JP2000295297A - Communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a communication system and its reception circuit where a received signal is accurately obtained from a signal sent through a 2-wire transmission line without much reducing a transmission rate. SOLUTION: The communication system using 2-wire transmission lines 1, 2 through which transmission signals of inverted phases to each other are transmitted, is provided with a plurality of nodes connected to the 2-wire transmission lines 1, 2 and each of the nodes builds in a termination resistor corresponding to the 2-wire transmission lines 1, 2. Furthermore, the reception circuit to receive a transmission signal as a node is provided with AC coupling circuits 15, 16 that extract an AC component of the transmission signal received via the 2-wire transmission lines 1, 2, bias circuits 17, 18 that apply a bias voltage to the output signal from the AC coupling circuits 15, 16, and clip circuits 24, 25 that clip the output signal level of the bias circuits 17, 18, which respectively correspond to the 2-wire transmission lines 1, 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication system having a plurality of nodes commonly connected to a transmission line.

[0002]

In conventional communication systems, as shown in FIG. 1, the transmission line 1 and 2 of the two-wire transceiver circuit 3 ₁ to 3 _n is connected as a plurality of nodes. Both transmitting and receiving circuit 3 ₁ to 3 _n has the same configuration. A positive potential Vcc (for example, 5V) is applied to one end of the transmission line
, And the other end is similarly supplied with the positive potential Vcc via the terminating resistor 5. A ground potential Vg (for example, 0 V) is supplied to one end of the transmission line 2 via a terminating resistor 6, and the ground potential Vg is similarly supplied to the other end via a terminating resistor 7.

[0003] In the transceiver circuit 3 _1, the transmission line 1,
2, a bidirectional input / output filter 11 is connected via a connector 12. The transmission line 1 of the input / output filter 11
2 and the connection terminals B1 and B2 on the opposite side of the connection terminals A1 and A2.
A transmission signal is supplied to B2 via the non-inverting amplifier circuit 13 and the inverting amplifier circuit 14 individually. Also, the filter 11
Are connected to connection terminals B1 and B2 respectively through AC coupling circuits 15 and 16 each composed of a resistor and a capacitor.
7, 18 are connected. Each signal obtained from the bias circuits 17 and 18 becomes a reception signal via the differential amplifier 19.

When a transmission signal is output, the transmission signal is amplified by the non-inverting amplifier circuit 13 and inverted and amplified by the inverting amplifier circuit 14. Transmission signals having phases opposite to each other are supplied to the filter 11 from the non-inverting amplifier 13 and the inverting amplifier 14. The filter 11 individually low-passes these transmission signals. The output transmission signal of the non-inverting amplifier 13 is supplied to the transmission line 2 after passing through the filter 11, and the inverting amplifier 14 is supplied to the transmission line 1 after passing through the filter 11.

On the other hand, signals transmitted by the transmission lines 1 and 2 are supplied to a filter 11. The filter 11 individually lower-passes these transmission signals to form an AC coupling circuit 1.
Output to 5 and 16. In each of the AC coupling circuits 15, 16, the AC component of the transmission signal is extracted and removed, and the bias circuits 17, 1
8 is supplied. For example, as shown in FIG. 2A, when the signal A transmitted on the transmission line 1 and the signal B transmitted on the transmission line 2 change in opposite phases, the bias circuit 17 shown in FIG. ), A bias voltage is applied to the transmission signal A to generate a bias signal BIASA.
In the bias circuit 18, a bias voltage is applied to the transmission signal B to generate a bias signal BIASB. Each output signal of the bias circuits 17 and 18 is detected by the differential amplifier 19 as a reception signal as shown in FIG.

When the transmission line 1 is disconnected, the transmission line 2
2D, the bias signal BIASA is constant and does not change as shown in FIG. 2D, but the bias signal BIAS is applied to the signal B transmitted through the transmission line 2 by applying a bias voltage. The signal BIASB changes in the same manner as the signal B. The differential amplifier 19 compares the fixed bias signal BIASA and the bias signal BIASB to obtain a reception signal as shown in FIG. This is the same when the transmission line 1 is grounded or when the transmission line 2 is disconnected or grounded.

If the transmission circuits 1 are not provided without the bias circuits 17 and 18, the signals A and B input to the differential amplifier 19 become as shown in FIG. Not detectable. Such a transmitting and receiving circuit 3 ₁
The configurations and operations are the same for transmitting and receiving circuit 3 ₂ to 3 _n. The above-mentioned conventional communication system is disclosed, for example, in Japanese Patent Laid-Open Publication No. Hei 3-171849.

[0008]

By the way, the transmission lines 1 and 2 of the two-wire type can be represented by an equivalent circuit as shown in FIG. 3 with a resistance R0 per unit length, an inductance L0 and a capacitance C0.
It can be represented by 0. The transmitting and receiving circuit 3 ₁ to 3 _n each capacitance C1 also exists as shown in FIG. Therefore,
The rising edge and the falling edge of the transmission signal change transiently under the influence of these capacitances. Looking at the transmission line 1, as shown in FIG.
6 and the capacitance C composed of the capacitance C0 and the capacitance C1 act as a time constant, and FIG.
As shown in (1), the waveform of the transmission signal on the transmission line 1 changes transiently at the time of falling and rising.

However, for example, if any part of the transmission line 1 is disconnected, the resistance value R is doubled. Therefore, if the change in the capacitance C is ignored, the time constant is doubled. The waveform of the transmission signal on 1 becomes more distorted. This is the same in the case of a contact failure between each transmission / reception circuit and the transmission line 1, and also in the case of a disconnection or a contact failure not only in the transmission line 1 but also in the transmission line 2, the waveform of the transmission signal is similarly large. It is affected by a certain time constant. The transmission / reception circuit has a problem that it is impossible to obtain an accurate reception signal from the transmission signal of the transient waveform affected by such a large time constant without lowering the communication speed.

An object of the present invention is to provide a communication system capable of accurately obtaining a received signal from a signal transmitted by a two-wire transmission line without greatly reducing the communication speed, and a receiving circuit thereof. It is.

[0011]

SUMMARY OF THE INVENTION A communication system according to the present invention is a communication system using a two-wire transmission line for transmitting transmission signals having phases opposite to each other, and is connected to the two-wire transmission line. A plurality of nodes are provided, and each node has a built-in terminating resistor corresponding to a two-wire transmission line.

According to the communication system of the present invention, since each node has a built-in terminating resistor corresponding to the two-wire transmission line, the transmission line is disconnected or a contact failure occurs between the node and the transmission line. Also, since the time constant when the transmission line is viewed from the node does not increase, the received signal can be accurately obtained from the signal transmitted through the two-wire transmission line without greatly reducing the communication speed.

The communication system according to the present invention includes a receiving circuit for receiving a transmission signal as a node, the receiving circuit including an AC coupling circuit for extracting an AC component of the transmission signal input via the transmission line, and an AC coupling circuit. A bias circuit for applying a bias voltage to an output signal of the circuit and a clip circuit for clipping the output signal level of the bias circuit are provided for each two-wire transmission line.

According to the communication system of the present invention, even when a transmission signal having a transient waveform affected by a large time constant is received, the characteristics of the trailing edge of the received signal can be improved, and high-speed communication can be performed. It becomes possible. Further, a receiving circuit of the present invention is a receiving circuit for receiving a transmission signal in a communication system using a two-wire transmission line for transmitting transmission signals having phases opposite to each other, wherein the transmission circuit receives the transmission signal input via the transmission line. An AC coupling circuit for extracting an AC component of a signal, a bias circuit for applying a bias voltage to an output signal of the AC coupling circuit, and a clip circuit for clipping an output signal level of the bias circuit correspond to each of the two-wire transmission lines. It is characterized by having.

According to the receiving circuit having such a configuration, even when a transmission signal having a transient waveform affected by a large time constant is received, the characteristics of the trailing edge of the received signal can be improved, and high-speed communication can be performed. A simple receiving circuit can be configured.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 7 shows a communication system according to the present invention, and the same parts as those of the conventional communication system shown in FIG. No terminating resistor is directly connected to the two-wire transmission lines 1 and 2. In the transmitting and receiving circuit 3 _1, and the connection terminals A1, A2 of the transmission line 1 and 2 of the filter 11 the inverting amplifier circuit 14 and an AC coupling circuit 15 is connected to the connection terminal B1 of the opposite, the connection terminal B2 The non-inverting amplifier circuit 13 and the AC coupling circuit 16 are connected, which is the same as in the conventional system. In the communication system according to the present invention, the connection terminal B
A distribution termination circuit 21 is further connected to 1 and B2.
The distributed termination circuit 21 includes termination resistors 22 and 23. The termination resistor 22 supplies the positive potential Vcc to the connection terminal B1, and the termination resistor 23 is provided so as to supply the ground potential Vg to the connection terminal B2.

From the AC coupling circuits 15 and 16, the differential amplifier 1
9 are connected to bias circuits 17 and 18
And the clip circuits 24 and 25 are connected. The clipping circuit 24 suppresses the biasing signal BIASA to the first clipping level CLIP1 when the biasing signal BIASA of the line L1 falls below the first clipping level CLIP1, and the clipping circuit 25 sets the biasing signal BIASB of the line L2 to the first clipping level CLIP1. 2 is higher than the clip level CLIP2 of the bias signal BIAS.
B is suppressed to the second clip level CLIP2.

The configuration of the transceiver circuit 3 ₁ also applies to the transceiver circuit 3 ₂ to 3 _n. In the communication system having the above-described configuration, when a transmission signal is output, the transmission signal is amplified by the non-inverting amplifier circuit 13 and is also inverted and amplified by the inverting amplifier circuit 14. Transmission signals having phases opposite to each other are supplied to the filter 11 from the non-inverting amplifier 13 and the inverting amplifier 14. The filter 11 individually low-passes these transmission signals. Non-inverting amplifier circuit 13
Is transmitted to the transmission line 2 after passing through the filter 11, and the inverting amplifier circuit 14 passes through the filter 11,
The signal is supplied to the transmission line 1.

On the other hand, the signals transmitted by the transmission lines 1 and 2 are supplied to a filter 11. The filter 11 individually lower-passes these transmission signals to form an AC coupling circuit 1.
Output to 5 and 16. In each of the AC coupling circuits 15, 16, the AC component of the transmission signal is extracted and removed, and the bias circuits 17, 1
8 is supplied. The transmission of the transmission signal in this way is the same as that of the conventional communication system.

On the transmission line 1 or 2, usually, FIG.
As shown in (1), the rising and falling waveforms of the transmission signal are obtained. The total resistance R of the terminating resistor 22 or 23 for each transceiver circuit 3 within _one to 3 _n in this waveform, the above-mentioned electrostatic capacitance C0 and the electrostatic capacitance C and each transceiver circuit 3 ₁ consisting of the capacitance C1 Acts as a time constant when the transmission line 1 is viewed from ３3 _n .

[0021] However, in the communication system according to the present invention, the terminating resistor in the transceiver circuit 3 within _one to 3 _n 22,
Since 23 is provided, for example, when somewhere in the transmission line 1 is broken, it is possible to prevent the time constant is increased by the terminating resistor 22 in each transceiver circuit 3 ₁ to 3 _n. In other words, in the case of a terminating resistor directly connected to the transmission line 1 as in the conventional communication system, the resistance value R is doubled, so that the time constant is doubled. , without time constant is increased as twice during disconnection of the transmission line by the terminating resistors 22 and 23 is provided in each transceiver circuit 3 within _one to 3 _n, the transmission signal on the transmission line 1, 2 The rising and falling waveforms hardly change as shown in FIG.
Therefore, it becomes possible to obtain an accurate received signal from the transmission signal when the disconnection of the transmitting and receiving circuit 3 ₁ to 3 _n In this way the transmission line. In FIG. 8B, a broken line waveform shows a case where a transmission line is broken in a conventional communication system.

Further, the transmission line 1 and the transceiver circuit 3 ₁ to 3 _n
Also, in the case of a contact failure between the two, the increase of the time constant can be prevented in the same manner, and the transmitting / receiving circuit to be received can obtain an accurate received signal from the transmitted signal. Further, in the communication system according to the present invention, the clip circuits 24 and 25 are connected to the lines L1 and L2 from the AC coupling circuits 15 and 16 to the differential amplifier 19 together with the bias circuits 17 and 18 as described above. Therefore, in the clipping circuit 24, as shown by the broken line X1 in FIG.
When the first bias signal BIASA falls below the first clip level CLIP1, the bias signal BIASA of the line L1 becomes the first bias signal BIASA as shown by the solid line Y1 in FIG.
At the clip level CLIP1 in the clipping circuit 25, the line L2 as shown by the broken line X2 in FIG.
Of the bias signal BIASB of the second clip level C
When LIP2 is exceeded, the bias signal BIASB of the line L2 is suppressed to the second clip level CLIP2 as shown by the solid line Y2 in FIG.

At the trailing edge of the transmission signal, the characteristics of the solid lines Y1 and Y2 are changed by the clipping circuits 24 and 25 to the broken lines X1 and X2.
The characteristic changes earlier by the time T than the characteristic No. 2.
Therefore, the waveform of the received signal output from the differential amplifier 19 is as shown by the solid line Y3 in FIG. 9B, and is earlier by the time T than the waveform without the clipping circuits 24 and 25 (broken line X3). It becomes a falling pulse waveform. As a result, the characteristics of the trailing edge of the received signal can be improved.

When the transmission line 1 is disconnected, only the signal B is transmitted by the transmission line 2, so that the signal
As shown in (a), the biasing signal BIASA is constant and does not change, but a bias voltage is applied to the signal B transmitted through the transmission line 2 so that the biasing signal BIASB is applied.
Is obtained as Even in this case, the clip circuit 25
In FIG. 10A, as shown by a broken line X2 in FIG. 10A, the bias signal BIASB of the line L2 is changed to the second clip level CL.
When the voltage exceeds IP2, the bias signal B of the line L2
The IASB is suppressed to the second clip level CLIP2 as indicated by the solid line Y2 in FIG. Differential amplifier 1
In FIG. 9, the level of the fixed bias signal BIASA and the level of the solid line Y2 are compared to obtain a reception signal that falls quickly as shown in FIG. 10B. As a result, the characteristics of the trailing edge of the received signal can be improved.

FIG. 11 shows the filter 11, the non-inverting amplifier 13, and the inverting amplifier 1 in the transmitting / receiving circuit.
4. Bias circuits 17, 18 and clip circuits 24, 2
5 shows a specific configuration example. That is, filter 1
1 includes resistors 31 to 34 and capacitors 35 and 36. The non-inverting amplifier 13 includes resistors 41 and 42, a PNP transistor 43, and a diode 44, and the inverting amplifier 14 includes resistors 46 and 47, an NPN transistor 48, and a diode 49. The bias circuit 17 has a resistor 5
1 to 53 and a PNP transistor 54, and the bias circuit 18 includes resistors 56 to 58 and an NPN transistor 5
Consists of nine. The clip circuit 24 includes resistors 61 to 63, PN
The clip circuit 25 includes resistors 66 to 68 and a PNP transistor 6.
9 and a diode 70.

In the above embodiment, the node is described as a transmission / reception circuit. However, the node may be provided separately for the transmission circuit and the reception circuit.

[0027]

As described above, according to the present invention, each node has a built-in terminating resistor corresponding to a two-wire transmission line, so that the transmission line is disconnected or the contact between the node and the transmission line is poor. Even so, the time constant when the transmission line is viewed from the node does not increase, so that the received signal can be accurately obtained from the signal transmitted by the two-wire transmission line without greatly reducing the communication speed. .

Further, according to the present invention, an AC coupling circuit for extracting an AC component of a transmission signal input via a transmission line, a bias circuit for applying a bias voltage to an output signal of the AC coupling circuit, Since a clipping circuit for clipping the output signal level is provided for each of the two-wire transmission lines, even if a transmission signal having a transient waveform affected by a large time constant is received, the trailing edge of the reception signal Characteristics can be improved, and high-speed communication can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a conventional communication system.

FIG. 2 is a waveform diagram showing signal transmission in a conventional communication system.

FIG. 3 is a diagram showing an equalization circuit of a two-wire transmission line.

FIG. 4 is a diagram illustrating a capacitance in a transmission / reception circuit.

FIG. 5 is a diagram showing a time constant circuit when a transmission line is viewed from a receiving side.

FIG. 6 is a diagram showing a waveform of a transmission signal.

FIG. 7 is a block diagram showing an embodiment of the present invention.

FIG. 8 is a diagram illustrating a waveform of a transmission signal.

FIG. 9 is a waveform diagram showing a clip operation.

FIG. 10 is a waveform diagram showing a clip operation when a transmission line is disconnected.

FIG. 11 is a circuit diagram showing a specific configuration of a transmission / reception circuit.

[Explanation of symbols]

1, 2 transmission line 3 _{1 to} 3 _n transmission / reception circuit 11 filter 12 connector 15, 16 AC coupling circuit 19 differential amplifier 21 distributed termination circuit

 ────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kazuya Iwamoto 1-4-1 Chuo, Wako-shi, Saitama F-term in Honda R & D Co., Ltd. (Reference) 5K029 AA11 CC01 DD13 JJ06 LL00 LL05

Claims (4)

[Claims] 1. A communication system using a two-wire transmission line for transmitting transmission signals having opposite phases to each other, comprising: a plurality of nodes connected to the two-wire transmission line; A communication system including a terminating resistor corresponding to each of the two-wire transmission lines. 2. The two-wire transmission line includes a first termination resistor that applies a first predetermined potential to one of the two-wire transmission lines, and a second one that transmits the first predetermined potential to the other of the two-wire transmission line. 2. The communication system according to claim 1, further comprising a second terminating resistor for providing a different second predetermined potential. 3. A receiving circuit for receiving the transmission signal as the node, wherein the receiving circuit extracts an AC component of a transmission signal input via the transmission line, and the AC coupling circuit. 2. A bias circuit for applying a bias voltage to the output signal of claim 2, and a clip circuit for clipping an output signal level of the bias circuit, corresponding to each of the two-wire transmission lines. Communications system. 4. A receiving circuit for receiving a transmission signal in a communication system using a two-wire transmission line for transmitting transmission signals having phases opposite to each other, wherein a reception signal of the transmission signal input via the transmission line is provided. An AC coupling circuit for extracting an AC component, a bias circuit for applying a bias voltage to an output signal of the AC coupling circuit, and a clip circuit for clipping an output signal level of the bias circuit, for each of the two-wire transmission lines. A receiving circuit correspondingly provided.