JPH0683303B2 - Telephone with echo suppression circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a telephone with an echo suppression circuit, and more particularly to a telephone communication circuit for telephones, such as a digital telephone or a telephone communication circuit for automobile telephones, in which the voice communication path is an equivalent four-wire system. In the above, the present invention relates to a telephone that prevents the echo of the talker caused by the delay of the transmission system and the wraparound of the 2-wire / 4-wire system from being heard.

[Outline of Invention]

The present invention provides a transmission / reception signal detection control circuit between a transmission path and a reception path of a telephone in order to suppress a speaker echo generated in a digital telephone that talks with an analog telephone or a wireless telephone such as a car telephone. By detecting the condition that the transmission signal is higher than the threshold value and the reception signal is lower than the threshold value, and inserting a loss circuit in the reception channel for a preset time, excellent speech quality can be obtained. It's something I got to get.

[Prior art]

In a call between digital telephones, since the call is consistently made through the four lines via the relay terminal station, the receiving signal is cut off during transmission and the transmission signal is cut off during reception. Call quality is very good. On the other hand, when a telephone call is made between a digital telephone and an analog telephone, or when a telephone call is made between wireless telephones, a 2-wire / 4-wire conversion circuit is inserted in the transmission line, so the transmission signal is inevitably generated. Flows into the receiving path through the conversion circuit, the echo of the talker is superimposed on the reception signal, which deteriorates the communication quality, and the transmission signal is heard.

FIG. 4 is a block diagram of a conventional digital telephone. In FIG. 4, 1 is a transmitter, 2 is a transmitter amplifier, 3 is a receiver, 4 is a receiver amplifier, 5 is a sidetone amplifier, 8 is a digital signal transmission / reception circuit, 9 is a 2-wire 4-wire conversion circuit, and 10 is Terminal station, 11
Is a 2-line to 4-line conversion circuit for analog telephones, and 12 and 13 are transmitters and receivers. 101 is a circuit of a digital telephone, 102
Is a digital analog signal transmission line, and 103 is an analog telephone circuit.

Digital telephones are equivalent to four-line telephones because the transmission / reception signals are encoded and then transmitted in a time-division manner, as shown at 101 in FIG. 4 (for example, literature: Nishino, Nomura). ， Amemiya “Call quality design of digital telephone equipment”
Tsuken Jikken, 33.No.8.p1855, 1984).

In FIG. 4, the transmission signal input from the transmitter 1 is amplified by the amplifier 2, encoded into a digital signal by the signal transmission / reception circuit 8, and then transmitted to the transmission line 102. The signal converted into the analog signal after the digital exchange point 31 in the transmission line becomes two lines in the two-line / four-line conversion circuit 9, and passes through the terminal station 10 to the two-line / four-line conversion of the analog telephone 103. The circuit 11 separates the transmission / reception signal line, and the signal is received via the receiver 13. Further, a transmission signal from the analog telephone 103 is collected by the transmitter 12, is sent to the analog subscriber line through the 2-line / 4-line conversion circuit 11 in the telephone, and is transmitted to the terminal station 10. After that, from the terminal station 10 via the 2-wire / 4-wire conversion circuit 9 of the transmission line 102,
It is converted to a digital signal at the digital exchange point 32. Four
A signal input to the signal transmission / reception circuit 8 in the digital telephone 101 from the transmission line 102 of the line transmission system is converted into an analog signal, amplified by the reception amplifier 4, and then added to the reception handset 3 for listening. Further, a part of the transmission signal of the digital telephone 101 is added and input to the reception circuit via the sidetone circuit 5 and is received by forming the sidetone path.

FIG. 5 is a block diagram of a conventional wireless telephone connection system. In FIG. 5, 81 and 88 are radio telephone transmitters, 82 and 87 are radio telephone receivers, 102 'is a signal transmission path including radio station equipment, 104 is a radio telephone circuit, and other symbols are shown in FIG. Represents the same thing as.

A wireless telephone represented by a car telephone is constructed as shown in FIG. Although the basic communication path configuration is the same as that of the digital telephone shown in FIG. 4, it is transmitted via the telephone side transmitters 81 and 83 and the base station receivers 85 and 87 for receiving the signals. Then, it is sent to the transmission system 102 ′ and sent to the terminal station 10 via the 2-wire / 4-wire conversion circuit 9.
Further, a signal sent from another terminal via the terminal station 10 is separated into transmission / reception by the 2-wire / 4-wire conversion circuit 9 of the transmission system 102 ', and then the base station transmitters 88, 86 to the telephone receiver. It is input to the receiving circuit via 84 and 82, and is received by the handset 3.

By the way, 2 of the transmission systems 102 and 102 'shown in FIGS.
The line-to-four-line conversion circuit 9 is composed of a bridge circuit that connects the higher-ranking four-wire transmission line and the lower-ranking two-wire transmission line. Here, a value equivalent to the impedance when looking at the terminal station 10 including the analog telephone 103 and the subscriber line is set in the entire transmission band and under all subscriber conditions (subscriber line loss, telephone type, etc.)
It cannot be realized by the 2-wire / 4-wire conversion circuit 9.
Therefore, a part of the transmission signal of the 4-wire system wraps around to the reception signal and is listened to by the digital telephone 101 side through the same route as the reception signal. This phenomenon is the same not only in the wired system shown in FIG. 3 but also in the wireless telephone shown in FIG. This wraparound signal is called a speaker reverberation, deteriorates the S / N of the speaker signal, affects the utterance level of the speaker, and interferes with normal conversation. As a result, it becomes a factor of deteriorating the quality of telephone calls, and the quality degradation is more remarkable as the echo with a particularly long time delay. Therefore, conventionally, when designing a digital telephone or a wireless telephone, the influence of echo cannot be ignored, which makes the design difficult.

Here, CCITT SGX II makes the following recommendations in order to deal with factors causing deterioration due to echoes in digital telephones and wireless telephones. That is, the echo volume that reaches the inside of the speaker's ear via the transmission path for the volume of the speaker's mouth and the 2-wire / 4-wire conversion circuit, and is called the echo volume, is measured by the opinion test. It is recommended that the calculated allowable limit value be used and that the echo amount of the telephone used does not exceed the limit value. In order to comply with this recommendation, in telephones, measures such as reducing the gain of the transmission / reception circuit or increasing the gain of the sidetone to mask the echo with sidetone are adopted. Meanwhile, CCITT
With SGX II, good call quality in telephone transmission
It is evaluated by using the scale of the transmission loss of the volume of the ear in the ear of the other party from the volume of one speaker's mouth, and a desirable range of numerical values is also recommended for this.

[Problems to be solved by the invention]

Thus, in the past, digital telephones that talk with analog telephones and wireless telephones such as car telephones have been
A part of the transmission signal wraps around the reception signal through the 4-wire conversion circuit and is listened to by the telephone via the same route as the reception signal, which deteriorates the communication quality. Also, with a 4-wire telephone, sufficient volume cannot be obtained for the above-mentioned reasons, and CCIT
There were some problems such as not being able to achieve the desired volume for transmitting and receiving recommended by T SGX II, surrounding noise and side noise being too loud, the S / N of the receiving signal being deteriorated, and the transmission level being low.

Furthermore, in the future, transmission delay tends to increase further in digital telephones that perform digital signal processing of voice, such as using high-efficiency encoders and decoders, and wireless telephones that use a spread spectrum method and have a confidential communication function. It is expected that the propagation delay will be further increased due to the one-way propagation delay time of 250 mS due to the use of satellite communication.
On the other hand, it becomes more and more difficult and impossible to deal with the gain of the transmission / reception circuit and the side volume.

An object of the present invention is to solve such a problem, prevent a speaker echo from being heard by an echo caused by a propagation delay in a digital telephone or a wireless telephone, and realize a sufficiently large listening volume. , To provide a telephone with an echo suppression circuit having a natural sidetone volume.

[Means for solving problems]

In order to achieve the above object, the echo suppression circuit telephone according to the present invention is a telephone for handset communication through a handset, a transmission / reception amplifier, and a transmission / reception channel, and an echo signal suppression loss means serially connected to the reception channel, It is provided between the receiving channel and the transmitting channel, detects the levels of the transmitting signal and the receiving signal, compares the transmitting signal with the transmitting threshold level, and compares the receiving signal with the receiving threshold value. And a transmission / reception signal detection control means for controlling the insertion / removal of the echo signal suppression loss means to / from the reception path for a preset time according to the comparison result.

[Action]

According to the present invention, when a four-line telephone call is made using a digital telephone, a wireless telephone, or the like, the echo of the talker heard on the four-line telephone side is suppressed, and the transmission / reception telephone call circuit and the side channel gain of the four-line telephone are suppressed. A reverberation level suppressing circuit for a telephone is provided in the four-line telephone so that can be set to a desired value in terms of call quality. As a result, the gain of the transmitter / receiver circuit can be increased, the sound can be heard at a sufficient volume, the sound can be transmitted so that the other party can hear it at a sufficient volume, and the echo of the speaker can be prevented from being heard. .

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. First
The figure shows the digital telephone and digital
An analog signal transmission line is shown, 14 is a loss circuit for echo signal suppression, 16 is a transmission / reception signal detection control circuit, and other symbols are the same as those in FIG. Further, A shows a part of the flow of the transmission signal, B shows a part of the flow of the echo and the reception signal, and C shows the flow of the loss control signal. With the loss control signal C, a loss circuit for suppressing echo signal is provided.
14 is controlled and the loss of the receiving channel is inserted or extracted.

The transmission signal from the transmitter 1 passes through the transmission amplifier 2, is encoded from the output terminal 6 into a digital signal in the digital signal transmission / reception circuit 8, and is transmitted to the digital / analog transmission line via the digital exchange point 31. It A transmission signal (that is, ...
Echo), and the reception signal input from the terminal station 10 via the 2-wire / 4-wire conversion circuit 9, the digital signal transmission / reception circuit 8
Is converted into an analog signal by the loss circuit for echo signal suppression 14
After that, it passes through the reception amplifier 4 and is received by the receiver 3. The transmission / reception signal detection control circuit 16 determines the presence / absence of the transmission / reception signal by using a part A and B of the input transmission / reception signal. this is,
It is for judging whether or not the transmitted voice signal is heard as an echo and is large enough to hinder the call.
The determination is made by comparing the threshold value of the set level with the input signal value. When the transmitted voice signal is large enough to hinder the call, the loss control signal C flows, so that the echo signal suppressing loss circuit 14 is inserted in the circuit and the received signal is attenuated. The echo signal suppression loss circuit 14
Is a loss circuit such as a resistor that is connected / isolated by the loss control signal C.

FIGS. 2A and 2B are detailed configuration diagrams showing an example of the echo signal suppressing loss circuit and the transmission / reception signal detection control circuit in FIG.

The echo signal suppressing loss circuit 14 includes a resistor R ₀ connected in series to the receiving path and a resistor connected between the output side of the resistor R ₀ and the ground potential as shown in FIG. 2 (a). It is composed of R ₁ and a switch circuit 40 such as a transistor connected in parallel with the resistor R ₁ . For example, when a high level signal is input as the loss control signal C, the switch 40 is closed and the resistor R ₁ is bypassed by the switch circuit 40. Therefore, the output terminal of the resistor R ₀ connected in series to the receiving path is grounded. When the potential drops to 0, the output signal becomes 0, and the reception signal is not heard. Therefore, when there is an echo signal, if the switch 40 is closed, no echo is heard. When a low level signal is input as the loss control signal C, the switch 40 remains open, so that an L-shaped resistor is inserted in the receiving path. Now, if R _{0 is set} to 1 KΩ and R _{1 is set} to 1 KΩ, the received signal is reduced to a half size and can be heard. If R ₀ is 1KΩ and R ₁ is 10KΩ, the received signal is 90%.
It will be heard in the above size.

Next, the transmission / reception signal detection control circuit 16 of FIG. 2 (b) has a function of detecting the levels of the transmission signal and the reception signal, a function of comparing the transmission signal and the transmission threshold with a level, It has a function of comparing the level of the signal with the threshold value of the reception, and a function of outputting the loss control signal C for a preset time according to the comparison result. That is, the transmission signal A and the transmission threshold value X are compared by the comparison circuit 32. When the transmission signal A is larger than the threshold value X, the comparison circuit 31 is activated so that the transmission signal A is larger than the threshold value. Even when it is small, the comparison circuit 32 is activated, and when it is immediately after the end of transmission, the counter is
At the same time as starting 33, the loss control signal C is set to a high level to insert a loss in the receiving channel. The comparison circuit 31 compares the reception signal B and the reception threshold Y in magnitude to determine the reception signal B.
Is larger than the threshold value Y, the loss control signal C is set to the low level and the counter 33 is reset. When the reception signal B is smaller than the threshold value Y, the loss control signal C is set to the high level to insert the loss in the reception path. In addition, when it is not immediately after the end of the transmission, the content of the counter 33 is monitored, and if the preset time is exceeded, the loss control signal C
Is set to a low level and the counter 33 is reset. The loss control signal C is kept at a high level until a preset time is reached. These operations can be realized by hardware or program control.

FIG. 3 is a flow chart showing the operation of the transmission / reception signal detection control circuit of FIG.

The transmission / reception signal detection control circuit 16 first determines the presence / absence of the transmission / reception signal by using parts A and B of the transmission / reception signal input to the transmission / reception signal detection control circuit 16 (step 21). If it is determined that there is a transmission signal, then it is determined whether or not there is a reception signal (step 22). The judgment of the presence or absence of the reception signal is made by judging whether it is the voice of the partner talker or the echo signal. The partner talker's voice is output from the partner talker (in this case, the analog telephone 103) and the terminal station 10 The level is lowered due to the subscriber line loss between the analog telephone 103 and the analog telephone 103 and the relay line loss from the terminal station 10 of the transmission line 102 toward the terminal 32, and the signal is input to the digital telephone 101. On the other hand, the reverberant signal is a relay line loss from the terminal 31 of the transmission line 102 toward the 2-wire / 4-line conversion circuit 9, and a loss when the 2-wire / 4-wire conversion circuit 9 goes around the reception line, and the transmission line.
The level is lowered due to the relay line loss from the 2-wire / 4-wire conversion circuit 9 of 102 toward the terminal 32. Therefore, the transmission / reception signal detection control circuit 16 can determine the presence / absence of a reception signal because the level of the echo signal is reduced by the loss difference between the two. Here, if it is determined that the reception signal is present, the loss amount to be inserted in the reception circuit of the echo signal suppression loss circuit 14 is set to 0 dB.
And reset the counter (step 29). This counter is built in the transmission / reception signal detection control circuit 16,
It starts operating at the same time as the end of transmission, and counts the time corresponding to the round-trip propagation delay time in the transmission path 102. Until the count ends, the loss circuit 14 is continuously inserted in the receiving channel. On the other hand, if it is determined that there is no reception signal, the loss circuit 14
Insert (step 24).

On the other hand, if it is judged that there is no transmission signal after the first return,
The presence or absence of the reception signal is judged (step 23), and as a result,
If it is judged that there is a received signal, the insertion loss of the echo signal suppression loss circuit 14 is set to 0 dB, and the counter is reset (step 29). If it is determined that there is no reception signal, it is determined whether or not the transmission signal has just stopped (step 25). If it is determined that the speech has just been stopped, the counter is started and the echo signal suppressing loss circuit 14 is inserted (step 26). Then, the process returns to step 21 again. If it is judged that it is not immediately after the stop of the talk, it means that the silent state is continuing, and it is judged whether or not the counter started immediately after the stop of the talk reaches the set echo delay time. If not reached (step 27), the echo signal suppression loss circuit 14 is continuously inserted (step 28). If the echo delay time has passed, the echo signal suppression loss circuit 140 is set to 0 dB and the counter is stopped. Allow (Step 29).

The echo delay time that defines the upper limit of the counter is
Depending on the equipment used, the maximum number of round trips is 70 mS for a digital telephone using a terrestrial line, the maximum is 300 mS for a round trip with a signal processing wireless telephone, and the maximum is 600 mS for a round trip using a satellite line. is there. Therefore, the loss is inserted in the receiving circuit by the delay time of these values.

In this way, the transmission signal of the 4-wire telephone is transmitted to the partner analog telephone at a sufficiently large level, and the echo returned via the 2-wire / 4-wire conversion circuit is The loss insertion circuit provided in the reception circuit of the 4-wire telephone operates effectively for a time period in anticipation of the round-trip transmission delay and prevents the reception of echoes. That is, whether or not there is a transmission signal on the 4-wire telephone side, the echo of the talker is suppressed as long as there is an echo, so that the deterioration of the call quality is prevented and the call is disturbed. The impact will also disappear.
Also, if the receiving signal interrupts while the 4-wire telephone is transmitting, the loss inserted in the receiving circuit is immediately removed, so there is no disconnection of the receiving signal and the other party's voice can be heard at an appropriate and sufficient volume. Even if the echo of the talker is superimposed on the received signal, the level of the echo is smaller than that of the received signal, so that the echo is masked by the received signal and cannot be heard.

In this way, 4
When the line telephone and the analog telephone communicate with each other, the echo of the talker deteriorates the call quality. However, conventionally, the gain of the transmission / reception circuit on the side of the 4-wire telephone cannot be increased, and the sound blocking volume has an appropriate value. On the contrary, the side volume is increased to mask the echo, whereas in the present embodiment, the echo can be suppressed by the echo signal suppression loss, so that excellent call quality can be realized. it can.

Also, regarding the optimum value of the side volume, CCITT SGX II is also considering, but there is a desirable recommended value that does not interfere with the call. In the past, the sidetone was increased to some extent with the idea that the echo of the talker could be masked by the sidetone, but in this embodiment, the optimum side volume recommended by CCITT SGX II can be set. Here, an example is described in which the transmission / reception signal is applied to an equivalent 4-wire telephone of a digital telephone in which the transmission / reception signal is transmitted in a time-division manner. be able to. In addition to the circuit shown in FIG. 2, the configurations of the transmission / reception signal detection circuit and the echo signal suppression loss circuit are compared by comparing the detected voice with the respective thresholds, and comparing the resistance and the semiconductor element. The method of controlling an attenuator, or a digital telephone, can be realized by calculation using a coded voice signal in particular.

〔The invention's effect〕

As described above, according to the present invention, the echo of the talker heard on the 4-wire telephone side is suppressed by using the transmission / reception signal detection control circuit and the echo level suppression loss circuit. Can be heard at a sufficient volume and can be heard at a sufficient volume for the other party, and the echo of the talker can be prevented from being heard, and excellent call quality can be realized. .

[Brief description of drawings]

FIG. 1 is a block diagram of a digital telephone showing an embodiment of the present invention, FIG. 2 is a detailed block diagram of a loss circuit for echo signal suppression and a transmission / reception signal detection control circuit in FIG. 1, and FIG. An operation flow chart of the transmission / reception signal detection control circuit in the figure, FIG. 4 is a connection configuration diagram of a conventional digital telephone, and FIG. 5 is a connection configuration diagram of a conventional wireless telephone. 1: Transmitter, 2: Transmitter amplifier, 3: Receiver, 4: Receiver amplifier, 5:
Sidetone amplifier, 6: Output terminal of transmitter amplifier, 7: Input terminal of receiver amplifier, 8: Digital signal transmitting / receiving circuit, 9: 2-wire / 4-wire converting circuit, 10: Terminal station, 11: 2 in analog telephone Line-to-line conversion circuit, 14: Echo signal suppression loss circuit, 16: Transmission / reception signal detection control circuit, 81: Wireless telephone transmitter, 82: Wireless telephone receiver, 101: Digital telephone circuit block, 102: Digital analog Signal transmission line, 103: analog telephone circuit, 10
2 ': signal transmission path including wireless station equipment, 104: wireless telephone circuit block.

Claims (3)

[Claims] 1. In a telephone set for handset communication through a handset, a handset amplifier, and a handset, a reverberation signal suppressing loss means connected in series to the handset and provided between the handset and the handset. , The level of the transmission signal and the reception signal is detected, the comparison level of the transmission signal and the transmission threshold value is compared, the comparison level of the reception signal and the reception threshold value is compared, and the comparison result is set in advance. A transmission / reception signal detection control means for controlling the insertion / removal of the echo signal suppression loss means to / from the reception path for a predetermined time. 2. The transmission / reception signal detection control means, when it is determined that the transmission signal is larger than the transmission threshold and the reception signal is smaller than the reception threshold, the echo signal suppressing loss means. Is inserted in the reception channel, and when the reception signal is judged to be greater than the reception threshold, the echo signal suppressing loss means is removed from the reception channel. Telephone with suppression circuit. 3. The transmission / reception signal detection control means, if the reception signal level is smaller than the reception threshold value after the transmission signal level becomes smaller than the transmission threshold value, the echo signal suppression loss means is previously set. The telephone set with an echo suppression circuit according to claim 1, wherein the telephone set is continuously inserted into a receiving channel for a set time.