JPH0122776B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transmission circuit that converts a signal to be transmitted into a current and transmits the current.

Generally, when transmitting signals between wired broadcasts, intercoms, or electronic circuits in automobiles, a common ground line (GND) is set, and a common power supply is connected to each circuit connected by the transmission line to transmit voltage. is being carried out.

FIG. 1 shows an equivalent circuit of a conventional transmission circuit.
A signal source 6 of a transmission signal is connected to the transmission terminals 4A, 4B of the transmission circuit 2, and a reception circuit 10 is connected to the reception terminals 8A, 8B of the transmission circuit 2.
Transmission lines 12A, 1 constituting the transmission circuit 2
2B has its own resistors 14, 16 interposed therein. In such a transmission circuit 2, the transmission line 12B forming a common reference potential line is a common ground line, and there is a drawback that signal transmission cannot be performed unless such a common reference potential is provided.

Furthermore, such voltage transmission is susceptible to external noise and power supply hum, which causes waveform distortion in the transmitted signal. Moreover, transmission line 1
If 2A and 12B are long, the transmission line 12
The influence of the resistor 16 included in A and 12B is likely to appear,
Waveform distortion, etc. of the transmitted signal occurs, so a circuit is required to improve this, and it has the disadvantage of requiring countermeasures such as using thick conductor wire to lower the impedance of the ground line. .

Therefore, the present invention aims to provide a transmission circuit that performs current transmission by converting a transmission signal into a current, eliminates the influence of external noise and the influence of ripple components from the power supply, and enables highly reliable signal transmission. .

That is, the transmission circuit of the present invention includes: a transistor differential pair that converts a signal to be transmitted into a current; a first current mirror circuit that flows out a signal current obtained from one transistor of the transistor differential pair;
A second current mirror circuit that draws a current corresponding to the signal current flowing through the other transistor of the transistor differential pair is installed on the transmitting circuit side, and the signal current is transmitted from the first current mirror circuit to the first transmission line. and a fourth current mirror circuit into which a current corresponding to the signal current is drawn into the second current mirror circuit via a second transmission line, on the receiving circuit side. The signal current corresponding to the signal to be transmitted is transmitted from the transmitting circuit side to the receiving circuit side.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings.

FIG. 2 shows an embodiment of the transmission circuit of the present invention. The transmitting circuit 20 and the receiving circuit 22 are individually equipped with power supplies 24 and 26, and the transmitting circuit 20 and the receiving circuit 22 are linked through current paths 28A and 28B, so that the signal current from the transmitting circuit 20 is transmitted through the current paths 28A and 28B.
It is received by the receiving circuit 22 via 28B.

The transmission circuit 20 includes a transistor differential pair 30 as a voltage-current conversion circuit that converts a transmission signal into a current.
is installed. This transistor differential pair 30
is composed of a pair of transistors 32 and 34 whose emitters are connected in common, and an input terminal 36 is formed at the base of the transistor 32.
A constant DC bias is set from a bias circuit 40 via a resistor 38. On the other hand, transistor 3
A feedback circuit 42 is formed between the base of 4 and the output point. That is, this feedback circuit 42 has a resistor 4
A resistor 44 is connected between the base of the transistor 34 and the output point, and the base of the transistor 34 is connected to a bias circuit 40 via the resistor 46. Further, a constant current source 48 is connected between the emitters of the transistors 32 and 34 and a power supply line connected to the negative electrode side of the power supply 24.

The output of the transistor differential pair 30 is taken out from the collector side of each transistor 32, 34, and current mirror circuits 50, 52 are provided as first current mirror circuits for taking out this output.
That is, between the collectors of the transistors 32 and 34 and the power supply line to which the positive side of the power supply 24 is connected, transistors 54 and 56 whose bases and collectors are connected in common are connected.
Transistors 58 and 60 are connected to the base and collector of
The bases of the transistors 62 and 62 are connected in common to the bases and collectors of the transistors 56 and 62, respectively. Each transistor 58,
The emitters 60 and 62 are commonly connected to the power supply 24 via the positive power supply line, and the transistor 5
Transistors 58 and 6 are connected to the collectors of transistors 8 and 62.
2 currents, and the transistor 62
A second current mirror circuit 64 is installed in order to extract the current flowing through the circuit to the outside. This current mirror circuit 64 is composed of transistors 66, 68, and 70, and the base and collector of the transistor 66 and the bases of the transistors 68 and 70 are connected in common, and each of the transistors 66, 6
Both emitters 8 and 70 are connected to the power supply 24 via the negative power supply line. An output terminal 72 for taking out the amplified output of the transmitting circuit 20 is formed at the collector of each transistor 58, 68.

Current paths 28 as first and second transmission lines are connected to the collectors of the transistors 60 and 70.
Output terminals 74A, 74B are formed to connect A, 28B, and input terminals 76A, 76B of the receiving circuit 22 are connected to these output terminals 74A, 74B via current paths 28A, 28B.

In addition, the receiving circuit 22 includes current paths 28A and 28B.
In order to extract the signal current applied from the third
A current mirror circuit 80 and a fourth current mirror circuit 78 are installed. Third current mirror circuit 8
0 consists of transistors 86 and 88, the base of the transistor 88 is commonly connected to the base and collector of the transistor 86, and an input terminal 76A is formed.
The emitter No. 8 is connected to the power supply 26 via the negative power supply line.

The fourth current mirror circuit 78 is composed of transistors 82 and 84, and the base of the transistor 84 is commonly connected to the base and collector of the transistor 82, and an input terminal 76B is formed. The emitter is connected to the power supply 26 via the positive power supply line.

The collectors of the transistors 84 and 88 are connected in common, and an output terminal 90 is formed, which is connected via a resistor 92 to a bias circuit 94 for applying a constant DC bias.

The operation will be explained based on the above configuration.
The signal to be transmitted applied to the input terminal 36 is amplified by the transistor differential pair 30, and is converted into a current that changes according to the signal amplitude by the voltage-current conversion function of the transistor differential pair 30. be done. The current flowing through each transistor 32, 34 flows through the transistor 58, 62 via the first current mirror circuit 50, 52, and the current flowing through each transistor 58, 62 flows through the transistor 66, 68 of the second current mirror circuit 64. The combined current output is taken out from the output terminal 72.

The current flowing through the transistor 32 is extracted from the current mirror circuit 50, flows to the transistor 60, is applied from the output terminal 74A to the input terminal 76A of the receiving circuit 22 via the current path 28A, and flows to the transistor 86. On the other hand, the current flowing to the transistor 34 flows to the transistor 70 via the current mirror circuit 52 and the current mirror circuit 64, and this current flows to the transistor 82 of the current mirror circuit 78.
The current is drawn in through the current path 28B. The currents flowing through the transistors 84 and 88 are combined between the collectors of the transistors 84 and 88, and are taken out from the output terminal 90. Therefore, the transmission signal applied to the input terminal 36 is converted into a current by the transistor differential pair 30, and then combined by the current mirror circuits 78, 80 via the current paths 28A, 28B, and then output to the output terminal 9.
It can be extracted from 0, and signal transmission is performed using current as a medium.

According to such a configuration, power supplies 24 and 26 are individually set for the transmitting circuit 20 and the receiving circuit 22,
Each of the circuits 20 and 22 is maintained in a potential floating state. That is, the power supplies 24 and 26 are not connected with respect to the reference potential point, but
Since the transmitter circuit 20 and the receiver circuit 22 are individually set, external noise and ripples generated in the power supply can be eliminated. In particular, there is no need to lower impedance by using a thick conductor for the reference potential line (earth line) as in the past.
Since a special connection cable for transmission is not required, the cost of the transmission line can be reduced. Therefore, such a transmission circuit can be used for intercoms, transmission circuits for public address systems, CATV, telephone lines, transmission lines for various circuits in industrial equipment such as automobiles, etc., to perform highly reliable signal transmission. .

As explained above, according to the present invention, a transistor differential pair that converts a signal to be transmitted into a current is installed on the transmitting circuit side, and the signal current obtained by one transistor of the transistor differential pair is transferred to the first transistor. The signal current obtained by the other transistor of the transistor differential pair is passed from the current mirror circuit to the third current mirror circuit on the receiving circuit side via the first transmission line, and the signal current obtained by the other transistor of the transistor differential pair is passed to the second current mirror circuit. By drawing the current from the fourth current mirror circuit on the receiving circuit side through the transmission line, the signal current obtained corresponding to the signal to be transmitted is transmitted from the transmitting circuit side to the receiving circuit side. Both the transmitting circuit and the receiving circuit can be set in a floating state, and the signal to be transmitted can be converted into a current and transmitted from the transmitting circuit to the receiving circuit, and there is no need to set up a common installation line. Since it is possible to prevent the incorporation of unnecessary components such as external noise and hum, and there is no need to form a ground line with impedance in mind, the configuration can be simplified and the transmission circuit can be constructed at low cost. can.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional general transmission circuit, and FIG. 2 is a circuit diagram showing an embodiment of the transmission circuit of the present invention. 20... Transmission circuit, 22... Receiving circuit, 28A... Current path (first transmission line), 28B... Current path (second transmission line), 30... Transistor differential pair, 50,5
2...First current mirror circuit, 64...Second current mirror circuit, 78...Fourth current mirror circuit, 80...
Third current mirror circuit.

Claims (1)

[Claims] 1 A transistor differential pair that converts a signal to be transmitted into a current, a first current mirror circuit that flows out a signal current obtained in one transistor of this transistor differential pair, and the other transistor of the transistor differential pair. a second current mirror circuit that draws in a current corresponding to the signal current flowing through the transmission circuit; A current mirror circuit and a fourth current mirror circuit in which a current corresponding to the signal current is drawn into the second current mirror circuit via a second transmission line are installed on the receiving circuit side, and the current mirror circuit is connected to the transmitting circuit side. A transmission circuit characterized in that the signal current corresponding to the signal to be transmitted is transmitted to the receiving circuit side.