JPH08186798A - Skew distortion correction device in VTR - Google Patents

Abstract

(57) [Abstract] [Purpose] To minimize the skew distortion due to the horizontal sync phase shift that occurs when switching between the recording and playback heads, and to set the most stable operating conditions against interference such as noise. To aim. A skew distortion correction device in a helical scan type VTR, which includes an AFC2 that receives a reproduced video signal from the VTR1, a μ-COM4 that receives a head switching pulse from the VTR1, and an AFC2 and a μ-COM4.
And a monitor circuit 3 for displaying a horizontal synchronizing signal on the screen.
Based on the VCO control voltage, the COM4 detects the horizontal synchronization phase shift amount included in the playback video signal when switching between recording and playback heads, and supplies a current corresponding to the phase shift amount to the AFC2 during head switching. , A monitor circuit is controlled to correct skew distortion on the display screen.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a skew distortion correction device in a video tape recorder (hereinafter referred to as VTR), and particularly in a VTR of a helical scan system, a horizontal sync phase shift of a sync signal generated at head switching between recording and reproduction. The present invention relates to a skew distortion correction device that detects a quantity and controls a monitor circuit that monitors a reproduced video signal to correct skew distortion on a display screen.

[0002]

2. Description of the Related Art As is well known, a helical scan VTR is a magnetic tape which is alternately attached to a magnetic tape by a head mounted on a rotary cylinder so as to face each other at a 180 ° positional relationship. It is designed to be recorded or played back. On the other hand, considering the current VHS system as the magnetic tape format,
When the relative positional relationship of 80 ° is deviated by 1 ° between recording and reproducing, it becomes clear that the phase of the horizontal synchronizing signal of the reproduced video signal is shifted by 1.5 cycles before and after the head switching between recording and reproducing. ing. That is, in compatible reproduction with recording, at present, no matter how the relative mounting position of the head is managed, a horizontal synchronization phase shift of the horizontal synchronization signal occurs when the head is switched between recording and reproduction.

FIG. 3 shows a general automatic frequency control (AFC).
It is a principal part block diagram of a circuit. In the figure, 1 is a VTR, 21 is a sync separation circuit, 22 is an AFC detector, 23 is a voltage control circuit, and 24 is a frequency divider. Furthermore, 5 is a filter circuit. The AFC circuit 2 includes a sync separation circuit 21, an AFC detector 22, a voltage control circuit 23, and a frequency divider 24.

The AFC circuit 2 is usually built in a display device together with a monitor circuit. That is, VTR
In order to output a stable screen against interference due to noise or the like in a display device that monitors the reproduced video signal that has reproduced, the horizontal synchronization signal in the reproduced video signal output from the VTR is used in the AFC circuit 2 as shown in the figure. To generate a stable synchronization signal H-SYNC. The synchronization signal H-SYNC is sent to the monitor circuit.

In the circuit shown in the figure, the reproduced video signal from the VTR 1 is input to the AFC detector 22 via the sync separation circuit 21, and the output of the AFC detector 22 is a voltage controlled oscillator (V
CO) 23. On the other hand, the output of the VCO 23 is output as a horizontal synchronizing signal to the monitor circuit via the frequency divider 24. At this time, the rise of the output of the VCO 23 is adjusted by the filter constant of the filter circuit 5.

By the way, with respect to the horizontal synchronization phase shift that occurs when the recording and reproducing heads are switched as described above, this AF
The C circuit 2 may not be able to follow sufficiently and may be bent at the upper part of the display screen, that is, skew distortion may occur. Conventionally, in order to solve the above problems, an AFC as shown in this figure
By setting the circuit constant of the filter circuit 5 in the circuit so as to increase the control sensitivity by the output of the AFC detector 22 of the VCO 23, the VCO 23 is sharply synchronized with the input signal (that is, the output of the sync separation circuit 21). It corresponded.

However, if the response characteristic of the AFC circuit 2 is increased by the above measures, a video signal with deteriorated S / N (a TV tuner output in a weak electric field, a VTR reproduction output in which dubbing is repeated many times, etc.) is input. Sync separation circuit 2
When the S / N of the output of 1 deteriorates and the output of the AFC detector 22 has a large noise component, the filter circuit 5 cannot remove this noise component, and the VCO 23 becomes in an unstable oscillation state. As a result, the AFC circuit 22 has a characteristic of being weak against noise interference, and when a video signal with deteriorated S / N is input, jitter or an unstable phenomenon of horizontal synchronization occurs. For this reason, countermeasures are taken at a compromise point in consideration of both skew distortion and noise resistance, and it is difficult to obtain a sufficient effect on skew distortion.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and in a helical scan type VTR, skew distortion due to horizontal sync phase shift occurring at the time of switching between recording and reproducing heads is minimized, and noise and the like are minimized. The purpose is to set the most stable operating conditions against the interference of.

[0009]

SUMMARY OF THE INVENTION The present invention is a skew distortion correction device in a helical scan type video tape recorder, wherein an automatic frequency control circuit 2 for receiving a reproduced video signal from the video tape recorder 1 and the video. A microcomputer 4 that receives a head switching pulse from the tape recorder 1, and a V connected between the automatic frequency control circuit 2 and the microcomputer 4.
A CO control filter 5 and a monitor circuit 3 for displaying a horizontal synchronizing signal on a screen are provided, and the microcomputer 4 supplies the automatic frequency control circuit 2 with a VCO control voltage which is an end voltage of the VCO control filter 5. On the basis of the above, the horizontal sync phase shift amount generated at the time of head switching between recording and playback included in the playback video signal is detected, and a current corresponding to the phase shift amount is supplied to the automatic frequency control circuit 2 at the time of head switching. Thus, the skew distortion on the display screen is corrected by controlling the monitor circuit.

Further, the automatic frequency control circuit 2 detects the frequency difference between the sync separation circuit for receiving the reproduced video signal, the horizontal sync signal from the sync separation circuit, and the output obtained by dividing the output of the voltage controlled oscillator. AFC detector, voltage controlled oscillator for generating reference frequency, frequency divider for dividing output of the voltage controlled oscillator, and voltage controlled oscillator by the AFC detector for stable operation of the automatic frequency control circuit And a filter circuit for determining the control sensitivity characteristic of the video tape recorder, which is a VCO control voltage of the filter circuit when the head is switched between storage and reproduction of the video tape recorder.
After detecting the phase shift amount of the horizontal synchronizing signal based on the FC error signal, a current corresponding to the phase shift amount is supplied to the voltage controlled oscillator when the head is switched.

[0011]

In the present invention, the phase shift amount of the horizontal synchronizing signal is detected from the VCO control voltage of the AFC circuit (voltage at the filter end = AFC error signal, see FIG. 1) at the time of switching the recording / reproducing head of the VTR. A current corresponding to the amount is supplied to the VCO when the head is switched.

By this operation, the AFC circuit immediately responds to the horizontal sync phase shift at the time of switching the head between recording and reproduction, and as a result, it is possible to set the most stable operating condition against interference such as noise. Become.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of the main portion of a skew distortion correction device according to the present invention, and FIG. 2 is a signal timing chart at each point of the device of FIG. In FIG. 1, 1 is a video tape recorder (VTR), 2 is an automatic frequency control circuit (AFC), 3 is a monitor circuit (MON), 4 is a microcomputer (μ-COM), and 5 is a VCO control filter. Further, in FIG. 2, is a head switching pulse, is a reproduced video signal, is a horizontal synchronization signal, is AF
C error signal, VCO control signal, and corrected horizontal synchronizing signal.

In FIGS. 1 and 2, the reproduced video signal is output from the VTR 1 to the AFC circuit 2. This reproduced video signal contains a horizontal sync phase shift when the head is switched. Further, the head switching pulse from the VTR 1 is input to the microcomputer 4. On the other hand, the reproduced video signal has a horizontal sync phase shift each time the head is switched, so that an AFC error signal is generated at the end of the VCO control filter 5 every time the head is switched. This AFC error signal is input to the microcomputer 4. The microcomputer 4 detects the horizontal sync phase shift amount contained in the reproduced video signal based on the AFC error signal.

As shown in FIG. 2, the phase difference of the horizontal synchronizing signal is detected by the voltage difference of the AFC error signal before and after the rising and falling edges of the head switching pulse. The larger the phase difference, the larger the voltage difference. The terminal for detecting the AFC error signal is the control terminal of the VCO 23 in the AFC circuit 2, and when this signal is operating as the AFC circuit, the filter circuit 5 controls the phase shift of the horizontal synchronizing signal as shown in the figure. The effect is a signal that rises sharply first and gradually converges. In the present invention, the phase shift amount is detected based on this AFC error signal, and the VC is instantly detected.
The current that causes the output of O23 to follow the input signal is VC
Supply to the control terminal of O23.

Since a certain time is recorded on a video tape under a certain condition, a VT is generally used at present.
Based on the same concept as the auto tracking mounted on the R, it is considered that once detected, almost the same state will continue thereafter. That is, the phase difference shown in FIG. 2 occurs when the recording and reproducing VTRs are different. In other words, when a tape recorded on one VTR is reproduced, the phase difference from the beginning to the end of the tape is almost the same.
If the phase difference is detected once, only the correction operation needs to be performed thereafter. However, when a plurality of VTRs are recorded on one tape, the phase difference is deviated depending on the recording position. Therefore, in order to automatically perform skew distortion, this abnormality is detected and the position is again detected. It is necessary to detect the phase difference. The detection of this abnormality is generally the same as the re-detection of the auto-tracking mounted on the VTR, and it is possible to utilize this.

Therefore, a current corresponding to the detected phase shift is supplied from the microcomputer port to VC.
If the O control filter 5 is supplied at the same timing as the head switching pulse, a stable horizontal synchronizing signal can be obtained at all times. In this case, H of microcomputer
i, OPEN, and Low ports (not shown) are used to detect OPEN and to correct H when the correction
Either i or Low mode is set.

According to the present invention, it is not necessary to consider the case where the response speed of the AFC circuit is large, such as the phase shift of the horizontal synchronizing signal at the time of head switching. It is stable against disturbances such as.

[0019]

As described above, according to the skew distortion correcting apparatus of the present invention, the helical scan type VTR is used.
In the above, the horizontal sync phase shift that occurs when switching between the recording and reproducing heads can be minimized, and the most stable operating condition against interference such as noise can be set. It can be corrected effectively.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a main part of a skew distortion correction device according to the present invention.

FIG. 2 is a signal timing chart at each point of the apparatus shown in FIG.

FIG. 3 is a configuration diagram of a main part of a general automatic frequency control (AFC) circuit.

[Explanation of symbols]

 1 ... Video tape recorder (VTR) 2 ... Automatic frequency control circuit (AFC) 3 ... Monitor circuit (MON) 4 ... Microcomputer (μ-COM) 5 ... VCO control filter

Claims (2)

[Claims] 1. A skew distortion correction device for a helical scan type video tape recorder, comprising: an automatic frequency control circuit (AFC, 2) for receiving a reproduced video signal from the video tape recorder (VTR, 1).
And a microcomputer (μ-COM, 4) for receiving a head switching pulse from the video tape recorder (1)
A VCO control filter (5) connected between the automatic frequency control circuit (2) and the microcomputer (4), and a monitor circuit (MO for displaying a horizontal synchronization signal on the screen).
N, 3), the microcomputer (4) outputs the reproduction video signal based on a VCO control voltage which is an end voltage of the VCO control filter (5) to the automatic frequency control circuit (2). A horizontal sync phase shift amount generated at the time of head switching between recording and reproduction included therein is detected, and a current corresponding to the phase shift amount is detected at the time of head switching by the automatic frequency control circuit (2).
To the monitor circuit (MON,
A skew distortion correction device characterized by controlling 3) to correct skew distortion on a display screen. 2. The automatic frequency control circuit (2) calculates a frequency difference between a sync separation circuit for receiving the reproduced video signal, a horizontal sync signal from the sync separation circuit and an output obtained by dividing the output of the voltage controlled oscillator. An AFC detector for detecting, a voltage controlled oscillator for generating a reference frequency, a frequency divider for dividing the output of the voltage controlled oscillator, and a voltage by the AFC detector for stably operating the automatic frequency control circuit. A filter circuit that determines the control sensitivity characteristic of the control oscillator, and detects the phase shift amount of the horizontal synchronizing signal based on the AFC error signal that is the VCO control voltage of the filter circuit when the recording and reproducing heads of the video tape recorder are switched. The skew distortion correction device according to claim 1, wherein a current corresponding to the phase shift amount is supplied to the voltage controlled oscillator after head switching. .