JPH0693709B2 - Telephone - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a telephone capable of conference call in which two or more telephone lines are simultaneously connected.

2. Description of the Related Art In recent years, an increasing number of devices can connect two or more telephone lines to one telephone. In such a telephone, first use one telephone line to talk to the other party, then use the other telephone line to call a second party, and three people including the person themselves talk at the same time. There is a telephone that can make (so-called conference call).

Hereinafter, a conventional conference call circuit having a telephone line as described above will be described with reference to the drawings.

FIG. 2 shows a configuration of a main part of a conventional telephone capable of conference call. In FIG. 2, 1 and 2 are connection terminals to the first telephone line, and 3 and 4 are connection terminals to the second telephone line. Reference numeral 5 is a first telephone line selection switch operated when making a call with the first telephone line,
It has two contacts 5a, 5b. Reference numeral 6 denotes a second telephone line selection switch which is operated when making a call with the second telephone line, and has two contacts 6a and 6b, and is mechanically connected to the first telephone line selection switch 5. They are interlocked and configured to operate reciprocally. Reference numeral 7 denotes a conference call switch which is operated when the other party of the first telephone line, the other party of the second telephone line, and the caller of the apparatus simultaneously talk with each other, and four contact points 7a, 7b, 7c, Composed of 7d. Reference numeral 8 is a low frequency transformer, which is a winding connected to the first telephone line.
8a, a winding 8b connected to the second telephone line, and a secondary winding 8c. 9 is a bridge diode, 10
Is a dial signal transmission circuit for transmitting a dial signal to the telephone line, 11 is a telephone circuit network composed of a dial button (not shown) and a control circuit connected to the dial signal transmission circuit 10, 12 is a transistor, and 13 is a zener diode. ,
Reference numeral 14 is a bias resistor connected between the collector and base of the transistor 12, 15 is a coupling capacitor, and 16, 17, 18 are impedance network networks having impedances Z1, Z2, and Z3, respectively. Reference numeral 19 is a transmission signal input terminal, 20 is a reception signal output terminal, and 21 is a common terminal. Further, 22 is a hook switch, which contacts when a handset (not shown) is lifted.
22a and 22b are configured to be turned on. or,
Reference numerals 25 and 26 are switches operated when holding the first and second telephone lines, respectively, and resistors 23 and 24 are connected to the respective telephone lines.

Regarding the telephones that are capable of conference calls configured as above,
The operation will be described below.

First, the case of making a call to the first telephone line will be described. When the first telephone line selection switch 5 is operated, its contacts 5a and 5b are closed. When the handset (not shown) is lifted, the contacts 22a and 22b of the hook switch 22 are turned on, and the current of the first telephone line is the contact of the hook switch 22.
22b, bridge diode 9, dial signal transmission circuit 1
0, flows to the telephone network 11 via the power switch 14. In addition, a part of the current also flows through the Zener diode 13 to generate a constant voltage (approximately 5V), which is the telephone network.
The operating voltage is 11. When a dial button (not shown) is operated, the dial signal transmitting means 10 interrupts the line current and transmits a dial pulse to the first telephone line. When connected to the other party, a handset (not shown) connected to the telephone network 11 can make a call. Here, the operation of the side soundproof circuit composed of the transistor 12 and the impedance networks 16 to 18 will be described. Now the transistor 12 has a resistor 14
The base is biased by and is in operation. When a transmitter signal of a handset (not shown) is applied to the transmitter signal input terminal 19, an output signal appears in the collector of the transistor 12, and the secondary side winding 8c of the low frequency transformer 8 to the office line side winding. It is transmitted to 8b, and a transmission signal is transmitted to the first telephone line. In addition, the reception signal from the first telephone line is transmitted from the winding 8b on the station line side of the low frequency transformer 8 to the winding on the secondary side.
8c, taken out from the connection point of the impedance networks 16 and 17, and applied to the handset receiver (not shown) for listening. On the other hand, the sneak of the transmission signal to the reception signal (so-called side tone) is expressed as Z1: Z2 = ZL: Z3, where ZL is the impedance when the telephone line is viewed from the secondary side of the low-frequency transformer. When is established, it becomes zero. Therefore, the circuit constants that compose the impedance network 16 to 18 satisfy the above relational expression (actually, the impedance of the telephone line changes depending on the state of the line, so that the side sound attenuation that can be satisfied within that range is To be obtained).

Here, a case where the first telephone line is put on hold and another person is called by the second telephone line to make a call will be described. First, the first telephone line is put on hold. When the first hold switch 25 is operated to close the contact, the resistor 23 is connected to the telephone line. Next, when the second telephone line selection switch 6 is operated, in response to this, the contacts 5a and 5b of the first telephone line selection switch 5 are opened, and the telephone network 11 and the like are disconnected from the first telephone line. However, since the resistor 14 is connected, the first telephone line will not be disconnected. Also, the second
The contacts 6a and 6b of the telephone line selection switch 6 are turned on, and since the handset is still lifted, the hook switch 22 is turned on so that the second telephone line is closed. Second telephone line current is hook switch 22
Via the contact 22b, the bridge diode 9, the dial signal transmission circuit 10, and the power source changeover switch 14
Flow to. In addition, a part of the current also flows through the Zener diode 13 to generate a constant voltage (approximately 5V), which becomes the operating voltage of the telephone network 11. When a dial button (not shown) is operated, the dial signal transmitting means 10 interrupts the line current and transmits a dial pulse to the second telephone line. When connected to the other party, you can talk using a handset (not shown). Next, description will be made on a case where three parties talk with each other on the first and second telephone lines (so-called conference call). When the conference call switch 7 is operated, the contacts 7a to 7d are turned on, the winding 8a of the low frequency transformer 8 is the first telephone line, the winding 8b is the second telephone line, and the winding 8c is the telephone. It is connected to the network 11 and the contacts 25 and 26 of the hold switch open and the resistor 23
And 24 are respectively disconnected from the telephone line, and the current of each telephone line flows through the windings 8a and 8b of the low frequency transformer 8 to maintain the closed state. On the other hand, the voltage (approximately 5V) generated between the terminals of the Zener diode 13 is applied to the telephone network 11,
The current for operation is supplied. When a transmitter signal of a handset (not shown) is applied to the transmitter signal input terminal 19, an output signal appears in the collector of the transistor 12, and the secondary side winding 8c of the low frequency transformer 8 to the office line side winding. The transmission signal is transmitted to 8a and 8b, and the transmission signal is transmitted to the first and second telephone lines. In addition, the reception signal from the first telephone line is transmitted from the winding 8a on the office line side of the low frequency transformer 8 to the winding 8c on the secondary side, is taken out from the connection point of the impedance networks 16 and 17, and is not shown in the handset. It is applied to the handset of No. 2 and can be listened to, and further transmitted to the winding 8b on the office line side and also transmitted to the second telephone line. The reception signal from the second telephone line is transmitted from the winding 8b to the electromagnetically coupled secondary winding 8c, taken out from the connection point of the impedance networks 16 and 17, and applied to the handset receiver not shown. Can be listened to, and the winding point on the station line side
It is transmitted to 8a and is also transmitted to the first telephone line. More information is transmitted to the second telephone line and the telephone network 11, respectively. The conference call can be performed as described above.

Problems to be Solved by the Invention However, in the above-mentioned configuration, since the impedance seen from the secondary side of the low-frequency transformer is connected to two telephone lines during a conference call, only a single telephone line is called. Compared to the time when it is being performed (it is reduced to about 1/2), it largely deviates from the above relational expression, and the volume of the sidetone increases. As a result, the user cannot easily speak because his / her own voice is loud, and because of this, the user tends to speak in a small voice, and the volume transmitted to the other party becomes low. In addition, when the handset is placed face down on a desk or on the side of a wall, there is a problem that a side tone may generate a sound.

The present invention has been made in view of the above-mentioned prior art, and it is possible to keep sidetones at an almost constant optimum volume regardless of the number of connected telephone lines, thereby making it difficult to talk or to make a ringing sound. The purpose of the present invention is to provide a telephone that can be used for comfortable conference calls without any loss.

Means for Solving the Problems In order to solve the above-mentioned conventional problems, the present invention provides a plurality of impedance circuits and a telephone line selection switch for selecting a single or a plurality of telephone lines to be connected. A switch for switching the impedance network inserted between the input end of the transmission signal and the output end of the reception signal is provided.

Operation The present invention can insert an impedance circuit network that reduces sidetone even if the number of connected telephone lines is changed by the above configuration.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a configuration of a main part of a telephone capable of conference call according to the present embodiment. In FIG. 1, 1 and 2 are connection terminals to the first telephone line, 3 and 4 are connection terminals to the second telephone line, and 5 is an operation for making a call with the first telephone line. It is the first telephone line selection switch
It has one contact 5a, 5b. Reference numeral 6 denotes a second telephone line selection switch which is operated when making a call with the second telephone line, and has two contacts 6a and 6b, and is mechanically connected to the first telephone line selection switch 5. They are interlocked and configured to operate reciprocally. Reference numeral 7 is a conference call switch which is operated when the other party of the first telephone line, the other party of the second telephone line, and the caller of the present apparatus make a call at the same time, and five contact points 7a, 7b, 7c, It is composed of 7d and 7e. 8
Is a low-frequency transformer, which is composed of a winding 8a connected to the first telephone line, a winding 8b connected to the second telephone line, and a winding 8c on the secondary side. 9 is a bridge diode,
Reference numeral 10 is a dial signal transmitting circuit for transmitting a dial signal to the telephone line, 11 is a telephone circuit network composed of a dial button (not shown) and a control circuit connected to the dial signal transmitting circuit 10, 12 is a transistor, and 13 is a zener. Diode, 14 is a bias resistor connected between the collector and base of transistor 12, 15 is a coupling capacitor, 16a, 16
Reference numerals b, 17 and 18 are impedance networks whose impedances are Z1, Z1, Z2 and Z3, respectively. Reference numeral 19 is a transmission signal input terminal, 20 is a reception signal output terminal, and 21 is a common terminal.
Reference numeral 22 is a hook switch, which is configured so that the contacts 22a and 22b are turned on when a handset (not shown) is lifted. In addition, 26 and 26 are switches operated when holding the first and second telephone lines, respectively.
3 and 24 are connected to each telephone line.

Regarding the telephones that are capable of conference calls configured as above,
The operation will be described below.

First, the case of making a call to the first telephone line will be described. When the first telephone line selection switch 5 is operated, its contacts 5a and 5b are closed. When the handset (not shown) is lifted, the contacts 22a and 22b of the hook switch 22 are turned on, and the current of the first telephone line is the contact of the hook switch 22.
22b, bridge diode 9, dial signal transmission circuit 1
0, flows to the telephone network 11 via the power switch 14. In addition, a part of the current also flows through the Zener diode 13 to generate a constant voltage (approximately 5V), which is the telephone network.
The operating voltage is 11. When a dial button (not shown) is operated, the dial signal transmitting means 10 interrupts the line current and transmits a dial pulse to the first telephone line. When connected to the other party, a handset (not shown) connected to the telephone network 11 can make a call. Here, the operation of the side soundproof circuit composed of the transistor 12 and the impedance networks 16 to 18 will be described. Now the transistor 12 has a resistor 14
The base is biased by and is in operation. When a transmitter signal of a handset (not shown) is applied to the transmitter signal input terminal 19, an output signal appears in the collector of the transistor 12, and the secondary side winding 8c of the low frequency transformer 8 to the office line side winding. It is transmitted to 8b, and a transmission signal is transmitted to the first telephone line. In addition, the reception signal from the first telephone line is transmitted from the winding 8b on the station line side of the low frequency transformer 8 to the winding on the secondary side.
8c, taken out from the connection point of the impedance networks 16 and 17, and applied to the handset receiver (not shown) for listening. On the other hand, the sneak of the transmitted signal to the received signal (so-called sidetone) is Z1: Z2 = ZL: Z3 (1), where ZL is the impedance when the telephone line is viewed from the secondary side of the low-frequency transformer. It becomes zero when the relational expression Therefore, the circuit constants that compose the impedance network 16 to 18 satisfy the above relational expression (actually, the impedance of the telephone line changes depending on the state of the line, so that the side sound attenuation that can be satisfied within that range is To be obtained).

Here, a case where the first telephone line is put on hold and another person is called by the second telephone line to make a call will be described. First, the first telephone line is put on hold. When the first hold switch 25 is operated to close the contact, the resistor 23 is connected to the telephone line. Next, when the second telephone line selection switch 6 is operated, in response to this, the contacts 5a and 5b of the first telephone line selection switch 5 are opened, and the telephone network 11 and the like are disconnected from the first telephone line. However, since the resistor 23 is connected, the first telephone line is never disconnected. Also, the second
The contacts 6a and 6b of the telephone line selection switch 6 are turned on, and since the handset is still lifted, the hook switch 22 is turned on so that the second telephone line is closed. Second telephone line current is hook switch 22
Via the contact 22b, the bridge diode 9, the dial signal transmission circuit 10, and the power source changeover switch 14
Flow to. In addition, a part of the current also flows through the Zener diode 13 to generate a constant voltage (approximately 5V), which becomes the operating voltage of the telephone network 11. When a dial button (not shown) is operated, the dial signal transmitting means 10 interrupts the line current and transmits a dial pulse to the second telephone line. When connected to the other party, you can talk using a handset (not shown). Next, description will be made on a case where a call is made with the other parties of the first and second telephone lines to three persons (so-called conference call). When the conference call switch 7 is operated, the contacts 7a to 7d and 7e are turned on, and the winding 8a of the low frequency transformer 8 is the first telephone line, the winding 8b is the second telephone line, and the winding 8c. Telephone network 11
Connected to. Also, the contacts 25 and 26 of the hold switch are opened, the resistors 23 and 24 are disconnected from the telephone line, respectively, and the current of each telephone line flows through the windings 8a and 8b of the low frequency transformer 8 to maintain the closed state. . On the other hand, a voltage (approximately 5V) generated between the terminals of the Zener diode 13 is applied to the telephone network 11, and a current for operation is supplied. The transmission signal is transmitted from the transmitter of the handset (not shown) to the transmission signal input terminal 19
The output signal appears at the collector of the transistor 12 when applied to the secondary side winding 8c of the low frequency transformer 8
The transmission signal is transmitted to 8a and 8b, and the transmission signal is transmitted to the first and second telephone lines. In addition, the reception signal from the first telephone line is transmitted from the winding 8a on the office line side of the low frequency transformer 8 to the winding 8c on the secondary side, is taken out from the connection point of the impedance networks 16 and 17, and is not shown in the handset. It is applied to the handset of No. 2 and can be heard, and further transmitted to the winding 8b on the office line side and also transmitted to the second telephone line. The reception signal from the second telephone line is transmitted from the winding 8b to the electromagnetically coupled secondary winding 8c, taken out from the connection point of the impedance networks 16 and 17, and applied to the handset receiver not shown. Then, it is transmitted to the winding 8a on the office line side and transmitted to the first telephone line.
Further, since the fifth contact 7e of the conference call switch is turned on, the impedance network 16b is connected in parallel with the impedance network 16a. For this reason, (Z1) circuits with almost the same impedance are connected in parallel, so the combined impedance is approximately 0.5Z1. Therefore, the above relational expression (1) becomes 0.5Z1: Z = ZLa: Z3 (2), and the impedance of the line that can obtain the optimum side sound attenuation in this state is ZLa = 0.5 (Z1 Z3 / Z2) (3). On the other hand, from equation (1), ZL = (Z1 ・ Z3 / Z2) (4), so ZLa = 0.5ZL (5), and the impedance of the telephone line seen from the secondary side of the low-frequency transformer 8 is 1 When it drops to / 2, the optimum sidetone attenuation will be obtained. On the other hand, during a conference call, two telephone lines with almost the same impedance are connected in parallel in terms of AC, so the impedance of the telephone line seen from the secondary side of the low-frequency transformer 8 is about 1/2. It is falling. Therefore, the amount of sidetone attenuation is kept optimal, and a call can be made in the same manner as a normal call. The conference call can be performed as described above.

EFFECTS OF THE INVENTION The present invention provides a plurality of impedance circuits between an input end of a transmission signal and an output end of a reception signal according to the selection of a telephone line selection switch for selecting a single or a plurality of telephone lines to connect. Since it has a switch for switching the impedance circuit network to be inserted, if the number of connected telephone lines changes, the impedance circuit network will also switch, keeping the sidetone almost constant and preventing ringing. You can

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a main part of a telephone capable of conference call according to the present invention, and FIG. 2 is a circuit diagram showing a main part of a conventional telephone. 1, 2 ...... Connection terminal to the first telephone line 3, 4 ...... Connection terminal to the second telephone line 5 ...... First telephone line selection switch 6 ...... Second field telephone line selection switch 7 ... Conference call switch 8 Low frequency transformer 9 Bridge diode 10 Dial signal sending circuit 11 Telephone network 12 Transistor 13 Zener diode 14, 23, 24 Resistor 15 Capacitor 16a , 16b, 17, 18 ...... Impedance circuit network 19 ...... Transmit signal input terminal 20 …… Receive signal output terminal 21 …… Common terminal 22 …… Hook switch 25, 26 …… Hold switch

Claims (1)

[Claims] 1. A selection switch for selecting a single or a plurality of telephone lines to be simultaneously connected, and a coupling means for coupling the telephone line selected by the selection switch to an output end of a reception signal and an input end of a transmission signal. A plurality of impedance circuits inserted between the input end of the transmission signal and the output end of the reception signal, and between the input end of the transmission signal and the output end of the reception signal according to the switching of the selection switch. And a switch for switching the impedance network to be inserted in the telephone