JPH0481907B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a conference telephone device that is equipped with a speaker for amplifying the audio from the other party in the conference, a plurality of microphones, and an audio switch for preventing howling. More specifically, by using speakers and multiple microphones installed in the same room, conference participants in that room can communicate with participants in remote conference rooms connected by communication lines. The present invention relates to a conference telephone device that performs hands-free conference calls.

[Conventional technology]

In a conventional hands-free conference telephone device using a microphone and amplification speaker (hereinafter referred to as a speaker), an audio switch circuit is used to prevent howling caused by acoustic coupling between the microphone and the speaker. The level of the transmitted audio signal collected by the microphone is compared with the level of the received audio signal from the other party, and the loss is removed for the channel with the higher signal level, resulting in a steady gain. On the other hand, a loss is inserted into the channel with the lower signal level, and the system operates so that the loop gain of the system is 1 or less.

For this reason, when controlling the audio switch, we always compare the levels of the speaker's transmitted signal collected in the conference room and the received signal from the other party's conference room.
Either a transmitting state (a state in which there is no insertion loss on the transmitting side and an insertion loss on the receiving side) or a receiving state (a state in which there is an insertion loss on the transmitting side and no insertion loss on the receiving side). Control is performed so that the state is maintained.

That is, when the level of the transmitting signal is higher than the level of the receiving signal, the transmitting state is set, and in the opposite case, the receiving state is set.

This level comparison will be explained using FIG. 3. FIG. 3 is a block diagram for explaining the operating principle of the conference telephone device.

In the figure, 1 is a 2-wire to 4-wire conversion circuit, 2 is a line connected to the 2-wire side of this 2-wire to 4-wire conversion circuit 1, 3 is a microphone that collects the transmitting audio signal Ti, and 4 is this A variable gain amplifier receives the output of the microphone 3 as an input, 5 is a speaker, and 6 is a variable gain amplifier provided before the speaker 5. The output terminal of the variable gain amplifier 4 is connected to one of the 4-wire sides of the 2-wire to 4-wire conversion circuit 1, and the input terminal of the variable gain amplifier 6 is connected to the 4-wire side of the 2-wire to 4-wire conversion circuit 1.
It is connected to the local area on the line side. Note that Tc indicates the level detection point of the transmitting signal, and Rc indicates the level detection point of the receiving signal.

Next, the operation of level comparison in the apparatus shown in FIG. 3 will be explained.

First, at the received signal level detection point Rc,
The outgoing signal from the speech in the conference room is divided into a wrap-around signal Se that comes from the 2-wire to 4-wire conversion circuit 1 due to mismatching on line 2, and a receive signal Ri from the other conference room that is sent from line 2. will be detected.

Next, when the speaker in the conference room interrupts from the other conference room in the transmitting state when speaking, the level of the receiving signal Ri is the same as the transmitting signal that has been routed by the 2-wire to 4-wire conversion circuit 1. In other words, it must be higher than the level of the loop signal Se.

The level of this loop signal Se depends on the impedance balance between the 2-wire and 4-wire conversion circuit 1 and the circuit 2, but since the impedance of the connected lines is different,
The level of the loop signal Se is set assuming a standard line.

[Problem that the invention seeks to solve]

In the conventional conference telephone device using the audio switch circuit described above, the impedance of the line is fixed within a certain assumed range, so the level of the loop signal Se in the 2-wire to 4-wire conversion circuit 1 is also fixed. value.

Therefore, even under line conditions where the level of the loop signal Se is better than the expected value, interactivity due to interrupts is not improved at all, and the loop signal Se
Under a line where the level of the signal is worse than the expected value, there is a serious problem in that the transmitting signal causes the system to switch to the receiving state, causing blocking of the transmitting signal.

[Means for solving problems]

The conference telephone device according to the present invention performs control to automatically vary the circuit constants of the 2-wire to 4-wire conversion circuit using audio signals sent from the conference room to adapt to the line in use. The device is equipped with a control means.

[Effect]

The present invention includes a control means that can vary the constant of the Harance circuit in the 2-wire to 4-wire conversion circuit, calculates the amount of wraparound in the 2-wire to 4-wire conversion circuit by calculation, and varies the constant of the balance circuit. By doing so, control is performed to optimally match the line currently in use.

〔Example〕

Embodiments of the present invention will be described in detail below based on the drawings.

FIG. 1 is a block diagram showing an embodiment of a conference telephone apparatus according to the present invention, and FIG. 2 is a block diagram showing an example of a 2-wire to 4-wire conversion circuit used in the present invention.

First, in order to facilitate understanding of the present invention, this second
The diagram will be explained.

In this Fig. 2, 10 and 11 are transmitter terminals;
12, 13 are receiver terminals, 14, 15 are fixed impedances R ₁ , R ₂ , 16 are variable impedances R _f ,
17 is a transformer, and the line 2 is connected to the 2nd line side of the transformer 17. Further, T indicates the transmitting side, and R indicates the receiving side.

Next, the operation of the circuit shown in FIG. 2 will be explained.

First, the transmitting audio signal collected in the conference room passes through the transmitting channel, enters between the transmitting terminals 10 and 11 of the 2-wire to 4-wire conversion circuit, and is connected to the fixed impedance 14.
The signal is sent to the line 2 from the transformer 17 through the .

Also, the reception signal of the other party's conference room sent from line 2 is transmitted through variable impedance 1 through transformer 17.
6 and between the receiving terminals 12 and 13.

Here, when the transmission signal applied between the transmission terminals 10 and 11 satisfies the condition of balance of the bridge circuit, that is, R _f = R ₂ /R ₁ · R _L where, R _f : variable impedance R ₁ : Value of fixed impedance 14 R ₂ : Value of fixed impedance 15 R _L : If the conditions for impedance fluctuation are satisfied, the receiving terminal 1 of the receiving side R
It does not go around between 2 and 13. In other words, the transmitting signal does not go around to the receiving/receiving side.

Here, the values R ₁ of impedances 14 and 15,
Since R ₂ is fixed, matching can be achieved by correcting the change in impedance R _L for each line using the variable impedance R _f .

Now, the present invention is implemented as follows. In FIG. 1 showing an embodiment of the present invention, the same reference numerals as those in _{FIG .} an analog-to-digital conversion circuit (A/D conversion circuit) connected to each of 8 and converting the signals of the sending and receiving channels into digital data;
is a control circuit that receives the output of this analog-to-digital conversion circuit 7 as an input, and this control circuit 8 automatically changes the circuit constants of the 2-wire to 4-wire conversion circuit 1 using the audio signal sent from the conference room. It constitutes a control means that performs variable control to adapt to the line in use.

Next, the variable impedance control operation in the embodiment shown in FIG. 1 will be explained.

First, the level of the transmitting signal in the transmitting state is detected at the level detection point _C of the transmitting signal and the level detection point R _C of the receiving signal.

Then, the level of this detected signal is converted into a digital signal by the analog-to-digital conversion circuit 7, and is taken into the control circuit 8 as data.

Next, the control circuit 8 calculates the average value of the data detected at each level detection point T _C and R _C of the transmit signal and the receive signal, and calculates the difference between the two data.

Then, when the difference becomes small, that is, when the amount of wraparound in the 2-wire to 4-wire conversion circuit 1 becomes larger than the specified value, this control circuit 8
, the 2-wire to 4-wire conversion circuit 1 is controlled.

That is, while performing variable control of the impedance value R _f of the variable impedance 16 in FIG. 2 showing an example of the configuration of this 2-wire to 4-wire conversion circuit 1,
The amount of wraparound in the 2-wire to 4-wire conversion circuit 1 is detected.

That is, the transmitting and receiving signals at the level detection point _Tc of the transmitting signal and the level detection point of the receiving signal are converted into data by the analog-to-digital conversion circuit 7, and the control circuit 8 calculates the data. Control is performed until the difference exceeds the specified value.

Through this control, the impedance value R _f of the variable impedance 16 in FIG. 2 is varied,
The impedance value R _f that matches the impedance of each line can be calculated, and the amount of wraparound in the 2-wire to 4-wire conversion circuit 1 due to the difference in impedance of each line can be minimized.

〔Effect of the invention〕

As explained above, according to the present invention,
By converting the received signal into data using analog-to-digital conversion, performing calculations on the data, and controlling until the difference exceeds the standard,
It is possible to minimize the amount of interference caused by mismatching in the transmitting 2-wire to 4-wire converter circuit due to the impedance of the line to which the conference telephone device is connected, and it always maintains the switchability and interactivity between transmitting and receiving calls. Since it can be optimized, the practical effect is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a conference telephone device according to the present invention, FIG. 2 is a block diagram showing an example of a 2-wire to 4-wire conversion circuit used in the present invention, and FIG. 3 is a block diagram showing an example of a 2-wire to 4-wire conversion circuit used in the present invention. FIG. 3 is a block diagram for explaining the principle of operation. 1...2-wire-4-wire conversion circuit, 2...line, 3...
...Microphone, 4...Variable gain amplifier, 5...
Loudspeaker, 6... variable gain amplifier, 7... analog-to-digital conversion circuit, 8... control circuit.

Claims (1)

[Claims] 1. A conference telephone device that uses speakers and multiple microphones installed in the same room to allow conference participants in the same room to conduct handle-free conference calls with participants in remote conference rooms connected by communication lines. means for comparing the level of a transmission signal collected by the microphone, the level of a reception signal sent from the conference room on the other side, and the level of the reception signal sent from the conference room on the other side; In a conference telephone device having an audio switch circuit configured with a control circuit that performs control to reduce loss for the communication path with a higher signal level obtained by this means, the signal is transmitted from the conference room. A conference telephone device characterized by comprising a control means for automatically varying the circuit constants of a 2-wire to 4-wire conversion circuit using audio signals to adapt the circuit constants to the line in use. .