JPH02301388A - Video reproducing device - Google Patents

Abstract

PURPOSE:To correct an error of a time axis of a reproduced FM signal and to suppress a bent picture or flickering by converting a dither signal exciting a head into a signal cancelling a time axis error with a head excitation at an equalizer circuit, controlling an output frequency of a voltage controlled oscillator to supply it as a clock for a variable delay line. CONSTITUTION:The device is provided with a time axis correction device consisting of a variable delay line 6 retarding an FM signal reproduced from a video head 1, a voltage controlled oscillator 7 generating a clock signal supplied to the variable delay line 6 and an equalizer circuit 8 controlling the voltage controlled oscillator 7 based on a dither signal. Then as a voltage of the dither signal gets higher, the output of the equalizer circuit 8 is decreased, the oscillating frequency gets lower and the delay time of the delay line 6 is increased. Conversely when the voltage is lowered, the output of the equalizer circuit 8 is increased, the oscillated frequency gets higher and the delay time is decreased. Thus, the time axis error is corrected with high accuracy and production of a bent picture or flickering on the screen is suppressed.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a video playback device equipped with a time axis correction device for correcting screen shaking, screen curvature, etc. that occur during playback of a video tape recorder. be.

[Conventional technology]

Figure 2 is the Television Journal Society Journal, 1978, Vol. 32, No. 1O.
In Figure 0, which is a block diagram showing the auto-tracking device shown in Tracking automation (pages 839-841) in the special feature on magnetic recording described in the issue, 1 is a video head, 2 is a head deflector that excites the head, 3 is a head deflector driving amplifier, 4 is a head amplifier that amplifies the FM signal reproduced by the head, 5 is a limiter, 15
9 is a demodulator for the reproduced FM signal; 9 is a reference signal source that generates a dither signal to excite the head; IO is a flat equalizer that corrects fast fluctuations in the envelope of the FM signal; 11 is an automatic gain adjuster (AGC amplifier); 12 13 is an envelope detector that detects the envelope of the FM signal, 13 is a synchronous detector, and 14 is an adder.

FIGS. 3 and 4 are diagrams for explaining the operation of the above circuit.

FIG. 3 shows the situation when the video head is scanning with a certain amount of deviation from the recording track, and FIG. 4 shows the situation when the video head is scanning the recording track normally.

In both figures, (a) shows the dither signal generated from the reference signal source 9, and (b) shows the trajectory of the playback video head relative to the recording track. (C) is the waveform of the reproduced FM signal, (the peaks are the waveforms obtained by detecting the envelope from the waveform in (C), and (e) are the waveforms obtained by synchronously detecting (b) with the dither signal (a).

Furthermore, FIGS. 5 and 6 are explanatory diagrams showing the travel locus of the video head and its enlarged view when the video head has a tilted azimuth angle in a conventional auto-tracking device.

Next, the operation will be explained. In FIG. 2, an FM signal reproduced from a head 1 is amplified by a head amplifier 4, subjected to amplitude limitation by a limiter 5, and demodulated to a baseband video signal by an FM demodulator 15.

On the other hand, the FM signal output from the head amplifier 4 passes through a flat equalizer 1O that corrects fast fluctuations in the envelope and an AGC amplifier 11 that corrects slow fluctuations, and an amplitude modulation component is detected by an envelope detector 12. This variation is then input to the synchronous detector 13, which synchronously detects it with the dither signal output from the reference signal source 9, and detects it as an error signal indicating which side of the recorded track the video head has deviated to. The above dither signal is added to this error signal by an adder 14 and supplied to the head deflector drive amplifier 3 to cause the head to follow the recording track while exciting the head deflector 2.

The above operation will be explained with reference to FIGS. 3 and 4. FIG. 3(B) shows a state in which the head during reproduction is shifted leftward from the center of the recording track (off-track) with respect to the traveling direction. At this time, the FM signal reproduced from the head has the maximum signal amplitude when the trajectory of the head excited by the dither signal (a) is closest to the center of the track, as shown in (C) (at the Max position in the figure). ), the signal amplitude is minimum when it is farthest from the center (position Min in the figure), and when the dither signal is at a positive potential, the head moves to the left of the track in the traveling direction. This FM signal (C) is converted to flat equalizer 1.
0. If the signal is input to the envelope detector 12 after passing through the AGC amplifier 11, an envelope waveform as shown in (b) is obtained. This waveform (b) is synchronously detected to obtain the waveform (e), and by removing the dither signal frequency and higher frequency components, the voltage error signal indicated by the dotted line (←) in (e) can be obtained. It will be done. The magnitude of this error signal represents the amount of deviation of the head from the track center. After adding a dither signal to this error signal, the drive amplifier amplifies it by an appropriate amount and moves the head deflector so that the head follows the recording track.In this way, the head completely follows the recording track as shown in Figure 4. A stable state follows.

In FIG. 4, the position of the ← mark in (e) is at a potential of 0 (v) and represents the operation in a state where the error signal is zero.

In the above description, it has been assumed that the video head has no tilt gap angle, so that the video head accurately scans the recording track and a video signal without time axis error can be obtained.

However, when recording with a video head having a certain tilt gap angle and reproducing with almost the same video head, a time axis error will occur if the conventional method is used. This will be explained with reference to FIGS. 5 and 6.

In Figure 5, (a) is equivalent to (a) in Figure 3 or Figure 4.
) is the same dither signal waveform as (6), and f is a trajectory of the video head as in (6). PI, P2, P
3 represents an inclined gap video head, and the inclination of the head represents a helad gap, and the dotted line in the track indicates a recording state with an inclined gap video head, and has a constant angle with respect to the track width direction. Here, the intervals between the dotted lines are constant and represent unit time, and the recording state is assumed to have no time axis error.

On the other hand, when the head is excited with a dither signal, as shown in Figure 5(f), when the head is at position P2, the head gap is at a position delayed with respect to the recording signal, and at position P3, the head gap is at a position delayed with respect to the recording signal. The gap is in an advanced position. In other words, P2
At position P3, only the signal that is originally scanned can only be reproduced, resulting in a temporally expanded signal, and at position P3, even signals after the signal that should originally be scanned are reproduced, compressed temporally. This is a signal.

FIG. 6 is an enlarged view of FIG. 5(f) in the track width direction. y represents the track width direction, and X represents the traveling direction of the head.

Here, the displacement (distance) of the head from the center of the track
As shown in the figure, if Y is the amount of displacement of the head from the track center in the width direction, the position of the head shifts by X in the direction of movement, that is, the time axis error Δτ occurs by a time proportional to X. occurs.

The amount is Δτ−kX −−Y−tanθ−(1) θ: Head gap angle−−Relative velocity of the head Here, since the head gap angle is constant, tanθ is a constant, and the relative velocity of the head is also a constant. Since the gain of the drive amplifier 3 and the electro-mechanical conversion efficiency of the head deflector 2 are also predetermined values (constants), Y becomes a function of the dither signal. Therefore, the time axis error Δτ is also proportional to the dither signal.

If the gain of the drive amplifier 3 is 01, the electromechanical conversion efficiency of the head deflector 2 is G2, and the dither signal is sinωt, then Δr- is -tanθ-Gt -Gt ・sinωt
-P -s i nωt...(2) (The time axis error will be P-tanθ'G+'G*.

[Problem to be solved by the invention]

The tracking device of a conventional video playback device is configured as described above, so that when an FM signal is recorded with a video head having a certain inclined gap angle and played back with almost the same video head, the FM signal is There were problems such as errors in the time axis and distortion or shaking of the image on the screen.

This invention was made in order to solve the above-mentioned problems, and it is an object of the present invention to provide a video playback device that can correct errors in the time axis of reproduced FM signals and suppress image distortion and shaking. purpose.

[Means to solve the problem]

A video playback device according to the present invention includes a variable delay line that delays an FM signal played back from a video head, a voltage controlled oscillator that generates a clock signal to be supplied to the variable delay line, and a voltage controlled oscillator that controls the voltage based on a dither signal. It is equipped with a time base correction device consisting of an equalizer circuit that controls an oscillator.

[Effect]

In this invention, the dither signal that excites the head is converted into a signal that cancels the time axis error due to head excitation using an equalizer circuit, and the output frequency of the voltage controlled oscillator is controlled and supplied as a clock for the variable delay line.
The time axis error can be corrected by passing the M signal through a variable delay line.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a time axis correction device for a video playback device according to an embodiment of the present invention. In the figure, 6 is a variable delay line (such as a CCD) that is approximately one horizontal period of a television signal. It has a delay time of .

7 is a voltage controlled oscillator, and 8 is an equalizer circuit. Also, the same reference numerals as in FIG. 2 indicate the same or corresponding parts. However, the video head 1 has an inclined gap.

The operations of the components having the same numbers as those in the conventional example will be omitted. The FM signal reproduced from the head is amplified by the head amplifier 4 and input to the variable delay line 6.

On the other hand, the dither signal output from the reference signal source is given -2 times the characteristic by the equalizer circuit 8 and the voltage controlled oscillator 7 so as to cancel out the time axis error Δ2 expressed by equation (2). The equalizer circuit amplifies only the dither signal component and blocks unnecessary components (for example, high-order harmonics).

As the voltage of the dither signal increases, the output of the equalizer circuit 8 decreases, the oscillation frequency decreases, and the delay time in the delay line 6 increases. Conversely, when the voltage decreases, the output of the equalizer circuit 8 increases, and the oscillation power increases.When the head is at the (0 P) position, the reproduced signal is further advanced in the direction of travel of the head than its original position. is compressed in time.At this time, the output voltage of the equalizer 8 is small, so the output frequency of the voltage controlled oscillator is lowered, and the variable delay line acts to lengthen the signal delay time. .

Conversely, when the voltage of the dither signal is low, the head
Since the signal to be reproduced is temporally expanded, the variable delay line acts to shorten the delay time.

The FM signal that has passed through the variable delay line is amplitude limited by a limiter 5 and demodulated into a baseband video signal by a demodulator 15. Since time axis correction is performed in the state of the FM signal, there is no time axis error in the baseband video signal.

Furthermore, since the dither signal output from the reference signal source 9 that excites the head is used to obtain the time axis error due to head displacement, time axis correction can be performed with high precision.

In addition, in the above embodiment, a CCD was used for the variable delay line, but an A/D converter, a line memory, a D/A
Using a converter, the write clock of the A/D converter and line memory is used as the output signal of the voltage controlled oscillator 7,
The reading of the line memory and the clock of the D/A converter may be operated using a clock made with a highly accurate crystal.

Further, although the delay time of the variable delay line is set to be about one horizontal period, it may be any value that can correct the time axis error caused by the dither signal.

Further, the explanation has been made assuming that there is no time delay element in the response during electromechanical conversion in the head deflector 2, but if there is a time delay element, the equalizer circuit 8 may absorb the time delay element.

Furthermore, in the above embodiment, an example of a VTR that records a composite video signal in FM mode is shown, but a system that records a luminance signal in a home VTR using FM and converts and records a color signal in a low frequency range may also be used. A similar effect can be obtained by passing the converted color signals together through a variable delay line.

(Effects of the Invention) As described above, according to the present invention, the reproduced FM signal is passed through a variable delay line, and the delay time is controlled by a dither signal from a stable reference signal source. This has the effect of providing a video playback device that can correct axis errors.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a time axis correction device of a video playback device according to an embodiment of the present invention, and FIG. 2 is a block diagram showing a tracking device of a conventional video playback device.
3 to 6 are explanatory diagrams of the operation of the conventional device. 1 is a video head, 2 is a head deflector, 3 is a drive amplifier, 4 is a head amplifier, 5 is a limiter, 6 is a variable delay line, 7 is a voltage controlled oscillator, 8 is an equalizer, 9 is a reference signal source, 10 is a flat equalizer , 11 is an AGC amplifier, 12 is an envelope detector, 13 is a synchronous detector, 1
4 is an adder circuit, and 15 is an FM demodulator. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] (1) When reproducing a video signal recorded with a tilted gap video head having a certain tilted gap angle with respect to the track width direction, the tilted gap video head is excited and its position is moved to move the tilted gap video head to the recorded track. A video playback device having a tracking device that completely tracks the video head, comprising: a variable delay line that delays an FM signal played from the video head; a voltage controlled oscillator that generates a clock signal to be supplied to the variable delay line; 1. A video playback device comprising a time axis correction device comprising an equalizer circuit that receives a dither signal used to excite a head and controls a voltage controlled oscillator.