HK1019830B - A method and arrangement for minimizing skew - Google Patents

Description

Method and apparatus for minimizing skew distortion

The present invention relates to a method and apparatus for minimizing skew distortion when transmitting signals at high transmission rates to achieve low bit error rates. For example, low error rates are required in data transmission links of switching cores of telecommunications switching centers or switches.

In some cases, the requirements for "fault-free" signal transmission in the field of telecommunications are very high. For example, in the data transmission links of the switching core of the above-mentioned telecommunications switching centers or switches, the bit error rate must be very low.

Reliability can be further improved by using triple transmission, in which three separate links are used, each link transmitting the same information. By comparing the signals/bits received on the three links with each other and applying a majority decision method, it is often possible to sort out the majority of the errors that occur when the three sets of received information differ.

However, at the moment most decision methods are taken, the three sets of signals must arrive at the same time. However, the requirement for precise simultaneity may be difficult to achieve for several reasons. In parallel signal transmission, time deviations or so-called skew distortions can occur in the electronic components and also in the signal transmission lines. By properly configuring the electronic component, skew distortion in the electronic component can be minimized.

At a signal transmission rate of 1 gigabit/second, the "one bit time" is 1 nanosecond. This corresponds to a bit length of 0.2 meters of fiber. When skew distortion is not allowed to exceed one tenth of a bit length, this means that the length difference between different wires in the transmission line does not exceed 2 cm. Therefore, in order to minimize skew distortion that may occur in a transmission line, the transmission line and its individual conductors have been connected/bundled in triplets into a ribbon or flat cable, wherein the length difference between the different conductors in the transmission line does not exceed 2 cm. By providing such a transmission line, for example, a rolled flat ribbon cable that has been divided into accurate, appropriate lengths, e.g. 10 meters, 20 meters, 30 meters, and a maximum length difference between different conductors of ± 1 centimeter, the skew distortion can be minimized when using such a cable. Here, by conductor is first of all meant an optical fiber, although other conductors, such as coaxial conductors or bifilars, are also possible.

For example, when a conductor is to be installed on the end of an optical fibre in a transmission line, the transmission line is first cut to an appropriate length substantially perpendicular to its longitudinal axis, so that the difference in length between the optical fibres, the total length of which is not critical, but only the difference in length between the optical fibres, the maximum of which has been predetermined, will be negligible. The three fibers in the transmission line are then separated from each other along a short distance from the end of the transmission line and coupled to the desired device. Having the correct mutual position of the connectors of the cable after connecting the optical fibres can be very easy to perform and compared with the control measurements of three separate connector-fitted cables. To facilitate separation of the different conductors or fibres, they may be provided with different identifying indicia, symbols and/or different colours. When three optical fibres are secured together along a substantial part of their length, they can be easily brought together for installation, which is advantageous in large scale installations, and the cable sections can be easily separated so that the sections can be installed separately. Skew distortion can be controlled while ensuring a maximum length deviation of 1 cm per optical fiber, and thus it is possible to achieve more reliable signal transmission by means of most decision methods.

Fig. 1 illustrates a three-fiber optical cable provided with a connecting portion and having a prescribed length according to the present invention.

Fig. 2 illustrates one end of the three-fiber optical cable shown in fig. 1, and shows a length deviation of the optical fiber provided with the connection portion.

FIG. 3 illustrates a ribbon cable or ribbon cable stacked upon one another in accordance with the present invention.

FIG. 4 illustrates three rows of side-by-side ribbon cables or ribbons according to the present invention.

Fig. 5A-C illustrate different insulated fiber optic assemblies or insulated conductor assemblies that make up a cable according to the present invention.

Fig. 1 and 2 illustrate a possible configuration of a ribbon or flat cable 1 comprising optical fibers 2. Each optical fibre is surrounded by an insulating protective sheath 3 and is provided with connectors 4 at both ends of the fibre, as shown in the figure. The 3 different sheaths 3 of the optical fiber ribbon 1 are joined to one another in such a way that the central sheath is joined to the two outer sheaths and thus forms an optical fiber ribbon or a flat optical fiber ribbon. When manufacturing the optical fiber ribbon cable, 3 optical fibers having the same length as each other, which are adjacent to each other, are placed in their respective sheaths, and then the sheaths are combined with each other. This enables flat three-fiber cables of various lengths, e.g. 10, 15, 20 or 25 meters, each with an absolute length accuracy of less than ± 1 cm, where a maximum deviation of 5, e.g. 1 cm per side, can be measured and the skew distortion/time deviation will not exceed one tenth of a one-bit time slot at a rate of 1 gigabit/second. When the connector is to be mounted to the end of an optical fiber, the appropriate length of the three-fiber cable is first removed. This will result in negligible length deviation between the fibers. Three jacketed optical fibers are then separated along a short length from the end of the cable and the connector is secured to the cable. This is easily achieved by correctly positioning the connectors in the optical fibres with respect to each other after fixing the connectors. Alternatively, the manufacture of a flat optical cable having a defined length and provided with connectors at its respective ends can be fully automated, wherein the optical fibers, the sheathing material and the connectors are supplied to a flat optical cable or ribbon cable manufacturing apparatus which is capable of producing a finished, measured, connector-provided flat optical cable having three or more optical fibers. It is apparent that, for example, a flat cable or a ribbon cable for a digital telecommunications signaling system may be configured in a similar manner with three or more conductive wires instead of optical fibers. Applying most decision methods when transmitting the same information while precisely manufacturing optical fibers or wires will provide highly reliable and fault-free signal transmission with low error rates.

Fig. 3 and 4 illustrate cables having optical fibers or electrical conductors, respectively, and arranged in triads, wherein fig. 3 illustrates overlapping flat cables 6, and fig. 4 illustrates flat cables 7 arranged side by side in a horizontal plane, each flat cable containing a plurality of optical fibers 8 or electrical conductors. The ribbons of the cable can be easily separated from each other and their individual optical fibers or wires can be easily separated to enable the connector to be mounted thereon. Even in the case of multi-layer ribbon cables, or cables arranged side-by-side in a horizontal plane, the cables can be pre-fabricated with optical fibers/conductors having substantially the same length with a maximum length deviation of ± 1 cm in order to minimize skew distortion.

Fig. 5A-C illustrate another form of a three fiber ribbon cable. Fig. 5A illustrates the optical fiber/conductor jacket bonded together with an intermediate piece of material 10, as opposed to the illustration of fig. 5B, which is absent from fig. 5B. Fig. 5C shows the sheaths arranged in a triangle, seen in cross-section, wherein each sheath 9 is combined with two other sheaths 9. The cables illustrated in fig. 5A-C may be provided with an outer protective sheath. Even in these cases, the sheaths incorporating the optical fibers/wires arranged in a ribbon form or a triangular cross-sectional form, each having an absolute length accuracy of less than ± 1 cm so as to minimize skew distortion, and mounted on the connector, may be configured or prefabricated using the optical fibers/wires having the same length as each other.

Claims (8)

1. A method for minimizing skew distortion when transmitting digital signals at a transmission rate of ultra-high speed information transmission of 1 gigabit/second or more,

securing three or more conductors in parallel and spaced relation to each other, wherein any length difference between said conductors will not exceed a maximum value such that time offset/skew distortion will not exceed a fraction of a bit slot one tenth of a bit slot when transmitting information; and

the wires transmit the same information in parallel at the same time so that majority decision methods are used to avoid bit errors when the information from different wires is different.

2. An apparatus for minimizing skew distortion when transmitting a digital signal at a transmission rate of ultra-high speed information transmission of 1 gigabit/second or more,

securing three or more conductors in parallel and spaced relation to each other, wherein any length difference between said conductors will not exceed a maximum value such that time offset/skew distortion will not exceed a fraction of a bit slot one tenth of a bit slot when transmitting information; and

the wires transmit the same information in parallel at the same time so that majority decision methods are used to avoid bit errors when the information from different wires is different.

3. A device according to claim 2, characterized in that the wires (2) are arranged as a part of a ribbon cable (1).

4. A device according to claim 3, characterized in that three or more ribbon cables (6) are joined together.

5. A device according to claim 3, characterized in that three or more ribbon cables (7) are joined together in a side-by-side relationship.

6. A device according to any of claims 2-5, characterized in that said conductors are equipped with connectors (4).

7. A device according to any of claims 2-5, characterized in that the wires (2) are separated from each other.

8. A device according to any of claims 2-7, characterized in that the length difference (5) is less than 2 cm when transmitting at a rate of 1 gigabit/second or higher.