CN101136660B - Matching absorber for reducing damage of bridge tap to cable transmission performance - Google Patents

Abstract

This invention relates to a match absorber used in reducing harm of cable transmission performance by bridge taps including an impedance match circuit matching the total impedance with the cable bridged on the circuit of the tap for absorbing the electromagnetic signal of a specific frequency coupled in the tap, optionally, said absorber includes a serial structure of inductor, resistor and a capacitor and adjusts capacitance value according to the length of the tap by an adjustable capacitor to suit taps of different lengths, when an electromagnetic wave signal coupled to the tap is transmitted to the end of the tap, the absorber can absorb a wave of specific frequency, reduce its reflection rate and interference generated by the wave reflecting to the primary loop, improve its frequency response character and increase the transmission ability of the DSL system.

Description

Be used to reduce the matching absorber of bridge tap to the cable transmission performance damage

Technical field

The present invention relates to the telecommunications access network system, relate more specifically to a kind of matching absorber.

Background technology

Along with new business such as Internet fast development and IPTV, new application and development, access bandwidth to be had higher requirement, broadband access network becomes the emphasis of telecom operators' networking and business development.For making full use of existing copper cash resource, to the user broadband inserting service is provided with lower cost, telecom operators both domestic and external generally adopt DSL (DSL) technology, comprise ADSL/ADSL2+, VDSL, SHDSL, HDSL etc.Wherein ADSL is present topmost broadband access method, and the whole world is used and surpassed 100,000,000 lines, also surpasses 1,500 ten thousand lines in China.Various DSL technology all are to have utilized untapped high-frequency band in the plain old telephone copper cash, adopt advanced modulation technique, and broadband access is provided, and adopt the frequency spectrum of 26KHz～138KHz and 138KHz～1.1MHz to be respectively applied for the uplink and downlink transfer of data like ADSL.

In the DSL system based on copper cash, some factors like bridge tap, crosstalk etc., have relatively the transmission performance of DSL system to seriously influence.

Mainly because multiple distribution causes, it is in tearing the telephone-moving process open, not have in time to remove original distribution to cause that part is also arranged to bridge tap on the local cable.Multiple connection is in order to make wiring have versatility and flexibility, to make things convenient for the user to insert from different places, because can't clearly know user's physical location in the future in many cases.The bridge tap that multiple connection causes is seen Fig. 1.Among this figure, connect through cable (such as, twisted-pair feeder) 13 as the digital subscriber line access multiplex (DSLAM) of local side apparatus 11 and the modulator-demodulator (Modem) that is used as family end equipment 12, the open circuit cable that is connected on the cable 13 is a bridge tap 14.Because bridge tap is connected in parallel on the former circuit; And the tap terminal open circuit, thus a unmatched pip of impedance appears, transmission signals is produced echo; Make the signal attenuation characteristic of circuit fluctuation occur; Influence transmission performance, gently then reduced transmission rate and track stability (causing user easier to go offline), heavy then cause the user to open.

Particularly; Signal from the local side to the user side (or from user side to the local side) will be divided into two parts along the main line transmission through bridge contact, and a part gets into bridge tap; Another part still transmits along main line; The signal that gets into bridge tap can produce stronger reflection at the end of bridge tap after the bridge tap transmission, produce in this reflected signal meeting feed-in main line and with original signal and interfere, and can produce additional attenuation to some frequency range; The influenced more serious frequency (paddy in the frequency response curve) and the length (be equivalent to signal and return caused phase change) of bridge tap are inverse relation, that is:

$f_n=\frac{(n+\frac{1}{2})\×0.64\×c}{2l}(n=\mathrm{0,1,2},...)$

Wherein, f _nN decay trough in the frequency response curve of expression circuit, c representes the light velocity in the vacuum, the 0.64th, the group velocity that signal is propagated in cable, l representes the length of bridge tap.Because along with the increase of n, the pad value of the frequency response curve of circuit is decayed rapidly, so only need here to consider that frequency is f ₀Additional attenuation.Therefore,

$f_0=\frac{0.16\×c}{l}$

Along with new business and new application and development such as IP TV, the transmission quality of DSL circuits such as ADSL is also had higher requirement, to improve line speed, improve the stability of a system.How reducing even eliminate bridge tap to DSL system transmissions Effect on Performance, is a very important technical problem.Consider bridge tap removed fully to exist improvement cost high, it is big to implement difficulty, and the fast-changing situation of incompatibility business demand is so the influence of adopting other means to reduce bridge tap is reasonable selection.

Summary of the invention

In order to overcome the bridge tap that exists in the prior art and influence the above-mentioned defective of circuit Frequency Response, the signal transmission impairment that the present invention provides a kind of bridge tap that is used for effectively reducing copper cash to cause improves the matching absorber of DSL broadband access network transmission performance.

According to the present invention; A kind of matching absorber of bridge tap to the cable transmission performance damage that be used to reduce is provided; Said matching absorber comprises the impedance phase match circuit of its total impedance and cable; This circuit jumps on the circuit of bridge tap, is used for absorbing the electromagnetic signal of the CF that is coupled to bridge tap, and wherein said matching absorber comprises the series arrangement of inductance, resistance and electric capacity; Said electric capacity is tunable capacitor, comes capacitance value according to bridge tap length, makes the total impedance of matching absorber and the impedance phase coupling of cable; Wherein, said CF is the 0th corresponding centre frequency f of decay trough in the frequency response curve of circuit ₀

The impedance of said match circuit is equal to said CF f ₀Under line impedance, that is:

R＝R _L(f ₀)

$2\mathrm{\π}{f}_{0}L=\frac{1}{2\mathrm{\π}{f}_{0}C}$

Wherein, L is the inductance value of inductance, and C is the electric capacity capacitance; R is the resistance value of resistance; R _L(f ₀) be line impedance, be the function of frequency.

Preferably, above-mentioned matching absorber of the present invention, in the ADSL system, satisfy:

R=100, and $C=\frac{{\mathrm{<figure-callout\; id="2"\; label="l"\; filenames="H061C6177120060906E000012.png"\; state="\{\{state\}\}">l</figure-callout>}}^2}{{0.32}^2{\mathrm{\&pi;}}^2{c}^{2}L}$

Wherein, c is a light speed in a vacuum, and l is the length of bridge tap, and L is an inductance value, and R is a resistance value, and C is a capacitance, and π is a circumference ratio.

Because matching absorber of the present invention comprises the impedance phase match circuit of its total impedance and cable; And this circuit jumped on the circuit of bridge tap; The electromagnetic signal that is coupled to the CF in the bridge tap is sponged; Reduce its reflection, and then reduce the decay trough of these frequency band signals in the circuit frequency response curve.

In addition, (electromagnetic wave) of the present invention matching absorber can reduce the end face reflection of bridge tap, improves the transmission performance and the stability of a system of circuit, improves the transmission rate of DSL system, extends transmission distance.Have simple in structure, be easy to realize, volume is little, cost is low, completely without source structure, implement convenient, do not influence advantage such as plain old telephone service.

The present invention can utilize the electromagnetic wave signal that impedance matching principle will be coupled in the bridge tap to absorb, and reduces the end face reflection coefficient of cable, improves the transmission rate and the stability of ADSL and other DSL systems.Can be used for the telecommunications access network system, belong to broadband access based on copper cable.

A significant advantage of the present invention is only to adopt the passive structures of circuit (for example inductance, resistance and electric capacity), realizes simply need not power supply, and cost is low, is fit to wide-scale adoption.

Another advantage of native system is easy for installation.The end that only need be connected across bridge tap gets final product, and it is little to take up room, and the set-up time is short, removes also very convenient.

Description of drawings

Fig. 1 illustrates copper twisted pairs bridge tap sketch map on the telecommunications network of the prior art;

Fig. 2 schematically illustrates matching absorber principle and the application mode based on the LRC loop that the present invention is used to eliminate the bridge tap influence.

Embodiment

Specifically describe the embodiment of matching absorber of the present invention below in conjunction with accompanying drawing, wherein same or analogous drawing reference numeral is represented same or analogous parts.

Now, specifically describe matching absorber principle and the application mode that the present invention is used to eliminate the bridge tap influence with reference to figure 2.As shown in the figure, the matching absorber 4 based on the LRC loop of the present invention mainly is made up of inductance 1, resistance 2 and electric capacity 3.Inductance 1, resistance 2 are contacted with electric capacity 3 threes and are connected, and the across after the connection of will contacting is to the line of bridge tap 14.

Introducing according to the front, is the absworption peak of f0 in order to eliminate the most serious centre frequency of systematic influence, and the impedance of LRC match circuit will be equal to the line impedance under the corresponding frequencies.For ease of making, adopt the resistance of definite value, and make the AC impedance of inductance and the AC impedance equal and opposite in direction of electric capacity, therefore opposite in sign has:

R＝R _L(f ₀)

$2\mathrm{\&pi;}{f}_{0}L=\frac{1}{2\mathrm{\&pi;}{f}_{0}C}$

Wherein, L is the inductance value of inductance 1, and C is electric capacity 3 capacitances; R is the resistance value of resistance 2; R _L(f ₀) be line impedance, be the function of frequency.

With ADSL is example; Calculate for simplifying; Line impedance is got 100ohm; And with substitution, (for ISDN, line impedance is about 120 ohm as follows in the calculating formula simplification.All be example below with ADSL.)：

R＝100

$C=\frac{{\mathrm{<figure-callout\; id="2"\; label="l"\; filenames="H061C6177120060906E000012.png"\; state="\{\{state\}\}">l</figure-callout>}}^2}{{0.32}^2{\mathrm{\&pi;}}^2{c}^{2}L}$

Wherein, c is a light speed in a vacuum, and l is the length of bridge tap, and L is an inductance value, and R is a resistance value, and C is a capacitance, and π is a circumference ratio.

In addition, can be through adopting adjustable resistance, controllable impedance or tunable capacitor, regulate the resistance value of resistance, inductance or electric capacity according to bridge tap length, the total impedance that makes matching absorber is mated with the impedance phase of cable.

The present invention comprises scheme (if the employing parallel circuits or a simple resistance of inductance, resistance and electric capacity polyphone through the matching absorber based on the LRC loop; Can cause the plain old telephone can't ring; So this patent adopts LRC polyphone scheme), and with this LRC circuit jump to bridge tap on, thereby the electromagnetic signal that will be coupled to the CF in the bridge tap sponges; Reduce its reflection, and then reduce the decay trough of these frequency band signals in the circuit frequency response curve.Thereby reduced interference to the signal of some frequency of transmitting on the circuit, and improve the Frequency Response of circuit, improved the transmission performance of DSL system.

But the present invention specifically is not limited to the concrete formation of above-mentioned execution mode; Those of ordinary skills it is contemplated that also other circuit constitutes; As long as constituting, such circuit can the electromagnetic signal that be coupled to the CF in the bridge tap be sponged; Reduce its reflection, and then reduce the decay trough of these frequency band signals in the circuit frequency response curve.

In addition, if the terminal of bridge tap is inconvenient to install LRC circuit of the present invention, also can be installed in other convenient positions of installing, as long as the LRC circuit is connected across on the bridge tap.

Although present invention is described, foregoing description the invention is not restricted to the above-mentioned specific descriptions that combine accompanying drawing just for illustrative purposes.Those of ordinary skills can carry out various changes and not break away from spirit of the present invention it, and protection scope of the present invention is limited the accompanying Claim book.

Claims (3)

1. one kind is used to reduce the matching absorber of bridge tap to the cable transmission performance damage; It is characterized in that; Said matching absorber comprises the impedance phase match circuit of its total impedance and cable; This circuit jumps on the circuit of bridge tap, is used for absorbing the electromagnetic signal of the CF that is coupled to bridge tap; Wherein said matching absorber comprises the series arrangement of inductance (1), resistance (2) and electric capacity (3); Said electric capacity (3) is tunable capacitor, comes capacitance value according to bridge tap length, makes the total impedance of matching absorber and the impedance phase coupling of cable;

Wherein, said CF is the 0th corresponding centre frequency f of decay trough in the frequency response curve of circuit ₀

The impedance of said match circuit is equal to said CF f ₀Under line impedance, that is:

R＝R _L(f ₀)

$2\mathrm{\&pi;}{f}_{0}L=\frac{1}{2\mathrm{\&pi;}{f}_{0}C}$

Wherein, L is the inductance value of inductance (1), and C is electric capacity (a 3) capacitance; R is the resistance value of resistance (2); R _L(f ₀) be line impedance, be the function of frequency.

2. matching absorber as claimed in claim 1, wherein in the ADSL system, satisfy:

R=100, and $C=\frac{l^2}{{0.32}^2{\mathrm{\&pi;}}^2{c}^{2}L}$

Wherein, c is a light speed in a vacuum, and l is the length of bridge tap, and L is an inductance value, and R is a resistance value, and C is a capacitance, and π is a circumference ratio.

3. matching absorber as claimed in claim 2, wherein said inductance (1), resistance (2) and electric capacity (3) adopt adjustable resistance, controllable impedance and tunable capacitor.

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