BACKGROUND OF THE INVENTION

This invention relates to electrical cables, and, in particular, to an electrical cable system used for transmitting both digital and analog electrical signals.

Systems using both digital and analog electrical signals have become increasingly popular in consumer applications. In one example, multimedia presentations can be made using digital electrical signals to generate visual images and analog electrical signals to generate the audio portion of the presentation. The presentation is provided on a mass storage device such as a CD/ROM. A computer reads the presentation as data from the storage device. The digital portion is transmitted to a visual display device in digitized form. The audio portion is transmitted to conventional speakers or earphones in analog form. Such systems can also include other inputs and outputs in either digital or analog form.

Digital and analog signals are transmitted between various devices in such systems. It has been the conventional practice to use a number of cables to transmit these signals, typically one type of cable for digital signals and another for audio signals. The multiplicity of cables can be unsightly and inconvenient. Additionally, there may be interference from external sources that degrades the quality of the transmitted information, particularly in the case of the analog signals used to produce the audio portion of the presentation.

There is therefore a need for an improved approach to the transmission of analog and digital signals over cables for use in consumer electronics applications. The present invention fulfills this need, and further provides related advantages.

SUMMARY OF THE INVENTION

The present invention provides a cable system for transmitting digital and audio information over a single cable. The cable is compact and convenient to use. Interference and distortion of the signals is reduced as compared with the conventional use of separate cables for digital and audio signals. The cable system of the invention is readily fabricated and tested, and thereafter adapted for specific applications.

In accordance with the invention, a cable system comprises a central core and an annular sheath overlying at least a portion of the length of the central core. The core comprises digital electrical signal conductor means for carrying digital signals, a core ground plane conductor overlying the digital electrical signal conductor means, a first digital connector electrically communicating with a first end of the digital electrical signal conductor means, a second digital connector electrically communicating with a second end of the digital electrical signal conductor means, and a core ground plane connector electrically communicating with the core ground plane conductor. The annular sheath comprises analog electrical signal conductor means for carrying analog signals, a sheath ground plane conductor overlying the analog electrical signal conductor means, a first analog connector electrically communicating with a first end of the analog electrical signal conductor means, a second analog connector electrically communicating with a second end of the analog electrical signal conductor means, and a sheath ground plane connector electrically communicating with the sheath ground plane conductor.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic, partially exploded, end-to-end view of the cable system of the invention;

Figure 2 is a schematic sectional view of the cable system of Figure 1, taken along line 2-2 of Figure 1; and

Figure 3 is a schematic view of the electrical interconnection and grounding of the cable system of Figure 1.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 depicts a cable system 20, and Figure 2 is a cross section through a portion of the cable system 20. The cable system 20 includes a flexible portion 22 formed of a central core 24, an annular sheath 26 overlying the core 24, and an outer covering 28 overlying the annular sheath 26. Connectors of various types, as will be described, are found at the ends and, in a preferred embodiment, at an intermediate location along the length of the flexible portion 22.

The central core 24 includes a plurality of insulated digital electrical signal conductors 30, usually manufactured as a twisted bundle of the conductors 30. Each of these conductors 30 is typically a copper wire surrounded by an electrically insulating material such as rubber. When the cable system 20 is used, digital electrical signals, typically in SCSI (small computer systems interface) format, are transmitted across the digital electrical signal conductors 30.

A core ground plane conductor 32 overlies the plurality of insulated digital electrical signal conductors 30. The core ground plane conductor 32 is preferably a metallized foil wound tightly over the digital electrical signal conductors 30. As used herein, a "metallized foil" can include a thin metal (e.g., aluminum) foil, a nonmetallic material that has been coated with a metallized coating (e.g., aluminum-coated mylar), or other electrically conducting, flexible material suitable for use as a ground plane conductor in a flexible cable.

The function of the core ground plane conductor 32 is to provided an electrically conducting barrier overlying the plurality of insulated digital electrical signal conductors 30, which barrier is grounded as will be discussed. This grounded barrier shields the insulated digital electrical signal conductors 30 from external electromagnetic interference. The term "wound tightly" is used in the manner known to those who build electrical cables, meaning that the metallized foil is wound over the conductors 30 with sufficient tension applied during winding that the metallized foil closely contacts the bundle of conductors 30. Because each of the conductors 30 is itself electrically

insulated, the presence of the metallized foil does not cause shorting of the conductors 30.

The annular sheath 26 includes a plurality of insulated analog electrical signal conductors 34. Each of these conductors 34 is typically a copper wire surrounded by an electrically insulating material such as rubber. When the cable system 20 is used, analog electrical signals are transmitted across the analog electrical signal conductors 34. The analog electrical signal conductors 34 are preferably wound around the central core 24 in a spiral fashion. The analog electrical signal conductors 34 are wound upon, and closely contact, the core ground plane conductor 32.

A sheath ground plane conductor 36 overlies the plurality of insulated analog electrical signal conductors 34. The sheath ground plane conductor 36, like the core ground plane conductor 32, is preferably a metallized foil, but in this case wound tightly over the analog electrical signal conductors 34. The function of the sheath ground plane conductor 36 is to provided an electrically conducting barrier overlying the plurality of insulated analog electrical signal conductors 30, which barrier is grounded as will be discussed. This grounded barrier shields the insulated analog electrical signal conductors 34 from external electromagnetic interference. As shown in Figure 2, the insulated analog electrical signal conductors

34 serve to separate the sheath ground plane conductor 36 from the core ground plane conductor 32 and to electrically isolate the sheath ground plane conductor 36 from the core ground plane conductor 32. Stated in another way, the analog electrical signal conductors 34 are captured between the core ground plane conductor 32 and the sheath ground plane conductor 36. Each of the analog electrical signal conductors 34 is closely contacted on at least two sides by the ground plane conductors 32 and 36. Because each of the conductors 34 is itself electrically insulated, the presence of the ground plane conductors 32 and 36 does not cause shorting of the conductors 34. The close contact by the ground plane conductors 32 and 36 to each of the analog electrical signal conductors 34 serves to shield the conductors 34 more effectively and to prevent electrical cross-talk between the conductors 34 more effectively than if the conductors 34 were simply bundled (and twisted) and covered by a single ground plane

conductor, as in a conventional shielded analog cable.

The annular sheath 26 is covered by the outer covering 28, which is preferably a flexible insulating material such as rubber, an artificial polymer, or a woven fabric. Various electrical connectors are positioned at the ends of the signal conductors 30 and 34, and the ground plane conductors 32 and 36. At a first end 38 of the flexible portion 22 of the cable system 20, a first digital connector 40 electrically communicates with a first end of each of the plurality of insulated digital electrical signal conductors 30. At the first end 38 of the cable, a core ground plane connector 42 electrically communicates with a first end of the core ground plane conductor 32. At the first end 38 of the cable, a first analog connector 44 electrically communicates with a first end of each of the plurality of insulated analog electrical signal conductors 34. At the first end 38 of the cable, a sheath ground plane connector 46 electrically communicates with a first end of the sheath ground plane conductor 36. In a preferred embodiment, the connectors 40, 42, 44, and 46 are all incorporated into a single first-end connector 48, and are depicted as pins of that first-end connector 48.

In a preferred version of the cable system 20, the sheath 26 extends less than the entire length of the central core 24. A portion 50 of the central core 24 therefore extends beyond a second end 52 of the sheath 26 to a second end 54 of the core 24. (The outer covering 28, which overlies the annular sheath 26 when present, instead overlies the central core 24 in the portion 50.)

At the second end 52 of the sheath 26 a second analog connector 56 electrically communicates with a second end of each of the plurality of insulated analog electrical signal conductors 34. At the second end 54 of the core 24 a second digital connector 58 electrically communicates with a second end of each of the plurality of insulated digital electrical signal conductors 30. In the preferred embodiment, the second analog connector 56 are captured within an analog connector housing 60 and extend through openings therein. The second digital connectors 58 are incorporated into a second-end connector 62, and are shown as pins therein.

This arrangement of connectors is used so that the second-end connector

62 can be plugged into a digital video display device. The second analog connectors 56 can be separately plugged into various analog input or output devices such as earphones, a microphone, a mass storage device, or the like. Placement of the second analog connectors 56 at an intermediate location between the first end 38 and the second end 52 provides space for the user of the system to conveniently make the plug connections.

In a preferred embodiment, an analog signal processing circuit 64 electrically communicates with the plurality of insulated analog electrical signal conductors 34. The analog signal processing circuit 64 is positioned along the length of the plurality of analog electrical signal conductors 34 at a location intermediate the first analog connector 44 and the second analog connector 56. In the illustrated version, the analog signal processing circuit 64 is positioned immediately adjacent to the second analog connector 56 on a small card that fits within the analog connector housing 60. The analog signal process circuit typically is an amplifier so that amplified signals can be transmitted along the length of the insulated analog signal conductors 34.

Figure 3 illustrates the connection of the first end of the cable system 20 to a system, such as a computer system 70, that transmits and/or receives the digital and analog signals over the cable system 20. The ground plane conductors 32 and 36 are grounded to the respective digital and analog circuits within the computer system 70 that communicate with the digital signal conductors 30 and analog signal conductors 34. This grounding approach ensures the most effective shielding of the digital signal conductors 30 and the analog signal conductors 34, because any noise on the respective conductors 30 and 34 will also be impressed upon their respective ground plane conductors 32 and 36.

More specifically, the first end connector 48 is plugged into a corresponding connector 72 of the computer system 70. The digital signal conductors 30 communicate (via paths 30') with a digital processing region 74 of a processing card 76 within the computer system 70. The core ground plane conductor 32 communicates (via path 32') with a digital ground 78 in the same digital processing region 74. Similarly, the analog signal conductors 34 communicate (via paths 34') with an analog processing region 80 of the

processing card 76. The sheath ground plane conductor 36 communicates (via path 36 ^* ) with an analog ground 82 in the same analog processing region 80. The digital ground 78 and the analog ground 82 are connected to a common ground 84, or they may be independently grounded. However, even when they are connected to the common ground 84, the signal on each ground 78 and 82 reflects the interference found on the respective lines 32 and 34 because substantially no current flows between the grounds 78 and 82.

The cable system 20 provides a convenient, neat packaging, within a single cable, of the digital and analog conductors that are used in driving a multimedia system. Multiple individual cables are not required. Additionally, the cable system 20 provides important technical benefits in providing improved shielding for the analog signal conductors 34. The digital ground plane conductor 32 and the sheath ground plane conductor 36 have the same interference imposed thereon as found on the respective digital signal conductors 30 and analog signal conductors 34, ensuring effective shielding of the conductors 30 and 34. Lastly, positioning of the second analog connectors 56 at an intermediate location permits convenient plug attachments of analog devices to the cable system.

Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.