JPH0438096A - Dial pulse transmission circuit - Google Patents

Abstract

PURPOSE:To improve the reliability of a trunk circuit by providing a resistance equipped with a lower resistance value than a charge path and an opening/ closing element set to a conductive state during a direct current loop opening/ closing element transmits a dial pulse against a two-wire type call line and set to an interruption state except the above-mentioned period. CONSTITUTION:When a photocoupler 5 is set to the conductive state ON in the case that a central office is sent to a public communication network not shown in the figure, base current flows to a transistor 66 in a direct current loop circuit 6a to set to the conductive state, and the direct current loop formed by the transistor 66 set to the conductive state and a resistance 63 is connected to a two-wire type call line 1. When a photocoupler 68 is set to the conductive state ON, a resistance 67 is parallely connected to a resistance 61. Every time when the photocoupler 5 is set to the interruption state OFF, a condenser 64 is discharged through a resistance 62, and every time when the photocoupler 5 is set tot he conductive state ON, the condenser 64 is charged through parallely connected resistance 61 and 67.

Description

[Detailed Description of the Invention] [Summary] Regarding a dial pulse sending circuit in a trunk circuit such as a central office line trunk connected to a DC two-wire trunk line, the present invention provides a dial pulse sending circuit for a capacitor in a DC loop circuit without using a relay contact. It is designed to be disconnected during transmission, and is set in a conductive state with a DC loop circuit that exhibits a predetermined resistance value to the DC signal applied to both ends, and a high impedance value to the audio signal applied to both ends. In this case, by connecting the DC loop circuit to the two-wire communication line and repeating the conduction state and cut-off state at a predetermined intermittent cycle and intermittent ratio, dial pulses can be transmitted to the two-wire communication line via the DC loop circuit. In a trunk circuit equipped with a DC loop opening/closing element that sends out an audio signal, a charging path for a capacitor provided in the DC loop circuit to exhibit a high impedance value for audio signals is provided with a resistance value lower than that of the charging path. The resistor having the resistor and the DC loop opening/closing element are set to a conductive state during a period when the dial pulse is sent to the two-wire communication line, and are set to a cutoff state except for the period,
By connecting in series and then connecting in parallel a switching element formed by a semiconductor element such as a photocoupler, the charging time of the capacitor is shortened.

[Industrial application field]

The present invention is a DC two-wire system! This invention relates to a dial pulse sending circuit in a trunk circuit connected to an 11 line.

[Conventional technology]

FIG. 4 is a diagram showing an example of a conventional central office line trunk.

FIG. 4 shows, as an example of a trunk circuit to which the present invention is applied, a central office line trunk installed in a home device connected to a public communication network (not shown) via a calling and receiving office line. .

The two-wire communication line 1 of the office line trunk includes an office line polarity detection circuit 2, a calling signal detection circuit 3, a diode bridge 4, a photocoupler 5, a DC loop circuit 6, a capacitor 7, a relay ring 8, and a two-wire four-wire A conversion circuit 9 is connected.

The office line polarity detection circuit 2 identifies the call setting process by detecting the polarity of the DC voltage supplied from the public communication network to the two-wire communication line 1 of the office line trunk via the originating and receiving office line. .

When a call arrives from the public communication network, the ringing signal detection circuit 3 detects the ringing signal sent from the public communication network via the originating/terminating station line.

The diode bridge 4 keeps the polarity of the DC voltage applied to the photocoupler 5 and the DC loop circuit 6 constant even when the polarity of the DC voltage supplied from the public communication network changes.

The photocoupler 5 is set to a disconnected state when the central office line trunk is in an empty state, and set to a conductive state when making a call to a public communication network or responding to an incoming call from a public communication network. By this, the DC loop circuit 6 is connected to the two-wire communication line 1, and when making a call, it is intermittent a required number of times at a predetermined intermittent cycle (for example, 10 times per second) and at a predetermined intermittent ratio (for example, a meter rate of 33%). As a result, dial pulses are sent to the public communications network via the originating and terminating station lines.

The capacitor 7 and the relay ring 8 separate the two-wire communication line 1 connected to the public communication network from the communication line on the home equipment side.

The two-wire/four-wire conversion circuit 9 converts a two-wire communication line l connected to a public communication network into a four-wire communication line inside a home device (not shown).

The DC loop circuit 6 includes resistors 61 to 63 and a capacitor 6.
4, a relay contact 65 and a transistor 66.

The transistor 66 is in a state where, for example, the office line trunk is in an empty state, the photocoupler 5 is set to a cutoff state, and no DC voltage is supplied to the DC loop circuit 6 from the public communication network via the originating and receiving office line. However, when the photocoupler 5 is set to the conductive state when the office line trunk makes a call to the public communication network, for example, the above-mentioned DC voltage is applied across the resistors 61 and 62. As a result, the base current flows through the transistor 66 to the resistor 63.
, and transistor 66 is set to a conductive state.

When transistor 66 is set to a conductive state, resistor 63
are each set to conductive state.
The central office line trunk is connected to the two-wire telephone line 11 via the photocoupler 5 and diode bridge 4, and forms a DC loop with a predetermined resistance value for the originating and receiving office line, so that the central office line trunk is in the outgoing state for the public communication network. becomes.

Since the photocoupler 5 maintains a conductive state until the telephone call ends and the office line trunk is restored, the DC loop circuit 6 connects the DC loop formed by the transistor 66 and the resistor 63 to the two-wire communication line 1 during the telephone call. However, due to the effect of the capacitor 64 connected between the base and emitter of the transistor 66, it exhibits high impedance to the audio signal transmitted via the two-wire communication line 1.
Guarantees low loss for audio signals.

Before a call is established, the photocoupler 5 intermittently sends dial pulses as described above in order to send the telephone number of the called subscriber from the central office line trunk to the public communications network via the originating and receiving office line. If the capacitor 64 is connected between the base and emitter of the transistor 660 during that time, the capacitor 64 will be discharged via the resistor 62 every time the photocoupler 5 is turned on and off, and the capacitor 64 will be discharged via the resistor 61. In order to repeat charging, when the photocoupler 5 becomes conductive, the transistor 66 is activated after a delay while the capacitor 64 is being charged.
The base current begins to flow in , and the point at which transistor 66 is set to conductive is also delayed, resulting in distortion of the dial pulse.

In order to eliminate such adverse effects, the capacitor 64 is disconnected from the DC loop circuit 6 by setting the relay contact 65 to a cutoff state while the photocoupler 5 sends out the dial pulse.

[Problem to be solved by the invention]

As is clear from the above explanation, in a conventional central office line trunk, the capacitor 64 provided to make the DC loop circuit 6 high impedance with respect to the voice signal is connected to the DC loop by the relay contact 65 during dial pulse transmission. Although it was disconnected from the circuit 6, since the relay contact 65 involves mechanical operation, it wears out over a long period of time, and there is also the risk of causing poor contact, which poses a problem that impairs the reliability of the central office line trunk. there were.

The present invention aims to disconnect a capacitor in a DC loop circuit during dial pulse delivery without using relay contacts.

[Means to solve the problem]

FIG. 1 is a diagram showing the principle of the present invention.

In FIG. 1, 100 is a DC loop circuit, 101 is a capacitor, 102 is a charging path for the capacitor 101, 200 is a DC loop switching element, and 300 is a two-wire communication line, all of which are provided in the trunk circuit.

103 is a resistor provided in the DC loop circuit 100 according to the present invention.

104 is a switching element provided in the DC loop circuit 100 according to the present invention.

[Effect]

The DC loop circuit 100 exhibits a predetermined resistance value to a DC signal applied to both ends, and exhibits a high impedance value to an audio signal applied to both ends.

When the DC loop opening/closing element 200 is set to a conductive state, the DC loop circuit 100 is connected to a two-wire communication! 300 and repeats the conduction state and cutoff state at a predetermined intermittent cycle and intermittent ratio, a dial pulse is sent to the two-wire communication and vI 300 via the DC loop circuit 100.

The capacitor 101 is provided so that the DC loop circuit 100 exhibits a high impedance value to the audio signal.

The resistor 103 is a resistor having a lower resistance value than the charging path 102.

The switching element 104 is set to a conductive state during a period when the DC loop switching element 200 is sending out a dial pulse to the two-wire communication line 300, and set to a cutoff state during a period other than the period.

Resistor 103 and switching element 104 are connected in series with each other and in parallel with charging path 102 .

As a result, the DC loop switching element 200 is connected to the two-wire communication line 3.
During the period when the dial pulse is being sent to 00, the charging time of the capacitor 101 is shortened, and the distortion to the dial pulse sent to the two-wire communication line 300 is reduced due to the interruption of the DC loop opening/closing element 200.

Note that by forming the switching element 104 using a semiconductor element such as a photocoupler, there is no possibility of wear and poor contact occurring as in relay contacts.

Further, the trunk circuit may be a central office line originating trunk connected to a central office line exclusively for originating, or a central office line originating/receiving trunk connected to an originating/receiving office line.

Therefore, elements that cause wear and contact failure, such as relay contacts, are removed from the DC loop circuit, and the reliability of the trunk circuit is improved.

〔Example〕

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

FIG. 2 is a diagram showing a central office line trunk according to an embodiment of the present invention, and FIG. 3 is a diagram showing an example of the photocoupler conduction state in FIG. 2. Note that the same reference numerals refer to the same objects throughout the plan.

In FIG. 2, a central office line trunk is shown as the trunk circuit in FIG. 1, a DC loop circuit 6 is shown as the DC loop circuit 100 in FIG. 1, and a DC loop switching element 200 in FIG. A photocoupler 5 is shown, a two-wire communication line 1 is shown as a two-wire communication line 300, and a capacitor 64 and a resistor 6 are shown as the capacitor 101 and charging path 102 in FIG.
1 is shown, a resistor 67 is provided as the resistor 103 in FIG. 1, and a photocoupler 68 is provided as the switching element 104 in FIG.

In FIGS. 2 and 3, when the central office line trunk is in the restored state, both photocouplers 5 and 68 are set to the disconnected state OFF.

In such a state, when the central office line trunk makes a call to a public communication network (not shown), when the photocoupler 5 is set to the conductive state at time t, the current in the DC loop circuit 6 is turned on in the same process as described above. A base current begins to flow through the transistor 66 and the transistor 66 becomes conductive, and a DC loop formed by the conductive transistor 66 and the resistor 63 is connected to the two-wire communication line 1 .

At this point, the photocoupler 68 is still in the disconnected state.
Since it is set to FF, the resistor 67 does not participate in the DC loop for the two-wire communication line 1 at all.

Subsequently, the photocoupler 68 is set to the ON state at a time point tub just before the photocoupler 5 sends out a dial pulse corresponding to the number "3" to the public communication network.

When the photocoupler 68 is set to the ON state, the resistor 67 is connected in parallel to the resistor 61.

In this state, the photocoupler 5 sends a dial pulse corresponding to the number "3" to the public communication network from time t to time t. It is intermittent three times at a predetermined intermittent cycle and a predetermined intermittent ratio.

Each time the photocoupler 5 is set to the cutoff state OFF, the capacitor 64 is discharged via the resistor 62, and each time the photocoupler 5 is set to the conduction state ON, the capacitor 64 is discharged.
is charged via resistors 61 and 67 connected in parallel.

Note that since the resistance value of the resistor 67 is set to a sufficiently low resistance value compared to the resistance value of the resistor 61, the capacitor 64 is rapidly charged, and as a result, after the photocoupler 5 is set to the conductive state, the transistor is turned on. The delay time until the base current begins to flow through 66 is also significantly reduced, and the distortion imparted to the dial pulses sent to the calling and receiving office lines becomes almost negligible.

Time point t when the dial pulse corresponding to the number "3" finishes being transmitted. At a subsequent time point tab, the photocoupler 68 is again set to the cutoff state OFF, and the resistor 67 is again disconnected from the DC loop circuit 6m.

Then, from time L4m to tsa, the photocoupler 5 changes the number "2".
'', the photocoupler 68 is set to the conductive state from time t41+ to tsbO, as described above, and the distortion imparted to the dial pulse is removed by the capacitor 64, as described above.

When the telephone call via the originating and receiving office line is eventually terminated and the office line trunk is restored, the photocoupler 5 is set to the cut-off state and the DC loop circuit 63 is disconnected from the two-wire communication line 1.

As is clear from the above description, according to this embodiment, while the photocoupler 5 is sending out the dial pulse, the photocoupler 68
Since the conduction state is set to ON, the resistor 67 has a sufficiently low resistance.
is connected in parallel to the resistor 61, and the capacitor 64 is rapidly charged, so that the delay time when the transistor 66 is set to the conductive state after the photocoupler 5 is set to the conductive state ○゛N is also significantly shortened. The distortion imparted to the dial pulse can also be almost ignored.

Furthermore, since the photocoupler 68 has no fear of wear and poor contact like the relay contacts 65 (FIG. 4), the reliability of the central office line trunk is also improved.

Note that FIGS. 2 and 3 are merely embodiments of the present invention, and for example, the configuration of the DC loop circuit 100 is the same as that of the DC loop circuit 6. Although the present invention is not limited to this and many other modifications may be considered, the effects of the present invention remain the same in any case. Further, the trunk circuit to which the present invention is applied is not limited to the central office line trunk shown in the drawings, and the effects of the present invention will remain the same as long as the trunk circuit includes a DC loop circuit.

〔Effect of the invention〕

As described above, according to the present invention, elements that cause wear and poor contact, such as relay contacts, are removed from the DC loop circuit in the trunk circuit, and reliability of the trunk circuit is improved.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the principle of the present invention, FIG. 2 is a diagram showing a central office line trunk according to an embodiment of the present invention, FIG. 3 is a diagram showing an example of the photocoupler conduction state in FIG. 2, and FIG. 1 is a diagram showing an example of a conventional central office line trunk. In the figure, 1 and 300 are two-wire communication lines, 2 is a central office line polarity detection circuit, 3 is a calling signal aspect ratio circuit, 4 is a diode bridge, 5 and 68 are photocouplers, 6.6. and 100 are DC loop circuits, 7.64 and 101 are capacitors, 8 is a relay ring, 9 is a two-wire and four-wire conversion circuit, and 61.
62, 63, 67 and 103 are resistors, 65 is a relay contact, 66 is a transistor, 102 is a charging path, 104 is a switching element, and 200 is a DC loop switching element. The principle of the present invention is shown in Fig. 1 and Fig. 2.

Claims (2)

[Claims] (1) A DC loop circuit (100) that exhibits a predetermined resistance value to a DC signal applied to both ends and a high impedance value to an audio signal applied to both ends; By connecting the loop circuit (100) to the two-wire communication line (300) and repeating the conduction state and cutoff state at a predetermined intermittent cycle and intermittent ratio,
In a trunk circuit comprising a DC loop opening/closing element (200) that sends a dial pulse to the two-wire communication line (300) via the DC loop circuit (100), , a resistor (103) having a lower resistance value than the charging path (102) for the capacitor (101) provided to exhibit a high impedance value for the audio signal.
and a switching element that is set to a conductive state during a period when the DC loop switching element (200) is sending out dial pulses to the two-wire communication line (300), and set to a cutoff state outside of the period. (104) in series and then in parallel, the capacitor (101)
A dial pulse sending circuit characterized by shortening the charging time. (2) The dial pulse sending circuit according to claim 1, wherein the switching element (104) is formed by a photocoupler.