Electricity: conductors and insulators – Conduits – cables or conductors – Insulated
Utility Patent
1997-06-06
2001-01-02
Kincaid, Kristine (Department: 2831)
Electricity: conductors and insulators
Conduits, cables or conductors
Insulated
C174S1130AS
Utility Patent
active
06169251
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a quad cable having at least one quad of signal conductors extending within an encircling insulating buffer, and the buffer being encircled by a conducting shield.
BACKGROUND OF THE INVENTION
According to U.S. Pat. No. 5,574,250, a known, quad cable of high frequency performance is constructed with signal transmitting, insulated signal conductors that are radially spaced from a central axis of the cable. The signal conductors are closer to the central axis of the cable than to an encircling shield. An insulation layer separates the signal conductors from a shield by a lengthy distance, to reduce both signal attenuation, and signal skew, of high frequency signals being transmitted by the known cable. For example, the insulated conductors are spaced by the insulation layer from the shield by at least the same distance, and farther, than they are spaced from the central axis of the cable.
SUMMARY OF THE INVENTION
According to a quad cable of the invention, a cable of at least one quad comprises two pairs of insulated signal conductors, an insulating buffer encircling the conductors, and a conducting shield encircling the buffer. A compact quad cable is achieved. For example, the buffer has a lower dielectric constant than that of insulation on each of the signal conductors. The buffer separates the shield from each of the signal conductors by a distance less than another distance between a central axis of the shield and each of signal conductors. Closer spacing of the shield to the signal conductors provides a compact quad cable.
An embodiment of the invention provides a quad cable with a skew value of 2 picoseconds per foot (2 ps/ft.), and less.
An embodiment of the invention provides a quad cable of desired characteristic impedance.
An embodiment of the invention provides a quad cable of desired characteristic impedance and of a lowered signal skew, and of minimized size, meaning overall diameter of the cable.
An embodiment of the invention provides a technique for lowering signal skew values of a quad cable while maintaining the same size and same characteristic impedance.
An embodiment of the invention provides a quad cable comprising, solid insulation on insulated conductors of the cable with a uniform dielectric constant and a uniform signal skew value, as required without undue control over manufacturing processes for producing an expanded insulation with a uniform dielectric constant.
An embodiment of the invention provides a quad cable with a dielectric buffer between a conducting shield and insulated conductors with uniform signal skew, the conductors being encircled by the buffer, and the buffer being of lower dielectric constant than that of insulation on the conductors to provide the cable with low signal skew at a desired characteristic impedance.
An embodiment of the invention provides a quad cable with solid insulation on insulated conductors of the cable, and an insulating buffer bridging between each of the insulated conductors and a conducting shield, the buffer having a lower dielectric constant that that of the insulation, and the buffer having a thickness that results in the distance between the shield and any conductor being less than the distance between a center axis of the shield and any of the conductors.
An embodiment of the invention provides a quad cable with lower signal skew while maintaining a given characteristic impedance without an increase in size of the cable.
An embodiment of the invention provides a quad cable with solid insulation on the conductors of the cable, and color coding on the insulation having insubstantial effect on dielectric constant, and inconsequential effect on signal skew.
According to an embodiment of the invention, the signal conductors of a quad cable are spaced closer to a shield than they are spaced from a central axis of the cable, and an insulating buffer separating the insulated conductors from the shield has a dielectric constant less than that of insulation on the signal conductors. A quad cable of low skew value is attained.
Marking individual conductors of a cable with color coding is desirable to distinguish among the conductors, for example, to prevent undesired, cross over connections at opposite ends of the cable. In the known cable, the signal conductors are insulated with a foamed or otherwise expanded insulation. Marking the expanded insulation with color coding contributes to inconsistencies in the dielectric constant and the signal skew. For example, marking with ink will adhere to an insulation when it is at an elevated temperature. When the ink is applied to extrudate insulation during expansion of the insulation, the ink produces further inconsistencies in the dielectric constant of the expanded insulation. When the ink is applied after expansion of the insulation, the expanded insulation must be heated, which significantly weakens the self supporting strength of the expanded insulation, to produce an inconsistent dielectric constant. Thus, the application of color coding on expanded insulation presents further inconsistencies in dielectric constant and inconsistent skew values. Marking of the known cable has been restricted to an exterior jacket of the known cable, leaving the individual conductors unmarked and thus indistinct from one another.
According to another embodiment of the invention, the solid insulation on each of the conductors of a quad is suitable for marking, for example, to provide color coding.
Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, according to which:
REFERENCES:
patent: 3610814 (1971-10-01), Peacock
patent: 3643007 (1972-02-01), Robert et al.
patent: 3885380 (1975-05-01), Hacker
patent: 4629285 (1986-12-01), Carter et al.
patent: 4755629 (1988-07-01), Beggs, et al.
patent: 5521333 (1996-05-01), Kobayashi et al.
patent: 5574250 (1996-11-01), Hardie et al.
patent: 5777273 (1998-07-01), Woody et al.
patent: 1 088 108 (1955-03-01), None
Grant Charles Lloyd
Patel Mukesh M.
Kincaid Kristine
Nguyen Chau N.
The Whitaker Corporation
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