Patent Application
20140027155
This invention relates to electrical connectors and cables for signal transmission.
As signal bandwidth demands have increased, the issue of signal cross-contamination, commonly referred to as “crosstalk”, has become ever more challenging. Increasing bandwidth requires a proportional increase in signal frequency, which in turn makes it easier for signal energy to jump the dielectric barrier between adjacent signal transmission lines.
Examples of methods generally employed to prevent external interference of signal transmission include twisted pair cabling and differential mode signal transmission. Twisted pair cabling is a type of wiring in which two conductors of a single circuit are twisted together for the purposes of canceling out electromagnetic interference from external sources. Differential mode signal transmission, or the simultaneous transmission of a signal on one line conductor and an equal and opposite signal on the other, was introduced in twisted pair and parallel conductor transmission applications to provide a simple means of cancelling undesired external noise.
RS-422, USB, and Ethernet protocols, which are common protocols for high-speed signal transmission, all employ differential mode signals. In those protocols where multiple transmission lines are bundled together for collective data transmission, the problem of crosstalk becomes an issue. Because all signals are differential mode, the possibility of the differential signal in one twisted pair inducing differential interference within an adjacent pair is considerable.
Ethernet in particular, which has rapidly progressed from 10 Mbps to 1000 Mbps service bandwidths, has created the need of ever more stringent control of signal contamination between adjacent pairs. Most high-end Ethernet connections employ a registered jack (RJ) connector to minimize crosstalk. However, even with RJ connectors, each connection point creates a means by which crosstalk can occur, the magnitude of which is proportional to the physical and electrical lengths of that connection.
As differential signal connectors have been introduced into military and industrial applications, the demand has increased for specifically designed differential signal connectors to reliably operate in harsh usage environments and conditions, also known as “ruggedized” connectors. As used herein, “ruggedized” means specifically designed to reliably operate in harsh usage environments and conditions, such as strong vibrations, extreme temperatures, wet conditions, and/or dusty conditions. Some designs for such connectors included placing an RJ connector within a larger protective connector, preventing dust and water ingress, but those designs maintained the RJ connector's spring contacts which were not ideal when subjected to mechanical shocks or vibrations. More traditional pin-and-socket connectors, such as M12 style connectors, offer a much more robust, reliable, and compact interface with similar ingress protection. However, the crosstalk introduced by lengthy connections limit performance.
The Telecommunications Industry Association (“TIA”) has set new category protocols increasing the difficulty in the production of a cable and connectors that meets performance demands with respect to crosstalk. The transmission standards for “Category 6” cable has proven elusive for manufacturers of differential signal connectors. Category 6 Ethernet is far less tolerant of crosstalk than the earlier Category 5e, which is necessary for the clear transmission of information at high frequencies in all four data pairs of such connectors operating in full duplex mode.
Embodiments of the inventive differential mode signal connectors and cable assemblies described herein overcome the disadvantages of previous differential mode signal connectors and cable assemblies.
In accordance with one embodiment of the invention, there is provided a cable assembly including a cable and a plurality of conductor pairs extending therethrough, wherein each conductor in a first conductor pair is equidistant to each conductor in a second conductor pair adjacent to the first conductor pair. A connector assembly attached to an end of the cable includes a plurality of connector contact pairs extending through the connector, wherein each connector contact is associated with a conductor.
In accordance with another embodiment of the invention, there is provided a connector assembly comprising a housing and a plurality of connector contact pairs extending through said housing, wherein each connector contact in a first connector contact pair is equidistant to each connector contact in a second connector contact pair adjacent to the first connector contact pair. An odd number of connector contact pairs may be present in the connector assembly.
The connector assembly according to one embodiment of the invention is preferably a hermetically sealed connector.
Other aspects and advantages of the invention will be apparent from the following detailed description wherein reference is made to the accompanying drawings. In order that the invention may be more fully understood, the following figures are provided by way of illustration, in which:
a is a cross-sectional view of two adjacent conductor pairs according to an embodiment of the present invention;
b is a cross-sectional view of two conductor pairs according to a second embodiment of the present invention;
c is a cross-sectional view of two conductor pairs according to a third embodiment of the present invention;
a is a cross-sectional view of a prior art connector demonstrating a spatial optimum pattern;
b is a cross-sectional view of another prior art connector demonstrating a spatial optimum pattern;
a is a cross-sectional view of a contact pattern according to one embodiment of the present invention;
b is a cross-sectional view of a contact pattern according to another embodiment of the present invention;
c is a cross-sectional view of a contact pattern according to yet another embodiment of the present invention;
a is a cross-sectional view of a first contact pattern tested for Category 6 Near-End Crosstalk;
b is a cross-sectional view of a second contact pattern tested for Category 6 Near-End Crosstalk;
c is a cross-sectional view of a third contact pattern tested for Category 6 compliance;
d is a cross-sectional view of a fourth contact pattern tested for Category 6 compliance;
e is a cross-sectional view of a fifth contact pattern tested for Category 6 compliance;
f is a cross-sectional view of a sixth contact pattern tested for Category 6 compliance;
g is a cross-sectional view of a seventh contact pattern tested for Category 6 compliance;
h is a cross-sectional view of an eighth contact pattern tested for Category 6 compliance;
i is a cross-sectional view of a ninth contact pattern tested for Category 6 compliance;
j is a cross-sectional view of a tenth contact pattern tested for Category 6 compliance;
k is a cross-sectional view of a contact pattern according to an embodiment of the present invention tested for Category 6 compliance; and
l is a cross-sectional view of a contact pattern according to another embodiment of the present invention tested for Category 6 compliance.
a is a cross-sectional view of four conductors 10a, 10b, 12a, and 12b arranged in a “T” pattern. According to one embodiment of the invention, a first conductor pair 10a, 10b is oriented perpendicular to a second conductor pair 12a, 12b, such that each conductor in the first conductor pair is equidistant to the conductors in the adjacent second conductor pair. As used herein, the term “equidistant” means that each conductor in a first conductor pair is substantially the same distance to each conductor in a second conductor pair. Preferably, the difference between lengths L1 and L2 or H1 and H2 is within 5% of either length and more preferably 2% or less of either length.
In the embodiment illustrated in
b is a cross-sectional view of four conductors 10a, 10b, 12a, and 12b arranged in a “+” pattern. According to an embodiment of the invention, a first conductor pair 10a, 10b and a second conductor pair 12a, 12b are oriented such that the two pairs share a midpoint and each conductor in one pair is equidistant to the conductors in the other pair. Similar to
By arranging the conductor pairs according to an embodiment of the present invention, crosstalk between adjacent pairs can be resolved to common mode. Thus, crosstalk is prevented by the implementation of a design in which conductor pairs 10, 12 are laid out not in a flat pattern, but in an alternating pattern of horizontally and vertically arranged pairs. The vertical pairs will receive a noise signal from the adjacent horizontal pairs which is purely a common mode signal, and will induce no net signal in those adjacent pairs for the entirety of the length of a cable. Common mode interference is cancelled by differential signal processing architecture and, thus, constitutes no undesired noise. The differential signal transmitted through the second pair of conductors 12a, 12b self-cancels noise induced in the first pair of conductors 10a, 10b, while noise received by the second conductor pair 12a, 12b is resolved to common mode.
When manufacturing cable, parallel conductors make for inexpensive and efficient construction because such cables, such as ribbon cable, can be produced from continuous processes involving well-known fabrication equipment. Wires can be pulled through and the insulation material can then be continuously extruded over them. Twisted pairs, on the other hand, need wires to be constantly wound about each other, and, in multiline cables, pairs need to be further wound about each other in a helical lay. Twisted pairs require more elaborate tooling and are more difficult to build in longer runs. As such, the process of making cables including twisted conductor pairs is ordinarily much more expensive than parallel conductor cable.
The disadvantage associated with parallel conductors, as noted above, is their susceptibility to noise, not only from external sources, but also between adjacent transmission lines. Because each wire of a given pair induces and in turn receives noise from one and only one adjacent unpaired conductor, crosstalk is by nature a differential noise signal, which can degrade the available data transmission bandwidth. However, ribbon cable manufactured in accordance with aspects of the present invention demonstrate acceptable crosstalk levels between adjacent unpaired conductors for differential signal transmission applications, such as Gigabit Ethernet.
The ability to feed high-quality differential signals on parallel conductors allows Ethernet and other data protocols to be implemented more easily and more cost effectively than what has previously been achieved. Less expensive cables and simpler connectors could be developed to take advantage of the conductor or connector pattern made according to an embodiment of the present invention. In addition to cable, layered circuit boards and other transmission lines can take advantage of this conductor geometry. On a layered circuit board, horizontal conductor pairs may be printed on a single layer along a first plane, while each conductor forming a vertical pair and extending in the same direction as the horizontal pair would be printed on separate planes either above or below the plane of the horizontal pairs, such that each conductor in the vertical pair is equidistant to each of the conductors in the horizontal pair and all of the conductors are substantially parallel to each other. The conductors may have any form, so long as the cross-sectional area of the conductors are similar in size and shape.
With respect to the connector assembly affixed to the end of the cable, patterns for the connector contacts or “contacts” extending through the body of the connector assembly may be arranged to minimize the overall size of a connector. Crosstalk readings can be affected by connection length, insulation material, contact spacing, wiring arrangement, termination style, and termination quality. However, proximity is the main driver of crosstalk, such that adjacently-wired data pairs will likely have the worst crosstalk performance. Since size and weight can be factors in connector selection, spatially optimized contact patterns are conventionally used, and very little attention has been paid to the impact of contact pattern geometry on crosstalk performance. Examples of spatial optimum patterns for contacts currently used in the art are shown in
One embodiment of the present invention provides a connector assembly that includes pairs of connector contacts in a “T” pattern, such as the connector “T” pattern described above with respect to
In
For two-pair differential mode signal transmission, the “T” or “+” pattern arrangement is theoretically perfect for purposes of avoiding crosstalk. When adding additional data pairs beyond two, the challenge becomes more difficult. However, it is still possible, regardless of the number of pairs or the overall shape of the desired connector package, to ensure that all adjacent contact pairs are arranged in a manner which enforces the basic “T” pattern. As illustrated in
Although crosstalk between adjacent pairs within a repeating “T” pattern will be zero, crosstalk between non-adjacent pairs will be non-zero. Since nonadjacent pairs are further separated, and are often buffered by adjacent-pair field effects, the magnitude of this crosstalk is an amount such that these contact patterns might be regarded as an optimal balance of data performance and spatial efficiency. In both instances, additional space may be needed over and above what is needed for a spatially optimized contact configuration.
For example, to accommodate the repeating “T” pattern of four contact pairs illustrated in the embodiment of
As the present invention provides a connector that may incorporate a traditional pin and socket design, the connector may be made using various methods of insulating and retaining the contacts within the connector housing known to those skilled in the art. One method of connector retention employs resilient plastic or metal spring clips to locate and retain the individual contacts. Each clip is designed to allow a contact to be inserted from one direction, and retain that contact once inserted to the proper depth. While this type of connector may be ideal for electrical applications where noise and signal cross-contamination need to be carefully controlled, retainer clip inserts have the drawback of being relatively difficult to seal hermetically, and are not particularly robust mechanically. Some designs may show susceptibility to vibration and there are applications where a tamper-resistant connector will be highly desirable. Therefore, while any method known to those skilled in the art may be employed for retention or insulation of the contacts in the connectors of the present invention, methods that will produce a ruggedized connector are employed in one embodiment. In one embodiment, the connector is hermetically sealed.
The electrical contacts may be insulated by encapsulating them within a molded insulation material. Encapsulation may be performed using techniques that will be understood by one of ordinary skill in the art from the description herein. This material could be rubber or a rigid plastic, e.g. thermoplastic, thermoset, etc. The contact may be completely and intimately surrounded by the dielectric to hermetically seal the contact. Some molded inserts, such as MIL-C-24231 receptacles, must be terminated prior to molding the insulator, while others, such as MIL-C-24231 plugs, can be terminated afterwards. In almost all instances of the latter case, multi-contact inserts must be solder-terminated. Because of the nature of the molding processes involved, the dielectric insulation may be a solid material.
Molded inserts are mechanically robust because they are composed of a uniform piece of material and are not susceptible to damage which may occur when contacts are inserted. They are also easier to seal hermetically because many materials can be bonded to metal contacts and a smooth outside surface condition is easier to achieve for elastomeric seals. Molded connectors are tamper-resistant, mechanically robust, and the insulation material can be chosen to suit any particular thermal or chemical environment. They also are relatively inexpensive in large volumes because the molding process can be automated.
The connectors may also be glass to metal seal connectors according to one embodiment of the present invention. Glass to metal seal connectors are currently the style of choice when end users require a connector that will be put into a harsh environment, e.g. oil & gas drilling, extreme underwater depths with submarines and ROV's, high altitude aircraft, nuclear reactors, etc., because the connectors are mechanically robust and can perform well in such harsh environments. In conditions of over 30,000 PSI of pressure or at temperatures in excess of 300° C., the connectors exhibit little to no degradation of performance. They achieve this by using metal housings typically of high grade materials, e.g. stainless steel 316L, K500 Monel, titanium alloy, etc. Glass preforms and electrical contacts are then loaded into the metal housings into differing configurations, and the assembly is then placed into a furnace at a temperature high enough to melt the glass around the contacts, but low enough to not melt or distort the contacts or the metal housings. If the glass and metal have substantially different coefficients of thermal expansion, the part is subjected to a specific cooling cycle after the glass is melted to form a compression seal. If the coefficients are substantially similar, the materials will form a matched seal upon cooling.
Glass to metal seals can come in various shapes, sizes, and styles. The glass used can be configured in many different ways to achieve particular design objectives. There are low temperature glasses that will melt at lower temperatures, which can be useful if the final assembly requires multiple glass seal steps. A high temperature glass can then be glass sealed into a larger assembly using a lower temperature glass. Low temperature glass can also be useful if the metals being used have lower melting points or annealing temperatures. The glass can be drawn and cut to size, sintered from glass powder, or cast from a molten state. The glass is the insulation dielectric in a glass to metal seal, and will typically have a dielectric constant between 5 and 6.
Embodiments of the invention that incorporate a conductor pair or connector contact pair pattern, such as illustrated in
Embodiments of the invention also include differential mode signal connectors and cable assemblies that may be adequately ruggedized for military and industrial applications that are easily manufactured, and are therefore a cost-effective alternative to present differential mode signal connectors and cable assemblies.
The present invention may be best understood in view of the following non-limiting example. Using like materials (the same dielectric insulation material, pin contacts, socket contacts, and cable were employed), and varying only the contact pattern geometry, various different contact arrangements, as shown in
As shown in Table 1, spatially optimized contact configurations fared much worse than those which spread the contact pairs a greater distance, but ultimately the configuration which performed the best were the contact configurations according to the present invention in
This “T” pattern geometry incorporated into the various designs of the present invention has implications wherever differential mode communications are used in cables and traditional pin and socket contact connectors. For Ethernet applications, which are perhaps the most common use of such communications, this technology places Category 6 performance within easy reach of traditional connector designs. Traditional pin and socket connectors are much more robust and reliable than RJ connectors; therefore, the present invention which incorporates pin and socket connectors may be easily ruggedized for military or industrial applications. Despite the need to provide additional space to accommodate the optimal contact pattern for the connector assembly of the present invention, the present invention provides a connector design having a more efficient use of space than encapsulated RJ designs. Further, this technology provides a clear set of design guidelines for arranging contacts and conductors for multiple differential mode communication lines, whether used by themselves, or in combination with other elements within the same connector package. Lastly, by reducing crosstalk, higher transmission frequencies will be made available for RS-422, Ethernet, and other differential signal data transmission protocols, which may in turn lead to the development of less expensive, more robust, and higher bandwidth extensions of these protocols.
While preferred embodiments of the invention have been shown and described herein, it will be understood that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will occur to those skilled in the art without departing from the spirit of the invention. Accordingly, it is intended that the appended claims cover all such variations as fall within the spirit and scope of the invention.
