JPS6136434B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a burst signal separation circuit for separating a burst signal from a color television signal, and particularly to a burst signal separation circuit useful when the horizontal synchronization period varies.

One of the methods for recording television video signals on magnetic tape is to wrap the magnetic tape around a cylinder (drum) containing a rotating head and run it. There is a helical scanning video tape recorder device that forms a video track), and it has come to be widely used not only for consumer use but also as a professional device for industrial and broadcasting purposes.

In the case of this helical scanning video tape recorder device, it is common to record one field or multiple fields of video signals on one video track, and the rotating head is arranged perpendicular to the input video signal to be recorded. It is designed to rotate in synchronization with a synchronization signal. Since there are many devices in which one field of video signal is recorded on one video track, this case will be described below, but the present invention records one field of video signal on one video track. Needless to say, this is not limited to the case.

When one field of video signals is recorded on one video track, as shown in Figure 1, the rotary head is set so that the vertical blanking section is located at the end of each video track (the edge of the tape). controlled.
This control is performed by controlling the rotation of the rotary head by comparing the phase of a tachometer signal generated by detecting the rotational phase of the rotary head with a vertical synchronization signal of the input video signal. Therefore, during recording, the vertical synchronization signal of the input video signal and the tachometer signal always have a constant phase relationship.

If one main video recording/reproducing rotary head is attached to the rotary body to which the rotary head is attached (so-called one-head system), the video track is formed by only one rotary head. , a small portion of the video signal is missing from the top end of the tape to the bottom end of the tape. However, in cases where two or more main video recording/playback rotary heads are mounted on a rotating body (in the case of a so-called 2-head system, etc.)
After one rotating head finishes scanning the tape,
For example, just before exiting from the top of the tape, the next head enters from the bottom of the tape, and the top of the video track and the bottom of the next video track overlap and record the same signal. In some cases, it may be done. In this case, no missing portion of the video signal occurs.

When reproducing recorded video signals, the rotary head is controlled to rotate at a constant rotation speed, such as by rotating in synchronization with a synchronization signal sent from a reference synchronization signal generator or other reference signals. Ru.
Also, the phase of tape travel is controlled such that the rotating head tracks directly over the video track, such as by controlling the rotation of a capstan that drives the tape.

If only the running of the tape were to be stopped during playback, the rotary head would repeatedly scan the same part of the tape in the direction of arrow A, drawing a trajectory as shown by straight line PQ' in Figure 1, for example. . This means that when the tape is running steadily in the direction of arrow B in Figure 1, after the rotary head that was scanning the previous video track has finished its run and passed point Q', the next rotary head will move forward. It is approximately the same time that the tape passes point P and starts scanning, and the tape advances one video track pitch while the rotary head scans the tape once, so the rotary head moves from point P to Q. During one scan of the tape up to the point, Q
This means that the point has moved to point Q', and one video track from point P to point Q is formed on the tape. When the tape stops running at this point, the rotating head similarly scans from point P to point Q', but the tape does not move, so the tape is also scanned from point P to point Q'. That's what happens. Therefore, in this case, the rotary head that was scanning directly above the video track at point P gradually falls off the track, and then gradually moves onto the adjacent track, and so on.
At point Q', it will scan directly above the adjacent track.

The width of the video track is, for example, 180 μm, and the gap between the tracks (guard band) is often selected to be approximately 2:1, for example, 90 μm. Therefore, as the rotary head falls from the track, the S/N ratio of the signal deteriorates, and beat disturbance occurs while the rotary head is scanning over two tracks.

However, as shown in Figure 1, if the phases of the horizontal synchronizing signals _S Even when running in the opposite direction (direction) or in the opposite direction, the image can be monitored on the video monitor even if there is a noise band due to beat interference. This is called still or slow-motion playback, and is convenient for finding the start and end points of necessary scenes when editing a program. One of the features of a helical scanning video tape recorder device that records one field or a plurality of fields of video signals on one video track is that such static or slow motion playback can be easily performed.

Furthermore, if a digital time base corrector equipped with an instantaneous lock type clock generator is used, the program on the tape can be viewed as an image even during fast forwarding or rewinding.

If the tape is run in the opposite direction at the same speed as when running normally, the rotating head will move from point P in Figure 1.
Since point Q'' moves to point Q' while scanning to point Q', the rotary head appears to scan from point P to point Q'' on the tape.

In the case of static playback (playing the tape stationary to obtain a still image), the rotating head scans the tape from point P to point Q', but in the case of steady playback, it scans from point P to point Q. Compared to the case shown in FIG. 1, the scanning length is shorter by 1.5H (horizontal synchronization period). For convenience of explanation, the video track width and angle are exaggerated in Figure 1.
The number of horizontal synchronization signals in one video track is also much smaller than in the actual case.
Actual equipment is often designed so that the amount of time required for static playback is 2.5H less than for steady playback. In this case, if the tape is similarly run in the opposite direction at the same speed as the steady run, 5H will be reduced.

However, since the rotating head always rotates at a constant speed, the time it takes to scan the tape from point P to point Q is equal to the time it takes to scan the tape from point P to point Q' or from point P to point Q''. If the number of horizontal synchronization periods played while the rotary head scans the tape once is reduced, one horizontal synchronization period becomes longer by that amount. When the number of horizontal synchronization periods is increased (which occurs when the tape runs in the forward direction at a speed higher than the normal running speed), one horizontal synchronization period becomes shorter.

When playing in a stationary state, slow motion, fast forwarding, or rewinding, the length of the horizontal synchronization period changes considerably. A video signal with a changed horizontal synchronization period is normally processed into a regular video signal by a digital time base corrector (timebase collector).

A system diagram of this type of digital time axis correction device is shown in FIG. The input video signal 11 is converted into an 8- to 10-bit digital signal by an A/D converter 12 with a clock frequency of, for example, four times or three times that of the color subcarrier. On the other hand, a synchronization separation circuit 17 separates a horizontal synchronization signal 18 and a burst signal 19 from the input video signal 11. A write clock 20 and a write address clear pulse 21 are generated from the horizontal synchronizing signal 18 and the burst signal 19 by a write clock generating circuit 22. Write clock 20 is also used as a conversion clock for A/D converter 12.

The memory 13 consists of a memory cell, a write address counter, and a read address counter, and the input digital video signal is stored in the memory cell specified by the write address counter, and is stored in the memory cell specified by the read address counter. specified and read. The address counter is clocked by the input clock and cleared by the address clear pulse. For example, based on the reference video signal 23, the read clock generation circuit 24 generates the read clock 26 and the read address.
Generate clear pulse 25. This read clock 26 and read address clear pulse 2
The digital video signal read out from the memory 13 by the D/A converter 14 is converted back into a video signal, and the synchronizing signal portion is shaped by the process amplifier circuit 15 to become an output video signal 16. In this case, the output video signal 16 is locked to the reference video signal 23.

The present invention relates to an improvement of the burst signal separation circuit of this digital time base correction device. FIG. 3 shows a system diagram of a burst signal separation circuit according to an embodiment of the present invention. This circuit corresponds to the synchronous separation circuit 17 shown in FIG. FIG. 4 shows the signal phase relationship of each part in FIG. 3.

A horizontal synchronization separation circuit 31 clips the synchronization part from the input video signal 11 to extract a horizontal synchronization signal 32. In FIG. 4, ``A'' is an input video signal, and ``B'' is a horizontal synchronizing signal. Variable delay pulse generation circuit 33
is a variable delay one-shot multivibrator that is triggered on the leading edge of horizontal sync signal 32 and a pulse 34 (fourth pulse) that gates the trailing edge of horizontal sync signal 32.
The trailing edge of the horizontal synchronizing signal is gated by a gate circuit 35, and the gated pulse 36 (FIG. 4 D) triggers a burst gate pulse generation circuit 39, and a burst gate pulse generator circuit 39 is activated. - Gate pulse 40 (FIG. 4E) gates a burst from input video signal 11 in burst gate circuit 38 to generate burst signal 19.

Pulse 3 gated from trailing edge of horizontal sync signal
6 controls the pulse delay time (τ in FIG. 4C) of the variable delay pulse generation circuit 33 via a branch circuit 37. If the width of the pulse 36 gated from the trailing edge of the horizontal synchronizing signal is adjusted to approximately half in the normal state of the gate pulse 34, and if the pulse delay time of the variable delay pulse generation circuit 33 is shortened, the horizontal The width of the pulse 36 gated from the trailing edge of the synchronization signal becomes wider, and conversely, the width of the pulse becomes narrower when the delay time increases. Therefore, by integrating the gated pulse 36 from the trailing edge of the horizontal synchronizing signal, the variable delay pulse generating circuit 33 can be controlled to always correctly gate the trailing edge of the horizontal synchronizing signal. Conversely, the trailing edge of the horizontal sync signal can always be gated correctly even if the width of the horizontal sync signal changes (by re-correcting the video signal during standstill, slow motion, fast forward, or rewinding). .

The need to gate the trailing edge of the horizontal sync signal correctly at all times is because the burst signal determines the phase of the clock for the digital conversion of the video signal, and the re-alignment signal of the video tape recorder equipment is dropped. In order to gate bursts without error, it is necessary to check the trailing edge of the horizontal synchronization signal, which is the source of the burst, because it contains unnecessary signals that can be confused with synchronization signals, such as beats that occur when a rotary head plays signals from two video tracks at the same time. It is necessary to always take it out accurately.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating a video track on a tape of a helical scanning video tape recorder device in which the present invention is implemented, FIG. 2 is a system diagram of a digital time axis correction device, and FIG. 3 is an embodiment of the present invention. An example system diagram, FIG. 4, is a diagram showing waveforms and phase relationships of various parts of the embodiment shown in FIG. 3.

Claims (1)

[Claims] 1. Delay the leading edge of the horizontal synchronizing signal of the input video signal through a variable delay circuit, generate a gate pulse with this delayed signal, gate the trailing edge of the horizontal synchronizing signal with this gate pulse, and extract this signal. burst based on the trailing edge of the horizontal sync signal
A gate pulse is generated to gate and separate the burst signal from the input video signal, and the trailing edge of the extracted horizontal synchronizing signal and the output signal of the variable delay circuit are phase-compared, and the error signal is used to separate the burst signal from the input video signal. A burst signal separation circuit for video signals, characterized in that the circuit controls a variable delay circuit.