JPH09312596A - Echo canceller - Google Patents

Abstract

(57) Abstract: The degree of echo suppression by an echo canceller provided in a 4-wire section of a 2-wire to 4-wire conversion unit of a private branch exchange,
It is possible to reduce the possibility that the call is disturbed due to the length of the two-line subscriber line. SOLUTION: The transmission signal output from a codec 6 is 5
LPF11 extracts low frequency components below 00Hz,
The level detector 12 detects whether the level is high or low. When the level is high, the switch 13 is turned on and the switch 15 is turned on.
Is turned off and the phase of the component of the transmission signal of 500 Hz or less is corrected by the phase corrector 16 and given to the subtractor 5.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a private branch exchange or the like.
The present invention relates to an echo canceller used in a line / line conversion unit.

[0002]

2. Description of the Related Art A private branch exchange has a hybrid transformer for converting a two-wire telephone line (subscriber line) for bidirectional transmission into a four-line section of a transmission path and a reception path on the premises, and a transmission path and a reception path, respectively. There is a 2-wire / 4-wire conversion unit including an amplifier such as an operational amplifier inserted in the. FIG. 2 is a block diagram of a 2-line to 4-line conversion unit to which the present invention is applied. In the figure, 1 is a hybrid transformer (H), 2 is an amplifier of a transmission path, 3 is an amplifier of a reception path, 4 is an echo canceller which is an object of the present invention, 5 is a subtractor, 6 is a codec (codec), 7,8
Is a PCM highway, and 9 is a subscriber line. The codec 6 decodes the digital signal input from the PCM highway 7 and outputs an analog signal, and also encodes the analog signal output from the downlink amplifier 3 to generate a downlink P signal.
It is sent to the CM highway 8. In addition, the subscriber line 9 in the two-line section is a bidirectional transmission line having a D standard, that is, a band of 300 to 3400 Hz.

The analog transmission signal output from the codec 6 is amplified by the amplifier 2 in the transmission path and is transmitted to the subscriber line 9 as the transmission voice signal X via the hybrid transformer 1. At that time, part of the transmitted audio signal X leaks into the reception path and wraps around. If the leakage component, that is, the level of the echo Y is large, a ringing sound is generated and the communication quality is deteriorated. The echo canceller 4 is provided to suppress the echo Y. As shown in the figure, the echo canceller 4 is connected between the transmission path and the reception path of the 4-wire section, branches and inputs the transmission signal output from the codec 6, adjusts the level and inverts the phase, and the subtracter 5 The echo Y is canceled (cancelled) by inputting it to one side and adding the opposite phase to the leakage component Y of the other side.

[0004]

In the above-mentioned conventional circuit, the length (distance) of the subscriber line in the two-line section differs depending on the communication partner, and the impedance seen from the side of the four-line section changes depending on the length. Is disturbed and the leakage component Y becomes large, and it becomes an echo, which hinders the call.

SUMMARY OF THE INVENTION An object of the present invention is to provide an echo canceller which improves the communication quality by suppressing the echo generated by the length of the subscriber line in the two-line section, which is the above-mentioned conventional drawback. .

[0006]

An echo canceller according to the present invention comprises a transmission amplifier and a reception amplifier provided in each of a transmission path and a reception path in a 4-wire section of a private branch exchange, and a transmission path and a reception in the 4-wire section. In order to cancel the leakage of the outgoing voice signal to the receiving path in the two-wire to four-wire converting section equipped with the hybrid transformer for converting the path to the two-wire subscriber line, the input signal of the transmission amplifier is branched and In an echo canceller for adding the leakage component from the hybrid transformer, which is input to one of the subtracters inserted in the receiving path and is input to the other of the subtractors, in an opposite phase, the input signal of the transmission amplifier is branched and input. A low-pass filter for extracting frequency components of 500 Hz or less and an output level of the low-pass filter is compared with a preset threshold value, and when the output level is larger than the threshold value, the on-signal is turned on. And a level detector that outputs an off signal when the output signal is smaller than a threshold value, and a first signal that turns on / off a signal obtained by branching the input signal of the transmission amplifier according to an on / off signal output from the level detector. Switch and 500H of the signal output from the first switch
The level detector connected between the input end of the first switch and the output end of the phase corrector, and the phase corrector for correcting the phase of the frequency component of z or less and inputting it to the other of the subtractor. OFF / inverted ON / OFF signal output from
A second switch that is turned on / off according to an on signal, and turns on the first switch when a frequency component of 500 Hz or less is detected from the input signal of the transmission amplifier at a predetermined level or more and the second switch is turned on. Is turned off and the phase corrector performs phase correction of a preset correction amount for the frequency component of 500 Hz or less and outputs it. When the frequency component of 500 Hz or less is below a predetermined level, the first It is characterized in that the switch is turned off and the second switch is turned on to output the input signal of the transmission amplifier as it is to cancel the echo.

[0007]

1 is a block diagram showing an embodiment of the present invention. In the figure, parts other than the echo canceller 4'are indicated by the same reference numerals as in FIG. Reference numeral 11 in the echo canceller 4'of the present invention is a low-pass filter (LPF), and its cutoff frequency is 500 Hz. 12 is a level detector, 13 and 15 are ON / OFF switches, 14 is an inverting circuit, and 16 is a phase corrector.

According to the present invention, in the conventional circuit, the subscriber line 9 is used.
Focusing on the point that the impedance matching cannot be achieved due to the length of the distance is because the phase of the low frequency part of the transmission band is shifted, the signal component of 500 Hz or less is extracted, the phase is corrected, and the signal is added again. Then, a signal for echo cancellation is generated.

5 of the transmission signals output from the codec 6
The LPF 11 extracts a component of 00 Hz or less, and the level detector 12 detects whether the level is higher than a preset threshold value. When the detection level is large, an ON signal is output from the level detector 12, the ON / OFF switch 13 is turned ON, and the ON / OFF switch 15 is turned OFF by the signal inverted by the inverting circuit 14 to phase the transmission signal. Input to the compensator 16, 500Hz
The phases of the following frequency bands are corrected and given to the subtractor 5.

When the detection level is low, the ON / OFF switch 13 is turned off and the ON / OFF switch 15 is turned on to give the transmission signal to the subtractor 5 as it is. In this way, the echo canceller 4 responds to the length of the subscriber line 9 of the line to be connected with the transmission signal by 500.
When there is a component below Hz, the phase of the low frequency component is corrected and output as a suppression signal. Phase corrector 16
The amount of phase correction in the low frequency band of
It is set by experimentally obtaining the phase shift amount corresponding to the distance.

[0011]

As described in detail above, by implementing the present invention, the optimum echo canceling signal can always be obtained even if the length of the subscriber line of the line to be connected is different. The decrease can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram of a conventional 2-line to 4-line conversion unit.

[Explanation of symbols]

 1 Hybrid Transformer 2,3 Amplifier 4,4 'Echo Canceller 5 Subtractor 6 Codec 7,8 PCM Highway 9 Subscriber Line 11 LPF 12 Level Detector 13,15 Switch 14 Inversion Circuit 16 Phase Corrector

Claims (1)

[Claims] 1. A transmission amplifier and a reception amplifier provided in each of a transmission line and a reception line of a four-wire section of a private branch exchange, and a transmission line and a reception path of the four-line section are converted into a two-wire subscriber line. In order to cancel the leakage of the transmitted audio signal to the receiving path in the 2-wire to 4-wire converting unit including the hybrid transformer, one of the subtracters inserted in the receiving path by branching the input signal of the transmission amplifier In an echo canceller for adding a leak component from the hybrid transformer, which is input to the other of the subtractor, in anti-phase, the input signal of the transmission amplifier is branched and input to 500 Hz.
A low-pass filter for extracting the following frequency components and an output level of the low-pass filter are compared with a preset threshold value, and an ON signal is output when the output level is higher than the threshold value. A level detector that outputs an off signal when it is smaller than a threshold value; a first switch that turns on / off a signal obtained by branching the input signal of the transmission amplifier according to an on / off signal output from the level detector; A phase corrector for correcting the phase of a frequency component of 500 Hz or less of the signal output from the first switch and inputting the result to the other of the subtractors, an input end of the first switch and an output end of the phase corrector. And a second switch connected between the switch and the ON / OFF signal output from the level detector and turned OFF / ON according to an OFF / ON signal obtained by inverting the ON / OFF signal. When a frequency component equal to or lower than z is detected at a predetermined level or higher, the first switch is turned on and the second switch is turned off, and the phase corrector is preset for the frequency component equal to or lower than 500 Hz. The phase of the correction amount is corrected and output, and when the frequency component of 500 Hz or less is below a predetermined level, the first switch is turned off and the second switch is turned on.
An echo canceller configured to cancel the echo by directly outputting the input signal of the transmission amplifier by turning on the switch.