Patent Document

BACKGROUND  
         [0001]    This description relates to electromagnetic bus coupling.  
           [0002]    Digital devices such as memory or input/output (I/O) devices are commonly connected to communication buses through sockets that are wired to the buses. A user can insert a device into a socket and remove it as needed.  
           [0003]    Devices can also be coupled to buses electromagnetically as suggested in U.S. Pat. No. 5,638,402. That patent describes the use of connectors for an electromagnetically coupled bus that permit live insertion or withdrawal of device modules. 
       
    
    
     DESCRIPTION  
       [0004]    Each of the following figures shows only examples of one or some implementations.  
         [0005]    [0005]FIG. 1 is a three-dimensional view of a fragment of a motherboard and daughter cards mounted in sockets on the motherboard.  
         [0006]    [0006]FIG. 2 is a sectional end view of a socket on a motherboard.  
         [0007]    [0007]FIG. 3 is a sectional side view of a socket mounted on a motherboard.  
         [0008]    [0008]FIG. 4 is a three-dimensional view of the top of a fragment of a coupler.  
         [0009]    [0009]FIG. 5 is a three-dimensional view of the bottom of a fragment of a coupler.  
         [0010]    [0010]FIG. 6 is a sectional end view of another socket.  
         [0011]    [0011]FIG. 7 is a sectional end view of a portion of another socket.  
         [0012]    [0012]FIG. 8 is a block diagram of a multi-drop signal distribution system using electromagnetic couplers.  
         [0013]    [0013]FIG. 9 is an electrical model of electromagnetic couplers. 
     
    
       [0014]    As shown in FIGS. 1 and 2, in some implementations a digital device  10 , such as a memory card, may be electromagnetically coupled to a bus  14  using a socket  16  which permits insertion or removal of the digital device and provides the electromagnetic coupling between the bottom of the socket and the top of the bus across a coupling interface  12 . Additional digital devices  11 ,  13  may be inserted into additional sockets  17 ,  19  that are also electromagnetically coupled to the bus  14  at other coupling interfaces  23 ,  25  located along the length of the bus. Signals carrying, for example, data, address, and control information may then be communicated between the digital devices and a processor  21  coupled to the bus  14 . The invention is not limited to memory cards and is applicable to any kind of digital device that may need to communicate. Similarly, although we mention a processor as one example of a device with which the digital device is communicating, any sort of digital component may be communicating with the digital device.  
         [0015]    The motherboard  22  on which the processor  21  and sockets  16 ,  17 , and  19  are mounted may have multiple conductive layers separated by dielectric layers. The bus  14 , e.g., a multi-drop parallel bus, may include signal, power, and ground conductors arranged on the conductive layers of the motherboard. The signal lines (e.g.,  31 ,  33 ,  35 ) may run generally parallel along the length of the bus on the surface of the motherboard, and the ground and power may be carried on internal conductive layers of the motherboard. The reference planes on the motherboard may provide impedance control for the signal lines.  
         [0016]    Additional details of some implementations of a multi-drop signal distribution system  100  are shown in FIGS. 8 and 9 and discussed later.  
         [0017]    At each of the coupling interfaces  12 ,  23 ,  25 , the bus may include an electromagnetic coupler for each of the signal lines at that coupling interface. Example couplers  24 ,  26 ,  28  are shown in FIG. 1 at locations that are not occupied by sockets. Each of the electromagnetic couplers may interact across the interface with a corresponding electromagnetic coupler on the bottom of the sockets to permit signals to be communicated between the digital device held in that socket and the bus. A variety of configurations are possible for the couplers, including linear and zig-zag. Additional information about possible configurations of the couplers is set forth below and in U.S. patent application Ser. Nos. 09/792,502, 09/714,899, and 09/792,546, filed on Nov. 15, 2000.  
         [0018]    As shown in FIG. 3 each of the sockets may be mounted on the motherboard by inserting, for example, three sets of pins  36 ,  38 ,  40  into corresponding through-holes in the motherboard and soldering the pins to the respective conductive layers, which may include ground and power layers. Thus, some of the pins in the three sets may carry ground and power to the digital devices while other pins may only provide mechanical support.  
         [0019]    Each of the digital devices may hold one or more integrated circuits and other circuit components  41  and may carry conductors that correspond to lines of the bus and terminate at contact pads  43  along an edge of the board.  
         [0020]    Socket  16  may be similar to a typical digital device or I/O card socket and may include metal traces  50 ,  52 . The upper end  54  of each of the metal traces may be bent to form a spring that presses against a corresponding contact pad  43  when the card is inserted into the socket. At the other ends, some of the metal traces may pass through the body of the socket and form the ground and power pins of pin sets  36 ,  38 ,  40 .  
         [0021]    Others of the metal traces, which carry signals to and from the card, may have ends  61 ,  63  that are soldered to a rigid coupler  70  that is seated within a cavity  72  in the bottom of the socket  16 .  
         [0022]    As shown in FIG. 4 (seen from the top) and FIG. 5 (seen from the bottom), some implementations of the rigid coupler may include a core  80  formed of a rigid epoxy laminated glass cloth sheet, such as grade FR 4 . (FIGS. 5 and 6 show only a portion of the full width of the rigid coupler. FIG. 6 does not show the detail of the layers of the coupler.) The upper and lower faces of the rigid coupler may bear metalization layers  73 ,  75 . The lower metalization layer  75  may bear the electromagnetic coupler traces  97 ,  99 ,  101  of the electromagnetic coupler (as seen in FIG. 5). The lower metalization layer may be mechanically coupled to, but electrically isolated from, the upper metalization layer by through vias  79 ,  81  that form conductive electrical links to solder pads  83 ,  85  that are formed in the upper metalization layer (but not in contact with the rest of the upper metalization layer).  
         [0023]    The upper metalization layer  73  of the rigid coupler may provide a reference plane for impedance control of the electromagnetic coupling traces on the bottom of the rigid coupler. On the upper metalization layer, a solder mask  82  may have apertures that define areas at which solder connections are made between the termination ends  50 ,  52  of the metal traces and the solder pads  83 ,  85 . (The solder joints are not shown in FIG. 4, for clarity.) The bottom metalization layer also may bear a solder mask  84 . The solder mask layer may act as a dielectric in the electromagnetic coupler. The dielectric material characteristics may be important for coupler performance. The solder mask layer may also prevent a direct electrical connection with the traces on the motherboard.  
         [0024]    As shown in FIG. 2, a position spacer  88  may be placed in cavity  72  with its upper surface in contact with the floor  73  of the socket and its lower surface in contact with the solder mask of the rigid spacer. The spacer may have a carefully controlled thickness  74  so that when the rigid coupler is mounted on the socket and the socket is mounted on the motherboard, the coupler traces  97 ,  99 ,  101  are parallel to and a predetermined distance  90  from the electromagnetic coupler traces on the upper surface  92  of the motherboard. The spacer  88  may be designed to prevent arbitrary “floating” of the vertical position of the rigid coupler while the rigid coupler is being soldered to the socket body.  
         [0025]    To achieve the desired electromagnetic coupling at the interfaces  12 ,  23 ,  25 , any potential air gap between the respective coupler traces should be eliminated. Warping of the motherboard and shrinking of the socket body during the molding process may cause air gaps between the respective coupler traces. By applying a thickness  86  of a viscous material  89  to the bottom of the rigid coupler or to the top of the motherboard or both before the socket is mounted, the force applied to the socket when it is mounted may cause the viscous material to be squeezed and to flow to fill the air gaps. The viscous material is selected to be one that (a) has a dielectric constant similar to the dielectric constant of the substrates of the mother board and the rigid coupler, (b) has a viscosity that will achieve the filling of air gaps, its bonding strength being secondary, (c) has good temperature stability and an ability to withstand the heat associated with soldering the pins to the motherboard, and (d) is separable from the motherboard, perhaps by heating, to permit reworking of the mounting.  
         [0026]    To make the socket, the socket body  100  may be formed in a conventional way with the metal traces embedded in the body. High temperature solder balls may be placed on the upper surface of the rigid coupler. The position spacer may be placed in the cavity. The rigid coupler may be placed in the cavity touching the spacer and a clamping force may be applied to hold the rigid coupler in place against the bottom face of the spacer. Heat may be applied to reflow the solder. After the socket is formed, it may be attached to the motherboard by applying the thickness of viscous material, placing it on the board with the pin sets in through-holes of the motherboard, and soldering the pins to the motherboard.  
         [0027]    In use, the digital device may be repeatedly inserted in and removed from the socket. Once inserted the signals can pass across the electrometrically coupled interface.  
         [0028]    As shown in FIGS. 8 and 9, some implementations of a multi-drop bus system may include a device  110  and other devices  120 ,  130 , and  140 . Device  110  may have a bus  112  coupled to device  110 . Devices  120 ,  130 , and  140  may each comprise a bus  122 ,  132 , and  142 , respectively, and a component  124 ,  134 , and  144 , respectively. Buses  122 ,  132 , and  142  may be coupled to components  124 ,  134 , and  144 , respectively.  
         [0029]    Devices  120 ,  130 , and  140  are each electromagnetically coupled to bus  112  by an electromagnetic coupler  160 ,  170 , and  180 , respectively. Electromagnetic couplers  160 ,  170 , and  180  electromagnetically couple buses  122 ,  132 , and  142 , respectively, to bus  112 , allowing components  124 ,  134 , and  144 , respectively, to communicate with device  110 . Electromagnetically coupling each device  120 ,  130 , and  140  to bus  112  forms a data channel having substantially uniform electrical properties for transferring signals among devices  110 ,  120 ,  130 , and  140  and allows use of relatively high frequency signaling without significantly increasing noise attributable to transmission line effects.  
         [0030]    Although illustrated with three devices  120 ,  130 , and  140  electromagnetically coupled to bus  112 , bus  112  may have any suitable length and may accommodate any suitable number of devices to be electromagnetically coupled to bus  112 . For one embodiment, bus  112  is approximately  50  centimeters (cm) in length, allowing up to  16  devices each to be electromagnetically coupled along approximately  1  cm of the length of bus  112  with each device spaced on a pitch of approximately 1.5 cm.  
         [0031]    Each device  120 ,  130 , and  140  maybe fixedly coupled to bus  112  or, alternatively, may be removably coupled to bus  112 . As devices  120 ,  130 , and  140  are electromagnetically coupled to bus  112 , each device  120 ,  130 , and  140  may be added to or removed from bus  112  with minimized effect on the communication bandwidth of bus  112 .  
         [0032]    Buses  112 ,  122 ,  132 , and  142  may each comprise any suitable number of lines of any suitable conductive material. Devices  110 ,  120 ,  130 , and  140  may each comprise any suitable circuitry to perform any suitable function. As one example, device  110  may comprise a memory controller and devices  120 ,  130 , and  140  may each comprise a memory module, for example. Devices  110 ,  120 ,  130 , and  140  may communicate over buses  112 ,  122 ,  132 , and  142  using any suitable signaling scheme. Each device  110 ,  120 ,  130 , and  140  for one embodiment communicates using differential signal pairs to help minimize power and electromagnetic interference (EMI) and to help increase noise immunity.  
         [0033]    Each component  122 ,  132 , and  142  may comprise any suitable circuitry. Each component  122 ,  132 , and  142  for one embodiment serves as an interface for each device  120 ,  130 , and  140  to communicate with device  110 .  
         [0034]    Although illustrated in multi-drop signal distribution system  100 , each device  120 ,  130 , and  140  for another embodiment may communicate with device  110  in a point-to-point manner by electromagnetically coupling each device  120 ,  130 , and  140  to a respective bus coupled to device  110 .  
         [0035]    For one embodiment, as illustrated in FIG. 8, electromagnetic coupler  160  is formed by a portion  162  of the length of bus  112 , a portion  164  of the length of bus  122 , and a dielectric  166  between portions  162  and  164 . Electromagnetic coupler  170  is formed by a portion  172  of the length of bus  112 , a portion  174  of the length of bus  132 , and a dielectric  176  between portions  172  and  174 . Electromagnetic coupler  180  is formed by a portion  182  of the length of bus  112 , a portion  184  of the length of bus  142 , and a dielectric  186  between portions  182  and  184 . Each dielectric  166 ,  176 , and  186  may comprise any suitable dielectric material such as, without limitation, air, various polyimides, various epoxies, various polymeric materials, various plastics, various ceramics, polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE) such as Teflon® by E. I. du Pont de Nemours and Company of Wilmington, Del., RT/Duroid® by World Properties, Inc. of Lincolnwood, Ill., and/or alumina, for example. Each electromagnetic coupler  160 ,  170 , and  180  may be formed to have any suitable coupling coefficient, such as in the range of approximately 0.15 to approximately 0.45 for example.  
         [0036]    [0036]FIG. 9 illustrates, for one embodiment, an electrical model  100  for electromagnetic coupler  160  coupling a single conductive line  212  of bus  112  and a single conductive line  222  of bus  122 , for electromagnetic coupler  170  coupling line  212  of bus  112  and a single conductive line  232  of bus  132 , and for electromagnetic coupler  180  coupling line  212  of bus  112  and a single conductive line  242  of bus  142 .  
         [0037]    Line  212  is terminated with a parallel resistor  216  coupled between the end of line  212  distant from device  110  and a suitable voltage reference, such as ground for example. Resistor  216  for one embodiment has a resistance approximately equal to the characteristic impedance of line  212 . Line  222  is terminated with a parallel resistor  226  coupled between the end of line  222  distant from device  120  and a voltage reference. Resistor  226  has a resistance approximately equal to the characteristic impedance of line  222 . Line  232  is terminated with a parallel resistor  236  coupled between the end of line  232  distant from device  130  and a voltage reference. Resistor  236  has a resistance approximately equal to the characteristic impedance of line  232 . Line  242  is terminated with a parallel resistor  246  coupled between the end of line  242  distant from device  140  and a voltage reference. Resistor  246  has a resistance approximately equal to the characteristic impedance of line  242 . Lines  212 ,  222 ,  232 , and  242  are each terminated with a matched impedance for transmitting relatively high frequency signals.  
         [0038]    As device  110  transmits a signal on line  212 , a corresponding signal is induced on lines  222 ,  232 , and  242  through electromagnetic coupler  160 ,  170 , and  180 , respectively, due to the electromagnetic fields generated by driving the signal on line  212 . Similarly, as component  124 ,  134 , or  144  transmits a signal, on line  222 ,  232 , or  242 , respectively, a corresponding signal is induced on line  212 .  
         [0039]    Lines  222 ,  232 , and  242  each absorb only a fraction of the power of a corresponding signal driven on line  212 . Each line  222 ,  232 , and  242  terminates the received power using resistor  226 ,  236 , and  246 , respectively. Similarly, line  212  absorbs only a fraction of the power of a corresponding signal driven on line  222 ,  232 , and  242 . Line  212  terminates the received power using resistor  216 . Each electromagnetic coupler  160 ,  170 , and  180  may absorb any suitable amount of power depending, for example, on the amount of driven power and the coupling coefficient of the electromagnetic coupler. Each electromagnetic coupler  160 ,  170 , and  180  for one embodiment absorbs less than approximately one percent of the power of a signal driven on any line coupled to the electromagnetic coupler. Because any capacitive load of devices  120 ,  130 , and  140  and their respective lines  222 ,  232 , and  242  are isolated from one another and from line  212 , a generally constant impedance environment may be maintained on line  212  and any disturbance or impact of communication system parasitics on lines  212 ,  222 ,  232 , and  242  is minimized or avoided.  
         [0040]    Bus  112  for one embodiment is mounted on or integrated in a circuit board, and device  110  is mounted on or otherwise coupled to the circuit board such that device  110  is electrically coupled to bus  112 . Each electromagnetic coupler  160 ,  170 , and  180  is formed by positioning bus portions  164 ,  174 , and  184 , respectively, relative to bus portions  162 ,  172 , and  182  with dielectric  166 ,  176 , and  186  between the electromagnetically coupled portions.  
         [0041]    Among the advantages of the invention are one or more of the following. The socket need not take up any more space (or require any more spacing from socket to socket) on the motherboard than a conventional non-electromagnetically coupled socket mounted on a conventional motherboard. The space on the motherboard need not be reallocated to accommodate the socket. Existing memory component packaging configurations can be used. The socket is rigid and therefore provides reliable and stable mechanical performance. The socket can be made and installed simply and at low cost.  
         [0042]    Although the above description mentions some implementations, other implementations are also within the scope of the following claims.  
         [0043]    For example, a reference plane may not be required on the rigid coupler if the metal trace is made short enough and with a low enough profile spring contact The length of the spring may be optimized by simulation so that its effect on rise time of a high speed signal will be minimized. The exact length of the spring may be determined by system requirements on output rise time and by the available IC technology on input rise time. Through such optimization, the uncontrolled impedance of the metal spring will have limited overall effect on electrical performance. Otherwise, measures such as a reference plane molded inside the socket frame may have to been taken for full impedance control.  
         [0044]    In addition, the spring shape may be changed to reduce friction force during digital device insertion since the friction force (vertical force) is exerted onto interconnects between the spring and the rigid coupler, which may increase the likelihood of solder ball damage.  
         [0045]    In laptop computers and some servers, digital devices are often mounted parallel to the motherboard to minimize the projection of the cards above the motherboard. As shown in FIG. 6, in some implementations, a low-profile version of the socket can be constructed with an insertion slot  121  that is oriented horizontally rather than vertically. The bottom portion of the socket and the rigid coupler are similar to the ones described earlier, but the metal traces  123 ,  125  on the two sides of the connector may have different contours as shown.  
         [0046]    As shown in FIG. 7, in alternative implementations for the rigid coupler, instead of soldering the terminations of the metal traces to the upper surface of the coupler and making electrical connections by vias to the coupler traces on the bottom of the rigid coupler, the metal traces may be soldered into plated-through holes  140 ,  142  in the core and in that way make direct contact to the coupler traces  146 . Such an arrangement may avoid possible reliability concerns about the soldered joints between the metal trace terminations and the top of the rigid connector described earlier.  
         [0047]    Although the implementations described above refer to memory cards, and motherboards of computers, the socket arrangement may be used in any environment in which an insertable device is to be electromagnetically coupled to a bus for communication of signals.

Technology Category: 5