JPS5820508B2 - 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 three times that of the low-converted carrier chrominance signal and which is primarily upper sideband. , relates to a method for reproducing a color video signal recorded on a recording medium by a composite signal of a low-pass converted carrier color signal and a pilot signal having a frequency twice the carrier frequency, and in particular, a method for reproducing a color video signal recorded on a recording medium in a stable manner. This ensures that the signal can be obtained reliably.

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

FIG. 1 is an example of this, in which the color video signal from the input terminal 1 is supplied to the low-pass filter 2A, and the original carrier frequency of the carrier color signal is ts, and the carrier frequency after low-pass conversion as described later is If fL is the component up to fs(L, for example, this color video signal is an NTSC signal and fS
-3,58MHz, and when its horizontal frequency is fH, fL1 -TfH-0,4MH2, 3.18MHz
The luminance signal YA (FIG. 3A) of up to 2 components is extracted and supplied to the modulator 3, while f s=
The 3.58 MHz signal and the f L = 0.4 MHz signal from the variable frequency oscillator 5 are transferred to the frequency converter 6A.
From this, the frequency becomes fs-fL-3, respectively.
, 18MHz, fs + fL = 3.98
MHz and fs+2 f L = 4.38 MHz
Obtain three signals of f s−f L=3.18MH
The signal z is supplied to the modulator 3 and subjected to amplitude modulation, for example balanced modulation, using the luminance signal YA, thereby obtaining a modulated luminance signal YB (FIG. 3B).

This balanced modulation, for example, as shown in FIGS. 7A and B,
The white level shown by the straight line a of the luminance signal YA and the horizontal synchronization signal s
At a level intermediate between the peak value level of H, the amplitude becomes zero,
The amplitude is maximized at the white level and the peak level of the horizontal synchronizing signal sH.

Then, this modulated luminance signal YB is expressed as fs−f L =
It is supplied to a low-pass filter 7A having a characteristic of lowering the frequency by 6 dB at 3.18 MHz.
Figure C) is taken out and supplied to the frequency converter 8Y, and fs12 f L = 4.38 from the frequency converter 6A.
Frequency conversion is performed using a MHz signal, and the carrier frequency becomes (f
s+2fr, )-(fs-fL)=3 fL=
1.2 MHz mainly upper sideband modulated luminance signal Y
D (FIG. 3D) is obtained and supplied to the synthesizer 10 through the low-pass filter 9Y.

The input color video signal is also passed through a bandpass filter 11.
and extracts a carrier color signal C8 having a carrier frequency fs=3.58 MHz, and supplies it to the combiner 12,
Furthermore, fs-f L = 3 from the frequency converter 6A
．． A 18 MHz signal is supplied to the amplitude modulator 13, while an input color video signal is supplied to the horizontal synchronization signal separation circuit 14 to extract the horizontal synchronization signal sH, which is sent to the amplitude modulator 1.
3 and t4. -fL-3, 18, MHz signal is amplitude-modulated with the horizontal synchronization signal sH to obtain a modulated pilot signal PC, which is supplied to the combiner 12.

Then, in the synthesizer 12, the carrier color signal C8 and the modulated pilot signal Po are frequency-multiplexed, and the multiplexed signal cs+pc (Fig. 3E) is supplied to the frequency converter 8C, and the frequency converter 6A outputs fs+fL. =3.98MHz signal, carrier frequency is (fS+fL)-
f s = f L = 0.4 MHz carrier color signal CL
and the carrier frequency is (fs + fL) - (fs - fL) -2
A modulated pilot signal PD of fL-0.8 MHz is obtained (FIG. 3F) and is supplied to the synthesizer 10 through the low-pass filter 9C.

Then, polyphonic signals (FIG. 3G) of the signals YD, cL, and PD are taken out from the synthesizer 10, and supplied to the magnetic head 16 through the recording amplifier 15 to be recorded on, for example, a magnetic tape.

In this case, the carrier color signal C from the bandpass filter 11
8 is supplied to the burst gate circuit 17 to take out a burst signal, which drives the oscillator 4 in synchronization 1.Furthermore, the horizontal synchronization signal sH from the circuit 14 is supplied to the phase comparator circuit 18, and the variable frequency 1 A signal of fL-T2fH=0.4MHz from the oscillator 5 is supplied to the frequency divider 19 and divided into 100] to obtain the horizontal frequency fH.
This signal is supplied to the phase comparison circuit 18, and the comparison error voltage is supplied to the variable frequency oscillator 5 to control its oscillation frequency.

During reproduction, as shown in Fig. 2, the magnetic head 2
1, the above-mentioned carrier frequency is 3 f L
= 1.2 MHz mainly upper sideband modulated luminance signal YD and carrier frequency f I, = 0.4 MHz
The carrier color signal CL and the carrier frequency are 2 f L = 0.8
Multiplexed signal with MHz modulated pilot signal PD (
G) in FIG. 3 is supplied to a frequency converter 24Y through a regenerative amplifier 22 and an automatic gain control circuit 23, while a signal of f s = 3.58 MHz from a fixed oscillator 25 is supplied to another frequency converter 26A. In addition, a signal of f L = 0.4 MHz from the variable frequency oscillator 27 is supplied to this other frequency converter 26A through the switch circuit 28, so that the frequencies are respectively f s + f L
=3.98MHz, f S+2 f L-4, 38
MHz and fB−fL=3.18MHz are obtained, and the f3+2fL=4.38MHz signal is supplied to the frequency converter 24Y to frequency convert the reproduced multiplexed signal. Carrier frequency is (f3+2fL)-
3fL=fs-fL=3.18 MHz mainly lower sideband modulated luminance signal Y.

(H in FIG. 3), which is taken out through a low-pass filter 29A and supplied to a demodulator 30 to be output to a frequency converter 26A.
The demodulated luminance signal is demodulated using a signal of fs−f L = 3.18 MHz, and the demodulated luminance signal is supplied to the synthesizer 31.

The regenerated multiplexed signal is sent to another frequency converter 24C.
fs+f L from the frequency converter 26A
= 3.98 MHz signal to this frequency converter 24C
The frequency of the multiplexed signal supplied to and reproduced is converted so that the carrier frequency becomes (f S + f L ) - f L = f S
A carrier color signal Cs of 3.58 MHz and a carrier frequency (f
s+f L ) -2f L=f s-f L=3.
18 MI (z modulated pilot signal PQ is obtained (Fig. 3 ■), and the band pass filter 32 changes the carrier frequency to f3-
A carrier color signal Cs of 3.58 MHz is taken out and supplied to a synthesizer 31 to obtain a reproduced color video signal at an output terminal 33.

In this case, the bandpass filter 34 changes the frequency to f s
-f L=3.18 MHz pilot signal P.

The output voltage is taken out and supplied to the detection circuit 35, 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.

On the other hand, the pilot signal P from the filter 34.

is supplied to the phase comparison circuit 36, and the frequency converter 26A
A signal of fs-fL=3.18 MHz is supplied to the phase comparison circuit 36, the comparison error voltage is supplied to the variable frequency oscillator 27 to control its oscillation frequency, and the luminance signal from the demodulator 30 is supplied to the phase comparison circuit 36. The signal is supplied to the gate circuit 37, and the amplitude-modulated pilot signal P from the filter 34 is supplied to the detection circuit 38 as shown in FIG. The horizontal synchronizing signal sH of the demodulated luminance signal is extracted and supplied to the polarity discrimination circuit 39 to generate the horizontal synchronizing signal sH.
When the polarity of is inverted with respect to the normal polarity, the switch circuit 28 is switched by the output of the circuit 39, and the f L = 0.4 MHz signal from the variable frequency oscillator 27 is sent to the frequency converter 26A through the phase inversion circuit 40. supply

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

Now, assume that the carrier wave is ACO53ωLt. 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 cosp t, and the modulated luminance signal is A (1+
mC03P t )CO33(IJ L t).

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

Here, A (1+mC03P t )CO33ωL is −AC
O33ωL t+LmAcO3(3(Z)L+P)
t2 ±7mACO8(3ωL-P)t.

Among these, the residual sideband component YD of the modulated luminance signal is
−EYCO8(3ωL×P)t.

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

Further, if the pilot signal PD is EPCO52ωLt, the signal from the fixed oscillator 25 is COSωSt, and the signal from the variable frequency oscillator 27 is CO3(ωLt10), the signal supplied from the frequency converter 26A to the frequency converter 24Y is cos((ωS+2ωL)t+20), so
Modulated luminance signal Y obtained from filter 29A.

is E Ycos (3ωL0P) t -CO3(
(ωS+2ωL)t+2θ) →E Ycos ((ωS-ωL-P)t+2θ), and the signal supplied from the frequency converter 26A to the demodulator 30 becomes cos((ωS-ωL)t-θ). , the demodulated luminance signal obtained from the demodulator 30 is expressed as EYCO3((ωS-ωL-P)t+2θ)・C08(
(ωS-ωL) becomes -θ) →B Ycos(P t -3θ).

On the other hand, since the signal supplied from the frequency converter 26A to the frequency converter 24C is cos ((ωS+ωL) is 10θ), the pilot signal Pc obtained from the filter 34 is E pC,O3((ωS (IJ L ) t+θ
), and in the phase comparison circuit 36, the signal cos((
ωS−ωL) and −θ) and this pilot signal EPCO3
((ωS-ωL)t+θ) is compared in phase, and the phase difference 2θ is variable so that it becomes 2nπ (n-0, 1, 2, ...), that is, θ-nπ. A frequency oscillator 27 is controlled.

Therefore, the demodulated luminance signal is θ-0, 2π,...
When..., E YCO3p t, θ=π, 3
When π..., it becomes -E YCO8P 1.

However, when the demodulated luminance signal becomes -Ey CO8p t due to θ-π, 3π, . Phase inversion circuit 40
The phase of the demodulated luminance signal is immediately inverted and supplied to the frequency converter 26A as θ-0, 2π, . . . , and the demodulated luminance signal is immediately converted into E Therefore, a demodulated luminance signal of a predetermined polarity is always obtained.

In addition, in FIG. 2, the carrier frequency fL after low-frequency conversion,
If the pilot signal frequency 2fl and the carrier wave frequency 3fl of the modulated luminance signal include jitter fluctuations in the tape drive system, the output of the automatic gain control circuit 23 of the reproduction circuit will have △fl, △2fL, and △3fl, respectively. These phase fluctuation components include the fixed oscillator 25, the phase comparator circuit 36, and the variable frequency oscillator 27.
Needless to say, it is absorbed by the automatic phase adjustment system including the following.

The example in FIG. 4 is an example in which a modulated luminance signal, a carrier color signal, and a pilot signal are frequency-converted together, and the color video signal from the input terminal 1 is supplied to the low-pass filter 2B. -2 fj = 2.78 MHz, the luminance signal YA (Fig. 6A) is taken out and sent to the modulator 3.
while f s−=3.58 from oscillator 4
MHz signal and f L= from variable frequency oscillator 5
A 0.4 MHz signal is supplied to the frequency converter 6B, and from this the frequency becomes fs-2f L=2.
．． 78 MI (7, obtain three signals of fs-f L = 3.1.8 MHz and f s + f L = 3.98 MHz, and supply the f s-2f L = 2.78 MHz signal to modulator 3. Then, the luminance signal YA is subjected to amplitude modulation, for example, balanced modulation as described above, and from this, the modulated luminance signal Y
B (Figure 6B) is obtained.

And this modulated luminance signal YB is fs 2fL=2.7
It is supplied to a low-pass filter 7B with a characteristic of lowering the frequency by 6 dB at 8 MHz, and its main component is the lower sideband component Yc (Fig. 6C).
is taken out and supplied to the synthesizer 20.

The input color video signal is also passed through a bandpass filter 11.
A carrier color signal C8 having a carrier frequency f s = 3.58 MHz is extracted from the carrier color signal C8, and is supplied to the synthesizer 20.

Furthermore, f s−f L = from the frequency converter 6B
3.1.8 MHz signal is supplied to the amplitude modulator 13, while the input color video signal is supplied to the horizontal synchronization signal separation circuit 1.
4, extracts the horizontal synchronizing signal S F (and supplies it to the amplitude modulator 13 to amplitude modulate the fs-fL=3.18 MHz signal with the horizontal synchronizing signal S H to generate the modulated pilot signal PC. and supplies it to the synthesizer 20.

Then, in the synthesizer 20, the modulated luminance signal Yc,
The carrier color signal C8 and the modulated pilot signal Pc are frequency-multiplexed to produce the multiplexed signal Yc+C8+PC (FIG. 6D)
is supplied to the frequency converter 8, and f from the frequency converter 6B is
The carrier frequency is (fs+fL)-(fs-
2fL)=3 fL=1.2MHz mainly upper sideband modulated luminance signal YD and carrier frequency (f s+
fL) f5=fL-'1.4MHz carrier color signal CI, and the carrier frequency is (fs+fLknee (fs
-f L ) -2f L = 0.8 MHz modulated pilot signal PD is obtained (FIG. 6E).

These signals YD1CL are then filtered through the low-pass filter 9.
and PD multiplexed signal (FIG. 6F) is extracted and supplied to the magnetic head 16 through the recording amplifier 15 and recorded on, for example, a magnetic tape.

During reproduction, as shown in FIG.
1, the above-mentioned carrier frequency is 3 f L
= a mainly upper sideband modulated luminance signal YD of 1.2 MHz, a carrier chrominance signal CL with a carrier frequency of f L = 0.4 MHz, and a carrier frequency of 2 f L , = o,
A multiplexed signal (FIG. 6F) with the modulated pilot signal PD of 8 MHz is supplied to the frequency converter 24 through the regenerative amplifier 22 and the automatic gain control circuit 23, while f s = 3 from the fixed oscillator 25. A signal of .58 MHz is supplied to another frequency converter 26B, and a signal of fL = O-4 MHz from the variable frequency oscillator 27 is supplied to this other frequency converter 26A through the switch circuit 28, from which the frequency are respectively f s+f L=3
．． 98MHz, fs-2fL = 2.78MH
We obtained three signals of z and f3-fL = 3.18 MHz, and that f3 + fL = 3.98 MHz.
The signal is supplied to the frequency converter 24, and the reproduced multiplexed signal is frequency-converted so that the carrier frequency becomes (fs+fL).
−3fL−f B 2 f L = 2.78 MH
The modulated luminance signal Yc is mainly a lower sideband of z, and the carrier frequency is (fs+fL) -fL=fs=3.58M
Hz carrier color signal Cs and carrier frequency (f s + fL
)-2fI, -f s-f L=3.18MI (obtain the pilot signal PC of z (Fig. 6G).

Then, the carrier frequency is changed to f s by the low-pass filter 29
2 f I, = 2.78 MHz modulated luminance signal y
o is taken out, and supplied to the demodulator 30, demodulated with the fs-2f L = 2.78 MHz signal from the frequency converter 26B, and the demodulated luminance signal is supplied to the synthesizer 31, and the band The carrier frequency is f in the pass filter 32.
Take out the carrier color signal C8 of s=3.58 MHz,
This is supplied to a synthesizer 31, and a reproduced color video signal is obtained at an output terminal 33.

In this case, the frequency of the band pulse filter 34 is f
s-f L = 3.18 MHz pylon] - Take out the signal Pc and perform the same control as in the case of Fig. 2.

According to the method of the invention described above, a low-pass converted carrier chrominance signal, a balanced modulated luminance signal whose carrier frequency is three times that of the low-pass 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 three 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, although the recording/reproducing characteristics of magnetic tape etc. exhibit a peak at a relatively low frequency, for example, around 1 MHz, if the carrier frequency of the modulated luminance signal is three times that of the carrier chrominance signal that has been low-band converted, for example, Since it concerns a low frequency of 1.2 MHz, its carrier frequency comes before and after this peak, and therefore the S of the luminance signal
/N gets better.

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.

Furthermore, it is possible to extract and record luminance signals up to a relatively wide band of around 3 MHz.

In addition, as shown in the example in the figure, if the horizontal synchronizing signal position is detected during playback by amplitude modulating this pilot signal, the modulation of the luminance signal is performed by adjusting the white level and horizontal synchronizing signal as shown in Figure 7. The amplitude can be maximized at the peak level of sH, and as shown in Figure 8A and B, the amplitude becomes zero at a level halfway between the white level and black level shown by the straight line, and the synchronization signal sH. It is possible to perform deeper modulation than in the case where the corresponding portion is modulated to have a larger amplitude than the other portions and the horizontal synchronization signal position is detected based on this amplitude difference during reproduction.

Although the above example is a case where the luminance signal is amplitude-modulated, it may also be phase-modulated.

[Brief explanation of drawings]

FIG. 1 is a system diagram of a recording system as an example of the method of the present invention, FIG. 2 is a system diagram of its reproducing system, FIG. 3 is a spectrum diagram for explaining the same, and FIG. 4 is another example of the method of the present invention. FIG. 5 is a system diagram of the recording system, FIG. 5 is a system diagram of the reproducing system, FIG. 6 is a spectrum diagram for explaining the same, and FIGS. 7 and 8 are waveform diagrams showing the modulation state. 1 is the color video signal input end, 2A, 2B. 7A, 7B, 9Y, 9C and 9 are low pass filters, 3
and 13 are amplitude modulators, 8Y, 8C and 8 are frequency converters, 11 is a band pass filter, and 14 is a horizontal synchronizing signal separation circuit.

Claims (1)

[Claims] 1 a low-band-converted carrier chrominance signal CL, a balanced modulated luminance signal YD whose carrier frequency is three times that of this low-band-converted carrier chrominance signal and is mainly in the upper band, and the above-mentioned low-converted carrier; In order to reproduce a color video signal recorded on a recording medium, a composite signal of the color signal CL and a pilot signal PD having a frequency twice the carrier frequency is connected to at least an automatic gain control circuit and the automatic gain control circuit. A first frequency conversion circuit converts the carrier color signal CL subjected to the low frequency conversion and the pilot signal PD to a high frequency frequency; and a first frequency conversion circuit connected to the automatic gain control circuit converts the carrier wave of the balanced modulated luminance signal YD into a high frequency a second frequency conversion circuit that converts the frequency into a frequency; 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 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 conversion/demodulation signal generation circuit for supplying a signal having a predetermined frequency and phase to a demodulation circuit for the balanced modulated luminance signal Yc; controlling the amplitude of the signal reproduction signal with the automatic gain control circuit, and controlling the frequency and phase of the output signal of the conversion/demodulation signal generation circuit based on the phase comparison signal of the phase comparison circuit;
This frequency and phase controlled oscillation signal is transmitted to the first.
A method for reproducing a color video signal, the signal being 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.