Telephonic communications – Subscriber line or transmission line interface – Protective circuit
Reexamination Certificate
1998-08-19
2001-11-06
Chan, Wing Fu (Department: 2643)
Telephonic communications
Subscriber line or transmission line interface
Protective circuit
C439S616000, C333S185000, C333S202000
Reexamination Certificate
active
06314182
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a system for connecting a multiplicity of cables to an electronic device. The system provides electromagnetic compatibility (EMC) which is typically required in the telecommunication field for the reduction of electromagnetic interference. The cables used with the system are preferably of the twisted pair type commonly used for telecommunication signal transmission.
BACKGROUND OF THE INVENTION
The technical advances occurring in the field of electronics, and more particularly in the telecommunication field, increasingly requires the connection of a multiplicity of cables to all kinds of electronic equipment. In the case of high-frequency or high-bit rate data transmission, fiber-optic cables and coaxial cables are used. Specific connector systems have been developed for these fiber-optic and coaxial cables which allow the connection of a multiplicity of cables. On the other hand, there is also a broad field in which the frequencies and bit-rate transmissions are lower. Primarily for cost reasons, the cables which are used for lower frequencies and lower bit-rate transmissions are neither of the fiber-optic type nor of the coaxial type, which means that the cables are not individually shielded in some way. However to provide some electromagnetic compatibility, these “low speed” cables are formed into so-called “twisted pairs” which provide a minimum of electronic shielding. Such electronic shielding is supposed to prevent an electronic shielding is supposed to prevent an interaction between the individual communication lines {known as cross-talk), as well as interaction between the cable and the outside environment (typically referred to as electromagnetic compatibility).
When using twisted pair cables, a multiplicity of cables are typically brought into the form of a bundle of cables which has a common outer sheath. To meet the requirements for the necessary electromagnetic compatibility, one possibility is to make the outer sheath a common electromagnetic shield for the entire bundle of cables. Such systems for connecting the multiplicity of cables to electronic equipment then include such a shielded bundle which is connected to a connector having a multiplicity of contacts. Such cable assemblies and connectors are well known and are described, for example, in the German Offenlegungsschrift DE 42 44 225 and the European Patent Application EP 0 041 595.
Another possibility for meeting the electro-magnetic compatibility requirements is to utilize cables where the conductor is surrounded by an insulation layer which itself provides a contribution to the shielding. This can be achieved, for example, by adding ferrite particles to the insulation layer as described in U.S. Pat. Nos. 5,170,010 and 5,313,017. Alternatively, the insulating layer may consist of a material that has a relatively high dielectric constant (e.g., more than 4) as described in the European Patent Application EP 0 190 939. Yet another alternative is to give the insulation layer a high magnetic permeability as referred to in the German Offenlegungsschrift DE 40 41 374 or to build in an electrically conductive resin layer using carbon fibers as described in the European Patent Application EP 0 596 896.
A certain level of electromagnetic shielding can generally be obtained by simply twisting the signal conductor and the ground conductor around each other (thereby giving rise to the term “twisted pair cable”). The twisted pairs can, for example be bundled together and provided with a common shield as it can be seen in the U.S. Pat. No. 4,218,580.
A number of variations for twisted pair cables can be devised. One possibility is to have two signal conductors and one ground conductor, with the three conductors being twisted around each other as referred to in the Japanese Patent Application JP 7-326 229.
Another possibility is described in the references JP 9-259 655, JP 8-321 220 and U.S. Pat. No. 5,659,152. In all these references, bundles of twisted pair cables are used in which the individual twisted pairs have different pitches. It has been shown that through these configurations it is possible to reduce the cross-talk and to meet certain levels of the above mentioned standards for electromagnetic compatibility.
Although special cables having specific dielectric or twisted pair configurations with a complex geometrical structure may provide the needed electro-magnetic compatibility, the use of such special cables is not generally acceptable. Specifically, such special cables typically have either a high material cost or their somewhat complicated configuration does not allow the utilization of these cables in great quantities and without a specific adjustments. Thus, the general practice is to operate with standardized twisted pair cables having a simple configuration, and bringing multiple cables into a bundle of cables which, however, is not additionally protected with an outer conductive shield.
Therefore, as a possible solution to provide the necessary electro-magnetic compatibility another approach has been taken. Specifically, it has become common to utilize additional electrical or electronic filters to reduce cross-talk and signal noise. The filters are typically passive filters comprising at least a capacitor, and preferably a combination of capacitors and inductors. Currently, these filters are known to be built into the cable connectors. This can, for example, be seen from the German Offenlegungsschrift DE 36 24 571, the European Patent Application EP 0 467 400 and the European Patent Application EP 0 366 965. Typically, these filters are built into the contact pin configuration of the connector. EP 0 366 965 shows a somewhat more advanced configuration in which the contact pin
50
(see
FIG. 5
) is surrounded with three cylindrical components, the middle component providing an inductor, the two outer components having the form of a concentric capacitor. The inner electrode of this concentric capacitor is electrically and mechanically connected to the central pin, while the outer electrodes are connected to the common ground of the entire connector system into which the filter is built. Typically, filters with this configuration are inserted into a holder (see
FIG. 2
) which allows the connection to a common electrical ground.
The connectors with built in filters are also described in the European Patent Applications EP 0 410 5 769, EP 0 339 802, EP 0 601 327 and EP 0 382 148, the German Offenlegungsschrift DE 38 08 330 and the Japanese Patent Application JP 9-199 238. In all these cases, the general construction is more or less as described above utilizing essentially cylindrical capacitors.
Connector configurations which utilize built-in filters, however, have disadvantages. In particular, a certain minimum spacing between the contact pins of the connector must be maintained, as the capacitors which are assembled onto the contact pins require additional space. This is, for example, particularly critical when higher currents (e.g., on the order of several amps) have to be transmitted (such as for the power supplies of high-power fluorescent lamps which are driven with higher frequencies), and where simultaneously electro-magnetic compatibility is required. Therefore, connectors with built-in filters cannot be utilized when a miniaturized connector is required. Furthermore, connectors with built-in filters are typically pre-designed and pre-assembled and, therefore do not allow for any modification of the built-in filters. Thus, it is necessary to build different connectors for each different electrical requirement. Building different connectors for each different electrical requirement is clearly not practical given the almost limitless variations of capacities and inductances which may be needed.
On the other hand, the utilization of filters offers a relatively simple way to meet the requirements for electro-magnetic compatibility as compared to the above-described alternative solutions. An additional possibility would be to build the f
3M Innovative Properties Company
Chan Wing Fu
Florczak Yen Tong
McNutt Matthew B.
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