JPH02143696A - Non-linear emphasis circuit and non-linear de-emphasis circuit - Google Patents

Abstract

PURPOSE:To prevent generation of distortion in a signal waveform after nonlinear de-emphasis by combining a circuit adding an output of an LPF and an input signal and a circuit subtracting an output of the LPF from the input signal. CONSTITUTION:The input signal is fed to a limiter 3 via an HPF 2, fed to an LPF 4 after amplitude limit, a harmonic component generated in the limiter 3 is attenuated and the result is fed to an adder 5 and the input signal and the output of the LPF 4 are added and outputted. On the other hand, the output signal is returned to an HPF 11 in a de-emphasis circuit and fed to an LPF 9 via a limiter 10 and the harmonic component generated in the limiter 10 is attenuated and then fed to a substractor 8 and the output of the LPF 9 is subtracted from the input signal and the result is outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a nonlinear emphasis circuit and a nonlinear deemphasis circuit used in video tape recorders (hereinafter abbreviated as VTR), communication devices, and the like.

(Conventional technique vfI) As a means of improving the S/N ratio of the transmission line.

There is a method that uses a combination of a non-emphasis circuit that changes the amount of emphasis according to the amplitude of the signal and a non-linear de-emphasis circuit that has the characteristics of a non-linear emphasis circuit, and this method has been widely used in recent years.

A conventional non-linear emphasis circuit and a conventional non-linear de-emphasis circuit will be explained below.

FIG. 3(a) is a block diagram of a conventional nonlinear emphasis circuit, and FIG. 3(b) is a block diagram of the same nonlinear deemphasis circuit. In the figure, a signal input from an input terminal 101 is transmitted through a high-pass filter 1.
02 emphasizes high frequency components, limiter 1.0
Sent to 3. The limiter 103 limits the amplitude of the output signal of the high-pass filter 102 and sends the result to the adder 104. The adder 104 adds the signal input from the input terminal and the output signal of the limiter 103, and sends the output signal to the output terminal tOS.

Therefore, in a nonlinear emphasis circuit,
When the amplitude of the signal input from the input terminal is large, the amplitude is limited by the limiter 103, so that the effect of emphasizing high frequency components by the high-pass filter 102 is reduced. Further, when the amplitude of the signal input from the input terminal is small, the amplitude is not limited by the limiter 103, so that the effect of emphasizing high frequency components by the high-pass filter 102 is not reduced.

In the conventional nonlinear emphasis circuit configured as described above, a signal with an emphasis amount changed according to the amplitude of the signal input from the input terminal 101 can be output from the output terminal 105. That is, the smaller the amplitude of the signal input from the input terminal, the stronger the effect of emphasizing the high frequency components of the input signal.

FIG. 4 shows frequency characteristics of the nonlinear emphasis circuit when the input level is large and small.

Next, a block diagram of a conventional nonlinear de-emphasis circuit will be described.

In FIG. 3(b), the signal output from the output terminal 106 is returned to the high-pass filter 107, the high frequency components are emphasized, and the signal is sent to the limiter 108. The limiter 108 limits the amplitude of the output signal of the high-pass filter 107 and sends the result to the subtracter 109. The subtracter 109 subtracts the output signal of the limiter 108 from the signal input from the input terminal 110 and sends the output signal to the output terminal 106.

In the conventional non-linear de-emphasis circuit configured as described above, for the same reason as the non-linear emphasis circuit, a signal with a de-emphasis amount changed according to the amplitude of the signal input from the input terminal 110 is output to the output terminal. It can be output from 106.

Next, the reason why the SN ratio of the transmission path is improved by combining a nonlinear emphasis circuit and a nonlinear deemphasis circuit whose characteristics are complementary to those of the nonlinear emphasis circuit will be explained.

Figure 5 shows a case where the non-linear emphasis circuit shown in Figure 3 and a non-linear de-emphasis circuit, which has characteristics complementary to those of the non-linear emphasis circuit, are actually used in combination to improve the S/N ratio of the transmission line. It is a block diagram. By using the high-pass filter 102, the high-pass filter 107, and the limiter 103 and limiter 108 shown in the figure, which have exactly the same characteristics, a non-linear de-emphasis circuit having complementary characteristics to the non-linear emphasis circuit can be realized.

A signal input from the terminal 101 has high frequency components emphasized by the non-linear emphasis circuit according to the amplitude of the input signal, is output from the output terminal, and is sent to the transmission line 111. The signal passing through the transmission line 111 is sent to the input terminal 11.
0, is returned to its original characteristic by a nonlinear de-emphasis circuit, and is output from an output terminal 106.

6(a), (b)-(c)-(d) are frequency characteristic diagrams at the respective terminals 101, 105, 106, and 110 in FIG. 5 when the level of the input signal is fixed. As shown in Figure 6(a), when a signal with flat frequency characteristics is applied to the 5 input terminals, the high frequency components are emphasized by the non-linear emphasis circuit, so
The frequency characteristic diagram at the terminal 105 is as shown in FIG. 6(b). Therefore, in the transmission line, as shown in Fig. 6 (
Even when noise exhibiting the noise distribution in the 0 part of c) occurs, the nonlinear de-emphasis circuit, which has characteristics complementary to those of the non-linear emphasis circuit, reduces the high frequency components emphasized by the non-linear emphasis circuit and restores the original sound. In order to return to the flat characteristic of , noise is also reduced at the same time. The 0 part in FIG. 6(d) indicates the amount of noise reduction. Therefore, the more high-frequency components are emphasized by the nonlinear emphasis circuit, the more the noise reduction effect by the nonlinear de-emphasis increases, and the SN
ratio is improved.

Next, in the nonlinear emphasis circuit.

The effect of changing the amount of emphasis and outputting it according to the amplitude of the signal input from the input terminal will be described.

Normally, when a high frequency component of a signal is emphasized by an emphasis circuit, a peak appears in the waveform after the emphasis. FIG. 7 shows a waveform after emphasis when a step input signal is input to the emphasis circuit. The waveform peak value is shown in part (■) of FIG.

Normally, in linear emphasis, if the amount of emphasis is set to a large value in hopes of improving the signal-to-noise ratio, the peak value of the waveform increases, causing various problems when the signal passes through the transmission path.

It is thought that an input signal with a large amplitude has a better signal-to-noise ratio than an input signal with a small amplitude. Therefore, in a nonlinear emphasis circuit, when the amplitude of the input signal is large, the amount of emphasis is increased more than when the amplitude of the input signal is small. This prevents the peak value of the waveform from increasing, thereby preventing various adverse effects associated with an increase in the peak value of the waveform.

(Problems to be Solved by the Invention) In the conventional configuration described above, when improving the S/N ratio of a transmission line by combining a non-linear emphasis circuit and a non-linear de-emphasis circuit, the transmission line is configured as a band-limited system. In this case, the harmonic components of the signal generated by the limiter of the nonlinear emphasis circuit are no longer transmitted, resulting in distortion of the signal waveform after nonlinear deemphasis.

In other words, if the transmission path is a system with unrestricted bandwidth, harmonics generated in the nonlinear emphasis circuit can be completely canceled by a nonlinear deemphasis circuit whose characteristics are complementary to those of the nonlinear emphasis circuit. However, if the transmission path is a band-limited system, the harmonics generated in the nonlinear emphasis circuit will be attenuated in the transmission path, so the characteristics of the nonlinear emphasis circuit and the nonlinear deemphasis circuit with complementary characteristics will be opposite. As a result, harmonics are generated, resulting in distortion of the signal waveform.

An object of the present invention is to provide a non-linear emphasis circuit which eliminates the drawbacks of the conventional technology and which does not cause distortion in the signal waveform after non-linear de-emphasis even when the transmission path is configured with a band-limited system. An object of the present invention is to provide a non-linear de-emphasis circuit.

(Means for Solving the Problems) A nonlinear emphasis circuit of the present invention includes a high-pass filter that passes high frequency components of an input signal;
A configuration including a limiter that limits the amplitude of the output signal of this high-pass filter, a low-pass filter that passes the low frequency component of the output signal of this limiter, and an adder that adds the output signal of this low-pass filter and the input signal. 1. The nonlinear de-emphasis circuit of the present invention includes a high-pass filter that passes high-frequency components of an output signal, a limiter that limits the amplitude of the output signal of this high-pass filter, and a low-frequency component of the output signal of this limiter. It has a low-pass filter that passes frequency components and a subtracter that subtracts the output signal of the low-pass filter from the input signal.

(Function) According to the present invention, when a nonlinear emphasis circuit and a nonlinear deemphasis circuit are used in combination to improve the S/N ratio of a transmission line, the transmission line is configured in a band-limited system. Even if
It is possible to prevent distortion from occurring in the signal waveform after non-linear de-emphasis.

(Example) An example of the present invention will be described based on FIGS. 1 and 2.

FIG. 1(a) is a block diagram of a non-linear emphasis circuit of the present invention, and FIG. 1(b) is a block diagram of a non-linear de-emphasis circuit of the present invention.

First, FIG. 1(a) will be explained. A signal input from an input terminal 1 is sent to a limiter 3 after its high frequency components are emphasized by a high-pass filter 2 . Limiter 3
, the amplitude of the output signal of the high-pass filter 2 is limited, and the result is sent to the low-pass filter 4. The low-pass filter 4 attenuates the harmonic components generated in the limiter 3 and sends the result to the adder 5.

The adder 5 adds the signal input from the input terminal 1 and the output signal of the low-pass filter 4, and sends the output signal to the output terminal 6.

The operation of the non-linear emphasis circuit configured as described above is similar to that of a conventional non-linear emphasis circuit, except for the operation of attenuating harmonics generated by the limiter 3 with the low-pass filter 4. That is, input terminal 1
It is possible to output from the output terminal 6 an output signal in which the amount of emphasis is changed according to the amplitude of the input signal.

Next, a block diagram of a non-linear de-emphasis circuit according to the present invention will be explained.

The signal output from the output terminal 12 is returned to the high-pass filter 11, where the high frequency components are emphasized and the signal is sent to the limiter 1.
Sent to 0. The limiter 10 includes a high-pass filter 1
1 and the result is sent to a low-pass filter 9. The low-pass filter 9 attenuates the harmonic components generated by the limiter 10,
The result is sent to subtracter 8. The subtracter 8 subtracts the output signal of the low-pass filter 9 from the signal input from the input terminal 7 and sends the output signal to the output terminal 12.

The operation of the non-linear de-emphasis circuit configured as described above is the same as that of a conventional non-linear de-emphasis circuit, except for the operation of attenuating the high frequency generated by the limiter 10 with the low-pass filter 9. That is,
An output signal having a de-emphasis amount changed according to the amplitude of the signal inputted from the input terminal 7 can be outputted from the output terminal 12.

FIG. 2 is a block diagram of the case where the S/N ratio of the transmission path is improved using the nonlinear emphasis circuit and nonlinear deemphasis circuit configured as shown in FIG. 1. High pass filter 2 and high pass filter 1 shown in the figure
1. Limiter 3 and Limiter 10. By using low-pass filters 4 and 9 that have exactly the same characteristics, a non-linear de-emphasis circuit having characteristics complementary to those of the non-linear emphasis circuit and the non-linear emphasis circuit is realized.

If you use a non-linear emphasis circuit and a non-linear de-emphasis circuit configured as above.

The reason why distortion does not occur in the signal waveform after non-linear de-emphasis will be explained even when the transmission line shown in FIG. 2 is constructed of a band-limited system.

In other words, in the conventional example, even in the limiter of the nonlinear emphasis circuit, the generated harmonics are attenuated in the transmission path, so in the nonlinear deemphasis circuit, which has characteristics complementary to those of the nonlinear emphasis circuit, the harmonics are attenuated. This resulted in waveform distortion.

Therefore, according to this embodiment of the present invention, in order to prevent harmonics that would be attenuated in the transmission path from occurring in the nonlinear emphasis circuit or the nonlinear deemphasis circuit, the low-pass filter 4, By providing 9 on the output side of the limiters 3 and 10, it is possible to prevent distortion from occurring in the signal waveform after nonlinear de-emphasis even if the transmission line is configured with a band-limited system. be.

(Effects of the Invention) According to the present invention, when improving the S'N ratio of a transmission line by using a combination of a non-linear emphasis circuit and a non-linear de-emphasis circuit, the band of the transmission line is limited. It is possible to realize an excellent non-linear emphasis circuit and non-linear de-emphasis circuit that can prevent distortion from occurring in the signal waveform after non-linear de-emphasis, even when the system is configured with a non-linear de-emphasis system.
Its practical effects are great.

[Brief explanation of the drawing]

FIG. 1(a) is a block diagram of a nonlinear emphasis circuit according to an embodiment of the present invention, FIG. 1(b) is a block diagram of the same nonlinear de-emphasis circuit, and FIG.
Figure 3(a) is a block diagram of a conventional non-linear emphasis circuit, and Figure 3(b) is a block diagram of the conventional non-linear emphasis circuit. A block diagram of the emphasis circuit. Figure 4 is a frequency characteristic diagram of the nonlinear emphasis circuit when the input level is high and low. Figure 5 is a diagram of Figures 3 (a) and (b).
A block diagram when the S/N ratio of a transmission line is improved using the circuit shown in Figure 6 is a frequency characteristic diagram when the input signal level is fixed, and Figure 7 is a diagram showing a step input signal input to the emphasis circuit. FIG. 1.7...Input terminal, 2.11...High pass filter, 3,10...Limiter, 4,9...Low pass filter, 5...Adder, 6゜12...
- Output terminal, 8... Subtractor, 13... Transmission line. Patent applicant: Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] (1) a high-pass filter that passes high-frequency components of an input signal; a limiter that limits the amplitude of the output signal of the high-pass filter; and a low-pass filter that passes low-frequency components of the output signal of the limiter; A non-linear emphasis circuit comprising an adder for adding an output signal of the low-pass filter and an input signal, and outputting an amount of emphasis changed according to the amplitude of the input signal. (2) a high-pass filter that passes high-frequency components of the output signal; a limiter that limits the amplitude of the output signal of the high-pass filter; and a low-pass filter that passes the low-frequency components of the output signal of the limiter; A non-linear de-emphasis circuit comprising a subtracter that subtracts the output signal of the low-pass filter from the input signal, and outputting a de-emphasis amount that is changed according to the amplitude of the input signal. (3) The non-linear emphasis circuit and the non-linear de-emphasis circuit according to (1) and (2), wherein the output signal of the non-linear emphasis circuit is used as an input signal of a transmission line, and the output signal of the transmission line is used as an input signal of the non-linear de-emphasis circuit. Emphasis circuit.