Abstract:
A signal connector assembly with a plug contact within a plug having a high resistive portion. When the plug of the assembly first makes contact with the electrical receptacles within a mating receptacle, the high resistive portion prevents a voltage surge. As the plug is further inserted into the receptacle, the energy passing from the plug to the receptacle is gradually increased. Eventually, the receptacle contacts within the receptacle pass the high resistive portion and make contact with the conductive portion of the plug contact, thereby permitting transmission of valid signals without the generation of spurious errors.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates generally to electrical connectors for electronic devices. More particularly, the invention relates to electrical contacts for use in electrical connectors to prevent the generation of spurious signals upon mating of the connector.  
           [0003]    2. Description of the Related Art  
           [0004]    Electrical connectors for use with peripheral electronic devices are well known in the art. A recurrent problem with many prior art connectors is the generation of spurious signals upon mating of a peripheral electronic device to an electronic system which is already energized. The connector may induce a voltage pulse into the energized electronic system. The voltage pulse may travel through the electronic system, thereby introducing spurious errors into the system. This problem is known in the art as the “hot plug” problem.  
           [0005]    This condition that causes errors in electronic systems results from the very high data rates and very low energy of the signals within the systems. The input capacitance of the connector, printed circuit board lines and device capacitance of the buffer integrated circuit devices are the basis of the problem. Energy must flow from the system bus to charge this input capacitance, (generally tens of picofarads). When energy is removed from the system bus, a voltage pulse to an adjacent device on the bus occurs, thereby creating errors in the system. The voltage pulse may be no greater than normal signals so no new radiated noise problem is introduced. However, it can cause data to be incorrectly transferred. Accordingly, the interconnections themselves are a large portion of the problem. This problem is universal since it affects both digital and analog electronic devices.  
           [0006]    The prior art has generally addressed the “hot plug” problem by using logic and timing control circuitry, such as that which is disclosed in U.S. Pat. No. 4,245,270, to slowly ramp up the voltage within the connecting line. However, providing the additional circuitry is complex and expensive.  
           [0007]    Many connecting schemes require certain portions of the connector to be mated prior to other portions, or in a particular sequence. For example, with respect to power applications, U.S. Pat. No. 4,079,440 discloses a circuit board having two connector plugs of differing lengths. The longer connector plug makes initial contact with a power line prior to the shorter plug, which reduces the onset of power surges. However, this scheme requires manual dexterity and specific insertion and removal timing for proper operation.  
           [0008]    A connector assembly disclosed in U.S. Pat. No. 4,747,783 attempts to eliminate timing and control circuitry for power applications. This connector assembly uses a long pin in the “plug” to first make contact with its mating “socket” to gradually increase the voltage to the socket until the entire plug makes mating contact with the socket. The plug comprises a pin having a thin insulating material covering the surface and a thin low resistive material covering the insulating material. When the plug makes initial contact with the socket, the current must pass through the resistive portion of the plug. This permits the electronic components in the peripheral device to charge gradually and eliminates the current surges which may result.  
           [0009]    This device is undesirable for several reasons. First, it requires the use of several contacts of differing lengths, thereby raising manual dexterity problems. Secondly, although the low resistance (i.e. 2-60 ohms) is sufficient to eliminate current surges in power transmissions, it is not sufficient to eliminate the voltage pulse from being introduced into the electronic system. In addition, the thin layer of low resistive material surrounding the thin layer of insulating material introduces an additional problem into the connection between the peripheral device and the electronic system; short capacitance. As explained previously, capacitance is undesirable in a connector.  
           [0010]    It would be desirable to provide a signal connector assembly that would not introduce errors into an electronic system during a hot plug.  
         SUMMARY OF THE INVENTION  
         [0011]    The present invention provides a plug contact having a high resistive portion within a plug for use in a signal connector assembly. When the plug of the assembly first makes contact with the receptacle contacts within a mating receptacle, the high resistive portion of the plug contact prevents a voltage spike. To prevent voltage pulses, resistive portions with resistances ranging from 10 KW to 1 GW are necessary depending upon the application. As the plug is further inserted into the receptacle, the energy flow is gradually increased. Eventually, the receptacle contacts within the receptacle pass the high resistive portion and make contact with the conductive portion of the plug contact, thereby permitting transmission of valid signals without the generation of spurious errors. In an alternative embodiment, the receptacle contact, or both the plug contact and the receptacle contact, may have the high resistive portion.  
           [0012]    It is an object of the present invention to provide a connector assembly which permits connection of a peripheral device to an energized electronic system without introducing any spurious errors into that system.  
           [0013]    Other objects and advantages of the present invention will become apparent after reading the detailed description of the presently preferred embodiment. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is an isometric view of a simplified illustration of the present invention.  
         [0015]    [0015]FIG. 2 is a graph of voltage versus distance traveled along the high resistive portion.  
         [0016]    [0016]FIG. 3 is a graph of megaohms versus distance traveled along the high resistive portion with curves depicting varying thicknesses of the portion.  
         [0017]    [0017]FIG. 4 is a graph of megaohms versus distance traveled along the high resistive portion with curves depicting varying resistivities of the portion.  
         [0018]    [0018]FIG. 5 a  is an alternative embodiment of the present invention with a tapered high resistive portion.  
         [0019]    [0019]FIG. 5 b  is an alternative embodiment of the instant invention with a stepwise-tapered high resistive portion.  
         [0020]    [0020]FIG. 5 c  is an alternative embodiment of the present invention with a resistive portion of mixed high resistive materials.  
         [0021]    [0021]FIG. 5 d  is an alternative embodiment of the present invention with a conductive barb in the high resistive portion.  
         [0022]    [0022]FIG. 5 e  is an alternative embodiment of the present invention with the high resistive portion extending into a hole in the conductive portion.  
         [0023]    [0023]FIG. 5 f  is an alternative embodiment of the present invention with a high resistive housing.  
         [0024]    [0024]FIG. 5 g  is an alternative embodiment of the present invention with a high resistive inset in the housing.  
         [0025]    [0025]FIGS. 5 h  and  5   i  are an alternative embodiment of the present invention with a high resistance inset in the housing.  
         [0026]    [0026]FIG. 6 is an illustration of the instant invention utilized on a circuit board.  
         [0027]    [0027]FIG. 7 is an illustration of the instant invention being used on a cylindrical connector.  
         [0028]    [0028]FIG. 8 is an illustration of the various prior art connectors. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0029]    The preferred embodiment will be described with reference to the drawing figures wherein like numerals represent like elements throughout.  
         [0030]    Referring to FIG. 1, the preferred embodiment of the connector assembly of the present invention comprises a plug  6  for mating with a corresponding receptacle  8 . It should be recognized that although only one plug contact  7  is shown in detail for simplicity, there are typically at least two or more plug contacts  7  within every plug  6  for mating with corresponding receptacle contacts  15 . The shape of the plug  6  is not central to the present invention. For simplicity, the plug  6  and plug contact  7  are illustrated as rectangular, although those of skill in the art will realize that many other shapes could be used without departing from the spirit of the present invention. The plug contact  7  comprises a conductive portion  14  which can be made from any conductive material, (such as brass, nickel, gold, copper or a superconductor, etc.) and a highly resistive portion  12 . The resistive portion  12  is generally rectangular shaped and extends across the width W of the plug contact  7 . The resistive portion  12  comprises a layer of highly resistive material inset into the surface  16  of the plug  6 , with a first end  11  of the resistive portion  12  exposed to the receptacle  8  and a second end  13  of the resistive portion  12  in contact with the conductive portion  14 .  
         [0031]    A typical receptacle  8  includes a receptacle contact  15  for each corresponding plug contact  7  which electrically mates with its corresponding receptacle contact  15  as the plug  6  of the peripheral device (not shown) is inserted into receptacle  8  of the electronic system (not shown).  
         [0032]    In operation, the first end of the plug  6  is inserted into the cavity of the receptacle  8 . The receptacle contact  15  will make first contact with the resistive portion  12 . Since it is contemplated that the electronic system will be energized, this will permit energy from the electronic system to begin flowing from the receptacle contact  15 , through the resistive portion  12  and into the conductive portion  14  of the plug contact  7 . The resistive portion  12  reduces the magnitude voltage pulses such that they will not present errors into the electronic system, as will be explained in detail hereinafter. A portion of the voltage “seen” by the plug  6  will drop across the resistive portion  12 . As the plug  6  is inserted further into the receptacle  8 , the receptacle contact  15  passes along the surface  16  of the resistive portion  12  until it finally reaches the conductive portion  14  of the plug contact  7 . When the plug  6  is fully inserted into the receptacle  8 , the receptacle contact  15  will be in direct contact with the conductive portion  14  of the plug contact  7 . Accordingly, there will be no voltage drop across the resistive portion  12  of the plug contact  7 . With respect to capacitance, the arrangement of the present invention specifically limits the capacitance between the metallic portions of the plug and receptacle contacts  7 ,  15 , (it bypasses the high resistance), to an acceptably low level. It does this by minimizing their effective coupling area and the effective dielectric constant between them, which is primarily air.  
         [0033]    A primary aspect of preventing a voltage pulse is to reduce the initial voltage seen by plug contact  7  upon insertion of the plug  6  into the receptacle  8 . Referring to the test setup  94  and the graph of FIG. 2, it can clearly be seen that the resistive portion  12  reduces the initial voltage seen by the receptacle contact  15 . The graph represents the voltage seen by the receptacle contact  15  as the plug  6  is removed from the receptacle  8 . Referring to the portion of the graph to the left of point  92 , this shows a short circuit voltage of 0V across the plug contact  7  while the plug contact  7  is in full contact with the receptacle contact  15 . At point  92 , the receptacle contact  15  contacts the resistive portion  12 . The resistive portion  12  permits the voltage as seen across the receptacle contact  15 , to increase gradually along the sloped (or curved) portion  93  of the graph as the plug  6  is removed from the receptacle  8 . At point  91 , the receptacle contact  15  no longer contacts the plug contact  7 . Accordingly, 5V is seen by the receptacle contact  15 . Curve  93  shows the gradual transition between points  91  and  92  which prevents voltage pulses which will prevent the introduction of errors into the system. Obviously, one skilled in the art would clearly recognize that the graph would be reversed upon insertion of a plug  6  into a receptacle  8 .  
         [0034]    The high resistance of resistive portion  12  limits the rate of flow of current from the system bus to the “cold” device being hot-plugged into the system. The evidence of too fast a current transfer is a transient voltage pulse at the connection to the operating system. The transient voltage pulse decays as it propagates along the system bus, primarily because the bus and other attached devices are sources of charge. Accordingly, the high resistance slows the charge transfer enough to provide time for the charge to be adequately replaced. If the voltage cannot dip below the sensing threshold of an adjacent device, an error cannot occur.  
         [0035]    [0035]FIG. 3 is a graph of the electrical resistance as measured from the end of the plug contact  7 . This graph is based on a resistive portion  12  of a rectangular shape 13 mils wide and 15 mils long. The high resistive material had a resistivity of 9×10 10  ohm-inches. As shown, the resistance increases as the thickness of the resistive portion  12  increases. Referring to curve  20 , when a resistive portion thickness of 8 mils is used, a resistance of 10 MW is achieved at the first end  11  of the plug contact  7 , which gradually decreases until the second end  13  is reached where the resistance is nominally zero. Curves  21 ,  22  and  23  illustrate that the resistance decreases with a decrease in resistive portion thickness. The shape of the curves also differs as the resistive portion thickness is changed.  
         [0036]    Referring to FIG. 4, the thickness of the resistive portion  12  was kept constant at 4 mils while the resistivity of the resistive portion  12  was varied. Curve  31  illustrates a high resistivity of 1.8×10 11  ohm inches. The resistance measured at the first end  11  of the plug contact  7  is almost 16 megohms, which decreases gradually to zero at the second end  13 . Curves  32  and  33  illustrate that as the resistivity of the material is decreased, the resistance measured along the plug contact  7  will also decrease.  
         [0037]    By changing both the resistivity and the thickness of the resistive portion  12 , as those skilled in the art will realize, the present invention can be adapted to different uses and applications. However, it is also extremely important to reduce the short capacitance to a negligible level. The short capacitance is reduced by keeping the thickness of the inlay  12  relatively thick, (i.e. in applying the present invention to a SCSI Bus, typically approximately 5 mils). By adjusting the resistivity and thickness of the portion, connector assemblies can be created with desirable characteristics by preventing voltage surges for various types of signals and applications.  
         [0038]    Alternative embodiments of the present invention are shown in FIGS. 5 a - 5   h.  In the embodiment depicted in FIG. 5 a,  the resistive portion  12  has a tapered profile. By varying the shape of the tapered profile  13 , the resistive transition curves that result as the receptacle contact  15  passes over the resistive portion  12  can be varied as desired for a particular application.  
         [0039]    [0039]FIG. 5 b  depicts an alternative embodiment with the resistive portion  12  in a stepwise-tapered profile  17 . By varying the steps between the steps, the resistive transition curves can be varied as desired.  
         [0040]    A third alternative embodiment is shown in FIG. 5 c.  The resistive portion  12  consists of two or more materials with varying resistivities.  
         [0041]    [0041]FIG. 5 d,  a fourth alternative embodiment shows, the resistive portion  12  extending from the conducting portion  14 . A conducting barb  18  extends from the conducting body  14  into the resistive portion  12 . A fifth alternative embodiment, FIG. 5 e,  has the resistive portion  12  extending into a hole  19  in the conducting portion  14 . As those skilled in the art will note many other variations are possible without departing from the spirit of the invention. These varying embodiments can be used for varying the resistive transition curves for differing applications.  
         [0042]    [0042]FIG. 5 f  depicts a sixth embodiment. The conductive body  14  is surrounded by a high resistive housing  30 . Receptacle contact  15  first makes contact with high resistive housing  30 . As the receptacle contact  15  makes contact with conducting portion  14 , the receptacle contact sees essentially no resistance.  
         [0043]    In FIG. 5 g,  the housing  30  is non-conductive. However, high resistive portions  12  make initial contact with receptacle contact  15 . The high resistive portions  12  are electrically connected and may be physically connected (not shown) to conducting portion  14 .  
         [0044]    [0044]FIGS. 5 h  and  5   i  depict a plug  7  having a housing  85  surrounding a first high resistance  31  portion and a second low resistance portion  32 . Upon full mating, the receptacle contact  15  is in full contact with the low resistance portion  32 .  
         [0045]    [0045]FIG. 6 illustrates that the present instant invention may also be used with the contacts on a printed circuit board. The resistive portions  70 A-N of the instant invention may be employed in one or more plug contacts  72 A-N on a conventional printed circuit board  71 . FIG. 7 shows that the present invention may be adapted to various shaped applications. For instance, a plug  83  with a cylindrical shape with a resistive portion  81  and conductive portion  82 . Receptacle contacts  84  within the receptacle  85  make contact with the resistive portion  81  prior to the conductive portion  82 .  
         [0046]    [0046]FIG. 8 illustrates some prior art electrical connectors. The size and shape of the connectors vary. As those skilled in the art will realize, the present invention can be used with the contacts within these various connectors.  
         [0047]    Although the invention has been described in part by making detailed reference to certain specific embodiments, such details are intended to be instructive rather than restrictive. It will be appreciated by those skilled in the art that many variations may be made in the structure and mode of operation without departing from the spirit and scope of the invention as disclosed in the teachings herein.