CN100508416C - Adjustable echo remover for whole duplex communication system - Google Patents

Abstract

An echo cancellation device used in complete douplex communication system. It includes a transmitting terminal to transmit the transmitting signal, and a receiving terminal to receive a received signal. The device includes: the filter to output filtrating wave signal according to the transmitting signal; the echo cancellation circuit coupling connected with the filter to output echo cancellation signal according to the filtrating signal; at least a echo cancellation resistance coupling connected with the transmitting and receiving terminals and the echo cancellation circuit; and the echo residue detecting circuit to output controlling signal according to the echo residue of the receiving terminal in order to control the filter.

Description

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

Technical field

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

Background technology

Because the progress of science and technology, the application of internet is also more and more wide.More and more big in view of the frequency range of network is required, the Ethernet that is commonly used at present (ethernet), the transfer rate of its packet also is promoted to more than the 1Gbps from the past 10/100Mbps.

Please refer to Fig. 1, it shows the functional block diagram of Fast Ethernet (faste thernet) device of 1Gbps.In the Fast Ethernet device of 1Gbps, each connectivity port (port) has four passages (channel) 100.Each passage has a conveyer (transceiver) 102, and utilizes line interface (line interface) 116 and twisted-pair feeder (twistl ines) 118 to couple.Conveyer 102 comprises transmission end 104 and receiving terminal 106.Wherein, transmission end 104 comprises a digital analog converter 108 (Digital-to one Analog Converter DAC), in order to after will transmitting signal and converting analog form to, is sent to long-range another network equipment by line interface 116 and twisted-pair feeder 118.And receiving terminal 106 comprises an AFE (analog front end) (Analog Front End, AFE) circuit, carrying out signal earlier in order to the analog signal that line interface 116 is received handles, utilize analog-digital converter (Analog-to-DigitalConverter again, ADC) 114 convert digital signal to after, deliver to late-class circuit again.Fast Ethernet device and long-range another network equipment use four channels simultaneously, and each channel is carried out transmission and the function that receives simultaneously.So Fast Ethernet is an a kind of full duplex communication system.

Each channel of Fast Ethernet network device is carried out simultaneously and is transmitted and receiving function.When channel transmits signal, can receive signal simultaneously to this channel and exert an influence, this phenomenon is called as echo and disturbs (echoimpairiment).Minimum for the echo disturbing effect is dropped to, can set acho in the general conveyer and eliminate circuit (echo cancellation) 110 and echo cancellation resistance R p, as shown in Figure 1.Echo cancellation circuit coupling 110 also is a D/A conversion circuit usually, in order to the transmission signal corresponding elimination signal (cancellation signal) of output with D/A conversion circuit 108 outputs, this elimination signal can offset and transmit the influence that signal is caused receiving terminal 106, to reach the effect of echo cancellation.

Please refer to Fig. 2, it shows the equivalent circuit diagram of Fast Ethernet device shown in Figure 1.Wherein, the digital analog converter in the conveyer 100 108 and echo cancellation circuit coupling 110 respectively circuit equivalent be current source Id and Ic.For receiving terminal 106, if reach the purpose of echo cancellation, the output current of current source Ic and Id must mutually offset the effect that receiving terminal 106 is caused.

Please refer to Fig. 3, it shows the little signal model of equivalent circuit diagram shown in Figure 2.Wherein, Zo is an equivalent output impedance, in Fig. 2, equivalent output impedance comprises the equivalent resistance Rc in order to the build-out resistor Rm of matched impedance and passage, and Vo is an output signal, the transmission signal of transmission end 104 outputs just, Vi is an input signal, just imports the reception signal of receiving terminal 106.Can obtain following equation by the circuit diagram shown in Fig. 3:

$\mathrm{Vi}=\frac{-\mathrm{Zi}[\mathrm{IdZo}+(\mathrm{Zo}+\mathrm{Rp})\mathrm{Ic}]}{\mathrm{Rp}+\mathrm{Zi}+\mathrm{Zo}}---\left(1\right)$

Will be with echo cancellation, Vi=0 just, then must satisfy:

IdZo+(Zo+RP)Ic＝0 (2)

Therefore, when the pass of Ic and Id be:

$\mathrm{Ic}=\frac{-\mathrm{Zo}}{\mathrm{Rp}+\mathrm{Zo}}\mathrm{Id}---\left(3\right)$

Then echo can be eliminated fully.

The shortcoming of known echo cancellation circuit coupling is for to be considered as simple load resistance Re with equivalent output impedance Zo, and its electricresistance effect is that the equivalent resistance Rc by build-out resistor Rm and passage is determined.But except the equivalent resistance Rc of build-out resistor Rm and passage, unavoidable parasitic capacitance Ce effect when equivalent output impedance also need be considered the side circuit realization.If only equivalent output impedance Zo is considered as simple load resistance RE, then the echo disturbing effect can't be dropped to minimum.

Summary of the invention

In view of this, purpose of the present invention is providing a kind of full duplex communication system that is used for exactly, can further reduce the echo eliminating device of echo disturbing effect.

According to purpose of the present invention, a kind of echo cancellation (echocancellation) device that is used for the 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 signal.This echo eliminating device comprises: filter, in order to export the filtering signal according to transmitting signal; Echo cancellation circuit coupling couples with filter, in order to foundation filtering signal output echo cancellation signal; At least one echo cancellation resistance is with transmission end, receiving terminal and echo cancellation circuit; And the residual echo testing circuit, in order to residual echo (echo residue) the output controlling signal of foundation receiving terminal, with control filters.

For above-mentioned purpose of the present invention, feature and advantage can be become apparent, a preferred embodiment cited below particularly, and formula is described in detail as follows in conjunction with the accompanying drawings.

Description of drawings

Fig. 1 shows the functional block diagram of the Fast Ethernet device of 1Gbps;

Fig. 2 shows the equivalent circuit diagram of Fast Ethernet device shown in Figure 1;

Fig. 3 shows the little signal model of the equivalent circuit diagram shown in Fig. 2;

Fig. 4 is the functional block diagram according to the Fast Ethernet device shown in first embodiment proposed by the invention;

Fig. 5 is a schematic diagram of realizing the low pass filter among Fig. 4 with digital circuit;

Fig. 6 is a schematic diagram of realizing the low pass filter among Fig. 4 with analog circuit; With

Fig. 7 is the functional block diagram according to the Fast Ethernet device shown in second embodiment proposed by the invention.

The reference numeral explanation

100,400,700 passages

102,402,702 conveyers

104,404,704 transmission ends

106,406,706 receiving terminals

108,408,708 digital analog converters

110 echo cancellation circuit coupling

112,412,712 analog front circuits

114,414,714 analog-digital converters

116,416,716 line interfaces

118,418,718 twisted-pair feeders

310,350 impedance components

320,340 current sources

330 resistance

420,720 low pass filters

Embodiment

Referring again to Fig. 3, the present invention is that the consideration side circuit is realized unavoidable parasitic capacitance effect, so load resistance Re that equivalent output impedance Zo is formed for the equivalent resistance Rc by build-out resistor Rm and passage and (Zo=Re//Ce) in parallel of parasitic capacitance Ce, so the size of equivalent output impedance Zo is shown in following equation:

$\mathrm{Zo}=\frac{\mathrm{Re}}{\mathrm{sReCe}+1}---\left(4\right)$

With equation (4) substitution equation (3), then obtain equation (5):

$\mathrm{Ic}=\frac{-\mathrm{Re}}{\mathrm{Rp}+\mathrm{Re}+\mathrm{sReRpCe}}\mathrm{Id}=H\left(s\right)\·\mathrm{Id}---\left(5\right)$

By equation (5) as can be known, in fact the H (s) that concerns of Ic and Id is a low pass transfer equation formula (lowpass transfer function).Please refer to Fig. 4, it is the functional block diagram according to the device of the Fast Ethernet (fast ethernet) shown in first embodiment proposed by the invention.Echo eliminating device proposed by the invention comprises: echo cancellation circuit coupling 410, in order to produce the corresponding elimination signal of exporting with D/A conversion circuit 408 of transmission signal; Echo cancellation resistance R p is coupled between transmission end 404 and the receiving terminal 406, and low pass filter 420, couples with echo cancellation circuit coupling 410, as its front stage circuits.Wherein, echo cancellation circuit coupling 410 can be digital analog converter, and low pass filter 420 can be selected to realize with the numeral or the mode of analog circuit.If the mode with digital circuit realizes, then is wave digital lowpass filter (digital low pass filter), as shown in Figure 5.If the mode with analog circuit realizes, then is resistance-capacitance network low pass filter (RC networklow pass filter), as shown in Figure 6.By low pass filter 420, can be so that the transmission signal of the elimination signal payment D/A conversion circuit 408 of echo cancellation circuit coupling 410 (equivalence is current source Ic on the circuit) output (equivalence is current source Id on the circuit) output, to the influence that receiving terminal 406 is caused, the phenomenon that echo is disturbed drops to minimum.Wherein, the electric capacity of Fig. 6 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 grid voltage Vd.

Please refer to Fig. 7, it is the functional block diagram according to the Fast Ethernet device shown in second embodiment proposed by the invention.When actual conditions, the size of parasitic capacitance Ce, passage equivalent resistance Rc and impedance matching resistance R m can be subjected to operational environment, working temperature, processing procedure difference ... or the like the influence of factor, so can in the transmission/receiving course of network data, all can change at any time.In order to reach the effect of echo cancellation more accurately, in second embodiment that the present invention proposes, also be provided with residual echo testing circuit 722, in order to detect the residual echo (echoresidue) that receiving terminal 706 is received at receiving terminal 706.Residual echo testing circuit 722 can be according to detected residual echo output controlling signal to low pass filter 720, to form a loop.If low pass filter 720 is a wave digital lowpass filter, as shown in Figure 5, then can adjust its finite impulse response (FIR) (Finite Impulse Response, FIR) or infinite impulse response (Infinite Impulse Response, IIR) coefficient, if low pass filter 720 is the resistance-capacitance network low pass filter, then can adjust resistance capacitance (RC) value of resistance-capacitance network low pass filter by control gate pole tension Vd, come dynamically to adjust low pass filter 720, 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, so it is not that those skilled in the art without departing from the spirit and scope of the present invention in order to qualification the present invention; can be used for a variety of modifications and variations, so protection scope of the present invention is looked accompanying Claim and is as the criterion.

Claims (7)

1. echo eliminating device that is used for the full duplex communication system, wherein, this full duplex communication system comprises a transmission end, in order to transmitting signal, and a receiving terminal, in order to receive signal, this echo eliminating device comprises:

One filter is in order to export a filtering signal according to this transmission signal;

One echo cancellation circuit coupling couples with this filter, in order to export an echo cancellation signal according to this filtering signal; And

At least one echo cancellation resistance is coupled between this transmission end and this receiving terminal, and this filter and this echo cancellation circuit, as its front stage circuits.

2. device as claimed in claim 1, wherein this echo cancellation signal is offset the transmission signal of D/A conversion circuit output.

3. device as claimed in claim 1, wherein this echo cancellation circuit coupling is a digital analog converter.

4. device as claimed in claim 1, wherein this filter is a digital filter.

5. device as claimed in claim 1, wherein this filter is a resistance-capacitance network filter.

6. device as claimed in claim 1, wherein this filter is a low pass filter.

7. device as claimed in claim 1, wherein this echo eliminating device also comprises a residual echo testing circuit, exports a controlling signal in order to the residual echo according to this receiving terminal, to control this filter.

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