JPH0379893B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is connected between a 2-wire or 4-wire line, a modem, a maintenance telephone, etc. in a data transmission device, and is used for branching and receiving signals. The present invention relates to a transmitting/receiving signal branching circuit for performing coupling.

(Prior art) Conventionally, in a data transmission device using a voice line, when transmitting and receiving signals are branched between a two-wire line and a modem, a maintenance telephone, etc., it has been generally used because of its advantages such as reducing leakage inductance. It uses a hybrid transformer. Figure 4 shows such a conventional data transmission device.
1 is a two-wire line (shown in a single-line diagram; the same applies hereinafter); 12 is a data transmission device; 13 is a hybrid transformer; 14 is a maintenance telephone; 15 is a 4-wire modem; and 16 is an adder. are shown respectively.

In this data transmission device 12, the modem 15 and transmission signal is added to the transmission signal of the maintenance telephone 14 in an adder 16, and sent to the two-wire line 11 via the hybrid transformer 13. At this time, as is well known, if impedance matching is achieved between the hybrid transformer 13 and the circuit connected to it, the output signal of the adder 16 will be
It is designed so that it does not go around to the receiving circuit side of No. 5.

On the other hand, the transmission signal from the line 11 is branched via the hybrid transformer 13 only to the receiving circuit of the modem 15 and the receiving circuit of the maintenance telephone 14.

(Problems to be Solved by the Invention) Here, even if the hybrid transformer 13 is an ideal transformer with no loss, the transmission and reception signals are each attenuated by -3 dB due to its insertion.
Furthermore, if the modem 15' in the data transmission device 12' is of a two-wire type as shown in FIG.・The received signal is further −
This will result in 3dB of attenuation.

In addition, the hybrid transformer 13, 13'
It is difficult to miniaturize compared to ICs, etc., and the cost is generally high.

On the other hand, as a device for branching transmitting/receiving signals without using a hybrid transformer, for example,
There is a bidirectional relay device described in No.-23683.

According to this relay device, the circuit configuration can be simplified by not using the above-mentioned transformer, but it is only intended for communication between multiple two-wire circuits, and Since the configuration is such that a sum signal of signals from the circuits is transmitted, there is a problem in that an adding circuit is required.

The present invention was proposed to solve the above problems, and its purpose is to eliminate attenuation of transmitted and received signals by using a branch circuit consisting of an operational amplifier and a resistor instead of a hybrid transformer. Furthermore, it is an object of the present invention to provide a transmitting/receiving signal branching circuit that can be miniaturized and reduced in cost by using an IC, and can be applied to two-wire lines and four-wire lines.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a device that is connected between a communication line and first and second transmitter/receivers, and that branches a received signal from the communication line. to cause the first and second transmitting/receiving devices to receive it, and
In a transmission/reception signal branch circuit that combines transmission signals from a first and second transmission/reception device and transmits them to a communication line, one input terminal is connected to the first transmission/reception device, and the other input terminal is connected to a second transmission/reception device. a first operational amplifier connected to a transmission circuit of a second transmitting/receiving device via a resistor, and having an output terminal connected to a communication line via a sixth resistor for impedance matching;
One input terminal is connected to a communication line, the other input terminal is connected to an output terminal of the first operational amplifier via a third resistor, and the output terminal is connected to a receiving circuit of a second transmitting/receiving device, and , a second operational amplifier connected to the first transmitting/receiving device via a seventh resistor for impedance matching, and a first operational amplifier connected between the other input terminal and output terminal of the first operational amplifier. a fourth resistor connected between the other input terminal of the first operational amplifier and the output terminal of the second operational amplifier and whose resistance value is equal to that of the first resistor; and the other of the second operational amplifier. The fifth resistor is connected between the input terminal and the output terminal of the fifth resistor and has a resistance value equal to that of the third resistor.

(Function) In the present invention, the transmission/reception signals are branched by the first and second operational amplifiers without using a hybrid transformer. In this case, the present invention focuses on the fact that the line impedance and the modem impedance are known, and prevents the transmitted signal from going around to the receiving circuit and the received signal from going around to the transmitting circuit.

That is, when the output terminal of the first operational amplifier for transmission is connected to a communication circuit via an impedance matching resistor, the voltage across this resistor is determined because the impedance of the line is known. Therefore, by extracting this voltage and applying it to the second operational amplifier for reception and performing appropriate calculations, the transmitted signal component of the output terminal voltage of the first operational amplifier is removed and the received signal from the communication line is can only be obtained.

Further, since the impedance of the modem is also known, it is possible to similarly obtain only the transmission signal from which the received signal component from the communication line has been removed by calculation by the first operational amplifier.

Furthermore, by appropriately setting the values of the input resistance and feedback resistance of each operational amplifier, attenuation of transmitted and received signals is prevented.

Furthermore, the present invention can achieve the above-mentioned effects with a single branch circuit, and can be applied not only to two-wire lines but also to four-wire lines.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.
First of all, FIG. 1 shows a first embodiment of the present invention. This embodiment is a data system that combines or branches transmission/reception signals between a two-wire line, a modem, and a maintenance telephone. This is applied to transmission equipment. In the figure, 11 is a two-wire line as described above, 12' is a data transmission device, and the transmitting/receiving signal branching circuit 1 according to the present invention has a terminal A connected to the line 11, and a first transmitting/receiving device. A terminal C is connected to a two-wire modem 15' as a second transmitting/receiving device, and terminals B and D are respectively connected to a transmitting circuit and a receiving circuit of a maintenance telephone 14 as a second transmitting/receiving device.

To explain its circuit configuration, first, terminal C is connected to the non-inverting input terminal of the first operational amplifier OP ₁ that constitutes the differential amplifier, and is also connected to the differential input terminal via impedance matching resistor R ₇ . It is connected to the output terminal of the second operational amplifier PO ₂ that constitutes the amplifier. The input terminal of this operational amplifier PO ₂ is connected to the terminal D and is also connected via a resistor R ₄ to the inverting input terminal of the first operational amplifier OP ₁ . Further, this inverting input terminal is connected to terminal B via a resistor _R2 .

Furthermore, a resistor _R1 is connected to the feedback loop of the first operational amplifier _OP1 , and the output terminal of the operational amplifier _OP1 is connected to the terminal A through an impedance matching resistor _R6 and also through a resistor _R3 . second
is connected to the inverting input terminal of the operational amplifier OP ₂ . Further, the terminal A is connected to the non-inverting input terminal of the operational amplifier _OP2 , and the resistor _R5 is connected to the feedback loop of the operational amplifier _OP2 .

Note that in this circuit, the value of each resistor is R ₃ =
Let R ₅ , R ₁ =R ₄ and assume that the value of resistor R ₆ is equal to the known impedance of line 11 and the value of resistor R ₇ is equal to the input impedance of modem 15', which is also known.

To explain this operation, first, a transmission signal from the modem 15' and a transmission signal from the maintenance telephone ₁₄ are operated on by the first operational amplifier OP1, and then sent out from the terminal A. Also, the received signal from line 11 and the output signal of operational amplifier OP ₁ are connected to the second operational amplifier.
It is calculated at OP ₂ and output to terminal D and terminal C.

Now, as a result of the calculation by operational amplifier OP ₂ , among the voltages Vd and Vc appearing at terminals C and D, line 11
Find the components Vdr and Vcr of the received signal from.
In Figure 1, the output terminal voltage of operational amplifier OP ₁
The component of V ₁ due to the transmitted signal is V ₁ s, and the component of the voltage Va at terminal A due to the transmitted signal is Vas
Then, since the resistance R ₆ is equal to the impedance of the line 11, the following relationship holds between them.

Vas=V ₁ s/2 ...(1) Here, if the component of the voltage V ₁ due to the received signal from the line 11 is V ₁ r, and the component of the voltage Va due to the received signal is Var, then V ₁ r Since the output impedance of the operational amplifier OP ₁ is very small, V ₁ r=0. Therefore, V ₁ and
Va is expressed by the following formula.

V ₁ = V ₁ s + V ₁ r = V ₁ s ... (2) Va = Vas + Var = (V ₁ s / 2) + Var ... (3) On the other hand, the output voltage Vdr of operational amplifier OP ₂ is expressed by the following formula .

Vdr=(1+ _R5 / _R3 )Va-( _R5 / _R3 ) _V1 ...(4) Since _R5 = _R3 in equation (4), Vdr=2Va- _V1 ...(5 ) Substituting equations (2) and (3) into equation (5), Vdr = 2 {(V ₁ s/2) + Var} − V ₁ s = 2Var ……(6) In other words, from this equation (6) As is clear, terminal D
The transmission signal component _{V 1 s} of the output terminal voltage V 1 of the operational amplifier OP ₁ does not appear in , the transmission signal does not go around, and only the reception signal Var from the line 11 is doubled and output.

Also, since the resistor _R7 is equal to the impedance of the modem 15', Vcr=Vdr/2...(7), and from equations (6) and (7), Vcr=Var...(8) and the terminal The received voltage at A will appear as it is at terminal C on the modem 15' side without being attenuated.

This is almost the same for the transmission signal, and regarding the components Vds and Vcs due to the transmission signal among the voltages Vd and Vc at terminals D and C, since Vds = 0, Vd = Vds + Vdr = Vdr ... (9) Vc = Vcs + Vcr = Vcs + (Vdr / 2) ... (10) The output voltage V ₁ s of operational amplifier OP ₁ is V ₁ S = (1 + R ₁ / R ₄ ) Vc - (R ₁ / R ₄ ) Vd
...(11) Here, since R ₁ = R ₄ , V ₁ s = 2Vc - Vd ... (12) Substituting equations (9) and (10) into equation (12), V ₁ s = 2 {(Vdr/2)+Vcs}−Vdr=2Vcs...(13) i.e. the output voltage of op amp OP ₁
The received signal component Vdr of the output voltage Vd of the operational amplifier OP ₂ does not pass around to V ₁ s. Also, the voltage
V ₁ s becomes 1/2 at terminal A, so from terminal A
A voltage equal to Vcs is output towards line 11. Furthermore, the transmission signal Vb of the maintenance telephone 14 is -
It is multiplied by (R ₁ /2R ₂ ) and output from terminal A.

The flow of each of the above signals is shown in FIG. 2.

In this embodiment, since impedance matching between the line 11 and the modem 15' is performed by mutually separate resistors R ₆ and R ₇ , the present invention is applicable to the line 11 and the modem 15' which have different impedances. It can also be easily applied to

Next, FIG. 3 shows a second embodiment of the present invention. In this embodiment, the present invention is applied to a four-wire line consisting of a transmitting line 11' and a receiving line 11''.
This is the case when connecting with a wire modem 15,
The transmitting/receiving signal branching circuit 1' is newly provided with terminals E and F, respectively. Among these, a resistor _R8 is connected between the terminal E and the connection point of the resistors _R1 and _R2 , and a resistor _R9 whose one end is grounded and the other end is connected to the terminal E. Further, a resistor R10 is connected between the terminal F and the connection point of the resistors _R3 and _R5 , and a resistor _{R11 whose} one end is grounded is connected to the terminal F.
the other end is connected.

In this embodiment, the input impedance of terminals E and F is the combined resistance of R ₃ , R ₅ , R ₁₀ , and R ₁₁ of R ₁ , R ₄ , R ₈ , and R ₉ , respectively, so these and the modem 15 or the receiving line 11'', terminal E is used as the transmitting terminal of the modem 15, terminal C is used as the receiving terminal, and terminal A is used as the transmitting terminal for the 4-wire line. Terminal F can be used as a receiving terminal.

According to this embodiment, whether the line and modem are two-wire or four-wire, they can be connected by a single circuit configuration, which has the advantage of being highly versatile and economical.

(Effects of the Invention) As described in detail above, according to the present invention, transmission and reception signals can be branched without using a hybrid transformer, and the signals are not attenuated at that time.

Furthermore, since the circuit configuration is mainly composed of operational amplifiers and the like, it can be implemented as an IC, and the size and cost of the circuit device can be reduced.

Furthermore, the present invention branches transmission and reception signals independently without using signals from other communication lines, and there is no need for signal lines or addition circuits for connection with other lines, so the configuration can be further simplified. Simplification and cost reduction can be achieved. In addition, the present invention provides two
Since it can be applied not only to wire lines but also to four-wire lines, it has the advantage of being highly versatile.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention, FIG. 2 is an explanatory diagram showing the flow of signals, FIG. 3 is a circuit diagram showing a second embodiment of the present invention, and FIGS. FIG. 5 is a circuit diagram showing a conventional example. 1, 1'... Transmission/reception signal branch circuit, 11, 1
1', 11''... Line, 12', 12''... Data transmission device, 14... Maintenance telephone, 15, 15'...
Modem, OP ₁ , OP ₂ ... operational amplifier, R ₁ to _{R 11} ...
...Resistance, A to F...terminals.

Claims (1)

[Scope of Claims] 1. Connected between a communication line and first and second transmitting/receiving devices, and branching a received signal from the communication line to be received by the first and second transmitting/receiving devices; In the transmitting/receiving signal branch circuit that combines transmission signals from the first and second transmitting/receiving devices and transmitting the combined signals to the communication line, one input terminal is connected to the first transmitting/receiving device, and the other input terminal is connected to the first transmitting/receiving device. a first operational amplifier connected to the transmission circuit of the second transmitter/receiver via a second resistor, and whose output terminal is connected to the communication line via a sixth resistor for impedance matching; one input terminal; is connected to the communication line, the other input terminal is connected to the output terminal of the first operational amplifier via the third resistor, the output terminal is connected to the receiving circuit of the second transmitting/receiving device, and impedance matching is performed. a second operational amplifier connected to the first transmitting/receiving device via a seventh resistor for the first operational amplifier; a first resistor connected between the other input terminal and the output terminal of the first operational amplifier; a fourth resistor connected between the other input terminal of the first operational amplifier and the output terminal of the second operational amplifier and whose resistance value is equal to that of the first resistor; and the other input terminal of the second operational amplifier. A transmitting/receiving signal branch circuit comprising: a fifth resistor connected between the output terminal and the fifth resistor having a resistance value equal to that of the third resistor.