JPS6336689B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an echo rejection device for use in telephone lines having long propagation delays, such as long distance terrestrial lines or satellite lines. In particular, it is used in 4-wire transmission lines to suppress the echoes that return to the caller late via the 2-wire/4-wire converter, and to enable smooth calls without sensing echoes. This relates to an echo prevention device that is inserted and removed.

In long-distance terrestrial lines or satellite lines, two-wire and four-wire converters are placed at both ends of the line to prevent increases in line loss, and most of the line is configured as a four-wire transmission line that can easily compensate for losses. An ideal 2-wire 4-wire converter has the impedance of the 2-wire transmission line and the 4-wire
A bridge balanced state is formed between the output impedance on the receiving side of the wire transmission line, the input impedance on the transmitting side, and the 2-terminal impedance of the balanced circuit inside the 2-wire 4-wire converter, and 4-wire transmission To prevent transmission signals from leaking from the receiving side to the transmitting side of the channel. However, since actual 2-wire and 4-wire converters cannot achieve perfect impedance balance, such leakage of the transmitted signal cannot be completely prevented, and a portion of the transmitted signal is returned to the original speaker as an echo. Return to Moreover, the echoes generated at the far end are returned and heard after a delay after the transmission, which may make it difficult to communicate.

For this reason, echo blocking devices have traditionally been used in long-distance lines to prevent echoes from returning. An echo suppression device is generally inserted into a 4-wire transmission line and inserts transmission loss depending on the call condition.
Alternatively, it is a device with a function to remove this.

Conventional echo suppression devices are of the all-analog type according to the CCITT (Consultative Committee for International Telegraph and Telephone) standard G.161, or of the digital processing type according to the CCITT standard G.164. In particular, the digital processing type has a so-called interrupt operation that removes the suppression loss in the sending channel when transmitting a call, so that the analog type has a All interrupts (Full
In addition to the partial break-in function, a new temporary interrupt (partial break-in) function is provided.

Here, "temporary interruption" means that the level of the sending channel input of the echo prevention device is compared to the receiving channel input level,
If it is determined that the noise is too loud, an interrupt operation is performed immediately, and if it is determined that the error was caused by impulsive noise, etc., the transmitting and receiving channels are restored to the state before the interrupt operation with a short hangover time, and If the determination is correct and the level of the input channel is sufficiently higher than the level of the input channel of the receiving channel, an interrupt state is established in which the transmitting channel and the receiving channel are restored to the state before the interrupt operation with a long hangover time; This refers to an interrupt that is configured to transition to a so-called all-interrupt state. When the time required for interrupt operation is shortened, it is necessary to instantaneously compare the input level of the transmitting line and the input level of the receiving line to determine which one is greater, which reduces the risk of transmission line impulse noise, click noise, etc. Misjudgments are likely to occur, but the above-described provisional interrupt can reduce the effects of such misjudgments.

Conventional devices of this kind set two large and small thresholds corresponding to the receiving channel input level in order to determine that the transmitting channel input level is higher than the receiving channel input level, and set the threshold value of the smaller level among them. A high-level threshold is used for temporary interrupts, and a high-level threshold is used for all interrupts (Japanese Patent Application Laid-Open No. 54-60514, IEEE Trans.
COM February 1972 issue P.55-60, E. FARIELLO et al.).
For this reason, (1) the configuration of the level comparison circuit becomes complicated, which tends to increase the cost; and (2) the interrupt operation time cannot be sufficiently shortened in the case of an actual audio signal that exhibits complex behavior between the two threshold values. There were disadvantages such as the fact that there were cases where this was not possible.

The present invention is an improvement on this, and aims to provide a stable echo suppression device that has a simple configuration, is inexpensive, has a short interrupt operation time, and is less affected by disturbances such as impulsive noise. .

The present invention includes a comparison circuit that compares an input level of a sending line and an input level of a receiving line, and has one threshold value each, and uses the output of a timer circuit controlled by the output of this comparing circuit as a temporary interrupt operation. The present invention is characterized in that the output of another timer circuit, which is controlled when the comparator circuit has an output for a long time, is used as a control signal for all interrupt operations.

The embodiment drawings will be described in detail below.

FIG. 1 is a block diagram of a device according to an embodiment of the present invention. 1 is an input terminal of the handset, 2 is an output terminal of the receiving line, 3 is an input terminal of the sending line, and 4 is an output terminal of the sending line. Reference numeral 5 denotes a telephone loss circuit for attenuating the signal passing through the receiving path when it is determined that each input of the sending path and the receiving path is at a certain level and a two-way communication state is established. 6 is a suppression loss circuit for blocking the signal passing through the sending channel when the receiving channel input level is greater than the sending channel input level and it is determined that the receiving channel is in a one-way communication state. It is.

Reference numeral 7 denotes a suppression threshold detection circuit, which determines whether the input level of the receiving channel exceeds a certain threshold. Reference numeral 8 denotes an interrupt threshold generation circuit that generates a unique interrupt threshold corresponding to (preferably approximately proportional to) the output level of the reception loss circuit 5. 9 is an interrupt threshold detection circuit;
It is determined whether the transmission channel input exceeds the output of the interrupt threshold generation circuit 8, and when this exceeds the output, the built-in timer circuit is sequentially controlled and temporary interrupt and total interrupt control signals are output.

Reference numerals 10 and 11 are signal lines for temporary interrupt and full interrupt control signals, respectively, and signal lines 12 and 13 are for channel input and interrupt threshold, respectively. A control circuit 14 controls the suppression loss circuit 6 and the receiving loss circuit 5 by receiving the output of the suppression threshold detection circuit 7 and the output of the interrupt threshold detection circuit 9 supplied through the signal lines 10 and 11 as inputs.

Here, terminals 1 to 4 of the circuit shown in FIG. 1 are each shown as one line, but each consists of two wires, L ₁ and L ₂ . terminals 1 and 4 are respectively connected to the 4-wire terminals of the long-distance line. Furthermore, 1
Considering a long-distance line, for example, Tokyo and New York, Tokyo and New York are connected by a 4-line line as mentioned above, and there is a 2-line and 4-line conversion point in Tokyo, and a 2-line and 4-line conversion point in New York. In each case, an echo rejection device of similar standard as shown in FIG. 1 is used.

The reception signal output from the output terminal 2 passes through the transmission line, passes through a 2-wire/4-wire converter (not shown) at the end of the line, and is mostly transmitted to a 2-wire transmission line that terminates at the telephone set. However, some of the components are reflected due to the impedance mismatch and leak to the transmitting side, and reach the input terminal 3 of the transmitting line via the four-wire transmission line again, becoming an echo related to the receiving line input. If the suppression threshold detection circuit 7 determines that there is a receiving channel input, and the interrupt threshold detection circuit 9 determines that the transmitting channel input does not reach the interrupt threshold, the suppression loss is transmitted to the suppression loss circuit 6 via the control circuit 14. The echoes inserted and reaching the input terminal 3 of the transmission path are blocked by the suppression loss circuit 6 and are not output to the output terminal 4 of the transmission path.

Further, when the suppression threshold detection circuit 7 determines that there is a receiving channel input, and the interrupt threshold detecting circuit 9 detects that the transmitting channel input exceeds the interrupt threshold, the control circuit 14 sends the signal to the receiving loss circuit 5. Receiving loss is inserted into the signal, and the telephone signal is also attenuated. but,
The echoes at this time are attenuated twice by this receiving loss circuit 5 and a receiving loss circuit corresponding to the receiving loss circuit 5, which is a circuit with the same characteristics as the circuit in FIG. 1 installed at the far end of the line. In addition, by the time it completes one round of the line, it suffers both the balance loss and the passing loss of the 2-wire/4-wire converter. Therefore, even if the echo becomes sufficiently small that it returns to the sender, it will not be heard. Thus, according to the circuit of FIG. 1, echo feedback is always prevented, and when the receiving channel input level is greater than the sending channel input level, the receiving channel input reaches the receiving telephone, and the sending channel input In a two-way conversation state in which the level is higher than the receiving channel input level, both the transmitting channel input and the receiving channel input reach the telephone of the other party, resulting in a transmitting interrupt state, allowing a smooth conversation.

FIG. 2 shows an example of the configuration of the interrupt threshold detection circuit 9. Signal lines 10, 11, 12, and 13 correspond to signal lines 10, 11, 12, and 13 in FIG. 1, respectively. 15 is a level comparison circuit which compares the channel input from 12 with the interrupt threshold from 13, and outputs a trigger signal when the channel input level exceeds the interrupt threshold. 16 is a timer circuit which has a short time constant and outputs a control signal for temporary interrupt operation when the trigger signal supplied from the level comparison circuit 15 continues for a time corresponding to this time constant;
If it does not last, it is reset to the initial state. 17 is a timer circuit which also has a long time constant, and when the provisional interrupt operation control signal supplied from the timer circuit 16 continues for a time corresponding to this time constant, it outputs a control signal for all interrupt operations. is output, and if it does not persist, it is reset to the initial state.

In this way, the circuit shown in FIG. 2 provides provisional interrupt operation control that has sufficiently fast interrupt operation time and that is resistant to impulsive noise from the transmission line by utilizing the integral effect of the duration of the trigger signal in the timer circuit 16. Signals can be obtained with a simple configuration. Further, due to the integration effect over a relatively long time due to the persistence of the temporary interrupt operation signal, all interrupt operation control signals that are reliably determined without being affected by impulsive noise etc. can be realized using a simple circuit.

FIG. 3 shows another example of the configuration of the interrupt threshold detection circuit. Signal lines 10, 11, 12, and 13 correspond to signal lines 10, 11, 12, and 13 in FIG. 2, respectively. 17' is a timer circuit. In the configuration of FIG. 3, the timer circuit 17' has a longer time constant than the timer circuit 17, and when the trigger signal supplied from the level comparison circuit 15 continues for a time corresponding to this time constant, all interrupt operations are terminated. Outputs control signals for

As explained above, according to the present invention, the threshold value is 1
Thus, an echo suppression device of economical construction is obtained. The device of the present invention is capable of high-speed detection of transmitted and received signals and can execute temporary interrupt operations that meet the CCITT standards, so it can be applied to various long-distance terrestrial lines or satellite lines that can be connected internationally , an economical telephone line with good call quality can be obtained. Furthermore, since there is an integral effect in the detection operation of transmitted and received signals, it is possible to construct a stable telephone line that is less affected by disturbances such as impulsive noise.
In particular, since an echo prevention device is used for each communication path even in a multiplex circuit with a large number of communication paths, the effect obtained by making this circuit economical is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing an example of the configuration of an interrupt threshold detection circuit. Third
The figure shows another example of the configuration of the interrupt threshold detection circuit. 1... Receiving channel input terminal, 2... Receiving channel output terminal, 3... Sending channel input terminal, 4... Sending channel output terminal, 5... Receiving channel loss circuit, 6... Suppression loss circuit,
7... Suppression threshold detection circuit, 8... Interrupt threshold generation circuit, 9... Interrupt threshold detection circuit, 10, 11,
12, 13...Signal line, 14...Control circuit, 15
... Level comparison circuit, 16 ... Timer circuit, 1
7, 17'...Timer circuit.

Claims (1)

[Claims] 1 A telephone loss circuit 5 inserted between the input terminal of the receiving line and the output terminal of the receiving line and attenuating the signal passing through the handset, and between the input terminal of the transmitter and the output terminal of the sending line. A suppression loss circuit 6 that attenuates the inserted signal passing through the transmitting channel, a suppression threshold detection circuit 7 that determines that the input level of the receiving channel exceeds a certain threshold, and the output of this suppression threshold detection circuit. and a control circuit 14 that receives as an input and controls the attenuation amount of the reception loss circuit and the suppression loss circuit, an interrupt threshold generation device that generates an interrupt threshold voltage corresponding to the input level of the reception path. a circuit 8, a level comparison circuit 15 that compares the interrupt threshold voltage with the input level of the transmission path, and an input level of the transmission path detected by this level comparison circuit that exceeds the interruption threshold voltage. A first timer circuit 16 sends out an output when the time is a predetermined short time, and a time period in which the input level of the transmission path exceeds the interrupt threshold voltage, which is detected by the level comparison circuit, is determined in advance. a second timer circuit 17 or 17' that sends out an output when a predetermined long time has elapsed, the outputs of both the timer circuits are given to the control circuit, and the control circuit An echo prevention device characterized in that the two loss circuits are controlled for a short time by the output of the circuit, and the two loss circuits are controlled for a long time by the output of the second timer circuit. .