JPH0627023Y2 - Noise reduction circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a noise reduction circuit in a video tape recorder (VTR).

(B) Conventional technology In a home VTR, a noise cancel circuit is provided in a luminance signal processing system during reproduction for the purpose of visually reducing the influence of noise. FIG. 3 shows an example of a conventionally used circuit (high-pass filter type noise cancel circuit).

In the figure, (1) is the input terminal for the reproduced FM signal, and (2) is the FM
A demodulator, (3) is a de-emphasis circuit, (4) is a noise canceling circuit, and (5) is an output terminal of a luminance signal. Noise cancel circuit (4) is a high pass filter (6), limiter
(7) and a subtractor (8) are provided.

This noise cancellation circuit (4) is "home video technology"
As described in pp. 102-103 (published by the Japan Broadcasting Corporation), the high-frequency components of the de-emphasized reproduced luminance signal are taken out, and the one with the smaller level is derived by the limiter (7). It subtracts from the original signal. That is, a high-frequency component and a low-level component in the output of the de-emphasis circuit (3) are regarded as noise components, and the polarity is inverted and added to the original signal to cancel the noise components.

However, as a matter of course, there is a true signal component in the signal derived by the high-pass filter (6), and if the cancellation amount (depending on the limiter level and the size of the limiter output) is increased, the true signal component is increased. The signal component is also canceled. By canceling the true signal component,
The signal waveform may be distorted. Therefore, the amount of cancellation cannot be increased and the effect of noise reduction is small.

(C) Purpose of the Invention The present invention has been made in view of the above points, and an object thereof is to provide a noise reduction circuit having a large noise reduction effect.

(D) Configuration of the invention The present invention uses a non-linear emphasised video signal to FM.
In a noise reduction circuit of a magnetic recording / reproducing apparatus for reproducing the video signal from a medium which is modulated and recorded, a demodulation means for demodulating a reproduced FM signal, a high-pass filter type noise cancellation circuit having an output of the demodulation means as an input, A noise reduction circuit comprising: a non-linear de-emphasis circuit having an output of a high-pass filter type noise cancellation circuit as an input.

(E) Embodiment An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit block diagram of the embodiment. In the figure, (1) is an input terminal for a reproduced FM signal, (2) is an FM demodulator, (10) is a high-pass filter type noise canceling circuit (high-pass filter (11), limiter (12)) described in the section of the prior art. , Subtractor
(Including (13)), (14) is a non-linear de-emphasis circuit, (15) is a second high-pass filter type noise cancel circuit, and (5) is a luminance signal output terminal.

Next, the operation will be described. At the time of reproduction, the reproduction luminance signal from the FM demodulator (2) is emphasized as shown in FIG. 2 due to the non-linear emphasis at the time of recording (in the case of β system). That is, in general, high-frequency components are emphasized, but the degree of emphasis is higher for components with lower original levels,
The higher the original level, the smaller the emphasis amount. In other words, the high frequency components are emphasized and compressed. Further, the output of the FM demodulator (2) contains so-called "triangular noise", the level of which increases in the higher frequency range.

This reproduction luminance signal is supplied to the high pass filter type noise cancel circuit (10). Then, of the high frequency components, the components not applied to the limiter are canceled. Therefore, the noise component is reduced and the reproduced luminance signal waveform is distorted.

The output of the first high pass filter type noise cancel circuit (10) is de-emphasized by the non-linear de-emphasis circuit (14). This de-emphasis operation is the second
It is set so as to have a characteristic completely opposite to the characteristic shown in the figure.
Therefore, high frequency suppression and expansion operations are performed. Specifically, the suppression amount of the high-frequency component having a high level is small, and the suppression amount of the high-frequency component having a low level is large.

Therefore, the noise component reduced by the noise cancel circuit (10) is further reduced. Further, it can be considered that the portion of the waveform distortion caused by the cancellation of the true signal component includes the high frequency signal component. Therefore, the degree of this waveform distortion is also suppressed because the high frequency component is suppressed.

The following is a comparison with the case where the de-emphasis circuit and the noise cancel circuit are arranged as in the conventional example. The rate of noise reduction in the de-emphasis circuit (14) is higher in the present invention than in the conventional example. Because the noise component level at the input of the de-emphasis circuit (14) is smaller in the case of the embodiment than in the conventional example,
Non-linear de-emphasis characteristics (reverse characteristics of Fig. 2)
Therefore, the reduction amount becomes larger in the case of the embodiment. Therefore,
It can be seen that the noise reduction effect in the present invention is greater if the proportion of noise canceled by the noise canceling circuit is the same.

Further, as in the embodiment, the second high-pass filter type noise canceling circuit (15) is provided after the de-emphasis circuit (14).
By providing the above, the noise reduction effect can be increased and the waveform distortion can be improved by appropriately selecting the amount of cancellation and the cutoff frequency in the two noise cancellation circuits (10) and (15). Even if the cancellation amount of the first noise cancellation circuit (10) is increased, the waveform distortion is reduced as described above,
Noise is also reduced. Second noise cancellation circuit
Since the noise level is low at the input of (15), it is not necessary to increase the cancellation amount, and therefore the waveform distortion can be reduced. In addition, since it is considered that higher frequency noise remains in the output of the de-emphasis circuit (14),
Set the cutoff frequency of the noise cancellation circuit (15) of the first
If it is set higher than the cutoff frequency of the noise canceling circuit (10), the waveform distortion becomes smaller. Also, the demodulator
Along with (2), 1H delay type noise canceling circuit
9-2228).

(F) Effect of the Invention As described above, according to the present invention, the noise reduction effect can be enhanced without increasing the distortion of the waveform, which is useful.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a characteristic diagram of nonlinear emphasis, and FIG. 3 is a block diagram of a conventional example. (2) …… FM demodulator, (10) …… Noise cancel circuit,
(14) …… De-emphasis circuit.

Claims (1)

[Scope of utility model registration request] 1. A noise reduction circuit of a recording / reproducing apparatus for reproducing the video signal from a medium in which the video signal is FM-modulated and recorded, after the demodulating means for demodulating the reproduced FM signal,
The first high pass filter type noise cancel circuit, the de-emphasis circuit and the second high pass filter type noise cancel circuit are connected in cascade, and the cutoff frequency of the high pass filter in the second high pass filter type noise cancel circuit is set to the above. A noise reduction circuit characterized by being set to a frequency higher than a cutoff frequency of a first high-pass filter type noise cancellation circuit.