JPS63229995A - Two-wire/four-wire conversion circuit - Google Patents

Abstract

PURPOSE:To increase the quantity of mismatching attenuation on the side of two-wire line by setting the impedance on the side of a four wire to a pure resistance and providing an equilibrium connection network on an infiltrating cancellation line part. CONSTITUTION:For matching the load impedance 12 of the two-wire analogue line in an analogue trunk 11, the impedance 13 on the side of the four-wire is set to the pure resistance, and the equilibrium connection network 14 which prevents a reception signal from a four-wire digital channel 10 form infiltrating into the channel 10 is provided in the infiltrating cancellation line part 15 with the least influence of the impedance on the pure resistance. Thus, the equilibrium connection network 14 does not influence the quantity of mismatching attenuation on the side of the two-wire, and the input impedance 13 on a return loss on the side of the four-wire. Since a two-wire/four-wire conversion circuit can be designed without the consideration of influence on both, the quantity of mismatching attenuation on the side of the two-wire can freely be increased.

Description

[Detailed Description of the Invention] [Summary] In an analog trunk in a digital exchange,
By using pure resistance as the impedance on the four-wire side to match the load impedance of the two-wire analog line, and by providing a balanced connection network in the wrap-around canceling line section, the amount of mismatch attenuation on the two-wire line side can be reduced. something that has been increased.

[Industrial application field]

The present invention relates to a two-wire to four-wire conversion circuit for analog trunks in a digital exchange.

In analog trunks in digital exchanges, the communication path of the exchange is a digital communication path, so it is a four-wire configuration, whereas analog lines are often two-wire systems, so two-wire
A hybrid function that performs four-wire exchange is required. At this time, it is necessary to insert a balanced connection m (BN) to match the impedance of the two-wire side and to prevent the reception signal from the four-wire side from going around to the four-wire transmitting side. However, since the insertion of the BN deteriorates the matching with the game and leads to a decrease in the amount of mismatch attenuation on the second line side, improvements are desired.

[Conventional technology]

A conventional two-wire to four-wire conversion circuit is shown in FIG.

In FIG. 2, 1, 2, 3, and 4 are operational amplifiers, 5 is a balanced wiring network (BN), 6 is a transformer, and 7 is a terminal resistor of the opposite station including line resistance. The input terminal a on the four-wire side is connected to a digital exchange network via a D/A converter (not shown).

The output terminal on the four-wire side is connected to a network of digital exchanges via an A/D converter (not shown).

The impedance of BN5 is 211%, the sum of the terminating resistance on the two-wire side and the line resistance is ZI-1, and the voltage at the input terminal a on the four-wire side is e. Here the input voltage e.

is amplified by operational amplifier 2 and the gain of operational amplifier 3 is 1), and the voltage between points C and d, which are the outputs of operational amplifiers 2 and 3, is Ae, then the voltage between the input voltage and c-d is A
becomes. Therefore, if the gain of the operational amplifier 4 is B, the signal is input to the operational amplifier 1 through the operational amplifier. The differential input, which is the output of the operational amplifier 4, is amplified by the operational amplifier 1, and a signal of voltage e0 is outputted to the output terminal.

In order to maximize the return loss, that is, to minimize the wraparound on the four-wire side, the differential input of the operational amplifier 1 only needs to be zero. The conditions for impedance matching between the four-wire side and the two-wire side are Zl, = Z! +
Therefore, if ZI=Zll and A-B=2 are satisfied, impedance matching can be achieved, and e. = 0, and the return loss becomes maximum. Therefore, operational amplifier 2.3. and 4 are considered so that A−B=2.

(Problems to be Solved by the Invention) In the conventional two-wire to four-wire conversion circuit described above, BN5 is directly connected to the four-wire side winding of the transformer 6, and the impedance matching condition is 2.=211. be.

Therefore, the impedance ZR of BN5 is designed to match the terminating resistance on the two-wire side. However, the impedance ZL on the two-wire side includes not only the terminating resistance but also the line resistance, and the value of this line resistance varies depending on the system. For this reason, the impedance Z of BN5 does not necessarily match ZI, and it is difficult to adjust the impedance of BN5 according to the line impedance on the second line side, resulting in a mismatch and the impedance on the second line side. There is a problem that the amount of matching attenuation becomes small.

[Means for solving problems]

The present invention will be explained in detail using FIG.

In FIG. 1, an analog trunk 11 in a digital exchange connecting a two-wire analog line 9 and a four-wire digital communication path 10 is shown.

In this analog trunk 11, the impedance 13 on the four-wire side is a pure resistance to match the load impedance 12 of the two-wire analog line. In addition, a balanced connection network 14 that prevents the received signal from the four-wire digital communication path 10 from going around to the four-wire digital communication path 10,
It is provided in the loop cancellation line section 15 where the influence of impedance on the pure resistance is least.

[For production]

The impedance on the four-wire side for matching the load impedance on the two-wire side is a pure resistance, and the balanced resistance vAm14 is provided in the loop cancellation circuit section where the impedance has the least influence on the pure resistance, thereby suppressing loop loop.
Since impedance matching can be easily achieved while reducing the amount of heat, the amount of mismatch attenuation can be increased.

〔Example〕

An embodiment of the invention will now be explained with reference to the circuit diagram of FIG.

In FIG. 1, 9 is a two-wire analog line, 10 is a four-wire digital communication line, 11 is an analog trunk, 13 and 1
6 is a resistor, 15 is a loop cancellation line, 14 is a balanced wiring network (BN), 17, 18, 19 and 20 are operational amplifiers,
21 is I. Lance.

A D/A converter 22 is connected between the input terminal a on the four-wire side of the analog trunk 11 and the digital communication path IO, and an A/D converter 23 is connected between the output terminal and the digital communication path 10. is connected.

The four-wire side input terminal a is connected to one input of the operational amplifier 19 via the operational amplifier 17 and the four-wire side winding of the transformer 21 . The output of the operational amplifier 17 is connected to the one input of the operational amplifier 19 via an operational amplifier 18 and a pure resistor 13 for matching. The output of operational amplifier 17 is also directly connected to the other input of operational amplifier 19.

The output of the operational amplifier 19 is connected to one input of the operational amplifier 20, and the input terminal a is connected to the other input of the operational amplifier 20 via a loop cancellation line 15 including a resistor 16. Between the detour cancellation line 15 and the earth,
A balanced wiring network (BN) 14 is connected.

The resistance value of the c-d resistor 13 is R3, and the load impedance on the two-wire side, that is, the sum of the terminating resistance and line resistance, is ZI.
If the voltage at the input terminal a on the four-wire side is e, then the input voltage el is amplified by the operational amplifier 18, and the voltage between the output of the operational amplifier 18 and the output of the operational amplifier 17 is AeH, then the input voltage vs. c − The voltage between d becomes A. Therefore,
Become an operan.

Assuming that the gain of the operational amplifier 19 is B, it is operationalized and input to one input of the operational amplifier 20.

On the other hand, the impedance of BN14 is Z*, Fir;
If the resistance value of the resistor 6 is <R, which is the same as that of the resistor 13, then the other input voltage of the operational amplifier 20 is such that if the output voltage e0 of the operational amplifier 20 is set to zero, the return loss on the four-wire side will be maximized, and the wrap-around will be canceled. For this purpose, it is sufficient that the output voltage of the operational amplifier 19 and the voltage of the loop canceling line 15 are made equal to each other. In order to satisfy the above formula, it is necessary that A-B=1 in ZL-ZB, and the operational amplifier 17, 1
The gains of 8, 19, and 20 satisfy A-B=1.

is designed to.

The resistor 13, which is the input impedance on the four-wire side, does not affect the return loss. Furthermore, since the impedance of the BN 14 has almost no effect on the resistor 13, which is the input impedance, matching can be achieved simply by adjusting tl (resistance value R3).

〔Effect of the invention〕

As explained above, according to the present invention, the balanced connection M? Change the position of 4 (BN),
By making it possible to adjust impedance matching using only pure resistance, BN can adjust the amount of mismatch attenuation on the two-wire side, and
The input impedance has no effect on the return loss on the four-wire side, and it is possible to design a two-wire to four-wire conversion circuit without considering their effects on each other. Therefore, the mismatch attenuation on the two-wire side and the return loss on the four-wire side are reduced. It is possible to improve both without sacrificing both.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a two-wire to four-wire conversion circuit according to the principles and embodiments of the present invention, and FIG. 2 is a circuit diagram of a conventional two-wire to four-wire conversion circuit. 9... Two-wire analog line, 10... Four-wire digital communication path, 12... Load impedance, 13... Pure resistance, 14... Balanced connection network, 15... Detour cancellation line.

Claims (1)

[Claims] Two-wire analog line (9) and four-wire digital communication line (10)
), the load impedance (12) of the two-wire analog line (9) is
), the impedance on the four-wire side is a pure resistance (13), and the balanced connection prevents the received signal from the four-wire digital communication path (10) from going around to the four-wire digital communication path. A two-wire to four-wire conversion circuit characterized in that a network (14) is provided in a loop canceling line section (15) where the influence of impedance on the pure resistor (13) is least.