Abstract:
Embodiments of the invention use a small piece of flex or rigid PCB as the cable plug. The wires of the cable are soldered onto the pads on the PCB with the pads so arranged that all the ground pads are tied together without needing a separate grounding bar. The signal and GND pads are so aligned such that minimum strip length is required for soldering and the symmetry of the differential signals is maintained.

Description:
FIELD OF THE INVENTION 
       [0001]    Embodiments of the present invention are directed to cable termination and, more particularly, to cable wire termination for high speed interfaces. 
       BACKGROUND INFORMATION 
       [0002]    Electrical cables are often used to carry electrical data signals or power from one device to another. At some point the cable must be terminated where it connects to the device or to a plug or connector which may be plugged into the device. It is well known that high speed electrical performance heavily depends on proper cable termination in order to insure mechanical and electrical integrity. 
         [0003]    Referring to  FIG. 1 , there is illustrated a popular method for terminating cables, such as micro-coaxial cables, commonly referred to simply as micro-coax. A micro-coax cable  100  may include a central signal wire  102  covered in a signal wire insulator  104 , a conductive coaxial shield  106  surrounding the insulator  104 , a shield insulator  107  may be present, and finally an outer insulative sheath  108 . The cables  100  are stripped as shown. Often, the cables  100  occur in differential pairs with one cable signal wire  102  carrying signal Ss+ and the other carrying Ss−. 
         [0004]    One current cable termination solution typically involves soldering the wires  102  to stamp-and-formed contacts  112  in a cable plug. In some cases, a small piece of printed circuit board (PCB)  110  may be inserted in the cable plug and the wires  102  are soldered  114  onto the PCB pads. The contacts or the PCB pads are arranged in a row, and long strip length of wire  102  is often necessary in order to solder the wire  102  onto the contacts or pads  112 . In the case of a micro-coax cable, an additional metal ground bar  116  is needed to tie the cable shields  106  to the ground  118 . The ground bar  116  may be a conductive metal strip runs across all of the cable shields and ties them to a ground cable  118 , in some cases. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    The foregoing and a better understanding of the present invention may become apparent from the following detailed description of arrangements and example embodiments and the claims when read in connection with the accompanying drawings, all forming a part of the disclosure of this invention. While the foregoing and following written and illustrated disclosure focuses on disclosing arrangements and example embodiments of the invention, it should be clearly understood that the same is by way of illustration and example only and the invention is not limited thereto. 
           [0006]      FIG. 1  is a plan view of a typical wire termination scheme; 
           [0007]      FIG. 2  is a plan view of a wire termination device for a coaxial or micro-coaxial cable according to one embodiment; and 
           [0008]      FIG. 3  is a plan view of a wire termination device for a twinax or twisted pair cable according to one embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    It is well known that cable assembly high speed electrical performance heavily depends on cable termination. Developing a simple method for cable wire termination will improve the cable assembly high speed performance to support high speed interfaces such as SATA3, USB3, and PCIe3 that may involve cables. Embodiments of the invention provide a solution to allow cable wires to be cleanly terminated onto a cable plug with a minimum strip length (i.e. the length over which the shielding is removed). 
         [0010]    Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. 
         [0011]    Referring now to  FIG. 2 , there is shown one embodiment of the invention for cable termination. As shown, a plurality of cables  200  may be terminated. For illustrative purposes, four cables  200  are shown comprising two differential pairs  202  and  204 . Of course in practice any number of cables or a single cable may be terminated within the teachings of the invention. In one embodiment a small piece of flex or rigid printed circuit board (PCB)  206  may be used as for a cable plug  208 . The cable plug  208  may be inserted into a receptacle connector on, for example, a motherboard. The PCB  206  may be of one or more layers with or without a ground plane. 
         [0012]    Parallel traces comprising a one or more differential pair signal pads  212  may be patterned or stamped on the PCB  206 . A ground (GND) network  214  may also be patterned on the PCB  206  symmetrically surrounding the differential signal pads  212 . As shown, the ground network  214  surrounds each of the differential pairs  212  on at least three sides with a parallel strips of the ground network  214  on either side of the parallel traces forming the differential pair  212  and perpendicular part of the ground network  214  lying in front of the differential pairs  212 . 
         [0013]    In one embodiment, a wire termination area  210  includes the perpendicular part of the GND network  214  which lies in front of the differential signal pads  212 . The micro-coax cables  200  may be stripped as shown in the bubble  250  with a length of the inner core  252  protruding out in front followed by a length of the core insulator  254 , followed by an exposed length of the coax shield  256 . When terminating a micro-coax cable onto the PCB  206 , the coax shield  256  in front of the conductor core  252  is soldered onto the GND pad in the termination area  210  and becomes a part of the GND network  214 . The conductor core  252  is soldered onto the signal pad on one of the differential pairs  212 , in-line with the shield  256 . 
         [0014]    There are many advantages to this cable termination scheme including, there is no longer the need to have a GND bar  116  to tie shields to GND, as shown in  FIG. 1 , saving materials and costs, In addition, the GND traces/pads  214  on the PCB  206  are directly in contact with the coax cable shields  256  forming a smooth return path. Further, the GND/guide trace network  214  on the PCB  206 , and if necessary, the GND plane on the PCB  206  further improves return path, reducing crosstalk and emission. 
         [0015]      FIG. 3  shows yet another embodiment of the invention for twinax or twisted pair cables. The termination is done similarly to the micro-coax case, as shown in  FIG. 2 . As before, parallel traces comprising a one or more differential pair signal pads  312  may be patterned or stamped on the PCB  306 . A ground (GND) network  314  may also be patterned on the PCB  306  symmetrically surrounding the differential signal pads  312 . As shown, the ground network  314  surrounds each of the differential pairs  312  on at least three sides. 
         [0016]    In this case, each cable  300  may comprise first wire  302  and a second wire  304  forming the twinax or the twisted differential pair. In addition a third wire, known as the drain wire,  305  may also make up part of the cable  300 . The differential pair  302  and  304  of the cable  300  is soldered onto the differential pads/traces  312  on the PCB  306 . The drain wire  305  of the cable differential pair is soldered onto the GND network  314  as shown. 
         [0017]    Again, this termination scheme has many advantages including, the symmetry of differential pair  302  and  304  is maintained in the termination area; this is usually not the case for other termination schemes. Plus, the termination is very clean with minimum wire stripping and no wire cross-over. The termination area may be protected with over-molding or potting, which is not shown in the diagram. 
         [0018]    Thus, according to embodiments flex or rigid PCB may be used for wire termination with all GND pads tied together. The GND and signal solder pads are aligned in-line such that the symmetry of differential signaling is maintained and the cable stripped length is kept to a minimum. Further, in the case of micro-coax cable, there is no need for grounding bar to tie the ground together. 
         [0019]    The above description of illustrated embodiments of the invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. 
         [0020]    These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification and the claims. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.