Abstract:
Switchable grounded terminal loads are built into, or otherwise coupled to, connectors on motherboards and control devices. The terminal loads are coupled to the bus termination at the connector when the connector is “stuffed” (connected to a mating connector). The switchable grounded terminal loads replace dummy connectors in preventing empty “unstuffed” connectors from increasing error risks on active channels.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority from U.S. Non-Prov. patent application Ser. No.  14 / 757 , 951  filed Dec.  26 ,  2015  which is entirely incorporated by reference herein. 
     
    
     FIELD 
       [0002]    Related fields include electrical connectors, and more particularly techniques for controlling impedance in empty slots, tabs, plugs, or sockets connected to central processing units (CPUs) or other processors or controllers. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0003]      FIG. 1  is a block diagram of stuffed (connected) and unstuffed (empty) fixed connectors on a motherboard. 
           [0004]      FIG. 2  is a state diagram for a connector with a switchable terminated load. 
           [0005]      FIGS. 3A-3C  illustrate a terminal load engaged and disengaged by spring forces in a compression clip. 
           [0006]      FIGS. 4A-4B  are views of a mechanical switch. 
           [0007]      FIG. 5  is a connector with switchable grounded terminal loads on two receptacle walls. 
           [0008]      FIG. 6  is an adaptation of the two-switch, two-load schema for male fixed connectors. 
           [0009]      FIG. 7  is a connector with a single switchable terminal load. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    For purposes herein, the following terms shall be associated with the following definitions: 
         [0011]    Detachable Connector: A connector that can engage to, and disengage from, a Fixed Connector; for example, a tab on a memory card that mates with a slot on a motherboard or a plug at the end of a cable that mates with a socket in a device housing. 
         [0012]    Fixed Connector: A connector permanently attached, directly or through a cable, to a controlling component such as a motherboard or a controlling device such as a desktop computer or mobile phone which may or may not be accessible through a device housing. 
         [0013]    Computers and electronic devices are made with various fixed connectors both inside and outside the housing. Connectors accessible only from inside the housing provide flexibility for manufacturing, upgrading, and repair. For example, a motherboard may have several expansion slots for memory cards, audio/video cards, networking cards, and the like. The same motherboard may be installed with most of the expansion slots empty in a basic model, or with most of the expansion slots full in a higher-end model. An end user who initially buys a basic model can fill up more of the expansion slots later to improve or expand functionality. If either a card or a slot is damaged, the bad card may be swapped for a good card or the good card may be moved from the bad slot to an empty good slot. Storage devices that can be easily attached to and detached from motherboards provide similar configuration flexibility. 
         [0014]    Connectors accessible from outside the housing enable connection of the device to peripheral devices, peer devices, and networks. Portable devices in particular may be connected to, and disconnected from, multiple power sources, display devices, scanners, printers, keyboards, mice, and docking stations several times a day. 
         [0015]    In many devices, some of the fixed connectors are likely to be disconnected (empty, or “unstuffed”) at any given time. Some systems may tolerate emptiness of some types of fixed connectors, but others may increase noise, degrade signal quality, or cause other problems that would be absent if the connector were connected (occupied, or “stuffed”). Accordingly, passive “dummy” cards or plugs are made for a variety of connector types. They do not add any new functionality to the device, but they provide a terminal load, sometimes with grounding, so that the fixed connector performs as if it were engaged with a detachable connector rather than being empty. Although they remedy some of the problems, dummy cards may add significant cost to the system. 
         [0016]    To avoid exposing unconnected pins and plugs to external environments or foreign objects, many fixed connectors may be female, with recessed electrical contacts. However, embodiments of the disclosed concepts may be adapted for fixed male connectors as well as fixed female connectors. 
         [0017]      FIG. 1  is a block diagram of stuffed (connected) and unstuffed (empty) fixed connectors on a motherboard. The baseboard routing  101  is shown connecting the CPU  105  to each of a pair of T-topology buses  109 . 1  ad  109 . 2 . 
         [0018]    The branches of T-topology bus  109 . 1  terminate in one of the simplest fixed connector types. The fixed connector  102  is “stuffed,” i.e., a mating detachable connector  103 . 1  having one or more pins or contacts is engaged with fixed connector  102 . The fixed connector  104  is “unstuffed,” i.e., empty or unconnected. The absence of a contact leaves termination  107  “floating,” i.e., unloaded and ungrounded. 
         [0019]    Floating termination  107  may introduce an impedance mismatch that degrades the performance of T-topology bus  109 . 1  and increases the risk of error for the component connected to CPU  105  by detachable connector  103 . 1  and stuffed fixed connector  102 . For example, some dual in-line memory modules (DIMMs) may have a “Low” (0-1%) risk of write errors and a “Medium” (1-10%) risk of read errors on a T-topology bus  109 . 1  if both fixed connectors are stuffed, but if one fixed connector is unstuffed the risk of both read and write errors may increase to “High” (10-50%). Changing the design of T-topology bus  109 . 1  for better performance with one stuffed fixed connector  102  and one unstuffed fixed connector  104  may unsatisfactorily compromise the bus performance with two stuffed fixed connectors while never quite reaching the desired performance level with one stuffed and one unstuffed. 
         [0020]    At the terminations of T-topology bus  109 . 2 , stuffed fixed connector  112  and unstuffed fixed connector  114  eliminate floating terminations. Grounded terminal loads  119 . 1  and  119 . 2  are switchably coupled to the terminations of T-topology bus  109 . 2 . The switch  117 . 1  is open when the fixed connector  112  is stuffed with detachable connector  103 . 2 , disconnecting grounded terminal load  119 . 1  from its branch of T-topology bus  109 . 2  so that the only connection of stuffed fixed connector  112  is with detachable connector  103 . 2 . Stuffed fixed connector  112  may thus behave like conventional stuffed fixed connector  102 . The unstuffed fixed connector  114  has switch  117 . 2  that is closed so that its termination of T-topology bus  109 . 2  is connected to grounded terminal load  119 . 2  instead of floating. The grounded terminal load  119 . 2  may be designed to match the impedance of detachable connector  103 . 2  so that T-topology bus  109 . 2  may behave as if both fixed connectors are stuffed even if one or both fixed connectors are in fact unstuffed. 
         [0021]    The grounded terminal loads  119 . 1 ,  119 . 2  are illustrated as schematic resistors, but in some embodiments they may include other types of impedance-matching components, depending on the characteristics of detachable connector  103 . 2 . The grounded terminal loads  119 . 1 ,  119 . 2  and/or switches  117 . 1 ,  117 . 2  may be positioned in, on, or around fixed connectors  112 ,  114  in any suitable location and orientation. Additionally, in some embodiments, switches  117 . 1 ,  117 . 2  may be actuated by any convenient effect that may be made to coincide with engagement and disengagement of the detachable connector  103 . 2  from the fixed connector  112 . In some embodiments, switches  117 . 1 ,  117 . 2  actuate mechanically, such as by a spring which has the advantage of not requiring any added electrical power to operate the switch. 
         [0022]    For example, detachable connector  103 . 2  may be the connector tab on a memory card, e.g., a DIMM card. In some embodiments, detachable connector  103 . 2  may be a connector tab for an audio-visual (A/V) card, an option card, a graphics card, a Peripheral Component Interconnect Express (PCIe) card, a PCIe card raiser. In other embodiments, detachable connector  103 . 2  may be a Serial AT Attachment (SATA) detachable connector. In yet other embodiments, detachable connector  103 . 2  may be a Universal Serial Bus (USB) plug or a DisplayPort (DP) plug. 
         [0023]      FIG. 2  is a state diagram for a connector with a switchable terminated load. In state  202  (e.g., when initially installed), the grounded terminal load is engaged by default and the fixed connector is terminated and grounded. State  202  may be a default state whenever the system power is on and the fixed connector is unstuffed. In some embodiments, state  202  may persist when the power is off and the fixed connector is unstuffed, to make it the default power-up state. 
         [0024]    Stimulus  203 , in which the detachable connector is engaged (optionally followed by stimulus  205 , in which an actuator opens the switch), triggers a state change to state  206 , in which the fixed connector is disconnected from the grounded terminal load. From there, stimulus  207 , in which the detachable connector is disengaged (optionally followed by stimulus  209 , in which the actuator closes the switch, triggers a state change back to state  202 ). The actuator inputs are optional because some embodiments change states without requiring an “actuator” per se as a separate part. In such embodiments, the switching is actuated by a mechanical reaction of existing parts to the insertion or removal of the detachable connector. 
         [0025]      FIGS. 3A-3C  illustrate a terminal load engaged and disengaged by spring forces in a compression clip.  FIG. 3A  is a perspective view of stuffed and unstuffed fixed connectors with cutaways to show interior compression clips. These connectors are generic and not intended to represent any particular manufacturer&#39;s product. Fixed connectors  312  and  314  are mounted on baseboard  301 , which may be, for example, a printed circuit board (PCB). They may be enclosed in casings  342  and  344  with (or, alternatively, without) end latches  332 . 1 ,  332 . 2 ,  334 . 1 , and  334 . 2 . 
         [0026]    Inside the casings  342 ,  344  (which are shown partially cut away to show the interior structure), the fixed connectors  312  and  314  may include spring-loaded clips with compression jaws  322 . 2 ,  324 . 2 . The detachable connector  303  may be a tab extending from another PCB or a packaged module. Clip jaws  322 . 1 ,  322 . 2  of stuffed fixed connector  312  expand to admit detachable connector  303  and exert a compressive restoring force to hold detachable connector  303  securely in place. Latches  332 . 1  and  332 . 2  are shown in a horizontal locked position, which also acts to hold the detachable connector in place. 
         [0027]    In some embodiments, fixed connectors  312  and  314  may include conductive pins or leads such as fixed connector contacts  352 ,  354 . In stuffed fixed connector  312 , fixed connector contacts  352  make electrical contact as well as mechanical contact with detachable connector contacts  313  (e.g., pins or “goldfingers”) of detachable connector  303 . For simplicity, very short connectors with only a few pins are illustrated, but those skilled in the art understand that the same type of connector may be made in a variety of lengths with varying numbers of pin, strip, or similar connections. 
         [0028]    In unstuffed fixed connector  314 , the absence of a detachable connector allows clip jaw  324 . 2  to relax to an equilibrium position angled further toward a longitudinal midplane than the position of clip jaw  322 . 2 . The latches  334 . 1  and  334 . 2  are shown tilted outward from the ends, which position allows the detachable connector to be inserted or released. 
         [0029]      FIG. 3B  is a sectional view of stuffed fixed connector  312  through section A-A of  FIG. 3A , omitting the casing. In some embodiments, fixed connector contacts  352  may be connected to vias  311  that extend through one or more layers of baseboard  301 . The grounded terminal load for stuffed fixed connector  312  may include terminal contact  309 , impedance element  319 , and ground connection  329 . In some embodiments, ground connection  329  may connect to a ground plane of baseboard  301 . 
         [0030]    When detachable connector  303  is inserted in the clip, it exerts expansion force  310  on clip jaws  322 . 1  and  322 . 2 . Clip jaws  322 . 1  and  322 . 2  “push back” with a restoring force to hold detachable connector  303  in place, but are held too far apart by detachable connector  303  to touch terminal contacts  309 . Therefore, when fixed connector  312  is stuffed, the fixed connector contacts  352  connect only with the detachable connector contacts  313 , and the grounded terminal load is unconnected to the fixed connector contacts  352 . 
         [0031]      FIG. 3C  is a sectional view of unstuffed fixed connector  314  through section A-A of  FIG. 3A . When detachable connector  303  is absent from the clip, it exerts no expansion force on clip jaws  324 . 1 ,  324 . 2 . Without that opposing force, restoring force  320  pushes clip jaws  324 . 1 ,  324 . 2  inward toward their equilibrium position. Somewhere along the path of relaxation of clip jaws  324 . 1 ,  324 . 2 , the fixed connector contacts  354  touch terminal contacts  309 . Therefore, whenever fixed connector  314  is unstuffed, the restoring force of clip jaws  324 . 1 ,  324 . 2  automatically connects the grounded terminal load  309 ,  319 ,  329 , terminating the fixed connector contacts  352  so that unstuffed fixed connector  314  does not have a floating termination. 
         [0032]      FIGS. 4A-4B  are views of a mechanical switch. The switches shown in the figures may be made small enough to build into some types of connectors.  FIG. 4A  shows two different magnifications of part of an unstuffed fixed connector with the switch closed to connect the terminal load. Unstuffed fixed connector  414  includes a cavity  444 . Cavity  444  holds two arms, stationary arm  424  and moveable arm  434 , that constitute the switch. The moveable arm  434  has a first conductive contact  433 , which in unstuffed fixed connector  414  touches a second conductive contact  423  on stationary arm  424 . When the first conductive contact  434  and the second conductive contact  424  are touching, current can flow between stationary arm  424  and moveable arm  434 . One of stationary arm  424  or moveable arm  434  may be connected to a grounded terminal load (not shown). Moveable arm  434  also features a bend  435  that protrudes through an opening into receptacle  454  of unstuffed fixed connector  414 , where the detachable connector is normally inserted with a running-and-sliding fit or an interference fit, depending on the type of connector. 
         [0033]      FIG. 4B  shows two different magnifications of part of a stuffed fixed connector with the switch open to disconnect the terminal load. Detachable connector  403  is inserted in the receptacle of fixed connector  412  using downward pressure  410 . When detachable connector  403  encounters bend  435  of moveable arm  434 , it pushes bend  435  out of the receptacle and back into the cavity in direction  420 . Meanwhile, second contact  423  is held in place by locating feature  422  in the cavity wall of the connector body. The rigidity of moveable arm  434 , including bend  435 , moves the first contact  433  off of and away from second contact  423  in direction  430 , thereby opening the switch and disconnecting the grounded terminal load (not shown in this view). 
         [0034]    Materials for the first contact and second contact may be any conductive material that can withstand the expected number of couplings and uncouplings over the life of the connector. Gold or silver may be chosen for connectors that are connected and disconnected less often. Copper, aluminum, or harder alloys containing gold or silver may be preferred where connecting and disconnecting will be done more often. The bend and contact-end section of the moveable arm may preferably be a rigid material for repeatable motion while the section of the moveable arm below the bend may either provide an elastic restoring force itself (e.g., work-hardened metal) or be rigid and coupled to a spring that provides the restoring force. 
         [0035]      FIG. 5  is a connector with switchable grounded terminal loads on two receptacle walls. The connector  512  has switches on opposing sides of receptacle  554 . Alternatively, switches may be on adjacent walls; preference may depend on the location of the bus terminations that benefit from termination loads. Unstuffed connector  512  has a pair of mirror-image cavities  544 . 1  and  544 . 2 . Each one has a stationary arm  524 . 1  or  524 . 2  connected to a terminal load that includes an impedance element  519 . 1  or  519 . 2  and a ground connection  529 . 1  or  529 . 2 . The grounded terminal loads  519 . 1 + 529 . 1 ,  519 . 2 + 529 . 2  may be coupled to either the stationary arms  524 . 1 ,  524 . 2  or the movable arms  534 . 1 ,  534 . 2 . However, in some embodiments, it may be preferable to use the stationary arm  524 . 1 ,  524 . 2  to avoid transferring repeated stresses to the grounded terminal loads  519 . 1 + 529 . 1 ,  519 . 2 + 529 . 2 . 
         [0036]    While receptacle  554  is empty, first contacts  533 . 1  and  533 . 2  on movable arms  534 . 1 ,  534 . 2  will touch second contacts  523 . 1  and  523 . 2  on stationary arms  524 . 1  or  524 . 2  to provide electrical couplings to the grounded terminal loads  519 . 1 + 529 . 1 ,  519 . 2 + 529 . 2 . If detachable connector  503  is inserted in receptacle  554 , it will displace two bends  535 . 1  and  535 . 2  of moveable arms  534 . 1  and  534 . 2 . When bends  535 . 1  and  535 . 2  are pushed back into cavities  544 . 1 ,  544 . 2 , first contacts  533 . 1  and  533 . 2  on movable arms  534 . 1 ,  534 . 2  will move away from second contacts  523 . 1  and  523 . 2  on stationary arms  524 . 1  or  524 . 2  to eliminate electrical couplings to the grounded terminal loads  519 . 1 + 529 . 1 ,  519 . 2 + 529 . 2 . 
         [0037]      FIG. 6  is an adaptation of the two-switch, two-load schema for male fixed connectors. At this writing, a majority of fixed connectors are female because the recessed contacts on a female connector are less exposed, and thereby may be less vulnerable to accidental shorting and other problems. However, the disclosed approach may also work with male fixed connectors. 
         [0038]    Connector  614  is a male connector compatible with mating connector  613 . Instead of an inner receptacle, the space to be occupied by the mating connector  613  is an outer perimeter  664 . The configuration may be very much like  FIG. 5 —dual mirror-image cavities  644 , stationary arms  624 , first contacts  623 , moveable arms  634 , second contacts  633 , impedance elements  619 , and ground connections  629 —except that the bends and openings face outward rather than inward. Bends may be replaced with solid (e.g., molded) tabs  645  in any of the designs. 
         [0039]      FIG. 7  is a connector with a single switchable terminal load. This approach may be especially suitable for slots that mate with tabs  703  with contacts  713  on the side, so that the bottom surface may be used to switch the terminal load, which may include impedance element  719  and ground connection  729 . This terminal load is coupled to stationary arm  724  at a right angle. As with the other illustrated examples, bend  735  in moveable arm  734  protrudes into the space for the currently absent mating connector  703 , and first contact  733  touches second contact  723  to close the switch and couple the bus termination(s) to the terminal load. When inserted, mating connector  703  will push bend  735  down to move first contact  733  away from second contact  723  to decouple the connector from the grounded terminal load. 
         [0040]    Non-limiting examples of the types of connectors that could potentially be customized with switchable terminal loads include Peripheral Component Interconnect Express (PCIe), USB, DisplayPort, SATA, raiser, option cards, and AN boards. Models predicted that connectors with switchable terminal loads yield about the same error rate as connectors with more expensive dummy mating connectors installed. 
         [0041]    The preceding Description and accompanying Drawings describe examples of embodiments in some detail to aid understanding. However, the scope of protection may also include equivalents, permutations, and combinations that are not explicitly described herein. Only the claims appended here (along with those of parent, child, or divisional patents, if any) define the limits of the protected intellectual-property rights.