JPS5880990A - Recording and reproducing device for color television signal - Google Patents

Abstract

PURPOSE:To prevent deterioration in the picture quality of a reproduced color signal due to a decrease in color output level and an increase in mixed disturbing wave due to high-density recording, by emphasizing and recording the side band wave of a low frequency converted color signal and suppressing the side band wave on a reproduction side. CONSTITUTION:A luminance signal component in an input video signal 1 is separated through an LPF2 and a modulate by an FM modulator 3. Color components are separated by a BPF4 and converted to low frequency through a balanced modulator 5, oscillator 6, and LPF7. The low-frequency converted color signal has its color signal side- band wave emphasized by a side-band emphasizing circuit 8 and is mixed by a mixer 9 with the FM signal and the output signal of an auto tracking pilot signal generator 12. A three-frequency mixed signal reproduced by a reproducing head 11, on the other hand, is mixed by a head amplifier 13, and said emphasized component emphasized during recording is suppressed by a side-band suppressing circuit 16 to separate the reproduced color signal into a low frequency color signal through an LPF17. Consequently, the influence of a disturbing wave signal generated between the circuit 8 and circuit 16 is reduced without deteriorating the color picture quality.

Description

DETAILED DESCRIPTION OF THE INVENTION The main objects of the present invention are to reduce interference waves to a reproduced color signal in a recording/reproducing apparatus that records and reproduces a color television signal on a recording medium, and to improve the 87IIT ratio of the reproduced color signal. In household magnetic recording and reproducing devices (hereinafter referred to as VTRs), the luminance signal component in the composite color video signal is generally FM on the high frequency side.
The color signal is frequency-converted to the lower frequency side, and the two signals are superimposed and recorded on the same magnetic head.

Technological progress in home VTRs has been rapid in recent years, and the trend is towards higher density recording. In order to achieve this high-density recording, new technological developments are underway: 0) automatic tracking control technology that can realize narrow track width recording and playback; @) short wavelength, narrow track recording technology; High emphasis recording technology to prevent deterioration of luminance signal reproduction S/H, (3) development of optimal recording media for short wavelength recording and reproduction, and the above three items.

Each item will be briefly explained below.

(1) Automatic tracking control allows the head to faithfully on-track the recording track during playback of the VTR and perform playback scanning! In order to achieve this, an electromechanical transducer is used to automatically shift the head height position according to curves in the recording trajectory. When recording and reproducing data with a narrow track width, it becomes difficult to perform accurate tracking using only the mechanical precision of the device. Therefore, in a VTR having a tape format with a track pitch of approximately 10 μm or less, auto-tracking control is considered essential in consideration of compatibility and the like.

FIG. 1 is an explanatory diagram of auto-tracking on a tape pattern of a rotating two-head type V'J'H.

This is the trajectory with the same head.

Now, the normal tracking position when the dome is scanning on the track of the track is the position shown in a, and in the case of off-tracking, it is the position shown in b when it straddles the B track, and the position shown in C. In some cases, the signal may be shifted in two directions when it straddles the B track. In this way, when the track is off-track, the reproduction trajectory attempts to span one of the adjacent tracks, so it is corrected to a normal track trajectory using a tracking error signal obtained by some means. In this case, typical methods for obtaining the tracking error signal include (1) a method using an auxiliary head, (2) a method using a pilot signal for detecting track deviation, and (2) a search signal method.

As a means for obtaining a tracking error signal for a home VTR, the method using the above-mentioned number lot signal for detecting track deviation is most often used.

A typical example of the pilot method is illustrated in FIGS. 2 and 3.

Figure 2 shows the recording frequency spectrum when recording a pilot signal. No band, e.g. 10
0 configured as a signal with a frequency of 0 to 200 KHz
In Fig. 3, the pilot signals fl, f2 are
A tracking error signal detection method using four frequency signals of ゜t, , f, will be explained.

Insert for each recording track recorded with two rotating heads.
This is a method in which the frequency of the pilot signal is changed and two pilot signals having a repetition period of every four tracks are recorded. Now, if we record frequencies f and ~f4 from track ~ // track as shown in Figure 3, when playing back, A'
When the head scans on the track, when on track like head q, f2. A three-frequency pilot signal of fs and fa is obtained, and the Cf2 fs) component and Cfa f
s) When the two frequencies of the component are obtained by the reproduction processing circuit, (f2
The level of Cf4-fs) becomes equal to the level of Cf4-fs). Similarly, when off-track like head h, f
2 and f.

A two-frequency signal is obtained, and the level of Cf2-fs) is ・
If q is large, the level of Cf4fs) becomes zero. Similarly, in head 1, only the (f4fs) component is obtained. As is clear from this result, (f2−
When the signal level of f3) and the signal level of (f4-f5) are the same, the on-track condition is met. The beat frequency (f2 of the adjacent track signal)
If the four-signal pilot frequencies are selected so that f5) and Cfa-fs) are different, then the following can be obtained.

As you can see, in response to high-density recording, new technology has become available for home use.
Although it is introduced in TR, recording and reproduction of color signals, on the other hand, causes various problems such as interference and 8/N reduction, so this will be explained with reference to the drawings.

o)) In the racking control method, when a method is used in which the pilot signal is superimposed and recorded with the FM signal/low frequency converted color signal for tracking error signal detection as explained in accordance with Fig. 2, the color signal FIG. 6 shows the reproduced spectrum near the color signal when frequency 9 is 630 KHz and pilot signal frequency fp is 150 KH2 (representative frequency among four frequencies). In FIG. 6, O is a regenerated pilot signal,
n is a reproduced color signal and is a sideband wave of the sb, m ij F M signal. Additionally, p and q signals are generated at frequencies of 330 KHz and 930 KHz. This signal is a cross-modulation component generated by the third-order distortion of the tape head system when the color signal f and pilot signal fp are recorded and reproduced by the tape head system, and f, -2fp = 330
KHz and fB +21p = 930 KHz. Bandwidth of reproduced color signal is ±500 KH centered on f8
z sideband signal band, but the aforementioned cross-modulation signal occurs within the color signal band. Further, the pilot signal is also within the band and is removed through a trap circuit for pilot removal, but since the reproduction level of the pilot signal is high, if it is not removed sufficiently, it will also affect the color signal. Although the cross-modulation signal can be reduced by lowering the recording level of the pilot signal, the S/N ratio of the reproduced pilot signal deteriorates, so that the level exceeds the allowable limit.

In this way, when the pilot signal is used for auto-tracking, interference such as cross-modulation components and fundamental wave components will occur in the reproduced color signal. , the sidebands of the FM signal become an emphasized and broadened spectrum. As a result, Figure 6H
A portion where the components of the lower sideband of the FM signal and the upper sideband of the color signal are shared occurs. If the F'M signal sideband mixes into the color signal in such an H part,
The reproduced color signal produces crack-like beats even at the edges, making it very unsightly. In addition, tapes with extremely thin magnetic layers, such as ME tapes, have a narrow track width in the short wavelength region, and are difficult to reproduce at low relative speeds. However, in the case of color signals having long wavelengths, since the tape thickness becomes thinner, the amount of tape magnetization decreases, and the reproduced color output level does not increase. Rather, the narrower track width reduces the reproduced color output level.

In this way, various technologies are introduced for high-density recording, but in addition to lowering the color output signal, cross-modulation components of the auto-tracking pilot signal and color signal, and the lower side band of the high-emphasis N signal The image quality of the reproduced color signal is significantly degraded due to the contamination of wave components.

The present invention eliminates such interference waves and also eliminates color S/
The present invention relates to a means for improving color reproduction and providing good color reproduction image quality.

In order to prevent the image quality of the reproduced color signal from deteriorating due to the accompanying drop in color output level and increase in interfering interference waves, means to emphasize and record the sidebands of the low frequency converted color signal to be recorded, and to suppress the sidebands during reproduction. It is intended to provide

The structure of the present invention will be explained by referring to one embodiment along with the drawings.

FIG. 7 is a block diagram of a recording and reproducing system of a VTR in which the color signal sideband emphasis and suppression method according to the present invention is adopted.

To explain the operation from the recording side block side, the luminance signal component in the input video signal No. 1 is separated by the LPF No. 2, subjected to high frequency emphasis, and then modulated by the FM modulator No. 3.

Further, the color signal components are separated by 4 BPFs, and converted to a low frequency by 6 balanced modulators, 6 oscillators, and 7 LPFs.

The low frequency converted color signal is mixed with the output signal of the device by a mixer 9 by a sideband emphasizing circuit 8, amplified by a recording amplifier 1o, and recorded by a head 11.

Next, the reproduction side block will be explained.

The three-frequency mixed signal reproduced by head No. 11 is amplified by head amplifier No. 13, and the reproduced luminance signal therein is separated into an FM signal by HPF No. 14, and obtained as de-emphasis after demodulation by FM demodulator No. 16. It will be done. The reproduced color signal is processed by 16 sideband suppression circuits, after suppressing the emphasis during recording, 1
The color signal is separated into a low frequency converted color signal by a 7 LPF, the 18 balanced modulator, the 19 oscillator, the 2o BPF performs frequency conversion to the original color signal, and the 021 mixer converts the color signal and luminance signal. are mixed, and 22 reproduced video output signals are obtained. 23 is a reproduced pilot signal detection circuit. 〇 Figure 8 shows a specific example of the frequency characteristics of the color signal sideband emphasizing circuit shown in Figure 7. show. f in the figure.

is the low-transform subcarrier frequency. The degree of emphasis at this time, that is, the recording frequency characteristics, can be selected arbitrarily, but if the level is 9, the weight ratio of the FM signal will be higher when it is recorded overlapping with the FM signal, and the tape head system will record and reproduce it. In the process, the influence of color signal sidebands causes a decrease in the reproduced FM signal level and an increase in cross-modulation in the luminance signal band.Experimentally, the maximum emphasis gain is f. ±500kHz
In this respect, it is desirable that the level is approximately 6 dB.The frequency characteristics of the color signal reproduction sideband suppression circuit shown in FIG. The overall frequency characteristic becomes flat.

As shown in Fig. 7, Fig. 9 shows the frequency spectrum of the playback head amplifier output when recording and playing back three-frequency signals of FM signal, color signal, and pilot signal. is the FM luminance signal, J is the color signal,
V is the pilot signal, and the respective carrier frequencies are f, ~
In the spectrum of the zero-power error signals f2, fa, and fp, the broken line part is the spectrum before sideband emphasis, and the solid line part is the spectrum after emphasis.

In other words, the energy highlighted in the shaded area! Some OW and 2 are intermodulation components and f. It has a frequency of ±2fp.

The level of the color sideband having the same frequency as the cross-modulation component of W is Y when not emphasized, and the level is X when emphasized. Regardless of sideband emphasis, the cross-modulation component is a component generated in the tape head system and remains constant, so the degree of improvement in the influence of cross-modulation is X-Y. Similarly, considering the influence of the FM signal at the current frequency of f5, it means that only T-U has been improved. Further, during reproduction, since sideband waves are suppressed, the total image quality of color recording and reproduction remains unchanged, and the influence of interference waves mixed from the recording emphasis circuit to the reproduction suppression circuit is suppressed. In addition, in order to suppress cross-modulation components such as W and z in Figure 9, the center frequency of the sideband emphasis in Figure 8 is set to the low-pass conversion color frequency, and the sidebands on both sides are emphasized in a well-balanced manner. It is clear that this is more effective.

FIG. 10 shows a specific configuration example of a sideband enhancement/suppression circuit according to the present invention. The block portions in the figure have the same functions as in FIG. 7. Figure 10a shows a sideband emphasizing circuit.
The main carrier wave is attenuated in a trap circuit consisting of LS + '2 and whose resonance frequency is the color low-pass conversion subcarrier frequency, that is, the sideband is emphasized, and the maximum amount of emphasis is R.
5+R5/Rs. The transistor JTR2 is an emitter follower circuit of a buffer, and its output signal passes through a clip circuit composed of "7+D++"2 and is mixed with an FM signal, etc. This clipping circuit is a circuit that clips the large signal level.If the color signal level is high and the sideband level is also high, if the sideband is emphasized, the sideband level will be slightly higher than the main carrier. This is to prevent cross-modulation noise (in the FM luminance signal) that occurs due to the increased superimposition ratio with the FM signal when the FM signal is recorded in a superimposed manner. This clip level is set to a level that will not cause ripping or clipping even if the sidebands of a normal color par signal are emphasized.

Figure 10 shows a sideband suppression circuit on the reproduction side. In the amplifier composed of the transistor TR5, sideband suppression is performed on the output signal on the collector side by the resonant circuit composed of R12y L2 #'5 on the emitter side. It will be done. The resonant frequency and frequency characteristics must be under the same conditions as recording.In addition, the overall frequency characteristics of this emphasis/suppression circuit,
It is desirable that the phase characteristics be flat.

In this way, by emphasizing and recording the sidebands of the low-frequency conversion color signal and performing sideband suppression on the playback side, the interference signal generated between the recording emphasis circuit and the playback suppression circuit can be suppressed. For example, it is possible to reduce the effects of interference signals such as cross-modulation noise between the auto-tracking pilot signal and color signal, and lower sideband waves of FM waves without changing the color image quality, and it is possible to obtain good reproduced color image quality. .

Similarly, 87N deterioration due to noise within the color signal band generated in the tape head system, head amplifier, etc.
It is natural that it will be improved. Especially when high-density recording is performed using magnetic media such as MIE tape, the reproduced color level is low and 37N deterioration is likely to occur due to the influence of amplifier noise. Using the circuit has the effect of suppressing noise generated in the tape head system and head amplifier that enters the color band in the same way as cross-modulation components, and it is possible to obtain good color reproduction image quality.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the auto-tracking method, Figure 2 is a spectrum diagram of the pilot signal for auto-tracking,
Figure 3 is an explanatory diagram of the auto-tracking method using the pilot method, Figure 4 is a diagram showing high emphasis characteristics, and Figure 6 is a diagram showing the high emphasis characteristic.
The figure is a spectrum diagram of FM high emphasis recording, Figure 6 is a spectrum diagram showing the influence of the auto-tracking pilot and the 7M lower sideband on the color signal, Figure 7 is a basic block diagram of an embodiment of the present invention, Figure 8 is a diagram showing the frequency characteristics when color sideband emphasis is performed according to the present invention.
FIG. 10 is a spectrum diagram showing the effects of the present invention, FIG. 10a is a specific circuit diagram of the main part of the recording system of the present invention, and FIG. 1...Input terminal, 2, 7, 17...L
PF, 3...FM modulator, 4,2o...
・BPF, 5, 18...Balanced modulator, 6, 19
...... Oscillator, 8... Sideband emphasizing circuit,
9, 21... Mixer, 1o... Recording amplifier, 11... Magnetic head, 12... Pilot signal generator, 13... Head Amplifier, 1
4...HPF, 16...FM demodulator,
16... Sideband suppression circuit, 23... Regenerated pilot signal detection circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 4 Figure //'l tis ts Illi4 ((Hz Figure 5 Figure 6 Figure 7 Figure 8 Figure 9)

Claims (1)

[Claims] (1) A color television signal consisting of a luminance signal and an amplitude-modulated modulated chrominance signal is separated into a luminance signal and a modulated chrominance signal, and the luminance signal is subjected to frequency modulation (FM) in a high frequency band.
When recording on a recording medium by at least frequency multiplexing the FM luminance signal and the modulated color signal frequency-converted to a frequency band lower than the lower sideband of the FM luminance signal wave, the sideband spectrum of the modulated color signal is By emphasizing and recording 87H compared to the center frequency, and by passing the reproduced modulated color signal through a circuit having opposite characteristics to the sideband emphasizing circuit during recording, it is possible to obtain a reproduced modulated color signal with a good 87H. A recording/reproducing method of a color television signal characterized by: Claims characterized in that the recorded frequency multiplexed signal includes a pilot signal for tracking detection in addition to an FM luminance signal and a low frequency conversion modulation color signal. The recording and reproducing method for color television signals according to item 1. (3) The color television signal recording and reproducing method according to claim 1, wherein the modulated color signal with sideband emphasis is recorded after passing through an amplitude limiting circuit. -) Modulated color signal center frequency f. againstfa±600K
4. The color television signal recording and reproducing system according to claim 1, wherein the sideband level at a Hz point is emphasized by approximately edB.