Patent Publication Number: US-7909613-B2

Title: Coaxial connecting device

Description:
TECHNICAL FIELD 
     The present invention relates to a coaxial connecting device and, in particular, to a coaxial connecting device for making an electrical connection between a coaxial cable and a device under test. 
     BACKGROUND ART 
     Coaxial cable is an electrical cable consisting of an inner signal conductor, an insulator surrounding the signal conductor, and an outer cylindrical conducting shield surrounding the insulating spacer such that the inner conductor and the outer shield shares the same axis. 
     The coaxial cable is often used for precise electric and electronic devices and test devices due to its low electrical interference and transmission stability relative to other types of cables. In a case of usage with a test device, a coaxial connecting device for securing signal transmission reliability of the coaxial cable even with repeated attachment and detachment to the test objects. 
       FIG. 1  shows a conventional coaxial connecting device. As shown in  FIG. 1 , the conventional coaxial connecting device includes an inner conductive contact assembly contacting a signal conductor of a coaxial cable, a conductive ground plunger containing the inner conductive contact assembly in its cylindrical inner space, an isolator for electrically isolating the inner conductive contact assembly and the conductive ground plunger from each other, and an interface element fixed to an outer conductor of a coaxial cable so as to make electrical connection to the plunger. The interface element is arranged in an exterior barrel by means of a ground sleeve such that the ground sleeve slides along the interface element fixed inside the exterior barrel. 
     In the conventional coaxial connecting device, however, the interface element is fixed on the exterior barrel such that, when approaching the exterior barrel to a test object without cutting off the electricity on the coaxial cable, the contact assembly and ground plunger are likely to contact the conductors of the test object before fixing the exterior barrel in place so as to cause unstable electric current, whereby it is required to laboriously switch on and off the electricity whenever changing test target devices. 
     Meanwhile, a connection member is required for electrically connecting the test equipment, which generates test signals, to a test target device. Particularly, as the devices to be tested are highly advanced, the connection link vulnerable to weak signals and interferences causes to degrade the test result reliability. 
     Therefore, there has been a requirement for a coaxial connecting device capable of transferring test signals to test target device, without degrading the signal strength and causing frequency interferences. 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     The present invention has been made in an effort to solve the above problems, and it is an object of the present invention to provide a coaxial connecting device that is capable of minimizing the signal contact path between a coaxial cable and an external pad and reducing signal loss and interference. 
     Technical Solution 
     In one aspect of the present invention, the above and other objects of the present invention are accomplished by a coaxial connecting device electrically connecting a coaxial cable to a signal pad and a ground pad. The coaxial connecting device includes a signal pin for electrically connecting a signal conductor of the coaxial cable to the signal pad; a ground connector for electrically connecting a ground conductor of the coaxial cable to the ground pad; a cylindrical guide tube surrounding the ground conductor for elastically contacting the ground pad while maintaining a predetermined distance with the signal pin; and a dielectric member surrounding a part of the signal pin for electrically isolating the cylindrical guide tube and the signal pin from each other and coaxially maintaining the guide tube and the signal pin. 
     Preferably, the ground connector is directly connected to the ground conductor of the coaxial cable at one end and tightly inserted into the cylindrical guide tube, the ground connector having a first protrusion. 
     Preferably, the cylindrical guide tube includes a main body connected to an end of the ground connector by means of shrink fit and fixed by the first protrusion; a ground contact part elastically connected to the ground pad; a bridge part electrically connecting the ground contact part to the main body; and an elastic member arranged between the main body and the ground contact part, the elastic member surrounding the bridge part. 
     Preferably, the signal pin is a spring probe pin. 
     Preferably, the signal pin includes a first part which is elastically contacting with the signal pad; a second part longitudinally connected to a proximal end of the first part and having a fixation protrusion for limiting movement of the dielectric member, the second part being formed with a diameter larger than that of the first part such that the first part reciprocates within the second part; and a third part longitudinally connected to the second part at one end and having an insertion hole formed at the other end for receiving the signal conductor, the third part having a diameter larger than that of the second part. 
     Preferably, the second part is arranged such that a beginning end of the second part is positioned below a finishing end of the bridge part of the cylindrical guide tube. 
     Preferably, the main body has a second protrusion protruded inward for limiting movement of the dielectric member in cooperation with the fixation protrusion and limiting a movement of the bridge member; the bridge member is connected to the main body at one end by means of shrink fit and fixed by the second protrusion and is provided with a third protrusion at the other end for defining movement of the ground contact part; and the ground contact part includes a stopper for restricting movement of the ground contact part and an elongate member for maintaining electrical contact with the third protrusion while the ground contact part reciprocates along the bridge part. 
     Preferably, the elongate member has a cylindrical shape of which inner surface is electrically contacting with the third protrusion. 
     Preferably, the elongate member has a cylindrical shape having a guide hole elongated in a longitudinal direction, the guide hole being slightly skewed relative to a longitudinal axis of the coaxial connecting device and the bridge part has an engagement pin which is engaged with the guide hole, the engagement of the engagement pin and the guide hole providing electrical contact point. 
     Preferably, the elongate member has a cylindrical shape tapered to a distal end and slit in a longitudinal direction with predetermined intervals along its circumference, the elongate member electrically contacting the third protrusion while moving back and forth. 
     Preferably, the dielectric member is blocked to move in a direction by the second protrusion of the main body and the fixation protrusion and in the other direction by an end of the ground connector and the third part, and the signal pin and the cylindrical guide tube are isolated from each other by the dielectric member and space in between. 
     Preferably, the ground connector is directly connected, at its one end, to the ground conductor of the coaxial cable and has a connection protrusion formed on its inner wall for fixing the cylindrical guide tube inside thereof; and the cylindrical guide tube comprises a ground contact part which is elastically contacting with the ground pad, a bridge part connected to the ground contact part by means of shrink fit and fixed by the connection protrusion and electrically connecting the ground contact part and to the ground connector, and an elastic member interposed between the ground contact part and the ground connector and surrounding the bridge part. 
     Preferably, the signal pin includes a first part which is elastically contacting with the signal pad; and a second part which a diameter larger than that of the first part and is connected to the first part at one end and has a insertion hole formed at the other end for receiving the signal conductor of the coaxial cable, the one end of the second part being positioned below one end of the bridge part of the cylindrical guide tube. 
     Preferably, the bridge part of the cylindrical guide tube is connected to the ground connector at one end by means of shrink fit and fixed by the fixation protrusion, limits movement of the ground contact part by biasing force of the elastic member, and has a contact protrusion protruded on an outer surface thereof; and the ground contact part comprises a stopper facing one end of the elastic member and an elongate member integrally formed with the stopper and maintaining electrical contact with the contact protrusion while the ground contact part moves back and forth. 
     Preferably, the dielectric member is connected to the second part of the signal pin by means of shrink fix, and the signal pin and the cylindrical guide tube are electrically isolated from each other by the dielectric member and space formed between the signal pin and the cylindrical guide tube. 
     ADVANTAGEOUS EFFECTS 
     The coaxial connecting device of the present invention has an effect to minimize contact path between the ground conductor of a coaxial cable and a ground pad of a device under test, resulting in improvement of impedance match and frequency characteristics. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a perspective view illustrating a conventional coaxial connecting device; 
         FIG. 2  is a perspective view illustrating a coaxial connecting device according to an exemplary embodiment of the present invention; 
         FIG. 3  is a cross sectional view illustrating the coaxial connecting device of  FIG. 2 ; 
         FIGS. 4 to 6  are partial cross sectional views illustrating how to operate the coaxial contractor of  FIG. 1 ; 
         FIG. 7  is a perspective view illustrating a coaxial connecting device according to another exemplary embodiment of the present invention; 
         FIG. 8  is a perspective view illustrating a coaxial connecting device according to an exemplary embodiment of the present invention; 
         FIG. 9  is a partial cross sectional view of the coaxial connecting device of  FIG. 8 ; and 
         FIG. 10  is a cross sectional view illustrating a coaxial connecting device according to another exemplary embodiment of the present invention. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Exemplary embodiments of the present invention are described with reference to the accompanying drawings in detail. The same reference numbers are used throughout the drawings to refer to the same or like parts. Detailed descriptions of well-known functions and structures incorporated herein may be omitted to avoid obscuring the subject matter of the present invention. 
       FIG. 2  is a perspective view illustrating a configuration of a coaxial connecting device according to an exemplary embodiment of the present invention. 
     In this embodiment, the present invention is a coaxial contractor  200  for electrically connecting a signal pad and a contact pad of an external printed circuit board (not shown) to a coaxial cable  305 . As shown in  FIG. 2 , the coaxial connecting device according to an embodiment of the present invention includes a signal pin  310 , a ground connector  320 , a cylindrical guide tube  330 , and a dielectric member (not shown). 
     If a pressure is applied while the guide tube  330  and signal pin  310  are contact the respective ground and signal pads, the guide tube  330  and the signal pin  310  are elastically compressed. The guide tube  330  is connected to a ground and functions as a ground, and the signal pin  310  is connected to a signal conductor (not shown) of the coaxial cable  305 . 
       FIG. 3  is a cross sectional view illustrating the coaxial connecting device of  FIG. 2 , and  FIGS. 4 to 6  are partial cross sectional views illustrating how to operate the coaxial contractor of  FIG. 1 . A structure and function of the coaxial connecting device of the present invention is described hereinafter with reference to  FIGS. 2 to 6 . 
     A coaxial cable  305  includes a signal conductor  305   c , a dielectric insulator  305   b  surrounding the signal conductor  305   c , and a ground conductor  305   a  surrounding the dielectric insulator  305   b . The signal pin  310  of the coaxial connecting device is elastically contacting with a signal pad (PS) of an external printed circuit board (PCB)  350  so as to make an electrical connection between the signal conductor  305  of the coaxial cable  305  and the signal pad (PS). 
     The signal pin  310  can be any of a variety of materials that are conductive to transfer electrical signals. The signal pin  310  is configured such that the tip of the signal pin  310  is contracted and extended. 
     The signal pin  310  includes a first part  310   a , a second part  310   b , and a third part  310   c  formed with different diameters. The first part  310   a  can elastically reciprocate in longitudinal direction against the signal pad (PS). 
     The second part  310   b  is connected at one end of the first part  310   a  such that the first part  310   a  reciprocates inside the second part  310   b . The second part  310   b  is also provided with a fixation protrusion  410  formed around an outer surface at one end for fixing the dielectric member  340 . The third part  310   c  is connected at the other end of the second part such that the second part  310   b  is fixed inside of the third part  310   c . The third part  310   c  is provided with a contact hole  345  at the other end for tightly receiving the signal conductor  305   c  of the coaxial cable  305 . The third part  310   c  has a diameter larger than that of the second part  310   b  so as to fixedly contact with the dielectric member. 
     The signal conductor  305   c  of the coaxial cable  305  is inserted into the contact hole  345  of the third part  310   c  of the signal pin  310  and then fixed by means of soldering. Although the soldering is used in this embodiment, the signal conductor  305   c  and the signal pin  310  can be abutted with each other using various techniques. 
     The ground connector  320  surrounds a part at which the signal pin  310  and the coaxial cable  305  are connected to each other. The ground connector  320  is connected to the ground conductor  305   a  of the coaxial cable  305 . The ground connector  320  is directly connected to the ground conductor  305  of the coaxial cable  305  by surrounding the ground conductor  305  such that the entire cylindrical guide tube  330  functions as a ground. 
     The ground connector  320  has a shape of a cylindrical sleeve having a protrusion  320   a  formed around its outer circumferential surface. One end of the ground connector  320  is connected to the ground conductor  305   a  of the coaxial cable  305  and the other end of the ground connector  320  is connected to the guide tube  330 . 
     The dielectric member  340  is arranged to contacted with the ground connector  320  around the signal pin  310 . The dielectric member  340  surrounds at a part of the signal pin  310  so as to electrically insulate the signal pin  310  from the guide tube  330  and maintain the guide tube  330  and the signal pin  310  in a concentric manner. The dielectric member  340  is fixed by means of the second protrusion  420  and the first protrusion  410  arranged at one end of the guide tube  330  and one end of the ground connector  320  and the third part  310   c  of the signal pin  310  arranged at the other end. 
     The signal pin  310  is insulated against the cylindrical guide tube  330  by means of air except for a region surrounded by the dielectric material. The signal pin  310  and the guide tube are isolated from each other by the dielectric member  340  and the air. 
     A start point of the second part  310   b  of the signal pin  310  is arranged below the upper end of a middle part  330   c  of the guide tube  330 . Accordingly, even when the first part  310   a  of the signal pin  310  contacts the signal pad (PS) so as to be retreated, the start point of the second part  310   b  is prevented from directly contacting the signal pad (PS). 
     The cylindrical guide tube  330  contacts with an outer surface of the ground connector and surrounds the signal pin  310  while maintaining a predetermined distance. Also, the guide tube  330  is elastically contact with the ground pad (PG). 
     The structure of the cylindrical guide tube  330  is described hereinafter in more detail. The cylindrical guide tube  330  includes a main body  330   a , a ground contact part  330   b , a bridge part  330   c , and an elastic member. The main body  330   a  is coupled with a ground connector  320  by means of shrink fit and fixed by the first protrusion  320   a . The ground contact part  330   b  is elastically contacted with the ground pad (PG). The bridge part  330   c  is electrically connecting the main body  330   a  and the ground contact part  330   b . The elastic member  330   d  is arranged between the main body  330   a  and the ground contact part  330   b  by surrounding the bridge part  330   c.    
     The main body  330   a  is provided with a second protrusion  420  for fixing the dielectric member  340  with the first protrusion  410  and fixing one end of the bridge part  330   c  at the other side. 
     The bridge part  330   c  is connected, at its one end, to the main body  330   a  by means of shrink fit and is provided with a third protrusion  430  at the other end for defining movement of the ground contact part  330   b.    
     The ground contact part  330   b  includes a stopper  440  which is hooked with the third protrusion  430  to restrict the movement of the ground contact part  330   b  and an elongate member  450  for maintaining the electrical contact with the third protrusion  430  while the ground contact part  330   b  reciprocates along the bridge part  330   c.    
     The bridge part  330   c  is connected to the ground contact part  330   b  such that the ground contact part  330   b  can slide along the bridge part  330   c . The movement of the ground contact part  330   b  is limited by the third protrusion  430  of the bridge part  330   c  and biased by the elastic member  330   d . The elastic member  330   d  can be any of various types of springs. 
     The bridge part  330   c  is fixed to the main body  330   a  together with elastic member  330   d  by means of shrink fit and fixed by the second protrusion  420 . The coaxial cable  30  coupled with the ground connector  320  and the signal pin  310  is connected to the main body  330   a  by means of shrink fit. The ground connector  320  is fixed to the main body  330   a  by the first protrusion  320   a.    
     After the ground connector  320  is connected to the main body  330   a , the ground conductor  305   a  of the coaxial cable  305  is soldered to the ground connector  320 . The elongate member  450  of the ground contact part  330   b  has a cylindrical shape and its inner surface is contacted with the third protrusion so as to maintain the electrical connection, thereby functioning as a ground. 
       FIG. 4  shows a state of the coaxial connecting device  200  before contacting with a device on the PCB  350  to be tested;  FIG. 5  shows a state of the coaxial connecting device  200  contacting with a device on the PCB  350  to be tested; and  FIG. 6  shows a state of the coaxial connecting device  200  when the coaxial contractor  200  is pressed to the PCB  350  such that the first part  310   a  of the signal pin  310  and the elongate member  450  of the ground connect part  330   b  are elastically withdrawn. 
     The elongate member  450  maintains the contact with the third protrusion  430  of the bridge part  330   c  while being withdrawn. That is, when the coaxial connecting device  200  is pushed to the PBC  350 , the ground contact part  330   b  is biased by the elastic member  330   d  so as to be tightly contacted with the ground pad (PG) while the elongate member  450  is maintaining the electrical connection with the third protrusion  430 . 
     Since the elongate member  450  is connected to the ground conductor  305   a  of the coaxial cable  305 , it functions as a ground. Also, the signal pin  310  is electrically connected to the signal conductor  305   c  of the coaxial cable  305  so as to make a signal line. 
       FIG. 7  is a perspective view illustrating a coaxial connecting device according to another exemplary embodiment of the present invention. 
     Referring to  FIG. 7 , an elongate member  450  of the ground contact part  330   b  is formed having a cylindrical shape. The elongate member  450  is provided with a guide hole  610  elongated in its longitudinal direction, the guide hole  610  being slightly skewed relative to a longitudinal axis of the coaxial connecting device  200 . 
     The guide hole  610  receives an engagement pin  620  formed on the surface of the bridge part  330  such that the elongate member  450  is rotatively reciprocating. 
     The contact point of the bridge part  330  and the elongate member  450  is established by the guide hole  610  and the engagement pin  620  such that the elongate member  450  contacts the contact pad (PG) with low contact resistance. 
       FIG. 8  is a perspective view illustrating a coaxial connecting device according to an exemplary embodiment of the present invention, and  FIG. 9  is a partial cross sectional view of the coaxial connecting device of  FIG. 8 . 
     Referring to  FIG. 8 , the elongate member  450  has a cylindrical shape tapered to its distal end and slit in a longitudinal direction along its circumference with regular intervals, whereby the distal end can be leaned inward. 
     The inner wall of the slit elongate member  450  is electrically contacted with the third protrusion  430  such that multiple contact points secure contact stability. 
       FIG. 10  is a cross sectional view illustrating a coaxial connecting device according to another exemplary embodiment of the present invention. 
     As shown in  FIG. 10 , the coaxial connecting device  700  is provided with a ground connector  710  and a signal pin  730  that are different from those of coaxial connecting device of  FIG. 3 . Detailed descriptions of functions and structures of other elements are omitted. 
     The ground connector  710  is directly connected, at its one end, to the ground conductor  305   a  of the coaxial cable and is provided with an engagement protrusion formed on an inner surface thereof for fixing a bridge part  720  of a cylindrical guide tube. 
     The cylindrical guide tube includes a ground contact part  330   b  which is elastically contacting with a ground pad, a bridge part  720  coupled with the ground connector  710  by means of shrink fit and fixed by a fixation protrusion so as to make an electrical connection to the ground contact part  330   b , and an elastic member  330   d  arranged between the ground contact part  330   b  and the ground connector  710 , the elastic member  330   d  winding the bridge part  720 . 
     As shown in  FIG. 7 , the ground connector  710  of the coaxial connecting device  700  has a shape formed by integrating the ground connector  320  with the main body  330   a  of the coaxial connecting device of  FIG. 3 . 
     The signal pin  730  includes a first part  730   a  and a third part  730   c  formed with different diameters. The first part  730   a  can elastically reciprocate in longitudinal direction against the signal pad (PS). The second part  730   b  is connected at one end of the first part  730   a  such that the first part  730   a  can reciprocate inside the second part  730   b . The second part  730   b  is provided with a hole formed at its other end for receiving the signal conductor  305   c.    
     The signal pin  730  has no fixation protrusion, which is provided in  FIG. 3  for fixing the dielectric member since there is no third part. A dielectric member  740  is coupled with the second part  730   b  by means of shrink fit. Also, the ground connector  710  has no protrusion for fixing the dielectric member  740 . 
     The bridge part  720  and the ground contact part  330   b  of the cylindrical guide tube are identical with those of  FIG. 3  in structures and functions. The protrusion  720   a  of the bridge part  720  is identical with the third protrusion  430  of  FIG. 3 . 
     In the coaxial connecting device  700  of  FIG. 10 , the signal pin  730  and the cylindrical guide tube are isolated from each other by means of the dielectric member and air. 
     Unlike the coaxial connecting device  200  of  FIG. 3  in which the dielectric member is fixed by means of protrusions provided on the cylindrical guide tube and the signal pin, the dielectric member of the coaxial connecting device  700  of  FIG. 10  is fixed by means of shrink fit. 
     Although not depicted in the drawings, it is obvious to those in the art that the protrusion for fixing the dielectric member can be provided on at least one of an inner wall of the cylindrical guide tube and surface of the signal pin. 
     Although exemplary embodiments of the present invention have been described in detail hereinabove, it should be clearly understood that many variations and/or modifications of the basic inventive concepts herein taught which may appear to those skilled in the present art will still fall within the spirit and scope of the present invention, as defined in the appended claims. 
     As described above, the coaxial connecting device of the present invention minimizes a contact length between the ground conductor of a coaxial cable and a ground pad and provides impedance matched coaxial signal transmission link, resulting in improvement of frequency characteristics. 
     INDUSTRIAL APPLICABILITY 
     The coaxial connecting device of the present invention is applicable to various types of device testing systems.