JPH05315998A - Method for reducing distortion on transmission line - Google Patents

Abstract

PURPOSE:To reduce distortion generated on a transmission line and to execute correct reception at the time of transmitting digital data. CONSTITUTION:A predistortion circuit 5 is provided at the prestage of a driver 6 for converting transmission data 4 in a transmitting equipment 01 to a transmitting signal 1S. The circuit 5 accelerates the transmission time of a low frequency signal component in the data 4 than that of a high frequency signal component only by a delay time difference obtained by subtracting the delay time of the high frequency component from that of the low frequency component in the signal 1S which is generated on the transmission line 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission line distortion reducing method for performing correct reception by reducing transmission line distortion in pulse code communication (baseband transmission) or data communication using modulation / demodulation. In the following figures, the same reference numerals indicate the same or corresponding parts.

[0002]

2. Description of the Related Art Conventionally, there are roughly two types of techniques for reducing transmission line distortion and performing correct data communication.
One method is to reduce distortion on the receiving side as shown in FIG. In the figure, 01 is a transmitting circuit, 02 is a receiving circuit, 1 is a transmission line connecting the transmitting circuit 01 and the receiving circuit 02,
Reference numeral 2 is an equalizer provided in the receiving circuit 02, and 3 is a demodulator.

That is, the receiving circuit 02 side is provided with an equalizer 2 as a filter having characteristics opposite to those of the transmission line 1 through which a signal is transmitted, and a received signal from the transmission line is transmitted by passing through the filter 2. This is a method of removing the path distortion and trying to demodulate correctly through the demodulator 3. The other method is to reduce distortion by changing the transmission waveform in advance on the transmission side. This is the pre-distortion technology with 10BASE-T.

FIG. 7 is a waveform diagram for explaining this predistortion technique. In FIG. 7, the dotted line waveform is the transmission / reception waveform when no predistortion is performed, and the solid line is the transmission / reception waveform when predistortion is performed. That is, in the predistorted solid line waveform, the zerox time points of the transmission waveform and the reception waveform coincide with each other.

[0005]

However, these methods have problems. That is, in the case of the former method, it is impossible to first create an equalizer whose characteristics are completely opposite to those of the transmission line.Moreover, the input impedance of the equalizer is kept high and the signal is not attenuated by the equalizer. However, it is necessary to provide a buffer at the first stage of the receiving device or to configure an equalizer using active elements, which has a drawback that the circuit configuration becomes complicated in any case.

In the latter method, it is necessary to create a step (intermediate level) in the transmission waveform. For that purpose, there are a method of preparing two kinds of voltage to be supplied to the transmission driver to form the step, or a method of forming the step using resistance voltage division as a usual method, but this involves transmission loss. There is a problem. Therefore, it is an object of the present invention to provide a method for reducing transmission line distortion, which eliminates the above-mentioned drawbacks, has a simple circuit system, has a small transmission loss, and can accurately remove transmission line distortion.

[0007]

In order to solve the above-mentioned problems, a transmission line distortion reducing method according to the present invention uses a transmission line (a transmission line through which a signal is transmitted when transmitting digital data (such as transmission data 4)). 1)) and the group delay time difference obtained by subtracting the group delay time of the high frequency component from the group delay time of the low frequency component in the signal (predistortion circuit 5, The low frequency signal component in the transmission signal (such as 1S) is transmitted earlier than the high frequency component (via the modulation circuit with predistortion 15 or the like).

[0008]

On the transmitting side, the low frequency component in the transmission signal is compared with the high frequency component by the amount of jitter due to the transmission path (group delay time difference = low frequency group delay time−high frequency group delay time).
The output is performed as early as possible so that the transmission line distortion on the receiving side via the transmission line becomes zero.

[0009]

Embodiments of the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram showing a configuration of a main part as a first embodiment of the present invention, FIG. 2 is a waveform diagram of each part in FIG. 1, and FIG. 3 is a waveform diagram of each part when the present invention is not applied in FIG. is there. 2 and 3, the transmission signal 1 is actually
Although the received signal 1R should be delayed from S, the position of the received signal 1R is shifted to the front for easy understanding.

FIG. 1 shows an example in which the present invention is implemented in the case of baseband transmission with Manchester code. In the figure, reference numeral 5 denotes a predistortion circuit which is the main subject of the present invention and which is newly installed in the transmitter 01. In addition, 6 is a driver for inputting the transmission signal 1R to the transmission line 1 in the transmission device 01,
Reference numeral 8 denotes a reception signal 1R from the transmission line 1 in the reception device 02.
It is a receiver that takes out and outputs the detection signal 9.

Next, the operation of FIG. 1 will be described with reference to FIG. 2. In the transmitter 01, the transmission data 4 having the waveform shown in FIG.
Through the predistortion circuit 5 and sent to the transmission driver 6 as a predistorted signal (predistortion signal) 5a having the waveform shown in FIG. Then, the transmission driver 6 sends out the transmission signal 1S having the waveform shown in FIG. This transmission signal 1S becomes a reception signal 1R having a waveform as shown in FIG. 2 via the transmission line 1, and this reception signal 1R is input to the receiver 8 of the receiving apparatus 02 and the reception signal 1R has the waveform shown in FIG. The detection signal 9 is output. This detection signal 9 is further demodulated by means not shown to obtain received data.

Next, the predistortion circuit 5 of FIG. 1 will be described. 3 is a transmission signal 1 in the case where the same transmission data 4 as in FIG. 2 is transmitted without passing through the predistortion circuit 5 (that is, without suppressing jitter) in FIG.
The waveforms of S, the received signal 1R, and the detection signal 9 are shown, and the waveform of the received signal 1R is distorted, so that the detection signal 9 has a jitter Tj. On the other hand, FIG. 2 is a diagram showing the relationship between the predistortion signal 5a, the transmission signal 1S, the reception signal 1R and the detection signal 9 when passing through the predistortion circuit 5 according to the present invention. That is, the predistortion circuit 5 operates so that the low frequency component is output earlier than the high frequency component by the predicted jitter amount Tj of the transmission line 1 based on the input transmission data 4. The signal thus produced is the predistortion signal 5a in FIG. Since it operates in this way, the received signal 1R passing through the transmission line 1 and the detection signal 9 detected through the receiver 8 become a correct target signal waveform with distortion removed.

As can be seen from the pre-distortion signal 5a, when the next low frequency signal comes after the high frequency signal, the first half cycle of the low frequency signal becomes slightly higher in frequency than the normal frequency of the low frequency signal. On the contrary, when the next high frequency signal comes after the low frequency signal, the first half cycle of the high frequency signal is slightly lower in frequency than the normal frequency of the high frequency signal.

FIG. 4 is a block diagram showing the configuration of the essential parts of the second embodiment of the present invention. Reference numeral 15 is a modulation circuit with predistortion, which is the main subject of the present invention, provided in the transmitter 01. This is a demodulation circuit provided in the receiving device 02. FIG. 5 is a waveform diagram of each part for explaining the operation of FIG. In FIG. 5, the received signal 1R is actually changed from the transmitted signal 1S.
Should be delayed, and the received signal 1R due to attenuation
The crest value should be low, but in order to make it easier to understand, the positional relationship is shifted and the crest value is made the same.

FIG. 4 shows an example in which the present invention is carried out when data is transmitted using modulation (phase continuous FSK). In the transmission device 01, the transmission data 4 having the waveform shown in FIG. 5 is transmitted to the transmission line 1 as the transmission signal 1S having the waveform shown in FIG. 5 through the modulation circuit 15 with predistortion according to the present invention. Then, the transmission signal 1S enters the receiving device 02 via the transmission path 1 and obtains the detection signal 9 via the demodulation circuit 18.

Next, the predistortion method in the case of the second embodiment will be described. FIG. 5 shows the relationship between the waveforms of the transmission signal 1S and the reception signal 1R when passing through the modulation circuit 15 with predistortion.
The modulation circuit 15 with predistortion operates so as to output the low frequency component earlier than the high frequency component by the predicted jitter amount Tj of the transmission line based on the input transmission data 4. Because it works that way,
The received signal 1R passing through the transmission line 1 has a correct target modulation waveform with distortion removed. As can be seen from the waveform of the transmission signal 1R, when the low frequency signal comes next to the high frequency signal, the first half cycle (fL2) of the low frequency signal has a frequency slightly smaller than the normal frequency (fL1) of the low frequency signal. Get higher On the contrary, when the next high frequency signal comes after the low frequency signal, the first half period (fH
In 2), the frequency is slightly lower than the normal frequency (fH1) of the high frequency signal. In other words, there is a relationship such as fH1> fH2 fL2> fL1 ─────────── (1).

[0017]

According to the present invention, the group delay difference (jitter) between the high frequency component and the low frequency component generated in the transmission line can be predicted from the transmission line length or the material and shape of the transmission line. Since the predicted group delay difference occurring on the transmission path is added in reverse, the reception signal passing through the transmission path is accurately removed of the transmission path distortion, and the target correct signal duty can be obtained. It becomes easier to perform correct reception.

[Brief description of drawings]

FIG. 1 is a block diagram showing a main part configuration as a first embodiment of the present invention.

FIG. 2 is a waveform diagram of signals at various parts in FIG.

FIG. 3 is a waveform diagram of signals at various parts in FIG. 1 when the present invention is not applied.

FIG. 4 is a block diagram showing a main configuration of a second embodiment of the present invention.

FIG. 5 is a waveform diagram of signals at various parts in FIG.

FIG. 6 is a block diagram for explaining an example of a conventional transmission distortion reduction method.

FIG. 7 is a waveform diagram for explaining another example of the conventional transmission distortion reduction method.

[Explanation of symbols]

 01 transmitter 02 receiver 1 transmission path 1S transmission signal 1R reception signal 4 transmission data 5 predistortion circuit 5a predistortion signal 6 driver 8 receiver 9 detection signal 15 modulation circuit with predistortion 18 demodulation circuit

Claims (1)

[Claims] 1. At the time of digital data transmission, the transmitter side is equal to a group delay time difference which is generated on a transmission path through which a signal is transmitted and which is obtained by subtracting a group delay time of a high frequency component from a group delay time of a low frequency component in the signal. In the method of reducing transmission line distortion, the low frequency signal component in the transmission signal is transmitted earlier than the high frequency component.