Patent Application
20060054334
The present invention relates to shielded electric cables for the transmission of electrical signals through the cables. In particular, the present invention provides an improved shielded parallel pair cables for achieving low insertion loss performance and method of making the cables.
Electrical cables for data transmission are well known. One common cable is a coaxial cable. Coaxial cables generally comprise an electrically conductive wire surrounded by an insulator. The wire and insulator are surrounded by a shield, and the wire, insulator and shield are surrounded by a jacket. Coaxial cables are widely used and best known for cable television signal transmission and ethernet standard communications in local area networks. Coaxial cables can transmit at much higher frequencies than a standard twisted pair wire and, therefore, have a much greater transmission capacity. In addition, coaxial cables have very little crosstalk, and therefore, provide a very reliable medium for data transmission. Other types of cables are also well known, such as twisted pair cables used for telephone signal transmission, and fiber optic cables.
With the proliferation of high-speed, powerful personal computers and the availability of advanced telecommunications equipment, there is a need for cables which are capable of transmitting data at ever faster speeds. Fiber optic cables provide optimum data rate and performance for long distance and high data rate transmissions, since fiber optic cables provide very high data rate transmission with low attenuation and virtually no noise. Fiber optic cables provide data transmission at data rates up to and beyond 10 Gbps. However, despite the increased availability of fiber optic cables, the price of fiber optic cables and transceivers have not dropped to a level where it is always practicable to use. Accordingly, other less expensive cables capable of high speed data transmission are still in demand.
One such cable used for high speed data transmission between two points or devices is a shielded parallel pair cable. Parallel pair cable designs provide two separately insulated conductors arranged side by side in parallel relation, the pair being then helically wrapped in a shield. However, a helically applied shield has many discontinuities. The signal path within the shield is interrupted each time the signal encounters an overlap in the spiral. These repeated interruptions cause signal loss, measured as increased attenuation. A common usage of these cables is to interconnect a mainframe computer to a memory device. As is well known, the speed and data rate with which the computer must communicate with the memory is critical to the computer's performance capabilities. Parallel pair cables are usually used for differential signal transmission. In differential signal transmission, two conductors are used for each data signal transmitted and the information conveyed is represented as the difference in voltage between the two conductors.
U.S. Pat. No. 6,677,518 to Hirakawa et al. discloses a data transmission cable having a pair of conductors, each coated with an insulation, and a drain wire. The pair of conductors and drain wire are successively covered by a shielding tape, which can be longitudinally or spirally wrapped, having a thickness of between 1 μm and 10 μm; and a resin layer. There is no disclosure of polymeric tape layers intermediate to the shielding tape and resin layer.
U.S. Pat. No. 5,483,020 to Hardie et al. discloses parallel pair cable having a pair of conductors, each covered with an insulation to electrically insulate the conductors from each other. The insulated conductors are then covered with a metal shield, preferably constructed of a plurality of interwoven electrically conductive strands to prevent radiated energy from escaping the cable construction. The shield is surrounded by a jacket to protect the cable. There is no disclosure of polymeric tape layers intermediate to the shielding tape and resin layer or of a drain wire.
Even with recent advances in parallel cable construction, there remains a need for a high speed parallel pair cable that reduces skew and also minimizes the pair shield discontinuities in order to achieve low insertion loss performance.
The present invention relates to shielded electric cables for the transmission of electrical signals through the cables. In particular, the present invention provides an improved shielded parallel pair cables for achieving low insertion loss performance.
The cable of the present invention contains at least one pair of insulated conductors and an optional drain wire. The insulated conductors are laid parallel to one another, forming a common axis. The insulated conductors and drain wire are longitudinally covered by a shielding tape, which preferably comprises a metallic sheet having an adhesive applied on selected portions of its surface. The adhesive is most preferably applied in a checker board pattern so that the surface contains areas of uncoated, exposed metal forming contact pads. The shielding tape is then covered with two layers of polymeric tapes spirally wrapped around the shielding tape in opposite helical directions. The polymeric tape is preferably constructed of a polymeric sheet having a layer of adhesive disposed on one surface.
Methods of making the cable are also disclosed. In an embodiment the cable is made by providing a core having a pair of insulated conductors and a drain wire, wrapping a shielding tape longitudinally around the core, successively wrapping two layers of polymeric tapes around the shielding tape in opposite helical directions. Preferably, the shielding tape comprises a metallic sheet having an adhesive applied in a checker-board pattern on its surface.
The foregoing background and summary, as well as the following detailed description of the drawings, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings:
a shows a cross-sectional view of the shielding tape of the present invention.
b shows a top view of the shielding tape of the present invention.
As shown in
In this embodiment, each of the conductors 110 is coated with an insulation 112, such as a plastic material. The outer periphery of the insulation 112 is successively covered with a shielding tape 114, two layers of polymeric tapes 116 and 118, and a jacket 120 as an optional component.
In a preferred embodiment, a grounding drain wire 122 is also provided along the insulated conductors 110, so as to be contained inside the shielding tape 114 together with the conductors 110. The conductors 110 (coated with the insulation 112) and the drain wire 122 constitute the core of the cable. The position of the drain wire 122 is not confined as shown in
Various methods can be considered for covering the conductors 110 (coated with the insulation 112) with the shielding tape 114. Preferably, the conductors 110 may be longitudinally wrapped with the shielding tape 114 such that both ends of the shield tape 114 overlap each other along the longitudinal direction of the conductors 110, as shown in
When the data transmission cables according to the present invention are differential data transmission cables, at least a pair of conductors contained inside the cable 100 are located in a state parallel to each other.
The conductors 110 are composed of a single wire conductor formed of, for example, a soft copper wire, a tin-plated soft copper wire, a silver-plated copper alloy wire, and the like or of a stranded wire conductor made by stranding the single wires. Other metal materials, such as aluminum, steel, and the like that are commonly used in making conductors for cables, are appropriate for the present invention. The preferred conductor material is silver plated copper.
The insulation 112 is preferably composed of a polymeric material which can be, but is not limited to, polyethylene, polypropylene, copolymer of ethylene and tetrafluoroethylene (ETFE), copolymer of tetrafluoroethylene and hexafluiropropylene (FEP), polytetrafluoroethylene (PTFE) resin, copolymer of tetrafluoroethylene and perfluoroalkoxy (PFA), fluorine-containing rubber, or mixtures thereof. The preferred insulation material is polyethylene.
Referring to
Referring back to
The jacket 120, although optional, is preferably composed of a polymeric resin, which can be, but is not limited to, polyvinyl chloride (PVC), polyethylene, polypropylene, copolymer of ethylene and tetrafluoroethylene (ETFE), copolymer of tetrafluoroethylene and hexafluiropropylene (FEP), polytetrafluoroethylene (PTFE) resin, copolymer of tetrafluoroethylene and perfluoroalkoxy (PFA), fluorine-containing rubber, and combinations thereof. The jacket 120 can be extruded around the outer periphery of the polymeric tapes 116 and 118 in a uniform thickness by an extruder, or the like.
Although
Referring to
Without further description, it is believed that one of ordinary skill in the art can, using the preceding description and the following illustrative examples, make and utilize the composition of the present invention and practice the methods. The following example is given to illustrate the present invention. It should be understood that the invention is not to be limited to the specific conditions or details described in this example.
The following Examples compare cables of the present invention with other cables.
Overall, the examples show that the cable of the present invention provides superior operational characteristics by achieving low insertion loss performance.
Although certain presently preferred embodiments of the invention have been specifically described herein, it will be apparent to those skilled in the art to which the invention pertains that variations and modifications of the various embodiments shown and described herein may be made without departing from the spirit and scope of the invention. Accordingly, it is intended that the invention be limited only to the extent required by the appended claims and the applicable rules of law.
