Parallel Elastic Wave Filter Circuit for High-Band Edge Loss Reduction

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Conventional filters experience increased insertion loss at the high band edge of their passband due to capacitive impedance and bulk wave losses in elastic wave resonators, which deteriorate the Q characteristics and overall performance.

Innovation Solution

A filter device is designed with a parallel connection of a first and second filter, where the second filter's passband has a higher center frequency, and a capacitor is connected in parallel with an elastic wave resonator in the low band sided filter to reduce bulk wave loss and improve Q characteristics.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a parallel connection of two filters with different passbands is used to achieve a wider passband, then the passband coverage is improved, but the insertion loss at the high band edge deteriorates due to bulk wave loss in the elastic wave resonator

Engineering Contradiction:

Improvepassband coverageVSAvoidinsertion loss at high band edge

Core Design Contradiction:

Adaptability or versatilityVSLoss of energy

Solution Approach 1:

A capacitor is introduced as an intermediary component connected in parallel with the elastic wave resonator in the low band sided filter. This capacitor mediates the energy distribution by providing an alternative current path that reduces the bulk wave loss in the elastic wave resonator at high frequencies, thereby reducing insertion loss at the high band edge while preserving the wide passband coverage achieved through parallel filter connection

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention changes the electrical parameters of the low band sided filter by adding a capacitor in parallel with the elastic wave resonator. This parameter modification alters the impedance characteristics and Q-factor of the resonator circuit, reducing the bulk wave loss effect at high frequencies and improving insertion loss performance without compromising the overall passband structure

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If the second filter's passband is positioned at a higher center frequency to extend the high band coverage, then the frequency range is improved, but the Q characteristics of the elastic wave resonator deteriorate due to capacitive impedance

Engineering Contradiction:

Improvefrequency rangeVSAvoidQ characteristics

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The capacitor serves as an intermediary that compensates for the capacitive impedance effect in the elastic wave resonator at high frequencies. By providing a parallel resonant path, it maintains the Q characteristics of the overall circuit even when the elastic wave resonator alone would exhibit degraded performance due to bulk wave loss and capacitive effects

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The capacitor is预先 configured to counteract the capacitive impedance that arises in the elastic wave resonator at high frequencies. This preliminary anti-action prevents the Q characteristics from deteriorating by establishing a compensating reactive element before the frequency range extension fully manifests its adverse effects

Inventive Principle:

Principle #9Preliminary anti-action

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 effectively reduces insertion loss at the high band edge of the passband by mitigating capacitive impedance and bulk wave losses, enhancing the filter's performance and maintaining a desired passband.

Implementation Method 1

this elastic wave resonator has a capacitive impedance at frequencies within the passband of the second filter, and so this elastic wave resonator functions as a capacitor

Methodology Applied

Scientific EffectCapacitive impedance: Capacitance

Implementation Method 2

at a frequency band higher than the antiresonance frequency of the elastic wave resonator, however, a loss (bulk wave loss) occurs due to a bulk wave generated in the piezoelectric substrate of the elastic wave resonator

Methodology Applied

Scientific EffectBulk wave loss: Damping

Implementation Method 3

a loss (bulk wave loss) occurs due to a bulk wave generated in the piezoelectric substrate of the elastic wave resonator

Methodology Applied

Scientific EffectBulk wave: Ultrasonic Vibration

Implementation Method 4

bulk wave generated in the piezoelectric substrate of the elastic wave resonator

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS11728787B2Filter device, radio-frequency front-end circuit, and communication apparatus

Publication Date: 2023.08.15 MURATA MFG CO LTD

AI summary

A filter device includes a first filter and a second filter. The first filter and the second filter are disposed in parallel between a first terminal and a second terminal. A first passband of the filter device includes at least part of a second passband of the first filter. The first passband includes at least part of a third passband of the second filter. The second passband is narrower than the first passband. The third passband is narrower than the first passband. The third passband has a center frequency higher than a center frequency of the second passband. The first filter includes multiple elastic wave resonators and a first capacitive element. The first capacitive element is connected in parallel with the first elastic wave resonator.