JPH0478227B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for reproducing television composite video signals on a magnetic disk.

[Prior Art] When one field or one frame of a television composite video signal is recorded on one track per revolution of a magnetic disk using the frequency modulation (hereinafter referred to as FM) method, the beginning and end of recording on each track are There will always be a seam between records. This recording seam appears as flickering on the television screen when played back, so the seam exists 7H (however, H is one horizontal synchronization cycle period) before the vertical synchronization signal. is set as,
Care has been taken not to appear on the actual TV screen.

[Problems to be Solved by the Invention] However, if the FM recorded signal has a gap at the seam as shown in Figure 7, when it is reproduced and demodulated, the recorded seam will appear as shown in Figure 8. Noise is generated in the vicinity including the eyes, and that noise is also generated in the sync signal part (a part lower than the pedestal level), and depending on the sync separation circuit method of commercially available televisions, this noise can be The problem was that it could be mistaken for an equalization pulse, disrupting vertical synchronization and causing the screen to vibrate up and down.

This invention was devised in order to eliminate these drawbacks, and it is a magnetic system that eliminates demodulation noise caused by recording seams and eliminates disturbances in vertical synchronization of composite video signals to obtain clear images. An object of the present invention is to provide a method for reproducing a television composite video signal on a disc.

[Means for Solving the Problems] The present invention records one field or one frame of a television composite video signal on one track per rotation of a magnetic disk using a frequency modulation method, and reads out the composite video signal from the magnetic disk. and demodulate it.
The composite video signal includes at least the recording seam of the demodulated composite video signal in the range from the horizontal synchronization signal position that does not appear on the television screen before the vertical synchronization signal of the demodulated composite video signal to before the start of the vertical blanking period. The problem is that the video signal level was forcibly set above the pedestal level.

Further, the present invention records one field or one frame of a television composite video signal on one track per rotation of a magnetic disk using a frequency modulation method, reads out the composite video signal from the magnetic disk, demodulates it, and demodulates the demodulated composite video signal. The level of the composite video signal includes at least the recording seam of the composite video signal in the range from the position of the horizontal synchronization signal that does not appear on the television screen before the vertical synchronization signal of the signal to before the start of the vertical blanking period. The purpose of this method is to forcibly set the signal level above the pedestal level, detect a synchronization signal defective portion of the composite video signal, and superimpose a pseudo synchronization pulse on the synchronization signal defective portion.

[Function] In the present invention having such a configuration, the composite video signal read from the magnetic disk is demodulated, and the level in the vicinity of the recorded joint of the demodulated composite video signal is forcibly pedestalized. Set above level.

Further, in the present invention, after the level in the vicinity of the recording joint of the composite video signal including the joint is forcibly set to be equal to or higher than the pedestal level, a pseudo synchronization pulse is superimposed on that part.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a magnetic disk on which, for example, a television composite video signal of n fields (=n/2 frames) on n tracks is recorded using the FM method, with one field per rotation and one track.
A composite video signal recorded on the magnetic disk 1 is read by a reproduction head 2 and supplied to a reproduction demodulation circuit 4 via a head amplifier 3. The composite video signal reproduced and demodulated by the reproduction demodulation circuit 4 is supplied to one contact 5a of the first changeover switch 5. The other contact 5b of the first changeover switch 5
A voltage E having a level corresponding to the gray color of a television signal, for example, which is higher than the pedestal level of the composite video signal, is input to the input signal.

The magnetic disk 1 is attached to a flange 8 fixed to a rotating shaft 7 of a motor 6, as shown in FIG. A disk core 9 is provided at the center of the magnetic disk 1, and this core 9 is attached to the flange 8. A permanent magnet 10 is embedded in the flange 8, and a permanent magnet 10 is embedded at one point of the disk core 9.
A magnetic piece 11 for PG is buried, and the permanent magnet 10
It is magnetized by A PG coil 12 is provided above a portion through which the magnetic piece 11 passes as the magnetic disk 1 rotates. The point where the magnetic piece 11 is buried approximately coincides with the joint of recording of the composite video signal of each track on the magnetic disk 1.

The PG coil 12 detects the passage of the magnetic piece 10 and supplies its detection output to a monostable multivibrator 14 via a pulse shaping circuit 13. The output of the multivibrator 13 is supplied to the first changeover switch 5. The first changeover switch 5 normally closes the contact 5a, and switches the contact to the contact 5b only when a signal is input from the multivibrator 14. The oscillation period of the multivibrator 13 is set, for example, to several H (where 1H is one horizontal synchronization period).

The demodulated composite video signal outputted through the first changeover switch 5 is sent to one contact 16a of the second changeover switch 16 via a 0.5H delay circuit 15 that delays the demodulated composite video signal by 1/2 of the horizontal synchronization period. At the same time, the other contact 16 of the changeover switch 16
directly supplied to b. The second changeover switch 16 switches its contacts 16a and 16b in response to a switching pulse SWP which alternately goes high and low for each field. Then, it is output as the final reproduced composite video signal Sv via the second changeover switch 16. In addition, here, alternately for each field
For example, the 0.5H delay or no delay is due to the 1/2 interlaced system in the normal television standard system, and in the NTSC system, 1 frame = 2 fields, which is 525H, so 1 field = 262.5H. This is to correct the fact that the horizontal synchronization will be off by 0.5H at the recording seam.

In the embodiment of the present invention having such a configuration, a composite video signal recorded on a certain track of the magnetic disk 1 is read out by the playback head 2, and is transmitted via the head amplifier 3 and the playback demodulation circuit 4 to the signal shown in FIG. A signal having a waveform as shown in a is supplied to one contact 5a of the first changeover switch 5. In this operation, when the magnetic piece 11 of the disk core 9 passes the position of the PG coil 12, the third
A waveform as shown in b in the figure is generated. This waveform is shaped by the pulse shaping circuit 13 into a rectangular wave as shown in FIG.
is supplied to As a result, the multivibrator 14 oscillates with a pulse width of several H as shown in d of FIG. 3, during which time the first changeover switch 5 is switched to the contact 5b side. The timing of this switching is set to fall within a range that includes the recording seam of the composite video signal and its vicinity. As a result, the reproduced and demodulated composite video signal outputted from the first changeover switch 5 is converted into a television signal so as to cover the range of noise generated by the recording seam, as shown in e of FIG. A voltage E corresponding to the gray level of is forcibly superimposed, and the noise is erased. Therefore, this portion will be displayed as gray on the television screen. This superimposition of the gray level signal also prevents noise from occurring in the synchronization signal portion, and there is no risk of vertical synchronization being disturbed due to noise being mistakenly detected as an equalization pulse. Therefore, the screen is prevented from vibrating up and down due to the recording seams,
You can get a clear screen.

Next, another embodiment of the invention will be described with reference to the drawings. Note that the same parts as in the above embodiment are given the same reference numerals, and detailed explanations will be omitted.

As shown in FIG. 4, an adder 17 is provided, and the composite video signal from the first changeover switch 5 is directly supplied to the adder 17, and a synchronization separation circuit 18, a synchronization loss detection circuit 19, and a pseudo synchronization It is supplied via a generating circuit 20.

The synchronization loss detection circuit 19 and the pseudo synchronization generation circuit 20 are specifically constructed as shown in FIG. That is, the synchronization loss detection circuit 19
NPN type transistors Tr1, Tr2 and PNP type transistor Tr3 are provided, the signal from the synchronous separation circuit 18 is input to the base of the transistor Tr1, the signal is taken out from the collector side of the transistor Tr1, and the signal is passed through the diode D. The said transistor Tr2
supplies to the base of Furthermore, a signal is taken out from the collector of the transistor Tr2 and supplied to the base of the transistor Tr3, and the signal is output from the collector of the transistor Tr3 to the pseudo synchronization generating circuit 20.

The pseudo synchronous generation circuit 20 includes an NPN type transistor Tr4, a PNP type transistor Tr5, and
It is composed of an unstable multivibrator consisting of NPN type transistors Tr6 and Tr7, and the output from the synchronization loss detection circuit 19 is connected to the transistor Tr.
The output of the multivibrator is supplied to the base of the transistor Tr5, and the pseudo synchronous pulse is supplied from the collector of the transistor Tr5 to the base of the transistor Tr5, and the operation of the unstable multivibrator is controlled by the on/off operation of the transistor Tr4. It is output to the adder 17.

In this device, when the first changeover switch 5 outputs the composite video signal shown in FIG. are separated. This synchronization signal is input to the synchronization loss detection circuit 19, and the synchronization signal causes the transistor to
Since Tr1 operates, the output at point P of the integrating circuit changes as shown in the sixth c. At this time, the potential at point P does not rise to the emitter potential of transistor Tr2 during normal synchronization intervals, and transistor Tr2 remains off. However, if there is a missing part of the synchronization signal, the potential at point P will continue to rise, causing the transistor to
Exceeds the emitter potential of Tr2 and that transistor Tr
2 will turn on. As a result, the synchronization loss detection circuit 19 outputs a signal corresponding to the loss portion of the synchronization signal, as shown in d of FIG. When the signal from the synchronization loss detection circuit 19 is input, the pseudo synchronization generation circuit 20 operates as an unstable multivibrator, and outputs a synchronization pulse close to a substantially normal synchronization signal as shown in e of FIG. Therefore, the adder 17 superimposes the composite video signal from the first switch 5 and the pseudo synchronization pulse from the pseudo synchronization generation circuit 20 to produce a composite video without loss of synchronization signal as shown in f in FIG. It will start outputting a signal. Therefore, even if there is a receiver whose vertical synchronization is affected by synchronization loss, for example, it is possible to prevent the vertical synchronization from being disturbed.

Note that the pseudo synchronization pulse is generated by the synchronization loss detection circuit 19.
Although there will be a slight deviation from the correct synchronization pulse due to the configuration of the system, there is no risk that this degree will adversely affect the vertical synchronization of the receiver.

Of course, this embodiment also provides the same effects as the previous embodiment.

In the above embodiments, the signal level to be superimposed is set to a level corresponding to the gray color of the television signal, but this is not necessarily the case. It's good if you get used to it.

Furthermore, in the above embodiment, the range of several H before and after the seam of recording of the composite video signal was set to a level corresponding to the gray of the television signal, but the invention is not necessarily limited to this. In some television receivers, the period from 15H before the leading edge of the vertical sync signal is hidden at the bottom of the screen and is not displayed on the screen. The signal level including the recording seam may be set to a level corresponding to the gray color of the television signal. In other words, in the present invention, at least a complex signal is generated in the range from the horizontal sync signal position that does not appear on the television screen before the vertical sync signal to before the start of the vertical blanking period (before the equalization pulse that precedes the vertical sync signal). It is sufficient to set the signal level including the recording seam of the video signal to a level corresponding to the gray color of the television signal.

[Effects of the Invention] As detailed above, the present invention provides a magnetic disk that eliminates demodulation noise caused by recording seams and eliminates disturbances in vertical synchronization of composite video signals to obtain clear images. A method for reproducing a television composite video signal can be provided.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a schematic diagram showing the configuration of a magnetic disk section in the same embodiment, Fig. 3 is an output waveform diagram of each part in the embodiment, and Fig. 4 5 is a block diagram showing another embodiment of the present invention, FIG. 5 is a specific circuit diagram of the synchronization loss detection circuit and pseudo synchronization generation circuit in FIG. 4, and FIG. 6 shows the output waveforms of each part in the same embodiment. FIG. 7 is a waveform diagram showing a waveform near the recording seam of a composite video signal conventionally recorded on a magnetic disk, and FIG. 8 is a waveform diagram showing a conventionally demodulated composite video signal. 1... Magnetic disk, 2... Playback head, 4...
...Regeneration demodulation circuit, 5...First changeover switch, 1
2...PG coil, 14...monostable multivibrator, 19...synchronization loss detection circuit, 20...pseudo synchronization generation circuit.

Claims (1)

[Claims] 1. Recording one field or one frame of a television composite video signal on one track per rotation of a magnetic disk using a frequency modulation method, reading out the composite video signal from the magnetic disk and demodulating it, and demodulating the composite video signal. The composite video signal includes at least the recording seam of the composite video signal in the range from the horizontal synchronization signal position that does not appear on the television screen before the vertical synchronization signal of the composite video signal to before the start of the vertical blanking period. A method for reproducing a television composite video signal for a magnetic disk, characterized in that the signal level is forcibly set to a level higher than a pedestal level. 2. Set the signal level set in the range from the horizontal synchronization signal position that does not appear on the television screen before the vertical synchronization signal of the composite video signal to before the start of the vertical blanking period to a level corresponding to the gray color of the television signal. A method for reproducing a television composite video signal from a magnetic disk as claimed in claim 1. 3 One field or one frame of a television composite video signal is recorded on one track per rotation of a magnetic disk using a frequency modulation method, the composite video signal is read out from the magnetic disk and demodulated, and the vertical the level of the composite video signal including at least the recording seam of the composite video signal in the range from the horizontal synchronization signal position that does not appear on the television screen before the synchronization signal to before the start of the vertical blanking period; A television composite video signal for a magnetic disk is forcibly set to a level higher than the pedestal level, furthermore, a synchronization signal defective portion of the composite video signal is detected, and a pseudo synchronization pulse is superimposed on the synchronization signal defective portion. How to play.