Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
2000-12-04
2001-12-25
Gaffin, Jeffrey (Department: 2841)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C361S767000, C361S777000, C361S792000
Reexamination Certificate
active
06333472
ABSTRACT:
This invention relations to the reduction of crosstalk in data transmission systems, and more particularly to the reduction of crosstalk associated with connectors in data communication systems.
It is well recognised that when a signal is applied to a pair of unshielded conductors a signal will be induced in adjacent conductors. This phenomenon is known as “crosstalk” and the induced signal is, so far as the conductor in which it is induced is concerned, a noise signal which reduces the signal-to-noise ratio of the conductor.
Data communication systems frequently use cables consisting of four pairs of conductors. Each pair of conductors is twisted together and such cables are generally known as “UTP” (standing for “Unshielded Twisted Pair”) cables. The problem of crosstalk within such cables is adequately addressed by varying the twist rate of the individual pairs and by other expedients known to those skilled in the art. A problem arises, however, at points within a system where connections must be made between the UTP cable and another cable or fixed installation. Within the zone of such connections the pairs must be separated from each other, and, at least to some extent, each pair must be untwisted in order to form a connection. This disruption of the standard pattern of the UTP cable produces crosstalk in the zone of the connection.
The problem is particularly acute, but is not limited to, connectors which comprise a plug and jack socket for forming a releasable connection. In the most commonly used wiring convention (known as RJ45) the conductors of a four pair UTP cable are separated and are connected to eight parallel contacts of a plug. A socket of the jack, into which the plug is in use, inserted, has eight parallel contacts for mating with the eight contacts of the plug. This arrangement of parallel contacts on the plug and parallel contacts on the jack gives rise to significant crosstalk. Further, in many installations it is impractical to connect a cable direct to the jack and accordingly the jack socket is mounted on a circuit board on which is also mounted one or more connectors for receiving conductors to be connected to the jack. Tracks on the circuit board connect the connectors to the contacts of the socket. These tracks may also give rise to crosstalk.
The problem is particularly acute in the case of the RJ45 wiring convention since in this case the conductors of one twisted pair are connected to the center two contacts of the jack (by convention pins
4
and
5
) whilst the conductors of another twisted pair are connected to the contacts which are located immediately outwardly of pins
4
and
5
(i.e. Pins
3
and
6
). This arrangement whereby the contacts of the jack associated with one twisted pair are located between the contacts associated with another twisted pair gives rise to particularly high levels of crosstalk between the respective twisted pairs.
A number of solutions to the above problems have been proposed. Notably, United Kingdom patent publication GB-A-2269941 proposes a number of connection arrangements in which the tracks on a circuit board are specially routed with a view to reducing crosstalk. Two distinct arrangements are described within the patent publication. According to one arrangement, if conductors are presented to the circuit board in the order ABCD the tracks are routed on the circuit board so that the tracks associated with conductors A and C are close to each other, but are spaced from the tracks associated with conductors B and D, which are also close to each other. In the second arrangement proposed in GB-A-2269941 the tracks on the board associated with conductors A and C crises-cross each other so as to simulate a twisted effect. Likewise, tracks associated with conductors B and D crises-cross each other to simulate a twisted effect.
In an alternative solution which has been used successfully for a number of years by R.W. Data Limited of 43-45 Salt house Road, Cornwell Business Park, Brackmills, Northampton, NN4 7EX, the circuit board is provided with relatively large areas of copper sheet connected to the respective tracks so that areas of copper sheet on one side of the board associate with areas of copper sheet on the opposite side of the board to form parallel plate capacitors. By appropriately selecting the areas and the tracks to which they are connected a substantial reduction in crosstalk can be obtained.
We have now discovered a further method of reducing crosstalk in such circumstances. The new method offers the advantage that relatively short and direct conductive tracks may be used for connecting the pins of the jack to the pins of the connectors on the circuit boards, but at the same time crosstalk can be reduced to an acceptable level. Further, the new arrangement provides a significant increase in flexibility in circuit board design as compared with either the techniques of GB-A-2269941 or the previous technique of R.W. Data referred to above. It is accordingly believed that the new method can lead to a better overall reduction in crosstalk, eliminating or substantially reducing not only crosstalk associated with the jack itself but also crosstalk induced by the disruption to the normal twisted pair arrangement of conductors which occurs in the immediate vicinity of the Jack and the immediate vicinity of the connections on the circuit board to the cable.
Accordingly, one aspect of the present invention provides a circuit board for use in a connector between cables of a data transmission system, the circuit board comprising at least one array of input terminals for incoming signals, at least one array of output terminals for outgoing signals; a respective conductive track connecting each input terminal to a respective output terminal; and closed loops of conductive material connected to at least some of the terminals or conductive tracks, the loops being positioned on the circuit board to reduce crosstalk from the levels which would exist within the connector in the absence of such closed loops.
The exact size, shape and position of the closed loops will be determined by the crosstalk to be reduced and may vary in light of the particular characteristics of the installation in which the circuit board is to be used. In a typical installation in which a plug and jack socket is used to provide a releasable connection between cables, the closed loops will be sized and positioned so as to eliminate so far as possible the overall crosstalk within the system induced by all conductor arrangements from the point where the conductors of the UTP cable are separated from their standard laid arrangement for connection to the plug to the point where the conductors of the UTP cable are separated from their usual laid arrangement for connection to the connectors provided on the circuit board. Since it is envisaged that the invention will be capable of eliminating or substantially reducing crosstalk of the overall connector it will be appreciated that the exact position and layout of the loops must to some extent be empirically derived once the particular arrangement of the incoming and outgoing cables has been settled. As a general guide, however, it is envisaged that a loop provided on one side of the circuit board and connected to the terminals associated with one conductor of one pair will be matched on the opposite side of the circuit board by a loop connected to the terminals associated with a conductor of another pair.
In some cases a single loop will be provided connected to the terminals associated with one conductor. In other cases, a plurality of loops will be provided. In the case where a plurality of loops are provided, the different loops associated with one pair of terminals may be located on the opposite side of the circuit board and overlying loops associated with a plurality of other terminals. For example, a total of three loops may be connected to the input terminal
1
/output terminal
1
pair, and of these three loops one may be matched on the opposite side of the circuit board by a loop associated wi
Alcala José H
Dykema Gossett PLLC
Gaffin Jeffrey
LandOfFree
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