JPH01318395A - Trunk line interface circuit - Google Patents

Abstract

PURPOSE:To reduce the number of parts and to increase a maximum AC undistorted power output by changing the method for connection between a loop detecting/polarity discriminating circuit and a DC sink circuit. CONSTITUTION:A two wire-one wire converting circuit 20 is directly connected to a pair of subscriber terminals 71 and 72, and one end of a loop detecting/ polarity discriminating circuit 40 is connected to the first subscriber terminal 71, and the other end is connected to one end of a DC sink circuit 30. The other end of the DC sink circuit 30 is connected to the second subscriber terminal 72. Thus, a polarity coincidence detecting circuit is eliminated, and the maximum AC undistorted power output is increased by the voltage drop due to the polarity coincidence detecting circuit, namely, the offset voltage corresponding to two diodes in comparison with a conventional maximum AC undistorted power output.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is provided in the main device of a key telephone system,
The present invention relates to a central office line interface circuit for connecting a pair of subscriber terminals of a central office line to a communication path switch via one line.

[Conventional technology]

As is well known, a key telephone system consists of a main device and a plurality of key telephones connected to the main device. The main device is connected to a plurality of subscriber lines (office lines), and controls connections between the office lines and key telephones, connections between key telephones, that is, between extension lines, and the like. In order to control these connections, the main device is equipped with a communication path switch. The communication path switch - generally consists of a CMOS matrix, 11! It is controlled by a control circuit. On the other hand, the central office line consists of 2a. A central office line interface circuit is provided in the main unit to connect the pair of subscriber terminals of the two-wire central office line to the communication path switch via one line.

The main functions that the central office line interface circuit must have are (1) converting the signals on the second line of the central office line and the signals on the first line of the communication path switch (2nd line); 1
line conversion function), (2) forming a DC loop of the central office line during a call with the central office line (DC loop formation function), (3) loop detection function that detects a loop of the central office line), and (
4) To determine the polarity of the office line (polarity determination function).

FIG. 2 shows the configuration of a conventional station line interface circuit 10'. The conventional station line interface circuit 10'' has two wires.
2-wire to 1-wire conversion circuit 20 that realizes 1-wire conversion function
, a DC sink circuit 30 for realizing the DC loop forming function, and a loop detection and polarity determination circuit 8! A loop detection/polarity determination circuit 40' is provided to realize the function, and a polarity-number circuit 50 is provided to match the polarity of the station line side with the polarity of the DC sink circuit 30'.

The 2-wire to 1-wire conversion circuit 20 is connected to the communication path switch 60 via a single wire, and also connects a pair of central office lines via a loop detection/polarity determination circuit 40' and a polarity switch 60'. terminals 77 and 72.

The DC synchro path 30° is connected in parallel between the 2-wire to 1-wire conversion circuit 20 and the polarity/number circuit 50.

In other words, the DC synchro path 30', like the 2-wire to 1-wire conversion circuit 20, connects the pair of subscriber terminals 7 via the loop detection/@gender determination circuit 40' and the polarity-several times 1it@50.
1 and 72. The loop detection/polarity determination circuit 40' has one end or one of a pair of subscriber terminals (the first
subscriber terminal) 71, and the other end or polarity-number circuit 5
0 first input terminal. Polarity-number circuit 5
The second input terminal 0 is connected to the other (second subscriber terminal) 72 of the pair of subscriber terminals.

The 2-wire to 1-wire conversion circuit 20 includes a transformer 21 and a low impedance circuit 22. The transformer 21 is a device that enables conversion and transmission of an AC signal on the central office line and an AC signal on one line of the communication path switch 60. transformer 21
has a first winding 21a and a second winding 21b. One end of the first winding 21a is connected to the communication path switch 6 via one wire.
0, and the other end is grounded. Second winding 21
One end of b is connected to the first subscriber terminal 71 through the polarity-number circuit 50 and the loop detection/polarity determination circuit 40°, and the other end is connected to the second subscriber terminal 71 through the low-impedance circuit 22 and the polarity-number circuit 50. is connected to the subscriber terminal 72 of.

The low impedance circuit 22 is for lowering the input impedance for alternating current signals on the central office line. For example, it is terminated with 600Ω.

That is, the low impedance circuit 22 is a circuit for impedance matching with the station line. The low impedance circuit 22 has a first capacitor 22a connected in series with the second winding 21b of the l-lance 21. One end of the first capacitor 22a is connected to one end of the second winding 21b, and the other end is connected to the second subscriber terminal 72 via the polarity-number circuit 50. Low impedance circuit 2
2 also has a series circuit of a second capacitor 22b and a first resistor 22c connected in parallel to the first capacitor 22a. One end of the first resistor 22c is connected to one end of the first capacitor 22a, that is, one end of the second winding 22b, and the other end is connected to one end of the second capacitor 22b. The other end of the second capacitor 22b is connected to the second subscriber terminal 72 via the other end of the first capacitor 22a, ie, the polarity - several times #150.

The polarity-number circuit 50 consists of four diodes 51.52.5
A bridge rectifier circuit consisting of 3 and 54,
It has the above-mentioned first and second input terminals, a positive output terminal Tp, and a negative output terminal T''n.The first input terminal is connected to the first subscriber terminal 71 via the loop detection/polarity determination circuit 40°. connected, the second input terminal directly connects to the second subscriber terminal 72
It is connected to the.

The DC sink circuit 30° consists of a series circuit of an NPN transistor 31 and a second resistor 32. The collector of the NPN transistor 31 is connected to the iE pole output terminal Tp of the polarity-number circuit 50, and the emitter is connected to one end of the second resistor 32. The other end of the second resistor 32 has a polarity of −
It is connected to the negative output terminal Tn of the several circuit 50. NP
The base of the N-type transistor 31 is connected to the second:1 resistor 22b and the first resistor 22c of the low impedance circuit 22.
connected to the connection point.

The DC sink circuit 30' connects the central office line (between a pair of subscriber terminals 71 and 72) with a DC voltage of, for example, 100Ω to 40Ω.
Terminate with 0Ω.

The loop detection/polarity determination circuit 40' consists of first and second light emitting diodes (LEDs) 41 and 42 of first and second photocouplers connected in parallel with opposite polarities. In particular, the anode of the first L E I ) 41 is connected to the first subscriber terminal 71 and the cathode is connected to the first input terminal of the polarity-number circuit 50 . Second
The cathode of L E D 42 is connected to the first subscriber terminal 7
1 and its anode is connected to a first input terminal of the polarity-number circuit 50. Note that the first and second photo-transistors (not shown) of the first and second photocouplers
is connected to a control circuit (not shown) that controls the communication path switch 60.

[Problem to be solved by the invention]

As is well known, in the telephone system, the DC standard at the time of central line acquisition is defined by the subscriber voltage Von, which is, for example, 48V DC voltage, applied to a pair of subscriber terminals 71 and 72. The AC undistorted maximum output VFax' in the conventional station line interface circuit 10' is expressed by the following equation.

Vmax'-Von-Vp (40') -2Vp (
50) Veg (30°) ... (1) Here, V, (40°) is the loop detection/polarity determination circuit 4
0' is the offset voltage of each of the first and second LEDs 41 and 42, V F (50) is the polarity - several times F
Offset voltage 1 of each diode configuring I@50,
and V and E (30°) respectively represent the base-emitter voltage of the NPN transistor 31 constituting the DC sink circuit 30'.

Therefore, the conventional station line interface circuit 10° has the disadvantage that the AC undistorted maximum output is not very large. In addition, since it has a polarity-number circuit 50 that is not directly related to the function of the office line interface circuit, the number of components that make up the circuit will increase in the conventional office line interface circuit 10°. There are some drawbacks.

An object of the present invention is to provide a station line interface circuit that can increase the AC undistorted maximum output.

Another object of the present invention is to provide an inexpensive station line interface circuit that can reduce the number of components that make up the circuit.

[Means to solve the problem]

A central office line interface circuit according to the present invention is a central office line interface circuit for connecting a pair of subscriber terminals of a central office line consisting of two wires to a communication path switch via one line, and wherein a 2-wire-to-1-line conversion means for converting the signal on the 1-line of the communication path switch; a DC sink group for forming a DC loop of the station line; In the central office line interface circuit, the central office line interface circuit includes a loop detection/polarity determining means for detecting a line loop and determining the polarity of the central office line, wherein the two-wire to one-wire converting means is connected to a communication path switch via the one line. and directly connected to the pair of subscriber terminals, one end of the loop detection/polarity determination means being connected to one end of the pair of subscriber terminals, and the other end of the loop detection/polarity determination means is connected to one end of the DC sink means, and the other end of the DC sink means is connected to the other ends of the pair of subscriber terminals.

[For production]

By configuring as described above, the polarity-number circuit is deleted, and thereby the AC undistorted maximum output is reduced by the voltage drop due to the polarity-number circuit, that is, the offset voltage of two diodes, compared to the conventional AC non-distortion circuit. It can be made larger than the maximum distortion output.

〔Example〕

゛Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Referring to FIG. 1, a central office line interface circuit 10 according to an embodiment of the present invention includes a 2-wire to 1-wire conversion circuit 20, a DC sink circuit 30, and a loop detection/igi! It has a sex determination circuit 40.

The 1-wire to 2-wire conversion circuit 20 of this embodiment has a configuration similar to that shown in FIG. Identical parts have the same reference numerals as shown in FIG. 2, and their description will be omitted for the sake of brevity. However, the 2-wire to 1-wire conversion circuit 20 from IrYl has a polarity-number circuit 50 and a loop detection/polarity determination circuit 40.
In contrast, the 2-wire to 1-wire conversion circuit 20 of this embodiment is directly connected to the pair of subscriber terminals 71 and 72. There is.

One end of the loop detection/polarity determination circuit 40 is connected to the first subscriber terminal 71, and the other end of the loop detection/polarity determination circuit 40 is connected to one end of the DC sink circuit 30. The other end of the DC sink circuit 30 is connected to a second subscriber terminal 72.

The loop detection/polarity determination circuit 40 includes first and second LPs of first and second photocouplers connected to opposite polarities,
Consisting of D41 and D42. Specifically, the first LED
41 is connected to the first subscriber terminal 71;
The cathode is connected to a DC sink circuit 30. Second
The cathode of the LED) 42 is connected to the first subscriber terminal 71, and the anode is connected to the DC sink circuit 30. Note that the first and second photocouplers of the first and second photocouplers
The phototransistor (not shown) is connected to a control circuit (not shown) that controls the communication path switch 60.

The DC sink circuit 30 includes an NPN transistor 31,
It has a second resistor 32 and a PNP transistor 33. The collector of the NPN transistor 31 is connected to the cathode of the first LED 41 of the loop detection/polarity determination circuit 40, and the emitter is connected to one end of the second resistor 32. The other end of the second resistor 32 is connected to the second subscriber terminal 72.
It is connected to the. The collector of the PNP transistor 33 is connected to the second L E of the loop detection/polarity judgment circuit v@40.
D 42 is connected to the anode, and its emitter is connected to one end of the second resistor 32 .

NPN transistor 31 and PNP transistor 3
3 base is common to the second low impedance circuit R22.
It is connected to the connection point between the capacitor 22b and the first resistor 22c.

In this way, since the loop detection/polarity determination circuit 40 and the DC sink circuit 30 are connected, the polarity
The several circuits 50 can be deleted, and the two photocoupler LEDs 41 and 4 of the loop detection/polarity determination circuit 40 can be removed.
2 and the two transistors 31 and 33 of the DC sink circuit 30, so that a reverse voltage is not applied to each transistor 31 and 33 of the DC sink circuit 30, and the loop detection/polarity determination circuit 40 performs polarity determination. I can do it.

Compared to the conventional office line interface circuit 10° (FIG. 2), the office line interface circuit 10 of this embodiment includes a DC sink circuit 30 or a PNP type transistor 33.
The number of components is one more than the conventional DC sink circuit 30, but since the polarity-number circuit 50 can be deleted and the four diodes 51 to 54 can be omitted, the total number of components is reduced to three. You can save money and it will be cheaper.

The AC undistorted maximum output vlIla× in the station line interface circuit 10 of this embodiment is expressed by the following equation.

Vmax = Von-Vp (40)-V[IF, (3
0)-(2) Here, Vp(40) is the first and second LEIs constituting the loop detection/polarity determination circuit 40)/1
1 and 42 -14 = respective offset voltages, and ■IIF, (30) represent the base-emitter voltages of each of the NPN transistor 31 and the PNP transistor 33 constituting the DC sink circuit 30, respectively. .

As is clear from comparing equations (2) and (1), the office line interface circuit 10 of this embodiment has a larger AC undistorted maximum output than the conventional office line interface circuit 10. It is possible to do so. That is, the AC undistorted maximum output can be increased by an offset voltage corresponding to two diodes constituting the polarity-number circuit 50.

〔Effect of the invention〕

As explained above, according to the present invention, the 2-wire to 1-wire conversion means is connected to the communication path switch via the 1-wire, and
Connect directly to a pair of subscriber terminals and loop detection/fl! One end of the sex determination means was connected to one end of a pair of subscriber terminals, the other end was connected to one end of a DC sink means, and the other end of the DC sink means was connected to the other end of a pair of subscriber terminals, so that the parts It becomes possible to provide an inexpensive office line interface circuit that is small in number and can increase the AC undistorted maximum output.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a station line interface circuit according to an embodiment of the present invention, and FIG. 2 is a block diagram showing the configuration of a conventional station line interface circuit. 10... Office line interface circuit, 20... 2 wire -
1-wire conversion circuit, 30... DC sink circuit, 40...
Loop detection/polarity determination circuit, 60...communication path switch, 71.72... subscriber terminal.

Claims (1)

[Scope of Claims] A central office line interface circuit for connecting a pair of subscriber terminals of a central office line consisting of one and two wires to a communication path switch via one line, the circuit comprising: 2-wire to 1-line conversion means for converting a signal and a signal on one line of the communication path switch; DC sink means for forming a DC loop of the office line; detecting the loop of the office line; In a central office line interface circuit having a loop detection/polarity determining means for determining the polarity of a central office line, the two-wire to one-wire converting means is connected to the communication path switch via the one line, and The loop detection/polarity determination means is directly connected to the pair of subscriber terminals, one end of the loop detection/polarity determination means is connected to one end of the pair of subscriber terminals, and the other end of the loop detection/polarity determination means is connected to the DC sink means. A central office line interface circuit characterized in that the DC sink means is connected to one end of the DC sink means, and the other end of the DC sink means is connected to the other end of the pair of subscriber terminals. 2. The loop detection/polarity determination means includes a first light emitting diode of a first photocoupler having an anode connected to one end of the pair of subscriber terminals, and a cathode connected to one end of the pair of subscriber terminals. a second light emitting diode of a second photocoupler, and the DC sink means includes an NPN type transistor whose collector is connected to the cathode of the first light emitting diode; A PNP transistor having a collector connected to an anode; and a resistor having one end connected to the NPN transistor and the emitter of the PNP transistor, and the other end connected to the other end of the pair of subscriber terminals. The station line interface circuit according to item 1.