SAW Ladder Filter Resonator Layout for Lower Passband Insertion Loss

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Solution Overview

Problem

Conventional filter devices with multiple acoustic wave resonators face challenges in increasing the maximum combined Q value, leading to increased insertion loss on the low-frequency side within the passband.

Innovation Solution

A band-pass filter device with specific configurations of parallel arm resonators, including a first parallel arm resonator with a higher resonant frequency and narrower overlap width, and a second parallel arm resonator with a lower resonant frequency and wider overlap width, positioned within the passband, to enhance the combined Q value and reduce insertion loss.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If conventional SAW filter with ladder circuit is used, then the filter structure is simple, but the combined Q value cannot be sufficiently increased leading to increased insertion loss on low-frequency side

Engineering Contradiction:

Improveinsertion loss on low-frequency sideVSAvoidcombined Q value

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The patent changes the electrical parameters of the parallel arm resonators by configuring different numbers of electrode finger pairs and different overlap widths. Specifically, the first parallel arm resonator has more electrode finger pairs with narrower overlap width, while the second has fewer pairs with wider overlap width. This parameter differentiation optimizes the combined Q value across the frequency band, particularly improving performance on the low-frequency side where conventional filters suffer from high insertion loss.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If parallel resonators with same number of electrode fingers are used, then the manufacturing process is simplified, but the combined Q value is limited and insertion loss increases

Engineering Contradiction:

Improvecombined Q valueVSAvoidresonator configuration uniformity

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent applies local quality by making each parallel arm resonator have distinct characteristics tailored to its specific function in the frequency spectrum. The first parallel arm resonator is designed with more electrode finger pairs and narrower overlap width to target specific frequency ranges, while the second resonator has fewer pairs with wider overlap width for complementary coverage. This localized optimization of resonator properties achieves superior combined Q value without requiring complex manufacturing processes.

Inventive Principle:

Principle #3Local quality

3Reliability

If resonators with different resonant frequencies are used, then the frequency response is improved, but the device complexity increases

Engineering Contradiction:

Improvefrequency response characteristicsVSAvoidresonator configuration diversity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent segments the frequency response requirements by assigning different resonant frequencies to different parallel arm resonators. The first parallel arm resonator operates at a higher resonant frequency while the second operates at a lower resonant frequency, allowing each to be optimized for its specific frequency range. This segmentation approach improves overall frequency response characteristics while maintaining manageable device complexity through systematic frequency division.

Inventive Principle:

Principle #1Segmentation

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 proposed configuration effectively increases the combined Q value on the low-frequency side within the passband, reducing insertion loss and promoting miniaturization while maintaining high steepness and out-of-band attenuation.

Implementation Method 1

an input terminal and an output terminal, at least one ground terminal, and a plurality of parallel arm resonators

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

Japanese Unexamined Patent Application Publication No. 11-312951 discloses an example of a surface acoustic wave (SAW) filter

Methodology Applied

Scientific EffectSurface acoustic wave: Surface Acoustic Wave

Implementation Method 3

Anti-resonant frequencies of the first parallel arm resonator and the second parallel arm resonator are both positioned within the passband. A resonant frequency of the first parallel arm resonator is higher than a resonant frequency of the second parallel arm resonator.

Methodology Applied

Scientific EffectResonance: Resonance

Data Source

PatentUS12512820B2Filter device and multiplexer

Publication Date: 2025.12.30 MURATA MFG CO LTD

AI summary

A filter device includes a series arm connecting input and output terminals. Parallel arms branch from the series arm to a ground terminal. The parallel arms include first and second parallel arms branching from portions of the series arm. The first and second parallel arm resonators are respectively provided in or on the first and second parallel arms. The parallel arm resonators each include an IDT electrode including electrode fingers. Each IDT electrode includes an overlap region. A number of pairs of electrode fingers of the IDT electrode in the first parallel arm resonator is greater than a number of pairs of electrode fingers of the IDT electrode in the second parallel arm resonator. An overlap width of the IDT electrode in the first parallel arm resonator is narrower than the overlap width of the IDT electrode in the second parallel arm resonator.