JPS6218097B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a two-wire bidirectional amplifier whose purpose is to repair a two-wire relay line with large losses.

Conventionally, two-wire bidirectional amplifiers utilize negative impedance and audio power comparison.
VODAS, loudspeaker telephones, and related devices include echo suppressor devices and the like. Here, when realizing a call forwarding service (a service that forwards a call to a called party to another pre-registered subscriber phone), which is considered as a new telephone service, the forwarding line is further connected to a long-distance transmission line. In this case, the transmission loss from the caller to the final destination increases, making it impossible to maintain the good call quality that was available in the past. Therefore, for such a call transfer service, a bidirectional amplifier for loss compensation is required in the trunk line.

FIG. 1 shows an example of the configuration of a trunk line for a call transfer service. A, B, and C are switching stations, which in this case represent a calling subscriber station, a terminating subscriber station, and a transfer subscriber station, respectively. a, b, and c indicate respective subscriber telephones. A bidirectional amplifier D, which compensates for the increased line loss for this service, is inserted on the switching trunk side of the terminating subscriber station B. Now, the line losses of each subscriber line and each transmission line are as shown in the figure: l _a , l _b , l _c , l _AB , l _BC ,
Then, existing telephone transmission systems are designed so that l _a +l _AB +l _b does not exceed a predetermined maximum value in order to ensure a predetermined speech quality. However, when a forwarding service is provided as shown in Figure 1, the transmission loss from the caller to the final forwarding destination is l _a +l _AB +l _BC
+l _C , and the above maximum value cannot be guaranteed.
Some kind of loss compensation means is required, and it is necessary to install a bidirectional amplifier in the trunk section of the receiving subscriber station B. In this case, the repeater has a predetermined gain in the transmitting direction when transmitting a call, and inserts a predetermined loss in the opposite direction based on the sound condition of the four-wire closed circuit. Conventional
It is possible to use a voice switch-type bidirectional repeater used in VODAS, etc., but the gain of the necessary amplifier varies depending on the transfer line and is not constant, and in Figure 1, there is almost no l _BC . Case (B
(for example, when transferring to the same area), a gain is not required; however, when a long-distance line is configured with a large _BC , a large gain is required, and therefore the call side of the bidirectional amplifier is If the gain is set to compensate for maximum loss, the output level of the bidirectional amplifier will be excessive when configured with a low-loss line, not only overloading the circuitry after the amplifier, but also significantly reducing speech quality. This is inconvenient because it reduces the On the other hand, due to its nature as a relay line, the amplifier has
It is desirable that the gain during a call be the same in both directions.

In view of these demands, an object of the present invention is to have a function of compensating for loss in a trunk line with a simple configuration, and also to prevent an excessive output level from increasing even when no gain is required. An object of the present invention is to provide a two-wire bidirectional trunk line with an automatic gain control function capable of always keeping the loss in the same direction.

The present invention solves the above-mentioned increase in loss by two points.
A voice switch-type 2-wire system with a 2-wire to 4-wire conversion transformer on both sides in the relay line section, and a voice switch type that operates to gain gain in the communication direction by comparing the magnitude of the communication power in each direction in the 4-wire section. It is a bidirectional amplifier.

FIG. 2 shows an embodiment of the invention. In the figure, 1 and 2 are 2-wire to 4-wire conversion circuits, and 3 and 4 are 2-wire to 4-wire conversion circuits.
is a variable gain/loss circuit, and depending on external control information,
Complementarily results in loss or gain. 5 compares the magnitude of the audio force taken out from a part of the main signal path of the variable gain/loss circuits 3, 4, and sends control information to the variable gain/loss circuits 3, 4 based on the comparison information obtained as a result. This is a voice detection control circuit that provides 6,7
are level control audio detection control circuits connected to the output points of the four-wire circuits, respectively, for comparing the respective average call strengths with a predetermined average level set in advance;
Reference numerals 8 and 9 are variable loss circuits controlled by the control circuits 6 and 7 and inserted on the 4-wire side.

FIG. 5 shows a specific example of the voice detection control circuit 5.
The audio signal on the transmitting (hereinafter referred to as S) side and the audio signal on the receiving (hereinafter referred to as R) side enter detectors 201 and 202 from output points m and n, respectively, and are rectified and extracted as direct current, after which they are brought to a reference level. After being compared and determined by the comparators 203 and 205 with V _TH and the magnitude comparator 204 of the S and R levels, the NAND circuit 2
06, 207, inverter circuit 208, 209,
201 and outputs to control lines s ₁ , s ₂ , r ₁ , r ₂ that control the variable loss circuits 3 and 4.

Now, when there is a call signal on the S side, this signal is compared in magnitude with the R side signal level by the voice detection control circuit 5. For example, if it is determined that the S side level is not smaller than the R side level, the circuit 3 is a gain, and at the same time the same amount of loss is given in the circuit 4, giving a predetermined gain a dB in the communication direction and a predetermined loss a dB in the opposite direction. When the average voice call level at the output point of the variable gain/loss circuit 3 exceeds a preset level due to this increase in gain in the speech direction, the output of the level control audio detection control circuit 6 causes the variable loss circuit on the S side to 8 is given a loss. This operation is controlled continuously or stepwise to ensure that the S-side call average level does not exceed a preset average level at all times. Variable loss circuit 8, 9
The value of is retained until one call ends, or
It operates to return to the original value little by little at regular intervals. The operation when the R side is talking is exactly the same as the S side talking operation described above, and each variable loss circuit is controlled in accordance with the direction. By the above operation, for example, when the present amplifier circuit is connected to a relay line with low loss, loss is inserted into the corresponding line input section to prevent overload of the line due to the amplification operation.

According to this embodiment, the average level at the output point of the 4-wire section is operated so as not to exceed a certain predetermined level. A large amount of loss is introduced in the variable loss circuit, and the losses inserted in each direction are not the same in both directions. Therefore, the gains between the two lines in the communication direction are not necessarily the same.

FIG. 3 shows a second embodiment according to the invention.
The difference from the first embodiment is that a second level control variable loss circuit is inserted in series to each output section of the 4-wire section, and each is configured to be controlled by the output level detection information of the other side. It's what I did. That is, for example, due to the level excess information at the S side output point p, the S
At the same time as giving a loss to the side input level control variable loss circuit 8, the same amount of loss is also given to the second variable loss circuit 14 provided at the R side output point. The operation on the R side is similar. Due to the above operation, even if the call level in each direction is different, the same amount of loss is inserted into the other side as that inserted into each other's input side, so the gain in the call direction is always the same. becomes.

FIG. 4 shows an example of the level control audio detection control circuits 6 and 7 in the first and second embodiments.
In order to detect the average call strength in a relatively short time and with high accuracy, this circuit uses a method of detecting the call level within a fixed time interval window.
The detection input is rectified by the detection circuit 101 and becomes one input of the comparator 102. The reference level V is applied to the other input of the comparator 102. The output of comparator 102 is input to sample circuit 103. A timing pulse with a cycle sufficiently narrower than the time interval window for calculating the average level is supplied from the timing generation circuit 106 to the sampling circuit, and a reference level V that provides a reference speech force is applied to each sampling pulse for sampling the rectified output.
It is compared with _TH , and the number of times the reference voltage is exceeded during the time window is counted by the next connected counting circuit 104, and when the counted value exceeds a preset value,
An output is given to shift register 105. The output of the shift register 105 is connected to the variable loss circuit inserted on the 4-wire side, and a predetermined amount of loss is inserted. The shift register 105 is
It has a memory function, and the value of the variable loss circuit is held until the contents of the shift register change next time. In this embodiment, the analog input signal is directly detected at predetermined time intervals to determine the average call power, but a method of A/D converting the audio input signal and comparing and detecting the digital signal is also conceivable. It is clear that there is no need to have separate timing generation circuits for the S side and the R side, and even one timing generation circuit can be provided in common.

According to the present invention, with a simple configuration, the system is suitable for compensation for loss of trunk lines necessary for call transfer service.
A two-wire bidirectional amplifier of the audio switch type is obtained.

[Brief explanation of the drawing]

Fig. 1 is a block diagram for explaining the transmission line side of the call transfer service, Fig. 2 is a block diagram showing the first embodiment of the present invention, and Fig. 3 is a block diagram showing the second embodiment of the present invention. Figures 4 and 4 are Figures 2 and 3.
FIG. 5 is a block diagram showing an example of the audio detection control circuit for level control, and FIG. 5 is a circuit diagram showing a specific example of the audio detection control circuit. a, b, c are subscriber telephones, A, B, C are switching offices corresponding to the subscribers, respectively, l _a , l _b , l _c , l _A
B and l _BC are respectively line losses, 1, 2... 2-wire to 4-wire conversion circuit, 3, 4... gain/loss variable circuit, 5... audio detection control circuit, 6, 7... audio detection control circuit for level control, 8, 9...variable loss circuit, 10, 11...2
Line variable loss control line, 12, 13... Audio detection input line for level control, 101... Detection circuit, 102... Comparator, 103... Sample circuit, 104... Counting circuit,
105...Shift register, 106...Timing generation circuit, 14 and 15 are respectively variable loss circuits for second level control, 201, 202...Detector, 203,
205... Comparator, 204... Size comparator, 206,
207...NAND circuit, 208-210...inverter circuit.

Claims (1)

[Claims] 1 a first conversion means for transmitting a call signal from a first two-line line to a second two-line line and a call signal from a third two-line line to the first two-line line;
a second conversion means for transmitting a call signal from a fourth two-line line to a fifth two-line line, and a second converting means for transmitting a call signal from a sixth two-line line to the fourth two-line line; a first gain/loss variable means for varying the gain or loss for the speech signal from the second two-line line and transmitting it to the sixth two-line line; and a first gain/loss variable means for varying the gain or loss for the speech signal from the fifth two-line line; or a second gain/loss that is varied and transmitted to the third two-wire line;
In the two-wire bidirectional amplifier comprising loss variable means, the first gain/loss variable means is configured to cancel the excess level when the speech signal level at the output end of the first gain/loss variable means exceeds a predetermined level. controlling the gain/loss variable means so that when the speech signal level at the output end of the second variable gain/loss means exceeds a predetermined level, the second variable gain/loss means cancels the excess; A two-wire bidirectional amplifier, characterized in that it comprises means for controlling.