JPH0220992A - Time base correcting circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is characterized in that the color signal of a video signal is frequency-converted to a low frequency band.
The present invention also relates to a time axis correction device that can be used in a device that reproduces a video signal from a magnetic recording medium in which a luminance signal is recorded with high frequency modulation.

2. Description of the Related Art In conventional consumer VTRs, the chrominance signal of a video signal is frequency-converted to a low frequency band, and the luminance signal is frequency-modulated to a high frequency band, and then recorded on a magnetic recording medium. During playback, in the process of converting the frequency of the color signal converted to the low frequency range back to the original high frequency range, time axis fluctuations (phase fluctuations) included in the color signal are removed.
Adding to the frequency modulated and recorded/reproduced luminance signal,
It was outputting to a monitor television receiver. this is,
This is because in the recording and reproducing system of a consumer VTR, a certain amount of time axis fluctuation occurs, and the phase of the color signal changes significantly due to the time axis fluctuation, so it is necessary to remove this phase. In addition, since the time axis fluctuations included in the luminance signal have a low frequency and are removed by the FC circuit included in the monitor television receiver, it is necessary to remove the time axis fluctuations included in the luminance signal. There was no (“Time axis fluctuation and its correction method” Konishi et al., Journal of the Television Society, p4g5
~6031 Volume 3, No. 6 (1981)).

Problems to be Solved by the Invention However, in such conventional consumer VTRs, as mentioned above, time axis fluctuations (phase fluctuations) included in color signals
is corrected, but the time axis fluctuation included in the luminance signal is not corrected, so the color signal and the luminance signal have different time axis fluctuations, causing image quality deterioration.

In particular, the color signal contains high-frequency components of the luminance signal,
Since the high frequency component and the low frequency component of the luminance signal have different time axis fluctuations, on the monitor television receiver,
The high-frequency component of the luminance signal is not used effectively, and there is a problem in that it acts as a kind of interference signal.

In view of the above, an object of the present invention is to provide a time axis correction device that corrects time axis fluctuations of color signals and luminance signals and does not cause image quality deterioration.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention uses a magnetic recording medium in which the color signal of a video signal is frequency-converted to a low frequency band, and the luminance signal is frequency-modulated to a high frequency band and recorded. , a variable delay device that takes the reproduced signal as an input signal and changes the delay time of the reproduced signal; a luminance separator that separates a frequency-modulated luminance signal from the output signal of the variable delay device; An FM demodulator that FM demodulates a luminance signal from the output signal, a sync separator that separates horizontal synchronization from the output of the FM demodulator, and an FM demodulator using the signal output from the sync separator as a control signal. A sample-and-hold device samples and holds the voltage of the pedestal portion of the output luminance signal or the sync-tip voltage, a low-pass filter detects the time axis fluctuation component from the output of the sample-and-hold device, and according to the output of this low-pass filter, It is equipped with a voltage controlled oscillator that generates a clock that drives a variable delay device, and is configured to eliminate time axis fluctuations in a reproduced signal reproduced from a magnetic recording medium.

Effect of the Invention With the above-described configuration, the present invention detects the time axis fluctuation of the reproduced signal reproduced from the magnetic recording medium by the change in the pedestal voltage or the sync tip voltage of the luminance signal. Detection is performed starting from a portion with good H, improving detection accuracy. In particular, the frequency used for the pedestal portion of the luminance signal is around 4 MHz in some systems, making it possible to detect high frequency components of time axis fluctuations with a good S/N ratio. Furthermore, since the time axis fluctuations of the color signal and the time axis fluctuations of the luminance signal are corrected at the same time, the high frequency components of the luminance signal included in the color signal can be effectively used.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the main parts of a time axis correction device according to an embodiment of the present invention.

In FIG. 1, a chrominance signal of a video signal is frequency-converted to a low frequency band, and a luminance signal is frequency-modulated to a high frequency band and recorded on a magnetic recording medium. The reproduced signal is input. The variable delay device 2 varies the delay time of the reproduced signal according to the clock output from the voltage controlled oscillator 8, thereby correcting the time axis fluctuation of the reproduced signal. Next, the signal output from the variable delay device 2 is input to the brightness separator 3. Brightness separator 3
Then, the frequency-modulated luminance signal multiplexed with the reproduced signal is separated and output to the 7M demodulator 4. The 7M demodulator 4 demodulates the luminance signal and outputs it to the sync separator 5 and sample-and-hold device 6. The sync separator 6 separates the horizontal sync signal included in the luminance signal, and the sample and hold unit 6 uses the horizontal sync signal output from the sync separator 5 to separate the luminance output from the 7M demodulator 4. Sample and hold through the pedestal voltage of the signal.

That is, as shown in FIG. 2, the sample and hold pulse shown in (b) is generated for the luminance signal of one horizontal synchronization period shown in (a), and the sampled and held pedestal voltage shown in (C) is output. . Next, the Lohas filter 7 separates and detects the time axis fluctuation component from the output of the sample and hold device 6 in frequency, and outputs the detected component to the voltage controlled oscillator 8 . Next, the voltage controlled oscillator 8 varies the frequency of the clock according to the time axis fluctuation component output from the low-pass filter 7 and outputs it to the variable delay unit 2. Therefore, with the above-described configuration, the time axis fluctuation component can be detected from the pedestal voltage of the luminance signal, and by varying the delay time of the variable delay device 2, it is possible to obtain a reproduction signal of the magnetic recording medium without time axis fluctuation.

Next, the variable delay device 2 shown in FIG.
Mu/D conversion circuit 12 shown in FIG. Memory circuit 13.
D/MU conversion circuit 14. It is constituted by a low-pass filter 15, and the delay time changes depending on the frequency of the clock input from the terminal 17.

The variable delay device 2 shown in FIG. 1 also has a limiter circuit 22 . shown in FIG. 3(b). It can also be configured by an n-stage inverter circuit 23, but in this case, the signal input to the terminal 24 for controlling the delay time is a DC voltage. Therefore, the output of the low-pass filter 7 shown in FIG. 1 is amplified and used as a control voltage.

In this embodiment, the variable delay device 2 shown in FIG.
It may also be configured using a CAN (charge coupled device).

Further, in this embodiment, a configuration has been described in which the time axis variation component is detected from the pedestal voltage of the luminance signal, but the time axis variation component may be detected from the sync tip voltage in the same manner as the above-described configuration.

Effects of the Invention As described above, according to the present invention, since the time axis fluctuation component is detected from the pedestal voltage or sync tip voltage of the luminance signal, the best transmission C/N of the magnetic recording medium can be detected. can be used to improve detection accuracy. In particular, the frequency used for the pedestal portion is about 4 MH2 in some systems, which increases the output of high frequency components of time-axis fluctuations and further improves detection accuracy. Furthermore, according to the present invention, since the time axis fluctuations of the luminance signal and the time axis fluctuations of the color signal are corrected simultaneously, the high frequency components of the luminance signal included in the color signal can also be effectively used. Extremely useful.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a main part showing a time axis correction circuit according to an embodiment of the present invention, FIG. 2 is a waveform diagram showing time timing in each part of the same, and FIG. 3 is a block diagram of a main part showing the same variable delay device. It is. 2...Variable delay device, 3...Brightness separator, 4...FM demodulator, 6...Sync separator, 6...・Sample hold device, 7.16...
...Low pass filter, 8...Voltage controlled oscillator, 12...M/D conversion circuit, 13...
・Memory circuit, 14...D/person conversion circuit, 22
・・・・・・Limiter circuit, 23...group n-stage inverter circuit. Name of agent: Patent attorney Shigetaka Awano and 1 other person 1st
Figure 2 (C-n

Claims (1)

[Claims] A reproduction signal reproduced from a magnetic recording medium in which the color signal of the video signal is frequency-converted to a low frequency band and the luminance signal is frequency-modulated to a high frequency band is used as an input signal, and the delay time of the reproduction signal is calculated. a brightness separator that separates a frequency-modulated brightness signal from the output signal of the variable delay device; and an FM demodulator that performs FM demodulation of the brightness signal from the output signal of the brightness separator; a sync separator that separates horizontal synchronization from the output of the FM demodulator; and a sync separator that separates horizontal sync from the output of the FM demodulator;
a sample-and-hold device that samples and holds the voltage of the pedestal portion of the luminance signal output from the demodulator or the sync-tip voltage; a low-pass filter that detects a time-axis fluctuation component from the output of the sample-and-hold device; A time axis correction device comprising: a voltage controlled oscillator that generates a clock for driving the variable delay device according to an output.