JPH01241262A - Subscriber circuit - Google Patents

Abstract

PURPOSE:To adjust the earth impedance connecting to both lines A, B by providing a comparison means for feeding current of both the subscriber lines A, B and a control means controlling a transistor (TR) so as to make both the feeding currents equal to each other. CONSTITUTION:When the earth impedance of a power supply circuit 4a is smaller than that of the power supply circuit 4b, the relation of power supply current Ia>Ib exists. Thus, the relation of voltage Va>Vb exists and the relation of output voltage Va' of the operational amplifier 7a > output voltage Vb' of the operational amplifier 7b exists and an output voltage Va'-Vb' of an operational amplifier 8 is biased toward the positive polarity. A base current of a TR 44 is decreased and then the base current of the TR 41a is reduced, resulting that the current 1a is reduced, the earth impedance of the circuit 4a is increased and the currents Ia, Ib are adjusted so as to be equal to each other. When the impedance to the circuit 4a is opposite, the opposite control is applied to adjust the earth impedance of both the circuits 4a, 4b equal to each other automatically.

Description

[Detailed Description of the Invention] [Summary] Regarding the improvement of a subscriber circuit that supplies power supply current to an accommodated subscriber line, the present invention relates to an improvement of a subscriber circuit that accommodates a subscriber line without expending much effort and expense at the manufacturing stage of the subscriber circuit. The purpose is to adjust the impedance to the ground connected to the A line and B line of the subscriber line. In the exchange, a comparison means for comparing the value of the power supply current supplied to the A line and the value of the power supply current supplied to the B line and outputting a comparison result, and based on the comparison result output from the comparison means, A control means is provided for controlling the base current of at least one of the two transistors so that both feed currents are equal.

[Industrial application field]

The present invention relates to a digital exchange, and more particularly to an improvement in a subscriber circuit that supplies power supply current to an accommodating adder line.

In a digital exchange, power supply current is supplied from each subscriber circuit to the subscriber line accommodated, but if the impedance of the power supply circuit to the A line and B vA that constitute the subscriber line is not balanced, This generates noise on the subscriber lines and causes crosstalk between the subscriber lines.

[Conventional technology]

FIG. 3 is a diagram showing an example of a conventional subscriber circuit.

In addition, in FIG. 3, among the various functional units included in the subscriber circuit 1, only the parts related to the power supply function for the subscriber line 2 accommodated are mainly shown, and the other parts are omitted.

In FIG. 3, a transistor 41a and a resistor 42a
A power supply circuit 4a comprising a transistor 41b and a resistor 42bG is provided between the A line 21a of the subscriber line 2 and the DC power supply 5 whose positive terminal is grounded, and a power supply circuit 4b comprising a transistor 41b and a resistor 42bG is connected to the subscriber line 20B. It is provided between the line 21b and the earth.

A base current is supplied to each transistor 41a and 41b through resistors 43a and 43b, respectively.
Collector currents proportional to the base current are supplied to the A line 21a and the B line 21b via resistors 42a and 42b as feed currents ra and rb, respectively.

Also, the transistor 41a and the resistor 4 in the power supply circuit 4a
2a and the connection point between the transistor 41b and the resistor 42t) in the power supply circuit 4b are connected to the two-wire/four-wire conversion circuit 6, and the audio signal sent from the telephone 3 is transferred to the subscriber line. 2, and power supply circuits 4a and 4
The audio signal transmitted to the two-wire/four-wire conversion circuit 6 via the line 6 and output from the two-wire/four-wire conversion circuit 6 is transmitted to the telephone set 3 via the reverse path described above.

Note that since the subscriber line 2 and the telephone 3 have a finite ground impedance, the power supply current Ta supplied from the power supply circuit 4a to the A line 21a and the power supply current Ta supplied from the power supply circuit 4b to the B line 21
The power supply current Ib supplied to the power supply current Ib is not necessarily the same as that supplied to the power supply current Ib.

If the power supply currents 1a and rb do not fail, the power supply circuit 4
This means that the ground impedance of a and the ground impedance of the power supply circuit 4b are not equal, and the subscriber line 2
This causes noise to occur between the A line 2La and the B line 21b of the subscriber line 2 accommodated in the other subscriber circuit 1.
This may cause crosstalk between the

Therefore, at the stage of manufacturing the subscriber circuit 1, the power supply circuit 4a
In order to completely reduce the ground impedance of the power supply circuit 4b, it is necessary to adjust the resistance values of the resistors 42a and 42b, and also adjust the resistance values of the resistors 43a and 43b.

[Problem to be solved by the invention]

As is clear from the above description, in some conventional subscriber circuits, in order to prevent noise or crosstalk from occurring in the subscriber line 2 accommodated, the ground impedances of the feeder circuits 4a and 4b are made equal. Resistors 42a, 42b
It is necessary to adjust the resistance values of , 43a and 43b,
There was a risk that much effort and expense would be lost in the manufacturing stage of the subscriber circuit.

SUMMARY OF THE INVENTION An object of the present invention is to make it possible to adjust the ground impedance connected to the A line and B line of subscriber lines to be accommodated without spending much effort and expense at the manufacturing stage of the subscriber circuit.

[Means to solve the problem]

FIG. 1 is a diagram showing the principle of the present invention.

In FIG. 1, 2 is a subscriber line accommodated in the subscriber circuit, 21a and 21b are A lines and B lines constituting the subscriber line 2, and 41a and 41b are respectively collector currents as feeding currents 1a and Ib. , A line 21a and ByA
21b.

Reference numeral 100 represents comparison means provided in the subscriber circuit according to the present invention.

200 is a control means provided in the subscriber circuit according to the present invention.

[Effect]

The comparison means 100 compares the power supply current 1 supplied to the A line 21a.
The value of a is compared with the value of the power supply current IbO supplied to the B line 21b, and the comparison result is output.

Based on the comparison result output from the control means 200, the control means 200 controls the base current of at least one of the two transistors 41a and 41b so that the refeed currents ia and Ib are equal.

Therefore, in the subscriber circuit, the A and B lines of the subscriber line
So that the impedance to ground connected to the line is equal,
It is automatically adjusted without any effort, and it becomes possible to prevent the occurrence of noise and crosstalk, thereby improving the economic efficiency of the digital communication device.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a diagram illustrating a subscriber circuit according to one embodiment of the present invention. Note that the same reference numerals indicate the same objects throughout the figures. Also, in FIG. 2, only the parts related to the power supply function of the subscriber circuit are mainly shown, and other parts are omitted.

In FIG. 2, operational amplifiers 7a, 7b and 8 are provided as the comparison means 100 in FIG.
A transistor 44 is provided as the control means 200 in the figure.

In FIG. 2, a base current is supplied to a transistor 41a provided in a power supply circuit 4a through a resistor 43a1 and a transistor 44, and a transistor 41b provided in a power supply circuit 4b is supplied with a base current via a resistor 43a1 as described above.
A base current is supplied to the subscriber line 2 through resistors 42a and 42b, and collector currents proportional to the base current are supplied as feed currents 1a and Ib, respectively, to the lines constituting the subscriber line 2 to be accommodated. 21a and B line 21
b.

As a result, both ends of the resistor 42a in the power supply circuit 4a,
Voltages Va and v proportional to the feed currents Ia and rb are applied across the resistor 42b in the feed circuit 4b, respectively.
b occurs.

The operational amplifier 7a outputs a voltage Va' proportional to the voltage Va applied manually through the resistors 71a and 72a, and inputs the voltage Va' to the non-inverting input terminal (+) of the operational amplifier 8 through the resistor 81.

Further, the operational amplifier 7b outputs a voltage "b" proportional to the voltage vb inputted through the resistors 71b and 72b,
It is input to the inverting input terminal (-) of the operational amplifier 8 via the resistor 82 .

The operational amplifier 8 receives a voltage Va input through a resistor 81.
' is compared with the voltage Vb' input through the resistor 82, and a voltage (V
Output a"-vb")°.

On the other hand, the output voltage of the operational amplifier 8 (
A base current proportional to Va"-vb')" is supplied, and a collector current proportional to the base current is supplied to the resistor 43.
A is supplied to the transistor 4.1a as a base current through the transistor 4.1a.

Now, the ground impedance of the power supply circuit 4a is
If it is smaller than the ground impedance of b, the value of the power supply current 1a that the power supply circuit 4a supplies to the A line 21a is larger than the value of the power supply current rbO that the power supply circuit 4b supplies to the B line 21b.

As a result, the voltage VaO value becomes larger than the voltage vbO value, the value of the output voltage Va' of the operational amplifier 7a becomes larger than the value of the output voltage vb'' of the operational amplifier 7b, and the output voltage (Va -Vb') " will be biased to the positive side.

The base current of the transistor 44 decreases in proportion to the bias of the output voltage (Va''-Vb')'' to the positive side.
Further, the collector current of the transistor 44, that is, the base current of the transistor 41a also decreases in proportion to the decrease in the base current, and as a result, the power supply current 1a decreases.

A decrease in the power supply current Ia corresponds to an increase in the ground impedance of the power supply circuit 4a.

Therefore, the power supply currents Ia and Ib of power supply circuits 4a and 4b become equal (automatically adjusted,
The ground impedances of 4b and 4b also become equal.

On the other hand, when the ground impedance of the feed circuit 4a is larger than the ground impedance of the feed circuit 4b, the value of the feed current Ia that the feed circuit 4a supplies to the A line 21a is the value of the feed current Ia that the feed circuit 4b supplies to the B line 21b. becomes smaller than the value of the current rb, so that the voltage VaO value is the voltage V ))
The value of the voltage Va" output by the operational amplifier 7a is smaller than the value of the voltage vb' output by the operational amplifier 7b.
The output voltage of the operational amplifier 8 (Va'
-vb")' will be biased to the negative side.

The base current of the transistor 44 increases in proportion to the deviation of the output voltage (Va"-vb')' to the negative side, and the collector current of the transistor 44, that is, the collector current of the transistor 41a increases in proportion to the increase in the base current. The base current also increases, and as a result, the feed current 1a increases until it becomes equal to the feed current rb supplied by the feed circuit 4b, and the ground impedances of the feed circuits 4a and 4b are automatically adjusted to be equal.

As is clear from the above description, according to this embodiment, the power supply currents 1a and rb supplied by the power supply circuits 4a and 4b, respectively, are set to the voltages Va and vb, and the operational amplifier 7a
and 7b, and compared by an operational amplifier 8,
The transistor 44 controls the base current of the transistor 41a in proportion to the output voltage (Va'-Vb')', which is the comparison result, so that the power supply currents 1a and Ib become equal (automatically adjusted and the power supply The ground impedances of circuits 4a and 4b become equal.

Note that FIG. 2 is only one embodiment of the present invention, and for example, the first control means 200 is not limited to controlling the base current of the transistor 41a, but may also control the base current of the transistor 41b, etc. Although many other modifications may be considered, the effects of the present invention remain the same in any case.

〔Effect of the invention〕

As described above, according to the present invention, in the subscriber circuit, the impedance to the ground connected to the A line and the B line of the subscriber line is automatically adjusted to be equal without any effort, and the generation of noise and crosstalk is prevented. This makes it possible to prevent this, and improves the economic efficiency of the digital exchange.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle of the present invention, FIG. 2 is a diagram showing a subscriber circuit according to an embodiment of the present invention, and FIG. 3 is a diagram showing an example of a conventional subscriber circuit. In the figure, 1 is a subscriber circuit, 2 is a subscriber line, 3 is a telephone, 4a and 4b are power supply circuits, and 5 is a direct line. A power supply, 6 is a two-wire four-wire conversion circuit, 7a, 7b and 8 are operational amplifiers,
21a is the A line, 21b is the B line 41a, 41b and 44
are transistors, 42a, 42b, 43a, 43a',
43b, 45.71a, 71b, 72a, 72b, 73
a, 73b, 81, 82 and 83 are resistors, 100 is a comparison means, and 200 is a control means. 4 Principles of Small Inventions 1) Figure 3

Claims (1)

[Claims] The respective collector currents of the two transistors (41a, 41b) are used as feeding currents (Ia, Ib) to be connected to the A line (21a) and the B line (21b) of the subscriber line (2) to be accommodated. In the respective digital exchanges, the value of the power supply current (Ia) supplied to the A line (21a) and the power supply current (Ib) supplied to the B line (21b) are determined.
Comparison means (100
), and controlling the base current of at least one of the two transistors (41a, 41b) so that the two feed currents (Ia and Ib) are equal, based on the comparison result output from the comparison means (100). A subscriber circuit characterized in that it is provided with control means (200).