JPH051673B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a rotating head helical scan type magnetic recording and reproducing apparatus (VTR) for recording and reproducing video signals having a positive synchronizing signal.

[Background of the invention]

Methods for recording current composite video signals, including NTSC signals, on VTRs are detailed in books such as VTR Technology (Japan Broadcasting Publishing Association, October 1980), edited by the Japan Broadcasting Corporation. , it is common to directly record video signals as FM modulated signals. The current composite video signal is shown in Figure 1a.
As shown in , it has so-called negative polarity synchronization, which is the opposite polarity to the video, and if you compare it with a fixed threshold level, it will be difficult to detect signals with time axis fluctuations such as skew, such as the playback signal of a VTR. Even if there was a problem, it was possible to easily perform synchronization separation.

Currently, a high-definition television system with significantly higher definition than current television systems such as NTSC has been proposed, and as a method for transmitting wideband signals, a technical report of the Television Society
MUSE detailed in TEBS95-2 (March 1984)
method will be adopted. This method uses a positive synchronization format with a trapezoidal waveform as shown in Figure 1b, and the center (50% level) of the trapezoidal wave during the horizontal synchronization period is determined based on the phase of the reference signal within the vertical blanking period. Detects and performs synchronous separation.

However, when this type of signal is directly recorded and reproduced on a VTR, it may become impossible to separate the synchronization from the reproduced signal due to skew at the head switching point that occurs in the VTR. In particular, in order to record wideband signals, one field signal is recorded on multiple tracks, which is the so-called segment recording format.
In the case of a VTR, this was a serious problem, and the problem was that the time base correction circuit at the rear of the VTR or the receiver could not function at all.

[Purpose of the invention]

The purpose of the present invention is to solve the above-mentioned problems,
The object of the present invention is to provide a signal recording method that makes it possible to separate the synchronization from the VTR playback signal even in positive polarity synchronization format signals such as the MUSE system.

[Summary of the invention]

For the above purpose, in the present invention, an overlap section on the entry side of the head of each recording track on a magnetic tape (for example, a two-head helical scan type VTR) is provided.
In this case, it is necessary to wrap the magnetic tape around the rotating cylinder by at least 180 degrees, but in reality it is wound an additional 10 degrees or more to ensure operating margin. This section is called an overlap section. ) to solve the problem that synchronization separation becomes impossible after the head switching point during playback until the next vertical synchronization signal arrives. It is.

The present invention is also effective for non-segment recording VTRs, which are commonly used in the past, in which one field of video signal is recorded on one track.
This can be expected to be particularly effective in segment recording VTRs that record on multiple tracks.

[Embodiments of the invention]

Next, embodiments of the present invention will be described with reference to the drawings. Here, as an example, a 2-head helical scan type VTR with 4-segment recording in which one field of video signals is recorded on four tracks will be described.

FIG. 2 conceptually shows a recording pattern that remains on a magnetic tape when the present invention is used. 1 is a magnetic tape, and 2 is a recording track for one field period (four tracks in total). In addition, the section 2a surrounded by the broken line in 2 is the recording part of the video signal (including the positive synchronization signal) corresponding to the 180° winding on the rotating cylinder, 2b is the head inlet side, and 2c is the head outlet side. Each indicates an overlap section. The arrows in the figure indicate the running direction of the head and tape.
3 is a recording part of a vertical synchronization signal (including a reference signal for horizontal synchronization separation) included in the input video signal, and 4 is a recording part of a horizontal synchronization signal (including a reference signal for horizontal synchronization separation) included in the input video signal. This is the recording part of the reference signal for.

If the present invention were not used (i.e. 4
For tracks with recording pattern 3 of the vertical synchronization signal during playback, the head switching point (one head becomes two
It is possible to perform synchronization separation from the signal from the moment when the remaining head is at the boundary between 2b and 2a of the next track, but after that, it is possible to separate the synchronization from the signal between Until the synchronization signal is reproduced (after four tracks), synchronization separation is impossible. This is because skew (discontinuity in the phase of the reproduced horizontal synchronizing signal) occurs at the head switching point due to expansion and contraction of the tape.

In the present invention, such a problem does not occur because a reference signal for horizontal synchronization separation is inserted and recorded in the overlap section on the head input side of each track. It goes without saying that this reference signal should also be recorded on a track having a vertical synchronization signal.

Further, although the case of 4-segment recording using 2-head helical scan is shown here, the present invention can also be applied to other cases, such as non-segment recording. In general, this invention can be applied to a VTR that records and reproduces a positive synchronization type video signal included in a reference signal for horizontal synchronization separation during vertical blanking, and is within the scope of the present invention.

Next, an embodiment of the present invention will be described in more detail using the block diagram of FIG. 5 is a video signal input terminal, 6 is a vertical synchronization separation circuit, 7 and 8 are reference signal addition circuits, 9a and 9b are pre-emphasis circuits, 10a and 10b are FM modulation circuits, 11a and 1
1b is a recording amplifier; 12a and 12b are recording heads; 13 is a magnetic tape; 14a and 14b are reproduction heads; 15a and 15b are reproduction amplifiers;
6b is an FM demodulation circuit, 17a and 17b are de-emphasis circuits, 18a and 18b are time axis correction circuits, 19 is a switch circuit, and 20 is a switch circuit 1
9 is an input terminal for a control signal, and 21 is an output terminal for a video signal.

The video signal input from the input terminal 5 is applied to the vertical synchronization separation circuit 6. Here, a pulse whose phase is locked to vertical synchronization is obtained and applied to the reference signal addition circuits 7 and 8. Although not shown in the figure, the rotation phase of the rotary cylinder is controlled based on this pulse,
Either head 12a or 12b is 3 in Figure 2.
(within the range of 2a, and between 2a and 2)
The vertical synchronization signal (near the border of b) is recorded. In the reference signal addition circuit 7, head 1
2a is 8, the head 12b is 4 in FIG.
A signal is added to record the reference signal at the position shown (in the input side overlap section). Of course, since this signal serves as a reference for horizontal synchronization separation during reproduction, it must be phase-locked to the horizontal synchronization signal recorded on the same track. The high-frequency components of the two video signals to which the reference signal has been added are emphasized in pre-emphasis circuits 9a and 9b, and become recording FM signals in FM modulation circuits 10a and 10b, which are sent to recording amplifiers 11a and 11b, recording heads 12a, The data is recorded onto the magnetic tape 13 via the magnetic tape 12b.

During reproduction, the reproduction signals of the reproduction heads 14a and 14b (which may be the same as those of the recording heads 12a and 12b) are demodulated via reproduction amplifiers 15a and 15b and FM demodulation circuits 16a and 16b, respectively, and are demodulated by de-emphasis circuits 17a and 17b. to suppress high frequencies, S/
N is improved and inputted to the time axis amplification circuits 18a and 18b. Here, skew, jitter, etc. of the reproduced signal are removed, and the horizontal synchronization signal used to detect it can be separated regardless of the skew based on the reference signal added during recording, so it is necessary to perform the intended operation. I can do it. The signals 18a and 18b corrected in time axis are applied to a switch circuit 19, respectively. This switch is switched in response to a control signal from an input terminal 20 in accordance with the rotational phase of the rotary cylinder. Therefore, a continuous reproduced video signal appears at the output terminal 21, but this has been time-axis corrected as described above, and the reference signal added at the time of recording has been removed. This corresponds to the recorded video signal and can be connected directly to the receiver.

In the signal shown in FIG. 1b, the video luminance signal and chromaticity signal are time-axis multiplexed, and the zero level reference of the chromaticity signal may be multiplexed in the vertical blanking period. In this case as well, it is effective to record the zero level reference in the input side overlap section of each recording track in a similar manner.

Finally, an example of a method for separating the horizontal synchronization signal during playback based on the reference signal added during recording is shown in Section 4.
This will be explained using FIG. As shown in the signal waveform diagram of FIG. 4, the reference signal 22 is a negative pulse having a polarity opposite to that of the video signal. This pulse 22 is inserted so as to be phase-locked to the positive synchronizing signal every 2H (horizontal period) having a positive (or negative) slope of the video signal shown in the figure.

FIG. 5 is a block diagram of a synchronization separation circuit during reproduction. A reproduced video signal (a signal obtained by recording and reproducing the signal shown in FIG. 4) is inputted from the input terminal 23. 24
This is a separation circuit for Hasaki's reference signal. Since the reference signal is a negative pulse, it can be easily separated by comparing it with a constant DC potential threshold level. The separated pulses are applied to a voltage controlled oscillator (VCO) 25. The VCO 25 first generates a pulse every 2H that is phase-locked with the separation pulse, and opens and closes the gate circuit 26.

When the VCO 25 generates a pulse, the gate circuit 26 detects the level of the reproduced video signal during a period of a positive synchronization signal having a positive (or negative) slope. Next, the level comparator 27 detects the difference from the 50% level, and its output controls the output pulse phase of the VCO 25 so that the detected level becomes 50%. By doing this, the phase of the reproduced horizontal synchronization signal can be detected without being affected by device skew, jitter, etc., and a separated output can be obtained at the output terminal 28, making it possible to use, for example, a time axis correction circuit. You can make it work as expected.

〔Effect of the invention〕

As explained above, according to the present invention, in a VTR for recording and reproducing a video signal having positive polarity synchronization and in which a reference signal for separating the horizontal synchronization signal is multiplexed with vertical blanking, It is not impossible to separate the synchronization signal from the reproduced video signal due to skew or the like, and the desired operation can be expected in the time axis correction circuit and the receiver.

[Brief explanation of the drawing]

FIG. 1 is a waveform diagram of a video signal, FIG. 2 is a recording pattern diagram on a magnetic tape of a VTR according to the present invention, FIG. 3 is a block diagram showing an embodiment of the present invention, and FIG. 4 is a video signal according to the present invention. FIG. 5 is a block diagram of the synchronous separation circuit according to the present invention. 7, 8... Reference signal addition circuit, 18... Time axis correction circuit, 22... Reference pulse.

Claims (1)

[Claims] 1. In a rotating head helical scan type magnetic recording and reproducing device that records and reproduces a composite video signal in which the synchronization signal has the same polarity as the video signal and is a positive synchronization that does not exceed its maximum amplitude, overlap of each recording track on the recording medium is avoided. It is characterized by having means for recording a reference signal phase-locked with the positive synchronization signal in the section, and means for separating the synchronization signal from the reproduced signal of each track during reproduction based on the phase of the reference signal. magnetic recording and playback device.