Bandpass Filter Topology for Steeper Out-of-Band Attenuation

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing band pass filters do not achieve sufficient attenuation outside the pass band, leading to inadequate isolation when used in multiplexers.

Innovation Solution

A band pass filter design that includes a ladder filter connected in series with a longitudinally coupled resonator filter, featuring separate ground terminals and an inductor between specific nodes, which shifts the attenuation pole to a low frequency side, enhancing attenuation outside the pass band and reducing apparatus size.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If the first ground terminal is separated from the second ground terminal, then the attenuation characteristics at the low pass end of the pass band are steepened, but the apparatus size increases

Engineering Contradiction:

Improveattenuation characteristicsVSAvoidapparatus size

Core Design Contradiction:

Manufacturing precisionVSVolume of moving object

Solution Approach 1:

The second ground terminal and third ground terminal are integrated into a single common ground terminal, reducing the number of separate ground connections while maintaining the necessary electrical isolation and ground stability for achieving steep attenuation characteristics

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

An inductor is introduced as an intermediary element to electrically connect the ladder filter and longitudinally coupled resonator filter while providing the necessary ground reference, enabling compact design without compromising attenuation performance

Inventive Principle:

Principle #24Intermediary (Mediator)

2Stability of the object's composition

If the second ground terminal is integrated with the third ground terminal, then the ground potential of the longitudinally coupled resonator filter is stabilized, but the isolation outside the pass band is insufficient

Engineering Contradiction:

Improveground potential stabilityVSAvoidisolation

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The inductor value is optimized to shift the attenuation pole to a lower frequency, thereby improving isolation in the frequency bands of interest while maintaining ground potential stability

Inventive Principle:

Principle #35Parameter changes

3Reliability

If an inductor is added between the parallel arm resonator and longitudinally coupled resonator filter, then the attenuation pole is shifted to low frequency side improving attenuation outside pass band, but the device complexity increases

Engineering Contradiction:

Improveattenuation outside pass bandVSAvoidfilter structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The inductor serves multiple functions simultaneously: it acts as an electrical connector between filter stages, provides ground reference, and shifts the attenuation pole frequency, thereby improving isolation without requiring additional dedicated components for each function

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 design achieves significant improvement in attenuation outside the pass band and provides excellent inter-band isolation when combined with another filter, reducing the size of the apparatus and stabilizing ground potential.

Implementation Method 1

an inductor that is electrically connected between the first node on the first signal path and the second ground terminal or between the second node on the second signal path and the third ground terminal

Methodology Applied

Scientific EffectInductance: Inductor

Implementation Method 2

separating the first ground terminal from the second ground terminal reduces the influence of parasitic inductance

Methodology Applied

Scientific EffectParasitic inductance: Parasitic Capacitance

Implementation Method 3

integrating the second ground terminal with the third ground terminal stabilizes ground potential of the longitudinally coupled resonator filter

Methodology Applied

Scientific EffectGround potential stabilization: Earthing

Data Source

PatentUS11405018B2Filter and multiplexer

Publication Date: 2022.08.02 MURATA MFG CO LTD

AI summary

A filter includes a ladder filter including a first parallel arm resonator and a second parallel arm resonator, a longitudinally coupled resonator filter electrically connected in series to the ladder filter, a first ground terminal electrically connected to the first parallel arm resonator, a second ground terminal electrically connected to the second parallel arm resonator, a third ground terminal electrically connected to the longitudinally coupled resonator filter, a third signal path electrically connected to a first node on a first signal path electrically connecting the second parallel arm resonator to the second ground terminal and a second node on a second signal path electrically connecting the longitudinally coupled resonator filter to the third ground terminal, and an inductor electrically connected between the first node on the first signal path and the second ground terminal or between the second node on the second signal path and the third ground terminal.