Abstract:
A method for assembling an impedance controlled connector using conventional connector shells and inserts and corresponding connector pins and sockets. Controlled impedance cables are prepared and physically arranged for termination in a conventional connector shell in a configuration which enhances the impedance control characteristic of the assembled connector. Assembly of the connector is effected using conventional materials and tools.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from U.S. Provisional Patent Application Serial No. 60/181,719, filed on Feb. 11, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to electrical connectors and, more particularly, to a method for assembling a controlled impedance electrical connector using conventional components. 
     2. The Prior Art 
     Electrical signals operating at very high frequencies require controlled impedance and energy containment in their associated wiring and connectors. Commonly, controlled impedance and energy containment is effected by using shielded or coaxial cable and/or special electrical connectors or connector inserts. Such connectors typically are custom-made for particular applications and, therefore, often are expensive and not readily available when needed. 
     It would be beneficial to provide a method for fabricating a controlled impedance connector for a variety of applications using readily available, conventional components. 
     SUMMARY OF THE INVENTION 
     The present invention provides a novel method for assembling a controlled impedance electrical connector, such as the connector disclosed in co-pending U.S. patent application Ser. No. 09/607,487. More particularly, the present invention provides a method for assembling a controlled impedance electrical connector using conventional connector components, including conventional connector shells and inserts. The method of the present invention can be used in connection with connector shells having nearly any cross-section, including, without limitation, circular, square, and rectangular. The method of the present invention can be used to assemble an impedance controlled connector for use with conductors carrying a variety of signals, including single-ended signals, differential signals, and bidirectional differential signals. Test results indicate that a controlled impedance electrical connector assembled using the process of the present invention provides appropriate energy containment for signals varying in frequency from direct current (DC) to approximately 3.5 GHz. 
     In a preferred embodiment, the method of the present invention can be used to terminate an impedance controlled cable, such as a cable having a center conductor and a surrounding shielding braid, to a conventional insert in a conventional electrical connector shell. Preferably, the impedance controlled cable is prepared for termination by first stripping a length of outer jacket away from an end of the impedance controlled cable, leaving all but a short length of the underlying shielding braid in place. The exposed shielding braid then can be pushed back against the end of the remaining outer jacket, exposing the inner dielectric insulation. A short length of the inner dielectric insulation (and center conductor protective wrap, if present) is removed to expose the center conductor. Preferably, the center conductor is folded back upon itself to provide an adequate diameter for crimping. 
     In a preferred embodiment, a standard M39029/56-348 connector socket or M39029/58-360 connector pin (or the respective, suitable alternative) then is crimped onto the center conductor using a conventional crimping tool and die. A small section of shrinkable tubing can be installed across the gap between the crimp contact, i.e., the connector socket or connector pin, and the inner dielectric insulation to provide additional mechanical strength to the connection. 
     The shielding braid then is replaced over the inner dielectric insulation. Preferably, the shielding braid is spread evenly over the inner dielectric insulation, ensuring that no opening in the braid has a dimension larger than {fraction (1/20)} of a wavelength corresponding to the highest frequency to be handled by the connector (or, in a time domain, {fraction (1/20)} of the fastest transition speed of a signal, as would be known to one skilled in the art). A wire can be wrapped around the braid to cover any opening of excessive size. If such a cover wire is used, it preferably is soldered to the shielding braid to improve the overall shielding characteristic and to hold the wire in place, thus ensuring the opening remains covered. A drain wire preferably is added around the shielding braid near the end of the outer cable jacket and soldered in place. 
     The foregoing steps describe the preferred method for preparing a cable carrying a single-ended signal for termination at a connector insert. The method of the present invention also can be used in connection with, for example, multiple cables or a multi-wire cable carrying differential signals and bidirectional differential signals, among others. In a differential signal application, a second cable or wire is prepared and terminated in the same manner as for the single-ended signal application described above. The drain wires of the two cables or wires then are twisted and preferably soldered together. A standard M39029/56-348 connector socket or M39029/58-360 connector pin (or the respective, suitable alternative) is crimped onto the twisted and soldered drain wires using conventional tools. In a bidirectional differential signal application, a second pair of cables or wires for the second signal path also is prepared, as described above. 
     The prepared cables and/or wires are arranged into a predetermined pattern in which they will be configured when installed into the connector. This pattern is selected to ensure that the assembled connector will exhibit adequate impedance control characteristics. This pattern can be determined using any suitable parameter extraction software, such as the Maxwell® program available from the Ansoft Corporation of Pittsburgh, Pa., or other commercial or proprietary program. One suitable alternative software package is available from Innoveda of Redmond, W.Va. 
     The prepared and arranged wires are inserted into a conventional insert in a conventional connector housing in the predetermined pattern. Preferably, all of the conductor termination components (i.e., connector sockets or pins) associated with a particular cable or group of cables are pressed into the connector insert substantially simultaneously, a little bit at a time, to avoid placing excessive strain on any of the wiring. Any practical number of conductors can be prepared for and terminated at a connector in the foregoing manner. Once installed into a connector, individual connector sockets and/or pins can be removed and reinserted using conventional insertion and removal tools. 
     If reference planes are needed for impedance control within the connector, as would be known to those skilled in the art, they may be provided by inserting signal pins into the connector insert in a predetermined configuration and grounding them to the connector shell, thus forming a Faraday Cage around the signal wires requiring such impedance control measures. Preferably, the grounds (or drains) of the relevant signal wires are connected to any of these grounded pins. 
     Overall shielding of the cable also can be accomplished using conventional connector fittings in a novel manner. More particularly, the shielding can be bunched at the location where the shielding normally ends. This allows the shield to continue within the connector to provide impedance control right up to the inner face of the connector housing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a perspective view of a conventional connector for use in accordance with the present invention; 
     FIG. 1B is an end elevation view of a conventional connector for use in accordance with the present invention; 
     FIG. 2 is a side elevation view of an insulated conductor partially prepared for termination to a connector in accordance with the method of the present invention; 
     FIG. 3 is a side elevation view of an insulated conductor partially prepared for termination to a connector in accordance with the method of the present invention; 
     FIG. 4 is a side elevation view of an insulated conductor partially prepared for termination to a connector in accordance with the method of the present invention; 
     FIG. 5 is a side elevation view of an insulated conductor partially prepared for termination to a connector in accordance with the method of the present invention; 
     FIG. 6 is a side elevation view of an insulated conductor partially prepared for termination to a connector in accordance with the method of the present invention; 
     FIG. 7 is a side elevation view of an insulated conductor partially prepared for termination to a connector in accordance with the method of the present invention; 
     FIG. 8 is a side elevation view of an insulated conductor partially prepared for termination to a connector in accordance with the method of the present invention; 
     FIG. 9 is a side elevation view of an insulated conductor partially prepared for termination to a connector in accordance with the method of the present invention; 
     FIG. 10 is a side elevation view of an insulated conductor partially prepared for termination to a connector in accordance with the method of the present invention; 
     FIG. 11 is a side elevation view of a pair of insulated conductors partially prepared for termination to a connector in accordance with the method of the present invention; 
     FIG. 12 is a side elevation view of a pair of insulated conductors partially prepared for termination to a connector in accordance with the method of the present invention; 
     FIG. 13 is a side elevation view of a pair of insulated conductors partially prepared for termination to a connector in accordance with the method of the present invention; 
     FIG. 14 is an end elevation view of a plurality of conductors prepared for insertion into a connector in accordance with the method of the present invention; 
     FIG. 15 is a partial end elevation view of a connector shell and insert for use in connection with the method of the present invention; 
     FIG. 16 is another partial end elevation view of a connector shell for use in connection with the method of the present invention; 
     FIG. 17 is an end elevation view of a controlled impedance connector prepared in accordance with the method of the present invention using a conventional connector shell and insert; 
     FIG. 18 is a side elevation view of a conventional shield termination; and 
     FIG. 19 is a side elevation view of an impedance controlled shield termination according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention provides a method for assembling a controlled impedance electrical connector  40  using conventional components, including, for example, a conventional connector shell  44  and a conventional connector insert  42 , as illustrated in FIG.  1 A and FIG.  1 B. In a preferred embodiment, the method of the present invention can be used in connection with an impedance controlled cable, such as cable  50  having center conductor  52 , surrounding inner dielectric insulation  58 , and surrounding shielding braid  54 , as illustrated in, for example, FIG.  5 . In this embodiment, impedance controlled cable  50  is prepared for termination at connector  40  by first stripping a length (preferably about one inch) of outer jacket  56  away from a free end of impedance controlled cable  50 , leaving underlying shielding braid  54  in place, as illustrated in FIG. 2. A short length (preferably about ⅛ inch) of shielding braid  54  then is removed, as illustrated in FIG.  3 . The exposed portion of shielding braid  54  then is pushed back towards the end of previously cut-back outer jacket  56 , i.e., away from the free end of cable  50 , thus exposing inner dielectric insulation  58  covering center conductor  52 . Typically, when shielding braid  54  is pushed back in this manner, a bulge B is formed therein, as illustrated in FIGS. 4-8. A short length (preferably about ⅛ inch) of inner dielectric insulation  58  and the center conductor protective wrap, if present (not shown), is removed to expose center conductor  52 , as illustrated in FIG.  5 . The portion of center conductor  52  thus exposed can be then folded back upon itself, as illustrated in FIG. 6, if necessary to provide an adequate diameter for crimping, as described below. 
     In a preferred embodiment, a conductor termination component, such as a connector socket  62  or a connector pin  64 , then is crimped onto center conductor  52  using a conventional crimping tool and die (not shown). Connector socket  62  can be a standard connector socket, such as an M39029/56-348 connector socket or a suitable alternative. Similarly, connector pin  64  can be a standard connector pin, such as an M39029/58-360 connector pin or a suitable alternative. The resulting gap  68  between inner dielectric insulation  58  and connector socket  62  or connector pin  64  (and, therefore, the exposed length of center conductor  52 ) should be kept to a minimum. Preferably, a short section of shrinkable tubing  66  is installed across gap  68  to provide additional mechanical strength to the connection. See FIGS. 7 and 8. 
     Shielding braid  54  then is replaced over inner dielectric insulation  58 . Shielding braid  54  preferably is spread evenly over inner dielectric insulation  58 , ensuring that no opening in shielding braid  54  has a dimension larger than {fraction (1/20)} of a wavelength of the highest frequency to be handled by the connector (or, in a time domain, {fraction (1/20)} of the fastest transition speed of a signal, as would be known to one skilled in the art). See FIG. 9. A cover wire  70  can be wrapped around shielding braid  54  to cover any opening of excessive size. If such a wire  70  is used, it preferably is soldered to shielding braid  54  to improve the energy containment characteristic and, therefore, the impedance control of the overall cable and connector structure. A drain wire  72  preferably is installed around shielding braid  54  near the end of outer cable jacket  56  and soldered in place to the shielding braid. See FIG.  10 . The free end of drain wire  72  preferably is terminated to a conductor termination component, such as a connector socket  62  or a connector pin  64 . 
     The foregoing steps describe the preparation of a typical impedance controlled cable  50  carrying a single-ended signal for termination to a connector  40 . An impedance controlled cable (or group of cables) carrying more than one signal path and, therefore, having more than one conductor, can be prepared in a similar manner. For example, a differential signal can be transmitted using a pair of impedance controlled cables  50 . In such a differential signal application, each of the cables  50  is prepared as described above, and the drain wires  72  of the two cables  50  preferably are twisted and soldered together. See FIGS. 11 and 12. A connector socket  62  or connector pin  64 , as described above, preferably is crimped onto the twisted and soldered drain wires  72 , as illustrated in FIG.  13 . When twisting and soldering the drain wires  72 , consideration should be given to the pattern and spacing of the prepared cables  50  and connectors sockets  62  and/or pins  64  into the connector insert  42 , as will be further discussed below. The foregoing technique also may be used in an application involving a bidirectional differential signal and, therefore, two pairs of impedance controlled cables  50 , by preparing a second pair of cables  50 , as described above, for the second signal path. See FIG.  14 . The method of the present invention can be used in other applications, as well. 
     The prepared cables  50  and connector sockets  62  and/or pins  64  are arranged into a predetermined pattern in which they will be routed when installed into the connector, as would be known to one skilled in the art. See FIG.  14 . The predetermined pattern is selected to ensure that the completely assembled connector will exhibit adequate energy containment and impedance control characteristics. This pattern can be determined using suitable parameter extraction software, such as the Maxwell® program available from Ansoft Corporation of Pittsburgh, Pa. or other similar commercial or proprietary program. 
     The prepared connector sockets  62  and/or pins  64  are inserted into a conventional connector insert  42  in a conventional connector housing  44  in the predetermined pattern. In multiple-signal/multi-wire applications, such as the two conductor plus drain differential configuration or the four conductor plus two drains bidirectional differential conductor configuration, all connector sockets  62  and/or pins  64  are pressed into connector insert  42  substantially simultaneously, a little bit at a time, to avoid placing excessive strain on any of the wiring. See FIG.  15 . Any practical number of cables  50  can be prepared for and terminated at a connector  40  in the foregoing manner. Once installed into a connector, individual connector sockets  62  and pins  64  can be removed and reinserted using conventional insertion and removal tools. 
     If reference planes are required for impedance control within a connector  40 , they may be provided by inserting grounding pins  74  in the connector insert  42  in a predetermined configuration and grounding them to the connector shell  44 , thus forming a Farady cage  76  around the signal paths requiring such impedance control measures, as would be known to one skilled in the art. See FIGS. 16 and 17. Preferably, the grounds (drains wires  72 ) of the applicable cables  50  are connected to any of the corresponding grounding pins  74 . 
     Overall shielding of an impedance controlled cable  50  also can be accomplished using conventional connector fittings in a novel manner. In a conventional cable-to-connector termination, as illustrated in FIG. 18, a length of shielding braid  54  is cut back from the free end of cable  50  and terminated between a shield collar  78  and a retainer ring  80  adjacent to connector shell  44 . A novel impedance controlled termination can be realized by preparing the end of cable  50  to be terminated so that the length of shielding braid  54  is sufficient to extend to, and preferably into, the end of connector shell  44  and to form a bulge B′ of shielding braid  54  in the region between shield collar  78  and retaining ring  80  prior to securing retaining ring  80  in place. 
     The foregoing techniques have been described and shown for use with connectors having circular cross sections. However, these techniques also may be used with connectors having other cross sections, including, without limitation, square or rectangular. 
     Whereas the present invention has been described with respect to specific embodiments thereof, it is understood that various changes and modifications will be suggested to one skilled in the art and it is intended that the invention encompass such changes and modifications as fall within the scope of the appended claims.