JP2507652B2 - Eco-canceller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] The present invention relates to an echo canceller used for a long distance telephone system, a conference telephone system, a television / voice conference telephone system, etc., even when the echo canceller falls into a divergent state due to disturbance or the like. An echo that is configured to generate a pseudo echo signal based on the received signal and subtract the pseudo echo signal from the input signal on the transmission side to obtain the output signal on the transmission side for the purpose of enabling automatic self-recovery. In the canceller,
A divergence detecting unit that compares the pseudo echo signal and the input signal on the transmitting side and detects divergence when the pseudo echo signal exceeds a predetermined ratio of the input signal on the transmitting side, and when divergence is detected by the divergence detecting unit. A reset means for resetting the echo canceller is provided.

[Field of Industrial Application] The present invention relates to a long distance telephone system, a conference telephone system,
Alternatively, the present invention relates to an echo canceller used in a television / voice conference telephone system or the like.

The echo canceller was developed for the purpose of preventing the deterioration of the communication quality due to the echo that occurs in long-distance telephone lines such as satellite communication and submarine cable communication. This echo canceller technology is currently applied to two-way repeaters for call transfer services, repeaters for conference calls, etc. for the purpose of improving ringing margin, and to improve the efficiency of transmission lines. It is also required for the purpose of canceling problematic echoes by applying a high efficiency encoder having a long coding delay.

Further, in a television / conference telephone system, a loudspeaker telephone, etc., the output sound from a speaker is used for the purpose of canceling an echo sound generated when the sound is reflected by a wall of a room and goes around to a microphone.

[Prior Art] The principle of the echo phenomenon and echo canceller will be described below in the case of a long-distance telephone line.

FIG. 13 is a diagram for explaining the echo phenomenon. Generally, in long-distance lines, the subscriber lines at both ends of the line are two-wire lines that send and receive signals using two lines, and the long-distance lines that connect them are 4-wire lines that use separate lines for transmission and reception. Composed of. Hybrid transformer 4 for conversion between 2-wire and 4-wire
Although 1 and 42 are used, a phenomenon occurs in which a part of the input signal on the reception side leaks to the transmission side via the hybrid transformers 41 and 42 due to the impedance mismatch at the connection point of the 2 and 4 lines. This leaked signal is generally called an echo.

In the case of domestic calls, this echo has a short propagation time of the voice signal, and the time difference between the transmitted signal and the echo returned via the connection point on the other side is as small as about 50 msec at the maximum, so the speaker Is heard as a sidetone and does not interfere with the call, so there are few problems.

On the other hand, on an international line such as a satellite line, the round-trip signal between callers may have a propagation time of about 300 msec or more, so the caller can speak while listening to the echo of his voice with a delay. It becomes difficult to talk and it becomes impossible to make a smooth call.

The echo canceller suppresses such an echo, and its operating principle is shown in FIG. The echo cancellers 43 and 44 are placed at both ends of the 4-wire line, and the echo cancellers 43 and 44 estimate the characteristics of the echo path and generate pseudo echo signals 431 and 441.
And subtracting units 432 and 442 for subtracting the pseudo echo signal from the actual echo signal.

The pseudo echo generators 431 and 441 generally use a transversal filter to estimate the impulse response of the echo path.However, in order to respond to changes in the impulse response, the received signal is usually used to adaptively adjust the coefficients of the adaptive filter. It has a changing structure. As an adaptive algorithm of the adaptive filter, generally, a learning identification method having a simple hardware configuration and relatively good characteristics is often used.

[Problems to be Solved by the Invention] However, when a learning identification method or an adaptive algorithm similar thereto is used, estimation is performed when a narrow band signal such as a low bit rate modem signal or a single frequency signal by FM modulation is input. The value of the impulse response (tap coefficient of the filter) may become large, and a divergence phenomenon may occur in which the bit limit defined by the hardware configuration is exceeded.

When the echo canceller is applied to the real line,
Not only when the line is connected and the echo path exists, but there is also the case where the echo path does not exist because the line is switched. Therefore, the echo canceller is always in a state where it can correctly estimate the impulse response. Not necessarily.

In order to deal with such a case, the echo canceller usually has a control function inside for judging the situation and always performing a stable operation. However, these limiting functions cannot be applied to all situations, and if the adaptive operation is continued for a long time when the impulse response cannot be estimated for some reason, the calculation error gradually accumulates. Finally, it may fall into the divergence phenomenon.

When such a divergence phenomenon occurs, the echo canceller forms a closed loop between two echo cancellers forming a pair, as shown in Fig. 14, so that once the filter coefficient diverges. Then, it can be said that it is very difficult to automatically return to normal operation.

Further, such a divergence phenomenon also occurs in the following cases. That is, since the echo canceller performs complicated processing in real time, it is usually realized by using a digital signal processing circuit, and the signal to be handled is a digital signal. On the other hand, the signals handled by the telephone network are analog signals.

Therefore, a circuit for converting an analog signal into a digital signal is required before and after the echo canceller, and in most cases, a PCM codec is used as this conversion circuit as shown in FIG. This PCM codec uses a non-linear 8-bit signal such as a μ-law code as an output signal, and its maximum value is limited.

Since the input signal on the transmission side of the echo canceller is the output signal of the PCM codec, even at the maximum level, the maximum output value of this PCM codec will not be exceeded. Since the pseudo echo is an estimate of the echo, it does not exceed the maximum value of the PCM codec if it operates normally.

In the echo canceller, when the digital signal processing is performed using the non-linear 8-bit output signal of the PCM codec, it is usually converted into a linear signal before the processing. At that time, the 8-bit PCM codec is used. Is extended to a 14-bit signal. In addition, when performing echo cancellation processing with an echo canceller,
Calculations are often performed with a system of 14 bits or more, and in such cases, if the echo path is not estimated correctly, a value exceeding the maximum value of the PCM codec will be calculated as a pseudo echo signal. There is also.

As a result, the output signal on the transmission side, which is a residual echo, may exceed the maximum value of the PCM codec. Even in such a case, if the output signal on the transmission side is converted again to 8 bits by the PCM codec and transmitted to the opposite echo canceller, it does not affect the opposite echo canceller.

However, when a high-efficiency encoder is inserted instead of the PCM codec, the output signal on the transmission side may be transmitted to the opposite echo canceller while exceeding the maximum value of the PCM codec.

As a result, a value exceeding the maximum value of the PCM codec is input as the receiving side input signal of the opposite echo canceller, but this signal passes through the echo path (that is, from the opposite echo canceller through the PCM codec, hybrid transformer, and PCM codec). The value is suppressed by the PCM codec when it is output to the path that wraps around to the transmission side of the original counter echo canceller), which causes non-linearity between the reception side input signal and the transmission side input signal. Therefore, the correct echo canceling operation becomes impossible, which may cause the opposite echo canceller to diverge.

When the divergence phenomenon occurs for some reason as described above, it actually appears as an obstacle to the call. In such a case, conventionally, there is a method other than resetting the echo canceller by human judgment. There was no

The present invention has been made in view of such circumstances, and it is an object of the present invention to automatically restore itself even when the echo canceller falls into a divergent state due to a disturbance or the like.

[Means for Solving the Problems] FIGS. 1 to 4 are explanatory views of the principle according to the present invention. 1 to 4, reference numeral 91 is an adaptive filter that generates a pseudo echo based on a received signal, and 92 is a subtraction unit that subtracts the pseudo echo signal of the adaptive filter 91 from a transmission side input signal and outputs a transmission side output signal. , 93, 95, 96 are divergence detecting means, respectively, and 94 is a reset means for resetting the echo canceller circuit including the adaptive filter 91 according to the detection signal from the divergence detecting means.

As shown in FIG. 1, the echo canceller according to the present invention, as shown in FIG. 1, generates a pseudo echo signal based on a received signal, subtracts the pseudo echo signal from a transmission side input signal, and outputs the transmission side output signal. In the echo canceller configured to, comparing the pseudo echo signal and the transmission side input signal, the divergence detection means 93 for detecting divergence when the pseudo echo signal becomes a predetermined ratio or more of the transmission side input signal, And reset means for resetting the echo canceller when divergence is detected by the divergence detecting means 93
With 94.

The echo canceller according to the present invention, as another form,
As shown in FIG. 2, in a echo canceller configured to generate a pseudo echo signal based on a received signal and subtract the pseudo echo signal from a transmission side input signal to obtain a transmission side output signal, a pseudo echo A divergence detecting means for comparing at least one of the signal and the output signal on the transmitting side with a predetermined threshold value determined based on the maximum value of the input signal on the transmitting side, and detecting divergence when the compared signal exceeds the threshold value.
95, and reset means 94 for resetting the echo canceller when divergence detection means 95 detects divergence.

As another form of the echo canceller according to the present invention, in the echo canceller of the form of FIG. 2 described above, the divergence detecting means 95 compares the pseudo echo signal and the transmission side output signal with a threshold value, and Are both configured to detect divergence when they exceed the threshold.

Further, as yet another embodiment, the echo canceller according to the present invention, as shown in FIG. 3, generates a pseudo echo signal based on the received signal, and subtracts this pseudo echo signal from the input signal on the transmission side for transmission. In the echo canceller configured to be the side output signal, comparing the transmission side input signal and the transmission side output signal, the transmission side input signal is a predetermined ratio or more of the transmission side output signal, and the transmission side output signal, A divergence detecting means 96 for detecting divergence by exceeding a predetermined threshold value determined based on the maximum value of the input signal on the transmitting side, and a reset for resetting an echo canceller when divergence is detected by the divergence detecting means 96 Means 94
Be equipped with.

Furthermore, as another form of the echo canceller according to the present invention, as shown in FIG. 4, in each of the above-mentioned forms, an echo canceller amount judging means 97 for judging the echo canceller amount of the echo canceller, and a band-limited low-noise canceller. Noise generating means 98 for generating level noise (around line noise) and noise generating means as a transmitting side output signal to be sent to the other side when the echo canceling amount judging means 97 judges that the echo canceling amount is small. Further comprising switch means 99 for selecting low level noise from 98.

Incidentally, the divergence detecting means 93, 95, 96 in each of the above modes
In the signal comparison in (1), signal power, signal amplitude, or the like can be used as the signal, and when using the signal amplitude, it is preferable to use the temporal average value.

[Operation] In the echo canceller of the form shown in FIG. 1, the divergence detecting means
93 monitors the pseudo echo signal and the input signal on the transmission side, and when divergence of the echo canceller occurs, the divergence state is detected because the pseudo echo signal is larger than a predetermined ratio of the input signal on the transmission side. The detection circuit outputs a detection signal, and the reset circuit receiving the detection signal clears the tap value and the tap coefficient of the adaptive filter 91 to initialize the echo canceller. This causes the echo canceller to recover itself.

The echo canceller of the form shown in FIG.
95 monitors whether the pseudo echo signal or the output signal on the transmission side exceeds a predetermined threshold value.When the divergence state occurs, the pseudo echo signal or the output signal on the transmission side exceeds the predetermined threshold value. The divergence detecting means 95 detects this, and the reset circuit 94 resets the echo canceller.

In this case, both the pseudo echo signal and the output signal on the transmitter side can be configured to be judged to be in a divergent state when both exceed a predetermined threshold value. In this case, the reliability of detection of the divergent state is high. Go up.

In the echo canceller of the form shown in FIG. 3, the divergence detection signal
96 detects a divergence state when the input signal on the transmission side exceeds a predetermined ratio of the output signal on the transmission side and the output signal on the transmission side exceeds a predetermined threshold value, and resets the echo canceller by the reset circuit 94. .

Furthermore, in the echo canceller of the form shown in FIG. 4, when the echo canceller is reset at the time of divergence detection, echoes that have not been canceled during the period until the tap coefficient of the adaptive filter 91 converges and sufficient echo cancellation is performed. Echo cancellation amount judging means 97 so that it is not sent to the other party.
Judges this state and switches the switch circuit 99 to send the low level noise of the noise generating means 98 to the other side as an output signal of the transmitting side. As a result, the echo canceling characteristic of the echo canceller can be stabilized.

Embodiments Embodiments of the present invention will be described below with reference to the drawings. Throughout the following drawings, all circuit elements having the same reference numerals represent circuits having the same function.

FIG. 5 shows an echo canceller as an embodiment of the present invention. In FIG. 5, a block surrounded by a dotted line is an echo canceller, and a tap value storage unit 1 that sequentially holds a received signal sequence as a tap value, a tap coefficient storage unit 3 that holds a tap coefficient of each tap, and this tap Pseudo-echo generation unit 4 that generates a pseudo-echo signal based on a value and a tap coefficient, a subtracter 5 that subtracts the pseudo-echo signal from a transmission-side input signal and outputs a transmission-side output signal (that is, a residual echo signal), a reception signal and a transmission side A tap coefficient updating unit 2 that updates the tap coefficient so that the estimated impulse response is converged based on the output signal, and a divergence detection that detects the divergence of the filter based on the input of the transmission side input signal and the pseudo echo signal It is configured to include a container 6.

The detection signal of the divergence detector 6 is transmitted to the tap value storage unit 1 and the tap coefficient storage unit 3, and at the time of divergence detection, the tap value and the tap coefficient held by these are cleared. Note that here, the tap value storage unit 1, the tap coefficient updating unit 2, the tap coefficient storage unit 3, and the pseudo echo generating unit 4 are provided.
Is composed of a transversal type adaptive digital filter.

The configuration example of the divergence detector 6 in the apparatus of this embodiment is the sixth.
As shown in the figure. As shown, the signal power of the pseudo echo signal
A signal power calculation unit 61 that calculates Ppe, a signal power calculation unit 62 that calculates the signal power Psi of the transmission side input signal, and a predetermined coefficient K (from 1 from the transmission side input signal power Psi calculated by the signal power calculation unit 62 A coefficient unit 63 for multiplying by a slightly larger value), and the pseudo echo signal power Ppe from the signal power calculation unit 61 and the coefficient unit 6
Transmitting side input signal power Psi multiplied by a predetermined coefficient K through 3
And a comparator 64 that outputs a divergence detection signal based on the result of the comparison.

As shown in FIG. 7, the signal power calculating section 61 or 62 calculates the signal power by the mean square of the amplitude of a certain section, that is, Can be used.

Alternatively, a method of obtaining the leaky integral or the like can be used. When the leaky integral is used, the signal power calculators 61 and 62 multiply the input signal Xi by the coefficient α as shown in FIG. , An adder 613 that receives the output of the coefficient unit 612 and outputs a signal power P, a delay unit 614 that delays the output of the adder 613, and an output of the delay unit 614 is multiplied by a coefficient 1-α to be given to the adder 613. It can be configured by the coefficient unit 615 and the like.

FIG. 9 shows a configuration example of the hold data clear circuit in the tap value storage unit 1 and the tap coefficient storage unit 3.
As shown, these circuits include a RAM 21 for sequentially storing tap values and tap coefficients, and the read / write mode of this RAM 21 is controlled by the R / W control circuit 22. Reference numeral 23 is an address counter that sequentially updates the address of the RAM 21, and the 0 register 24 holds a "0" value as write data at reset.

The detection signal from the divergence detector 6 is input to the R / W control circuit 22, and when the divergence is detected, this R / W is detected.
Under the control of the control circuit 22, the address counter 23 is reset and sequentially incremented from address 0 to the final address, and the “0” value of the 0 register 24 is input to the RAM 21. All the data held in RAM21 can be cleared to "0".

The pseudo echo signal generated by the pseudo echo generator 4 is
It is calculated by estimating the echo signal sneaking from the receiving side to the transmitting side by the adaptive filter section, and it is considered that the signal power will be almost the same as the input signal on the transmitting side after the echo canceller converges during one-way communication. Also, even during the transient period until the echo canceller converges, as long as the tap coefficient converges in the correct direction, the pseudo echo signal power
It is not considered that Ppe becomes larger than a certain ratio with respect to the transmission side input signal power Psi.

Further, during a two-way simultaneous call, the near-end talker input signal is added to the echo signal as the transmission-side input signal, so that the transmission-side input signal Psi is considered to be sufficiently larger than the pseudo echo signal power Ppe.

Therefore, when the pseudo echo signal power Ppe exceeds the transmission side input signal power Psi, the tap coefficient of the adaptive filter unit is updated in the wrong direction, and a signal unrelated to the echo is internally generated. It can be determined that the state is a divergent state.

The divergence detector 6 determines the presence / absence of this divergence state. The signal power calculators 61 and 62 respectively calculate the signal powers of the transmission side input signal and the pseudo echo signal to calculate the transmission side input signal power Psi and the pseudo echo. After obtaining the signal power Ppe, the coefficient signal 63 is applied to the input signal power Psi on the transmission side by a coefficient K with a certain margin, and the comparator 64 compares both signal powers to obtain Psi × K-Ppe. If ≧ 0, it is determined that the normal state where no divergence has occurred, and if Psi × K−Ppe <0, the divergence state is determined.

When the divergence detector 6 determines that the adaptive filter section is diverging, a detection signal is sent from the comparator 64 to the tap value storage section 1 and the tap coefficient storage section 3, and the tap value of the adaptive filter section is output. Since the tap coefficient is cleared, and the echo canceller is reset by this, even if it falls into a divergent state, it becomes possible to automatically restore itself.

Various modifications can be made in implementing the present invention. These will be described below.

FIG. 10 shows another embodiment of the present invention. This circuit is obtained by changing the configuration of the divergence detector 6 in the apparatus of the embodiment shown in FIG. 5, and the overall configuration of the echo canceller is almost the same as that shown in FIG. Is the transmission side output signal output from the subtractor 5 and the pseudo echo signal from the pseudo error generating unit 4,
The difference is that the transmitter input signal is not input.

In the divergence detector shown in Fig. 10, the output signal (residual echo signal) on the transmission side and the pseudo echo signal are compared with comparators 66 and 67, respectively.
Is input to each comparator 66, 67 as a comparison reference.
The maximum value of the PCM codec (for example, +3.17 dBmO) is input.

As described in Fig. 15, this PCM codec performs A / D conversion and D / A conversion of the signal between the echo canceller and the line, and its output signal is the input to the echo canceller on the transmission side. It is a signal, and the maximum value of this output signal is limited.

Each of the comparators 66 and 67 compares the output signal on the transmission side and the pseudo echo signal with a reference value that is the maximum value of the PCM codec, and outputs a detection signal to the OR circuit 68 when these signals exceed the reference value. It is supposed to do.

 The operation of this embodiment will be described below.

Pseudo-echo signal generated by the pseudo-echo generation unit 4 or transmission-side output signal (residual error) created by subtracting the pseudo-echo signal from the transmission-side input signal by the subtractor 4.
When the echo canceller is operating normally,
It is unlikely that the maximum value of the M codec will be exceeded. Therefore, when the maximum value of the PCM codec is exceeded, it can be determined that the adaptive filter unit malfunctions and is in the divergent state.

Each comparator 66, 67 of the divergence detector makes this determination, and if at least one of the output signal on the transmission side and the pseudo echo signal exceeds the maximum value of the PCM codec output, the detection signal is sent via the OR circuit 68. This detection signal is output and sent to the tap value storage unit 1 and the tap coefficient storage unit 3 to reset the echo canceller as described above so that the divergence state is self-recovered.

In this embodiment, the divergence detector determines that the output signal or the pseudo echo signal is in the divergent state when the PCM codec maximum value exceeds the PCM codec.
By replacing the circuit 68 with an AND circuit, divergence detection can be performed only when both the output signal on the transmission side and the pseudo echo signal exceed the PCM codec maximum value. In this case, divergence detection is more reliable. Become. Further, the divergence detector may detect divergence only with one of the output signal on the transmission side and the pseudo echo signal.

FIG. 11 shows still another embodiment of the present invention. The difference of this embodiment apparatus from that of FIG. 5 is that the divergence detector 7
The configuration is different, and a mechanism for transmitting a dummy audio signal to the opposite device is provided before the adaptive filter unit sufficiently converges when the echo canceller is reset.

In FIG. 11, the divergence detector 7 is supplied with a transmission side input signal and a transmission side output signal, respectively. Reference numeral 8 denotes an echo cancellation amount determination unit, to which the detection signal of the divergence detector 7 is input, so that it can be determined whether or not the echo cancellation operation in the adaptive filter unit is properly performed.

The determination signal of the echo cancellation amount determination unit 8 is a switch circuit.
Used as a control signal to control 10 switching.
The switch circuit 10 switches the transmission signal output to the line side to either the transmission side output signal from the subtractor 5 or the low level noise from the low level noise generating section 9. The low-level noise of the low-level noise generation unit 9 is low-level noise that is band-limited to the voice band, and becomes a pseudo transmission signal.

A configuration example of the divergence detector 7 of the apparatus of this embodiment is shown in FIG. As shown in the figure, the divergence detector 7 has signal power calculators 71 and 72 for calculating the signal powers of the transmission side input signal and the transmission side output signal, respectively, and a constant coefficient K (slightly larger than 1) for the transmission side input signal power Psi. Value), a comparator 74 for comparing the transmission-side input signal power Psi multiplied by the coefficient K with the transmission-side output signal power Pso, and a transmission-side output signal power Pso for a predetermined transmission-side output power threshold value. It is configured to include a comparator 75 for comparing with TH and an AND circuit 76 for receiving a comparison result signal of the comparators 74 and 75 and outputting a detection signal.

As the signal power calculation units 71 and 72, the configuration shown in FIG. 6 or 7 described above can be used.

Here, the coefficient K of the coefficient unit 73 is a value slightly larger than 1, and is determined in consideration of a certain margin. Further, the threshold TH of the output signal power Pso on the transmission side of the comparator 75 is
Based on the maximum value of the output signal of the CM codec, it is determined to have a certain margin in the signal power corresponding to this maximum value.

 The operation of the apparatus of this embodiment will be described below.

The divergence detector 7 monitors the signal power Psi of the input signal on the transmission side and the signal power Pso of the output signal on the transmission side. In the comparator 74, the output signal power Pso on the transmission side is a fixed ratio of the input signal power Psi on the transmission side. When the output signal power Pso exceeds the threshold TH of the output signal power of the transmission side, the comparator 75 outputs the detection signal to the AND circuit 76 when it exceeds the threshold value TH of the output signal power of the transmission side.
Output to AND circuit 76.

Accordingly, the divergence detector 7 considers that the adaptive filter unit is in the divergent state when Pso> TH and Psi × K <Pso, and outputs a detection signal to the tap value storage unit 1 and the tap coefficient storage unit 3.

The detection of such a divergent state is possible for the following reasons.

That is, the output signal on the transmission side becomes maximum when both speakers are talking at the maximum level during two-way simultaneous communication, and when the echo canceling operation by the echo canceller is performed accurately, It does not exceed the maximum value of the PCM codec mentioned above.

The threshold TH of the output signal power of the transmission side is set to a value that allows a certain margin for the power corresponding to the maximum value of the PCM codec, assuming that the pseudo echo signal is not subtracted inside the echo canceller. Therefore, as long as the tap coefficient of the adaptive filter section converges in the correct direction, the transmission side output signal power Pso is the threshold TH
I can't think of over. Further, during normal operation of the echo canceller, the pseudo echo signal is subtracted from the transmission side input signal to obtain the transmission side output signal. Therefore, the transmission side output signal power Pso is equal to the transmission side input signal power Psi.
It is not possible to exceed a certain ratio of.

Therefore, if the transmission side output signal power Pso exceeds both the threshold value TH of the transmission side output signal power Pso and a certain ratio of the transmission side input signal power Psi, the tap coefficient is updated in the wrong direction inside the echo canceller. Therefore, it can be considered that it is a divergent state in which a signal unrelated to the echo is generated inside.

As described above, when divergence is detected by the divergence detector 7, the tap values and tap coefficients in the tap value storage unit 1 and the tap coefficient storage unit 3 are cleared and the circuit is initialized, whereby the echo canceller diverges. It is possible to recover from the state and re-converge.

However, at the time of this initialization, echo is not sufficiently canceled during the transition period until the tap coefficient converges to an appropriate one, so echo that could not be canceled will be output to the other side, It is not preferable as the characteristic of the echo canceller.

Therefore, in the apparatus of this embodiment, the echo cancellation amount determination unit 8
Determines the amount of echo cancellation inside the echo canceller, and switches the switch circuit 10 to the low-level noise generation unit 9 side until the echo cancellation is performed to a certain extent, whereby the output signal of the transmission side is output. Low-level noise limited to the voice band is output to the other party, thereby stabilizing the cancellation characteristics of the echo canceller.

[Effects of the Invention] According to the present invention, even when the echo canceller falls into a divergent state due to a disturbance or the like, it becomes possible to detect the divergent state and automatically restore itself to a normal position. The reliability of the canceller can be increased.

[Brief description of drawings]

1, FIG. 2, FIG. 3, and FIG. 4 are explanatory views of the principle according to the present invention, FIG. 5 is a block diagram showing an echo canceller as one embodiment of the present invention, and FIG. 7 is a block diagram showing a configuration example of a divergence detector in the apparatus, FIG. 7 is a block diagram showing a configuration example of a signal power calculation unit of the divergence detector of the embodiment, and FIG. 8 is a signal power calculation of the divergence detector of the embodiment. FIG. 9 is a block diagram showing another configuration example of the section, FIG. 9 is a block diagram showing an example of a tap value and tap coefficient clearing circuit of the embodiment, and FIG. 10 is a divergence detector of another embodiment of the present invention. Block diagram showing a configuration example, FIG. 11 is a block diagram showing still another embodiment of the present invention, FIG. 12 is a block diagram showing a configuration example of a divergence detector in the embodiment apparatus of FIG. 11, FIG. Shows the principle of the echo phenomenon, and Fig. 14 shows the principle of the echo canceller. FIG. 15 to be described and FIG. 15 are block diagrams showing a configuration when the echo canceller is applied to a telephone network. In the figure, 1 ... Tap value storage unit 2 ... Tap coefficient updating unit 3 ... Tap coefficient storage unit 4 ... Pseudo echo generating unit 5 ... Subtractor 6, 7 ... Divergence detector 8 ... Echo cancellation amount Judgment unit 9 …… Low-level noise generator 10 …… Switch circuit 21 …… RAM 22 …… R / W control circuit 23 …… Address counter 24 …… 0 register 61, 62, 71, 72 …… Signal power calculator 64, 66, 67, 74, 75 ... Comparator 63, 73 ... Coefficient unit

 ─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-63-98226 (JP, A) JP-A-3-178227 (JP, A) JP-A 62-163428 (JP, A) JP-A 61- 72419 (JP, A) JP-B-62-58574 (JP, B2) US Patent 5305309 (US, A)

Claims (5)

(57) [Claims] 1. An echo canceller configured to generate a pseudo echo signal based on a received signal and subtract the pseudo echo signal from a transmission side input to obtain a transmission side output signal. Side input signals are compared, and divergence detection means (93) for detecting divergence when the pseudo echo signal is equal to or higher than a predetermined ratio of the transmission side input signal, and divergence detection means (93) An echo canceller comprising reset means (94) for resetting the echo canceller when detected. 2. An echo canceller configured to generate a pseudo echo signal based on a received signal and subtract the pseudo echo signal from a transmission side input signal to obtain a transmission side output signal. A divergence detecting means for comparing at least one of the output signals on the side with a predetermined threshold value determined based on the maximum value of the input signal on the transmission side, and detecting divergence when the compared signal exceeds the threshold value. ) And reset means (94) for resetting the echo canceller when divergence is detected by the divergence detecting means (95). 3. The echo canceller according to claim 1, wherein the divergence detecting means (95) compares the pseudo echo signal and the output signal on the transmitting side with a threshold value, and when both of them exceed the threshold value. It is designed to detect divergence. 4. An echo canceller configured to generate a pseudo echo signal based on a received signal and subtract the pseudo echo signal from a transmission side input signal to obtain a transmission side output signal. The transmission-side output signal is compared, the transmission-side input signal is equal to or higher than a predetermined ratio of the transmission-side output signal, and the transmission-side output signal has a predetermined value determined based on the maximum value of the transmission-side input signal. Echo comprising divergence detecting means (96) for detecting divergence when the threshold is exceeded, and reset means (94) for resetting the echo canceller when divergence is detected by the divergence detecting means (96) Canceller. 5. An echo cancellation amount judging means (97) for judging an echo cancellation amount of an echo canceller, a noise generating means (98) for generating band-limited low level noise, and the echo cancellation amount judging means ( 97) further comprising a switch means (99) for selecting a low level noise from the noise generating means (98) as a transmission side output signal to be transmitted to the other side when it is determined that the echo cancellation amount is small. Item 5. The echo canceller according to any one of items 1 to 4.