JPH03113974A - Video signal recording and reproducing device - Google Patents

Abstract

PURPOSE:To reduce the deterioration in picture quality due to moire by detecting a phase error or an FM modulation signal at a reference point in a horizontal blanking based on a vertical horizontal synchronizing signal separated from an inputted video signal and retarding the video signal so as to make the phase error zero. CONSTITUTION:A recording signal processing circuit 2 converts the inputted video signal into a recording signal suitable for the recording format based on vertical and horizontal synchronizing signals H, D inputted from a synchronizing separator circuit 1 and a synchronizing signal and a burst signal being the reference for time axis correction at the reproduction are inserted in a horizontal blanking period of a recording video signal. A video signal (d) outputted from a variable delay circuit 3 is converted into an FM modulation signal (e) by an FM modulation circuit 4. The FM modulation signal (e) whose phase is compensated is retarded at a variable delay circuit 6 by (TD-Td) and the delay is compensated so that the period of the horizontal synchronizing signal H is constant, the result is amplified by a recording amplifier 7 and recorded on a magnetic tape 9 with a rotary head 8.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a video signal recording and reproducing device that modulates and records a recording signal by FM modulating the recording signal. This invention relates to a device for phasing.

[Prior Art] As a video tape recorder (hereinafter referred to as rVTRJ), a video signal is FM-modulated and recorded on a magnetic tape by a magnetic head, and a reproduced signal reproduced from the magnetic tape by the magnetic head is FM-demodulated. A device for obtaining a reproduced video signal is known.

Such VTRs have a problem in that moiré occurs at the edge portions of the reproduced video signal, particularly where the white level changes from the black level.

The process of moire generation will be explained below. For example, if the video signal supplied to the FM modulation circuit of the recording system is
Assume that there is an etched portion that falls from white to black as shown in a). At this time, moiré as shown by diagonal lines in FIG. 8(b) occurs in the edge portion of the FM demodulated video signal output from the FM demodulation circuit of the reproduction system. The reason why such moiré occurs is as follows.

- When performing FM modulation on a video signal, the frequency on the white level side is selected to be higher. The period of the white level portion of the FM modulation signal is, for example, TV, and the period of the black level portion is, for example, T8 (>Tw). In this case, since the phase of the FM carrier is not locked to the video signal, the phase of the FM modulation signal can take various phases at the point of change from the white level to the black level.

FIGS. 8(C) to 8(e) are waveform diagrams showing examples thereof, respectively. As is clear from these figures, when the video signal a changes sharply from the white level to the black level, the FM
The period of the modulation signal e changes from Tw to 71%, but due to the phase relationship between the FM carrier and the change point of the video signal, the period of the FM modulation signal immediately after the change point is T I""
It will vary like T s. Therefore, if a pulse count type FM demodulation circuit that counts zero crossing points is used in the FM demodulation circuit of the reproduction system, moiré occurs in the edge portion of the video signal after FM demodulation as described above.

Note that when the video signal changes sharply from the black level to the white level, the period of the FM modulation signal changes from TB to Tw, so the zero cross point of the FM modulation signal immediately after the change point varies. is small, and moiré at the edge of the video signal after FM demodulation does not pose much of a problem.

The moiré described above looks like jitter, especially on a still screen, and is very unsightly. Also, JP-A-58-
In order to correct the time axis error (jitter) during playback, as in the time axis correction device of Publication No. 124385, the method shown in FIG.
), there is a method of adding a horizontal synchronization signal and a burst signal in advance during recording and using those signals during playback to absorb time axis errors. For the same reason as in the case of the video signal described above, moiré as shown by diagonal lines in FIG. 9(b) occurs, and the accuracy of the time axis correction operation deteriorates.

[Problems to be Solved by the Invention] Since the conventional video signal recording and reproducing apparatus is configured as described above, the effect of moire looks like jitter, especially in still images, making it very unsightly. Further, when performing time axis correction, the influence of moire becomes residual jitter, which has a negative effect on the time axis correction operation.

The present invention was made to solve the above-mentioned problems, and an object of the present invention is to provide a magnetic recording/reproducing device in which image quality is less degraded by moiré.

[Means for solving the Li2 problem] The video signal recording and reproducing device according to the present invention has an FM
The present invention is characterized in that it includes a phase error compensating means for compensating the signal phase of the modulated signal during the horizontal blanking period so that it becomes the same phase every horizontal scanning period.

[Operation] The phase error compensating means in the present invention detects the phase error of the FM modulation signal with respect to the phase reference signal every horizontal scanning period, and delays the video signal so that this phase error becomes zero. Therefore, the occurrence of moiré at the trailing edge of each signal is reduced, and a visually good reproduced image with less influence of moiré can be obtained.

[Embodiments of the Invention] Hereinafter, one embodiment of the present invention will be described with reference to the drawings. 1st
In the figure, (1) is a synchronization separation circuit that separates vertical and horizontal synchronization signals from the input video signal, and
A phase detection position designation signal b (shown in FIG. 2(b)) is output. (2) is the recording signal processing circuit, and the synchronization separation circuit (1)
Based on the vertical and horizontal synchronization signals H and D input from the (3) is a variable delay circuit that adds a synchronization signal and a burst signal that serve as a reference for the recording video signal, and performs emphasis etc. is delayed by Td. (4) is an FM modulation circuit that performs FM modulation on the delayed recording video signal d, and (5) is a phase detection circuit, which generates an FM modulation modulation signal based on the phase detection position designation signal inputted from the synchronization separation circuit (1). The tube phase is detected and a delay time setting signal ve corresponding to the detected phase difference φ is output. (6)
is the delay time setting signal V input from the phase detection circuit (5). (7) is a recording amplifier, (8) is a rotary head, (9 ) is a magnetic tape.

Figure 3 is a block circuit diagram of a configuration example of the phase detection circuit (5), where (20) is a capacitor that removes the DC component of the input signal, (21) is a fixed delay circuit, and (22) is a capacitor (20). A divider (23) divides the output of the divider (22) by the output of the fixed delay circuit (21). This is a sample value hold circuit that samples and holds the value of ).

FIG. 4 is a circuit diagram of a configuration example of the variable delay circuit (3), in which the delay time Td is set according to the voltage of the delay time setting signal vc. FIG. 5 is a diagram showing the delay characteristics of the variable delay circuit (3).

Next, the operation will be explained. The input video signal is input to a synchronization separation circuit (1) and a recording signal processing circuit (2). The recording signal processing circuit (2) converts the input video signal into a recording signal conforming to the recording format based on the vertical and horizontal synchronization signals H and D manually inputted from the synchronization separation circuit (1). As shown in (a), a synchronization signal and a burst signal are inserted into the horizontal blanking section of the recorded video signal to serve as a reference for time axis correction during playback, and after applying emphasis etc., the variable delay circuit ( 3) Output to. The variable delay circuit (3) is composed of a variable delay line, and the delay amount is set to Td based on the delay time setting signal ve input from the phase detection circuit (5). It is configured to be reset at the same time as the video signal ends.

The video signal d output from the variable delay circuit (3) is FM
The 0 phase detection circuit (5), which is subjected to FM modulation signal tube conversion by the modulation circuit (4), converts the FM modulation signal tube phase into a phase detection position designation signal, as shown in the enlarged waveform diagram of FIG. 2(C). The phase error φ is detected using the rising edge of the signal as a reference.

The FM modulation signal e0 shown by the broken line in FIG. 2(c) shows the FM modulation signal when the phase error φ is 0.

In this embodiment, the position for detecting the phase error φ is set at the black level portion of the horizontal blanking interval, so the frequency of the FM modulation signal tube FM carrier at that phase detection position is known. Therefore, it becomes possible to detect the FM modulation signal tube phase.

Next, the operation of the phase detection circuit (5) shown in FIG. 3 will be explained.

First, the DC component included in the FM modulation signal tube is removed using a capacitor (20) to obtain a signal φ(t) x Asin (2πωet+φ) (ωe = carrier frequency of the black level FM video signal), and this signal φ (1), fixed delay circuit (
21), the black level FM carrier frequency ωC is delayed by 174 phases to obtain the signal ψ(t) = A cos (2πω, 1+φ), and these signals are divided by the divider (22) to obtain the signal Then, based on the phase detection position designation signal S, sample and hold the value of this signal, obtain a delay time setting signal ve based on this hold value, and send this signal VC to the variable delay circuit (3) and ( 6). In this embodiment, it is assumed that when the sample hold value is 0, the phase error φ of the FM modulation signal is 0.

The above detailed operation will be explained using FIG. 6.

FIG. 6(a) is a waveform diagram of the horizontal synchronizing signal portion of the video signal al with a phase error φ output from the recording signal processing circuit (2), and FIG. 6(b) is a waveform diagram of the horizontal synchronizing signal part when the phase error φ is 0. Waveform diagram of FM modulation signal e0, the same figure (c) is video signal a with phase error φ1
This is a waveform diagram of the FM modulation signal tube when phase compensation is not performed. In this case, moiré occurs at the edge portions as in the conventional example. Therefore, in order to compensate for the phase error φ1 of the FM modulation signal e1, the time T corresponding to the phase difference φ is required.
It is sufficient to delay the video signal a1 by d1, that is,
The length of the black level section from the end of the video signal to the horizontal synchronization signal H in FIG. 2(a) is determined by the phase detection circuit (5).
Tdl based on the delay amount setting signal Vel output from
Figure 6(d) shows a waveform obtained by delaying the video signal a by Tdl, and this signal d1
The waveform obtained by FM modulating is shown in FIG. 6(e). With this configuration, the phase of the FM modulation signal e is determined by the phase error φ
is compensated to 0 every horizontal scanning period, and each signal in the horizontal blanking period after the horizontal synchronization signal, for example, the waveform of the FM modulation signal of the burst signal, has exactly the same phase every -horizontal scanning period. Then, the phase-compensated FM modulation signal e is processed by the variable delay circuit (6) by (To-Td).
After the delay amount is compensated so that the period of the horizontal synchronizing signal H becomes constant, it is amplified by a recording amplifier (7) and recorded on a magnetic tape (9) by a rotary head (8).

If such a circuit configuration is adopted, the FM modulation signal e becomes a signal whose phase is compensated for each -horizontal scanning period, and it is possible to reduce image quality deterioration due to moiré as shown in the conventional example. Since the waveform of the FM modulation signal of each signal in the horizontal blanking period after the synchronization signal H is the same for each -horizontal scanning period, the time axis correction operation can also be performed satisfactorily.

FIG. 7 is a block circuit diagram of another embodiment of the present invention, in which the variable delay circuit (6) is omitted from the embodiment of FIG. This means that when the FM modulation signal e is delayed by (TO-Td) in the variable delay circuit (6) in FIG.
To prevent the waveform from becoming distorted when the amount of delay is changed, the video signal a is delayed by the variable delay circuit (3) during recording.
The delay amount Td is absorbed together with the jitter on the reproduction system side. Even with such a circuit configuration, the same effects as in the above embodiment can be obtained.

In the above embodiment, an analog delay circuit as shown in FIG. 4 was used as the variable delay circuit, but an analog memory such as a CCD may also be used to delay the recorded video signal. It may be D-converted and delayed using digital memory.

Further, in the above embodiment, the phase detection circuit (5) is configured as shown in FIG. 3, but the configuration is not limited to this.

In addition, in the above embodiment, all the signals added to the horizontal blanking period of the recorded video signal are sent to the recording signal processing circuit (2).
), but it is not limited to this, and the same effect can be applied even when adding a part of the horizontal blanking period (for example, adding only a burst signal) or when not modifying the horizontal blanking period at all. be effective.

[Effect of the Invention 1 As described above, according to the present invention, the phase error of the FM modulation signal at the reference point within horizontal blanking is detected based on the vertical and horizontal synchronization signals separated from the input video signal. However, since the video signal input to the FM modulation circuit is delayed so that the phase error becomes 0, -
The phase of the FM modulation signal can be aligned to a constant phase for each horizontal scanning period, and there is an effect that a magnetic recording/reproducing device can be obtained in which image quality deterioration due to moiré is reduced.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram of an embodiment of the present invention, FIG. 2 is a signal waveform diagram for explaining the operation of this embodiment, and FIG.
The figure is a block circuit diagram of the phase detection circuit of this embodiment.
Figure 5 is a circuit diagram of the variable delay circuit of this embodiment, Figure 5 is a characteristic diagram of this variable delay circuit, Figure 6 is a signal waveform diagram for explaining the operation of this embodiment, and Figure 7 is a diagram of the variable delay circuit of this invention. The block circuit diagrams of other embodiments, FIGS. 8 and 9, are signal waveform diagrams for explaining the reason why moiré occurs in the conventional device. (1)...Synchronization separation circuit, (2)...Recording signal processing circuit, (3), (8)...Variable delay circuit, (4)
...FM modulation circuit, (51--phase detection circuit. In each figure, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] (1) In a video signal recording and reproducing device that records a video signal by FM modulating the video signal, vertical and horizontal synchronization signals are separated from the video signal, and based on the vertical and horizontal synchronization signals, the horizontal FM modulation signal of the video signal is means for generating a reference signal for detecting the phase within the blanking period every horizontal scanning period; means for detecting the phase error of the FM modulation signal based on the reference signal; and the detected phase error signal. A video signal recording and reproducing device comprising at least means for delaying an input video signal so that the phase error in the horizontal blanking section of the FM signal becomes 0 based on the above.