JPS6187496A - Trunk circuit of telephone switching device - Google Patents

Abstract

PURPOSE:To obtain a prescribed call level without depending on the set condition of an office side telephone line by providing a call current detecting circuit for detecting the DC call current of the office side telephone line and controlling the gain of a transmission and reception amplifier by this detecting output. CONSTITUTION:A telephone switching device 10 is constituted with a trunk circuit 20, a subscriber's circuit 30 and a time division multichannel switch 40. In this case, the circuit 20 is provided with a call current detecting circuit 24 and the detecting output of the circuit 24 controls the gain of a reception amplifier 28 and a transmission amplifier 29. In case when a loss in office side telephone lines 51, 52 become large, that is to say, if office side telephone line resistance values R1, R2 become large, a call current formed by a battery 61, the line 51, a trunk capture relay contact 23, the circuit 24, the line 52 and the battery 61 is reduced. Accordingly, the circuit 24 detects the decrease of this call current, increases the gain of the amplifiers 28, 29 by the output of the detecting signal, and compensates the decrease portion of the call current.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention is utilized in a central office line circuit of a private branch exchange (PBX). In particular, the present invention relates to a central office line circuit that can control the speech level of a telephone line on the central office side to a constant level in a telephone exchange having a time division multiplex communication path switch.

[Conventional technology]

A block diagram of a conventional telephone exchange device is shown in FIG.

The telephone exchange apparatus 10 is comprised of a central office line circuit 20, a subscriber circuit 30, and a time division multiplex communication path switch 40. The office line circuit 20 is connected to a central office exchange 60 via an office telephone line 51.52, and the time division multiplexing path switch 40 includes an analog-to-digital converter 21.1' and a digital-to-analog converter 22. Connected by The subscriber circuit 30 is connected to a subscriber telephone 70 via a subscriber-side telephone line 53, and the time division multiplex communication path switch 40 is
An analog-to-digital converter 31 and a digital-to-analog converter 32 are connected.

In the office line circuit 20, the office side telephone line 51 is connected to the office line terminating coil 204 via the office line capture relay contact 23, and is further connected to the two lines of the two-wire/four-wire conversion circuit 27 via the capacitor 25 and lance 26. The line side is connected. The four-wire side of the two-wire/four-wire conversion circuit 27 includes an amplifier 28, an analog/digital converter 21, a time division multiplex channel switch 40,
A reception path connected to the four-wire side of the two-wire/four-wire conversion circuit 34 via the digital-to-analog converter 32 and amplifier 36 in the subscriber circuit 30, and the amplifier 35, analog-to-digital converter 31, and time division multiplexing. A transmission path is formed which is connected to the four-wire side of the two-wire/four-wire conversion circuit 27 via the communication path switch 40, the digital/analog converter 22 in the office line circuit 2o, and the amplifier 29.

A subscriber-side telephone line 5 is connected to the two-wire side of the two-wire/four-wire conversion circuit 34 in the subscriber circuit 30 via a communication line current supply circuit 33.
3 is connected.

Among the above routes, the loss of the communication signal due to the telephone lines 51 and 52 on the central office side is between 0 and 7 CdB), and the loss within the telephone exchange 10 is normally designed to be around 0 to I C, dB). has been done.

[Problem that the invention seeks to resolve] However, in the central office line circuit of such conventional telephone exchange equipment, losses due to the central office telephone line are not compensated for, and therefore, depending on the conditions of the central office telephone line, There were problems such as the call level for outgoing and receiving calls varied greatly depending on where the telephone exchange equipment was installed.

The present invention has been made in view of these conventional problems, and aims to provide a central office line circuit for a telephone exchange that can provide a constant speech level regardless of the installation conditions of the telephone line on the central office side. purpose.

[Means for solving problems]

The central office line circuit of the telephone exchange device of the present invention detects the line resistance value (directly the talking current value) by focusing on the fact that the loss caused by the telephone line on the central office side has a correlation with the direct current resistance value of this line. Accordingly, the present invention is characterized by having means for controlling the gain of the transmitting/receiving amplifier and canceling the loss caused by the telephone line resistance on the office side.

In other words, there is a two-wire/four-wire conversion circuit connected to the two-wire office telephone line, a transmitting amplifier and a receiving amplifier connected to the four-wire side of this circuit, and a circuit connected to the output of the transmitting amplifier. It comprises an analog-to-digital converter and a digital-to-analog converter connected to the human power of the receiver amplifier, and the output of the analog-to-digital converter and the input of the digital-to-analog converter are connected to the subscriber line. In a central office line circuit of a telephone exchange connected to a time division multiplex communication path switch that performs exchange connections, the transmitting side amplifier and the receiving side amplifier are variable gain amplifiers, and detect the DC talking current of the central office telephone line. The present invention is characterized by comprising: a communication current detection circuit for detecting a communication current; and means for controlling the gains of the transmitting-side amplifier and the receiving-side amplifier based on the detection output of the detection circuit.

[For production]

The present invention provides that the losses in the two-wire central office telephone line connecting the central office exchange and the private branch exchange account for most of the loss in the four-wire line connecting the central office exchanges, and that Since the loss is due to the direct current resistance of the line, the loss can be detected by connecting a communication current detection circuit in place of the office line termination coil and detecting the communication current of the office side telephone line. Furthermore, by outputting the detection signal to the gain control terminals of the variable gain amplifiers for transmitting and receiving, and increasing the gain, it is possible to compensate for the loss of communication current due to the telephone line on the office side.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a block diagram (IXX) showing an embodiment of the present invention. In FIG. The office line circuit 20 is connected to the office side exchange 60 via office side telephone lines 51 and 52, and is connected to the time division multiplexing path switch 40 through an analog-to-digital converter 21 and a digital-to-analog converter 22. The subscriber circuit 30 subscribes ':Fii!1.!
It is connected to the subscriber telephone Mn 70 via the I telephone line 53, and the telephone division multiplex path switch 40 has an analog-to-digital converter 31 and a digital-to-analog converter 32.
Connected by

Inside the central office exchange 60, there is a battery 6 for supplying communication current.
1 are connected to the telephone lines 51 and 52 on the central office side.

In the office line circuit 20, the office side telephone line 51, 52 is DC terminated at the office line capture relay contact 23 and the call current detection circuit 24, and is connected to an AC bone (call signal) or two wires via a capacitor 25 and a transformer 26. It is connected to the two-wire side of the four-wire conversion circuit 27. An analog/digital converter 21 and a digital/analog converter 22 are connected to the four-wire side of the two-wire/four-wire conversion circuit 27 via variable gain amplifiers 28 and 29. The detection signal of the communication current detection circuit 24 is connected to gain control terminals of variable gain amplifiers 28 and 29.

In the subscriber circuit 30, the subscriber-side telephone line 53 is connected to the two-wire side of the two-wire/four-wire conversion circuit 34 via the communication path current supply circuit 33, and to the four-wire side via amplifiers 35 and 36. An analog-to-digital converter 31 and a digital-to-analog converter 32 are connected.

Note that parts not directly related to the present invention, such as the control circuit of the time division multiplex channel switch 40, are omitted.

Next, the operation of the circuit of this embodiment will be explained.

The flow of call signals for sending and receiving calls on the central office line is as already explained in connection with the conventional device. In other words, the receiving route is: central exchange 60 - central telephone line 51.52 - central line capture relay contact 23 - capacitor 25 - transformer 26
Two-wire four-wire conversion circuit 27 - Variable gain amplifier 28 - Analog-to-digital converter 21 Temporary division multiplex channel Suinochi 4
0-Digital-analog converter 32-Amplifier 36-Two-wire four-wire conversion circuit 34-Speech line current supply circuit 33-Subscriber side telephone line 53-Subscriber telephone line [70] party telephone a7〇 - subscriber side telephone line 53 - communication path current supply circuit 33 - two-wire four-wire conversion circuit 34 - amplifier 35 - analog-to-digital converter 31 temporary division multiplex communication path switch 4〇 - digital-to-analog converter 22-
Variable gain amplifier 29 - two-wire four-wire variable t'A circuit 21 - transformer 26 - capacitor 25 - station line capture relay contact 23
- The route is from the telephone lines 51 and 52 on the central office side to the central office exchange 60.

Here, the features of the present invention are that the circuit for terminating the communication current of the office line is changed from the conventional office line termination coil 204 to the communication current detection circuit 24;
Amplifiers 20B and 20.9 within 0 are variable gain amplifiers 2 whose gains change according to the detection signal of the communication current detection circuit 24.
This is the point where it became 8.29.

When the loss in the telephone lines 51 and 52 on the office side becomes large, it can be considered that the resistance values R+ and Rz on the telephone line on the office side become large. In other words, the office side telephone line resistance value R+
, Rz becomes large, the hatch U-61-office side telephone line 51-one-office line capture relay contact 23-talk current detection circuit 2
The communication current generated by 4-office side telephone line 52-battery 61 is reduced. Therefore, the communication current detection circuit 24 detects this decrease in the communication current, and increases the gain of the variable gain amplifiers 28 and 29 by outputting a detection signal to compensate for the decrease in the communication current.

〔Effect of the invention〕

As explained above, in the present invention, by increasing the gain of the variable gain amplifier, the loss due to the telephone line on the office side is compensated for, and a uniform speech level can be provided. That is, there is an excellent effect in that the loss caused by the telephone line on the central office side can be automatically compensated for.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 21 is a block diagram of a conventional device. 10... Telephone exchange equipment, 20... Office line circuit, 21.
31...Analog-digital converter, 22.32.
...Digital-to-analog converter, 23... Office line capture relay contact, 24... Call current detection circuit, 25...
Capacitor, 26...Transformer, 27...Flat wire four-wire conversion circuit, 28.29...Variable gain amplifier, 30...
・Subscriber circuit, 33...Call path current supply circuit, 34・
...Two-wire four-wire conversion circuit, 35.36...Amplifier, 40
...Time division multiplex communication path switch, 51.52... Office side telephone line, 53... Subscriber side telephone line, 60...
Central office exchange, 61... Buffer telephone, 70... Subscriber telephone, 204... Central office line termination coil, 208.209
...Amplifier, R,, R2... Office side telephone line resistance value.

Claims (1)

[Claims] (1) A two-wire/four-wire conversion circuit connected to the two-wire central office telephone line, a transmitting amplifier and a receiving amplifier connected to the four-wire side of this circuit, and a circuit connected to the output of the transmitting amplifier. an analog-to-digital converter connected to the input of the receiving amplifier, and an output of the analog-to-digital converter and an input of the digital-to-analog converter connected to the subscriber line. In the central office line circuit of a telephone exchange connected to a time division multiplex communication path switch that performs exchange connections, the transmitting side amplifier and the receiving side amplifier are variable gain amplifiers, and detect the DC talking current of the central office telephone line. What is claimed is: 1. A central office line circuit for a telephone exchange apparatus, comprising: a communication current detection circuit for detecting a communication current; and means for controlling the gains of the transmitting-side amplifier and the receiving-side amplifier based on the detection output of the detection circuit.