WO2004030158A2

WO2004030158A2 - Impedance-tuned terminal contact arrangement and connectors incorporating same

Info

Publication number: WO2004030158A2
Application number: PCT/US2003/030106
Authority: WO
Inventors: David L. Brunker; Daniel L. Dawiedczyk; Maxwill P. Bassler; Patrick R. Casher
Original assignee: Molex Incorporated
Priority date: 2002-09-25
Filing date: 2003-09-25
Publication date: 2004-04-08
Also published as: EP1459414B1; CN1742411A; CN100474708C; WO2004030158B1; AU2003282873A8; JP4068618B2; EP1459414A2; AU2003282873A1; DE60325325D1; WO2004030158A3; JP2006500749A

Abstract

A terminal contact arrangement for a connector promotes reduction in deviation of the impedance of the connector when mated to an opposing connector and energized. The connector has an insulative housing with a plurality of terminal-receiving passages disposed in it. Conductive terminals are supported in some, but not all of the passages. The terminal contain distinct terminal sets that include a pair of differential signal terminals and at least two associated ground reference terminals. The two associated ground reference terminals are interconnected together so that electrically, they act as a single ground terminal having a width equal to the sum of the widths of the two connected ground reference terminals. The ground reference terminals of the sets are disposed in a single row of terminals, while the differential signal terminals of the same terminal set are disposed in another row of terminals spaced apart from the row of ground reference terminals. The differential signal terminals are separated from each other within their terminal row by an empty passage so that the two differential signal terminals of each terminal set are spaced farther apart from each other than they are spaced apart from their associated ground reference terminals.

Description

IMPEDANCE-TUNED TERMINAL CONTACT ARRANGEMENT AND CONNECTORS INCORPORATING SAME

Background of the Invention

The present invention relates generally to terminations for connectors and more particularly to connectors having selected impedances that are used in connection with signal cables, such as in an automotive environment.

Many electronic devices rely upon transmission lines to transmit signals between related devices or between peripheral devices and circuit boards of a computer. These transmission lines incorporate signal cables that are capable of high-speed data transmissions.

These signal cables may use what are known as one or more twisted pairs of wires that are twisted together along the length of the cable, with each such twisted pair being encircled by an associated grounding shield. These twisted pairs typically receive complementary signal voltages, i.e., one wire of the pair may see a +1.0 volt signal, while the other wire of the pair may see a -1.0 volt signal. Thus, these wires may be called "differential" pairs, a term that refers to the voltage difference between the two conductors in a signal pair. Such a twisted pair construction minimizes or diminishes any induced noise voltage from other electronic devices and thereby eliminates electromagnetic interference.

As signal cables are routed on a path to an electronic device, they may pass by or near other electronic devices that emit their own electric field. These devices have the potential to create electromagnetic interference to transmission lines such as the aforementioned signal cables. Automotive environments are particularly harsh in electromagnetic interference. Such interference is frequently caused by high voltage ignition signals. Other sources of interference in the automotive environment include alternator charging systems and many switched devices, such as air conditioning. However, this twisted pair construction tends to minimize or diminish any induced electrical fields and thereby substantially eliminates electromagnetic interference.

In order to maintain electrical performance integrity from such a transmission line, or cable, to the circuitry of an associated electronic device, it is desirable to obtain a substantially constant impedance throughout the transmission line, from circuit to circuit or to avoid large discontinuities in the impedance of the transmission line. The difficulty of controlling the impedance of a connector at a connector mating face is well known because the impedance of a conventional connector typically drops through the connector and across the interface of the two mating connector components. Although it is relatively easy to maintain a desired impedance through an electrical transmission line, such as a cable, by maintaining a specific geometry or physical arrangement of the signal conductors and the grounding shield, an impedance discontinuity is usually encountered in the area where a cable is mated to a connector. It is therefore desirable to maintain a desired impedance throughout the connector and its connection to the cable.

Typical signal cable terminations involve the untwisting of the wire pairs and the unbraiding of the braided shield wire and/or foil surrounding the wire pairs. These wires are unbraided manually and this manual operation tends to introduce variability into the electrical performance. This is caused by unbraiding the grounding shield wires, then typically twisting them into a single lead and subsequently welding or soldering the twisted tail of a connector terminal. This unbraiding and twisting often results in moving the signal conductors and grounding shield out of their original state in which they exist in the cable. This rearrangement may lead to a decoupling of the ground and signal wires from their original state that may result in an increase of impedance through the cable-connector junction. Moreover, this twisting introduces mechanical variability into the termination area in that although a cable may contain multiple differential pairs, the length of the unbraided shield wire may vary from pair to pair. This variability and rearrangement changes the physical characteristics of the system in the termination area which may result in an unwanted change (typically an increase) in the impedance of the system in the area.

Additionally, it is common for the signal and ground termination tails of a connector to be arranged into whatever convenient space is present at the connector mounting face without any control of the geometry or spatial aspects of the signal and ground terminals being considered. When signal wires and ground shields are pulled apart from the end of a cable, an interruption of the cable geometry is introduced. It is therefore desirable to maintain this geometry in the termination area between the cable and the cable connector to reduce any substantial impedance increase from occurring due to the cable termination.

The present invention is therefore directed to a terminal contact arrangement and function directed at providing improved connections between connectors and between the mating portions of two interengaging connectors that provides a high level of performance and which maintains the electrical characteristics of the cable in the termination area, particularly in an automotive environment.

Summary of the Invention

Accordingly, it is a general object of the present invention to provide an improved termination structure for use in high-speed data transmission connections in which the impedance discontinuity through the cable termination and connector is minimized so as to attempt to better match the impedance of the transmission line.

Another object of the present invention is to provide an improved connector for effecting a high-performance connection between a circuit board and an opposing connector terminated to a transmission line, wherein the transmission line includes multiple pairs of differential signal wires, each such pair having an associated ground, the connector having pairs of signal terminals and ground terminals associated therewith arranged in triangular fashions so as to reduce impedance discontinuities from occurring when the connector is mated to the opposing connector and further, by inverting adjacent triangular associated sets of signal and ground terminals, the connector is given a specific density characteristic while maintaining a desired preselected impedance through the connector.

Another object of the present invention is to provide a termination assembly for use in conjunction with signal cables that provides a connection between the twisted wire pairs and grounding shield of the cable and the connector, the termination assembly having an improved electrical performance due to its structure.

It is a yet further object of the present invention is to provide a connector for connecting cables, such as in accordance with the IEEE 1394b standard, to a circuit board of an electronic device, wherein the connector has a number of discrete, differential signal wires and associated grounds equal in number to those contained in the cables, the ground terminals of the connector being configured in quantity and location with respect to the signal terminals of the connector in order to minimize the drop in impedance through the connector.

A still another object of the present invention is to provide a connector for termination to a cable, wherein a plurality of ground terminals are positioned within the cable connector housing and are spaced apart from two associated signal terminals in the connector housing, the plurality of ground terminals being commoned to effectively provide a singular ground terminal that is of a similar or greater effective width as compared to the distance between the signal terminals. A yet further object of the present invention to provide a cable connector for use with differential signal wire pairs, wherein a plurality of ground terminals are commoned together and in a spaced-apart relationship to the terminals for the differential signal wire pairs, with the terminals for the differential signal wire pairs spaced from each other by one vacant terminal position so that the differential signals are decoupled from each other and the differential signals are each more closely coupled to the plurality of commoned ground terminals.

Another object of the present invention is to provide a cable connector for use with differential signal wire pairs extending the length of the cable, the cable connector having a plurality of ground terminals that are commoned together and two signal terminals that are arranged and maintained in an essentially triangular orientation with the commoned ground terminals through the connector and at the termination areas thereof.

The present invention accomplishes these objects by virtue of its structure. In order to obtain the aforementioned objects, one principal aspect of the invention that is exemplified by one embodiment thereof includes a first connector for a circuit board which has a housing that supports, for each twisted pair of wires in the mating signal cable, three conductive terminals in a unique pattern of a triplet, with two of the terminals carrying differential signals, and the remaining terminal being a ground terminal that serves as a ground plane or ground return to the differential pair of signal wires. The first connector supports multiple terminal triplets, in an inverted fashion (widthwise along the connector mating face) so that two rows of terminals are defined in the first connector, the signal terminals of a first triplet are disposed in one row in the connector and the ground terminal of that first triplet is disposed in the other row of the connector, while the signal terminals of a second, or of adjacent triplets, are disposed in the other row of the connector and the ground terminal of this second triplet or of two adjacent triplets are disposed in the one row of the connector. The signal and ground terminals of adjacent triplets are arranged in an inverted fashion. A second connector for a cable is provided that mates with the first connector and their second connector has multiple terminal triplets arranged to mate with their corresponding terminal triplets of the first connector.

The arrangement of these terminals in sets of three within the first connector permits the impedance to be more effectively controlled throughout the first connector, from the points of engagement with the cable connector terminals to be points of attachment to the circuit board. [0025] In this manner, each such triplet of the first connector includes a pair of signal terminals having contact portions that are aligned together in side-by-side order, and which are also spaced apart a predetermined distance from each other. The ground terminal is spaced apart from the two signal terminals in a second row.

In another principal aspect of the present invention, the width of the ground terminals and their spacings from the signal terminals of each such triplet maybe chosen so that the three terminals may have desired electrical characteristics such as capacitance and the like, all of which will affect the impedance of the connector.

By this impedance-regulating ground structure, a greater opportunity is provided to reduce the impedance discontinuity which occurs in a connector without altering the mating positions or the pitch of the differential signal terminals. Hence, this aspect of the present invention may be aptly characterized as providing a "tunable" terminal arrangement for each differential signal wire pair and associated ground wire arrangement found either in a cable or in other circuits.

In another principal aspect of the present invention, these tunable triplets are provided within the connector housing in an inverted fashion. That is, the ground terminals of adjacent terminal triplets lie in different terminal rows of the connector, as do the signal terminals in alternating fashion along the width of the connector. When multiple terminal triplets are utilized in the connectors, other terminals of the connector such as power and reference terminals may be situated in the connector at a midpoint thereof between the terminal triplets.

In another principal aspect of the invention, as exemplified by another embodiment thereof, a receptacle connector for a circuit board which has a housing having at least three conductive terminals arranged in an effective pattern of a triplet, with two of the terminals carrying differential signals, and the remaining terminal being a ground terminal that is comprised of a plurality of individual ground terminals. Preferably, the plurality of individual ground terminals are interconnected or "commoned" together at the connector, and in a preferred embodiment, this interconnection occurs along the body or tail portions of the ground terminals. A plug connector for the end of a cable mates with the receptacle connector, and this plug connector also has the differential signal and ground terminals effectively arranged in a complementary triplet pattern of conductive terminals which are terminated to the signal and ground wires of the cable. Preferably, an unused terminal position is interposed between the two differential signal terminals in both the receptacle connector and the plug connector so that the differential signals are decoupled from each other, and so that the differential signals are more closely coupled to the plurality of ground terminals. The plurality of ground terminals are electrically in common so that the plurality of ground terminals acts a single wide terminal, or a common ground path disposed in a spaced-apart plane from the two differential signal terminals.

The arrangement of these three terminals within the connector permits the impedance to be more effectively controlled throughout the receptacle connector, from the points of engagement with the plug connector terminals to the points of attachment to the circuit board. In this manner, each such effective triplet includes a pair of signal terminals that are aligned together in side-by-side order, and which are also spaced apart a predetermined distance from each other. The plurality of ground terminals extend along a different plane than that defined by the differential signal terminals, with the signal terminals located closer to the plurality of ground terminals than to each other.

The effective width of this plurality of ground terminals and its spacing from the signal terminals may be chosen so that the signal and ground terminals may have desired electrical characteristics such as capacitance and the like, which affect the impedance of the connector. The effective width of the plurality of ground terminals is thereby increased in the contact mating area of the terminals and may also be increased in the transition area that occurs between the contact and termination areas of the terminals. By this structure, a greater opportunity is provided to reduce the impedance discontinuity which occurs in a connector without altering the mating positions or the pitch of the differential signal teπninals. Hence, this aspect of the present invention may be aptly characterized as providing a "tunable" terminal arrangement for each differential signal wire pair and associated ground wire arrangement found either in a cable or in other circuits.

In another principal aspect of the present invention, two or more such tunable effective triplets may be provided within the connector housing, but inverted with respect to each other. Alternatively, additional ground terminals maybe interposed between the two sets of triplets, or terminals that supply electrical power through the connector may be located between and provide separation of the effective triplets. Such power supply terminals generally act as additional low impedance terminals, in a manner substantially similar to the plurality of ground terminals, to provide coupling to the differential signal terminals and to thereby control impedance.

These and other objects, features and advantages of the present invention will be clearly understood through consideration of the following detailed description. Brief Description of the Drawings

In the course of the following detailed description, reference will be made to the accompanying drawings wherein like reference numerals identify like parts and in which:

FIG. 1 is a diagram illustrating the typical impedance discontinuity experienced throughout a high-speed cable connection and also the reduction in this discontinuity that would be experienced with the connectors of the present invention;

FIG. 2 is an elevational view of a cable connector assembly of the invention in place on a circuit board of an electronic device illustrating an "internal" environment in which the present invention has utility;

FIG. 3 is an elevational view of a cable connector assembly of the invention in place on a circuit board of an electronic device and extending to the exterior of the device to illustrate an "external" environment in which the present invention has utility;

FIG. 4 is a schematic view of the connector interface area between a cable and board connector;

FIG. 5 is a cross-sectional view of the interior construction of a cable for use with the connectors of the present invention;

FIG. 6 is a front perspective view of another embodiment of a connector constructed in accordance with the present invention, and suitable for mounting on a printed circuit board;

FIG. 7 is a rear perspective view of the connector illustrated in FIG. 6;

FIG. 8 is a rear elevational view of the connector illustrated in FIGS. 6 and 7;

FIG. 9 is a front elevational view of another embodiment of the connector illustrated in FIGS. 6-8 and which is suitable for mounting to a printed circuit board, but with the unused terminal locations between the pairs of signal terminals vacant in accordance with another aspect of the present invention;

FIG. 10 is a diagrammatic view of the arrangement and the placement of two pairs of signal terminals disposed adjacently to pairs of ground terminals of the connector illustrated in FIGS. 6-8, with a vacant or unused terminal interposed between the pairs of signal terminals, in accordance with the invention;

FIG. 11 is a diagrammatic view of the arrangement and placement of the terminals, similar to FIG. 10, but illustrating the diagonal placement of the power terminals between inverted pairs of signal terminals in accordance with the invention;

FIG. 12 is another diagrammatic view of the arrangement and the inverted placement of two pairs of signal terminals disposed adjacently to three ground terminals in modified triplet configurations, with a vacant or unused terminal interposed between the pairs of signal terminals, in accordance with the invention;

FIG. 13 is a rear perspective view of the connector illustrated in FIG. 9;

FIG. 14 is a rear elevational view of the connector illustrated in FIGS. 9 and 13;

FIG. 15 is an exploded perspective view of the connector illustrated in FIGS. 6-8 with a mating plug including wires extending from each used terminal position;

FIG. 16 is a perspective view of the connector portions illustrated in FIG. 15, but with the connector and the mating plug connected together; and,

FIG. 17 is a perspective view, similar to FIG. 16, but with two multiple- wire signal cables terminating in the mating plug, and two individual power wires also terminating in the mating plug in a diagonal orientation between the two signal cables.

Detailed Description of the Preferred Embodiments

The present invention is directed to an improved connector particularly useful in enhancing the performance of high-speed cables, particularly in input-output ("I/O") applications as well as other types of applications. More specifically, the present invention attempts to impose a measure of mechanical and electrical uniformity on the termination area of the connector to facilitate its performance, both alone and when combined with an opposing or mating connector.

Many peripheral devices associated with an electronic device, such as a video camera or camcorder, transmit digital signals at various frequencies. Other devices associated with a computer, such as the CPU portion thereof, operate at high speeds for data transmission. High speed cables are used to connect these devices to the CPU and may also be used in some applications to connect two or more CPUs together. A particular cable may be sufficiently constructed to convey high speed signals and may include differential pairs of signal wires, either as twisted pairs or individual pairs of wires.

The use of high speed electronics is becoming more prevalent in the automotive environment. For example, automotive manufacturers are considering implementing a central data communications backbone in vehicles to provide a convenience port to interface with consumer entertainment devices and personal computers. Ultimately, such a backbone may also interface with other vehicular operations. Data transmission speeds generally range from 100 Mbps (megabits per second) to 1.6 Gbps (gigabits per second). Thus, while the connectors of the present invention are generally based upon an automotive grade 0.64 mm terminal system, the present invention is also suitable for use in many other types of connectors.

However, this environment is known to have considerable electromagnetic interference (EMI). While shielded cables with internal twisted pair wires are fairly immune to such EMI, connecting such cables to the printed circuit boards (PCBs) of electronic devices presents a variety of potential problems, including potentially significant impedance discontinuities at the connector.

One consideration in high speed data transmissions is signal degradation. This involves crosstalk and signal reflection which is affected by the impedance of the cable and connector. Crosstalk and signal reflection in a cable may be easily controlled in a cable by shielding and the use of differential pairs of signal wires, but these aspects are harder to control in a connector by virtue of the various and diverse materials used in the connector, among other considerations. The physical size of the connector in high speed applications also limits the extent to which the connector and terminal structure maybe modified to obtain a particular electrical performance.

Impedance mismatches in a transmission path can cause signal reflection, which often leads to signal losses, cancellation, or the like. Accordingly, it is desirable to keep the impedance consistent over the signal path in order to maintain the integrity of the transmitted signals. The connector to which the cable is terminated and which supplies a means of conveying the transmitted signals to circuitry on the printed circuit board of the device is usually not very well controlled insofar as impedance is concerned and it may vary greatly from that of the cable. A mismatch in impedances between these two elements may result in transmission errors, limited bandwidth and the like.

FIG. 1 illustrates the impedance discontinuity that occurs through a conventional plug and receptacle connector assembly used for signal cables. The impedance through the signal cable approaches a constant, or baseline value, as shown to the right of FIG. 1 at 51. This deviation from the baseline is shown by the solid, bold line at 50. The cable impedance substantially matches the impedance of the circuit board at 52 shown to the left of FIG. 1 and to the left of the "PCB Termination" axis. The vertical axis "M" represents the point of termination between the socket, or receptacle, connector and the printed circuit board, while the vertical axis "N" represents the interface that occurs between the two mating plug and socket connectors, and the vertical axis "P" represents the point where the plug connector is terminated to the cable.

These corresponding regions defined by the axes "M", "N" and "P" can be seen in FIG. 4 for a typical connector assembly 100 of the socket and plug type that is disposed between a cable 105 and a printed circuit board (PCB) 103. As shown in FIG. 4, a connector 100 has a plurality of terminals 102 extending through through-holes in the PCB 103 for electrical connection to various portions of the PCB and to electronic circuitry typically mounted thereon. Of course, connector 100 could alternatively have its terminals 106 configured for a surface mount to the PCB 103.

The curve 50 of FIG. 1 represents the typical impedance "discontinuity" achieved with conventional connectors and indicates three peaks and valleys that occur, with each such peak or valley having respective distances (or values) H_x, H₂ and H₃ from the baseline as shown. These distances are measured in ohms with the base of the vertical axis that intersects with the horizontal "Distance" axis having a zero (0) ohm value. In these conventional connector assemblies, the high impedance as represented by H_l5 will typically increase to about 150 ohms, whereas the low impedance as represented by H₂ will typically decrease to about 60 ohms. This wide discontinuity between H-i and H₂ of about 90 ohms affects the electrical performance of the connectors with respect to the printed circuit board and the cable.

The present invention pertains to a connector and to connector termination structures that are particularly useful in I/O (" input-output") applications that has an improved structure that permits the impedance of the connector to be set so that it emulates the cable to which it is mated and reduces the aforementioned discontinuity. In effect, connectors of the present invention maybe "tuned" through their design to improve the electrical performance of the connector.

The effect of this tunability is explained in FIG. 1, in which a reduction in the overall impedance discontinuity occurring through a cable to circuit board connector assembly. The impedance discontinuity that is expected to occur in the connectors of the present invention is shown by the dashed line 60 of FIG. 1. The solid line of FIG. 1 represents the typical impedance discontinuity that is experienced in the connector system, and by comparing the dashed and solid lines, the magnitudes of the peaks and valleys of this discontinuity, H_π, H₂₂ and H₃₃ are greatly reduced. The present invention is believed to significantly reduce the overall discontinuity experienced in a conventional connector assembly. In one application, it is believed that the highest level of discontinuity will be about 135 ohms (at H_π) while the lowest level of discontinuity will be about 85 ohms (at H₂₂). The target baseline impedance of connectors of the invention will typically be may vary from about 28 to about 150 ohms, but will preferably be in the range of between about 100 to about 110 ohms with a tolerance of about +/- 5 to +/- 25ohms.

It is contemplated therefore that the connectors of the present invention will have a total discontinuity (the difference between H_u and H₂₂)of about 50 ohms or less, which results in a decrease from the conventional discontinuity of about 90 ohms referred to above of as much as almost 50%. This benefit is believed to originate from the capacitive coupling that occurs among the two differential signal terminals and their associated ground terminal. It will be understood, however, that capacitive coupling is but one aspect that affects the ultimate characteristic impedance of the terminals and the comiector supporting them.

Turning to FIG. 2, one "internal" environment is depicted in which the present invention maybe used. In this environment, the connectors of the present invention are disposed inside of the exterior wall 1108 of an electronic device, such as a computer 1101. Hence, the reference to "internal." The connectors of the present invention may also be used in an "external" application, as illustrated in FIG. 3, wherein one of the connectors 1110 is mounted to the PCB 1103, but extends partly through the exterior wall 1108 of the device 1101 so that it may be accessed by a user from the exterior of the device 1101. The connector assembly 1100 includes a pair of first and second inter-engaging connectors, described herein as a respective receptacle (or socket) connector 1110 and a plug connector 1104. One of these two connectors 1110 is mounted to the PCB 1103 of the device 1101, while the other connector 1104 is typically terminated to a cable 1105 that leads to a peripheral device.

The structure of the socket connector 1110 illustrated in FIG. 3 permits it to be used in the "internal" application shown in FIG. 2, as well as in "external" applications where the connector 1110 is mounted to the circuit board 1103, but where the connector 1110 extends partially through and is accessible from an exterior wall 1108 of the electronic device.

FIG. 5 is a cross-sectional view of a typical cable, generally designated by reference numeral 1105. The illustrated cable complies with the IEEE 1394b standard for use in interconnecting high speed electronic equipment, specifically in an automotive environment. Cable 1105 may contain two pairs of twisted pair wires 1114 and 1115 disposed within cable 1105 in side-by-side relationship, such as along a generally horizontal axis in the orientation shown in FIG. 5. For example, the signals present on the twisted pair 1114 may be referred to as A+ and A- and the signals present on the twisted pair 1115 may be referred to as B+ and B-. Twisted pairs 1114 and 1115 extend the length of the cable and may be of #24 AWG wire that is surrounded by an electrically insulating cover. The twisted pairs may be disposed in an electrically conductive shield 1118 and 1119, respectively, such as a metal foil, braided wire, or the like.. Such conductive shields 1118 and 1119 may utilized as a ground in cable 1105. If used, a pair of power conductors 1116 and 1117 may also be disposed within cable 1105, such as along the vertical orientation depicted in FIG. 5. An electrically insulating cover 1120 typically encases the twisted pairs 1114 and 1115, and the power conductors 1116 and 1117. Additionally, another conductive shield (not shown) such as conductive foil or braided wire may be disposed underneath the cover 1120 of cable 1105.

FIGS. 6-8 are views of a receptacle or socket connector 1130, constructed in accordance with the principles of the present invention, that is particularly suitable for use in automotive applications. As seen in FIG. 6, the connector 1130 includes a mating cavity, generally designated 1132, for receiving a complementary shaped plug connector 1140 (FIG. 15). Connector 1130 includes an electrically insulative housing 1133 that may be formed from a dielectric material. If desired, portions of the outer surfaces of connector 1130 maybe fabricated with a metallic conductive coating or shield to provide electromagnetic shielding for the electrically conductive terminals therein. A back wall 1134 of connector 1130 is configured with a plurality of cavities for receiving and supporting a plurality of electrically conductive terminals 1141 through 1152. These terminal-receiving cavities preferably extend completrely through the connector housing 1133.

As mentioned earlier, one of the objects of the present invention is to provide a connector having an impedance that more closely resembles that of the system (such as the cable) impedance than is typically found in multi-circuit connectors. The present invention accomplishes this by way of what shall be referred to herein as a modified or pseudo "triplet". A conventional triplet is an arrangement of three distinct terminals in a generally triangular configuration. Such a conventional triplet further involves the use of two differential signal terminals and a single associated ground terminal that are arranged to mate with corresponding terminals of the plug connector 1140 which are terminated to the wires of a differential (preferably a twisted pair of wires), such as one of the twisted pairs 1114 or 1115 in FIG. 21 and a ground. The terminals that form the triplet carry signals that are complements of each other; for example, +1.0 volts and -1.0 volts as well as a ground complement.

In accordance with a primary aspect of the present invention, the terminals 1141-1152 of the connector 1130 in FIG. 6 are selected to provide an equivalent triplet. In order to "tune" the electrical characteristics of the connector 1130 and more closely emulate the impedance of the system, a plurality of ground terminals is provided in association with each set of differential signal terminals. For example, in the connector 1130 of FIG. 6, two terminals 1147 and 1149 may be selected for the differential pair signals A+ and A- and terminals 1141 and 1142 may be selected as ground terminals associated with the A+ and A- signals to form a first equivalent triplet. As is understood in the art, this set of differential signal terminals 1147, 1149 and the pair of associated ground terminals 1141, 1142 define a single differential signal transmission line, or channel.

Similarly, the terminals 1144, 1146, 1151 and 1152 may constitute a second differential signal transmission line or channel, with terminal 1144 & 1146 being chosen for the differential pair signals B+ and B- and terminals 1151 & 1152 being chosen as the ground terminals associated with the B+ and B- signals to form a second equivalent triplet. Note that the signals A+ and A- are selected to be at the left of the lower row of terminals 1147-1152 while the signals B+ and B- are selected to be at the right of the upper row of terminals 1141- 1146 so that the two differential signal transmission channels are located in different areas of the connector. In this respect, the triplet formed by terminals 1144, 1146 and 1151-1152 may be said to be inverted from the triplet formed by terminals 1141-1142, 1147 and 1149. This provides better isolation of the nearest signal terminals of the respective triplets, such as terminals 1144 and 1149 than if these signal terminals were adjacently disposed in the same row. These triplets may also be described in terms of their spatial location in that imaginary lines drawn through the centers of the two differential signal terminals of one signal transmission channel and one of the two ground terminals of that same channel define a triangular pattern and the centers of these terminal define vertices of the imaginary triangle. Such imaginary triangular patterns may be inverted as shown in the drawings. Terminals 1143 and 1150 may be reserved for electrical power, or may be additional ground terminals. If reserved for power, terminals 1143 and 1150 will emulate the low impedance of the ground terminals at the higher frequencies of the signals on the signal terminals 1144, 1146-1147 and 149. For this reason, terminals 1143 and 1150 may be referred to as "power grounds".

In accordance with another primary aspect of the present invention, the terminal position between the differential signal terminals is left vacant or unused. For example, the terminal position 1145' between differential signal terminals 1144 and 1146 is unused. This causes the horizontal spacing between terminals 1144 and 1146 to be greater than the vertical spacing between terminals 1144 and 1146 and the nearest ground or power ground terminal, such as terminals 1150-1152. The horizontal spacing between the differential signal terminal of each signal channel is also greater than the horizontal spacing between the associated ground terminals of that same signal channel. The result is that the differential signal terminals 144 and 146 will be somewhat decoupled. By contrast, the differential signal terminals will be more closely coupled to the ground and power ground terminals 1150-1152 which will lower the impedance in connector 1130 to the signals present on differential signal terminals 1144 and 1146 at the signal frequencies of interest.

Similarly, a vacant or unused terminal position 1148' is interposed between the differential signal terminals 1147 and 1149 in the other triplet for the same reasons and to the same effect. Preferably, no terminals are inserted into the vacant terminal positions 1145' and 148' since any terminals inserted into these positions would tend to defeat the desired level of decoupling between the respective signal teπninals 1144, 1146 and 1147, 1149. Thus, when all of the terminals in connector 1130 are collectively referred to herein as terminals 1141- 1152, it will be understood that there may be no terminals in terminal positions 1145' and 1148'.

As seen in FIGS. 7 & 8, ground terminals 1141 and 1142 are preferably bridged by a conductive metal portion 1154 to provide a common ground, thereby further reducing the impedance seen at the connector. Similarly, ground terminals 1151 and 1152 are bridged by a conductive metal portion 1155 to provide a common ground for the same purpose and to the same effect. The metal bridging portions 1154 and 1155 may be integrally formed at the time that the ground terminals are manufactured, or may thereafter be added, such as by known welding techniques. It can be seen from the drawings that the bridging portions 1154, 1155 are located on what may be referred to as the body portions of the terminals and these body portions are portions that interconnect the tails and contact portions of each terminal together. Although the bridging portions are illustrated on the vertical extend of the terminals and not the horizontal extent in which the terminal contact portions lie, it will be understood that they maybe located in other areas of the two ground terminals, including the horizontal extents thereof. Preferably the interconnection occurs between the contact and tail portions of the terminals. The interconnection of two teπninals cooperatively defines a common ground path for the pair of differential signal terminal associated with the ground tenninals. If terminals 1143 and 1150 are not needed for power, these terminals may also be used as ground terminals, and the bridging portions 1154 and 1155 may extend from the other adjacently located ground terminals to terminals 1143 and 1150, thereby providing three adjacent bridged and common ground terminals 1141-1143 in the upper row associated with differential signal teπninals 1147 and 1149. Similarly, three adjacent bridged and common ground terminals 1150-1152 in the lower row will be associated with the differential signal teπninals 1144 and 1146.

Although the preferred embodiment illustrates terminals 1141-1152 arranged in two parallel rows, or in two spaced apart and parallel planes, it will be understood that such these terminals need not lie in exact parallel rows or spaced apart and parallel planes to obtain the advantages of the invention. For example, connector 1130 may be provided with only one set of triplets instead of the two sets illustrated in FIGS. 6-8. Since one of the primary aspects of the invention is to provide a plurality of ground terminals in closer spatial relationship with the signal terminals than with each other, the two inverted triplets in FIG. 6 may be separated or spaced apart with the benefits of the invention continuing to be maintained. Also, there is no need that the rows defined by the ground teπninals and by the signal terminals of the two triplets be in alignment, i.e., the triplets could be in staggered relationship as long as each triplets remains in effect.

With this equivalent triplet structure, each pair of the differential signal terminals of the cable or circuit have an individual ground terminal associated with them that extends from end-to-end through the connector, thereby more closely emulating both the cable and its associated plug connector from an electrical performance aspect. Such a structure keeps the signal wires of the cable "seeing" the ground in the same manner throughout the length of the cable and in substantially the same manner through the plug and receptacle connector interface and on to the circuit board. This connector interface is shown schematically in FIG 4. and may be considered as divided into four distinct Regions, I-IN, insofar as the impedance and electrical performance of the overall connection assembly or system is concerned. Region I refers to the cable 105 and its structure, while Region II refers to the termination area between the cable connector 104 and the cable 105 when the cable is terminated to the connector. Region III refers to the mating interface existent between the cable connector and the board connector 110 that includes the mating body portion of the connectors 104, 110. Region IN refers to the area that includes the termination between the board connector 110 and the circuit board 103. The lines "P, N, and M" of FIG. 4 have been superimposed upon FIG. 1.

The presence of an associated ground with the signal terminals importantly imparts capacitive coupling between the three terminals. This coupling is one aspect that affects the ultimate characteristic impedance of the terminals and their connector. The resistance, terminal material and self-inductance are also components that affect the overall characteristic impedance of the connector insofar as the triplet of terminals is concerned. In the embodiment shown in FIG. 6, the effective width of the ground terminals 1141-1142, combined with the power ground terminal 1143, is sufficiently broad to extend over the signal terminals 1147 and 1149. Collectively, teπninals 1141-1143 provide an effective ground plane in proximity to the signal terminals 1147 and 1149. This ground plane defined by terminals 1141-1143 is closer to the signal terminals than the signal terminals are to each other, and hence like coupling between the signal terminals is maintained. This permits the impedance of the connector to be tuned from a spacing aspect.

The effect of this tunability is explained in FIG. 1, in which a reduction in the overall impedance discontinuity or variation occurring through the connector assembly is demonstrated. The impedance discontinuity that is expected to occur in the connectors of the present invention is shown by the dashed line 60 of FIG. 1. It will be noted that the magnitude of the peaks and valleys, H_π, H₂₂ and H₃₃ is greatly reduced. The present invention is believed to significantly reduce the overall discontinuity experienced in a conventional connector assembly. In one application, it is believed that the highest level of discontinuity will be about 135 ohms (at H_n) while the lowest level of discontinuity will be about 85 ohms (at H₂₂). The target baseline impedance of connectors of the invention will typically be about 110 ohms with a tolerance of about +/- 25 ohms. It is contemplated therefore that the connectors of the present invention will have a total discontinuity (the difference between H and H₂₂)of about 50 ohms, which results in a decrease from the conventional discontinuity of about 90 ohms referred to above by as much as almost 50%.

Returning now to FIGS. 6-8, as teπninals 1141-1152 pass through the back wall 1134 of connector 1130, each terminal bends through about 90 degrees to extend downwardly (FIG. 7) to make electrical connection with a printed circuit board, such as PCB 1103 in FIGS. 1 & 2. As the teπninals extend downwardly, it is important to maintain the same spatial relationship of the terminals to one another, as discussed above with respect to the terminal location and spatial relationships within the cavity 1132 in FIG. 6. This will maintain the equivalent triplet relationships, and therefore the improved impedance perfoπnance. No matter what planes the teπninals lie in, it is desired to maintain the triplet arrangement of the terminals. By manipulating the distance between the ground and signal terminals, the impedance of the system maybe changed, or "tuned." This is done because capacitive coupling occurs between the two signal wires (and terminals) as well as each of the signal lines and the ground lines (and terminals). The spacing of the terminals also affects the impedance of the system. The widths of the ground and signal terminals also affects the coupling and the impedance of the system, which also includes the resistance of the terminals, which in turn is also a function of the dimensions of the terminals.

Prior to insertion in a printed circuit board, the downwardly depending terminals 1141- 1152 in FIG. 7 are maintained in the desired spatial relationship by perforations in an insulative membrane 1158 that is attached to the underside of connector 1130. After the connector 1130 is inserted in a printed circuit board, the through-holes and solder provide a stronger means of maintaining the spatial relationships amongst the various terminals.

The relationships among the various terminals are shown in diagrammatically in FIGS. 10-12. Each of these diagrams illustrates two rows of six terminals, with the rows being parallel to one another. Each diagram also shows that terminals 1141, 1142, 1151 and 1152 are selected to be ground terminals G, that terminal positions 1145 and 1148 are unused or vacant terminals X, that terminal positions 1144 and 1146 are the differential signal terminals B+ and B-, respectively, and that terminal positions 1147 and 1149 are the differential signal terminals A+ and A-, respectively. In FIGS. 19 & 11, terminal positions 1143 and 1150 are the terminals power ground Gp. In FIG. 12, terminal positions 1143 and 1150 are additional ground terminals G, as in those situations where power is not supplied through the connector 1130. In FIG. 11, a diagonal line 160 indicates the diagonal orientation or placement of the ground power terminals between the triplet defined by terminals 1141-1142, 1147 and 1149, and the triplet defined by terminals 1144, 1146 and 1151-1152. This diagonal line may be considered as a line of symmetry that separates the differential pairs and their associated grounds. Five terminal passages are on each side of the line of symmetry and the orientation of the signal and ground terminals. However, as previously stated above, the ground power terminals Gp act as additional ground terminals due to the typical low impedance of a power supply.

An alternative embodiment of a connector 1170 constructed in accordance with the invention is illustrated in FIGS. 9-14. This alternative embodiment is substantially identical in structure and operation to the connector 1130 of FIGS. 6-8, except that connector 1170 is formed without the unused or vacant tenninal positions 1145' and 1148' of FIGS. 6-8. However, this embodiment continues to maintain the spacing between the differential signal terminals as though the vacant terminal positions 1145' and 1148' were present, as in FIGS. 6- 8. The absence of the vacant terminal positions 1145' and 1148' in the embodiment illustrated in FIGS. 9 & 13 may assist in avoiding mistakes during assembly, such as by inserting terminals into the desired vacant terminal positions. As is illustrated in FIG. 9, in this embodiment, the connector is formed without the terminal-receiving passages that are left vacant so that mis-insertion of terminals into these vacant positions may be avoided during assembly of the connector.

FIGS. 15-17 illustrate the socket connector 1130 of FIGS. 6-8 in combination with an opposing mating connector 1140. Mating connector 1140 has an insulative connector housing 1171 formed from a dielectric material in a complementary configuration to the cavity 1134 of the receptacle connector 1130 so as to facilitate and ensure the proper mating therebetween. The housing 1171 contains a plurality of internal cavities for securing and supporting mating terminals (not shown) that electrically engage the terminals 1141-1152 of the connector 1130 when the mating connector is fully inserted into the cavity 1134 of connector 1130. In this respect, the internal cavities and the terminals of mating connector 1140 are configured and spaced to align with the coπesponding tenninals 1141-1152 of connector 1130. Thus, mating connector 1140 also maintains the desired triplet configuration between the differential signal terminals and the plurality of ground terminals. Accordingly, mating connector 1140 also provides a relatively low impedance deviation as shown by the impedance curve 60 in FIG. 1.

The wires from the cable may be individually terminated in mating connector 1140, as shown in FIGS. 15 and 16. Alternatively, as shown in FIG. 17, each of the triplets in the form of a cable 1173 and 1174, and consisting of the differential signal pairs and the plurality of grounds, may be terminated at the mating connector 1140, with the power wires 1175 and 1176 individually terminated.

Claims

Claims:

1. A connector for providing a connection between differential signal circuits, wherein each differential signal circuit includes a pair of differential signal conductors and two associated ground conductors, the connector comprising: an electrically insulative housing, the housing having a plurality of terminal- receiving cavities disposed in said housing, the terminal-receiving cavities being disposed in a pattern within said housing for supporting electrically conductive terminals in at least first and second distinct rows within said housing; a plurality of electrically conductive terminals supported in some of said terminal-receiving cavities of said housing, said terminals including at least one distinct teπninal set that includes a pair of differential signal terminals and at least two associated ground reference terminals, the pair of differential signal terminals of the one terminal set being disposed in terminal-receiving cavities in said first row and the two ground reference terminals of the one terminal set being disposed in terminal-receiving cavities in said second row , said two ground reference terminals of said one terminal set being further interconnected to cooperatively define a common ground path fof said pair of differential signal terminals; and, said pair of differential signal terminals having a empty terminal-receiving cavity interposed between such that said differential signal terminals are spaced apart a first distance and said differential signal terminals are spaced apart from said two associated ground terminals a second distance, the first distance being greater than the second distance.

2. The connector of claim 1 , wherein each of said terminal includes a contact portion, a tail portion and a body portion that interconnects the contact and tail portions together.

3. The connector of claim 2, wherein said body and tail portions of each terminal extend at an angle to said contact portions thereof..

4. The connector of claim 2, wherein said two ground reference terminals are interconnected by a bridging piece along their body portions

5. The connector of claim 4, wherein said bridging pieces are integrally formed as part of said two ground reference terminals.

6. The connector of claim 4, wherein said contact portions extend horizontally through said housing and said body portions extend vertically, said bridging pieces interconnecting said two ground reference terminals together along their vertical extent.

7. The connector of claim 1, further including a circuit board engaging said terminal tail portions.

8. The connector of claim 1, further including a second distinct terminal set that includes a second pair of differential signal terminals and at least two second associated ground reference terminals, the second pair of differential signal terminals of the one terminal set being disposed in terminal-receiving cavities in said second row and the two second ground reference terminals of the second teπninal set being disposed in terminal- receiving cavities in said first row , said two ground reference terminals of said one terminal set being further interconnected together; and, said second pair of differential signal terminals also having a empty terminal- receiving cavity interposed between them such that said second pair of differential signal terminals are spaced apart by a third distance and said second pair of differential signal terminals are spaced apart from said second two associated ground terminals a fourth distance, the third distance being greater than the fourth distance.

9. The connector of claim 8, wherein said first and third distances are equal.

10. The connector of claim 9, wherein said second and fourth distances are equal.

11. The connector of claim 8, wherein said plurality of terminals further includes first and second power terminals, the first power terminal being disposed in said first row adjacent to said two associated ground reference terminals of said one terminal set, the second power terminal being disposed in said second row adjacent said two associated ground reference terminals of said second teπninal set.

12. The connector of claim 11, wherein said first and second power terminals are respectively disposed in said first and second rows in an offset manner so that an imaginary line drawn through the first and second power terminals extends at an angle across said first and second rows.

13 The connector of claim 8, wherein said plurality of terminals further includes first and second additional ground terminals power terminals, the first additional ground terminal being disposed in said first row adjacent to said two associated ground reference terminals of said one teπninal set, the second additional ground terminal being disposed in said second row adjacent said two associated ground reference terminals of said second terminal set.

14. The connector of claim 13, wherein said first and second additional ground terminals are respectively disposed in said first and second rows in an offset manner so that an imaginary line drawn through the first and second power terminals extends at an angle across said first and second rows.

15. A contact arrangement for a differential signal connector having an insulative housing and a plurality of conductive terminals supported in the housing, each of the terminals including a t least opposing contact and tail portions, the contact portions contacting opposing terminals of a mating connector, the arrangement comprising: the terminals defining at least a first differential signal channel that includes a first pair of differential signal terminal and a first pair of associated ground terminals, the first differential signal set terminals being disposed in first and second rows in said housing, the first row including said first pair of differential signal terminals and said second row including said first pair of associated ground terminals, said first pair of associated ground terminals being disposed in said second row adjacent each other and spaced apart from each other by a first distance, said first pair of differential signal terminals being disposed in said first row adjacent each other but spaced apart from each other a second distance that is greater then the first distance.

16. The contact arrangement of claim 15, wherein said first pair of associated ground terminals are interconnected together.

17. The contact arrangement of claim 16, wherein said first pair of associated ground terminals are interconnected to each other between said contact and tail portions thereof.

18. The contact arrangement of claim 15, wherein said housing includes a plurality of terminal-receiving passages, and said first pair of differential signal terminals are received within two of the terminal-receiving passages and are separated from each other by an intervening, empty terminal-receiving passage.

19. The contact aπangement of claim 15, wherein said the terminals further define a second differential signal channel that includes a second pair of differential signal terminals and a second pair of associated ground terminals disposed in said first and second rows of said housing, the second pair of associated ground terminals being spaced apart from each other by said first distance, and said second pair of differential signal terminals being spaced apart from each other by said second distance.

20. The contact aπangement of claim 19, wherein said second pair of differential signal terminals are disposed in said second row of said housing and said second pair of associated ground terminals are disposed in said first row of said housing..

21. An electrical connector comprising: a housing which holds signal contacts and ground contacts that are arranged in at least two rows, each of the rows including at least a pair of differential signal contacts lying adjacent each other, and at least a pair of said ground contacts, wherein each said pair of differential signal contacts in one of said rows is opposed to a respective pair of ground contacts in another of said rows to form a signal transmission channel, the signal transmission channels being arranged consecutively along the rows in an alternating inverted sequence such that, within each said row, said pair of adjacent said signal contacts of one said signal transmission channel is spaced apart within said row from a pair of said ground contacts of a different said signal transmission channel, said ground contact pairs of each of said signal transmission channels being interconnected together to cooperatively define a common ground path associated with said pair of differential signal terminals of said signal transmission channel.

22. The electrical connector as recited in claim 21 , wherein, for each of said signal transmission channels, said pair of differential signal terminals are spaced apart from each other widthwise a first distance and said two rows of terminals are spaced apart from each other a second distance, the first distance is greater than said second distance.

23. The electrical connector as recited in claim 21, wherein imaginary lines drawn through vertices of said pair of said differential signal terminals and either of said pair of associated ground contacts in any of said signal transmission channels form an imaginary triangular pattern.

24. The electrical connector as recited in claim 23, wherein the triangular shaped pattern for consecutive said signal transmission channels are inverted with respect to said triangular shaped pattern for a previous said signal transmission channel.