RF Multiplexer Resonator Layout for Rayleigh Ripple Suppression

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Solution Overview

Problem

Existing multiplexers in communication devices face degradation of insertion loss due to Rayleigh wave ripples in acoustic wave resonators, particularly when multiple bandpass filters are connected in common, leading to interference and reduced performance across frequency bands.

Innovation Solution

A multiplexer design that includes a first filter with a series of series arm resonators and a parallel arm resonator on a path connecting a common terminal to a terminal, utilizing shear horizontal waves as the main mode, with the number of electrode finger pairs minimized on the series arm resonator closest to the common terminal to reduce ripple generation, and a second filter with a passband overlapping the ripple generation frequency to mitigate interference.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If multiple bandpass filters are connected in common to enable multiband compatibility, then the communication device can handle multiple frequency bands, but Rayleigh wave ripples from one filter's acoustic wave resonator degrade the insertion loss in another filter's passband

Engineering Contradiction:

Improvemultiband compatibilityVSAvoidinsertion loss degradation

Core Design Contradiction:

Adaptability or versatilityVSLoss of energy

Solution Approach 1:

The patent introduces a specific resonator configuration as an intermediary element between the common connection point and other filters. The parallel arm resonator with connection node closer to the terminal acts as a mediator that suppresses Rayleigh wave ripple propagation, preventing energy loss in adjacent passbands while maintaining multiband operation.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent applies local quality by making the series arm resonator connected closest to the common terminal have the fewest electrode finger pairs compared to other series arm resonators. This localized differentiation reduces Rayleigh wave generation at the critical position nearest to the common connection, thereby protecting other filters' passbands from ripple interference.

Inventive Principle:

Principle #3Local quality

2Loss of energy

If the number of electrode finger pairs in series arm resonators is increased to improve filter performance, then the insertion loss in the passband improves, but Rayleigh wave ripple generation increases and degrades other filters' passbands

Engineering Contradiction:

Improveinsertion loss in passbandVSAvoidRayleigh wave ripple generation

Core Design Contradiction:

Loss of energyVSObject-generated harmful factors

Solution Approach 1:

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent changes the parameter of electrode finger pairs non-uniformly across different series arm resonators. Specifically, the resonator closest to the common terminal has fewer pairs than others, creating a parameter gradient that suppresses Rayleigh wave propagation to adjacent filters while maintaining adequate insertion loss performance.

Inventive Principle:

Principle #35Parameter changes

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 reduces or prevents the degradation of insertion loss in the passband caused by Rayleigh wave ripples, improving signal reflection efficiency and maintaining high performance across multiple frequency bands.

Implementation Method 1

a plurality of series arm resonators and a first parallel arm resonator utilize a shear horizontal (SH) wave as a main mode

Methodology Applied

Scientific EffectShear horizontal wave:

Implementation Method 2

Rayleigh wave ripples are generated, for example, in the case where a bandpass filter that makes up a demultiplexer utilizes leaky waves as primary acoustic waves

Methodology Applied

Scientific EffectRayleigh wave: Surface Acoustic Wave

Data Source

PatentUS11811393B2Multiplexer, radio frequency front-end circuit, and communication device

Publication Date: 2023.11.07 MURATA MFG CO LTD

AI summary

A multiplexer includes a filter on a first path connecting a common terminal and an input/output terminal, and a second filter on a second path connecting the common terminal and a second terminal, the second filter having a passband that overlaps a generation frequency of Rayleigh wave ripples in the filter. The filter includes series arm resonators on the first path and a parallel arm resonator, the series arm resonators and the parallel arm resonator utilize an SH wave as a main mode, and a number of electrode finger pairs of the series arm resonator is fewest among numbers of electrode finger pairs of the series arm resonators.