WO1999019886A1

WO1999019886A1 - Isolated and floating shielded cable system

Info

Publication number: WO1999019886A1
Application number: PCT/US1998/021903
Authority: WO
Inventors: Matthew Bond
Original assignee: Tara Labs, Inc.
Priority date: 1997-10-16
Filing date: 1998-10-16
Publication date: 1999-04-22

Abstract

A shielded cable system for delivering an audio and/or video signal from a source component (15) to a load component (17) with a minimum of RF and/or EMI interference. The shield in the cable is not connected at its ends to the connectors of the cable. Instead, the RF and EMI interference which is picked up by the shield is attenuated through a connection to the shield which is external to both the signal-carrying conductor in the shield and the shield itself.

Description

ISOLATED AND FLOATING SHIELDED CABLE SYSTEM

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to shielded cable systems which reduce radio frequency (RF) and electromagnetic interference (EMI) . This invention more specifically relates to shielded cable systems of this type which transmit audio and/or video signals.

Description of Related Art

Today's¹ audio and/or video systems often consist of a set of physically-separated components. This is particularly true in high-end systems.

Among the components which are typically separated are the source of the audio and/or video signal, such as a CD player, tape deck, FM tuner, TV tuner or VCR, and the load to which that source is connected, such as a pre-amplifier or amplifier.

The voltage level of the source signal is typically low. The impedance of the source, on the other hand, is typically high. The combination of a relatively- low level signal delivered over a relatively-high impedance line makes the signal particularly susceptible to interference from undesirable outside sources, such as RF and EMI . The interference becomes more pronounced as the separation distance between the source and load components increases. This is particularly problematic in high-end systems where the separation distance is often several feet .

One technique which has been used for many years to reduce this interference is to shield the signal-carrying conductor. In a typical system, connectors are fixed to each end of a conductor which mate with corresponding connectors on the source and load components. The shield is formed with a wire mesh or metallic foil which surrounds the conductor, but is electrically isolated from it. The ends of the shield are also electrically and mechanically connected to the connectors at the end of the conductor, but to a portion of the connectors which is electrically isolated from the portion of the connectors which carries the signal . The isolated portion of the connectors is typically provided with a low potential upon connection to the component, thus providing a pathway for directing the interference which the shield picks up away from the signal-carrying conductor.

This configuration, however, is not without problems. Interference current traveling through the shield still causes interference to the signal traveling through the signal-carrying conductor due to the coupling between the two. That same coupling similarly attenuates the signal which is traveling through the signal-carrying conductor, attenuation which is particularly problematic because the magnitude usually varies as a function of the frequency of the signal .

In an effort to reduce the problems caused by the coupling between the shield and the signal-carrying conductor, filters have been inserted in the path of the shield and/or the signal-carrying conductor, including ferrite filters and network filters. Although helpful, the problems caused by the coupling of the shield to the signal-carrying conductor continue at discernible levels.

SUMMARY OF THE INVENTION

One object of the present invention is to obviate these as well as other problems in prior art shielded cable systems . Another object of the present invention is to provide a shielded cable system which substantially attenuates interference from RF and EMI .

Another object of the present invention is to provide a shielded cable system which effectively reduces outside interference, while having minimal effect upon the signal which the system is carrying.

Another object of the present invention is to provide a shielded cable system which is inexpensive to manufacture and easy to install . A still further object of the present invention is to provide an effective shielded cable system which is readily adaptable to existing audio and/or video components . These as well as still further objects, features and benefits of the present invention are achieved by using a floating shield which is isolated and not terminated at either end of the signal -carrying conductor. An attenuator for attenuating the RF and/or EMI picked up by the shield is electronically connected to the shield, but located remotely from it .

In one embodiment, the attenuator includes a block, also external to the shield and signal-carrying conductor, which is electrically connected to ground. In another embodiment, the attenuator includes a filter tuned to filter out the interference, but not the signal which is being carried by the signal -carrying conductor. These as well as still further features, objects and benefits of the present invention will now become apparent upon a study of the attached drawings and the description of the preferred embodiments which will now be set forth.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 illustrates a typical prior art shielded cable system.

Fig. 2 is a cross-section of one of the cables shown in Fig. 1.

Fig. 3 is a cross-section of a prior art twin-axial cable.

Fig. 4 illustrates a prior art cable using a ferrite filter.

Fig. 5 illustrates a prior art cable using a network filter. Fig. 6 illustrates a portion of a shielded cable system incorporating one embodiment of the present invention which uses an external connection to ground.

Fig. 7 illustrates a portion of a shielded cable system incorporating a still further embodiment of the present invention in which the ends of the shields are not electrically interconnected.

Fig. 8 illustrates a portion of a shielded cable system incorporating another embodiment of the present invention which does not use an external connection to ground .

Fig. 9 illustrates a ferrite filter which may advantageously be used in connection with one embodiment of the present invention. Fig. 10 illustrates a network filter which may advantageously be used in connection with another embodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS Fig. 1 illustrates a typical prior art shielded cable system.

As shown in Fig. 1, the shielded system includes a shielded cable 1 containing a signal -carrying conductor 3 and a shield 5. A connector 7 is mechanically attached to one end of the cable 1 and a connector 9 is mechanically attached to the other end of the cable 1. The connector 7 includes a tip 11 electrically connected to one end of the signal-carrying conductor 3. The connector 9 includes a tip 13 electrically connected to the other end of the signal -carrying conductor 3. The cable 1 further includes a shield 5 substantially surrounding the signal-carrying conductor 3 and electrically and mechanically connected at one end to the connector 1 and at the other end to the connector 9. The shielded cable 1 is typically used to electrically connect a signal source 15, such as a CD player, FM tuner, TV tuner, or VCR, to a signal load 17, such as a pre-a plifier or amplifier. As is well known in the art, this is typically accomplished by inserting the connector 7 into a mating connector 19 which is part of the signal source component 15 and inserting the connector 9 into a mating connector 21 which is part of the signal load component 17. As is also well known, the cylindrical outer-surface of the connectors 19 and 21 area usually connected to a ground or a near-ground source of potential, thus providing a pathway for attenuating the interference which is picked up by the shield 5. Within the center of the connectors 19 and 21, of course, is also a connection (not shown) for electrically and mechanically mating with the tips 11 and 13, respectively.

The shielded cable system shown in Fig. 1 also often includes a second shielded cable 23 containing components essentially the same as the first shielded cable 1. The second shielded cable 23 is typically advantageously used to interconnect a second source of signal information from a connector 25 on the signal source component 15 to a connector 27 on the signal load component 17. The signals delivered over shielded cables 1 and 23 could be the left and right audio channels. Alternatively, one signal could be audio, while the other could be video. A third connection (now shown) is also frequently used on the signal source component 15 and the signal load component 17, two of the connections typically carrying the left and right audio channels and the third (not shown) carrying a baseband video signal . Audio and video could also be mixed into a single signal. Signals unrelated to each other could also be delivered over the pair of cables 1 and 23. Alternatively, a single signal could be delivered in a highly-balanced system over two signal-carrying wires, one being delivered by the cable 1 and the other being delivered by the cable 23. A broad variety of other assortments of audio, video and/or audio and video signals are also advantageously channeled over the signal cable 1 or the pair of cables 1 and 23.

Fig. 2 is a cross-section of the cable shown in Fig. 1. As shown in Fig. 2, the cable 1 includes the signal - carrying conductor 3, the shield 5, and insulating material 29 to insulate the signal-carrying conductor 3 from the shield 5.

Fig. 3 is a cross-section of a twin-axial prior art cable 31. As is well known in the art, such a cable includes a first signal-carrying conductor 33, a second signal-carrying conductor 35, and a shield 37. The signal-carrying conductors 33 and 35 are insulated from one another and from the shield by insulating material 39. Shielded cables of the type shown in Fig. 1 have also been advantageously used in the prior art in connection with twin-axial cables, such as the twin-axial cable illustrated in Fig. 3. As is also well known in the art, there are a broad variety of other configurations of shielded cables, including cables with more than two signal-carrying conductors, cables containing multiple shields, and cables having cross- sections which are not circular.

As is also well known in the art, a broad variety of mating connectors can advantageously be used to mechanically and electrically connect the shielded cables to the signal source component and the signal load component. Examples of these include RCA-type connectors and [describe other types] .

In almost all of these shielded cable systems, however, RF and EMI interference are not entirely shielded from the signal-carrying conductor. In part, this is due to the coupling which exists between the shield and the signal-carrying conductor. In some cases, the shielded cable works poorly because the electrical connection which is made to the shield through the connector on the signal source component and/or the signal load component is not at true ground potential.

Another typical problem with this type of shielded cable system is that it causes attenuation of the signal being carried by the signal-carrying conductor in amounts which often differ depending upon the frequency of that signal. This constitutes an additional source of undesired signal distortion. One attempt which has been made in the prior art to reduce these distortions has been to insert a filter inline with the shielded cable. Fig. 4 illustrates a prior art cable using such filter, a ferrite filer. As shown in Fig. 4, the shielded cable 33 is run through the center of a ferrite filter 35 just before the shielded cable 33 is connected to a connector 37.

Fig. 5 illustrates another type of in-line filter which has been used in the prior art, a network filter. As shown in Fig. 5, an C network 39 is connected to the signal-carrying leads 41 and 43 of a shielded cable 45. The components in the network 39 are selected to allow the signal in the signal -carrying conductors 41 and 43 to pass without substantial alteration, but to attenuate any RF and/or EMI interference which has been induced into the signal-carrying conductors, notwithstanding the presence of a shield (not shown) around the signal - carrying conductors .

Even with filters, such as the filters illustrated in Figs. 4 and 5, however, RF and/or EMI continue to cause discernible distortions to the signal being carried in the signal-carrying conductor. The shield surrounding the signal-carrying conductor also continues to cause discernible attenuation in the signal being carried by the signal-carrying conductor in amounts which often differ as a function of the frequency of that signal . In-line filters also often cause additional distortions.

Fig. 6 illustrates a portion of a shielded cable system incorporating one embodiment of the present invention which uses an external connection to ground. As shown in Fig. 6, this embodiment includes a shielded cable 51 containing a shield 53, insulating material 55, a signal-carrying conductor 57, and end connectors 59 and 60.

With one significant exception, the shielded cable 51 is in all ways like the shielded cable 1 shown in Fig. 1, as well as all of the variations of the shielded-cable 1 which have been discussed above or are otherwise known in the prior art. The one significant exception, however, is that the shield 53, unlike the shield 5 shown in Fig. 1, is not electrically connected at its ends to the connectors 59 and 60. Rather, the shield 55 is electrically floating. Floating and isolating the shield 53 from the grounded ends of the shielded cable 51 minimizes the coupling between the shield 53 and the signal-carrying conductor 57. This minimizes the effect of RF and EMI currents flowing through the shield 53 on the signal in the signal-carrying conductor 57, while at the same time minimizes the attenuation which the shield 53 causes to the signal being carried by the signal -carrying conductor 57.

At the same time, of course, it is necessary to attenuate the RF and EMI interference which is picked up by the shield 53 in order to protect the signal-carrying conductor 57 from this interference. To enhance the degree of isolation between the shield 53 and the signal - carrying conductor 57, however, this is done by connecting the shield 53 through an interference conductor 60 to an attenuator 63 located remotely from the signal-carrying conductor 57 and the shield 53. This permits the shield 53 to maintain a substantially isolated and floating relationship to the signal-carrying conductor 57, while at the same time provides a pathway for the attenuation of RF and EMI interference which is picked up by the shield 53.

There are a broad variety of embodiments which the attenuator 63 can take, only one of which is illustrated in Fig. 6. The attenuator 63 which is illustrated in Fig. 6 is simply a block which functions to interconnect the interference conductor 60 to a ground source 65 through a ground conductor 67. As shown in Fig. 6, the ground source 65 is a connection to a ground potential on the chassis of a signal load component 69. Although the chassis of the signal load 69 is illustrated in Fig. 6 as the electrical ground, it is, of course, to be understood that numerous other sources of an electrical ground could instead be used. For example, the ground could be the chassis of the signal source (not shown in Fig. 6) , the chassis of another component in the system, the center of a star- ground, a water pipe, or the ground conductor in the wall outlet. Preferably, the ground connection represents as low a potential as is available in the system. Typically, the external ground connection which is used in connection with the present invention will be at a potential which is lower than the potential of the ground connection provided by the connectors on the signal source component or the signal load component to which the signal-carrying conductor is connected, such as the connectors 19, 21, 25 or 27 shown in Fig. 1. As also illustrated in Fig. 6, a detachable set of mating connectors 71 and 73 are advantageously used to connect the interference conductor 60 to the block 63. Similarly, a detachable set of connectors 75 and 77 are advantageously used to connect the ground conductor 67 to the block 63. Although banana-type connectors are shown, other connectors, preferably having very low resistance, can also advantageously be used. These connectors facilitate quick and easy installation of the shielded cable system of the present invention. Of course, connectors are not needed in all embodiments.

As with the prior art system shown in Fig. 1, a second cable 79 configured identically or similarly to the first cable 51 is also shown in Fig. 6. As with the shielded cable 51, a shield 81 on the second cable 79 is also isolated and floating and connected through an interference conductor 83 through a detachable set of connectors 85 and 87 to the ground block 63. Although the interference conductors 60 and 83 are shown in Fig. 6 as both being connected to the same block, it is, of course, to be understood that separate attenuators could be used to attenuate the RF and EMI interference in the shields 53 and 81. In the configuration shown in Fig. 6, however, a single block connected to a single ground is utilized to perform both attenuating functions, thus providing a more economical approach.

The interference conductors 61 and 83 are shown in

Fig. 6 as being connected to one end of the respective shields 53 and 81. In other embodiments of the invention, however, these interference conductors could be connected to other portions of the shields.

In the embodiment shown in Fig. 6, the ends of the shields 53 and 81 which are not connected to the interference conductors are electrically connected to one another by a shield interconnection conductor 91. Although advantageous in some embodiments, other embodiments of the invention will not utilize this shield interconnection conductor, but rather will function with this end of the shields completely unconnected electrically. This alternate embodiment is partially illustrated in Fig. 7.

As mentioned above, the block 63 embodiment shown in Fig. 6 for the attenuator is but one example of the many forms which the attenuator can take. Fig. 8 illustrates a portion of a cable system incorporating a still further embodiment of the present invention utilizing a different form of an attenuator in which no connection to an external ground is made. As shown in Fig. 8, a first shielded cable 101 and a second shielded cable 103 made in accordance with one embodiment of the present invention are shown as connected to a form of attenuator called a floating block 105 through an interference conductor 107 and an interference conductor 109, respectively. To effectuate attenuation, the floating block 105 can advantageously use a filter 111. The filter 111 can advantageously include a ceramic composite device, such as a ferrite filter 113 shown in Fig. 9. It can in addition or alternatively include a network filter 115 as illustrated in Fig. 10, i.e., a filter containing components such as an inductor 117 and a capacitor 119. Resistive elements could also be included, the elements being selected and interconnected in accordance with well-known techniques to attenuate the RF and EMI interference, while minimizing the attenuation of the signal being carried by the signal-carrying conductor.

Although having now described certain embodiments of the present invention, it is, of course, to be understood that the present invention encompasses numerous other embodiments. For example, although only passive filters have thus-far been described as being used in conjunction with the present invention, it is to be understood that active filters could instead or in addition be used. Although only a single shield has been illustrated in the shielded cable of the invention, multiple shields could also be used, all, some or only one of which is connected and processed in accordance with the concepts of the present invention. In a multiple shield configuration, for example, one shield could be left floating and isolated and could then be externally attenuated in accordance with the concepts of the present invention, while the other shield could be electrically-connected to the connectors at the end of the shielded cable, as was done in the prior art. The invention is also applicable to a broad variety of cable configurations, other than the configurations which have been illustrated in the drawings, such as cables containing multiple signal - carrying conductors, signal-carrying conductors which are individually and/or collectively shielded, and cables terminating in connectors other than the types shown in the drawings. A broad variety of shields could also be used, such as metallic or foil shields. The filter networks which are used could be of the multiple-pull variety, as well as other types. In short, the present invention is limited solely by the claims which are now set forth.

Claims

I CLAIM :

1. A shielded cable system for delivering the

audio, video, or audio and video signal from a source

component connector to a load component connector while

minimizing RF and/or EMI intereference with the signal,

the source component connector being part of a source

component and the load component connector being part of

a load component, said shielded cable system comprising:

an elongated signal-carrying conductor for

conducting the signal between the source component

connector and the load component connector, said signal-

carrying conductor having a source conductor end and a

load conductor end;

a source cable connector electrically and

mechanically connected to said source conductor end for

electrically and mechanically connecting said source

conductor end to the source component connector, said

source cable connector having a configuration which

electrically and mechanically mates with the source

component connector; a load cable connector electrically and

mechanically connected to said load conductor end for

electrically and mechanically connecting said load

conductor end to the load component connector, said load

cable connector having a configuraton which electrically

and mechanically mates with the load component

connector;

an electrical shield substantially shielding

said signal-carrying conductor, but electrically

isolated therefrom and not being electrically terminated

to either said source cable connector or to said load

cable connector;

an interference conductor electrically

connected to said shield, said interference conductor

not being terminated to either said source cable

connector or to said load cable connector; and

an attentuator connected to said interference

conductor and located remotely from said signal-carying

conductor and said shield to attenuate RF and/or EMI

interference picked up by said shield.

2. The system of Claim 1 wherein said attenuator

includes a block located remotely from said signal-

carrying conductor and said shield to which said

interference conductor is connected.

3. The system of Claim 2 wherein the connection

between said interference conductor and said block is

made through a detachable set of connectors .

4. The system of Claim 2 further including a

ground conductor connected to said block for

electrically connecting said block to an electrical

ground .

5. The system of Claim 4 wherein the connection

between said block and the ground is made through a

detachable set of connectors.

6. The system of Claim 4 wherein the source

component connector includes a ground terminal and

wherein the point to which said ground condutor is grounded is closer to ground potential than the ground

terminal .

7. The system of Claim 1 wherein said attenuator

includes a filter.

8. The system of Claim 7 wherein said filter includes a ceramic composite device.

9. The system of Claim 8 wherein said ceramic composite device includes a ferrite filter.

10. The system of Claim 7 wherein said filter includes an network filter.

11. The system of Claim 7 wherein said filter is

passive.

12. A shielded cable system for delivering the

audio, video, or audio and video signals from a first

and second source component connector to a first and second load component connector while minimizing RF

and/or EMI intereference with the signals, the source

component connectors being part of a source component

and the load component connectors being part of a load

component, said shielded cable system comprising:

a first elongated signal-carrying conductor

for conducting the signal between the first source

component connector and the first load component

connector, said first conductor having a first source

conductor end and a first load conductor end;

a second elongated signal-carrying conductor

for conducting the signal between the second source

component connector and the second load component

connector, said second conductor having a second source

conductor end and a second load conductor end;

a first source cable connector electrically

and mechanically connected to said first source

conductor end for electrically and mechanically

connecting said first source conductor end to the first

source component connector, said first source cable

connector having a configuration which electrically and mechanically mates with the first source component

connector;

a second source cable connector electrically

and mechanically connected to said second source

conductor end for electrically and mechanically

connecting said second source conductor end to the

second source component connector, said second source

cable connector having a configuration which

electrically and mechanically mates with the second

source component connector;

a first load cable connector electrically and

mechanically connected to said first load conductor end

for electrically and mechanically connecting said first

load conductor end to the first load component

connector, said first load cable connector having a

configuraton which electrically and mechanically mates

with the first load component connector;

a second load cable connector electrically and

mechanically connected to said second load conductor end

for electrically and mechanically connecting said second

load conductor end to the second load component connector, said second load cable connector having a

configuraton which electrically and mechanically mates

with the second load component connector;

a first electrical shield substantially

shielding said first signal-carrying conductor, but

electrically isolated therefrom and not being

electrically terminated to either said first source

cable connector or to said first load cable connector;

a second electrical shield substantially

shielding said second signal-carrying conductor, but

electrically isolated therefrom and not being

electrically terminated to either said second source

cable connector or to said second load cable connector;

a first interference conductor electrically

connected to said first shield, said first interference

conductor not being terminated to either said first

source cable connector or to said first load cable

connector;

a second interference conductor electrically

connected to said second shield, said second

interference conductor not being terminated to either said first source cable connector or to said second load

cable connector;

a first attentuator connected to said first

interference conductor and located remotely from said

first signal-carying conductor and said first shield to

attenuate RF and/or EMI interference picked up by said

first shield; and

a second attentuator connected to said second

interference conductor and located remotely from said

second signal-carying conductor and said second shield

to attenuate RF and/or EMI interference picked up by

said second shield.

13. The system of Claim 12 including a shield

interconnector conductor electrically connecting said

first and said second shields.

14. The system of Claim 13 wherein said first and

said second sheilds each have two ends; wherein said

first and said second interference condutors are

connected to said first and second shields, respectively, at one end thereof; and wherein said

shield interconnector conductor is connected to said

first and said second shields at the other end thereof.

15. The system of Claim 12 wherein said first and

said second attenuators include a block located remotely

from said first and second signal -carrying condutors and

said first and said second shields to which said first

and said second interference conductors are connected.

16. A shielded cable system comprising a signal-

carying conductor having two ends, a shield for

shielding said signal-carying conductor which is

floating and not terminated at either end of said

signal -carrying conductor, and an attenuator

electrically connected to said shield, but located

remotely from said signal-carying condutor and said

shield for attenuating RF and/or EMI picked up by said

shield.

17. A shielded cable system for delivering the audio, video, or audio and video signal from a source component connector to a load component connector while minimizing RF and/or EMI interference with the signal, the source component connector being part of a source component and the load component connector being part of a load component, said shielded cable system comprising:

an elongated signal-carrying conductor for conducting the signal between the source component connector and the load component connector, said signal- carrying conductor having a source conductor end and a load conductor end;

a source cable connector electrically and mechanically connected to said source conductor end for electrically and mechanically connecting said source conductor end to the source component connector, said source cable connector having a configuration which electrically and mechanically mates with the source component connector;

a load cable connector electrically and mechanically connected to said load conductor end for electrically and mechanically connecting said load conductor end to the load component connector, said load cable connector having a configuration which electrically and mechanically mates with the load component connector;

an electrical shield substantially shielding said signal-carrying conductor, but electrically isolated therefrom and not being electrically terminated to either said source cable connector or to said load cable connector; and

an interference conductor electrically connected to said shield, said interference conductor not being terminated to either said source cable connector or to said loan cable connector.

18. A shielded cable system comprising:

a signal-carrying conductor having two ends ;

a shield for shielding said signal - carrying conductor which is floating and not terminated at either end of said signal- carrying conductor; and

an interference conductor electronically

connected to said shield for re-routing RF and/or EMI

picked up by said shield.