JPH01103328A - 2/4-wire converting circuit - Google Patents

Abstract

PURPOSE:To decrease the number of taps of an echo canceller by inserting a resistor between a common return for a reception circuit and a transmission circuit and other terminal of a primary winding of a transformer, and connecting an equalizer to an output terminal of the reception circuit. CONSTITUTION:A resistor R2 is inserted between the common return (earth) of transmission circuit 10 and a reception circuit 20 and other terminal of the primary winding of the transformer T and an equalizer 4 is connected to the output terminal of the circuit 20. In such a case, the transmission characteristic from the output point of the amplifier 2 to the input point of the amplifier 3 is expressed in equation I, where L is the self inductance and Z1 is the input impedance of the line. Thus, the transmission characteristic at DC (omega=0) is derived as R2/R1+R2 from the equation I and shows a large value. Thus, the echo tail due to DC interruption is decreased. Since the frequency characteristic in the band at the output of the equalizer 4 is made flat, the tail of the echo signal is zero. Thus, the number of tap of the echo canceller is reduced further.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a two-wire and four-wire conversion circuit for an echo canceller used in baseband digital transmission.

[Prior Art] Conventionally, this type of two-wire/four-wire conversion circuit uses a hybrid transformer as shown in FIG. That is,
A transmission line is connected between the secondary windings of the transformer T, and one terminal of the primary winding of the transformer T is connected to an amplifier 2 and a resistor R1.
The output terminal of a transmitting circuit (line driving circuit) 10 consisting of the above and the input terminal of the receiving circuit 20 consisting of the amplifier 3 are connected.

The other terminal of the primary winding of the transformer T is directly connected to ground, ie to the common return of the receiving circuit 20 and the transmitting circuit 10. Note that 1 is an input terminal and 5 is an output terminal.

[Problems to be Solved by the Invention] Incidentally, in the conventional hybrid transformer type two-wire four-wire conversion circuit having such a configuration, the transfer characteristic from the output point of amplifier 2 to the input point of amplifier 3 is as follows: is lossless, its self inductance and mutual inductance are L, and the input impedance of the line is 21
Then, it is expressed by the following formula.

(R+ +L) ・jωL+R+ 'L Therefore, the (ω=0) transfer characteristic in direct current is zero according to the above equation,
Inverse characteristics cannot be defined. Therefore, in the conventional 2-wire 4-wire conversion circuit, direct current and low frequency components are blocked by the transformer T. Therefore, when this conventional 2-wire 4-wire conversion circuit is applied to an echo canceller system for baseband data transmission, an echo signal (at point A in Figure 2) generated in response to the transmission signal sent out from the transmission circuit. As shown in Figure 3, the single pulse response of the signal (signal) is accompanied by an extremely long tail. Therefore, in a conventional 2-wire 4-wire conversion circuit, the number of taps in the echo canceller must be increased. First, there is a drawback that the structure of the echo canceller becomes large.

[Means for Solving the Problems] The two-wire four-wire conversion circuit according to the present invention includes a transmitting circuit for transmitting a transmitting signal, and one output terminal of the transmitting circuit connected to one of the primary windings. a transformer having terminals connected to it and a transmission line coupled between the secondary windings; and an input signal to one terminal of the primary winding of the transformer in order to receive a received signal from the transmission line via the transformer. In a two-wire four-wire conversion circuit having a receiving circuit connected to a terminal, a resistor is inserted between a common return line of the receiving circuit and the transmitting circuit and the other terminal of the primary winding of the transformer, It is characterized in that an equalizer is connected to the output terminal of the receiving circuit.

[Examples] Examples of the present invention will be described below with reference to the drawings.

Referring to FIG. 1, the 2-wire 4-wire conversion circuit according to the first embodiment of the present invention has a common return wire (ground) of the receiving circuit 20 and the transmitting circuit 10 and the other of the primary winding of the transformer 1'. The circuit is similar to the conventional 2-wire 4-wire conversion circuit shown in FIG. It has a configuration.

Transmission 73 sent out from the transmission circuit (line drive circuit) 10
The signal is transmitted to the transmission path via the transformer T, and at the same time leaks to the receiving circuit 20 as an echo signal.

In this embodiment, the transfer characteristic from the output point of amplifier 2 to the input point of amplifier 3 is expressed by the following equation.

[R+ +R2+2+ 11#L+(R+ +R
2) ・L Therefore, the transfer characteristic in DC (ω=0) is 1, and according to E formula, it becomes R, +R2, which is a large value. Therefore, the 2-wire 4-wire conversion circuit of this embodiment can reduce the influence of echo tail due to DC cutoff, and can reduce the number of taps of the exhaust canceller.

In the following, since the above transfer characteristic does not have a zero point, the zero equalizer 4, which can define an inverse characteristic, has this inverse characteristic.

At the output of the equalizer 84, the frequency characteristics within the band become flat, so the tail of the echo signal becomes zero. Therefore, the number of taps of the echo canceller can be further reduced.

Referring to FIG. 4, in the 2-wire 4-wire conversion circuit according to the second embodiment of the present invention, the amplifier 3 of the receiving circuit 20 is a differential amplifier 3a, and one input terminal of the differential amplifier 3a and A resistor R3 is connected between the transmitting circuit 10 and the output terminal of the amplifier 2.
This embodiment has the same configuration as the first embodiment described above, except that a network Z and a network Z are provided.

According to such a configuration, the transfer characteristic can be approximated to Ri +1, so that echoes can be further suppressed.

[Effects of the Invention] As explained above by Sosusu, according to the present invention, the common return wire of the receiving circuit and the transmitting circuit and the terminal of the primary winding of the transformer on the side where the receiving circuit and the transmitting circuit are not connected By inserting a resistor between the
The effect is that the echo tail can be shortened, and as a result, the number of taps of the echo canceller can be reduced.

[Brief explanation of the drawing]

1 is a circuit diagram showing the configuration of a 2-wire 4-wire conversion circuit according to the first embodiment of the present invention, FIG. 2 is a circuit diagram showing the configuration of a conventional 2-wire 4-wire conversion circuit, and FIG. 3 is a circuit diagram showing the configuration of a conventional 2-wire 4-wire conversion circuit. FIG. 4 is a diagram showing an example of the echo signal of the two-wire 4 according to the second embodiment of the present invention.
FIG. 2 is a circuit diagram showing the configuration of a line conversion circuit. 1...Input terminal, 2...Amplifier, 3...Amplifier,
3a...Differential amplifier, 4...Equistop device, 5...Output terminal, 10...Transmission circuit (line drive circuit), 20...
・Reception circuit, T...Transformer, RI, R2, Rs・
...Resistance, 2...Network. Figure 1 ko0 Figure 2

Claims (1)

[Claims] 1. A transmission circuit for transmitting a transmission signal, a transformer in which one terminal of a primary winding is connected to the output terminal of the transmission circuit, and a transmission line is connected between the secondary windings, and the transmission line A 2-wire 4-wire conversion circuit includes a receiving circuit whose input terminal is connected to one terminal of a primary winding of the transformer in order to receive a received signal from the transformer via the transformer. 2, characterized in that a resistor is inserted between the common return line of the transmitting circuit and the other terminal of the primary winding of the transformer, and an equalizer is connected to the output terminal of the receiving circuit.
4-wire conversion circuit.