JPS61247191A - Video signal reproducing system - Google Patents

Abstract

PURPOSE:To improve the resolution by leaps and bounds by controlling the phase of a carrier for frequency conversion so that phase relations between a synchronizing signal of a demodulated reproduced low band luminance signal and a high band component of a synchronizing signal included in a high band luminance signal are fixed. CONSTITUTION:The output of a frequency demodulator 5 has the frequency converted with jitter by the carrier for frequency conversion which passes a phase shifter 73 on a basis of a horizontal synchronizing signal obtained by a synchronizing signal separator 11 to take out only a luminance signal by a luminance signal comb line filter 8. This signal and a low band luminance signal YL of the output of the demodulator 5 are synthesized to obtain a chrominance signal without jitter and a luminance signal whose high band component and low band component have the same jitter. Phase relations between the synchronizing signal and the high band component of the synchronizing signal included in the high band luminance signal are detected by a phase detector 70, and the phase shifter 73 is controlled so that they are fixed. Thus, the phase of the carrier is kept correct, and the phase of a high band luminance signal YH and that of a low band luminance signal YL coincide with each other.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for reproducing video signals recorded using a low frequency conversion method.

2. Description of the Related Art A conventional low frequency conversion video signal recording and reproducing system has a configuration as shown in FIGS.

This will be explained using FIG. 4.

Figure 4a shows an NTS signal in which the luminance signal Y and chromaticity signal C are combined.
Although a composite color video signal such as C or PAL is shown, the following explanation will be based on an NTSC signal. The NTSC signal is applied to input terminal 2o in FIG.

Then, a low pass filter (hereinafter referred to as LPF) of about sMHz is applied.
As shown in FIG. The composite color video signal that has passed through the bandpass filter (hereinafter referred to as BPF) 24 is composed of the high-frequency components YH of K, luminance signal Y, and carrier color signal C, as shown in FIG. 4C. become something. If we consider the chromaticity signal C by dividing it into a subcarrier frequency f8 and a sideband component element 0, this can be expressed as f, +fC+YH. From this signal, only the burst signal is extracted by the burst gate 26, and a continuous wave of the burst frequency and the subcarrier frequency f is obtained by a PLL (phase locked loop) consisting of a phase comparator 26, an LPF 27, and a voltage controlled crystal oscillator 28. A PLL consisting of a phase comparator 32, an LPF 33, a voltage controlled oscillator (hereinafter referred to as VCO) 34, and a frequency divider 36 converts the horizontal synchronization signal fH extracted from the composite color video signal by the synchronization separator 31 into a low-frequency subcarrier. Obtain f1 and balance modulator (hereinafter referred to as BM)
The signal obtained by 29 is a continuous wave with a frequency of f8+f1, so this and the output of BPF24 are combined with BM3.
0 to obtain a low-frequency converted signal centered on the low-frequency subcarrier f1. This signal and the FM signal are combined, as shown in FIG. 4d, which is amplified by the recording amplifier 23 and recorded on a magnetic tape or the like by the head 1.

FIG. 6 is a block diagram of the playback side, in which the playback signal obtained by the head 1 is amplified by a preamplifier 2, and then sent to a bypass filter (hereinafter referred to as HPF) 3 and an LPF 6 to produce an FM signal and a low-frequency conversion signal, respectively. It can be divided into

The FM signal is amplitude limited by a limiter 4 to suppress amplitude fluctuations, demodulated by an FM demodulator 6, and then converted to the original low-band luminance signal YL.
get.

However, it includes jitter Δ in the drive system of the magnetic tape, etc.

On the other hand, the low frequency conversion signal is returned to the carrier color signal C centered on the original subcarrier f by the output of the local oscillator 95 and the chromaticity processing unit (APC) s, and is combined with the low frequency luminance signal YL. At the output terminal 12, the original composite color video signal is obtained. At this time, the APC 9 operates to stabilize the phase of the subcarrier so that colors can be reproduced correctly on the receiver side. In other words, in APC9, BM
From the signal that has undergone frequency conversion at step 91 and passed through BPF 92, only the burst portion is taken out at burst gate 93, and its phase is compared with the output of subcarrier fixed oscillator 96 at phase comparator 94. The obtained error signal is output at LPFse. It is smoothed and drives VCOsy.

The output of the VCOs 7 is a frequency obtained by adding an error to the low subcarrier f1, which is the frequency of the subcarrier fixed oscillator 9.
The output of 6 is frequency-converted by BM98, and the frequency is converted by low-frequency conversion signal and BMel. Then, the conveyed color signal f, +fc+YH is obtained as shown in the following equation.

Cf +f +Δ)-Cf1-fC-YH+Δ)2f
8+fc+YH Since this loop performs a negative feedback operation to eliminate errors, a signal without jitter components is obtained as an output. This is generally called an APC loop. These are described in Japanese Patent Publication No. 50-14852.

Now, since the jitter of the carrier color signal has been removed, the colors are correctly reproduced, and the FM demodulated low-band luminance signal YL+Δ
Although it contains jitter, it can be tracked on the receiver side, so the image can be reproduced.

By the way, jitter has been removed from the high-frequency luminance signal YH, which is included in the carrier color signal band signal by frequency-converting the low-frequency conversion signal, but the receiver follows the jitter of the low-frequency luminance signal YL+Δ. Therefore, it appears to be distorted, as if there is jitter, and the reproduced high-frequency luminance signal YH
I can't make the most of it. A method of making use of this high-range luminance signal YH is also described in JP-A-57-89387-8, but it requires setting the frequency of the carrier wave for frequency conversion to be an integral multiple of the synchronization signal. As described above, this method cannot be applied to cases where the subcarrier fs of the NTSC signal is used as the carrier wave.

Problems to be Solved by the Invention When using the subcarrier f8 of the NTSC signal, (1
), there are two types of phase relationships with the synchronization signal. Therefore, even if the phases of the high-range luminance signal YH and low-range luminance signal YL are adjusted to match, the phase relationship of the other side will be different. If this happens, the phases of YH and YL will be out of phase by 1800.

f8=2 fH・・・・・・・・・・・・・・・・・・
(1) The present invention has been made in view of the above points, and is a video signal that can obtain a reproduced composite color video signal in which a high-range luminance signal YH and a low-range luminance signal YL are in phase with each other with a simple configuration. The purpose is to provide a playback method.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention focuses on the fact that there is always a constant phase relationship between the synchronization signal and the luminance signal. The phase relationship between the high frequency component of the synchronization signal included in the high frequency luminance signal is detected, and the phase of the carrier wave for frequency conversion is controlled so that the phase relationship is constant. Then, the present invention can reproduce a composite color video signal without shifting the phase of the low-frequency luminance signal and the high-frequency luminance signal by the above-described method, and the high-frequency luminance signal included in the low-frequency converted signal can be reproduced. It is possible to effectively restore components and dramatically improve resolution.

FIG. In FIG. 1, the same components as in FIG. 6 are given the same numbers, and their explanations will be omitted.

The two APCs 901 and 902 in Figure 1 are the APCs in Figure 6.
Same as 9.

The case of an NTSC signal will be explained with reference to FIG. Signals passing through the LPFs are input to APC901 and APC902. In the APC 902, as described above, the fixed oscillator 96 removes the jitter component and converts the frequency, and the chromaticity signal comb filter (CCF) 1o outputs only the chromaticity signal. As is well known, in this method, the chromaticity signal and the luminance signal have a frequency interleaving relationship as shown in Figure 3, and the chromaticity signal comb filter (CCF) 1
0 has the frequency characteristics shown by the solid line in the figure a, and can easily pass only the chromaticity signal.

On the other hand, in the APC901, based on the horizontal synchronization signal obtained from the output of the FM demodulator 6 and the synchronization separator 11, a 455 multiplier 71 consisting of a PLL. The carrier wave for frequency conversion, which becomes the frequency of the subcarrier f8 which is 5 times higher than that of the subcarrier f8 and passes through the phase shifter 73, performs frequency conversion with jitter. )s
extracts only the luminance signal. By combining these two signals and the low-frequency luminance signal YL that is the output of the FM demodulator 6, the output terminal 12 receives a carrier color signal without a shifter, and both the high-frequency component and the low-frequency component of the luminance signal. A luminance signal with the same jitter is obtained, and when viewed on a receiver, the color is correctly reproduced because the chromaticity signal has no jitter, and it follows the jitter of the luminance signal, so the high-frequency range of the luminance signal is You will be able to see it without wavering.

Further, a phase detector 70 detects the phase relationship between the synchronization signal and the high frequency component of the synchronization signal included in the high frequency luminance signal, and controls the phase shifter 73 so that the phase relationship is constant. By doing this, the phase of the carrier wave is maintained correctly, and the high-band luminance signal YH and the low-band luminance signal YL are in phase.

FIG. 2 shows an example using a time pace collector with a subcarrier feedback terminal, and shows a method of inputting an external carrier wave to the APC 9. In this case, a luminance signal and a carrier color signal both with jitter are outputted to the output terminal 12, and the jitter is removed by the connected time base collector to obtain a jitter-free composite color video signal. Even in this case, the phase detection section 7o
Then, there will be a phase shift.

Also, if the phase is adjusted correctly, the phase relationship between the synchronization signal and its high-frequency component can only be in two ways: Oo or 18oo, so if it deviates by 1800, use a phase shifter to invert it. You can also do it. In this case, the phase shifter may be a simple circuit that switches between inversion and non-inversion, and a flip-flop may be used for phase detection.

Effects of the Invention As described above, according to the present invention, with an extremely simple configuration, the high-frequency components of the low-frequency converted luminance signal are reproduced with correct phase, and the resolution is dramatically improved, making it extremely useful. It is.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a video signal reproducing method in one embodiment of the present invention, FIG. 2 is a block diagram showing a video signal reproducing method in another embodiment, and FIG. 3 is a comb filter characteristic and frequency. Diagram showing interleaving relationship, 4th
6 is a diagram showing the frequency spectrum of each signal, FIG. 6 is a block diagram showing a conventional video signal recording method, and FIG. 6 is a block diagram showing a conventional video signal reproducing method. To... Phase detection unit, 73... Phase shifter, 11... Synchronization separation unit. Name of agent: Patent attorney Toshio Nakao and one other name
Figure 3 Figure 4 Evening Figure 6

Claims (1)

[Claims] A carrier wave is frequency-modulated using a low-frequency conversion signal obtained by frequency-converting a carrier color signal band signal separated from a composite color video signal to a low frequency band, and a luminance signal separated from the composite color video signal by a low-pass filter. The reproduction carrier color signal band signal obtained by frequency converting the reproduced low-pass conversion signal separated from the reproduced signal obtained by reproducing it into the original frequency band, and the reproduced A video recording and reproducing method that obtains a reproduced composite color video signal by mixing a reproduced luminance signal obtained by demodulating a reproduced frequency modulated signal separated from the signal, wherein a synchronization signal of the reproduced luminance signal and the reproduced carrier color signal are mixed. By controlling the phase of the carrier wave used for frequency conversion so that the phase difference with the high frequency component of the synchronization signal included in the band signal is a constant value, the phase of both the carrier color signal band and the reproduced luminance signal is adjusted. A video signal reproduction method that is characterized by