JPS6331969B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a 2-wire to 4-wire conversion circuit that couples a 2-wire line and a 4-wire line used in wired communications.

<Prior art> In wired communication, a two-wire line for bidirectional communication and a four-wire line for one-way communication are combined,
Guides the signal from the wire line to the 4-wire output line, guides the signal from the 4-wire input line to the 2-wire line, and eliminates the wraparound signal from the 4-wire input line to the 4-wire output line. A 2-wire to 4-wire conversion circuit is used.

Conventionally, a so-called transformer hybrid circuit using a transformer is well known as a first example of this type of circuit.

As a second example, with the electronicization of communication equipment in recent years, an impedance network is used to simulate a signal transmitted to a 2-wire line from a signal on a 4-wire input line, and the signal is actually transferred to a 2-wire line. Keiichi Yasuda has developed an electronic hybrid circuit that uses an electronic circuit to subtract this simulated signal from the signal generated on the line, thereby eliminating the wraparound signal.
Koichi Hasegawa and Hiroyuki Endo
“Design and Performance of Subscriber Line
Interface Module for Digital Switching
System” was proposed in ISSCC'80.

Furthermore, as a third example, from the point of view of electronically synthesizing the input impedance of a two-wire line, it is possible to detect the differential voltage of the two-wire line and apply feedback to the signal source that generates the signal to the two-wire line. DWAULL, DASPIRES, PCDAVIS and
SFMOYER “A High-Voltage IC for a
Transformerless Trunk and Subscriber Line
Interface”IEEE Journal of Solid-State
Circuits, Vol.SC−16.4, August 1981.

The impedance values that determine the signal transfer characteristics in such a hybrid circuit include the terminal impedance Z _T of the two-wire line, the signal transmission impedance Z _S to the two-wire line, and the two-wire line connecting to the hybrid circuit. There is a load impedance Z _L which is the composite impedance of the terminal and the load of the hybrid circuit, and a balance impedance Z _B which simulates this load impedance. this house,
It is well known that it is especially important that the values of Z _L and Z _B match from the point of view of attenuating the wrap-around signals from the 4-wire input line to the 4-wire output line. Also, Z _T and Z _S take the same value as one number.

By the way, in existing hybrid circuits, Z _T ,
Three or more impedance networks are required to synthesize Z _S and Z _B. For example, in the transformer hybrid circuit of the first example, one impedance network (e.g., 600Ω is used) between the four-wire input line and one terminal of the four-wire line-side winding of the transformer; An impedance network (e.g. 600Ω) is connected between the opposite terminal of the 4-wire line winding of the transformer and ground, and a balance network is connected between the midpoint of the 4-wire line winding of the transformer. For example, three impedance networks are required.

In addition, in the second example of electronic hybrid, 2
Z _T is constructed by the impedance of the impedance network connected between the lines of the wire line, and the differential voltage of the 2-wire line is detected by a high-impedance amplifier. In addition to transmitting the signal to the line, the signal is used to simulate the two-wire line voltage using an operational amplifier, etc. using an impedance network proportional to Z _S and Z _B , and the difference with the detected differential voltage is calculated. , cancels the wraparound signal, but also requires three impedance networks.

Furthermore, even when using the feedback circuit of the third example, there is one impedance network for _ZT synthesis, two impedance networks proportional to ZT and _ZB for wraparound prevention, and a 4-wire input line. In order to achieve the desired transfer characteristics from the 4-wire input line to the 2-wire line, a total of 4 impedance networks are used, including one impedance network proportional to Z _T attached to the 4-wire input line. are doing.

Furthermore, the second and third examples of the latter are
The aim of these circuits was to make the circuits more compact through computerization, but the feature of these circuits was that the wraparound cancellation circuit was constructed so as not to affect the transfer characteristics from the 4-wire input line to the 2-wire line. The point is that
As a result, Z _T and Z _B can be used to prevent wraparound, independently of the single impedance network for combining Z _T and Z _S.
Two impedance networks are required proportional to , essentially requiring three or more impedance networks.

Further, in the hybrid circuits of the first, second, and third examples, even if the balance impedance Z _B matches the load impedance Z _L , if Z _T ≠ Z _L , then 4
There is a drawback that the transfer characteristic from the linear input line to the two-wire output line has frequency characteristics and causes waveform distortion. In other words, this drawback is the same as the first, second, and third
The transfer characteristics from the 4-wire input line to the 2-wire output line in the example are multiplied by an equivalent circuit that supplies a signal from a signal source with impedance Z _S = Z _T to load impedance Z _L , so Z _B = Even if it is Z _L , Z _L /L _S
If is not a real number, this is due to the fact that the transfer characteristic has a frequency characteristic.

<Object of the Invention> An object of the invention is to provide a 2-wire to 4-wire conversion circuit in which the number of impedance circuit networks for synthesizing Z _T , Z _S , and Z _B is two or less.

Another object of the present invention is to synthesize the power consumption of the circuit by using an impedance network that is a constant multiple of the actual Z _T , Z _S , and Z _B in a way that synthesizes Z _T , Z _S , and Z _B . It is an object of the present invention to provide a 2-wire to 4-wire conversion circuit that achieves a reduction in noise and high accuracy.

Still another object of the present invention is to provide a 2-wire to 4-wire conversion circuit having a frequency-free transfer characteristic from a 4-wire input line to a 2-wire output line for any _ZL . .

<Summary of the Invention> The 2-wire to 4-wire conversion circuit of the present invention includes: a first means for detecting a difference signal of a two-wire line;
a second means for erasing only the signal component of the four-wire input line from the difference signal obtained from the first means and detecting it as a signal of the four-wire output line; proportional to the signal, the first 2
a signal inversely proportional to the impedance of the terminal impedance network; a signal proportional to the signal of the four-wire input line and inversely proportional to the impedance of the second two-terminal impedance network;
a third means for generating a feedback signal as a weighted sum with a difference signal of the wire line; fourth and fifth means for respectively generating voltages of opposite polarity using the feedback signal as input; third and fourth impedance networks coupling one of the means and one of the two-wire lines, and one of the fifth means and the other of the two-wire lines; transmitting a signal on a formula input line to the two-wire line, transmitting a signal arriving from the two-wire line to a four-wire output line, and transmitting a signal from the four-wire input line to the four-wire output line. It is characterized by minimizing the amount of wraparound.

<Description of Embodiments> Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the basic configuration of an embodiment of the 2-wire/4-wire conversion circuit of the present invention. Block 1 is connected to two-wire lines T and R and is means for detecting a difference signal S1 between input signals S0 from these two-wire lines T and R. Block 2 outputs the difference signal 71 detected by block 1 and the signal S on the 4-wire input line RX.
2 and 2 are weighted with polarity that eliminates the wraparound amount, and the signal to the 4-wire output line TX is
This is a means of detecting it as S3. Block 3 is
operating in conjunction with a first two-terminal impedance network 8 with an impedance Z _T ′ and a second two-terminal impedance network 9 with an impedance Z _B ′, proportional to the signal S3 on the four-wire output line TX;
A signal S4 inversely proportional to the impedance Z _T ′ of the first two-terminal impedance network 8 and a signal S2 of the four-wire input line RX and inversely proportional to the impedance Z _B ′ of the second two-terminal impedance network 9 The weighted sum of the signal S5 detected by the block 1 and the difference signal S1 of the two-wire line detected by the block 1 is calculated as the feedback signal S6.
This is a means to do so. Block 4 and Block 5
are two-wire line voltage generating voltage sources that each receive the feedback signal S6 as input and generate signal voltages having mutually depolarized polarities. Blocks 6 and 7 are impedance networks that couple the outputs of the two-wire line voltage generating voltage sources 4 and 5 and the T or R of the two-wire line, respectively.

The weight in the weighted sum used in the explanation of each block above is determined by how the magnitude of the signal level in the circuit is determined, and when realizing the circuit, phase inversion, constant multiplication, etc. Various variations are possible, but as long as they are based on the operation according to the principle formula as described later, they are included in the scope of the present invention.

Next, the qualitative operation of the first circuit will be explained.

Block 1 removes the in-phase signal generated at the end of the two-wire line and detects only the difference signal S1. This difference signal S1 is the sum of the signal S2 input from the four-wire input line RX and transmitted to the two-wire line, and the signal arriving via the two-wire line. Therefore, in block 2, from this difference signal S1, the 4-wire input line
By subtracting the RX signal S2, 2
Only the signal S0 that has arrived via the wire line can be detected and used as the signal S3 of the four-wire output line TX.

Input impedance of the circuit seen from the 2-wire line
If block 1 has a high input impedance, Z _T is determined by the variation of the two-wire line voltage generating voltage source with respect to variations in the input voltage and the impedance Z _F of the impedance network existing therebetween. Among these, the voltage fluctuation of the two-wire line voltage generation voltage source is variable by the first impedance network 8 that constitutes the feedback system, and as described later, the input impedance Z _T is It can be set to 1/constant of the impedance value Z _T ' of the network 8. The path directly from block 1 to block 3 feeds back signal S1, which is a component of the feedback signal S6 that does not have frequency characteristics.

Considering the transfer characteristics from the 4-wire input line to the 2-wire line, from the 4-wire input line RX to block 2,
The feedback system enters the feedback system via the second impedance network 9, and as described later, the first impedance network 8 provides a variable output impedance.
Generates a signal to the wire line. This signal can correct the frequency characteristics of the load impedance Z _L of the two-wire line by the impedance value Z _B ' of the second impedance network 9, and as described later, the impedance Z _B ' can be corrected. By setting the impedance Z _L to a constant multiple, it is possible to
Transmission without frequency characteristics to wire lines is possible.

The operating principle of the circuit according to the invention is as follows. In this explanation, for the sake of simplicity, block 1 in FIG. 1 detects the difference signal S1 of the two-wire line at 1 times the amplitude, and block 4 detects the voltage with the amplitude 1 times that of the feedback signal S6 output by block 3. block 5 generates a voltage with an amplitude -1 times that of this feedback signal S6, and the transfer function from the 4-wire input line RX to the 2-wire line and from the 2-wire line to the 4-wire output. line tx
A circuit with a characteristic that the transfer function and the transfer function are both 1 is set.

In order to obtain this characteristic, block 2 in Figure 1,
Block 3, 2-terminal impedance network 8,
9.Includes 4-wire input line RX, 4-wire output line TX,
Output S1 of block 1 to output S6 of block 3
It is sufficient to construct the portion leading to the circuit with a circuit having characteristics as shown in FIG. That is, the output S1 of block 1 in FIG.
RX signal S2 is subtracted and the 4-wire output line TX
becomes the signal S3. This part corresponds to block 2 in FIG.

The signal S2 input from the four-wire input line RX is multiplied by Z _F '/Z _B ' in block 8 and added in adder AD2, and becomes part of the feedback signal S6. 4-wire output line
The TX signal S3 is multiplied by Z _F '/Z _T ' in block 9, subtracted by adder AD2, and becomes part of the feedback signal S6. Also, the input signal S1 is input to the block D.
The signal is multiplied by 1/2 by the adder AD2, and becomes part of the return signal S6. The feedback signal S6 obtained by the weighted sum in the adder AD2 is sent to block 3 in FIG.
generates an output corresponding to the output of .

In such a circuit, the input impedance Z _io of the circuit as seen from the two-wire line is as follows.

When the differential voltage of the two-wire line changes by V, the voltage between the two two-wire line voltage generating voltage sources changes by 2(1/2 - Z _F ′/Z _T ′)V, and I={ Since a current of V-2(1/2- Z _F ′/Z _T ′)V}/2Z _F flows in, Z _io = V/I=Z _F Z _T ′/Z _F ′...(1), Here, by setting Z _T ′=mZ _T and Z _F ′=mZ _F , Z _io =Z _T ……(2).

Next, when the load impedance of the 2-wire line is Z _L , the transfer function H ₄₂ from the signal voltage V _RX of the 4-wire input line RX to the signal voltage V _2W of the 2-wire line is calculated as follows. Become. The feedback signal is (1/2−Z _F ′/Z _T ′
) V _2W + (Z _F ′ / Z _T + Z _F ′ / Z _B ) V _RX , which becomes a voltage with opposite polarity in two two-wire line voltage generation voltage sources, and the potential difference is Z _L / ( Since the product multiplied by Z _L + 2Z _F becomes V _2W , the following formula holds true.

2Z _L /Z _L +2Z _F {(1/2-Z _F ′/Z _T ′)V _2W +(Z _F ′/Z
_T + Z _F ′/Z _B ) V _RX } = V _2W ...(3) If we transform equation (3) and set Z _T ′=mZ _T and Z _F ′=mZ _F , then H ₄₂ =V _2W / V _RX = Z _L /Z _T +Z _L Z _T +Z _B /Z _B ...(4) That is, by setting Z _B = Z _L , H ₄₂ = 1
Therefore, the frequency characteristics become flat.

In addition, when the load impedance of the 2-wire line is Z _L , the transfer function H ₄₄ of the amount of signal wraparound from the signal S2 on the 4-wire input line RX to the signal S3 on the 4-wire output line TX is Z _B If = Z _L , then from equation (4) H ₄₂
= 1, so adder AD1 connects the 4-wire input line
By subtracting the signal S2 of RX, H ₄₄ =0
becomes. Similarly, from the 2-wire line to the 4-wire output line TX
The transfer function leading to is 1.

The number of impedance circuit networks required in the above circuit configuration is two, impedance circuit networks 8 and 9. In addition, the impedance network 6, 7
Since the impedance of can be selected as any value,
A simple resistor is sufficient without requiring a reactance element, and there is no need to count it as an impedance network in practice.

Next, the basic configuration shown in FIG. 1 will be explained in more detail with reference to the circuit diagram shown in FIG.

Operational amplifier 11 detects difference signal S1 of two-wire line signal S0 together with resistors R11 to R14. Here, if R11/R12=R13/R14 and the voltages of the two-wire lines T and R are V _T and V _R , respectively,
The amplitude of the output of the operational amplifier 11 is -1 times the difference signal V _T -V _R. The block 10 detects only the DC component of this difference signal S1 and, in response, operates an operational amplifier 4 to cause an appropriate loop current to flow through the two-wire line.
Although this is a means for determining the DC operating point of No. 1 and 51, the details are omitted here.

The output S1 of the operational amplifier 11 is connected to the capacitor C1.
The direct current is cut off, and only the alternating current is transmitted to the subsequent stage. The operational amplifier 21, together with the resistors R21 to R23, receives the difference signals S1 to 4 detected by the operational amplifier 11.
Subtract signal S2 of wire input line RX, and convert to 4-wire output line
Let it be the TX signal S3.

The operational amplifier 31 includes a first impedance network 8, a second impedance network 9, and a resistor R3.
1 and R32 to generate a feedback signal S6 to the operational amplifiers 41 and 51. Here resistors R31 and R32
By setting the resistance value of R32=2R31, a 1/2 component in block D in FIG. 2 is created. Operational amplifier OP1, together with resistors R1 and R2, inverts signal S2 on four-wire input line RX.
Further, the operational amplifier OP2 inverts the output signal S6 of the operational amplifier 31 together with the resistors R3 and R4 to generate a signal 6. Operational amplifiers 41 and 51 are connected to resistors R41 and R42 and resistors R51 and R52, respectively.
Together, they form a line voltage generation voltage source that generates voltages of opposite polarity. The output signal 6 of the operational amplifier OP2 is applied to the operational amplifier 41 side, and the output signal S6 of the operational amplifier 31 is applied to the operational amplifier 51 side, with DC components cut off by capacitors C2 and C3. Resistors R61 and R71 connect the two-wire lines T and R to the two line voltage generating voltage sources 4 and 5.

By selecting R11 to R14>>R61 and R71, the differential voltage detection circuit 1 including R11 to R14 is equivalently regarded as high impedance. As an example, in this circuit R11=R12=R13
=R14, R21=R22=R23, R32=R2R31, R1=
R2, R3=R4, R41=R42, R51=R52, R31=
By setting the conditions mR61=mR71, Z _T ′=mZ _T , and Z _B ′=mZ _B , the characteristics shown in the above-mentioned principle can be obtained.

<Effects of the Invention> As explained above, the present invention has the above-described circuit configuration, thereby reducing the number of impedance elements required by the 2-wire to 4-wire conversion circuit to two.
Further, there is an effect of making the frequency characteristics from the 4-wire input line to the 2-wire line flat for any load impedance _ZL .

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the basic configuration of an embodiment of the present invention, FIG. 2 is a block diagram specifically showing the main parts of FIG. 1, and FIG. FIG. 2 is a circuit diagram showing one embodiment in further detail. T, R...2-wire line, RX...4-wire input line, TX...4-wire output line, 1...first means,
2... second means, 3... third means, 4... fourth means, 5... fifth means, 6, 7... third,
fourth impedance network, 8, 9...first;
A second impedance network.

Claims (1)

[Claims] 1. In a circuit network that couples a two-wire line, a four-wire input line, and a four-wire output line, a first means for detecting a difference signal of the two-wire line; 4 from the difference signal obtained from the means of 1.
a second means for erasing only the signal component of the wire input line and detecting it as a signal on the four-wire output line;
a signal inversely proportional to the impedance of the terminal impedance network; a signal proportional to the signal of the four-wire input line and inversely proportional to the impedance of the second two-terminal impedance network;
a third means for generating a feedback signal as a weighted sum with a difference signal of the wire line; fourth and fifth means for respectively generating voltages of opposite polarity using the feedback signal as input; third and fourth impedance networks coupling one of the means and one of the two-wire lines, and third and fourth impedance networks coupling one of the fifth means and the other of the two-wire lines, A signal on a 4-wire input line is transmitted to the 2-wire line, a signal arriving from the 2-wire line is transmitted to a 4-wire output line, and from the 4-wire input line to the 4-wire output line. A 2-wire to 4-wire conversion circuit designed to minimize signal wraparound.