Longitudinally Coupled Resonator Filter Layout for High-Side Attenuation

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Solution Overview

Problem

Conventional longitudinally coupled resonator acoustic wave filters require bridge capacitances that increase the chip surface area, leading to an increase in filter size, which is undesirable.

Innovation Solution

The filter design includes a configuration where hot-side comb-shaped electrodes of IDT electrodes are connected to reflectors, allowing for improved attenuation characteristics on the high frequency side of the pass band without increasing the filter size by utilizing internal capacitance within the filter structure.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If bridge capacitance is connected in parallel with the longitudinally coupled resonator acoustic wave filter, then attenuation characteristics on the high frequency side of the pass band are improved, but the chip surface area and filter size are increased

Engineering Contradiction:

Improveattenuation characteristicsVSAvoidchip surface area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent merges the bridge capacitance function with the existing IDT electrode structure by electrically connecting the hot-side comb-shaped electrode of the first IDT electrode to the reflector. This integration eliminates the need for separate bridge capacitance components while achieving the same attenuation effect, thereby resolving the contradiction between improved attenuation characteristics and reduced chip surface area.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The IDT electrode structure is given multiple functions: it serves both as the primary transducer for acoustic wave generation and as the bridge capacitance element for improving attenuation characteristics. The hot-side comb-shaped electrode connected to the reflector provides both the transduction function and the capacitance function, allowing one component to fulfill multiple roles and avoid additional area consumption.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Reliability

If bridge capacitance is provided to improve attenuation characteristics, then the filter performance is enhanced, but the device size is increased

Engineering Contradiction:

Improvefilter performanceVSAvoidfilter size

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent combines the bridge capacitance functionality into the existing IDT electrode structure. By connecting the hot-side comb-shaped electrode of the first IDT electrode to the reflector, the same structural element serves dual purposes: maintaining acoustic wave transduction and providing the necessary capacitance for improved attenuation characteristics, thus avoiding additional device complexity and size increase.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The IDT electrode structure serves itself by utilizing its own hot-side comb-shaped electrode as the bridge capacitance element. The electrode connected to the reflector provides the capacitance function internally without requiring external or additional components, allowing the filter to improve its own performance while maintaining compact dimensions.

Inventive Principle:

Principle #25Self-service

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 enhances attenuation on the high frequency side of the pass band without enlarging the filter size, achieving improved performance without the need for additional bridge capacitances.

Implementation Method 1

IDT (Interdigital Transducer) electrodes that include a first IDT electrode and a second IDT electrode

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

first reflector and a second reflector that are provided on respective sides of the plurality of IDT electrodes in an acoustic wave propagating direction

Methodology Applied

Scientific EffectAcoustic wave reflection: Reflection

Implementation Method 3

The hot-side comb-shaped electrode of the first IDT electrode is electrically connected to at least one of the first reflector and the second reflector

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS12574014B2Longitudinally coupled resonator acoustic wave filter and acoustic wave filter

Publication Date: 2026.03.10 MURATA MFG CO LTD

AI summary

A longitudinally coupled resonator acoustic wave filter including IDT electrodes including a first IDT electrode and a second IDT electrode, and first and second reflectors, in which the IDT electrodes have respective hot-side comb-shaped electrodes and respective ground-side comb-shaped electrodes, the hot-side comb-shaped electrodes of the first IDT electrodes are electrically connected to at least one of the first and second reflectors, the second IDT electrodes are between the IDT electrode and the first reflector and between the IDT electrode and the second reflector respectively, the hot-side comb-shaped electrodes of the IDT electrodes are connected to one of an input end and an output end, and the hot-side comb-shaped electrodes of the IDT electrodes are connected to the other of the input end and the output end.