GB2314466A

GB2314466A - Capacitor array for reducing cross-talk in connectors

Info

Publication number: GB2314466A
Application number: GB9711853A
Authority: GB
Inventors: Golam Mabud Choudhury; Theodore Alan Conorich; Michael Gregory German; Amid Ihsan Hashim; Ronald William Kohl; Julian Robert Pharney
Original assignee: Lucent Technologies Inc
Current assignee: Nokia of America Corp
Priority date: 1996-06-21
Filing date: 1997-06-09
Publication date: 1997-12-24
Anticipated expiration: 2017-06-09
Also published as: AU2492097A; AU717619B2; GB2314466B; NZ328143A; GB9711853D0

Abstract

A capacitor array 15 is formed from a board 16 having multiple layers 17, 18, 19 with conductive paths 20, 30, 40, 21, 31, 41, 22, 32, 42, 62, 72, 82 on selected layers. Paths across the layers are aligned and sufficiently close that each aligned array e.g. 20, 30, 40 acts as a single solid capacitor plate. Capacitive coupling between pairs of plates e.g. 20, 30, 40 and 21, 31, 41 produces crosstalk. A conductor of a connector may be connected to each plate, for example by a through-plated vias T, R and short traces 28, 29. The crosstalk between the plates is equal and opposite to the crosstalk between the conductors thereby cancels the crosstalk of conductors. Crosstalk cancellation between adjacent pairs of plates may occur.

Description

DEVICE FOR REDUCING NEAR-END CROSSTALK Field of the Invention This invention relates to electrical connectors, and in particular to a device for reducing crosstalk in connectors.

Background of the Invention Standards for crosstalk in connectors has become increasingly stringent.

For example, in category 5 of ANSVIIAgA-568A Standard, it is required that a 25 pair ribbon cable connector exhibit pair to pair near-end crosstalk loss which is better than 40dB at 100MHz. Since the 25 pair miniature ribbon connector is designed to carry the signals for a multitude of work stations, this requirement has to be met on a power sum basis. This is a more stringent requirement since for each pair, crosstalk couplings from all the other pairs must be consider Recently, it has been proposed to produce a category 5 connector by inclusion of conductors in a side-by-side relation to provide crosstalk of a polarity opposite to that of the mating section of the connector. (See U.S. Patent Application Serial No. 08/263,111 filed June 21, 1994.) It has also been proposed to reduce crosstalk, for example in modular jacks, by crossing over certain conductors. (See U.S. Patent No. 5,186,647 issued to Denkmann et al.).

It has also been suggested that certain conductors in a modular jack could be mounted above certain other conductors to provide capacitive coupling and thereby induce opposite polarity crosstalk. The conductors could be formed as lead frames or printed on a printed circuit board (See British Patent No. 2,271,678 issued to Pinney et al.) It has also been suggested that a printed wiring board connector could compensate for crosstalk in its mating section by including capacitive coupling unbalance between conductor pairs which produced crosstalk of an opposite polarity.

(See, U.S. Patent Application of Conorich et al, case 5-8-1, filed on an even date herewith.) Since most multi-pair printed circuit board connectors, however, are not capable of category 5 performance, it is desirable to provide a device which can economically convert such connectors to category 5 by reducing the crosstalk exhibited by the connectors.

Summary of the Invention The invention is a device for compensating for near-end crosstalk of a first polarity exhibited by an electrical connector including contacts. The device comprises an insulating board including a plurality of layers. At least selected layers include on a surface thereof a plurality of pairs of essentially parallel conductive paths. Each path is vertically aligned with corresponding paths in other layers of the device to form an array which comprises a capacitor plate so that a plurality of capacitor plates is fonned. The capacitor plates are arranged to provide capacitive coupling unbalance between adjacent pairs when a voltage is supplied thereto to produce near-end crosstalk of a second plurality which is opposite to the first polarity. The device further includes means for electrically connecting the connector contacts to the paths.

Brief Description of the Figures These and other features of the invention are delineated in detail in the following description. In the drawing: FIG. 1 is a frontal exploded view of an assembly in accordance with an embodiment of the invention; FIG. 2 is a partly schematic plan view of a device in accordance with the same embodiment; FIG. 3 is a cross sectional view taken along line 3-3 of FIG. 2; FIG. 4 is a cross sectional view taken along line 4 4 of FIG. 2; and FIG. S is an enlarged, schematic view of a portion of the device.

It will be appreciated that, for purposes of illustration, these figures are not necessarily drawn to scale.

Detailed Description Referring now to the drawings, in which like reference numerals identify similar or identical elements, FIG. 1 illustrates an assembly which will result in reduced crosstalk in accordance with an embodiment of the invention A standard connector, 10, includes an insulating housing, 11, which encloses a plurality of contacts. The contacts at one end, 12, form a mating section for receiving a standard cable connector (not shown), for example, a 25 pair cable connector. The other ends of the contacts are formed into pins or eyelets, e.g., 13. Device 15 and printed circuit board 14 provide means of attachment and electrical connection to each pin or eyelet, 13. It is known that the connector, 10, will produce a certain amount of crosstalk in the form of induced voltage of a certain polarity in the mating section, 12. Unless some means are provided within the connector, 10, for reducing crosstalk, the connector will usually not provide category S performance. However, by providing a device, 15, to be described, between the connector, 10, and circuit boared, 14, a category 3 or 4 connector, for example, which exhibits 28-32 dB power sumnearendcrosstalkat at 100 MHz, can be used in combination with the device, 15, to produce category 5 performance exhibiting better than 40 dB power sum near-end crosstalk loss at 100 MilL An example of the device, 15, is shown in more detail in the views of FIGS. 2-5. The device comprises an insulating substrate, 16, which in this example is a printed circuit board material such as FR-4. The substrate, 16, is made up of several dielectric layers, e.g., 17 and 18, separated by epoxy layers, e.g., 19 in a manner known in the art On at least selected dielectric layers, and in this example on each dielectric layer, are formed a plurality of pairs of conductor paths, e.g., 20 and 21, 22 and 23, and 30 and 31, which can be deposited on each major surface of each dielectric layer and patterned by standard techniques such as photolithography.

While eight layers of conductor paths are shown in this example, it will be appreciated that any number can be employed. Each path, e.g., 20, is essentially parallel to the other path, 21, in the pair, and typically is made of copper with a length, 1, of 0.01143 meters, a width, a, of 0.0002 meters and a thickness, h, of 0.00004 meters. Each path, e.g., 20, is also vertically aligned with corresponding paths, e.g., 30, in all the layers of the device, as best seen in FIG. 3. The thicknesses of the layers, 17-19, are chosen to provide a separation, t, between aligned paths in the vertical direction. This separation is typically .025-25 mm. On at least one end of each of the paths, and in this example on both ends, is a via hole, e.g., 24,23,26, and 27. The via holes permit a common electrical connection between each path, e.g., 20 and 30, which is vertically aligned in the several layers. Each path has approximately the same length, but in this embodiment, for reasons discussed later, the paths of adjacent pairs on each layer are shifted in the horizontal direction by an amount, u, as illustrated in FIG. 2.

Between each path in a conductor pair is a pair of plated through holes, e.g., T1 and R1. Each hole is labelled with a 'T" or an "R" and a subscript to indicate that the hole will receive a pin, e.g., 13 of FIG. 1, from the connector which corresponds to a Tip ( I) or Ring (R) contact. Consequently, the holes T1 - T5 and R1 - R5 are aligned in corresponding rows to match the footprint of the connector, 10. Conductive traces, e.g., 28 and 29, are provided between each plated through hole, T1 and R1, respectively, and its corresponding path, 20 and 21, respectively, on at least one layer to permit electrical connection between the pins of the connector, 10, and their appropriate path when the pins are inscrted into the plated through holes.

In accordance with a primary feature of the invention, when the connector pins are inserted through the plated tbrough holes, Tl -T5 and R 1 -R5, and a voltage is supplied thereto, each array of vertically aligned paths, e.g., 21, 31, and 41, in the several layers will electrically act as a single solid capacitor plate.

Each capacitor plate coupled to a connector pin of one type, e.g., Ring, will provide capacitive coupling to an adjacent plate, e.g., 22, 32, and 42, which is coupled to a pin of another type, e.g., Tip to produce capacitive coupling unbalance between the pairs. This phenomenon is made possible by the overlapping of the electric fields associated with each path as illustrated schematically in FIG. 5. As shown, even though each path, e.g., 21 and 31, is a physically separate element, the vertical separation, t, of the paths is sufficiently small so that the electric fields (illustratcd by arrows) between the adjacent paths, e.g., 21 and 22, and 31 and 32, will overlap sufficiently in the vertical direction so that each vertically aligned array of paths acts like a single plate. It is known from Walker, Capacitance, Inductance and Crosstalk Analysis (Artech House 1990) at page 51 that the capacitive coupling, C1, between adjacent inner layer paths, e.g., 31 and 32, is, given by:

where 0 iS the dielectric constant of free space, , is the dielectric constant of the layers 17-19,1 is the length of the paths, and d is the horizontal spacing of the paths. The capacitive coupling, C2, which would occur between, e.g., 31 and 32, paths if the vertical paths, e.g., 21 and 31, and 22 and 32, were single plates, is given by: C2 = (2) Equations 1 and 2 can be solved for "t" by setting C1 equal to C2 to give the appropriate maximum separation for the vertically aligned paths to electrically act as single solid plates. In one example, the spacing, d, was 203 microns, the width, a, of each path was 152 microns, and the thickness, h, of the paths was 35.6 microns giving a maximum separation of 394.9 microns.

This capacitive coupling between unlike paths, e.g., R1 andT2, produces crosstalk which is opposite in polarity to the crosstalk produced in the mating section, 12, of the connector, 10, since the mating section produces crosstalk between adjacent tip conductors or adjacent ring conductors. Thus, an appropriate choice of the size of the paths and distance, d, between the paths will produce sufficient crosstalk in the element, 15, to essentially cancel out the crosstalk produced in the connector, 10. The primary objective is to cancel out enough crosstalk from the mating region to produce power sum near-end crosstalk loss performance of better than 40 dB at 100 MHL It should be appreciated that there will also be coupling between each vertically aligned array of paths, e.g., 21, 31, and 41, and the vertically aligned unlike paths, 62,72, and 82, in the next adjacent pair. The coupling will not be as great as that between adjacent pairs since the distance, dl, between the paths will be much greater. Therefore, to increase the coupling between non-adjacent paths, the conductor pairs are staggered by an amount, u, as shown in FIG. 2. The area of capacitive coupling between adjacent unlike paths, e.g., 21 and 22, is illustrated by the cross hatched region, 60, and the area of coupling between unlike paths in the next adjacent pair, 21 and 62, is illustrated by the speckled region, 61. As shown, the staggering of the positions of adjacent pairs offers a wider area for coupling between non adjacent pairs to at least partially overcome the larger separation.

Once the appropriate layer thickness is chosen so that each vertical array of paths can be treated as a single capacitor plate, the parameters for producing the desired power sum perforrnance can be determined according to the analysis described in U.S. Patent Application of Conorich et al, case 5-8-1, filed on an even date herewith and incorporated by reference herein.

Various modifications are possible. For example, the via holes, e.g., 24-27, can be eliminated and electrical connection between the connector, 10, and the paths on each layer provided by including trace conductors such as 28 and 29 from the plated through holes, e.g., T1 and R1, to the appropriate paths on each layer. Further, each path on a layer can be aligned rather than offset as shown in FIG. 2 if desired In addition, the device 15 could be integrated into a portion of the printed circuit board, 14, to which the connector, 11, is mounted.

Claims

Claims:

1. A device for compensating for nw-end crosstalk of a first polarity and first magnitude exhibited by an electrical connector (10) including contacts, said device CHARACI ERIZED BY: an insulating board (16) including a plurality of layers (e.g, 17, 18,19); a plurality of pairs of essentially parallel conductive paths (e.g., 20, and 21, 22 and 23, and 30,31) formed on a surface of at least selected layers, each path being vertically aligned with corresponding paths in other layers to form an array which comprises a capacitor plate so that a plurality of capacitor plates are formed in the device, the capacitor plates being arranged to provide capacitive coupling unbalance between adjacent pairs when a voltage is supplied thereto to produce near-end crosstalk of a second polarity which is opposite to the first polarity; and means (e.g., 24,25,26 and 27) for electrically connecting the connector contacts to the paths.

2. The device according to claim 1 wherein the crosstalk of a second polarity has a second magnitude which is essentially equal to the first magnitude.

3. The device according to claim 1 wherein the vertical separation (t) between the paths is such that any electrical fields between adjacent paths overlap sufficiently in the vertical direction to provide the electrical equivalent of a solid plate from the vertically aligned paths.

4. The device according to claim 3 wherein the vertical separation is within the range .025 to 25 mm.

5. The device according to claim 1 wherein the means for connecting the connector contacts comprises a plurality of plated through holes (r,R)extending through the board arranged to receive the contacts from the connector, and conductive traces (e.g., 28,29) extending from each hole to a responding path on at least one surface of the board

6. The device according to claim 5 wherein the means for coupling further comprises a plurality of plated via holes (e.g., 24,25,26 and 27), each via hole electrically connecting the paths in a corresponding vertically aligned array.

7. The device according to claim 1 wherein at least some of the arrays of vertically aligned paths are also positioned to providt additional capacitive coupling unbalance between next adjacent pairs.

8* The device according to claim 7 wherein the conductive pairs are horizontally offset in position relative to adjacent conductive pairs.

9. The e device according to claim 1 further comprising the connector and a printed circuit board to which the connector and device are mounted