Abstract:
A scheme for compensating for both near-end (NEXT) and far-end (FEXT) crosstalk within a communication connector having first and second pairs of contact wires. A first stage of compensation includes capacitive coupling that corresponds in magnitude to a sum of offending capacitive and offending inductive crosstalk both of which originate from a mating connector. At a second stage of compensation, both (a) inductive coupling corresponding in magnitude to the offending inductive crosstalk, and (b) capacitive coupling corresponding in magnitude and of opposite polarity to the inductive coupling, are produced. In the disclosed embodiment, the first and the second compensation stages are implemented in an industry type RJ-45 communication jack to meet or surpass Category 6 NEXT/FEXT loss levels.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to communication connectors that are configured to compensate for offending crosstalk. 
     2. Discussion of the Known Art 
     Communication connectors that are configured to suppress or to compensate for crosstalk that originates from within a mating connector, are generally known. As defined herein, crosstalk arises when signals conducted over a first path, e.g., a pair of contact wires in a communication plug connector, are partly coupled electromagnetically into a second signal path (e.g., another pair of contact wires) within the same connector. The signals coupled from the first path may be detected as “crosstalk” in the second path, and such crosstalk degrades existing signals that are being routed over the second path. 
     Applicable industry standards for rating connector crosstalk performance are given in terms of near-end crosstalk (NEXT) and far-end crosstalk (FEXT). The ratings are usually specified for mated plug and jack combinations, and input terminals of the plug connector may be used as a reference plane. NEXT is defined as crosstalk whose power travels in an opposite direction to that of an originating, disturbing signal in a different path. FEXT is defined as crosstalk whose power travels in the same direction as the disturbing signal in the different path. See, e.g., “Transmission Systems For Communications”, Bell Telephone Laboratories (5th ed. 1982), at page 130. Communication links using unshielded twisted pairs (UTP) of copper wire are now expected to meet industry “Category 6” standards which call for at least 54 dB NEXT loss and 43 dB FEXT loss, each at 100 MHz, with respect to any two signal paths through the mated connectors. 
     Crosstalk compensation circuitry may be provided on or within layers of a printed wire board to which the contact wires of a communication jack are connected. See U.S. Pat. No. 5,997,358 (Dec. 7, 1999), all relevant portions of which are incorporated by reference. U.S. Pat. No. 6,139,371 (Oct. 31, 2000), also incorporated by reference, relates to a communication connector assembly having capacitive crosstalk compensation. The assembly features a number of terminal contact wires at least first and second pairs of which have free end portions that extend to define leading portions. A leading portion of a first pair of contact wires, and a leading portion of a second pair of contact wires, are dimensioned and arranged for capacitively coupling to one another so as to produce capacitive crosstalk compensation. See also commonly owned U.S. application Ser. No. 09/583,503, filed May 31, 2000, and entitled “Communication Connector with Crosstalk Compensation”, and U.S. Pat. No. 5,700,167 (Dec. 23, 1997) which discloses inductive crosstalk compensation circuitry in the form of conductive loops that are printed in mutual coupling relation on a printed wire board. 
     It is also known that in conventional modular communication plugs, capacitively coupled and inductively coupled signal components add for NEXT, while they subtract for FEXT. That is: 
     
       
         NEXT= Xc+Xm   
       
     
     and 
     
       
         FEXT= Xc−Xm,   
       
     
     wherein: 
     Xc is the capacitively coupled component, and 
     Xm is the inductively coupled component. 
     It is also known that the effectiveness of any NEXT cancellation scheme is limited by the amount of delay between the offending crosstalk and the compensating crosstalk, and that NEXT cancellation may be improved by reducing such delay with optimum cancellation occurring when the delay is effectively zero. The connector configuration in the mentioned U.S. Pat. No. 6,139,371 minimizes the delay for capacitive crosstalk compensation by deploying the capacitive compensation coupling at non-current carrying free ends of the contact wires in a modular jack, effectively at the connection interface where the offending crosstalk is introduced by the mating plug. 
     If all existing NEXT is compensated using capacitive coupling at the non-current carrying wire free ends, NEXT would be effectively canceled because delay is minimized. But FEXT performance may be degraded, however, since the compensation being provided is totally capacitive in nature. 
     Further, if a configuration such as in the &#39;371 patent is used only to cancel the capacitive component of the original crosstalk, and inductive coupling is also provided to compensate for the offending inductive component (see, e.g., U.S. Pat. No. 6,196,880 issued Mar. 16, 2001), FEXT would be minimized but the efficiency of NEXT cancellation may be reduced due to a time delay caused by the remote placement of the inductive compensation which is effectively distributed over the length of the inductive coupling region. Thus, the need to maintain adequately low FEXT levels has been a constraint on the degree to which NEXT levels can be reduced. 
     SUMMARY OF THE INVENTION 
     According to the invention, a method of compensating for near-end and far-end crosstalk in a communication connector, includes producing capacitive compensation coupling at a first stage in. the connector wherein the capacitive compensation coupling corresponds in magnitude to a sum of offending capacitive crosstalk and offending inductive crosstalk both of which originate from a mating connector, and producing, at a second stage, both (a) inductive compensation coupling corresponding in magnitude to the offending inductive crosstalk from the mating connector, and (b) capacitive coupling corresponding in magnitude and of a polarity opposite to that of the inductive compensation coupling. 
     For a better understanding of the invention, reference is made to the following description taken in conjunction with the accompanying drawing and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     In the drawing: 
     FIG. 1 is a vector representation of the compensation scheme of the invention, as applied in a communication connector; 
     FIG. 2 is a perspective view of a portion of the connector of FIG. 1; 
     FIG. 3 is a side view of the connector shown in FIG. 2, 
     FIG. 4 represents a first configuration of intermediate portions of contact wires in the connector; 
     FIG. 5 represents a second configuration of the intermediate portions of the contact wires in the connector; 
     FIG. 6 is a view of a front surface of a printed wiring board in the connector; and 
     FIG. 7 is a view of a rear surface of the printed wiring board in FIG. 6, as viewed from the front. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a vector representation of a crosstalk compensation scheme according to the invention, as deployed in a communication connector  10 , for example, a modular jack. Two stages  12 ,  13  of compensation coupling are defined within the connector  10 . A mating connector  11 , e.g., a communication plug, is assumed to introduce offending crosstalk onto terminal contact wires of the connector  10  at a plug/jack contact line  16 . The offending crosstalk, labeled “Stage 0” in FIG. 1, includes an inductive component Xmo and a capacitive component Xco. Typically, the capacitive component Xco follows the inductive component Xmo after only a relatively short delay. 
     As shown in FIG. 1, capacitive compensation coupling Xc 1  of a value the same or approximately equal to Xco+Xmo and of opposite polarity, is introduced at the first stage  12  (Stage  1 ) of compensation coupling at the plug/jack contact line  16 . Such coupling may be implemented, for example, by producing the required value of capacitive compensation coupling at non-current-carrying free ends of the contact wires of the connector  10  according, for example, to the mentioned U.S. Pat. No. 6,139,371. Since the capacitive compensation coupling provided by the first stage  12  is at a minimal delay with respect to the total offending crosstalk introduced at the plug/jack contact line  16  (stage  0 ), and because the compensation coupling provided by the first stage  12  is equal in magnitude and of opposite polarity to the total offending crosstalk, optimum NEXT cancellation is achieved. 
     To cancel FEXT without degrading NEXT, the second stage  13  of compensation coupling is provided as shown in FIG.  1 . Part  14   a  of the second stage is configured to produce an inductive compensation coupling component Xm 2  that is equal in magnitude and of opposite polarity to the inductive component Xmo of the. offending crosstalk introduced by the mating connector at the plug/jack contact line  16 . Part  14   b  of the second stage  13  is configured to produce a capacitive coupling component Xc 2  that is equal in magnitude to the inductive compensation component Xm 2 , but of opposite polarity. To be self-canceling, the two components Xc 2 , Xm 2  should be introduced at substantially the same physical location in the connector  10 . 
     It can be seen in FIG. 1 that the second stage  13  produces the required capacitive-for-capacitive and inductive-for-inductive compensations needed to cancel FEXT. Although the first and the second stages  12 ,  13  are delayed from one another, FEXT cancellation is substantially delay insensitive and is not significantly affected. Also, the second stage  13  is selfcanceling, and can be conveniently positioned in time or distance with respect to the first stage  12 , without degrading NEXT performance. Further, the parts  14   a,    14   b  of the second stage  13  can be placed at an offset from one another, to fine tune any remaining residual crosstalk resulting from a finite delay between the offending crosstalk introduced at stage  0 , and the first stage  12  of compensation coupling in the connector  10 . 
     Accordingly, to compensate for both NEXT and FEXT simultaneously, the capacitive component Xco of the offending crosstalk is effectively canceled by capacitively coupled crosstalk of equal magnitude and opposite polarity, and the offending inductive component Xmo is effectively canceled by inductively induced crosstalk of equal magnitude and opposite polarity. Since the components Xc 2  and Xm 2  have opposite polarity, their relative delay may be favorably chosen for canceling any residual NEXT. 
     Actually, three compensations may be considered as occurring simultaneously. A part of the first stage  12  component Xc 1  cancels the capacitive component Xc 0  of the offending crosstalk. The remaining part of Xc 1  cancels the compensation coupling component Xc 2  of the second stage  13  with a residual crosstalk vector shifted by +90 degrees, and the inductive compensation coupling component Xm 2  of the second stage  13  cancels the inductive component Xmo of the offending crosstalk with a residual crosstalk vector of like magnitude but shifted by −90 degrees. Since the two residual crosstalk vectors have opposing phase, they cancel one another. 
     In other, more generalized implementations of the present scheme, the components Xc 1  and Xc 2  may be varied in magnitude about their initially determined values for purposes of fine tuning. 
     FIG. 2 is a perspective view of a front portion of one embodiment of the connector  10 , showing four pairs of contact wires  20 , a first printed wiring board  22 , and a second printed wiring board  24 . An outer connector housing and associated structure are omitted in the figure for purposes of clarity. 
     The first printed wiring board  22  has an array of contact pads  26  in proximity to a front edge of the board. The pads  26  are aligned beneath corresponding free ends of the contact wires  20 . When terminals of a mating plug connector (not shown) engage the contact wires at the plug/jack contact line  16 , the contact wires deflect resiliently downward and their free ends establish electrical contact with the corresponding pads  26 . Certain values of capacitance are provided on or within the board  22 , between selected pairs of the contact pads  26  in order to implement the first stage  12  of compensation coupling in the connector  10 . For example, a capacitance of 1.02 pf between pads labeled T(tip) 1  and T 3 , and a capacitance of 1.02 pf between the pads labeled R(ring) 1  and R 3 . See commonly owned U.S. application Ser. No. 09/664,814 filed Sep. 19, 2000, and entitled “Low Crosstalk Communication Connector”, all relevant portions of which are incorporated by reference. 
     In FIG. 2, the fourth and the fifth contact wires from the left are aligned with contact pads labeled T 1  and R 1 , and they define a first signal path (pair  1 ) through the connector  10 . The third and the sixth contact wires, aligned with pads labeled R 3  and T 3 , define a different signal path (pair  3 ) through the connector  10 . In typical industry type RJ-45 communication connectors using TIA wiring method T568B, a greatest amount of offending crosstalk is developed in plug connectors among the pair  1  and the pair  3  signal paths. 
     The terminal contact wires  20  are supported above the first printed wiring board  22  by the second printed wiring board  24 . As seen in FIG. 3, bases  30  of the contact wires  20  are press-fit or otherwise fixed in corresponding terminal openings  32  formed in the wiring board  24 . The wiring board  24  has a second set of terminal openings  34  arrayed next to vertical side edges of the board  24  for supporting connector terminals (not shown) which are coupled via wire traces on the board to the bases  30  of the contact wires. 
     The second wiring board  24  includes circuitry (shown in FIGS. 6 and 7) used to implement both parts  14   a  and  14   b  of the second stage  13  of compensation coupling. Because the second stage  13  at the second wiring board  24  is physically separated from the first wiring board  22 , it is preferred that no significant crosstalk be allowed to develop among intermediate portions of the contact wires between the plug/jack contact line  16  and the wiring board  24 . 
     Thus, as shown in FIGS. 4 and 5, the cross-sections of the pair  1  contact wires ( 1 T and  1 R), are aligned at right angles to and bisect a line drawn between the cross-sections of the pair  3  contact wires ( 3 R and  3 T). FIG. 4 represents a “square” pattern, and FIG. 5 shows a “stagger” pattern for the contact wires, both of which satisfy a symmetric and mutually orthogonal alignment for the pair  1  and the pair  3  contact wires between the plug/jack contact line  16 , and the bases  30  of the contact wires at the second wiring board  24 . 
     FIG. 6 is a view of a front surface  40  of the second wiring board  24 , and FIG. 7 is a view of a rear surface  42  of the wiring board  24  as viewed from the front. As seen in FIGS. 6 and 7, the pair  1  and the pair  3  contact wires enter the wiring board  24  with the square pattern of FIG.  4 . The capacitive component part  14   b  of the second stage  13 , is at or near a centroid of the inductive component part  14   a  and of opposite polarity. The embodiment of FIGS. 6 and 7 uses a wiring board trace layout that generates inductive coupling using mutually facing loop traces, as in the mentioned U.S. Pat. No. 5,700,167. Opposite polarity capacitive coupling is implemented by interdigital comb traces on the board at  14   b,  and is applied at the centers of the inductive loops at  14   a.  Also, if necessary, a capacitive compensation element (not shown) may be provided on the wiring board  24  at the bases  30  of the contact wires, to compensate for any undesired crosstalk coupling among the intermediate portions of the pair  1  and the pair  3  contact wires. 
     EXAMPLE 
     The two-stage crosstalk compensation scheme of FIG. 1 was simulated using a SPICE simulation program. Offending crosstalk was introduced at the plug/jack contact line  16  with a capacitive component Xco=10 mv/v, and an inductive component Xmo=6 mv/v. Stage  1  compensation coupling with Xc 1 =16 mv/v was produced at the plug/contact line  16 . Stage  2  compensation coupling was simulated at a distance corresponding to a delay of 100 picoseconds from the stage  1  location, with Xc 2 =6 mv/v and Xm 2 =6 mv/v. Results showed that NEXT loss was 65.1 dB at 100 MHz, and FEXT loss was 101 dB at 100 MHz. Without the stage  2  compensation, NEXT and FEXT losses were measured at 58.2 dB and 39.2 dB, respectively. Thus, according to the simulation results, the stage  2  compensation enabled Category 6 performance to be attained for the connector  10 . 
     While the foregoing description represents preferred embodiments of the invention, it will be appreciated that various changes and modifications may be made without departing from the spirit and scope of the invention pointed out by the following claims.