Patent Publication Number: US-RE47460-E

Title: Controlled-impedance cable termination using compliant interconnect elements

Description:
This application is a Divisional Reissue Application of Reissue application Ser. No. 15/248,438 filed on Aug. 26, 2016, both of which are Reissue Applications of U.S. Pat. No. 9,160,151 issued on Oct. 13, 2015 from application Ser. No. 14/534,241 filed on Nov. 6, 2014. The entirety of the above-mentioned patent applications are hereby incorporated by reference herein and made a part of this application.  
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     REFERENCE TO A SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISK APPENDIX 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to electrical cable terminations, more particularly, to controlled impedance cable terminations which are generally used to transmit high-frequency signals in electronic equipment. 
     2. Description of the Related Art 
     The purpose of a cable termination is to provide an interconnect from the cable to the electrical device and to provide a separable electrical interconnection between the cable and its operating environment. The characteristic of separability means that the cables are not interconnected by permanent mechanical means, such as soldering or bonding, but by temporary mechanical means. 
     Currently cables are terminated using a conventional type connector which is also controlled-impedance, such as an SMA (SubMiniature Version A) connector, or the cables are soldered to a printed circuit board (PCB) which is then separably connected to the working environment. The SMA connectors, while being generally the same impedance environment as the cable, have impedance mismatches which cause high-frequency attenuation at the point of interface between the cable and the connector and the connector and its working environment, such as like a PCB. Additionally, these cable terminations often require through holes in PCB&#39;s for mounting and, consequently, it can be difficult to design the best possible controlled impedance environment. These types of cable terminations are generally for a single cable and require a substantial amount of PCB area to terminate, thus decreasing the density capability of connections. 
     Another form of prior art is a system which uses two independent parts to mate several cables to its electrical environment. This system uses one part that is generally soldered to a printed circuit board and another part that is generally mated to several cables. The two pieces can be plugged together to form the controlled impedance interconnection. These systems are better-controlled impedance environments but are limited in the densities at which the cables can be used. That is, the cables require a minimum space between them to achieve the controlled impedance environment and thus only a small number of cables can be terminated in a given area. 
     Another form of prior art, disclosed in U.S. Pat. No. 7,544,093, is a system which employs removable cables that are held to the device by means of a spring. The cable has a terminal end which makes the signal conductor protrude from the cable terminal end. The terminal is then pressed to the device by means of a spring and the ground shield of the cable is connected to the device by a conductive rubber ground shield that shorts the terminal ground to the device ground. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is an apparatus and method for terminating a controlled-impedance cable that uses a compliant contact element at the point of termination minimizes detrimental electrical effects of the termination. 
     The present invention includes a cable terminator that employs compliant electrical contacts to provide an interface between the controlled-impedance cable (hereinafter, simply “cable”) and another device. The assembly is removably attached to the electrical device by a compression force in a direction of compression typically provided by jack screws that may not compress the assembly and device together linearly. Compliant contacts compensate for noncoplanarities between the conduction points of the electrical device. 
     Each embodiment of the terminator includes an anchor block for securing the cable, one or more compliant signal contacts for making the electrical connection between the cable center conductor(s) and the electrical device, optional compliant ground contacts for making the electrical connection between the cable shield and the ground plane of the device, and a plate mounted to the anchor block that holds the contacts. 
     The anchor block can be either electrically conductive or nonconductive. When conductive, the ground shield of all of the cables are electrically connected to the anchor block. The present invention contemplates several different methods to accomplish this including soldering the cable ground shield, crimping the ground shield, potting with a conductive adhesive, insert molding, press fitting a rigidized ground shield, threading, and twist-lock. Once the cables are anchored in the anchor block, the anchor block face and cable ends are dressed to make a reliable electrical contact with compliant contacts. Dressing may include polishing by some mechanical means, such as by milling, grinding, or sanding, in order to make sure that the cable center conductor is positioned at a known depth with respect to the anchor block face. 
     When the anchor block is nonconductive, a conductive ferrule is installed on the ground shield of each cable. The cable ends are dressed to make a reliable electrical contact with compliant contacts and the ferrule/cable assemblies are installed into holes in the anchor block. The present invention contemplates several different methods to accomplish this including, press fitting, threading, and twist-lock. 
     Example compliant contacts for use with the present invention include spring probes, electrically-conductive rubber contacts, fuzz button contacts, stamped metal contacts, chemically etched contacts, and skewed coil contacts. 
     The plate holds the contacts. Features of the plate include a face surface that abuts the anchor block face, a device surface that generally abuts the device, and at least one through aperture for the contacts. Each aperture has an anchor block face opening and a device face opening. The apertures for the signal contacts are aligned with the corresponding cable hole in the anchor block. 
     The cable center conductor is connected to the signal conduction point of the electrical device by the compliant signal contact. In most configurations, the signal contacts are surrounded by a number of ground contacts that connect either the conductive anchor block or the cable shield to the device in a pattern that closely mimics the impedance environment of the cable. The impedance of the system can be changed by changing the position of the ground contacts with respect to the signal contact or by changing the insulating material. 
     The skewed coil contact is captured in a through aperture in the plate. The aperture has a larger center section that narrows to a smaller block opening at the side adjacent to the anchor block and to a smaller device opening at the other end. The length of the contact leads is such that the leads extend from the openings. Alternatively, the block opening is as wide as the center section. Optionally, the contact area between the center conductor and device and the corresponding contact lead can be increased by a pair of conductive bosses that the contact is captured in that is as wide as the cable center conductor. Optionally, the remaining space of the aperture is filled with a compliant, electrically conductive elastomer that adds resiliency and aids in electrically shorting the coil loops. 
     The fuzz button contact is cylindrical and forced into an aperture that is narrower at the center than the ends. The contact ends extend from the plate. 
     The conductive rubber contact for the signal contact can be cylindrical with a centrally-located annular depression that fits on an annular protrusion in the aperture. The contact ends extend from the plate. The conductive rubber contact for the ground contact can be the same structure as the signal contact or can be circular, surrounding the signal contact. 
     The etched or stamped contact is a strip of conductive material in a C shape that is captured in a C-shaped aperture. 
     The electrical connection between the center conductor and the signal contact and the electrical connection between the ground block/cable shield ferrule and the ground contacts are compression connections. With the contacts installed in the plate, the plate is mounted to the anchor block with mechanical attachments, thereby forcing the end of the signal contact against the end of the center conductor and the ends of the ground contacts against the anchor block/cable shield ferrule. Alternatively, the electrical connection between the center conductor and the signal contact is a solder connection. Alternatively, the end of the center conductor is formed into a compliant spring like the skewed coil contact. 
     The plate can be either insulating or conductive. The insulating plate is made of a non-electrically-conductive material. A conductive plate is preferably composed of an electrically-conductive metal that couples the ground contacts, thereby providing more precise impedance matching to the signal contact. Alternatively, the conductive plate is composed of a non-conductive material plated with a conductive coating. The signal contact is insulated from the conductive plate by an insulating centering plug or a non-conductive coating. 
     Alternatively, the signal contact aperture is within a conductive boss. The boss is surrounded by an insulating annulus that insulates the boss from the conductive plate. 
     Also disclosed is a method and apparatus for assembling cables to the anchor block so that the cables are the same length to within a very small tolerance. To facilitate the method, a soldering fixture is used that has a frame, a connector jig, a block jig, and legs. The frame is generally rectangular and stands vertically. The connector jig is mounted to the lower cross piece of the frame. The block jig is mounted to the upper cross piece of the frame. Four legs extend from the bottom corners of the frame in generally opposite directions at an angle of at least 10° from horizontal so that they prevent the frame from falling over but allow the user to tilt the frame. 
     The connector jig locks the cable connectors at a fixed distance away from where the other end of the cable will be soldered to the anchor block. The connector jig locks the connectors in an upwardly open arc so that the cables are the same length to the anchor block. 
     The anchor block is secured to the block jig, face up, which is secured to the upper cross piece. A tensioning plate is mounted to the upper cross piece. Jack screws are threaded into holes at the end of the tensioning plate. 
     The cable sheath is stripped and the stripped portion is fed through the hole in the anchor block and a corresponding cable hole in the tensioning plate. A coil spring is placed on each cable and a collar is tightly secured to the cable. 
     After putting the connectors in the connector jig, the jack screws are tightened until there is adequate tension on the cables. Each cable shield is soldered to the anchor block. The angled legs allow the user to tilt the fixture for easier access to each side of the anchor block. After the solder and anchor block have cooled sufficiently, the jack screws are loosened, and the collars, springs, and tensioning plate are removed. The anchor block is removed from the frame and the connectors are removed from the connector jig. 
     The anchor block face is finished smooth and evenly flat by sanding, milling, planing, skiving, broaching, or any other appropriate method. 
     Objects of the present invention will become apparent in light of the following drawings and detailed description of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a fuller understanding of the nature and object of the present invention, reference is made to the accompanying drawings, wherein: 
         FIG. 1  is an isometric view of the cable termination assembly of the present invention for use with coaxial cables; 
         FIG. 2  is a front view of the cable termination assembly of  FIG. 1  connected to a device; 
         FIG. 3  is a cross-sectional detail view of the cable termination assembly connected to a device; 
         FIG. 4  is a side view of the cable termination assembly of  FIG. 1 ; 
         FIG. 5  is an exploded view of the cable termination assembly of  FIG. 1  with a conductive anchor block; 
         FIG. 6  is a top cross-sectional view of the cable termination assembly of  FIG. 2  taken along the line A-A; 
         FIG. 7  is a front cross-sectional view of the cable termination assembly of  FIG. 4  with a conductive anchor block taken along the line B-B; 
         FIG. 8  is a cross-sectional view of a method of removably attaching the cable to the anchor block; 
         FIG. 9  is a cross-sectional view of another method of removably attaching the cable to the anchor block; 
         FIG. 10  is an exploded view of the cable termination assembly of  FIG. 1  with a nonconductive anchor block; 
         FIG. 11  is a front cross-sectional view of the cable termination assembly of  FIG. 4  with a nonconductive anchor block taken along the line B-B; 
         FIG. 12  is a cross-sectional view showing the common features of the plate; 
         FIG. 13  is an isometric view of an angled anchor block; 
         FIG. 14  is an isometric view of a parallel anchor block; 
         FIG. 15  is an isometric view of a right-angle anchor block; 
         FIG. 16  is a cross-sectional side view of a configuration of a right-angle anchor block; 
         FIG. 17  is bottom view of the cable termination assembly of  FIG. 1  with an insulating plate; 
         FIG. 18  is a detail view of a configuration of the bottom of the coax cable termination assembly of  FIG. 17  taken at C; 
         FIG. 19  is a detail view of another configuration of the bottom of the coax cable termination assembly of  FIG. 17  taken at C; 
         FIG. 20  is a detailed view of  FIG. 7  taken at D showing the coax cable termination using a skewed coil contact with a conductive anchor block and an insulating plate having mirror-image sheets; 
         FIG. 21  is a detailed view of  FIG. 7  taken at D showing the coax cable termination using a skewed coil contact with a nonconductive anchor block and an insulating plate having mirror-image sheets; 
         FIG. 22  is a detailed view of  FIG. 7  taken at D showing the coax cable termination using a skewed coil contact with an insulating plate having asymmetrical sheets; 
         FIG. 23  is a detailed view of  FIG. 7  taken at D showing the coax cable termination using a skewed coil contact with an insulating plate having an elongated center section; 
         FIG. 24  is a detailed view of  FIG. 7  taken at D showing the coax cable termination using a skewed coil contact with an insulating plate and conductive bosses; 
         FIG. 25  is a detailed view of  FIG. 7  taken at D showing the coax cable termination using a fuzz button contact with an insulating plate; 
         FIG. 26  is a detailed view of  FIG. 7  taken at D showing the coax cable termination using a conductive rubber contacts with an insulating plate; 
         FIG. 27  is a cross-sectional view of  FIG. 26  taken at E-E; 
         FIG. 28  is a cross-sectional view of  FIG. 27  taken at F-F; 
         FIG. 29  is bottom view of the cable termination assembly of  FIG. 1  using stamped or etched contacts embedded in an insulating plate; 
         FIG. 30  is a detail view of the bottom of the coax cable termination assembly of  FIG. 29  taken at H; 
         FIG. 31  is a cross-sectional view of the plate of  FIG. 29  before installation on the anchor block; 
         FIG. 32  is a detailed view of  FIG. 7  taken at D showing the coax cable termination using stamped or etched contacts embedded in an insulating plate; 
         FIG. 33  is an exploded view of the cable termination assembly using the anchor block of  FIG. 14  with an insulating plate; 
         FIG. 34  is a cross-sectional view of the cable termination assembly using the anchor block of  FIG. 14  with an insulating plate; 
         FIG. 35  is a detailed view of  FIG. 7  taken at D showing the coax cable termination using a skewed coil contact for the ground contacts and a shaped cable center conductor for the signal contact with an insulating plate; 
         FIG. 36  is bottom view of the cable termination assembly of  FIG. 1  with coaxial cables, a conductive plate, and insulating plug for the signal contact; 
         FIG. 37  is a detail view of the bottom of the coax cable termination assembly of  FIG. 36  taken at J with a conductive plate and insulating plug for the signal contact; 
         FIG. 38  is a detailed view of  FIG. 7  taken at D showing the coax cable termination using a skewed coil contact with a conductive plate and insulating plug for the signal contact; 
         FIG. 39  is bottom view of the cable termination assembly of  FIG. 1  with coaxial cables, a conductive plate, dielectric annulus, and conductive boss for the signal contact; 
         FIG. 40  is a detail view of the bottom of the coax cable termination assembly of  FIG. 39  taken at K with a conductive plate, dielectric annulus, and conductive boss for the signal contact; 
         FIG. 41  is a detailed view of  FIG. 7  taken at D showing the coax cable termination using a skewed coil contact with a conductive plate, dielectric annulus, and conductive boss for the signal contact; 
         FIG. 42  is an isometric view of the cable termination assembly of the present invention for use with twin-axial cables; 
         FIG. 43  is a front view of the cable termination assembly of  FIG. 42 ; 
         FIG. 44  is a top cross-sectional view of the cable termination assembly of  FIG. 43  taken along the line M-M; 
         FIG. 45  is a side view of the cable termination assembly of  FIG. 42 ; 
         FIG. 46  is a front cross-sectional view of the cable termination assembly of  FIG. 45  taken along the line N-N; 
         FIG. 47  is bottom view of the cable termination assembly of  FIG. 42  with an insulating plate; 
         FIG. 48  is a detail view of the bottom of the cable termination assembly of  FIG. 47  taken at R with an insulating plate; 
         FIG. 49  is a detailed view of  FIG. 46  taken at P showing the twin-axial cable termination using skewed coil contacts with an insulating plate; 
         FIG. 50  is bottom view of the cable termination assembly of  FIG. 42  with twin-axial cables, a conductive plate, and insulating plugs for the signal contacts; 
         FIG. 51  is a detail view of the bottom of the twin-axial cable termination assembly of  FIG. 50  taken at S; 
         FIG. 52  is a detailed view of  FIG. 46  taken at P showing the twin-axial cable termination using skewed coil contacts, a conductive plate, and insulating plugs for the signal contacts; 
         FIG. 53  is a bottom view of an alternative cable termination assembly of  FIG. 42  with twin-axial cables, a conductive plate, and insulating plugs for the signal contacts; 
         FIG. 54  is a detail view of the bottom of the alternative twin-axial cable termination assembly of  FIG. 53  taken at T; 
         FIG. 55  is a detailed view of  FIG. 46  taken at P showing the alternative twin-axial cable termination of  FIG. 53 ; 
         FIG. 56  is an isometric view of a soldering fixture of the present invention with cables and anchor block; 
         FIG. 57  is a front view of the fixture of  FIG. 56 ; 
         FIG. 58  is a side view of the fixture of  FIG. 56 ; 
         FIG. 59  is a detail view of the connector jig of  FIG. 57 ; 
         FIG. 60  is a detail view of the block jig and tensioning plate of  FIG. 57  with the anchor block attached; 
         FIG. 61  is a detail view of a cable threaded through the block and tensioning plate; 
         FIG. 62  is a detail view of the screw and collar installed on a cable; and 
         FIG. 63  is a detail view of the tensioning plate in tension. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present application hereby incorporates by reference in its entirety U.S. patent application Ser. No. 14/238,215, on which this application is based. 
     The present invention is an apparatus and method for terminating a controlled-impedance cable that minimizes detrimental electrical effects of the termination by using a compliant or compressible contact element at the point of termination. With the present invention, impedance mismatches are minimized, allowing the cable to be more useful in high-frequency signal ranges. The present invention can be used with any cable structure where the impedance between the inner conductor(s) and the ground shield is controlled. 
     In addition, the present invention increases the density at which the controlled-impedance cables can be used. That is, with the present invention, more cables can be terminated in a given amount of space than with terminations of the prior art. Further, the interface between the components of the present invention may not require through-hole mounting, which may further enhance density capability. 
     The present invention calls for proper dressing of the cable end so that small, compliant contacts can be used for separably interconnecting the controlled-impedance cables to whatever electrical device the user desires. A prime example is connecting two printed circuit boards which must communicate with each other at high frequency, such as connecting a computer central processing PCB with its random access memory PCB or another central processing PCB. 
     As shown in  FIGS. 1-11 , the present invention includes a cable terminator  10  that employs compliant electrical contacts  12 ,  14  to provide an interface between the controlled-impedance cable (hereinafter, simply “cable”)  30  and another device  2 , typically an integrated circuit (IC) or a printed circuit board (PCB). The terminator  10  is installed on the cable  30  as described below. The combination of terminator  10  and cable(s) is referred to as the cable termination assembly  8 . As shown in  FIGS. 2 and 3 , the assembly  8  is removably attached to the electrical device  2  by a compression force  22  in a direction of compression  24 . Typically, jack screws  26  provide the compression force  22 . Jack screws  26  may not compress the assembly  8  and the electrical device  2  together linearly. Compliant contacts  12 ,  14  facilitate an adequate connection between the cables  30  and the electrical device  2 , compensating for noncoplanarities in the conduction points  4  of the electrical device  2 . 
     The present invention is for use with controlled-impedance cables having one or more center conductors. A coaxial cable  30  has a center conductor  32  surrounded by a dielectric  34  with a ground reference shield  36  outside the dielectric  34 . Optionally, a sheath  38  covers the shield  36 . A twin-axial cable  30  has two center conductors  32  surrounded by a dielectric  34  with a ground reference shield  36  outside the dielectric  34  and a sheath  38  covering the shield  36 . Cables with more than two center conductors are available. Although not specifically described, the present invention can be adapted to accommodate cables having more than two center conductors. 
     The terminator  10  of the present invention has several embodiments. Each embodiment includes an anchor block  16  for securing the cable  30 , one or more compliant signal contacts  12  for making the electrical connection between the cable center conductor(s)  32  and the electrical device  2 , optional compliant ground contacts  14  for making the electrical connection between the cable shield  36  and the ground plane of the device  2 , and a plate  18  mounted to the anchor block  16  that holds the contacts  12 ,  14 . 
     In one embodiment, the anchor block  16  is conductive and provides a common ground for the cables  30 , as in  FIG. 5 . The ground shields  36  of all of the cables  30  are electrically connected to the anchor block  16 . The present invention contemplates several different methods to accomplish this. The ground shield  36  may be soldered into a hole  40  in anchor block  16 . The cable sheath  38  is stripped back at least the length of the anchor block hole  40 . The cable  30  is inserted into the hole  40  up to the end of the sheath  38  and the shield  36  is soldered to the anchor block  16 . 
     Alternatively, the cable  30  may be crimped into the anchor block hole  40 . After the sheath  38  is stripped back, the cable  30  is inserted into the hole  40 . The hole  40  may have the path through which the cable  30  runs geometrically altered after insertion of the cable  30  to a point where the size of the path is smaller than the size of the cable  30 , thereby anchoring the cable  30  to the anchor block  16  and electrically connecting the shield  36  to the anchor block  16 . 
     Other methods of anchoring the cable  30  to the anchor block  16  include potting the ground shield  36  with a conductive adhesive once it is placed in the hole  40 , insert molding the anchor block  16  with the cable  30  in place at the time of molding, and press fitting a rigidized, for example, pretinned, ground shield into the hole  40 . 
     Once the cables  30  are anchored in the anchor block  16 , the face  20  of the anchor block  16  and cable ends  136  are properly dressed to make a reliable electrical contact with small compliant contacts. The cable ends  136  and the anchor block face  20  may need to be polished and planarized by some mechanical means, such as by milling, grinding, or sanding, in order to make sure that the cable center conductor  32  is positioned at a known depth with respect to the anchor block face  20 , in this case flush with the anchor block face  20 . The cable ends  136  and face  20  may also require noble metal plating to prevent the polished surface from oxidizing or otherwise degrading so as to inhibit acceptable electrical connection to the center conductor  32  and the anchor block  16 . 
     Methods of removably attaching the cable  30  to the anchor block  16  are shown in  FIGS. 8 and 9 . These methods permit replacement of individual cables  30  so the entire assembly does not have to be replaced. The first method calls for attaching a ferrule at or near the end of the cable  30  for dressing the cable end. The sheath  38  is stripped back and a threaded ferrule  134  is slipped over the shield  36 . The ferrule  134  is attached to the cable by soldering, crimping, or other mechanical means that electrically couples the ferrule  134  to the shield  36 . The cable end  136  is then dressed by polishing so as to achieve a flat surface on the cable end  136 . The ferrule  134  is then threaded into a threaded hole  138  in the anchor block  16  until the center conductor  32  is pressed to the signal contact  12  in order to produce an electrical connection between the center conductor  32  and the signal contact  12 . 
     In the configuration of  FIG. 8 , the anchor block  16  has two parts  140 ,  142 . The top part  140  has the threaded hole  138  into which the ferrule  13  is threaded. The bottom part  142  is for precisely aligning the cable end  136  so that the center conductor  32  is directly over the signal contact  12 . This method can be use for precisely terminating individual cable on very tight pitch as in 1 mm or less spacing between cable center conductors  32 . 
     The second method of removably attaching the cable  30  to the anchor block  16  calls for the use of a twist-lock attachment  300 , as shown in  FIG. 9 . A twist-lock component  302  is slipped over the cable  30  such that the component  302  can slide freely over the cable  30 . A coil spring  304  is slipped over the cable  30 . After the sheath  38  is stripped back, a ferrule  306  is attached to the shield  36  by soldering, crimping, or other mechanical means that electrically couples the ferrule  306  to the shield  36 . The cable end  308  is then dressed by polishing so as to achieve a flat surface on the cable end  308 . 
     The cable end  308  is inserted into a hole  310  in the anchor block  16 . Protrusions  312  from the twist-lock component  302  slide down opposed notches, not shown, in the sides of the hole  310  until they align with an annular depression  316  in the hole  310 . With this alignment, the spring  304  is compressed so that it presses the center conductor  32  to the signal contact  12  in order to produce an electrical connection between the center conductor  32  and the signal contact  12 . The twist-lock component  302  is turned so that the protrusions  312  are captured by the annular depression  316 , thereby retaining the cable  30  in the hole  310 . 
     In another embodiment, the anchor block  16  is nonconductive and merely provides an anchor for the cables  30 , as in  FIGS. 10 and 11 . The anchor block  16  is composed of a nonconductive material. The cable sheath  38  is stripped back and an electrically-conductive ferrule  330  is slipped over the shield  36 . The ferrule  330  is attached to the cable by soldering, crimping, or other mechanical means that electrically couples the ferrule  330  to the shield  36 . 
     The cable end  332  is then dressed by polishing so as to achieve a flat surface on the cable end  332 . The ferrule  330  is then inserted into a hole  334  in the anchor block  16  until the center conductor  32  is pressed to the signal contact  12  and the ferrule  330  is pressed against the ground contacts  14 . 
     The present invention contemplates a number of different ways for the ferrule/cable assembly to be retained in the anchor block  16 . Two such methods are described above with reference to removable cables and  FIGS. 8 and 9 . The first uses a threaded attachment and the second uses a twist-lock attachment. 
     Another method is via a press fit. Optionally, the side  340  of the ferrule  330  is knurled or otherwise roughened. The ferrule/cable assembly is forced into the hole  334 , which is slightly smaller, until the cable end  332  is flush with the block face  338 . 
     Another method is shown in  FIG. 11 . The ferrule  330  has an annular ridge  342  either at the end  344  of the ferrule  330  or away from the end  344 , as in  FIG. 11 . The anchor block  16  has two sections, a bottom section  346  and a top section  348 . The upper end of the hole  334  in the bottom section  346  has an annular groove  352 . When the ferrule/cable assembly is inserted into the hole  334 , the ridge  342  fits into the groove  352  with the cable end  332  flush with the block face  338 . The block top section  348  is installed on the bottom section  346  and attached via screws, clips, or any other acceptable method. The top section  348  captures the ferrule/cable assembly in the anchor block  16 . Optionally, the ridge  342  and groove  352  can be keyed to prevent the ferrule/cable assembly from rotating in the hole  334 . 
     In some designs, particularly with removable attachments, the cable end may not be exactly flush with the anchor block face  20 , that is, it may be slightly recessed into or protruding from the anchor block face  20 . That recession or protrusion can be as much as 0.05 inch. The present specification and claims use the term, “flush”, to indicate that the cable end is actually flush with, slightly recessed into, or slightly protruding from the anchor block face  20  by as much as 0.05 inch. 
     In most of the present figures, the anchor block  16  is generally a rectangular solid where the cables  30  are perpendicular to the anchor block face  20 . However, the anchor block  16  can have other shapes.  FIG. 13  shows an angled anchor block  16  where the cables  30  are at an angle to the anchor block face  20 .  FIG. 14  shows a parallel anchor block  16  that can be used with a device edge attachment. 
       FIG. 15  shows a generic right angle anchor block  16  where the cables  30  bends through 90°.  FIG. 16  shows a right angle anchor block  16  with a strain relief. The anchor block  16  has a base  280  that is composed of a conductive or non-conductive, generally rigid material. The cable  30  rests in a channel  284  in the base  280 . A cover  282  that is composed of a conductive or non-conductive, relatively rigid material is attached to the base  280 . The manner of attachment depends on the base and cover materials. For example, if the base  280  and cover  282  are both metallic, the attachment can be by screws. If the base  280  and cover  282  are both plastic, the attachment can be the cover  282  snapping onto the base  280  with tabs and slots. The channel  284  has a bend  286  that provides strain relief when the base  280  and cover  282  are assembled. 
     These are only examples of other anchor block shapes. The present invention contemplates that the anchor block  16  can have any shape that works for a particular application. 
     Example compliant contacts for use with the present invention include spring probes, electrically-conductive rubber contacts, fuzz button contacts, stamped metal contacts, chemically etched contacts, and skewed coil contacts. 
     A typical spring probe consists of a hollow barrel with a spring and one or two plungers. The spring is housed in the barrel with the end of the plungers crimped in opposed open ends of the barrel at the ends of the spring. The spring biases the plungers outwardly, thereby providing a spring force to the tip of the plungers. 
     Conductive elastomer bumps are made of rubber and/or silicones of varying types with embedded conductive metal elements. The elastomer bump can work when the device conduction point is elevated off the device, thus sometimes requiring a protruding feature from the device or the addition of a third conductive element to the system to act as a protruding member. 
     Alternatively, the contact can be made of a single sheet of anisotropic conductive elastomer which is an elastomeric sheet that only conducts electricity through its thickness. 
     A fuzz button is a wire that is crumpled into a cylindrical shape. The resulting shape looks very much like tiny cylinder made of steel wool. When the cylinder is placed within a hole in a sheet of nonconductive material, it acts like a spring that is continuously electrically shorted. Like elastomer bumps, the fuzz button can be used with a third element needed to reach inside the hole of the nonconductive sheet to make contact with the fuzz button. 
     Skewed coil contacts of various types and configurations are described in U.S. Pat. Nos. 7,126,062 and Re41,663, both of which are incorporated herein by reference. Briefly, the skewed coil contact includes a coil of conductive, inherently elastic wire with a pair of oppositely extending leads. The leads extend in a direction angled from the coil axis. During compression, the coil loops are electrically shorted together while they slide along each other. 
     The figures illustrate the use of skewed coil contacts, fuzz button contacts, conductive rubber contacts, and stamped metal or a chemically etched contacts. As indicated above, the plate  18  holds the contacts  12 ,  14 . The structure of the plate  18  depends on the type of contact. Regardless of the type of contact, the plate  18  has several common features. These features are shown in  FIG. 12  with reference to the skewed coil contact as a signal contact  12 , but apply to all types of contacts as well as the ground contacts  14 . The plate  18  has a face surface  170  that abuts the anchor block face  20  when the terminator  10  is assembled. The plate  18  has a device surface  172  that generally abuts the device  2  when the terminator  10  is connected to the device  2 . The plate  18  has at least one through aperture  174  for the contacts  12 ,  14 . The apertures are either signal apertures or ground apertures, depending on the type of signal that is carried in the contact in that aperture. Each aperture  174  has an anchor block face opening  176  and a device face opening  178 . The signal apertures for the signal contacts  12  are aligned with the corresponding cable hole  40  in the anchor block  16 . Prior to assembling the plate  18  to the anchor block  16 , the anchor block contact point  180  of the contact  12  extends from the anchor block face opening  176 . Prior to connecting the terminator  10  to the device  2 , the device contact point  182  of the contact  12  extends from the device face opening  178 . 
       FIGS. 17-41  show configurations of the present invention for a coaxial cable. The center conductor  32  of the cable  30  is connected to the signal conduction point  4  of the electrical device  2  by the compliant signal contact  12 . As shown in  FIGS. 17-19 , the signal contacts  12  are surrounded by a number of ground contacts  14  that connect either the conducting anchor block  16  or the cable ferrule  330  to the device in a pattern that closely mimics the impedance environment of the cable  30 , e.g. 50 ohms, 75 ohms, 85 ohms, or 100 ohms. The impedance of the system can be changed by changing the position of the ground contacts  14  with respect to the signal contact  12  or by changing the insulating material, thereby changing the dielectric constant of the material or both. Changing the locations of the ground contacts with respect to the signal contact is like changing the diameter of the ground shield on a coaxial cable from 2.5 mm for 50-ohm cable to 6 mm for 75-ohm cable. Alternatively, the dielectric may be changed so that the lower the dielectric constant of the material, the closer the ground shield can be to the cable signal conductor while the cable maintains the same impedance environment. 
     When there are two or more cables  30  and a conductive anchor block  16 , there may be ground contacts  14  that are “shared” between cables  30 . For example, in the coaxial structure of  FIG. 19 , the ground contact  14 ′ between the two signal contacts  12  is common to both cables. The common ground contact can also been seen in  FIG. 20 , where the right side ground contact  14  is between the ground shields  36  of adjacent cables  30 . Another example is shown in the twin-axial structure of  FIG. 48 , where the ground contacts  14 ′ between the two signal contacts of adjacent cables  30  are common to both cables. 
     As shown in  FIGS. 20-22 , the skewed coil contact  42  is captured in a through aperture  44  in the plate  18 . The aperture  44  has a larger center section  48  that narrows to a smaller block opening  46 b at the side adjacent to the anchor block  16  and to a smaller device opening  46 a at the other end. In one configuration, shown in  FIGS. 20 and 21 , the plate  18  has two mirror image sheets  50  where each sheet  50  has one opening  46 a,  46 b and a half of the center section  48 . The contact  42  is placed in the center section  48  of one sheet  50  and the sheets  50  are sandwiched together to capture the contact  42 . In another configuration, shown in  FIG. 22 , the plate  18  has a base sheet  52  with one of the openings  46 a and the center section  48  and a top sheet  54  with the other opening  46 b. The contact  42  is placed in the center section  48  and the sheets  52 ,  54  are sandwiched together, capturing the contact  42  within the aperture  44 . The length of the contact leads  56  is such that the leads  56  extend from the openings  46 a,  46 b. 
     An alternative configuration is shown in  FIG. 23 . Rather than a wider center section with smaller openings at both ends, the center section  48  extends its full width from the block opening  46 b to a smaller device opening  46 a on the opposite side of the plate  18  from the anchor block  16 . When the plate  18  is mounted to the anchor block  16 , as described below, the contact  12 ,  14  is secured in the plate  18 . If all of the apertures  44  are of this design, the plate  18  does not have to have two sheets  50 . Since the contacts  12 ,  14  can be installed from the block opening  46 b, the plate  18  can be a single sheet. 
     Because of the very small size of the wire used to make the skewed coil contact  42 , the contact area between the skewed coil signal contact  12  and the cable center conductor  32  is small. This can cause a capacitive reactance at the interface of the contact leg  56  and the cable center conductor  32  which can cause reflections at high frequencies. To help alleviate this problem, the through aperture  44  is wide for its entire length, as in  FIG. 24 . Each end has an annular shoulder  60 . A pair of conductive bosses  62  with a shoulder  64  fit into the aperture  44 , with the shoulders  60 ,  64  retaining the bosses  62  in the aperture  44 . The boss  62  has a through hole  66  that narrows from the center of the aperture  44  to a smaller device opening  46 a and a smaller block opening  46 a at the ends through which the contact leads  56  extend. The bosses  62  increase the effective area of the contact lead  56 . 
     In  FIG. 24 , the conductive bosses  62  are shown spaced from each other, that is, they do not touch each other. In an alternative configuration, the conductive bosses  62  are made long enough to touch each other, either around the entire circumference of the aperture  44  or only portions of the circumference, such as with extending fingers. This can alleviate the potential problem of the conductive bosses  62  acting as a capacitive device if the contact  12  does not short them together. 
     Optionally, in any skewed coil contact configuration, after the contact  42  is installed, the remaining space of the aperture  44  is filled with a compliant, electrically conductive elastomer that adds resiliency and aids in electrically shorting the coil loops. 
     As shown in  FIG. 25 , the fuzz button contact  70  is cylindrical. The plate  18  has a through aperture  72  that is narrower at the center than the ends, as at  74 . The contact  70  is forced into the aperture  72 . The length of the contact  70  is such that the ends  76  extend from the plate  18 . 
     As shown in  FIGS. 26-28 , the conductive rubber contact  100  for the signal contact  12  can be cylindrical with a centrally-located annular depression  102 . The plate  18  has a through aperture  104  with a centrally-located annular protrusion  106 . The rubber contact  100  is radially compressed and placed in the aperture  104  such that the protrusion  106  fits into the depression  102  to retain the contact  100  in the aperture. The length of the contact  100  is such that the ends  108  extend from the plate  18 . 
     The conductive rubber contact for the ground contact  14  can be of the same structure as the signal contact  12 . Alternatively, the conductive rubber contact  112  for the ground contact  14  is circular, surrounding the signal contact  12 , as in  FIG. 27 . The conductive rubber contact  112  has a circular top sheet  114  adjacent to the anchor block  16  and a circular bottom sheet  116  for interfacing to the device  2 . The two sheets  114 ,  116  are electrically connected by a plurality of plugs  118  in through apertures  120  in the plate  18 . The number of plugs  118  can vary by application and is typically four or eight spaced evenly around the signal contact  100 . As with the signal contact  100 , each plug  118  has an annular depression  122  that fits into an annular protrusion  124  for retention. Optionally, knobs  126  extending from the sheets  114 ,  116  into depressions  128  in the plate  18 , as in  FIG. 28 , help retain the sheets  114 ,  116  in position. 
     In  FIGS. 29-32 , the contact  150  is a strip of conductive material in a C shape. The contact  150  can be formed by chemical etching, by stamping and forming, or by any other means practical. The contact  150  is captured in a through aperture  160  in the plate  18 . In their quiescent state, the contact leads  152  extend outwardly of the plate  18 , as in  FIG. 31 . When the anchor block  16  is attached to the plate  18 , the upper lead  152  deforms toward the plate  18  and into a depression  156 , as in  FIG. 32 , thereby providing electrical contact by the signal contact  12  to the center conductor  32  and by the ground contacts  14  to the anchor block  16 . When the assembly is connected to the device  2 , the lower lead  154  deforms toward the plate  18  and into a depression  158 . 
     An alternate terminator assembly  10  using the anchor block of  FIG. 14  is shown in  FIGS. 33 and 34 . The compliant contacts  12 ,  14  fit into apertures  44  in the plate  18 . The signal contact  12  presses against the center conductor  32  that has been bisected longitudinally and dressed. 
     The electrical connection  80  between the center conductor  32  and the signal contact  12  and the electrical connection  82  between the anchor block  16  and the ground contacts  14  are compression connections. With the contacts  12 ,  14  installed in the plate  18 , the plate  18  is mounted to the anchor block  16  with mechanical attachments  28 , such as screws, rivets, and the like. Installing the plate  18  forces the end of the signal contact  12  against the end of the center conductor  32  and forces the ends of the ground contacts  14  against the anchor block  16 . 
     Alternatively, the electrical connection  80  between the center conductor  32  and the signal contact  12  is a solder connection while the electrical connection  82  between the anchor block  16  and the ground contacts  14  is a compression connection. 
     Alternatively, as shown in  FIG. 35 , the end of the center conductor  32  is formed into a compliant spring like the skewed coil contact, as at  84 . The plate  18  is configured like that of  FIG. 23 , where the block opening  46 b is the same size as the center section  48 . The plate  18  is assembled without a signal contact  12  and, when the plate  18  is installed, the end of the center conductor  32  extends through the device opening  46 a. The electrical connection  82  between the anchor block  16  and the ground contacts  14  is a compression connection. 
     The plate  18  can be either insulating or conductive.  FIGS. 20-35  show an insulating plate  86 . The insulating plate  86  is made of a non-electrically-conductive material, preferably a plastic, so as to not electrically couple the signal contacts  12  and ground contacts  14 . 
     A conductive plate  88 , shown in  FIGS. 36-41 , is preferably composed of an electrically-conductive metal. Alternatively, the conductive plate is composed of a non-conductive material plated with a conductive coating. The conductive plate  88  electrically couples the ground contacts  14 , thus providing more precise impedance matching to the signal contact  12 . The signal contact  12  is insulated from the conductive plate  88  by an insulating centering plug  90  which prevents the signal contact  12  from electrically shorting to the conductive plate  88 . The plug  90  includes the through aperture  44 , the device opening  46 a, the anchor block opening  46 b, and the center section  48 . The plug  90  is typically made from an insulating plastic. 
     The plug  90  may be press fit into a through hole  92  in the conductive plate  88  or it may be bonded into the hole  92  with an adhesive. Alternatively, as shown in  FIG. 38 , the plug  90  is has two parts  94 , each of which fit into one plate sheet  50 . Mating shoulders  96 ,  98  retain the plug parts  94  in the plate sheets  50 . 
       FIGS. 39-41  show a configuration where the signal contact aperture  44  is within a conductive boss  190 , like that of  FIG. 24 . The boss  190  is surrounded by an insulating annulus  192  that insulates the conductive boss  190  from the conductive plate  88 . The annulus  192  can be composed of any dielectric material, but a better match can be had if the annulus  192  is composed of the same material as the cable dielectric  34 . 
     Alternatively, the signal contact  12  can be insulated from the conductive plate  88  by a non-conductive coating such as powder coating. In this case the signal contact aperture may be made larger such that the coating reduces the aperture size to the appropriate size for use. As with the plug  90 , the impedance of the system can be changed by either changing the thickness of the coating or by changing the coating material, thereby changing the dielectric constant of the material. 
       FIGS. 42-55  show configurations of the present invention for a twin-axial cable. The twin-axial configurations are illustrated using the skewed coil contacts. The present invention contemplates that any of the various available compliant contacts, including those described with reference to the coaxial cable assembly, can be used with twin-axial cables, as well as cables with more than two center conductors. 
     The center conductors  32  of the cable  30  are connected to the signal conduction points  4  of the electrical device  2  by the compliant signal contacts  12 . As shown in  FIGS. 47-52 , the signal contacts  12  are surrounded by a number of ground contacts  14  in a pattern that closely mimics the impedance environment of the cable  30 , e.g. 50 ohms, 75 ohms, 85 ohms, or 100 ohms. As described above with reference to the coaxial cable assembly, the impedance of the system can be changed by changing the position of the ground contacts  14  with respect to the signal contact  12  or by changing the insulating material, thereby changing the dielectric constant of the material or both. 
     As with the coaxial cable configurations, the plate  18  can be either insulating or conductive.  FIGS. 47-49  show an insulating plate  86  and  FIGS. 50-55  show a conductive plate  88 . With the conductive plate  88 , the signal contacts  12  are insulated from the conductive plate  88  by an insulating plug  90  which prevents the signal contacts  12  from electrically shorting to the conductive plate  88 . The plug  90  has two apertures  44 , one for each signal contact  12 . As described above with reference to  FIGS. 36-38 , the twin-axial cable plug  90  can be anchored by any conceivable means, such as by press fit, as shown in  FIG. 52 , adhesive, or capture. 
       FIGS. 53-55  show an alternative to the configuration of  FIGS. 50-52 . This configuration does not use ground contacts, only signal contacts  12 . The ground signal conducts directly through the conductive plate  88  to the device  2 . 
     The present specification describes a number of different compliant contacts that can be used in the present invention. These are merely examples. The present invention contemplates that any form of compliant contact that has the appropriate characteristics for the particular application can be used. In addition, the present specification contemplates that different types of contacts can be use in the same assembly. For example, a skewed coil contact can be used as the signal contact and a circular conductive rubber contact can be used as the ground contact. 
     The present invention produces a controlled-impedance, compliant cable to device interface which can be less than 1 mm thick (the length of the compliant contacts  12 ,  14 ) and mimics the controlled-impedance environment of the cable  30 , thereby ensuring the highest possible signal rates through the termination. 
     The present invention can also produce a controlled-impedance device to device interface because the cables  30  can have terminators  10  at both ends. 
     When working with very high frequencies, for example, frequencies in the Gigahertz range and above, electrical cable lengths are very critical. In order to maintain phase synchronization between signals on different cables, the cables must have as close to the exact same length, mechanically and electrically, as is practical. The present specification describes a method and apparatus for assembling cables  202  to the anchor block  200  so that the cables  202  are the same length to within a very small tolerance, on the order of 0.001 inch for cables  202  that are 6 inches long from the cable connector  204  to the block face  206 . The present method can be used for cables of any length. Longer cables result in larger tolerances. At a given temperature, a cable length can be controlled to within 0.03% to 0.05% of the cable&#39;s overall length. 
     To facilitate the method, a soldering fixture  210  is used. The fixture includes a frame  212 , a connector jig  214 , a block jig  216 , and legs  218 .  FIGS. 56-58  illustrate a fixture  210  for use with 16 cables  202  and a rectangular solid anchor block  200  for two rows of cables  202 . The fixture  210  can be modified for a different number of cables, different shape anchor block  200 , different cable connector  204 , different cable length, etc. 
     The frame  212  is generally rectangular and stands vertically. The connector jig  214  is mounted to the lower cross piece  222  of the frame  212  inside the frame  212 . The block jig  216  is mounted to the upper cross piece  224  of the frame  212  outside of the frame  212 . Four legs  218  extend from the bottom corners of the frame  212  in generally opposite directions. The legs  218  are angled from the frame  212  by at least 10° from horizontal so that they prevent the frame  212  from falling over but allow the user to tilt the frame  212 . The preferred angle is about 20° so that the frame can be tilted between 70°, 90°, and 110° from vertical to facilitate use, as described below. The present invention contemplates that the angle of the legs  218  can vary from application to application. 
     The fixture  210  locks the connector  204  of each cable  202  at a fixed distance away from where the other end of the cable  202  will be soldered to the anchor block  200 . The connector jig  214  locks the connectors  204  and can be designed appropriately for any particular type of connector  204 .  FIG. 59  shows a portion of a connector jig  214  for locking coaxial connectors. There is a connector securement  226  for each cable  202 . The securement  226  includes a channel  228  with an upper narrow section  230  for the cable  202  and a lower wide section  232  for the connector  204 . The narrow section  230  is defined by outwardly extending upper fingers  234 . The wide section  232  is defined by outwardly extending lower fingers  236 . When there is upward tension on the cable  202 , the connector  204  catches on the bottom surface  238  of the upper fingers  234 . 
     Because the distance (pitch) between cables  202  at the anchor block  200  is smaller than the diameter of the connectors  204 , the cables  202  cannot be secured parallel to each other to achieve equal length. To solve this problem, the connector jig  214  locks the connectors  204  in an upwardly open arc  240  so that the cables  202  are the same length to the anchor block  200 . 
     As shown in  FIG. 60 , the block jig  216 , a C-shaped component, is secured by screws  250  to the top surface  244  of the upper cross piece  224  of the frame  212 , straddling a C-shaped cutout  246 . The anchor block  200  is secured by screws  242  to the block jig  216  such that the anchor block face  206  is up and straddles the cutout  246 , which provides access to the cable holes  248  in the anchor block  200 . 
     A tensioning plate  252  is mounted to the upper cross piece  224 . There are threaded holes  254  at each end of the tensioning plate  252  into which the jack screws  256  are threaded. The tensioning plate  252  is placed over the anchor block face  206  and the jack screws  256  are turned into the holes  254  so that the tensioning plate  252  rests on the anchor block face  206 . The tensioning plate  252  has a cable hole  258  for each cable  202  that is aligned with the anchor block cable hole  248  for the same cable  202 . Optionally, the tensioning plate  252  is machined out above the anchor block  200 , as at  270 , to facilitate access to the face  206 . 
     Each cable  202  is trimmed so that it is at least 1.4 inches longer that the assembled length of the cable  202 . The cable  202  is stripped at the end so that the length from the connector  204  to the stripped portion remains constant. The non-stripped portion of the cable  202  extends into the anchor block hole  248  approximately 0.06 inches. 
     As shown in  FIG. 61 , after trimming, each cable  202  is fed through the hole  248  in the anchor block  200  corresponding to the connector securement  228  into which the cable connector  204  will be placed and through the corresponding cable hole  258  in the tensioning plate  252 . 
     As shown in  FIG. 62 , a coil spring  260  is placed on each cable  202  and a collar  262  is placed over each cable  202  so it touches the spring  260 . Alternatively, the spring  260  and collar  202  can be a unified component. A set screw  264  is turned into the collar  262  to tightly secure the collar  262  to the cable  202 . 
     The connectors  204  are placed into the corresponding securement  228  and the two jack screws  256  are tightened until the cables  202  have enough tension to be pulled against their securements  226 , making sure that the cables  202  are straight between the connector  204  and the anchor block  200  with no kinks or bends. Optional stops  266  prevent the jack screws  256  from being tightened too much. In the illustrated configuration, the stops  266  are spacers  292  on the jack screws  256  between the tensioning plate  252  and the jack screw heads  294 , as shown in  FIG. 63 . 
     The springs  260  independently keep each cable  202  tight so that the distance from the connector  204  anchor block face  206  remains consistent for all of the cables  202 . 
     Each cable shield  208  is soldered to the anchor block  200  such that the solder flows into the hole  248 . The angled legs  218  allowing the user to tilt the fixture  210  permit easier access to each side of the anchor block  200  for soldering. 
     After the solder and anchor block  200  have cooled sufficiently, the jack screws  256  are loosened until tension on the springs  260  is released. The collars  262 , springs  260 , and tensioning plate  252  are removed. The anchor block  200  is removed from the frame  212  and the connectors  204  are removed from the connector jig  214 . The excess cable is cut off. 
     Next, the anchor block face  206  is finished smooth and evenly flat. There are a number of ways known in the art to accomplish this, including sanding, milling, planing, skiving, and broaching. Once the cables  202  are secured in the anchor block  200 , any conceivable method can be used to dress the face  206  of the anchor block  200  which achieves the desired surface finish and/or planarity. 
     Thus it has been shown and described a controlled-impedance cable termination and a method and apparatus for attaching controlled-impedance cables to the termination. Since certain changes may be made in the present disclosure without departing from the scope of the present invention, it is intended that all matter described in the foregoing specification and shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense.