JPH04124997A - Key telephone system - Google Patents

Abstract

PURPOSE:To prevent from feeling a sense of incompatibilitly by providing a control means outputting a control signal against a sidetone generation means to operate the sidetone generation means and generating the sidetone in an extention communication similar to the one in a trunk line communication. CONSTITUTION:When a key telephone system 22 is in an extension calling, a control circuit 18b recognizes it and closes an analog switch 37 by its control signal. A part of a transmitting signal outputted from a transmitting amplifier 17 is supplied through a sidetone generation circuit and input resistance R3 to the inversion input terminal of an arithmetic amplifier 140 as the sidetone. A part of the above-mentioned transmitting signal is added to a receiving signal supplied from a codec 13 through resistance R4. Thus, the sneak path of the sidetone is generated similarly to the trunk line communication of the key telephone system 22 even at the time of the extension calling of the key telephone system 22, there is no difference in the feeling of communication between the trunk line communication time and the extension communication time.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Field of Application) The present invention generally relates to a button telephone device, and particularly relates to a plurality of key telephone devices each having a configuration in which a sending signal and a receiving signal are processed independently. The present invention relates to a button telephone device connected to a base.

(Prior Art) FIG. 3 is a block diagram showing the overall configuration of a conventional key telephone device.

The following explanation will explain the operation of each part of the button telephone device having the configuration shown in FIG. , and the operations of each part when the speaker of the key telephone 22 attempts to make a telephone call over a central office line.

First, the operation of each part when the speaker of the key telephone 22 makes an extension call will be considered. When the speaker of the button telephone 22 takes the handset off-hook and then presses the extension key switch 19, the extension key switch 1
A signal indicating that a pressing operation has been performed from 9 is sent to the control circuit 18.
The a1 ping pong transmission circuit 12 is provided to the central control circuit 9 through a button telephone interface unit 8 containing a ping pong transmission circuit. When the central control circuit 9 receives the above signal, it recognizes that the extension key switch 19 has been pressed and sends an LED lighting control signal to the control circuit 18a through the above path. When the control circuit 18a receives the above I and ED lighting control signals, it lights up an extension key switch LED (not shown). In this state, when the button on the dial pad 21 is pressed by the speaker (that is, when a specific extension number: in this case, the extension number corresponding to the button telephone 23 is dialed),
A dial signal resulting from this suppression operation is given to the control circuit 18a. This dial signal is then transmitted to the control circuit 18a.
The dial signal is then sent to the central control circuit 9 through the above-mentioned route, and the central control circuit 9 recognizes that a call is being made from the key telephone 22 to the key telephone 23 based on this dial signal. The central control circuit 9 thereby notifies the key telephone 23 of the incoming call. That is, the central control circuit 9 provides a data signal indicating that there is a call from the button telephone 22 to the control circuit 30 through the button telephone interface unit 10, which includes a ping pong transmission circuit, and the ping pong transmission circuit 24. When the control circuit 30 receives this data signal, it turns on the extension key switch LED (
The button telephone 23
The speaker is informed that an extension call is being made from the key telephone 22. In response to this notification, when the speaker of the key telephone 23 takes the handset off the hook and presses the extension key switch 32, a signal generated by this pressing operation is given to the control circuit 30 as a response signal to the notification. This signal is applied from the control circuit 30 to the central control circuit 9 through the above path in the opposite direction.

When the central control circuit 9 receives the above signal, it transmits the control circuit 18a through the button telephone interface unit 8, etc.
A signal is given to notify that a response signal has been sent from the control circuit 30a side of the button telephone 23. Then, the time switch 7 is controlled to enable extension calls between the key telephones 22 and 23.

On the other hand, when the speaker of the key telephone 22 makes a telephone call over the central office line, the operations of each part are as follows.

When the speaker of the button telephone 22 takes the handset off-hook and then presses the central line key switch 20, a signal indicating that the central line key switch 20 has been suppressed is transmitted to the control circuit 18a1, the ping-pong transmission circuit 12, and the button telephone It is provided to the central control circuit 9 through the interface unit 8 and the like. When the central control circuit 9 receives the above signal, it recognizes that the central line key switch 20 has been suppressed, and sends out an LED lighting control signal through the above path to the control circuit 18a, and also sends the LED lighting control signal to the central line interface circuit. In order to cause the station line interface unit 6 to acquire the station line, a station line acquisition command signal is output to the control circuit 35 of the station line interface unit 6. The central control circuit 9 performs the above-mentioned control and also controls the time switch 7 to allocate time slots for the key telephone 22 to make a telephone call over the central office line. The control circuit 18a controls the LED
When the lighting control signal is input, the LED for the central line key switch
(not shown) lights up. In this state, when a button on the dial pad 21 is pressed by the speaker (that is, when an arbitrary office line number is dialed), a dial signal resulting from this pressing operation is given to the control circuit 18a.

This dial signal is sent from the control circuit 18s to the central control circuit 9 through the above-mentioned path. In response to this diamond small signal, the central control circuit 9 outputs a control signal to the control circuit 35 of the office line interface unit 6 to cause the office line interface unit 6 to transmit a dial pulse to the office line 1. When the dial pulse output from the central office line interface unit 6 is given to the central office exchange (not shown) through the central office line 1, the central office exchange (not shown) sends a message to the other party's terminal (not shown) corresponding to this dial pulse. Outputs a calling signal.

When the speaker of this terminal takes the handset off-hook, the central office exchange (not shown) recognizes this and sends a DC voltage signal with the polarity reversed to the other party (not shown) to notify that it has been connected. Main device 11 through line 1
Send to. As a result, a state is established in which a central office line call can be made between the key telephone 22 and the other party's terminal (not shown). Note that, contrary to the above, when a dial pulse for calling the key telephone 22 is sent from the other party's terminal (not shown) to the central office exchange (not shown), the dial pulse is sent from the central office exchange (not shown) to the main unit through the central office line 1] A calling signal is sent to 1. When the central office line interface circuit 33 detects the arrival of this calling signal and supplies the incoming call detection signal to the central control circuit 9 through the control circuit 35, the central control circuit 9 sends an incoming call to the control circuit 18g through the button telephone interface unit 8, etc. , sends out a data signal indicating that there is a call from the central office line side. Along with this, the central control circuit 9
By controlling the time switch 7, the key telephone 22 allocates a time slot for making a telephone call over the central office line. When the speaker of the button telephone 22 takes the handset off-hook, the received voice signal transmitted through the central office line 1 is transferred to the 2-wire 4-wire conversion circuit 2, the received receiver amplifier 3.
, the codec 5, the time switch 7, the button telephone interface unit 8, the ping-pong transmission circuit 12, the codec 13, and the receiver amplifier 14, and are transmitted to the receiver 15 of the handset.

Each part of the configuration shown in FIG. 3 that was not mentioned in the above description will be described in detail later.

(Problems to be Solved by the Invention) In the button telephone device having the above configuration, when the key telephone 22 (or the button telephone 23) is in the state of talking on a central office line, the 2-wire/4-wire conversion circuit 2 of the main device 11 , a part of the transmitting signal output from the transmitter 16 (or transmitter 27) goes around the receiving signal from the other party's terminal transmitted through the office line 1, which is an analog line, and is output as sidetone to the receiver. 15 (or the receiver 26). On the other hand, when the key telephone 22 (or the key telephone 23) is in an extension call state, the transmitter 1
The transmit signal output from the receiver 6 (or the receiver 27) and the receiver signal output from the receiver 15 (or the receiver 26) are each processed independently in the codec 13,
transmitted. Therefore, as in the case of a telephone call over a central office line, part of the transmitting signal output from the handset 16 (or handset 27) is output from the other party's key telephone to the handset 15 (or handset 26). Sidetone at a level that does not creep into the signal and is therefore clearly perceptible to the caller, with the exception of negligible sidetone due to acoustic effects between the handset's transmitter and receiver. does not occur.

In this way, even if the same button telephone is used, sidetone is generated when talking to a central office line, but no sidetone is generated when talking to an extension line. There is a problem in that the feeling of talking differs depending on whether there is sidetone or not, and this makes the person making the call feel uncomfortable.

Therefore, the present invention has been made to solve the above-mentioned problems, and its purpose is to provide a button telephone to which a plurality of button telephones are connected, each of which is configured to process a sending signal and a receiving signal independently. By making the device produce the same sidetone during an extension call as when talking to a central office line, there will be no difference in the feel of the call between the office line call and the extension call, thereby making the caller feel more comfortable. To provide a button telephone device that does not make you feel uncomfortable.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a plurality of extension telephones each having a configuration in which transmitting signals and receiving signals are processed independently, and which are connected to a central office line. In the button telephone device, the button telephone device includes a main device for setting an extension call for connecting the plurality of extension telephones to each other and a central office line call for connecting the extension telephones to a central office line, wherein each of the extension telephones has: a sidetone generating means that operates in response to a control signal given from the outside and causes a part of the sending signal transmitted from the extension telephone to be included in the receiving signal received by the extension telephone; and a control means for operating the side sound generation means by outputting a control signal to the side sound generation means when the side sound generation means is in the state.

(Function) In the above configuration, the sidetone generating means is operated by a control signal given from the outside, and passes a part of the transmitting signal transmitted from the extension telephone to the receiving signal received by the extension telephone. The control means operates the sidetone generation means by outputting a control signal to the sidetone generation means when each extension telephone is in an extension call state. In a pushbutton telephone device to which a plurality of extension telephones are connected, the transmitting signal and the receiving signal are processed independently, and the same sidetone as that during the central office telephone call is generated during the extension telephone call. By doing so, there is no difference in the feel of a call between a central office line call and an extension call, so that the caller no longer feels uncomfortable.

(Example) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram showing the overall configuration of a general key telephone device to which an embodiment of the present invention is applied.

The key telephone device shown in FIG. 2 includes a plurality of key telephones each having a configuration in which a sending signal and a receiving signal are processed independently.

The internal configuration of the key telephone will be detailed later. As is clear with reference to FIG. 2, a key telephone device generally includes a main device 11 and a plurality of key telephones 22, 23 connected to the main device 11 (in FIG. 2, for convenience of illustration). , only two units are listed). The main device 11 includes a central office line interface unit 6 connected to the central office line 1, a button telephone interface unit 8 provided corresponding to the button telephone 22, and a button telephone set corresponding to the button telephone 23. It comprises an interface unit 10 and a central control circuit 9 which brings under control the central office line interface unit 6 and the button telephone interface unit 8.10.

The above configuration will be described in more detail as follows.

The office line interface unit 6 is provided for connecting the office 1i1 and the button telephone device, and includes the office line interface circuit 33, transformer 34.2, etc.
It includes a four-wire conversion circuit 2, a receiving amplifier 3, a transmitting amplifier 4, a codec 5, and a control circuit 35. Under the control of the control circuit 35, the office line interface circuit 33 detects the arrival of a calling signal from the office line, captures the office line, and sends out a dial pulse signal. transformer 3
4 is connected between the office line interface circuit 33 and the 2-wire/4-wire conversion circuit 2. The 2-wire 4-wire conversion circuit 2 is
It receives an analog signal (receiving voice signal, etc.) provided from the office line 1 through the office line interface circuit 33 and transformer 34 and outputs it to the receiving amplifier 3. The 2-wire 4-wire conversion circuit 2 also receives an analog signal (such as a transmitted audio signal) output from the transmitting amplifier 4 and converts it into a transformer 3.
4 and the office line interface circuit 33 to the office line 1. The receiving amplifier 3 is
It receives and amplifies an analog signal (received voice signal, etc.) given from the four-wire conversion circuit 2, and then outputs it to the codec 5. On the other hand, the transmitting amplifier 4 receives an analog signal (such as a transmitting audio signal) output from the codec 5, amplifies it, and then outputs the signal to the 2-wire/4-wire conversion circuit 2. The codec 5 receives the analog signal (received audio signal, etc.) amplified by the receiving amplifier 3 and digitizes it.
Convert to CM signal. Then, this PCM signal is
The time switch 71 outputs through the time slot assigned on the CM highway. The codec 5 also receives the PCM signal output from the time switch 7 through time slots assigned on the outgoing PCM highway. Then, this PCM signal is converted into an analog signal (
After converting the signal into a transmitting voice signal (such as a transmitting voice signal), the signal is output to a transmitting amplifier 4. The control circuit 35 is placed under the control of the central control circuit 9 together with the above-mentioned time switch 7. That is, the control circuit 35 sends and receives control signals to and from the central control circuit 9 through the data highway. When the control circuit 35 receives a control signal to capture the office line 1 from the central control circuit 9 via the data highway, it controls the office line interface circuit 33 to capture the office line 1 in accordance with this control signal. When the central office line interface circuit 33 detects that a paging signal has arrived from the central office line 1, the control circuit 35 transmits a data signal indicating that the paging signal has arrived to the central control circuit via the data highway. It is designed to output to 9.

The time switch 7 consists of a call memory, a counter circuit, and the like. By multiplexing, separating, or phase converting the signals output through the plurality of input PCM highways under the control of the central control circuit 9, time division is performed between the corresponding input PCM highways and output PCM highways. It is designed to be connected in an exchange. That is, the time switch 7 receives the PCM signal given from the time slot allocated on the outgoing PCM highway, and transmits the signal through the outgoing time slot allocated on the PCM highway to form the button telephone interface unit 8. Output to ping pong transmission circuit. The time switch 7 also receives the PCM signal output from the Bing Bong transmission circuit of the button telephone interface unit 8 through the time slot assigned on the incoming PCM highway, and transmits it through the time slot assigned on the outgoing PCM highway. It is designed to output to codec 5. The time switch 7 further transmits the PCM signal output from the codec 5 through the time slots assigned on the incoming PCM highway and the time slots assigned on the outgoing PCM highway, making up the button telephone interface unit 10. The codec codecs the PCM signal output from the Bing Bong transmission circuit constituting the key telephone interface unit 10 through the time slots assigned to the input PCM highway and the time slots assigned to the output PCM highway. Give to 5.

The central control circuit 9 includes the above-mentioned time switch 7,
Each part forming the central office line interface unit 6,
Button telephone interface unit 8.10 (As mentioned above, for convenience of illustration, only two button telephones are shown in FIG. 2, so two button telephone interface units are provided corresponding to each button telephone. The various parts constituting the main device 11 of the key telephone device, such as the various parts constituting the main unit 11 (only shown in the figure), are placed under its control. As already explained, the central control circuit 9 communicates with the control circuit 35 through the data highway, controlling signals for acquisition of the central office line, control signals for transmitting dial pulse signals, and detecting incoming call signals from the central office line 1. It sends and receives signals, etc. that notify the The central control circuit 9 not only controls the button telephone interface unit 8 by sending control signals to the button telephone interface unit 8, but also controls the control information sent from the button telephone interface unit 8 side through the data highway. receive. Similarly to the above, the central control circuit 9
The button telephone interface unit 10 is not only controlled by sending control signals to the button telephone interface unit 10, but also receives control information sent from the button telephone interface unit 10 through the data highway.

The button telephone interface unit 8 includes a ping-pong transmission circuit, a control circuit, and a ping-pong transmission data transformer (none of which are shown).

The above-mentioned ping-pong transmission circuit is controlled by the control circuit.
The serial digital data of the PCM signal (audio signal data) sent from the time switch 7 and the control data given from the control circuit through the time slot assigned on the M highway is sent to the button telephone 22.
Transmit using ping-pong transmission method (digital transmission method). The ping-pong transmission circuit also receives serial digital data of a PCM signal (audio signal data) and control data transmitted from the button telephone 22 by the ping-pong transmission method, and allocates the PCM signal to the input PCM highway. The control data is outputted to the time switch 7 through the assigned time slot, and the control data is outputted to the control circuit of the button telephone interface unit 8. The control circuit receives the control data sent from the central control circuit 9 through the data highway and outputs it to the ping-pong transmission circuit of the button telephone interface unit 8, as described above.

The control circuit also receives control data on the button telephone 22 side given from the ping-pong transmission circuit, and outputs this to the central control circuit 9 through the data highway.

The button telephone interface unit 10 has a similar configuration to the button telephone interface unit 8.

That is, under the control of the control circuit, the ping-pong transmission circuit of the button telephone interface unit 10 transmits the PCM signal (voice signal data) sent from the time switch 7 through the time slot assigned on the outgoing PCM highway and the signal given from the control circuit. The serial digital data together with the received control data is transmitted to the button telephone 23 using a ping-pong transmission method. The above ping pong transmission circuit is
In addition, upon receiving serial digital data of a PCM signal (audio signal data) and control data transmitted from the button telephone 23 by the ping-pong transmission method, the PCM signal is transmitted to the time slot assigned on the incoming PCM/1 way. The control data is outputted to the time switch 7 through the button telephone interface unit 10, while the control data is outputted to the control circuit of the button telephone interface unit 10. The control circuit receives the control data sent from the central control circuit 9 through the data highway and outputs it to the ping-pong transmission circuit of the button telephone interface unit 10, as described above. The control circuit also receives control data on the button telephone 23 side given from the ping-pong transmission circuit, and transmits it to the central control circuit 23 through the data highway.
It is designed to output to .

The button telephone 22 includes a ping-pong transmission circuit 12, a control circuit 18b1, a dial pad 21, an extension key switch 19,
Office line key switch 20, codec 13, receiver amplifier 1
4, a transmitting amplifier 17, an analog switch 37, a handset receiver 15, a handset transmitter 16, and the like.

The ping pong transmission circuit 12 is under the control of the control circuit 18b,
Receiving serial digital data of a PCM signal (voice signal data) and control data sent from the button telephone interface unit 8 using a ping-pong transmission method, the PCM signal is output to the codec 13,
On the other hand, control data is output to the control circuit 18b. The ping-pong transmission circuit 12 also transmits the PCM signal (audio signal data) output from the codec 13 and the control circuit 1.
The control data output from 8b is converted into serial digital data, and this serial digital data is output to the button telephone interface unit 8. The codec 13 receives the PCM signal (audio signal data) output from the ping-pong transmission circuit 12, converts it into an analog signal (receiving audio signal, etc.), and then transmits the signal to the receiving amplifier 1.
Output to 4. The codec 13 also includes a transmitting amplifier 17
It receives an analog signal (transmission audio signal, etc.) output from the ping-pong transmission circuit 12, converts it into a PCM signal (audio signal data), and then outputs it to the ping-pong transmission circuit 12.

The receiver amplifier 14 receives an analog signal (receiver audio signal, etc.) output from the codec 13, amplifies it, and then outputs it to the receiver 15 of the handset. The transmitting amplifier 17 receives an analog signal (such as a transmitting audio signal) output from the transmitter 16 of the handset, amplifies it, and then outputs the amplified signal to the codec 13 . The extension key switch 19 is connected to the button telephone 22
When the extension key switch 19 is pressed, a signal indicating that the extension key switch 19 has been pressed is sent to the control circuit 18b. It is now output.

The central line key switch 20 is pressed when the speaker of the button telephone 22 wants to make a central line call (an outside line call).When the central line key switch 20 is pressed,
A signal indicating that the central line key switch 20 has been pressed is output to the control circuit 18b.

The dial pad 21 sends a dial signal corresponding to the button pressed by the speaker of the button telephone 22 to the control circuit 18.
b.

The analog switch 37 is provided in a sidetone generation circuit that connects the output side of the transmitting amplifier 17 and the input side of the receiving amplifier 14. The analog switch 37 is the control circuit 1
8b, when the key telephone 22 is in an extension call state, it is closed by a control signal output from the control circuit 18b. analog switch 3
7 is closed, a part of the output signal from the transmitting amplifier 17 is added as sidetone to the receiving signal input from the codec 13 to the receiving amplifier 14. The above content will be explained in detail later using FIG.

The button telephone 23 also has the same configuration as the button telephone 22. That is, the ping-pong transmission circuit 24, the control circuit 30
b1 dial pad 29, extension key switch 32, office line key switch 31, codec 40, receiving amplifier 25,
It includes a transmitting amplifier 28, an analog switch 37, a handset receiver 26, and a handset transmitter 27. The functions of the above-mentioned parts making up the button telephone 23 are similar to those of the parts making up the button telephone 22.

The operation of the above configuration is such that, for example, when the key telephone 22 is in an extension call state, the analog switch 37 is closed by a control signal from the control circuit 18b, and the received call from the codec 13 is input to the receive amplifier 14. The operation is similar to that of the button telephone device having the configuration shown in FIG. 3 above, except that a part of the output signal from the transmitter amplifier 17 is added to the signal as a sidetone. Therefore, a description of the operation of the button telephone device having the configuration shown in FIG. 2 will be omitted.

FIG. 1 is a block diagram showing a sidetone generation circuit provided inside a button telephone 22 according to an embodiment of the present invention (the sidetone generation circuit provided inside the button telephone 23 is similar to the sidetone generation circuit provided inside the button telephone 23). Since the configuration is the same as that of the sidetone generation circuit provided inside the key telephone 22, illustration and detailed explanation of the sidetone generation circuit on the button telephone 23 side will be omitted).

In FIG. 1, the transmitting amplifier 17 has a circuit configuration of an inverting amplifier circuit as shown. That is, an input resistor R1 is connected to the inverting input terminal side of the operational amplifier 170, which is a main component of the transmitting amplifier 17. The inverting input terminal of the operational amplifier 170 is connected to the handset's transmitter 16 through the input resistor R1. A non-inverting input terminal of operational amplifier 170 is grounded. The output terminal side of the operational amplifier 170 is not only connected to the input side of the codec 13 but also connected to a sidetone generation circuit that connects the output side of the transmitting amplifier 17 and the input side of the receiving amplifier 14. . Further, a negative feedback resistor R2 is connected between the output terminal of the operational amplifier 170 and the inverting input terminal of the operational amplifier 170.

On the other hand, the receiving amplifier 14 has a circuit configuration of an inverting and adding circuit, as shown in the figure. That is, input resistors R3 and R4 are connected to the inverting input terminal side of the operational amplifier 140, which is a main component of the receiving amplifier 14. The inverting input terminal of the operational amplifier 140 is connected to the output side of the codec 13 through an input resistor R3, and to the above-mentioned sidetone generation circuit through an input resistor R4. Operational amplifier 14
The non-inverting input terminal of 0 is grounded.

The output terminal side of the operational amplifier 140 is connected to the receiver 15 of the handset. Further, a negative feedback resistor R5 is connected between the output terminal of the operational amplifier 140 and the inverting input terminal of the operational amplifier 140.

An analog switch 37 is connected to the sidetone generation circuit described above. This analog switch 37 uses various semiconductor switching elements that open/close in response to control signals output from the control circuit 18b. This analog switch 37 is closed by a control signal output by the control circuit 18b when the control circuit 18b recognizes that the key telephone 22 is in an extension call state. Then, a part of the transmission signal output from the transmission amplifier 17 is converted into sidetone to the operational amplifier 140 through the sidetone generation circuit to which the closed analog switch 37 is connected and the input resistor R3.
is applied to the inverting input terminal of Some of the above transmission signals are
In the operational amplifier 140, it is added to the reception signal provided from the codec 13 through the input resistor R4.

The operation of the above configuration will be explained below. It is assumed that the caller of the button telephone 22 presses the extension key switch 19 and takes the handset off-hook to conduct an extension call. A transmitting signal v1 output from the handset's transmitter 16 is input to the operational amplifier 170 of the transmitting amplifier 17 through an input resistor R1. Then, when the negative feedback resistor R2 and the input paper telephone 22 are in an extension communication state, the voltage is applied even when the analog switch 37 of the sidetone generating circuit is closed. In other words, a portion of the signal goes around to the received signal side as sidetone. This becomes a signal expressed by the anal mouth.

On the other hand, the reception signal output from the output side of the codec 13 is input to the operational amplifier 140 through the input resistor R4. Then, the amplification factor is determined by the negative feedback resistor R5 and the input resistor R4.

It will be. As a result, when making an extension call using the key telephone 22, the sidetone will be heard in the same way as when making a call to the office line using the button telephone 22, so there will be no difference in the feel of the call between when making a call using the office line and when making an extension call. , callers no longer feel any discomfort.

On the other hand, when the caller on the button telephone 22
0 is pressed, the handset is off-hook, and a call is being made over the central office line. In this case, the analog switch 37 of the sidetone generating circuit does not go around to the receiver amplifier 14 side. That is, a part of the transmitting signal sent from the transmitter 16 of the handset passes through the 2-wire/4-wire conversion circuit 2 of the main device 11 into the receiving signal provided from the central office line 1 as sidetone. It is. Therefore, the receiver amplifier 14
The 2-wire to 4-wire conversion circuit 2 is used for this purpose.

Incidentally, the sidetone level adjustment during an extension call using the button telephone 22 is performed using an input resistor R that constitutes the receiver amplifier 14.
This can be done by changing the value of 3. The value of the input resistance R3 may be converted by selecting a fixed resistance element with a desired resistance value from among fixed resistance elements having various resistance values, or by selecting a variable resistance element (volume). There is no problem in performing this by varying the resistance value of the element.

When a variable resistance element is used as the input resistor R3, there are advantages as described below.

The impedance of the central office line 1 that connects the central office exchange and the main equipment 11 is the distance between the central office exchange and the main equipment, that is, the central office line 1.
The value varies depending on the length.

Therefore, if the impedance of the 2-wire 4-wire conversion circuit 2 of the main device 11 is set to match the impedance of the central office line 1, the level value of the sidetone that goes around the 2-wire 4-wire conversion circuit 2 will also change. It's coming.

However, if a variable resistance element (volume) is connected as the input resistor R3 as described above, the central office exchange and the main device 11
Depending on the distance between the above variable resistance element (volume)
By changing the resistance value, for example, adjustment work such as making the sidetone level during an internal line call substantially equal to the sidetone level during a local line call can be performed relatively easily.

〔Effect of the invention〕

As explained above, according to the present invention, a plurality of extension telephones each having a configuration in which a sending signal and a receiving signal are processed independently are operated by a control signal given from the outside, and sidetone generating means for causing a part of the transmitted speaking signal to be included in the receiving signal received by the extension telephone;
Since it is decided to provide a control means for operating the side sound generating means by outputting a control signal to the side sound generating means when each extension telephone is in an extension call state,
In a button telephone device to which a plurality of key telephones are connected, each of which has a configuration in which the sending signal and the receiving signal are processed independently, the same sidetone as that during a central office line call is generated during an extension call. By doing so, it is possible to prevent a difference in the feeling of talking between a central office line call and an extension line call, thereby providing a button telephone device in which the caller does not feel uncomfortable.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a sidetone generation circuit provided inside a button telephone according to an embodiment of the present invention, and FIG.
FIG. 3 is a block diagram showing the overall structure of a key telephone device according to an embodiment of the present invention. FIG. 3 is a block diagram showing the overall structure of a key telephone device according to the prior art. DESCRIPTION OF SYMBOLS 1... Office line, 11... Main device, 14... Receiving amplifier, 15... Handset receiver, 16... Handset transmitter, 17... Transmitting amplifier, 18b...
- Control circuit, 22. 23... button telephone, 37.
...Analog switch, R1, R3, R4...Input resistance, R2゜R5...Negative feedback resistance.

Claims (1)

[Scope of Claims] 1. A plurality of extension telephones configured to independently process outgoing and received signals, and an extension connected to a central office line to exchange and connect the plurality of extension telephones to each other. A button telephone device comprising a main device for setting telephone calls and central office telephone calls for switching and connecting each of the extension telephones and a central office line, wherein each of the extension telephones is operated by a control signal given from the outside, sidetone generating means for causing a part of the transmitting signal transmitted from the telephone to be included in the receiving signal received by the extension telephone; control means for operating the sidetone generating means by outputting a control signal. 2. The button telephone device according to claim (1), wherein the sidetone generating means includes a gain adjusting means for adjusting the gain of a part of the transmitted signal that is passed around to the received signal. Telephone device.