Patent Publication Number: US-11646135-B1

Title: High performance differential cable

Description:
BACKGROUND 
     Field of the Disclosure 
     This disclosure relates generally to information handling systems and, more particularly, to differential cables for communication between information handling systems. 
     Description of the Related Art 
     As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems. 
     Cables have become an integral part of server design. Within a server, cables connect PCBs. Within a rack, multiple servers may be installed and communication between servers and racks can occur over cables. 
     Cables provide a lower loss mode for signal propagation compared to PCB which makes them popular. Internal cables have been popular in rack servers for a while. 
     SUMMARY 
     Embodiments disclosed herein may be generally directed to a high performance differential signal cable and a method for manufacturing a high performance differential cable. 
     A method of manufacturing a high performance differential cable may comprise forming a dielectric core with a central cavity, a plurality of wire guides arranged on an outer perimeter and a polarity key located on the outer perimeter. The method further comprises positioning two sets of wires in the plurality of wire guides, wherein a first set of wires corresponds to a first differential signal conductor (DSC) and a second set of wires corresponds to a second DSC. The method also comprises surrounding the dielectric core and the plurality of wires with a dielectric layer and surrounding the dielectric layer with a shield to form a bulk differential cable. The method further comprises forming a paddle board with two pads on a first end and an interconnecting structure on a second end, the interconnecting structure configured for interconnecting the two or more wires of each DSC and isolating the two DSCs. The method may also include forming a slot in the dielectric core, positioning the paddle board in the slot, connecting a first wire of a first DSC to a first pad of the two pads, connecting a first wire of a second DSC to a second pad of the two pads, connecting a second wire of the first DSC to a first lead that is connected to the first pad, and connecting a second wire of the second DSC to a second lead that is connected to the second pad, wherein the interconnecting structure divides each pair of signals for transmitting through the first set of wires and the second set of wires and combines signals received from multiple wires into a single set of signals. 
     In some embodiments, the cavity comprises a plurality of sides based on a combined number of wires of the two DSCs. In some embodiments, the combined number of wires of the two DSCs is four and the cavity comprises four sides. In some embodiments, each side of the plurality of sides of the cavity is oriented relative to a wire guide of the plurality of wire guides. In some embodiments, the polarity key is located on the outer perimeter relative to the cavity. 
     In some embodiments, the interconnecting structure comprises a first pad for coupling to a first wire associated with a first DSC and a first lead, a first transverse member and a first crossover member for coupling to a second wire associated with the first DSC. The interconnecting structure may comprise a second pad for coupling to a first wire associated with a second DSC and a second lead, a second transverse member and a second crossover member for coupling to a second wire associated with the second DSC. 
     In some embodiments, a diameter of each wire is approximately half a diameter of a corresponding differential signal conductor. 
     In some embodiments, each wire extends outward of the outer perimeter and the dielectric layer contacts each wire such that a dielectric pocket is formed between the outer perimeter of the dielectric core and the dielectric layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the invention and its features and advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: 
         FIG.  1    is a cross-section view of a common cable for communicating between information handling systems; 
         FIG.  2    is a cross-section view of a differential signal conductor separated into two pairs of differential signal conductors each, illustrating horizontal and vertical coupling that can cancel crosstalk between channels; 
         FIG.  3    is a perspective view of a dielectric core with a cavity, four wire guides and a polarity key according to one embodiment of a high-performance differential cable; 
         FIG.  4    is a perspective view of the dielectric core of  FIG.  3    with two pairs of two wires positioned in the four wire guides according to one embodiment of a high-performance differential cable; 
         FIG.  5    is a perspective view of the dielectric core of  FIG.  4    with a dielectric layer surrounding the dielectric core and the four wires to form a bulk differential cable according to one embodiment of a high-performance differential cable; 
         FIG.  6    is a perspective view of the bulk differential cable of  FIG.  5    with a shield surrounding the dielectric layer according to one embodiment of a high-performance differential cable; 
         FIG.  7    is a perspective view of an end of the bulk differential cable of  FIG.  6    with portions of the dielectric layer and shield removed from the bulk differential cable for manufacturing one embodiment of a high-performance differential cable; 
         FIG.  8    is a perspective view of the bulk differential cable of  FIG.  7    with a slot formed in the dielectric core for manufacturing one embodiment of a high-performance differential cable; 
         FIG.  9 A  is a perspective view of two pairs of two wires with an interconnect connecting each pair of wires for manufacturing one embodiment of a high-performance differential cable; 
         FIG.  9 B  is an alternate perspective view of two pairs of two wires with an interconnect connecting each pair of wires for manufacturing one embodiment of a high-performance differential cable; 
         FIG.  10    is a perspective view of a paddle board with the interconnect of  FIGS.  9 A and  9 B  for manufacturing one embodiment of a high-performance differential cable; 
         FIG.  11    is a perspective view of a paddle board connected to the bulk cable to form one embodiment of a high-performance differential cable; 
         FIG.  12    is a graph depicting normalized losses for differential cables with wires of different diameters, illustrating benefits of one embodiment of a high-performance differential cable; 
         FIG.  13    is an end view of a dielectric core configured with two pairs of three wires positioned in six wire guides according to one embodiment of a high-performance differential cable. 
     
    
    
     DESCRIPTION OF PARTICULAR EMBODIMENT(S) 
     In the following description, details are set forth by way of example to facilitate discussion of the disclosed subject matter. It should be apparent to a person of ordinary skill in the field, however, that the disclosed embodiments are exemplary and not exhaustive of all possible embodiments. 
     For the purposes of this disclosure, an information handling system may include an instrumentality or aggregate of instrumentalities operable to compute, classify, process, transmit, receive, retrieve, originate, switch, store, display, manifest, detect, record, reproduce, handle, or utilize various forms of information, intelligence, or data for business, scientific, control, entertainment, or other purposes. For example, an information handling system may be a personal computer, a consumer electronic device, a network storage device, or another suitable device and may vary in size, shape, performance, functionality, and price. The information handling system may include memory, one or more processing resources such as a central processing unit (CPU) or hardware or software control logic. Additional components of the information handling system may include one or more storage devices, one or more communications ports for communicating with external devices as well as various input and output (I/O) devices, such as a keyboard, a mouse, and one or more video displays. The information handling system may also include one or more buses operable to transmit communication between the various hardware components. 
     Cables are used to connect information handling systems and cards or components on information handling systems. 
     Referring to  FIG.  1   , a typical cable  100  comprises two differential signal conductors  10 , an insulator  12  surrounding each DSC  10 , ground wire  14 , all surrounded by shield  16 . A pair of DSCs  10  may be referred to as a differential pair structure. 
     Traditional differential pair structures are coupled in one direction; either horizontally (edge coupled) or vertically (broadside coupled), which results in some fringing, since the electromagnetic fields use more space to terminate. This increases crosstalk and lowers density since it requires more space to isolate. 
     A challenge for server designs involves lowering the signal loss through cables. While ultra-low loss materials are being considered on one end, the materials add cost. Furthermore, even though cables provide a low loss medium, the loss is not adequate to address crosstalk concerns for cables with greater than 700 mm cable lengths. Due to the density of servers, increasing the size of the cables is undesirable and might not be a choice. 
     Particular embodiments are best understood by reference to  FIGS.  2 - 8 ,  9 A- 9 B and  10 - 13   , wherein like numbers are used to indicate like and corresponding parts. 
     Referring to  FIG.  2   , embodiments disclosed herein may divide each DSC  10  into two or more interconnected wires  202 A,  202 B and  204 A,  204 B, whereby the outer diameter of a high performance differential cable is not increased (and may be decreased) but signal losses are reduced. As depicted in  FIG.  2   , the symmetry tightens up the coupling and reduces fringing, between fields  206 , which results in lower crosstalk. As the number of conductors is doubled, loss is reduced as well, even when using thinner conductors. In cable applications the tight coupling allows drainless operation, and the low leakage enables a simple wrapped shield without having to worry about resonances. 
     Bulk Differential Cable 
       FIGS.  3 - 6    may be associated with steps in a manufacturing process for constructing a bulk differential cable.  FIGS.  3 - 6    depict bulk differential cable  300  having two pairs of wires for a combined four total wires, but larger numbers are possible (and may have increasing performance capabilities). 
     Referring to  FIG.  3   , manufacturing a bulk differential cable may start with extruding a dielectric core  302 . Embodiments of dielectric core  302  may comprise a plurality of wire guides  304  on an outer perimeter of dielectric core  302 , polarity key  308  and central cavity  306 . Wire guides  304  may be formed as grooves configured to retain wires  202 A,  202 B,  204 A and  204 B during the build process. 
     Cavity  306  may comprise multiple sides. As depicted in  FIG.  3   , cavity  306  may have four sides. Cavity  306  having sides may be used as a tooling feature to align the end of bulk differential cable during cable termination to prepare bulk differential cable for coupling to a connector. Cavity  306  contains air, which reduces dielectric losses. Cavity  306  also makes bulk differential cable lighter and more flexible. 
     Polarity key  308  may be formed as a thicker section of dielectric core  302 . Polarity keys  308  may be used for matching polarity of wires  202 A,  202 B,  204 A and  204 B and add mechanical strength of bulk differential cable for cable termination. 
       FIG.  4    depicts bulk differential cable  300  with wires  202 A,  202 B,  204 A and  204 B positioned in wire guides  304  of dielectric core  302 . As depicted in  FIG.  4   , wires  202 A,  202 B,  204 A and  204 B may extend partially outward of an outer perimeter of dielectric core  302 . 
       FIG.  5    depicts bulk differential cable  300  with wires  202 A,  202 B,  204 A and  204 B positioned in wire guides  304  of dielectric core  302  and dielectric layer  310  surrounding wires  202 A,  202 B,  204 A and  204 B and dielectric core  302 . As depicted in  FIG.  5   , in some embodiments, dielectric layer  310  may contact wires  202 A,  202 B,  204 A and  204 B but not contact dielectric core  302  such that air may be present in spaces between wires  202 A,  202 B,  204 A and  204 B and dielectric layer  310 . In some embodiments, dielectric layer  310  comprises a dielectric tape wrap. 
       FIG.  6    depicts bulk differential cable  600  with wires  202 A,  202 B,  204 A and  204 B positioned in wire guides  304  of dielectric core  302 , dielectric layer  310  surrounding wires  202 A,  202 B,  204 A and  204 B and dielectric core  302 , and shield  312  surrounding dielectric layer  310 . In some embodiments, because of the strong coupling and well contained fields, a simple foil wrap  312  may be sufficient. 
     Bulk Differential Cable Termination 
       FIGS.  7 - 8 ,  9 A- 9 B and  10 - 11    depict embodiments of a high performance differential cable during various stages of cable termination in a manufacturing process. 
     Referring to  FIG.  7   , slot  802  may be formed in an end of bulk differential cable  600 . Shield  312  and dielectric layer  310  may be stripped a distance  314  to expose wires  202 A,  202 B,  204 A and  204 B. One or more of cavity  306  and polarity key  308  may be used to align each end of bulk differential cable  600  to a cutter such that, when slot  802  is formed, the same wires (e.g., wires  204 A and  204 B) are on the same side of slot  802 . Additionally, when slot  802  is formed, dielectric spaces  804  may be retained between adjacent wires (e.g., wires  204 A and  204 B) on the same side of slot  802 . 
     High Performance Cable End Connectors 
       FIGS.  9 A,  9 B,  10  and  11    depict views of high performance cable manufactured using bulk differential cable  600  and a paddle card interface with an interconnecting structure. 
       FIGS.  9 A and  9 B  depict images illustrating one strategy to combine four wires  202 A,  202 B,  204 A and  204 B into one pair of differential signal conductors  202 ,  204 . As depicted in  FIGS.  9 A and  9 B , interconnecting structure  900  comprises first pad  902  for coupling to a first wire (e.g.,  202 B) and second pad  904  for coupling to second wire (e.g., wire  204 A). Additionally, first pad  902  may be coupled to a second wire ( 202 A) through first lead  902 A, first crossover member  902 B and first transverse member  902 C. Similarly, second pad  904  may be coupled to a second wire ( 204 B) through second lead  904 A, second crossover member  904 B and second transverse member  904 C. Thus, interconnecting structure  900  at a first end of bulk differential cable  600  may divide a single pair of signals for transmitting through multiple wires in bulk differential cable  600  and combine signals received from multiple wires in bulk differential cable  600  into a single pair of signals. 
       FIG.  10    depicts one embodiment of paddle board  1000  comprising interconnecting structure  900 . As depicted in  FIG.  10   , paddle board  1000  may comprise base  1002 , first pad  902  for coupling to a first differential signal connector  202  (not shown), second pad  904  for coupling to a second differential signal connector  204  (not shown) and grounding pads  1006 . Interconnecting structure  900  may be integrated with base  1002 . Impedance and length matching all happens in paddle board  1000 . Planes and GND vias are omitted for clarity. 
       FIG.  11    depicts a perspective partial view of one embodiment of an end of a high performance differential signal cable configured with paddle board  1000  positioned in slot  802  of bulk differential cable such that wires  202 A,  202 B (not visible),  204 A, and  204 B (not visible) are connected to one of first pad  902  or second pad  904 . Solder  1102  may further couple wires  202 A,  202 B,  204 A, and  204 B to first pad  902  or second pad  904 . Solder  906  may couple shield  312  to grounding pads  1006 . Paddle board  1000  can be made compatible with all edge-based connector types such as high-speed signal conductors such as Mini Cool Edge  10  (MCIO) connectors, SATA interface connectors such as Slimline connectors and high volume universal connectors such as Gen-Z connectors. 
     In some embodiments (not shown) an overmold may be applied to the end of a high performance differential signal cable for mechanical strength and to protect the connections between wires  202 A,  202 B,  204 A, and  204 B and first pad  902  and second pad  904 . 
     Referring to  FIG.  12   , air is the best medium for high-speed signals as it has Dk=1 and loss tangent of 0. Embodiments disclosed herein allow air to be present in cavity  306 , between dielectric core  302  and dielectric shield  310 , and spaces  804 , which reduce signal loss drastically. The diameter of each wire  202 A,  202 B,  204 A and  204 B may be half the diameter of a differential signal conductor such as differential signal conductor  10  (shown in  FIG.  1   ), which typically results in more signal losses of a high performance differential signal cable. However, having four wires instead of two increases the surface area and reduces skin effect losses, which results in a net improvement over two thicker wires.  FIG.  12    depicts a graph of normalized losses for wires of different diameters. For example, point P 1  represents a conductor (such as depicted in  FIG.  1   ) with a diameter of 16 mils and normalized losses of 1. Points P 2 -P 5  represent losses for wires of smaller diameters. For example, point P 2  represents a conductor with a 14 mils diameter, resulting in normalized losses of 0.57. Many cables today are around 8-11 mils in diameter. Comparing the losses of a wire with an 8 mils diameter represented point P 5  and the losses of a wire with for a wire with a 16 mils diameter represented by point P 1 , the losses represented by point P 5  are about 30% lower. Thus, embodiments that use two smaller wires instead of a single large wire may have significantly lower losses. Notably,  FIG.  12    depicts a simulation for a model that did not include air in air pockets or a dielectric core. Thus, for embodiments with air present, the losses associated with point P 5  for a cable with 8 mils diameter as compared with point P 1  for a cable with 16 mils diameter may be less than 30%. 
     Alternate Configurations 
     Referring to  FIGS.  4  and  13   , embodiments may comprise two or more wires for each differential signal conductor. As mentioned above with respect to  FIG.  4   , embodiments may have two pairs of wires for a combined total number of four wires  202 A,  202 B,  204 A and  204 B. Embodiments may have more wires as well. As depicted in  FIG.  13   , embodiments may have two sets of three wires for a combined total number of six wires  202 A,  202 B,  202 C,  204 A,  204 B and  204 C. Dielectric core  1302  may be configured with six wire guides  1304  and cavity  1306  may have three or more sides. Dielectric key  1308  may be used for aligning dielectric core  1302  relative to a cutter. 
     The above disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments which fall within the true spirit and scope of the disclosure. Thus, to the maximum extent allowed by law, the scope of the disclosure is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.