JPH0425264A - 2/4-wire conversion circuit - Google Patents

Abstract

PURPOSE:To reduce the effect of noise generated in the circuit on a bypass quantity from a transmission system to a reception system by forming the circuit with a line transformer separating a DC current supplied from an exchange installation from a DC current supplied from its internal power supply and a reception system operational amplifier having a resistance hybrid at its input point. CONSTITUTION:A line transformer 1 is connected between a transmission system operational amplifier 2 and a line impedance 11. Then a DC current supplied from an exchange installation is separated from a DC current supplied from its internal power supply. Then a resistance hybrid HB separating signals of the transmission system and the reception system via the line transformer 1 and a termination resistor 9 having a resistance equal to the line impedance 11 is provided to an input point of the reception system operational amplifier 3. Thus, the circuit withstands line noise and common mode noise on the line without much effect of a change in the impedance of the telephone line.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a transmission system in an information communication processing device that satisfies terminal technical standards and is connected to switching equipment.

This invention relates to a 2-wire to 4-wire conversion circuit that performs 2-wire to 4-wire conversion between receiving systems.

[Conventional technology]

FIG. 3 shows a conventional 2-wire to 4-wire conversion circuit, and in the figure, 11 is line impedance, which is usually 600Ω in telephone lines. 15 is line impedance 1
A balance network for matching with 1.
A resistive bridge has a complex impedance, usually consisting of a resistor and a capacitor. 16. 17 represents the resistance value R□, R2 forming one side of the bridge, 18 represents the signal voltage of the transmitting system, and is the point A of the bridge.

Occurs between 0 and 0. Reference numeral 19 indicates a signal voltage source for the receiving system, which is generated between point B of the bridge and ground.

Next, the operation will be explained.

First, the line impedance 11 forms one side of the resistance bridge, and the size of this line impedance 11 is Z
, the impedance of the balance network 15 is BN, then this resistance bridge is Z: R,=BN:
Since the conditional expression H□ is satisfied, the transmitting signal and the receiving signal existing on the line are separated within the range where this condition is satisfied. First, when a transmitting signal is generated as a voltage at points A and C of the resistor bridge, there is a resistor 1 on the line for the voltage between A and C.
A voltage dropped by a resistance value R2 of 7 is sent onto a line having a line impedance of 11.

At this time, from the above conditional expression, the voltage between point B and the ground becomes O', and if this voltage is taken out as a receiving system signal, the signal sent from the transmitting system will not go around to the receiving system. Therefore, based on the principle of this resistance bridge, only the signal on the line can be taken out as a signal for receiving a call. In addition, the impedance of a telephone line is designed with the assumption that it is 600Ω, but in reality it is simply 60Ω due to the impedance of the power supply circuit on the exchange equipment side, line loss, etc.
It is not equivalent to a 0Ω resistance.

[Problem to be solved by the invention]

Since the conventional 2-wire to 4-wire conversion circuit is configured as described above, the point where the amount of signal looping from the transmitting system is uniquely minimized is determined relative to the impedance of the telephone line. Changes (particularly fluctuations in line loss) have a large effect on loopback, and since the receiving system is connected to the telephone line in a direct current manner, it is susceptible to line noise, especially in-phase noise that occurs on the circuit. There were issues such as being affected by component noise. A technique partially similar to the conventional 2-wire to 4-wire conversion circuit is disclosed in Japanese Patent Application Laid-open No. 300686/1986.

This invention was made to solve the above problems, and is a 2-wire to 4-wire conversion that is not significantly affected by changes in telephone line impedance and can deal with single-line noise and common-mode component noise on the circuit. The purpose is to obtain a circuit.

[Means to solve the problem]

The 2-wire to 4-wire conversion circuit according to the present invention is connected between a transmitting system operational amplifier that amplifies a transmitting system signal and a line impedance and is supplied from exchange equipment. A line transformer that separates the direct current from the direct current supplied from the internal power supply, and a terminating resistor with a resistance equal to the line impedance.

It consists of a receiving operational amplifier that has a resistor hybrid at its input point that separates the transmitting and receiving signals.

[Effect]

In the 2-wire to 4-wire conversion circuit according to the present invention, the resistance hybrid at the input point of the operational amplifier in the receiving system operates differentially with respect to the operational amplifier, so that noise generated on the circuit is transferred from the transmitting system to the receiving system. Reduce the influence on the wraparound amount.

[Embodiments of the invention]

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

In FIG. 1, 1 is a line transformer, which separates the DC current supplied from the exchange equipment from the operating power source of the circuit inside the device. Since the impedance of the telephone line is normally designed considering 600Ω, a 600Ω line transformer 1 is used. 2 is a transmitting operational amplifier that amplifies the signal from the terminal device and sends it to the telephone line. 3 is a receiving operational amplifier that receives signals on the telephone line. 4°5.6 is the resistance value R, the resistances R2 and R3, and 7.8 is the variable resistance. Resistor 4 and variable resistor 7 are transmitting operational amplifier 2
The gain is determined by adjusting the variable resistor 7. The resistors 5 and 6 and the variable resistor 8 have the same function, that is, gain adjustment, for the receiving system operational amplifier 3, but here they are not used to determine the gain of the receiving system, but to adjust the gain from the transmitting system to the receiving system. This is to prevent the signal from looping around, and by adjusting the variable resistor 8, the amount of looping around can be adjusted. 9 is a terminating resistor with a resistance value R4 of 600Ω to match the impedance of the telephone line.

10 is a capacitor with a capacity of C□, which functions as an element for adjusting impedance. Note that the resistors 5 and 6 and the variable resistor 8 constitute a resistance hybrid HB.

Next, the operation will be explained. The transmission system operational amplifier 2 and its peripheral circuitry, ie, a resistor 4 and a variable resistor 7, amplify the transmission system signal and send power to the telephone line.

At this time, the variable resistor 7 is adjusted to determine the transmission power.

This transmitting system is connected to the telephone line via the line transformer 1, and the impedance seen from the telephone line is the line transformer 1. Including each impedance component of the resistor 9 and capacitor 10, R4°C, the total is 60
It is selected to be 0Ω.

Further, the above-mentioned transmission system signal goes out from the transmission system operational amplifier 2 to the telephone line via these termination circuits. On the other hand, the receiving system operational amplifier 3 and its peripheral circuits form a 2-wire to 4-wire conversion circuit, and by differentially inputting the transmitting system signals to the receiving system, only the signals on the telephone line can be input. It is extracted as a receiving signal. Now, for convenience of explanation, variable resistor 8
Let the resistance value of
．． When the composite impedance of the capacitor 10 is Z and the voltage of the signal sent from the transmitting operational amplifier 2 is V, the (-) input terminal of the receiving operational amplifier 3 has (Ra /
A voltage of R2+R1) x v is generated, and (Z/R, +z) is generated at the (+) input terminal of the receiver operational amplifier 3.
A voltage of xv is generated.

If R,: R, = R4: Z, no voltage is generated at the output terminal of the operational amplifier 3 of the receiving system.

That is, the transmitting system signal does not go around to the receiving system. Therefore, the situation is usually like this.

The variable resistor 8 is adjusted, and the receiving system operational amplifier 3 performs 2-wire to 4-wire conversion so that only the signal on the telephone line can be extracted as a receiving system signal.

In this embodiment, a case where a resistive hybrid is configured differentially for the receiver operational amplifier 3 has been explained.
In this case, if the impedance 2 on the line side fluctuates, the balance condition of the resistive hybrid collapses and one round trip occurs. In the case of a general public network, the distance from the switching equipment is
Since the maximum loss is 7 dB and cannot be uniquely replaced with a 600 Ω resistor, the circuit of the above embodiment may not be able to sufficiently prevent the loop-around operation. Therefore, by making the balance of the resistance values of the peripheral circuits of the receiving operational amplifier 3 sufficiently large with respect to the terminating resistance, it is possible to obtain a greater effect of preventing loopback.

This embodiment will be explained below with reference to FIG.

12 and 13 are resistors with resistance values R,,R, and 14 is a variable resistor, which is connected in series with the resistor 12, thereby adjusting the balance of the resistance values. In the explanation of FIG. 1, R,:
R, = R,: It has been explained that Z is the principle of balance, but in Fig. 2, the resistance value R4 of the resistor 9 is included in the impedance Z on the line side seen from the transmitting operational amplifier 2, and is the principle of balance. The principle is to set the resistance value of variable resistor 14 to VR□
, VR3: R, = RG: Z.

According to this embodiment, in FIG. 1, the resistance value of the resistor 9 forming one side of the bridge is 600Ω in accordance with the impedance of the telephone line, and z# is 600Ω, so the left and right ratio in the above equation is 1. :1, and the fluctuation of Z remains as it is (1
:1 ratio), which affects the above balance. on the other hand,
In Figure 2, by changing this balance, the influence of Z fluctuations is further reduced. In other words, the resistor 13 in FIG. 2 is a resistor forming one side of the bridge that functions in the same way as the resistor 9 in FIG. The balance of the resistance values in is determined by VR,>R,=R,>Z, and it can be ensured that fluctuations in Z have almost no influence.

〔Effect of the invention〕

As described above, according to the present invention, by connecting a line transformer between the transmitting system operational amplifier and the line impedance, the DC current supplied from the exchange equipment and the DC current supplied from the internal power supply are separated. A resistor hybrid is provided at the input point of the receiving operational amplifier to separate the transmitting system and receiving system signals via the line transformer and a terminating resistor having a resistance value equal to the line impedance. This has the effect of being able to perform the desired 2-wire to 4-wire conversion without being greatly affected by changes in the impedance of the telephone line, making it resistant to line noise and in-phase component noise on the circuit.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a 2-wire to 4-wire conversion circuit according to one embodiment of the present invention, FIG. 2 is a circuit diagram showing another embodiment of the 2-wire to 4-wire conversion circuit of the present invention, and FIG. is a circuit diagram showing a conventional 2-wire to 4-wire conversion circuit. 1 is a line transformer, 2 is a transmitting operational amplifier, 3 is a receiving operational amplifier, 9 is a terminating resistor, 11 is a line impedance, and HB is a resistance hybrid. In Figure 1, the same reference numerals indicate the same or equivalent parts. (2 others)

Claims (1)

[Claims] a transmitting system operational amplifier that amplifies the transmitting system signal, and a transmitting system operational amplifier connected between the transmitting system operational amplifier and the line impedance,
A line transformer separates the direct current supplied from the exchange equipment and the direct current supplied from the internal power supply, and the transmitting and receiving systems are connected via the line transformer and a terminating resistor with a resistance equal to the line impedance. A 2-wire to 4-wire conversion circuit comprising a receiver operational amplifier having a resistor hybrid at the input point to separate signals.