JPH0526375B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an echo canceller for automatically canceling unnecessary reflected waves (echoes).

[Technical background of the invention and its problems]

When attempting to perform simultaneous two-way communication of data using a two-wire telephone line such as a subscriber's telephone line, the four-wire section between the four-wire section to which the terminal is connected and the subscriber's line.
Echo signals generated in the two-wire converter (hybrid transformer) pose a major problem. An echo canceller is known as a means for canceling the echo signal, which is a leaked signal from the transmitting side of the local station to the receiving side of the local station. This generates a pseudo echo signal by weighting and adding tap coefficients (convolution calculation) to the own station's transmitted signal, and subtracts this pseudo echo signal from the own station's received signal to eliminate the echo signal included in the own station's received signal. It is something to do.

By the way, in conventional echo cancellers, a signal obtained by subtracting a pseudo echo signal from a received signal of the local station is used as an error signal for controlling the tap coefficient. However, in this method, when there is a transmission from the other station, the error signal is superimposed with the signal sent from the other station in addition to the residual component of the echo signal, so the echo cancellation performance is poor when transmitting simultaneously in both directions. The drawback was that it deteriorated significantly.

[Purpose of the invention]

An object of the present invention is to provide an echo canceller whose echo cancellation performance does not deteriorate even during simultaneous bidirectional transmission.

[Summary of the invention]

The present invention further eliminates the own station received signal component from a signal obtained by combining the own station received signal and the pseudo echo signal, extracts only the residual component of the echo signal, and generates a pseudo echo based on this. The main point is to control the tap coefficient of the transversal filter in the circuit.

That is, the present invention provides an echo canceler for a simultaneous two-way communication system that modulates a local station transmission signal, sends the modulated signal to a transmission path, and receives a local station reception signal inputted from the transmission path. A pseudo-echo generation circuit generates a pseudo-echo signal by passing the transmitted signal through a transversal filter with a variable tap coefficient and then modulating the signal; and a pseudo-echo generation circuit generates a pseudo-echo signal by combining the pseudo-echo signal and the own-station received signal, and receives the received signal at the own-station. a first synthesis circuit that demodulates and outputs the signal after canceling an echo signal component included in the signal; and an equalization circuit that eliminates transmission distortion in the transmission path included in the output signal of the first synthesis circuit. a sign judgment circuit which judges the sign of the output signal of this equalizer and outputs it as a reference signal; and a transversal filter whose tap coefficient is variable and which inputs the reference signal from this sign judgment circuit and taps this reference signal. a transmission distortion generation circuit that outputs a signal with transmission distortion added thereto; an output signal of this transmission distortion generation circuit;
a second synthesizing circuit that synthesizes the output signal of the synthesizing circuit and outputs a residual component of the echo signal and a residual component of the signal to which the transmission distortion has been added; station transmission signal and the second
The tap coefficient of the transversal filter is controlled so that the residual component of the echo signal is minimized based on the correlation value with the output signal of the synthesis circuit.

〔Effect of the invention〕

According to the present invention, it is possible to generate a pseudo echo signal that minimizes the residual component of the echo signal based only on the residual component of the echo signal, thereby eliminating the influence of the transmitted signal from the other station even during simultaneous bidirectional transmission. A good echo cancellation effect can be obtained.

Further, in the present invention, the transfer function (determined by the tap coefficient of the transversal filter) of the pseudo-echo generation circuit is controlled so that the output signal of the second synthesis circuit becomes minimum (zero). Therefore, the transfer function of the pseudo-echo generation circuit is ultimately equal to the transfer characteristic of the hybrid, which is the echo path, and does not depend on the transfer function of the transmission path, so the echo signal cancellation performance changes depending on the transfer function of the transmission path. There's nothing to do. That is, it is possible to compensate for the influence of the transfer function of the transmission line in the echo signal cancellation operation.

[Embodiments of the invention]

FIG. 1 shows the configuration of an echo canceller according to an embodiment of the present invention. In the figure, the baseband transmission signal applied to input terminal 1 is modulated by modulation circuit 2, and then transferred to hybrid transformer 3.
The signal is transmitted to the other station via the echo generator 4, and is also input to the pseudo echo generation circuit 4. The pseudo-echo generation circuit 4 includes a transversal filter 5 with a variable tap coefficient and a modulation circuit 6 consisting of a phase rotation circuit, and generates a voice-band pseudo-echo signal from the baseband transmission signal. This pseudo echo signal is input to the first combining circuit 7 together with the received signal input via the hybrid transformer 3.
In the first synthesis circuit 7, a difference circuit 8 subtracts the pseudo echo signal from the received signal to eliminate the echo signal component generated in the hybrid transformer 3, and a demodulation circuit 9 consisting of a phase rotation circuit performs demodulation. Obtain baseband reception signal. The output of the first synthesis circuit 7 is given as one input signal to the second synthesis circuit 16 via the delay circuit 10, and
Automatic equalizer using transversal filter 1
1 eliminates transmission distortion caused by the received signal on the telephone line, and further removes phase disturbances such as phase jitter in a carrier phase tracking circuit 12 consisting of a phase rotation circuit, after which the received signal is input to a sign determination circuit 13. The sign determination circuit 13 is a zero level slicer that converts the input signal into a digital signal with a fixed positive value or negative value depending on whether it is above or below the zero level. The digital signal output from the sign determination circuit 13 is guided to the output terminal 14 as a baseband reception signal from the partner station. Further, this digital signal is given to the transmission distortion generation circuit 15 as a reference signal. The transmission distortion generating circuit 15 is constituted by a transversal filter having a variable tap coefficient, and each reference signal is multiplied by its corresponding tap coefficient, and the sum thereof is determined. Here, the tap coefficient is changed by the output signal of the difference circuit 18, as will be described later, and is controlled to have a value corresponding to the transmission distortion in the transmission path. Therefore, the output signal of the transmission distortion generation circuit 15 is a signal obtained by adding pseudo transmission distortion to the baseband reception signal from the partner station. The output of this transmission distortion generating circuit 15 is sent to the second combining circuit 1.
6 other input signals. The second synthesis circuit 16 calculates the difference between the signal from which phase disturbances such as phase jitter of the baseband reception signal applied through the delay circuit 10 are removed by the phase rotation circuit 17 and the baseband signal output from the transmission distortion generation circuit 15. The difference signal is obtained by a difference circuit 18 and outputted through a phase rotation circuit 19 which provides an opposite phase correction of the phase rotation circuit 17. Second
The output of the combining circuit 16 is the sum of (the difference between the actual echo signal and the pseudo echo signal) and (the difference between the actual received signal with transmission distortion and the received signal with pseudo transmission distortion). This output becomes a signal for controlling the tap coefficient of the transversal filter 5 in the pseudo echo generating circuit 4. Here, the transversal filter 5 changes the tap coefficient for the output of the second synthesis circuit 16 using only (the difference between the actual echo signal and the pseudo echo signal). On the other hand, the output signal of the difference circuit 18 becomes a signal for controlling the tap coefficient of the transversal filter in the transmission distortion generating circuit 15. Transmission distortion generation circuit 1
In step 5, the tap coefficient is changed for the above output using only the difference between the actual received signal with transmission distortion and the received signal with pseudo transmission distortion.

The operation of this embodiment will be explained using equations. The baseband transmission signal given to input terminal 1 is x _i
(i is sampling time), tap coefficient of transversal filter 5 is a _o (n is tap coefficient number)
Then, the output u^ _u of the pseudo echo generation circuit 4 is: u^ _i = e ^j 〓 ⁱ _N 〓 ⁿ⁼¹ a _o x _io ...(1) (Here, N is the number of taps, and θ _i is the modulated carrier wave. is given by the real part of the phase rotation angle, i=√−1. On the other hand, from the hybrid transformer 3, the transmission signal υ _j e ⁱ⁽ 〓 ⁱ⁺ 〓 ¹⁾ from the other station and the voice band echo signal _{u i} generated in the hybrid transformer 3 are transmitted.
The real part of the sum of e ^j( 〓 ⁱ⁺ 〓 ⁰⁾ is input (here θ _p ,
θ ₁ is constant phase). Therefore, the output of the difference circuit 8 is the real part of u _i e ⁽ 〓 ⁱ⁺ 〓 ⁰⁾ −e _j 〓 _iN 〓 ⁿ⁼¹ a _o x _io +υ _i e ^j( 〓 ⁱ⁺ 〓 ¹⁾ ……(2) This is then demodulated in the demodulation circuit 9, that is, subjected to phase rotation such as e _-j 〓 _i , so that from the first synthesis circuit 7, γ _i (u′ _i − _N 〓 ⁿ⁼¹ a _o x _io ) +υ′ _i ...(3) Here, u′ _i =u _i e ^j 〓 ⁰ , υ′ _i =υ _i e ^j 〓 ¹ ...(4) are output.

The part in parentheses on the right side of equation (3) is the residual component of the echo signal, and υ' _i is the signal transmitted from the other station (the signal received by the local station) that has been subjected to transmission distortion due to the telephone line. this
The signal γi given by equation (3) is waveform-equalized by the automatic equalizer 11 as described above to remove transmission distortion, and is further configured using a carrier phase tracking circuit using a phase rotation circuit (PLL). By the circuit 12,
After the phase is controlled so as to follow the original carrier phase of the transmission signal from the other station and phase disturbances such as phase jitter are removed, the sign determination circuit 13
The sign is determined as described above, and the determination result is input to the transmission distortion generation circuit 15 as a reference signal. At this time, in the automatic equalizer 11, a time delay M _p occurs only for the central tap position of the transversal filter. Therefore, we decided to use the judgment result as a reference signal.
It will be displayed as Z _i-Mp . Next, if the tap coefficient of the transversal filter in the transmission distortion generation circuit 15 is b _k (k=1,...,K), then from this circuit 15, u^ _i-Mp = _K 〓 ^k=1 b _k Z _{i -Mp-k} ...(5) is output. In this transmission distortion generating circuit 15 as well, a time delay K ₀ corresponding to the central tap position of the transversal filter occurs. The delay circuit 10 is
This is provided to correct the delay amount M _p +K _p =L _p caused by the automatic equalizer 11 and the transmission distortion generation circuit 15, and its output is calculated as r _i-L0 = (u′ _{i- L0} − _N 〓 ⁿ⁼¹ a _o x _i-L0-o )υ′ _i-L0 ……(6). The output of this delay circuit 10 is further passed through a phase rotation circuit 17 for correcting phase disturbances such as phase jitter, which functions equivalently to the carrier phase tracking circuit 12.
A phase rotation of e ^-j 〓 ⁱ is applied. In the difference circuit 18,
Perform the difference calculation between equations (5) and (6), and obtain ε _i = r _i-Lp e ^-j 〓 ⁱ −u^ _i-Mp = e ^-j 〓 ⁱ (u′ _i
-L0 − _N 〓 ⁿ⁼¹ a _o x _i-L0-o ) + (e ^-j 〓 ⁱ v′ _i-Lp − _K 〓 ^k=1 b _k Z _i-Mp-k ……(7) Error Obtain signal ε _i . Then, phase rotation circuit 1
9, a phase rotation of e ⁱ 〓 ⁱ is applied to ε _i , and the error signal ε′ _i = (u′ _i-L0 − _N 〓 ⁿ⁼¹ a _o x _i-L0-o ) + (υ′ _{i- L0} −e ^j 〓 ⁱ _K 〓 ^k=1 b _k Z _i-M0-k ...(8) is output as an error signal ε′ _i .

Here, the tap coefficient a _o of the transversal filter 5 in the pseudo echo generation circuit 4 is controlled by (8)
Assuming that the square of the error signal in the equation is minimized based on the steepest descent method, the gradient of the evaluation functions ε' _i and ε' _i ^* (* is the complex conjugate) is calculated as ∂/ using equation (8). ∂a _o ε′ ₁ ε′ ₁ ^* =−2ε′ _i x ^* _i-Lp-o ...(9) Therefore, the tap coefficient correction formula is a _o ^{(i+1 )} = a _o ⁽ⁱ⁾ + αε′ _i x ^* _i-Lp-o ……(10). In other words, the following formula calculates the correlation between the error signal ε′ _i output from the second synthesis circuit 16 and the complex conjugate of the transmission baseband signal x _i-L0 input to terminal 1, and then multiplies this by a constant. This shows that a new tap coefficient value at time i+1 can be successively determined by adding the tap coefficient a ⁽ⁱ⁾ _o at time i to the tap coefficient a (i) o at time i.

As described above, the error signal ε _i ' is the sum of (the difference between the actual echo signal and the pseudo echo signal) and (the difference between the actual received signal with transmission distortion and the received signal with pseudo transmission distortion). Here (actual echo signal)
and (pseudo echo signal) are each generated from the transmission baseband signal X _i-L0 of the local station. However, both the (actual received signal with transmission distortion) and (pseudo received signal with transmission distortion) are generated from the received baseband signal Z _i-M0 from the partner station. Therefore, as shown in equation (10), the error signal ε _i ′ and the transmission baseband signal
By correlating with the complex conjugate of X _i-L0 , only the difference between the actual echo signal and the pseudo echo signal is extracted, and the tap coefficient is changed to minimize this.

From equation (10), it can be seen that the configuration of the transversal filter 5 in the pseudo echo generating circuit 4 can be as shown in FIG. In FIG. 2, terminal 21
The transmission baseband signal x _i sample value series is input to the sample memory 22, and the sample values at each time are stored in the sample memory 22. Each of these sample values is multiplied by a tap coefficient a _o in a weighting circuit 23, then added and synthesized in an adding circuit 24, and inputted from a terminal 25 as an equalized vane band pseudo echo signal. on the other hand,
The terminal 26 is connected to the second synthesis circuit 1 given by equation (8).
The error signal ε′ _i obtained in step 6 is input to the multiplier 27.
Then, the correlation ε' _i x ^* _i-Lp-o with the complex conjugate of the transmission baseband signal stored in the sample memory 22 is taken, and the integration circuit 28 performs the calculation of equation (10). The tap coefficient is updated sequentially. The configuration shown in FIG. 2 is different from the configuration known as a conventional transversal automatic equalizer, in that, for the delay circuit 10 in FIG. The difference lies in that the signal stored in the sample memory is used to change the weighting.

Next, the tap coefficient b _k of the transversal filter in the transmission distortion generating circuit 15 is controlled by similarly minimizing the square of the error signal ε _i in equation (7) based on the steepest descent method. Can be executed. Using equation (7), the gradient of the evaluation function ε _{i ε i} ^* is: ∂/∂b _k ε _i ε _i ^* =−2ε _i Z ^* _i-Mp-k ……(11) Therefore, the tap coefficient The correction formula for b _k is as follows, where β is a positive tap gain: b _k(i+1) = b _k ⁽ⁱ⁾ + βε _i Z ^* _i-Mp-k ...(12) The tap coefficient b _k is successively updated with the correlation value between the error signal ε _i outputted from the difference circuit 18 and the complex conjugate of the reference signal Z _{i -Mp-k} stored in the transmission distortion generating circuit 15 . In this equation (12), by correlating the error signal ε _i with the complex posterior of the reference signal (received baseband signal) Z _i-Mp , in contrast to the above equation (10), Only the difference (between the distorted received signal and the pseudo-transmission distorted received signal) is extracted, and the tap coefficient is changed to minimize this difference. The configuration of the transmission distortion generating circuit 15 may be the same as that commonly known as a transversal automatic equalizer.

In other words, in the configuration of the transversal filter 5 shown in FIG.
The stored signals in the sample memory that are correlated and used to change the weightings are the same. (For example, in FIG. 2, the stored signal of the first sample memory 22 is supplied to the first multiplier 27. The same applies to the second and subsequent eyes.) Transmission distortion generation circuit 1
5, the reference signal is connected to terminal 21 in FIG.
A sample value series of Z _i-Mp is input, and sample values at each time are stored in the sample memory 22. Each of these sample values is given a tap coefficient by a weighting circuit 23.
After being multiplied by b _k , the signals are added and combined in an adding circuit 24, and outputted from a terminal 25 as a baseband reception signal to which pseudo transmission distortion has been added. On the other hand, the error signal _ε i obtained by the difference circuit 18 given by equation (7) is input to the terminal 26, and the multiplier 27
The correlation ε _i Z _i-Mp-k with the complex conjugate of the reference signal stored in 2 is taken, and the integration circuit 28 calculates equation (12), thereby updating the tap coefficients one by one. .

In this way, in this embodiment, the transmission distortion generation circuit 15
In this step, a signal to which pseudo transmission distortion is added is created using the determination result (baseband received signal) of the determination circuit as a reference signal. Next, this transmission distortion generating circuit 15
and (received signal with pseudo transmission distortion), the first
The output signal of the combining circuit 7 (the sum of (the difference between the actual echo signal and the pseudo echo signal) and (the actual received signal with transmission distortion)) is combined in the second combining circuit 16, and the difference is taken. . The output signal of this second combining circuit 16 (the sum of (the difference between the actual echo signal and the pseudo echo signal) and (the difference between the actual received signal with transmission distortion and the received signal with pseudo transmission distortion)) is The signal is supplied to an echo generating circuit 4 and a transmission distortion generating circuit 15. The pseudo echo generating circuit 4 changes the tap coefficient so that the difference between the actual echo signal and the pseudo echo signal is minimized. In the transmission distortion generation circuit, the tap coefficient is changed so that the difference between the actual received signal with transmission distortion and the received signal with pseudo transmission distortion is minimized.

Through such control, the transfer function (tap coefficient) of the pseudo-echo generation circuit will eventually become equal to the transfer characteristic (coefficient for generating an echo signal according to the own station's transmitted signal) of the hybrid, which is the echo path, and Since it does not depend on the transfer function of the transmission line (a coefficient that generates transmission distortion according to the transmission signal from the other station), the echo signal cancellation performance does not change depending on the transfer function of the transmission line. That is, it is possible to compensate for the influence of the transfer function of the transmission line in the echo signal cancellation operation.

Note that if the transmission signal from the other station and the transmission signal from the own station are asynchronous, a speed conversion circuit may be provided in the second synthesis circuit 16. That is, the calculations on the receiving side up to finding the error signal ε′ _i in equation (8) are operated in synchronization with the signal transmitted from the other station, and the error signal ε′ _i that controls the pseudo echo generation circuit 4 is buffered.・
After storing the data in memory and converting the speed, the second synthesis circuit 16 outputs a control signal to the pseudo echo generation circuit 4, and if the pseudo echo generation circuit 4 is operated in synchronization with the own station transmission signal, the problem of asynchronization can be solved. can be easily solved.

Further, in FIG. 1, the delay circuit 10 is provided independently of the automatic equalizer 11, but the delay circuit 10 can also be constructed using the memory within the automatic equalizer 11. FIG. 3 shows the configuration of a part of the transversal automatic equalizer. The γ _i signal of equation (3) is input to the terminal 31, and the sample value at each time is stored in the sample memory 32. are multiplied by a variable tap coefficient in a weighting circuit 33, and an adder 34 adds and synthesizes all the multiplication results, and outputs the result to a terminal 35. Therefore, for example, when there is an insufficient amount of delay as shown in FIG. 3, if the sample memory 36 is added for that amount, a signal corresponding to the output of the delay circuit 10 given the necessary amount of delay can be obtained from the terminal 37. I can put it out. On the contrary, if the output from the final stage of the sample memory 32 is delayed too much, the delay circuit 1
It is sufficient to extract a signal corresponding to an output of 0.

Further, the second synthesis circuit 16 can be modified in various ways, and FIG. 4 shows examples of the modifications. In FIG. 4a, the output of the transmission distortion generating circuit 15 inputted from the terminal 42 is given phase disturbance by the phase rotation circuit 44, and this is output from the output of the delay circuit 10 inputted to the terminal 41 and the difference circuit 43. Subtracted. This subtraction result is output as a control signal to the pseudo echo generation circuit 4 through a terminal 45, and is also phase-corrected in the opposite direction to the phase rotation circuit 44 through a phase rotation circuit 46, and is sent from a terminal 47 to the transmission distortion generation circuit 1.
It is output as an error signal for controlling 5.
At this time, the error signal output from terminal 45 is (8)
Since the error signal output from the terminal 47 is given by the equation (7), it is possible to obtain exactly the same operation as in Fig. 1 even if the second synthesis circuit with the configuration shown in Fig. 4 a is used. I understand.

Furthermore, if a phase rotation circuit that provides phase disturbance is inserted between the sign determination circuit 13 and the transmission distortion generation circuit 15 in FIG. As shown in FIG. 4b, the output of the transmission distortion generation circuit 15 input from the terminal 42 and the output of the delay circuit 10 with phase disturbance input from the terminal 41 are connected to a difference circuit. 48, and a phase-disturbed error signal for controlling the transmission distortion generation circuit 15 is sent from the terminal 47 to the pseudo echo generation circuit 4.
It is clear that the same operation as shown in FIG. 1 can be obtained by removing the phase disturbance component by the phase rotation circuit 49 and outputting the control error signal via the terminal 47.

In the above explanation, the transversal filter 5 in the pseudo echo generation circuit 4, the transmission distortion generation circuit 1
5 and the automatic equalizer 11 are all operated in the baseband band, but it is of course possible to configure any of them to operate in the passband band of the audio band. For example, when only the automatic equalizer 11 is operated in the passband, the phase rotation circuit as the demodulation circuit 9 in the first synthesis circuit 7 in FIG. A circuit that inputs a signal expressed as a real number in a band and outputs a signal expressed as a complex signal. It is known that this circuit can be constructed with a Hilbert filter, etc., and has been commonly used for telephone line models.) , a passband signal is output from the first synthesis circuit 7, passes through a passband automatic equalizer 11, and then is removed by a carrier phase tracking circuit 12, which removes phase disturbances such as phase jitter and also performs a demodulation operation.
The sign determination circuit 13 may determine the result. At this time, the delay circuit 10 also serves as a passband delay circuit, and the second combining circuit 16 may perform phase disturbance correction and demodulation in the same manner as the circuit 12.

Furthermore, a passband signal is input from the terminal 1, and the pseudo echo generation circuit 4 is configured only with a transversal filter 5 that operates in the passband.
In order to perform baseband operation, the phase rotation circuit 19 in the second synthesis circuit 16 in FIG.
It is obvious that it is sufficient to provide not only the operation e ^j 〓 ⁱ that causes phase disturbance but also a function of converting the frequency of the error signal ε′ _i in the baseband band to the passband band. Similarly, for the transmission distortion generation circuit 15, it is also possible to use this as a passband band.
Of course, it is possible to operate the automatic equalizer 11 and the transmission distortion generating circuit 15 in the passband band, and the first,
The second synthesis circuit and other constituent circuits may be modified as appropriate.

In addition, during initial tap coefficient training of the automatic equalizer 11, transmission distortion generation circuit 15, and pseudo echo generation circuit 4, the reference signal input to the transmission distortion generation circuit 15 is used as a training signal for judgment by the sign judgment circuit 13. It may be used instead of the result and switched to the judgment result after the training is completed. Furthermore, instead of using variable tap coefficients for the automatic equalizer 11 and transmission distortion generation circuit 15, they may be configured to have fixed tap coefficients that respectively provide predicted transmission distortion correction and transmission distortion.

Furthermore, in the above explanation, the amount of delay in the first synthesis circuit 7 has been ignored, but if there is a delay, it is sufficient to further correct the amount of delay as shown in FIG. 2 to the pseudo echo generation circuit 4. .

[Brief explanation of drawings]

FIG. 1 is a block diagram of an echo canceller according to an embodiment of the present invention, FIG. 2 is a diagram showing a specific configuration example of a pseudo echo generation circuit in the same embodiment, and FIG. FIGS. 4a and 4b are diagrams showing an example of the configuration of the delay circuit, and FIGS. 4A and 4B are diagrams showing other examples of the configuration of the second synthesis circuit used in the present invention. 4...Pseudo echo generation circuit, 7...First synthesis circuit, 15...Transmission distortion generation circuit, 16...Second synthesis circuit.

Claims (1)

[Claims] 1. In an echo canceler for a simultaneous two-way communication system that modulates a local station transmission signal and sends it to a transmission path, and receives a local station reception signal input from the transmission path, a pseudo echo generation circuit that generates a pseudo echo signal by passing the local station transmission signal through a transversal filter with a variable tap coefficient and then modulating the signal; and combining the pseudo echo signal and the local station reception signal. , a first synthesis circuit that demodulates and outputs the echo signal component included in the received signal of the own station, and a transmission distortion in the transmission path included in the output signal of the first synthesis circuit. An equalizer to be erased, a sign judgment circuit which judges the sign of the output signal of this equalizer and outputs it as a reference signal, and a reference signal from this sign judgment circuit is input, and the tap coefficient of this reference signal is variable. A transmission distortion generation circuit outputs a signal with transmission distortion added by passing it through a transversal filter, and the output signal of this transmission distortion generation circuit and the output signal of the first synthesis circuit are combined to generate the echo. a second synthesis circuit that outputs a residual component of the signal and a residual component of the signal to which the transmission distortion has been added, and the pseudo echo generation circuit combines the own station transmission signal and the output signal of the second synthesis circuit. An echo canceller characterized in that a tap coefficient of the transversal filter is controlled so that a residual component of the echo signal is minimized based on a correlation value between the transversal filter and the echo signal. 2. The transmission distortion generating circuit controls the transversal filter so that the residual component of the signal to which the transmission distortion is added is minimized based on the correlation value between the reference signal and the output signal of the second combining circuit. 2. The echo canceller according to claim 1, wherein a tap coefficient is controlled.