JP2003077345A - Time skewless multicore unshielded twisted pair cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multicore unshielded twisted pair cable of which, respective twisted pair cables have unified signal propagation properties (signal transmission rate, as well as wave form) between themselves, time skew is made to become very small, and wave form correction is enabled to perform with an identical circuit. SOLUTION: The number of pitch n (turns/m) is made to smoothly change, and the number of pitch n (turns/m) in average at respective twisted pair cables are made to become identical with each other, and respective cables are made to be adjacent with each other with different pitch.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is a device for eliminating a difference in signal propagation time between pairs in a multi-core twisted pair cable (hereinafter referred to as multi-core TWP).

[0002]

2. Description of the Related Art In recent years, a communication line using an inexpensive TWP has been actively applied as a technique for economically transmitting a high-speed digital signal. For example, Ethernet (registered trademark) uses a cable in which four pairs of non-shielded TWPs are integrated.

On the other hand, in the DVI standard, which is a standard for digital signals on a computer screen, a typical 1280X
When a 1024-dot screen is transmitted at a refresh rate of 60 Hz, RGB signals for one dot are transmitted at time intervals of about 10 nSec. Since the signal for 1 dot is expressed by 10 bits, the 1-bit restoration clock of the digital data operates at 1 nSec (1 GHz), and the time tolerance is ± 0.5 nSec. For this reason, the DVI standard uses a shielded TWP to provide a clock signal and
Seed video data is being sent. In this case all T
Since WP uses twisted wires of the same pitch, there is no signal propagation time difference (hereinafter referred to as time skew). However, it is necessary to shield each TWP, which increases the cost. The time skew of an unshielded TWP for Ethernet (registered trademark) currently on the market is as follows. 15nSec to 20nSec (100MBP for 50m cable)
S Ethernet (registered trademark) 10nSec to 13nSec (1GBP with a cable length of 50m
S Ethernet (registered trademark)) Even if an attempt is made to transmit a DVI signal over a long distance using these lines, it is difficult to transmit only a distance of 3 m to 5 m due to a delay time difference between data.

In the present invention, it is recognized that this time skew is caused by the difference in twist pitch between twisted pairs, and by equalizing the average twist pitch of each twisted pair, this time skew is removed, and the twisted pair is twisted. It minimizes crosstalk. This makes it possible to inexpensively produce a cable that does not require a shield and has a small time skew. Figure 1 shows the structure of an existing unshielded TWP cable. The features are as follows. (1) With the structure in which the differential signal lines are stranded, the signal components of the radiation noise to other parties and the radiation noise from other parties are canceled and reduced. (2) In order to accommodate a plurality of TWPs in one cable, the pitch of each TWP is changed to reduce interference between TWPs. (3) Since the structure is simple, the cost can be greatly reduced and it is currently mass-produced.

[0005]

However, due to the structure of the above (2), there is a time difference in signal propagation between the TWPs. The measured values are as follows. Propagation of 50 m 15 nSec to 20 nSec 30 MHz pulse (for 100 MBPS Ethernet (registered trademark)) Propagation of 50 m 10 nSec to 13 nSec 30 MHz pulse (for 1 GBPS Ethernet (registered trademark)) The twist pitch is a cause of the difference in propagation time. It is conceivable that the finer the line length, the longer it becomes. Commercially available TWP for 100 MHz Ethernet (registered trademark)
An example of the pitch of the stranded wire is as follows. Length per twist (λ) Number of twists per 1 m (n) First wire 21 mm / time 47.6 times / m Second wire 19 mm / time 52.6 times / m Third wire 16 mm / time 62.5 Times / m 4th line 14mm / times 71.4 times / m

[0006]

As a method of eliminating the delay time difference due to the pitch difference, a method of changing the pitch on the way is effective.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION For example, the first line is replaced with a fourth line every several meters, (n ₁ and n ₄ are averaged), or the first line is (n ₁ → n ₂ → n ₃ → The time skew difference can be made extremely small (1 ns or less) by cyclically replacing with n ₄ ) and averaging. FIG. 2 shows the case of cyclic replacement. With this method, there are still problems in production when the pitch is suddenly changed, and there is a concern about reflection and crosstalk at the pitch change point. Therefore, in the present proposal, by changing this pitch (n) spatially smoothly, Minimize the cue and set the crosstalk between twisted pairs at the same position on the cable (same cross section on the cable)
So that each TWP is adjacent with a different number of twists (n),
Each n is spatially modulated. This is equivalent to the same TWP being spatially displaced and integrated into a single cable.

N is the number of twists per 1 m, and Λ is n
(1) The twist pitch n of each TWP is as follows: Spatial modulation like. n = no + Δn · cos (2πx / Λ) (2) By providing a spatial phase difference q between the TWPs, the twist pitches n are different between the TWPs at the same x point. ni = no + Δn · cos (2π (x−q) / Λ) For example, in four pairs of standard cables, q = (1/4) Λ
When shifted by (corresponding to 90 °), Δn = (71-47) / 2 = 12 times / m (deviation of pitch number of one commercially available product) no = (71 + 47) / 2 = 59 times / Assuming that m (the average number of pitches of one commercially available product), the first line = no + Δn · cos (2πx / Λ) the second line = no + Δn · cos (2π (x− (1/4) Λ) / Λ) the third line = no + Δn · cos (2π (x− (2/4) Λ) / Λ) 4th = no + Δn · cos (2π (x− (3/4) Λ) / Λ) As a result, the first TWP and the other three TWPs The interference between them becomes an average when there is no modulation, and it is expected that the crosstalk characteristics are basically the same as in the case of the conventional simple twisted wire. Moreover, each TWP has the same characteristic impedance, and the time skew between the TWPs is only the time skew of the fractional length portion with respect to the pitch modulation wavelength (Λ), and a set of TWPs with a time skew of practically zero (0.5 nSec or less) is set. Cable can be realized.

[0009]

EXAMPLE λ = 20 mm, q = 250 mm, Λ = 1 m,
The fractional length is 1 m or less. The time skew in this case is about 50 m time skew × (1/50), which is about (10 to 20 nSec) × (1/50), that is, (1 /
2) It can be kept below nSec. FIG. 3 shows a schematic diagram of the embodiment.

[0010]

EFFECT OF THE INVENTION A multi-core cable in which the signal time skew is extremely small can be constructed by inexpensive non-shielded twisted cables. In addition, since each TWP has the same structure, all characteristics such as waveform distortion are made uniform, which facilitates the design of a circuit for waveform correction.

[Brief description of drawings]

FIG. 1 is a conventional TWP cable. The structure of a non-twisted pair cable that is frequently used in Ethernet (registered trademark) or the like is shown.

FIG. 2 shows averaging of delay times by the alternating method. A method of equalizing the delay times by alternating TWP with a small signal delay time (small n) and TWP with a large signal delay time on the way.

FIG. 3 shows averaging of delay times by a smooth alternation method. An example of a method of integrating the TWPs of which the pitch is smoothly changed according to the present invention by shifting the spatial phase to make the delay times uniform will be described.

[Explanation of symbols]

1 1st TWP line n = 71 times / m 2 2nd TWP line n = 62 times / m 3 3rd TWP line n = 52 times / m 4 4th TWP line n = 47 times / m 5 5th TWP line Average by pitch change 6 6th TWP line Averaging by changing pitch 7th TWP line Averaging by changing pitch 8th TWP line Averaging by changing pitch 9th TWP line 5th TWP line Smoothly changed pitch 10 10th TWP line 6th TWP line Smoothly changed pitch 11 11th TWP line Smoothly changed pitch of 7th TWP line 12 12th TWP line Smoothly changed pitch of 8th TWP line

Claims (2)

[Claims] 1. A multi-core non-shielded twisted pair cable in which the pitch of each twisted pair cable is changed smoothly to average and equalize the signal delay times between the twisted pair cables. 2. The twisted pair cables are integrated while being spatially displaced from each other, and in the vicinity of an arbitrary cross section, the twisted pair cables of the constituent elements are arranged so that the pitches thereof are different from each other, and the twisted pair cables are arranged. Multi-core non-shielded twisted pair cable that minimizes crosstalk between paired cables.