Abstract:
An improved electrical connector for connecting bus lines to a card such as a memory card or media card, including a multi-level connector comprising a latching device having a plurality of insertable latch positions that advantageously allows for selectively connecting or isolating an electrical path to an adjoining connector. The connectors of unpopulated DIMM slots are disconnected from the network along with the traces that would normally form a stub with associated undesirable signal reflections that would otherwise disturb the signal transmitted to the receiving end if not properly terminated. The contacts of the edge connector itself are used as a means to selectively connect or disconnect adjacent/downstream cards in a serially cascaded architecture. The burden of the stubs due to unpopulated card slots and the need to place one card at the far end of the network are thus eliminated.

Description:
This application is a continuation of U.S. patent application Ser. No. 13/492,115 filed on Jun. 8, 2012. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The disclosure relates generally to apparatus and techniques for mitigating signal reflections for signals in a data processing system, and more specifically relates to a connector and associated connector usage that mitigates signal reflections by eliminating stubs in a signal path. 
     2. Description of the Related Art 
     As processor speeds increase, there is a growing need to make improvements in the card and connector interface that connect to a plurality of cards and connects. As but one example, dual inline memory modules (DIMM) are plugged into various DIMM connectors on a system or motherboard to increase the amount of memory that is usable in a data processing system. The DIMM connectors are typically connected in a serial fashion on the system or motherboard, and introduce reflection-points or stubs in the electrical path or bus.  FIG. 1A  shows a traditional DIMM connector  100  without a DIMM card inserted within a cavity  115  of such DIMM connector. This DIMM connector has a plurality of attachment points  102  and  104  (only two are shown for ease in clarity) for connecting the DIMM connector  100  to a system or motherboard (not shown). The DIMM connector  100  also has a plurality of pins  106  and  108  (only two are shown for ease in clarity) for providing an electrical pathway from the attachment points  102  and  104  to a DIMM card when inserted in such DIMM connector. This connection can be seen in  FIG. 1B  that depicts a traditional DIMM connector  100  with a DIMM card  110  inserted therein. The pins  106  and  108  positively engage with wiring vias or connecting points (not shown) on the DIMM card  110 , thereby providing an electrical connection from the DIMM card  110  to the system or motherboard by way of pins  106 / 108  and attachment points  102 / 104 . 
     Certain connector assemblies for facilitating connection of a card or board inserted therein to a planar or motherboard also contemplate use of different lengths for the wires, strips, or wiring vias within the connector assembly to make it easier to insert and remove cards or boards. For example, as described in U.S. Pat. No. 4,095,866 entitled “High Density Printed Circuit Board and Edge Connector Assembly” which is hereby incorporated by reference as background material, two different strip lengths—a long strip length and a short strip length—are used to provide an electrical connection from the connector assembling to a card/board inserted into such connector assembly, as shown by elements  101 / 103  (long pins) and  105 / 107  (short pins) in  FIG. 1C , that are part of the connector assembly  109  that is attached to a system or motherboard  111 . The greater length of the spring contact members/strips reduces the force required for insertion of a card/board  113  into a cavity  115  within the connector assembly  109 . 
     A depiction of signal paths within the system or motherboard interconnected to a DIMM card is generally shown at  200  of  FIG. 2 . Here, there are two DIMM connectors  100 , specifically Connector 1 and Connector 2, with one (Connector 1) having a DIMM card  110  inserted therein, and the other (Connector 2) not having a DIMM card inserted therein. Only two representative bus signals  202  and  204  are shown for clarity, although in practice there are many bus signals including both address and data signals. The bus signals provide an electrical path between the system or motherboard and the memory devices. For example, Sig 1 element  202  provides an electrical path from the system/motherboard to Connector 1 through attachment point  102  and pin  106 . Similarly, Sig 2 element  204  provides an electrical path from the system/motherboard to Connector 1 through attachment point  104  and pin  108 . Connector 2 is arranged in a serial fashion with respect to Connector 1, and therefore Sig 1 element  202  also extends to element  102  of Connector 2 and Sig 2 element  204  also extends to element  104  of Connector 2 to provide an electrical path between the system/motherboard and Connector 2 in the event that a DIMM card were to be plugged into Connector 2 to increase memory capacity for the data processing system. Additional connectors can also be provided in this serial arrangement, and in such a case the Sig 1 element  202  and Sig 2 element  204  (as well as all other bus signals) would extend to such other connectors as indicated by the dotted lines for Sig 1 and Sig 2. 
       FIG. 3  provides a conceptual wiring view of series connections among multiple DIMM connectors on a system/motherboard at  300 , where connector pads on the system/motherboard are shown and each path includes short or long traces and vias of the system/motherboard that provide the bus nodes to each of the connectors (not shown) mounted on the system/motherboard. When all of the connectors are not populated with a DIMM card, these wiring traces and vias present stubs  302  that act as reflection points, where the electrical signal that is activated to access a given DIMM card continues to travel along wiring traces and vias to its end, and then reflects back along the same wiring path back to the signal&#39;s originating point, as is known in the art. Current solutions to this stub-reflection problem include either providing some type of impedance-terminator at the end of the stub to absorb the electrical signal at the end of the stub, or to use the very end connector as the first DIMM card that is connected/plugged-in to reduce the length of the stub. 
       FIG. 4  shows at  400  a traditional DIMM connector with the numerous pins that support the numerous bus signals used to electrical interconnect with a DIMM card (not shown) when such DIMM card is inserted into the DIMM connector by using of a latching mechanism  402 . 
     As shown above and summarized in  FIG. 5 , a problem exists when all card connectors are not populated with cards due to undesirable stub-reflections that adversely impact the maximum operational speed of the bus, thus negatively impacting overall system performance of a data processing system. Also note in  FIG. 5  that when only one DIMM is populated in position C3 shown in the far-end configuration, stubs caused by the presence of the connector fingers of C1 and C2 will still adversely effect system performance. This technique is typically used if only one DIMM were used. However, this places the DIMM further away from the driver/receiver circuitry and forces the longest signal path and thus degrades system performance due to the longer path. 
     BRIEF SUMMARY OF THE INVENTION 
     According to one embodiment of the present invention, there is provided an improved electrical connector for connecting bus lines to a card such as a memory card or media card. In particular, an apparatus is provided that comprises a multi-level connector comprising a latching device having a plurality of insertable latch positions. The multi-level connector advantageously allows for selectively connecting or isolating an electrical path to an adjoining connector thus allowing for a single card to connect with the shortest possible path to a processor or other net driving source. The connectors of unpopulated DIMM slots are disconnected from the network along with the traces that would normally form a stub with associated undesirable signal reflections that would otherwise disturb the signal transmitted to the receiving end if not properly terminated. The contacts of the edge connector itself are used as a means to selectively connect or disconnect adjacent/downstream cards in a serially cascaded architecture. The burden of the stubs due to unpopulated card slots and the need to place one card at the far end of the network are thus eliminated. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1A  depicts a conventional DIMM connector without an installed card; 
         FIG. 1B  depicts a conventional DIMM connector with an installed DIMM card; 
         FIG. 1C  depicts a conventional high-capacity connector with a plurality of connections provided within such connector; 
         FIG. 2  depicts a conventional DIMM connectivity and routing technique; 
         FIG. 3  depicts printed circuit board routing using convention DIMM placement; 
         FIG. 4  depicts a card edge connector with levers that may be used with DIMM modules or cards; 
         FIG. 5  depicts a serial daisy chain net topology having undesired stub effects; 
         FIG. 6A  depicts an embodiment with a near-end populated configuration; 
         FIG. 6B  depicts an embodiment with a two-DIMM populated configuration; 
         FIG. 6C  depicts an embodiment with a fully populated configuration; 
         FIG. 7A  depicts a front and back view of a dual in-line design; 
         FIG. 7B  depicts a side view of a dual in-line design with cards mounted in connectors at different depths; 
         FIG. 7C  depicts another side view of a dual in-line design with cards mounted in connectors at different depths; 
         FIG. 7D  depicts logical wiring between connector pins for multiple connectors in a first shunting embodiment; 
         FIG. 8  (including  FIGS. 8A and 8B ) depicts a positioning and latching arrangement that provides multiple levels or depths for a card or module installed in a connector; 
         FIG. 9A  depicts a front and back view of an alternative dual in-line design; 
         FIG. 9B  depicts a side views of the alternative dual in-line design of  FIG. 9A  with a single-contact approach in a shunting environment with finger contact through-vias; and 
         FIG. 10  depicts an alternative embodiment where the first/partial level/depth provides a shunting/closed contact for electrical connection to other connectors, and the second/full level/depth provides no contact—and thus provides electrical isolation—to other connectors to thereby mitigate undesired signal reflections. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as a system or methodology. Aspects of the present invention are described below with reference to flowchart illustrations and/or block diagrams of methods and apparatus (systems) according to embodiments of the invention. 
     Referring now to  FIGS. 6A ,  6 B, and  6 C, there is shown a near-end populated configuration, a two DIMM populated configuration, and a fully populated configuration according to a preferred embodiment, respectively, that provides an improved connector with dual-contact pins C1, C2 and C3 for connecting bus lines to a card such as a memory card or media card. In particular, an apparatus is provided that comprises a multi-level connector comprising a latching device having a plurality of insertable latch positions. In a preferred embodiment, two (2) different physical levels are provided, although more are possible. When a card/module is only partially inserted in a given connector slot, that is herein called a first level, a pair of connector pins associated with a given bus signal of the connector slot and main printed circuit board are electrically isolated from one another. When a card/module is fully inserted in a given connector slot, that is herein called a second level, a pair of connector pins associated with a given bus line of the connector slot and main printed circuit board are electrically connected together by finger contacts provided on the card/module, as will now be shown in detail. 
     Referring specifically to  FIG. 6A  and the near-end populated configuration, where a DIMM module/card  602  is provided in Slot 1, the DIMM  602  is only inserted into a first level of a multi-level connector, the first level being provided at the curved portion of pin  604  of Slot 1. Since there is no electrical continuity between pin  604  of Slot 1 and pin  606  of Slot 1 when DIMM  602  is inserted in the first or top level position of Slot 1, there is no stub that would otherwise provide undesirable signal reflections. In essence, the bus wiring for Slot 2 and Slot 3 is electrically isolated from the bus wiring for Slot 1 when DIMM  602  is only inserted down into the first level of Slot 1. 
     Referring specifically to  FIG. 6B  and the two-DIMM populated configuration, where a DIMM module/card  612  is provided in Slot 1 and a DIMM module/card  614  is provided in Slot 2, the DIMM  612  is fully inserted down into a second level of a multi-level connector, the second level being provided at the curved portion of pin  606 . The DIMM  614  in Slot 2 is only inserted into a first level of a multi-level connector, the first level being provided at the curved portion of pin  604  of Slot 2. Since there is no electrical continuity between pin  604  of Slot 2 and pin  606  of Slot 2 when DIMM  602  is inserted in the first or top level position of Slot 2, there is no stub that would otherwise provide undesirable signal reflections. In essence, the bus wiring for Slot 3 is electrically isolated from the bus wiring for Slot 1 and Slot 2 when DIMM  612  is fully inserted in Slot 2 and DIMM  614  is only inserted down into the first level of Slot 2. 
     Referring specifically to  FIG. 6C  and the fully populated configuration, where a DIMM module/card  622  is provided in Slot 1, a DIMM module/card  624  is provided in Slot 2 and a DIMM module/card  626  is provided in Slot 3, the DIMM  622  is fully inserted down into a second level of the multi-level connector, the second level being provided at the curved portion of pin  606  of Slot 1. The DIMM  624  in Slot 2 is fully inserted down into a second level of the multi-level connector, the second level being provided at the curved portion of pin  606  of Slot 2. The DIMM  626  in Slot 3 is only inserted into a first level of a multi-level connector, the first level being provided at the curved portion of pin  604  of Slot 3. Here, there is electrical connectivity between pin  604  of Slot 1 and pin  606  of Slot 1, as well as electrical connectivity between pin  604  of Slot 2 and pin  606  of Slot 2 that continues on to pin  604  of Slot 3. In essence, all of Slots 1-3 are electrically connected together in this fully populated configuration shown in  FIG. 6C . Of course, if there were more than three (3) slots, the same techniques are applicable to slots further down the serial cascaded bus. 
     Turning now to  FIGS. 7A-7C , there is shown a front view and back view in  FIG. 7A , and corresponding side views in  FIGS. 7B and 7C , of a representative dual in-line design of a DIMM memory module  702  containing a plurality of SDRAM memory modules on both sides of the DIMM memory module and associated finger contacts (preferably gold contacts, but another conductive material such as copper could also be used for the finger contacts) used to connect the DIMM module to a DIMM connector, where the above describe multi-level connectivity is provided for signals on both sides of the DIMM module. Alternatively, the Bit&lt;x&gt; bus signals could be provided on the back side of the DIMM module, and the Bit&lt;y&gt; bus signals could be provided on the front side of the DIMM module. The techniques described herein are also applicable to other types of electronic modules or cards other than a DIMM module. 
     Referring specifically to the front and back DIMM module views of  FIG. 7A , snap-in depth control slots are shown along the edges of the DIMM module that provide support for snapping the DIMM module into a DIMM connector at either a first level (partially inserted) or a second level (fully inserted), as previously described. Snap-in depth control slots  703  facilitate positioning the DIMM module at a first (partial) level/depth within a DIMM connector, and snap-in depth control slots  705  facilitate positioning the DIMM module at a second (full) level/depth within a DIMM connector. The depth control function of either slot could be interchanged. An alternate means of controlling the depth could be achieved by another method such as an insert that is placed in the socket prior to inserting the card which prevents the card from being inserted to the second level. Another method may use a pin that could be inserted through a hole or notch that limits the travel of the module and prevents it from being inserted to the second level. These two sets of slots are operable to mate with one of two corresponding protruding portions ( FIG. 8  elements  806  and  808 , respectively) of a DIMM connector that the DIMM module is inserted into, as further shown below with respect to the  FIG. 8  description. 
     Referring specifically to a representative side view shown in  FIG. 7B , where the depicted view is similar to the near-populated configuration shown in  FIG. 6A , but with multi-level connections being provided on both sides of the DIMM card. Here, a single card is shown that is inserted to a first level or depth in a given connector such that the wiring for the second connector is electrically isolated from the wiring of the first connector in similar fashion to that described above with respect to  FIG. 6A . 
     The depicted view in  FIG. 7C  is similar to the two-DIMM populated configuration shown in  FIG. 6B , but with multi-level connections being provided on both sides of the DIMM card. Here, two cards are shown that are inserted into respective DIMM connectors, where DIMM card  612  is fully inserted at a second depth or level and DIMM card  614  is partially inserted at a first depth or level such that the wiring for the second connector is electrically connected to the wiring of the first connector in similar fashion to that described above with respect to  FIG. 6B . Here, representative bus Bit(x) and Bit (y) are shown being sourced from a controller driver/receiver (not shown), and following internal printed circuit board wiring to the two connector pins  604  associated with the card inserted to the second depth. Shunts  810  each provide an electrical path—since the card is fully inserted to the second depth—between pins  604  and  606  on each side of the card, to thus provide an electrical connection from each of pins  606  back down to the printed circuit board wiring that provides an electrical path to each of pins  604  on the next connector in the serially cascaded set of connectors. While only two bits are shown for ease of clarity, there are numerous bits so configured to provide a fully functional bus that is driven by a controller driver/receiver, as will now be shown. 
       FIG. 7D  element  710  depicts a conceptual view of multiple connector pin pairs for a given connector, and the logical wiring between pads of multiple connectors connected in a serially cascaded fashion. The rectangular pads for the connectors are electrically connected to associated connector pins  604  and  606  (not shown, except for the pin numbers along the bottom of the Figure that the respective pads are associated with). Here, a controller  712  reads/writes to the bus  714 , and such signal travels along internal wiring to the first set of pins  604  of a pin pair  604 / 606  for both side 1 and side 2 of connector 1. Each of pins  606  of a pin pair  604 / 606  for both side 1 and side 2 of connector 1 are then electrically connected to respective pins  604  of a pin pair  604 / 606  for both side 1 and side 2 of connector 2, where connector 2 is configured the same as connector 1 in order to provide card insertion-level based selective electrical connectivity or isolation to another downstream connector, as previously described. 
       FIG. 8  (including  FIGS. 8A and 8B ) depicts details of the dual-level retainer portion of a connector that is operable for providing two depths or levels for inserting a card or module therein. Snap-in slots  703  for the deep (fully inserted, second) depth and snap-in slots  705  for the shallow (partially inserted, first) depth are depicted along the side of DIMM card/module  702 . When a card is partially inserted and snapped into the slots  705  as shown on the left of  FIG. 8B , contacts of long pins are made on Gold fingers  810  along the bottom portion of such Gold fingers along both the front side and back side as marked with ‘x’s on the left side of  FIG. 8A . When a card is fully inserted in the connector at the second depth/level to provide the electrical connectivity to a subsequent connector in a serially cascaded bus connection, as previously described, two rows of contacts are made as marked with ‘x’ along the bottom and the upper parts of the Gold fingers  810  as shown on the right of  FIG. 8A , providing a short between short and long pins such as is shown by elements  604  and  606  of  FIGS. 6 and 7 . 
     As shown at  820  of  FIG. 8B , DIMM module/card  702  is inserted to a first level or depth in DIMM connector  811 . A spring clip  806  of DIMM connector  811  engages with the first level snap-in depth control slot  703  to position the DIMM module/card  702  at a first depth/level. As shown at  830  of  FIG. 8B , DIMM module/card  702  is inserted to a second level or depth in DIMM connector  811 . A spring clip  808  of DIMM connector  811  engages with the second level snap-in depth control slot  705  to position the DIMM module/card  702  at a second depth/level. 
       FIGS. 9A and 9B  depict an alternative embodiment where extra-long contacts  910  are provided along the bottom edge on the front side of DIMM module/card  902  (per  FIG. 9A ), and shorter (normal) length contacts  920  are provided along the bottom edge on the back side of DIMM module/card  902  (per  FIG. 9A ). Of course, the front and back sides could be reversed or switched, where the front side has the shorter length contacts and the back side has the extra-long contacts. 
     In this embodiment shown in  FIG. 9A , a set of through-vias  930  are provided to interconnect the extra-long contacts  910  on the front side of DIMM module/card  902  to the shorter/normal length contacts  920  on the back side of DIMM module/card  902  (as can further be seen by the side views in  FIG. 9B ). In this configuration, the spring clips within the DIMM connector can be shaped/sized different than previously shown by elements  604  and  606  in  FIGS. 7B and 7C . In this shunting embodiment, as contrasted to the embodiment shown in  FIGS. 7B and 7C , the set of through-vias  930  provide electrical connection from a front side connector pin to an associated back side connector pin for a given card. Thus, the shape/size of the spring clips used in this embodiment can be different than previously shown by elements  604  and  606  in  FIGS. 7B and 7C , since a connection is provided from the front to the back side of the card using such through-vias  930 , as will now be shown. 
     For example, as shown by the configuration  950  with its associated DIMM connector  960  in  FIG. 9B , spring clip  914  includes a single v-shaped protrusion for engaging with the DIMM module/card, and spring clip  916  similar includes a single v-shaped protrusion for engaging with the DIMM module card  902 . This single-contact implementation  950  of  FIG. 9B  also shows an example of the DIMM module/card inserted in both a first and second depth. The first (partial) depth card insertion is shown by the left-side of configuration  950 , resulting in a closed contact on one side of the DIMM card  902  and an open contact on the other side of the DIMM card  902  and thus providing electrical isolation with associated stub removal. The second (full) depth card insertion is shown by the right-side of configuration  950 , resulting in a closed contact on both sides of the DIMM card  902  and thus providing electrical continuity to the next DIMM connector in the serial daisy chain but. Also shown is a representative bus bit connection  965  between a given bus signal on a daughter card and a module mounted on such daughter card, thus depicting a complete bus signal path from printed circuit board wiring to a connector that a daughter card is plugged into for electrical interconnect there between, and then from the daughter card to a module mounted on such daughter card. 
     Turning now to  FIG. 10 , an alternative embodiment is shown where the first/partial level/depth provides a shunting/closed contact for electrical connection to other connectors, and the second (full) level (depth) provides no contact—and thus provides electrical isolation—to other connectors to thereby mitigate undesired signal reflections. 
     As shown by the configuration at  1000  with its associated DIMM connector  960  in  FIG. 10 , spring clip  904  includes a v-shaped protrusion for engaging with the DIMM module/card, and spring clip  906  also includes a v-shaped protrusion for engaging with the DIMM module card  902 , but the contact point has been extended upward/higher than the previously described embodiments. This configuration at  1000  of  FIG. 10  shows an example of the DIMM module/card inserted in both a first and second depth, but with the connection/isolation functionality being reversed from what was previously described in earlier embodiments. The first (partial) depth card insertion is shown by the left-side of configuration  940 , resulting in a closed contact on both sides of the DIMM card  902  and thus providing electrical continuity to the next DIMM connector in the serial daisy chain. The second (full) depth card insertion is shown by the right-side of configuration  940 , resulting in a closed contact on both sides of the DIMM card  902  and thus providing electrical isolation with associated stub removal in this alternative embodiment. 
     Thus, illustrative embodiments of the present invention provide a computer implemented method and computer system for providing an improved connector for connecting bus lines to a card such as a memory card or media card. In particular, a multi-level connector comprising a latching device having a plurality of insertable latch positions is provided and described herewith. 
     The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiment. For example, back-drilling vias at the connector pins could further minimize the effect of those vias stubs on the printed-circuit card. The terminology used herein was chosen to best explain the principles of the embodiment, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed here. 
     The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems and methods according to various embodiments of the present invention. It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, occur substantially concurrently, or the blocks may occur in the reverse order, depending upon the functionality involved.