Electrical connectors provide signal connections between electronic devices using signal contacts. In many applications of electrical connectors, for example electrical connectors associated with printed wiring boards (PWB), the physical characteristics and close proximity of the signal contacts within the electrical connector may cause degradation of signal integrity. Two causes of signal degradation in electrical connectors are commonly referred to as “skew” and “crosstalk.”
Degradation of signal integrity may be caused by signal propagation delay in one conductor with regard to a related conducted. Signal propagation delay is commonly referred to as “signal skew” or “skew.” One cause of skew in an electrical connector is varying electrical paths within the connector through which signals are conducted. In particular, the electrical path of one conductor will be different than the electrical path of another conductor if the physical length of the conductors in the respective paths are not equal. For example, in differential signal transmission where one signal is carried over two conductors, if the first electrical path for the signal is through a conductor that is physically longer than a conductor used in the second electrical path, the propagation time for each signal through the paths may not be equal. The unequal signal propagation time causes signal skew and degrades signal integrity.
Skew is a particular concern when connecting co-planar devices such as printed wiring boards or printed circuit boards. Often, two right-angle connectors are used when connecting co-planar devices. Each right angle connector may inherently create skew, and therefore, the use of two such connectors in combination intensifies the skew, creating significant degradation of signal integrity. FIG. 1 shows skew associated with prior art, co-planar connectors. FIG. 1 is a side cross section view of prior art, right-angle connectors 173, 174 used to connect two substantially co-planar devices 171, 172. FIG. 1 shows two transmission paths 175, 176 through connectors 173, 174 from device 171 to device 172. In right angle-connector 173, transmission path 175 is longer than transmission path 176, creating signal skew. Likewise, right angle connector 174 suffers from signal skew as well because transmission path 175 is also longer than transmission path 176. Connecting devices 171, 172 using right angle connectors 173, 174 increases the skew that would be present if the devices were connected in a perpendicular manner using just one of the right angle connectors 173, 174.
Another cause of signal degradation is commonly called “crosstalk.” Crosstalk occurs when one signal contact induces electrical interference in another signal contact that is in proximity to it. The electrical interference is caused by intermingling electrical fields between the two contacts. Such interference is a particular problem when signal contacts are closely spaced in electrical connectors. Like skew, crosstalk also may cause significant degradation of signal integrity.
Solutions to the problems of signal skew and crosstalk in an electrical connector are generally in tension. It is well-known in the art of electrical connectors that one way of minimizing skew is to decrease the physical spacing between signal contacts. Decreasing the spacing minimizes skew because the differences in the electrical path—and therefore signal propagation time—are minimized. Decreasing spacing is a welcome solution to skew because, by decreasing spacing, the signal contact density—that is, the number of signal contacts per unit area—of the connector increases.
Minimizing skew by decreasing contact spacing, however, may create or further intensify crosstalk. Crosstalk, as explained, is caused by intermingling electric fields, and therefore placing signal contacts closer together intensifies the intermingling. The solution to the problem of crosstalk is generally to place signal contacts further apart and if possible, to place ground contacts between signal contacts. The solution to crosstalk, therefore, may create or intensify skew and decrease the signal density of the electrical connector.
With electronic device miniaturization and the omnipresent and accelerating need for high speed electronic communications, the reduction of skew and crosstalk are significant goals in electrical connector design. Therefore, there is a need for an electrical connector that minimizes skew and crosstalk while maximizing the signal density of the connector.