JPS589415A - Automatic equalizer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic equalizer that compensates for waveform distortion due to line frequency characteristics.

Generally, the line frequency characteristics of a communication line are flat in a relatively low frequency range and sloped in a relatively high frequency range. Therefore, when transmitting a digital signal having a certain frequency distribution via a communication line, it is necessary to compensate for the waveform distortion due to the line frequency characteristics described above.

Conventionally, automatic equalizers have been known to compensate for such external waveform distortion. This automatic equalizer focuses on the fact that the line loss due to communication lines (the amount of operational attenuation at the Nyquist frequency) is approximately proportional to the amount of change in the peak value of the transmitted signal. AGC(
automatic gain control). In other words, the peak value is controlled to be constant.

However, in the conventional type described above, since a single type of variable equalization circuit is used to equalize the flat loss part and the slope loss part of the line frequency characteristic, it cannot be applied to various communication lines. There is a problem in that it is not possible to accurately represent the gain characteristic that is opposite to the frequency characteristic, and there are many equalization residuals. In other words, lines used in communication lines have various wire diameters, and as a result, the rate of change in the flat loss portion and the rate of change in the slope loss portion differ, and the slope of the slope loss portion varies depending on the line length of the communication line. This is because they are different.

The purpose of the present invention is to realize a gain characteristic as close as possible to the gain characteristic opposite to the line frequency characteristic', based on the concept of using a variable equalization circuit with three types of different gain characteristics, and to achieve equal gain characteristics throughout the transmission band. The purpose of this invention is to solve the problems of the above-mentioned conventional type by reducing the possibility of oxidation.

Hereinafter, the present invention will be explained in comparison with a conventional type with reference to the drawings.

FIG. 1(4) to FIG. 1(C) are graphs showing line frequency characteristics. Figure 1 (4) to Figure 1 (0), the horizontal axis shows frequency and the vertical axis shows loss. For example, as the line length increases, the curve AI,
The loss increases in the order of A2*As.

Furthermore, when the flat loss portion and the slope loss portion in the case of Figure 1 are shown separately, Figure 1(B) and 1
It will be as shown in the figure (Q. However, the straight line Ble B
l #B3 (Figure 1 (B)) is #JA1-' on each side.
l # A3 (Fig. 1 (A)), and the curve C1°C2a c3 (Fig. 1 (C)) corresponds to each curve AI
+ A, aAs (to Figure 1)).

What should be noted here is that when the line loss becomes large, the slope of the slope loss portion becomes large and the curvature also becomes large, as shown in FIG. 1(C). In other words, the slope (average) of curve C3 is the slope (average) of curve C1
average), and the curvature of curve C3 is larger than the curvature of curve C1. The digital signal is shown in Figure 1 (A
) When transmitted via a communication line having line frequency characteristics shown in ), waveform distortion occurs on the receiving side.

In order to compensate for such waveform distortion, it is sufficient to realize a gain characteristic opposite to the loss characteristic shown in FIG. 1(A) on the receiving side. An automatic equalizer is a means for this purpose.

FIG. 2 is a block circuit diagram of a conventional automatic equalizer. In FIG. 2, a digital signal "a#" transmitted via a communication line is supplied to a variable equalization circuit 1, and an output signal 1b of the variable equalization circuit 1 is supplied to a peak detector 2. In this case, the peak voltage detected by the peak detector 2 is replaced by a resistance change of the variable resistor 14 (not shown in FIG. 2, but shown in FIG. 3) of the variable equalization circuit 1. That is, it utilizes the fact that line loss due to a communication line, t't, is proportional to the amount of change in the peak value of the transmitted signal.

FIG. 3 is a circuit diagram of the variable equalization circuit 1 of FIG. 2. Third
In the figure, a CR circuit is provided which is composed of resistors 11 and 12, a capacitor 13, and a variable resistor 14.
The output of the circuit is connected to the non-inverting input of amplifier M.

The characteristics of this variable equalization circuit 1 are shown in Figure 4. Fourth
In the figure, for ease of understanding, a line A'I H1% g showing the loss characteristic opposite to the gain characteristic of the variable equalizer circuit 1 is shown.
A'3 is shown. That is, the line A'l*A
/, l k's, the slope of the slope loss portion is approximated by a constant value, for example, 6 dBloCT. Therefore, the line loss is curve A1.

As shown in A2pA3, when both the slope and the curvature change, the equalization shown in the shaded area increases. That is, the application range of the automatic equalizer shown in FIG. 2 using the variable equalization circuit 1 shown in FIG. 3 is limited to communication lines having a short line length and a constant wire diameter.

In contrast, in the present invention, three types of variable equalization circuits are used to equalize the flat loss portion of the line frequency characteristic, the slope (average) of the slope loss portion, and the curvature of the slope loss portion.

FIGS. 5(A) to 5) are gain characteristic diagrams for explaining the present invention in detail. According to the present invention, FIG.
, FIG. 5(B), and FIG. 5(C) are approximated as a gain characteristic that compensates for the loss characteristic as shown in FIG. 1(4). That is, the fifth
Figure (A) shows the gain characteristic that compensates for the flat loss characteristic, and Figure 5 (
B) is a gain of 4! that compensates for the slope of the slope loss characteristic. Figure 5 (C) shows the curvature of the slope loss characteristic. This is an advantageous characteristic. The gain characteristic in FIG. 5 (FIG. 50) is shown to make it easier to understand that the gain characteristic of Q compensates for the curvature of the slope loss portion. i.e. in Figure 5)
In this case, the flat portion is ignored from the gain characteristics shown in FIG. 5(C).

FIG. 6 is a block circuit diagram of an automatic equalizer as an embodiment of the present invention. In FIG. 6, elements that are the same as those in FIG. 2 are given the same reference numerals.

That is, in FIG. 6, three anisotropic variable equalization circuits 3, 4.5 are provided, and these are commonly controlled by the peak detector 2. In this case, variable equalization circuit 3
, 4゜5 are Fig. 5 (A), Fig. 5 middle) and Fig. 5, respectively.
(Has a gain characteristic of Q.Hereinafter, variable equalization circuits 3 and 4
5 will be explained in detail.

FIG. 7(4) is a circuit diagram of the variable equalization circuit 3 of FIG. In FIG. 7(4), the resistors 31 and 32 are configured in an inverted shape, and the variable resistor 33 is connected in parallel to the resistor 2. Furthermore, the connection point of the resistors 31, 32 is connected to the normal input of the amplifier AMP1. The peak voltage detected by the peak detector 2 is applied to the variable resistor 33.
In this case, when the peak voltage is large (corresponding to when the line length is short), the value of the variable resistor 33 is small, and conversely, when the peak voltage is small (corresponding to when the line length is long),
The value of the variable resistor 33 is set to a large value. In this way, as the value of the variable resistor 33 increases, the gain increases as shown in the direction of the arrow in FIG. 5(A). That is, the flat loss portion shown in ) in FIG. 1 can be equalized.

FIG. 7(B) is a circuit diagram of the automatic equalization circuit 4 of FIG. The circuit of FIG. 7B is similar to the circuit of FIG.

In FIG. 7(B), resistors 41 and 42, capacitor 4
3. A 908 circuit is provided by the variable resistor 44. In this case, when the peak voltage decreases and the value of the variable resistor 44 increases, the gain increases as shown in the direction of the arrow in FIG. 5(B). However, as shown in FIG. 5), the slope of the gain changing portion is constant. That is, the slope of the slope loss portion shown in FIG. 1 (C) can be equalized.

FIG. 7 (Q is a circuit diagram of the variable equalization circuit 50 in FIG. 6).

In FIG. 7(C), a coil 51 and a resistor 52 are connected in series, and a parallel circuit of a capacitor 53 and a variable resistor 54 is connected in series. The circuit constructed in this way is connected to the inverting input of amplifier AMP2. In this case, when the value of the variable resistor 54 changes, the coil 51 . Resistance 52. The Q of the tuning characteristic of the capacitor 53 changes. That is, as shown in FIG. 5(C), when the peak voltage decreases and the value of the variable resistor 54 increases, the Q value increases.

In other words, the curvature of the gain characteristic exerts a large influence. In this way, the variable equalization circuit 4 having the gain characteristic shown in FIG. 5(B) and the variable equalization circuit 5 having the gain characteristic shown in FIG. It is possible to equalize

As shown in FIG. 5(C), the variable equalizer circuit 5 has a steep attenuation characteristic at frequencies higher than the frequency f, so it also acts as a filter to remove out-of-band noise. .

As explained above, according to the present invention, a gain characteristic close to a gain characteristic opposite to the line frequency characteristic can be realized.
Therefore, equalization can be reduced, which is useful for solving the problems of the conventional type described above.

[Brief explanation of drawings]

Figures 1 (4) to 1 (C) are graphs showing line frequency characteristics, Figure 2 is a block diagram of a conventional automatic equalizer, and Figure 3 is a circuit diagram of the variable equalizer circuit 10 in Figure 2. , Figure 4 is a characteristic diagram of the variable equalizer circuit 1 in Figure 2, Figure 5 (4) to Figure 5 O')
) is a gain characteristic diagram for detailed explanation of the present invention, FIG. 6 is a block diagram of an automatic equalizer as an embodiment of the present invention,
7(A) to 7(C) are circuit diagrams of the variable equalization circuits 3 and 4.5 of FIG. 6, respectively. 1: variable equalization circuit, 2: peak detector, 3: first variable equalization circuit, 4: second variable equalization circuit, 5: third variable equalization circuit. Category 1 Loss (A) 1 (aB Loss (B) Loss (dB) (C) Loss (dB Frequency

Claims (1)

[Claims] 1. In an automatic equalizer that compensates for waveform distortion due to line frequency characteristics, a first variable equalization circuit that equalizes the flat loss portion of the line frequency characteristic and compensates for the slope of the slope loss portion of the line frequency characteristic. a second variable equalization circuit that compensates for the curvature of the slope loss portion of the line frequency characteristic; and a peak detector that detects the peak value of the output signal of the automatic equalizer. according to the output signal of the peak detector. An automatic equalizer characterized in that the second and third variable equalizer circuits are automatically gain controlled.