Abstract:
A differential data cable for high-speed signals includes a connector PCB with angled pads cable connection pads connected to a pair of differential data cable conductors, wherein the symmetrical angled configuration minimizes lead lengths, interface discontinuities, and common mode imbalance. A third pad may be connected to a return signal wire. The connector PCB may have a similar arrangement on the other side, and may have a ground plane in between. The cable may be placed over the ground plane and away from the edge. Pads may have a bump to shorten wire lengths. Wires are glued to the bumps using a UV-curable adhesive. Wires are positioned in an angle with the PCB.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. Provisional Patent Application Ser. No. 62/281,059, entitled “A Data Connector”, filed on Jan. 20, 2016, which is hereby incorporated by reference as if set forth in full in this application for all purposes. 
     
    
     BACKGROUND 
       [0002]    The present application relates in general to data communication systems, and more specifically to cables and connectors for transferring data between one system and another. 
         [0003]    Data cables, their connectors, and connector form factors are often specified in industry standards related to specific data communication protocols. These industry standards usually take performance into account. 
         [0004]    An aspect partially left to individual manufacturers is the final performance, provided that the minimums specified in an industry standard are met. The performance is impacted both by the raw cable and its connectors. Innovations, such as described in the present document, improve the quality of connectors without significant impact on their cost. 
         [0005]    One example of a high-speed data cable is the quad small form-factor pluggable (QSFP) cable that supports hot-pluggable transceivers in 40 and 100 Gbits/second data communication systems. The data travels through four channels of nominally 10 or 25 Gbits/second each. The QSFP standard supports various communication protocols. QSFP connecters have 38 pins, including 4 high-speed transmit (TX) and 4 high-speed receive (RX) pairs. QSFP cables are often used in data centers, and to connect servers and switches. Embodiments of the invention are applicable to many industry standards for form factors that are used for high-speed data transmission. A few of those are small form-factor pluggable (SFP), QSFP, QSFP DD (double density), microQSFP, and miniature serial-attached small computer system interface high density (Mini-SAS HD). 
       SUMMARY 
       [0006]    Embodiments of the invention provide a connector printed circuit board (PCB) for high-speed signals carried in a differential data cable. The connector PCB comprises two high-speed cable connection pads on a first side. Two differential data cable conductors are electrically coupled to the high-speed cable connection pads. The connection pads are positioned in a symmetrically angled configuration to minimize differential data cable lead lengths and to minimize discontinuity for high-speed signals traveling between the differential data cable conductors and the high-speed cable connection pads. The connector PCB may further include a third pad positioned between the high-speed cable connection pads. A third differential data cable conductor electrically coupled to the third pad. The two high-speed cable connection pads are positioned symmetrically around the third pad. 
         [0007]    The differential data cable may be a high-speed data twin-axial cable; the two differential data cable conductors may be signal wires; and the third differential data cable conductor may be a return signal wire, such as a drain wire or a twin-axial cable outer conductor. In some embodiments, the cable connection pads may be made with silver-plated copper. 
         [0008]    The connector PCB may have a similar arrangement of pads and conductors (wires) on a second side. Embodiments may include a ground plane in between. The differential data cable may be placed over the ground plane and away from a connector PCB edge. Pads may include a bump to shorten wire lengths. Wires may be glued to the pads or bumps using a UV-curable adhesive. Cable conductors may be positioned in an angle with the connector PCB. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Various implementations will be described with reference to the drawings, in which: 
           [0010]      FIG. 1  illustrates an example connector according to an embodiment of the invention; 
           [0011]      FIG. 2  illustrates the geometry of connections between cable wires and a PCB according to one embodiment of the invention; and 
           [0012]      FIG. 3  illustrates a cross-cut side view of connections between cable wires and a PCB according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Data cables, their connectors, and connector form factors are often specified in industry standards related to specific data communication protocols. These industry standards usually take performance into account. An aspect partially left to individual manufacturers is the final performance, provided that the minimums specified in an industry standard are met. The performance is impacted both by the raw cable and its connectors. Innovations, such as described in the present document, improve the quality of connectors without significant impact on their cost. 
         [0014]      FIG. 1  illustrates an example connector  100  according to an embodiment of the invention. Example connector  100  includes metal bracket  110  and printed circuit board (PCB)  120 . PCB  120  includes connector pads  130  and cable connection pads  140  (both are encircled). PCB tracks electrically couple connector pads  130  to cable connection pads  140 . Metal bracket  110  holds PCB  120 . Connector  100  conforms to the 28QSFP standard. It has 38 connector pads  130 ,  19  on each side of PCB  120 . In normal use, connector  100  has another metal bracket (not shown), with the two brackets mounted to each other enveloping PCB  120  and an end of a raw cable (not shown) connected to the PCB as described herein. A raw cable may hold, for example, eight high-speed data twin-axial cables. In some embodiments, a single metal bracket may envelope PCB  120  and the cable end. In most embodiments, part of the bracket(s) and part of the cable end may be surrounded, held together, and protected by a plastic holder.  FIG. 1  shows an example of how four of the eight high-speed data twin-axial cables may connect to PCB  120  on one side, whereas the other four of the eight high-speed data twin-axial cables may connect to PCB  120  on the other side. In various implementations, to minimize the cable&#39;s lead length (the length of a twin-axial cable&#39;s inner conductor that protrudes from the coaxial insulator), two high-speed cable connection pads  140  may be positioned in a symmetrically angled configuration. The angle may vary. 
         [0015]    In some embodiments, the two high-speed cable connection pads  140  may surround a third cable connection pad  140  that connects a return signal wire to PCB  120 &#39;s ground plane. The return signal wire may be a drain wire or outer conductor of the twin-axial cable pair. Distances between cable connection pads  140  may vary, depending on the embodiment. In some embodiments, connector pads  130 , cable connection pads  140  and the PCB tracks may be made of silver-plated copper to improve connector  100 &#39;s high-speed performance. Various embodiments minimize a discontinuity for high-speed signals traveling between the signal wires and cable connection pads  140  by using the angled configuration alone, the two high-speed cable connection pads  140  surrounding the third cable connection pad  140  alone, the cable connection pads  140  and the PCB tracks made of silver-plated copper alone, or any combination thereof. 
         [0016]      FIG. 2  illustrates the geometry  200  of connections between cable wires and a PCB according to one embodiment. The embodiment is suitable for transferring a differential pair of high-speed signals from a differential data cable via the PCB to a matching connector.  FIG. 2  shows PCB  210 , high-speed data twin-axial cable  220 , coaxial insulator  230  around signal wire  250  and coaxial insulator  235  around signal wire  255 , return signal wire  240 , high-speed cable connection pads  260  and  265 , and return signal wire connection pad  270 . Whereas conventional connectors include parallel pads with the return signal wire connector on the outside, embodiments of the invention place high-speed cable connection pads symmetrically angled around a return signal wire connection pad. Embodiments keep cable connection pads short, to minimize bare wire length and coaxial insulator length. 
         [0017]    The distances a and b in  FIG. 2  between signal wire  250  and return signal wire  240 , respectively signal wire  255  and return signal wire  240 , are variable. They are equal (a=b), to implement the symmetry. In embodiments, the electrical field coupling of high-speed cable connection pad  260  (to which signal wire  250  is connected) to return signal wire connection pad  270  equals the electrical field coupling of high-speed cable connection pad  265  (to which signal wire  255  is coupled) to return signal wire connection pad  270 . Equal coupling reduces common mode imbalance, which can suffer from any inadvertent common-mode-to-differential-mode conversion. 
         [0018]      FIG. 3  illustrates a cross-cut side view  300  of connections between cable wires and a PCB  310  according to an embodiment of the invention. In prior-art cable-to-PCB connection arrangements, the cable wires are typically connected to pads situated at the edge of the PCB. A prior-art connector may include a notch in which the cable conductor&#39;s insulator may sink to allow for a short connection. In contrast, in embodiments of the present invention cables are positioned further from the edge of PCB  310 , which has a ground plane  320  between its top and bottom to reduce crosstalk between cables on both sides.  FIG. 3  further shows part of a first high-speed data twin-axial cable at the top, with coaxial insulator  330 , and signal wire  340 . A high-speed cable connection pad features bump  360 , to which signal wire  340  is connected. A part of a second high-speed data twin-axial cable is shown at the bottom of PCB  310 . 
         [0019]    In embodiments of the present invention in which the cables are positioned further from the edge of the board, the signal wires are angled slightly ( FIG. 3  shows angle α between coaxial insulator  330  and PCB  310 , with the angle α in a plane orthogonal to the PCB  310  surface) and connected to the pads using UV-curable adhesive  350  to make the shortest connections to the pads. Embodiments of the invention may further include a bump  360  to allow the shortest connection. 
         [0020]    Although the invention may be described with respect to specific types of cables and connectors (e.g., QSFP and differential data cables), it should be apparent that many other types of cables and connector designs can be used with features described and claimed herein. For example, embodiments of the invention are suitable for any connector that conforms with an industry standard for connector form factors used for high-speed data transmission. Although the description has been described with respect to particular embodiments thereof, these particular embodiments are merely illustrative, and not restrictive. Embodiments of the invention may single out, or combine, any of the techniques described herein. Use of the techniques described herein does not in any way prevent the simultaneous use of conventional best practices such as keeping PCB traces short. 
         [0021]    It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. These different combinations constitute various alternative aspects of the invention. 
         [0022]    Although the description has been described with respect to particular embodiments thereof, these particular embodiments are merely illustrative, and not restrictive. 
         [0023]    It will also be appreciated that one or more of the elements depicted in the drawings/figures can also be implemented in a more separated or integrated manner, or even removed or rendered as inoperable in certain cases, as is useful in accordance with a particular application. 
         [0024]    As used in the description herein and throughout the claims that follow, “a”, “an”, and “the” includes plural references unless the context clearly dictates otherwise. Also, as used in the description herein and throughout the claims that follow, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise. 
         [0025]    Thus, while particular embodiments have been described herein, latitudes of modification, various changes, and substitutions are intended in the foregoing disclosures, and it will be appreciated that in some instances some features of particular embodiments will be employed without a corresponding use of other features without departing from the scope and spirit as set forth. Therefore, many modifications may be made to adapt a particular situation or material to the essential scope and spirit.