Acoustic Wave Filter Topology for Frequency Shift and Passband Width

Solution Overview

Problem

Frequency-variable acoustic wave filters with series-arm circuits face issues due to increased off capacitance when a switch element is non-conductive, leading to reduced frequency shift and pass band width, limiting the ability to effectively switch between frequency bands.

Innovation Solution

An acoustic wave filter device incorporating a series-arm circuit and a parallel-arm resonant circuit with a frequency-variable circuit, utilizing a second acoustic wave resonator with higher resonant and anti-resonant frequencies, and a switch element to vary filter characteristics, ensuring sufficient frequency shift and pass band width by switching between conduction and non-conduction states.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a series-arm circuit with a switch element is used to vary frequency, then the filter can switch between frequency bands, but as off capacitance increases, the frequency shift amount decreases and pass band width decreases

Engineering Contradiction:

Improvefrequency band switching capabilityVSAvoidfrequency shift amount

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The patent applies dynamics by making the resonant frequency and anti-resonant frequency of the parallel-arm resonant circuit variable through a frequency variable circuit. This circuit includes a second acoustic wave resonator and a switch element that, when switched between conduction and non-conduction states, dynamically adjust the resonant and anti-resonant frequencies. This dynamic adjustment ensures that the frequency shift amount remains sufficient while maintaining the pass band width, resolving the contradiction between frequency band switching capability and frequency shift precision.

Inventive Principle:

Principle #15Dynamics

2Adaptability or versatility

If a series-arm circuit with a switch element is used to vary frequency, then the filter can switch between frequency bands, but the pass band width at non-conduction state decreases

Engineering Contradiction:

Improvefrequency band switching capabilityVSAvoidpass band width

Core Design Contradiction:

Adaptability or versatilityVSLength of moving object

Solution Approach 1:

The patent applies dynamics by making the resonant frequency and anti-resonant frequency of the parallel-arm resonant circuit variable through a frequency variable circuit. This circuit includes a second acoustic wave resonator and a switch element that, when switched between conduction and non-conduction states, dynamically adjust the resonant and anti-resonant frequencies. This dynamic adjustment ensures that the frequency shift amount remains sufficient while maintaining the pass band width, resolving the contradiction between frequency band switching capability and frequency shift precision.

Inventive Principle:

Principle #15Dynamics

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 enables effective switching between two frequency bands with increased frequency shift and pass band width, reducing insertion loss and allowing for compact, low-profile filter designs with high steepness transmission characteristics.

Implementation Method 1

acoustic wave filters using acoustic waves have been widely used as band pass filters arranged in a front end unit of mobile communication equipment

Methodology Applied

Scientific EffectAcoustic wave: Acoustics

Implementation Method 2

Switching between the first filter characteristics and the second filter characteristics is performed by switching between conduction and non-conduction of the switch element

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Data Source

PatentUS11031921B2Acoustic wave filter device, duplexer, radio frequency front end circuit and communication apparatus

Publication Date: 2021.06.08 MURATA MFG CO LTD

AI summary

The acoustic wave filter (10A) includes a parallel-arm resonant circuit (12p). The parallel-arm resonant circuit (12p) includes a parallel-arm resonator (p1) and a frequency variable circuit (72p) that are connected in parallel. The frequency variable circuit (72p) includes a parallel-arm resonator (p2) that has a resonant frequency higher than that of the parallel-arm resonator (p1) and a switch (SW1) element. A frequency difference between a resonant frequency on a higher frequency side of the parallel-arm resonant circuit (12p) in a case where the switch (SW1) is OFF and a resonant frequency on a higher frequency side of the parallel-arm resonant circuit (12p) in a case where the switch (SW1) is ON is equal to or more than a frequency difference between a low frequency end frequency of the second attenuation band and a low frequency end frequency of the first attenuation band.