JPH06311072A - Two-way balanced transmission circuit - Google Patents

Abstract

PURPOSE:To prevent a signal from being leaked in an opposite direction with a transmission input of other terminal by devising the circuit such that a signal from the other terminal is applied in a forward direction in a polarized light emitting element and a signal of the same terminal is applied in the opposite polarity so as to attain the transmission of a DC component and signal transmission with less waveform distortion. CONSTITUTION:Transmission sections 3a, 3b and reception sections 6a, 6b are arranged to both terminals of a balanced line L to attain semi-duplex transmission of a monopolar signal in two-ways. Since the coupling system by an optical signal is adopted for the transmission sections 3a, 3b, it is prevented that the signal sent from transmission inputs Ai, Bi of its own terminal is not reversely leaked to transmission inputs Bi, Ai of the other terminal. Moreover, light emitting elements 1a, 1b stimulated by the monopolar signal and polarized current generating light receiving elements 2a, 2b are provided to one end of the balanced line L and polarized current generating light receiving elements 4a, 4b and light receiving elements 5a, 5b receiving the light to provide an electric output are provided to the other terminal. Thus, the 2-way transmission of the monopolar signal including a DC component and the signal transmission with less waveform distortion are attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bidirectional balanced transmission circuit for transmitting a signal through a balanced line such as a twisted pair cable.

[0002]

2. Description of the Related Art Conventionally, a balanced line is used to transmit a signal in both directions.
As an example of a transmission circuit for transmitting, a high circuit as shown in FIG.
There was a method using a brid trance. Tran at the end of A
Ta is a pair of primary windings T₁ , T₂ And secondary winding T₃ Equipped
I am. The turn ratio of each winding is T ₁ ²= T₂ ²= T₃ ²/ 2
Is set to. Secondary winding T of transformer Ta₃
Is the characteristic impedance Z₀ Connected to the balanced line L of
It Primary winding T₁ , T₂One end of is connected with the polarity shown
Is the center tap on the primary side, and Z₀ /
It is grounded through the impedance of 2. Primary winding
T₁ The other end of is the transmission end Tx,
Z₀ Is connected to the signal source Va. Primary winding T₂ 
The other end of is the receiving end Rx, and the characteristic impedance
Z₀ Grounded by. The transformer Tb at the B end is the same.
Have a configuration. The input signal at the end A is the transmission end Tx at the end A
Is output from the B-side receiving end Rx.
Be done. On the contrary, the input signal at the B end is transmitted from the transmitting end Tx at the B end.
The output is received, and is received and output at the receiving end Rx at the A end.

As described above, the transformer used for transmission and reception utilizes magnetic field coupling. That is, since the signal induced in the output is transmitted by the current change of the input electric signal, in the method using the transformer, both the balanced and unbalanced signal forms of the input and output of the transformer can be realized. Whether the signal form of the input or the received output is balanced or unbalanced, the signal form on the balanced transmission path side can be balanced. Further, since the input and output of the transformer are insulated, it is possible to prevent the influence of noise caused by the ground voltage (ground current), and it is easy to remove common mode noise superimposed on the line by balanced transmission.

As described above, in the transformer system, balancing and insulation can be realized at the same time. However, as described above, the signal transmission on the input / output side of the transformer is performed by the current change of the electric signal.
In principle, direct current cannot be transmitted. On the other hand, the square wave of the digital signal has many DC components. For this reason, when transmitting a digital signal using a transformer, as shown in FIG.
When the square wave including the DC component is the input signal as shown in (a), the DC component of the output signal is attenuated, the waveform distortion occurs, and the accurate signal transmission is performed as shown in FIG. 13 (b). The drawback is that it cannot be done.

In the circuit shown in FIG. 12, the signal transmitted from one end to the other end depends on the directionality of the transformer winding.
It cancels itself and does not appear. On the other hand, the signal transmitted to the other end is output from the receiving unit at the other end, but since the transmitting unit at the other end has the same configuration as the receiving unit, the signal leaks in the opposite direction to the input of the transmitting unit. Will come out. This backward signal has an adverse effect such as giving an excessive voltage to the circuit depending on the configuration of the circuit connected to the next stage (that is, the circuit for applying the signal to the transmitting unit).

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks, and an object of the present invention is to have the advantages of the conventional transformer system and to enable transmission of a DC component. The purpose is to realize signal transmission with less waveform distortion and to prevent the signal from leaking in the opposite direction at the transmission input at the other end.

[0007]

According to the present invention, in order to solve the above-mentioned problems, a unipolar signal is applied to one end of a balanced line L terminated by a terminating resistor Ra, as shown in FIG. A light emitting element 1a driven to emit light, a transmitter 3a including a polar current generating light receiving element 2a for receiving an optical signal emitted from the light emitting element 1a and sending it as an electrical signal to the balanced line L, and a balanced transmission line. A polar light emitting element 4a that is driven to emit light by an electric signal from L, and a receiving unit 6a that includes a light receiving element 5a that receives the optical signal emitted from the polar light emitting element 4a and outputs it as an electric signal, Termination resistance Rb
A light emitting element 1b driven to emit light by a unipolar signal, and a light signal emitted from the light emitting element 1b at the other end of the balanced line L terminated by Of the current generating light receiving element 2b
And a polar light emitting element 4b which is driven to emit light by an electric signal from the balanced transmission line L, and a light receiving element 5b which receives an optical signal emitted from the polar light emitting element 4b and outputs it as an electric signal. The polar light emitting element 4a is provided with a signal from a polar current generating light receiving element 2b at the other end in the forward direction, and a signal from the polar current generating light receiving element 2a at the same end. Are connected so as to be applied in reverse polarity, and the polar light emitting element 4b is applied with a signal from the polar current generating light receiving element 2a at the one end in the forward direction, It is characterized in that the signals from the current generating light receiving element 2b are connected so as to be applied in opposite polarities.

[0008]

According to the present invention, in the transmitters 3a and 3b,
Since the coupling method using the optical signal is used, the signal transmitted from the transmission inputs Ai and Bi at the self-end is the transmission input B at the other end.
i and Ai do not leak in the opposite direction. Also,
Provided at one end of the balanced transmission line L are light emitting elements 1a and 1b that are driven to emit light by a unipolar signal, and polar current generation light receiving elements 2a and 2b that receive the light and send it to the balanced line L as an electrical signal. Since the polar light emitting elements 4a and 4b driven to emit light by the electric signal from the balanced line L and the light receiving elements 5a and 5b that receive the light and output the light as electric signals are provided at the other end, a single component including a DC component is provided. Bidirectional transmission of a polarity signal is possible, and signal transmission with less waveform distortion is possible.

[0009]

1 is a circuit diagram of an embodiment of the present invention, in which a transmitting section 3a, 3b and a receiving section 6a are provided at both ends of a balanced line L, respectively.
6b shows a transmission circuit for bidirectionally performing half-duplex transmission of a unipolar signal. Both ends of the balanced line L are respectively terminated by resistors Ra and Rb having a characteristic impedance Z _{0 of the} line. Transmitters 3a arranged at both ends of the balanced line L,
In 3b, the light emitting elements 1a and 1b driven to emit light by a unipolar signal containing a large amount of direct current components, and the light emitting elements 1a and 1a,
After receiving the optical signal emitted from 1b, there are provided light receiving elements 2a and 2b which generate a polar current and send it to the balanced line L as an electric signal. Such a light receiving element 2
There is a photodiode as an example of a and 2b. In the receivers 2a and 2b arranged at both ends of the balanced line L, the polar light emitting elements 4a and 4b driven to emit light by the electric signal from the balanced transmission line L and the polar light emitting elements 4a and 4b are emitted. It is provided with light receiving elements 5a and 5b which receive an optical signal and then output it as an electric signal. As an example of the polar light emitting elements 4a and 4b, for example, a light emitting diode (LED), a laser diode (LD), or a light bulb in which diodes are connected in series is used.

Here, the polar light emitting element 4a is applied with a signal from the light receiving element 2b for generating a polar current at the other end in the forward direction, and the light receiving element 2a for generating a polar current at the same end.
Are connected so that the signals from the. A signal from the light receiving element 2a that generates a polar current is applied in the forward direction to the polar light emitting element 4b at the other end,
The signals are connected so that the signals from the light receiving elements 2b that generate a polarized current at the same end are applied in opposite polarities. For example, in the case of transmission from the A end to the B end, after receiving the optical signal emitted from the light emitting element 1a driven to emit light by a unipolar signal, the light receiving element 2a generates a polar current and balances as an electric signal. Send to line L. The terminal Sa ₁ has a positive potential with respect to the terminal Sa ₂ in the potential generated in the terminating resistor Ra at the A end by the current from the light receiving element 2a that generates a polar current. Since the polar light emitting element 4a of the A-end receiver 6a is connected as shown in the figure, no current flows through this light emitting element 4a. Therefore, neither the optical signal nor the output signal is generated in the A-end receiver 6a. In addition, since no current flows through the polar light emitting element 4a of the A-terminal receiving unit 6a (that is, a high impedance is exhibited), it does not affect the terminal resistance Ra at the A-terminal.

On the other hand, the signal transmitted through the balanced line L is terminated by
The potential generated by the resistor Rb is the terminal Sb ₁ Is the terminal Sb₂ Against
Then it is terminated so that it becomes positive. Polarization of B-end receiver 6b
Since the luminescent element 4b is connected as shown,
The voltage generated by the end resistor Rb is applied to the polar light emitting element 4b.
It is applied in the forward direction. Therefore, at the B-end receiver 6b
Generate an optical signal and an output signal. At the B end transmitter 3b
In addition, the polar current generating light receiving element 2b is as shown in the figure.
Since it is connected to the
Is applied in the opposite direction to the current generating light receiving element 2b.
Therefore, in the polar current generating light receiving element 2b at the B end,
No current flows (ie exhibits high impedance)
Therefore, the terminal resistance Rb at the B end is not affected. Well
In addition, the signal does not leak to the B-end transmitter 3b in the opposite direction.
Yes.

Since the terminal resistance Ra at the A end is a resistance for shunting the current source (that is, the polar current-generating light-receiving element 2a), it has a role of a signal source resistance. Also,
The terminating resistor Rb at the B end has a role of terminating the load of the balanced line L as described above. As a result, both ends of the balanced line L are terminated by the characteristic impedance Z ₀ of the line, so that signal transmission without reflection is possible.

FIG. 2 shows an example of connection of light emitting elements for inputting a unipolar signal in each transmitting section. As shown in FIG. 2A, when a light emitting element 1a such as an LED (light emitting diode) or an LD (semiconductor laser) is used, a signal from a signal source is connected via a resistor Ri, and a current limiting action, It has an impedance matching function. Further, as shown in FIG. 2B, even when the light emitting element 1a having no polarity such as a lamp is used, the signal from the signal source is connected through the resistor Ri to achieve the current limiting action and the impedance matching action. To have.

FIG. 3 shows a connection example of the light receiving element 5a which outputs a signal in each receiving section. As shown in FIG. 3A, when the light receiving element 5a is a voltage generating element such as a solar cell, the light receiving element 5a is connected to the next stage circuit via an output resistor Ro having an impedance matching action. Further, as shown in FIG. 3B, when the light receiving element 5a is a current generating element such as a photodiode, it is terminated (shunted) with a resistor Ro that converts a photocurrent into a voltage and has an impedance matching action. And connect to the next stage circuit.

FIG. 4 is a signal waveform showing the operating state of each part in FIG. In FIG. 4, (a) is an input signal at the A terminal, (b) is an optical signal from the transmitting section at the A terminal, (c) is a voltage across the terminating resistor at the A terminal connected to one end of the balanced line, (d) )
Is the voltage across the terminating resistor at the B end connected to the other end of the balanced line, (e) is the optical signal at the receiving end at the B end, (f) is the output signal at the B end, and (g) is the input at the B end. A signal, (h) is an optical signal of the transmitting unit at the B end, (i) is an optical signal of the receiving unit at the A end, and (j) is an output signal of the receiving unit at the A end. As shown in this waveform diagram, the light emitting element produces an optical signal intensity proportional to the drive signal intensity, and the light receiving element produces an electrical signal intensity proportional to the received light signal intensity. Therefore, the signal (intensity) waveforms of the respective parts are all similar. It can be seen that signals are transmitted in half duplex from the A end to the B end and from the B end to the A end.

FIG. 5 shows the termination resistance Ra at both ends of the balanced line L,
It is a circuit diagram when the middle point of Rb is grounded. That is,
The termination resistor Ra connected to one end of the balanced line L Z _0/2
It is divided into resistors Ra ₁ and Ra ₂ having the impedance of, and the middle point is grounded. Further, the other end connected to the termination resistor Rb of the balanced line L is divided into resistor Rb _1, Rb ₂ having an impedance of Z _0/2, it is grounded its midpoint. Details of the operation of this embodiment are the same as those described with reference to FIG.

FIG. 6 is a circuit diagram of another embodiment of the present invention. In the present embodiment, a plurality of balanced lines L ₁ , L ₂ , ..., Ln are provided between the A end and the B end, and the transmission signal for each balanced line is input from one light emitting element 1 a at the A end. Further, the received signal from each balanced line is output from one light receiving element 5a. That is, each balanced line L ₁ ,
The polarized current generating light receiving element 2a connected to the terminating resistor on the A end side of L ₂ , ..., Ln is optically coupled to the light emitting element 1a in the light distributing portion indicated by the broken line, and The transmission signal given to the transmission input Ai of
_1, L _2, ..., are respectively distributed to Ln, receiving the output of the B-end Bo _1, Bo _2, ..., is transmitted to Bon. Also,
The light emitting element 4a connected to the terminating resistor on the A end side of each of the balanced lines L ₁ , L ₂ , ..., Ln is optically coupled to the light receiving element 5a at the optical coupling portion indicated by the broken line. As a result, the reception output Ao at the A terminal is converted into the transmission input Bi at the B terminal.
_The transmission signal input to any one of ₁ , ₁ , Bi ₂ , ..., Bin is transmitted. In this embodiment, one-to-many signal transmission can be performed between the A terminal and the B terminal.

Such a transmission method is shown in FIG.
In addition, one computer on the host side that communicates by polling method
Computer processing device H and a plurality of computer terminal devices C
₁ , C ₂ Suitable for concentrator D for connecting Cn
It is something. FIG. 8 shows each part in the system of FIG.
Shows the operation waveform of. Host computer processing
The signal output from the device H is output by the concentrator D to a plurality of
Balanced line L₁ , L₂ , ..., Ln are distributed to each equilibrium
Track L₁ , L₂ , ..., Computer end connected to Ln
End device C₁ , C₂ , ..., Cn are transmitted. In addition,
Computer terminal C₁ , C₂ , ..., Sent from Cn
Signal is balanced line L₁ , L₂ ,,, Host via Ln
Is transmitted to the computer processing unit H on the side. Where the concentrator
Position D is a plurality of balanced lines C₁ , C₂ ,…, Message from Cn
No. is combined and transmitted to the computer processing unit H on the host side
However, the communication right is given because of the polling method of communication.
Of computer terminal devices Ci (i = 1, 2, ..., N)
Since only one sends the signal, there is no possibility of signal collision.
Absent. Also, normal computer signals are unbalanced signals.
However, by using the present invention, it is transmitted as a balanced signal.
It is possible. From the above description, the embodiment of FIG.
When applied to the system of FIG. 7, the concentrator, unbalanced-flat
It can be seen that it also has the functions of an equilibrium converter and a transmission line.

FIG. 9 is a circuit diagram showing another embodiment of the present invention. At the A terminal, one unipolar signal given to the transmission input Ai is electrically distributed to drive the plurality of light emitting elements 1a. Further, after the light receiving element 5a receives the optical signal emitted from the polar light emitting element 4a driven by the electrical signals from the plurality of balanced lines L ₁ , L ₂ , ..., Ln, it is electrically coupled and received. The output Ao is configured to be output as one signal. That is,
In the embodiment of FIG. 6, signals are spatially distributed / coupled, but the embodiment of FIG. 9 is different in that they are electrically distributed / coupled. Here, as an example of a connection for electrically distributing a signal on the transmission side at the A terminal, in addition to the parallel connection method as shown in FIGS. 10 (a) and 10 (b), FIGS. A serial connection method as shown in is possible. In addition, as an example of a connection in which signals are electrically coupled on the receiving side at the A terminal, FIG.
A parallel connection system as shown in FIG. 11A and a series connection system as shown in FIG. 11B are possible. When the light receiving element is a current generating element such as a photodiode, these are connected in parallel and the voltage appearing across the common shunt resistor is used as an output. This shunt resistance serves as a signal source resistance. When the light receiving element is a voltage generating element such as a solar cell, these are connected in series and output through a resistor. This resistance becomes the signal source resistance.

[0020]

According to the present invention, a bidirectional balanced transmission circuit can be provided without supplying power from the outside, and since a signal is transmitted with an insulation amount of electric signal strength, a DC component can also be transmitted and a DC component can be transmitted. It is possible to transmit a digital signal containing a lot of waveforms with little waveform distortion, and the signal does not leak in the opposite direction at the input of the transmitter at the other end, and the input and output of the transmitter and receiver are balanced and unbalanced. Either signal form can be easily realized, and the input and output of the transmitter and receiver can be isolated.
Also, since both input and output can be isolated from the ground, it is possible to prevent the effects of noise caused by ground voltage (ground current),
Furthermore, since the balanced cable is used for signal transmission, it is easy to remove the common mode noise to be superimposed, and it is possible to perform signal transmission that cannot be realized by the conventional transmission method.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a connection example of a light emitting element used in the present invention.

FIG. 3 is a circuit diagram showing a connection example of a light receiving element used in the present invention.

FIG. 4 is an operation waveform diagram of an embodiment of the present invention.

FIG. 5 is a circuit diagram of another embodiment of the present invention.

FIG. 6 is a circuit diagram of still another embodiment of the present invention.

FIG. 7 is a circuit diagram showing an example of use in the communication system of the present invention.

FIG. 8 is an operation waveform diagram of a usage example in the communication system of the present invention.

FIG. 9 is a circuit diagram of another embodiment of the present invention.

FIG. 10 is a circuit diagram showing a connection example of a plurality of light emitting elements used in the present invention.

FIG. 11 is a circuit diagram showing a connection example of a plurality of light receiving elements used in the present invention.

FIG. 12 is a circuit diagram of a conventional example.

FIG. 13 is an operation waveform diagram of a conventional example.

[Explanation of symbols]

 1a, 1b light emitting element 2a, 2b polar current generating light receiving element 3a, 3b transmitter 4a, 4b polar light emitting element 5a, 5b light receiving element 6a, 6b receiver

Claims (2)

[Claims] 1. A light-emitting element driven to emit light by a unipolar signal at both ends of a balanced line terminated by a terminating resistor, and an optical signal emitted from this light-emitting element is received and sent to the balanced line as an electrical signal. Transmitter consisting of a polar current generating light receiving element, a polar light emitting element driven to emit light by an electric signal from a balanced transmission line, and an optical signal emitted from this polar light emitting element is received and output as an electric signal. The polar light emitting element is provided with a signal from the polar current generating light receiving element at the other end in the forward direction and the polar current generating light receiving element at the same end. A bidirectional balanced transmission circuit, characterized in that the signals from are connected so as to be applied in opposite polarities. 2. A bidirectional balanced transmission circuit comprising a plurality of the transmission circuits according to claim 1, wherein one end of the balanced line has a transmission signal input end and a reception signal output end connected in common.