Acoustic Wave Filter Circuit With Equal Inductors for Lower-Band Attenuation

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Solution Overview

Problem

Existing acoustic wave filter devices face challenges in increasing the attenuation amount of the attenuation band when the frequency of the pass band and the frequency of the attenuation band are shifted to lower frequencies, particularly due to differences in inductance values of paths connecting parallel arm resonators and switches.

Innovation Solution

The acoustic wave filter device incorporates a configuration with equal inductance values for the first and second inductors, and additional parallel arm resonance circuits, allowing for tunable filter characteristics by switching the impedance elements, thereby increasing the attenuation amount and maintaining steepness of the attenuation slope.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If the inductance values of paths connecting parallel arm resonators and switches are made different, then the device complexity is reduced, but the attenuation amount of the attenuation band decreases when switching to lower frequencies

Engineering Contradiction:

Improveinductance value configurationVSAvoidattenuation amount

Core Design Contradiction:

Device complexityVSLoss of energy

Solution Approach 1:

The patent applies homogeneity by setting the inductance values of the first and second inductors to be substantially equal. This uniform inductance configuration ensures that when switches are toggled to shift the pass band and attenuation band frequencies to lower frequencies, the attenuation amount is maintained at a high level. The equal inductance values create symmetric electrical characteristics that preserve the filter's attenuation performance during frequency switching operations.

Inventive Principle:

Principle #33Homogeneity

2Adaptability or versatility

If the frequency of the pass band and the frequency of the attenuation band are shifted to lower frequencies by switching, then the adaptability is improved, but the attenuation amount decreases due to inductance differences

Engineering Contradiction:

Improvefrequency tuning capabilityVSAvoidattenuation amount

Core Design Contradiction:

Adaptability or versatilityVSLoss of energy

Solution Approach 1:

The patent maintains homogeneous inductance values across parallel arm paths to ensure that frequency switching operations preserve attenuation characteristics. By making the inductance values substantially equal, the filter achieves consistent electrical behavior during frequency reconfiguration, allowing adaptable frequency tuning without sacrificing attenuation performance.

Inventive Principle:

Principle #33Homogeneity

Solution Approach 2:

The patent implements dynamic frequency tuning capability through switches that can change the electrical characteristics of the parallel arm resonance circuits. The switches enable the filter to dynamically shift both the pass band and attenuation band frequencies to lower frequencies while the equal inductance values ensure that this dynamic reconfiguration maintains the required attenuation amount.

Inventive Principle:

Principle #15Dynamics

3Loss of energy

If additional parallel arm resonance circuits are added to increase attenuation, then the filter performance is improved, but the device complexity increases

Engineering Contradiction:

Improveattenuation amountVSAvoidcircuit configuration

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The patent achieves improved attenuation performance by adding parallel arm resonance circuits with substantially equal inductance values. This homogeneous configuration allows the additional circuits to work synergistically, enhancing the attenuation amount through constructive interference of the electrical characteristics while maintaining a relatively compact and manageable circuit structure.

Inventive Principle:

Principle #33Homogeneity

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 increases the attenuation amount of the attenuation band when switching frequencies, while suppressing insertion loss and maintaining filter characteristics, enabling flexible frequency tuning.

Implementation Method 1

an acoustic wave filter device includes a series arm resonance circuit and parallel arm resonance circuits

Methodology Applied

Scientific EffectAcoustic wave resonance: Resonance

Implementation Method 2

acoustic wave filter devices that employ acoustic waves are widely used in band pass filters

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS10944381B2Acoustic wave filter device, multiplexer, radio-frequency front end circuit, and communication device

Publication Date: 2021.03.09 MURATA MFG CO LTD

AI summary

A filter includes a series arm resonator, a first parallel arm resonance circuit and a second parallel arm resonance circuit. The each of the first parallel arm resonance circuit and the second parallel arm resonance circuit includes: a parallel arm resonator that is connected to a node; a pair of elements consisting of a capacitor and a switch, which are connected in parallel with each other, that is connected in series with the parallel arm resonator; and an inductor that is provided on a path that connects the node and ground to each other via the switch. The inductance value of the inductor of the first parallel arm resonance circuit and the inductance value of the inductor of the second parallel arm resonance circuit are substantially equal to each other.