RF Multiplexer Inductor Layout for Spurious Wave Isolation

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Solution Overview

Problem

In multiplexers with multiple elastic wave filters connected to a common terminal, spurious waves generated by one filter can degrade the bandpass characteristics of another filter, leading to increased insertion loss and poor reflection characteristics.

Innovation Solution

Incorporating an inductance element in series between the first elastic wave filter and the common terminal, with the parallel arm resonator closest to the common terminal having the largest capacitance, to reduce the impact of spurious waves on the second elastic wave filter, while maintaining low loss in the first filter.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If multiple elastic wave filters are connected to a common terminal, then multiband communication capability is achieved, but spurious waves from one filter degrade the bandpass characteristics of another filter

Engineering Contradiction:

Improvemultiband communication capabilityVSAvoidbandpass characteristics

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

An inductance element is introduced as an intermediary component between the first elastic wave filter and the common terminal. This inductance element acts as a mediator that blocks spurious waves from propagating to the common terminal while allowing the desired signal to pass through, thereby preventing degradation of the second filter's bandpass characteristics without compromising multiband communication capability

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The harmful spurious waves are extracted or removed from the signal path by the inductance element, which selectively blocks these unwanted frequency components generated by the first filter before they can reach the common terminal and interfere with the second filter's operation

Inventive Principle:

Principle #2Taking out (Extraction)

2Reliability

If spurious waves are blocked to protect another filter, then bandpass characteristics are maintained, but insertion loss increases

Engineering Contradiction:

Improvebandpass characteristicsVSAvoidinsertion loss

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The inductance element is strategically placed only at the connection point of the first filter to the common terminal, providing localized suppression of spurious waves. This targeted approach ensures that only the harmful frequency components are blocked while the desired signal frequencies pass through with minimal attenuation, thus maintaining low insertion loss in the passband

Inventive Principle:

Principle #3Local quality

3Reliability

If the inductance element is connected in series between the first filter and common terminal, then spurious wave impact is reduced, but device complexity increases

Engineering Contradiction:

Improvebandpass characteristicsVSAvoidcircuit structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

A single inductance element serves as a simple intermediary component that provides effective spurious wave suppression. This minimalistic approach achieves the desired protection function with just one additional component, avoiding the need for complex filter structures or multiple additional elements, thus limiting the increase in device complexity

Inventive Principle:

Principle #24Intermediary (Mediator)

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 prevents the degradation of bandpass characteristics in the second elastic wave filter due to spurious waves from the first filter, while ensuring low insertion loss and improved impedance matching across the multiplexer.

Implementation Method 1

an inductance element. The first elastic wave filter includes two input-output terminals, one or more series arm resonators disposed in a path between the two input-output terminals

Methodology Applied

Scientific EffectInductance: Inductor

Implementation Method 2

The one parallel arm resonator has a largest capacitance, among the two or more parallel arm resonators

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 3

Elastic wave filters having low loss in their pass bands are used as multiple band pass filters defining the multiplexer

Methodology Applied

Scientific EffectSurface acoustic wave: Surface Acoustic Wave

Implementation Method 4

one or more series arm resonators disposed in a path between the two input-output terminals, and two or more parallel arm resonators disposed between the path and ground

Methodology Applied

Scientific EffectResonance: Resonance

Data Source

PatentUS10305449B2Multiplexer, high-frequency front end circuit, and communication apparatus

Publication Date: 2019.05.28 MURATA MFG CO LTD

AI summary

A multiplexer includes a common terminal, a Band66 transmission-side filter, a Band30 transmission-side filter, and an inductance element. The Band66 transmission-side filter includes series arm resonators and parallel arm resonators. The frequency of spurious waves generated by the Band66 transmission-side filter is included in a pass band of the Band30 transmission-side filter. A transmission output terminal is connected to a common terminal with the inductance element interposed therebetween and is directly connected to one parallel arm resonator. The one parallel arm resonator has a largest capacitance, among the parallel arm resonators.