Electricity: conductors and insulators – Conduits – cables or conductors – Insulated
Reexamination Certificate
2001-11-28
2003-11-25
Nguyen, Chau N. (Department: 2831)
Electricity: conductors and insulators
Conduits, cables or conductors
Insulated
Reexamination Certificate
active
06653570
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cable for the transmission of electrical signals. In particular, the present invention relates to an electrical cable having one or more ribbon conductor assemblies for improved signal transmission properties.
2. Discussion of Background
Electrical cables and interconnects are important but frequently overlooked components of audio and video playback systems. Well-chosen cables and interconnects can help users get the best performance from their systems, whereas poor or incompatible cables result in poor performance. The terms “cable” and “electrical cable” are often used to refer to any wiring in an audio or video system, most commonly to a power cord that connects a component to a source of electrical power such as a wall outlet, or a conductor that carries a high-current signal from a power amplifier to a loudspeaker. The term “interconnect” refers to a conductor that connects line-level signals in an audio or video system. For example, interconnects are used between source components (CD player, turntable, tape deck tuner) and the preamplifier, and between the preamplifier and the power amplifier of a typical audio system. For purposes of this specification, the terms “cable,” “electrical cable” and “interconnect” are used interchangeably.
Ideal cables are “neutral,” that is, they transmit electrical signals essentially instantaneously and without imposing significant distortion or degradation on the signals. However, real-world cables have electrical resistance, capacitance, and self-inductance properties which color the signals transmitted through the cables. Therefore, discriminating consumers select cables for their compatibility with the other system components, and (in some cases) for their ability to enhance the overall sound or video output of the system. Similar considerations apply to cables used in high-end computer systems, servers, and other applications where distortion-free signal transmission is a priority.
Many different types of electrical cables are available. Cables are frequently shielded to minimize the effects of electromagnetic interference on the signal-carrying conductors. Typically, shields of metal foil or braided strands of electrically-conducting material enclose the signal-carrying conductors and are electrically connected to ground potential at one or both ends of the cable. As noted above, all cables exhibit some signal degradation due to the effects of resistance/impedance, capacitance, and inductance. The most important sources of signal degradation arise from the interaction between the individual strands of multi-stranded conductors and a phenomenon known as the “skin effect.” A well-known problem with multi-stranded cable is the tendency for the signal to jump from strand to strand if the cable is twisted. Each strand interface acts like a small electrical circuit that adds capacitance to the cable, resulting in degradation of the signal. In addition, the flow of electrical current sets up a magnetic field in each conductor which induces a signal in adjacent conductors and further degrades the signal.
The skin effect is a factor at audio and higher frequencies: because the self-inductance of an electrical conductor is greatest at the center of the conductor, higher-frequency signals encounter a lower-impedance path towards the outside of the conductor, which reduces the effective cross-sectional area of the conductor at those frequencies, which in turn increases the impedance of the conductor at those frequencies. Because higher-frequency signals encounter higher impedances than lower-frequency signals, the relative amplitudes of different-frequency signals are distorted during transmission. This problem is particularly evident for mixed-frequency signals: the greater the bandwidth of the signal, the greater the distortion.
Cable designers seek to minimize these effects and (particularly for cables used to transmit audio and video signals) optimize the effective bandwidth of their cables using a variety of techniques. For example, ribbon-type conductors are used in many applications. Brunt (U.S. Pat. No. 5,900,589) shows an audio transmission cable with a signal-carrying conductor of pure (or nearly pure) silver ribbon enclosed by an insulating material, where the width of the conductor is at least five times its thickness. A ground conductor lies alongside the ribbon conductor, placed so that the cross-sectional width of each the two conductors lies facing the other. The resulting assembly is enclosed by a second insulating layer, a conductive shield, and an outer insulating material.
Shah, et al. (U.S. Pat. No. 5,500,489) provide a thin, flexible cable for electronic retailing applications. Their cable includes three ribbon conductors on one side of a dielectric ribbon, and a flame-resistant, electrically-insulating jacket enclosing the ribbon with the conductors.
Haldeman, Jr. (U.S. Pat. No. 3,586,757) discloses a flexible stripline transmission line having individual conducting and insulating portions which are free to move relative to each other. The stripline consists of a pair of ribbon conductors sandwiched between three insulators, with a flexible outer cover that holds them in place. There appears to be a small air space on each side of the conductor/insulator stack.
Eisler (U.S. Pat. No. 3,317,657) shows several designs for flat electric cables for heating applications. The cables include flat conductor strands, each enveloped in a sheath of insulating film. A plurality of such sheaths are secured to a wider insulating film by an adhesive or by welding.
Hoover's flat cable (U.S. Pat. No. 2,200,776) has three pairs of insulated copper ribbons that serve as power conductors, and two additional insulated conductors for connection to motor control devices. The ribbon conductors are enclosed by fiber insulation and linen tape; the cable structure is enclosed by a copper tube.
Weaver (U.S. Pat. No. 2,060,913) and Guilleaume (U.S. Pat. No. 531,614) provide telephone cables. Weavers self-coiling cable includes one or more strands of an elastic material such as phosphor bronze alloy which can be wound in a resilient helix. The conductors are insulated and bound together by braided textile covers or otherwise. Guilleaume's telephone cable has several strands of ribbon conductors twisted together and sheathed with paper or other insulator, followed by an outer sheath of lead. The ribbon conductors in each strand are insulated from each other by paper.
Trazyik (U.S. Pat. No. 5,872,334) and King (U.S. Pat. No. 2,586,345) use conductive shields in their devices. The Trazyik high-speed cable includes a pair of cables, each having a copper wire core surrounded by a dielectric layer (such as PTFE), a ground conductor, and a conductive shield. The cables are encased in a polymeric jacket, which is impregnated with a conductive material such as carbon. King discloses a three-core paper insulated mine shaft cable. The cable has three sets of conductors, each set consisting of a plurality of metal strands surrounded by paper insulation impregnated with micro-crystalline petroleum wax and cable-impregnating mineral oil. The conductor sets are encased in (in sequence) a metallized paper screen, a lead sheath, a layer of jute, steel wire armouring, and another layer of jute.
Despite the many types of cables available to consumers, there is a need for a wide-bandwidth, low-distortion electrical cable that can be used as a power cable or interconnect cable in a variety of different applications (audio and video systems, home theater systems, computer systems, servers, etc.). Such a cable would have a low overall impedance combined with low self-inductance, and, optionally, a dedicated ground conductor.
SUMMARY OF THE INVENTION
According to its major aspects and broadly stated, the present invention includes a ribbon conductor assembly having a ribbon conductor with an approximately rectangular cross-section transverse to a longitudinal axis of the cabl
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