Patent Application
20140206230
The Present Disclosure relates generally to cable interconnection systems, and, more particularly, to improved cable assemblies for use in high speed data transmission applications.
Conventional cable interconnection systems are found in electronic devices such as routers, servers and the like, and are used to form signal transmission lines. These transmission lines may extend between chip members and connectors, connectors in two different devices, and between devices themselves. Often, differential signal wires are used for each such transmission line in a cable and although it is easy to maintain a desired impedance profile along the length of the cable due to the cable geometry, it is difficult to maintain such a profile at the termination ends of the wires. In some instances, these terminations occur at circuit board that takes the form of an edge, or paddle, card. The wires are terminated to contact pads along the trailing edge of the circuit board. In such a situation, the exterior insulation is stripped back and the bare conductors are terminated to solder pads or the like. Removing the exterior insulation also requires removing the outer shield of the cable wires so that the termination area is left poorly grounded. This ungrounded area has been known to contribute to and increase the crosstalk between the wires in high speed applications. It is desirable to therefore have a cable termination with a structure that lessens the discontinuities in impedance profiles.
The Present Disclosure is therefore directed to a cable assembly particularly suitable for high speed data transmission applications.
Accordingly, there is provided an improved high speed cable assembly having an improved termination structure suitable for beneficial termination in high speed data transmission applications.
In accordance with an embodiment described in the Present Disclosure, a cable assembly is disclosed that utilizes a specially configured circuit board, or paddle card, to which the wires of the cable are terminated. The circuit board is formed with two distinct sections, the first of which may be considered a base portion on which a majority of the circuit board circuitry resides, including the front contact pads which engage terminals of an opposing mating connector, as well as the contact pads to which cable wires are terminated. The second portion may be considered an extension of the first portion but it has a different and lesser thickness than the circuit board base portion. It extends rearwardly of the base portion and the contact pads.
One or more ground plane layers are preferably extended into the area of the circuit board extension portion, rearwardly of the contact pads, and these ground plane layers may be the only circuitry of the circuit board that is supported by the extension portion. Ordinarily the cable wires have their insulation covering and exterior shields stripped from the ends thereof in order to expose free ends of the cable wire conductors, so that the conductors may be easily terminated to the circuit board along the rearmost set of contact pads thereof. In stripping the cable wires, the conductors have a bare extent, and the insulative or dielectric covering of the wires also has a given extent that extends between the leading edge of the insulative covering and the leading edge of the exterior shield. Ordinarily in dense cable connectors, differential signal pairs are arrayed in rows along the top and bottom surfaces of the circuit board. The conductors of the wire pairs are terminated to contact pads on opposite sides of the circuit board and the ends of the insulation of the wire pairs are disposed rearwardly of the circuit board trailing edge. The ends of the exterior shielding are likewise disposed rearwardly of the circuit board trailing edge and rearwardly of the ends of the cable wire insulation and as such, a gap occurs between the wire pairs attached to the top and bottom surfaces of the circuit board. This area is prone to increasing crosstalk and negatively influencing discontinuities in the impedance profile of the cable assembly.
The extension portion of the circuit board extends rearwardly into this gap between the leading edge of the shield and the trailing edge of the circuit board. It fills the intervening space between top and bottom pairs of cable wires, and because the extension portion supports at least one ground plane layer, it provides shielding between aligned pairs in the vertical direction of the cable assembly. This shielding reduces crosstalk in the termination area, without the need for additional, separate shielding components. The extension portion has a thickness that is less than the thickness of the circuit board base portion so that the circuit board has a stepped configuration when it is viewed from the side. The thickness of this extension portion may be chosen to provide a spacing template for the cable wires as it will preferably fit snugly in the horizontal gap that exists in the vertical direction between wires on opposite surfaces of the circuit board. The reduction in crosstalk between the vertically aligned wires without utilizing additional components, offers a cost saving in manufacturing of cable assemblies of the Present Disclosure. Moreover, the stepped profile of the circuit board provides for an intervening element that can assist in providing strain relief to the cable assembly when the circuit board is overmolded with an insulative material at least in the termination area. Suitable overmolding materials include plastics and/or epoxies.
These and other objects, features and advantages of the Present Disclosure will be clearly understood through a consideration of the following detailed description.
The organization and manner of the structure and operation of the Present Disclosure, together with further objects and advantages thereof, may best be understood by reference to the following Detailed Description, taken in connection with the accompanying Figures, wherein like reference numerals identify like elements, and in which:
While the Present Disclosure may be susceptible to embodiment in different forms, there is shown in the Figures, and will be described herein in detail, specific embodiments, with the understanding that the Present Disclosure is to be considered an exemplification of the principles of the Present Disclosure, and is not intended to limit the Present Disclosure to that as illustrated.
As such, references to a feature or aspect are intended to describe a feature or aspect of an example of the Present Disclosure, not to imply that every embodiment thereof must have the described feature or aspect. Furthermore, it should be noted that the description illustrates a number of features. While certain features have been combined together to illustrate potential system designs, those features may also be used in other combinations not expressly disclosed. Thus, the depicted combinations are not intended to be limiting, unless otherwise noted.
In the embodiments illustrated in the Figures, representations of directions such as up, down, left, right, front and rear, used for explaining the structure and movement of the various elements of the Present Disclosure, are not absolute, but relative. These representations are appropriate when the elements are in the position shown in the Figures. If the description of the position of the elements changes, however, these representations are to be changed accordingly.
Turning to
In termination, the free ends of the cable wire conductors 27 are exposed by removing a given length of their outer covering 26, and the outer shield member 29 also has a portion of it removed. This removal defines respective leading edges 28, 31 of both the wire insulation 26 and the shield member 29, both of which are spaced apart from the ends of the cable wire conductors. These leading edges 28, 31, as best shown in
In this gap area G, the cable wire shields 29 are removed and when the cable wires 25 are terminated to the circuit board 15, they are typically aligned with each other in pairs, vertically. That is, some pairs of the cable wires 25 are attached to the top surface of the circuit board 15, while a like amount of cable wires 25 are attached to the bottom surface of the circuit board 15. The pairs are arranged both side by side in two, generally horizontal planes, but the pairs in these planes are separated from each other by a vertical spacing that is at least equal to the thickness of the circuit board. In the gap area, G, where the cable wire shielding has been removed the signal wires of the cable are closely spaced apart from each other, and any ground plane that may be utilized in the circuit board construction stops near the trailing edge of the circuit board 15. Hence, there is no shielding in this gap area between the vertically spaced apart wire pairs. Even though the gap distance is relatively small, at high data transfer speeds, such as 10 Gigabits per second (Gbps) crosstalk occurs and rises to a level that is deleterious to efficient signal transmission and may lead to discontinuities in the impedance profile of the cable assembly. This crosstalk is even greater at data transfer speeds of 25 Gbps.
As best shown in
Two such ground plane layers 36a, 36b are illustrated in
Such a structure reduces the crosstalk that occurs in this area, especially at high data transfer speeds of 10 Gbs up to 25 Gbps and above. The use of the circuit board extension portion 35 to solve this problem does so without increasing the complexity of assembly and manufacturing costs as it accomplishes a reduction in crosstalk without attaching any extra component. Crosstalk has been able to be reduced up to 15 dB between the adjacent top and bottom rows of twin-ax wires without adding any extra components to the cable assembly.
This new development also provides the user with the ability to integrate a strain relief aspect into the termination area. This may be done by forming a body portion utilizing a suitable material such as a plastic or an epoxy. As shown in
Preferably, the circuit boards of the Present Disclosure are integrally formed as one piece as shown in
Although the Present Disclosure has described our new development in terms of twin-ax wires, it will be understood that the principles thereof apply equally to pairs of differential signal wires used in cables where each wire had a center conductor surrounded by an insulative covering and the two wires are enclosed within an outer shielding member. In such an instance, the wires are arranged to align with corresponding contact pads and the insulation on each wire is trimmed back as is the outer shielding member for each such pair of wires, so that the leading edges of the wire insulation and the outer shielding members are disposed rearwardly of the circuit board base portion trailing edge so that the circuit board extension portion may be positioned therebetween in the manner described above.
Finally, while a preferred embodiment of the Present Disclosure is shown and described, it is envisioned that those skilled in the art may devise various modifications without departing from the spirit and scope of the foregoing Description and the appended Claims.
