JPS613533A - Two-wire two-way automatic gain controller - Google Patents

Abstract

PURPOSE:To prevent singing and cut-off of the head and tail of speech by starting the gain control of a gain variable circuit after an echo erasing amount or a sum between the echo erasing amount and an echo loss reaches a prescribed value. CONSTITUTION:Echo calcellers 7, 7' utilize a talking signal of start of talking, starts an echo cancelling operation, generate a signal to cancel an echo signal and superimpose it on the echo signal so as to erase the echo. In this case, until the echo cancelling attenuation of the canceller 7 is increased gradually and then reaches a prescribed, the gain of a gain variable circuit 8 is kept to 0, then no singing is generated and no cut-off of the start and tail of speech is caused. Then when the echo cancelling attenuation reaches a prescribed value or over, a control circuit 9 starts the gain control of the gain variable circuit 8.

Description

TECHNICAL FIELD The present invention relates to a two-wire bidirectional automatic gain control device for adjusting 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 line is not fixed, the gain of the bidirectional repeater may be variably controlled. For example, in a call transfer connection as shown in No. 11il, an incoming call from the calling telephone S1 to the telephone S2 of the receiving station EO2 via the calling station EOI is automatically designated via the transfer device T. Transfer destination phone S with transfer destination height EO3
Transfer connection to 3. Therefore, the loss between the originating telephone S1 and the transfer destination telephone 53 is as shown in FIG.
The loss L1dB between l and the terminating station EO2 and the terminating station EO2
and the loss L2dB between the transfer destination phone @S3. In order to compensate for the above losses, two lines are placed between the incoming line and the forwarding line.
It is necessary to insert a wire-type bidirectional repeater, but since the loss and impedance of the incoming line and transfer line differ each time the connection is made, the repeater gain is made variable according to the loss, and noise is generated due to impedance mismatch. must be prevented.

FIG. 3 is a block diagram showing an example of a conventional 21!1 type 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 signal transmitted from the first outgoing call WtS1 to the forwarding destination telephone S3 is transmitted from the hybrid conversion circuit 12 through the TTI and amplifier AMP+ to the resistive attenuator. The transmission signal sent to the transfer line from the transfer destination telephone S3 to the originating telephone Sl is converted into four wires by the hybrid conversion circuit 12 and then passed through the resistance attenuator ATT.
2 and amplifier AMP2 from hybrid conversion circuit 2 to calling telephone S1. Amplifier AIIIP
I and AMP2 are fixed gain amplifiers, and the attenuation amount of the resistive attenuators ATTI and ATT2 is controlled by the control unit C0NT.
It has automatic gain control by controlling.

The resistive attenuators ATTI and ATT2 are connected to the control unit C0NT.
It has a built-in voice switch that can be inserted and removed by the control unit C0.
NT monitors the level at input point A of resistive attenuator ATTI and the level at input point B of resistive attenuator ATT2, and adjusts resistive attenuators ATTI and AT so that the volume in both directions is constant.
It is designed to control T2. 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 when the voice switch is inserted or removed, the speech quality deteriorates due to cutting at the beginning and end of the speech, which is a phenomenon peculiar to voice switches.Also, in the convergence process of automatic gain control, the amplifier is overloaded. It may become overloaded and generate overload noise.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a two-wire bidirectional automatic gain control device that solves the above-mentioned conventional drawbacks, prevents the generation of overload noise and ringing, and does not cause truncations at the beginning and end of speech. It is in.

Structure of the Invention The two-wire bidirectional automatic gain control device of the present invention includes a pair of hybrid conversion circuits that convert a two-wire line to a four-wire line, and a four-wire section connected between the pair of hybrid conversion circuits. a control circuit for controlling the gain of the variable gain circuit; and an attenuation measurement circuit for measuring the echo cancellation attenuation or the sum of the echo cancellation attenuation and the turn loss of the echo canceller. prepare for,
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 required 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 l and 11 to convert them into a four-wire system, and a code circuit 5 and an echo The canceller 7, the variable gain circuit 8, and the decoding circuit 6 are connected. The input signal from the two-wire line l is
The signal is converted into a four-wire signal by the hybrid conversion circuit 2 and inputted to the code circuit 5, where it is converted into a digital signal. The output signal of the encoder circuit 5 is echo-cancelled by an echo canceller 7 and sent to a variable gain circuit 8. The signal is amplified by a variable gain circuit 8 and inputted to a decoding circuit 6 through an echo canceller 7', converted to an analog signal by the decoding circuit 6, and sent to a two-wire line 11 via a hybrid conversion circuit 12. Ru. The signal input from the two-wire line 11 is converted into a four-wire signal by the hybrid conversion circuit 12 and input to the encoder circuit 5, and then similarly sent to the echo canceller 7', variable gain circuit 8. Passes through echo canceller 7, decoding circuit 6, and hybrid conversion circuit 2
- is sent to the two-wire line l via -.

The control circuit 9 monitors the input and output signal levels of the variable gain circuit 8 in one direction, and the signal level in both directions is 1'i.
The gain of the variable gain circuit 8 is controlled so that the pl value is achieved.

However, until the output signal of the attenuation measurement circuit 10 reaches a certain value, the gain of the variable gain circuit 8 is set to O, and the above gain control is started after the output value of the attenuation measurement circuit 1o reaches a certain value or more. .

The attenuation measurement circuit 10 measures the echo cancellation attenuation based on the level difference between the signal level at the input point from the encoder circuit 5 to the echo canceller 7 and the signal level at the output point from the echo canceller 7 to the variable gain circuit 8. Control circuit 9
to notify. 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 the point of failure and the received signal reflected from the 2FF1 type line l are connected to the hybrid conversion circuit 2. It may be possible to measure the level difference between the echo signal transmitted through the echo canceller 7 and the signal output after being canceled by the echo canceller 7. In this case, the sum of the echo loss and the echo cancellation attenuation amount may be measured. become.

As described above, the control circuit 9 starts the gain control after the output value of the attenuation amount measuring circuit 10 reaches a certain value or more. This constant value may be set to a value such that when the variable gain circuit 8 is at its maximum gain, no noise is generated by the loop circuit constituted by the four-wire section and the hybrid conversion circuit. That is, when the attenuation measurement circuit IO measures the echo cancellation attenuation, the above-mentioned constant value is, for example, a hybrid loss (approximately 7 dB) from the maximum gain of the variable gain circuit 8.
), and the control circuit 9 sets 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 certain value, no noise will be generated.Also, when the attenuation measurement circuit IO measures the echo cancellation amount and the echo loss. In this case, the same effect can be obtained by setting the above-described constant value to, for example, the maximum gain of the variable gain circuit 8.

Next, the operation of this embodiment will be explained. 2-wire line 1
is connected to the two-wire line 11 through this device, the originating telephone and the transfer destination telephone are connected, and in response to a response from the transfer destination, a communication path is formed and a call is started. The echo cancellers 7 and 7' start an echo canceling operation using the call signal at the start of the call, create a signal for canceling the echo signal, and cancel the echo by superimposing it on the echo signal. 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 the generation of ringing while the echo canceller 7 is converging, thereby improving the quality of the call. In addition, there is no phenomenon in which one word is cut off at the beginning or end of episode 5.

Then, as shown in FIG. 5, the control circuit 9 starts gain control of the variable gain circuit 8 from the time point tc when the amount of echo cancellation attenuation exceeds a certain value, and the gain of the variable gain circuit 8 gradually increases. At time ts, the gain stabilizes at such a level that the output level (average value) becomes 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, so that noise may be generated or overload noise may occur during automatic gain control convergence. Never occurs. That is, there is no truncation at the beginning or end of the speech, and the occurrence of ringing or overload noise during the convergence of the echo canceller 7 and variable gain circuit 8 is prevented, resulting in improved speech quality. In addition, due to the effect of the echo canceller 7, the characteristics during a bidirectional call are improved and the call quality is improved, and furthermore, the sound stability is improved, which makes it possible to increase the upper limit of the gain of the variable gain circuit 8. Another advantage is that the application area of the automatic call forwarding service can be expanded.

Of course, when the attenuation measurement circuit 10 measures the echo cancellation amount+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 V of the echo canceller is adjusted. Since the configuration is configured so that the gain control of the variable gain circuit is started after the sum of echo losses reaches a predetermined value, there is no phenomenon of disconnection at the beginning and end of the first and second words, and noise generation and overload during the transition period leading to stable operation are avoided. This has the effect of preventing 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 the drawing]

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: two-wire line, 2, 12 bihybrid conversion circuit, 5: encoding circuit, 6: decoding circuit, 7.
7': Echo canceller, 8: Variable gain circuit, 9: Control circuit, 10: Attenuation reed measurement circuit.

Claims (1)

[Claims] a pair of hybrid conversion circuits that convert a two-wire line to a four-wire line; a variable gain circuit and an echo canceller connected to the four-wire portion between the pair of hybrid conversion circuits;
The control circuit includes a control circuit that controls the gain of the variable gain circuit, 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. A two-wire bidirectional automatic gain control device, characterized in that the automatic gain control function is stopped until the output value of the measurement circuit reaches a predetermined value.