Electrical connectors – With insulation other than conductor sheath – Plural-contact coupling part
Reexamination Certificate
1999-12-02
2002-06-25
Sircus, Brian (Department: 2839)
Electrical connectors
With insulation other than conductor sheath
Plural-contact coupling part
C439S941000, C439S620040
Reexamination Certificate
active
06409547
ABSTRACT:
This invention relates to modular, multi-component connectors for high frequency data transmission, and particularly to connectors with compensation structures that balance cross-talk generated within the connectors.
BACKGROUND
Over the last decade, the deployment of new computer network architectures has increased the demand for improved data communication cables and connectors. Initially, conventional cables and connectors were used for voice transmission and for low speed data transmission in the range of a few megabits per second. However, because conventional data cables and connectors were inadequate for high speed, bit-error-free data transmission within current or proposed network architectures, new types of high speed data communication cables and connectors have been developed. Such new cables or connectors need to meet specific requirements such as low attenuation, acceptable return loss, low cross-talk and good EMC (ElectroMagnetic Compatibility) performance parameters. They also need to meet specific requirements with respect to impedance, delay, delay skew and balance.
Cables for transmitting high speed digital signals frequently make use of twisted pair technology, because twisted pairs eliminate some types of cross-talk and other noise. Near end cross-talk (NEXT) in one twisted pair arises from the neighboring “disturbing” pairs inside the same cable. The cross-talk depends inversely on the square of the distance between the twisted pairs. In a twisted pair, each wire of the pair carries an information signal that is equal in amplitude and 180° out of phase with the counter-part signal carried by the pair. That is, each twisted pair carries differential signals. Ideally, the proximity of the twisted pairs to each other causes cross-talk to affect both wires of the pair equally. Thus, this noise ideally appears in both wires of the twisted pair creating a common mode signal. Cross-talk coupled to the same pair within the same cable can be compensated by adaptive amplifier techniques that substantially reject common mode signals. However, differential noise coupled to a twisted pair cannot be compensated for.
Cross-talk is a measure of undesirable signal coupling from one signal-carrying medium to another. Several different measures of cross-talk have been developed to address concerns arising in different cables, communications systems and environments.
One useful measure of cross-talk is near-end cross-talk (NEXT). NEXT is a measure of the signal coupled between two media, e.g., two twisted pairs, within a cable. Signal is injected into one end of the first medium and the coupled signal is measured at the same end of the second medium. Another useful measure of cross-talk is far-end cross-talk (FEXT). Like NEXT, FEXT is a measure of the signal coupled between two media within a cable. A signal is injected into one end of the first medium and the coupled signal is measured at the other end of the second medium. Other measures of cross-talk, including cross-talk of other types exist. For example, so called alien cross-talk, which is coupling into a signal-carrying medium from outside of a cable, may also be of interest. However, issues pertaining to alien cross-talk are not addressed here.
A modular connector usually includes a modular plug that is mated with a jack that has a receptacle-type opening. The modular plug includes a set of contacts and a dielectric housing having a wire-receiving end, a contact-terminating end, and a passageway used for both communicating internally between the respective ends and receiving a plurality of conductors (or a set of rear terminals to be connected to the wires). Some plugs may include a passageway with two surfaces that separate selected pairs of the wires within the limits of the housing. A patch cord cable assembly includes a data transmission cable, typically with four twisted wire pairs, and two plugs. The four twisted pairs may be wrapped in a flat or a round insulating sheath. The bundle may optionally include a drain wire and a surrounding shield for use with a shielded plug. The goal is to minimize the EMC issues and EMI coupling to the outside environment as required by various regulations.
Modern data networks have the data transmission cables built into the walls of a building and terminated by a modular connector system to enable flexible use of space. Individual computers are connected to the network, using a patch cord cable assembly, by inserting a connector plug into a connector jack (or a receptacle).
Many prior art connector systems have been used to transmit low frequency data signals, and have exhibited no significant cross-talk problem between conductor wires of different twisted pairs at these low frequencies. However, when such connectors are used for transmission of high frequency data signals, cross-talk between different pairs increases dramatically. This problem is caused basically by the design of the prior art connectors, wherein the connector electrical paths are substantially parallel and in close proximity to each other, producing excessive cross-talk.
A number of popular modular, multi-conductor connectors have been used in telecommunication applications and data transmission applications. Such connectors include 4-conductor, 6-conductor and 8-conductor types, commonly referred to as RJ-22, RJ-11 and RJ-45 as well as other types of connectors of similar appearance. In the detailed description provided below, we will illustrate various novel concepts in connection with an 8-conductor connector system designed for high-frequency data transmission.
An 8-conductor connector system (e.g., an RJ-45 type connector system) includes a modular jack and a plug made from a plastic body surrounding and supporting eight signal-carrying elements. Specifically, an RJ-45 type plug has eight conductive elements located side-by-side. Each conductive element has a connecting portion, attached to a signal-carrying conductor, and a contact portion. An RJ-45 type jack also has eight conductive elements located side-by-side, and each conductive element has a connecting portion and a contact portion arranged as a cantilever spring. The eight conductive elements are connected to four twisted pairs in a standard arrangement. The entire connector may include a conductive shield.
As mentioned above, the modular connector system has the conductive elements placed straight in parallel and in close proximity to each other. The close proximity increases the parasitic capacitance between the contacts, and the straight parallel arrangement increases the mutual inductance between the contacts. These are a principle source of differential noise due to coupling. Specifically, the connector cross-talk occurs between the electric field of one contact and the field of an adjacent contact within the jack or the plug. The cross-talk coupling is inversely proportional to the distance between the interfering contacts. The signal emitted from one conductive element is capacitively or inductively coupled to another conductive element of another twisted pair. Since the other contact element is at a different distance from the emitting element, this creates differential coupling.
Standardization of equipment is in the interest of both manufacturers and end users. The performance requirements are specified in IEEE 802.3 for both the 10Base-T and the 100BaseTX standards, where the data is transmitted at 10 Mbps and 100 Mbps at frequencies above 10 MHz and 100 MHz, respectively. The transmission parameters, including attenuation, near-end cross-talk and return loss, are defined in EIA/TIA-568-A for unshielded twisted pair (UTP) connectors.
In an attempt to reach cross-manufacturer compatibility, EIA/TIA mandates a known coupling level (Terminated Open Cross-talk) in a Category 5 plug. The modular connector system may include counter-coupling or compensation structures designed to minimize the overall coupling inside the connector system. Counter-coupling, as used herein, relates to the generation of a signal within a pair of elements of th
NORDX/CDT Inc.
Sircus Brian
Wolf Greenfield & Sacks P.C.
Zarroli Michael C.
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