Elastic Wave Filter Circuit With Even-IDT Impedance Matching

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing variable-frequency elastic wave filter devices face challenges in achieving sufficient attenuation in bands separated from the pass band while minimizing loss within the pass band, due to impedance mismatching issues between longitudinally coupled resonators and parallel arm resonance circuits.

Innovation Solution

The implementation of a variable-frequency elastic wave filter device with a longitudinally coupled resonator and a parallel arm resonator, where the parallel arm resonator is connected to the even-numbered IDT terminal of the longitudinally coupled resonator, and a variable frequency circuit is used to switch between ON and OFF, ensuring impedance matching and reducing loss by satisfying a conjugate relationship between the resonators' impedances.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If the parallel arm resonance circuit is connected to the odd-numbered IDT terminal of the longitudinally coupled resonator, then the structure is simplified, but sufficient impedance matching cannot be obtained and loss increases

Engineering Contradiction:

Improveconnection structureVSAvoidinsertion loss

Core Design Contradiction:

Device complexityVSLoss of energy

Solution Approach 1:

Instead of connecting the parallel arm resonance circuit to the odd-numbered IDT terminal as in conventional designs, this patent inverts the connection to the even-numbered IDT terminal. This inversion enables proper impedance matching between the longitudinally coupled resonator and the parallel arm resonance circuit, thereby reducing insertion loss while maintaining structural simplicity.

Inventive Principle:

Principle #13The other way round (Inversion)

2Object-affected harmful factors

If a longitudinally coupled resonator is added to achieve sufficient attenuation in separated bands, then attenuation performance improves, but impedance matching becomes difficult and loss increases

Engineering Contradiction:

Improveattenuation in separated bandsVSAvoidinsertion loss

Core Design Contradiction:

Object-affected harmful factorsVSLoss of energy

Solution Approach 1:

The patent applies the inversion principle by connecting the parallel arm resonance circuit to the even-numbered IDT terminal rather than the odd-numbered terminal. This inverted connection configuration enables both sufficient attenuation in bands separated from the pass band and proper impedance matching, thereby achieving low insertion loss without compromising attenuation performance.

Inventive Principle:

Principle #13The other way round (Inversion)

3Adaptability or versatility

If the impedance of the parallel arm resonator is made variable by changing frequency, then adaptability improves, but impedance matching with the longitudinally coupled resonator becomes more difficult

Engineering Contradiction:

Improvevariable frequency capabilityVSAvoidimpedance mismatching loss

Core Design Contradiction:

Adaptability or versatilityVSLoss of energy

Solution Approach 1:

The patent inverts the connection configuration to the even-numbered IDT terminal, which enables the parallel arm resonance circuit to properly match the variable impedance of the longitudinally coupled resonator across different frequencies. This inverted connection maintains conjugate impedance relationships even as frequency changes, thereby preserving both adaptability and low loss.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent utilizes parameter changes by designing the parallel arm resonance circuit with variable capacitance (through switches and capacitors) that adjusts according to frequency changes. This allows the circuit to maintain proper impedance matching with the longitudinally coupled resonator across a wide frequency range, reducing loss while maintaining adaptability.

Inventive Principle:

Principle #35Parameter changes

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 reduces loss within the pass band while achieving sufficient attenuation in separated bands, enhancing impedance matching and maintaining low insertion loss across varying frequencies.

Implementation Method 1

The plurality of IDT electrodes are disposed along a propagating direction of elastic waves

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

a first parallel arm resonator that is an elastic wave resonator connected between a node on the path and a ground and determines a pass band together with the longitudinally coupled resonator

Methodology Applied

Scientific EffectElastic wave resonance: Resonance

Data Source

PatentUS10601401B2Elastic wave filter device, radio-frequency front-end circuit, and communication apparatus

Publication Date: 2020.03.24 MURATA MFG CO LTD

AI summary

A filter includes a longitudinally coupled resonator device, a parallel arm resonator, and a variable frequency circuit. The parallel arm resonator is connected between a ground and a node provided on a path connecting input-output terminals. The variable frequency circuit is connected to the first parallel arm resonator. The longitudinally coupled resonator device includes three or more odd-number IDT electrodes, an odd-numbered IDT terminal, and an even-numbered IDT terminal. The even-numbered IDT terminal is a first signal terminal connected to at least one IDT electrode located at an even-numbered position from an edge of an arrangement order of the plural IDT electrodes. The odd-numbered IDT terminal is a second signal terminal connected to two or more IDT electrodes located at odd-numbered positions from the edge. The longitudinally coupled resonator device is disposed so that the even-numbered IDT terminal is connected to the node.