Ladder Variable RF Filter With Fixed Attenuation Pole Control

Solution Overview

Problem

Ladder-type frequency-variable filters struggle to achieve desired attenuation in specific frequency bands outside the pass band due to variations in sub-resonance frequency caused by variable impedance elements, leading to inadequate attenuation in harmonic regions.

Innovation Solution

Incorporating a series-arm resonator, a first and second parallel-arm resonator, and a variable impedance element connected in series with the first parallel-arm resonator, along with a fixed inductor connected in series with the second parallel-arm resonator, which maintains a sub-resonance point at a fixed frequency, ensuring attenuation poles are positioned at desired frequencies outside the pass band.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a variable impedance element is connected in series with a parallel-arm resonator to vary the pass band frequency, then the frequency of the pass band can be adjusted, but the sub-resonance frequency varies causing insufficient attenuation at specific frequency bands outside the pass band

Engineering Contradiction:

Improvefrequency adjustment capabilityVSAvoidattenuation performance

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The filter is divided into multiple parallel-arm resonators (first, second, third) with different configurations. The first parallel-arm resonator has a variable impedance element for frequency tuning, while the second and third parallel-arm resonators have fixed inductors to provide stable attenuation poles. This segmentation allows independent optimization of each resonator's function.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different parts of the filter have different characteristics: the first parallel-arm resonator is designed for frequency variability (with variable impedance element), while the second and third parallel-arm resonators are designed for frequency stability (with fixed inductors). Each component has locally optimized properties to fulfill its specific role in the overall filter performance.

Inventive Principle:

Principle #3Local quality

2Reliability

If multiple floating inductors are connected in series with parallel-arm resonators to achieve desired attenuation characteristics, then attenuation poles are generated, but the device complexity increases

Engineering Contradiction:

Improveattenuation characteristicsVSAvoidcircuit configuration

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The fixed inductors connected to the second and third parallel-arm resonators serve multiple functions: they generate attenuation poles for harmonic suppression and maintain stable sub-resonance frequencies. This multi-functional design reduces the need for additional separate attenuation components, thereby managing device complexity while achieving desired attenuation characteristics.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Adaptability or versatility

If the capacitance of a variable capacitor is varied to change the pass band frequency, then frequency tuning is achieved, but the attenuation pole frequency shifts causing inadequate attenuation in harmonic regions

Engineering Contradiction:

Improvefrequency tuning capabilityVSAvoidattenuation pole positioning

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The filter is divided into multiple parallel-arm resonators (first, second, third) with different configurations. The first parallel-arm resonator has a variable impedance element for frequency tuning, while the second and third parallel-arm resonators have fixed inductors to provide stable attenuation poles. This segmentation allows independent optimization of each resonator's function.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different parts of the filter have different characteristics: the first parallel-arm resonator is designed for frequency variability (with variable impedance element), while the second and third parallel-arm resonators are designed for frequency stability (with fixed inductors). Each component has locally optimized properties to fulfill its specific role in the overall filter performance.

Inventive Principle:

Principle #3Local quality

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 allows for consistent attenuation across multiple communication bands, even when the pass band shifts, by maintaining a fixed attenuation pole frequency, thereby ensuring sufficient attenuation at harmonic frequencies and reducing attenuation loss.

Implementation Method 1

Sub-resonance in the present disclosure represents LC series resonance of a capacitive capacitance of a resonator and an inductance of an inductor or LC series resonance of an inductive inductance of a resonator and a capacitance of a capacitor

Methodology Applied

Scientific EffectLC series resonance: Resonance

Data Source

PatentUS10886895B2Ladder-type frequency-variable filter, multiplexer, radio-frequency front end circuit, and communication terminal

Publication Date: 2021.01.05 MURATA MFG CO LTD

AI summary

Even when frequency characteristics are changed in association with multiple communication bands, an attenuation required for a specific frequency band outside a pass band is obtained. A frequency-variable filter (10) includes multiple series-arm resonators (111, 112, 113), multiple parallel-arm resonators (121, 122, 123), a variable capacitor (21), and an inductor (31) having a fixed inductance. The multiple series-arm resonators (111, 112, 113) and the multiple parallel-arm resonators (121, 122, 123) are connected in a ladder shape. The variable capacitor (21) is connected in series with the parallel-arm resonator (121). The fixed inductor (31) is connected in series with the parallel-arm resonator (123).