JPS6218096B2 - - 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 exchanges, and in this case, respectively.
They are a calling subscriber station, a terminating subscriber station, and a transfer subscriber station.
a, b, and c indicate respective subscriber telephones. A bidirectional amplifier to compensate for the increased line loss for this service is inserted on the switched trunk side of the terminating subscriber station B. Now, assuming that the losses of each subscriber line and each transmission path are l _a , l _b , l _c , l _AB , l _BC as shown in the figure, the existing telephone transmission system has l _a +l _AB +l _b is designed not to exceed a predetermined maximum value. However, when a forwarding service is provided as shown in Figure 1, the transmission system loss from the caller to the final forwarding destination is l _a + l _AB + l _BC + l _C ,
Since the maximum value cannot be guaranteed, some kind of loss compensation means is required, and a bidirectional amplifier is required in the trunk line section of the receiving subscriber station B. The characteristics of the repeater in this case are that it has a predetermined gain in the sending direction when transmitting a call, and it inserts a predetermined loss in the opposite direction due to the sound condition of a 4-wire closed circuit, which is used in conventional VODAS etc. A voice switch-type two-way repeater can be considered, but the gain of the necessary amplifier varies depending on the transfer line and is not constant _.
If there is almost no gain (such as when transferring to station B within the same area), no gain is necessary, but if the long-distance line consists of a large l _BC , a large gain is required, and Therefore, if the calling side gain of the bidirectional amplifier is set to compensate for the maximum loss, the output level of the bidirectional amplifier will be excessive when configured with a low-loss line, leading to overload of the line after the amplifier. Not only that, but it is also inconvenient because it significantly reduces the quality of the call. On the other hand, due to the nature of the amplifier as a repeater, it is desired that the gain during communication 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 used. An object of the present invention is to provide a two-wire bidirectional repeater with an automatic gain control function that can always keep the loss in the communication direction the same.

The present invention provides a 2-wire to 4-wire conversion transformer on both sides of the 2-wire relay line to cope with the increase in loss as described above, and increases the gain in the communication direction by comparing the magnitude of the communication power in each direction in the 4-wire section. The present invention provides an audio switch type two-wire bidirectional amplifier that operates to obtain the following.

FIG. 2 shows an embodiment of the invention. In the figure, 1 and 2 transmit the call signal from the external 2-wire side to one 2-wire side of the 4-wire side, and transmit the call signal from the other 2-wire side of the 4-wire side to the external 2-wire side. 3 and 4 are variable gain/loss circuits which are complementary to a loss state or a gain state depending on external control information. Reference numeral 5 denotes an audio detection control circuit that compares the magnitude of the audio power taken out from part of the main signal path of the variable gain/loss circuits 3 and 4, and provides control information to the variable loss circuit based on the comparison information obtained as a result. It is. Reference numerals 6 and 7 are level control audio detection control circuits connected to the output points of each two-line line on the four-line side, respectively, for comparing each average call strength with a predetermined average level set in advance; Reference numeral 9 denotes a two-wire variable loss circuit inserted on the two-wire side controlled by the control circuit.

Now, when there is a call signal on the transmitting (hereinafter referred to as S) side, this signal is compared in magnitude with the R side signal level by the voice detection control circuit 5, and for example, the S side level is the receiving (hereinafter referred to as R) side signal. ) When it is determined that the level is not lower than the level, the gain of circuit 3 is increased by a certain amount to put the S side in the gain state, and at the same time, the same amount of loss is given in circuit 4, and the predetermined gain in the speech direction is set to a dB.
gives a predetermined loss a dB in the opposite direction. When the average voice call level at the 4-wire output point in that direction exceeds a preset level due to this gain increase in the speech direction, the output of the level control audio detection control circuit 6 causes the 2-wire variable loss circuit 8 to loss is given. 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. The output of the level control voice detection control circuit 6 is held until the end of one call, or is operated to return to the original value little by little at certain fixed time intervals. The operation when the R side is making a call is exactly the same as the S side call operation described above.
Each variable loss circuit is controlled according to the direction. Due to 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 two-wire input section in order to prevent overload of the line due to the amplification operation. Further, since the loss is inserted into the second line side, the same amount of loss is also inserted in the opposite direction, and the loss can always be kept the same in the line in the communication direction.

FIG. 3 shows an example of the level control audio detection control circuits 6 and 7 shown in FIG. Since the average call strength is detected accurately in a relatively short time,
A method is adopted in which the call level is detected at fixed time intervals. The detection input is rectified and detected by the detection circuit 101, and becomes one input of the comparator 102. The other input of this comparator 102 has a reference level V _TH
is given, and its output enters the sample circuit 103. In the comparator 102, the reference voltage V _TH that provides the reference communication power and the rectified detection output from the detection circuit 101 are compared. The output of the comparator is input to a sampling circuit 103 and sampled by a timing pulse from a timing generation circuit 106 for calculating the average level. This sampling result is counted by a counting circuit 104 to count the number of times the reference voltage is exceeded within a time window, and when the counted value exceeds a preset value, an output is given to a shift register 105. The shift register output is connected to the two-wire variable loss circuit to insert a predetermined amount of loss. The shift register 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 obtain 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. The timing generation circuit is S
It is clear that there is no need to have separate ones for the R side, and it is possible to have one in common.

FIG. 4 shows an example of the audio control circuit 5 shown in FIG. The audio inputs of S and R are rectified from output points m and n to detectors 201 and 202, respectively, and taken out as direct current, and then set at a reference level V for determining the presence or absence of a call.
After being compared and judged by the comparators 203 and 205 with _TH and the level comparator 204 of the S side and R side, it is converted by the NAND circuits 206 and 207 and the inverter circuits 208 to 210, and then the variable loss circuits 3 and 4 is output to the control lines s ₁ , s ₂ , r ₁ , r ₂ that control the
Control ON-OFF.

As described above, according to the present invention, it is possible to obtain a voice switch type two-wire bidirectional amplifier suitable for compensation of losses in trunk lines necessary for call transfer services with a simple configuration.

[Brief explanation of the drawing]

Fig. 1 is a block diagram for explaining an example of a transmission path for a call transfer service, Fig. 2 is a block diagram showing an embodiment of the present invention, and Fig. 3 is a level control voice detection control circuit of Fig. 2. A block diagram showing an example of
FIG. 4 is a block diagram showing an example of the voice detection control circuit of FIG. 2. a, b, c are subscriber telephones, A, BC are switching offices corresponding to the subscribers, l _a , l _b , l _c ,
1, 2... 2-4 wire conversion circuit, 3, 4... variable gain/loss circuit _, 5... audio detection control circuit, 6, 7... audio detection control circuit for level control, respectively _. , 8, 9...2-wire variable loss circuit, 10, 1
DESCRIPTION OF SYMBOLS 1...2-wire 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 circuit, 201, 2
02...Detector, 203, 205...Comparator, 204
...Size comparator, 206, 207...NAND circuit, 2
08-210...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, when the output level of the first gain/loss variable means exceeds a predetermined reference level, the output level of the first two-wire line is increased by approximately the excess amount. and, when the output level of the second variable gain/loss means exceeds a predetermined reference level, means for applying a loss to the fourth two-line line by approximately the excess amount. A two-wire bidirectional amplifier characterized by: