JPS6192042A - Two-wire bidirectional repeating installation - Google Patents

Abstract

PURPOSE:To equalize two reception levels of an automatic gain control circuit to stabilize the operation by controlling the gain of a variable gain attenuator or a variable gain amplifier, which is inserted onto a transmission line in the four-wire side of a two-wire four-wire converting circuit, with the automatic gain control circuit. CONSTITUTION:Audio signals transmitted from telephone sets 11 and 21 are subjected to the line loss on transmission lines a1 and a2. Reception levels are observed by level detecting circuits 15 and 25, and respective under sound volumes (g) and g' are determined by an automatic gain control circuit 30. Gains of variable gain amplifiers 14 and 24 are equalized to larger one. That is, G=max(g, g') is true, and a variable gain attenuator 17 or 27 on a transmission line b1 or b2 in the four-wire side of the smaller under sound volume between variable gain attenuators 17 and 27 is attenuated by the same quantity as a difference DELTA between under sound volumes, namely, DELTA=g-g'. By this structure, the input reception level of the automatic gain control circuit 30 is made uniform independently of balance or unbalance of the line loss to stabilize the operation of the automatic gain control circuit 30.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a two-wire bidirectional repeater including an echo canceller circuit. In particular, the present invention relates to a two-wire bidirectional relay device that can obtain good communication quality characteristics with a simple configuration and can operate stably.

[Conventional technology]

FIG. 3 is a block diagram showing a conventional two-wire bidirectional relay device, which is used in a relay device for transferring incoming calls and the like.

Telephone 11.21, transmission line a, at, two-wire four-wire conversion circuit 12.22, four-wire side transmission line b of the two-wire four-wire conversion circuit
l, bt, four-wire side reception path C3cz of the two-wire four-wire conversion circuit,
An echo canceller circuit 13.23 that removes a loop signal (echo) from the four-wire side reception path to the four-wire side transmission path of the two-wire four-wire conversion circuit, a variable gain amplifier 14.24, a level detection circuit 15.25, It is composed of lines d1 and d2 that set the gain of the variable gain amplifier, and an automatic gain control circuit 30 that compensates for line losses of transmission lines a, , and az.

To simplify the explanation of the operation of this conventional two-wire bidirectional repeater, it is assumed that the echo canceller circuits 13 and 23 are both in a steady state using a known method and that sufficient echo cancellation has been achieved. do. The voice signal sent from the telephone 11 at a level of
B), and is received as an input to the variable gain amplifier 14 at a level of XL(tfB). However, in this explanation, the conversion loss of the two-wire/four-wire conversion circuit 12 is compensated by a fixed amplifier, or the line loss L
(dB).

Now, from the two-wire four-wire conversion circuit 12 to the four-wire side transmission path b1
The received signal sent out is detected by the level detection circuit 15 and is notified to the automatic gain control circuit 30 that it is at the level of XL (dB). The difference g between the reference output level Remember.

On the other hand, regarding the signal level X' transmitted from the telephone 21, the insufficient volume g' of the signal transmitted from the telephone 21 to the telephone 11 is g' = Xo - (X' - L'). However, L' is the line loss of the transmission path a2.

Now, it is assumed that the automatic gain control circuit 30 determines the gain G of the variable gain amplifier 14.24 from the insufficient sound volume g and g' based on the smaller value of the insufficient sound volume g or g'. That is, G=min(g, g'). Therefore, if the line losses on both sides of the device are equal, the line loss compensation bones in the variable gain amplifiers 14.24 will also be equal, and the operating and speech characteristics in both directions will be equal.

[Problem that the invention seeks to solve]

However, in such a conventional two-wire bidirectional relay device, if the line loss on both sides of the device is different, the telephone
If the receiving level of 1.21 is determined based on the smaller of the insufficient sound volumes, the larger the unbalance of the 88 FJ loss, the less gain can be obtained for the larger of the missing sounds. In addition, since the level detection circuit 15.250 input level difference for operating the automatic gain control circuit 30 becomes large, voice detection is performed.

If the level darkness value is set high, the reception level cannot be observed correctly when one side has a high line loss, or if it is set low, malfunctions may occur due to background noise other than the signal on the line side where the line loss is low. There was a problem.

Therefore, when the line loss is unbalanced, the operating points of the level detection circuits 15 and 25 depending on the voices of the callers on both sides will be equally constrained, and as a result, the call quality will not be equal and the quality of one side will deteriorate. There were drawbacks such as:

By the way, as a method for determining the gain of the automatic gain control circuit 30, when adjusting the gain to the one with the larger level difference between the two lines, contrary to the above, G=max(g,
g'), the one with the lower reception level will be relieved, but on the other hand, the one with the higher reception level will be saturated at the relay device output point because a larger gain is given. However, there were problems such as deterioration of characteristics.

The present invention has been made in view of these conventional problems, and aims to provide a two-wire bidirectional relay device that has a simple configuration, can obtain good call quality, and is capable of stable operation. do.

[Means for solving problems]

The present invention provides a variable gain attenuator or a variable gain attenuator that corrects the unbalance of line loss in transmission lines connected to both sides of a two-wire bidirectional repeater, and operates the automatic gain control circuit by inputting a signal of the same reception level to the automatic gain control circuit. It is characterized by being equipped with a variable gain amplifier.

In other words, a double terminal connected to each bidirectional two-wire transmission line, two two-wire four-wire conversion circuits that convert the signal of this terminal to four-wire, and these two two-wire four-wire conversion circuits. Two echo canceller circuits are connected to each other and cancel echo signals from the four-wire receiving side to the four-wire transmitting side, and the output terminals of these two echo canceller circuits are connected to compensate for the line loss of the above transmission line. two variable gain amplifiers, two level detection circuits that branch the outputs of the two echo canceller circuits and detect their output signal levels, and detect outputs of these two level detection circuits and the two variable gains In a two-wire bidirectional repeater equipped with an automatic gain control circuit that takes the output of an amplifier as an input and controls the gain of the variable gain amplifier to a required value, the four-wire output of the two two-wire and four-wire conversion circuits and two variable gain attenuators connected between the input terminals of the two variable gain amplifiers, the two variable gain attenuators input the output of the automatic gain control circuit, and the two variable gain attenuators The present invention is characterized in that it includes means for varying the amount of attenuation so that the signal detection levels of the two level detection circuits are substantially equal.

Alternatively, two variable gain amplifiers are provided that are connected between the four-wire output terminals of the two two-wire four-wire conversion circuits and the input terminals of the two variable gain amplifiers, and the two variable gain amplifiers are , characterized in that it includes means for inputting the output of the automatic gain control circuit and varying the gain so that the signal detection levels of the two level detection circuits become substantially equal.

[For production]

The present invention provides a variable gain attenuator or By controlling the gain of the variable gain amplifier by the automatic gain control circuit, it is equivalent to equalizing the line loss in both directions connected to this repeater. Therefore, the two reception levels of the automatic gain control circuit become equal, and the operation becomes stable.

Furthermore, the two variable gain amplifiers that compensate for line loss under the control of the automatic gain control circuit amplify signals at the same level, ensuring high relay quality.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the first aspect of the present invention. In FIG. 1, a telephone 11.21 is connected to an input/output terminal 10.20 of a two-wire bidirectional relay device via transmission lines al and ag, and this input/output terminal 10.2
0 is connected to the two-wire side of the two-wire/four-wire conversion circuit 12.22. The four-wire side outputs of the two-wire and four-wire conversion circuits 12 and 22 are guided to the four-wire side transmission paths b1 and b2, and the echo canceller circuit 13
．． It is inputted to the Sin terminal of 23, and further outputted from the 5out terminal, and connected to the inputs of the variable gain amplifier 14.24 and the level detection circuit 15.25. The output of the variable gain amplifier 14.24 is guided to the four-wire side receiving paths C1 and Cg of the two-wire/four-wire conversion circuit 12.22, and then to the R1n0i terminal of the echo canceller circuit 13.23 and the two-wire/four-wire conversion circuit 12.
．． Connected to the four-wire side input of 22. Automatic gain control circuit 3
0 is connected to the output of variable gain amplifier 14.24 and the output of level detection circuit 15.25, and
The signal output that sets the gain of 4.24 is connected to the lines d, , d2
Connect via.

Here, the features of the present invention are that the two-wire/four-wire conversion circuit 12.22 and the echo canceller circuit 13.23 on the four-wire side transmission path of the two-wire/four-wire conversion circuit 12.22, , bz.
A variable gain attenuator 17, 27 controlled by the output of the automatic gain control circuit 30 is connected between the two.

In this device, an analog-to-digital conversion circuit is installed in the four-wire side transmission path of the two-wire four-wire conversion circuit 12.22, and a digital-to-analog conversion circuit is installed in the four-wire side receiving path c, , Cm. Insert the circuit to create a two-wire and four-wire conversion circuit 12.
The parts other than 22 are constructed of digital circuits, but the details are omitted here.

The operation of the automatic gain control circuit 30 of the two-wire bidirectional relay device of the present invention will be described in detail below. It is assumed that the echo canceller circuits 13 and 23 are already in a steady state and have a sufficient amount of echo cancellation. In addition, the variable gain attenuator 17
．． The attenuation amount of No. 27 is initially set to OCdB).

The audio signal sent from telephone 11.21 is transmitted through transmission path a.
,, az suffers line loss. The received level is observed by the level detection circuit 15.25, and the automatic gain control circuit 30
Determine the respective insufficient volumes g and g'. This adjusts the gain of the variable gain amplifier 14.24 to the larger of the two. That is, G”max(g+g
), and the difference Δ in the insufficient volume of the variable gain attenuator 17 or 27 on the four-wire side transmission path or b2, whichever has the smaller insufficient volume among the variable gain attenuators 17 and 27, is gives the same amount of attenuation as Δ=g~g'.

With this structure, automatic gain control circuit 3
The 00 Å power reception level can be kept at a uniform level regardless of whether the line loss is balanced or unbalanced, and the operation of the automatic gain control circuit 30 is stabilized.

In this embodiment, the variable gain attenuator 17.27 includes a two-wire/four-wire conversion circuit 12.22 and an echo canceller circuit 13.27.
Although the echo canceller circuit 13 is inserted between the echo canceller circuit 13 and the echo canceller circuit 23, the present invention can be implemented by connecting it to either the input side or the output side of the echo canceller circuit 13.23.

However, in consideration of the wide range and echo cancellation characteristics of the echo canceller circuit 13.23, it is preferable to connect it to its input side.

FIG. 2 is a block diagram showing an embodiment of the second aspect of the present invention. The feature of the present invention is that the two-wire/four-wire conversion circuit 12
．． A variable gain amplifier 18.28 controlled by the output of the automatic gain control circuit 30 is connected to the output side of the echo canceller circuit 13.23 on the four-wire side transmission path 22, i, b.

The gain of the variable gain amplifier 18.28 is adjusted to the smaller value of the above-mentioned insufficient sound volume. That is, G=min(g+
g'). In addition, the variable gain amplifier 18.28 is initially set to a gain of 0 (dB), and the variable gain amplifier 18.28 is set to the variable gain amplifier 18.28 on the four-wire side transmission path or b2, whichever has the greater insufficient volume. gain amplifier 18 or 28
gives the same amount of gain as the difference Δ in the undersound volume, that is, Δ=g″′g′.

Similarly, the present invention can be implemented by connecting this variable gain amplifier 18.28 to either the input side or the output side of the echo canceller circuit 13.23 due to its function.
Considering the dynamic range and echo cancellation characteristics of the echo canceller circuit 13.23, it is preferable to connect it to its output side.

〔Effect of the invention〕

As explained above, the present invention is applicable to
Since the automatic gain control circuit balances the reception levels of both sides, it is possible to stably improve call quality, and
Line loss in the transmission line can also be completely compensated for. This makes it possible to ensure high relay quality8! It has a small effect. .

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a first embodiment of the two-wire bidirectional relay device of the present invention. FIG. 2 is a block diagram showing a second embodiment of the two-wire bidirectional relay device of the present invention. FIG. 3 is a block configuration diagram showing the configuration of a conventional two-wire bidirectional relay device. 10.20... Input/output terminal of relay device, 11.21.
...Telephone, 12.22...Two-wire four-wire conversion circuit, 13
．． 23...Echo canceller circuit, 14.24...
Variable gain amplifier, 15.25...Level detection circuit, 1
7.27... Variable gain attenuator, 18.28... Variable gain amplifier, 30... Automatic gain control circuit, a 1 ,
az...Transmission path, bl, b2...Four-wire side transmission path of the two-wire/four-wire conversion circuit, C1%C2...Four-wire side reception path of the two-wire/four-wire conversion circuit, d,, d2 ...Line for setting the gain of a variable gain amplifier.

Claims (2)

[Claims] (1) Two terminals each connected to a bidirectional two-wire transmission line, two two-wire/four-wire conversion circuits that convert the signals of these terminals to four-wire, and these two two-wire/four-wire conversion circuits. There are two echo canceller circuits that are connected to the four-wire receiving side and cancel echo signals from the four-wire transmitting side, and an echo canceller circuit that is connected to the output terminals of these two echo canceller circuits and cancels the line loss of the transmission line. two variable gain amplifiers for compensation, two level detection circuits that branch the outputs of the two echo canceller circuits and detect their output signal levels, and the detection outputs of these two level detection circuits and the two variable gain amplifiers In a two-wire bidirectional repeater equipped with an automatic gain control circuit that takes the output of a gain amplifier as an input and controls the gain of the variable gain amplifier to a required value, the four wires of the two two-wire and four-wire conversion circuits Two variable gain attenuators are connected between the output terminal and the input terminals of the two variable gain amplifiers, and the two variable gain attenuators receive the output of the automatic gain control circuit as input, and the two variable gain attenuators receive the output of the automatic gain control circuit as input. A two-wire bidirectional relay device comprising means for varying the amount of attenuation of two level detection circuits so that the signal detection levels of the two level detection circuits are substantially equal. (2) Two terminals each connected to a bidirectional two-wire transmission line, two two-wire/four-wire conversion circuits that convert the signals of these terminals to four-wire, and these two two-wire/four-wire conversion circuits. and two echo canceller circuits that cancel echo signals from the four-wire receiving side to the four-wire transmitting side, and are connected to the output terminals of these two echo canceller circuits to compensate for the line loss of the above transmission line. two level detection circuits that branch the outputs of the two echo canceller circuits and detect their output signal levels, and detect outputs of these two level detection circuits and the two variable gain In a two-wire bidirectional repeater equipped with an automatic gain control circuit that takes the output of an amplifier as an input and controls the gain of the variable gain amplifier to a required value, the four-wire outputs of the two two-wire and four-wire conversion circuits and two variable gain amplifiers connected between the terminal and the input terminal of the two variable gain amplifiers, the two variable gain amplifiers input the output of the automatic gain control circuit, and the two variable gain amplifiers input the output of the automatic gain control circuit, and A two-wire bidirectional relay device comprising means for varying the gain of the detection circuit so that the signal detection levels of the detection circuit are substantially equal.