Communications connector with multi-stage compensation

[0001] This application claims the benefit of U.S. Provisional Application No. 61/088,548, filed Aug. 13, 2008 and is incorporated herein in its entirety.

[0002] There is a need to improve near-end crosstalk NEXT performance of communications connectors at higher frequencies in a robust design that can be relatively easily manufactured. This description is directed to a method of improving NEXT performance in a communication connector by employing specific capacitive and inductive couplings on a printed circuit board (PCB) within the connector.

[0014] Some embodiments of the present invention employ a PCB in a modular jack assembly 10, which includes two-stage capacitor compensation/crosstalk with time delay and a version of a “lattice network.” More particularly, a PCB designed according to embodiments of the present invention may be employed as a rigid board 12 in a communication connector as shown in FIG. 1 and schematically in FIG. 2.

[0015] Other portions of the modular jack assembly 10 include the front housing 14, a contact nose 16 which holds plug interface contacts that are electrically connected to the rigid board 12, insulation displacement contacts (IDCs) 18 which terminate wires of a communication cable (not shown) and also make electrical contact with the rigid board 12, a rear housing 20, and a wiring cap 22. In a completed assembly, the plug interface contacts of the contact nose 16 and the IDCs 18 are inserted via compliant pins into the rigid board 12. The front housing 14 is clipped onto the rear housing 20, and the wiring cap 22 is clipped into the rear housing 20 thereby terminating wires of a communication cable at the IDCs 18.

[0016] The self-inductive stubs of the present invention employ the distributed electrical parameter of inductance per unit length of the circuit trace to produce the inductive elements. Although this configuration is modeled in the schematics below as a discrete inductor (which is appropriate as it has an equivalent effect) it is a distributed inductive component produced by the length of the traces as opposed to turns of a wire coil, for example. In contrast, the capacitors shown herein are discrete capacitors although both the capacitors and the inductors shown can be realized by discrete or distributed components, or as a combination thereof. The lattice network generally includes a crosstalk circuit component and a compensation circuit component, each of which has a different coupling rate versus frequency. A “crosstalk circuit component” is a circuit component in which coupling occurs with the same polarity as crosstalk-producing coupling within a plug, while a “compensation circuit component” is a circuit component in which coupling occurs in an opposite polarity to the crosstalk coupling that occurs within a plug.

[0017] The version of the lattice network used in embodiments of the present invention utilizes a second self-inductive stub connected between a capacitor and the second signal trace to the 2^nd stage crosstalk network. FIG. 3 illustrates a capacitor positioned between two inductors according to one embodiment of the present invention. Positioning the capacitor between the two stubs improves NEXT performance, relative to the opposite transmission direction (IDC to PIC), compared to putting the inductor on only one side of that capacitor, where the inductance of the single inductor, L1, is about equal to L2+L3 as shown in FIG. 3. Additionally, the second stub shows improvements in return loss, also relative to using only a one-sided inductor.

[0018] Self-inductive stubs (shown in FIG. 3) as described herein refer to traces that are made specific lengths to take advantage of their self-inductance. The term “stub” refers to the fact that these traces are not part of the main current-carrying path. They are stubs off of the current carrying path. Preferably, a self-inductive stub ends at a capacitor (i.e., there is no DC connection at the endpoint of the stubs). Current-carrying paths as described herein are traces that allow a DC current to flow between two points (such as the RJ45 plug and the insulation displacement contacts 18 (IDCs) in the jack).

[0019] EIA/TIA Category 6 (“CAT6”) products generally have 8 wires that make up 4 differential pairs. These wires are numbered numerically 1 through 8, and the differential pairs are 45, 36, 12, and 78 (pairs 1, 2, 3, and 4, respectively). The layout of these wires within an RJ45 plug causes crosstalk between these differential pairs that must be compensated for within a jack. Since there are 4 differential pairs, near end crosstalk (NEXT) can form between the six different pair combinations. These pair combinations are 45-36, 45-12, 45-78, 36-12, 36-8, and 12-78.

[0020] Referring to FIGS. 2, 4, and 5, the general design of a CAT6 jack according to one embodiment of the present invention uses time delay compensation for pair combinations 45-36, 36-12, 36-78, and 45-12. Pair combinations 45-36, 36-12, and 36-78 also make use of the lattice compensation technique. The type of lattice network for pair combination 45-36 described here is shown in FIG. 6. The lattice network here utilizes the self-inductance on C34 and C56 to create a “growing vector” in order to increase the overall NEXT bandwidth. Note that in FIG. 6, the effect of the nose 16 is ignored.

[0021] This description takes into account the following:

• • [0022] All capacitor dimensions given are referenced relative to the amount of overlap occurring between the pads. According to some embodiments of the present invention, one conductive pad of each capacitor is oversized 5 mils per side in each direction, for example, to help account for layer-to-layer registration. The dimensions given herein are for the smaller layer. According to one embodiment, capacitors are formed across a 4 mil core, generally made of an FR4 material having a dielectric constant of approximately 4.4.
  • [0023] The capacitance and inductance values given here are for use with one embodiment of an electrical connector. It is to be understood that the principles of the present application can be applied using other capacitance and inductance values. For example, different nose or IDC designs, including different material selection, may make alternative capacitance and inductance values beneficial.
  • [0024] Aspects of the present disclosure may be applied to shielded and/or punchdown-style connectors.
  • [0025] The schematics shown for each description include only the intentional capacitance added by design. For example, mutual inductance between wires is purposely not shown for schematic clarity and due to the fact that any mutual inductance that results from the design is not intentionally used for compensation.
  • [0026] These schematics do not show parasitic capacitances caused by the geometry of the setup unless this parasitic capacitance is deemed important to note (values greater than 0.1 pF). These values are noted, but not labeled with reference characters.
  • [0027] The schematics shown for each pair combination (FIGS. 6-11) do not show all connections since they are only showing two pairs at once. A full schematic of rigid board 12 is shown in FIG. 2. Note that for pair combinations 45-36, 36-12, and 36-78 the stub inductances are split between some of the capacitors. These connections are not completely shown in FIGS. 6-11 and the nomenclature for the inductance reflects which inductors are being used for which capacitors.
  • [0028] The schematics shown attempt to approximate a “middle plug” which refers to a plug whose crosstalk value is in the middle of the range of crosstalk specified for that pair combination.
  • [0029] All circuit board dimensions described in this RS are each individually subject to change (estimates up to 20%). One reason for this is variability of circuit board build tolerances from different circuit board manufacturers. Different material or different processes may be used to manufacture the circuit boards. Therefore, the performance of the circuit board may change even though the artwork is identical due to the capacitance changing. Another reason is to allow for design changes required to compensate for different jack designs that might be needed. Consequently, good engineering practice requires the ability to change the area of overlap for the pad capacitors by the specification tolerance (about ±20%). This change in area may be done on a capacitor-by-capacitor basis; however, it is preferred for the overall board design (trace layout, use of time delay, lattice) to remain constant even though capacitance values may be changed according to some embodiments. Some variants may only require changing the size of one or two capacitors (either smaller or larger), and some may require changing the size of all capacitors.

[0030] Referring to the Figures, and particularly to FIGS. 4 and 5, which show the individual rigid PCB layers' artwork and combined rigid PCB artwork, respectively, the PCB shown here has the following features. Dimensional tolerances for capacitive pads are given for both dimensions.

• • [0031] 1. Current carrying traces are routed between PIC vias and IDC vias with the respective pin numbers. PIC vias refer to the vias where the compliant pins from nose 16 interface with the rigid circuit board 12 in FIG. 1. The IDC vias refer to the vias where the IDCs 18 interface with the rigid circuit board 12 in FIG. 1.
  • [0032] 2. Improved manufacturability of the circuit board that has been achieved over previous CAT6 rigid circuit boards. This improved manufacturability has been achieved through moving capacitors further away from the vias so that they are less susceptible to manufacturing tolerances arising from layer-to-layer registration and tolerances in the drilling (such as capacitors C35 and C46 shown in FIGS. 4 and 5). Additionally, square capacitors are found to be less susceptible to manufacturing tolerances than rectangular capacitors, so most capacitors on the board have been made square.
  • [0033] 3. Crosstalk having the opposite polarity of the net crosstalk caused by the plug for pair combination 45-78 is provided by pad capacitor C47 connected between the 4 and 7 PIC vias, and by pad capacitor C58 connected between IDC via 5 and pin PIC via 8. A schematic for pair connection 45-78 is shown in FIG. 7. Pad capacitor C47 is sized 0.025″ by 0.025″ (±20%), and pad capacitor C58 is sized 0.027″ by 0.027″ (±20%).
  • [0034] 4. Crosstalk compensation for pair combination 45-12 is achieved by using the time delay model. A schematic for pair combination 45-12 is shown in FIG. 8. Pad capacitor C25 has the opposite polarity of the net crosstalk caused by the plug for pair combination 45-12 that connects between PIC vias 2 and 5. Pad capacitor C15 has the same polarity of the net crosstalk caused by the plug for pair combination 45-12 that connects between IDC vias 1 and 5. C15 is time delayed from C25 by approximately 0.395″ (average distance between the 1, 2, 4, and 5 PIC vias to their respective IDC vias). Pad capacitor C25 is 0.042″ by 0.042″±20%, and pad capacitor C15 is 0.033″ by 0.033″±20%.
  • [0035] 5. Crosstalk compensation for pair 45-36 is achieved by using the time delay model and by a lattice network compensation technique. A schematic for pair combination 45-36 is shown in FIG. 9. This time delay and lattice network includes:
    • [0036] a. A pad capacitor C35 connected between PIC vias 3 and 5 having the opposite polarity of the net crosstalk caused by the plug for pair combination 45-36. The pad capacitor C35 is 0.068″ by 0.068″±20%.
    • [0037] b. A pad capacitor C46 is connected between PIC vias 4 and 6 having the opposite polarity of the net crosstalk caused by the plug for pair combination 45-36. The pad capacitor C46 is 0.050″ by 0.093″±20%.
    • [0038] c. A pad capacitor C34 is connected between PIC vias 3 and 4 having the same polarity of the net crosstalk caused by the plug for pair combination 45-36. The pad capacitor C34 is 0.046″ by 0.046″±20%. This capacitor is time delayed from the C35 and C46 capacitors by approximately 0.39″ (the average distance between the 3, 4, 5, and 6 PIC vias to their respective IDC vias). The lattice network is achieved here by the addition of self-inductive stub L3U (approximately 0.9″ in length) and another self-inductive stub L4 (approximately 0.5″ in length).
    • [0039] d. A pad capacitor C56 having the same polarity of the net crosstalk caused by the plug for pair combination 45-36 that connects between IDC vias 5 and 6. The pad capacitor C56 is 0.0304″ by 0.093″±20%. This capacitor is time delayed from the C35 and C46 capacitors by approximately 0.39″ (average distance between the 3, 4, 5, and 6 PIC vias to their respective IDC vias). The lattice network is achieved here by the addition of self-inductive stub L6U and L6L (total length together of about 1.4″). Note that the self-inductance L5 is ignored due to the fact the stub length is minimal.
  • [0040] 6. Crosstalk compensation for pair combination 36-12 is achieved by using the time delay model and by a lattice network compensation technique. A schematic for pair combination 36-12 is shown in FIG. 10. This time delay and lattice network includes:
    • [0041] a. A pad capacitor C13 having opposite polarity of the net crosstalk caused by the plug for pair combination 36-12 that connects between PIC vias 1 and 3. The pad capacitor C13 is 0.046″ by 0.046″±20%.
    • [0042] b. A pad capacitor C26 having opposite polarity of the net crosstalk caused by the plug for pair combination 36-12 that connects between PIC vias 2 and 6. The pad capacitor C26 has an area of 0.00394 square inches±44%.
    • [0043] c. A pad capacitor C16 having the same polarity of the net crosstalk caused by the plug for pair combination 36-12 that connects between IDC vias 1 and 6. The pad capacitor C16 is 0.0335″ by 0.0945″±20%. This capacitor is time delayed from the C13 and C26 capacitors by approximately 0.38″ (the average distance between the 1, 2, 3, and 6 PIC vias to their respective IDC vias). The lattice network is achieved here by the addition of a self-inductive stub L6L (approximate length of 1″) (this is the same L6L stub used by pad capacitor C56).
  • [0044] 7. Crosstalk compensation for pair combination 36-78 is achieved by using the time delay model and by a lattice network compensation technique. A schematic for pair combination 36-78 is shown in FIG. 11. This time delay and lattice network includes:
    • [0045] a. A pad capacitor C37 having opposite polarity of the net crosstalk caused by the plug for pair combination 36-78 that connects between PIC vias 3 and 7. The pad capacitor C37 is 0.058″ by 0.058″±20%.
    • [0046] b. A pad capacitor C38 having the same polarity of the net crosstalk caused by the plug for pair combination 36-78 that connects between IDC via 3 and PIC via 8. The pad capacitor C38 is 0.034″ by 0.034″±20%. This capacitor is time delayed from the C37 capacitor by approximately 0.25″ (average physical distance along the trace between the 3, 6, 7, and 8 PIC vias to their respective IDC vias). The lattice network is achieved here by the addition of self-inductive stub L3U and L3L (total length together of about 1.1″) (this is the same L3U stub used by pad capacitor C34). Note that the self-inductance L8 is ignored due to the fact the stub length is minimal.

[0047] The self inductive stubs, along with corresponding capacitors (for example, the L5-C56-L6 combination and L3-C34-L4 combination n FIG. 6), are an LC circuit with a resonance effect, having a resonant frequency if f_o=1/(2π√LC). The selection of the inductance, L, and capacitance, C, values is generally a nonlinear multivariable optimization with multiple objective functions (NEXT, FEXT, return loss, etc.). Consequently, selection of a given L or C value is not made independent of other circuit considerations. Some of the considerations for selecting a given L value include that if it is too low the resonance point moves to a higher frequency and there may be no desired NEXT improvement in the signal frequency operation range of interest; and if the inductance is too high: a) the inductive traces can become to long to fit on a typical rigid board, b) the resonance can move into the frequency operation range of interest, possibly introducing deleterious effects; and c) there can be a degradation of return loss.