Surface Acoustic Wave Filter Ground Layout for Sharp Attenuation

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Surface acoustic wave filters with shared ground lines suffer from degraded attenuation characteristics due to parasitic inductance, leading to reduced performance and increased size.

Innovation Solution

Independent ground lines are used to connect interdigital transducer electrodes and parallel arm resonators to the ground, reducing parasitic inductance and enhancing attenuation characteristics while minimizing the number of ground terminals, thus allowing for a smaller filter size with improved transmission characteristics.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of stationary object

If ground lines are shared between the longitudinally coupled filter unit and the parallel arm resonators to reduce wiring area, then the filter size is reduced, but parasitic inductance increases and attenuation characteristics are degraded

Engineering Contradiction:

Improvewiring areaVSAvoidattenuation characteristics

Core Design Contradiction:

Area of stationary objectVSReliability

Solution Approach 1:

The ground connection paths are segmented into separate independent lines: one ground line connects the parallel arm resonators to ground, and another ground line connects the longitudinally coupled filter unit to ground. This segmentation prevents the ground lines from sharing common impedance, thereby eliminating parasitic inductance effects while maintaining compact wiring area.

Inventive Principle:

Principle #1Segmentation

2Device complexity

If ground lines are shared between the longitudinally coupled filter unit and the parallel arm resonators, then the number of ground terminals is reduced, but parasitic inductance increases and attenuation characteristics are degraded

Engineering Contradiction:

Improvenumber of ground terminalsVSAvoidattenuation characteristics

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The ground connection paths are segmented into separate independent lines that converge at a common ground terminal. This allows multiple ground connections without requiring multiple ground terminals, maintaining simplicity while preventing parasitic inductance through independent current paths.

Inventive Principle:

Principle #1Segmentation

3Reliability

If independent ground lines are provided for the parallel arm resonators and longitudinally coupled filter unit, then parasitic inductance is reduced and attenuation characteristics are improved, but wiring area increases

Engineering Contradiction:

Improveattenuation characteristicsVSAvoidwiring area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The independent ground lines for the parallel arm resonators and longitudinally coupled filter unit are merged at a common ground terminal. This combining approach allows the ground lines to remain independent throughout most of their length (preventing parasitic inductance) while converging at the end to minimize the overall wiring area.

Inventive Principle:

Principle #5Merging (Combining)

4Reliability

Engineering Contradiction:

Improveattenuation characteristicsVSAvoidnumber of ground terminals

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

Multiple independent ground lines are merged and connected to a single common ground terminal. This approach maintains the benefits of independent ground paths (reduced parasitic inductance) while avoiding the need for multiple ground terminals, thus not increasing 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

The solution achieves sharp attenuation at the low-frequency side of the band and reduces the filter size while maintaining excellent transmission characteristics, thereby improving the overall performance of the surface acoustic wave filter.

Implementation Method 1

a surface acoustic wave filter includes a longitudinally coupled filter that is connected between an input terminal and an output terminal on a main surface of a piezoelectric substrate

Methodology Applied

Scientific EffectSurface acoustic wave: Surface Acoustic Wave

Implementation Method 2

on a main surface of a piezoelectric substrate and that includes at least one longitudinally coupled resonator

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS10868516B2Surface acoustic wave filter

Publication Date: 2020.12.15 MURATA MFG CO LTD

AI summary

A surface acoustic wave filter includes a longitudinally coupled filter connected between an input terminal and an output terminal on a main surface of a piezoelectric substrate and that includes longitudinally coupled resonators and a parallel arm resonator connected between a node between the input terminal and the longitudinally coupled filter and ground. A line connecting IDT electrodes at an input side of a portion of the longitudinally coupled resonators to the ground and a line connecting the parallel arm resonator to the ground are independently provided and are connected to the same ground terminal.