Differential Transmission Cable Spiral Shielding Mode Conversion
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Solution Overview
Problem
High-speed differential transmission cables face challenges in reducing mode conversion noise and maintaining sufficient differential mode bandwidth, especially at data transmission rates of 25 Gb/s, due to issues with existing shielding methods such as longitudinal wrapping-type shielding causing increased mode conversion and spiral wrapping-type shielding leading to differential-mode suck-out.
Innovation Solution
A differential transmission cable with a pair of signal lines covered by a single insulation and a shielding tape helically wound around the insulation, where the signal line diameter is thinner than 30 AWG and the differential characteristic impedance is between 80Ω and 120Ω, utilizing the spiral wrapping-type shielding method to reduce mode conversion noise and maintain sufficient differential mode bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If longitudinal wrapping-type shielding method is used, then ease of manufacture is improved, but mode conversion noise increases
Solution Approach 1:
The patent inverts the conventional longitudinal wrapping-type shielding method by adopting a spiral wrapping-type shielding method. This inversion changes the shielding tape orientation from longitudinal to spiral, which fundamentally alters the electromagnetic field interaction and reduces mode conversion noise while maintaining manufacturing feasibility through a slightly modified process.
Solution Approach 2:
The patent changes the critical parameter of shielding tape wrapping angle from 0 degrees (longitudinal) to a spiral angle, and optimizes the signal line diameter to 30 AWG or thinner. These parameter changes transform the shielding effectiveness and reduce mode conversion noise to not more than -24 dB while keeping the manufacturing process relatively simple.
2Length of moving object
If signal line diameter is reduced to achieve thinner cable, then cable flexibility and compactness are improved, but mode conversion noise increases
Solution Approach 1:
The patent identifies signal line diameter as a critical parameter and sets it to 30 AWG or thinner, combined with specific insulation dimensions. This parameter optimization, together with the spiral shielding configuration, ensures that mode conversion noise remains at or below -24 dB even in thin cables suitable for high-speed transmission applications.
3Object-generated harmful factors
If spiral wrapping-type shielding method is used, then mode conversion noise is reduced, but differential-mode loss increases due to suck-out effect
Solution Approach 1:
The patent optimizes multiple parameters including signal line diameter (30 AWG or thinner), insulation dimensions (major axis not more than 1.5 mm, minor axis not more than 0.8 mm), and shielding tape configuration. These coordinated parameter changes reduce mode conversion noise to not more than -24 dB while preventing excessive differential-mode loss, achieving a balance between the two competing requirements.
Data Source
AI summary
A differential transmission cable includes a pair of signal lines, an insulation covering the pair of signal lines, and a shielding tape that includes a conductor layer and an insulation layer formed on one surface of the conductor layer and is helically wound around the insulation. The diameter of the signal line is thinner than at least 30 AWG (American Wire Gauge), and differential characteristic impedance is not less than 80Ω and not more than 120Ω.