JPS61208391A - Central office line circuit for telephone exchange - Google Patents

Abstract

PURPOSE:To provide good and uniform damping of singing of a two-line/ four-line converting circuit for a wide range of the central office line distance and to improve call properties, above all side tone properties and singing allowance within the telephone exchange by using a balancing network corresponding to the central office line distance. CONSTITUTION:A balancing network selecting circuit 11 is connected to a balancing network circuit selecting relay winding 10, an oscillator 18 and a receiver 17. The contact point of the relay winding 10 is balancing network selection relay contact 14. To this contact point are connected two balancing network circuits 15, 16 for selection as the balancing network circuit for the two-line/four-line converting circuit 13. The impedances of the balancing networks 15, 16 are decided as the balancing network circuit 16 for the mean line impedance between the central office lines of 4-7 dB and the balancing network circuit 15 which is optimum and corresponds to the mean line impedance between the office lines of 0-4 dB.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a central office line circuit of a telephone exchange, and more particularly to a two-wire/four-wire conversion circuit within the central office line circuit.

[Conventional technology]

Conventionally, in the NJ line accommodating section of a telephone exchange, a station M3 connected to a central office exchange 1 is accommodated in a central office line circuit 5 of a telephone exchange 4, as shown in FIG. The communication current from the battery 2 flows through the line capture relay contact 6 to the letter coil 7, forming a loop. On the other hand, the call signal system is connected to a two-wire/four-wire conversion circuit 113 via a capacitor 8 and a transformer 9. This two-wire/four-wire conversion circuit 113 includes a transmitting amplifier 21. A receiving amplifier 19 is connected to the receiving side.

Receiving amplifier 19. The transmitting amplifiers 21 are each connected to a time division mode (TDM) channel switch 23 via a codec 20, 21 to form a channel.

The two-wire/four-wire conversion circuit 113 of the office line circuit 5 has one balancing network circuit 116, and the transmitting amplifier 21
from the receiver amplifier 19 via the two-wire and four-wire conversion circuit 113.
The amount of sound attenuation applied to the circuit is dependent on this balancing network circuit 116.

[Problem that the invention seeks to solve]

The above-mentioned conventional two-wire/four-wire conversion circuit of the central office line circuit maintains balance using only two balancing network circuits, so if there is a change in line impedance due to line distance, the change in line impedance for each installed telephone exchange Results 1c with different sound attenuation amounts! The drawback is that the side volume of the handset varies greatly depending on the telephone exchange.

[Means for solving problems]

The station line circuit of the present invention divides the shortest and longest line distances that may be connected into several parts, and the average line impedance of each divided line section is
Multiple balancing network circuits are prepared in the two-wire/four-wire conversion circuit, and the line distance has a correlation with the line impedance.The line impedance is connected from the transmitting amplifier to the receiving amplifier via the two-wire/four-wire conversion circuit. Since there is a correlation with the amount of sound attenuation that goes around to the line, a balancing network circuit selection circuit is provided that detects this amount of sound attenuation and selects a balancing network circuit corresponding to the line distance.

〔Example〕

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

FIG. 1 is a block diagram of one embodiment of the present invention, and the control section of the station line circuit and the like which are not directly related to the present invention are omitted. The central office line 3#i connected to the central office exchange 1 is accommodated in the central office line circuit 5 of the telephone exchange 4. The communication current from the battery 2 flows through the line capture relay contact 6 to the letter coil 7 to form a loop.

On the other hand, the call signal system is connected to a two-wire/four-wire conversion circuit 13 via a capacitor 8 and a transformer 9. This two-wire/four-wire conversion circuit 13 includes a transmitting amplifier 21 and an oscillator 18 on the transmitting side.
The receiving amplifier 19 and the input of the receiver 17 are connected to the output and the receiving side, and each amplifier is connected to the TDM channel switch 23 via the codec 20 and 21.

Balancing network circuit selection circuit 11 is a balancing network circuit selection relay winding 10° oscillator 18
and connected to receiver 17. The contact of the relay winding 10 is a balancing network circuit selection relay contact 14 located inside the two-wire/four-wire conversion circuit 13 , and two balancing network circuits 15 and 16 are attached to the contact to select the balancing network of the two-wire/four-wire conversion circuit 13 . It is wired to be selected as a circuit.

The office line 3 is divided into two sections, 0 to 4 dB and 4 to 7 dB, and an optimal balancing network circuit 15 corresponding to the average line impedance between the office lines of 0 to 4 dB is used.
The impedance of each balancing network circuit 15, 16 is determined as the optimum balancing network circuit 16 for the average line impedance between station lines of 4 to 7 dB.

When a line between O and 4 dB is connected as station line 3,
A communication current flows through the path of battery 2 - office line 3 - line capture relay contact 6 - letter coil 7 - office line 3 - battery 2. On the other hand, the oscillator 18 outputs a signal, and the receiver 17 detects the amount of sound attenuation that is transmitted to the receiver amplifier 19 via the two-wire/four-wire conversion circuit 13. Balancing network circuit selection circuit 11h When the value of the sound attenuation detected by receiver 17 is less than a preset value (for example, 4 dB), current from relay drive power supply 12 to balancing network circuit selection relay winding 10 is cut off.

In other words, the two-wire and four-wire conversion circuit 13 does not operate the contact 14.
, a balancing network circuit 15 for O to 4 dB is connected to the office line 3.

In addition, when a line between 4 and 7 dl is connected as the office line 3, the balancing network circuit selection circuit 11 performs balancing because the value of the sound attenuation detected by the receiver 17 is greater than the preset value. A current is applied to the network circuit selection relay winding 10 to operate its contact 14, and a 4-7 dB balancing network circuit 16 is connected to the office line 3 as a balancing network circuit for the two-wire/four-wire conversion circuit 13.

〔Effect of the invention〕

As explained above, the present invention uses a balancing network circuit corresponding to the distance of the office line, thereby providing a uniform and good sound attenuation amount of the two-wire/four-wire conversion circuit over a wide range of the distance of the office line. This has the effect of improving call characteristics of telephones, especially sidetone characteristics and ringing margin within telephone exchanges.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional station line accommodation section. 1... Central exchange, 2... Battery,
3... Central office line, 4... Telephone exchange, 5...
....-Station line circuit, 6...Line capture relay contact, 7...Letter coil, 8...Capacitor, 9...Transformer, 10 ...Balancing network circuit selection relay winding, 11...
...Balancing network circuit selection circuit, 12
... Receiver, 1°8 ... Oscillator, 19 ...
... Receiving amplifier, 21... Transmitting amplifier,
20.22... Codec, 23...
TDM channel switch. Agent Patent Attorney So Uchihara

Claims (1)

[Claims] At least one office line and a plurality of telephones are exchanged and connected by a time division multiplexing method, the office line is accommodated on the two-wire side of the two-wire/four-wire conversion circuit, and the four-wire side of the two-wire/four-wire conversion circuit is connected. In a central office line circuit of a telephone exchange having a transmitting circuit and a receiving circuit connected to the side, a plurality of balancing network circuits built into the two-wire/four-wire conversion circuit, and a transmission on the four-wire side of the two-wire/four-wire conversion circuit. an oscillator connected to the circuit; a receiver connected to the receiving circuit on the four-wire side of the two-wire/four-wire conversion circuit; the receiver detects the signal output from the oscillator; and a balancing network circuit selection circuit for selecting a balancing network.