JPS6359145A - Transmission system for local area network - Google Patents

Abstract

PURPOSE:To allow the titled system being immune to external noise aud to increase the amplitude of a transmission signal by driving a coupler in response to an original signal, opening/short-circuiting a line via the coupler so as to change a line voltage and sending the line voltage change as a transmission signal of the original signal onto the line. CONSTITUTION:When a pulse of the original signal S1 is inputted to a base of a transistor (TR)1, the TR1 is turned on only when the pulse rises, a current is given and a light emitting diode D is lighted. Then a photo TR 0 receives the light and is turned on, transmission lines 1, 1' are short-circuited and a line voltage Vs is zero. Then the original signal S1 and the inverted line voltage change are sent to the transmission lines 1, 1' as the transmission signal S2 with respect to the original signal S1. Since the signal source is coupled to the lines 1, 1' via the photocoupler 2 in the isolating state in parallel, the system is immune to external noise. Moreover, the amplitude of the signal S2 is increased as from DC bias voltage to zero voltage. 3, driver.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a local area network transmission system, and in particular, transmits a transmission signal from a transmission signal source to a transmission line of a local area network to which a predetermined DC bias voltage is applied. This relates to a local area network transmission method.

[Prior Art] A local area network (hereinafter referred to as the abbreviation LA-M) is a communication network that performs communication between multiple information processing devices such as computers within a unified area such as within the same building or the same factory. With the progress of office automation in recent years, the number has increased to 91% and has been steadily increasing.

In a conventional LAN, a method of transmitting a transmission signal from a multiple source such as a computer to a transmission line to which a predetermined DC bias voltage is applied is to couple the signal source to the transmission line via a coupling capacitor. A method of transmitting the signal through a capacitor as described in No. 111j, or a method of coupling through a coupling transformer and performing the signal through this transformer is adopted.

[Problems to be solved by the invention] However, in the method of transmitting signals via a coupling capacitor, the transmission line side and the signal source side are electrically connected in an alternating current manner via the coupling capacitor, so external noise is generated. It has the disadvantage of being weak against Furthermore, the method using a coupling transformer has the problem that the amplitude of the transmission signal cannot be increased very much.

[Means for Solving the Problems] In order to solve the above-mentioned problems, according to the local area network transmission method of the present invention, a transmission signal is transmitted to the transmission line of the local area network to which a predetermined DC bias voltage is applied. signal sources are coupled in parallel in an insulated state via a photocoupler, the coupler is driven according to the original signal output from the signal source, and the voltage of the line is reduced by shorting and opening the line via the coupler. A configuration is adopted in which the voltage change is used as a transmission signal of the original signal to be transmitted through the line.

[Function] According to such a configuration, the signal source is coupled to the transmission line in an insulated state via the photocoupler, so that the signal source is resistant to external noise. Also short the transmission line.

Since the voltage of the transmission line is changed by opening it and the voltage change is used as the transmission signal, the amplitude of the transmission signal can be increased by changing the voltage of the transmission signal from the DC bias voltage described in 4-4 to the zero-1 voltage. .

[Embodiments] Hereinafter, details of embodiments of the present invention will be described with reference to the attached drawings.

The figure shows the configuration of an embodiment of a signal transmitting circuit that sends a transmitting signal to a LAN transmission line according to the method of the present invention.

The symbol 1.1' is a LAN transmission line, and there are two
A terminating resistor R is composed of a pair and has an equal resistance value at both ends.
1, connected as a loop via R1 and grounded. In addition, a predetermined DC voltage Vcc is applied to the transmission line 1 on one side.
A DC constant voltage power supply (not shown) that generates Vcc is connected via a voltage dividing resistor RO, and the DC voltage Vcc is set to a predetermined value by the voltage dividing resistor RO, the terminating resistors R1, R1, and the combined resistance of the transmission line 1.1'. A predetermined DC line bias voltage divided at a voltage division ratio is applied between the transmission lines 1 and 1'.

On the other hand, in the configuration shown below the transmission line 1.1' in Figure 1, the transmission line 1,
It is a transmitting unit that sends out signals to the photocoupler 2 and the original signal S.
1, the transistor Tri drives the photocoupler 2 according to
and a driver 3 consisting of protective resistors R3 and R4.

The photocoupler 2 is a known one consisting of a phototransistor TrO and a light emitting diode D.
The phototransistor TrO is connected in parallel to the transmission line 1 on the O side, and the collector of the phototransistor TrO is connected to one transmission line 1, and the emitter is connected to the other transmission line 1'. Further, the 7 nodes of the light emitting diode D are connected via a protective resistor R2 to a DC chamber (not shown) that generates a predetermined DC voltage Vc that drives the photocoupler 2, and a cardiac pressure power source, and the cathode is connected to the collector of the transistor Tri of the driver 3. It is connected to the.

The emitter of the transistor Tri is grounded, and the base receives an original signal S1 from an undisclosed signal source via protective resistors R3 and R4.

Next, the operation at the time of transmission with such a configuration will be explained.

When no pulse of the original signal Sl is input, the transistor Tri of the driver 3 is in an off state, no current is applied to the light emitting diode D of the photocoupler 2, the light emitting diode D is turned off, and the phototransistor TrO is not able to receive light. It is turned off because it is not available. Phototransistor TrO
Since the transmission line 1.1' is open in some parts, the line voltage Vs between the transmission line 1.1' is the line bias voltage described above.

Next, when a pulse of the original signal Sl is applied to the base of the transistor Tri, the transistor Trl is turned on only while the pulse is rising, a current is applied, the light emitting diode D emits light, and the phototransistor TrO emits light. It receives light and turns on.

As a result, the transmission line 1.1" is short-circuited, and the line voltage V
s becomes zero.

In this way, the change in the line voltage Vs, which is inverted from the original signal St, from the line bias voltage to zero voltage, is transmitted to the transmission line l as the transmission signal S2 of the original signal St.

1' is transmitted. That is, the original signal S1 is inverted to the transmission signal S2 with a full swing from the bias voltage to zero voltage,
The transmission signal S2 is sent to the transmission line 1.1''.The transmission signal S2 is received by a receiving side computer (not shown) via a signal receiving circuit (not shown).

According to this embodiment, since the signal source is coupled to the transmission line 1.1' via the photocoupler 2 in an insulated state, the signal source is resistant to external noise.

Further, the amplitude of the transmission signal S2 can be increased from a DC bias voltage to zero voltage.

Furthermore, when a large number of the above-mentioned transmitters are connected to the transmission line 1.1', even if one transmitter becomes inoperable due to a power failure in the photocoupler 2, the failure will not affect the other transmitters because they are connected in parallel. .

Furthermore, the configuration of this embodiment is extremely simple and can be implemented at low cost.

In addition, in the above explanation, the phototransistor T of the photocoupler 2
Although rO is directly connected to the transmission lines 1 and 1', a resistor may be inserted in series between them to reduce the amplitude of the transmission signal S2. In addition, a choke coil is connected in series to blunt the pulse shape of the transmission signal S2, and the transmission lines 1 and 1 are
Waveform control such as suppressing unnecessary radiation from ' is also possible.

In addition, an inverter is connected before the driver 3 to generate the original signal S1.
It is also possible to make the transmission signal S2 a non-inverted signal of the original signal Sl by inverting it and inputting it to the driver 3.

Further, the photocoupler 2 is not limited to the light emitting diode D and the phototransistor, but may be composed of other suitable light emitting elements and light receiving elements.

[Effects] As is clear from the explanation below, according to the local area network transmission method of the present invention, the signal source of the transmission signal is connected to the transmission line of the local area network by a photocoupler to which a predetermined DC bias voltage is applied. The voltage of the line is changed by connecting the coupler in parallel with an insulated IE, and driving the coupler according to the original signal output from the signal source to short-circuit or open the line via the coupler, and change the voltage of the line. Since a configuration is adopted in which the signal is transmitted through the line as the transmission signal of the original signal, it has excellent effects such as being strong against external noise, increasing the amplitude of the transmission signal, and being able to be implemented at low cost with a simple configuration. can get.

[Brief explanation of the drawing]

The figure is a circuit diagram showing the configuration of an embodiment of a signal transmission circuit that sends a transmission signal to a LAN transmission line according to the method of the present invention. 1.1”...Transmission line 2...Photocoupler 3...
Driver R1-R4...Resistor D...Light emitting diode TrO...Phototransistor Tri...Transistor

Claims (1)

[Claims] A signal source of a transmission signal is coupled in parallel in an insulated state via a photocoupler to a transmission line of a local area network to which a predetermined DC bias voltage is applied, and the coupler is driven in accordance with the original signal output from the signal source. A transmission method for a local area network, characterized in that the voltage of the line is changed by short-circuiting or opening the line via the line, and the voltage change is used as a transmission signal of the original signal to be transmitted through the line.