RF Multiplexer Attenuation Pole Design for Harmonic Suppression

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Solution Overview

Problem

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

Innovation Solution

A multiplexer configuration that includes a first filter with a parallel-arm resonator and a variable capacitor, and a second filter with a capacitive component, connected through a common point and a fixed inductor forming an LC series resonance circuit, which adds a desired attenuation pole to the frequency characteristics, ensuring adequate attenuation for harmonic frequencies.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a variable capacitor is connected in series with a parallel-arm resonator to vary the pass band frequency, then the frequency characteristics can be adjusted for multiple communication bands, but the sub-resonance frequency varies causing inadequate attenuation in harmonic regions

Engineering Contradiction:

Improvefrequency characteristics adjustmentVSAvoidattenuation characteristics

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The filter is divided into multiple independent resonators (first parallel-arm resonator, second parallel-arm resonator, series-arm resonators) that can be configured separately. Each resonator group can be independently adjusted or selected to achieve desired frequency characteristics while maintaining stable attenuation properties through the fixed inductor connections.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent uses variable capacitors to change the capacitance parameters for adjusting pass band frequency, while simultaneously employing fixed inductors to maintain stable sub-resonance frequencies. This parameter separation allows independent optimization of frequency tuning and attenuation characteristics.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If an inductor is connected in series with a parallel-arm resonator to achieve desired attenuation characteristics, then attenuation poles are formed, but the sub-resonance frequency varies when variable impedance elements are adjusted

Engineering Contradiction:

Improveattenuation characteristicsVSAvoidfrequency characteristics

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

Fixed inductors are introduced as intermediary elements between the variable capacitor-based resonators and the output. These fixed inductors serve as mediators that provide stable sub-resonance frequencies and consistent attenuation characteristics, while allowing the variable capacitors to freely adjust the pass band frequency without affecting attenuation stability.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Adaptability or versatility

If the capacitance of a variable capacitor is varied to adjust the pass band frequency, then multiple communication bands are supported, but the attenuation required for specific frequency bands outside the pass band cannot be obtained

Engineering Contradiction:

Improvecommunication band supportVSAvoidharmonic interference

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

Fixed inductors are pre-configured in series with parallel-arm resonators before the variable capacitor adjustment takes place. This preliminary configuration establishes stable sub-resonance frequencies that will consistently provide attenuation at harmonic regions regardless of how the variable capacitors later adjust the pass band frequency for different communication bands.

Inventive Principle:

Principle #10Preliminary 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

This configuration ensures consistent attenuation across multiple communication bands, including harmonics, by setting the attenuation pole frequency close to harmonic frequencies, thereby improving filter characteristics both within and outside the pass band.

Implementation Method 1

a circuit configuration in which an LC series resonance circuit including the capacitance of the second filter and the first inductor is connected to the first filter

Methodology Applied

Scientific EffectLC series resonance: Resonance

Implementation Method 2

an attenuation pole at a desired frequency is added to the frequency characteristics of the first filter

Methodology Applied

Scientific EffectAttenuation pole formation: Resonance

Data Source

PatentUS10700659B2Multiplexer, radio-frequency front end circuit, and communication terminal

Publication Date: 2020.06.30 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 multiplexer includes a transmission filter, a reception filter, and a common connection point. An antenna-side end of the transmission filter and an antenna-side end of the reception filter are connected to the common connection point. The transmission filter includes multiple resonators including a parallel-arm resonator and a variable capacitor that is connected in series with the parallel-arm resonator. An inductor for forming an attenuation pole is provided between the antenna-side end of the reception filter and the common connection point. By the inductor for forming an attenuation pole and the reception filter, which is capacitive, an attenuation pole at a frequency close to or equal to a specific frequency outside the pass band of a transmission signal is formed.