JPH03265344A - Extension incoming call reply monitor circuit for key telephone system - Google Patents

Abstract

PURPOSE:To make the operation stable by detecting a change in the impedance when viewing a terminal equipment from an electronic subscriber circuit so as to confirm a reply of the terminal equipment. CONSTITUTION:The circuit consists of an oscillation circuit 1, an analog switch 2, a 2/4-wire exchange circuit 3, a standby current circuit 11, a start signal detection circuit 8, and a balance circuit 10 or the like. When a tone transmission control signal of a master set is received and a start signal is sent to a terminal equipment 6, the circuit detects it that the impedance of the line of the terminal equipment 6 changes from a high value to a low value. The reply of the terminal equipment 6 with a tone transmission control signal is detected with a sufficient noise margin and the reliable reply monitor signal is sent to the master set. Thus, stable operation is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an incoming call response monitoring circuit that monitors incoming activation signals on an extension of a key telephone device that accommodates a facsimile (FAX).

(Prior Art) Conventionally, there has been a circuit as shown in FIG. 2 as this type of incoming call response monitoring circuit. 1 is an oscillation circuit that supplies a 1300 Hz activation signal to the first contact of the analog switch 2 forming the exchange switch section. 2nd of analog switch 2
The contact is connected to the not-illustrated exchange switch side (4-wire side) of the button telephone device that sends the tone sending control signal at startup, and the common contact is connected to the input of the following amplifier of the 2-wire 4-wire conversion circuit 3. It is connected to the. The 2-wire/4-wire conversion circuit 3 here has a normal function of converting a 2-wire signal to a 4-wire signal or vice versa. Furthermore, a 2-wire 4-wire conversion circuit 3
In order to obtain the function of sending a start signal from the terminal device side to the main device side, a start signal from the oscillation circuit 1 or a signal from an exchange switch (not shown) is inputted via the analog switch 2. Amplifier (-) 3a and amplifier (+)
) 3b, and an amplifier 3c that sends a start signal returned from the terminal device side (second battle side) to the main device side, which will be explained below.
It is equipped with

The outputs of the amplifiers 3a and 3b are respectively connected to the bases of transistors 4a and 4b forming the output stage of the electronic subscriber circuit. Transistors 4a, 4b
The collectors of are each connected to the line L l +L2. The emitter of the transistor 4a is connected via a resistor 4C to a power supply (not shown) that applies a voltage +V, and the emitter of the transistor 4b is grounded via a resistor 4d.

A phototransistor 5a of a preliminary current circuit 5 and a resistor 5b that limits the preliminary current flowing through the circuit are connected in series between the line L2 and the line L2. Input is connected. A photodiode 5c optically coupled to the phototransistor 5a has one end grounded via a resistor 5d, and the other end connected to a main device that sends out a tone sending control signal.

The emitter of the transistor 4b is connected to a non-inverting input of a current monitoring circuit 7 consisting of a comparator. A reference voltage is input to the inverting input of the current monitoring circuit 7. This reference voltage is obtained by dividing voltage +■ from a power source (not shown) by resistors 7a and 7b. The current monitoring circuit 7 sends a loop monitoring signal having a logic level of 1 to the main device when the voltage level at the emitter of the transistor 4b becomes equal to or higher than the reference voltage.

Here, the 2-wire 4-wire conversion circuit 3, the transistors 4a and 4
b, and the current monitoring circuit 7 are circuits that function as an electronic subscriber circuit section.

Next, the operation when starting up the FAX device 6 will be explained.

First, when a tone sending control signal is sent from the main device (not shown), a current flows through the diode 5c. For this purpose, the photodiode 5c emits light and turns on the phototransistor 5a, thereby activating the transistors 4a and 4b. Furthermore, by sending the tone sending control signal, the analog switch 2 is switched to the opposite position from the illustrated position, so that a 1300 Hz starting signal is sent from the oscillation circuit l via the analog switch 2 to the amplifiers 3a and 3b.
is input. Activation signals from amplifiers 3a and 3b are input to transistors 4a and 4b, and a tone is sent to the terminal device side. Furthermore, those collector outputs are connected to amplifier 3.
c. Amplifier 3c returns collector outputs from transistors 4a and 4b to the main device side as activation signals. Normally, the balance circuit 10 is used to minimize the amount of calls returned.

Further, the current monitoring circuit 7 monitors the emitter voltage of the transistor 4b, and sends out a loop monitoring signal having a voltage value corresponding to this to a main device (not shown). This emitter voltage has a correspondence relationship that satisfies the relationship It < IT < IL when the button telephone device is operating normally. However, ■
, is the loop current when the FAX device 6 captures the loop, ■. is a preliminary current, and (2) is a threshold current of the current monitoring circuit 7.

The main device (not shown) determines that "the button telephone device is operating normally" if such current relationships are satisfied.
I judge that.

(Problems to be Solved by the Invention) However, in the incoming call response monitoring circuit of the button telephone device having such a configuration, the loop current is connected to the line L1. L2~F
There has been a problem in that variations in line resistance between the AX devices 6, direct current resistance inside the FAX device 6, etc. have a non-negligible effect on the monitoring of incoming call responses. In order to solve this problem, it is conceivable to increase the noise margin by, for example, setting the level of the threshold current air high. However, since the conditions shown in the above equation still have to be satisfied, there is a limit to increasing the noise margin to a large value.

Also a preliminary electrician. is affected by the transmission efficiency of the photocoupler that constitutes the preliminary current circuit 5, so in order to make this preliminary current IE stable, it must be manufactured as a component that satisfies the specified specifications. must be sorted out from those who do. This is undesirable because it causes an increase in the cost of parts.

Furthermore, a typical electronic subscriber circuit section is designed so that stable characteristics can be obtained when a loop current of about 20 mA flows through the loop formed by the FAX machine. I
Since E is a smaller value and the loss in the 2-wire/4-wire conversion circuit 3 is large, there is a problem in that the noise margin of the circuit is reduced.

Furthermore, since the influence of variations in the characteristics of the transistors 4a and 4b is large, there is a problem in that variations in these characteristics also cause large variations in the level of the FAX activation signal.

As described above, the present invention eliminates the problem of having to set the detection current threshold value of the FAX response monitoring circuit to a low value that is undesirable from the noise margin point of view due to the loop current value. In addition, it is an object of the present invention to provide an incoming call response monitoring circuit for a button telephone device which is designed to eliminate the problem that the signal-to-noise ratio is low due to variations in the sending level of the activation signal of the terminal device, and whose operation is stable. With the goal.

(Means for Solving the Problems) The extension call response monitoring circuit of the button telephone device of the present invention has the following features:
A 2-wire 4-wire conversion circuit that converts a 2-wire signal on the terminal device side into a 4-wire signal on the main device side, and a tone transmission control circuit connected to the 4-wire transmission side of the 2-wire 4-wire conversion circuit to control tone transmission from the main device. a startup signal sending circuit that sends a startup signal for starting a terminal device to the 2-wire 4-wire conversion circuit in response to the signal; An extension call response monitoring circuit in a button telephone device, comprising a preliminary current circuit that supplies a preliminary current to the terminal device for the activation signal to be applied to the terminal device in response to a sending control signal, wherein the preliminary current circuit The line impedance of the circuit is set higher than the input impedance at the time of response of the terminal device, and is further connected to the 4-wire receiving side of the 2-wire 4-wire conversion circuit, and detects impedance change due to activation of the terminal device. The present invention is characterized in that it has an activation signal detection circuit.

(Function) According to the incoming call response monitoring circuit of the present invention configured as described above, when the activation signal is sent to the terminal device side by receiving the tone sending control signal from the main device, the terminal device side Based on detecting a change in the impedance of the loop spring from a high value to a low value, it is possible to determine that this terminal device has responded to the tone transmission control signal without being limited by the loop current value of the line. Detection is performed with a sufficient noise margin, thereby allowing a reliable response monitoring signal to be sent to the main device.

(Embodiment) FIG. 1 shows an incoming call response monitoring circuit of a key telephone device according to an embodiment of the present invention. The incoming call response monitoring circuit shown in FIG. 1 has the following circuit parts added to the circuit shown in FIG. 2. Here, the explanation will focus on such added circuit parts.

8 is a starting signal detection circuit connected to the output side of the amplifier 3c. The activation signal detection circuit 8 consists of an amplifier 8a that inputs and amplifies the output signal of the amplifier 3c, an integration circuit 8b that integrates the output signal of the amplifier 8a so as to remove the 1300 Hz AC component, and an operational amplifier. circuit 8b
and a reference voltage set so as not to detect noise by dividing the voltage +V, and output a response monitoring signal that becomes logic 1 when the former exceeds the latter.

Reference numeral 9 denotes a gate, which includes an inverter 9a that inverts the tone sending control signal, and an AND gate that performs a logical AND operation between the output of the inverter 9a and the output signal of the current monitoring circuit 7, and outputs the result as a disconnection (loop) monitoring signal. It consists of a gate 9b.

Reference numeral 10 denotes a balance circuit, which balances the impedances of the wires and L of the analog switch 2. This balance circuit 10 is connected. The balance circuit 10 has an impedance of 600Ω between the lines L1 and L2.
It functions best when it is balanced. 11 is the preliminary current circuit 5 shown in FIG. 2 as a conventional example.
This is a preliminary current circuit in which an inductance 5d is added to. This inductance 5d is the phototransistor 5a
and the resistor 5b, so that the AC impedance of the preliminary current circuit 11 becomes high.

Here, when the FAX device 6 is viewed from the lines L1 to L2, its input impedance is high impedance (for example, 2Ω or more) during the reception period of the activation signal,
It is approximately 600Ω during the period in response to the activation signal.

Next, the operation will be explained. First, a tone sending control signal is sent from the main device for activation, and the analog switch 2
is switched from the illustrated position to the opposite position, that is, to connect to the transmitting circuit 1. As a result, 1300 of oscillation circuit 1
Hz activation signal is routed through analog switch 2 to 2 wires 4
The signal is input to the amplifier 3a of the line conversion circuit 3. Since the tone sending control signal is also supplied to the photodiode 5C of the preliminary current circuit 11, the photodiode 5C emits light and turns on the phototransistor 5a. For this purpose, a preliminary current flows through the phototransistor 5a, the inductance 5e, and the resistor 5b, putting the transistors 4a and 4b into the operating state. Also, the activation signal from the analog switch 2 is applied to the amplifier 3a and 3b1 transistor 4a.
and 4b to the FAX device 6, and also to the activation signal detection circuit 8 and the main device (not shown) via the amplifier 3c. When the FAX device 6 is not responding, its input impedance is 2Ω or more, so the input level of the amplifier 3c is high.

The output of the amplifier 3c is sent to the main device (not shown), and at the same time is input to the activation signal detection circuit 8. In this activation signal detection circuit 8, the output of the amplifier 3c is inputted to a non-inverting input of a comparator 8c via an amplifier 8a and an integrating circuit 8b. In this state, the human power level of the comparator 8c is such that the non-inverting input level is higher than the inverting input level, that is, the reference voltage. Therefore, comparator 8
c sends a response monitoring signal of logic 1 to a main device (not shown).

On the other hand, the gate 9 functions to ignore the loop current while transmitting the tone transmission control signal, so as not to allow the output of the current monitoring circuit 7 to pass to the main device (not shown). That is, since the tone sending control signal is inverted by the inverter 9a and input to the AND gate 9b, the output of the gate 9b becomes φ while the tone sending control signal is being sent. In this way, while the main device is sending out the tone sending control signal, the activation signal detection circuit 8 sends a logic 1 output, and the gate 9 sends a logic φ output to the main device.

Next, the FAX machine 6 is started by receiving a start signal through the lines L1 and L2. Fax device 6 starts up
The impedance of is 600Ω. For this reason, the input level of the comparator 8c in the activation signal detection circuit 8c is such that the non-inverting input level is lower than the inverting input, that is, the reference voltage. Therefore, the activation signal detection circuit 8 has a logic φ
A response monitoring signal is sent to the main device.

When the main device transmits the activation signal in this manner and confirms the response of the FAX device 6 by detecting a change in the response monitoring signal, it stops transmitting the tone transmission control signal. This causes analog switch 2 to return to the position shown and 2! ! The supply of the activation signal to the four-wire conversion circuit 3 is stopped. Furthermore, since the tone transmission control signal to the gate 9 is also stopped, the gate 9 is opened, and from now on, the disconnection monitoring signal of the current monitoring circuit 7 is sent to the main device, so that the main device can monitor the loop disconnection. state.

(Effects of the Invention) As explained in detail above, the present invention is configured to check the response of the terminal device by detecting the change in impedance when the terminal device is viewed from the electronic subscriber circuit section. Therefore, the response of the terminal device can be checked without being restricted by the current value that flows when the terminal device captures the loop, and therefore, the value of the preliminary current for starting the terminal device can be Since it is also possible to select a value that can be stably activated, it is expected that the reliability of the button telephone device will be improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the button telephone device of the present invention, and FIG. 2 is a block diagram showing an embodiment of the conventional button telephone device. ...Oscillation circuit, ...Analog switch, ...2-wire 4-wire conversion circuit 1. 11...Preliminary current circuit,...Start signal detection circuit, O...Balance circuit.

Claims (1)

[Scope of Claims] A 2-wire 4-wire conversion circuit that converts a 2-wire signal on the terminal device side into a 4-wire signal on the main device side; a startup signal sending circuit that sends a startup signal for starting a terminal device to the 2-wire 4-wire conversion circuit in response to a tone transmission control signal from the device; and a 2-wire side of the 2-wire 4-wire conversion circuit. and a standby current circuit connected to the tone sending control signal and supplying a standby current to the terminal device so that an activation signal is applied to the terminal device in response to the tone sending control signal. The line impedance of the preliminary current circuit is set higher than the input impedance at the time of response of the terminal device, and is further connected to the 4-wire receiving side of the 2-wire 4-wire conversion circuit, and the impedance due to activation of the terminal device is An extension call response monitoring circuit in a button telephone device, comprising an activation signal detection circuit for detecting a change. The output of the amplifier 3c is sent to the main device (not shown) and at the same time is input to the activation signal detection circuit 8. In this activation signal detection circuit 8, the output of the amplifier 3c is inputted to a non-inverting input of a comparator 8c via an amplifier 8a and an integrating circuit 8b. In this state, the non-inverting input level of the comparator 8c is higher than the inverting input level, that is, the reference voltage. Therefore, comparator 8
c sends a response monitoring signal of logic 1 to a main device (not shown). On the other hand, the gate 9 functions to ignore the loop current while transmitting the tone transmission control signal, so as not to allow the output of the current monitoring circuit 7 to pass to the main device (not shown). That is, since the tone sending control signal is inverted by the inverter 9a and input to the AND gate 9b, the output of the gate 9b becomes φ while the tone sending control signal is being sent. In this way, while the main device is sending out the tone sending control signal, the activation signal detection circuit 8 sends a logic 1 output, and the gate 9 sends a logic φ output to the main device. Next, the FAX machine 6 is started by receiving a start signal via the lines L_1 to L_2. Upon startup, the impedance of the FAX device 6 becomes 600Ω. For this,
Regarding the input level of the comparator 8c in the activation signal detection circuit 8c, the non-inverting input level is lower than the inverting input, that is, the reference voltage. Therefore, the activation signal detection circuit 8 sends a response monitoring signal of logic φ to the main device.