JPS6331970B2 - - 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,
Guide the signal from the wire line to the 4-wire output line, guide the signal from the 4-wire output line to the 2-wire line, and eliminate 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” 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, and PCDAVIS are methods of controlling this amount of feedback using an impedance network inside the feedback circuit to achieve the required input impedance.
and SFMOYER “A High-Voltage IC for
a Transformerless Trunk and Subscriber
Line Interface” IEEE Journal of Solid−
State Circuits, Vo1.SC−16, No.4, August
Proposed in 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. Of these, 4
It is well known that it is particularly important that the values of Z _L and Z _B match from the point of view of attenuating the wrap-around signals from the wire input line to the four-wire output line. Additionally, Z _T and Z _S generally take the same value.

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; One impedance network (e.g. 600 Ω) between the opposite terminal of the transformer's 4-wire line-side winding and ground, and a balanced net between the midpoint of the transformer's 4-wire line-side winding and ground. Three impedance networks are required, such as the workpiece.

In addition, in the second example of electronic hybrid, Z _T is configured by the impedance of the impedance network connected between the lines of the two-wire line, and the differential voltage of the two-wire line is detected by a high-impedance amplifier. The signal on the 4-wire input line is transmitted to the 2-wire line, and the 2-wire line voltage is calculated using an operational amplifier or the like using an impedance network proportional to Z _S and Z _B. The wraparound signal is canceled by calculating the difference between the simulated and detected differential voltage, but this also requires three impedance circuit networks.

Furthermore, even when using the feedback circuit of the third example, there is one impedance network for Z _T synthesis, two impedance networks proportional to Z _T and Z _B for prevention of wraparound, 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 aimed at downsizing the circuits through electronicization, but the feature of these circuits is that the wrap-around cancellation circuit converts the 4-wire input line to the 2-wire input line. The point is that it is configured so as not to affect the transfer characteristics to the transmission line,
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 , the 2-wire input line can be changed from the 4-wire input line. The disadvantage is that the transmission characteristics to the output line have frequency characteristics and cause 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 shown in 2.2 are multiplied by an equivalent circuit that supplies a signal from a signal source with impedance Z _S = Z _T to a load impedance Z _L , so Z _B Even if = Z _L , Z _L /
If Z _S 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 provide a method for synthesizing Z _T , Z _S , and Z _B using an impedance network with a constant multiple of the actual Z _T , Z _S , and Z _B , which reduces circuit consumption. The object of the present invention is to provide a 2-wire to 4-wire conversion circuit that achieves reduced power consumption and increased 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 input line for any _ZL . be.

<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 2-wire line, and a difference signal obtained from the first means for detecting a difference signal of a 4-wire input line. a second means for erasing only the signal component and detecting it as a signal on the four-wire output line;
A third feedback signal that is a weighted sum of a signal that is inversely proportional to the impedance of the terminal impedance network and a signal that is proportional to the signal of the four-wire input line and inversely proportional to the impedance of the second two-terminal impedance network. and fourth and fifth means each receiving the feedback signal and generating currents of opposite polarity,
The fourth means is coupled to one of the two-wire lines, and the fifth means is coupled to the other of the two-wire lines, and the signal on the four-wire input line is transferred to the second line.
transmitting the signal to the 4-wire line, transmitting the signal arriving from the 2-wire line to the 4-wire output line, and routing the signal from the 4-wire input line to the 4-wire input line,
It is characterized by being minimized.

<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 S1 detected by block 1 and the signal S on the 4-wire input line RX.
This means performs weighted addition of 2 and 2 with a polarity that eliminates the amount of wraparound, and detects it as a signal S3 to the four-wire output line TX. Block 3 is
A first two-terminal impedance network 6 with an impedance Z _T ′ and a second two-terminal impedance network 6 with an impedance Z′ _B
is proportional to the signal S3 on the four-wire output line TX, and the first
A signal S4 inversely proportional to the impedance Z _T ' of the two-terminal impedance network 6 and the four-wire input line
This is means for generating a weighted sum of a signal S5 proportional to the RX signal S2 and inversely proportional to the impedance Z _B ' of the second two-terminal impedance network 7 as the feedback signal S6. Blocks 4 and 5 are two-wire line voltage generation current sources that receive the feedback signal S6 and generate signal currents of opposite polarity. The outputs of the current sources 4, 5 of the two-wire line voltage generation and T or R of the two-wire line are coupled.
Note that even if this coupling occurs through impedance, it does not affect the effects of the present invention.

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 circuit shown in FIG. 1 will be explained.

Block 1 removes the in-phase signal generated at the ends 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, this difference signal S1 is connected to the four-wire input line.
By subtracting the signal S2 of PX, 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
Z _T is determined by the current variation of the two-wire line voltage generating current source with respect to input voltage variation if Block 1 has a high input impedance. The current fluctuation of the current source for generating the two-wire line voltage is variable by the first impedance network 6 constituting the feedback system, and as described later, the input impedance Z _T
can be a constant divided by the impedance value Z _T ' of the first impedance network 6.

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 7, and as described later, the first impedance network 6 provides a variable output impedance.
Generates a signal to the wire line. This signal corresponds to the impedance value Z _B ′ of the second impedance network 7
It is possible to correct the frequency characteristics of the load impedance Z _L of the two-wire line by changing the impedance Z _B ′ to the impedance Z _L as described later.
By multiplying by a constant, transmission without frequency characteristics is possible from the 4-wire input line to the 2-wire line.

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 amplitude of the feedback signal S6 output by block 3 times gm. Block 5 outputs a current with an amplitude -gm times the 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 input Set up a circuit that has the characteristic that the transfer functions to the line TX are both 1.

In order to obtain this characteristic, block 2 in Figure 1,
Block 3, 2-terminal impedance network 6,
7.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 inputted from the four-wire input line RX is multiplied by 1/gm'·Z _B ' in block 6 and added in adder AD2, and becomes part of the feedback signal S6. The signal S3 on the 4-wire input line TX is 1/gm'・
It is multiplied by Z _T ' and subtracted by adder AD2, and becomes part of the feedback signal S6.

The feedback signal S6 produced by the weighted sum in adder AD2 produces an output corresponding to the output of block 3 in FIG.

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 two two-wire line voltage generating current sources have opposite polarities,
Since a current of I=gm/gm′Z _T ′・V is absorbed, Z _io =V/I=gm/gm′Z _T ′ ………(1) Here, Z′ _T =mZ _T , gm′=1 /mgm, 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 S6 is -
1/gm′Z _T ′V _2W + (1/gm′Z _T ′+1/gm′Z _B ′)V _RX
The two-wire line voltage generating current source causes current gm times this gm to flow through Z _L , and the voltage across Z _L becomes V _2W , so the following equation holds true.

{−1/gm′Z _T ′V _2W +(1/gm′Z _T ′+1/gm′Z _B ′
)V _RX }×gmZ _L = V _2W ......(3) If we transform equation (3) and set Z _T ′=mZ _T and gm′=1/mgm, 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 wrapping from the signal S2 of the 4-wire input line RX to the signal S3 of the 4-wire output line TX is Z If _B = 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 networks required in the above circuit configuration is 6 and 7 impedance networks.
There are two.

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, R11/R12=R13/R14, 2-wire line T, R
Assuming that the voltages of 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. Block 8 is a means for detecting only the DC component of this difference signal S1, and correspondingly determining the DC operating point of the operational amplifiers 41 and 51 so that an appropriate loop current flows through the two-wire line. It is 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 connect to 4-wire input line
Let it be the TX signal S3.

The operational amplifier 31 includes a first impedance network 6, a second impedance network 7, and a resistor R3.
1, and generates a feedback signal S6 to the operational amplifiers 41 and 51. Here, the resistor R31 is selected to be 1/gm'. Operational amplifier OP1 has resistors R1, R
2 and inverts the signal S2 on the 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. The operational amplifiers 41, 51, together with resistors R41, R42, R43, R44 and resistors R51, R52, R53, R54, constitute current sources 4, 5 for generating line voltages that generate voltages of opposite polarity. Regarding the operational amplifier 41 side,
To explain the operation of this current source 4, R42=R44,
By selecting R41=R43, the voltage-current conversion coefficient gm of the current source 4 becomes gm=1/R41=1/R43. The operation of the current source 5 on the operational amplifier 51 side is also similar. The output signal 6 of the operational amplifier OP2 is connected to the operational amplifier 41 side, and the output signal S6 of the operational amplifier 1 is connected to the operational amplifier 51 side.
2. The DC component is cut and added by C3. The outputs of current sources 4, 5 are directly connected to two-wire lines T, R. By selecting R11 to R14 to be large compared to the impedance of the two-wire line, the differential voltage detection circuit 1 including R11 to R14 has the following characteristics:
It can be equivalently regarded as high impedance. As an example, in this circuit, R11=R12=R13=R14, R21=
R22=R23, R31=mR41, R1=R2, R3=R4,
R41=R43=R51=R53, R42=R44=R52=R54,
By setting the conditions 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. 3 is an example of the present invention shown in FIG. FIG. 3 is a circuit diagram showing the 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... 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 third feedback signal that is a weighted sum of a signal that is inversely proportional to the impedance of the terminal impedance network and a signal that is proportional to the signal of the four-wire input line and inversely proportional to the impedance of the second two-terminal impedance network. and fourth and fifth means each receiving the feedback signal and generating currents of opposite polarity, the fourth means is coupled to one of the two-wire lines, and The fifth means is coupled to the other of the two-wire line, transmits the signal of the four-wire input line to the two-wire line, and transmits the signal coming from the two-wire line to a four-wire output. 2. A 2-wire to 4-wire conversion circuit configured to minimize signal wraparound from the 4-wire input line to the 4-wire output line.