JPH1174968A - Automatic converter for terminal device in telephone line and terminal device for telephone line - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively prevent noise that is caused by common mode noise from a commercial power supply by providing high pass filter circuits which bypass electronic switch circuits. SOLUTION: Automatic converters SW1 and SW2 for a terminal device in a telephone line consist of electronic switch circuits SWa and high pass filter circuits SWb that bypass the circuit SWa. The circuits SWa are provided with a trigger circuit which serially connects zener diodes ZD1 and ZD2 of reverse polarity and resistance R1 against a bidirectional triac T1. Also, the circuits SWb comprise a serial circuit of resistance R and a condenser C. The circuits SWa bypass a noise component and maintain the balance of ground impedance of telephone lines L1 and L2 even when the terminal device is not used and the circuits SWa do not operate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for switching a plurality of terminal devices connected to a single telephone line.
An automatic converter for a terminal device in a telephone line, which can effectively prevent noise mixed in a telephone during a call;
The present invention relates to a terminal device for a telephone line.

[0002]

2. Description of the Related Art When a plurality of telephones are connected in parallel to a single telephone line, an automatic converter for a telephone having a confidential function is used to automatically connect each telephone to the telephone line individually. (For example, Japanese Utility Model Publication No. 3-6063, FIG. 6).

[0003] This is based on telephone lines L1 and L2.
A plurality of telephones TEL1 and TEL2 are connected in parallel via automatic converters SW1 and SW2 having a secret function. Each automatic converter SWi (i = 1, 2) has a built-in electronic switch circuit composed of, for example, a bidirectional triac or a combination of a bridge rectifier circuit and a transistor or a unidirectional thyristor. TELi (i = 1,
It is inserted on one side of 2). The electronic switch circuit is
The operation is triggered by the normal line voltage of the telephone lines L1 and L2 and the ringing signal at the time of an incoming call, but any one telephone TELi is in a call and the line voltage of the telephone lines L1 and L2 is Is set not to be triggered when is reduced to a busy level. So, the telephone TELi
Means that when an incoming call is received from outside, the two units simultaneously ring a bell for calling, but if one unit goes off-hook, the other unit will ring.
The stand has become unusable, and mutual confidential functions have been realized.

[0004]

According to the prior art, when each telephone uses an external commercial power supply, unpleasant noise may be mixed into the telephone during a call, thereby deteriorating the call quality. There was a problem. Each telephone has an automatic converter on one side,
The balance of the ground impedance of the telephone line cannot be maintained when not in use, so the common mode noise from the commercial power supply is converted to normal mode noise, and becomes a nonnegligible noise level that enters the telephone during a call. It is because.

[0005] Such noise can be prevented by making the automatic converter a double-ended type and disconnecting both lines of the telephone not in use from the telephone line. A set of electronic switch circuits is required, which complicates the circuit configuration and inevitably increases the cost. Also, this kind of noise can occur when not only a telephone but also any terminal equipment using a commercial power supply such as a facsimile apparatus or a communication modem apparatus of a computer system is connected in parallel to a telephone line.

Accordingly, an object of the present invention is to provide a high-pass filter that bypasses an electronic switch circuit, or to use a converter only for one terminal device in view of the problems of the related art. Another object of the present invention is to provide an automatic converter for a terminal device in a telephone line and a terminal device for a telephone line that can effectively prevent noise caused by common mode noise from a commercial power supply.

[0007]

According to a first aspect of the present invention, an electronic switch circuit having a secret function and a high-pass filter circuit bypassing the electronic switch circuit are provided. Is the gist.

The high-pass filter circuit only needs to be able to pass through the audio band, and may be a series circuit of a resistor and a capacitor.

The gist of the second invention is to provide a terminal device connected in parallel to a single telephone line and a converter for inserting one of the terminal devices into one line.

[0010] The converter may be the automatic converter according to the first invention.

[0011]

According to the first aspect of the invention, the electronic switch circuit having the privacy function can disable one of a plurality of terminal devices connected in parallel to a single telephone line when the other is used. it can. In addition, the high-pass filter circuit can maintain the balance of the ground impedance of the telephone line by bypassing the noise component even when the terminal device is not in use and the electronic switch circuit is not operating. Therefore, the common mode noise from the commercial power supply that supplies power to the unused terminal device is not converted into a high-level normal mode noise.

The high-pass filter circuit only needs to be able to bypass a noise component corresponding to an audio frequency component in order to prevent noise from being sensed by a telephone during a call, and is capable of passing a noise component in a voice band. do it.
In addition, by using such a high-pass filter circuit, the noise resistance of the electronic switch circuit against high-frequency noise can be improved, and terminal equipment such as a facsimile apparatus can be provided by Nippon Telegraph and Telephone Corporation. The automatic ringing reception service can be used as it is. This is because the silent automatic reception service uses an audio signal of 1300 Hz as a calling signal.

On the other hand, the high-pass filter circuit has the simplest circuit configuration by using a series circuit of a resistor and a capacitor, and the manufacturing cost can be reduced.

According to the configuration of the second invention, the converter is
One terminal device is inserted only on one line side, and the other terminal device is directly connected to a telephone line. Therefore, even if the terminal device on the side directly connected to the telephone line cannot realize the confidential function, there is no fear of disturbing the balance of the ground impedance of the telephone line during use or non-use, It does not become a source of noise due to common mode noise from the commercial power supply to other terminal equipment, eliminates extra circuit loss due to the insertion of a converter, and provides a margin for limiting the burden on telephone lines. Can be bigger.

It is preferable to select a terminal device that does not require a secret function, such as a facsimile device or a communication modem device, for example, as the terminal device directly connected to the telephone line. This is because, when these devices are set to automatic transmission, when another terminal device is in use, the dial transmission function is automatically stopped, and there is no possibility of interference with other terminal devices. Also, the terminal device directly connected to the telephone line in this way can naturally use the silent automatic reception service.

The converter according to the second aspect of the present invention includes, in addition to the automatic converter according to the first aspect, an electronic switch circuit having only a confidential function, an electronic switch circuit having no confidential function, automatic or Any type, such as a manual mechanical switch, can be used.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

An automatic converter SWi (i = 1, 2) for a terminal device on a telephone line comprises an electronic switch circuit SWa,
And a high-pass filter circuit SWb which bypasses the electronic switch circuit SWa (FIG. 1). In addition, each automatic converter SW
i is inserted on one side of the telephone set TELi (i = 1, 2), and can connect the telephone set TELi to the telephone lines L1, L2. In addition, the telephone TELI here refers to any terminal device including a facsimile device, a communication modem device, and the like, in addition to the telephone.

The electronic switch circuit SWa includes a zener diode ZD having a reverse polarity to the bidirectional triac T1.
1, a trigger circuit for connecting ZD2 and a resistor R1 in series. Also, a high-pass filter circuit SWb
Is constituted by a series circuit of a resistor R and a capacitor C.

The Zener diodes ZD1 and ZD2 set the bidirectional trigger voltage of the triac T1. That is, the triac T1 is triggered when the line voltage of the telephone lines L1 and L2 is normal or when a ringing signal at the time of incoming call is received. Zener diode Z
A trigger voltage is set via D1 and ZD2.

When both telephones TELi are on-hook, no DC closed loop is formed in each telephone TELi. Therefore, the triac T1 of each electronic switch circuit SWa is not triggered even if the line voltage of the telephone lines L1 and L2 is at the normal DC level.

At the time of an incoming call from the outside, the telephone line L1
, L2, the triac T1 of both electronic switch circuits SWa, SWa is simultaneously triggered to conduct. This is because an AC closed loop capable of supplying a calling signal is formed in the telephone set TELi at the time of on-hook. That is, both of the telephone sets TELi can make a ringing bell sound.

One of the telephones T responds to the ringing tone for calling.
When ELi is off-hook, a DC closed loop is formed in the telephone set TELi, and the triac T1 of the electronic switch circuit SWa corresponding to the telephone set TELi is triggered. Therefore, the line voltage of the telephone lines L1 and L2 is reduced to the level during the call, and the call can be made by the telephone TELi. However, at this time, even if the other telephone TELj (j ≠ i) is off-hook, the corresponding electronic switch circuit SWa activates the internal triac T1.
Does not trigger, and a secret conversation function between the telephone sets TELi can be realized.

The resistor R and capacitor C of each high-pass filter circuit SWb have an appropriate time constant and can pass through the voice band. That is, even when the triac T1 of the electronic switch circuit SWa is not conducting, the high-pass filter circuit SWb bypasses a noise component corresponding to an audio frequency component, and at least in the frequency domain of the noise component, the telephone line L1, The balance of the impedance of L2 with respect to the ground is maintained to prevent the impedance from being extremely collapsed. Therefore, the high-pass filter circuit SWb is connected to the unused telephone T
It is possible to effectively prevent common mode noise from the commercial power supply that supplies power to ELi from being converted into high-level normal mode noise and from being mixed into another telephone TELj during a call.

In the above description, the high-pass filter circuit S
Wb may be constituted by any circuit element other than the resistor R and the capacitor C as long as it has appropriate frequency characteristics.

[0026]

[Other Embodiments] Each electronic switch circuit SWa may use a bridge rectifier circuit DB and a unidirectional thyristor SC connected to the output side of the bridge rectifier circuit DB as switching elements (FIG. 2). Thyristor SC anode,
A Zener diode ZD1 and a resistor R2 are connected between the gates, and a resistor R1 is connected between the gate and the cathode. Zener diode ZD1 sets the trigger voltage of thyristor SC. The thyristor SC short-circuits the output side of the bridge rectifier circuit DB, thereby making the input side of the bridge rectifier circuit DB conductive in both directions, and can operate in the same manner as the triac T1 in FIG. 1 as a whole.

In the electronic switch circuit SWa, a switching circuit composed of transistors TR1 and TR2 may be combined with the bridge rectifier circuit DB (FIG. 3).

On the output side of the bridge rectifier circuit DB, a zener diode ZD1, a series circuit of resistors R1, R2, a resistor R4, and a series circuit of a transistor TR1 are connected in parallel. The emitter of another transistor TR2 is connected to the connection point of the Zener diode ZD1 and the resistor R4, and the base and collector of the transistor TR2 are connected to the collector of the transistor TR1 via the resistor R3, respectively. It is connected to the connection point of the resistor R1. The base of the transistor TR1 is connected to a connection point between the resistors R1 and R2. Also,
A series circuit of a resistor R5 and a light emitting diode LED, and a zener diode ZD2 are connected in parallel to the resistor R4.

When the telephone TELi is off-hook, the transistor TR1 conducts through the Zener diode ZD1, and the telephone TELi becomes usable. On the other hand, the transistor TR2 is turned on when the transistor TR1 is turned on, and the transistor TR1 is turned on even if the line voltage of the telephone lines L1 and L2 drops to the busy level and the Zener diode ZD1 is cut off. Can be held. At this time, even if the other telephone TELj is off-hook, the corresponding electronic switch circuit S
Wa transistor TR1 is connected to Zener diode ZD1.
Do not conduct, and therefore do not conduct.

When an incoming call is received from the outside, the transistors TR1, T2 of the two electronic switch circuits SWa, SWa are turned on.
R1 conducts all at once, causing a bell sound. Further, the light emitting diode LED emits light to indicate the conduction of the transistor TR1, and this may be provided as needed.
You may delete it.

In FIG. 3, Zener diode ZD1,
The transistor TR2 may be omitted, and the photoswitch element PC2b may be provided between the base and the emitter of the transistor TR1 (FIG. 4). However, the photo switch element PC2b is the light emitting element PC2a on the other automatic converter SW2 side.
It is assumed that the optical coupling is performed.

In FIG. 4, a series circuit of a resistor R6 and a light emitting element PC1a is additionally connected in parallel to a resistor R4 on the automatic converter SW1 side. The light-emitting element PC2a and the photoswitch element PC1b are incorporated in the automatic converter SW2 in exactly the same manner as the automatic converter SW1. The photoswitch element PC1b is connected to the light-emitting element PC1 on the automatic converter SW1 side.
Optically coupled to 1a. In each automatic converter SWi, the resistor R2 between the base and the emitter of the transistor TR1 is also omitted.

Transistor TR1 on automatic converter SW1 side
Is turned on, the light emitting element PC1a emits light, and the photo switch element PC1b of the automatic converter SW2 on the other side is turned on.
The conduction of the corresponding transistor TR1 can be prevented. Conversely, the transistor TR1 on the automatic converter SW2 side
Is turned on, the light emitting element PC2a emits light and the automatic converter S
The W1 photoswitch element PC2b is turned on, and the corresponding transistor TR1 can be turned off. In addition, the light emitting diode LED of FIG. 4 may be provided as needed.

The automatic converter SWi of FIGS. 1 to 3 can be constructed as a terminal for a telephone line by inserting it as an automatic converter SW2 only on one side of one telephone TEL2 (FIG. 5). ). Since the telephone TEL1 is directly connected to the telephone lines L1 and L2, the telephone lines L1 and L2
(2) There is no risk of disturbing the ground impedance balance, and even if it is a telephone using an external commercial power supply (not shown), a facsimile machine, a communication modem, etc., it may become a noise source for the telephone TEL2 during a call. Absent. Note that the automatic converter SW2 in FIG. 5 may be any other type of automatic or manual converter.

[0035]

As described above, according to the first aspect of the present invention, by providing the high-pass filter circuit that bypasses the electronic switch circuit, the high-pass filter circuit operates the electronic switch circuit. Even when there is no such effect, the excellent effect that the noise component is bypassed to maintain the balance of the earth impedance of the telephone line, and thus the noise caused by the common mode noise from the commercial power supply can be effectively prevented. is there.

According to the second aspect of the present invention, by inserting a converter on one side of the terminal equipment, the other terminal equipment is directly connected to the telephone line, and is caused by common mode noise from a commercial power supply. There is an excellent effect that it does not become a source of noise.

[Brief description of the drawings]

FIG. 1 is a block diagram of the overall configuration

FIG. 2 is a main block diagram showing another embodiment (1).

FIG. 3 is a main block diagram showing another embodiment (2).

FIG. 4 is a view corresponding to FIG. 1, showing another embodiment.

FIG. 5 is a schematic view showing another embodiment.

FIG. 6 is a schematic block diagram showing a conventional technique.

[Explanation of symbols]

 L1, L2: telephone line SWi (i = 1, 2): automatic converter SWa: electronic switch circuit SWb: high-pass filter circuit R: resistor C: capacitor

Claims (5)

[Claims] An electronic switch circuit having a secret talk function;
An automatic converter for terminal equipment in a telephone line, comprising a high-pass filter circuit bypassing the electronic switch circuit. 2. The automatic converter according to claim 1, wherein the high-pass filter circuit is capable of passing a voice band. 3. The automatic converter according to claim 1, wherein said high-pass filter circuit is a series circuit of a resistor and a capacitor. 4. A terminal device for a telephone line, comprising: a terminal device connected in parallel to a single telephone line; and a converter inserted into one of the terminal devices on one side. 5. The converter according to claim 1, wherein
The terminal device for a telephone line according to claim 4, wherein the terminal device is an automatic converter according to any one of the above.