Passive-Element N-Path Filter for Low-Loss RF Bandpass

Solution Overview

Problem

Existing N-path filters experience increased loss within the passband and insufficient attenuation outside the passband, particularly in high frequency areas above 500 MHz, due to the non-linear characteristics of active elements used in the base filters.

Innovation Solution

The N-path filter design incorporates N-number signal paths with first and second modulators and band pass filters made of only passive elements, allowing for low loss within the passband and high attenuation outside the passband in high frequency areas.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If active elements such as operational amplifiers are used in base filters, then the N-path filter can be implemented with conventional circuit components, but loss increases within the passband and attenuation becomes insufficient outside the passband in high frequency areas of 500 MHz or more

Engineering Contradiction:

Improveease of manufactureVSAvoidloss within passband

Core Design Contradiction:

Ease of manufactureVSLoss of energy

Solution Approach 1:

The patent changes the fundamental parameter of the base filter from active to passive elements. This parameter change eliminates the non-linear characteristics and associated losses of active elements while maintaining the filter's functionality through the N-path modulation architecture.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent substitutes active electronic components (operational amplifiers) with passive components (inductors, capacitors, resistors). This substitution replaces the active amplification mechanism with a passive filtering mechanism that operates through the modulation and demodulation processes in the N-path structure.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Ease of manufacture

If active elements such as operational amplifiers are used in base filters, then the N-path filter can be constructed with standard components, but attenuation outside the passband becomes insufficient in high frequency areas of 500 MHz or more

Engineering Contradiction:

Improveease of manufactureVSAvoidinsufficient attenuation outside passband

Core Design Contradiction:

Ease of manufactureVSObject-generated harmful factors

Solution Approach 1:

The patent changes the fundamental parameter of the base filter from active to passive elements. This parameter change eliminates the non-linear characteristics and associated losses of active elements while maintaining the filter's functionality through the N-path modulation architecture.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent substitutes active electronic components (operational amplifiers) with passive components (inductors, capacitors, resistors). This substitution replaces the active amplification mechanism with a passive filtering mechanism that operates through the modulation and demodulation processes in the N-path structure.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 results in N-path filters with reduced loss within the passband and enhanced attenuation outside the passband, effectively addressing the limitations of existing filters in high frequency applications.

Implementation Method 1

The first modulator and the second modulator are operable to modulate the input signal in a phase of one period including different phases of the different N-number signal paths

Methodology Applied

Scientific EffectPhase modulation: Phase Modulation

Implementation Method 2

the base filter is a band pass filter including only passive elements

Methodology Applied

Scientific EffectResonance: Resonance

Implementation Method 3

Each of the base filters includes a capacitor and an inductor

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentUS20250080075A1N-path filter

Publication Date: 2025.03.06 MURATA MFG CO LTD

AI summary

An N-path filter includes N-number signal paths connected in parallel to each other between first and second input-output terminals. Each N-number signal path includes a first switch connected to the first input-output terminal to modulate an input signal, a second switch connected to the second input-output terminal to modulate the input signal in a same phase as that of the switch, and a base filter connected between the first and second switches. The first and second switches are operable to modulate the input signal in a phase of one period including different phases of the different signal paths. The base filter is a band pass filter including only passive elements.