JPH0430865Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Field of Industrial Application) The present invention relates to a videotape recorder, and more specifically, to a videotape recorder that automatically corrects vertical shaking or blurring of the screen when playing still images. Regarding recorders.

(Prior art and its problems) In a helical scan recording video tape recorder that uses a rotating magnetic head to record one field's worth of video signals on one inclined track of a magnetic tape, it is possible to perform still playback or slow playback. When performing variable speed playback that is different from the tape speed during recording, as in the case of the rotary magnetic head, the rotating magnetic head cannot scan the regular inclined track and reaches the adjacent track by straddling the inclined track. Therefore, in a tape format in which the H alignment (the arrangement of video signals in each horizontal period is always at equal intervals) with adjacent tracks is irregular, an H jump occurs at the change of tracks, resulting in a skew on the playback screen. Distortion appears.

Conventionally, in order to correct this irregularity in the H arrangement, in addition to two rotating magnetic heads for recording and reproducing, a disk drive having the same azimuth angle as one of these rotating magnetic heads, and having a predetermined distance from the other rotating magnetic head, has been proposed. An auxiliary rotary magnetic head and a delay circuit are installed at angularly distant positions to eliminate the H jump at a track change.

For example, in the case of a tape format in which adjacent tracks have a deviation of 0.25H as shown in FIG. 6, normal recording and recording as shown in FIG.
In addition to the reproducing rotary magnetic heads A and B, an auxiliary rotary magnetic head A' (having the same azimuth angle as the rotary magnetic head A) used exclusively for still reproduction is connected to the rotary magnetic head B.
The magnetic head drum 4 is offset by 1.25H in the direction of rotation of the magnetic head drum 4. Rotating magnetic head A during still playback
By using and the auxiliary rotating magnetic head A',
The reproduced video signal advances by 1.25H in the vicinity of the switching from the field F1 by the rotating magnetic head A shown at the left end of FIG. Does not occur. However, the field
When switching from F2 to the next field F3 (rotating magnetic head A), the reproduced video signal is delayed by 1.25H, so the horizontal synchronization signal interval becomes 1.5H, causing a 0.5H jump. Therefore, in the period of field F3, a 0.5H delay circuit is inserted and the reproduced video signal is processed to correct the H jump as shown in FIG. 8C. Note that correction is also performed in the delay circuit in field F4 following field F3, and H alignment correction is performed. That is, the H jump is eliminated by inserting a delay circuit for each frame.

By the way, as mentioned above, during variable speed playback, the rotating magnetic head deviates from the regular tilt track to be scanned, so the S/N of the re-video signal deteriorates.For example, in still playback, the rotating magnetic head switching pulse (hereinafter referred to as head switching pulse) The S/N ratio deteriorates in the vicinity of the pulse edge of the image (referred to as 1), causing noise bars to appear on the screen. Since there is a vertical synchronization signal after this pulse edge, the S/S of the video signal is
If N deteriorates, vertical synchronization will be disrupted, so during still playback, a pseudo vertical synchronization signal is inserted at the position of the vertical synchronization signal in the video signal to prevent S/N deterioration of the vertical synchronization signal.

This pseudo vertical synchronizing signal is inserted into the video signal after a predetermined time set by a time constant circuit after detecting the edge of the head switching pulse.

Therefore, if a fixed-phase pseudo vertical synchronization signal is inserted into the head switching pulse after performing the H alignment correction described above, the corrected field will have a pseudo vertical synchronization signal even though the video signal has been phase-shifted. Since the insertion position of the synchronization signal does not change, the interval between the adjacent horizontal synchronization signal and the pseudo vertical synchronization signal differs from the regular one, which appears as wobbling or blurring in the vertical direction of the reproduced screen.

(Object of the invention) The present invention solves the above-mentioned drawbacks of the prior art, and provides a video tape recorder equipped with a novel still playback means that improves the vertical shaking or blurring of the screen.

(Summary of the invention) This invention detects the period in which the time interval between the horizontal synchronization signal and the pseudo vertical synchronization signal is different from the normal value, causing skew distortion, and based on this detection, the time interval between the horizontal synchronization signal and the pseudo vertical synchronization signal is By correcting the generation timing, the time interval between the horizontal synchronization signal and the pseudo vertical synchronization signal is adjusted to a normal value.

(Example) The present invention will be described below based on the illustrated example.

FIG. 1 is a block diagram showing an embodiment of the present invention. Reference numeral 1 denotes a pseudo vertical synchronizing signal generator, which is used to generate a signal after a predetermined time from the arrival of the rising and falling edges of the head switching pulse (that is, when the vertical synchronizing signal originally generates a pseudo vertical synchronization signal VD at the position where 2 is a pseudo vertical sync signal inserter, which inserts a pseudo vertical sync signal output from the pseudo vertical sync signal generator 1 into the reproduced video signal during still playback.
Insert the VD. Reference numeral 3 denotes a timing correction circuit, which corrects the pseudo vertical synchronization signal generation timing of the pseudo vertical synchronization signal generator 1 in a field in which skew distortion is occurring based on the skew detection signal, that is, in a field for which H alignment correction has been performed. occurs. FIG. 2 is a circuit diagram showing a specific example of the pseudo vertical synchronization signal generator 1 and the timing correction circuit 3. The part surrounded by the one-dot chain line is the pseudo vertical synchronization signal generator 1, and the timing correction circuit 3 is It is composed of a monostable multivibrator MM and an AND gate AND.The monostable multivibrator MM is supplied with a head switching pulse and outputs a control pulse that continues the pulse edge of the head switching pulse for a predetermined period of time after arrival. Moreover, the control pulse and skew detection signal from the monostable multivibrator MM are supplied to the AND gate AND.
The control pulse input when the skew detection signal arrives is sent to the switch SW1 of the pseudo vertical synchronization signal generator 1.
Output for switching control.

The head switching pulse (FIG. 3a) supplied to input terminal 4 is obtained by diode D1 as a high level pulse representing the field of rotating magnetic head A, and by inverter I and diode D2 a high level pulse representing the field of rotating magnetic head A' is obtained. The representative low level pulse is phase inverted and a high level pulse is obtained, resulting in a high level signal for the entire period, which is supplied to the capacitor C via the resistor R1 to charge it. A changeover switch SW3 connected in parallel with the capacitor C is an instantaneous discharge switch for the capacitor C, and is turned ON by a trigger pulse from the pulse generator 5 every time the edge of the head switching pulse arrives. That is, a sawtooth wave generating circuit is constructed by an integrating circuit including a resistor R1 and a capacitor C, and a changeover switch SW3, and the third terminal voltage of the capacitor C is
As shown in FIG. 2, the change is a sawtooth wave whose period is one field scanning time.

The terminal voltage of capacitor C is given as a comparison input of comparator com. On the other hand, the reference input of the comparator com is connected to each reference power source SP via the changeover switch SW2.
1, selectively given by SP2. In the case of this embodiment, the voltage V1 of the reference power source SP1 corresponds to the terminal voltage of the capacitor C at the time when the pseudo vertical synchronizing signal VD is inserted during the still scanning period of the rotating magnetic head A, and the voltage V1 of the reference power source SP2 corresponds to V2 corresponds to the terminal voltage of the capacitor C at the time when the pseudo vertical synchronizing signal VD is inserted during the still scanning period of the auxiliary rotating magnetic head A'.

Therefore, as shown in Figure 3D, when the terminal voltage of capacitor C reaches V1, that is, after the time TA has elapsed from the rising edge of the head switching pulse, and when the terminal voltage of capacitor C reaches V2, that is, when the head switching pulse After time TB has elapsed since the falling edge, the pseudo vertical synchronization signal VD is output from the comparator com. Resistor R2, diode D3, switch
The SW1 path is a charging correction circuit for capacitor C. As shown in FIG. 3B, the switch SW1 is closed for a period TP during which the control pulse P obtained from the monostable multivibrator MM continues based on the arrival of the edge of the head switching pulse.

In this embodiment, by making the discharging time constant (=CR2) equal to the charging time constant (CR1), the capacitor C is not substantially charged, as shown in FIG. Period when terminal voltage is constant
Tq is formed, and the generation time of the pseudo vertical synchronization signal is delayed by TC as shown in FIG. 3E.

The configuration is as described above, and its operation will be explained next.

In the explanation of the operation, a case of still reproduction in which the video signal is delayed by 0.5H every two fields as H alignment correction as used in the explanation of the prior art will be explained.

When still reproduction is set, first, the rotating magnetic heads are switched, and still reproduction begins with the combination of rotating magnetic head A and auxiliary rotating magnetic head A'. As shown in FIG. 3A, the head switching pulse is at a high level during the scanning period of the rotating magnetic head A, and is at a low level during the scanning period of the auxiliary rotating magnetic head A'.
When the scanning period of the rotating magnetic head A arrives at a time of delay to, the reference power source is switched on by switching the changeover switch SW2 at the rising edge of the head switching pulse (time to).
Select SP1. The head switching pulse input from input terminal 4 is sent to capacitor C via resistor R1.
By charging the capacitor C, the voltage at its terminal becomes a sawtooth wave whose cycle is each scanning period, as shown in FIG. 3D.

Now, when the terminal voltage of the capacitor C reaches V1 after the magnetic TP has elapsed due to the magnetic _t0 , a pseudo vertical synchronizing pulse VD1 is outputted from the comparator com (FIG. 3(e)).
During this scanning period t ₀ - _{t 1} , the skew detection signal is at a low level as is clear from Figure 3C, that is, no skew distortion has occurred, so the control pulse P is not output and pseudo vertical synchronization is achieved. signal
VD timing correction is not performed. Next, at the arrival of the falling edge at time _t1 , the changeover switch SW2 is switched to the reference power source SP2 (reference voltage V2).
>V1). Furthermore, at this falling point, the output of the pulse generator 5 causes the changeover switch SW to
By turning on 3 for a short period of time, capacitor C is short-circuited and discharged.

The period from time t ₁ to _{t 2} is a scanning period of the auxiliary rotating magnetic head A', and during this period, the capacitor C is charged again, and its terminal voltage changes from the above-mentioned time t ₀ to t _{1 .}
Charging is performed with the charging time constant CR1 in the same way as before.

When the terminal voltage of the capacitor C reaches V2 after a time TB has elapsed since charging was started, the comparator com outputs a pseudo vertical synchronizing signal VD2.

The two fields explained so far correspond to fields F1 and _F2 in FIG.
A delay has been applied. Therefore, from time _t2 , the skew detection signal becomes high level in the field caused by the rotating magnetic head A, and the output pulse from the monostable multivibrator MM becomes an and gated signal.
The changeover switch is passed through AND as the control pulse P.
The changeover switch SW1 is turned on during the duration TP of the control pulse P (FIG. 3A). At the same time, capacitor C starts charging again, and its terminal voltage is applied to diode D3 of the discharge circuit.
When the voltage is increased to the point where it turns on, a charging compensation circuit for capacitor C is formed, and from this point on, for a time Tq,
The capacitor C becomes substantially uncharged. When the control pulse P disappears, the changeover switch
SW1 turns OFF, the discharge time constant circuit is released, and the capacitor C starts to be charged again. When the terminal voltage reaches V1, the comparator com outputs a pseudo vertical synchronizing signal VD3. That is, as shown in FIG. 3E, the pseudo vertical synchronizing signal VD3 changes from the rising edge of the head switching pulse at time _t2 to TA+TC (TC=0.5H).
Output after a certain amount of time has elapsed. Thereby, no interval deviation occurs between the predetermined horizontal synchronizing signal and the pseudo vertical synchronizing signal.

Further, the auxiliary rotating magnetic head at time t ₃ to _{t 4}
Since a delay of 0.5H is also applied to the scanning period of A', the pseudo vertical synchronization signal VD is delayed by the time TC using the control pulse P from the timing correction circuit 3, and the pseudo vertical synchronization signal VD is generated after the time TB+TC has elapsed from time _t3 . Output VD4.

Thereafter, the skew distortion can be removed by outputting the pseudo vertical synchronizing signal VD with a delay of time TC every two fields. In the above embodiment, the delay time for each field is common (TC), but it may be different for each field depending on the mounting position of the auxiliary rotary head A'. In such a case, the charging correction circuit is configured as shown in FIG. In other words, the charge correction circuit for capacitor C is connected to resistor R2.
and changeover switch SW1.
When SW1 is turned on, a discharge time constant path (time constant CR2) of capacitor C is formed. _In this case, if the relationship between each time constant is CR1>CR2, the total charging time constant becomes _CR1 - _CR2 , and as shown in FIG _. A delay time of Td and Te is added to each field in . Therefore, the charging time constant of the capacitor C can be set variously as required.

(Effects of the invention) According to the invention, in a field where the reproduction signal is delayed to correct skew distortion caused by discontinuity of the horizontal synchronization signal, the charging speed of the capacitor of the integrating circuit constituting the sawtooth wave generation circuit is corrected. Since the waveform of the sawtooth wave is modified and the phase of the pseudo vertical synchronization signal is changed, it is possible to avoid occurrence of vertical shift vibration on the playback screen due to correction of skew distortion.

In addition, by correcting the charging speed of the capacitor in the integrating circuit and modifying the waveform of the sawtooth wave, the phase of the pseudo vertical synchronization signal is changed. Phase adjustment can be easily done by adjusting the value of the resistor in the integrating circuit so that the monitor screen is stable.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention.
FIG. 2 is a circuit diagram showing a specific example of the pseudo vertical synchronization signal generation and timing correction circuit shown in FIG. 1, FIG. 3 is a waveform diagram for explaining the operation of the embodiment shown in FIG. 2, and FIG. A circuit diagram showing another embodiment of a pseudo vertical synchronization signal generator and a timing correction circuit, FIG. 5 is a waveform diagram for explaining the operation of the embodiment shown in FIG. 4, and FIG. FIG. 7 is a diagram showing the arrangement of rotating magnetic heads for performing H alignment correction, and FIG. 8 is a characteristic diagram for explaining H alignment correction. Explanation of symbols, 1... Pseudo vertical synchronization signal generator,
2... Pseudo vertical synchronization signal inserter, 3... Timing correction circuit, 5... Pulse generator.

Claims (1)

[Claims for Utility Model Registration] During still playback, a helical system that corrects skew distortion by delaying the playback signal of a predetermined field in which the horizontal synchronization signal is discontinuous for a predetermined period of time, and then inserting a pseudo vertical synchronization signal into the playback signal. In a scan type video tape recorder, there is a sawtooth wave generation circuit that outputs a sawtooth wave with a period of one field period based on a head switching pulse, and a sawtooth wave output from this sawtooth wave generation circuit and a reference level. a pseudo-vertical synchronization generation circuit that outputs a pseudo-vertical synchronization signal by comparing the above-mentioned sawtooth wave generation circuit; a charging speed correction circuit that corrects the charging speed of the capacitor of the integrating circuit constituting the sawtooth wave generation circuit; and a control circuit that operates the charging speed correction circuit according to the field in which the charging speed is corrected.