Abstract:
An electrical connector for terminating a shielded cable and connecting the cable to regularly arranged contact pins. The connector includes a connector body formed from an insulative material. The connector body has an upper surface and an opposing lower surface defined by a front edge, a back edge and two longitudinal side edges. The upper surface includes a plurality of longitudinal channels adapted to receive a plurality of socket contacts. A planar conductive ground plate engages the bottom surface of the connector body and extends across each of the plurality of socket contacts to establish a ground plane across the entire connector. A cover member encloses the longitudinal channels and socket contacts. A plurality of individual connectors may be stacked together and retained in a stack by a removable retaining rod.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a connector for coaxial, twin axial and/or twisted pair cables. The invention is especially suited for the termination of shielded cables of the type mentioned, such that controlled impedance is provided through the connector, from mating face to cable end. 
     A variety of connectors for terminating shielded cables are known in the art. Such connectors are typically designed for a single type of application and are not typically easily altered for use with, for example, different signal/ground configurations, or for use with different types of connection methods, e.g., soldering or welding. In addition, known connectors are typically difficult to assemble, often requiring multiple molding steps, over-molding of electrical contacts and the like, which add time and expense to the connector fabrication process. Finally, prior art connectors often do not provide adequate performance characteristics for high performance systems. Inadequate performance characteristics include, for example, the inability to control the impedance within the connector, or to match the connector impedance with that of the system in which the connector is used. What clearly is needed is a connector which provides greater flexibility in its use and which is easy and economical to produce. 
     SUMMARY OF THE INVENTION 
     Accordingly, the invention described herein provides an electrical connector which is easily assembled and configured for alternate uses, and which may be adjusted to provide a controlled impedance across each signal line of the connector. 
     Briefly, the present invention provides a connector for terminating a shielded cable and connecting the cable to regularly arranged contact pins. The connector comprises a planar connector body formed from an insulative material which has a plurality of longitudinal channels each adapted to receive a socket contacts. A planar conductive ground plate covers the bottom surface of the connector body and extends across each of the plurality of socket contacts. The ground plate makes electrical contact with the shield of the cable to establish a ground plane equidistant from each of the socket contacts. A cover member encloses the socket contacts. 
     A plurality of the connectors may be stacked together and held in a stacked configuration by a retaining rod which secures to mating engagement surfaces on the connector bodies. In a stack of connectors, the cover member may be provided with a conductive portion which is electrically connected to the ground plate, where the conductive portion of the cover member is formed to extend above the top side of the connector body and make electrical connection with the ground plate of the connector stacked above. In this manner, each of the ground plates in a stack of connectors may be assured of being at the same ground potential. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of one embodiment of the cable connector described herein. 
     FIG. 2 is an enlarged perspective view of the socket contact used in the connector of FIG.  1 . 
     FIGS. 3 a  and  3   b  are perspective views illustrating the insertion of a socket contact into the connector body. 
     FIG. 4 is a perspective view of the bottom side of the assembled connector of FIG.  1 . 
     FIG. 5 is a perspective view of the assembled connector without the cover member. 
     FIG. 6 is a perspective view of the assembled connector with the cover member. 
     FIGS. 7 a  and  7   b  are perspective views of a stack of assembled connectors. 
     FIGS. 8 a  and  8   b  are perspective views of stacked connectors engaged with a pin header. 
     FIG. 9 is an exploded perspective view of the connector showing an alternate embodiment of the cover. 
     FIG. 10 is a perspective view of the bottom side of the assembled connector of FIG.  9 . 
     FIG. 11 is an exploded perspective view of the connector showing another alternate embodiment of the cover. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The connector  18  of the present invention, shown in FIG. 1 in an exploded view, includes a connector body  20  formed from an insulative dielectric material, a plurality of socket contacts  22 , a planer conductive ground plate  24 , and cover member  26 . Retention rods  28  may be used when a plurality of connector bodies are stacked together. The connector  18  is shown in FIG. 1 in use with a pair of twin axial cables  30 . However, as will be discussed in greater detail below, the connector  18  of the present invention may be used with other types of shielded cables, such as coaxial or twisted pair cables. 
     Connector body  20  includes a top side  32  and an opposing bottom side  34 . The top and bottom sides  32 ,  34  are defined by a front edge  36 , a back edge  38  and two longitudinal side edges  40 . Top side  32  of connector body  20  includes a plurality of channels  42  separated by ribs  45  extending from openings  43  in front edge  36  toward back edge  38 . The channels  42  are adapted to receive socket contacts  22  and retain socket contacts  22  securely within the connector body  20 . 
     As best seen in FIG. 2, socket contact  22  includes resilient contact portions  44  which are adapted to engage a corresponding contact pin (not shown) inserted through opening  43  when the connector  18  is in use. Shank  46  extends from resilient contact portions  44  to socket terminal  48 . The width and height of shank  46  and terminal  48  may be selected to control the characteristic impedance in a known microstrip relationship with the ground plane provided by ground plate  24  described in greater detail below. The characteristic impedance may also be controlled by altering the thickness of the portion of connector body  20  which is between contacts  22  and ground plate  24 , or by altering the dielectric constant of the material of connector body  20 . 
     Socket contact. 22  also includes spring member  50  which locates socket contact  22  properly within channel  42 , and removably retains contact  22  within its respective channel  42  without damage to the housing, such that an individual socket contact  22  may be replaced without damaging the housing. Although socket contact  22  may be provided with additional contact retention features  52  which are shaped to frictionally engage the connector body  20  and aid in maintaining the position of socket contact  22 , such lance or sawtooth features may make replacement of contacts difficult. It is advantageous to have removable socket contacts  22 , so that damaged contacts may be replaced at relatively low cost, instead of causing the entire connector  18  to be rendered inoperable. 
     As can best be seen in FIGS. 3 a  and  3   b , socket contact  22  is adapted to slide longitudinally into a mating channel  42  in connector body  20 . As contact  22  slides into position, socket terminal  48  engages recesses  54  in the walls of channel  42 . In this manner, socket contact  22  is held securely against the bottom of channel  42 , thereby eliminating air gaps between socket contact and connector body  20  which may cause impedance variations across the connector. This is important, as the spring force of the signal conductors  74  of cables  30  may otherwise tend to lift terminals  48  away from connector body  20 . As socket contact  22  is moved further toward front edge  36  of connector body  20 , spring member  50  snaps into detent  56  in the wall of channel  42 . At this point, socket contact  22  is properly located and secured within its channel  42 . Socket contact  22  is prevented from moving out of channel  42  by spring member  50  which is engaged with detent  56 , and by terminal  48 , which is engaged with recesses  54 . A contact  22  is placed in each channel  42  in the above-described manner. 
     After socket contacts  22  are positioned within connector body  20 , ground plate  24  may be attached to the bottom side  34  of connector body  20 . Ground plate  24  is formed of a conductive material, such as metal. Ground plate  24  includes deformable grounding contacts  60  which may be selectively deformed to ground one or more of socket contacts  22 . One or more of the grounding contacts  60  may be deformed so as to ground a socket contact  22 . In this manner, connector  18  may be provided with a programmable grounding scheme. 
     Grounding contacts  60  make mechanical and electrical connection with socket contacts  22  through openings  62  in the bottom side  34  of connector body  20  (best seen in FIG. 3 b ). The grounding contacts  60  may make only spring force contact with socket contacts  22 , or they may alternatively be soldered or welded to socket contacts  22 . 
     Ground plate  24  is secured to the bottom side  34  of connector body  20  by locking tabs  64 . Locking tabs  64  engage slots  66  in the bottom side  34  of connector body  20  (FIG.  4 ). After locking tabs  64  are positioned in slots  66 , ground plate  24  is moved toward back edge  38  of connector body  20 . This sliding motion causes locking tabs  64  to engage ledges (not shown) in slots  66  and pull grounding plate  24  tightly against the bottom side  34  of connector body  20 . Locking tabs  64  are shaped so as to cause a camming action as ground plate  24  is moved toward back edge  38 . This camming action urges the ground plate against the connector body  20 , thereby eliminating air gaps, which may cause impedance variations across the connector. For this reason, it is preferred that the material of ground plate  24  be somewhat resilient. Beryllium-copper alloy is an example of one suitable material, although other suitable materials will readily be recognized by those skilled in the art. To further assure a tight fit between ground plate  24  and bottom side  34 , ground plate  24  is preferably formed so as to have a slightly concave shape when unattached to connector body  20 , such that locking tabs  64  tend to pull the edges of ground plate  24  toward bottom side  34  and thereby flatten ground plate  24  against bottom side  34 . When ground plate  24  is fully in position, a raised projection  70  on bottom side  34  engages opening  72  in ground plate  24 . In this manner, ground plate  24  is prevented from moving toward front edge  36  and possibly becoming disengaged from connector body  20 . 
     The direction in which ground plate  24  is installed onto connector body  20  (i.e., in the direction of axial pullout when connector  18  is engaged) assures ground plate  24  will not be dislodged while disconnecting an engaged connector  18 . Specifically, when cables  30  are attached to connector  18 , the cable shields  73  are attached to ground plate  24  by soldering or other means such as welding. Because ground plate  24  is installed in the direction of axial pullout force (which is applied to the cable when the connector  18  is disengaged from use), pulling on the cables tends to further secure ground plate  24  to connector body  20 , rather than tending to dislodge or loosen ground plate  24 . 
     As can be seen in FIG. 4, ground plate  24  extends across each of socket contacts  22  in the connector. This provides several advantages to the performance of connector  18 . Because ground plate  24  is part of the current return path, it is advantageous to provide as wide of a return path as possible to minimize the self-inductance generated in the connector. A long and narrow return path tends to cause greater self-inductance, which is detrimental to the connector performance. It will be noted that the deformable grounding contacts  60  of ground plate  24  are positioned such that the base of the deformed contact  60  is positioned close to front edge  36  of the connector. Because the ground plate  24  becomes part of the current return circuit of the connector, and any difference in the lengths of the signal and ground paths causes increased self-inductance in the connector (and hence an increase in impedance), it is advantageous to position the grounding contacts  60  as close as possible to the engagement point of the mating grounded component, e.g., the ground pin of the mating pin header  106 . In an alternate embodiment, the ground contact  60  could be shaped so as to make contact with the ground pin of the mating pin header. In this manner, the lengths of the signal and ground paths are kept as close as possible to the same length, thereby minimizing any self-inductance within the connector. 
     Finally, by extending ground plate  24  across each of the contacts  22 , a ground plane is established across the entire connector which allows the impedance of the connector to be closely controlled at each signal line. By securing ground plate  24  in the manner described above, it is ensured that the spacing between socket contacts  22  and the ground plane created by ground plate  24  is maintained at a constant and uniform distance. Socket contacts  22  form what is referred to as a microstrip geometry with the ground plane. The method for determining the impedance of a device having microstrip geometry is known in the art, and it will be recognized that by maintaining the spacing between the ground plane and socket contacts  22  at a uniform distance, the impedance of connector  18  can be closely controlled and adjusted for optimal connector performance. For example, the impedance can be adjusted by altering the width and thickness of the socket contact, by varying the dielectric constant of the material forming connector body  20 , or by altering the thickness of the material between contacts  22  and ground plate  24 . If the spacing between socket contacts  22  and the ground plane varies across the width of connector  18 , each of socket contacts  22  will experience a different impedance, thus causing degradation of a signal passing through the connector. Such impedance variations limit the bandwidth of the connector and are not acceptable in many high performance systems. 
     After the ground plate  24  is attached to connector body  20 , cables  30  may be attached to the connector  18 . The signal conductors  74  of cables  30  are connected to the terminals  48  of the appropriate socket contacts  22 , while the cable shields  73  are attached to ground plate  24 . This may be seen in FIGS. 4 and 5. In FIG. 5, it can be seen that the locking tab  64  may also function as a solder tab for the connection of cable shield  73 . Although the signal conductors  74  of cables  30  will typically be attached to contact terminals  48  by soldering, other methods of connection may be used. For example, it may be desired in some instances to weld the signal conductors  74  to the socket terminals  48 . For this reason, connector body  20  is provided with access openings  78  (best seen in FIG. 3 b ). Access openings  78  allow both sides of socket terminal  48  to be reached by electrodes so that the signal conductors  30  may be welded to the terminals  48 . Of course, such welding would have to occur prior to installation of ground plate  24 , as ground plate  24  covers access openings  78  after ground plate  24  has been installed onto connector body  20 . Alternately, access holes could also be provided in ground plate  24  for access to terminals  48 . Ground plate  24  also includes several access openings  80  near back edge  38 . Access openings  80 , for example, allow a solder paste to be used to connect the electrical shields  73  of cables  30  to ground plate  24 . Ground plate  24  may also be provided with raised ridges  82  which aid in positioning signal conductor  74  at the proper height for connection to terminals  48 . 
     It will be noted that ribs  45  which separate channels  42  function as cable organizers, helping direct cables  30  into channels  42  and properly position cable signal conductors  74  over terminals  48 . As best seen in FIG. 5, ribs  45  extend only so far toward back edge  38  as is necessary to property align signal conductors  74 . This allows signal conductors  74  to be more easily routed to any of a variety of contact terminals  48  without requiring significant bending of signal conductors  74 . 
     After cables  30  have been secured to contacts  22  and ground plate  24 , cover member  26  may be installed to finish assembling connector  18 . Cover member  26 , as best seen in FIG. 1, is secured to connector body  20  by sliding the cover member  26  from the back edge  38  toward the front edge  36  of the connector body  20 . As cover member  26  slides into position, guide rails  84  on cover  26  engage slots  86  in connector body  20  to properly position and secure cover member  26 . As cover member  26  becomes fully engaged with connector body  20 , latching features  88  on rails  84  securely engage detents  90  within connector body  20 , while lip  92  at the front edge of cover member  26  is secured under edge  94  of connector body  20 . The assembled connector  18  as thus described and shown in FIG. 6 is then ready for use. 
     In most applications, a plurality of assembled connectors  18  will be joined together for use as a “stacked” connector. An example of a set of stacked connectors is shown in FIGS. 7 a  and  7   b . As seen in the Figures, the connectors are secured to each other by retention rod  28 . Retention rod  28  is adapted to engage a mating recess  100  on side edges  40  of connector body  20 . Recesses  100  include a projecting rib  102  for engaging a mating groove  104  in retention rod  28 . The grooves  104  are spaced along retention rod  28  such that when a plurality of connectors  18  are stacked together and secured by retention rod  28 , the connectors  18  are held securely against one another. It is preferred that the material of retention rod  28  be somewhat resilient so that retention rod  28  may provide a compression force between the stacked connectors  18 . However, the material of retention rod must also be rigid enough to maintain the stacked connectors in proper alignment in all other dimensions. 
     Retention rod  28  is preferably formed of a polymeric material having a durometer less than the durometer of the material forming connector body  20 . 
     In this manner, retention rod  28  will yield to the material of connector body  20  as retention rod  28  engages connector body  20 . Alternately, retention rod  28  is may be formed of a material having a durometer greater than the durometer of the material forming connector body  20 , such that the material of connector body  20  yields to the material of retention rod  28 . 
     A set of stacked connectors may be engaged with a mating pin header  106 , as shown in FIGS. 8 a  and  8   b . It will be recognized by those skilled in the art that the configuration of retention rods  28  and recesses  100  may be altered to a variety of shapes while still performing their intended function. For example, rather than providing recess  100  in connector body  20  for receiving retention rod  28 , a projection (not shown) could extend from connector body  20  and retention rod  28  could be adapted to engage the projection. 
     The connector  18  and stacking method described herein make it possible to interchange a single connector  18  in a series of stacked connectors without disconnecting the entire stack of connectors from the pin header  106  of a powered system. Commonly referred to as “hot swapping”, this may be accomplished by simply removing the retention rods  28  from recesses  100  in the stacked connectors and pulling a single connector  18  from the pin header  106 . The removed connector  18  may then be re-inserted after any necessary adjustment is made, or a new connector my be installed in its place. The retention rods  28  are then reinstalled to secure the stack of connectors. This is a significant advantage over prior art stackable connectors which required that the entire stack of connectors  18  be removed from the pin header, and often further required that the entire stack of connectors be disassembled so that a single connector could be replaced. In addition, the manner in which ground plate  24  is installed, as described above, allows a single connector  18  to be removed by pulling on cables  30  without the possibility that ground plate  24  could be dislodged from connector body  20 . 
     To facilitate alignment of connector  18  with the pin field of pin header  106 , connector body  20  may be provided with an optional guide rail  108 , which is useful for guiding the assembled connector  18  into pin header  106 . Guide rail  108  is adapted to mate with grooves  110  in pin header  106 . The position and shape of guide rails  108  and grooves  110  may vary depending upon the particular use or application of connector  18 . Further, guide rails  108  may function as a connector polarization key to prevent an improper connection with pin header  106 . 
     Other features may be provided to connector  18  and pin header  106 . For example, as seen in FIG. 8 b , pin header  106  may be provided with a retaining latch  112  for securing a stack of connectors  18  within pin header  106 . Latch  112  is designed to engage lip  114  at the back edge  38  of connector body  20 . 
     Although the connector has been described above for use with two twinaxial type cables, other numbers and types of cables, such as coaxial cables or twisted pair cables may be used with the connector. The identical connector body  20  in ground plate  24  may be used with different types or numbers of cables. However, a slightly modified cover member  26 ′ may be desired for different numbers or types of cables. For example, FIGS. 9 and 10 illustrate use of three coaxial cables  30 ′ with the connector body  20 , contacts  22  and ground plate  24  described above. A slightly modified cover member  26 ′ is provided to accommodate the slightly different size and shape of the coaxial cables  30 ′. However, the guide rails  84 , latching mechanism  88  and lip  92  of cover member  26 ′ are identical to that described above for cover member  26 . 
     In some instances, it may be desired to form cover  26  from a conductive material or to provide cover  26  with a conductive section, such as by metal plating portions of cover  26 , and to then electrically connect the conductive portion of cover  26  to ground plate  24 . Such a modified connector  18 ″ and cover  26 ″ are shown in FIG.  11 . Cover  26 ″ is provided with a spring contact  116  which will make electrical contact with the ground plate  24  of a connector which is stacked above the cover  26 ″. Cover  26 ″ may make electrical contact with ground plate  24  of the connector  18 ″ by, for example, extending locking tabs  64  of ground plate  24  through connector body  20  to make contact with cover  26 ″. By electrically connecting cover  26 ″ with ground plate  24 , the connector  18 ″ is provided with additional shielding and it is possible to assure each individual connector in a stack of connectors  18 ″ is at the same ground potential. 
     The invention as described above provides numerous advantages compared to prior art connectors. The programmable grounding contacts  60  in ground plate  24  allow complete flexibility as to the arrangement of signal and ground contacts, without requiring design changes to the connector body or cover member. The wide ground plate  24  provides a low impedance current return path, and the uniform spacing between socket contacts  22  and the ground plane created by ground plate  24  allows the connector impedance to be controlled in a known microstrip relationship with the ground plane provided by ground plate  24 . The simplified stacking features allow any number of connectors  18  to stacked without extra components, while allowing the stack of connectors  18  to be easily disassembled and further allowing “hot swapping” of a single connector in a stack of connectors. 
     Although the present invention has been described herein with respect to certain illustrated embodiments, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention.