JPS6213858B2 - - 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 that use negative impedance, VODAS and loudspeaker telephones that use voice power comparison, and echo suppressor devices as related devices are known. Here, when realizing a call forwarding service (a service that forwards a call made to a called party to another subscriber phone that has already been registered), which is considered as a new telephone service, the forwarding line is used for long-distance transmission. 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, the above-mentioned loss-compensating bidirectional amplifier is required in the trunk line.

FIG. 1 shows the principle of a conventional audio switch type bidirectional amplifier. In the figure, when there is a transmitting signal from the S side, this signal is compared in magnitude with the signal level of the receiving (hereinafter referred to as R) side by the comparison control circuit CONT. By determining that the side level (denoted as S) is higher than the R side level, the loss of the variable loss means A2S and A3S is reduced to OdB.
At the same time, the S side is put into a gain state, and at the same time, the variable loss means A2R and A3R add the same amount of loss to the R side as the amount of change in loss at A2S and A3S. When the voice call average level exceeds a preset level at the four-wire output point p in that direction due to this gain increase in the call direction, a loss is given to the variable loss means A1S by the control information of the voice average level detection circuit DETS,
At the same time, when a call occurs in the opposite direction, the same amount of loss as A1S is given to the variable loss means A4R in the reverse direction in order to always keep the gain of the line in the communication direction the same. When the R side is making a call, each variable loss circuit is controlled in accordance with the direction in exactly the same way as the S-side call operation described above. When this amplifier is connected to a relay line with low loss through these operations, overload of the line due to the amplification operation is prevented.

The principle of the conventional voice switch type bidirectional amplifier has been shown above, but each time the average level of a voice call exceeds the reference level, the loop loss increases due to the loss given to the other party, and the loop gain is constant. It disappears. Even if you look at the loss that satisfies the sound condition, excessive loss will increase, and there is also a drawback that the level difference (level contrast) in both directions will increase.

SUMMARY OF THE INVENTION An object of the present invention is to provide an audio switch type two-wire bidirectional amplifier in which the loop gain is always kept constant and the level contrast is small.

In order to cope with the increase in loss described above, the present invention provides a 2-wire relay line with 2-4 wire transformers on both sides, and obtains a gain in the communication direction by comparing the magnitude of communication power in each direction in the 4-wire section. 2 working voice switch types
It is a wire bidirectional amplifier.

The present invention will be explained in detail below with reference to the drawings.
FIG. 2 shows an embodiment of the present invention. A3 in Figure 2
S' and A3R' are variable loss means capable of providing a loss of 0 to α _dB continuously or at step intervals. Now, S
When there is a transmission signal from the side, A1S, A2S, A
3S', A4S, A1R, A2R, A3R', A4R
In normal times, the losses are 0, 0, 0, 0, 0, respectively.
α, α, 0 _dB , but when the average voice call level at the 4-wire output point p exceeds the preset level by β _dB , the average audio level detection circuit DETS sends control information to cancel the excess level. s ₁ is sent.
This control information s ₁ sets the losses of the variable loss means A1S and A4R to β _dB . This control information _s1 is also sent to the comparison control circuit CONT.

FIG. 3 shows an example of this comparison control circuit CONT. Control information s ₁ sent to comparison control circuit CONT
is input to the decoder 10, and the control information γ corresponding to the value of (α−2β) _dB is input by the decoder 10.
3' and sent to the AND gate 12. Control information s ₂ indicating that the S-side level is not smaller than the R-side level from the voice communication strength determination circuit 14, which is composed of a comparison circuit, an inverter, etc.
Opened by The variable loss means A3R' is set to a loss of (α-2β) _dB by the control information γ3 sent from the AND gate 12. In other words, the loss is reduced by 2β _dB . This value is held until the voice call average level exceeds the preset level again.

In this state, the loss on the S side increases by β _dB due to the initial gain, and at the same time the loss on the R side is reduced by β _dB , so the gain of the 4-wire loop does not change and the loss on the S side increases by β dB.
The gain difference obtained by subtracting the gain on the R side from the gain on the R side is smaller than in normal times by 2β. Next, when changing from this state to the communication state on the R side, each variable loss means A1S, A2S, A3S', A4S, A1
The losses of R, A2R, A3R', and A4R are β, α, α, 0, 0, 0, 0, and β _dB , respectively, under normal conditions. If the state changes from this state and the average voice call level at the 4-wire output point q exceeds the preset level by γ _dB , control information r1 is sent by DETR to cancel the excess level, and the variable The loss of loss means A1R and A4S is γ _dB , and the control information
s ₃ sets A3S' to a loss of α-2γ _dB . Therefore, the gains on the S and R sides increase in loss by β-γ and β+γ from the initial state, respectively, and when the call is switched to the S side again, the gains on the S and R sides increase by γ+β and γ-β from the initial state, respectively. When talking in a steady state, both S and R can talk with the same gain state, and the level difference between the talking side and the non-talking side is 2α in the initial state, and the S side and R
When the side is talking, it decreases by 2γ and 2β, respectively.

In the above example, control information γ3 causes A3
R' is set to a loss of α-2β, but even if A2R is controlled to a loss of α-β and A3R' is a loss of α-β,
The amount of loss that is reduced on the R side is the same, and at this time A3S' and A2S are in the gain state, but the possible loss values are calculated in advance for only A3S' (α-2β).
Alternatively, it is also possible to set A2S to (α-β) and A3S' to (α-β). At this time, when switching from the S side talking state to the R side, the loop gain can be kept constant and the level difference between sending and receiving calls can be reduced, making it useful as a bidirectional amplifier for incoming call transfer. be.

As described above, according to the present invention, an audio switch type two-wire bidirectional amplifier which can keep the loop gain constant and reduce the level difference between sending and receiving calls with a simple configuration is obtained and is useful.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the principle of a conventional audio switch type two-wire bidirectional amplifier, Fig. 2 is a block diagram showing an embodiment of the present invention, and Fig. 3 is a block diagram of the comparison control circuit of Fig. 2. FIG. 2 is a block diagram showing an example. HYB1, HYB2...2-4 wire conversion circuit, A1
S, A2S, A3S', A4S, A1R, A2R,
A3R', A4R...variable loss means, VAS, VAR
... Fixed gain circuit, CONT ... Comparison control circuit,
DETS, DETR……Audio average level detection circuit,
DETS, DETR……Audio average level detection circuit, 1
0, 11... decoder circuit, 12, 13... AND gate circuit, 14... voice call determination comparison 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. While controlling the gain/loss variable means, the loss of the second gain/loss variable means is reduced by the excess amount, and the speech signal level at the output end of the second gain/loss variable means exceeds a predetermined level. The second variable gain/loss means is controlled to cancel the excess amount when the loss occurs, and means is provided for reducing the loss of the first variable gain/loss means by the excess amount. 2-wire bidirectional amplifier.