JP2003198433A - Echo canceler circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an echo canceler circuit in which an echo can be canceled in a simple configuration even in a transmission line having delay without making a transmitted voice unclear in the echo canceler circuit applied to a telephone system equipped with a two-wire/four-wire converting circuit and having the delay on a four-wire transmission line. <P>SOLUTION: On the hybrid circuit side of a counter station, a received signal level detecting circuit is provided, and an attenuation circuit is provided for applying attenuation corresponding to a level difference between the level of a received signal and a preset level to a transmitted signal outputted from a hybrid circuit to the four-wire transmission line when the detected level of the received signal is higher than the preset level. Thus, the echo can be canceled. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an echo canceling circuit used in a telephone system having a 2-wire to 4-wire converting circuit and having a delay in a 4-wire transmission line. 4-wire type transmission / reception transmission with a delay, which is circulated by the hybrid circuit on the station side and returns through the 4-wire type transmission / reception transmission line with a delay The present invention relates to a circuit for canceling an echo returned to a partner station via a path.

[0002]

[Related technical background] A conventional 2-wire / 4-wire conversion circuit is provided,
Referring to FIG. 1, which shows a schematic configuration of a telephone system having a delay in a 4-wire transmission line, a call partner station 1 is connected to a 2-wire transmission line 2. Then, in order to transmit a transmission / reception signal through the 4-wire type transmission line 3, the hybrid circuit 4 performs 2-line / 4-line conversion. The transmission signal of the call partner station 1 is transmitted on the reception side transmission line 3a of the 4-wire transmission line 3 and is input to the hybrid circuit 4 of the local station as a reception signal. The received signal input to the hybrid circuit 4 is converted into 4-line / 2-line and becomes the received signal of the own station 5. On the other hand, the transmission signal of the own station 5 is transmitted through the two-wire transmission line 2, and the hybrid circuit 4 separates the transmission signal and the reception signal. This transmission signal is transmitted through the four-wire transmission line. It is transmitted to the partner station 1 via the side transmission path 3b.

In the telephone system having such a configuration, a part of the reception signal input to the hybrid circuit 4 from the reception side transmission line 3a of the 4-wire transmission line 3 is on the transmission side of the 4-wire transmission line 3. It circulates around the transmission path 3b and becomes a side tone (echo), which interferes with the call of the called station 1. As a countermeasure against this sneak signal, the hybrid circuit 4 is connected via a 4-wire transmission line.
Generates a pseudo signal from the received signal input to
This pseudo signal is added to the transmission signal output from the hybrid circuit to the transmission side transmission line 3b of the four-wire type transmission line 3 to provide a side tone canceling circuit 6 for canceling the side tone circling through the hybrid circuit 4. Has been.

[0004]

The echo attenuation amount of the side-tone canceling circuit 6 is 20 to 30 [dB], and echo cancellation cannot be said to be sufficient. In particular, the larger the received signal,
There was a problem that call interference due to echo became noticeable. Therefore, when the level of the receiving signal of the receiving side transmission line 3a is detected by the receiving signal level detecting circuit 7 and the level of the receiving signal exceeds a predetermined standard level, the receiving signal level adjusting circuit 8 receives the receiving signal. Was suppressed, and the echo level sneaking into the transmission side transmission line 3b via the hybrid circuit 4 was reduced. For example, as shown in FIG. 2, the reception signal exceeding a predetermined level is attenuated, and the level of the reception signal input to the hybrid circuit 4 is limited to a certain value or less.

However, in this case, there is a problem that the voice signal of the partner station becomes unclear because the level of the received signal is suppressed. The present invention has been made in consideration of such conventional circumstances, and an object of the present invention is to provide an echo canceling circuit capable of reducing an echo generated in a hybrid circuit with a simple circuit configuration.

[0006]

In order to achieve the above-mentioned object, a hybrid circuit provided between a two-wire transmission line and a four-wire transmission line for converting a transmission / reception signal into a two-line / four-line signal,
A reception signal level detection circuit for detecting the level of a reception signal input to the hybrid circuit via the four-wire transmission line, and the hybrid when the level of the detected reception signal is higher than a preset level. The transmission signal attenuating circuit is provided for attenuating the transmission signal output from the circuit to the four-wire transmission line by an attenuation corresponding to the level difference between the level of the reception signal and a preset level.

Further, a hybrid circuit provided between the two-wire type transmission line and the four-line type transmission line for converting a transmission / reception signal into a two-line / four-line type, and the hybrid circuit via the four-line type transmission line. A pseudo signal is generated from the input voice signal, and this pseudo signal is added to the voice signal output from the hybrid circuit to the four-wire transmission line to cancel the sidetone sneaking around the hybrid circuit. A side-tone canceling circuit, a reception signal level detection circuit for detecting the level of a reception signal input to the hybrid circuit via the 4-wire transmission line, and a level of the detected reception signal from a preset level. Is larger, the transmission signal output to the 4-wire transmission line through the side tone canceling circuit is attenuated corresponding to the level difference between the level of the reception signal and a preset level. Is and a transmission signal attenuation circuit that.

Further, the transmission signal attenuating circuit is used to
A transmission signal level detection circuit for detecting the level of the transmission signal output to the wire transmission line, and a transmission signal output from the attenuation circuit to the 4-wire transmission line according to the detected level of the transmission signal. And a transmission signal level adjusting circuit for adjusting the level of the speech signal. In particular, the transmission signal attenuating circuit variably controls the attenuation amount at high speed when the level of the reception signal becomes high, and gradually controls the attenuation amount when the level of the reception signal becomes low.

Alternatively, a hybrid circuit provided between the two-wire type transmission line and the four-line type transmission line for converting a transmission / reception signal into a two-line / four-line type, and output from the hybrid circuit to the four-line type transmission line. And a transmission signal level detection circuit for detecting the level of the transmission signal, and when the detected level of the transmission signal is higher than a preset level, input to the hybrid circuit via the 4-wire transmission path. A reception signal attenuating circuit for attenuating the reception signal to be attenuated corresponding to the level difference between the level of the transmission signal and a preset level, and the time required for the round trip transmission of the signal through the 4-wire transmission path. A delay unit that delays the operation of the attenuation circuit by a time.

Further, a reception signal level detecting circuit for detecting the level of the reception signal input from the reception signal attenuating circuit to the hybrid circuit, and the reception signal attenuating circuit to the hybrid circuit according to the level of the detected reception signal. And a receiving signal level adjusting circuit for adjusting the level of the receiving signal input to. Therefore, according to the present invention, it is possible to eliminate the echo generated in the telephone system having the delay in the 4-wire transmission line with a simple structure by providing the 2-wire to 4-wire conversion circuit. Even if the transmission line has a delay,
An echo canceling circuit that cancels echo effectively can be provided.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION An echo canceling circuit according to the present invention will be described below with reference to the drawings. FIG. 3 is a schematic configuration diagram of an echo canceling circuit according to the first embodiment of the present invention. As shown in the figure, there is a hybrid circuit 4 provided between the 2-wire type transmission line and the 4-wire type transmission line for converting a transmission / reception signal into a 2 line / 4 line type. The receiving signal is input from the receiving-side transmission line 3a of No. 3 and the transmitting signal is output to the transmitting-side transmission line 3b of the 4-wire type transmission line.

A reception level detection circuit for detecting the level of the reception signal is connected to the reception side transmission line 3a of the 4-wire type transmission line 3. Then, the transmission signal attenuating circuit 10 is inserted in the transmission side transmission line 3b of the 4-wire type transmission line 3. The attenuation level of the transmission signal attenuation circuit 10 is adjusted according to the reception level detected by the reception signal level detection circuit 7. As shown in the attenuation characteristic of FIG. 4, the attenuation amount of the transmission signal attenuation circuit 10 detects the level of the reception signal, and when it is higher than a preset standard level, the attenuation amount greater than the standard level is taken as the attenuation amount. The attenuation circuit is configured to adjust the amount of attenuation.

In the echo canceling circuit thus constructed, the level of the reception signal input to the hybrid circuit 4 is detected by the reception signal level detecting circuit 7. Then, as described above, the echo that wraps around the transmission side transmission line 3b of the 4-wire transmission line 3 via the hybrid circuit 4 increases in proportion to the level of the reception signal. Therefore, when the level of the detected reception signal is equal to or higher than the preset signal level, the level of the echo that circulates in the transmission side transmission line 3b in the hybrid circuit 4 is suppressed to a certain level or less.
The attenuation amount of the transmission signal attenuation circuit 10 is increased. Specifically, as shown in the attenuation characteristics in FIG. 4, when a reception signal having a level higher than a predetermined standard signal level of 0 [dBr] arrives at the reception signal level detection circuit 7, the standard signal level is exceeded. The attenuation amount corresponding to the level difference is set as the attenuation amount of the transmission signal attenuation circuit 10. For example, in the case of a received signal whose level is 10 [dB] higher than the preset level,
The attenuation amount of the transmission signal attenuation circuit 10 is set to be 10 [dB].

By doing so, it is possible to suppress the echo due to the reception signal having a large reception level to a certain level or less. At this time, the control response time of the attenuation amount of the transmission signal attenuating circuit 10 is preferably 5 [m] when the level of the reception signal increases.
s], and when the level of the reception signal decreases, the fall time of the transmission signal attenuation circuit 10 may be set to about 50 [ms]. By controlling the response time of the attenuation amount of the transmission signal attenuating circuit 10 in this way, it is possible to suppress unnatural breaks in the beginning and end of the transmission signal.

The above-described operation is an explanation of the operation in the case where the signal from the partner station 1 suppresses the sneak in the hybrid circuit 4. On the other hand, the transmission signal from the own station 5 to the partner station 1 is converted into a signal on the transmitter side transmission path 3b of the 4-wire transmission path 3 by the hybrid circuit and transmitted to the partner station 1. At this time, since the transmission signal of the own station 5 does not flow to the reception side transmission line 3a, the reception signal level detection circuit 7 sets the attenuation amount of the transmission signal attenuation circuit 10 to 0 [dB]. Therefore, the transmission signal of the local station 5 reaches the partner station 1 without being attenuated by the transmission signal attenuating circuit 10.

As described above, when the level of the reception signal transmitted through the reception side transmission line 3a of the 4-wire type transmission line 3 becomes larger than the preset standard value, the portion larger than the standard level is transmitted. The attenuation amount of the signal attenuation circuit 10 is used. For this reason, the wraparound signal level, which becomes noticeable particularly in the case of a large level received signal, does not exceed a certain value. Also,
In the conventional echo canceling circuit, when the level of the reception signal exceeds a predetermined standard level, the reception signal level adjusting circuit 8 suppresses the reception signal level to reduce the echo level. There was a problem that the voice signal of was unclear. However, in the present embodiment, since the echo signal can be removed without attenuating the received voice signal, the received voice does not become unclear.

Further, if the level of the echo attenuated by the transmission signal attenuating circuit becomes a level below the audible limit, it is possible to prevent the echo from being heard. Therefore, when it is necessary to further reduce the level of the echo sound, for example, in FIG.
It is advisable to use the attenuation characteristic shown by the broken line in FIG. in this case,
It is preferable to set the level of the attenuation characteristic in the range where the sense of discomfort of the received voice is not increased in the partner station 1.

Since the echo canceling circuit according to the present invention provided in the vicinity of the hybrid circuit 4 suppresses the sneak signal, it is not affected by the delay 8 of the 4-wire type transmission line 3 and has a simple structure. An echo canceling circuit can be realized. Next, a second embodiment according to the present invention will be described. The present embodiment is different from the above-described embodiment in that, as shown in FIG. 6, in addition to the first embodiment, the reception input to the hybrid circuit 4 via the reception side transmission line 3a of the 4-wire transmission line 3 is performed. A pseudo signal is generated from the signal, and the pseudo signal is added to the transmission signal output from the hybrid circuit 4 to the transmission side transmission line 3b of the four-wire transmission line 3 to sneak through the hybrid circuit. Is provided with a side sound canceling circuit 6 for canceling.

The echo canceling circuit having such a configuration is
The sidetone that circulates through the hybrid circuit is canceled by the sidetone canceling circuit 6. The level of the sidetone that is canceled out is about -20 to -30 [dB]. And the first
As in the above embodiment, the echo is attenuated by the transmission signal attenuation circuit. Therefore, the echo can be attenuated more effectively.

Next, a third embodiment according to the present invention will be described. This embodiment differs from the first and second embodiments described above in that the first embodiment is shown in FIG.
Alternatively, in addition to the second embodiment, the transmission signal attenuation circuit 10
In order to further remove the echo attenuated by, the transmission signal level detecting circuit 11 and the transmission signal level adjusting circuit are provided on the output side of the transmission signal attenuating circuit 10.

The echo canceling circuit thus constructed is
As in the first or second embodiment, the level of the reception signal on the reception side transmission line 3a is detected by the reception signal level detection circuit 7. Then, in the case where the level of the detected reception signal exceeds the preset standard level, the transmission signal attenuating circuit 10 inserted in the transmission side transmission line 3b of the 4-wire transmission line 3 hybridizes by the transmission signal attenuation circuit 10. The signal level of the echo that circulates from the circuit 4 is suppressed. When the attenuation amount of the transmission signal attenuation circuit 10 has the same attenuation characteristic (FIG. 4) as that of the first or second embodiment and the level of the reception signal is detected and is larger than a preset standard level. , The attenuation amount of the transmission signal attenuation circuit 10 is adjusted with the difference from the standard level as the attenuation amount.

The present embodiment is characterized in that a transmission signal level detecting circuit 11 and a transmission signal level adjusting circuit 12 are provided in order to further attenuate the echo weakened by the transmission signal attenuating circuit 10. This circuit removes signals below a preset level. For example, as shown in the characteristics of the transmission signal level adjusting circuit 12 in FIG. 7, when the signal level passed through the transmission signal level adjusting circuit 12 without being attenuated is −23 [dBr] or more, a level signal smaller than this level signal is used. It is set so that the amount of attenuation increases. Therefore, the echo that has passed through the transmission signal attenuating circuit 10 and is reduced can be further reduced and erased.

Alternatively, in the transmission signal level adjusting circuit 12, the transmission signal level to be passed without being attenuated is -31.
When it is desired to be [dBr] or more, the attenuation characteristic shown by the broken line in FIG. 7 may be used. In this way, the attenuation amount of the transmission signal level adjusting circuit 12 may be adjusted so as to have the optimum value in accordance with the telephone system to which the echo canceling circuit of the present invention is applied.

Then, the transmission signal of the own station 5 is sent to the transmission side transmission line 3b of the 4-wire type transmission line 3 via the hybrid circuit 4. This transmission signal is not attenuated by the transmission signal attenuation circuit 10 as in the first or second embodiment. Therefore, the transmission signal level detected by the transmission signal level detection circuit 11 becomes a transmission signal of a certain level or higher, and is transmitted to the hybrid circuit 4 of the partner station 1 without being attenuated by the transmission signal level adjustment circuit 12.

Next, a fourth embodiment according to the present invention will be described. The first to third embodiments described above are echo canceling circuits focused on how to prevent the signal of the other station from being sneak in, but the present embodiment is largely in that echo cancellation is performed on the local station side. different. Specifically, as shown in the schematic configuration of FIG. 8, a transmission signal level detection circuit 11 is provided on the transmission side transmission line 3b of the 4-wire type transmission line, and the reception side transmission line 3a of the 4-wire type transmission line 3 is provided. The reception signal attenuation circuit 13 is inserted.
Then, when the level of the transmission signal detected by the transmission signal level detection circuit 11 is equal to or higher than the preset standard level, the reception signal attenuation circuit 13 uses the difference from the standard level as the attenuation amount.
To control.

At this time, the hybrid circuit 4 on the partner station side
The echo that wraps around the receiving-side transmission line 3a via the line is delayed by a delay 8 such as the transmission line. For this reason, a delay unit 14 for delaying the operation of the reception signal attenuation circuit 13 by the delay time of the transmission line is provided. The echo canceling circuit configured in this way is
The level of the transmission signal of the 4-wire transmission line 3 is detected by the transmission signal level detection circuit 11. When the level of the detected transmission signal is equal to or higher than the standard level set in advance, the reception signal attenuating circuit 13 suppresses the level of the echo circling in the hybrid circuit on the partner station side. Since this echo arrives at the reception signal attenuating circuit 13 after being delayed by the round-trip delay time in the 4-wire transmission line 3, the delay section 14 compensates the round-trip delay time and the reception signal attenuating circuit 1
Activate 3.

The feature of this embodiment is that, unlike the above-described first to third embodiments, the echo canceling circuit provided on the local station side can cancel the echo, and the system on the partner station side can be used. Need not be changed. Therefore, an optimum echo canceling circuit can be configured without being affected by the equipment condition of the partner station. Next, a fifth embodiment according to the present invention will be described. The present embodiment differs from the fourth embodiment as shown in the schematic configuration in FIG. 9 in that a reception signal level detecting circuit 7 for detecting the level of the reception signal attenuated by the reception signal attenuating circuit 13 and the reception signal The point is that the receiving signal level adjusting circuit 8 controlled by the level detecting circuit 7 is inserted in the receiving side transmission line 3a.

That is, the present embodiment is characterized in that the reception signal attenuating circuit 13 is further provided with a reception signal level detecting circuit 7 and a reception signal level adjusting circuit 8 in order to further attenuate the echo weakened by the reception signal attenuating circuit 13. The point is to remove signals below a preset level. For example, as shown in the attenuation characteristic of the transmission signal level adjusting circuit 12 in FIG.
When the level of the reception signal to be passed through the reception signal level adjusting circuit 8 without being attenuated is −23 [dBr] or more, the attenuation amount is set to be larger as the reception signal has a lower level. Therefore, the echo reduced by passing through the reception signal attenuation circuit 13 can be further reduced.

Alternatively, in the reception signal level adjusting circuit 8, the reception signal level to be passed without being attenuated is -31.
When it is desired to be [dBr] or more, the attenuation characteristic shown by the broken line in FIG. 10 may be used. As described above, the attenuation amount of the reception signal level adjusting circuit 8 may be adjusted so as to have the optimum value according to the telephone system to which the echo canceling circuit of the present invention is applied.

[0030]

As described above, according to the echo canceling circuit of the present invention, the level of the echo sneaking from the hybrid circuit when a signal having a magnitude higher than the preset standard level is input to the hybrid circuit. Since this method suppresses the unclear received voice, which is a problem with the conventional method, a good call can be made.

Further, even in the case of a transmission line having a transmission delay, since the delay section in consideration of the transmission time is provided, the echo is canceled even for the echo that wraps around behind the transmission signal. It is possible to obtain a great effect in practical use, such as being able to be configured with a simple circuit.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a conventional echo canceling circuit.

FIG. 2 is a diagram showing an attenuation characteristic of a reception signal level adjusting circuit.

FIG. 3 is a diagram showing a schematic configuration of an echo canceling circuit according to the first embodiment of the present invention.

FIG. 4 is a diagram showing characteristics of a transmission signal attenuation circuit according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a schematic configuration of an echo canceling circuit according to a second embodiment of the present invention.

FIG. 6 is a diagram showing a schematic configuration of an echo canceling circuit according to a third embodiment of the present invention.

FIG. 7 is a diagram showing characteristics of a transmission signal level adjusting circuit according to a third embodiment of the present invention.

FIG. 8 is a diagram showing a schematic configuration of an echo canceling circuit according to a fourth embodiment of the present invention.

FIG. 9 is a diagram showing a schematic configuration of an echo canceling circuit according to a fifth embodiment of the present invention.

FIG. 10 is a diagram showing characteristics of a reception signal level adjusting circuit according to a fifth embodiment of the present invention.

[Explanation of symbols]

1 partner station 2 2-wire transmission line 3 4-wire transmission line 3a Receiver side transmission line 3b Transmission side transmission line 4 hybrid circuit 5 own station 6 side sound cancellation circuit 7 Received signal level detection circuit 8 Received signal level adjustment circuit 9 delay 10 Transmission signal attenuation circuit 11 Transmission signal level detection circuit 12 Transmission signal level adjustment circuit 13 Received signal attenuation circuit 14 Delay section

Claims (6)

[Claims] 1. A hybrid circuit provided between a two-wire transmission line and a four-wire transmission line for converting a transmission / reception signal into a two-line / four-line signal, and the hybrid circuit via the four-wire transmission line. A reception signal level detection circuit for detecting the level of the reception signal input to the, and when the detected reception signal level is higher than a preset level, output from the hybrid circuit to the 4-wire transmission line An echo canceling circuit, comprising: a transmission signal attenuating circuit that attenuates a transmission signal by an amount corresponding to a level difference between the level of the reception signal and a preset level. 2. A hybrid circuit provided between a two-wire transmission line and a four-wire transmission line for converting a transmission / reception signal into a two-line / four-line signal, and the hybrid circuit via the four-wire transmission line. A pseudo signal is generated from the received voice signal input to the hybrid circuit, and the pseudo signal is added to the transmission signal output from the hybrid circuit to the four-wire transmission line to generate a sidetone that circulates through the hybrid circuit. A side sound canceling circuit for canceling, a receiving signal level detecting circuit for detecting a level of a receiving signal input to the hybrid circuit through the four-wire transmission line, and a level of the detected receiving signal set in advance If it is larger than the above, the side tone cancellation circuit
An echo canceling circuit, comprising: a transmission signal attenuating circuit for giving an attenuation corresponding to a level difference between the level of the reception signal and a preset level to the transmission signal output to the line type transmission line. . 3. The echo canceling circuit according to claim 1, further comprising a transmission signal level for detecting the level of the transmission signal output to the 4-wire transmission line via the transmission signal attenuating circuit. A detection circuit; and a transmission signal level adjusting circuit for adjusting the level of the transmission signal output from the attenuating circuit to the 4-wire transmission line according to the detected level of the transmission signal. Echo canceling circuit. 4. The transmission signal attenuator circuit variably controls the attenuation amount at high speed when the level of the reception signal becomes high, and gradually controls the attenuation amount when the level of the reception signal becomes low. The echo cancellation circuit according to claim 1. 5. A hybrid circuit provided between a 2-wire type transmission line and a 4-line type transmission line to convert a transmission / reception signal into a 2-line / 4-line type signal, and output from the hybrid circuit to the 4-line type transmission line. A transmission signal level detection circuit for detecting the level of the transmission signal to be generated, and a hybrid circuit via the 4-wire type transmission line when the level of the detected transmission signal is higher than a preset level. A receiving signal attenuating circuit that gives an attenuation corresponding to the level difference between the level of the transmitting signal and a preset level to the input receiving signal, and a round-trip transmission time of the signal through the 4-wire transmission path A delay unit that delays the operation of the attenuating circuit for a predetermined time. 6. The echo canceling circuit according to claim 5, further comprising: a receiving signal level detecting circuit for detecting a level of a receiving signal input from the receiving signal attenuating circuit to the hybrid circuit, and a level of the detected receiving signal. And a reception signal level adjusting circuit for adjusting the level of the reception signal input from the reception signal attenuating circuit to the hybrid circuit according to the above.