There is a problem in connectors designed for interconnecting multiple pairs of conductors, where each pair are required to carry individual signals, as there is the risk of cross coupling of signals due to electrostatic (capacitive) or magnetic (induction) coupling. Such cross coupling is called crosstalk and becomes worse as frequencies of signals are increased. The crosstalk results from the capacitive and inductive coupling between nearest lines of the pair which dominates the opposite phase and cancelling effect from the furthest lines of the other pair of a balanced two wire system. This results in effectively a differential capacitance between each line of each pair and the lines of the other pair. The problem is sometimes worsened by wiring conventions for example in the EIA/TIA 568B wiring practice for an eight contact in line connector, contacts 1 & 2 form the orange pair, contacts 3 & 6 form the green pair, contacts 4 & 5 form the blue pair and contacts 7 & 8 form the brown pair. It will be appreciated that in such a configuration crosstalk is a major problem between blue and green pairs as each line of each pair lies adjacent a line of the other pair and there is electrostatic and electromagnetic coupling between them.

To a lesser extent there is coupling between green and both orange and brown because one line of each pair lies adjacent a line of the other pair.

Attempts have been made to reduce the effect of crosstalk in adjacent lines of electrical connectors. For example in the ITT Industries Limited European Patent number 073199 there is disclosed an electrical connector which has four contacts extending between input terminals and output terminals. In order to reduce crosstalk between

pairs of contacts there is provided an overlapping of the mutually most distant terminals of different particularly assigned signal carrying pairs of the contacts to provide capacitive coupling therebetween to induce crosstalk in opposition to crosstalk induced between the mutually closest terminals. Whilst the construction described in that patent specification provides cross talk compensation which is reliable and relatively simple to manufacture it has been discovered that improvements in cross talk cancellation are possible. The present invention seeks to provide a connector having improved cross talk cancellation.

According to the invention there is provided an electrical connector comprising at least four contacts extending between input and output terminals, in which the mutually most distant contacts of different particular assigned signal carrying pairs of said contacts is arranged to provide coupling therebetween to induce crosstalk in opposition to crosstalk induced between the mutually closest contacts of the different assigned signal carrying pairs, wherein the path lengths of the mutually most distant contacts are extended to enhance a phase opposition relationship between the mutually opposed cross talks, thereby to reduce overall crosstalk.

One of each of said most distant contacts may be provided with a lateral extension which overlies the other cooperating contact of the other pair to provide overlapping and capacitive coupling therebetween. The other of said most distant contacts may have a portion of larger surface area where the lateral extension overlies, thereby to increase the capacitive coupling therebetween. In this way the differential capacitance between the cooperating contact and each of the contacts of the other pair is reduced. The contacts may be spaced apart transversely of the connector the mutually most distant ones of the contacts being assigned as one signal carrying pair and the lateral extension extending inwardly.

In a further embodiment of the invention two additional signal carrying pairs of contacts are disposed one to each side of said four contacts, and the outer contacts of said four contacts are arranged to overlap the most distant contact of the nearest additional pair to provide coupling therebetween to induce crosstalk in opposition to crosstalk induced between that outer contact and the nearest terminal of that additional pair.

In a refinement of the invention the most distant contacts are arranged to overlie one another, at least partially along their conductive path, to provide capacitive and inductive coupling therebetween. The contacts may be spaced apart transversely of the connector the mutually most distant ones of the contacts being assigned as one signal carrying pair. The arrangement may be such that two additional signal carrying pairs of contacts are disposed one to each side of said four contacts and the outer contacts of said four contacts are each divided to form two individual paths between input and output terminals which paths are arranged to overlie, at least partially along their conductive path, the first and fifth contacts and fourth and eighth contacts respectively to provide capacitive and inductive coupling therebetween.

The path lengths of the two individual paths of each divided outer contact may be extended to enhance a phase opposition relationship between the mutually opposed cross talks, thereby to reduce overall cross talk.

The contacts may be provided some on each side of an insulating separator which forms a dielectric between overlapping contacts. The separator may be a polyimide film.

In order that the invention and its various other preferred features may be understood more easily, embodiments thereof will now be described, by way of example only, with reference to the drawings in which, Figure 1 is a schematic diagram illustrating the major problem of crosstalk occurring in an eight contact

connector, Figure 2 is a plan view of a lead frame for providing six of the terminals of a connector constructed in accordance with the invention, Figure 3 is a plan view of a second lead frame for providing two additional terminals of a connector constructed in accordance with the invention.

Figure 4 is a plan view showing the arrangement of the lead frames of Figures 3 & 4 mounted one each side of an insulating dielectric film, Figure 5 is a plan view of a contact showing modification required, Figure 6 is a plan view of the contact of Figure 5 showing one step in the modification, Figure 7 is a plan view of the contact of Figure 6 showing a further modification step.

Figure 8 is a plan view of the contact of Figure 7 further modified, Figure 9 is a plan view of a completed modification of the contact illustrated in Figure 8, Figure 10 illustrates individual contacts for an eight contact connector, Figure 11 shows the contacts of Figure 10 with dielectric separators, Figure 12 shows an assembled disposition of the components of Figure 11, Figure 13 is an exploded view showing the component parts of a complete connector incorporating the construction of Figure 4 and employing the features of the invention, and Figure 14 shows the component parts of the connector of Figure 5 assembled in readiness, for the connection of insulated wires.

Figure 15 illustrates schematically two side by side transmission lines, Figure 16 illustrates the phase relationship of cross coupling between the transmission lines of Figure 15,

Figure 17 illustrates schematically extended lines of Figure 15, Figure 18 illustrates the phase relationship of cross coupling between the transmission lines of Figure 17, Figure 19 illustrates the phase relationship of cross coupling between transmission lines of extended length, Figure 20 illustrates the idealised phase cancellation introduced by extending the transmission lines, Figure 21 illustrates the actual phase relationship introduced by extending the transmission lines, Figure 22 illustrates schematically the various sections of connector coupling in a plug and socket connector, Figure 23 illustrates phase balancing of the crosstalk, Figure 24 illustrates crosstalk balancing by amplitude variation, Figure 25 illustrates crosstalk balancing by phase variation, and Figure 26 illustrates schematically the IDC termination of a connector.

Referring to Figure 1 there is illustrated an eight terminal in line connector intended for use with the EIA/TIA 568B wiring practice. As can be seen the lines 4 & 5 and 3 and 6 are close to each other and crosstalk is induced between them by electromagnetic and electrostatic coupling the capacitive element of which as simulated by capacitors C1 & C2. In order to compensate for such crosstalk compensating crosstalk can be introduced between 3 & 5 and 4 & 6 which is in antiphase to the unwanted crosstalk induced between the adjacent lines. This can be done by providing increased capacitive coupling between 3 & 5 and 4 & 6 as is shown in broken lines and identified as Cl'and C2'respectively. There is also crosstalk between the lines 2 & 3 and 6 & 7 of adjacent pairs of terminals as

represented by C3 and C4 and this can be similarly compensated by providing increased capacitive coupling between 1 & 3 and 6 & 7 as is shown in broken lines and identified as C3'and C4'respectively. The present invention is concerned with providing such compensation in a connector having four or more terminals. Referring now to Figure 2 there is shown in plan view a lead frame 10 formed by pressing from a thin sheet of metal e. g. beryllium copper to define six terminals numbered 1,2,4,5,7,8.

Figure 3 shows a plan view of another lead frame 11 similarly formed to define two terminals 3 & 6. In both lead frames one end of each of the terminals is formed as an elongate tail 12 the tails running in a substantially mutually parallel disposition and the other end is provided with an elongate cut out 13 which when separated from side rail 14 defines the fork of an insulation displacement connector. It will be seen in Figure 2 that the terminals 1,4,5 & 8 have portions 15A, 15B, 15C & 15D respectively of greater width and surface area which are intended for cooperation with lateral extensions 16A, 16B & 16C, 16D provided on terminals 3 & 6 respectively as will be seen from Figure 3.

Referring now to Figure 4 there is shown in plan view how the two lead frames are mounted one on top of another separated by an insulating film 17. In the illustration the lead frame 10 is shown on the bottom and is separated from the lead frame 11 by a transparent film for ease of illustration. The film may be of any suitable dielectric material for example polyimide such as is marketed under the trade name Kapton. the film may be 0.003 inches in thickness. Accurately defined thickness, dielectric constant and control of overlap is essential if effective cancellation of crosstalk is to be accomplished.

The frames are secured to the film by an adhesive for example by providing each side of the film with an acrylic coating and securing the frame thereto by heat bonding. In the drawing it can be seen that the lateral extensions 16A,

16B, 16C & 16D where they overlie the portions 15A, 15B, 15C & 15D respectively are shaded to aid identification.

The previously described arrangement is primarily concerned with capacitive cancellation which is most effective in cancellation of near end crosstalk (NEXT). In order to enhance far end crosstalk (FEXT) cancellation some degree of inductive cancellation is advisable.

This is accomplished by arranging signal current for both the sending and receiving lines to flow in adjacent wires (or contacts) which therefore share a similar magnetic space. If the wire of one pair is coupled into a wire of another pair that is not normally adjacent in the connector then cancellation occurs. The following description shows that the same wires that couple capacitively can also couple inductively. If it is therefore arranged that signal current flows through the capacitor plates then both capacitive and inductive cancellation will occur. This is effected as follows:- The contact illustrated in Figure 5 is the contact employed in previously mentioned European Patent Number 0731995 with capacitive spurs S and the signal current portion C. The shaded area shows a contact bridge that will be included to enable the signal current to flow through the capacitor plates. Figure 6 shows this bridge added and the original current carrying portion C of the contact shaded which must be removed to arrange all the signal current to flow through the capacitor plates (half through each plate). Figure 7 shows this final form.

It has been found advantageous to lengthen the portion of the contact (carrying half the current) and to narrow it to optimise the relationship between capacitance and inductance. This is shown in figure 8.

The wires that fit into the IDC portion of the contact generate crosstalk and balancing the phase of this crosstalk to enhance crosstalk cancellation can be effected by lengthening the electrical path at the rear end of the connector by folding back the contact as shown in Figure 9.

This is the final design of one of the green contacts (contacts 3 and 6) for improvement of the connector described in European Patent Number 0731995. A contact as shown in Figure 9 may be used for each of the contacts 3 and 6, as shown in Figure 10, with one being an upside down version of the other. Figure 10, further shows the 6 other contacts 1,2,4,5,7 & 8 similar to the design of the previously mentioned European Patent where contacts 1,4,5 and 8 have been narrowed more in line with contacts 3 and 6. In the present arrangement, as shown in Figure 11, there are three layers of contacts separated by two sheets of dielectric material D. Kapton is a suitable material for the dielectric. The assembled components are shown in Figure 12.

There is equilibrium of current in each split half of both contacts 3 and 6.

The length and width of each half of the split contacts is preferably different to effect the optimum balance between inductive and capacitive cancellation.

The foldback enables phase cancellation without any need to lengthen the connector. The wires at the rear of the connector, that protrude through the IDC's are of a controlled length, due to the assembly tooling used to install the connector, and enable repeatable phase balancing as previously described. Contact 3 and 6 are identical mirror images of each other.

Although the contact 3 illustrated in Figure 9 provides split paths and is intended for use in an eighth contact connector one side of the contact may be omitted to provide a single path. Such a construction may be advantageous with a four contact connector or for use with a group of four contacts in a multi-contact connector. The phase opposition enhancement capability provided by this invention will still result and provide a connector in accordance with the invention.

The two different constructions previously described have their lead frames bonded to the insulating film (s) and

are then encapsulated in a plastics material which as can be seen from Figure 13, where it is identified by the number 20, is of substantially rectangular block like form provided with eight parallel elongate slots 21 which are blind at one end and are for receiving insulated wires of a connecting cable. After encapsulation the rails of the lead frame are cut away to release the tails 12 and to open the end of the cut out 13 to define an insulation displacement fork 22. The fork end is bent upwardly at right angles as shown in the drawing and the tails are bent downwardly and backwardly so that they are inclined downwardly relative to the bottom of the block 20. It will be seen from the cut outs 13 in Figure 2 that they are relatively displaced longitudinally of the terminals such that by appropriate cutting during the separating from the rails of the lead frame they define forks which project at different distances such that when bent there are rows of forks at different heights to facilitate attachment of insulated wires as will be hereinafter described.

Referring now to the exploded view of Figure 13 the various additional components and their interconnection will now be described. A strain relief element 23 of shape similar to the rectangular block is provided and has slots 24A similar to slots 21 for receiving and supporting the insulation displacement connector forks 22 and the insulated wires. As can be seen the strain relief element forms effectively a continuation of the block when the insulation displacement forks are located in its slots.

A moulded plastics housing 24 has a top provided at one side with a recess 25 which is shaped to permit slidable insertion of the block 20 and strain relief element 23. In the bottom of the recess there are provided eight parallel slots 26 which extend along the recess from the insertion end and which are spaced apart similarly to the spacing of the tails 12 where they emerge from the block 20. The slots extend through to a recess in the bottom of the housing which has at the other side of the

housing an entry for receiving a cooperating connector. The slots 26 serve to each receive a tail 12, as the tail end of the block 20 is inserted into the recess 25, and to guide and separate the tails during and after insertion so that the tails are held in inclined disposition as contacts in the recess in the bottom of the housing for cooperation with a mating connector. The opposing walls of the recess 25 and the strain relief element are each provided with mutually engagable latch elements which in the described embodiments comprise inwardly tapered projections 27 on the opposing walls of the recess 25 and recesses 28 at opposite sides of the strain relief element into which the ends of the projections engage by snap action upon completion of insertion into the recess 25. Instead of providing the cooperating latch elements 28 on the strain relief element 23 they may be provided on the sides of the block 20, The housing 24 is also provided with an upwardly extending lid 29 which is formed during the moulding thereof and is linked with the housing top by a hinge line 30 and secured in the open position by a side connection portion 31 which is severed prior to closure of the lid.

The lid is provided with eight elongate projections 32 which align with the slots 21,24A and which serve to force insulated wires, when laid in the slot, into the insulation displacement connector forks 22 and to clamp the insulated wires when the lid is fully closed as the lid closed.

An outer shell 33 formed of metal or plastics and shaped to permit snug insertion of the hinge end of the housing 24 is also provided. This shell is effective to cause the connection of wires to the insulation displacement connectors, after laying in the slots 21 of the block 20 and slots 24A in the strain relief element after insertion in the housing 24, by just pushing the housing 24 into the shell which forces the lid closed and causes the projections 32 to force the insulated wires into the forks 22 which effect insulation displacement and connection to the wire and also causes the insulation of

the wires to be forced into the slots 24A of the strain relief element to aid retention of the wires. The shell acts as an electrical screen for the connector and the screening is further enhanced by a metal cable end screen 34 and securing clip 35.

The connector components assembled ready to receive insulated wires are shown in Figure 14.

The lid of the inner body moulding may differ from that illustrated in that a bar perpendicular to the wire may be provided which will push the wires into the IDC slots.

It has been found that the best compensation for crosstalk can be effected if the overlapping lateral extensions 16A-16D and wide portions 15A-15D are provided as close as possible to the tails 12 (Figures 2,3 and 4).

Although the embodiment described employs four pairs of wires it will be appreciated that the invention is effective for any connectors which include two or more pairs such as 3 & 6,4 & 5 where crosstalk is required to be reduced and can be employed in connectors having a large number of pairs.

In this respect crosstalk can be a problem in whatever configuration the contacts are paired. For simplicity considering a four contact in line connector the contacts being numbered 1 to 4 in sequence then the pairs can be designated as 1 & 4,2 & 3 (similar to 3 & 6,4 & 5, in the previously described embodiment) which is the worst case, but could be designated as 1 & 2,3 & 4 or 1 & 3,2 & 4. In each case there are wires close to each other relating to a different pair and crosstalk reduction or cancellation in accordance with the techniques of this invention can be effected. Such configurations are considered to fall within the scope of this invention.

The principles of the invention are applicable to connectors having large numbers of contacts and it will be appreciated that there is the possibility of crosstalk between each pair of contacts and all of the other pairs of

contacts and that the principles of this invention can be applied between each pair and any one or more of the other pairs of contacts.

Although the embodiment described employs lead frames mounted onto a dielectric film it will be appreciated that alternative constructions can be employed for example the contacts may be formed on opposite sides of a printed circuit board by etching or the contacts could be printed onto a dielectric film or board by for example screen printing a metallic pattern. Such configurations are considered to fall within the scope of this invention.

In order to clarify the operation of the embodiment of Figures 11 and 12 the following explanation may be helpful- Figure 15 shows two very short parallel twin wire transmission lines 40,41 spaced physically close to each other. Crosstalk is generated between the lines. We will view the Near end crosstalk (NEXT). The crosstalk generated is directly proportional to the length of the close proximity run. A 90° phase shift exists between the transmitted signal TX and NEXT when measured at the point 42 i. e. the start of the close proximity parallel run of the transmission line. The opposite ends of the lines are coupled to twisted pairs which do not generate crosstalk.

For simplicity we will assume that the length of the line is short enough so as not to cause the phase considerations that follow and the phase relationship is as illustrated in Figure 16. If another piece of Tx line 40A, 41A is added to the end of each of the lines 40 and 41 (of the same length), as illustrated in Figure 17, the crosstalk generated in the second section 40A, 41A will have the same amplitude as that generated in the first section. However, the Tx signal, being propagated to the Rx will arrive at the second section of transmission line after it was at the first section of line due to propagation delays. This represents a phase lag or delay.

This delayed Tx signal will introduce Next in the second

section of the lower transmission line. This Next is then propagated towards the label"NEXT"and is also phase delayed by the propagation delay in the lower line 41. The emerging Next has been delayed by twice the propagation delay of the"CABLE"line length (once there plus once back). Adding the Next generated in the second section of line 40A, 40B gives the phase relationship illustrated in Figure 18. (Note the phase is exaggerated for clarity). If many short sections of line were added the phase representation of each length would be as illustrated in Figure 19 where each section, further away from the Tx signal, is subjected to a greater delay. Note that if all the vectors for all the sections are added (as would be the case in practice) the total would have an amplitude of substantially n (No. of sections) times the amplitude for each section. The phase of the TOTAL would be the average of the phases for each section and is substantially half the phase of the last section. Also note that the line would not be made up sections-it would be continuous, The principle of sections is only used to aid the description.

This could be summarised by stating that the crosstalk generated suffers a phase delay equal to the length of the line (i. e. % x Twice the length of the coupled portion of lines).

In practice the vector does not sit on the 90° axis it suffers about a 10° delay in the connector described and sits at 80°.

If we now add a further length of transmission line to affect cancellation by allowing coupling of an opposite polarity line, this added length must be of the same length as the first to ensure that the crosstalk generated is equal in amplitude to that generated in the first length.

The antiphase nature of crosstalk cancels the crosstalk from the first length. It is assumed that the coupling in the first length is the same as the second length. This cancellation is shown in Figure 20.

Unfortunately, the idealised illustration in Figure

20 does not result because the second section of line (the cancellation part) is subjected to propagation phase delay as well and the actual phase relationship is shown in Figure 21. Due to the propagation delays described the resultant cancelled crosstalk is a little better than -40dB. Unless the phase delay is cancelled CAT 6 specification performance cannot be accomplished.

Phase cancellation is provided as follows with reference to Figure 22. Region A is the plug and the socket contacts making connection to the plug. This region produces crosstalk. Region B is part of the cancellation area of the socket and produces about twice the cancellation require to cancel region A. Region C is also in the socket, and produces crosstalk as at A. If the degree of crosstalk in each region (along with the correct phase relationship) is matched then absolute cancellation of NEXT occurs.

The vectors in Figure 23 show this: If the correct balance is obtained then Region B vector is identical in amplitude and exactly 180° to the addition of A to C so absolute cancellation results. The resultant NEXT is zero.

The illustration in Figure 23 is symmetrical but this need not be the case. By varying amplitudes and phases the same end result can be obtained as illustrated in Figures 24 and 25. In the connectors described the crosstalk (mainly capacitive) is generated in the IDC area by the IDC's themselves and the wires protruding through them as illustrated in Figure 26. For this crosstalk (as at C in Figure 23) to effect the correct degree of phase cancellation it is necessary to lengthen the path between regions B & C (Figure 22) to delay the C crosstalk as in Figure 25. This is done by looping back the contacts.