The present invention relates to the construction of shielded high speed data cables, which carry signal wires as well as ground and power wires.
Some high speed cable standards such as the High-Definition Multimedia Interface HDMI specification (High-Definition Multimedia Interface Specification Version 1.3, published by Hitachi, Ltd., Matsushita Electric Industrial Co., Ltd., Philips Consumer Electronics, International B.V., Silicon Image, Inc., Sony Corporation, Thomson Inc., and Toshiba Corporation, Jun. 22, 2006) have specific limits on the resistance of power and ground lines in the cable. For example, in HDMI cables a limit of 1.8 ohms is specified for the combined resistance of the Ground line and the Power line that provides 5V power and through which power may be provided to embedded circuitry in the cable. Another example of a similar resistance limit is contained in the Universal Serial Bus (USB) 3.0 specification (Universal Serial Bus 3.0 Specification, published by Hewlett-Packard Company, Intel Corporation, Microsoft Corporation, NEC Corporation, ST-NXP Wireless, and Texas Instruments, Revision 1.0, Nov. 12, 2008) according to which the combined resistance of the Power line and the Ground line is limited to 0.4 ohms.
To achieve the specified resistance limits, the conventional approach is to decrease the gauge of the wire, i.e. increase the wire thickness, in accord with increasing cable length.
A problem with the conventional approach of decreasing the gauge of the power and ground wires is that the resulting increase in the wire thicknesses has a direct impact on the cable outer diameter and the flexibility of the cable. This size increase can be significant when active equalization of the data lines is used, which allows higher loss and relatively high gauge (low diameter) wire to be used for the signal lines.
a shows a schematic diagram of a shielded high speed cable 100 of the prior art, including a raw cable 102, first and second terminating ends 104.1 and 104.2 at respective first and second ends of the raw cable 102. The raw cable 102 includes wires (conductors), which extend into the first and second terminating ends 104.1 and 104.2, namely a shield 106, a power wire 108, a group of signal wires 110, and a ground wire 112. The shield 106 is an conductive layer, implemented in a form of foil or braid, for example the cable 100 cable can be wrapped in a conductive foil, most often aluminum, or it can be wrapped in a braided mesh of tiny wires. Foil and braid have different characteristics, which accounts for the fact that many cables have both braid and foil as the shield 106.
The raw cable 102 is typically surrounded by an insulating layer (not shown in
b illustrates the raw cable 102 in a schematic cross-sectional view, in which the shield 106 surrounds the power line 108, the group of signal lines 110, and the ground wire 112. The group of signal lines 110 is shown to comprise 6 individual signal wires for illustrative purposes only. The actual number of signal wires varies according to the type of cable (HDMI or USB 3.0 for example). In addition to the signal wires there may also be so-called drain wires (not shown) included, which may be used for impedance control of the signal wires.
The shield 106 of the shielded high speed cable 100 is normally floating in the cable, and may be connected to a metal structure of the equipment to which the cable is connected.
Therefore there is a need in the industry for developing an improved high speed cable, which would avoid or mitigate the shortcomings of the prior art.
Therefore there is an object of the invention to provide an improved high speed cable with shield connection, which would have superior properties over existing prior art cables.
According to one aspect of the invention, there is provided a high speed cable, having a raw cable having a first end and a second end, and a first and second terminating assemblies at the first and second ends of the raw cable respectively, the high speed cable comprising:
In the embodiments of the invention, inductance values of the first and second inductive elements are substantially the same. Alternatively, the inductance values of the first and second inductive elements may be different. The inductance values of the inductive elements need to be selected so as to provide resistance, which is noticeably greater than resistance of the ground wire at electromagnetic frequencies of interest.
Conveniently, the first and second inductive elements comprise one or more of the following:
In the embodiments of the invention, the first and second inductive elements have inductance values selected from the following:
The first and second inductors can be formed on a printed circuit board (PCB) in one of the following ways:
In the high speed cable described above, the conductive layer is a shield, comprising one of the following:
The high speed cable further comprises a power wire enclosed by the conductive layer.
In different implementations of the high speed cable, the power wire may have a diameter, which is larger than a diameter of the ground wire. Alternatively, the power wire may have a diameter, which is substantially the same as a diameter of the ground wire. A diameter of the signal wire may be substantially the same as the diameter of the ground wire.
In one of the embodiments describing the high speed cable,
In the high speed cable described above, a diameter of the power wire and a diameter of the ground wire are specified approximately by American Wire Gauge (AWG) 22 and 36 respectively.
In one of the embodiments of the invention, the high speed cable has signal wires, which include one or more of the following:
The high speed cable of the embodiments of the invention includes a Universal Serial Bus (USB) 3.0 cable; and a High-Definition Multimedia Interface (HDMI) cable.
In yet another embodiment of the invention, the signal wire of the cable is shielded in a coaxial structure having a shield, and wherein the shield of the coaxial structure is used as the ground wire; or a power wire.
In one more embodiment of the invention, the high speed cable may further comprise an inner conductive layer within the conductive layer, which is insulated from the conductive layer, wherein the inner conductive layer is used as a power wire.
In the cable as described above, the signal wire comprises:
According to another aspect of the invention, there is provided a method for forming a cable having first and second ends, the cable having a ground wire and a conductive layer enclosing the ground wire, the ground wire and the conductive layer extending between the first and second ends, the method comprising:
According to yet another aspect of the invention, there is provided a cable having first and second ends, the cable comprising:
In the cable described above, inductance values of the first and second inductive elements may be the same, or alternatively the inductance values may be different as long as they are selected so as to provide resistance, which is noticeably greater than resistance of the ground wire at electromagnetic frequencies of interest.
Thus, an improved high speed data cable with shield connection has been provided.
Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which:
a shows a schematic diagram of a shielded high speed cable 100 of the prior art, including a raw cable 102;
b illustrates the raw cable 102 of
a shows a schematic diagram of an improved shielded high speed cable 200 according to one embodiment of the invention, including an improved raw cable 202;
b illustrates the improved raw cable 202 of
Embodiments of the present invention describe a high speed cable, in which the cable shield is used as a direct current (DC) path to reduce the combined resistance of the power and ground wires (conductors), as measured between the ends of the cable.
a shows a schematic diagram of an improved shielded high speed cable 200 according to one embodiment of the invention, including an improved raw cable 202 having improved first and second terminating ends, or terminating assemblies, 204.1 and 204.2 at respective first and second ends of the improved raw cable 202. Similar to the shielded high speed cable 100 of
Through the inductors H1 and H2, the thinner ground wire 212 is effectively shunted by the shield 206 providing a combined lower direct current (DC) resistance between the two terminating ends 204 than would a ground wire alone. This allows the thinner ground wire 212 to be constructed from a much thinner wire compared to the ground wire 112 of the shielded high speed cable 100 of the prior art.
The inductors H1 and H2 preferably have a negligibly low resistance, while their inductance may be typically be in the range of about 30-300 nH. If the thinner ground wire 212 were connected to the shield 206 directly without inductors H1 and H2, this would allow most of the high frequency noise current in the ground wire 212 to pass through the shield 206, which would then radiate electro-magnetic interference (EMI) and thus create problems with high frequency EMI. The high frequency noise current in the ground wire 212 could, for example, be caused by any active circuitry that obtain their power from the power wire 208 and return through the ground wire 212. The inductors H1 and H2 are designed to prevent the high frequency noise current from reaching the shield 206. The inductors H1 and H2 thus allow the shield 206 to decrease the low frequency resistance of the improved raw cable 202, and allow power to pass though the cable shield 206, but the inductors H1 and H2 will stop any high frequency energy from entering the shield 206 and stop the high frequency unwanted EMI.
b illustrates the improved raw cable 202 in a schematic cross-sectional view, in which the shield 206 surrounds the power wire 208, the group of signal lines 210, and the thinner ground conductor 212. Again, the group of signal lines 210 is shown to comprise 6 individual signal wires for illustrative purposes only.
Note the relative thickness of the thinner ground wire 212 compared to the power wire 208.
Following a description of a proposed cross section of a USB cable according to the prior art, specific example configurations for the improved raw cable 202 are described, according to embodiments of the invention.
The size of the central power wire 406 is preferably approximately American Wire Gage (AWG) 22, while the size of each of the insulated data signal wires (D0+, D0−, S0+, S0−, S1+, S1) may then be approximately Awg 36, and the Ground wires (G0, G1, and G2) are uninsulated Awg 30 wires. This arrangement allows the nine insulated wires 408 located inside of the concentric conductive layer 404 to be deposed evenly around the thicker central power wire 406 such as to fill the available space without the need for additional filler elements. Each of the pairs of insulated data signal wires (D0+, D0−) and insulated super-speed data signal wires (S0+, S0−, S1+, S1−) are deposed adjacent to each other, while the insulated ground wires (G0, G1, G2) are interposed between the pairs such as to provide shields between the data signal wire pairs. The insulation of the nine insulated wires 408 is chosen to give each data signal wire pair an impedance Z0 of 50 ohms.
Other wire sizes may be selected such that the nine additional insulated wires 408 fit neatly around the central power wire 406, and within the concentric conductive layer 404, comprising a braid or a foil, or a combination thereof.
In the following
Additional insulated wires (not shown), preferably, with the same diameter as the six insulated coax lines C0 to C5, can be added around the central power wire 606. This would allow an increase in the diameter of the central power wire 606, while maintaining the rotational symmetry. It is also contemplated that additional insulated wires may have a diameter, which is different from the diameter of the six insulated wires.
These additional insulated wires can then be used as ground conductors or power conductors. Connections between the concentric conductive layer 604 and any of the shields of the insulating wires that are used as ground conductors are again provided through inductors H1 and H2 in the terminating assemblies analogous to the arrangement shown in
Thus, reducing the end to end resistance of the ground conductor is achieved.
The arrangement shown in
It is understood that other types of cables may include only one of the wire bundles 816 or 818 and not necessarily both of them.
Common to all variations of the improved raw cable of the embodiments of the invention, i.e. the improved raw cable 202, the raw high speed USB cable 400, the high speed USB cable 500, the raw all-coax cable 600, the raw double-coax cable 700, and the mixed construction raw double-coax cable 800, is a terminating arrangement exemplified by the first and second terminating ends 204.1 and 204.2, which has been described in detail with regard to
This then results in the ability to use much thinner wire gauges for the ground wires. Similarly, the use of an inner conductive layer 706 in the raw double-coax cable 700, and an inner conductive layer 806 in the mixed construction raw double-coax cable 800 as a power conductor results in the avoidance of a power wire altogether.
All these measures are designed to contribute to making a thinner, lighter, and more flexible cable.
Thus, an improved high speed cable with shield connection has been provided.
Various modification and variations can be made to the embodiments of the invention described above.
For example, inductive elements H1 and H2 can be implemented as inductive (ferrite) beads instead of inductors, or they can be implemented as other suitable electrical/electronic elements possessing inductive properties.
Although it is preferred to have values H1 and H2 of the inductive elements to be approximately equal, it is contemplated that inductive elements H1 and H2 may have different inductive values, provided they result in a resistance, which is significantly greater, or at least noticeably greater, than the resistance of the thinner ground wire (for example, thinner ground wire 212) at EMI frequencies of interest.
Geometrical arrangements of wires and coaxial structures inside the cable, relative sizes of wires and coaxial structures inside the cable are shown for illustrative purposes only, and can be changed as required.
Although various exemplary embodiments of the invention have been disclosed, it should be apparent to those skilled in the art that various changes and modifications can be made which will achieve some of the advantages of the invention without departing from the true scope of the invention.
A person understanding this invention may now conceive of alternative structures and embodiments or variations of the above all of which are intended to fall within the scope of the invention as defined in the claims that follow.
The present application claims priority from the U.S. provisional application Ser. No. 61/202,869 filed on Apr. 14, 2009 for “High Speed Data Cable with Shield Connection”, the entire contents of which are incorporated herein by reference.
Number | Date | Country | |
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61202869 | Apr 2009 | US |