CN1649280B - Adjustable echo eliminator for full duplex communication system - Google Patents

Abstract

This invention relates to an echo-eliminating device for a duplex communication system. Said duplex communication system includes a transmission end for sending a signal and a receive end for receiving the signal. Said echo-eliminating device includes: a filter for outputting filtered signal based on the transmitted signal, a computing module coupling with said transmission end, receive end and the filter to output said received signal based on said filter signal and a for distance signal, a residual echo detection circuit for outputting a control signal to control the filter based on the residual echo at the receive end.

Description

The adjustable echo eliminating device that is used for full duplex communication system

Technical field

The present invention relates to a kind of full duplex (full duplex) communication system, and be particularly related to a kind of echo eliminating device that is used for full duplex communication system.

Background technology

Because the progress of science and technology, the application of internet is also more and more wide.In view of the bandwidth requirement to network more and more big, the Ethernet that is commonly used at present, the transfer rate of its data packet also is promoted to more than the 1Gbps from the past 10/100Mbps.

Each channel of Ethernet device can be carried out simultaneously and transmit and receiving function.When signal transmission channel, can exert an influence to this channel while received signal, this phenomenon is called as echo and disturbs (echoimpairment).Minimum for the echo disturbing effect is dropped to, can set acho in the general conveyer and eliminate circuit (echo cancellation), please refer to Fig. 1, it illustrates the equivalent circuit diagram that traditional line drive has an echo cancellation circuit coupling.Line drive is the conveyer of a kind of voltage mode (Voltage Mode).In Fig. 1, Rp be build-out resistor in order to matched impedance, Zo is a channel loading, Vi is an output signal, the transmission signal of transmission end (line drive Line Driver) 110 output just, Vo is the input signal of twisted-pair feeder.Because traditional echo cancellation circuit coupling only considers that this channel loading Zo is simple resistance, its resistance value is Re, for impedance matching, so Rp equals Re.Circuit diagram by Fig. 1 illustrates can obtain following equation by voltage divider principle:

$\mathrm{Vo}=\frac{\mathrm{Zo}}{\mathrm{Zo}+\mathrm{Rp}}\mathrm{Vi}$

Traditional echo cancellation circuit coupling is considered as simple load resistance Re with channel loading Zo.Be Zo=Re, bring equation (1) into

So Vo=1/2Vi (2)

The influence that this transmission signal Vi of i.e. this voltage mode transmission end 110 outputs is caused at receiving terminal 310 is 1/2Vi.Traditional echo cancellation circuit coupling is in order to produce this transmission corresponding echo cancellation signal of signal Vi (echo cancellation signal) of exporting with transmission end 110, this echo cancellation signal should be 1/2Vi, and this echo cancellation signal cancellation is transmitted the influence that signal caused by a subtracter, to reach the effect of echo cancellation.

And when considering side circuit, still need consider unavoidable parasitic capacitance Ce effect.If only this channel loading Zo is considered as simple load resistance Re, then the echo disturbing effect can't be dropped to minimum.In other words, the part that traditional echo cancellation circuit coupling 106 only can cancellation DC, residual echo (echo residue) that but can't the cancellation high frequency.

Summary of the invention

One of purpose of the present invention is exactly in that a kind of echo eliminating device that is used for full duplex communication system, can reduces the echo disturbing effect is provided, to solve the above problems.

According to purpose of the present invention, a kind of echo eliminating device that is used for full duplex communication system is proposed.This full duplex communication system comprises a transmission end, in order to transmitting signal, and a receiving terminal, in order to receive a received signal.This echo eliminating device comprises: an echo cancellation signal generator, in order to export the echo cancellation signal according to transmitting signal; One computing module couples with this transmission end, this receiving terminal and this echo cancellation signal generator, in order to according to this echo cancellation signal, with the radio-frequency component signal of this echo of eliminating this received signal.

In one embodiment of the invention, this echo eliminating device also includes a residual echo testing circuit, outputs control signals to the echo cancellation signal generator in order to the residual echo (echo residue) of foundation receiving terminal, to adjust this echo cancellation signal.

For above-mentioned purpose of the present invention, feature and advantage can be become apparent, a preferred embodiment cited below particularly, and conjunction with figs. are described in detail below.

The accompanying drawing summary

Traditional line drive that Fig. 1 illustrated has the equivalent circuit diagram of an echo cancellation circuit coupling.

Fig. 2 is the functional block diagram of the line drive that illustrates according to first embodiment proposed by the invention.

Fig. 3 is a schematic diagram of realizing the echo cancellation circuit coupling among Fig. 2 with analog circuit.

Fig. 4 is the functional block diagram of the line drive that illustrates according to second embodiment proposed by the invention.

Fig. 5 is a schematic diagram of realizing the echo cancellation circuit coupling among Fig. 4 with analog circuit.

The reference numeral explanation

102 build-out resistors

The equivalent load of 104 channels

106,320 echo cancellation circuit coupling

110 transmission ends

120,360,401,402,404,441, resistance

601、602、604、611

310 receiving terminals

330,530 computing modules

340 echo cancellation signal generators

370,412,612 electric capacity

403,603 operational amplifiers

410,540,610 low pass filters

420,620 subtracters

510 residual echo testing circuits

Embodiment

Referring again to Fig. 2, it is the functional block diagram of the Ethernet device that illustrates according to first embodiment proposed by the invention.This first embodiment considers that side circuit realizes real unavoidable parasitic capacitance effect, so the load resistance Re 360 that equivalent output impedance is made up of the equivalent resistance of build-out resistor Rp 102 and passage and parasitic capacitance Ce 370 (Zo=Re//Ce) in parallel.

$H\left(s\right)=\frac{\mathrm{Re}}{\mathrm{Rp}+\mathrm{Re}+\mathrm{sReRpCe}}---\left(3\right)$

Then echo can be eliminated fully.

Echo eliminating device proposed by the invention comprises: echo cancellation signal generator 340 couples with transmission end 110, in order to transmit signal output filtering signal according to this; And computing module 330, couple with transmission end 110, receiving terminal 310 and echo cancellation signal generator 340, in order to export this received signal according to this filtering signal and remote signal.Wherein, echo cancellation signal generator 340 can be selected to realize with the numeral or the mode of analog circuit.

If the mode with analog circuit realizes, then is resistance-capacitance network low pass filter (RCnetwork low pass filter) 410, as shown in Figure 3.Resistance-capacitance network low pass filter 410 comprises resistance R a 411 and capacitor C a 412, and it produces an echo cancellation signal in order to according to this output signal V i.Resistance-capacitance network low pass filter 410 is electrically coupled with resistance R 1 402, this echo cancellation signal is inputed to operational amplifier 403, and Vo inputs to operational amplifier 403 via resistance R 2 401.Resistance R _ f 404 has two ends, and an end is connected in the input of operational amplifier 403, and the other end is connected in the output of operational amplifier 403, with the magnification ratio of control transmission end and receiving terminal 310.The computing that utilizes operational amplifier to do low-pass filtering simultaneously and subtract each other can obtain after the calculating:

$\mathrm{Va}=\frac{R1}{\mathrm{Ra}+R1+\mathrm{sCaRaR}1}\mathrm{Vi}---\left(4\right)$

$\mathrm{Va}\·\frac{\mathrm{Rf}}{R1}+\mathrm{Vo}\·\frac{\mathrm{Rf}}{R2}=-\mathrm{Vr}---\left(5\right)$

Suppose Vr=0, merging aforesaid equation (2), (4) and (5) can obtain:

$\frac{1}{\mathrm{Ra}+R1+\mathrm{sCaRaR}1}=\frac{-\mathrm{Re}}{(\mathrm{Re}+\mathrm{Rp}+\mathrm{sCeReRp})R2}---\left(6\right)$

As long as therefore satisfy following two formulas (7), (8), then echo can be offseted fully:

CaRaR1＝CeRpR2 (7)

$\mathrm{Ra}+R1=(\frac{\mathrm{Rp}}{\mathrm{Re}}+1)R2---\left(8\right)$

To satisfy formula (7) and formula (8),, echo is offseted fully by resistance-capacitance network low pass filter 410 to adjust the value of capacitor C a, and the influence that receiving terminal 310 is caused, the phenomenon that echo is disturbed drops to minimum.Wherein, the electric capacity of Fig. 4 can be realized with metal sandwich electric capacity or parasitic capacitance, and resistance is to realize with a MOS transistor, and its resistance value is determined by the big or small of its gate voltage Vg.

Please refer to Fig. 4 and Fig. 5, it is the functional block diagram of the Ethernet device that illustrates according to second embodiment proposed by the invention.When actual conditions, the size of parasitic capacitance Ce 370, passage equivalent resistance Re 360 and impedance matching resistance R p 102 can be subjected to the influence of factors such as operational environment, working temperature, processing procedure difference, so can all can change at any time in the transmission/receiving course of network data.In order to reach the effect of echo cancellation more accurately, in second embodiment that the present invention proposes, echo eliminating device includes a residual echo testing circuit 510 in addition, in order to detect the residual echo (echoresidue) that receiving terminal is received.Residual echo testing circuit 510 can output control signals to echo cancellation signal generator 540 according to detected residual echo, to form a loop.If echo cancellation signal generator 540 is a wave digital lowpass filter, as shown in Figure 4, then can adjust its finite impulse response (FIR) (Finite ImpulseResponse, FIR) or infinite impulse response (Infinite Impul se Response, IIR) coefficient, if echo cancellation signal generator 540 is resistance-capacitance network low pass filters 610, as shown in Figure 5, then can adjust resistance capacitance (RC) value of resistance-capacitance network low pass filter by control grid voltage Vg, come dynamically to adjust low pass filter 610, to keep the effect of echo cancellation best according at that time circuit unit characteristic and network environment.

In sum; though the present invention discloses as above with a preferred embodiment; right its is not in order to limit the present invention; anyly have the knack of this skill person; without departing from the spirit and scope of the present invention; when can being used for a variety of modifications and variations, so protection scope of the present invention is as the criterion when looking accompanying the claim person of defining.

Claims (10)

1. the echo eliminating device of a full duplex communication system, in order to eliminate an echo of a received signal, this full duplex communication system comprises a link, is used for connecting channel, this channel has an equivalent load; One transmission end sends a signal to this channel in order to transmit one by a build-out resistor; And a receiving terminal, in order to receive this received signal, wherein, this build-out resistor is connected between this transmission end and this link, and this echo eliminating device comprises:

One echo cancellation signal generator couples with this transmission end, in order to receive and to transmit signal according to this, produces an echo cancellation signal; And

One computing module couples with this link, this receiving terminal and this echo cancellation signal generator, in order to receiving this received signal, and according to this echo cancellation signal, eliminates the radio-frequency component of this echo at least.

2. device as claimed in claim 1, wherein, this echo cancellation signal generator is a low pass filter.

3. device as claimed in claim 2, wherein, this low pass filter is a digital filter or a resistance-capacitance network filter.

4. device as claimed in claim 1, wherein, this computing module is a subtracter, it comprises an operational amplifier and a resistance.

5. device as claimed in claim 1, wherein, this echo eliminating device more comprises a residual echo testing circuit, be connected between this echo cancellation signal generator and this computing module, in order to detect a residual echo of this received signal, output one controls signal to this echo cancellation signal generator, to adjust this echo cancellation signal.

6. an echo eliminating device in order to eliminate an echo of a received signal, is arranged in a full duplex communication system, this full duplex communication system comprises a link, be used for connecting channel, a transmission end sends a signal to this link in order to transmit one by a build-out resistor, an and receiving terminal, in order to receive this received signal, wherein, this channel has an equivalent load, build-out resistor is connected between this transmission end and this link, and this echo eliminating device comprises:

One echo cancellation signal generator couples with this transmission end, in order to receive and to transmit signal according to this, produces an echo cancellation signal;

One computing module couples with this link, this receiving terminal and this echo cancellation signal generator, in order to receiving this received signal, and according to this echo cancellation signal, eliminates the radio-frequency component of this echo at least; And

One residual echo testing circuit, in order to detect a residual echo of this received signal, output one controls signal to this echo cancellation signal generator, to adjust this echo cancellation signal.

7. device as claimed in claim 6, wherein, this echo cancellation signal generator is a digital filter, and this control signal is in order to a plurality of coefficients of the finite impulse response (FIR) of adjusting this digital filter or a plurality of coefficients of infinite impulse response.

8. device as claimed in claim 6, wherein, this echo cancellation signal generator is a resistance-capacitance network filter.

9. device as claimed in claim 8, wherein, this resistance-capacitance network filter comprises a MOS transistor in addition, and this control signal is in order to control the gate electric current of this MOS transistor, to change a resistance value of this MOS transistor.

10. device as claimed in claim 8, wherein, this resistance-capacitance network filter comprises a capacitance module in addition, it is a capacitance that changes this capacitance module according to this control signal.

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