JPS6359146A - Reception system for local area network - Google Patents

Abstract

PURPOSE:To allow the titled system to be immune to external noise and to reduce distortion of a reception waveform by coupling a line and a device receiving a transmission signal in isolation state in parallel via a photocoupler connected in parallel with the line and receiving the signal via the photocoupler. CONSTITUTION:A reception signal S2 in a form being the inversion of the transmission signal S1 is obtained at a connecting point A and inputted to a Schmitt trigger circuit 4. Although the signal S2 includes a noise component shown in figure, the noise component is cut off by waveform shaping comprising the Schmitt trigger 4 and an inverter 5. Moreover, the signal S2 is inverted by the Schmitt trigger 4 and further inverted by the inverter 5 and corrected into the original polarity. Then the shaped signal S2' is outputted from output terminals 6, 7 and inputted to a device at the reception side. Moreover, the signal S2' is an inversion of the signal S1, but the signal S1 is the inversion of the transmission original signals, the signal S2' is the reproduction of the original signal with fidelity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a local area network reception system that receives transmission signals from a local area network transmission line.

[Prior Art] In recent years, local area networks (hereinafter referred to as LAN), which are communication networks that perform communication between information processing devices of multiple computers within a unified area such as within the same building or the same factory, have become popular. It has developed and spread with the advancement of office automation.

In a conventional LAN, a method of receiving a transmission signal sent from a transmission signal source such as a computer to a transmission line to which a predetermined DC bias voltage is applied is to connect the transmission line and the receiving side computer via a coupling capacitor. A method has been adopted in which devices such as the above are coupled and the transmission signal is received via the capacitor, or a method is used in which the devices are coupled via a coupling transformer and the signal is received via the transformer.

[Problems to be Solved by the Invention] However, the method using a coupling capacitor has the disadvantage that it is susceptible to external noise because the transmission line side and the signal receiving side are electrically connected in an alternating current manner via the coupling capacitor. be. Further, in the method using a coupling transformer, a large sag occurs due to the saturation phenomenon due to the bias DC, and there are problems such as large distortion of the received waveform.

[Means for Solving the Problems] In order to solve the above-mentioned problems, according to the local area network reception method according to the present invention, a transmission line is connected in parallel to the transmission line of the local area network so as to be driven by the transmission signal of the transmission line. A configuration is adopted in which the line and a device that receives the transmission signal are coupled in parallel in an insulated state via a connected photocoupler, and the transmission signal is received via the photocoupler.

[Function] According to such a configuration, the transmission line and the receiving side equipment are coupled in an insulated state via the photocoupler, so that the transmission line is resistant to external noise. Further, distortion of the received waveform does not occur as would be the case when a coupling transformer is used.

[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 receiving circuit that receives transmission signals from a LAN transmission line according to the method of the present invention.

71+1' is a LAN transmission line, which is composed of a set of two lines, which are connected as a loop through terminating resistors R1 and R1 having the same resistance value at both ends, and are grounded. In addition, on one side of the transmission line l, a DC constant voltage power supply (not shown) that generates a predetermined DC' heavy pressure Vcc is connected to a voltage dividing resistor R.
The DC voltage Vcc is connected through the voltage dividing resistor R.
A predetermined DC line bias voltage divided at a predetermined voltage division ratio by O, the combined resistance of the terminating resistors R1 and R1, and the transmission line 1.1' is applied between the transmission lines l and 1'.

A transmission signal is sent to the transmission line 1.1' from a device such as a computer on the transmitting side (not shown) via a signal transmission circuit (not shown), and is transmitted as a transmission signal indicated by the symbol Sl.

On the other hand, the configuration shown below the transmission line 1.1' in FIG. 1 is a signal receiver 2 for receiving the transmission signal 31 by a device such as a computer on the receiving side (not shown), and a photocoupler 3. It is composed of a Schmitt trigger 4 and an inverter 5, and a receiving side device is connected to an output terminal 6.7.

Photocoupler 3 is a light emitting diode D and a phototransistor T
It is a well-known device consisting of a transmission line 1.1', which is connected in parallel to the transmission line 1.1', and is driven by a transmission signal Sl. That is, the light emitting diode D of the photocoupler 3 is connected in parallel to the transmission line 1.1' via the protective resistor R2, and current is applied or cut off depending on the change in the voltage level of the transmission signal SL, and the light is turned on or off. It has become so. Further, a predetermined driving DC voltage Vc is applied from a DC constant voltage power source (not shown) to the collector of the phototransistor Tr via a protective resistor R3, and the emitter is grounded.

Then, the output of the photocoupler 3 is taken out as a reception signal S2 from the connection point A between the phototransistor Tr and the protection resistor R31m, and is then outputted from the output terminal 6.7 via the Schmitt trigger 4 for waveform shaping and the inverter 5. It has become.

Next, the operation at the time of reception with the above configuration will be explained.

Since the line bias voltage mentioned above is applied to the transmission line 1.1', the transmission signal Sl is generated in the form of an inversion of the original signal of the transmission signal, and the high level is approximately the line bias voltage,
It is generated and transmitted as a pulse signal whose low level is approximately O voltage. As can be seen from the waveform shown, the transmission signal S
l contains a noise component.

When the transmission signal Sl is at a high level, a current is applied to the light emitting diode D, one light emitting diode D emits light, and the phototransistor Tr receives light and turns on. Therefore, the connection point A is grounded via the phototransistor Tr, and the output voltage of the photocoupler 3 at the connection point A is approximately O.

Next, when the transmission signal S2 becomes low level, the power to the light emitting diode D- is cut off, and the light emitting diode D goes out.
Phototransistor Tr is turned off.

Therefore, the output voltage at the connection point A becomes approximately the power supply voltage Vc of the photocoupler 3.

In this way, the received signal S2 is obtained at the connection point A as an inverted version of the transmitted signal S1, and is input to the Schmitt trigger 4. Although the received signal S2 contains noise components as shown in the waveform, the Schmitt trigger 4 and the inverter 5
The noise component is cut by waveform shaping. Note that the received signal S2 is inverted by the Schmitt trigger 4, further inverted by the inverter 5, and returned to its original direction.

Then, the shaped received signal S2' is outputted from the output terminal 6.7 and inputted to the receiving side device.

Note that the received signal 32' is an inverted signal of the transmitted signal S1, but since the transmitted signal St is an inverted version of the original transmitted signal,
The received signal 32' is a faithful reproduction of the original signal.

According to this embodiment as described above, the transmission line l.

1' and the device on the receiving side are coupled in an insulated manner via the photocoupler 3, making it resistant to external noise. Further, distortion of the received waveform does not occur as in the case of passing through a coupling transformer.

Furthermore, except for the circuit of the light emitting diode D of the photocoupler 3, the signal receiver 2 is insulated from the transmission line 1.1', so even if a failure such as a power cut occurs in the signal receiver 2, the failure will not occur in the transmission line 1, 1' and other signal receivers, thus connecting multiple signal receivers to the transmission line l, 1'
You can continue.

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

In the above-described configuration, the amplitude of the received signal 32' can be adjusted by inserting a dividing resistor on the receiving output side of the photocoupler 3. In addition, for waveform shaping, a comparator configured to connect two stages of TTL or C-MOS and apply a positive feedback amount may be used instead of the Schmitt trigger 4. Also, it is limited to the light emitting diode D and phototransistor Tr. Alternatively, a photocoupler constructed from other suitable light emitting elements and light receiving elements may be used.

I would like to add that the transmission line 1 with the above configuration
．． Reception can be performed in the same manner even when no line bias voltage is applied to 1'.

[Effects] As is clear from the above explanation, according to the local area network reception method according to the present invention, a photocoupler connected in parallel to the transmission line of the local area network is driven by the transmission signal of the transmission line of the local area network. The line and the device that receives the transmission signal are coupled in parallel in an insulated manner through the photocoupler, and the transmission signal is received through the photocoupler. , excellent effects such as being able to be implemented at low cost with a simple configuration can be obtained.

[Brief explanation of the drawing]

The figure is a circuit diagram showing the configuration of a signal receiving circuit that receives transmission signals from a LAN transmission line according to the method of the present invention. 1.1'...Transmission line 2...Signal receiver 3...
・Photocoupler 4...Schmitt trigger 5...
Inverter 6.7...Output terminals R1-R3...
・Resistance D...Light-emitting diode Tr...Phototransistor

Claims (1)

[Claims] The transmission line and a device that receives the transmission signal are coupled in parallel in an insulated state through a photocoupler connected in parallel to the transmission line so as to be driven by the transmission signal of the transmission line of the local area network, and the transmission line is connected in parallel through the photocoupler. A receiving system for a local area network, characterized in that the transmission signal is received.