JPH01222550A - Hybrid circuit - Google Patents

Abstract

PURPOSE:To attain echo cancellation with high accuracy and simple adjustment by deciding 1st and 2nd resistances so that the gain of an inverse amplifier, the impedance of a terminal equipment, the impedance of a circuit element, the 1st resistance and the 2nd resistance satisfy a specific relation. CONSTITUTION:An inverse amplifier A2 amplifying inversely a reception signal and connecting to a reception side transmission line 4wyR and a voltage dividing circuit element I connecting between the output terminal of the inverse amplifier A2 and a 2-wire transmission line 2wy are provided on the circuit. Moreover, the 1st resistor B connected between the 2-wire transmission line 2wy and the transmission side transmission line 4wyS and the 2nd resistor C connected between the input terminal of the inverse amplifier A2 and the transmission side transmission line 4wyS are provided. Then the resistors R1, R2 are decided to satisfy equation I, where the inverse of G2 is the gain of the inverse amplifier A2, Z1 is the impedance at a terminal T, Z2 is the impedance of the circuit component I, R1 is the resistance of the 1st resistor B and R2 is the resistance of the 2nd resistor C. Thus, echo cancellation with high accuracy and simple adjustment is obtained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a hybrid circuit, and particularly relates to a two-wire transmission line to which a terminal such as a telephone is connected, and a four-wire system that connects the two-wire transmission line. The present invention relates to a hybrid circuit interposed between a transmission line and a transmission line.

[Conventional technology]

A conventional hybrid circuit, which is the basis of the present invention, will be explained with reference to FIGS. 2 and 3. As shown in Figure 2,
A telephone 10 as a terminal is connected to a two-wire transmission line 2wy consisting of a two-wire balanced pair cable. This two-wire transmission line 2wy is connected to a four-wire transmission line 4wy including a transmission side transmission line 4wyS and a reception side transmission line 4WyR via a hybrid circuit HYB.

As shown in FIG. 3, the hybrid circuit HYB has two
It is composed of coils L1 and L2 connected to the wire transmission line 2Wy, and a coil connected to the transmission side transmission line 4WyS. A balance resistor BNW is connected to the two-wire transmission line 2wy, and a connection point between the coil LI and the coil L2 and a connection point between the telephone 10 and the balance resistance BMW are connected to the reception side transmission line 4wyR. According to the above-mentioned hybrid circuit HYB, the main signal transmitted from the sending end is converted into two signals by mutual induction between the coil L+ and the coil L2.
It is transmitted from the wire transmission line 2wy to the transmission side transmission line 4wyS.

By the way, in recent years, voice transmission has been carried out over dedicated lines using high-speed digital lines, but analog signal transmission over digital lines requires a long delay time when performing A/D conversion, D/A conversion, and multiplexing. As shown in Fig. 2, the signal transmitted from the transmitting end becomes an echo signal and is transmitted to the transmitting end via the receiving transmission line 4wyR, so there is a problem that it is felt as an echo and the quality of the call deteriorates. be. Echoes caused by this delay time also occur in international lines using satellite communications, and in this case, a pseudo echo signal is generated and the echo is subtracted from the human signal to eliminate the echo. An echo canceller is used to ensure line quality.

[Problem to be solved by the invention]

However, although it is effective to use echo cancellers on international lines where line costs are high, it is not practical to use expensive echo cancelers on large-capacity digital lines aimed at reducing costs. Also, in a conventional hybrid circuit, it is theoretically possible to eliminate echoes by changing the impedance ratio of the coils Lls and 2 or by changing the balance resistor, but making the impedance of the coil variable is There are problems in that it is difficult and the cost increases if the balance resistance is continuously changed.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a hybrid circuit with an echo canceling function that can perform highly accurate echo cancellation with simple adjustment and can be manufactured at low cost.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a four-wire transmission line comprising a two-wire transmission line 2wy to which a terminal T is connected, a transmission line 4wyS on the transmitting side, and a transmission line 4WyR on the receiving side, as shown in FIG. and supplies the transmission signal transmitted via the two-wire transmission line 2Wy to the transmission side transmission line 4wyS, and the reception signal transmitted via the reception side transmission line 4wyR to the two-wire transmission line 2Wy. In the hybrid circuit that supplies the wire transmission line 2wy, an inverting amplifier A2 connected to the receiving side transmission line 4WVR and inverting and amplifying the received signal.
and the output terminal of the inverting amplifier A2 and the two-wire transmission line 2.
voltage dividing circuit element ■ connected between wy and the above-mentioned 2
A first resistor B connected between the wire transmission line 2wy and the transmitting side transmission line 4wyS, and a second resistor B connected between the input end of the inverting amplifier A2 and the transmitting side transmission line 4wyS. , the gain of the inverting amplifier A2 is -62, the impedance value of the terminal T is Zl, the impedance value of the circuit element (2) is Z2, and the value of the first resistor B is R1%. The present invention is characterized in that, when the value of the second resistor C is R2, R+ and R2 are determined so as to satisfy the following equation.

R*　　　　Zl　+22 [Effect] Next, the present invention will be explained in detail with reference to FIG.

If the potential of the received signal is V, then amplifier A with gain G
The potential V1 at the output terminal of the inverting amplifier A2 and the potential V at the output terminal of the inverting amplifier A2 are expressed as follows.

V 4 = G + ・Vl ... (2) Vs
= G2 ・Va = G+ −G2 ・V
a - (3) Also, if the voltage at the terminal is V2, the impedance z2 of the circuit element and the internal impedance z of the terminal
1, the potential V6 at the connection point between the terminal and the circuit element is as follows.

Zl + Z2 Zl + 7Z2 Based on the potential V1 at the connection point between the first resistor B and the second resistor C (0)
Then, the currents I+ and L flowing through each of the first resistor B1 and the second resistor C are expressed as follows.

Therefore, the current I flowing through the resistance is as follows.

I3 = II + I2 Z.

In Equation (7) above, if the following is true, it is possible to prevent the transmitted signal (V3) from including the component (V, ) of the received signal in the transmitted signal, thereby canceling the echo.

Therefore, in the present invention, so as to satisfy the above formula (8),
Echoes are eliminated by determining the values Rr and R2 of the first and second resistors.

〔Effect of the invention〕

As explained above, according to the present invention, since the resistance value is changed in order to cancel the echo, the echo can be canceled with high precision with simple adjustment, and the hybrid circuit can be manufactured at low cost. is obtained.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 4 shows a circuit diagram of the hybrid circuit of this embodiment, which includes operational amplifiers 20, 22, 24, 26, 28, and 30.

The receiving side transmission line 4WyR is connected to the non-inverting terminal of the operational amplifier 20.
is connected to one cable, and the inverting terminal of the operational amplifier 20 is grounded through a resistor 32 and connected to a resistor 34.
It is connected to the output terminal of the operational amplifier 20 via. The output terminal of the operational amplifier 2o is connected to the operational amplifier 2 through the resistor 40.
4, and is also connected to the inverting terminal of the operational amplifier 28 via a variable resistor 60. Also,
The non-inverting terminal of the operational amplifier 20 is connected to the inverting terminal of the operational amplifier 22 via a series circuit of a resistor 38 and a resistor 36. The connection point between the resistor 36 and the resistor 38 is grounded.

The inverting terminal of the operational amplifier 240 is connected to the output terminal via a resistor 48, and the non-inverting terminal is connected to the non-inverting terminal of the operational amplifier 26 via a resistor 44 and a resistor 46.

The connection point between the resistor 44 and the resistor 46 is grounded.

The output terminal of the operational amplifier 24 is connected to one table of the two-wire transmission line 2wy through a circuit element 52 with an impedance value of 22, and is connected to the inverting terminal of the operational amplifier 28 through a resistor 58 with an impedance value of R3. ing. This operational amplifier 24 performs inversion amplification with a gain of -02.

The inverting terminal of the operational amplifier 22 is connected to the other cable of the receiving transmission line 4wyR. The output terminal of the operational amplifier 22 is connected to the inverting terminal of the operational amplifier 26 via a resistor 42, and is connected to the operational amplifier 300 via a variable resistor 62.
Connected to the inverting terminal. This movable resistor 62 is configured so that its resistance value can be varied in conjunction with the variable resistor 60 described above. A non-inverting terminal of the operational amplifier 22 is grounded via a resistor 74 and connected to the output terminal of the operational amplifier 22 via the resistor 72.

The output end of the operational amplifier 26 is connected to the other cable of the two-wire transmission line 2wy via a circuit element 54 having the same impedance as the circuit element 52, and a resistor 56 having a value of R2.
It is connected to the inverting terminal of the operational amplifier 30 via.

The inverting terminal of the operational amplifier 260 is connected to the output terminal via the resistor 50. Like the operational amplifier 24, this operational amplifier 26 performs inversion amplification with a gain of -02.

The output end of the operational amplifier 28 is connected to one cable of the transmission side transmission line 4wyS and also connected to the inverting terminal via the resistor 64, and the non-inverting terminal of the operational amplifier 28 is connected to the resistor 66.
and a non-inverting terminal of the operational amplifier 30 via a resistor 68. The connection point between the resistor 66 and the resistor 68 is grounded.

The output end of the operational amplifier 30 is connected to the other cable of the transmission line 4wyS on the transmission side, and is also connected to a non-inverting terminal via a resistor 70.

The signal transmitted through the receiving side transmission line 4wyR is sent to the operational amplifier 20.
．． After being amplified by 22, the signal is inverted and amplified by operational amplifiers 24 and 26, and is input to the two-wire transmission line 2wy, and is also input to the transmission side transmission line 4wyS via operational amplifiers 28 and 30. Further, the output signal of the operational amplifier 20.22 is input to the operational amplifier 28.30 via a variable resistor 60.62.

Here, variable resistor 60.62 whose resistance value changes in conjunction with
By adjusting the resistance value R2 so as to satisfy the above equation (8), it is possible to prevent the signal transmitted through the receiving side transmission line 4wyR from being manually input to the transmitting side transmission line 4wys, thereby reducing the echo. can be erased.

As explained above, according to this example, a highly accurate hybrid circuit can be manufactured because no coil is used, and impedance matching is performed using a variable resistor, so it can be completely adjusted on site. Can be done. Furthermore, it is possible to reduce costs by incorporating the hybrid circuit into an IC.

Note that in the above, the resistor 60.62 is a variable resistor, but the resistor 56.58 may be used as a variable resistor whose resistance value changes in conjunction with the resistor 60.62, or the resistor 56.58 may be a variable resistor whose resistance value changes in conjunction. A fixed resistance may be used as long as it is determined by calculation.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram for explaining the present invention in detail, Fig. 2 is a circuit diagram showing a conventional transmission line, Fig. 3 is a circuit diagram showing a conventional hybrid circuit, and Fig. 4 is a circuit diagram for implementing the present invention. FIG. 3 is a circuit diagram showing an example. 20.22.24.26.28.30 ... operational amplifier, 32.34.36.38.40.42.44.46.4
8.50...Resistance, 52.54...Circuit element, 60.62...Variable resistance.

Claims (1)

[Claims] (1) Interposed between a 2-wire transmission line to which the terminal is connected and a 4-wire transmission line equipped with a transmitter-side transmission line and a receiver-side transmission line, and transmitted via the 2-wire transmission line. In a hybrid circuit that supplies a transmission signal to the transmission line on the transmission side and also supplies a received signal transmitted via the transmission line on the reception side to the two-wire transmission line, the hybrid circuit is connected to the transmission line on the reception side and the reception side an inverting amplifier for inverting and amplifying a signal; a circuit element for voltage division connected between the output end of the inverting amplifier and the two-wire transmission line; a first resistor connected between the input terminal of the inverting amplifier and the transmitting side transmission line;
, and the gain of the inverting amplifier is −G_2.
, when the impedance value of the terminal is Z_1, the impedance value of the circuit element is Z_2, the value of the first resistor is R_1, and the value of the second resistor is R_2, the following formula is satisfied. A hybrid circuit characterized in that R_1 and R_2 are defined as follows. R_1/R_2=(Z_1・G_2)/(Z_1+Z_
2)