JPH0729261A - System for controlling drum servo - Google Patents

Abstract

PURPOSE:To reduce a maximum amount of an initial drum phase error at the time of switching to a VSYNC reference mode by supplying a first, a second set signals from first, second signal generation circuits to an AND circuit, generating a third set signal and controlling a switch circuit. CONSTITUTION:By the first signal generation circuit 5, counting is started making a vertical synchronizing signal a reset signal, and a mask signal PM1 falling by the reset signal and rising at eleventh count is outputted, and the first set signal PS1 is outputted after the period of the signal PM1. The second signal generation circuit 6 is reset when a PG signal PG1 is inputted, and the second set signal PS2 starting the counting from l, rising at tenth count and falling at twenty-twoth count is outputted. By the outputs of the circuits 5, 6, the third set signals PS3, PS'3 signals and a third mask signal PM3 are outputted through the AND circuit, and the switch 3 is turned on/off by the third set signals PS3, PS'3, and the vertical synchronizing signal is supplied to a drum control circuit 8 for the period of the signal PS, and the drum phase error is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a VTR drum servo control system, and more particularly to a drum servo control system having a circuit for masking every other vertical synchronizing signal input from the outside.

[0002]

2. Description of the Related Art In a drum servo control circuit of a VTR, a vertical synchronizing signal of 50 Hz or 60 Hz input from the outside is formed in a vertical synchronizing signal input path in order to form a half frequency (25 Hz or 30 Hz). As shown, a synchronization signal regulation circuit 50 is provided to mask every other synchronization signal.

In the figure, reference numeral 51 is an input path for a vertical synchronizing signal from the outside, and 52 is a switch. This switch 52 is turned ON / OFF by the switch control signal generation circuit 5
3 output. The switch control signal generation circuit 53 uses the vertical synchronization signal output from the switch 52 as shown in FIG.
The drum FG signal “FIG. 5 (b)” given through the line 55 as a reset signal “(c)” in (c) is counted, and from the reset signal to 20 counts,
A low level is set and a high level is set for 20th and subsequent counts. However, since the vertical synchronization signal (e) is reset at the 24th count, a signal "FIG. 5 (d)" that sets the low level for the 24th count and thereafter is output. .

The switch 52 is turned on only during the high level period and turned off during the low level period. Therefore, the next vertical synchronizing signal (d) shown in FIG. 5C is masked. By repeating the same operation for (e) and (e), (e) is permitted and (e) is masked. Figure 5
(E) is an output signal generated on the output path 54 of the switch 52,
That is, the vertical synchronizing signal of 25/30 Hz is shown.

[0005]

By the way, in the VTR, the drum APC (automatic phase control) at the time of recording is changed from the mode based on the reference signal (D-REF reference mode) to the mode based on the vertical synchronization signal. (VSY
NC reference mode), but when the reference mode is switched, the synchronization signal regulating circuit of the above-mentioned conventional example uses D
-Head switching signal in REF standard mode
Since the mask period switching setting is performed with reference to the vertical sync signal at an arbitrary position with respect to (a), the first vertical sync signal and head switching signal when switching to the VSYNC reference mode. The phase between (a) and
In some cases, the difference from the target value (phase) of the drum APC (hereinafter referred to as "drum phase error") becomes large. And
When this large drum phase error occurs, it takes a long time to pull in the target value. This obviously causes deterioration of image quality at the start of recording.

The present invention has been made in view of the above circumstances, and provides a novel drum servo control system devised so as to reduce the maximum amount of the first drum phase error at the time of switching to the VSYNC reference mode. The purpose is to do.

[0007]

In order to achieve the above object, a drum servo control system of the present invention inputs a drum servo control circuit of a VTR and a vertical synchronizing signal input from the outside to the drum servo control circuit. A switch means provided in the input path and a vertical synchronizing signal input to the drum servo control circuit as a reset signal, the drum FG signal is counted from the reset signal, and a first width having a width corresponding to a time up to a predetermined count value is obtained. First signal generating means for generating a mask signal and for generating a first set signal except during the first mask signal period, and a drum FG signal is counted from the reset signal by using the drum PG signal as a reset signal, and a first count is performed. A second mask signal having a width determined by the value and the second count value is generated, and a second mask signal is generated except for the second mask signal. And a second signal generating means for outputting a third set signal having a width of a period in which both the first and second set signals are present, and a third mask signal is generated in a period other than the third set signal period. Logic means for controlling the switch means so that the switch means is turned on by the third set signal and the switch means is turned off by the third mask signal.

[0008]

According to this structure, the second mask signal is generated by the vertical synchronizing signal which has passed through the switch means, and the vertical synchronizing signal next to this vertical synchronizing signal is within the period of the third set signal obtained from the logic means. Since it does not exist, it cannot pass through the switch means and is masked. The second set signal can set the drum phase target in a relationship such that the drum phase target is located approximately in the center of the second set signal, and by controlling the switch means by the logical product output of the second set signal and the first set signal, One of the vertical synchronizing signals positioned before and after the drum phase target is taken out and the other is masked. Therefore, the difference between the extracted vertical synchronizing signal and the drum position target can be kept small.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 embodying the present invention, reference numeral 1 is a synchronizing signal regulating circuit, which is a switch 3 provided on an input path 2 for transmitting a vertical synchronizing signal from an external circuit,
A vertical sync signal (vertical sync signal of 25/30 Hz) output to the line 4 on the output side of the switch 3 is used as a reset signal to count the drum FG signal, generate a first mask signal, and generate a signal other than the first mask signal period. Is a first signal generation circuit 5 that generates a first set signal, and counts the drum PG signal using the drum PG signal as a reset signal,
A logical product of the second signal generating circuit 6 that generates the second set signal and the second mask signal during periods other than the second set signal and the signals from the first and second signal generating circuits 5 and 6 Is taken, and the output of the switch turns ON / OFF.
It is composed of an AND circuit 7 for controlling F. The 25/30 Hz vertical synchronizing signal on the line 4 is supplied to the drum servo circuit 8.

The second signal generation circuit 6 is reset when the drum PG signal PG ₁ shown in FIG. 2 is input,
The second set signal PS ₂ starts counting from 1, rises at the 10th count, and falls at the 22nd count
Is output. The phase target of the drum is located substantially in the center of the second set signal PS ₂ . The second signal generation circuit 6 outputs the second mask signal PM ₂ during the period other than the second set signal. The second signal generating circuit 6 is reset again when the next drum PG signal PG ₂ comes, and the same operation is repeated.

On the other hand, the first signal generating circuit 5 starts counting by using the vertical synchronizing signal (a) shown in FIG. 2 as a reset signal, falls by the reset signal [hence, vertical synchronizing signal (a)], and counts 11 The first mask signal PM ₁ that rises visually is output, and the first set signal PS ₁ is output except during the period of the first mask signal PM ₁ .

The AND circuit 7 for inputting the outputs of the first and second signal generating circuits 5 and 6 has the third set signals PS ₃ and PS ₃ ′ and the third mask signal PM ₃ as shown in FIG. Is output. The third set signals PS ₃ and PS ₃ ′ are generated due to the simultaneous presence of the first and second set signals PS ₁ and PS ₂ .

The switch 3 is ON when the voltage applied from the AND circuit 7 is at high level, and OF when it is at low level.
It is configured to be F. Therefore, it is turned on during the period of the third set signals PS ₃ and PS ₃ ′. At this time, the vertical synchronizing signal in a period of PS ₃ (b) is supplied to the drum servo control circuit 8, the vertical synchronizing signal period PS ₃ '(ii) does not located, passing through the switch 3 Can not be masked. In the case of the signal relationship of FIG. 2, the maximum drum phase error W is smaller than that of the conventional example of FIG.

Next, FIG. 3 shows a vertical synchronizing signal (a) (b) ...
Shows the operation waveforms by the circuit of FIG. 1 when the symbol .smallcircle. In the case of this signal relationship, the vertical synchronizing signal (a) is masked and the vertical synchronizing signal (b) is passed. Also in this case, the maximum drum phase error W is smaller than that in the conventional example of FIG.

[0015]

As described above, according to the present invention, V
In TR, the maximum amount of the first drum phase error at the time of switching to the VSYNC standard mode can be reduced, so that the drum servo control circuit takes a short time to pull the drum phase error to the target value, and the VSYNC standard mode can be changed. It is possible to substantially suppress the deterioration of the image quality at the time of switching.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a sync signal regulation circuit portion of a drum servo control system of a VTR embodying the present invention.

FIG. 2 is a waveform diagram for explaining the operation.

3 is a waveform diagram for explaining the operation when the vertical synchronizing signal is deviated from the case of FIG.

FIG. 4 is a circuit diagram of a conventional example.

FIG. 5 is a waveform diagram for explaining the operation of the conventional example.

[Explanation of symbols]

 1 sync signal regulation circuit 2 vertical sync signal input path 3 switch 4 switch output line 5 first signal generation circuit 6 second signal generation circuit 7 AND circuit 8 drum servo circuit

Claims (1)

[Claims] 1. A drum servo control circuit of a VTR, a switch means provided in an input path for inputting a vertical synchronizing signal input from the outside to the drum servo control circuit, and a vertical input to the drum servo control circuit. Using the synchronization signal as a reset signal, the drum FG signal is counted from the reset signal to generate a first mask signal having a width corresponding to the time up to a predetermined count value, and a first set signal is generated except during the first mask signal period. A first signal generating means, a drum PG signal is used as a reset signal, and the drum FG signal is counted from the reset signal to obtain a first count value and a second count value.
Of the second signal generating means for generating a second mask signal having a width determined by the count value of the second mask signal and a second mask signal other than the second mask signal, and a period during which both the first and second mask signal are present. The third set signal of the width is output, and the third mask signal is generated except during the third set signal period, the switch means is turned on by the third set signal, and the switch means is turned off by the third mask signal. And a logic means for controlling the switch means, the drum servo control system.