High Speed Bypass Cable for Backplanes
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Solution Overview
Problem
Conventional cable interconnection systems using FR-4 material for high-speed signal transmission above 10 Gbps suffer from significant signal losses, leading to increased costs due to the need for custom materials and complex design requirements, including amplifiers and repeaters, which complicate the routing of transmission lines and introduce impedance discontinuities.
Innovation Solution
A high-speed bypass cable assembly utilizing twin-ax wires enclosed in an insulative covering, which provides a consistent signal path independent of the circuit board, minimizing signal loss and impedance discontinuities by terminating the wires directly to connector terminals and using ground shields for shielding and crosstalk reduction, thus allowing the use of inexpensive FR4 material for circuit boards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If FR-4 material is used for circuit board construction, then cost is reduced, but signal loss increases dramatically at data rates above 6 Gbps
Solution Approach 1:
The patent divides the signal transmission path into two separate segments: (1) a short trace on the FR-4 circuit board to reach the connector, and (2) a dedicated bypass cable with controlled impedance construction that carries the high-speed signal from the connector to the chip. This segmentation allows the inexpensive FR-4 material to be used for the board while the signal integrity-critical path uses specialized low-loss construction.
Solution Approach 2:
The patent extracts the high-speed signal transmission function from the FR-4 circuit board material and places it into a separate bypass cable assembly. The bypass cable is terminated directly to the connector, bypassing the FR-4 board material for the critical signal path, thereby eliminating the signal loss problem while retaining the cost advantage of using FR-4 for the board structure.
2Adaptability or versatility
If transmission line traces are routed on FR-4 material, then board integration is achieved, but impedance consistency and signal integrity deteriorate due to routing complexity and turns
Solution Approach 1:
The patent segments the transmission path so that the impedance-critical portion (the bypass cable) is physically separated from the board routing. The bypass cable is constructed with controlled impedance geometry that maintains consistency throughout its length, while the board trace is minimized to only what is necessary to reach the connector.
Solution Approach 2:
The patent extracts the high-speed signal path from the board routing system and places it in a dedicated bypass cable with predetermined controlled impedance. This extraction eliminates the problems of routing turns, vias, and transitions that plague board traces, while the cable connector provides the interface back to the board.
3Adaptability or versatility
If long transmission line traces are used to connect chip to connector, then board layout flexibility is improved, but signal loss increases and amplifiers/repeaters are required
Solution Approach 1:
The patent extracts the long-distance signal transmission function from the board trace and places it in a dedicated bypass cable. The cable is designed with low-loss characteristics appropriate for the required length, and its external placement allows it to span the necessary distance without consuming valuable board space or requiring additional active components.
Solution Approach 2:
The patent moves the signal transmission path from the two-dimensional board plane to three-dimensional space by using a cable that can route outside the board plane. This allows the signal to traverse longer distances without being constrained by board trace routing limitations, and eliminates the need for additional board space for amplifiers and repeaters.
4Loss of energy
If custom low-loss materials are used for high-speed applications, then signal loss is reduced, but device cost increases severely
Solution Approach 1:
The patent segments the system into two parts with different material requirements: the FR-4 circuit board for structural and low-speed functions, and a specialized bypass cable for high-speed signal transmission. This allows the expensive low-loss materials to be used only where absolutely necessary (in the cable construction) rather than throughout the entire device.
Solution Approach 2:
The patent applies different material qualities to different parts of the system: inexpensive FR-4 material is used for the circuit board where high-speed transmission is not required, while specialized low-loss cable construction is used locally for the bypass path where high-speed signals must travel. This local application of quality optimizes performance where needed while minimizing overall cost.
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 bypass cable assembly effectively maintains consistent impedance and reduces signal loss, enabling high-speed data transmission above 10 Gbps without the need for expensive custom materials or complex routing, thereby reducing overall system costs and simplifying design.
Implementation Method 1
using ground shields for shielding and crosstalk reduction
Data Source
AI summary
A cable bypass assembly is disclosed for use in providing a high speed transmission line for connecting a chip, or processor mounted on a circuit board to a backplane. The bypass cable assembly has a structure that maintains the geometry of the cable in place from the chip to the connector and then through the connector. The connector includes a plurality of conductive terminals and shield members arranged within an insulative support frame in a manner that approximates the structure of the cable so that the impedance and other electrical characteristics of the cable may be maintained as best is possible through the cable termination and the connector.