Patent Publication Number: US-7722400-B2

Title: Differential pair electrical connector having crosstalk shield tabs

Description:
RELATED APPLICATION 
     This patent application claims the benefit of U.S. Provisional Patent Application Nos. 60/817,857, filed Jun. 30, 2006, and 60/818,140 filed Jun. 30, 2006, which are both incorporated by reference in their entireties. 
     This application is related to U.S. patent application No. 11/771,666, entitled “Differential Pair Connector Featuring Reduced Crosstalk,” filed on the same date as the present application, assigned to the same assignee and identifying Craig A. Bixler, John C. Laurx and Neil A. Martin as the inventors. This related application is incorporated by reference in its entirety as though fully set forth herein for everything it describes. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to electrical connectors, and more specifically, to high-frequency electrical connectors where signal crosstalk is a performance consideration. 
     BACKGROUND 
     Electronic devices continue to shrink in size, yet increase in speed and complexity. This has lead to the widespread availability of small electronic components capable of driving high-speed signals (e.g., above one GHz) over printed circuit board (PCB) tracks. The increasing use of these high-speed components has created a significant demand for high performance electrical connectors that support such signal frequencies and denser PCB track configurations, while at the same time requiring less space. 
     Transmitting high speed signals over differential pair channels is an increasingly popular technique for high bandwidth transmission between PCBs. In a typical high bandwidth system, “daughter card” PCBs are connected to a backplane using mated connectors. The backplane is itself a layered circuit board having, among other things, differential pair tracks formed therein for carrying high frequency signals between the daughter cards. 
     In such systems, one critical variable that affects bandwidth between PCBs is crosstalk. Generally, crosstalk is the electrical interference in a channel caused by a signal traveling through a neighboring channel. Under many circumstances, the presence of excessive crosstalk degrades system performance and negatively impacts bandwidth. High-speed signaling standards, such the Institute of Electrical and Electronics Engineers (IEEE) 802.3 XAUI standard require four channels of differential pairs operating at 3.125 GHz. Additional high-speed standards incorporating differential pairs include PCI Express, SONET OC-12, SONET OC-48, Gigabit Ethernet, HD-SDI, Serial RapidIO, CEI-6G and SerialLite II. Proprietary protocols are also often implemented in backplanes and other environments. 
     Using conventional connector technology, it is difficult or impossible to reliably transmit multiple channels of differential signals in close proximity to one another at high speed. The data rates of computing equipment, such as networking gear, have been consistently increasing in speed. As data rates increase, crosstalk between channels becomes more of a problem as it tends to degrade bandwidth. Thus, in differential pair systems, it is important that daughter cards and backplanes minimize the amount of crosstalk between differential pairs. It is also important for the PCB connectors between the daughter cards and backplanes to minimize crosstalk. 
     In view of the foregoing, there is a substantial need for an electrical connector that yields reduced crosstalk in high signal density, high bandwidth applications. 
     SUMMARY 
     Embodiments of the invention provide an improved differential pair connector that includes means for significantly reducing crosstalk between differential pair channels. Further embodiments provide an improved differential pair connector that can be embodied in an economical, high-density connector suitable for use in demanding high bandwidth applications. 
     In accordance with an exemplary embodiment of the invention, as described infra, an electrical connector comprises a housing having receptacles for receiving differential pair conductors. Extending away from the housing, between the receptacles, are electrically conductive shielding tabs for reducing crosstalk between the differential pairs. The tabs insert into a mated connector when an interconnect is formed. By inserting into the second connector, the shield tabs extend a larger ground plane around each differential pair, thus significantly reducing crosstalk within the connector. In one embodiment, the connector can be a GbX®-style daughter card connector mated to a GbX®-style backplane connector. 
     Other aspects, features, embodiments, processes and advantages of the invention will be or will become apparent upon examination of the following figures and detailed description. It is intended that all such additional features, embodiments, processes and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings are solely for the purpose of illustration and do not define the limits of the invention. Furthermore, the components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. In the figures, like reference numerals designate corresponding parts throughout the different views. 
         FIG. 1  is a simplified side view of a daughter card connector and associated backplane connector in accordance with an exemplary embodiment of the present invention. 
         FIG. 2  is a perspective view of the daughter card connector shown in  FIG. 1 . 
         FIG. 3  is a perspective view of a single wafer of the daughter card connector shown in  FIG. 2 . 
         FIG. 4  is a back view of the wafer shown in  FIG. 3 . 
         FIG. 5  is a front view of the wafer shown in  FIG. 3 . 
         FIG. 6  is a partial side view of the daughter card shown in  FIG. 2 . 
         FIG. 7  is a partial top perspective view showing the daughter card connector ground plane inserted into the backplane connector. 
         FIG. 8  is a partial bottom perspective view showing the daughter card connector inserted into the backplane connector. 
         FIG. 9  is a detailed bottom perspective view showing the daughter card connector inserted into the backplane connector. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description, which references to and incorporates the drawings, describes and illustrates one or more specific embodiments of the invention. These embodiments are offered not to limit but only to exemplify and teach the invention, are shown and described in sufficient detail to enable those skilled in the art to practice the invention. Thus, where appropriate to avoid obscuring the invention, the description may omit certain information known to those of skill in the art. 
       FIG. 1  is a simplified side view of a high-density serial connector  10  comprising daughter card connector  12  and associated backplane connector  14  in accordance with an exemplary embodiment of the present invention. The exemplary serial connector  10  is illustrated as a GbX®-style 4-pair signal module having an 8×10 array of differential pins  22 . The connector  10  can have the same size, mating characteristics and pin configuration as a conventional GbX® 4-pair connector. One example GbX® 4-pair daughter card connector is Molex part number 75220. Molex part number 75235-0X0X is the corresponding backplane connector. 
     The backplane connector  14  includes an array of differential pins  32  and ground plane shields  24 . The backplane connector  14  is affixed to a backplane printed circuit board (PCB)  16  using a conventional technique such as soldering. The backplane PCB  16  can be a conventional PCB that typically includes one or more layers of conductive tracks for carrying signals provided by the differential-pair pins  22  and one or more ground signal tracks and/or planes connected to the ground shields  24 . 
     A daughter card PCB  18  is affixed to daughter card connector  12 . The daughter card connector  12  is designed to plug into or mate with backplane connector  14 . The daughter card connector  12  includes internal conductors (not shown) for carrying signals from the differential pin pairs  22  to corresponding signal tracks formed in the daughter card PCB  18 . The daughter card can be a conventional PCB having electrical components mounted thereon. 
       FIG. 1  shows eight differential pins  22 , which is a subset of all of the differential pins in the backplane connector  14 , and three ground shields  24  interposed between each pair of the pins. Each of the pin pairs is configured to either receive or transmit differential signals. Differential signaling uses two complementary signals sent on a pair of matched conductors. Differential signals are more resistant to noise than single ended signals. Noise introduced to a differential signal typically affects both of the complementary signals in the same way. Because of the differential nature of the signals on a pin pair  22 , however, the noise tends to be cancelled. However, at high data rates, the differential signaling configuration because increasing less effective to reduce noise, which includes crosstalk interference from other nearby differential signals. 
     For purposes of terminology convention, the metal pins  22  are part of a “column” in a two-dimensional differential-pair pin array. “Columns” extend across the illustration. Each ground shield  24  illustrated in  FIG. 1  is made up of a metal plate and is connected to ground to provide shielding between “rows” of the pin pairs. “Rows” extend in and out of the illustration in  FIG. 1 . Electromagnetic shielding such as the ground shield  24  limits the flow of electromagnetic fields. Although numerous techniques can be used to shield conductors in close proximity to one another, in this embodiment, a conductive ground shield  24  is placed between pin pairs. Although the example connector  10  shows only four pin pairs in a column, any suitable number of differential pairs may be used and arranged in any suitable two-dimensional array. 
     In accordance with an advantageous aspect of the invention, the daughter card connector  12  includes a plurality of electrically conductive shield tabs  20  extending downwardly between adjacent columns of differential pins  22  for reducing crosstalk among adjacent pairs of pins in a row. These shield tabs  20  are preferably grounded. When the daughter card connector  12  is plugged into the backplane connector  14 , the crosstalk shield tabs  20  insert into the backplane housing floor  26  between columns of differential pins  22 . This provides additional ground plane shielding around each differential pair, and when combined with the existing ground shields  24 , the shielding extends in both the column and row directions of the differential pin array within the backplane housing floor  26 . This additional shielding significantly reduces crosstalk between differential pairs. The backplane connector  14  includes female receptacle structures formed between adjacent differential pin columns for receiving the shield tabs  20  when the daughter card connector  12  and backplane connector  14  are attached together. 
     The backplane connector  14  also includes a non-conductive housing  29  having header sidewalls  28  extending from the housing floor  26  substantially parallel to each other. The differential-pair pins  22  and ground shields  24  are press-fitted into the floor  26  so as to pass through the floor  26 . Each of the differential pins  22  has a generally flat upper portion  23  and an eye-of-the-needle pin  32  as a lower portion. Eye-of-the-needle pins are a type of compliant pin, which are typically used in high-speed applications. However, solder pins can also be used. Compliant pins mechanically attach the connector while providing an electrical interface. Each of the ground shields  24  has a generally flat upper blade  25  and one or more lower eye-of-the-needle pins  34 . 
     The daughter card connector  12  has corresponding female structures for receiving the upper portion  23  of the pins  22 , and the upper portion  25  of the shields  24 . The housing sidewalls  28  have guide slots formed on their inside faces for receiving daughter card connector guides  30  when the daughter card connector  12  and the backplane connector  14  are plugged together. The guide slots and guides  30  help align the mating pairs of pins  22  with their corresponding female portions in the daughter card connector  12 . 
     The backplane housing  29  can be made of any suitable electrically non-conductive material such as liquid crystal polymer (LCP), and is preferably created using a thermoplastic mold (e.g., conventional molding press) using conventional injection molding techniques. 
       FIG. 2  is a perspective view of the daughter card connector  12  shown in  FIG. 1 . The daughter card connector  12  includes a backplane connector interface  57  comprising plural differential pair receptacles  52 , ground blade slots  54  and crosstalk tabs  20  for connecting to the backplane connector  14 . The daughter card connector  12  also includes a daughter card interface  59  comprising plural pins  50  for connecting to the daughter card  18  ( FIG. 1 ). 
     The exemplary daughter card connector  12  illustrated in  FIG. 2  is composed of ten identical “wafers”  51  stacked together. Each wafer  51  comprises a column of differential pin receptacles  52  and three ground blade slots  54  interposed between the differential pair receptacles  52 . The ground blade slots  54  receive the ground shield  24  ( FIG. 1 ) of the connector  14  ( FIG. 1 ). Within each differential pin receptacle  52  is mounted a resilient differential conductor  56  for making electrical contact with a corresponding differential pin blade  24  when the daughter card connector  12  is plugged into the backplane connector  14 . The differential conductors  56  pass through the wafer  51 , electrically isolated from one another, and terminate with a corresponding eye-of-the-needle daughter card pin  50 . 
     Within each ground blade slot  54  are resilient conductor tangs  70 , as best seen in  FIG. 4 , for making electrical contact with ground blades  25  ( FIG. 1 ) when the daughter card connector  12  is plugged into the backplane connector  14 . 
     Each wafer  51  also includes four crosstalk shielding tabs  20  extending along corresponding differential pair receptacles  52 . The crosstalk shielding tabs  20  are part of a ground plane shield  60  (see  FIG. 3 ) included in each wafer  51 . Each wafer  51  also includes insertion guides  30  mated to corresponding guide slots formed in the backplane header  28 . 
     Each wafer  51  includes a non-conductive body  53  and spacing rib  55 , each made of injection molded plastic. The electrically conductive components are assembled into the body  53 . 
       FIG. 3  is a perspective view of a single wafer  51  of the daughter card connector  12  shown in  FIG. 2 . This view of the wafer  51  shows the ground plane shield  60 , which is mounted to the wafer body  53  using alignment lugs  62  of the body and lugs  64  ( FIG. 3 ). The ground plane shield  60  is made of stamped metal and generally covers one side of the wafer  51  to provide electrical shielding between columns of differential pairs. The bottom portion of the ground plane shield  60  includes fingers  69  that terminate with the crosstalk tabs  20 . The fingers  69  have spaces there between defining slots  54  for receiving the ground blades  25  ( FIG. 1 ) of the backplane connector  14 . The wafer  51  includes pins  50  for connecting to the daughter card PCB  18 . 
       FIG. 4  is a detailed back view of the ground plane  60  side of the wafer  51  shown in  FIG. 3 . This view shows the resilient tangs  70  formed on each finger  69  of the ground plane shield  60 . The tangs  70  contact the ground shield planes  25  ( FIG. 1 ) when the ground shield planes are inserted into slots  54  of the wafer  51 . Therefore, the ground shields  24  are in electrical contact with the ground plane  60  through the tangs  70 . Additionally, shielding tabs  20  extend from the ground shield  60  and are therefore grounded at the same potential as the ground plane  60  and ground shields  24 . The daughter card connector  12  and backplane connector  14  are grounded at the same potential through the shield plates  25  contacting the tangs  70 . This grounding scheme significantly reduces differential pair crosstalk in the serial connector  10 . 
     The ground plane  60  in  FIGS. 3 and 4  includes lugs  64  and alignment lugs  62  for mounting to the wafer  51 . Connector guides  30  allow the wafer  51  to mate with a corresponding backplane connector  14  ( FIG. 1 ). The wafer  51  of  FIGS. 3 and 4  is a one-piece assembly formed by a two shot molding process. The lugs  62  and  64  assist in aligning and retaining the ground plane  60  to the body of the wafer  51  during the molding process so the ground plane and wafer body are integral. 
       FIG. 5  is a detailed front view of the other side of the wafer  51  shown in  FIG. 3 . This view shows the plastic body  53  of the wafer isolating each finger  69  ( FIG. 4 ) of the ground plane  60  ( FIG. 4 ) from the resilient differential conductors  56 . For clarity, the non-conductive portions of the wafer are shaded. The fingers  69  provide shielding for the differential conductors  56 , but must be electrically isolated from the connectors to prevent the connectors from shorting to ground. Tangs  70  protrude into slots  54  from the ground shield  60  ( FIG. 4 ). The backside of crosstalk tabs  20  are visible extending below wafer  51 . 
       FIG. 6  is a partial side view of the daughter card connector  12  shown in  FIG. 2 . The wafers  51  are fastened together using any suitable conventional technique, such as ultrasonic welding, adhesives, integral press-fitting lugs or the like. Connector guides  30  on each of the wafers  51  allow the daughter card to mate with a corresponding backplane connector  14  ( FIG. 1 ). Crosstalk tabs  20  extend from the daughter card connector  12 . 
       FIG. 7  is a partial top perspective view of the daughter card connector  12  showing the ground plane  60  ( FIG. 3 ) of the daughter card connector ( FIG. 1 ) inserted into the backplane connector  14  ( FIG. 1 ). The differential pins  22 , ground blades  24 , wafer body  53 , and daughter card differential conductors  56  are omitted from this figure for clarity purposes. The crosstalk shield tabs  20  are inserted into corresponding tab receptacles  93  formed in the backplane connector floor  26 . The length of the tabs  20  is selected so that the tabs  20  extend completely though the thickness of the floor  26 . Other lengths can be used where suitable. For example, it is frequently necessary to have various circuits engage electrically before other circuits. Therefore, in some instances taller pins are used to engage some circuitry early then others as the connectors are joined. In some embodiments the length of the tab varies with the length of the corresponding pins. However, preferably, the tab shields extend substantially through the backplane housing (e.g. 95% through the housing) when the daughter card connector and backplane connector are mated. The housing floor  26  also has differential pin receptacles  90  formed therein. The differential pins  22  are press-fitted into these receptacles  90 . Fingers  69  of ground plane  60  connect with tangs  70  in order to provide a ground connection to ground blades  24  ( FIG. 1 ). Sidewall  28  provides mechanical stability for the backplane connector  14  and the daughter card connector  12 . 
       FIG. 8  is a partial bottom perspective view showing the daughter card connector  12  ( FIG. 1 ) inserted into the backplane connector  14  including the non-conductive housing  53 . The ground plane blades  24  are omitted from this figure for clarity purposes. The bottom edge of tabs  20  are visible between the differential pair pins  32 . The eye-of-the-needle ends of the differential pair pins  32  connect to the differential conductors  56 . 
       FIG. 9  is a detailed bottom perspective view showing the daughter card connector  12  ( FIG. 1 ) inserted into the backplane connector  14  ( FIG. 1 ). The ground plane blades  24  of the backplane connector  14  are omitted from this figure for clarity purposes. However, this view shows through-hole receptacles  101  formed in the backplane housing floor  26  for receiving the ground blade pins  34  of the ground shields  25 , which are press-fitted into the through-holes. The bottom edges of tabs  20  are visible between the differential pair pins  32 . The eye-of-the-needle ends of differential pair pins  32  connect to the differential conductors  56  as shown in  FIG. 8 . The ground blades  25  are visible above the backplane conductor. The non-conductive housing  53  and differential pair receptacles  52  are also visible between the daughter card connector  12  and the backplane connector  14 . 
     In keeping with the invention, the backplane conductor  14  receives both daughter card connectors with and without the shield tabs  20 . In this regard, some applications of the connector may not require supporting high speed, broad bandwidth connections. The backplane connector still contains tab receptacles  93 . In this way, daughter boards  12  requiring high performance connectors can be mounted with daughter card connectors having shield tabs  20 , while daughter boards having lower performance requirements can be mounted with daughter card connectors without the shield tabs. Both types of daughter card connectors can be mated with the same backplane connectors. The tab receptacle is not occupied when the backplane connector is mated with a daughter card connector that does not have shield tabs  20 . 
     In some embodiments of the invention, the shield tabs  20  are located on the backplane connector. The daughter card connector has corresponding tab receptacles  93 . In these embodiments the shield tabs  20  extend upwards from the backplane connector and engage the daughter connector when the two connectors mate. 
     All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
     Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.