Abstract:
An adapter for interconnecting a Small Form Factor Pluggable (SFP) transceiver into a receptacle configured to receive a Small Form Factor (SFF) transceiver. The innovative adapter provides an interface for connecting an SFP transceiver to an SFF receptacle (e.g. footprint) on a printed circuit board. This enables manufacturers and customers with printed circuit boards originally designed to receive and interoperate only with SFF transceivers, to replace SFF transceivers with newer SFP transceiver models through the use of the innovative interface described herein.

Description:
TECHNICAL FIELD 
   The present invention relates generally to optical transceivers, and more particularly, to connecting optical transceivers to printed circuit boards. 
   BACKGROUND 
   Optical transceivers are electro-optic devices that generally convert optical signals from a fiber optic cable into electrical signals, and vice versa. Optical transceivers are typically used as an interface between a fiber optic cable and a communication device, such as a communications node in a network and as such is usually mounted (i.e., attached) to a printed circuit board of a communication device as well as a fiber optic cable. 
   The way in which transceivers are attached to a printed circuit board is usually controlled by an industry standard. Industry standards ensure that each manufacturer of a transceiver meets certain criteria to ensure consistency for designs of printed circuit boards configured to receive the transceiver and interchangeability of transceivers among different manufacturers of transceivers. For instance, industry standards typically govern the size of a transceiver, packaging (if any) for retaining the transceiver, and its input and output (I/O) pin configurations including: the number of pins, spatial relation of each pin, electrical signal assignments for each pin, and so forth. Each industry standard inherently controls how to interface (i.e., to connect) the transceiver to a printed circuit board. For example, holes of a receptacle located on the printed circuit board for receiving pins of a transceiver or transceiver housing, must be complementary and align with the pins of the transceiver or transceiver housing. Additionally, the receptacle holes must align electrically with the signal assignments of the pins of a transceiver or transceiver housing. 
   Most transceivers are either manufactured in accordance with one of two industry standards: the Small Form Factor (SFF) or Small Form Factor Pluggable (SFP). Transceivers manufactured in accordance with the SFF industry standard (“SFF transceivers”) are typically electrically and mechanically mounted directly to a printed circuit board. That is, the leads or pins of the SFF transceiver are soldered directly to a printed circuit board. The pins of the SFF transceiver are soldered to holes of a complimentary receptacle on the printed circuit. The holes of the printed circuit board are typically connected to conductive traces contained within the printed circuit board. 
   Increasingly, transceivers are being manufactured in accordance with the SFP standard (“SFP transceivers”). SFP transceivers have an advantage over SFF transceivers, as the SFP transceiver slides inside a housing and plugs into a connector located in the housing without the need for soldering or pin alignment. Accordingly, the SFP transceiver can be field replaced simply by pulling the SFP transceiver out of the housing and plugging in a replacement SFP transceiver. The housing and connector are mated to the printed circuit board, by mechanical and electrical mechanisms. Accordingly, when updates or improvements are made to a transceiver design, it can be installed onto the printed circuit board simply by pulling an older version of the SFP transceiver out of the SFP housing and inserting the updated version therein. 
   Unfortunately, customers that have printed circuit boards designed to connect with SFF transceivers cannot take advantage of the newer SFP transceivers, because the SFF and SFP transceiver footprints are not compatible with one another. That is, the housing and connector of an SFP transceiver has pins and fastening mechanisms that are not aligned with the holes of a receptacle configured to accept an SFF transceiver. Accordingly, replacing the SFF transceiver with an SFP transceiver is not possible, because even if the SFF transceiver is removed from the board, the SFP transceiver housing&#39;s footprint, and electrical pin assignment is incompatible with a receptacle on a printed circuit board configured to receive a SFF transceiver. 
   One possible solution to this problem involves redesigning the artwork of the printed circuit board and replacing the old SFF compliant printed circuit boards in their entirety. However, to design such a printed circuit board and replace the older ones is time consuming, expensive and inconvenient. This is especially problematic if there are multiple product lines each having different printed circuit board designs and sizes, as each must be customarily redesigned to include an SFP transceiver. 
   SUMMARY 
   To address the above-discussed deficiencies of the prior art, the present invention provides an adapter for interconnecting a Small Form Factor Pluggable (SFP) transceiver to a circuit pack of a communications device having a footprint intended to receive a Small Form Factor (SFF) transceiver. 
   In one exemplary implementation, the adapter includes a footprint that is formatted to accept complementary connector elements of an SFP transceiver housing/SFP connector, and is configured to electrically and mechanically connect with the SFP transceiver housing/SFP connector. The adapter may also include an SFF connector having leads that are complementary to a footprint formatted for SFF transceivers. The leads of the SFF connector are configured to electrically and mechanically connect with the SFF footprint on the printed circuit board. An electrical module of the adapter provides an electrical communication path between an SFP transceiver and the SFF footprint on the printed circuit board when an SFP transceiver is disposed in the SFP transceiver housing and connected to the SFP connector, and the SFF leads are connected to the receptacle of the printed circuit board. 
   As a result of using the innovative adapter described herein, manufacturers and customers can utilize printed circuit boards (such as motherboards of a communications device) originally designed to receive and interoperate only with SFF transceivers, to function now with newer SFP transceiver models. The adapter further eliminates the conventional problems of having to redesign printed circuit boards designed to function with SFF transceivers, which is a time consuming and costly process. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. It is emphasized that various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. Reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  illustrates a top view of a conventional circuit pack such as a motherboard for a communications device. 
       FIG. 2  shows a side-view of a conventional SFF transceiver. 
       FIG. 3  is a side view of an SFP transceiver housing with SFP transceiver and fiber optic cable installed. 
       FIG. 4  illustrates an exploded isometric view of an embodiment of the innovative adapter. 
       FIG. 5  is a high-level block diagram of the electrical module providing an interface between a circuit pack and an SFP transceiver when the SFP transceiver is inserted in an SFP transceiver connector. 
       FIG. 6  is a schematic block diagram of one embodiment of an electrical module. 
       FIG. 7  is an isometric view of the innovative adapter from the perspective of the connector side of the adapter. 
   

   DETAILED DESCRIPTION 
     FIG. 1  illustrates a top view of a conventional circuit pack  100  such as a motherboard for a communications device. Circuit pack  100  is typically a printed circuit board or card on which components  102  may be mounted and interconnected to provide a functional unit of the communications device when installed therein. Circuit packet  100  includes a Small Form Factor (SFF) transceiver footprint  104  (“SFF footprint”) configured to receive a conventional SFF transceiver. 
     FIG. 2  shows a side-view of a conventional SFF transceiver  202 . With reference to  FIGS. 1 and 2  two rows of holes  106 ( 1 ) and  106 ( 2 ) of SFF footprint  104  are spatially arranged in direct alignment with two rows of pins  204  (only one row can be seen in the side view of  FIG. 2 ) of a SFF transceiver  202 . In other words, holes  106 ( 1 ) and  106 ( 2 ) are complementary in terms of spatial, mechanical and electrical arrangement with the pins of a SFF transceiver  202 . Spacing dimensions between each successive pin (or each hole), as well as mechanical and electrical assignments, are dictated by the SFF industry standard. Accordingly, if an SFF transceiver  202  were mounted to a circuit pack  100 , pins  204  of SFF transceiver  202  would line-up to fit in holes  106 ( 1 ) and  106 ( 2 ) of SFF footprint  104 . It is also possible that SFF transceiver  202  could be surface-mounted to circuit pack  100 . 
     FIG. 3  is a side view of a Small Form Factor Pluggable transceiver housing  302  (SFP housing). SFP housing  302  is also commonly referred to in the industry as a cage in which an SFP transceiver  304  (shown as a dashed line) can be inserted and connected to a fiber cable  306  via a connector  308 . SFP housing  302  surrounds a SFP connector  310  (shown as a dashed line), which is configured to attach directly to a printed circuit board. SFP housing  302  and SFP connector  310  include fastening devices  312  such as electrical leads and pins spaced apart and positioned in accordance with the SFP industry standard. These fastening devices are not electrically or mechanically compatible with the SFF industry standard. As a result, SFP housing  302  and SFP connector  310  will not lineup and connect directly with holes  106  ( FIG. 1 ) of SFF footprint  104  ( FIG. 1 ). In other words, the SFP housing  302  and connector  310  have fastening devices  312  which are incongruent (electrically, mechanically, and spatially) and will not align or connect with SFF footprint  104  ( FIG. 1 ). 
   To resolve this problem, the inventors developed an innovative adapter configured to interconnect an SFP transceiver  304  to an SFF footprint  104  of a circuit pack  100 .  FIG. 4  illustrates an exploded isometric view of an embodiment of such an adapter  400 . Adapter  400  includes a printed circuit board  402 , a receptacle side  404 , a connector side  406 , an SFP footprint  408 , an SFF connector  412 , and an electrical module  416 . 
   Circuit board  402  is typically an FR 4  circuit board. Circuit board  402  includes conductive traces (not shown in  FIG. 4 ) for interconnecting electrical components that may be surface-mounted or through-hole mounted to circuit board  402  of adapter  400 . The interconnected components provide a direct electrical interface between SFP connector  310  and an SFF footprint  104  ( FIG. 1 ). Alternative suitable substrates may be used in place of FR 4 . 
   Referring now to receptacle side  404  of adapter  400  is SFP footprint  408 . SFP footprint  408  contains holes  410  configured to align in a complementary manner with counterpart pins and fastening mechanisms  312  of SFP transceiver housing  302  and SFP connector  310 . Accordingly, when SFP transceiver housing  302  and SFP connector  310  are attached to circuit board  402 , each pin/fastening mechanism  312  contacts a corresponding hole  410  or equivalent retention mechanism of SFP footprint  408 . SFP transceiver housing  302  and SFP connector  310  may be soldered to printed circuit board  402  to ensure a secure mechanical and electrical connection. Alternatively, in other implementations, clips or other fastening mechanisms may attach SFP transceiver housing  302  to printed circuit board  402 . 
   Connector side  406  of adapter  400  includes an SFF connector  412  including a set of leads  414 ( 1 ),  414 ( 10 ), . . . ,  414 ( 20 ), and  414 (G 3 ), arranged in spatial and electrical relation to connect with SFF footprint  104  ( FIG. 1 ) of a circuit pack  100  ( FIG. 1 ). Accordingly, when the leads, referred to generally as reference number  414 , are attached to the circuit pack  100  ( FIG. 1 ), each lead  414  aligns with a corresponding contact or hole of footprint  104  of circuit pack  100 . In one exemplary implementation, leads  414  may be pins or posts extending from connector  412  and intended to fit in holes  106  of circuit pack  100 . In alternative implementations, leads  414  may be formed into gull-wing configurations for surface mounting the connector to a surface mount equivalent of footprint  104  ( FIG. 1 ). In other alternative embodiments, it is possible for connector  412  to be attached to circuit pack  100  using other electrical and mechanical attachment mechanisms, such as employing traces of circuit pack  100  and leadless attachment techniques. For a better understanding of a technique for employing traces of a substrate as leads, see  A New Leadframeless IC Carrier Package using Metal Base Substrate , by Junsuke Tanaka et al., ISHM Proceedings (1995), incorporated herein by reference. 
   SFF connector  412  also includes gull-wing configuration leads  417  that provide an electrical and mechanical connection to circuit board  402  of adapter  400 . Alternatively, SFF connector  412  could include pins in place of gull-wing leads  417  that would connect to circuit board  402 . In other alternative embodiments, it is possible to attach connector  412  to circuit board  402  using other electrical and mechanical attachment mechanisms, such as employing leadless attachment techniques as mentioned above with respect to leads  414 . 
   Connector side  406  also includes an external heat-sink  418  that may be attached to circuit board  402  using threaded posts (not shown) or other fastening mechanisms, to dissipate heat from SFP transceiver housing  302  on receptacle side  404 . The heat-sink has two functions: it dissipates heat as well as provides a second attachment mechanism between the module and motherboard. This attachment increases the mechanical integrity of the assembly. It is possible that some less demanding environments will not need heat-sink  418 . 
   Also shown in  FIG. 4 , is electrical module  416 , configured to electrically interconnect SFP transceiver connector  310  to SFF connector  412 . That is, electrical module  416  provides an electrical communication path between an SFP transceiver  304  ( FIG. 3 ) (when disposed in the SFP transceiver housing  302 ), and leads  414  of SFF connector  412 , when SFF connector  412  is attached to SFF footprint  104  ( FIG. 1 ) of circuit pack  100 . A portion of electrical module  416  includes electrical traces (not shown in  FIG. 4 ) located on a layer of printed circuit board  402 . Additionally, it is possible for electrical module  416  to include more than one discrete component, even though only one such component is illustrated in  FIG. 4 . 
   It is noted in other implementations, the electrical module  416  may be positioned in other locations, such as on the connector side  406  of adapter  400 . Alternatively, electrical module  416  may be contained within circuit board  402  by superimposing electrical components into circuit traces of circuit board  402 . Other possible arrangements for the positioning of electrical module  416  (and components therefore) may include placing it partially or wholly on receptacle and connector sides  404  and  406 , and/or contained within circuit board  402 . The components comprising electrical module  416  may also be partially or wholly encapsulated. 
     FIG. 5  is a high-level block diagram of electrical module  416 , which provides an interface between circuit module  100  and SFP transceiver  304  ( FIG. 3 ) when inserted in SFP transceiver connector  310 . In particular, electrical module  416  provides an electrical communication pathway between SFF connector  412  and SFP connector  310 . 
     FIG. 6  is a schematic block diagram of one embodiment of an electrical module  416 . Besides traces in circuit board  402  forming part of a communication path between an SFP transceiver and circuit pack, electrical module  416  includes: a loss of signal (LOS) converter  608 , a Clock and Data Recovery module (CDR)  610 , a signal detector  620 , and power filters  624 . Transmission and reception of data to and from transceiver  304  via electrical module  416  shall now be explained in more detail. 
   Data emanating from circuit pack  100  ( FIG. 1 ) travels through SFF connector  412  to SFP footprint  408 , via a transmit data signal pathway  602 , which may include one or more circuit traces in circuit board  402  ( FIG. 4 ). As used herein a pathway generally includes one or more circuit traces in circuit board  402 . 
   Data received by SFP transceiver  304  is transmitted from SFP footprint  408  to CDR  610  via received data pathway  606 . Other information transmitted from SFP footprint  408  includes a LOS indicator signal  604  to LOS converter  608 . LOS indicator signal  604  indicates whether an optical signal level received by SFP transceiver  304  is at a proper level to receive data. The SFP standard dictates this signal to be a logical high when there is a loss of signal. Whereas the CDR  610  requires a logical low when there is a loss of signal. Accordingly, LOS converter  608  changes the positive logic LOS signal  604  to a negative logic signal  607 . 
   CDR  610  coordinates the transmission of received data from SFP footprint  408  to SFF connector  412 . For example, CDR  610  uses a phase locked loop (PLL) (not shown) to coordinate the transmission of received data and the recovered clock to circuit pack  100 . This is accomplished by synchronizing the PLL with a reference clock signal  611  transmitted by reference oscillator  612 . The CDR produces a lock detect signal, a recovered clock signal, and recovered data signal, which are transmitted via pathways  618 ,  616 , and  614 , respectively. Pathways  614  and  616  are connected to SFF connector  412  for interconnecting adapter  400  ( FIG. 4 ) to SFF circuit footprint  104  ( FIG. 1 ). 
   The lock detect signal is received by signal detector  620  which converts the signal level to a level required by circuit pack  100  configured for an SFF transceiver. The signal detect output is transmitted to SFF connector  412  via pathway  622  and ultimately to circuit pack  100  via footprint  104 . 
   Power filters  624  isolate and filter power from the circuit pack  100  for use by SFP transceiver  304  ( FIG. 3 ) and LOS converter  608 , CDR  610 , reference oscillator  612 , and signal detector  620 . Power filters  624  ensure there is compatible signal and power operation between an SFF centric circuit pack  100  and SFP transceiver  304 . 
   The electrical module  416  is only one example of a suitable communications environment and is not intended to suggest any limitation as to the scope of use or functionality of circuitry that could be used herein. Additionally, the exemplary communications environment should not be interpreted as having any dependency or requirement relating to any one or combination of components illustrated in electrical module  416 . 
     FIG. 7  is an isometric view of adapter  400  from the perspective of the connector side  406 . In this embodiment, gull-wing leads  417  are attached directly to circuit board  402  via pads (not shown). Again, leads  414  of connector  412  follow the SFF industry standard so that they match holes  106  ( FIG. 1 ) of SFF footprint  104  ( FIG. 1 ). 
   Accordingly, an innovative exemplary embodiment of an adapter has been presented that provides a way to salvage circuit packs that use SFF transceivers without having to redesign the circuit packs, artwork on the circuit packs, or faceplates of the circuit pack. This will allow communication equipment manufacturers and communication providers to update their transceivers to the latest SFP industry standard transceivers without having to redesign circuit packs. 
   It is also noted that the SFP connector  310 , SFP housing  302 , and SFF connector  412  may be located on either side of circuit board  402 . For example, in one alternative embodiment all connectors and the SFP housing  302  may be placed on the receptacle side  406  of circuit board  402 . 
   The described embodiments are to be considered in all respects only as exemplary and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.