JPS61276495A - Main wire circuit for telephone exchange - Google Patents

Abstract

PURPOSE:To improve side tone characteristic and singing margin by detecting speaking current value and selecting plural balancing network circuits provided in a two-wire four wire converting circuit. CONSTITUTION:Current level of a main wire 3 is detected by a balancing network selecting circuit 7 that forms the loop circuit of a telephone exchange and exciting and non-exciting of a relay is controlled through a balancing network circuit selecting relay winding 10. A balancing network 15 or 16 corresponding to the amount of attenuation for the change of impedance depending on line distance is selected through a relay contact 14 of a two-wire four wire converting circuit 13. Consequently, side tone characteristic and singing margin in the telephone exchange can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a central office line circuit for a telephone exchange. In particular, it relates to a two-wire/four-wire conversion circuit in a central office line circuit.

〔overview〕

The present invention improves call characteristics, sidetone characteristics, and This makes it possible to improve the sound characteristics, etc.

[Conventional technology]

As shown in FIG. 2, the conventional two-wire/four-wire conversion circuit of the office line circuit has only one balancing network circuit 15, and the receiving amplifier 19 passes the receiving amplifier 19 through the two-wire/four-wire conversion circuit 13. The amount of sound attenuation passed to the amplifier 17 was dependent on only one balancing network circuit 15.

[Problem that the invention seeks to solve]

The two-wire, four-wire conversion circuit of the conventional central office line circuit described above responds to changes in line impedance due to line distance, and the amount of ringing attenuation differs depending on the installed telephone exchange, resulting in a decrease in side volume at the telephone set. However, each telephone exchange had very different drawbacks.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and aims to provide a central office line circuit that improves telephone call characteristics, particularly sidetone characteristics, and ring margin between telephone exchanges.

[Means for solving problems]

The present invention connects at least one office line and a plurality of telephones by means of a time division multiplex communication system (TDM), accommodates this office line on the two-wire side of a two-wire/four-wire conversion circuit, and In the central office line circuit of a telephone exchange, in which codecs for sending and receiving calls are connected to the four-wire side of the two-wire, four-wire conversion circuit, the talking current value of the central line is detected, and the detected value is used to The present invention is characterized in that the line conversion circuit includes a balancing network circuit selection circuit for selecting one of a plurality of balancing network circuits prepared within the line conversion circuit.

[For production]

The balancing network circuit selection circuit is selectively connected according to the communication current. As a result, the balancing network corresponding to the distance of the central office line is properly connected, increasing the sound attenuation of the two-wire/four-wire conversion circuit, improving the sidetone characteristics of the telephone, and improving the ringing margin inside the exchange. .

〔Example〕

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

FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention.

The office line 3 is accommodated in the office line circuit 5 of the telephone exchange 4, and the communication current passes through the line capture relay contact 6 and forms a loop in the balancing network circuit selection circuit 7. 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 has the output of the transmitting amplifier 19 and the receiving amplifier 1.
7 input is connected. On the other hand, the balancing network circuit selection circuit 7 is connected to the balancing network/nodwork circuit selection relay winding 10, and the balancing network/nodwork circuit selection relay contact 14 connects the two balancing network circuits 15, 16 to the two-wire/four-wire conversion circuit 13. It is wired to be selected as a balancing network.

Note that the control section of the station line circuit and the like that are not directly related to the present invention are omitted.

Next, the operation of the embodiment of the present invention will be explained.

First, the office line 3 is divided into two sections of communication current levels, θ~4 dB and 4~7 dB. An optimal balancing network circuit 15 corresponding to the average line impedance between 0 and 4 dB of the office line 3 and the above 4 to 7 dB of the office line 3.
The impedance of each balancing network circuit 15,16 has been determined as the optimal balancing network circuit 16 for the average line impedance between.

Further, when the office line 3 is 4 dB, the communication current is about 50 mA.

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 - balancing network circuit selection circuit 7 - office line 3 - battery 2, and this current value is 50 mA or more. Since the communication current of the balancing network circuit selection circuit 7 is 50 mA or more, the balancing network circuit selection relay 10.14 is not operated.
The balancing network circuit of the two-wire/four-wire conversion circuit 13 is connected to a balancing network circuit 15 for the office line 3 of 0 to 4 dB.

On the other hand, when a line between 4 and 7 dB is connected as the office line 3, the communication current value becomes 50 mA or more, and the balancing network circuit selection circuit 7 detects this communication current of 50 mA or less and selects the balancing network circuit. Activate relay 10.14. A balancing network circuit 16 for the central office line 3 of 4 to 7 dB is connected to the balancing network circuit of the two-wire/four-wire conversion circuit 13.

〔Effect of the invention〕

As explained above, the present invention uses a balancing network circuit that corresponds to the office line depending on the distance of the office line, thereby achieving uniform and good sounding of the two-wire/four-wire conversion circuit over a wide range of the distance between the office lines. It can provide an amount of attenuation, and has the effect of improving speech characteristics of a telephone, particularly sidetone characteristics and ringing margin within a telephone exchange.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram of a conventional station line circuit. 1... Office exchange, 2... Battery, 3... Office line,
4... Telephone exchange, 5... Office line circuit, 6... Line capture relay contact, 7... Balancing network circuit selection circuit, 7'... Letter coil, 8... Capacitor, 9... ...Transformer, 10...Balancing network circuit selection relay winding, 12...Relay drive power supply, 13...Two-wire four-wire conversion circuit, 14...Balancing network circuit selection relay contact, 15.16.・
- Balancing network circuit, 17... Receiving amplifier, 18.20... Codec, 19... Transmitting amplifier, 21... Time division exchange switch.

Claims (1)

[Claims] (1) One or more office line terminals, a two-wire/four-wire conversion circuit whose two-wire side is connected to the office line terminal, a codec connected to the four-wire side of this two-wire/four-wire conversion circuit, and this codec. In a central office line circuit of a telephone exchange equipped with a time division switching device connected to 1. A central office line circuit for a telephone exchange, comprising: means for detecting a passing speech current; and means for switching and connecting the balancing network according to the speech current detected by the means.