JPH0846649A - Digital signal transmission system - Google Patents

Abstract

PURPOSE:To provide the digital signal transmission system in which an AMI code signal is sent through an optical fiber cable. CONSTITUTION:A transmission circuit 10 converts a positive signal TPD and a negative signal TND of an AMI code signal into signals with positive or negative polarity and generates a binary code signal PND by superimposing them. The binary code signal PND is sent through an optical fiber cable 30 being a transmission medium. A reception circuit 20 converts the received optical signal into a binary electric signal pulse pnd, which is separately detected as a positive signal RPD and a negative signal RND, which are used to recover the original AMI code signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital signal transmission system for transmitting a digital signal by wire, and more particularly to a digital signal transmission system for transmitting an AMI-encoded digital signal through an optical fiber cable.

[0002]

2. Description of the Related Art In a digital transmission circuit for transmitting a digital signal via a cable, an original information signal sequence is often converted into another pulse sequence for transmission. An AMI code (Alternate Mark Inversion code), which is one method of a transmission line code suitable for such wired transmission, does not have high transmission efficiency, but since the average value of the transmission waveform is 0, the DC component can be cut and It is widely used because it is easy to monitor errors.

The principle circuit of this AMI code and an example of encoding are shown in FIG. FIG. 3 is a diagram for explaining the AMI code, in which (A) is a principle circuit diagram and (B) is a circuit diagram.
3 is a time chart showing an example of AMI encoding. Binary input data Data sequentially input from the input terminal is J-
It is input to both the J and K terminals of the K flip-flop 61. As a result, every time 1 is input to the input data Data, the signal Q for inverting the positive / negative is changed to the JK flip-flop 6
It is output from 1. The logical product of this signal Q, the input data Data, and the signal TIM that is 50% -duty AMI Pulse,
By the AND element 62, a signal PD for applying a positive sign signal is obtained. Also, the negative signal of signal Q, input data Data, and 50% -duty
By obtaining the logical product of the signal TIM which is AMI Pulse by the NAND element 63, the signal ND for applying the signal of the negative sign is obtained. By applying a positive polarity pulse and a negative polarity pulse to the transmission line based on the signal PD and the signal ND, respectively, an AMI signal in which the input data is changed into a ternary data series can be obtained.

A conventional transmission system for transmitting this AMI-coded information sequence by using a metallic cable will be described with reference to FIGS. 4 and 5. FIG. 4 is a diagram showing a configuration of an example of a transmission / reception circuit that transmits / receives an AMI-coded signal. FIG. 5 is a time chart showing signal waveforms of the circuit shown in FIG. AMI code transmission / reception circuit 40
Is composed of an input terminal 46, drivers 41 and 42, a pulse transformer 43, receivers 44 and 45, and an output terminal 47. From the input terminal 46, the signal TPD for generating the AMI-coded positive polarity signal and the signal TND for generating the negative polarity signal are input. These signals are negative signals as shown in FIGS. 5 (A) and 5 (B). The input signals are the drivers 41, 4
2 is applied to the pulse transformer 43.

The pulse transformer 43 is a transformer for cutting off a direct current component, impedance matching, and supplying electric power to a transmission system, and a signal passing through this transformer is transmitted by the metallic cable 50. FIG. 5 (A),
The input signals TPD and TPN shown in FIG.
The AMI signal having positive and negative pulses shown in FIG. In addition, the signal transmitted by the metallic cable 50 passes through the pulse transformer 43 and the receiver 44,
It is output from the output terminal 47 through 45. The receiver 44 outputs a signal RPD corresponding to a positive polarity signal, and the receiver 45 outputs a signal RND corresponding to a negative polarity signal.

On the other hand, optical fiber cables are becoming popular as transmission media for digital communication systems. The optical fiber cable has characteristics such as low loss and wide band, as compared with other transmission media such as metallic cable, so that it is possible to transmit a large capacity over a long distance. Further, since the optical fiber cable is not an electric conductor, it has a feature that it does not have problems such as induction noise and radio wave interference. However, the practical optical transmission method using this optical fiber cable is currently performed by light intensity modulation in which the light quantity of the light source is simply changed according to the signal. Due to such a feature as a transmission medium that a transmission band can be sufficiently wide, a modulation method, and characteristics of a light emitting element, the method of digital transmission line coding using an optical fiber cable is 2 CMI code (Code Mark Invers
ion code) and mB1C code (m Binary with 1 Comple
ment insertion code) is used.

[0007]

However, the above-mentioned AM
In the transmission method using the I code, since the transmission is performed using a metallic cable, loss is large and inductive noise is likely to occur. Therefore, the relay distance cannot be increased, and a large number of relays must be installed. Moreover, there is a possibility that a transmission error may occur. As a means for solving the above problems, a method of transmitting using an optical fiber cable as a transmission medium is desired. However, the transmission method using an optical fiber cable is
Due to the various characteristics described above, the base code transmission of the binary code by the light intensity modulation is suitable, and it is not suitable for transmitting the signal of the AMI code which is a ternary signal.

Therefore, it is an object of the present invention to provide a digital signal transmission system capable of transmitting an AMI-coded signal using an optical fiber cable as a transmission medium. Another object of the present invention is to provide a digital signal transmission method that enables transmission of an AMI-coded signal with a long relay distance without a transmission error.

[0009]

The AMI code is a three-valued AMI code adjusted to have the same number of positive and negative signals in order to cut a DC component in consideration of transmission through a metallic cable. It is a signal. Therefore, the amount of information has redundancy, and this ternary signal can be converted into a binary signal without changing the frequency. In the digital signal transmission system of the present invention, by removing this redundancy, the AMI code signal is converted into a binary code signal and transmitted.

The digital signal transmission system of the present invention uses the AMI
The encoded input signal is inverted by superimposing one of the positive polarity signal and the negative polarity signal on the other signal,
A means for converting the binary coded signal, a means for converting the converted binary coded signal into an optical signal and transmitting it by an optical fiber cable, and a means for receiving the transmitted optical signal and converting it to a binary electrical signal. Means for converting, means for outputting a selection signal for determining whether the individual pulse of the received electric signal is a positive polarity pulse or a negative polarity pulse in the AMI-coded signal, and based on the selection signal Received the above 2
It comprises means for separately detecting a positive polarity signal and a negative polarity signal from the value electric signal and reproducing the AMI-coded signal.

[0011]

According to the digital signal transmission system of the present invention, the signal sequence in which the information to be transmitted is AMI-coded is further converted into a binary coded signal. Therefore, this signal can be transmitted by light intensity modulation. That is, it can be easily transmitted by a transmission system using an optical fiber cable as a transmission medium. In addition, the conversion from the signal of the AMI code to the signal of the binary code, which is performed by inverting one of the positive polarity signal and the negative polarity signal of the AMI code signal and superimposing it on the other signal, This is a conversion that uses the redundancy of the code. Therefore, there is no loss of information, and the original signal of the AMI code can be easily restored from the received signal.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the digital signal transmission system of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing the configuration of a digital signal transmission system according to an embodiment of the present invention. FIG. 2 is a time chart for explaining each signal of the digital signal transmission system shown in FIG. The digital signal transmission system of the present invention comprises a transmitter 10, a receiver 20, and an optical fiber cable 30.

The transmitter 10 sends the information sequence to be transmitted to A
The MI coded signal is input. This signal is input as a signal TPD for applying a positive polarity pulse and a signal TND for applying a negative polarity pulse. In this embodiment, it will be described that the digital signal transmission method of the present invention can be replaced with the above-mentioned conventional transmission method to perform transmission. Therefore, this input signal TP
As shown in FIGS. 2A and 2B, D and TND are
The same negative signal as shown in FIGS. 5A and 5B is used. Further, in the present embodiment, in order to synchronize with the receiving side, the bipolar violation signal is applied every two cycles of positive and negative before transmitting the first information sequence of the transmission signal.

The AND gate 11 receives the input signal TP
It is a circuit that superimposes D and the signal TND, converts them into a binary signal sequence, and outputs it. In the present embodiment, since the signal TPD and the signal TND are both signals of the same negative polarity, this AND gate is used as the superposition circuit. Figure 2
The AND gate 11 calculates the logical product of the signals TPD and TND shown in FIGS. 2A and 2B, and outputs a binary signal PND shown in FIG. Optical transmitter module 12
Is a module that converts the input signal PND into an optical signal and outputs it to the optical fiber cable 30. The input signal PND is converted into a signal for converting the intensity of light, the signal is applied to the semiconductor laser which is a light emitting element, and the light emitted by the semiconductor laser is emitted to the optical fiber cable. The light emitting element may be a light emitting diode other than the semiconductor laser, for example.

The optical fiber cable 30 is a transmission medium for transmitting an optical signal, and a general-purpose optical fiber cable may be used according to the transmission characteristics, the transmission distance, the mechanical strength and the like. Further, a repeater is appropriately provided as needed.
The optical signal transmitted by the optical fiber cable enters the optical receiving module 21 of the receiving circuit 20.

The receiving circuit 20 includes an optical fiber cable 30.
Is a receiving / converting circuit for converting the optical signal transmitted by the above into an electric signal, and further converting the electric signal into an AMI-coded signal. The optical receiving module 21 receives an optical signal transmitted by the optical fiber cable 30 by a light receiving element such as a photodiode, converts it into an electric signal, amplifies it, and outputs it. Figure 2
A signal pnd having the same waveform as the binary coded transmission signal PND shown in (C) is received.

The mask signal generation circuit 22 generates a mask signal S shown in FIG. 2D from the received signal pnd and outputs it to the inverter circuit 23 and the OR gate circuit 24. In the present embodiment, from the detection of the first pulse of the received signal, it changes to High-Low by 2 cycles corresponding to the bipolar violation signal, and thereafter,
A mask signal S shown in FIG. 2D, whose output is inverted each time a pulse is detected, is generated. Therefore, the mask signal S shows a low level when the pulse of the reception signal pnd is restored as a positive pulse, and a high level when it is restored as a negative pulse. The inverter circuit 23 inverts the mask signal S generated by the mask signal generation circuit 22.

The OR gate circuit 24 is a gate circuit for detecting a signal having a positive sign from the signal pnd received by the optical receiving module 21 based on the mask signal S generated by the mask signal generating circuit 22. is there. In the present embodiment, the selection signal S and the reception signal p
Due to the polarity of nd, the received signal pnd is passed when the mask signal S is at low level. Therefore, the signal RPD shown in FIG. 2E can be detected. This signal RPD is the same as the signal TPD for applying a positive polarity pulse.
The OR gate circuit 25, based on the mask signal S generated by the mask signal generation circuit 22,
It is a gate circuit for detecting a signal having a negative sign from the signal pnd received by the signal 1. In this embodiment, the signal output from the inverter circuit 23 is Low.
At the level, the received signal pnd is passed. Therefore, the signal RND shown in FIG. 2 (F) can be detected. This signal RND is a signal TND for applying a negative pulse.
Is the same as

In this way, the input signals TPD and TND are
It could be transmitted as output signals RPD and RND.
That is, the AMI-encoded information signal could be transmitted using the optical fiber cable as the transmission medium, only by adding a simple circuit. Therefore, in the transmission system using the AMI code, when the optical fiber cable becomes available as a transmission medium, by using this digital signal transmission method, the optical fiber cable can be used without changing the current AMI transmitter and receiver. Data can be transmitted.

The digital signal transmission system of the present invention is
The present invention is not limited to this example, and various modifications can be made. For example, the AND gate circuit 11, the inverter circuit 23, the OR gate circuit 24, and the OR of the present embodiment.
Each circuit such as the gate circuit 25 is a circuit illustrated as an example in conformity with the characteristics and polarity of the input signal of this embodiment. Therefore, when the polarities of the input signal and the output signal are changed, the respective circuits are also changed accordingly.
Further, the logical configuration of each circuit is not limited to that of this embodiment, and may be realized by any circuit configuration.

[0021]

As described above, according to the digital signal transmission system of the present invention, the AMI-coded signal can be transmitted by the optical fiber cable only by using a simple signal conversion circuit. Therefore, it is possible to eliminate the transmission error due to the induced noise and transmit the AMI-coded signal with a long relay distance.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a digital signal transmission system according to an embodiment of the present invention.

FIG. 2 is a time chart explaining each signal of the digital signal transmission system shown in FIG.

FIG. 3 is a diagram for explaining an AMI code, where (A) is A
A principle circuit diagram of the MI code, (B) is a time chart showing an example of the AMI code.

FIG. 4 is a diagram illustrating a conventional digital signal transmission system.

5 is a time chart for explaining each signal of the digital signal transmission system shown in FIG.

[Explanation of symbols]

 10 ... Transmission circuit 11 ... AND gate 12 ... Optical transmission module 20 ... Reception circuit 21 ... Optical reception module 22 ... Mask signal generation circuit 23 ... Inverter circuit 24, 25 ... OR gate circuit 30 ... Optical fiber cable 40 ... Transmission / reception circuit 41, 42 ... Driver 43 ... Pulse transformer 44, 45 ... Receiver 50 ... Metallic cable 60 ... AMI encoding circuit 61 ... JK flip-flop 62 ... AND element 63 ... NAND element

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Claims (1)

[Claims] 1. A signal conversion means for converting an AMI-encoded input signal into a binary coded signal by inverting one of a positive polarity signal and a negative polarity signal and superimposing the inverted signal on the other signal. A transmitting means for converting the binary coded signal converted by the signal converting means into an optical signal and transmitting the optical signal through an optical fiber cable; and an optical signal transmitted by the transmitting means for converting into a binary electric signal. A receiving unit and a selection signal for determining whether each signal pulse of the binary electric signal received by the receiving unit corresponds to a positive polarity pulse or a negative polarity pulse in the AMI coded signal. And a selection signal output means for outputting a positive polarity signal and a negative polarity signal from the received binary electrical signal based on the selection signal output by the selection signal output means. A digital signal transmission system having a reproducing means for detecting and reproducing an AMI-coded signal.