JPS585555B2 - Color video signal recording method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for modulating a color video signal and recording it on a magnetic tape, etc. The present invention relates to an improved method of modulating a color video signal and recording it on a magnetic tape or the like, and in particular, it has a simple configuration that provides a good S/N ratio and a small spacing loss. It concerns the recording method.

Conventionally, such a recording method, as shown in FIG. 1E,
For the luminance signal, the carrier frequency is, for example, fD=1.1
For example, the carrier chrominance signal is extracted as an amplitude-modulated signal YD mainly in the upper sideband as low as 8 MHz, and the carrier frequency is lower than the carrier frequency fD of the modulated luminance signal YD, for example fI = -0.59 MHz. The signal cI is frequency-converted so as to have a lower frequency, and a composite signal of the modulated luminance signal and the carrier color signal CI that has been low-frequency-converted is recorded on a magnetic tape or the like.

According to this method, the S/N ratio can be improved, and the loss caused by the gap between the head gap and the recording medium, so-called spacing difference, can be reduced.

That is, the recording/reproducing characteristics of magnetic tape etc. exhibit a peak at a relatively low frequency, for example, around IMHz, but in this method, the carrier frequency of the modulated luminance signal is lowered, so there is no signal before or after this peak. The carrier frequency of this signal comes to match, and therefore the S/N ratio of the luminance signal improves.

Furthermore, since the spacing loss increases as the signal frequency increases, the spacing loss can be reduced by lowering the carrier frequency of the luminance signal in this manner.

The present invention relates to an improvement in a method for recording such a color video signal, and is intended to obtain a color video signal having the above-described signal form to be recorded.

The recording method according to the present invention will be explained below with reference to FIG.

In FIG. 2, reference numeral 1 denotes an input terminal for a color video signal, and the color video signal from this input terminal is supplied to a low-pass filter 2 to obtain a luminance signal YA of components up to fB=2.99MHz, for example.
(A in FIG. 1) and supply it to the balanced modulator 3,
On the other hand, when the horizontal frequency from the variable frequency oscillator 4 is fH, the relationship is fL-2n+1/2fH (n is an appropriate positive integer), for example, fL=75/2fH-0.59.
MHz signal and f3 from oscillator 5 = 3.58MHz
fs-fL-fB=
2.99MHz signal and fj+fL-fc=4.17
Obtain MHz signal, fB=2.99MH from filter 7
The signal of z is taken out and the signal of f is extracted from the filter 8.

The first 4.17 MHz signal is taken out, and the fB=2.99 MHz signal from this filter 7 is supplied to the balanced modulator 3 for balanced modulation with the luminance signal YA. From this, the modulated luminance signal YB (first Figure B) is obtained.

In this case, for example, as shown in FIGS. 6A and 6B, in the modulated luminance signal YB, the amplitude of the portion 14 corresponding to the synchronization signal SH of the luminance signal YA is larger than that of other portions. That is, the amplitude is made larger than the amplitude of the portion corresponding to the white level and black level of the signal YA.

Then, this modulated luminance signal YB is expressed as fB=2.99MH
The lower sideband component Yc (FIG. 1C) is mainly extracted from the vestigial sideband filter 9 which has a characteristic of decreasing by 6 dB at z, and is supplied to the synthesizer 10.

The input color video signal is also passed through a bandpass filter 11.
A carrier color signal C8 (FIG. 1C) having a carrier frequency of fs=3.58 MHz is extracted, and is supplied to a combiner 10 to be combined with a modulated brightness variable signal Yc.

Then, the combined signal Yc+Cs is supplied to the frequency converter 12 and frequency-converted using a signal of fc=4.17MHz from the filter 8. As for the luminance signal, the carrier frequency is f
D-fc-fB-(f3+fi)-(rs-fL)=2
fl-1.18 MHz mainly upper sideband signal YD,
and the carrier frequency is fB=fc+fB=2fs=7.16
MHz mainly lower sideband signal YE, and carrier color signal, carrier frequency is fL=fc-fB=0.
59MHz signal CL and carrier frequency fH=fQ+
We get a signal C1 of fs=2fB+fL=7.75MHz (Fig. 1D) and these signals YT, YE, C■ Return C
H is supplied to the low-pass filter 13 so that the carrier frequency is f
The modulated luminance signal YD, which is mainly an upper band wave, is low at D-1.18 MHz, and the carrier color signal CL whose carrier frequency is fL-0.59 MHz, which has been frequency-converted to the lower frequency side, is taken out (Fig. 1E). , this is supplied to the magnetic head 15 through the recording amplifier 14 and recorded on, for example, a magnetic tape.

In this case, the input color video signal is supplied to the horizontal synchronization signal separation circuit 16 to extract the horizontal synchronization signal, which is supplied to the phase comparator circuit 17, and the fL from the variable frequency oscillator 4
A signal of =75/2fH=0.59MHz is supplied to the dividing frequency 18, divided by 75/2 to produce a signal of horizontal frequency fH, which is supplied to the phase comparator circuit 17, and the comparison error voltage is converted to a variable frequency The carrier color signal CS from the bandpass filter 11 is supplied to the oscillator 4 to control its oscillation frequency, and the carrier color signal CS from the bandpass filter 11 is supplied to the burst gate circuit 19.
A horizontal synchronizing signal is supplied to the waveform shaping circuit 20 to obtain a burst gate signal, which is then supplied to the burst gate circuit 19 to extract the burst signal, which drives the oscillator 5 synchronously.

In this manner, according to the present invention, the carrier color signal CS of the color subcarrier frequency is directly combined with the balanced modulated luminance signal Yc, and the frequency converter 12 generates the -converted signal f.

The modulated luminance signal, which is mainly an upper band wave having a low carrier frequency, and the carrier chrominance signal, which is frequency-converted to its lower frequency side, are obtained simultaneously.

FIG. 3 shows an example of a reproduction device for color video signals recorded according to the present invention, in which reproduction signals YD and CL (E in FIG. 1) from a magnetic head 21 are supplied to a frequency converter 23 through a reproduction amplifier 22. On the other hand, variable frequency oscillator 2
A signal of fL-0.59 MHz from oscillator 25 and a signal of fs=3.58 MHz from oscillator 25 are supplied to frequency converter 26, and a signal of f8-fL-fB=2.99 MHz and fs+fL=fo=4. A signal of 17 MHz is obtained, a signal of fB=2.99 MHz is taken out from the filter 27, and a signal of fB=2.99 MHz is taken out from the filter 28.

- A 4.17 MHz signal is supplied to the frequency converter 23 to frequency convert the reproduced signals YD and CL, and for the luminance signal, the carrier frequency is fB=fo-fI=2.99 MHz.
Mainly the lower sideband signal YF1 and the carrier frequency are fG
=fc+fD=5.35 MHz, which is mainly an upper sideband signal yo; and for the carrier color signal, a signal CS with a carrier frequency of fs=fc-fL=3.58 MHz, and a carrier frequency of fI=fc+fL=4. 76MHz signal c
I (Fig. 1F).

These signals YF, Yg, Cs, and C1 are then supplied to a low-pass filter 29 to filter mainly the lower band at the carrier frequency rB - 2.99 MHz, similar to the signal Yc (FIG. 1C) obtained from the filter 9 during recording. The modulated luminance signal YF of the wave is taken out (Fig. 1G) and sent to the synchronous detection circuit 3.
0 and fB from filter 27 = 2.99MHz
Synchronous detection is performed using the signals of , and the detected luminance signal is sent to synthesizer 3
1, and the signals YF, Y from the frequency converter 23
G, Cs, and CI are supplied to the bandpass filter 32 to obtain a carrier color signal CS with a carrier frequency of f8=3.58MHz.
(H in FIG. 1), and supplies it to a synthesizer 31 where it is combined with a luminance signal to obtain a reproduced color video signal at an output terminal 33.

In this case, the modulated luminance signal YF from the filter 29 is
Similar to the modulated luminance signal yB obtained from the balanced modulator 3 during recording, as shown in FIG. 5B, the amplitude of the portion MH corresponding to the synchronization signal is larger than the amplitude of other portions. , supplies this modulated luminance signal YF to the gate circuit 34, and supplies it to the envelope detection circuit 35,
The detected output is supplied to the synchronization signal position detection circuit 36 to obtain a gate signal at the synchronization signal position, which is then supplied to the gate circuit 34 to obtain the partial MF corresponding to the synchronization signal with a frequency of fB=2.99MHz. (FIG. 5C) and supplies it to the phase comparator circuit 37 to obtain fB from the filter 27 =
The phase is compared with a 2.99 MHz signal, and the comparison error voltage is supplied to the variable frequency oscillator 24 to control its oscillation frequency.

According to such a circuit configuration, the carrier frequency fD of the modulated luminance signal is now 2 times the carrier frequency fL of the low-pass converted carrier chrominance signal.
Therefore, the amount of phase variation for frequency fD due to the same time axis variation of the tape should be twice that for frequency fL.

Therefore, the reproduced carrier frequencies fD and fL including the amount of phase variation can be respectively expressed as follows.

fD+2Δψ fL+Δψ On the other hand, the oscillation frequency from the variable frequency oscillator 24 is selected as the oscillation frequency fL of the oscillator 24 because feedback control is applied to remove the amount of phase fluctuation from the signal from the frequency converter 26. If so, the oscillation frequency from the oscillator 24 will be fL+Δψ.

This oscillation signal is transmitted to the reference oscillator 2 in the frequency converter 26.
5 with a reference signal having a frequency f8, a converted signal having a frequency fC is obtained from the filter 28.

However, even if the frequency is converted from fL to fs+fL, the absolute magnitude of the phase variation remains Δψ because the frequency is converted from the reference signal.

Therefore, the converted signal fc can be expressed as follows.

fc=fS+fI+Δψ Therefore, the carrier color signal frequency-converted to the original frequency band by the frequency converter 23 is fo-(fL+Δψ)=(f8+fL+Δψ)-(fL
Since the jitter is removed, the jitter is removed.

Also, regarding the modulated luminance signal, fO-(fD+2Δψ)=(fD+fB+Δψ)-(f
D+2Δψ)=fB−Δψ, and the jitter remains by Δψ.

However, the modulated luminance signal is further processed by the synchronous detection circuit 30.
Since the signal is supplied to the filter 27 and detected by the synchronous detection signal from the filter 27, the remaining jitter Δψ is also removed.

That is, since the synchronous detection signal f3 is expressed as fS-(fL±Δψ)=fB-Δψ, no jitter appears in the detection output.

Furthermore, as shown in FIG. 5A, depending on whether the original video signal YA is on the white level side or on the black level side with respect to the intermediate level between the white level and the black level shown by straight line a, If it is a sawtooth wave like , it is either section TA or section TB.
Even if the phase of the balanced modulated signal YB, and hence the modulated luminance signal YF obtained from the filter 29, is inverted, the fB of the filter 27 is 2.99M.
Since the Hz synchronous detection signal is synchronized with the phase of the portion MH corresponding to the synchronous signal, the detected luminance signal cannot be detected by the filter 2 at the intended time, that is, at the time of recording.
A luminance signal similar to the signal YA obtained by the method is obtained.

Therefore, a stable and desired reproduced color video signal can be obtained at the output end 33.

As in the example of FIG. 4, the carrier color signal C from the filter 32
Similarly to the above, the modulated luminance signal YF from the filter 29 is supplied to the envelope detection circuit 35, and its detection output is supplied to the synchronization signal position detection circuit 36 to determine the synchronization signal position. obtains a gate signal, further supplies this to a delay circuit 39 to obtain a burst gate signal, supplies this to a burst circuit 38, extracts a burst signal from it, supplies it to a phase comparator circuit 40, and outputs a burst gate signal to the oscillator 25. It is also possible to compare the phase with a signal of fS-3.58 MHz, and supply the comparison error voltage to the variable frequency oscillator 24 to control its oscillation frequency.

During recording, the luminance signal may be subjected to normal amplitude modulation without being subjected to balanced modulation.

The carrier frequency fD of the modulated luminance signal recorded on the recording medium is the carrier frequency f of the carrier color signal converted to the lower frequency side.
If L can be lower than the above value, 3 times or 4 times that value.
You may choose twice.

Also, it is not necessarily necessary to select an integer multiple of the carrier frequency fL of this carrier color signal, but it is sufficient to select a low frequency within a range where the spectrum of the modulated luminance signal and the spectrum of the carrier color signal converted to the low frequency side do not overlap. It is something.

[Brief explanation of drawings]

FIG. 1 is a spectrum diagram for explaining the present invention, FIG. 2 is a circuit block showing an example of the recording method of the present invention, and FIGS. 3 and 4 are color video signals recorded by the recording method of the present invention. Circuit block 5 showing an example of a device for reproducing
The figure is a waveform diagram for explaining the present invention. 23 is a frequency converter, 29 is a low-pass filter, 30 is a synchronous detection circuit, and 32 is a band-pass filter.

Claims (1)

[Claims] 1 Balance modulation of the luminance signal of the human-powered color video signal, extracting the lower sideband signal of the modulated luminance signal,
This lower sideband signal is weighted with the carrier color signal of the input color video signal, and this weighted signal is frequency-converted by the conversion signal of - to produce a modulated luminance signal mainly of the upper sideband with a low carrier frequency. A color video image in which a frequency-converted carrier color signal is simultaneously extracted from the lower frequency side of the modulated luminance signal, and a composite signal of the extracted modulated luminance signal and the carrier color signal is recorded on a recording medium. How to record signals.