JP2648041B2 - Video signal processing circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal processing circuit of a video tape recorder at a reproduction speed different from the recording speed.

[0002]

2. Description of the Related Art In an LP (long time) mode of a VTR (video tape recorder) of the VHS-PAL system, in a recording track on a tape, a deviation amount αH from an adjacent track is equal to 0.75H (H is horizontal. Corresponding to the period of the synchronization signal). When field still reproduction is performed using a main head and a sub head (reverse azimuth) shifted by 2H from 180 degrees on a tape recorded in such a format, a horizontal synchronization signal is generated at a switching point for each field. A discontinuity of 0.25H occurs. As a result, a skew distortion and a phenomenon of discoloration occur on the reproduction screen.

For this reason, conventionally, 0.25H (glass delay line) and 0.5H (CCD delay line) are used to reduce
By sequentially giving a delay of 5H, 0.5H, 0.25H and 0H to the reproduced signal, discontinuity of the horizontal synchronizing signal is prevented.

Next, the above operation will be described with reference to FIG. FIG. 3 is an explanatory diagram showing a sequence of a horizontal synchronizing signal and a color signal of a reproduced video signal. A indicates the signal as it is reproduced. When performing field still reproduction, there are 313.25 horizontal synchronization signals included in a period in which head switching is performed. Therefore, when the main head and the sub head provided at a distance of 2H from 180 degrees are used, a deviation of 0.25H occurs. That is, the signal of the next field is delayed by 0.25H (advanced by 0.75H) with respect to the expected phase. In addition, * is given to indicate a sequence of color signals. In this example, since the signal is a PAL signal, for example, during the period marked with *, for example, the RY component is in a negative state with respect to the u axis. It is shown that.

[0005] (b) sequentially 0.75
H, 0.5H, 0.25H, and 0H show signals when delay times are given. At the timing a, there is a deviation of 0.25H as shown in a.
By giving a delay time of 5H, the horizontal synchronization signal is continuous. At the next timing b, 0.7 at timing a
Since the delay of 5H gives the lead of 0.5H, the horizontal synchronization signal can be made continuous by giving the delay time of 0.5H.

At the next timing c, a delay of 0.5H is given at the timing b, so that a lead of 0.25H occurs. Therefore, the horizontal synchronization signal can be made continuous by giving a delay of 0.25H. At the next timing d, since a delay of 0.25H is given at the timing c, there is no deviation, so the required delay amount is 0H.

By changing the delay time in this way,
The horizontal synchronization signal can be made continuous. However, as is apparent from b, the sequence of the chrominance signals remains out of order. Therefore, in (b), by giving a delay time of 1H to the periods represented by A and B, the sequence of the color signals can be made continuous.

For skew correction, for example,
This is disclosed in JP-A-55-33316 (H04N5 / 93).

[0009]

However, in the above method, although the delay lines of 0.25H and 0.75H are used, since the 0.25H delay line can use only the glass delay line, The circuit scale becomes large.
This is because the pass band of the glass delay line is narrow, and when trying to pass a video signal,
This is because the signal must be converted to On the other hand, a delay line using a CCD has a wide band and does not need to be such.

[0010]

According to the present invention, 0.75H
A delay time of 1.25H is created by using the delay line of 0.5H and the delay line of 0.5H, and by using this, the delay line of 0.25H becomes unnecessary. That is, 1.25H
By using the delayed signal and the signal delayed by 1H, the relative delay amount becomes 0.25H.

[0011]

Since a 0.25H delay line is not used, a glass delay line does not need to be used, and a frequency conversion circuit or a modulation circuit is not required, and the configuration can be simplified.

[0012]

An embodiment will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the embodiment, and FIG. 2 is an explanatory diagram showing the operation of the embodiment.

Among the reproduced video signals, a luminance signal is inputted from a terminal 1 and a chrominance signal is inputted from a terminal 2. 4 is a circuit for controlling the sequence of the color signal,
Correct the discontinuity of the color signal. After the input luminance signal and color signal are mixed by the mixing circuit 3, they are supplied to the 1H CCD delay circuit 5 and the first switch 6. Therefore, the first
The control of the changeover switch 6 controls whether to give a 1H delay to the video signal.

The output of the first changeover switch 6 is supplied to a second changeover switch 8, a 0.5H CCD delay line 7, and a fifth changeover switch 12. The second changeover switch 8 selects the output of the first changeover switch and the output of the 0.5H CCD delay line 7. The output of the second changeover switch 8 is 0.75H
After being delayed by the CCD delay line 9, the third switch 10
Given to. The third changeover switch 10 is provided with the 0.75
H.CCD delay line 9 output and 0.5H.CCD delay line 7 output are selected.

The fourth switch 11 selects the output of the third switch 10 and the output of the 0.75H CCD delay line 9. Then, the output is the other input of the fifth changeover switch. The control circuit 14 controls the first to fifth changeover switches. In each changeover switch circuit, when the control pulse from the control circuit is at the L level, the terminal on the black circle side is selected. The control circuit 14 also controls the color sequence control circuit 4.

Next, the operation will be described with reference to FIG. 2A is the same VHS-PAL VTR as FIG. 3A.
5 shows a signal at the time of field still reproduction in the LP mode. As described above, this signal has a discontinuity in the horizontal synchronizing signal at the joint of one field and a discontinuity in the sequence of the color signal. Symbols f to n are control pulses from the control circuit.

The signal (b) in FIG. 2 is a signal obtained by delaying the signal (1) by 1H, and represents a signal that has passed through the 1H CCD delay line 5. C indicates a signal at the terminal 13, which is obtained when only the continuation of the horizontal synchronizing signal is considered.

In the first field in FIG.
The first changeover switch 6 selects the black circle side, the second changeover switch 8 and the third changeover switch 10 select the black circle side, the fourth changeover switch 11 selects the black circle side, and the fifth changeover switch 12 selects the white circle side. Therefore, on the output terminal 13, a reproduced signal delayed by 1H is generated. In the next field, the first changeover switch 6 selects the black circle side, the second changeover switch 8 and the third changeover switch 10 select the black circle side, the fourth changeover switch 11 selects the white circle side, and the fifth changeover switch 12 selects the black circle side. I have. That is,
The output of the first changeover switch 7 is the second changeover switch 8,
A 0.75H delay time is given to appear at the terminal 13 via the 0.75H CCD delay line 9. Therefore, the horizontal synchronization signal at point e is continuous.

In the next field, the first changeover switch 6
Is the black circle side, the second changeover switch 8 and the third changeover switch 10
Indicates the white circle side, the fourth changeover switch 11 selects the black circle side, and the fifth changeover switch 12 selects the black circle side. That is, the output of the first changeover switch 6 passes through the 0.5H CCD delay line 7 and appears at the terminal 13. If the second field is 0.
The shift of 0.5H at the point f caused by the delay of 75H is eliminated by this.

In the next field, the first changeover switch 6
Is the white circle side, the second changeover switch 8 and the third changeover switch 10
Indicates the white circle side, the fourth changeover switch 11 selects the white circle side, and the fifth changeover switch 12 selects the black circle side. That is, 1H ・ C
The 1H delay by the CD delay line is not performed, and the output of the mixing circuit 3 is given a 1.25H delay time by the 0.5H delay line 7 and the 0.75H delay line 9. Since the delay time of 1H + 0.5H was substantially given in the previous field, the deviation of 0.25H caused by this is eliminated by the difference between the delay of 1.5H and the delay of 1.25H. You. Accordingly, the horizontal synchronizing signal is continuous at the point g.

Although the continuity of the horizontal synchronizing signal can be maintained by the above operation, the discontinuity of the color signal sequence is not eliminated. That is, in the periods D and E, the sequence of the color signal is inverted. To undo this,
Correction is performed using a control pulse such as nu. For example, the color signal correction circuit 4 delays the color signal by 1H when the null control pulse is at the H level. By this processing, as shown in FIG. 7E, in the field still reproduction, the horizontal synchronizing signal is continuous, and the sequence of the color signals can be continuous. The actual processing output is represented by E.

It is necessary to pay attention to the timing of the control pulse, except for the null control pulse, in relation to the vertical synchronizing signal of the original video signal (a in FIG. 2).
That is, it must be delayed by 1H.

The 0.75H delay line can be realized by increasing the frequency of the clock of the CCD delay line having a wide variable range for TBC (time base collector) by 4/3 by using the 1H delay line. . Therefore, only the 0.5H and 1H delay lines are actually required.

[0024]

As described above, according to the present invention, 0.2%
Since the skew correction in the LP mode of the VHS-PAL system can be realized without using the 5H delay line, the configuration is simplified and the effect is great.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an embodiment.

FIG. 2 is an explanatory diagram showing an operation of the embodiment.

FIG. 3 is an explanatory diagram showing an operation of a conventional example.

[Explanation of symbols]

 Reference Signs List 4 color signal correction circuit 5 1H CCD delay circuit 6 1st switch 7 0.5H CCD delay line 8 2nd switch 9 0.75H CCD delay line 10 3rd switch 11 4th switch 12 5th Selector switch

Claims (1)

(57) [Claims] 1. A video signal processing circuit for processing a video signal in which a horizontal synchronizing signal has a discontinuity of at least 0.25H at a joint of a field, a delay of 1H (H corresponds to a period of the horizontal synchronizing signal). Means and 0.5
H delay means, 0.75 H delay means, and 0.5
H delay means and 0.75H delay means are connected in a subordinate manner to obtain a 1.25H delay time, and the 1H delay means and the means for obtaining the 1.25H delay time are used for video. A switch means for giving a delay time of 0.25H to the signal.