Patent Publication Number: US-6663424-B1

Title: Ultra wideband interconnect solution

Description:
GOVERNMENT LICENSE 
     The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of Grant No. DAAD19-01-9-0001 awarded by the United States Army: Material Command Acquisition. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to the field of connections between an external source or load and an internal circuit. More particularly, the present invention relates to an interconnect for transferring an ultra wideband frequency signal between an external source or load and internal circuit components. 
     Coaxial cable is often used to transmit and receive data signals. Interconnects can be used to connect the coaxial cable to an internal circuit that can interpret and utilize the content of the data signal or can forward the data signal to other components. The internal circuit can additionally transmit information to a load through the interconnect. The interconnect&#39;s structure enables the data signal to travel from the coaxial cable through a housing to the internal circuit and from and internal circuit through the housing to an external load. 
     Heretofore, an interconnect included a pin emerging from the coaxial cable connector, and extending over an internal circuit trace on a circuit board. The coaxial cable connector is situated in an aperture through the housing containing the circuit board and is connected to the circuit board with a conductive media. The conventional interconnect provides a fixed, direct and continuous contact with the internal circuit trace. However, the conventional interconnect does not provide optimal signal performance, especially at higher frequencies. 
     For mmWave and higher frequencies, optimally transmitting an electrical signal to the inside of a package or housing can be difficult. Problems with current interconnect structures include high insertion loss, high VSWR, and large field discontinuities which can couple through cavities and promote instabilities in electrical circuits. 
     Therefore, there is a need for a simple and effective wideband, low loss, low VSWR interconnect structure for connecting an external source or load to an internal circuit. Further there is a need for a simple, easy to manufacture method to provide the interconnect structure. Yet further, there is a need for an interconnect for higher frequency signals which is low cost, efficient, and easy to manufacture. 
     SUMMARY OF THE INVENTION 
     One embodiment of the invention relates to an interconnect for an electric circuit. The interconnect can include an external cable including an external cable pin projecting from the termination of the external cable, an internal circuit housed inside a package having a wall, an aperture in the package wall housing a receptacle, a connector and a cavity, wherein the external cable pin passes through the receptacle to electrically couple the external cable pin to a first conductive pin of the connector, and a conductive media for electrically coupling a second conductive pin of the connector to the internal circuit. 
     Another embodiment of the invention relates to an ultra wideband interconnect for electrically coupling an external cable to an internal circuit. The ultra wideband interconnect includes a coaxial cavity in a package wall for receiving a conductive pin from a connector, and a conductive media for coupling the conductive pin from a connector to a circuit trace on an internal circuit. The conductive media can be positioned to couple with the conductive pin within the cavity. 
     Another embodiment of the invention relates to a method for providing an ultra-wideband interconnect between an external cable and an internal circuit. The method includes providing a internal circuit including a circuit trace for receiving a data transmission enclosed in a package having a wall, wherein the wall includes an aperture defining a cavity, providing connector including a conductive pin assembly for sending a data transmission electrically coupled to an external cable, wherein the connector is housed within the wall such that the conductive pin extends into the cavity, coupling a conductive media to the conductive pin within the cavity, and coupling the conductive media to the circuit trace so as to electrically couple the conductive pin to the circuit trace. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will become more fully understood from the following detailed description, taken in conjunction with the accompanying drawings, wherein like reference numerals refer to like parts, and in which: 
     FIG. 1 is a exploded cross sectional view of an interconnection between an external cable and an internal circuit in accordance with an exemplary embodiment; 
     FIG. 2A is a cross sectional view of a conductive pin situated within a wall cavity terminating at the exit to the cavity and coupled to an internal circuit by a conductive media; 
     FIG. 2B is a cross sectional view of a conductive pin situated within a wall cavity terminating prior to exiting the cavity and coupled to an internal circuit by a conductive media; and 
     FIG. 3 is a flow diagram illustrating the steps for providing an ultra wideband interconnect. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, an interconnect  100  is shown in accordance with an exemplary embodiment. Interconnect  100  provides a signal transition between a coaxial cable  110  and an internal circuit  130  through a wall  140 . Interconnect  100  provides an electrical coupling between internal circuit  130  and coaxial cable  110 . 
     Interconnect  100  can be used for both input and output functions. Interconnect  100  can be used to facilitate the transfer of information to or from internal  130  circuit to an external load or source. An external source can be any structure or device transmitting information. An external load can be any structure or device receiving information. 
     Coaxial Cable can be a standard coaxial cable as is well known in the art. Coaxial Cable  110  includes a signal line  112 , an insulating material  114 , an outer sheathing  116 , and a connective housing  120 . Connective housing  120  includes a female connector  122  surrounding a protruding conductive pin  124 . Connective housing  120  is shown as having female connector  122 , however it is understood that conductive housing  120  can be include any type of connector for securing coaxial cable  110  to wall  140 . Coaxial cable  110  is manufactured in a fashion to promote propagation and integrity of a signal. Signal line  112  can formed from any medium capable of transmitting an ultra wideband signal. Signal line  112  is electrically coupled to conductive pin  124  so as to transmit a data signal from signal line  112  to conductive pin  124  or from conductive pin  124  to signal line  112 . Coaxial cable  110  is traditionally utilized to transmit or send data to or from an external device to internal circuit  130 . External devices can include an antenna, an oscilloscope, another circuit, or any other data source. 
     Internal circuit  130  can be any type of passive or active electrical device, structure, integrated circuit, etc. Internal circuit  130  can include a dielectric substrate  132  having a conductive pattern  134  formed on a surface. According to an exemplary embodiment, dielectric substrate  132  can be formed of aluminum hydride. According to an exemplary embodiment, conductive pattern  134  can be a copper stripline circuit trace etched in accordance with standard lithographic techniques known in the art. 
     Wall  140  includes a aperture  142 . Aperture  142  can extend through wall  140  defining an aperture between coaxial cable  110  and internal circuit  130 . Wall  140  is positioned so as to abut or nearly abut internal circuit  130 . Aperture  142  is defined so as to provide access to conductive pattern  134 . 
     Aperature  142  houses a receptacle  150 , a connector  160 , and a cavity  170  to facilitate connection of coaxial cable  110  to internal circuit  130 . Receptacle  150  can be any receptacle capable of receiving and securing a coaxial cable to a wall  140 . According to an exemplary embodimnent, receptacle  150  can be a field replaceable two-hole flange mount jack receptacle. Receptacle  150  is positioned between coaxial cable  110  and connector  160 . 
     According to an exemplary embodiment, receptacle  150  can be mounted to wall  140  by any standard mounting means. According to an exemplary embodiment, receptacle  150  is mounted using standard screws. Receptacle  150  includes a conductive pin hole  152  to receive and pass through conductive pin  124 . Receptacle  150  further includes a male connector  154  to mate with female connector  122  to securely attach coaxial cable  110  to receptacle  150 . Male connector  154  can be an OS-50 Jack. 
     Connector  160  is positioned within aperture  142  between receptacle  150  and internal circuit  130 . Connector  160  includes a receptacle side conductive pin  162 , a seal  164 , and a internal circuit side conductive pin  166 . Connector  160  can be any type of connector capable of receiving and passing a data signal. According to an exemplary embodiment, connector  160  can be a solder-in thermally matched hermetic seal. 
     According to an exemplary embodiment, conductive pin  124  can be electrically coupled to receptacle side conductive pin  162  to permit transfer of data to or from coaxial cable  110 . 
     Connector  160  can also be positioned within aperture  142  such that internal circuit side conductive pin  166  is located within cavity  170  and terminates in close proximity to internal circuit  130 . Connector  160  is also positioned such that internal circuit side conductive pin  166  terminates at a point near the end of cavity  170  proximate to internal circuit  130 . According to an exemplary embodiment, internal circuit side conductive pin  166  terminates within 10 mm of the end of cavity  170 . 
     Cavity  170  is a cavity within wall  140  having a characteristic impedance defined by the physical size of the cavity and the dielectric constant of the insulating material. According to an exemplary embodiment, as shown in FIG. 1, the insulating material can be air. 
     Conductive media  180  electrically couples internal circuit side conductive pin  166  to conductive pattern  134 . Conductive media  180  can be any formable conductive media. According to an exemplary embodiment, conductive media  180  can be a singular or multiple gold ribbon or wire. Conductive media  180  can be coupled to internal circuit side conductive pin  166  within cavity  170  with a minimally short length of conductive media. Conductive media  180  does not maintain the characteristic impedance of the coax as the conductive media protrudes through wall  140 . This has the effect of minimizing the discontinuity in the electrical signal path. 
     In operation, according to an exemplary embodiment, a signal can be placed on coaxial cable  110  for transmission into and out of internal circuit  130 . The structure of interconnect  100 , as defined above, can be used to maximize the field containment of the electrical signal. The field containment is maximized by providing a coaxial structure for the signal all the way through cavity  170  in wall  140  and transitioning to internal circuit  130  directly at the edge of wall  140  . This allows for the physical alignment of the coax field with internal circuit  130 . 
     The transition between from internal circuit side conductive pin  166  to conductive media  180  occurs within the air coax of cavity  170 , slightly before protruding beyond wall  140  into the cavity occupied by internal circuit  130 . The physical alignment of the signal fields combined with the minimal distance of the interconnect where conductive media  180  is attached allows for superior performance. Superior performance can include an excellent return loss and an minimal insertion loss. 
     FIG. 2A is a cross sectional close up view of internal circuit side conductive pin  166  extending through the entire length of cavity  170 . According to an exemplary embodiment, this embodiment minimizes the interconnect distance between internal circuit side conductive pin  166  and internal circuit  130  while still providing a transition from internal circuit side conductive pin  166  to conductive media  180  within cavity  170 . 
     In FIG. 2A, internal circuit side conductive pin  166  is shown as rounded according to an exemplary embodiment. According to alternative embodiments, internal circuit side conductive pin  166  can be beveled or squared to maximize signal strength and integrity. 
     FIG. 2B is a cross sectional close up view of internal circuit side conductive pin  166  extending a distance short of the entire length of cavity  170 . According to an exemplary embodiment, this embodiment provides a transition from internal circuit side conductive pin  166  to conductive media  180  within cavity  170 , but not at the exact edge of cavity  170 . FIG. 2B illustrates that placement of internal circuit side conductive pin  166  along the entire length of cavity  170  is not required to provide the advantages of interconnect  100 . 
     FIG. 3 is a flow diagram  300  illustrating the steps in creating an ultra wideband interconnect according to an exemplary embodiment. Flow diagram  300  includes exemplary steps performed in the manufacture of an ultra wideband interconnect solution according to an exemplary embodiment. 
     In a step  310 , a circuit trace is provided on a dielectric surface of an internal circuit to receive a data transmission from an external cable. The internal circuit is further enclosed inside a package having a wall. The internal circuit can be position proximate to the wall. The wall includes an aperture extending from external to the package to the inside of the package. The aperture further defines a cavity. The cavity is a coaxial space defining an air coax within the cavity. According to alternative embodiments, the cavity can be backfilled with any other type of dielectric media. The cavity can be positioned proximate to the internal circuit so as to provide access for an electrical coupling with the internal circuit. The circuit trace can be formed using lithographic etching techniques that are well known in the art. 
     In a step  320  an external cable is provided having a conductive pin . The external cable can carry a data transmission signal for transfer to the internal circuit. The external cable also includes a coupling assembly for coupling the external cable to a receptacle. The receptacle can be coupled to a connector. The receptacle and connector can be housed within the an aperture in the wall of the package containing the internal circuit. The receptacle, which is housed within the aperture defined in the wall, can be positioned such that the conductive pin associated with the connector is position entirely within the cavity. 
     In a step  330 , a conductive media can be provided between the conductive pin associated with the connector and the circuit trace of the internal circuit. The conductive media can be coupled to the conductive pin associated with the connector within the cavity defined by the aperture in the wall of the package. The conductive media electrically couples the conductive pin associated with the connector to the circuit trace to allow transmission of a data signal. 
     While the exemplary embodiments illustrated in the FIGURES. and described above are presently preferred, it should be understood that these embodiments are offered by way of example only. For example, alternative embodiments may be suitable for use, wherein the internal circuit includes a die, or a transmission line other than a coaxial cable is used. Additionally, an air coax is described, but an alternative dielectric substrate can be backfilled into the cavity defined by the aperture in the cavity wall. Accordingly, the present invention is not limited to a particular embodiment, but extends to various modifications that nevertheless fall within the scope of the appended claims.