Abstract:
A communications jack assembly includes: a jack frame having a plug aperture; a dielectric mounting substrate attached to the jack frame; and a plurality of conductors engaged with the mounting substrate, each of the conductors including a fixed end portion mounted with the mounting substrate and a free end portion extending into the plug aperture for electrical contact with a mating plug, each of the free end portions having substantially the same profile and being substantially transversely aligned in side-by-side relationship. A first pair of conductors is sandwiched inside a second pair of conductors. The second pair of conductors includes a crossover, the positioning of crossover being selected to provide differential to common mode crosstalk compensation.

Description:
CLAIM OF PRIORITY 
     This application claims priority as a continuation-in-part application to U.S. patent application Ser. No. 11/088,044, filed Mar. 23, 2005 now U.S. Pat. No. 7,204,722, which in turn claims priority from U.S. Provisional Patent Application Ser. No. 60/636,595, filed Dec. 16, 2004, the disclosures of both of which are hereby incorporated herein in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to communication connectors and more particularly to crosstalk compensation in communication connectors. 
     BACKGROUND OF THE INVENTION 
     In an electrical communication system, it is sometimes advantageous to transmit information signals (video, audio, data) over a pair of wires (hereinafter “wire-pair” or “differential pair”) rather than a single wire, wherein the transmitted signal comprises the voltage difference between the wires without regard to the absolute voltages present. Each wire in a wire-pair is susceptible to picking up electrical noise from sources such as lightning, automobile spark plugs and radio stations to name but a few. Because this type of noise is common to both wires within a pair, the differential signal is typically not disturbed. This is a fundamental reason for having closely spaced differential pairs. 
     Of greater concern, however, is the electrical noise that is picked up from nearby wires or pairs of wires that may extend in the same general direction for some distances and not cancel differentially on the victim pair. This is referred to as crosstalk. Particularly, in a communication system involving networked computers, channels are formed by cascading plugs, jacks and cable segments. In such channels, a modular plug often mates with a modular jack, and the proximities and routings of the electrical wires (conductors) and contacting structures within the jack and/or plug also can produce capacitive as well as inductive couplings that generate near-end crosstalk (NEXT) (i.e., the crosstalk measured at an input location corresponding to a source at the same location) as well as far-end crosstalk (FEXT) (i.e., the crosstalk measured at the output location corresponding to a source at the input location). Such crosstalks occur from closely-positioned wires over a short distance. In all of the above situations, undesirable signals are present on the electrical conductors that can interfere with the information signal. When the same noise signal is added to each wire in the wire-pair, the voltage difference between the wires will remain about the same and differential cross-talk is not induced, while at the same time the average voltage on the two wires with respect to ground reference is elevated and common mode crosstalk is induced. On the other hand, when an opposite but equal noise signal is added to each wire in the wire pair, the voltage difference between the wires will be elevated and differential crosstalk is induced, while the average voltage on the two wires with respect to ground reference is not elevated and common mode crosstalk is not induced. 
     U.S. Pat. No. 5,997,358 to Adriaenssens et al. (hereinafter “the &#39;358 patent”) describes a two-stage scheme for compensating differential to differential NEXT for a plug-jack combination (the entire contents of the &#39;358 patent are hereby incorporated herein by reference, as are U.S. Pat. Nos. 5,915,989; 6,042,427; 6,050,843; and 6,270,381). Connectors described in the &#39;358 patent can reduce the internal NEXT (original crosstalk) between the electrical wire pairs of a modular plug by adding a fabricated or artificial crosstalk, usually in the jack, at one or more stages, thereby canceling or reducing the overall crosstalk for the plug-jack combination. The fabricated crosstalk is referred to herein as a compensation crosstalk. This idea can often be implemented by twice crossing the path of one of the differential pairs within the connector relative to the path of another differential pair within the connector, thereby providing two stages of NEXT compensation. This scheme can be more efficient at reducing the NEXT than a scheme in which the compensation is added at a single stage, especially when the second and subsequent stages of compensation include a time delay that is selected to account for differences in phase between the offending and compensating crosstalk. This type of arrangement can include capacitive and/or inductive elements that introduce multi-stage crosstalk compensation, and is typically employed in jack lead frames and printed wiring board (“PWB”) strictures within jacks. These configurations can allow connectors to meet, for example, “Category 6” performance standards set forth in ANSI/EIA/TIA 568, which are primary component standards for mated plugs and jacks for transmission frequencies up to 250 MHz. 
     Alien NEXT is the differential crosstalk that occurs between communication channels. Obviously, physical separation between jacks will help and/or typical crosstalk approaches may be employed. However, a problem case may be “pair 3” of one channel crosstalking to “pair 3” of another channel, even if the pair 3 plug and jack wires in each channel are remote from each other and the only coupling occurs between the routed cabling. To reduce this form of alien NEXT, shielded systems containing shielded twisted pairs or foiled twisted pair configurations may be used. However, the inclusion of shields can increase cost of the system. Another approach to reduce or minimize alien NEXT utilizes spatial separation of cables within a channel and/or spatial separation between the jacks in a channel. However, this is typically impractical because bundling of cables and patch cords is common practice due to “real estate” constraints and ease of wire management. 
     In spite of recent strides made in improving mated connector (i.e., plug jack) performance, and in particular reducing crosstalk at elevated frequencies (e.g., 500 MHz—see U.S. patent application Ser. No. 10/845,104, entitled NEXT High Frequency Improvement by Using Frequency Dependent Effective Capacitance, filed May 4, 2004, the disclosure of which is hereby incorporated herein by reference), channels utilizing connectors that rely on either these teachings or those of the &#39;358 patent can still exhibit unacceptably high alien NEXT, particularly at very high frequencies (e.g., 500 MHz). 
     SUMMARY OF THE INVENTION 
     The present invention can provide communications jacks with improved differential to common mode and differential to differential NEXT and FEXT performance, particularly at high frequencies. As a first aspect, embodiments of the present invention are directed to a wiring board for a communications jack, comprising: a dielectric mounting substrate; and a plurality of contact wires mounted in the mounting substrate, each of the contact wires including a fixed end portion mounted in the mounting substrate and a free end portion, each of the free end portions having substantially the same profile and being substantially transversely aligned in side-by-side relationship. A first pair of contact wires is sandwiched inside a second pair of contact wires. The second pair of contact wires includes a crossover, the positioning of crossover being selected to provide differential to common mode crosstalk compensation. 
     As a second aspect, embodiments of the present invention are directed to a wiring board for a communications jack, comprising: a dielectric mounting substrate; and first, second, third and fourth pairs of contact wires mounted in the mounting substrate, each of the contact wires including a fixed end portion mounted in the mounting substrate and a free end portion, each of the free end portions having substantially the same profile and being substantially transversely aligned in side-by-side relationship. The wires of the first pair of contact wires are immediately adjacent to each other and are sandwiched inside the third pair of contact wires, the wires of the second pair are immediately adjacent to each other, the wires of the fourth pair are immediately adjacent to each other, and the second and fourth pairs sandwich the third pair. The third pair of contact wires includes a crossover, the positioning of crossover being selected to provide differential to common mode crosstalk compensation. 
     As a third aspect, embodiments of the present invention are directed to a communications jack assembly, comprising: a jack frame having a plug aperture; a dielectric mounting substrate attached to the jack frame; and a plurality of conductors engaged with the mounting substrate, each of the conductors including a fixed end portion mounted with the mounting substrate and a free end portion extending into the plug aperture for electrical contact with a mating plug, each of the free end portions having substantially the same profile and being substantially transversely aligned in side-by-side relationship. A first pair of conductors is sandwiched inside a second pair of conductors. The second pair of conductors includes a crossover, the positioning of crossover being selected to provide differential to common mode crosstalk compensation. 
     Pursuant to further embodiments of the present invention, communications jacks are provided which include a housing having a plug aperture and a wiring board. These jacks further include a first contact wire and a second contact wire that form a first differential pair of contact wires, the first and second contact wires each having a fixed end portion that is mounted in the wiring board and a deflectable portion that is at least partially positioned in the plug aperture. These jacks also include a third contact wire and a fourth contact wire that form a second differential pair of contact wires, the third and fourth contact wires each having a fixed end portion that is mounted in the wiring board and a deflectable portion that is at least partially positioned in the plug aperture. In these jacks, at least a portion of the first differential pair of contact wires is sandwiched in between the contact wires of the second differential pair of contact wires, and the third contact wire crosses over the deflectable portion of the first contact wire and the deflectable portion of the second contact wire. 
     In some embodiments of these jacks the fourth contact wire may cross under the deflectable portion of the first contact wire and the deflectable portion of the second contact wire. Moreover, the fourth contact wire may also cross under the deflectable portion of the third contact wire and the third contact wire may also cross over the deflectable portion of the fourth contact wire. The portion of the third contact wire that crosses over the deflectable portions of the first and second contact wires may be a crossover segment, and the third contact wire may include a support finger. The crossover segment may be between the fixed end portion of the third contact wire and the support finger. The support finger may be supported by a separate support stricture. 
     In further embodiments of the present invention, communications jacks are provided which again include a housing having a plug aperture and a wiring board. The jacks also include a first contact wire and a second contact wire that form a first differential pair of contact wires, the first and second contact wires each comprising a wire segment that includes a fixed end mounted in the wiring board and a free end, as well as a third contact wire and a fourth contact wire that form a second differential pair of contact wires. The third and fourth contact wires, however, may each comprise a wire segment that includes a fixed end mounted in the wiring board and a free end, and a support finger that branches off of the wire segment between the fixed end and the free end. 
     In these jacks, the second differential pair of contact wires may include a crossover that is located in a deflectable portion of the contact wires. Moreover, the support finger of the third contact wire may engage a first support structure and the support finger of the fourth contact wire may engage a second support structure. These jacks may also include a stop that engages a distal end portion of the support finger of the third contact wire. 
     Pursuant to still further embodiments of the present invention, communications jacks are provided which include a housing having a plug aperture, a wiring board, a first contact wire and a second contact wire that form a first differential pair of contact wires, the first and second contact wires each having a fixed end portion that is mounted in the wiring board and a free end portion and a third contact wire and a fourth contact wire that form a second differential pair of contact wires, the third and fourth contact wires each having a fixed end portion that is mounted in the wiring board, a free end portion, an intermediate segment connecting the fixed end portion and the free end portion and a support finger branching off of the intermediate segment, the support finger including a base end that connects to the intermediate segment and a distal end opposite the base end. In these jacks, the support finger and the free end portion of the third contact wire may be substantially aligned in a longitudinal direction and may not be aligned with the fixed end portion of the third contact wire. 
     In these jacks, the third contact wire may be configured so that the support finger and the free end portion of the third contact wire form a beam that absorbs substantially all of the strain experienced by the third contact wire in response to insertion of a mating plug into the plug aperture. In addition, the distal end of the support finger of the third contact wire may not be fixedly mounted. These jacks may also include a first stop that engages the distal end of the support finger of the third contact wire and/or a second stop that engages the free end of the third contact wire when a mating plug is inserted into the plug aperture and then removed. 
     Pursuant to still further embodiments of the present invention, communications jacks are provided that include a housing having a plug aperture. These jacks further include a first contact wire and a second contact wire that form a first differential pair of contact wires, as well as a third contact wire and a fourth contact wire that form a second differential pair of contact wires. The first and second contact wires each including a first end, a second end and an intermediate portion connecting the first end and the second end. In addition, the jacks include a first conductive element branching off of the intermediate portion of the first contact wire. This first conductive element crosses over the third contact wire and the fourth contact wire. The jacks also include a second conductive element branching off of the intermediate portion of the second contact wire. The second conductive element similarly crosses under the third contact wire and the fourth contact wire. 
     In these jacks, the first ends and the second ends of the first and second contact wires may be free-floating. The jacks may also include a wiring board. The first conductive element may comprise a signal carrying path from the first contact wire onto the wiring board, and the second conductive element may comprise a signal carrying path from the second contact wire onto the wiring board. The jacks may further include a first stop that engages the first end of the first contact wire, a second stop that engages the first end of the second contact wire, a third stop that engages the second end of the first contact wire and/or a fourth stop that engages the second end of the second contact wire. In some embodiments of these jacks, the first conductive element may be a fixed end portion of the first contact wire, the first end of the first contact wire may be a distal end of a support finger of the first contact, the second conductive element may be a fixed end portion of the second contact wire, and/or the first end of the second contact wire may be a distal end of a support finger of the second contact. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is an exploded perspective view of a prior art communications jack. 
         FIG. 1A  is an enlarged perspective view of the prior art communications jack of  FIG. 1 . 
         FIG. 1B  is a top view of the wiring board of  FIG. 1A . 
         FIG. 2  is a side view of contact wires of the jack of  FIG. 1 . 
         FIG. 3  is a top schematic view of contact wires of the prior art jack of  FIG. 1 . 
         FIG. 4  is a top schematic view of contact wires of an embodiment of a communications jack according to the present invention. 
         FIG. 5  is an enlarged perspective view of contact wires following the configuration illustrated in  FIG. 4  according to embodiments of the present invention. 
         FIG. 6  is an enlarged side view of contact wires of  FIG. 5  in a wiring board. 
         FIG. 7  is a perspective view of a communications jack that includes the contact wires of  FIG. 5  according to embodiments of the present invention. 
         FIG. 7A  is an enlarged perspective view of the communications jack of  FIG. 7 . 
         FIGS. 8A-8D  are graphs plotting forward and reverse differential to common mode NEXT and FEXT as a function of frequency for pairs 3 and 2. 
         FIGS. 9A-9D  are graphs plotting forward and reverse differential to common mode NEXT and FEXT as a function of frequency for pairs 3 and 4. 
         FIG. 10  is a perspective view of contact wires of a communications jack according to further embodiments of the present invention. 
         FIG. 11  is a perspective view of two of the contact wires depicted in  FIG. 10  that shows how those contact wires engage a plurality of stops. 
         FIG. 12  is a perspective view of the two contact wires of  FIG. 11  mounted on a support structure of the communications jack. 
         FIG. 13  is an exploded perspective view of a communications jack according to embodiments of the present invention that includes the contact wire configuration of  FIG. 10  with all but two of the contact wires removed. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention will be described more particularly hereinafter with reference to the accompanying drawings. The invention is not intended to be limited to the illustrated embodiments; rather, these embodiments are intended to fully and completely disclose the invention to those skilled in this art. In the drawings, like numbers refer to like elements throughout. Thicknesses and dimensions of some components may be exaggerated for clarity. 
     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the description of the invention and the appended claims, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     This invention is directed to communications connectors, with a primary example of such being a communications jack. As used herein, the terms “forward”, “forwardly”, and “front” and derivatives thereof refer to the direction defined by a vector extending from the center of the jack toward the plug opening of the jack. Conversely, the terms “rearward”, “rearwardly”, and derivatives thereof refer to the direction directly opposite the forward direction; the rearward direction is defined by a vector that extends away from the plug opening toward the remainder of the jack. The terms “lateral,” “laterally”, and derivatives thereof refer to the direction generally parallel with the plane defined by a wiring board on which jack contact wires are mounted and extending away from a plane bisecting the plug in the center. The terms “medial,” “inward,” “inboard,” and derivatives thereof refer to the direction that is the converse of the lateral direction, i.e., the direction parallel with the plane defined by the wiring board and extending from the periphery of the jack toward the aforementioned bisecting plane. Where used, the terms “attached”, “connected”, “interconnected”, “contacting”, “mounted” and the like can mean either direct or indirect attachment or contact between elements, unless stated otherwise. Where used, the terms “coupled,” “induced” and the like can mean non-conductive interaction, either direct or indirect, between elements or between different sections of the same element, unless stated otherwise. 
     Referring now to the figures, a prior art jack, designated broadly at  10 , is illustrated in  FIGS. 1 and 1A . The jack  10  includes a jack frame  12  having a plug aperture  14  for receiving a mating plug, a cover  16  and a terminal housing  18 . These components are conventionally formed and not need be described in detail herein; for a further description of these components and the manner in which they interconnect, see U.S. Pat. No. 6,350,158 to Arnett et al., the disclosure of which is hereby incorporated herein in its entirety. Those skilled in this art will recognize that other configurations of jack frames, covers and terminal housings may also be employed with the present invention. Exemplary configurations are illustrated in U.S. Pat. Nos. 5,975,919 and 5,947,772 to Arnett et al. and U.S. Pat. No. 6,454,541 to Hashim et al., the disclosure of each of which is hereby incorporated herein in its entirety. 
     In addition, referring still to  FIG. 1  and also to  FIG. 2 , the jack  10  further includes a wiring board  20  formed of conventional materials. The wiring board  20  may be a single layer board or may have multiple layers. The wiring board  20  may be substantially planar as illustrated, or may be non-planar. 
     Referring again to  FIGS. 1 and 1A , contact wires  22   a ,  22   b ,  24   a ,  24   b ,  26   a ,  26   b ,  28   a ,  28   b  are attached to the wiring board  20 . As described in U.S. Pat. No. 6,350,158 referenced above, the contact wires  22   a ,  22   b ,  24   a ,  24   b ,  26   a ,  26   b ,  28   a ,  28   b  have free ends that have substantially the same profile, are substantially transversely aligned in side-by-side relationship, and that extend into the plug aperture  14  to form electrical contact with the terminal blades of a mating plug. The free ends of the contact wires  22   a ,  22   b ,  24   a ,  24   b ,  26   a ,  26   b ,  28   a ,  28   b  extend into individual slots  29   a - 29   h  in the forward edge portion of the wiring board  20 . The contact wires  22   a ,  22   b ,  24   a ,  24   b ,  26   a ,  26   b ,  28   a ,  28   b  are arranged in pairs defined by TIA 568B, with wires  22   a ,  22   b  (pair 1) being adjacent to each other and in the center of the sequence of wires, wires  24   a ,  24   b  (pair 2) being adjacent to each other and occupying the leftmost two positions (from the vantage point of  FIG. 1B ) in the sequence, wires  28   a ,  28   b  (pair 4) being adjacent to each other and occupying the rightmost two positions (from the vantage point of  FIG. 1B ) in the sequence, and wires  26   a ,  26   b  (pair 3) being positioned between, respectively, pairs 1 and 4 and pairs 1 and 2. The wires  22   a ,  22   b ,  24   a ,  24   b ,  26   a ,  26   b ,  28   a ,  28   b  are mounted to the wiring board  20  via insertion into respective apertures  32   a ,  32   b ,  34   a ,  34   b ,  36   a ,  36   b ,  38   a ,  38   b , which are arranged in the illustrated embodiment in a “dual diagonal” pattern known to those skilled in this art as described in U.S. Pat. No. 6,196,880 to Goodrich et al., the disclosure of which is hereby incorporated herein in its entirety. Those skilled in this art will appreciate that contact wires or other contacts of other configurations may be used. As one example, contact wires configured as described in aforementioned U.S. Pat. No. 5,975,919 to Arnett et al. may be employed. 
     As can be seen in  FIGS. 1A and 3 , each of pairs 1, 2 and 4 that comprise adjacent contact wires include a respective “crossover”  22   c ,  24   c ,  28   c , i.e., a location in which the contact wires of a pair cross each other without making electrical contact, typically such that the free end of one contact wire of the pair is substantially longitudinally aligned with the fixed end portion of the other contact wire of the pair. The crossovers  22   c ,  24   c ,  28   c  are located approximately in the center of their contact wires (between the free ends of the contact wires and their mounting locations on the wiring board  20 ). Crossovers are included to provide compensatory crosstalk between contact wires. In the illustrated embodiment, the crossovers are implemented via complementary localized bends in the crossing wires, with one wire being bent upwardly and the other wire being bent downwardly. The presence of a crossover, structural implementations thereof, and its effect on crosstalk are discussed in some detail in the &#39;358 patent described above and U.S. Pat. No. 5,186,647 to Denkmann et al., the disclosure of which is hereby incorporated herein by reference. In this prior art device, the contact wires of pair 3 (wires  26   a ,  26   b ) do not include a crossover. 
     Referring once again to  FIGS. 1 and 1A  and to  FIG. 1B , eight insulation displacement connectors (IDCs)  42   a ,  42   b ,  44   a ,  44   b ,  46   a ,  46   b ,  48   a ,  48   b  are inserted into eight respective IDC apertures  52   a ,  52   b ,  54   a ,  54   b ,  56   a ,  56   b ,  58   a ,  58   b . The IDCs are of conventional constriction and need not be described in detail herein; exemplary IDCs are illustrated and described in U.S. Pat. No. 5,975,919 to Arnett, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     Referring now to  FIGS. 1A ,  1 B and  2 , the each of the wire apertures  32   a ,  32   b ,  34   a ,  34   b ,  36   a ,  36   b ,  38   a ,  38   b  is electrically connected to a respective IDC aperture  52   a ,  52   b ,  54   a ,  54   b ,  56   a ,  56   b ,  58   a ,  58   b  via a respective conductor  62   a ,  62   b ,  64   a ,  64   b ,  66   a ,  66   b ,  68   a ,  68   b , thereby interconnecting each of the contact wires  22   a ,  22   b ,  24   a ,  24   b ,  26   a ,  26   b ,  28   a ,  28   b  to its corresponding IDC  42   a ,  42   b ,  44   a ,  44   b ,  46   a ,  46   b ,  48   a ,  48   b . The conductors  62   a ,  62   b ,  64   a ,  64   b ,  66   a ,  66   b ,  68   a ,  68   b  are formed of conventional conductive materials and are deposited on the wiring board  20  via any deposition method known to those skilled in this art to be suitable for the application of conductors. Some conductors are illustrated as being entirely present on a single layer of the wiring board  20  (for example, conductor  62   a ), while other conductors (for example, conductor  62   b ) may reside on multiple layers of the wiring board  20 ; conductors can travel between layers through the inclusion of vias (also known as plated through holes) or other layer-transferring structures known to those skilled in this art. 
     U.S. Pat. No. 5,967,853 to Hashim (the disclosure of which is hereby incorporated herein in its entirety) describes a technique whereby capacitive compensation is used to simultaneously compensate differential to differential and differential to common mode crosstalk. However, in order to effectively cancel both NEXT and FEXT it is typically necessary to provide both inductive and capacitive compensation. The prior art arrangement of contact wires disclosed in  FIGS. 1-3  has been proven to effectively and efficiently provide inductive differential to differential crosstalk compensation. However, it has been determined that this arrangement may be ineffective, and perhaps counterproductive, in providing inductive differential to common mode compensation in the jack  10 . More specifically, the prior art arrangement provides inductive differential to differential crosstalk compensation between pairs 1 and 3, pairs 2 and 3, and pairs 4 and 3, but in the development of the present invention it has been recognized that, due to the large physical separation between the conductors of pair 3 and their asymmetric placement relative to pair 2 (and similarly to pair 4 ), the highest levels of differential to common mode crosstalk in a mating plug, which can be the most problematic to channel performance, tend to occur on pairs 2 and 4 when pair 3 is excited differentially. The differential to common mode crosstalk occurring when any of the pairs 1, 2 and 4 is excited differentially tends to be much less severe, and consequently much less problematic, because the separation between the conductors in each of these pairs is one-third the separation between the conductors of pair 3. In the prior art arrangement of contact wires disclosed in  FIGS. 1-3 , crossover on each of pairs 1, 2 and 4 inductively compensates for the less severe differential to common mode crosstalk occurring when any of these pairs is differentially excited. However, due to the absence of a crossover on pair 3, this arrangement not only fails to inductively compensate for the more severe common mode crosstalk on pairs 2 and 4 when pair 3 is differentially excited, but can actually exacerbate this problem. This is especially true when the jack receives a conventional plug such as the one illustrated in U.S. Pat. No. 6,250,949 to Lin. 
     Turning now to  FIG. 4 , an arrangement of wires according to embodiments of the present invention, designated broadly at  120 , is illustrated schematically therein. The wiring arrangement  120  includes eight contact wires  122   a ,  122   b ,  124   a ,  124   b ,  126   a ,  126   b ,  128   a ,  128   b  that comprise, respectively, wire pairs 1, 2, 3 and 4. In contrast to the prior art arrangement of contact wires described above, in this embodiment the contact wires  122   a ,  122   b  of pair 1, the contact wires  124   a ,  124   b  of pair 2, and the contact wires  128   a ,  128   b  of pair 4 do not include a crossover, while the contact wires  126   a ,  126   b  include a crossover  126   c.    
     Like the prior arrangement, this arrangement of contact wires should provide compensatory inductive differential to differential crosstalk between pairs 1 and 3, pairs 2 and 3, and pairs 4 and 3. In addition, this arrangement, although not inductively compensating for the less severe differential to common mode crosstalk occurring when any of the pairs 1, 2 and 4 is differentially excited, can provide inductive compensation for the highly problematic differential to common mode crosstalk occurring on pairs 2 and 4 when pair 3 is differentially excited. Because the most problematic differential to common mode crosstalk can be inductively compensated, a jack employing this arrangement can meet higher performance standards, particularly at elevated frequencies. 
     An exemplary implementation of this arrangement is illustrated in  FIGS. 5-7A , in which a jack  200  according to embodiment of the present invention is shown. The jack  200  includes a jack frame  212  having a plug aperture  214 , a cover  216  and a terminal housing  218 . A wiring board  220  includes IDCs  242   a - 248   b  mounted thereon. Contact wires  222   a - 228   b  are mounted to the wiring board  220 . At their free ends, the contact wires  222   a - 228   b  fit within slots  229   a - 229   h  located at the forward end of the wiring board  220  and are positioned to mate with the blades of a plug inserted into the plug aperture  214 . With the exception of the crossover region  226   c , described in greater detail below, the contact wires  222   a - 228   b  follow generally the same profile until they bend downwardly into their respective mounting apertures in the wire board  220 . Conductive traces on the wiring board  220  provide signal paths between the contact wires  222   a - 228   b  and the IDCs  242   a - 248   b.    
     Referring now to  FIG. 5 , the contact wires  226   a ,  226   b  form the crossover  226   c  with the assistance of supports  227   a ,  227   b . Each of the contact wires  226   a ,  226   b  includes a transversely-extending crossover segment  231  that travels either over (in the case of the contact wire  226   a ) or under (in the case of contact wire  226   b ) the contact wires  222   a ,  222   b . Each of the contact wires  226   a ,  226   b  also includes a support finger  233  that extends rearwardly from the crossover segment  231  to rest atop a respective support  227   a ,  227   b . The supports  227   a ,  227   b  extend upwardly from the wiring board  220  from locations approximately halfway between the free ends of the contact wires  226   a ,  226   b  and their mounting locations  236   a ,  236   b  in the wiring board  220 . In some embodiments the support finger  233  of each contact wire  226   a ,  226   b  may extend from its crossover segment at substantially the same angle, such that the supports  227   a ,  227   b  are of different heights in order to support the crossover segment  231  of each contact wire  226   a ,  226   b  at the proper elevation. In other embodiments, the supports  227   a ,  227   b  may be of the same height, and the support finger  231  of each crossover segment may extend therefrom at different angles, or the supports may be of different heights and the fingers may extend at different angles. 
     This configuration enables the free ends of the contact wires  226   a ,  226   b  to deflect in response to the insertion of a plug in the plug aperture  214  without contacting the contact wires  222   a ,  222   b . The illustrated embodiment has the advantage of enabling the commencement of the inductive differential to differential and differential to common mode compensations at minimal delay from the corresponding crosstalk sources, which can be important to effective crosstalk compensation. The separation between the crossover segments  231  and the locations where the contact wires  222   a ,  222   b  intercept a mating plug is about 0.154 inches, but those skilled in this art will appreciate that a separation gap of a different size may also be suitable with the present invention. Typically the contact wires are between about 0.648 and 0.828 inches in length, and the crossover  226   c  occurs between about 0.3 and 0.4 inches from the free ends of the contact wires  226   a ,  226   b.    
     The skilled artisan will recognize that, although eight contact wires are illustrated and described herein, other numbers of contact wires may be employed. For example, 16 contact wires may be employed, and one or more crossovers that cross over a pair of contact wires sandwiched therebetween may be included in those contact wires. 
     Further, those skilled in this art will recognize that other jack configurations may also be suitable for use with the present invention. For example, as discussed above, other configurations of jack frames, covers and terminal housings may also be employed with the present invention. As another example, the contact wires may have a different profile (an exemplary alternative profile is depicted in U.S. Pat. No. 5,975,919 to Arnett et al.), or they may by replaced by conductive paths on a flexible circuit, and they may mount in locations that do not follow the “dual diagonal” mounting scheme illustrated herein (an exemplary alternative is illustrated in U.S. Pat. No. 6,116,964 to Goodrich et al). As a further example, the IDCs may mount in a different pattern on the wiring board, or some other type of connector may be used. Those skilled in this art will also recognize that embodiments of the wiring board described above may be employed in other environments in which a communications jack may be found. For example, jacks within a patch panel or series of patch panels may be suitable for use with such wiring boards. Other environments may also be possible. It may also be recognized that the contact wires may not include any crossovers on any of the pairs, but rather the wiring board to which they are attached can have its signal carrying conductive paths routed in accordance with the crossover scheme described generally in  FIG. 4 . 
     Moreover, those skilled in this art will further recognize that the crossover of pair 3 described above can be implemented, with similar beneficial effect on differential to common mode crosstalk conversion, by forming the conductor leads of jacks utilizing metallic lead-frame structures instead of printed wiring boards to achieve the required connectivity and crosstalk compensation. In such a configuration, the contact wires and/or the insulation displacement connectors may be formed integrally with the conductors as unitary members. 
     The configuration illustrated and described herein can provide connectors, and in particular communications jacks, that exhibit improved crosstalk characteristics, particularly at elevated frequencies. For example, a connector such as that illustrated in  FIGS. 5-7A  and mated with a conventional plug may have channel alien NEXT of less than −60 dB power sum at 100 MHz, and less than −49.5 dB power sum at 500 MHz. 
     Also those skilled in the art will recognize that in situations where it may not be critical to implement the differential to differential crosstalk compensation between pairs 3 and 2 and between pairs 3 and 4 in the contact wires, it is possible to provide instead compensation for the common mode crosstalk induced on pair 3, or pair 1, when either of pair 2 or pair 4 is differentially excited, by modifying the contact wire crossover scheme of  FIG. 4  to include crossovers in pairs 2 and 4 in addition to the crossover on pair 3. 
     Further, those skilled in the art will recognize the reciprocity that exists between the differential to common mode crosstalk induced on a first pair, when a second pair is excited differentially, and the common mode to differential signal induced on the second of these pairs when the first of these pairs is excited common-modally, with the common mode to differential crosstalk equaling the differential to common mode crosstalk multiplied by a constant, that constant being the ratio of the differential to common mode impedances. Consequently, when an improvement occurs, due to the current invention, in the differential to common mode crosstalk between two pairs when one of these pairs is excited differentially, a corresponding improvement occurs in the common mode to differential crosstalk between these two pairs, when the other of these pairs is excited common-modally. 
     The invention is described in greater detail herein in the following non-limiting example. 
     EXAMPLE 
     Communication jacks of the configuration illustrated in  FIG. 1 , mated with conventional plugs, were modeled and solved using finite element electromagnetic field simulation software. In one jack model designated “experimental jack”, the contact wire crossover configuration substantially matched the embodiment of the current invention illustrated in  FIGS. 5-7A . In a second jack model, designated “prior art jack”, the contact wire crossover configuration substantially matched the prior art jack illustrated in  FIGS. 1-3 . The jack models were then solved for differential to common mode NEXT and FEXT crosstalk. 
     Differential to Common Mode Results for the problematic 3-2 and 3-4 pair combinations, where pair 3 is the differentially excited pair, are shown in  FIGS. 8A-8D  and  FIGS. 9A-9D . For each of these pair combinations results are provided for forward NEXT, forward FEXT, reverse FEXT and reverse NEXT, wherein the term “forward” represents the testing orientation in which the excitation is injected from the cordage end of the plug and term “reverse” represents the testing orientation in which the excitation is injected from building cable end of the jack. It can be seen that in all these cases the experimental jack employing the pair 3 crossover exhibited significant improvements in differential to common mode crosstalk (i.e. lower decibel levels) over the prior art jack, within the frequency band of interest of 10-500 MHz. 
       FIGS. 10-13  illustrate a communications jack  300  according to further embodiments of the present invention. In particular,  FIG. 10  illustrates the contact wire configuration for the jack  300 ,  FIG. 11  shows how two of the contact wires of  FIG. 10  may interact with a plurality of stops,  FIG. 12  illustrates one implementation for two of the stops of  FIG. 11 , and  FIG. 13  is an exploded perspective view of the entire jack  300  with six of the contact wires removed. 
     As shown in  FIG. 13 , the jack  300  includes a jack frame  312  having a plug aperture  314  for receiving a mating plug, a cover  316 , a terminal housing  318 , a wiring board  320 , and a plurality of insulation displacement connectors (IDCs)  342   a ,  342   b ,  344   a ,  344   b ,  346   a ,  346   b ,  348   a ,  348   b . The wiring board  320  is located at least partially within the housing of the jack  300  (in jack  300  the housing comprises the jack frame  312 , the cover  316  and the terminal housing  318 ). These components are conventionally formed and/or are described above with respect to other embodiments of the present invention, and hence will not be described in further detail herein. Those skilled in this art will recognize that other configurations of jack frames, covers, terminal housings, wiring boards and IDCs may also be employed in further embodiments of the present invention. 
     As shown best in  FIG. 10 , the jack  300  further includes eight contact wires  322   a ,  322   b ,  324   a ,  324   b ,  326   a ,  326   b ,  328   a ,  328   b . In the jack  300  the free ends of the contact wires  322   a ,  322   b ,  324   a ,  324   b ,  326   a ,  326   b ,  328   a ,  328   b  have substantially the same profile and are substantially transversely aligned in side-by-side relationship. However, it will be appreciated that other configurations may also be used. As shown best in  FIG. 13 , the free ends of the contact wires  322   a ,  322   b ,  324   a ,  324   b ,  326   a ,  326   b ,  328   a ,  328   b  extend into the plug aperture  314  of the jack to form electrical contact with the blades of a mating plug (not shown in  FIGS. 10-13 ). The free ends of the contact wires  322   a ,  322   b ,  324   a ,  324   b ,  326   a ,  326   b ,  328   a ,  328   b  extend into individual slots  329   a - 329   h  in the forward edge portion of the wiring board  320 . The contact wires  322   a ,  322   b ,  324   a ,  324   b ,  326   a ,  326   b ,  328   a ,  328   b  are arranged in pairs defined by TIA 568B, and are mounted to the wiring board  320  via insertion into respective apertures (not shown) in the wiring board  320 . As in the above-described embodiments of the present invention, the contact wires  322   a ,  322   b ,  324   a ,  324   b ,  326   a ,  326   b ,  328   a ,  328   b  are electrically connected to the IDCs  342   a ,  342   b ,  344   a ,  344   b , 346   a ,  346   b ,  348   a ,  348   b  via conductors (not shown) formed on and/or in the wiring board  320 . 
     The eight contact wires  322   a ,  322   b ,  324   a ,  324   b ,  326   a ,  326   b ,  328   a ,  328   b  comprise, respectively, wire pairs 1, 2, 3 and 4. As with the previous embodiment, the contact wires  322   a ,  322   b  of pair 1, the contact wires  324   a ,  324   b  of pair 2, and the contact wires  328   a ,  328   b  of pair 4 do not include a crossover, while the contact wires  326   a ,  326   b  include a crossover. Thus, this contact wire arrangement should provide compensatory inductive differential to differential crosstalk between pairs 1 and 3, pairs 2 and 3, and pairs 4 and 3, as well as inductive compensation for the differential to common mode crosstalk occurring on pairs 2 and 4 when pair 3 is differentially excited. 
     As shown best in  FIG. 11 , the contact wires  326   a ,  326   b  of pair 3 each include a fixed end portion  362 ,  372  that includes a termination (also referred to as a “fixed end”)  361 ,  371  that is mounted in the wiring board  320 , a deflectable free end portion  363 ,  373 , and a support finger  366 ,  376 . The deflectable free end portion of each contact wire  326   a ,  326   b  includes a crossover segment  363 ,  373  and a plug contact region  364 ,  374  where each contact  326   a ,  326   b  contacts a respective blade of a mating plug. The portion of contact wire  326   a  forming a direct path between the fixed end  361  and the far end of the free end portion  363  comprises an intermediate portion of the contact wire  326   a . The support finger  366  branches off of this intermediate portion. Likewise, the portion of contact wire  326   b  forming a direct path between the fixed end  371  and the far end of the free end portion  373  comprises an intermediate portion of the contact wire  326   b . The support finger  376  branches off of this intermediate portion. In the embodiment of  FIGS. 10-13 , the crossover segments  363 ,  373  are transversely-extending crossover segments that travel either over (in the case of the contact wire  326   b ) or under (in the case of contact wire  326   a ) the contact wires  322   a ,  322   b . The support fingers  366 ,  376  each extend rearwardly from the crossover segment  363 ,  373 , and each support finger includes a respective distal end  367 ,  377 . As shown in  FIG. 12 , the distal ends  367 ,  377  of the support fingers  366 ,  376  rest atop respective supports  327   a ,  327   b . In the pictured embodiment, the supports  327   a ,  327   b  are at different elevations above the top surface of the wiring board  320  in order to support the respective crossover segments  363 ,  373  of contact wires  326   a ,  326   b  at the proper elevation. It will be appreciated, however, that in other embodiments, the supports  327   a ,  327   b  may be of the same height and/or that the support fingers  366 ,  376  of each crossover segment may extend therefrom at different angles, or the supports may be of different heights and the fingers may extend at different angles. 
     Referring now to  FIG. 12 , note that, because of the extended length of the transverse crossover segment, the plug contact region  364 ,  374  of contacts  326   a ,  326   b  may be offset by a relatively large distance from the respective fixed end  361 ,  371  of each contact. As such, the contacts  326   a ,  326   b  may not have sufficient support which, in certain circumstances, may allow one or both of the contacts  326   a ,  326   b  to make physical and electrical contact with one or both of contacts  322   a ,  322   b  when the contacts of the jack  300  are deflected as a mating connector is received within the plug aperture  314 . Thus, as discussed above, each contact  326   a ,  326   b  may include a respective support finger  366 ,  376  that engages a respective support element  327   a ,  327   b  to ensure that sufficient support is provided so that such short-circuiting of either or both contacts  326   a ,  326   b  will not occur. As shown best in  FIGS. 11 and 12 , the distal ends  367 ,  377  of the respective support fingers  366 ,  376  do not terminate into the wiring board  320  in this particular embodiment of the present invention, as the signal carrying path to the wiring board is through the crossover segment  363  and fixed end portion  362  for contact  326   a  and through the crossover segment  373  and fixed end portion  372  for contact  326   b . Instead, the distal ends  367 ,  377  of the support fingers  366 ,  376  engage respective supports  327   a ,  327   b  (see  FIG. 12 ) to provide sufficient support so that the contact wires  326   a ,  326   b  do not make physical contact with any of the other contact wires during normal operation of the jack  300 . 
     As shown in  FIG. 12 , pursuant to embodiments of the present invention, the support finger  366  and the free end  365  of contact  326   a  may form a beam structure  368 . This beam structure  368  may absorb all or practically all of the strain experienced by the contact wire  326   a  in response to insertion of a mating plug into the plug aperture  314 , and thus provides the contact force that holds the contact  326   a  against a corresponding blade of the plug such that a reliable electrical connection is established between the plug blade and contact  326   a . As such, the crossover segment  363  of contact  326   a  and the fixed end portion  362  need not absorb any of the strain for contact wire  326   a . In fact, in some embodiments, the crossover segment  363  of contact  326   a  and the fixed end portion  362  could be replaced by electrical lead wires (i.e., non-flexure members) that merely provide a conductive path from the contact  326   a  onto the wiring board  320 . Similarly, the support finger  376  and the free end  375  of contact  326   b  may form a beam structure  378 . This beam structure  378  may absorb all or practically all of the strain experienced by contact wire  326   b  in response to insertion of a mating plug into the plug aperture  314 , and thus provides the contact force that holds the contact  326   b  against a corresponding blade of the plug such that a reliable electrical connection is established between the plug blade and contact  326   b . As such, the crossover segment  373  of contact  326   b  and the fixed end portion  372  need not absorb any of the strain for contact wire  326   b.    
     As shown best in  FIGS. 11 and 12 , a plurality of stops  351 - 354  may be included in the connector  300 . In particular, a stop  353  may be provided adjacent the free end  365  of contact  326   a , a stop  351  may be provided adjacent the free end  375  of contact  326   b , a stop  354  may be provided adjacent the distal end  367  of the support finger  366  of contact  326   a , and a stop  352  may be provided adjacent the distal end  377  of the support finger  376  of contact  326   b . These stops  351 - 354  may be implemented, for example, as plastic walls in the contact dividing structure  369 , although it will be appreciated that numerous other ways of implementing these stops are possible. The plastic stops  354  and  352  may facilitate preventing over-bending of the crossover segments  363  and  373 , respectively, when a mating plug is inserted into the plug aperture  314 . The plastic stops  353  and  351  may facilitate preventing over-bending of the crossover segments  363  and  373  when a mating plug is removed from the plug aperture  314 . 
     Also, neither the distal ends  367 ,  377  of the support fingers  366 ,  376  nor the free ends  365 ,  375  of the contacts  326   a ,  326   b  are fixedly mounted in the embodiment of  FIGS. 10-13 . Instead, as shown best in  FIG. 12  the distal ends  367 ,  377  of the support fingers  366 ,  376  of the contacts  326   a ,  326   b  are supported by the supports  327   a ,  327   b , respectively. The free ends  365 ,  375  of the contacts  326   a ,  326   b  may likewise be supported by the top surface of the wiring board  320  when a mating plug is received in the jack aperture  314  (and may or may not engage the wiring board  320  in the absence of a mating plug). Thus, both the distal ends  367 ,  377  of the support fingers  366 ,  376  and the free ends  365 ,  375  of the contacts  326   a ,  326   b  may move some distance when a mating plug is inserted into and/or removed from the plug aperture until these ends engage the respective stops  351 - 354  which prevent further movement. By leaving both the distal ends  367 ,  377  of the support fingers  366 ,  376  and the free ends  365 ,  375  of the contacts  326   a ,  326   b  unclamped (i.e., not fixedly mounted), improved flexture may be provided and the overall length of the portion of the contacts  326   a ,  326   b  forming the beams  368  and  378  may be correspondingly reduced if desired. 
     In operation, the free ends  365 ,  375  of the contact wires  326   a ,  326   b  deflect in response to the insertion of a plug in the plug aperture  314  without contacting the contact wires  322   a ,  322   b . The illustrated embodiment has the advantage of enabling the commencement of the inductive differential to differential and differential to common mode compensations at minimal delay from the corresponding crosstalk sources, which can be important to effective crosstalk compensation. The separation between the crossover segments  363 ,  373  and the location where the contact wires  322   a ,  322   b  intercept a mating plug is about 0.15 inches, but those skilled in this art will appreciate that a separation gap of a different size may also be suitable with the present invention. 
     Those skilled in this art will recognize that various modifications may be made to the communications jack of  FIGS. 10-13  such as, for example, the modifications discussed above that could be made to the communications jack of  FIGS. 5-7 , and that such modifications are within the scope of the present invention. 
     The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the claims. The invention is defined by the following claims, with equivalents of the claims to be included therein.