Differential Transmission Line Common Mode Notch Filter

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Solution Overview

Problem

Differential signaling is susceptible to common mode noise due to high frequency alternating current components, leading to electromagnetic radiation and noise even when employing differential signals.

Innovation Solution

A differential transmission line with a common mode notch filter, comprising adjacently arranged repeating sections where the length of each section is half of the electric wavelength of the common mode electromagnetic wave to be suppressed, with varying conductor width and spacing patterns to maintain identical differential mode impedance while periodically changing common mode impedance, effectively suppressing common mode noise.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If differential signaling is used to improve noise resistance, then electromagnetic noise resistance is improved, but common mode noise susceptibility increases due to high frequency alternating current components

Engineering Contradiction:

Improveelectromagnetic noise resistanceVSAvoidcommon mode noise

Core Design Contradiction:

Object-affected harmful factorsVSObject-generated harmful factors

Solution Approach 1:

The transmission line is divided into multiple repeating sections, each with specific length equal to half the wavelength of the target common mode frequency. This segmentation creates periodic impedance variations that form notch filter characteristics, allowing the line to suppress specific common mode frequencies while maintaining differential mode signal integrity

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The conductor width and spacing are varied locally along the transmission line according to a periodic pattern. This creates positions with different common mode impedances while maintaining constant differential mode impedance, forming a common mode notch filter that suppresses high frequency common mode noise without affecting differential signaling

Inventive Principle:

Principle #3Local quality

2Object-generated harmful factors

If common mode impedance is periodically changed to suppress common mode noise, then common mode noise suppression is improved, but transmission line structure complexity increases

Engineering Contradiction:

Improvecommon mode noise suppressionVSAvoidtransmission line structure

Core Design Contradiction:

Object-generated harmful factorsVSDevice complexity

Solution Approach 1:

The transmission line employs periodic variations in conductor width and spacing that repeat at intervals corresponding to half the wavelength of the target common mode frequency. This periodic structure creates resonant cancellation effects that suppress common mode noise at specific frequencies while maintaining a relatively simple geometric progression pattern

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The physical parameters of the transmission line (conductor width, spacing between conductors) are systematically varied along the length of the line to create periodic impedance transformations. These parameter changes are designed to produce common mode reflection and cancellation at target frequencies while maintaining constant differential mode characteristics

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

The solution significantly reduces common mode noise by periodically changing the common mode impedance, thereby enhancing the suppression of common mode signals and their harmonics, improving signal integrity in differential signaling.

Implementation Method 1

Methodology Applied

Scientific EffectCommon mode notch filter: Filter (electronic)

Implementation Method 2

The sections have lengths that are each equal to half of an electric wavelength of a lowest frequency of a common mode electromagnetic wave to be suppressed

Methodology Applied

Scientific EffectElectromagnetic wave interference: Interference

Data Source

PatentUS9479362B2Differential transmission line with common mode notch filter

Publication Date: 2016.10.25 LENOVO ENTERPRISE SOLUTIONS (SINGAPORE) PTE LTD

AI summary

A differential transmission line with a common mode notch filter includes adjacently arranged, repeating differential transmission line pair sections. The sections have lengths that are each equal to half of an electric wavelength of a lowest frequency of a common mode electromagnetic wave to be suppressed during transmission of an electric signal over the differential transmission line. Each section includes a pair of conductors separated from one another by a spacing. The width of each conductor and the spacing between the conductors of each section vary over the length thereof according to a same pattern such that at every point over the length of each section a differential mode impedance of the differential transmission line is identical. A common mode impedance of the differential transmission line changes periodically in accordance with the lengths of the sections.