JPH0263355A - Loudspeaker telephone system - Google Patents

Abstract

PURPOSE:To devise the device such that a transmission signal is able to be reached to an opposite party even with a small transmission level by revising a changeover curve representing a crossover from a reception state into a transmission state to a lower position in the presence of reception noise. CONSTITUTION:Transmission loss and reception loss circuits are divided into two circuits 13, 14 and 15, 16 respectively, and a loss control circuit 17 is provided, which decreases the loss of the transmission loss circuits 13, 14 and increases the loss of the reception loss circuits 15, 16 in the reception state when the received noise level from a line 5 is larger than the reception threshold level. Then on each of the split transmission and reception loss circuits is controlled by the loss control circuit 17. Thus, even if the received noise is large or the transmission signal has a small level, the transmission signal without loss is sent to the opposite party.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a loudspeaker telephone device, and more particularly to a loudspeaker telephone device that enables appropriate transmission of calls.

(Prior Art) FIG. 3 is a block diagram showing an example of a conventional loudspeaker telephone device. The audio signal input from the microphone 1 is amplified by the transmitting amplifier 2, attenuated by the transmitting loss circuit 3, and then transmitted to the four-wire 5 via the hybrid circuit 4.
will be sent to.

On the other hand, the audio signal transmitted through the line 5 enters the reception loss circuit 6 via the hybrid circuit 4, is attenuated there, is amplified by the reception amplifier 7, and is output from the speaker 8.

The signal from the transmission loss circuit 6 is input to the transmission detection circuit 9. Further, the voice reception signal from the hybrid circuit 4 is input to the voice reception detection circuit 10 . Output signals from the transmitting call detection circuit 9 and the receiving call detection circuit 10 are input to the audio switch control circuit 11, respectively. The voice switch control circuit 11 receives the voice reception threshold level output from the voice reception threshold level setting circuit 12 . Voice switch control circuit 1
The control signal outputted by the transmitter 1 is input to the transmitting loss circuit 3 and the receiving loss circuit 6. The audio switch control circuit 11 is
The output levels of the transmitting speech detection circuit 9 and the receiving speech detection circuit 10 are compared, and the amount of loss of each of the transmitting speech loss circuit 3 and the receiving speech loss circuit 6 is controlled to increase or decrease in a reciprocal manner according to the result.

The microphone 1, the transmitting amplifier 2, the transmitting loss circuit 3, the hybrid circuit 4, and the line 5 form a transmitting path, and the line 5, the hybrid circuit 4, the receiving loss circuit 6, the receiving amplifier 7, and the speaker 8 A receiving channel is formed by

The receiving threshold level generated by the receiving threshold level setting circuit 12 is the input level on the line 5 at the point where the device changes from the transmitting state to the receiving state when there is no transmitting signal from the microphone 1.

Next, the operation of the circuit shown in FIG. 3 will be explained. First, line 5
When there is no reception signal from the microphone 1 and no transmission signal from the microphone 1, the input level from the line 5 is lower than the reception threshold level, so the audio switch control circuit 11 reduces the loss amount of the transmission loss circuit 3. Then, the loss amount of the reception loss circuit 6 is controlled to be large, and the circuit enters the transmission state. In this state, a reception signal is input from the line 5, the output level of the reception detection circuit 10 increases, and when the reception signal from the line 5 becomes higher than the reception threshold level set by the level setting circuit 12, the control circuit 11 Control is performed to increase the amount of loss in the loss circuit 3 and to decrease the amount of loss in the reception loss circuit 6. This puts the circuit in the receiving state.

When the reception signal is higher than the reception threshold level and there is also a transmission signal, the control circuit 11 compares the output levels of the transmission detection circuit 9 and the reception detection circuit 10, and depending on the comparison result, the transmission loss circuit 3 and the reception loss circuit 6 are increased/decreased reciprocally.

FIG. 4 is a diagram showing switching characteristics of the circuit of FIG. 3. The vertical axis indicates the transmitting level input from the microphone 1, and the horizontal axis indicates the receiving level input from the line 5.

Curve A shows the switching characteristics from the receiving state to the sending state, and curve B shows the switching characteristics from the sending state to the receiving state.

Now, in FIG. 4, it is assumed that a noise level of level N comes from line 5. Noise here means ambient noise that is input to the telephone receiver of the other party.

At this time, when there is no transmitting signal from the microphone 1, the output level of the receiving detecting circuit 10 is higher than the output level of the transmitting detecting circuit 9. Then, the loss amount of the reception loss circuit 6 is controlled to be small, and the reception state is established.

Here, in order to input a transmission signal from the microphone 1 and send the transmission signal to the line 5 at a level at which communication is possible, a level equal to or higher than point P in FIG. 4 is required. Above this level, the output level of the transmitting speech detection circuit 9 becomes higher than the output level of the receiving speech detection circuit 10, and the control circuit 11 reduces the loss amount of the transmitting speech loss circuit 3 and increases the loss amount of the receiving speech loss circuit 6. It is controlled so that it becomes a transmitting state.

The reason for reciprocally increasing and decreasing the amount of loss in the transmitting loss circuit 3 and the receiving loss circuit 6 is to prevent the transmission signal from passing through the hybrid circuit 4 to the receiving side and the acoustic coupling from the speaker 8 to the microphone 1. When considering, a microphone 1, a transmitting amplifier 2, a transmitting loss circuit 3, a hybrid circuit 4,
This is to ensure that the total gain of the loop of the receiving loss circuit 6, the receiving amplifier 7, the speaker 8, and the microphone 1 is 1 times or less in both the transmitting and receiving states. This prevents the device from oscillating.

(Problem to be Solved by the Invention) As described above, when the noise level N is higher than the reception threshold level R, the transmission state does not occur unless the input level of the microphone 1 is equal to or higher than the level P.

For example, consider a case where a call is made by voice using this loudspeaker telephone device, and a call is responded by voice.

A reception signal (voice call signal) from the other party is outputted from the speaker 8 via the line 5, the reception loss circuit 6, and the reception amplifier 7.

When answering a voice call output from the speaker 8 through the microphone 1, if the noise level N from the other party is lower than the receiving threshold level R, the transmitting state will occur when the receiving signal disappears, but the noise level N is the reception threshold level R
If it is larger, the transmitting state will not occur unless the microphone input level reaches point P or higher. In this case, the response from microphone 1 is sent to line 5 with a loss caused by transmission loss circuit 3.
go out to

In other words, if the caller is far away from the loudspeaker telephone device and the transmitting level is low, the transmitting state will not occur.
There is a problem in that the transmitting signal does not reach the other party.

The present invention has been made to solve these problems, and an object of the present invention is to provide a loudspeaker telephone device that allows a transmitted signal to reach the other party even if the transmitted voice level is low.

[Structure of the invention]

(Means for Solving the Problems) The present invention provides a transmission path for transmitting a transmission signal to a line via a first transmission loss circuit, and a transmission path for transmitting a reception signal from the line through a first reception loss circuit. The receiving path outputted from the speaker, the transmitting signal level, and the receiving signal level are compared with a predetermined receiving threshold level, and the first transmitting loss circuit and the first receiving loss circuit are controlled according to the results. In the loudspeaker telephone device equipped with a control circuit that reciprocally controls increase/decrease of respective losses, a second transmitting loss circuit and a receiving loss circuit are connected in series with the first transmitting loss circuit and the receiving loss circuit. The second transmitting loss circuit is provided in the talking path and the receiving path, and reduces the loss amount of the second sending loss circuit which is in the receiving state when the noise level from the line exceeds the receiving threshold. A loss control circuit is further provided to control the amount of loss to be large.

(Function) In the present invention, the transmitting loss circuit and the receiving loss circuit are divided into two, and the amount of loss in the transmitting loss circuit is determined in the receiving state when the noise level of the receiving voice from the line is higher than the receiving threshold level. A loss control circuit is provided that operates to reduce the amount of loss in the receiving loss circuit and increase the amount of loss in the receiving loss circuit, and one of the divided transmitting and receiving loss circuits is controlled by this loss control circuit. To send a transmission signal without loss to the other party even when the noise of the reception is large or the transmission signal is small.

(Example) Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention.
Components that are the same as those in the conventional circuit shown in the figure are given the same reference numerals, and detailed explanation thereof will be omitted.

In the present invention, the transmitting loss circuit and the receiving loss circuit are divided into first and second transmitting loss circuits 13.14 and first and second receiving loss circuits 16.15, respectively. A loss amount control circuit 17 is provided, and the outputs of the reception detection circuit 10 and reception threshold level setting circuit 12 as well as the output of the noise detection circuit 18 are inputted and compared, and a second
The amount of loss in the transmitting loss circuit 14 and the second receiving loss circuit 15 is controlled reciprocally.

FIG. 2 is a diagram showing the transmitting and receiving switching characteristics of the circuit of FIG. 1.

Next, the operation of the circuit shown in FIG. 1 will be explained. In Figure 2,
It is assumed that the same noise level as the conventional noise level N corresponding to FIG. 4 is input from the line 5. Noise level N
is detected by the noise detection circuit 18, and when there is no transmission signal from the microphone 1 and the reception signal is only a noise signal and there is no voice reception signal, the three inputs input to the loss amount control circuit 17 are: Since the level passing through the noise detection circuit 18 is the highest, the loss amount control circuit 17 reduces the loss amount of the second transmission loss circuit 14 and increases the loss amount of the second reception loss circuit 15. .

The control circuit 11 controls the first transmission loss circuit 13 and the first
The control of the reception loss circuit 16 is the same as the conventional one.

Therefore, in this case, the amount of loss in the first transmitting loss circuit 13 is increased, and the amount of loss in the first receiving loss circuit 16 is decreased.

In this state, since the amount of loss in the second transmission loss circuit 14 is small, the level input to the transmission loss circuit 9 is correspondingly large, and the voice switch control circuit 11 is in a state where it is easy to enter the transmission state. becomes.

In other words, the switching curve from the receiving state to the transmitting state is changed to curve C in Fig. 2, and the level difference between the P point and the Q point is equal to the level that reduces the amount of loss in the second transmitting loss circuit. .

Also, at this time, from microphone 1 through hybrid circuit 4,
In order for the total loop gain returned to the microphone l via the speaker 8 to be 1 times or less, the loss amount control circuit 17 needs to increase the second transmission loss by the amount of loss reduced by the second transmission loss circuit 14. It is necessary to add a loss to the reception loss circuit 15.

In this state, there is a loss in the reception output from the speaker 8, and the noise output is suppressed by that amount.

In this way, when the signal from line 5 is only a noise signal, the switching curve changes to curve C, and even a small microphone input level can result in a transmitting state.

Next, in this state, if a received voice signal comes in from the line 5 and its level is higher than the noise level, the output level of the received voice detection circuit 10 will be higher than the output level of the noise detection circuit 18, so the second By increasing the amount of loss in the transmission loss circuit 14 and decreasing the amount of loss in the second reception loss circuit 15, the switching curve can be returned to the position A.

As a result, the received signal output from the speaker 8 becomes a lossless received signal. When the received voice signal disappears and only noise remains, the switching curve returns to line C.

〔Effect of the invention〕

As explained above, in the present invention, when there is reception noise, the switching curve for switching from the receiving state to the speaking state is changed to a lower position than in the past, so there is an advantage that the transmitting state is less likely to occur than in the past. be.

Therefore, even if the person speaking is far away from the loudspeaker telephone device and the transmission level is low, the transmission signal will reach the other party without loss.

Further, when there is only noise, the noise level output from the speaker is suppressed due to loss, so there is an advantage that the noise is no longer harsh on the ears of the caller.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a switching characteristic diagram in the block diagram of FIG. 1, and FIG.
The figure is a block diagram showing an example of a conventional loudspeaker telephone device.
The figure is a switching characteristic diagram in the block diagram of FIG. 3. 1... Microphone, 2... Sending amplifier, 4... Hybrid circuit, 5... Line, 7... Receiving amplifier,
8...Speaker, 9...Talking detection circuit, 10...
Receiving call detection circuit, 11...Voice switch control circuit, 12
... Reception threshold level setting circuit, 13... First transmission loss circuit, 14... Second transmission loss circuit, 15...
Second reception loss circuit, 16... first reception loss circuit,
17... Loss amount control circuit, 18... Noise detection circuit.

Claims (1)

[Claims] A transmission path for transmitting a transmission signal to a line via a first transmission loss circuit, a reception path for outputting a reception signal from the line from a speaker via a first reception loss circuit, and a transmission signal level. and a reception signal level with a predetermined reception threshold level, and a control circuit that reciprocally controls the amount of loss of each of the first transmission loss circuit and the first reception loss circuit according to the result. In the loudspeaker telephone device, a second sending loss circuit and a second receiving loss circuit are provided in the sending path and the receiving path in series with the first sending loss circuit and the receiving loss circuit, and When the noise level from the line exceeds the reception threshold level, the loss of the second transmission loss circuit in the receiving state is reduced and the loss of the second reception loss circuit is controlled to be large. A loudspeaker telephone device characterized by being provided with a control circuit.