JPS6327194A - Subscriber circuit - Google Patents

Abstract

PURPOSE:To contrive to keep a two-wire side impedance to be constant without the aid of an ON/OFF by detecting the ON/OFF of a subscriber loop by means of a state detection circuit and providing a capacitor and a resistor which are connected in series with a switch to be controlled by the output of the state detection circuit. CONSTITUTION:A transmitter amplifier 12 and a receiver amplifier 14 are connected to a two-wire/four-wire converter circuit 4, and the circuit 4 has a balance network 13 which is approximately equal to the two-wire side impedance, e.g. the composite impedance of a telephone set 1 being in OFF hook state and a subscriber line 2. The state detection circuit 15 detects the ON/OFF state of the subscriber loop, and at the time of an ON hook state, it generates an output, drives a transistor 17 and operates a relay 18. After the relay 18 operates, the contact 18-1 of the relay closes and the capacitor 19 and the resistor 20 are inserted between a two-wire system line 2. The capacitor 19 prevents the resistor 21 from the flow of a direct current, and simultaneously, being combined with the resistor 20, keeps the impedance of the line 2 to be equal to a value of that in the OFF hook state.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a subscriber circuit provided for each subscriber line, and more particularly to a subscriber circuit of a digital exchange that serves as a four-wire communication path.

+c++ Conventional Technology Since the digital circuit portion of the communication path in a digital telephone exchange is a 4-wire system, a 2-wire/4-wire conversion circuit is required in the subscriber circuit connected to the telephone set. 2 lines 4
In the line conversion circuit, the impedance when looking at the two-wire line,
By matching the impedance of the balance network connected to the 2-wire and 4-wire conversion circuits, it is possible to prevent interference from the 4-wire receiving side to the 4-wire transmitting side. If this wrap-around prevention function deteriorates, the 4-wire loop attenuation deteriorates, causing 4-wire loop oscillation, speaker echo, and receiver echo, so care must be taken when designing the impedance of the balance network.

By the way, since this impedance is matched to the impedance at the time of loop formation when the subscriber is in a talking state, mismatching occurs in the 2-wire/4-wire conversion circuit when on-hook, resulting in a reduction in return loss. Therefore, if a four-wire loop is formed at this time, there is a problem in that oscillation or the like may cause interference to the other subscriber.

For this reason, a method has been proposed in which the 4-wire line is opened by detecting the on/off state of the subscriber loop (Japanese Patent Application Laid-open No. 60-2
(See Publication No. 47394). However, although cutting the four-wire loop is effective in preventing wrap-around, there is another problem in that it is impossible to test the continuity of the communication path in an on-hook state.

(/1 Problems to be Solved by the Invention The present invention solves the above problems, that is, mismatching occurs in the 2-wire 4-wire conversion circuit during on-hook, causing 4-wire loop oscillation, etc. This solves the problem of not being able to conduct continuity tests on communication channels that are connected to other channels.

(B) Means for Solving the Problems The present invention provides a state detection circuit for detecting the on/off state of the subscriber loop in a subscriber circuit having a 2-wire and 4-wire conversion circuit, and a state detection circuit for detecting the on/off state of the subscriber loop. '1l by the output of the detection circuit
lij! It has a switch that is turned on, and a capacitor and a resistor connected in series to the switch.

(E) Function: Regardless of whether the telephone connected to the subscriber circuit is on-hook or off-hook, the impedance of the 2-wire line does not change significantly, so the return loss in the 2-wire 4-wire conversion circuit is reduced. The occurrence of oscillations in the 4-wire loop can be suppressed.

(F) Example Hereinafter, an example of the present invention will be described with reference to the drawings. Figure 1 shows the communication path of a digital exchange.
Telephones (1-1) to (1-n) are analog type, 2
It is connected to subscriber circuits (3-1) to (3-n) of the exchange through wire lines (2-1) to (2-n). (4-1)
-(4-n) are 2-wire/4-wire conversion circuits, which convert a 2-wire line into a 4-wire line. The transmission signal (Tl) from the telephone (1-1) is a digital signal (P
CM) and digital highway (HWT) (7
-1). , (9) is a digital highway (
This is a digital switch that changes the time slots of the DA converter (HIT).
-n). In this way, some exchanges (4
-1) → (5-1) → (9) → (6-n) → (4-n)
→ (5-n) → (9) → (6-1) → (4-1) and a 4-wire loop is formed.

Continuity tests are performed on the D-A converter (6), A-D converter (5+), digital switch (9), and 2-wire 4-wire conversion circuit (4
) is a test to confirm the operation of the digital switch (9), and is performed using the oscillator a0 and level detector αD attached to the digital switch (9). During the continuity test, the central controller C (not shown), which controls the operation of the exchange, finds an empty subscriber circuit (3) (telephone (11 is on-hook)) and turns on the oscillator α.
α is connected to the subscriber circuit (3), and the subscriber circuit (3) is connected to the level detector U. In this way, the signal from the oscillator αα passes through the 2-wire and 4-wire conversion circuit (4) to the level detection circuit (11).
Detects the return and turns on the digital switch (9).
Determine whether the communication route bus including the communication route bus is normal.

Next, a subscriber circuit embodying the present invention will be explained according to FIG. A transmitting amplifier α2 and a receiving amplifier a41 are connected to the two-wire four-wire conversion circuit (4). The 2-wire 4-wire conversion circuit (41) includes a balance network ti3 whose impedance on the 2-wire side is approximately equal to the combined impedance of the off-hook telephone (11) and the subscriber line (2).

α is a state detection circuit that detects whether the subscriber loop is on or off and generates an output when it is on-hook. This detection output drives transistor a'n to operate a relay brocade. (18-1) is a contact point of a relay installed on a two-wire line, with a 1μF capacitor (1) and a 60μF capacitor (1).
A 0Ω resistor is connected in series.

Therefore, when the relay side operates, the relay contact (18-1
1 is closed capacitor Q! J and resistor are two-wire line (2)
inserted in between. Note that the capacitor (19 is a resistor (101)
The impedance of the two-wire line (21) is set to be equal to the value in the off-hook state in combination with the resistor (2).

(G) As described in detail, according to the present invention, the impedance on the 2-wire side can be kept almost constant whether the telephone is on-hook or off-hook, so return loss in the 2-wire to 4-wire conversion circuit can be reduced. Therefore, the gain of the 4-wire loop can always be kept low, which solves problems such as oscillation and echo during connection.
Since the wire loop can be formed even in the on-hook state, 2 wires 4
Continuity tests can be performed via a line conversion circuit.

[Brief explanation of drawings]

FIG. 1 is a diagram showing communication paths of a digital exchange, and FIG. 2 is a block diagram showing an embodiment of the subscriber circuit of the exchange according to the present invention. (11...Telephone, +2+...Subscriber line (2
wire line), (3)... subscriber circuit, (41・-2
4-wire conversion circuit, (5)...A-D converter, (6
)...D-A converter, (71, (8)...Digital highway (4-wire line), (9)...Digital switch, (1'2...Telephone amplifier, t13+-・・・
Balance network, (141-・Reception amplifier, a5
1...Status detection circuit, 0g...Relay, 9...
・Capacitor, COI...Resistance.

Claims (1)

[Claims] (1) In a subscriber circuit having a 2-wire 4-wire conversion circuit,
A state detection circuit for detecting the on/off state of the subscriber loop is provided, and a switch means controlled by the output of the state detection circuit is provided on the two-wire line, and a capacitor and a resistor connected in series with the switch means. and the capacitor and the resistor are inserted between the two-wire line when the subscriber loop is in an off state, and the impedance on the two-wire side is kept almost constant regardless of the state of the telephone. subscriber circuit.