JPS5820509B2 - Color video signal playback method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention comprises a low-converted carrier chrominance signal and a balanced modulated luminance signal whose carrier frequency is four times that of the low-converted carrier chrominance signal and which is primarily upper sideband. , regarding a method for reproducing a color video signal recorded on a recording medium using a composite signal of the low-pass converted carrier color signal and a pilot signal having a frequency twice the carrier frequency, in particular, a method for reproducing a color video signal recorded on a recording medium, in which a stable desired reproduced color is obtained. This ensures that a video signal can be obtained.

Hereinafter, the method for reproducing a color video signal according to the present invention will be explained with reference to the drawings.

Fig. 1 shows an example of this, in which the color video signal from the input terminal 1 is supplied to the low-pass filter 2, and the carrier frequency when the original carrier frequency of the carrier color signal is low-pass converted as fS1 as described later is fL. Then, the components up to fs-3fL,
For example, if this color video signal is an NTSC signal and f
When s = 3.58 MHz and its horizontal frequency is fH, fL = 迭ヱ f H = 0.37 MHz
In this case, the luminance signal YA (FIG. 3A) with components up to 2.47 MHz is extracted and supplied to the modulator 3, while f S = 3.58 MHz from the oscillator 4
and f L = 0. from the variable frequency oscillator 5.
A signal of 37 MHz is supplied to the frequency converter 6, from which the frequencies are respectively f s - 3f L = 2.
Obtain three signals of 47 MHz and fs+fL=3.95 MHz, supply the fs-3fL=2.47 MHz signal to the modulator 3, perform amplitude modulation, for example, balance modulation, with the luminance signal YA, and then modulate it. A luminance signal YB (FIG. 3B) is obtained.

Then, this modulated luminance signal YB is converted to fs-3fL=2.
It is supplied to a low-pass filter 7 which has a characteristic of lowering the frequency by 6 dB at 47 MHz, and its main component is the lower sideband component Yc (Fig. 3C).
is taken out and supplied to the synthesizer 8.

The input color video signal is also supplied to a bandpass filter 9 to extract a carrier color signal C8 having a carrier frequency of f s = 3.58 M) (z), which is supplied to a synthesizer 8 .

Furthermore, f S−f L=3.2 from the frequency converter 6
A 1 MHz signal is supplied to the combiner 8 as a pilot signal.

Then, in the synthesizer 8, the modulated luminance signal Yc, the carrier color signal Cs, and the pilot signal P.

is frequency-multiplexed, and the multiplexed signal Yc+C8+PC (D in FIG. 3) is supplied to the frequency converter 10.
The carrier frequency is (f3+fL)-(fs 3fL)-=4fL=1.4 by frequency conversion using a signal of f3+fI, = 3.95 MHz.
an 8 MHz mainly upper sideband modulated luminance signal YD;
Carrier frequency is (fs+fL) fs=fL=0.37MH
The carrier color signal CL of z and the frequency (f3+fL)(fs
−fL)=2fL=0.74MHz pilot signal F
Obtain D (Fig. 3E).

These signals YD, C are then filtered through a low-pass filter 11.
The L and PD multiplexed signal (FIG. 3F) is taken out and supplied to the magnetic head 13 through the recording amplifier 12 to be recorded on, for example, a magnetic tape.

In this case, the carrier color signal C8 from the bandpass filter 9
is supplied to the burst gate circuit 14 to extract a burst signal, which synchronously drives the oscillator 4. Furthermore, the input color video signal is supplied to the horizontal synchronization signal separation circuit 15 to extract a horizontal synchronization signal SH, which is Supplied to the phase comparator circuit 16, and also outputs 7 *8e* &'155 r F) (7) t L-T
-i -H-2°゛°'' MHz signal is supplied to the frequency divider 17, divided by 7 to produce a signal with horizontal frequency fH, which is supplied to the phase comparator circuit 16, and the comparison error voltage is It is supplied to the variable frequency oscillator 5 to control its oscillation frequency.

During reproduction, as shown in FIG.
= 1.48 MHz mainly upper sideband modulated luminance signal YD, carrier frequency f L - 0, carrier color signal CL of 37 MHz, and frequency 2 f L = 0.74]'v
Multiplexed signal with iHz pilot signal PD (Fig. 3F)
) is supplied to the frequency converter 24 through the regenerative amplifier 22 and the automatic gain control circuit 23, while the fixed oscillator 25
The fs=3.58MHz signal from the variable frequency oscillator 2T is supplied to another frequency converter 26, and the fs=3.58MHz signal from the variable frequency oscillator 2T is supplied to another frequency converter 26.
A signal of L=0.37 MHz is fed to this further frequency converter 26, from which the frequency is respectively f s
+f I, = 3.95 MHz, f s-3, f L =
Three signals of 2.47■h and fs-fI, = 3.21■h are obtained, and the signals of tsfL = 3.95MHz are supplied to the frequency converter 24 to generate the reproduced multiplexed signal. After frequency conversion, the carrier frequency becomes (f s + f L )-4
The modulated luminance signal Yc of mainly lower sideband of fL=fB-3fL=2.47MHz and the carrier frequency
s+fL)-fL=fS=3.58 MHz carrier color signal C8 and frequency (fs+fL)2fL
=f5-fL=3.21MH2 pilot signal PC
(Figure 3G).

Then, the carrier frequency is changed to fs- by the low-pass filter 28.
The modulated luminance signal Yc of 3fL-2, 47ME (z is taken out, supplied to the demodulator 29, demodulated by the fs3fL=2.47MHz signal from the frequency converter 26, and the demodulated luminance signal is It is supplied to the synthesizer 30, and the carrier frequency is fs=3.58MHz in the bandpass filter 31.
A carrier color signal CS is taken out and supplied to a synthesizer 30, and a reproduced color video signal is obtained at an output terminal 32.

In this case, the bandpass filter 33 has a frequency of f 5
A pilot signal pc of −fL=3.21 MHz is taken out and supplied to the detection circuit 34, and the voltage from this is supplied to the automatic gain control circuit 23 to control the level of the reproduced multiplexed signal to be constant.

Furthermore, the pilot signal PC from the filter 33 is supplied to the phase comparison circuit 35, and the f
A signal of s fL=3.21 MHz is supplied to the phase comparison circuit 35, and the comparison error voltage is supplied to the variable frequency oscillator 27 to control its oscillation frequency.

Next, the operation of the reproducing circuit shown in FIG. 2 will be explained using mathematical formulas.

Now, assume that the carrier wave is Acos4ωLt. Then, consider the angular frequency of the modulated luminance signal as a single frequency for simplicity,
If its angular frequency is P (P=2πf), the modulated luminance signal is expressed as cosPt, and the modulated luminance signal is A(1-hn
cosP t ) cos4 ωLt.

Note) A is the amplitude of the carrier wave, and m is the modulation degree.

Here, A(1+mcosPt) CO34ωL t
■ =Acos4ωL t +-HmA CO3(4ωL+
P) 10-HmA cos (4ωL-P) t.

Among these, the residual sideband component YD of the modulated luminance signal is
=Eycos(4ωL+P)t.

The component YD of this modulated luminance signal is
appears in the output of

Further, if the pilot signal PD is Epcos2ωLjN, the signal from the fixed oscillator 25 is cosω8''1, and the signal from the variable frequency oscillator 27 is cos (ωLt+θ),
Since the signal supplied from the frequency converter 26 to the frequency converter 24 is cos ((ω8+ωL)t+θ), the modulated luminance signal Yc obtained from the filter 28 is Eycos(4ωL+P) t +cos ((ωS
+ωL)t+θ)→EY-cos((ωs-3ωL-P
)t+θ), and the signal supplied from the frequency converter 26 to the demodulator 29 is cos((ωs-3ωL)t
-8θ), the demodulated luminance signal obtained from the demodulator 29 is Ey cosl (ωs-:3ωI, -p) t+θ
)・cos((ωs−3ωb) −3θ)→Ey c
os (Pt-4θ).

On the other hand, since the signal supplied from the frequency converter 26 to the frequency converter 24 is cos ((ωS+ωL)t+θ), the pilot signal PC obtained from the filter 33 is E
P cos ((ωs-ωL) is 10), and in the phase comparator circuit 35, the signal cos ((ωs-ωL) t
-θ) and this pilot signal Epcos(ωS-ωL)
t+θ), and the phase difference 2θ is 2nπ
The variable frequency oscillator 27 is controlled so that (n-0, 1, 2...), that is, θ-nπ.

Therefore, the demodulated luminance signal is EYcosPt, which corresponds to the original modulated luminance signal cosPt, so that a demodulated luminance signal of a predetermined polarity is always obtained.

In addition, in FIG. 2, the carrier frequency fL1 after low frequency conversion
When the pilot signal frequency 2fL1 and the carrier frequency 4fl of the modulated luminance signal include jitter fluctuations in the tape drive system, phase fluctuations of ΔfL, Δ2fL, and Δ4fL occur at the output of the automatic gain control circuit 23 of the reproduction circuit, respectively. These phase fluctuation components are
Needless to say, it is absorbed by the automatic phase adjustment system including the fixed oscillator 25, the phase comparison circuit 35, and the variable frequency oscillator 27.

According to the method of the present invention described above, a low-band-converted carrier chrominance signal, a balanced modulated luminance signal whose carrier frequency is four times that of this low-band-converted carrier chrominance signal and whose carrier frequency is mainly upper sideband, When a composite signal of the range-converted carrier color signal and a pilot signal with a frequency twice the carrier frequency reproduces a color video signal recorded on a recording medium, the pilot signal included in the reproduced composite signal is The amplitude of the reproduced signal of the composite signal is detected and the amplitude of the reproduced signal of the composite signal is controlled, and the phase of this pilot signal is compared with the reference phase of the reference signal generator, and the frequency of the signal is controlled based on this phase comparison signal. Since the balanced modulated luminance signal is demodulated at , a stable and desired reproduced color video signal can be obtained.

It should be noted that a carrier color signal that has been low-band converted, a balanced modulated luminance signal that has a carrier frequency four times that of the carrier color signal that has been low-band converted and is mainly an upper band, and a carrier color signal that has been low band converted. By recording on the recording medium a composite signal with a pilot signal having a frequency twice the carrier frequency of
So-called spacing loss can be reduced.

That is, the recording/reproducing characteristics of magnetic tape etc. exhibit a peak at a relatively low frequency, for example, around I MHz, but if the carrier frequency of the modulated luminance signal is set to four times that of the carrier color signal that has been low frequency converted, For example, since the frequency is set to be as low as 1.48 MHz, the carrier frequency comes before and after this peak, and therefore the S/N ratio of the luminance signal is improved.

Also, the spacing loss increases as the signal frequency increases, so by lowering the carrier frequency of the luminance signal, the spacing loss can be reduced. However, for example, phase modulation may also be used.

[Brief explanation of drawings]

FIG. 1 is a system diagram of a recording system according to an example of the method of the present invention, FIG. 2 is a system diagram of its reproducing system, and FIG. 3 is a spectrum diagram for explaining the same. 1 is an input end for a color video signal; 2, 7, and 11 are low-pass filters; 3 is an amplitude modulator; 9 is a band-pass filter; and 10 is a frequency converter.

Claims (1)

[Scope of Claims] 1. A low-band-converted carrier chrominance signal cL, a balanced modulated luminance signal YD whose carrier frequency is four times that of this low-band-converted carrier chrominance signal and whose carrier frequency is mainly an upper sideband; In order to reproduce a color video signal recorded on a recording medium by a composite signal of the low-pass converted carrier color signal cL and a pilot signal PD having a frequency twice the carrier frequency, at least an automatic gain control circuit and the above-mentioned automatic gain control circuit are required. a first frequency conversion circuit connected to the gain control circuit and converting the low frequency converted carrier color signal cL and the pilot signal PD to high frequency; a first frequency conversion circuit connected to the automatic gain control circuit and converting the balanced modulated luminance signal; a second frequency conversion circuit that converts the YD carrier wave to a high frequency; and a demodulation circuit that is connected to the second frequency conversion circuit and demodulates the balanced modulated luminance signal Yc frequency-converted by the second frequency conversion circuit. an amplitude detection circuit that is connected to the first frequency conversion circuit and detects the amplitude of the pilot signal Pc that has been high-frequency converted by the first frequency conversion circuit;
a phase comparison circuit that is connected to the frequency conversion circuit of the first frequency converter and compares the phase of the pilot signal PC with the reference phase of the reference signal generator; a second frequency conversion circuit and a balanced modulated luminance signal Y; a conversion/demodulation signal generation circuit that supplies a signal having a predetermined frequency and phase to the demodulation circuit of the automatic gain control circuit, and the amplitude of the reproduced signal of the composite signal is determined by the output of the amplitude detection circuit. At the same time, the frequency and phase of the output signal of the conversion/demodulation signal generation circuit are controlled based on the phase comparison signal of the phase comparison circuit, and the oscillation signal whose frequency and phase have been controlled is transmitted to the first oscillation signal. A method for reproducing a color video signal, which is supplied to a second frequency conversion circuit and a luminance signal demodulation circuit to convert the frequency of the carrier color signal cL and demodulate the balanced modulated luminance signal YC.