Differential signal cable assembly

A differential signal cable assembly includes a connector to be connected to a communication device, a first multi-pair cable that is connected to the connector at one end and includes a plurality of first differential signal cables for transmitting differential signals, a second multi-pair cable that includes a plurality of second differential signal cables having a larger conductor diameter than the first differential signal cables, and a connection that is connected to an other end of the first multi-pair cable and one end of the second multi-pair cable such that each of the first differential signal cables is electrically connected to a corresponding one of the second differential signal cables.

The present application is based on Japanese patent application No. 2017-231888 filed on Dec. 1, 2017, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a differential signal cable assembly.

2. Description of the Related Art

A differential signal cable assembly is known which is provided with a multi-pair cable having plural differential signal cables for transmitting differential signals and connectors provided at both ends of the multi-pair cable (see, e.g., US 2017/0194751).

It is known that in some differential signal cable assemblies, connectors having substantially the same shape as an optical transceiver module are used. For example, in a differential signal cable assembly having connectors compliant with the QSFP (Quad Small Form-factor Pluggable) standard, a multi-pair cable having eight differential signal cables is used to support four transmit and receive channels. Regarding the number of the differential signal cables, it is sometimes expressed as 1-pair, 2-pair . . . , 8-pair, and so on since each differential signal cable has two cores (signal lines).

SUMMARY OF THE INVENTION

Along with an increase in channel capacity in recent years, it is required to increase the number of available transmit and receive channels per differential signal cable assembly. In recent years, a technique allowing for transmission/reception with eight channels, called QSFP-DD, is under development and there is a demand for a differential signal cable assembly capable of transmission/reception with not less than eight channels.

However, an increase in size of connector is not desirable in view of achieving higher density and larger capacity even if more channels can be provided. According to the QSFP-DD standard mentioned above, the size of connector is substantially the same as that specified in the QSFP standard, which means that sixteen differential signal cables need to be connected to a connector having substantially the same size as before.

Thus, differential signal cables having a smaller conductor diameter than before have to be used. However, differential signal cables having a small conductor diameter have large losses (attenuation of signals) and a transmission distance thus needs to be short.

It is an object of the invention to provide a differential signal cable assembly that has a sufficient transmission distance even when the number of channels is increased.

According to an embodiment of the invention, a differential signal cable assembly comprise:a connector to be connected to a communication device;a first multi-pair cable that is connected to the connector at one end and comprises a plurality of first differential signal cables for transmitting differential signals;a second multi-pair cable that comprises a plurality of second differential signal cables having a larger conductor diameter than the first differential signal cables; anda connection that is connected to an other end of the first multi-pair cable and one end of the second multi-pair cable such that each of the first differential signal cables is electrically connected to a corresponding one of the second differential signal cables.

Effects of the Invention

According to an embodiment of the invention, a differential signal cable assembly can be provided that has a sufficient transmission distance even when the number of channels is increased.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment

An embodiment of the invention will be described below in conjunction with the appended drawings.

General Configuration of Differential Signal Cable Assembly

FIG. 1is a perspective view showing a differential signal cable assembly (hereinafter, simply referred to as “cable assembly”) in the present embodiment. A cable assembly1is provided with connectors2to be connected to a communication device, first multi-pair cables3connected to the connectors2, second multi-pair cables4, and connections5which connect the first multi-pair cables3to the second multi-pair cables4.

The connector2is, e.g., a pluggable module connector compliant with the QSFP-DD standard. The connector2has a connector housing21and a connector substrate22housed in the connector housing21. A card edge connector portion22aformed by aligning electrodes is provided at an edge of the connector substrate22.

For connection between the connectors2in the cable assembly1of the present embodiment, the first multi-pair cables3having a relatively small conductor diameter (small outer diameter) are used only at portions close to the connectors2and the second multi-pair cables4having a relatively large conductor diameter (large outer diameter) are used at the other portion. In other words, in the cable assembly1, the long second multi-pair cables4having large outer diameter and conductor diameter and suitable for long distance transmission are connected to the connectors2via the short first multi-pair cables3having small outer diameter and conductor diameter.

The first multi-pair cables3used as connection to the connectors2have small outer diameter and conductor diameter and thus can be connected to the small connectors2even when the number of channels is increased. Use of only the first multi-pair cables3having a small conductor diameter does not allow a sufficient transmission distance to be ensured due to large a loss, but since the second multi-pair cables4having a large conductor diameter are used at the middle portion of the cable, it is possible to ensure a sufficient transmission distance. Furthermore, the cable in the vicinity of the connectors2can be bent easily, which facilitates cable laying work. Next, each component of the differential signal cable assembly1will be described in detail.

The first multi-pair cable3is connected to the connector2at one end and to the connection5at the other end. In this example, two 8-pair first multi-pair cables3each having eight first differential signal cables30for transmitting differential signals are used to support transmission/reception with eight channels. However, the number of first differential signal cables30contained in the first multi-pair cable3and the number of the first multi-pair cables3to be used are not limited thereto. For example, one 16-pair first multi-pair cable3may be used.

FIG. 2Ais a cross sectional view showing the first multi-pair cable3. In the first multi-pair cable3, a tape-shaped separator31is wound around two twisted first differential signal cables30and six other first differential signal cables30are spirally twisted therearound, as shown inFIG. 2A. The first multi-pair cable3also has a shielding tape32wound around all the eight first differential signal cables30, braided wires33covering the shielding tape32, and a jacket34covering the braided wires33. All the plural first differential signal cables30are shielded by the shielding tape32and the braided wires33.

Materials used to form general cables can be used as the respective materials of the shielding tape32, the braided wires33and the jacket34. The separator31is formed of, e.g., paper, yarn or foam. The foam is, e.g., polyolefin foam such as polypropylene foam or ethylene foam.

The first differential signal cable30has a pair of first signal lines301, a first insulation302covering the pair of first signal lines301, and a first shield303covering the first insulation302.

The first signal line301is a conductor wire formed of copper, etc., and transmits a differential signal. The pair of first signal lines301are covered with the single first insulation302. In other words, the first differential signal cable30has a two cores-in-one coating structure.

Based on the study by the present inventor, the conductor diameter of the first signal line301needs to be at least not more than 30 AWG (American Wire Gauge) (not more than 0.254 mm) in order to be connectable to the connector2compliant with the QSFP-DD standard. In this regard, however, even when the conductor diameter is 30 AWG, connection is not possible unless the first differential signal cable30is largely squashed. Therefore, the conductor diameter of the first signal line301is preferably not more than 0.2 mm, more preferably, not more than 34 AWG (not more than 0.16 mm). In the present embodiment, the conductor diameter of the first signal line301is 34 AWG

Characteristic impedance needs to a predetermined value. Thus, the smaller the conductor diameter, the smaller the outer diameter (the size) of the first differential signal cable30and the outer diameter of the entire first multi-pair cable3. In other words, the conductor diameter and the outer diameter of the first differential signal cable30have a positive correlation, and when the conductor diameter is determined, the outer diameter of the first differential signal cable30is automatically determined. Therefore, in the present embodiment, the size of the first differential signal cable30is determined based on the conductor diameter.

The first insulation302has an elliptical shape or an racetrack shape (a shape formed of two parallel straight lines of the same length and semi-circular arcs connecting ends of the two straight lines, a rounded rectangular shape) in cross-section so that a major axis direction thereof coincides with an alignment direction of the first signal lines301and the center in the major and minor axis directions coincide with the center point of a line segment connecting between the centers of the first signal lines301. In this example, the first insulation302is formed in an elliptical shape.

It is possible to use the first insulation302formed of, e.g., an insulating material such as polyethylene, polytetrafluoroethylene (PTFE) or tetrafluoroethylene-hexafluoropropylene copolymer (FEP). It is also possible to use the first insulation302formed of a foamed insulating material such as polyethylene foam. The first insulation302having a permittivity of about 1.5 to 3 can be used.

Furthermore, to facilitate installation to the connector substrate22, it is possible to use the first insulation302formed of a fluorine resin such as Teflon (registered trademark). Use of fluorine resin for a long cable is not realistic since it is expensive. However, since the first multi-pair cables3are short in the present embodiment, an increase in the cost can be relatively small even when using the first insulation302formed of fluorine resin. By using a fluorine resin to form the first insulation302, heat resistance of the first insulation302is improved and the first insulation302is less likely to melt by heat during soldering to the connector substrate22, allowing, e.g., plural first signal lines301to be connected at a time by soldering and thereby facilitating connection work to the connector2. It is very effective to improve workability particularly in case that the connector2is compliant with the QSFP-DD standard, etc., since many first differential signal cables30need to be connected to the small connector2.

The first shield303is formed by winding a shielding tape around the first insulation302. The shielding tape has a conductor layer and an insulation layer formed on one surface of the conductor layer even though it is not shown in the drawing. A strip-shaped conductive metal foil such as copper foil or aluminum foil can be used as the conductor layer, and an insulating resin such as polyester can be used as the insulation layer. A copper-polyester tape formed by providing a polyester insulation layer on one surface of a copper conductive layer is used in this example.

The first shield303is desirably formed by spirally winding (spirally wrapping) a shielding tape around the first insulation302. This allows for easier bending as compared to when longitudinally wrapping the shielding tape. In addition, it is difficult to manufacture a thin first differential signal cable30when employing longitudinal wrapping due to extensibility of the shielding tape, but it is easy to manufacture a thin first differential signal cable30when spirally winding the shielding tape.

In case that the shielding tape is spirally wound, it is known that a phenomenon called suck-out, which is significant attenuation of differential signal, occurs in a specific high-frequency region. Thus, the length of the first multi-pair cable3is adjusted to the extent that the effect of suck-out does not cause any problem. In detail, the length of the first multi-pair cable3is preferably not more than 30 cm, more preferably, not more than 20 cm.

FIG. 2Bis a cross sectional view showing the second multi-pair cable4. As shown inFIG. 2B, the second multi-pair cable4has substantially the same structure as the first multi-pair cable3.

That is, in the second multi-pair cable4, a tape-shaped separator41is wound around two twisted second differential signal cables40and six other second differential signal cables40are spirally twisted therearound. The second multi-pair cable4also has a shielding tape42wound around all the eight second differential signal cables40, braided wires43covering the shielding tape42, and a jacket44covering the braided wires43.

The second differential signal cable40has a pair of second signal lines401, a second insulation402covering the pair of second signal lines401, and a second shield403covering the second insulation402. The materials of the second signal line401, the second insulation402and the second shield403are the same as those used for the first multi-pair cable3and the explanation thereof is omitted. However, use of an expensive fluorine resin to form the second insulation402is not preferable since the second multi-pair cable4is long.

The conductor diameter of the second signal line401is larger than that of the first signal line301. In view of increasing a transmission distance, the conductor diameter of the second signal line401is desirably as large as possible. In detail, the conductor diameter of the second signal line401is preferably not less than 0.4 mm, more preferably, not less than 26 AWG (not less than 0.404 mm). In addition, a difference between the conductor diameter of the second signal line401and the conductor diameter of the first signal line301is desirably not less than 1.5 mm.

To prevent the suck-out mentioned above, the second shield403is formed by longitudinally wrapping a shielding tape around the second insulation402. This suppresses the effect of suck-out in the second multi-pair cable4and allows for transmission of, e.g., not less than 25 Gbit/s (gigabit per second).

The connection5is provided for electrically connecting each first differential signal cable30of the first multi-pair cable3to the corresponding second differential signal cable40of the second multi-pair cable4.

FIG. 3is a plan view showing a connecting circuit board used in the connection5.FIGS. 4A and 4Bare diagrams illustrating the connection5, whereinFIG. 4Ais a plan view in which a connection case and a connection shield member are omitted andFIG. 4Bis a side view in which the connection case and the connection shield member are shown as the cross section.

The connection5has connecting circuit boards51on which the first differential signal cables30are connected to the second differential signal cables40, a connection shield member52surrounding the connecting circuit boards51, and a connection case53housing the connecting circuit boards51and the connection shield member52. In the present embodiment, the connection5has two connecting circuit boards51each of which connects one first multi-pair cable3(eight first differential signal cables30) to one second multi-pair cable4(eight second differential signal cables40). The connection shield member52and the connection case53are provided to surround both the two connecting circuit boards51.

The connecting circuit board51has signal patterns510connecting the signal lines301and401of the first differential signal cables30and the second differential signal cables40to each other, and ground patterns511connecting the shields303and403of the first differential signal cables30and the second differential signal cables40to each other.

The signal pattern510has first electrodes510ato which the first signal lines301are soldered, second electrodes510bto which the second signal lines401are soldered, and connecting portions510celectrically connecting the both electrodes510aand510bto each other. The ground pattern511is formed in a rectangular frame shape surrounding the signal patterns510. The shields303,403of the both differential signal cables30,40are soldered to the ground pattern511.

Although only the front surface of the connecting circuit board51is shown inFIG. 3, the same patterns510and511are formed on the back surface (seeFIG. 4B). The ground patterns511on the front and back surfaces of the connecting circuit board51are electrically connected by multiple through-holes512. Four pairs of differential signal cables30and40are connected to each of the front and back surfaces of the connecting circuit board51. In addition, the differential signal cables30,40for transmission and reception of the same channel are arranged to face each other with the connecting circuit board51sandwiched therebetween.

In the present embodiment, the two split ground patterns511are provided on the front and back surface of the connecting circuit board51. This is because if an area of the ground pattern511is too large, heat applied during soldering is likely to escape through the ground pattern511and soldering workability decreases. By providing the split ground patterns511, it is possible to promptly raise the temperature when heating, thereby improving soldering workability.

Although one ground pattern511is allocated for two channels (two pairs of differential signal cables30,40to be soldered) in the present embodiment, one ground pattern511may be allocated for each channel (each pair of differential signal cables30,40to be soldered).

The connection case53is provided to protect the connecting circuit boards51and is, e.g., a molded component formed of a resin. The connection case53has a structure easily attached so as to surround the connecting circuit boards51, e.g., a two-part structure or a structure with hinges.

The connection shield member52functions in the same manner as the shielding tapes32,42and the braided wires33,43of the multi-pair cables3,4. The connection shield member52is provided to surround all portions not covered with the shielding tapes32,42and the braided wires33,43in the connection5, i.e., to surround the differential signal cables30and40extending out of the ends of the multi-pair cables3and4and the connecting circuit boards51. In this example, the shielding tapes32,42are folded back over the jackets34,44at the ends of the multi-pair cables3,4, and the connection shield member52is provided so as to be electrically connected to the folded-back portions of the shielding tapes32,42.

In addition, in the present embodiment, the connection shield member52is provided integrally with the inner surface of the connection case53. As a result, it is possible to reduce the number of components, and it is also possible to configure so that the connection shield member52comes into contact with the folded-back portions of the shielding tapes32,42at the time of attaching the connection case53, which improves workability during assembly. The connection shield member52may be formed of a metal plating applied to the inner surface of the connection case53, or may be formed of a metal sheet attached to the inner surface of the connection case53.

However, it is not limited thereto. For example, after forming the connection shield member52by winding a metal tape such as aluminum tape, the connection case53for protection may be provided therearound.

Alternatively, the connection case53may be a molded resin provided to surround the connecting circuit boards51and the connection shield member52. Furthermore, the connector housing21and the connection case53may be integrated. For example, a molded resin may be provided to cover all the connector substrate22, the first multi-pair cable3, the connecting circuit boards51and the entire connection shield member52.

Functions and Effects of the Embodiment

As described above, the differential signal cable assembly in the present embodiment is provided with the connectors2to be connected to a communication device, the first multi-pair cables3which are connected to the connectors2at one end and have plural first differential signal cables30for transmitting differential signals, the second multi-pair cables4which have plural second differential signal cables40having a larger conductor diameter than the first differential signal cable30, and the connections5which are connected to the other ends of the first multi-pair cables3and one ends of the second multi-pair cables4so that each of the first differential signal cables30is electrically connected to the corresponding second differential signal cable40.

The first multi-pair cables3(the first differential signal cables30) to be connected to the connectors2thus can be reduced in diameter and can be connected to the small connectors2even when the number of channels is increased. In addition, since the first multi-pair cables3(the first differential signal cables30) have a reduced diameter, the cable in the vicinity of the connectors2can be bent easily after the connectors2are connected to the communication device and it is thus easy to lay the cable. In addition, by connecting the first multi-pair cables3to the second multi-pair cables4having a large conductor diameter, it is possible to reduce loss (attenuation of signals) and thereby ensure a sufficient transmission distance.

Modifications

Although the first multi-pair cables3each having plural twisted first differential signal cables30are used in the embodiment, a first multi-pair cable3aconstructed from a flat cable having non-twisted parallel first differential signal cables30may be used, as is a cable assembly1ashown inFIGS. 5A and 5B. Although the first multi-pair cable3aused in the example shown inFIG. 5is a 16-pair flat cable in which two rows (in the minor axis direction of the first insulation302) of eight first differential signal cables30(in the major axis direction) are arranged with a plate-shaped separator (base)35between the two rows, for example, two 8-pair flat cables each having two rows of four first differential signal cables30may be used.

In addition, although one connector2is provided at each end in the embodiment, the cable may be branched and provided with two or more connectors2. For example, as is a cable assembly1bshown inFIG. 6, an 8-channel transmit and receive connector2acompliant with the QSFP-DD standard may be provided at one end and two 4-channel transmit and receive connectors2bcompliant with the QSFP standard at the other end. In this case, since the number of channels of the connector2bis small, the connection5and the first multi-pair cables3on the connector2bside are omitted and the second multi-pair cables4are directly connected to the connectors2b.

Furthermore, although the connecting circuit boards51are used in the connection5in the embodiment, the connection5may be configured that the signal lines301,401of the differential signal cables30,40are directly connected to each other by welding, etc.

Furthermore, although it is not mentioned in the embodiment, a signal processing circuit such as amplifier circuit may be mounted on the connector substrate22of the connector2.

SUMMARY OF THE EMBODIMENT

Technical ideas understood from the embodiment will be described below citing the reference numerals, etc., used for the embodiment. However, each reference numeral described below is not intended to limit the constituent elements in the claims to the members, etc., specifically described in the embodiment.

[1] A differential signal cable assembly (1), comprising: a connector (2) to be connected to a communication device; a first multi-pair cable (3) that is connected to the connector (2) at one end and comprises a plurality of first differential signal cables (30) for transmitting differential signals; a second multi-pair cable (4) that comprises a plurality of second differential signal cables (40) having a larger conductor diameter than the first differential signal cables (30); and a connection (5) that is connected to an other end of the first multi-pair cables (3) and one end of the second multi-pair cables (4) such that each of the first differential signal cables (30) is electrically connected to a corresponding one of the second differential signal cables (40).

[2] The differential signal cable assembly (1) defined by [1], wherein the conductor diameter of the first differential signal cables (30) is not more than 0.2 mm.

[3] The differential signal cable assembly (1) defined by [2], wherein the conductor diameter of the second differential signal cables (40) is not less than 0.4 mm.

[4] The differential signal cable assembly (1) defined by any one of [1] to [3], wherein the first differential signal cables (30) each comprise a pair of first signal lines (301), a first insulation (302) covering the pair of first signal lines (301), and a first shield (303) comprising a shielding tape that comprises a conductor layer and an insulation layer formed on one surface of the conductor layer and is spirally wound around the first insulation (302).

[5] The differential signal cable assembly (1) defined by [4], wherein the first insulation (302) comprises a fluorine resin.

[6] The differential signal cable assembly (1) defined by any one of [1] to [5], wherein the second differential signal cables (40) each comprise a pair of second signal lines (401), a second insulation (402) covering the pair of second signal lines (401), and a second shield (403) comprising a shielding tape that comprises a conductor layer and an insulation layer formed on one surface of the conductor layer and is longitudinally wrapped around the second insulation (402).

[7] The differential signal cable assembly (1) defined by any one of [1] to [6], wherein the connection (5) comprises a connecting circuit board (51) electrically connecting the first differential signal cables (30) to the second differential signal cables (40), and a connection shield member (52) surrounding the connecting circuit boards (51).

[8] The differential signal cable assembly (1) defined by [7], wherein the connection (5) comprises a connection case (53) for housing the connecting circuit boards (51), and the connection shield member (52) is provided integrally with the connection case (53).

Although the embodiment of the invention has been described, the invention according to claims is not to be limited to the embodiment. Further, please note that all combinations of the features described in the embodiment are not necessary to solve the problem of the invention. In addition, the invention can be appropriately modified and implemented without departing from the gist thereof.