JPH02279091A - Line interface circuit - Google Patents

Abstract

PURPOSE: To prevent a bell from ringing temporarily on the occurrence of polarity inversion by connecting a capacitor that had been connected between a tip primary winding and a ring primary winding to a secondary winding. CONSTITUTION: In a conventional connection, if polarity inversion takes place in a subscriber telephone line, when polarity of a current supplied via a tip terminal 2 and a ring terminal 3 is inverted, a capacitor is discharged on the moment of polarity inversion to tend to have caused a short time bell ringing in a telephone set 100. Then the capacitor 7 having been connected to the primary winding conventionally is reconnected to a secondary winding 6 together with resistors 16, 16a, 17, 17a, 18. In this case, an impedance characteristic of a line interface circuit measured between the tip terminal 2 and the ring terminal 3 is equivalent to an impedance characteristic of a circuit for a voice frequency band consisting of the capacitor 7 and the resistors 16, 17 connected in series therewith. Thus, the bell ringing of a bell of a telephone subscriber caused on the occurrence of polarity inversion is temporarily prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to a line for supplying current to a subscriber's telephone line and for coupling signals between the subscriber's telephone line and switching equipment in the field of telephones. This relates to an interface circuit.

BACKGROUND OF THE INVENTION In a typical prior art telephone switching system, line interface circuits were used to interface with the subscriber telephone lines of the telephone switching system.

The line interface circuit is typically connected to the tip-side feed line and the ring-side feed line of the subscriber telephone line and has an identical primary winding split in two and a secondary winding connected to a hybrid circuit. Equipped with a transformer.

Direct current is supplied to the subscriber's telephone line through the divided primary winding, the tip-side feed resistor and the ring-side feed resistor to operate the telephone set and equivalent equipment connected to the end of the subscriber's telephone line.

The line interface circuit may further include a tertiary winding similar to that disclosed in US Patent No. 4.103.112, sometimes cited as a balanced winding.

In any case, one side of the divided primary winding is usually connected in series with a capacitor device, typically a capacitor.
Conducts alternating signal current.

If there is no capacitor, the alternating signal current will take another path,
In this example, it would flow through the tip and ring side feed resistors. In fact, in the lower part of the audio band, a portion of the AC signal current will flow through the tip and ring side feed resistors. This is because in these low frequency bands, the conductance of the capacitor is close to the conductance of the tip and ring side feed resistors.

This has a detrimental effect on the operation of the line interface and is the subject of US Patent No. 004.864.609. The value of the capacitor is an important factor in defining the termination impedance of the line interface circuit. Therefore, every telephone company has predetermined capacitor values for various types of line interface circuits.

Recently, some telephone companies have introduced telemetry services in which meter readings of supplied goods are made by communication from the subscriber's home via the telephone system to the supplier of the goods. Such products include water, gas or electricity.

In such services, a reversal of the polarity of the supply current applied to the line interface circuit switches from the telephone to the telemetry equipment located in the subscriber's home.

This can be easily done by switching between the chip side feed line and the ring side feed line connected to the ends of the primary windings of the divided transformer for a few seconds while the telemetry device responds. After the telemetry device responds, normal connection is restored.

[Problem to be Solved by the Invention] However, conventionally, in many such system configurations, the electric charge accumulated in the capacitor connected between one side of the two divided primary windings is transferred to the subscriber telephone. When the line polarity was switched, a surge current was generated that could momentarily activate the bell inside the telephone.

Because telemetry is performed while the subscriber unit is idle, it is typically performed for short periods of time during the night when the telephone is least likely to be used. A telephone subscriber who is a light sleeper but wants to keep his phone close to him will be disturbed by the first ringing sound when the polarity of the power supply is reversed. Then, after a second or two, a second bell will sound when the line interface circuits are restored to normal connectivity.
Telephone subscribers will once again be bothered by telephone rings.

The purpose of this invention is to connect the capacitor conventionally connected to the primary winding side of the transformer to the secondary winding side, thereby essentially avoiding the erroneous generation of a ringing sound due to accumulated charge that occurs when switching the power supply polarity. It provides a line interface circuit.

Yet another object of the invention is to provide an economical and attractive line interface circuit for use with telephone switching equipment used to collect telemetry data.

[Means for Solving the Problems] The present invention provides a hybrid circuit that supplies direct current from a power supply to a tip side supply line and a ring side supply line of a subscriber telephone line, and is connected to the subscriber telephone line and a telephone exchange. In a line interface circuit that couples AC signals between A chip side power supply resistor and a ring side power supply resistor connected to the , a chip primary winding and a ring primary winding connected to the chip side terminal and the ring side terminal respectively, and a secondary winding connected to the hybrid circuit. and a transformer connected in polarity such that the directions of the feeding currents of the chip primary winding and the ring primary winding are magnetically added; In this case, an external reactance having a value such that the primary winding is transformer-coupled with a constant complex impedance is provided.

[Function] In the present invention, without connecting a capacitor between the chip primary winding and the ring primary winding, a capacitor that operates in the same way is connected to the secondary winding side. Prevents the bell from ringing.

[Embodiment] A specific example of the present invention will be described in detail below using a configuration diagram of a line interface circuit according to an embodiment of the present invention.

The telephone 100 is connected to a telephone exchange (not shown) via a tip-side power supply line 24, a ring-side power supply line 25, and a line interface circuit.

The chip-side power supply line 24 and the ring-side power supply line 25 are connected to the chip-side terminal 2 and the ring-side terminal 3, respectively.

The transformer 10 includes a chip primary winding 4 and a ring primary winding 5. The chip primary winding 4 is connected to the ground terminal of the local power supply and the chip side terminal 2, and the ring primary winding 5 is connected to the local power supply. It is connected to the negative polarity (-■) terminal of the device and the ring side terminal 3. Such a connection typically allows phone 1
When the 00 is in the off-hook state, the power supply voltage is applied to the phone, and the DC supply current flows from the ground terminal to the chip side power supply resistor 12 to the chip primary winding 4 to the break contact 21 to the chip side terminal 2 to the chip side supply. Flows in the direction of the electric wire 24 → telephone 100 → ring side power supply line 25 → ring side terminal 3 → break contact 31 - ring primary winding 5 - ring side power supply resistor 13 - negative polarity (-■) terminal of the station power supply, Telephone 100 operates.

The transformer 10 further includes a secondary winding 6, which is connected to the hybrid circuit 50 via a capacitor 7 and resistors 16.16a, 17.17a, 18. The secondary winding is essential for coupling AC signals between the telephone exchange and telephone 100.

The AC signal flows through the same circuit elements as described above for the DC supply current. However, the chip side power supply resistor 12 and the ring side power supply resistor 13 are set to such values that the voltage drop of the AC audio band signal is small.

According to the traditional design of line interface circuits, points 4a and 5a in the drawing usually contain capacitor elements for carrying most of the AC signal energy between the chip primary winding 4 and the ring primary winding 5. was connected. However, in conventional connections, as mentioned above, if the polarity of the subscriber telephone line is switched, thereby reversing the polarity of the supply current supplied via the tip-side terminal 2 and the ring-side terminal 3; , the capacitor discharged at the moment of polarity switching, and the capacitor tended to cause a brief ringing operation within the telephone 100.

Therefore, the solution to this problem is to bring the capacitor 7, which was conventionally on the primary winding side, to the secondary winding 6 side, and to
6.16a, 17.17a, and 18.

There, the impedance characteristics of the line interface circuit measured between the chip side terminal 2 and the ring side terminal 3 are
In the audio band, a resistor (
16, 17).

Hybrid circuit 50 is connected as shown in the figure, and the effective input impedance of hybrid circuit 50 is determined by the values of resistors 16a and 17a.

Hybrid circuit 50 is operative to receive AC signals from the telephone exchange via receive path 51 and to transmit AC signals to the telephone exchange via transmit path 52. The signal from receive path 51 is amplified and applied via balanced voltage section terminal 53 and transformer 10 to the subscriber's telephone line.

Break contact 21 and make contact 22 operated by relay armature 19, break contact 31, and make contact 3
2, it is possible to control positive polarity and reverse polarity and give energy to the communication line. Said relay armature 19 is controlled by the telephone exchange. When connecting the telemetry device 101 to a communication line, the telephone 10
Connected in parallel with 0.

It is not necessary to understand the functionality of the line interface circuitry to understand the operation of telemetry device 101. That is, the telemetry device 101 only transmits data of any content via the subscriber's telephone line when a power reversal occurs. Data is transmitted in various signal formats, such as dial pulse signals, in-band single frequency signals, DTMF signals, or frequency shift keying data signals. To operate the telemetry device 101, lead 1 is activated by a signal from the telephone exchange side.
By grounding 9a, the relay 19 is operated, the break contact 21 and the break contact 31 are opened, and then the make contact 22 and the make contact 32 are closed. In that way, the supply current is rerouted via the board 23, 33, and a reversal of the power supply polarity occurs at the point of the tip-side terminal 2 and the ring-side terminal 3. Such operation takes place without any significant surge currents in the communication lines since the capacitor 7 is connected to the secondary winding and is isolated from the direct supply current path.

This line interface circuit is intended to be a direct replacement for the conventional line interface circuit normally used in telephone exchanges, and operates in the same way.
Even if it is replaced, it will not have any significant effect on operation.

Dial and monitoring are detected in the line interface circuit by using a differential amplifier circuit 40 comprising a differential amplifier 41 having an inverting input, a non-inverting input and an output 48.

Resistors 42-44 are connected to a differential amplifier circuit 40 as shown. The input of the differential amplifier circuit 40 is connected to a chip voltage divider made up of resistors 14a and 14b and a ring voltage divider made up of resistors 15a and 15b, as shown. This arrangement is similar to that described in the V. V. Korsky patent mentioned above. This configuration can also be realized by a combination of suitable circuits (not shown) to perform magnetic flux cancellation as is commonly used in many current line interface circuits.

Capacitor 47 is connected in parallel with resistor 44, and output 48
The dots show dial pulses and rising and falling characteristics, which are on-hook and off-hook state transitions. Its output point 48
The characteristics of the monitoring signal are generally the same as those that would be exhibited if a capacitor was connected between points 4a and 5a.

An example of the values of each element shown in the drawings in the configuration of the line interface circuit is shown below.

Resistance 12.13 200
Ω14a: 14b 15a, 15b・・・・・・・・・ Ω1 to 300
6 17・・・・・・・・・ Self 450Ω16a
17a・・・・・・・・・ Ω18 to 300
・・・・・・・・・・・・・・・ IOKΩ42
・・・・・・・・・・・・・・・・・・ 5.08Ω
43 ・・・・・・・・・・・・・・・ 8 to Ω4
4 ・・・・・・・・・・・・・・・ Ω capacitor in 14 7・・・・・・・・・・・・・・・ 2.16
μF47・・・・・・・・・・・・・033μF
Note that the present invention is not limited to the above-mentioned exemplary values.

[Effects of the Invention] The present invention provides a line interface circuit which temporarily prevents a telephone subscriber's bell from ringing due to the charge accumulated in the capacitor when the polarity is reversed by having the line ink face circuit configuration as described above. can be provided.

[Brief explanation of drawings]

The figure shows a block diagram of an embodiment of the invention. 2... Chip side terminal, 3... Ring side terminal, 4...
・Chip primary winding, 5...Ring primary winding, 6...
Secondary winding, 7... Capacitor, 10... Transformer,
12...Bachitsubu side power supply resistance, 13...Ring side power supply resistance, 21.31...Break contact, 22.32...
・Make contact, 24... Chip side feeder line of the subscriber's telephone line, 25... Ring side feeder line of the subscriber's telephone line, 4
0... Differential amplifier circuit, 41... Differential amplifier, 44...
...Resistor, 47...Capacitor, 50...Hybrid circuit, 100...Telephone, 101...Telemetry device

Claims (1)

[Claims] 1. Direct current from a power supply is supplied to the tip side supply line and ring side supply line of the subscriber telephone line, and AC current is supplied between the subscriber telephone line and the hybrid circuit connected to the telephone exchange. In a line interface circuit that couples signals, the chip-side terminal and ring-side terminal are connected to the chip-side feed line and the ring-side feed line, respectively, and the chip-side feed resistor and ring are connected to the positive and negative terminals of the DC power supply, respectively. A side power supply resistor, a chip primary winding and a ring primary winding connected to the chip side terminal and the ring side terminal, respectively, and a secondary winding connected to the hybrid circuit, and the chip primary winding A transformer is connected with polarity such that the directions of the feeding currents of the wire and ring primary windings are magnetically added together, and the transformer is connected in series with the secondary winding and has a constant complex impedance with the primary winding in the audio band. a capacitive reactance having a value such that transformer coupling is effected at 2. The line interface circuit 3 according to claim 1, further comprising a switch means operable to invert the polarity of the DC power supply current applied to the line, the switch means comprising a break contact and a make contact on the chip side; and a break contact and a make contact on the ring side, the line interface circuit 4 is connected in combination with the chip side power supply resistor and the ring side power supply resistor, and is connected to the chip side voltage terminal and the ring side power supply resistor. A differential voltage divider with a tip voltage divider and a ring voltage divider with side voltage terminals, an input terminal connected to the tip side voltage terminal and a ring side voltage terminal, and an output terminal supplying a supervisory signal used in a telephone exchange. a feedback path in which a resistor and a capacitor are connected in parallel between the amplifier, the output terminal and the negative input terminal of the differential amplifier, and performs waveform shaping of rising and falling characteristics of the on-hook, off-hook and dial pulse signals; The line interface circuit 5 according to claim 1, which is provided between the tip-side feeder line and the ring-side feeder line of the subscriber telephone line and the telephone exchange, and supplies current to the subscriber telephone line by a feed current. , a line interface circuit that provides a monitoring display of on-hook and off-hook states of a telephone connected to a subscriber telephone line, a tip-side terminal and a ring-side terminal connected to a tip-side feed line and a ring-side feed line, respectively; A transformer including a chip primary winding connected between a chip side terminal and a chip side power supply resistor, and a ring primary winding and a secondary winding connected between a ring side terminal and a ring side power supply resistor. a power supply terminal connected to a power source for supply current; a chip-side power supply resistor and a ring-side power supply resistor connected to each of the power supply terminals and having approximately the same resistance value; and a power supply terminal for transmitting a signal from the subscriber telephone line to the telephone exchange an active hybrid circuit having a transmitting terminal for transmitting a signal, a balanced voltage drive terminal for transmitting a signal from the telephone exchange and a receiving terminal for transmitting a signal to the telephone, and connected between the secondary winding and the balanced voltage drive terminal; A network consisting of a resistor and a capacitor for coupling audio band signals between the secondary winding and the primary winding, and a chip side voltage terminal connected to both ends of the chip side power supply resistor and the ring side power supply resistor. a tip voltage divider and a ring voltage divider having a ring-side voltage terminal and a tip-side voltage terminal and a ring-side voltage terminal; A line interface circuit comprising: a dynamic amplifier circuit; and a negative feedback network that includes a resistor and a capacitor and responds to the differential amplifier when the on-hook/off-hook change occurs.