Abstract:
A contact is provided for use in an interface connector. The contact comprises a contact beam  12  having a mating surface proximate a first end of the contact beam. The mating surface  16  is configured to join a contact pad, such as on a module board to carry high speed data signals therebetween. The contact further includes a tail portion configured to join a contact pad, such as on a host board. A leg portion of the contact joins and interconnects the tail portion and a second end of the contact beam. The leg portion includes a retention segment, through which a signal transmission path passes as data signals are carried through the leg portion between the tail portion and contact beam, thereby reducing signal degradation. The retention segment is configured to secure the leg portion within a connector.

Description:
RELATED APPLICATION 
   The present applications relates to, and claims priority from, provisional application Ser. No. 60/424,263, filed on Nov. 6, 2002, titled “CONTACT FOR HIGH SPEED SMALL FORM FACTOR PLUGGABLE CONNECTOR”, the full and complete subject matter of which is expressly hereby incorporated in its entirety by reference. 

   BACKGROUND OF THE INVENTION 
   The present invention generally relates to a contact and a connector configured to carry data at high speeds. More specifically, certain embodiments of the present invention relate to a contact for use in various connectors. 
   Recently, interface connectors have been developed that are capable of satisfying a common specification for multi-source applications, such as in the telecommunications field, data communications applications, storage area networks and the like. The connectors convey data at very high data rates and should satisfy very strict signal quality criteria. The connectors are used in applications that have very demanding space constraints and thus are developed to satisfy various form factor. 
   These connectors interconnect a variety of components, such as host boards and daughter boards that carry transceiver ASICs and the like. In certain applications, the connector may be a 20 to 70 position pluggable transceiver (PT) connector that carries digital data signals at high data rates, such as 2.5, 5, and 10 Gbps (gigabits per second ) or higher. 
   However, as data rate increases, the signal performance of the conventional connectors declines. The signal performance may be characterized in terms of jitter, return loss, insertion loss, attenuation, reflectance, signal to noise ratio and the like. The performance of the connector is affected by several factors, one factor of which is the shape and configuration of the contacts that carry the data signals through the connector. Contacts of conventional design have been found to exhibit declining performance characteristics once the data rate reaches and exceeds 5 or 10 Gbps and higher. 
     FIG. 9  illustrates a conventional contact  310  designed for small form factor pluggable connectors to carry digital signals at a data rate of up to 2.5 Gbps. The contact  310  is held in a housing of a connector  305 . The contact  310  includes a contact beam  312  that is joined to one end of a leg portion  320 . An opposite end of the leg portion  320  joins a tail portion  332 . The contact beam  312  and tail portion  332  define interfaces at which data signals are conveyed to mating contact pads  357  and  355  on a module board  358  and host board  354 , respectively. The contact  310  includes a retention stub  322  that holds the contact  310  in place in the connector  305 . The retention stub  322  includes a base end formed with the leg portion  320  at an intermediate point along the length of the leg portion  320 . The retention stub  322  projects at a right angle from the leg portion  320  with an outer end  324  terminating at a point remote from the contact  310 . 
   The contact  310  exhibits satisfactory performance at data rates of at least 2.5 Gbps. However, when the data rate is increased to near 10 Gbps and higher the retention stub  322  begins functioning as an electrical stub which causes signal degradation, such as increased jitter, insertion loss, return loss and the like. 
   A need exists for an improved contact configuration that overcomes the problems noted above and experienced heretofore by convention contacts. 
   BRIEF SUMMARY OF THE INVENTION 
   A contact is provided for use in an interface connector. The contact comprises a contact beam having a mating surface proximate a first end of the contact beam. The contact beam is configured to carry high speed data signals. The contact further includes a tail portion configured to carry high speed data signals. A leg portion of the contact joins and interconnects the tail portion and a second end of the contact beam. The leg portion includes a retention segment, through which a signal transmission path passes as data signals are carried through the leg portion between the tail portion and contact beam. The retention segment is configured to secure the leg portion within a connector. 
   Optionally, the retention segment many be U-shaped and include first and second stems extending parallel to one another and being joined at one end. The stems are open at an opposite end, at which the first and second stems join the tail portion and leg portion, respectively. The signal transmission path passes through the first and second stems continuously along the U-shape. When the retention segment is formed in a U-shape, the contact&#39;s overall shape forms a general S-shape through which the signal transmission path travels. 
   In accordance with an alternative embodiment, a connector is comprised of a housing having first and second ends configured to mate with adjoining elements, such as module and host boards. The connector includes a contact held in the housing that has a contact beam configured to join a contact pad on an adjoining element. The contact includes a tail portion also configured to join a contact pad on an adjoining element. The contact beam and tail portion are joined by a leg portion that includes a retention segment formed continuously within the signal transmission path through the leg segment between the tail portion and contact beam. The retention segment secures the leg portion within the housing. 
   In accordance with an alternative embodiment, a method is provided for transmitting a high speed data signal in a carrier wave through contacts in an electrical connector. The method comprises transmitting data signal pairs in a high speed data signal over contacts in the connector at a data rate of at least 10 Gbps. The method further includes directing the data signal pairs along corresponding signal transmission paths through corresponding contacts that maintain a predetermined signal performance such that the jitter of the data signal pair at the contacts does not substantially exceed 11 picoseconds. 
   In accordance with at least one alternative embodiment, a method is provided for transmitting a high speed data signal in a carrier wave through contacts in a connector. The method comprises transmitting a data signal in a high speed data signal over a contact in a connector at a data rate of approximately at least 10 Gbps (e.g., 9.9-10.7 Gbps). The method further includes directing the data signal along a signal transmission path through the contact that maintains a predetermined signal performance such that insertion loss does not substantially exceed −3 dB up to the third harmonic (e.g., 15 GHz) of the fundamental frequency (e.g., 5 GHz) of the 10 Gbps data rate. 
   In accordance with an alternative embodiment, a method is provided for transmitting a high speed data signal and carrier wave through a contact in a connector. The method comprises transmitting a data signal in a high speed data signal over a contact in a connector at a data rate of at least 10 Gbps. The method includes directing the data signal along a signal transmission path through the contact that maintains a predetermined signal performance such that the return loss does not substantially exceed the insertion loss for frequencies between 5 and 15 GHz. 

   
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  illustrates an isometric view of a contact formed in accordance with an embodiment of the present invention. 
       FIG. 2  illustrates a side sectional view of a contact held in a connector formed in accordance with an embodiment of the present invention. 
       FIG. 3  illustrates a graph plotting insertion loss at various data rates experienced by the contact of  FIG. 1  versus the contact of FIG.  9 . 
       FIG. 4  illustrates a graph plotting return loss at various data rates experienced by the contact of  FIG. 1  versus the conventional contact of FIG.  9 . 
       FIG. 5  illustrates an eye pattern representing the performance exhibited by a reference cable carrying data signals at 10 Gbps. 
       FIG. 6  illustrates an eye pattern representing the performance exhibited by the conventional contact of  FIG. 9  carrying data signals at 10 Gbps. 
       FIG. 7  illustrates an eye pattern representing the performance exhibited by a reference cable carrying data signals at 10 Gbps. 
       FIG. 8  illustrates an eye pattern representing the performance exhibited by the contact of  FIG. 1  formed according to an embodiment of the present invention carrying data signals at 10 Gbps. 
       FIG. 9  illustrates a side section view of a conventional contact held in a connector. 
   

   The foregoing summary, as well as the following detailed description of certain embodiments of the present invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings, certain embodiments. It should be understood, however, that the present invention is not limited to the arrangements and instrumentality shown in the attached drawings. 
   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  illustrates a contact  10  formed in accordance with an embodiment of the present invention. The contact  10  is configured to be secured in a housing of a connector, such as a small form factor pluggable connector. The contact  10  may be used in a variety of other connectors and applications that convey signals at high data rates and desire high quality signal performance. By way of example, the contact  10  may carry digital data having a fundamental frequency of 5 GHz and a data rate of 10 Gbps and higher, while exhibiting very little jitter, insertion loss and return loss. 
   The contact  10  includes a contact beam  12  having an outer end with an optional lead-in surface  14  adjacent a mating surface  16 . The lead-in surface  14  is curved upward to facilitate loading of another component, such as a host board, daughter board and the like. When the host board or other component is fully inserted, contact (mating) pads on the host board firmly engage the mating surface  16  in a tangential alignment. Optionally, the mating surface  16  may be on the top or outer end of the contact beam  12 , or may constitute a pin insertable into an adjoining contact. 
   The contact  10  also includes a leg portion  20  having one end joined at bend  18  with the contact beam  12 . The leg portion  20  has an opposite end joining a tail portion  32  that may extend beyond a rear face  60  of the connector  50 . As shown in  FIG. 2 , the tail portion  32  extends beyond the rear face  60  of the connector  50  into which the contact  10  is loaded. While tail portion  32  is shown bent to extend beyond the contact  10 , optionally the tail portion  32  may be 1) bent in the opposite direction under the contact  10 , 2) shortened to be even with rear face  60 , or 3) turned downward to serve as a pin or otherwise. The tail portion  32  is configured to join a contact pad on a mating component, such as a host board  54  and the like. Optionally, the tail portion  32  may be soldered, surface mounted, or inserted as a pin to join with the host board  54 . 
   The leg portion  20  includes a brace segment  34  having an upper end joining the contact beam  12  generally at a right angle. A lower end of the brace segment  34  is formed at bend  28  with a retention segment  22 . The retention segment  22  is configured to securely retain the contact  10  in a channel within the housing of a connector  50  (FIG.  2 ). The brace segment  34  spaces the contact beam  12  and retention segment  22  apart from one another by a distance sufficient to define a mating area  30  therebetween. A module board  58  ( FIG. 2 ) is inserted into the mating area. The retention segment  22  is oriented parallel to, and extends in the same direction as, the contact beam  12 . The retention segment  22  is generally U-shaped and includes upper and lower stems  26  and  27 , respectively. First ends of the upper and lower stems  26  and  27  are joined to one another proximate the contact beam  12 , while opposite rear ends  38  of the upper and lower stems  26  and  28  are open. The rear end  38  of the lower stem  28  joins the tail portion  32 , which extends downward and rearward in a stepped manner. 
   Optionally, the retention segment  22  may extend in the direction opposite to the contact beam  12 . Alternatively, the retention segment  22  may be oriented at an acute or obtuse angle with the contact beam  12 . The retention segment  22  may have other shapes, such as C-shaped, S-shaped, square, arc-shaped, triangular, and the like. 
   The upper and lower stems  26  and  27  provide an opening at the rear end  38  to define a signal transmission path through the entire retention segment  22  (as denoted by arrow A) that is continuous, uninterrupted and lacking in termination points. When data signals are conveyed through the contact  10 , they pass from the mating surface  16  along the contact beam  12 , through the brace segment  34 , and around the upper stem  26  and lower stem  27  until reaching the tail portion  32 . Of course, data signals may be conveyed in the reverse direction instead, beginning at the tail portion  32  and traveling to the contact beam  12 . 
   The upper stem  26  includes projections  36  formed on the upper edge thereof. The projections  36  are dimensioned such that they, in combination with a lower edge  29  of the lower stem  27 , form an interference fit within a channel in the connector. 
     FIG. 2  illustrates a side sectional view of a connector  50  that may utilize the contact  10 . The connector  50  includes a base  52  mounted on a host board  54  and includes a front face  56  that receives a module board  58 . The connector  50  includes a rear face  60  having a passage  62  formed therein that extends to the front face  56 . The contact beam  12  extends into the passage  62  to a depth proximate the front face  56 . The rear face  60  also includes a channel  64  that is dimensioned to firmly receive the retention segment  22 . The tail portion  32  is mounted to a contact pad  55  on the host board  54 , while the mating surface  16  on the contact beam  12  abuts against a contact pad  57  on the module board  58 . Optionally, a pin  66  may be mounted in the host board  54  to retain the connector  50  thereon. 
     FIG. 3  illustrates a graph plotting insertion loss in decibels (dB) on the vertical axis and frequency in Gigahertz (GHz) on the horizontal axis. Insertion loss represents an attenuation of the data signal that results from the addition of a device into a system characterized as a transmission line. The insertion loss represents the reciprocal of the ratio of 1) the signal power delivered to the point in the transmission line where the device is added and 2) the signal power at the same point in the transmission line before the device is added. 
   In  FIG. 3 , line  80  represents the insertion loss introduced by contact  10  ( FIG. 2 ) into a data signal carrying data at a rate of approximately 10 Gigabits per second (Gbps). The insertion loss of contact  10  is measured at the contact pad  57  on the module board  58  ( FIG. 2 ) and the contact pad  55  on the host board  54 . The line  82  represents the insertion loss introduced by contact  310  ( FIG. 9 ) into a data signal also carrying data at a rate of approximately 10 Gbps. The insertion loss of contact  310  is measured at the contact pads  357  and  355  on the module board  358  and host board  354 , respectively. 
   It is understood that the data signal is comprised of frequency components spanning a broad frequency range. Each frequency component experiences insertion loss to a different degree. In  FIG. 3 , the insertion loss is shown for the frequency components, between 0 and 16 GHz, that are comprised in a data signal having a 10 Gbps data rate. For example, the 2 GHz frequency component conveyed through contacts  10  and  310  experiences very little insertion loss. The frequency components between 7 and 8 GHz, conveyed through contacts  10  and  310  experience approximately 1 dB of insertion loss. Of particular interest, the insertion loss introduced by contact  10  does not substantially exceed −2.5 dB for any frequency component up to 12.5 GHz, and does not substantially exceed −3 dB for any frequency component up to 16 GHz. It should be noted that 10 GHz and 15 GHz frequency components are the second and third harmonics of the fundamental frequency (5 Ghz) of the data signal. As is apparent from  FIG. 3 , the conventional contact  310  exhibits substantially more insertion loss at frequencies above 10 GHz as compared to contact  10 . 
     FIG. 4  illustrates a graph plotting return loss in dB on the vertical axis and frequency in GHz on the horizontal axis. Return loss represents a summation of the reflected signal energy returning backward toward an end of a transmission line from which the signal originates (e.g., an echo signal). For example, in bi-directional signaling applications, a transceiver may be placed at each end of the transmission line. The transmitter within each transceiver sends a data signal through the transmission line and then begins “listening” over the same line for data that is transmitted from the opposite end. The reflected or echo signals interfere with the desired data signals. Return loss may be caused by discontinuities and impedance mismatches within the transmission line. For purposes of this exemplary embodiment, it may be assumed that the data path between the module board  58 , contact  10  and host board  54  form a transmission line. Discontinuities within a transmission line occur at connection points, such as at contact pad  57  and at contact pad  55 . Impedance mismatches may occur between components within a transmission line or within a single component, device or cable. 
   In the conventional contact  310  (FIG.  9 ), the retention stub  322  functioned as an electrical stub for the higher frequency components of the data signal. As the retention stub  322  functioned more and more as an electrical stub, it varies the electrical characteristics of the contact  310  including, among others, its impedance. As the electrical characteristics (such as, but not limited to, the impedance) of the contact  310  vary, insertion loss, return loss and the like increase. The line  90  (in  FIG. 4 ) represents the return loss of contact  10  ( FIG. 1 ) measured at and including the contact pad  57  on the module board  58  and, at and including the contact pad  55  on the host board  54  while carrying digital data signals at approximately 10 Gbps (e.g., 9.9-10.7 Gbps). The line  92  represents the return loss of a contact  310  ( FIG. 9 ) measured at the contact pads  357  and  355 . 
     FIG. 4  illustrates the frequency components between 0 and 16 GHz that comprised a data signal having a 10 Gbps data rate. The return loss of the contact  10  for the 5 GHz frequency component is no greater than −15 dB. The return loss of the contact  10  for the 10 GHz and 15 GHz frequency components at do not exceed −5 dB and −2.5 dB, respectively. The frequency components at 5 GHz, 10 GHz and 15 GHz represent the fundamental, second harmonic and third harmonic frequencies of the exemplary data signal. 
   The measurements plotted in  FIGS. 3 and 4  are taken at the contact pads  55 ,  355 ,  57  and  357  to account for the interconnections at the tail portions  32 ,  322  and mating surfaces  16 ,  316 . The contact pads  55  and  355  may represent solder pads, while the contact pads  57  and  357  may represent mating pads. 
     FIGS. 5-8  illustrate eye patterns for reference cables (FIGS.  5  and  7 ), the conventional contact  310  (FIG.  6 ), and contact  10  ( FIG. 8 ) at contact pads  55  or  57 , and  355  or  357 . The eye patterns in  FIGS. 5 and 7  represent the data signal introduced into the contacts  310  and  10  at contact pats  55  and  57 , and  355  or  357 . An eye pattern represents an oscilloscope display in which a pseudo-random digital data signal from a receiver is repetitively sampled and applied to the vertical input of the oscilloscope, while the data rate is used to trigger the horizontal sweep of the oscilloscope. In the example of  FIGS. 5-8 , the data rate is 5 Gbps. The reference signal included a data stream containing pseudo-randomly generated data words, where each data word contained 127 bits ( 2   7 −1 PRBS). The data signal was driven by a 5 GHz clock to produce a 10 Gbps data rate. As shown in  FIGS. 5 and 7 , the reference cables (without any contact attached thereto) exhibited a 9 ps (picosecond) jitter and contained an 887 mV eye amplitude). 
   With reference to  FIG. 5 , the eye pattern  500  includes top and bottom rails  502  and  504 , respectively. The distance  506  between the centers of the top and bottom rails  502  and  504  corresponds to the signal amplitude. The thickness or width of each of the top and bottom rails  502  and  504  corresponds to the noise amplitude. The eye opening  508  represents the distance between the top and bottom rails  502  and  504 . The temporal width (along the horizontal axis) of the crossing section  510  represents the amount of jitter in the signal. In the referenced cable of  FIG. 5 , the eye opening  508  has a value of 887 mV, while the jitter  510  has a value of 9 ps. 
   The rising edge  512  of the reference cable in  FIG. 5  completes a state transition of approximately 800 mV in approximately 45 ps (the divisions on the horizontal axis are 15 ps/division, and on the vertical axis are 200 mV/division.  FIG. 7  illustrates the performance of a reference cable substantially similar to that of  FIG. 5 , but attached to the contact  10  (shown in FIG.  1 ). The signal performance of the reference cable in  FIG. 7  exhibits an eye opening of 887 mV and a jitter of 9 ps. 
   With reference to  FIG. 6 , the conventional contact  310  exhibits an eye opening having a value of 808 mV, with a jitter equal to 12 ps. In addition,  FIG. 6  illustrates the rising edge  612  of the data signal passed through conventional contact  310 . The rising edge  612  of the data signal through contact  310  requires over 75 ps to complete the state transition of approximately 800 mV. 
   In  FIG. 8 , the contact  10  ( FIG. 1 ) exhibits a signal performance having an eye opening of 756 mV and a jitter of approximately 10 ps. In addition, the rising edge  812  of the data signal is less rounded as compared to the rising edge  612  ( FIG. 6 ) of the conventional contact  310 . The rising edge  812  of the data signal through contact  10  requires no more than 60 ps to complete the state transition. The data signal conveyed by contact  10  exhibits a steeper or faster rise/fall time to transition between states as compared to the conventional contact  310 . A steeper rise time affords more time for the transceiver circuitry to gate or acquire each data value (e.g., a logic 0 or a logic 1) in the data signal. The improvement in rise time is due in part to the reduction, by the contact  10 , of insertion and return losses. By reducing the insertion and return losses, the signal quality is improved which in turn affords a steeper or faster rise/fall time, reduces jitter and introduces less distortion. 
   As shown above, the insertion and return losses are reduced by providing an electrical contact with more stable electrical characteristics over a wider frequency range. By way of example, the contact  10  exhibits a substantially even impedance along its length and over a large frequency range, up through the third harmonic of the fundamental frequency of the data transmission rate. For example, a data rate of 10 Gbps which is driven by a clock operating at 5 GHz per second has a third harmonic of approximately 15 GHz. As shown in  FIGS. 3 and 4 , the insertion and return loss (lines  80  and  90 ) of contact  10  maintained a much more stable and even performance over frequencies of 5 GHz and higher, as compared to the insertion and return losses ( 82  and  92 ) exhibited by the conventional contact  310 . At frequencies above 5 and 10 GHz, the retention stub  322  ( FIG. 9 ) of the conventional contact  310  begins functioning as an electric stub. As an electrical stub, the retention stub  322  begins operating as a parallel transmission line that progressively interferes more with the characteristics of the higher frequency components. By way of example, when the length of the retention stub  322  equals ¼ th  of the wave length, the retention stub  322  forms a short circuit which drastically degrades the operation of the contact  310 . 
   The contact  10  ( FIG. 1 ) avoids stubs or other structure that would otherwise operate as an electrical stub, thereby avoiding the problems experienced by the conventional contact  310 . The structure of the contact  10  supports data transmission at high frequencies (as shown in  FIGS. 3 and 4 ) with less insertion and return loss, thereby improving the signal quality and affording a steeper/faster rise/rise time for the transition of the data signal between states, as well as reducing jitter and introducing less distortion. 
   While the invention has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims. Optionally, multiple contact  10  may be held in a common housing and configured to transmit data signal pairs.