Differential Signaling Cable Impedance Control

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Solution Overview

Problem

Conventional differential signaling cables face issues with signal skew, differential-to-common-mode conversion, and transmission loss when transmitting high-speed signals of several Gbps, leading to unstable characteristic impedance and difficulty in mounting, which affects signal integrity and electromagnetic interference performance.

Innovation Solution

A differential signaling cable design featuring parallel signal conductors with a specified interval, covered by an insulator and a shield conductor, where the even-mode impedance is 1.5 to 1.9 times the odd-mode impedance, and a drain wire is disposed to enhance grounding, allowing for stable production and easy mounting while reducing skew and transmission loss.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a twisted pair cable is used for differential signaling, then the cable is inexpensive, balanced, and easily bent, but the characteristic impedance is not stable and signal waveform collapses in high-frequency area

Engineering Contradiction:

Improvecable cost and flexibilityVSAvoidsignal integrity at high frequency

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent changes the geometric parameters of the cable structure by specifying a particular interval between signal conductors (0.3 to 0.8 times the outer diameter of the insulator) and controlling the ratio of even-mode to odd-mode impedance (1.5 to 1.9 times). These parameter changes stabilize the characteristic impedance and reduce signal skew, enabling reliable high-frequency transmission while maintaining the twin-axial cable structure.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent uses a composite structure combining insulator material with specific dielectric properties and metal shield conductors. The insulator material is selected and structured to provide both mechanical support and electrical isolation, while the shield conductor provides electromagnetic shielding. This composite approach achieves stable impedance characteristics and reduced differential-to-common-mode conversion.

Inventive Principle:

Principle #40Composite materials

2Manufacturing precision

If the interval between signal conductors is reduced to reduce skew, then skew decreases, but differential-to-common-mode conversion increases

Engineering Contradiction:

Improvesignal skew controlVSAvoiddifferential-to-common-mode conversion

Core Design Contradiction:

Manufacturing precisionVSObject-generated harmful factors

Solution Approach 1:

The patent optimizes the interval between signal conductors to be 0.3 to 0.8 times the outer diameter of the insulator, which balances the reduction of signal skew with the control of differential-to-common-mode conversion. Additionally, the even-mode to odd-mode impedance ratio is controlled at 1.5 to 1.9 times, which further optimizes the electromagnetic coupling characteristics to minimize harmful conversions while maintaining tight conductor spacing.

Inventive Principle:

Principle #35Parameter changes

3Object-affected harmful factors

If shield conductor is added to cover signal conductors, then noise resistance improves, but cable complexity and manufacturing difficulty increase

Engineering Contradiction:

Improvenoise resistanceVSAvoidcable structure complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent employs a thin film-like shield conductor that wraps around the insulator containing the signal conductors. This shield conductor is made as a continuous thin layer rather than a bulky structure, providing effective electromagnetic shielding and noise resistance while adding minimal complexity to the cable construction. The shield is integrated into the overall cable structure in a straightforward manner.

Inventive Principle:

Principle #30Flexible shells and thin films

4Manufacturing precision

If even-mode impedance is increased relative to odd-mode impedance, then electromagnetic coupling improves and skew reduces, but transmission loss increases

Engineering Contradiction:

Improvesignal skew and couplingVSAvoidtransmission loss

Core Design Contradiction:

Manufacturing precisionVSLoss of energy

Solution Approach 1:

The patent controls the even-mode to odd-mode impedance ratio to be 1.5 to 1.9 times, which optimizes the electromagnetic coupling between signal conductors to reduce skew and differential-to-common-mode conversion. Simultaneously, the interval between conductors is controlled at 0.3 to 0.8 times the insulator outer diameter, which balances coupling efficiency with transmission loss, preventing excessive energy dissipation while achieving the desired impedance ratio.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS9660318B2Differential signaling cable, transmission cable assembly using same, and production method for differential signaling cable

Publication Date: 2017.05.23 PROTERIAL LTD

AI summary

A differential signaling cable includes a pair of signal conductors provided in parallel, longitudinally within the differential signaling cable, an insulator covering a periphery of the pair of signal conductors as a whole, wherein only the insulator is between the pair of signal conductors, and a shield conductor provided on an outer periphery of the insulator. An interval between the pair of signal conductors is set so that an even-mode impedance of the pair of signal conductors having the interval fixed by embedment within the insulator and covered by the shield conductor, is in a range from 1.5 to 1.9 times an odd-mode impedance for improved skew and differential mode insertion loss experienced during a transmission of high-speed signals of at least 10 Gbps.