JPH03229532A - Signal transmission circuit - Google Patents

Abstract

PURPOSE:To automatically prevent the deterioration of quality in communication owing to a far-end crosstalk by previously storing waveform information corresponding to a distorted waveform in a digital memory, detecting the level of a reproduced reception signal and converting them into pulse waveforms corresponding to respective levels so as to transmit them. CONSTITUTION:The reception signal inputted from a connection terminal 8 with a transmission line is connected to an equalizer 10 via a switch circuit 11. The equalizer 10 generates level detection information 12 at every step which is previously decided in correspondence with the reception level. When level detection information 12 of the reception signal detected in the equalizer 10 is small level detection, a deciding circuit 17 selects digital information of a basic waveform pulse 20 in the digital memory 13 by judging the length of the transmission line to be long. In the case of large level detection, it selects digital information equivalent to the distorted waveform pulse 21 of the digital memory 13 by judging the length of the transmission line to be short. Thus, the characteristic of a pseudo line can automatically be selected in correspondence with the length of the transmission line to be applied.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is used in digital transmission, and in particular, a signal transmission circuit that can avoid far-end crosstalk in a digital transmission system using a transmission medium in which transmission loss depends on frequency. Regarding.

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The present invention provides waveform information corresponding to a distorted waveform that occurs when a transmission pulse of a fundamental waveform passes through the transmission medium in a signal transmission circuit that transmits digital information via a transmission medium whose transmission loss characteristics are frequency dependent. , the level of the reproduced seismic signal is stored in a digital memory in advance at each predetermined distance interval of the transmission medium, and if the level is small, the waveform corresponding to the fundamental waveform pulse is retrieved from the digital memory. By reading the information, and if the level is large, reading the waveform information corresponding to the distorted waveform, converting it to the corresponding pulse waveform and sending it out, it automatically prevents deterioration in communication quality due to far-end crosstalk, and This makes it possible to downsize the device by making it into an LSI.

[Conventional technology]

In order to transmit digital information to a long distance via a transmission medium, the digital information is converted into a code suitable for the transmission medium and the transmission means, and then sent to the transmission medium as a pulse waveform to be transmitted to a remote destination point. It is customary to use

In addition, the transmission loss characteristics of transmission media often depend on frequency, and it is convenient for the receiving side to correct pulse waveform distortion when receiving the pulse waveform transmitted via the transmission medium. In many cases, an equalizer and an amplifier are required to equalize the waveform.

On the other hand, when transmitting digital information to multiple destination points with different transmission distances using a transmission medium that is prone to far-end crosstalk (FEχT), it is necessary to avoid deterioration of communication quality due to mutual interference of far-end crosstalk. In addition, it is desirable that the reception level from any point be the same, and a level adjustment means is usually employed to adjust the transmission level to the other party depending on the length of the transmission distance.

As an example of a transmission medium whose transmission loss characteristics are frequency-dependent and prone to far-end crosstalk, twisted cotton-like cables, which are commonly used for digital transmission, are used.
pair cable). In digital transmission systems using twisted cotton-like cables, in order to avoid deterioration in communication quality due to far-end crosstalk, sufficient care must be taken in designing the level diagram on the cable to avoid extreme level differences in reception levels. In particular, copper cables installed for general telephone lines are
It is common for multiple lines to be bundled together, making it easy for crosstalk to occur between lines.

In recent years, with the increase in the amount of information, digital transmission systems using copper cables for general telephone lines are becoming popular.

When applying digital transmission systems to copper cables for general telephone lines, the cables with uneven line lengths are often placed on the east side, and reception level differences with adjacent lines are likely to occur due to far-end crosstalk. Requires measures to avoid interference.

Conventionally, in order to avoid such reception level differences, a pseudo line is often inserted on the transmitting side to compensate for level differences so that the level diagram on the cable ensures that the reception level from any point is the same. . This pseudo line is composed of passive elements such as LCR so that its transmission loss characteristics approximate those of the transmission medium, and from the receiving side, the length of the transmission medium is equivalent to the pseudo line loss. It only looks like the signal has been extended, and has no effect on the equalizer on the receiving side.

FIG. 3 is a block diagram showing an example of a digital transmission system to which the present invention is applied.

The line termination units 1 and 2 share the cable bundle 3 and are able to communicate independently with the line termination device 5 of the communication partner. The line termination section 1 is extended further away than the cable bundle 3 via an extension cable 4.

In the cable bundle 3, since two cables are installed side by side, they interfere with each other. For example, the signal sent from the line termination section 2 is superimposed on the signal from the line termination section 1 as far-end crosstalk FEXT and reaches the line termination section 6.

If the extension cable 4 is long, the S/N ratio between the level at which the signal transmitted from the line termination section 1 reaches the line termination section 6 and the far-end crosstalk FEXT deteriorates, and the line termination section 6 The quality of the signal received by the device is degraded.

Communication is performed between the line termination section 1 and the line termination section 6, as well as between the line termination section 2 and the line termination section 7, as shown in FIG. 3, by a time-division bidirectional multiplex transmission method (ping-pong transmission method).

In the time-division bidirectional multiplex transmission system, if the line termination units 6 and 7 of the line termination unit 5 are configured to send out transmission bursts all at once, the line termination units 1 and 2 will be in the receiving state at the same time, and the Far end crosstalk FEX between cables
The line termination section 1 is disturbed by T2. However, if the output level of the line termination section 6 and the line termination section 7 are the same,
The disturbance due to far-end crosstalk FEXT2 is small.

On the other hand, the modes in which line termination units 1 and 2 send signals and line termination units 6 and 7 receive signals include far-end crosstalk FEXT,
Since the signal level arriving from the line termination section 1 is reduced by an amount corresponding to the transmission loss of the extension cable 4, the influence of the interference increases and the S/N ratio deteriorates.

[Problem that the invention seeks to solve]

In the signal transmission circuit using the level adjustment method using the conventional pseudo-line mentioned above, when trying to implement it into an LSI for the purpose of downsizing and economical data transmission equipment, it is difficult to implement the pseudo-line made of LCR etc. into an LSI. However, there are drawbacks that discourage designs aimed at miniaturization and economy.

Additionally, in order to save costs when installing communication lines, it is necessary to automate the selection of pseudo lines.
The method of having a plurality of pseudo lines each made of passive elements such as LCR and selecting a desired pseudo line from among them has the drawback of increasing the circuit scale.

An object of the present invention is to eliminate the above-mentioned drawbacks, thereby realizing automation of level adjustment when applying a time-division bidirectional multiplexing transmission method as a digital transmission method to copper cables laid for general telephone lines. It is an object of the present invention to provide a signal transmission circuit that can avoid interference due to far-end crosstalk and is suitable for LSI integration.

[Means for solving problems]

The present invention provides a signal transmission circuit equipped with a means for transmitting digital information via a transmission medium whose transmission loss characteristic is frequency dependent, in which a transmission pulse of a basic waveform is transmitted via the transmission medium of a predetermined length. a storage means that stores a plurality of pieces of wave information corresponding to a pulse waveform including waveform distortion that occurs when digital-to-analog conversion means for reading out stored waveform information and converting it into a corresponding pulse waveform;
a driving means for setting the pulse waveform outputted from the digital-to-analog converting means to a predetermined level and outputting it as a transmission pulse; an equalizer that outputs level detection information for each level; a switch that connects and disconnects the earthquake signal to the equalizer based on switching control information that separates a transmission section and a reception section; and the level detection information. The present invention is characterized by comprising: determining means for selecting predetermined waveform information according to the length of the passage distance of the transmission medium based on the magnitude of the level, and controlling reading out from the storage means.

[Effect]

The equalization means detects the level of the reproduced earthquake signal and outputs level detection information. Based on this level detection information, when the level of the seismic signal is high, that is, when the distance of the transmission medium is short, the determining means selects waveform information corresponding to a distorted waveform equivalent to the required pseudo-line insertion. When the level of the seismic signal is low, that is, when the distance of the transmission medium is long, the waveform information corresponding to the fundamental waveform is controlled to be read out.

Then, the digital-to-analog conversion means converts the selectively read waveform information into a corresponding pulse waveform under the control of the determination means and sends it to the transmission medium.

Therefore, it is possible to realize the same function as a pseudo-line with a circuit configuration suitable for LSI integration, and the characteristics of the pseudo-line can be automatically selected according to the distance of the applied transmission medium, thereby preventing deterioration in communication quality due to far-end crosstalk. It can be prevented.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG.
The figure is an explanatory diagram showing an example of the output pulse waveform, and FIG. 3 is a block diagram showing an example of the digital transmission system to which the present invention is applied.

According to FIG. 1, the signal transmission circuit of this embodiment is a signal transmission circuit equipped with means for transmitting digital information via a transmission medium whose transmission loss characteristic is frequency dependent. A plurality of pieces of waveform information corresponding to a distorted waveform generated when a transmission pulse of a basic waveform is transmitted through the transmission medium of a predetermined length are stored for each predetermined distance interval of the transmission medium. A digital memo 3 as a storage means, and a digital-to-analog converter as a digital-to-analog conversion means for reading out the waveform information stored in the digital memory 13 and converting it into a corresponding pulse waveform based on the logic level of the digital information to be transmitted. (DA converter) 1
6, a drive circuit 14 as a drive means that sets the pulse waveform output from the digital-to-analog converter 16 to a predetermined level and outputs it as a transmission pulse, and a drive circuit 14 that equalizes the seismic signal input manually through the connection terminal 8. an equalizer 10 that plays back the earthquake signal, detects the level of the earthquake signal, and outputs level detection information 12 for each predetermined level; and switching control information 9 that separates the transmission section and the reception section. A switch circuit 11 serves as a switch means for connecting and disconnecting the seismic signal to the flower vase 10 based on the above, and waveform information is predetermined based on the magnitude of the level of the level detection information 12 and according to the length of the transmission medium passage distance. (
I'm getting better.

Digital Memo January 3 includes multiple types of digital information that can be used to create a mountain-like distorted waveform pulse 21 containing the waveform distortion generated by the transmission line as shown in FIG. Built-in.

As for the digital information, a plurality of types of digital information are prepared as equivalent to the distorted waveform pulse 21 by predicting the distortion when the basic waveform pulse 20 passes through each transmission path length interval of a predetermined cable length.

Next, the operation of this embodiment will be explained.

The seismic signal inputted from the connection terminal 8 with the transmission line is handled by the switch circuit 1 which cuts off the human input of the seismic signal to the flower vase 10 by switching control information 9 that separates the transmission section and the reception section.
It is connected to the flower vase 10 via 1. In the flower vase 10, level detection information 12 is created at each predetermined step corresponding to the reception level.

The determination circuit 17 selects digital information stored in the digital memory 13 based on the level detection information 12, reproduces the waveform with the digital-to-analog converter 16, and sends it as a pulse waveform to the transmission line from the connection terminal 8 by the drive circuit 14. do.

The digital-to-analog converter 16 reproduces pulses whose waveforms have been converted based on the digital information in the digital memory 13 for each logic "1" of the transmission information 15.

When the level detection information 12 of the seismic signal detected by the flower vase 10 is a small level, the determination circuit 17 determines that the transmission path length is long and outputs the digital information of the basic waveform pulse 20 of the digital memo January 3. is selected, and if a large level is detected, it is determined that the transmission path length is short and the digital memory 13 is
digital information corresponding to the distorted wave pulse 21 is selected.

Next, a case where the signal sending circuit of this embodiment is applied to the digital transmission system shown in FIG. 3 will be described.

In FIG. 3, when the line termination sections 1 and 2 are configured as the signal sending circuit of the embodiment shown in FIG. 1, the reception level is also becomes smaller, and the basic waveform pulse 20 is output.

On the other hand, since the line terminal part 2 is connected to a cable with a short transmission path length, the reception level becomes high, and the distorted waveform pulse 2
Outputs 1.

When the output level of the line termination section 2 becomes smaller, the far end crosstalk F
The interference caused by EXT is also reduced, making it possible for line termination section 6 to receive the signal from line #end section 1 with good quality.

On the other hand, the distorted waveform pulse 21 at the line termination section 2 is equivalent to that outputted by inserting a pseudo-line, and can be substituted for the function of the pseudo-line, and has no effect on the reception at the line termination section 7. I don't receive it.

〔Effect of the invention〕

As explained above, according to the present invention, by digitally generating a pulse waveform that is deformed to the same degree as the waveform distortion obtained due to the transmission loss frequency dependence of the pseudo line when the pseudo line is inserted, a pseudo line is generated. Functions equivalent to railroad tracks
It is possible to provide a signal transmission circuit that can be realized with a circuit configuration suitable for SI, and can automatically select the characteristics of the pseudo line according to the length of the transmission path to be applied, which is highly effective.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 2 is an explanatory diagram showing an example of the output pulse waveform. FIG. 3 is a block diagram showing an example of a digital transmission system to which the present invention is applied. 1.2.6.7...Line termination section, 3...Cable east, 4...Extension cable nope 5...Line termination device, 8.
...Connection terminal, 9...Switching control information, 1o...Vase, etc., 11...Switch circuit, 12...Level detection information, 13...Digital memory, 14...Drive circuit, 15 ... Transmission information, 16... Digital analog converter (DA converter), 17... Judgment circuit, 20...
- Basic waveform pulse, 21...distorted waveform pulse.

Claims (1)

[Claims] 1. In a signal transmission circuit equipped with means for transmitting digital information via a transmission medium whose transmission loss characteristics are frequency dependent, a transmission pulse of a basic waveform is transmitted to the transmission medium of a predetermined length. storage means for storing a plurality of pieces of waveform information corresponding to pulse waveforms including waveform distortion that occur when transmitted via the transmission medium for each predetermined distance interval of the transmission medium; Digital-to-analog conversion means for reading waveform information stored in the storage means and converting it into a corresponding pulse waveform; and driving means for setting the pulse waveform output from the digital-to-analog conversion means to a predetermined level and outputting it as a transmission pulse. , equalization means that equalizes the earthquake signal to reproduce the received signal, detects the level of the received signal, and outputs level detection information for each predetermined level, and switching control information that separates the transmission section and the reception section. switching means for connecting and disconnecting the received signal to the equalizing means based on the level detection information; and determining means for controlling reading from the storage means.