JPH02260864A - Ac signal call interphone set - Google Patents

Abstract

PURPOSE:To attain voice call without affect of a common impedance by providing a master set and plural slave sets connecting to the master set via a common speech line and having a transmission amplifier with high output impedance. CONSTITUTION:In the case of calling from a slave set 2-1 to, e.g. other slave sets 2-2, 2-3, a call AC signal iT such as a voice output signal outputted from a transmission amplifier A2 of the call slave set 2-1 is sent to at least one set of slave sets 2-2, 2-3 or the like via a speech line and the master set 1. Thus, the call message is sent from the slave set 2-1 to the other slave sets 2-2, 2-3 to apply voice call. In this case, since the transmission amplifier of the slave set has a high impedance, so-called, current drive is applied, the voltage generated in the common impedance Rc of a speech line is negligibly small and the voltage generated in the common impedance is fed back to the master set and no gain reduction nor oscillation is called.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an AC signal calling intercom device, and in particular, a device in which a base unit and a plurality of slave units are connected by a wiring format having a common impedance such as a multi-drop wiring system. The present invention relates to a technology that enables an AC signal call such as a voice call without being affected by the common impedance of an intercom device.

[Prior Art] Conventionally, in an intercom device, a base unit and a plurality of slave units are connected to a common call line using a multi-drop wiring method, etc., in order to simplify wiring and facilitate wiring work.

[Problems to be Solved by the Invention] However, in such an intercom device, for example, when one handset calls another handset, if a voice signal for the call is sent through the base phone, the call line is interrupted. Due to the common impedance, the voice call signal is fed back to the amplifier of the base unit, resulting in a decrease in gain or oscillation.

For this reason, so-called voice calling has not conventionally been performed in intercom devices having wiring and formats having a common impedance.

SUMMARY OF THE INVENTION In view of the problems with the conventional intercom devices described above, an object of the present invention is to enable voice calls to be made without being affected by the common impedance even in an intercom device having a wiring type having a common impedance. .

[Means for Solving the Problems] An AC signal calling intercom device according to the present invention includes a base unit and a plurality of slave units connected to the base unit via a common call line. Each handset is equipped with a high output impedance transmitting amplifier.

[Function] In such an intercom device, when one handset calls another handset, a calling AC signal such as a voice calling signal output from the transmitting amplifier of the calling handset is used as a voice call signal. It is transmitted to at least one or more other slave units via the line and the base unit. This allows one handset to send a calling message to another handset to make a voice call. In this case, since the transmitting amplifier of the handset has a high impedance, so-called current driving is performed.

Therefore, the voltage generated in the common impedance of the communication line becomes negligibly small, and the voltage generated in the common impedance is not fed back to the base unit and causes gain reduction or oscillation.

[Example] Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a schematic circuit diagram for explaining the principle of an intercom device according to the present invention. The intercom device in the figure includes a base unit 1 and slave units 2-1.2-2.2-3 connected to the base unit 1 through a common call line.・・・・・・
have. In addition, in FIG. 1, only the circuit part of the handset 2-1 that mainly transmits the calling signal is shown, and the other handsets 2-2, 2-3, etc. mainly show the circuit that receives the calling signal. Only shown schematically.

In the intercom device shown in Fig. 1, when calling another handset 2-2, 2-3, etc. from the handset 2-1, a calling voice signal is input from the transmitter T of the calling handset 2-1. . This calling voice signal is applied to the telephone line as a current signal IT by a transmitting amplifier A2 having a high output impedance. This current signal 11 flows from the power supply Vce of the base unit 1 to the communication line via the load resistor RL. Therefore, a voltage RLxt is generated across the load resistor RL of the base unit 1, and this voltage is amplified by the amplifier Al and supplied to each called slave unit 2-2, 2-3, etc.

As a result, a voice call is made from the handset 2-1 to the handset 2-2, 2-3, etc. In this case, even if there is a common impedance Re on the call line, the output impedance of the calling side handset 2-1 is sufficiently high, so the impedance Re
The voltage generated will be negligibly small. Therefore, in the device shown in FIG. 1, it is possible to make a voice call without being affected by the common impedance.

Note that in conventional intercom devices, a general NFB type amplifier is used as a transmitting amplifier for each handset, and the output impedance of this amplifier has a low value of, for example, 1 ohm or less. Therefore, the voltage generated at the common impedance Re is transmitted to the load resistance on the base unit side and fed back to the amplifier AI of the base unit 4, causing problems such as gain reduction or oscillation depending on the feedback phase.

FIG. 2 shows a specific configuration of an intercom device according to the present invention. The intercom device shown in the figure includes a base unit 1 and a plurality of slave units 5-1, 5-2, . It is equipped with... The base unit 1 includes a buffer amplifier 7 for amplifying a call signal, a power amplifier 9 for calling, and an analog switch 11 that is turned on when making a call. A telephone communication circuit 13 is provided. Moreover, the main unit 1 is connected between the power supply Vce and the transmission line LL of the communication line 3, and includes a transistor Tl and a diode Dl.

It has a power supply circuit composed of D2 and a resistor R2, and a load circuit composed of a series circuit of a resistor R1 and a capacitor Ct.

The handset 5-1 also includes a high output impedance transmitting amplifier composed of an operational amplifier A2k, a transistor T2, a choke coil CHI, a resistor R3, a capacitor 02, etc., a transmitting microphone M, and a receiver R. and a hook switch HS. In addition,
In this case, the transmitting amplifier connects the output of the operational amplifier A21 to the operational amplifier A2L through the emitter of the transistor T2.
A high output impedance circuit is constructed by feeding back to the inverting input terminal of the inverter. Note that the choke coil CHI and the capacitor C2 constitute a rectifying and smoothing circuit for supplying power to the operational amplifier A21. In addition, other handset 5-2. . . . can also have the same configuration as the handset 5-1.

Next, the operation of the intercom device having the above configuration will be explained. First, for example, from the slave unit 5-2 to the other slave unit 5.
-1, the telephone receiver 5-2 is lifted up and placed in an off-hook state, and the hook switch H3 becomes as shown in the figure. Then, the voice call signal manually inputted from the microphone M for speaking is applied from the amplifier for speaking to the speaking line L1 through the hook switch HS. As a result, the load resistance R1 of the main unit 1
An alternating current flows through the resistor R1, and a voice call signal voltage is generated across the resistor R1. In addition, when the handset 5-2 goes off-hook, DC power is supplied from the power supply VCC of the base unit 1 through the power supply circuit including the transistor TI and the transmission line LL, and the power supply for the transmission of the handset 5-2 is supplied. Amplifier works.

The voice call voltage generated across the load resistor R1 of the base unit 1 in this manner is applied to the communication circuit 13 and the buffer amplifier 7 of the base unit 1. The output of the buffer amplifier 7 is sent back to the handset R of the handset 52 at an appropriate level through the reception signal line L2, allowing the operator of the handset 5-2 to hear the voice call signal on the handset R. In addition, in the base unit 1, a call detection circuit (not shown) detects a current flowing through the transmission line L1 in response to the off-hook of the slave unit 5-2, and outputs a signal CD indicating the call state.

Then, this call detection signal CD is transmitted to the analog switch 11.
is applied, and the analog switch 11 is turned on.

That is, the analog switch 11 is turned on at the time of calling and applies the output of the buffer amplifier 7 to the calling power amplifier 9. Thereby, the calling voice signal output from the handset 5-2 is amplified by the buffer amplifier 7 and the power amplifier 9, and then transmitted to the handset side via the calling line L3. Among the handsets, in the handset that is in an off-hook state, for example, handset 5-1, a voice call signal is applied from the call line L3 to the receiver R through the hook switch H3, and a voice call is performed. In addition, when making such a voice call, the output impedance of the transmitting amplifier of the handset is high, so even if there is a common impedance on the call line 3 as described above, there will be no adverse effect. .

When the handset 5-1, which has received a call through such a calling operation, picks up the handset, the hook switch H3 is switched as shown by the dotted line in the figure. As a result, power is supplied to the handset 5-1 from the base unit 1 via the transmission line L1, and a call signal is applied to the handset R from the buffer amplifier 7 of the base unit 1 via the reception signal line L2. be done. As a result, for example, a call is made between handset 5-2 and handset 5-1. Note that the call circuit 13 of the base unit 1 can also be provided with the same call circuit and hook switch H3 as each slave unit, so that calls and conversations can be made between the slave unit and the base unit. I can do it.

[Effects of the Invention] As described above, according to the present invention, the output impedance of the transmitting amplifier of the handset is increased and AC signals such as voice call signals are transmitted using the M current drive method. Even in an intercom device having a wiring system having a common impedance, it is possible to perform AC signal calling without being adversely affected by the common impedance. Therefore, even when a wiring system having a common impedance, such as a multi-drop connection system, which was previously impossible, is used, stable and accurate voice calling can be performed.

[Brief explanation of drawings]

FIG. 1 is a schematic block circuit diagram for explaining the principle of an intercom device according to an embodiment of the present invention, and FIG. 2 is a block circuit diagram showing the configuration of an intercom device according to an embodiment of the present invention. It is a diagram. 1; Base unit, 2-1.2-2. 2-3. 5-1. 5-2.・・・
...; Child unit, 7; Buffer amplifier, 9; Power amplifier for calling, 11; Analog switch, H8; Hook switch, M; Microphone for speaking, A21. A22; Amplifier, TI, T2. T3; Transistor, CHI, CH2
, choke coil, CI, C2, C3, capacitor, R1, R2, R3, R4, resistor, DI, D2; diode. 13; Telephone circuit; 3; Telephone line; R; Receiver; Fig.

Claims (1)

[Claims] It is equipped with a base unit and a plurality of slave units connected to the base unit via a common communication line and each having a transmitting amplifier with a high output impedance. An AC signal calling intercom device, characterized in that the signal is transmitted to at least one or more other handsets via a call line and the base unit.