PLUG AND MATING SOCKET FOR DATA TRANSMISSION SYSTEMS

Abstract: A plug (9) and mating socket for data transfer has four pairs of contacts (1-8), two pairs (1, 2 and 5, 6) located on one side of the plug body (10) and the other two pairs (3, 4 and 7, 8) located on the other side of the plug body. The pairs of contacts are spaced from each other by a distance greater than the spacing of the contacts within each pair, the pairs (1, 2 and 5, 6) on one side of the plug body being offset from the pairs (3, 4 and 7, 8) on the other side of the plug body. Each pair of contacts is connected to one twisted pair of e.g. a UTP cable. The arrangement reduces inter-pair cross-talk.

Description: PLUG AND MATING SOCKET FOR DATA TRANSMISSION SYSTEMS This invention relates to a plug and to a corresponding mating socket which may be used to form a releasable connection between cables of a data transmission system. The so-called "RJ45" plug, and its corresponding socket, are extensively used as a means of forming connections between cables in both analogue and digital data transmission systems. The RJ45 plug has eight contacts each of which is in the form of an elongate bar. The bars are arranged as a parallel side by side array on one side of the central body of the plug. In data transmission systems data is supplied to the plug via one or more pairs of conductors. Accordingly, the RJ45 plug can accommodate up to four pairs of conductors. Depending upon the intended use of the plug there are a number of different conventions for connecting the conductors of each pair to their respective contacts. In the most commonly used convention (the 568B convention) the two central contacts are connected to one pair of incoming conductors, the two outermost contacts at one side of the array are connected to another pair of conductors; the two outermost contacts on the other side of the array are connected to another pair of conductors, and the two remaining contacts (numbers 3 and 6 measured from one end of the array) are connected to the final pair of conductors. Whilst the RJ45 plug has proved highly successful for relatively low frequency transmissions, as the required data transfer rate has increased the particular array of contacts used within the RJ45 plugs has lead to problems in that the parallel contact bars tend to increase crosstalk between the various pairs of conductors connected thereto. Whilst certain wiring conventions may lead to a slight reduction in cross-talk as compared with the 568B standard, the fact that certain adjacent contacts will inevitably be serving different conductor pairs means that the cross-talk problem cannot be reduced below a certain level. An object of the present invention is to provide a plug which retains the advantages of the RJ45 plug, but which is substantively less prone to cross-talk problems than the RJ45 plug. Another object of the present invention is to provide a socket which retains the advantages of the RJ45 socket, but which is substantively less prone to cross-talk problems than the RJ45 socket. The socket of the preferred embodiment has the additional advantage of presenting the contacts to a printed circuit board upon which it is mounted in a manner which leads to a particularly simple track configuration on the printed circuit board which in turn leads to a reduction in cross-talk without the need for complex compensation measures. According to one aspect of the present invention a plug for use in a data transmission system comprises a number of contacts arranged as a plurality pairs of two contacts, one of the pairs of contacts being located on one side of the plug body and another of the pairs of contacts being located on the other side of the plug body, the or each pair located on one side of the plug body being offset from the or each pair located on the other side of the plug body so as to reduce cross-talk therebetween. According to another aspect of the present invention there is provided a socket for use with the plug of the present invention, the socket comprising a plurality of contacts positioned to mate with the contacts of the plug of the present invention. It has been found that with the arrangement of contacts according to the present invention the advantage of simple construction and simple axial insertion and removal associated with the RJ45 plug are retained, and yet cross-talk is significantly reduced. Further, because of the reduced cross-talk between the contacts the previously relatively complex wiring schemes necessary to minimize cross-talk are not required and accordingly each pair of contacts may simply be connected to the corresponding conductors of a pair of incoming wires. In the case of the plug, this not only simplifies the wiring of the plug but means that the twisting of the incoming wire pairs need not be disturbed until immediately adjacent the point of connection to the contacts. This, in fact, assists in reducing cross-talk produced within the plug. In the case of the socket, the contact arrangement according to the present invention not only reduces the cross-talk but simplifies the track arrangements necessary on a circuit board upon which the socket is mounted. In this connection, it will be appreciated that the sockets used in data transmission systems are in general mounted on a printed circuit board on which is also mounted cable connectors, for example of the IDC type. It is necessary to connect the contacts of the socket with the contacts of the IDC connectors and this is accomplished by means of tracks on the printed circuit board. If a conventional RJ45 socket is wired e.g. in accordance with the 568B standard a relatively complex track arrangement must be provided on the PCB in order to provide connections between the socket contacts and the IDC connector contacts. Because of the conductor layout in the proposed socket according to the present invention this problem is simplified and simple short tracks can be provided leading from the socket contacts to IDC connectors. Each pair of tracks will be well spaced from the nearest adjacent pair of tracks and accordingly little mutual cross-talk will be induced between the tracks. Initial investigations indicate that a plug and socket according to the present invention having a size corresponding substantially to that of a standard RJ45 plug and socket can achieve a cross-talk improvement of at least 30dB as compared with a standard RJ45 plug and socket. The invention will be better understood from the following description of a preferred embodiment thereof, given by way of example only, reference being had to the accompanying drawing wherein: Figure 1 illustrates schematically and in perspective view one embodiment of a plug according to the present invention; Figure 2 is a front view of a socket in accordance with one embodiment of the invention for receiving the plug of Figure 1 ; Figure 3 is a perspective rear view of the socket of Figure 2 showing the contact layout; and Figure 4 shows the socket of Figures 2 and 3 mounted on a PCB with connections provided to IDC connectors. It will be appreciated that in Figures 1 , 3 and 4 of the drawings various contact and conductor layouts are illustrated which would not, in practice, be visible unless the materials from which the plug and socket bodies were made were transparent. The drawings are, however, intended only to be schematic and the position of the conductors has been shown for the purposes of a clear understanding of the invention. Referring to the drawing, the illustrated plug 9 comprises a body 10 having mounted thereon eight contact bars 1-8. The contact bars are secured to the body of the plug in a manner similar to that of conventional RJ45 plugs, and suitable means are provided at the rear of the plug for connecting conventional metal conductors to the contacts 1-8. In a conventional RJ45 plug the contacts are provided as a parallel array of bars located on one side only of the plug body. In contrast, in the case of the present invention four of the contacts are arranged on one side of the plug body, and four of the contacts are arranged on the other side of the plug body. The contacts on the respective sides of the plug body are arranged in pairs, that is to say contacts 1 and 2 form one pair, contacts 3 and 4 form a second pair, contacts 5 and 6 form a third pair and contacts 7 and 8 form a fourth pair. The first and third pairs of contacts are located on one side of the body whilst the second and fourth pairs of contacts are located on the opposite side of the body. The pairs of contacts located on the opposite sides of the body are mutually offset from each other, that is to say each pair of contacts is offset from the nearest contacts located on the opposite side of the body. In use, the proposed plug can be wired in accordance with a number of different conventions, but one preferred feature of its design is that each of four incoming conductor "pairs" can be wired directly to one of the pairs of contacts identified above. For example, if the plug is connected to standard Category 5 unshielded twisted pair (UTP) 4 pair cable the so called brown pair of conductors can be connected to contacts 1 and 2, the blue pair can be connected to contacts 3 and 4, the green pair can be connected to contacts 5 and 6 and the orange pair can be connected to contacts 7 and 8. Such an arrangement has the advantage that the pairs need only be untwisted at the immediate point of connection to the contacts. The proposed plug, wired in accordance with this scheme, has been found to provide an improvement in cross-talk as compared with the conventional RJ45 plug wired in accordance with the 568B convention. It will be noted that the advantages of the invention are achieved without any substantial increase in the size of the plug as compared with the standard RJ45 plug. In order to prevent inadvertent insertion of the plug of the present invention into a conventional RJ45 socket it will probably be desirable to make the plugs mutually incompatible and this can be achieved by appropriately increasing one of the dimensions of the proposed plug as compared with a standard RJ45 plug. However, such increase is not necessary in order to achieve the improved crosstalk of the present invention. Referring now to Figure 2 a socket for use with the plug of Figure 1 is illustrated viewed from the front - i.e. looking into the mouth into which the plug is inserted. It will be seen that the socket includes contacts 11 positioned to mate with the contact bars 1 -8 when the plug 9 is inserted into the body 12 of the socket. Clearly the lay-out of the contacts within the socket is complementary to that of the plug with the result that each pair of contacts in the socket is spaced a substantial distance from the nearest adjacent pair of contacts on the same side of the socket, and is offset relative to the nearest pair of contacts on the opposite side of the socket body. Referring now to Figure 3, it will be noted that the contacts 11 extend through the body and protrude as pins 13 from the rear surface of the body. These pins enable electrical connections to be made to the socket contacts and, in particular enable the socket to be mounted on a PCB 14 as illustrated in Figure 4 with the pins 13 connected to appropriate connector blocks 15 by way of tracks 16 provided on the PCB surface. It will be appreciated that the particular lay-out of conductors means that the pins 13 corresponding to contacts 1 and 2 may be connected to corresponding points on the connection block 15 by way of relatively short and direct tracks. Similarly, the pins 13 corresponding to each other pair of contacts can be connected to their respective portions of the connector blocks by relatively short and simple tracks. The short and simple tracks are spaced from each other by a significant distance and induced cross-talk between them is accordingly minimal . Means are preferably provided for releasably latching the jack to the socket. This can conveniently be provided by a spring loaded latch located on either the top or the bottom surface of the jack, or on one of the side surfaces. In the alternative, a pair of spring loaded latches located on the top and the bottom of the jack, or on both sides of the jack, may be provided for latching against corresponding abutment surfaces provided on the socket . In the illustrated embodiment of the invention a single latch 17 is provided on the lower surface of the plug and engages an abutment 18 provided on the socket body to latch the plug in position. It will be appreciated that in the case of the preferred embodiment of the present invention there are, on each side of the plug, four positions which in a standard RJ45 plug would be occupied by contacts. In the case of the preferred embodiment of plug these contact positions may be left empty or may be occupied by contacts which can be utilized for purposes other than high frequency signal transmission. For example, if contacts are provided in all possible contact positions (i.e. if two contacts are provided between contacts 2 and 5, two contacts are provided between contact 6 and the adjacent edge of the plug, two contacts are provided between contacts 4 and 7 and two contacts are provided between contact 3 and the adjacent edge of the plug) , the contacts other than contacts 1 -8 may be grounded or utilized in other ways to provide further reduction in cross-talk.

Claims: CLAIMS: 1. A plug for use in a data transmission system, the plug comprising: a number of contacts arranged as a plurality pairs of two contacts, one of the pairs of contacts being located on one side of the plug body and another of the pairs of contacts being located on the other side of the plug body, the or each pair located on one side of the plug body being offset from the or each pair located on the other side of the plug body so as to reduce cross-talk therebetween. 2. A plug according to claim 1 wherein two pairs of contacts are located on one side of the plug body, each pair being spaced from the other by a distance greater than the spacing between the contacts of either pair. 3. A plug according to claim 2 wherein one pair of contacts is located on the other side of the plug body directly opposite the space between the respective pairs of contacts on the said one side of the plug body. 4. A plug according to claim 2 wherein one pair of said two pairs of contacts is located adjacent one end of the one of the sides on which it is located and the other pair of said two pairs of contacts is located spaced from the opposite end of the one of the sides on which it is located. 5. A plug according to claim 4 wherein two pairs of contacts are located on the other side of the plug body, one pair directly opposite the space between the respective pairs of contacts on the said one side of the plug body and the other pair directly opposite the space between the said opposite end of the one side and the adjacent pair of contacts on the one side. 6. A plug according to any preceding claim wherein the contacts of each pair of contacts are connected to the respective conductors of a twisted pair of conducts of a cable having a plurality of twisted pairs. 7. A plug according to claim 6 wherein the conductors of each twisted pair remain twisted up to the point where the conductors are connected to the contacts. 8. A socket for the plug of any preceding claim, the socket having a passage for receipt of the portion of the plug upon which the contacts are located, and a contact for mating which each of the plug contacts.

Inventors: WEATHERLEY RICHARD, WEATHERLEY, RICHARD
Applicants: WEATHERLEY RICHARD, WEATHERLEY, RICHARD
Application year: 1998
Main classification: H01R23
IPC codes: H01R24