Composite Filter Layout With Shield Electrode for Stable Attenuation

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Solution Overview

Problem

Existing composite filter devices with acoustic wave resonators face variations in out-of-band attenuation due to fluctuations in the positional relationship between the longitudinally coupled resonator acoustic wave filter and the inductor, affecting the band pass filter's performance.

Innovation Solution

Incorporating a shield electrode not connected to any signal or reference potential, positioned between the inductor and the longitudinally coupled resonator acoustic wave filter, which overlaps the entirety of the inductor area, to reduce electromagnetic coupling variability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the inductor and longitudinally coupled resonator acoustic wave filter are positioned close to each other for impedance matching, then the band pass filter performance is improved, but the out-of-band attenuation varies due to positional variations

Engineering Contradiction:

Improveband pass filter performanceVSAvoidout-of-band attenuation

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

A shield electrode is introduced as an intermediary element between the inductor and the longitudinally coupled resonator acoustic wave filter. This shield electrode is connected to ground potential and positioned to overlap the inductor area in plan view, thereby mediating the electromagnetic interaction between the inductor and the acoustic wave filter. The shield electrode stabilizes the electromagnetic coupling, reducing variations in out-of-band attenuation while maintaining the beneficial close positioning for impedance matching.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of manufacture

If the position of the reception filter chip or transmission filter chip varies during mounting, then the manufacturing process becomes more flexible, but the electromagnetic coupling between the inductor and the acoustic wave filter varies

Engineering Contradiction:

Improvemounting flexibilityVSAvoidelectromagnetic coupling consistency

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The shield electrode serves as a buffer that decouples the electromagnetic interaction between the inductor and the acoustic wave filter. Even when the acoustic wave filter position varies during mounting, the shield electrode maintains a stable reference plane, thereby reducing the impact of positional variations on electromagnetic coupling consistency.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

By introducing the shield electrode connected to ground potential, the electromagnetic field distribution in the region between the inductor and the acoustic wave filter is modified. This parameter change in the electromagnetic environment reduces the sensitivity of the coupling to positional variations, thereby improving manufacturing precision without sacrificing mounting flexibility.

Inventive Principle:

Principle #35Parameter changes

3Area of stationary object

If the inductor area overlaps with the longitudinally coupled resonator acoustic wave filter in plan view, then the device area is reduced, but the out-of-band attenuation becomes sensitive to positional variations

Engineering Contradiction:

Improvedevice areaVSAvoidout-of-band attenuation stability

Core Design Contradiction:

Area of stationary objectVSReliability

Solution Approach 1:

The shield electrode is positioned between the inductor and the acoustic wave filter, overlapping the inductor area in plan view. This intermediary structure allows the inductor and acoustic wave filter to maintain their overlapping positions for area reduction, while the shield electrode stabilizes the electromagnetic coupling, preventing sensitivity to positional variations.

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 stabilizes the out-of-band attenuation of the band pass filter by minimizing the impact of positional variations between the inductor and the resonator, resulting in consistent frequency characteristics across a wide range.

Implementation Method 1

a shield electrode not connected to a signal potential and the reference potential and located between the inductor and the longitudinally coupled resonator acoustic wave filter

Methodology Applied

Scientific EffectElectromagnetic shielding: Faraday Cage

Implementation Method 2

a piezoelectric substrate, a first filter defining a band pass filter and including a longitudinally coupled resonator acoustic wave filter on the piezoelectric substrate

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS20240364308A1Composite filter device

Publication Date: 2024.10.31 MURATA MFG CO LTD

AI summary

A composite filter device includes a piezoelectric substrate, a first filter defining and functioning as a band pass filter and including a longitudinally coupled resonator acoustic wave filter located on the piezoelectric substrate, and a second filter including at least one resonator and an inductor connected to a reference potential. When an area inside an outer periphery of the inductor in a plan view is defined as an inductor area, at least a portion of the inductor area and the longitudinally coupled resonator acoustic wave filter overlap each other in the plan view. The composite filter device further includes a shield electrode located between the inductor and the longitudinally coupled resonator acoustic wave filter without being connected to a signal potential and the reference potential, and the shield electrode overlaps an entirety of the inductor area in the plan view.