JPS6258789A - Luminance signal processing circuit for video tape recorder - Google Patents

Abstract

PURPOSE:To improve the frequency characteristic and the sharpness of a picture by converting a high frequency component separated by a high pass filter into a square wave corresponding to an input amplitude by a level response limiter, mixing the result with a low frequency component, applying FM modulation and recording the result on a tape. CONSTITUTION:When a luminance signal A is separated by a Y/C separation means 2, a high frequency component B and a low frequency component C are separated from a luminance signal A by a separation means 3. The waveform as shown in figure D is converted from the high frequency component B by a level response limiter 6. The output of the level response limiter 6 and the low frequency component C are mixed by a mixing means 7 to obtain an output shown in E. Then the high frequency component B is attenuated by the recording/reproduction operation and the waveform is unsharpened when the high frequency component is formed in a square waveform as shown in E, the unsharpened waveform is compensated. Thus, the frequency characteristic of a reproducing signal is improved and the sharpness of a picture is increased. No deterioration of the S/N is caused as well.

Description

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

(B) Conventional technology In a VTR that records and regenerates television signals, the luminance signal is usually FM modulated, the color signal is frequency-converted to a low frequency range, and both are recorded in a superimposed manner.

Furthermore, in the luminance signal system, for the purpose of improving S/N, high frequencies are emphasized by pre-emphasis, then FM modulated and recorded, and during playback, it is configured to pass through a de-emphasis circuit after FM demodulation (for example, Corona Published, home VT
(See Introduction to R, p151).

By the way, the above-mentioned pre-emphasis and de-emphasis are intended to reduce one-triangular noise in FM modulation and demodulation. Theoretically speaking, the amounts of pre-emphasis and de-emphasis are set to be equal, but in reality the amount of de-emphasis is increased from the viewpoint of S/N improvement. As a result, high-frequency signals, which tend to be attenuated by recording and reproducing, are attenuated sharply, resulting in deterioration of frequency characteristics and unsatisfactory reproduced image quality.

(c) Problems to be solved by the invention, namely, in the present invention, the frequency characteristics of the VTR, S
The purpose is to improve /N.

(d) Means for Solving the Problems The present invention includes a bypass filter that extracts high-frequency components of a luminance signal, and a level-responsive limiter 7 that uses the output of this bypass filter as an input and outputs an output according to the amplitude of the input signal. A low-pass filter that extracts the low-frequency components of the luminance signal,
A mixing means is provided for mixing the output of the low-pass filter and the output of the level-responsive limiter.

(E) Effect The high-frequency component separated by the bypass filter is converted into a square wave corresponding to the input amplitude by the level responsive limiter. Then, it is mixed with low frequency components, FM modulated, and recorded on tape B-a. Therefore, since the high-frequency component is converted into a square wave, this component is recorded with emphasis.

(f) Examples Examples will now be described with reference to the drawings. FIG. 1 is a circuit block diagram of the embodiment, FIG. 2 is a waveform diagram of main parts, and FIG. 3 is a professional diagram showing a level responsive limiter.

In Figure 1, (1) is the input terminal for the video signal to be recorded, (2) is the luminance signal/chrominance signal separation means (Y/C separation means), and (3) is the high-frequency component and low-frequency component of the luminance signal. It is a separation means for separating the two, and includes a bypass filter (4) and a low-pass filter (5).

(6) is a level responsive limiter, and (7) is a mixing means. The output of this mixing means (7) has high frequency components emphasized and is recorded on tape via a subsequent pre-emphasis circuit, FM modulation circuit, etc.

The level responsive limiter (6) is a limiter that outputs an output with an amplitude corresponding to the amplitude of an input signal, and the output has a waveform like a square wave.

Therefore, it is assumed that a luminance signal as shown in FIG. 2 (A) is separated by the Y/C separation means (2). This luminance signal <A
), the high frequency component (B) and the low frequency component (C) are separated by separation means (
3). The waveform of the high frequency component (B) is converted by the level responsive limiter (6) as shown in (D). Then, the output of the level responsive limiter (6) and the low frequency component (C) are mixed by the mixing means (7).
) is obtained.

The high-frequency component (B) is attenuated by recording and reproducing operations, etc., and the waveform becomes dull. However, if the high-frequency component is shaped into a square wave as shown in (E), it is possible to compensate for the bluntness of the waveform. I can do it. Therefore, the frequency characteristics of the reproduced signal can be improved, the sharpness of the image increases, and S/H deterioration does not occur. This is because even if pre-emphasis and de-emphasis are provided in the same way as in the past, the frequency characteristics are improved.

The level responsive remic (6>) can be realized with the configuration shown in Figure 3. In Figure 3, (8) (9>) are the first and second clamp circuits, (10) and (11) are the first and second clip circuits. circuit,
(12) and (13) are first and second inversion circuits.

High-frequency components (
In B), the lower peak value is first clamped to a constant voltage by the first clamp circuit (8). This signal is amplified and the clamped side is clipped at a predetermined potential. By inverting the output of the first clip circuit (10), the second clamp circuit (9) and the second clip circuit (11)
Clamp and clip the upper peak value. The output of the second clipping circuit (11) is inverted by the second inverting circuit (13) to return it to the same polarity as the output of the bypass filter (4), and is used as the output of the level responsive limiter.

The first and second clamp circuits <8) <9) are 2 to 3M.
Constants are determined to respond to frequencies on the order of Hz.

Further, the bypass filter (4) allows components of 2 MHz or more to pass, and the low-pass filter (5) has a pass band of 2 MHz or less.

(g) Effects of the Invention As described above, according to the present invention, the waveform of the high frequency component of the luminance signal is shaped into a shape close to a square wave and is emphasized and recorded, so the S/N of the reproduced signal is This is practical because the frequency characteristics can be improved without deteriorating the image quality, and the sharpness of the image is improved.

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram of the embodiment, FIG. 2 is a waveform diagram, and FIG. 3 is a circuit diagram of a level responsive limiter. (3) Separation means, (6) Level responsive limiter, (7) Mixing means.

Claims (1)

[Claims] (1) In the luminance signal processing circuit before the FM modulation circuit of the video tape recorder, there is a separating means for separating the luminance signal into high frequency components and low frequency components, and a separating means for separating the luminance signal into high frequency components and low frequency components; A brightness signal processing circuit comprising: a level responsive limiter that outputs an output with a corresponding amplitude; and mixing means that mixes the low frequency component and the output of the level responsive limiter.