanced design to reduce unwanted signal components.

Innovation Solution

The acoustic wave filter incorporates a piezoelectric substrate with a filter body featuring a serial arm connected in a ladder shape, including serial and parallel resonators, where the serial arm is folded back and a shield conductor is positioned between the resonators to reduce electromagnetic coupling, and capacitor elements are used to adjust the layout for improved attenuation characteristics.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a ladder-type acoustic wave filter is used, then the filter structure is simple and compact, but electromagnetic coupling between serial resonators degrades attenuation characteristics outside the passing band

Engineering Contradiction:

Improvefilter structureVSAvoidattenuation characteristic

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

A shield conductor is introduced as an intermediary element between adjacent serial resonators in the ladder-type filter. This shield conductor, connected to ground potential, acts as an electromagnetic barrier that blocks coupling between resonators, thereby improving attenuation characteristics without fundamentally changing the ladder-type filter structure

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The filter structure is segmented into distinct sections with shield conductors placed between serial resonators. This segmentation divides the continuous ladder structure into isolated segments, preventing electromagnetic interference between adjacent segments while maintaining the overall compact filter design

Inventive Principle:

Principle #1Segmentation

2Area of stationary object

If the serial arm is folded back to improve layout, then the area is reduced, but electromagnetic coupling between resonators increases

Engineering Contradiction:

Improvefilter areaVSAvoidelectromagnetic coupling

Core Design Contradiction:

Area of stationary objectVSObject-affected harmful factors

Solution Approach 1:

When the serial arm is folded back to reduce area, shield conductors are strategically placed at the fold and between adjacent resonators. These shield conductors mediate the electromagnetic field interactions, allowing close spacing for area reduction while preventing harmful coupling through the grounded barriers

Inventive Principle:

Principle #24Intermediary (Mediator)

3Object-affected harmful factors

If shield conductors are added between resonators, then electromagnetic coupling is reduced, but device complexity and area increase

Engineering Contradiction:

Improveelectromagnetic couplingVSAvoidfilter structure

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The shield conductors are merged with the existing ground structure and interconnected to form a continuous electromagnetic shield. This integration approach reduces the number of discrete shield elements needed while achieving effective coupling reduction, thereby minimizing the increase in device complexity

Inventive Principle:

Principle #5Merging (Combining)

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 the attenuation characteristic outside the passing band by reducing electromagnetic coupling and allowing for improved layout adjustments without increasing the filter's area, effectively suppressing unwanted signal components.

Implementation Method 1

an acoustic wave filter configured by connecting a plurality of acoustic wave resonators in a ladder shape... a piezoelectric substrate, a filter body on the piezoelectric substrate

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

a shield conductor connected to a reference potential part... a portion which is located between at least one of the serial resonators included in the first divided arm and at least one of the serial resonators included in the second divided arm

Methodology Applied

Scientific EffectElectromagnetic shielding: Faraday Cage

Data Source

PatentUS10951194B2Acoustic wave filter, multiplexer, and communication apparatus

Publication Date: 2021.03.16 KYOCERA CORP

AI summary

A filter body includes a serial arm and one or more parallel resonators in a state where they are connected in a ladder shape. The serial arm includes a plurality of serial resonators connected in series to each other. A difference of resonance frequencies among the plurality of serial resonators is smaller than a half of a difference between the resonance frequency and an antiresonance frequency of each serial resonator. The serial arm includes a first divided arm which extends from one side toward the other side in a predetermined direction on the piezoelectric substrate, and a second divided arm which is folded back from the other side of the first divided arm and extends toward the one side. The shield conductor includes a portion which is located between at least one of the serial resonators included in the first divided arm and at least one of the serial resonators included in the second divided arm.