JPH0210613B2 - - Google Patents

Description

TECHNICAL FIELD The present invention relates to a two-wire bidirectional automatic gain control device that adjusts the gain of a two-wire bidirectional repeater.

Prior Art A two-wire bidirectional repeater is used to compensate for losses in a two-wire line, but when the connection of the two-wire circuit is not fixed, the gain of the bidirectional repeater may be variably controlled. Is required. For example, in a call transfer connection as shown in FIG.
An incoming call from No. 1 to the telephone S2 of the destination station E02 via the originating station E01 is automatically transferred and connected via the transfer device T to the destination telephone S3 of the designated destination station E03. Therefore, as shown in FIG. 2, the loss between the originating telephone S1 and the destination telephone S3 is the loss L1 dB between the originating telephone S1 and the terminating station E02.
Loss L2dB between receiving station E02 and forwarding destination phone S3
It becomes a harmony with In order to compensate for the above losses, it is necessary to insert a two-wire bidirectional repeater between the incoming line and the transfer circuit, but since the loss and impedance of the incoming line and transfer line differ each time they are connected, the repeater gain It is necessary to make it variable according to the loss, and also to prevent the generation of noise due to impedance mismatch.

FIG. 3 is a block diagram showing an example of a conventional two-wire bidirectional automatic gain control device. That is, the incoming line is connected to the hybrid conversion circuit 2 to convert it to a 4-wire system, and the incoming phone line is transferred from the calling phone S1 to the destination phone S.
The signal transmitted to the hybrid conversion circuit 1 passes through the resistive attenuator ATT1 and the amplifier AMP1.
2 to the transfer line, and the transmission signal from the transfer destination telephone S3 to the originating telephone S1 is converted into four wires by the hybrid conversion circuit 12 and then passed through the resistance attenuator ATT2.
and is sent from the hybrid conversion circuit 2 to the calling telephone S1 through the amplifier AMP2. amplifier
AMP1 and AMP2 are fixed gain amplifiers, and automatic gain control is performed by controlling the amount of attenuation of the resistive attenuators ATT1 and ATT2 by the control unit CONT. Resistance attenuator ATT1 and
ATT2 has a built-in audio switch that is inserted and removed by the control unit CONT, and the control unit CONT controls the level of input point A of the resistive attenuator ATT1 and the resistive attenuator.
The level at input point B of ATT2 is monitored, and the resistive attenuators ATT1 and ATT2 are controlled so that the volume in both directions is constant. Note that in a steady state, the gains in both directions are controlled to match the smaller gain.

The above-mentioned conventional device has the disadvantage that the speech quality deteriorates when the voice switch is inserted or removed due to cutting at the beginning and end of the speech, which is a phenomenon peculiar to voice switches. may be overloaded and generate overload noise.

OBJECT OF THE INVENTION The object of the invention is to solve the above-mentioned conventional drawbacks and
It is an object of the present invention to provide a two-wire bidirectional automatic gain control device that prevents overload noise and ringing from occurring and does not cause speech beginning or end cutting.

Structure of the Invention The two-wire bidirectional automatic gain control device of the present invention has two
A pair of hybrid conversion circuits for converting a wire line to a four-wire line; a variable gain circuit and an echo canceller connected to the four-wire section between the pair of hybrid conversion circuits; comprising a control circuit for controlling the echo canceller, and an attenuation measurement circuit for measuring the echo cancellation attenuation of the echo canceller or the sum of the echo cancellation attenuation and return loss,
The control circuit is characterized in that it is configured to stop the automatic gain control function until the output value of the attenuation measurement circuit reaches a predetermined value.

Embodiments of the Invention Next, the present invention will be described in detail with reference to the drawings.

FIG. 4 is a block diagram showing one embodiment of the present invention. That is, a pair of hybrid conversion circuits 2 and 12 are connected between two-wire lines 1 and 11 to convert it to a four-wire system.
A code circuit 5, an echo canceller 7, a variable gain circuit 8, and a decoding circuit 6 are connected to the line portion. The input signal from the 2-wire line 1 is converted into a 4-wire signal by the hybrid conversion circuit 2 and sent to the encoder circuit 5.
and is converted into a digital signal by the encoder circuit 5. The output signal of the encoder circuit 5 is echo-cancelled by an echo canceller 7 and sent to a variable gain circuit 8.
is input. The signal is amplified by the variable gain circuit 8 and input to the decoding circuit 6 through the echo canceller 7', where it is converted into an analog signal and sent to the two-wire line 11 via the hybrid conversion circuit 12. be done. The signal input from the two-wire line 11 is converted into four signals by the hybrid conversion circuit 12.
It is converted into a linear format and inputted to the encoder circuit 5, and then similarly sent to the echo canceller 7', variable gain circuit 8,
The signal passes through an echo canceller 7, a decoding circuit 6, and is sent to a two-wire line 1 via a hybrid conversion circuit 2.

The control circuit 9 monitors the input and output signal levels of the variable gain circuit 8 in both directions, and controls the gain of the variable gain circuit 8 so that the signal levels in both directions are constant. However, until the output signal of the attenuation measurement circuit 10 reaches a certain value, the variable gain circuit 8
The gain of the attenuation measurement circuit 10 is set to 0, and the gain control is started after the output value of the attenuation amount measuring circuit 10 reaches a certain value or more.

The attenuation measurement circuit 10 measures the echo cancellation attenuation based on the level difference between the level of the signal at the input point from the encoder circuit 5 to the echo canceller 7 and the level of the signal at the output point from the echo canceller 7 to the variable gain circuit 8. It measures and notifies the control circuit 9 of the measurement results. Alternatively, as shown by the dotted line in the figure, it is connected to the output point from the echo canceller 7 to the decoding circuit 6, and the received signal level at that point and the received signal reflected from the two-wire line 1 are connected to the hybrid conversion circuit. Alternatively, the level difference between the echo signal that has come in via the echo canceller 7 and the signal that has been canceled and output by the echo canceller 7 may be measured. In this case, the sum of echo loss and echo cancellation attenuation is measured.

As described above, the control circuit 9 starts the gain control after the output value of the attenuation measurement circuit 10 reaches a certain value or more. This constant value is determined by the variable gain circuit 8
It is only necessary to set the value to such a value that no noise is generated by the loop circuit composed of the four-wire section and the hybrid conversion circuit when the gain is the maximum. That is, when the attenuation measurement circuit 10 measures the echo cancellation attenuation, the above-mentioned constant value is, for example, a hybrid loss (approximately
7 dB), and the control circuit 9 controls the gain of the variable gain circuit 8 to 0 until the measured value of the attenuation measurement circuit 10 reaches the above-mentioned constant value, and the output of the attenuation measurement circuit 10 If the gain control of the variable gain circuit 8 is started after the value exceeds the above-mentioned fixed value, no noise will be generated. Furthermore, when the attenuation amount measuring circuit 10 measures the amount of echo cancellation plus the echo loss, the same effect can be achieved by setting the above-mentioned constant value to be the maximum gain of the variable gain circuit 8, for example.

Next, the operation of this embodiment will be explained. The two-wire line 1 is connected to the two-wire line 11 through the device, and the originating telephone and the forwarding destination telephone are connected,
A communication path is established based on the response from the transfer destination, and the communication is started. Echo cancellers 7 and 7' are
The echo canceling operation is started using the call signal at the start of the call, and a signal for canceling the echo signal is created and superimposed on the echo signal to cancel the echo. Since the gain of the variable gain circuit 8 is 0 until the echo canceling attenuation amount of the echo canceller 7 gradually increases and reaches the above-mentioned constant value, no sound is generated. In other words, it is possible to prevent ringing from occurring while the echo canceller 7 is converging, thereby improving the call quality. Furthermore, there is no phenomenon of cutting off at the beginning or end of speech. and,
As shown in FIG. 5, the control circuit 9 starts gain control of the variable gain circuit 8 from the time tc when the echo cancellation attenuation amount exceeds a certain value, and the gain of the variable gain circuit 8 gradually increases until the time ts. Here is the output level (average value)
The gain stabilizes at a constant value. In this embodiment, the gain control of the variable gain circuit 8 is started after the amount of echo cancellation of the echo canceller 7 reaches a certain level. will not occur. That is, there is no cutting at the beginning or end of a speech, and the occurrence of ringing or overload noise during convergence of the echo canceller 7 and the variable gain circuit 8 is prevented, and the speech quality is improved. In addition, the effect of the echo canceller 7 improves the characteristics during simultaneous calls in both directions, improving the call quality, and further improving the sound stability, making it possible to increase the upper limit of the gain of the variable gain circuit 8. This has the advantage of expanding the scope of application of the automatic call forwarding service.

Of course, when the attenuation measurement circuit 10 measures the echo cancellation amount plus the echo loss, the same effect can be achieved by the same operation. This case is advantageous because control of the variable gain circuit 8 can be started early when the actual echo loss is high. Further, it is also possible to effectively control the gain of the variable gain circuit 8 so as to prevent the generation of noise while sequentially measuring the echo loss + echo cancellation attenuation amount.

Effects of the Invention As described above, in the present invention, an echo canceller and a variable gain circuit are inserted into the 4-wire portion of a repeater connected to a 2-line line, and the echo cancellation amount or echo cancellation of the echo canceller is Since the structure is configured so that the gain control of the variable gain circuit is started after the sum of the echo loss and the echo loss reaches a predetermined value, there is no phenomenon of cutting at the beginning or end of speech, and the generation of ringing and noise during the transition period leading to stable operation is eliminated. This has the effect of preventing overload noise and improving call quality. Further, the effect of the echo canceller itself increases the sound stability, and furthermore, it becomes possible to increase the upper limit value of the gain of the variable gain circuit, and there is an advantage that the transfer service area can be expanded.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of a call transfer connection, FIG. 2 is a diagram showing transmission loss of a call transfer line, and FIG. 3 is a block diagram showing an example of a conventional two-wire bidirectional automatic gain control device. FIG. 4 is a block diagram showing one embodiment of the present invention, and FIG. 5 is a time chart showing gain control of the variable gain circuit in the above embodiment. In the figure, 1, 11: 2-wire line, 2, 1
2: Hybrid conversion circuit, 5: Code circuit, 6:
Decoding circuit, 7, 7': echo canceller,
8: variable gain circuit, 9: control circuit, 10: attenuation measurement circuit.

Claims (1)

[Claims] 1. A pair of hybrid conversion circuits for exchanging a 2-wire line to a 4-wire line, a variable gain circuit and an echo canceller connected to the 4-wire portion between the pair of hybrid conversion circuits, and a variable gain circuit and an echo canceller connected to the 4-wire portion between the pair of hybrid conversion circuits; The control circuit includes a control circuit that controls gain, and an attenuation measurement circuit that measures the echo cancellation attenuation of the echo canceller or the sum of the echo cancellation attenuation and return loss, and the control circuit controls the output of the attenuation measurement circuit. A two-wire bidirectional automatic gain control device, characterized in that the automatic gain control function is stopped until the value reaches a predetermined value.