Patent Publication Number: US-7211734-B2

Title: Quadrax to twinax conversion apparatus and method

Description:
This application is a continuation of U.S. application Ser. No. 10/899,515, Filed Jul. 26, 2004, now U.S. Pat. No. 7,019,219 entitled “QUADRAX TO TWINAX CONVERSION APPARATUS AND METHOD, which is a continuation of U.S. application Ser. No. 10/096,087, filed Mar. 11, 2002 now U.S. Pat. No. 6,794,578 entitled “QUADRAX TO TWINAX CONVERSION APPARATUS AND METHOD” and claims the benefit of U.S. Provisional Application No. 60/276,263 filed Mar. 14, 2001 entitled “QUADRAX TO TWINAX CONVERSION APPARATUS AND METHOD”, the entire contents of which is expressly incorporated by reference. 

   FIELD OF THE INVENTION 
   This invention relates to high-speed data transference and particularly to conversion from four wire (Quadrax) to two wire (Twinax). 
   SUMMARY OF THE INVENTION 
   High speed data transference requires transmission systems that minimize reflections. This is achieved through controlled characteristic impedance from source to load. In conventional microwave systems, this is accomplished with waveguide or coaxial transmission lines. However, with current high-speed data transfer, such as fiber channel, the source and load differential impedances are usually high and of the order of 100 to 150 ohms. Achieving these high impedances in coaxial transmission lines is size prohibitive. A more efficient transmission line for high-speed data transfer is Twinax wherein the signals are carried between a pair of conductors. 
   An even more efficient transmission line is four-channel Quadrax, wherein four wires are carried within a single enclosure. However, as described below, significant problems arise when the four channels must be physically separated. 
   The preferred embodiment of the present invention provides a solution to this problem and utilizes a novel combination of stacked stripline or microstrip and contact pins extending into the through-hole plated openings to locate a common ground plane between two trace layers to couple to two wire (Twinax) conductor without disturbing the relative positions of the diagonal pairs of the four wire (Quadrax) conductor. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1(A)  illustrates a single conductor coaxial transmission line in cross-section; 
       FIG. 1(B)  illustrates a two conductor (Twinax) transmission line in cross-section; 
       FIG. 1(C)  illustrates a four conductor (Quadrax) transmission line in cross-section; 
       FIG. 2  illustrates, in partial cross-section, the external configuration of one embodiment of the invention; 
       FIGS. 3(A) and 3(B)  respectively illustrate, in cross-section and in substantial enlargement, the stripline and the microstrip transmission line configurations; 
       FIG. 4  is an enlarged perspective view of a four layer stripline used in the preferred embodiment of this invention; 
       FIG. 5  is a horizontal elevational view of the stripline of  FIG. 4 ; 
       FIG. 6  illustrates a top plan view of the ground plane plans and trace layers of the stripline of  FIG. 4 ; 
       FIG. 7  illustrates the use of multiple layers of stripline board; 
       FIG. 8  illustrates a connector utilizing the multiple layers of  FIG. 7 ; 
       FIG. 9  is an elevational end view of another embodiment of the invention in which the Quadrax cable entry is bolted to a panel; 
       FIG. 10  is a perspective view of the Quadrax to Twinax connector including a connector for the Quadrax cable; 
       FIG. 11  is another perspective view of the apparatus of  FIG. 10  with the connector body removed to illustrate the internal connector pins; and 
       FIG. 12  is an enlarged view of the connector of  FIGS. 10 and 11  with the layer  2  of  FIGS. 5 and 6  exposed. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Currently, high-speed data transference requires transmission systems that minimize reflections. This is achieved through controlled characteristic impedance from source to load. In microwave systems, this is accomplished with waveguide or coaxial transmission lines. In both cases, the line geometry is the determining factor along with dielectric and conductor materials. Steps, bends, protrusions etc. will invariably cause reflections with consequent loss of transmission efficiency (insertion loss) and sending-end disturbance. In 2-wire differential-mode transmissions this is acceptable at lower data rates. When data rates become higher, such as fiber channel (into microwave frequencies), the line characteristic impedances become much more critical. 
   In fiber channel systems the source and load differential impedances are usually high (100–150Ω). Achieving these high impedances in a coaxial transmission line  20  ( FIG. 1(A) ) is size prohibitive. As a result, a line configuration such as Twinax  25  ( FIG. 1(B) ) wherein the signals are carried between a pair of conductors (usually round) critically spaced from each other and surrounded by a conductive enclosure. In this “differential line,” high impedances are easily obtained since the mutual capacitance between the conductors is minimized. 
   A more efficient development for fiber channel transmission is called Quadrax  30  (FIG.  1 (C)), having a single enclosure enclosing four wires  35 ,  36 ,  37 , and  38 . In Quadrax, a pair of conductors forms a Twinax differential pair. These respective pairs  35 ,  36  and  37 ,  38  must be diagonal because the paired conductor electric fields are mutually perpendicular and will therefore not couple. This condition eliminates cross talk, maintaining channel isolation. 
   Quadrax rather than Twinax is advantageously employed for longer line runs. However, a significant problem arises in the prior art when the two orthogonal channels of the Quadrax are physically separated into two separate pairs of Twinax. In the prior art, the pairs of the Quadrax  30  cross over when converted to Twinax resulting in impedance disturbance and reflections with some cross talk. At low frequencies or data rates, this is somewhat manageable, however, when data rates approach microwave frequencies, the resulting system degradation becomes unacceptable. 
   The preferred embodiments of this invention utilize a novel combination of transmission line configuration(s) of stripline  40  or microstrip  41  ( FIG. 3 ), to solve the problem of converting Quadrax to Twinax. Moreover, the embodiment described advantageously enables the conversion to be performed in a connector apparatus. As shown in  FIG. 2 , two Twinax conductors  25   a  and  25   b  are connected to one end  39  of a connector apparatus and the Quadrax cable  30  is connected to the other end  51  of a mating connector apparatus. Either stripline or microstrip configurations may be used, however, stripline will be described below. 
   Strip transmission line is a method of transmitting RF signals in a controlled impedance environment. The signal bearing line is a metal strip  42   a ,  42   b  between two ground planes  43   a ,  43   d  and separated by dielectric circuit boards  44   a ,  44   b  (see  FIG. 3 ). The conductive metal strips  42   a ,  42   b  are typically formed on the dielectric boards  44  by selective removal by chemical etching of the metal to leave the residual strips  42 . 
   The initial construction of one embodiment of the invention is best illustrated in  FIGS. 4 ,  5 ,  6  and  8  in which a multi-level stack comprises locating a first trace layer on level  2  between groundplanes  1  and  3  and a second trace layer on level  4  between ground planes  3  and  5 . The first traces  60 ,  61  on trace level  2  terminate at pad openings  65 ,  66  whereas a second set of traces  70 ,  71  on trace level  4  terminate at pad openings  75 ,  76 . The two conductors of a first Twinax line  25   a  connect to respective ends of  80 ,  81  of traces  60 ,  61 . The twin conductors of a second Twinax line  25   b  connect to respective ends  85 ,  86  of traces  70 ,  71 . The differential pair of conductors are soldered, or otherwise affixed to the surface pads on levels  2  and  4  shown in  FIGS. 5 and 6 . 
   The four conductors of the Quadrax cable  30  respectively electrically connect to one of the strips  60 ,  61 ,  70 ,  77  by contact pins  90 ,  91 ,  92 ,  93 . These contact pins are best shown in  FIG. 8 , which illustrates in cross section a connector adapted to connect to a pair of side-by-side Quadrax cables  30   a  and  30   b  and in  FIG. 12 , which illustrates a connector adapted to connect to a single Quadrax cable. Contact pins  90 ,  91 ,  92 ,  93  couple straight onto the stripline traces without crossing over or disturbing the relative positions of the selected diagonal pairs. This is accomplished by a series of plated through holes through the multi-level stack and is best shown in  FIGS. 4 and 5 . The diagonal pairs from the Quadrax interface are attached to the pad openings on their assigned traces, while merely passing through the through-holes in the other board having the traces and pads belonging to the other diagonal pair. Thus, referring to  FIGS. 8 and 12 , one pair of pins  90 ,  91  are in electrical contact with through-hole pad openings, such as pads  65 ,  66  of layer  2  (shown in  FIG. 6 ), but do not contact the traces on layer  4 . As noted above, these through-hole openings  65 ,  66  are respectively in contact with traces  60 ,  61 . The other pair of pins  92 ,  93  (best shown in  FIG. 8 ) are in electrical contact with through-hole pad openings of layer  4  (examples being pads  75 ,  76  shown in  FIG. 6 ), but merely pass through layer  2  without contacting the traces on this layer  2 . This maintains the impedance relatively consistent and therefore not frequency sensitive. 
   Referring to  FIGS. 2 and 8 , when connector body  52  engages connector body,  50  the pins  90 ,  91 ,  92 ,  93  of connector  50  are engaged by corresponding conductors in connector  52  which in turn are connected to the internal conductors of one or more Quadrax cables  30 . 
   Referring to  FIGS. 4 ,  5  and  6 , a common ground plane ( 3 ) is located between the two trace layers ( 2  and  4 ). As a result, the trace signal pairs  60 ,  61  and  70 ,  71  will be isolated with each signal pair in the controlled impedance of effectively two separate transmission systems. As described above and shown in  FIGS. 6 and 8 , these separated pairs run to respective surface pads  80 ,  81  and  85 ,  86  and selected through plated-through holes connect to the assigned embedded traces. 
   The configuration described and shown in  FIGS. 4 ,  5 , and  6  can be duplicated on a multiplicity of regions on a single multi-layered stripline board or several boards (as shown in  FIG. 7 ). 
   The embodiment shown in  FIGS. 2 and 8  includes a connector having sections  50 ,  52 . However, an embodiment of the invention can be also configured to attach directly to a panel with a header as shown in  FIG. 9 , wherein the Quadrax cable entry  100  is simply bolted to a panel  105 . 
   The 90° exit of the separate differential Twinax cables  25   a  and  25   b  shown in  FIGS. 8 ,  10  and  11  are examples of the invention. In other embodiments, the cables  25   a  and  25   b  can exit at any convenient angle including straight out the back, as shown in  FIG. 9 . 
     FIGS. 11 and 12  show the assembly of the connector of  FIG. 10  with the connector shell removed exposing the stripline assembly. 
   The dimensions and material properties of the boards shown in  FIGS. 5 and 6  are determined by the applicable well known equations. When the preferred conditions are achieved, the transmitted signal (source) is very efficiently delivered to its destination (load). 
   The equations for stripline are included in Appendix A(1) and A(2). The specifications for exemplary dielectric board  44  are provided by Appendix B. Manufacturing information of an exemplary embodiment are shown in Drawing No. 145-0097-000 (Appendices C1, C2 and C3). 
   Although this invention has been described in terms of certain preferred embodiments, other embodiments that are apparent to those of ordinary skill in the art, including embodiments which do not provide all of the benefits and features set forth herein, are also within the scope of this invention.