JPH0884355A - Subscriber's analog circuit - Google Patents

Abstract

PURPOSE: To prevent induction to a communication line of other channels even when a potential of the communication line fluctuates and an indicator signal such as a message waiting signal is sent from the subscribers analog circuit to a terminal equipment. CONSTITUTION: An inductive element LMW is inserted in series with an indicator signal transmission circuit 5. Furthermore, a 1st diode DA is interposed on the communication line in the vicinity of a connecting point between the communication line LA and the indicator signal transmission circuit 5A with a positive polarity with respect to a path through which a usual speech current flows. Moreover, a 2nd diode DB is interposed on the communication line in the vicinity of a connecting point between the other communication line LB to keep the balance with the one communication line and the indicator signal transmission circuit 5A with a positive polarity with respect to a path through which a usual speech current flows.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a PBX (Private Branch Exchange).
The present invention can be applied to, for example, an analog subscriber circuit having a message waiting signal transmission structure.

[0002]

2. Description of the Related Art In an analog subscriber circuit of a PBX used in a hotel or the like, a message that causes a lamp or the like attached to a terminal to perform a display operation to let the terminal user know that there is a message (standby message). In order to realize the waiting function, a message waiting signal transmission structure is provided.

FIG. 2 shows a conventional analog subscriber circuit having a message waiting signal transmitting structure, and also shows a message waiting signal receiving structure of a terminal.

In FIG. 2, the analog subscriber circuit 1 and the terminal 2 are connected to each other via a pair of a battery sending side communication line LA and a ground sending side communication line LB, and the pair of communication lines LA and LB. Various signals such as a call signal, a ringer signal, and a message waiting signal are transmitted and received via the.

In the terminal 2, a neon tube Ne for notifying that there is a message and a receiving resistor RT for a message waiting signal are connected in series between the pair of communication lines LA and LB. The neon tube Ne is not impressed by the power supply voltage for communication (for example, -48V), but is impressed by the message waiting voltage (for example, -144V) that is several times that (not necessarily an integral multiple). The neon tube Ne is connected in parallel with a filter circuit 3 composed of a parallel circuit of a resistor and a capacitor in order to prevent the neon tube Ne from being affected by a ringer signal which is a sine wave signal.

The analog subscriber circuit 1 includes an overvoltage protection circuit 4 for protecting the subscriber circuit from surge voltage and the like mixed in the pair of communication lines LA and LB, and a message waiting signal sending circuit 5 for sending a message waiting signal. And a subscriber circuit basic unit 6 that performs a basic operation as a subscriber circuit.

The subscriber circuit basic unit 6 is a so-called "BOR".
The subscriber line interface circuit 7 that performs the functions such as "B", "S", and "H" of the SCHT function, and the power lines mixed in the pair of communication lines LA and LB and the communication lines of other lines An overvoltage protection circuit 8 for protecting the subscriber circuit from the induced current, and a diode bridge structure which functions to fix the pair of communication lines LA and LB to the power supply potential (for example, -48V) VBB for communication and the ground potential, respectively. Each communication line LB, LA that supplies a call current to the terminal 2 in response to a drive command signal from the clamp circuit 9 and the subscriber line interface circuit 7 (the drive is always instructed except when the line is abnormal) Corresponding to the call current supply circuits 10 and 11, and the transmission / reception resistors RB and R for signals which are respectively inserted in series in the communication lines LB and LA.
It consists of A.

Message waiting signal transmission circuit 5
Includes a relay 12 that excites or demagnetizes in response to a relay control signal (message waiting control signal) MWCTL supplied from a control unit (not shown). The contact 12c of the relay 12 has a so-called c-contact configuration (three contact configuration), and is a connection point between the battery sending side communication line LA and the overvoltage protection circuit 4 and the battery sending side communication line L.
It is inserted in the battery sending side communication line LA between the connection point of A and the overvoltage protection circuit 8. That is, when the relay 12 is demagnetized, a call current path is formed. Relay 12
At the time of excitation, the relay contact 12c is connected to the series circuit of the message waiting signal sending resistor RMW and the message waiting negative power source (for example, -144V) VMW.

Thus, when the relay control signal MWCTL is intermittent, the terminal 2 is switched by the intermittent switching of the relay contact 12c.
The voltage VMW for message waiting (actually, the voltage drop due to the resistance is small) and the power supply voltage VBB for communication are alternately applied to the neon tube Ne of the above, and the neon tube Ne blinks. , Notify the terminal user that there is a message.

[0010]

However, the conventional analog subscriber circuit has a drawback in that the operation of sending a message waiting signal on a certain line adversely affects the communication line of another line.

FIG. 3 is a signal waveform diagram of each part of the analog subscriber circuit shown in FIG.

The relay control signal MWCTL is turned on (for example, 1
Second) and OFF (for example, 2 seconds) are repeated, the potential VLB of the ground transmission side communication line LB at the location where the analog subscriber circuit is pulled out maintains the ground potential G regardless of the ON / OFF operation. On the other hand, the potential VLA of the battery transmission side communication line LA changes between the power supply voltage VBB for communication and the potential different from the message waiting voltage VMW by the voltage drop due to the transmission resistance RMW, and the message waiting signal is transmitted. It becomes unbalanced transmission.
Therefore, the transmission of the message waiting signal induces the communication line to the adjacent line accommodated in the same cable due to the coupling of the line capacities. Actually, one cable has multiple lines (for example, 16 lines).
The battery sending side communication line LA and the ground sending side communication line LB are stored.

Further, the variation of the potential VLA of the battery transmission side communication line LA (variation of the message waiting signal) at the time of switching on and off is large (for example, -48V,-).
As shown in an enlarged scale in FIG. 3, the fall and rise of the potential change are steep and include high-frequency components, so that the induction, which is the coupling of the line capacitance, occurs. growing.

FIG. 4 shows a current path due to the line capacitance when the relay control signal MWCTL changes from OFF to ON. When the relay control signal MWCTL changes from OFF to ON, the potential VLB of the ground transmission side communication line LB
Is very small and gradual, so that almost no current flows due to the line capacity CB between the ground transmission side communication line LB and the other communication line. On the other hand, the battery transmission side communication line LA
Potential VLA of the power supply voltage VBB (for example, -48)
V) changes to a value close to the message waiting voltage VMW (for example, -144V), the current due to the line capacity CA between the battery sending side communication line LA and the communication line of the other line as shown in FIG. It flows toward the negative power source VMW of the waiting signal transmission circuit 5 (hereinafter,
The current in this path is called the charging current). Since the value of the transmission resistance RMW of the message waiting signal is usually as large as several tens of kΩ, the charging current is limited to some extent, but the signal falls sharply and contains high frequency components, so induction to other lines is suppressed. It was not enough to do.

FIG. 5 shows the current path due to the line capacitance when the relay control signal MWCTL changes from on to off. Even when the relay control signal MWCTL changes from on to off, the potential VLB of the ground transmission side communication line LB
Is very small and gradual, so that almost no current flows due to the line capacity CB between the ground transmission side communication line LB and the other communication line. On the other hand, the battery transmission side communication line LA
Potential VLA is the message waiting voltage VMW
(For example, -144V) from the value close to the power supply voltage V for communication
Since it changes to BB (for example, -48V), as shown in FIG. 5, the current due to the line capacity CA between the battery sending side communication line LA and the communication line of the other line is fed from the clamp circuit 9 or the overvoltage protection circuit 8. It flows out through a low resistance route toward the inter-capacitance CA side (hereinafter, the current in this route is called a discharge current). Even during this discharge, the battery sending side communication line L
Since the fluctuation of the potential VLA of A is large and steep, the induction to other lines was large.

In order to solve the inconvenience caused by such induction, it has been conventionally practiced to insert a common mode choke in the analog subscriber circuit. Induction from other lines
Battery transmission side communication line LA and geological transmission side communication line L
Occurs in phase with B. Therefore, by inserting a common mode choke that cancels the in-phase component and allows the differential component (for example, a call signal) to pass through as it is, the inductive component can be canceled and the call signal can pass through as it is.

However, the conventional common mode choke is intended to suppress the low-frequency inductive component from the power line or the like, and the high-frequency inductive component generated at the time of sending the message waiting signal is suppressed. The suppression characteristics were insufficient, and it affected the calls on other lines (audible noise). Further, a common mode choke which has a high inductance so that a direct current can be passed and an inductive component can be suppressed was expensive and large.

When a signal having a certain meaning is to be transmitted from the analog subscriber circuit 1 to the terminal 2,
It is conceivable that the potential of one of the communication lines is changed from the normal call potential as in the case of sending the message waiting signal, but the above-mentioned problem also occurs in such a case.

Therefore, even if the analog subscriber circuit 1 sends a signal to the terminal 2 by changing the potential of one communication line from the normal call potential, the analog line will not be adversely affected. A subscriber circuit is desired.

[0020]

In order to solve such a problem, a first aspect of the present invention is to provide an indicator power supply and an indicator signal transmission resistor having a voltage that is several times (not necessarily an integral multiple) the power supply voltage for communication. And a indicator switch for transmitting the indicator signal to the terminal by connecting the series circuit to one of a pair of communication lines connected to the terminal via the selector switch. In the analog subscriber circuit for sending to, the inductance element is inserted in the series circuit composed of the indicator power source and the indicator signal sending resistor.

The second aspect of the present invention is a series circuit composed of an indicator power source and an indicator signal transmitting resistor having a voltage that is several times (not necessarily an integer multiple) the power supply voltage for communication.
An analog subscriber that is provided with an indicator signal sending circuit consisting of a changeover switch, and sends the indicator signal to the terminal by connecting the series circuit to one of a pair of communication lines connected to the terminal via the changeover switch. In the circuit, a first diode is inserted on the communication line in the vicinity of the connection point between the indicator signal transmission circuit and one of the communication lines so as to be in the forward direction with respect to the path through which the normal call current flows. In addition, a second diode is inserted at a position on the other communication line where the balance with this one communication line can be maintained so that it is in the forward direction with respect to the path through which the normal call current flows. It is characterized by that.

An analog subscriber circuit according to a third aspect of the present invention is characterized in that it has both the characteristic configurations of the first and second aspects of the present invention.

[0023]

According to the first to third aspects of the present invention, a series circuit composed of an indicator power source and an indicator signal transmitting resistor having a voltage which is several times (not necessarily an integer) the power supply voltage for communication is provided,
An indicator signal sending circuit consisting of a changeover switch is provided, and the series circuit is connected to one of a pair of communication lines connected to the terminal via the changeover switch, and an indicator signal (for example, a message waiting signal corresponds thereto). ) To the terminal for analog subscriber circuits.

In such an analog subscriber circuit,
When the serial circuit in the indicator signal sending circuit is switched from the state where it is not connected to one communication line to the state where it is connected by the changeover switch, a current due to the line capacitance with the communication line of the other line tries to flow, Attempts to rapidly change the potential of one communication line. Therefore, in the first aspect of the present invention, an inductance element is inserted in the series circuit to limit the current, thereby slowing down the potential change of one communication line and suppressing induction to the communication line of the other line. It is a thing.

In the analog subscriber circuit as described above, when the serial circuit in the indicator signal sending circuit is switched from the state in which it is connected to one communication line to the state in which it is not connected by the changeover switch, A current due to the line capacitance between the communication line and the communication line of the other line flows out from the subscriber circuit basic portion, and the potential of one communication line is about to be changed suddenly. Therefore, the second
According to the present invention, the current is blocked by providing the first diode on the communication line in the vicinity of the connection point between the indicator signal sending circuit and the one communication line, and the potential change of the one communication line is slowed down. Then, it tried to suppress the induction to the communication line of other lines. Further, since the balance of both communication lines is impaired simply by providing the first diode, the second diode is also inserted in the other communication line.

The analog subscriber circuit according to the third aspect of the present invention is provided with both the characteristic features of the first and second aspects of the present invention, and exhibits the functions of the first and second aspects of the present invention.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of an analog subscriber circuit according to the present invention will be described in detail below with reference to the drawings. Here, FIG.
2 is a circuit diagram showing the configuration of the first embodiment, and the same or corresponding portions as those in FIG. 2 described above are designated by the same reference numerals.

In FIG. 1, in the analog subscriber circuit 1A of the first embodiment, the following circuit elements are added as compared with the conventional analog subscriber circuit 1.

That is, the inductance element L is connected in series in the series circuit of the message waiting signal sending resistor RMW and the message waiting negative power supply VMW which constitute the message waiting signal sending circuit 5A.
Inserting MW. The inductance element LMW may be inserted between the relay contact 12c and the sending resistor RMW,
It may be between the sending resistor RMW and the negative power supply for message waiting VMW (FIG. 1 shows this case), or between the negative power supply for message waiting VMW and ground. As is well known, the inductance element LMW has a characteristic that its impedance becomes large with respect to a change in current and remains low impedance with respect to a direct current component. The first embodiment utilizes this characteristic. ing.

The connection point between the battery sending side communication line LA and the subscriber circuit basic section 6 and the battery sending side communication line L
A diode DA is inserted in the forward direction with respect to the call current on the battery sending side communication line LA between the connection point between A and the overvoltage protection circuit 4. This diode D
The insertion point of A may be on the subscriber circuit basic unit 6 side from the message waiting signal transmission circuit 5A (see FIG. 1).
Indicates the case), and may be closer to the terminal 2 than the message waiting signal transmitting circuit 5A.
Further, on the ground line sending side communication line LB between the connection point between the ground line sending side communication line LB and the subscriber circuit basic unit 6 and the connection point between the ground line sending side communication line LB and the overvoltage protection circuit 4. , A diode DB is inserted in the forward direction with respect to the call current.

The operation of the analog subscriber circuit 1A according to the first embodiment will be described below, and the functions of the newly provided circuit elements LMW, DA, and DB will be clarified.

When a control unit (not shown) receives an instruction to execute a message waiting function from a certain operator to the terminal 2, the analog subscriber circuit 1A relating to the terminal 2 is received.
The relay control signal MWCTL applied to the message waiting signal sending circuit 5A is changed from the always off state to the state in which the on / off is periodically repeated.

The analog subscriber circuit 1A of the first embodiment
Also, as shown in the signal waveform diagram of each part in FIG. 6, when the relay control signal MWCTL repeatedly turns on and off, the potential VLB of the ground-side sending side communication line LB is almost grounded regardless of this on-off operation. While maintaining the potential G, the potential VLA of the battery transmission side communication line LA changes between potentials different from the power supply voltage VBB for communication and the voltage VMW for message waiting by the voltage drop due to the transmission resistance RMW. By the potential change of the battery sending side communication line LA,
At both ends of the neon tube Ne of the terminal 2, a voltage different from the message waiting voltage VMW and a power supply voltage VBB for communication are alternately applied by a voltage drop due to the sending resistance RMW, and the neon tube Ne blinks. Notify the terminal user that there is a message.

Here, when the relay control signal MWCTL changes from OFF to ON, the above-mentioned charging current (see FIG. 4) tends to flow. In the case of this embodiment, the message waiting signal sending circuit 5A Since the series inductance element LMW is inserted in the battery, the charging current is limited, and as shown in an enlarged view in FIG. 6, the change (falling change) of the potential VLA of the battery transmission side communication line LA is not steep. . That is, the high frequency component is reduced and the induction due to the line capacitance CA can be suppressed. In other words, it is possible to prevent the sending of the message waiting signal from adversely affecting the communication lines of other lines.

Further, when the relay control signal MWCTL changes from ON to OFF, the above-mentioned discharge current (see FIG. 5) tends to flow in the prior art. In the case of this embodiment, however, in the battery sending side communication line. Since the diode DA is inserted in LA, the reverse current blocking function of this diode DA prevents the discharge current from flowing through the route as shown in FIG. 5, and the charged electric charge is slowly discharged by the resistance of the terminal 2 or the like. It As a result, even during this change, FIG.
As enlarged and shown, the change (rise change) of the potential VLA of the battery transmission side communication line LA is not steep. That is, the high frequency component is reduced, the induction due to the line capacitance CA can be suppressed, and the message waiting signal is transmitted.
It is possible to prevent the communication line of another line from being adversely affected.

Although the function of suppressing the induction at the time of such discharge can be obtained only by inserting the diode DA,
The transmission between the analog subscriber circuit 1A and the terminal 2 is basically balanced transmission for signals other than the message waiting signal, and in order to maintain the balance of the pair of communication lines LA and LB at the time of transmission of a call signal or the like, A diode DB is also inserted on the ground transmission side communication line LB side.

Therefore, according to the first embodiment, even when the message waiting signal is transmitted, the falling changes and rising changes of the potential VLA of the battery sending side communication line LA are slowed down, and as a result, the high frequency components are reduced. However, it is possible to suppress the induction which is the coupling due to the line capacitance with the communication line of the other line. As a result, it is possible to prevent the call quality of the other line from deteriorating.

In order to exert such an effect, the newly provided inductance element LMW is inserted in the message waiting signal sending circuit 5A not related to the transmission of the call signal, and is newly provided. Since the diodes DA and DB are inserted in the forward direction with respect to the path of the call current, they do not hinder balanced transmission of the call signal or the like.

FIG. 7 is an explanatory diagram showing the characteristic construction of the second embodiment of the analog subscriber circuit according to the present invention.

In the first embodiment, the message waiting signal transmitting circuit 5A of each analog subscriber circuit 1A.
Although the inductance element LMW for limiting the charging current is provided for each of them, the analog subscriber circuit of the second embodiment has the inductance element LMW as shown in FIG.
The MW is shared by the message waiting transmission circuits (5B-1 to 5B-n) of the plurality of analog subscriber circuits (1A).

In FIG. 7, reference numerals 5B-1, ...,
The circuit parts denoted by 5B-n are the parts consisting of the relay contact 12c and the message waiting signal sending resistance RMW in FIG. 1, respectively.
... 5B-n shall also mean the entire message waiting transmission circuit.

As described above, the inductance element LMW has the characteristic that the impedance becomes large with respect to the change in current and remains low with respect to the direct current component. Therefore, even if the inductance element LMW is shared by the plurality of message waiting sending circuits 5B-1 to 5B-n, the sending operation of the message waiting signal of a certain message waiting sending circuit 5B-i (i is 1 to n) is different. It has almost no effect on the message waiting transmission circuit or communication line of the line.

According to the second embodiment, since the inductance element LMW for suppressing the charging current is shared by a plurality of analog subscriber circuits, the entire PBX and each analog subscriber circuit are simple in construction. Therefore, the cost can be reduced. Further, it is not necessary to add the inductance element LMW, which is a relatively large component, to each analog subscriber circuit, and the configuration can be made easy.

FIG. 8 is a circuit diagram showing the configuration of a third embodiment of the analog subscriber circuit according to the present invention, which is shown in FIG.
The same or corresponding portions as and are designated by the same reference numerals.

Analog subscriber circuit 1C of the third embodiment
Is compared with the analog subscriber circuit 1A of the first embodiment,
The configuration of the message waiting signal sending circuit 5C is different.

That is, in the message waiting signal sending circuit 5A of the first embodiment, the message sending negative power source VMW is connected to the battery sending side communication line LA.
Changeover switch (12, 12c) for connecting the sides
In the message waiting signal sending circuit 5C of the third embodiment, the changeover switch 12 for connecting the message waiting negative power source VMW side to the battery sending side communication line LA.
A two-contact configuration is applied as C. Where 2
The contact configuration changeover switch 12C may be a mechanical switch such as a relay and its contact (so-called b contact or a contact), or may be a semiconductor switch such as a switching transistor, a photocoupler, or an optical MOS switch. The latter is generally cheaper and can contribute to a lightweight and compact structure.

In the first embodiment, the diode DA is inserted from the message waiting signal transmitting circuit 5A to the subscriber circuit basic portion 6 side, but from the message waiting signal transmitting circuit 5A to the terminal 2 side. However, in the third embodiment, the insertion position of the diode DA is limited to the subscriber circuit basic section 6 side from the message waiting signal transmission circuit 5C.

Applicability of the changeover switch 12C having a two-contact structure is related to the fact that the diode DA is provided at such a position.

In the first embodiment, as described above,
It is characterized by the addition of new circuit elements LMW, DA, and DB, and the changeover switch follows the conventional circuit. Therefore, let us consider a case where the changeover switch (12, 12c) in the conventional circuit shown in FIG. 2 is replaced with a switch having a two-contact structure as in the third embodiment.

Under this assumption, it is assumed that the changeover switch is turned on in order to connect the message waiting negative power source VMW side to the battery sending side communication line LA. At this time, the electric potential V of the battery transmission side communication line LA
Although the LA can be changed to a predetermined potential, the negative terminal power supply VMW for message waiting is also connected to the subscriber circuit basic unit 6 which is designed to operate at the power supply voltage VBB for communication, and the subscriber circuit basic unit 6 is also provided. There is a risk that current will be drawn from the side and the subscriber circuit basic unit 6 will malfunction. Therefore, in the conventional circuit, the changeover switch (12, 12c) having a three-contact structure is applied, and the battery sending side communication line LA is used.
Even when the negative power supply VMW for message waiting is connected, the negative power supply VMW for message waiting is prevented from being connected to the subscriber circuit basic unit 6.

However, in the third embodiment, the diode DA is inserted from the message waiting signal transmitting circuit 5C to the subscriber circuit basic portion 6 side. for that reason,
Even when the changeover switch 12C is applied to the changeover switch 12C and the changeover switch 12C is turned on in order to connect the message waiting negative power source VMW side to the battery transmission side communication line LA, the diode DA is the basic circuit of the subscriber circuit. Negative power supply VMW for message waiting from section 6 side
It is possible to prevent a current from flowing toward the subscriber circuit basic unit 6 and prevent the subscriber circuit basic unit 6 from malfunctioning.

As described above, according to the third embodiment, the changeover switch of the message waiting signal transmitting circuit has a 2-contact structure which is smaller and cheaper than the 3-contact structure which cannot be applied in the conventional circuit. It can be applied to configure an analog subscription circuit. In particular, when a semiconductor switch is applied, the effect of downsizing and cost reduction is great.

In the above embodiment, the signal sent to the terminal is the message waiting signal, but the signal sent to the terminal may have a different meaning. In the claims, such a transmission signal is expressed as an indicator signal.

The configuration of the overvoltage protection circuit and the like which is not directly related to the function of transmitting the message waiting signal is as follows.
The invention is not limited to the above embodiment.

Further, the inductance element LMW for limiting the charging current is not limited to the coil but may be a microstrip line or the like.

[0056]

As described above, according to the present invention, the indicator signal sending circuit including the series circuit including the power source for the indicator and the indicator signal sending resistor and the changeover switch is provided, and the terminal is connected to the terminal through the changeover switch. In an analog subscriber circuit for sending an indicator signal to a terminal by connecting the series circuit to one of a pair of connected communication lines, an inductance element is provided in a series circuit composed of an indicator power supply and an indicator signal sending resistor. Since it has been inserted, even if the above series circuit is switched from the state where it is not connected to one communication line to the state where it is connected, the current due to the line capacity with the communication line of the other line can be limited, The potential change of the line can be blunted, and the induction to the communication line of other lines can be suppressed.

Further, according to the present invention, on the communication line in the vicinity of the connection point between the indicator signal transmitting circuit and one of the communication lines, the forward direction is set to the path along which the normal call current flows. The first diode is inserted into the communication line, and at the position on the other communication line where the balance with the one communication line can be maintained, the forward direction is set to the path through which the normal call current flows. Since the second diode is inserted in, while compensating the balanced transmission of the call signal,
Even if the above series circuit is switched from the state where it is connected to one communication line to the state where it is not connected, it is possible to prevent the current from flowing out from the basic part of the subscriber circuit, and slow down the potential change of one communication line. , It is possible to suppress the induction to the communication line of other lines.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a first embodiment.

FIG. 2 is a circuit diagram showing a conventional configuration.

FIG. 3 is a signal waveform diagram of each part of the circuit shown in FIG.

FIG. 4 is an explanatory diagram (Part 1) of a defect of the conventional circuit.

FIG. 5 is an explanatory diagram (part 2) of a defect of the conventional circuit.

FIG. 6 is a signal waveform diagram of each part of the first embodiment.

FIG. 7 is an explanatory diagram of the second embodiment.

FIG. 8 is a circuit diagram showing a configuration of a third embodiment.

[Explanation of symbols]

1A, 1C ... Analog subscriber circuit, 2 ... Terminal, 5A, 5
B-1 to 5B-n, 5C ... Message waiting signal sending circuit, 6 ... Subscriber circuit basic part, 12c ... Relay contact (3 contact configuration), 12C ... 2 contact configuration changeover switch, LMW ... Inductance element, DA, DB ... Diode, LA ... Battery sending side communication line, LB ... Ground sending side communication line, RMW ... Message waiting signal sending resistance, VMW ... Message waiting negative power source (message waiting voltage), VBB ... Call supply voltage .

Claims (5)

[Claims] 1. A serial circuit composed of an indicator power supply having a voltage several times higher than the power supply voltage for communication (not necessarily an integral multiple) and an indicator signal transmission resistance, and an indicator signal transmission circuit composed of a changeover switch, In the analog subscriber circuit for sending the indicator signal to the terminal by connecting the series circuit to one of a pair of communication lines connected to the terminal through the changeover switch, the indicator power supply and the indicator An analog subscriber circuit characterized in that an inductance element is inserted in a series circuit composed of signal transmission resistors. 2. A series circuit comprising an indicator power supply having a voltage several times higher than the power supply voltage for communication (not necessarily an integer multiple) and an indicator signal transmission resistor, and an indicator signal transmission circuit including a changeover switch, An analog subscriber circuit for sending an indicator signal to the terminal by connecting the series circuit to one of a pair of communication lines connected to the terminal via the changeover switch, and one of the indicator signal sending circuit and the indicator signal sending circuit. A first diode is inserted on the communication line in the vicinity of the connection point with the communication line so as to be in the forward direction with respect to a path through which a normal call current flows, and the one communication line At the position on the other communication line where the balance between the two can be maintained, and the second dial is provided so as to be in the forward direction with respect to the path through which the normal call current flows. Analog subscriber circuit, characterized in that it was inserted through the diode. 3. A series circuit comprising an indicator power supply having a voltage several times higher than the power supply voltage for communication (not necessarily an integer multiple) and an indicator signal transmission resistance, and an indicator signal transmission circuit comprising a changeover switch, In the analog subscriber circuit for sending the indicator signal to the terminal by connecting the series circuit to one of a pair of communication lines connected to the terminal through the changeover switch, the indicator power supply and the indicator An inductance element is inserted in a series circuit consisting of signal transmission resistors, and a normal call current flows on the communication line in the vicinity of the connection point between the indicator signal transmission circuit and one of the communication lines. The first to be forward
The second diode is inserted so that the equilibrium with one communication line can be maintained, and the second communication line is forwarded to a position on the other communication line where a normal call current flows. An analog subscriber circuit characterized by inserting a diode. 4. The analog subscriber circuit according to claim 1 or 3, wherein the inductance element is used in common with another analog subscriber circuit. 5. A switch having a two-contact structure, wherein the first diode is inserted on the subscriber circuit basic side from a connection point between the indicator signal sending circuit and one of the communication lines, and the changeover switch has two contacts. The analog subscriber circuit according to claim 2 or 3, characterized in that