JPS6228485B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a video tape recorder (VTR) for recording and reproducing video signals, and in particular provides an auto-tracking device that automatically tracks recording tracks during reproduction.

Conventionally, in a VTR, one field of video signals is sequentially recorded on a plurality of adjacent recording tracks, but in order to perform high-density recording, it is necessary to narrow the track pitch (distance between tracks). By the way, if this track pitch is narrowed, adjacent recorded tracks may be played back simultaneously due to tape speed fluctuations, tape meandering, etc., and the main signal may be interfered with by the reproduced signals from these adjacent recorded tracks. As a result, there was a problem in that the quality of the reproduced image deteriorated, and there was a limit to how narrow the track pitch could be.

Therefore, there is a method of detecting this track deviation and driving the magnetic head in the opposite direction to the track deviation using a drive device using a piezoelectric element or the like to perform accurate tracking.

There are various methods for detecting this track deviation.

For example, by memorizing the maximum value of the playback output level and detecting the difference between this maximum value and the current level,
There is a method of tracking control to reduce this difference. In this method, since it is not possible to detect in which direction the track deviation is occurring, the head is driven in an arbitrary direction, and if this level difference becomes large, the head is driven in the opposite direction. Therefore, tracking is performed at positions within a certain range around the maximum tracking position, and accurate tracking cannot be performed. Further, due to level fluctuations caused by fluctuations in the magnetic head and magnetic tape space, erroneous tracking control may occur even when the tracking position is accurate.

Therefore, as an alternative method, pilot signals of different frequencies are recorded for each track in advance, and when the main magnetic head is at the correct tracking position during playback, the main magnetic head is at the position straddling the adjacent tracks. These pilot signals are regenerated by an auxiliary magnetic head, and the difference in frequency is
There is a method of separating these two pilot signals and performing tracking control based on the level difference between them. In this method, even if there is a reproduction level fluctuation, the two pilot signals have similar level fluctuations, so there is no problem like the above method. However, it is necessary to record the pilot signal, which requires a circuit, and there is also the problem that unnecessary components are generated due to cross-modulation between the pilot signal and the recording signal, making it impossible to record at a high recording level. There is a drawback that the S/N ratio of the pilot signal is not sufficient and tracking control may be performed incorrectly due to noise.

The present invention is a method of separating the reproduced signals of these adjacent tracks and controlling tracking based on the difference, without recording a pilot signal.

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, a video signal to be recorded applied to an input terminal 1 is applied to an FM modulator 2 and a synchronization signal separation circuit 5.
Then, the synchronization signal is separated and applied to the reset signal generator 6 and the vertical synchronization signal separation circuit 8. The vertical synchronization signal separation circuit 8 separates the vertical synchronization signal and provides it to a 1/2 frequency divider 9, and the 1/2 frequency division signal is provided to the switching signal generator 7.

In the reset signal generator 6 (described later),
A horizontal synchronizing signal as shown in FIG. 2A is inputted, and a reset signal as shown in FIG.

In the FM modulator 2, the input video signal is FM modulated, and is reset to zero at the timing of the reset signal as shown in (c) by the reset signal, so that the input video signal is always zero during one horizontal scanning period (hereinafter referred to as C). 1H
FM signals with strong correlation are obtained for each (abbreviated as ).

This is because the video signal that is in phase and modulated by the timing of the reset signal is a signal that has a strong correlation between 1H, so this FM signal also becomes a signal that has a strong correlation between 1H.

Next, this FM signal is applied to the contact a of the changeover switch 4 and the polarity inverter 3, the polarity of which is inverted in the polarity inverter 3, and applied to the contact b of the changeover switch 4.

On the other hand, the switching signal generator 7 is supplied with a 1/2 frequency-divided signal of the vertical synchronizing signal as shown in FIG. 2D, and a reset signal as shown in FIG.
As the output signal, a signal as shown in (G) is obtained.

The configuration of the switching signal generator 7 is to divide the reset signal H by 1/2 to obtain a signal like F.
It consists of a 1/2 frequency divider and an AND circuit that performs AND logic on this signal and signal D to obtain output signal G.

Next, the changeover switch 4 is controlled by this output signal, and the output of the changeover switch 4 is as follows.
Every vertical scanning period (hereinafter abbreviated as 1V), the FM signal whose polarity is inverted every 1H and the FM signal as it is are alternately transmitted.
FM signal can be obtained.

The FM signal that is the output of this switch circuit 4 is
The recording magnetic head 10 sequentially records data on a magnetic recording medium in a conventionally known recording track arrangement as shown in FIG. 3 so that one field forms one recording locus.

FIG. 3 is a diagram showing the arrangement of recording tracks on a magnetic tape, in which the A track records an FM signal whose polarity is inverted every 1H, and the B track records an unchanged FM signal.

Next, to explain the reset signal generator 6 in more detail, in FIG. 4, a horizontal synchronizing signal A as shown in FIG. , is triggered at the rising edge of the pulse, and a signal RO with a pulse width T ₁ is obtained as an output. Next, this signal ``L'' is applied to the monostable multivibrator 29, which is triggered by the falling edge of the signal, and a reset signal with a pulse width T <sub>2</sub> as shown in ``C'' is obtained as an output.
The signal in FIG. 5C is the same as the signal in FIG. 2B.

Note that the pulse width _T1 means the timing of the reset signal and the synchronization signal, and this value may be any value as long as the reset signal falls within the horizontal blanking range. Further, the pulse width T ₂ must be less than or equal to 1/2 of the minimum period of the FM modulation signal.

During reproduction, the main reproduction magnetic head 11
The recorded signal of the main track is reproduced, and the FM demodulator 1
3 and is FM demodulated to obtain a reproduced video signal, which is then supplied to a noise remover 14. next,
The noise remover 14 removes phase discontinuous portions (same timing as the reset signal) caused by the reset signal forcing the FM signal to match the phase of the 1H during recording. The noise in the part) is removed and outputted to the output terminal 15 as a reproduced video signal.

To explain this noise remover 14 in detail, in FIG. 6, a reproduced video signal is input to an input terminal 31. This reproduced video signal is
As shown in Figure A, there is noise in the synchronization signal part, which is the phase-discontinuous part of the FM signal. This reproduced video signal is applied to the contact a of the switch 32, the output terminal 34, and the sync signal separation circuit 31, where the sync signal (FIG. 7b) is separated and controls the switch 32. The switch 32 is
This synchronizing signal causes the reproduced video signal of the synchronizing signal portion to be shot to the DC voltage source 33. Therefore, the noise is grounded to the potential of the DC voltage source 33, removed, and output to the output terminal 34.

On the other hand, when the main reproducing magnetic head 11 is at the accurate tracking position a as shown in FIG. The main reproducing magnetic head 11 is arranged in such a manner that the reproducing signal from the auxiliary reproducing magnetic head 12 is a mixture of the FM signal from the A track and the FM signal from the B track. . This reproduced signal is given to a 1H delay line 16, an adder 17, a subtracter 18,
A signal delayed by 1H by the 1H delay line 16 is applied to the adder 17 and subtracter 18.

Here, let the signal at any time be S _A for the A track reproduced signal and S _B for the B track reproduced signal, and as shown in Fig. 8, the phase of the signal at each H is expressed as A and B, respectively. Become.

However, for the sake of explanation, it is assumed that the video signals before and after 1H are equal (although they are actually different, it is true that they have a strong correlation, so it is safe to assume this).

That is, the reproduced signal A from the A track is a signal with the same phase for each H, and the reproduced signal B from the B track is a signal whose phase is inverted every 1H.

Therefore, the signal delayed by 1H and the added signal are S _A and the in-phase signals are added, resulting in 2S _A ,
S _B becomes zero when the opposite phases cancel each other out.

In other words, the adder 17 outputs a signal of 2S _A.

On the other hand, in the output of the subtractor 18, the in-phase signals of S _A cancel each other out and become zero, and the signals of S _B and the opposite phase signals are subtracted, resulting in signals of 2S _B and -2S _B , and as a result, 2S _B , -2S _B signal is output.

As a result, the signal _S'A from the A track and the signal _S'B from the B track are separated.

Next, these signals are given to amplitude detection circuits 19 and 20, respectively, and signals corresponding to the amplitudes are output.

Therefore, each output of the amplitude detection circuits 19 and 20 is
These are the signals 2S _A and 2S′ _B , and these signals are given to the subtracter 21, and the output is 2(S′ _A −S′ _B ).
An error signal of

This error signal is a signal corresponding to track deviation. For example, when the main magnetic head 11 is at the correct tracking position, S _A and S _B are equal, and this error signal is zero.

When the auxiliary reproducing magnetic head 12 deviates toward the A track, S _A >S' _B , resulting in a positive voltage signal corresponding to the deviation. When the auxiliary reproducing magnetic head 12 deviates toward the B track, S _A <S' B. S _B and becomes a negative voltage signal.

Therefore, accurate tracking can be achieved by moving the main reproducing magnetic head 11 and the auxiliary reproducing magnetic head 12 toward the B track in accordance with this error signal so that this signal is always zero. Become.

What should be noted here is that when the auxiliary reproducing magnetic head is at the position a as shown in Figure 9, if it is moved in the direction _D1 according to this error voltage as described above, Good, but when it is in a position like b,
It must be moved in the direction of D ₂ according to the error voltage.

In this case (position b), if it deviates toward the A track, the error voltage becomes a positive voltage, and a
If you move it in the direction of D ₁ in the same way as in the case of , it will shift more and more toward the A track.

Therefore, in this case, it is necessary to move in the direction _D2 , which is opposite to a.

In other words, the main reproducing magnetic head and the auxiliary reproducing magnetic head may be moved for each track (1V) in accordance with a signal obtained by inverting the polarity of this error signal.
To perform this inversion, the error signal from the subtracter 21 is applied to the polarity inverter 22 and the contact a of the changeover switch 23, and the signal whose polarity has been inverted by the polarity inverter 22 is applied to the contact b of the changeover switch 23. The changeover switch 23 is switched every 1V by the signal from the 1/2 frequency divider 25, and an error signal inverted every 1V is obtained at the output.

This error signal is applied to the drive device 26, and the drive device 26 moves the main reproducing magnetic head 11 and the auxiliary reproducing magnetic head 12 in accordance with this error signal, thereby enabling accurate tracking.

Note that the 1/2 frequency divider 25 is supplied with a vertical synchronization signal separated by a vertical synchronization signal separation circuit 24 from the reproduced video signal from the FM demodulator 13.

The above is an explanation of one embodiment of the present invention. Generally, a recording/reproducing system has a time axis variation factor, and it is normal that a frequency variation occurs in a reproduced signal.

Therefore, if the frequency fluctuation is large, a shift occurs in the phase relationship between the 1H delayed signal and the undelayed signal, making it difficult to separate the reproduced signals from the A and B tracks. Therefore, an embodiment that takes this frequency fluctuation into consideration will be described.

In FIG. 10, during reproduction, data is reproduced from the magnetic recording medium by the main reproduction magnetic head 11.
The FM signal is given to the FM demodulator 13 and the 1/2 frequency divider 35.

The FM demodulator 13 performs FM demodulation to obtain a reproduced video signal, and the synchronization signal separation circuit 43 separates the synchronization signal and supplies it to the gate signal generator 42 .

This synchronization signal causes the gate signal generator 42
generates a gate signal for gating the in-phase portion of the reproduced FM signal, that is, the signal portion of a certain period after being reset by the reset signal, and supplies it to the gate circuit 37.

On the other hand, the 1/2 frequency divider 35 divides the frequency of the FM signal by 1/2 and supplies the divided signal to the frequency converter 36.

Here, set the frequency of the part that is in phase during recording (the part after the reset signal in the sync signal part).
₁ and has a frequency fluctuation of Δ during reproduction, the output of the 1/2 frequency divider 35 is ( ₁ ,
The frequency is Δ)/2. This signal is frequency-converted by a frequency converter 36 using a signal with a frequency of ( ₂ - Δ)/2 from a 1/2 frequency divider 39, and the output is a signal with a frequency of ( ₁ + ₂ ). is obtained and applied to the gate circuit 37 , where only the signal of the aforementioned portion is separated by the gate signal from the gate signal generator 42 and applied to the phase comparator 38 .

On the other hand, the phase comparator 38 receives a stable frequency ( ₁ + ₂ )/2 from the fixed frequency number oscillator 41.
This signal and the signal from the gate circuit 37 are phase-compared, and the variable frequency oscillator 40 is controlled by the error signal.

Next, the output signal of this variable frequency oscillator 40 is
The signal is applied to a 1/2 frequency divider 39, divided into 1/2, and applied to a frequency converter 36.

As a result, due to the phase lock loop as described above, the frequency of the output signal of the variable frequency oscillator 40 becomes ( ₂ -Δ), and this signal is applied to the frequency converter 44.

On the other hand, the reproduction signal from the auxiliary reproduction magnetic head 12 similarly has a frequency fluctuation Δ, and the frequency of the above portion is also ( ₁ +Δ).

This reproduction signal is given to the frequency converter 44, and the signal from the variable frequency oscillator 40 ( ₂ - Δ
), the frequency is converted and a signal of frequency ( ₁ + ₂ ) with no frequency fluctuation is obtained as an output, which is output to the output terminal 45.

This signal is used for tracking control in a manner similar to that shown in FIG.

In this embodiment, a signal corresponding to the frequency fluctuation is obtained based on the FM signal whose frequency has been divided by 1/2 by the 1/2 frequency dividers 35 and 39.

The reason for this is that when using a signal that is not divided by 1/2, the phase is compared using an FM signal whose phase is inverted every 1H, and the phase error becomes a signal whose phase is inverted every 1H, causing a phase lock loop. Since the signal will not operate completely, the purpose is to divide the frequency by 1/2 so that the signal is in the same phase for 1H.

The above is an explanation of the embodiments of the present invention.According to the present invention, there is no need to record a pilot signal, etc. as in the past, and compared to methods that use burst signals of color signals, color It can also be used when recording and reproducing video signals without signals.

In addition, the modulation signal obtained by modulating the video signal itself is used as a tracking signal, and since it uses a modulation signal with a better S/N than when using a carrier color signal, stable tracking is achieved. be able to.

In the example, a method was used in which the FM signal was reset every 1H in order to create a signal with strong 1H correlation, but other signals with strong 1H correlation (for example,
PM modulation signal) is similarly possible.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG.
1 is a waveform diagram for explaining a part of the operation of FIG. 4 is a block diagram showing a partial configuration of FIG. 1, FIG. 5 is an operation waveform diagram of FIG. 4, FIG. 6 is a block diagram explaining a partial configuration of FIG. 1, and FIG. are the operating waveform diagrams in Figure 6, Figures 8 and 9.
The drawings are explanatory diagrams for explaining FIG. 1, and FIG. 10 is a block diagram of main parts of another embodiment of the present invention. 1...Input terminal, 2...FM modulator, 3, 22
...Polarity inverter, 4, 23...Switching circuit, 5...Synchronizing signal separation circuit, 6...Reset signal generator, 7...Switching signal generator, 8, 24...
... Vertical synchronization signal separation circuit, 9, 25 ... 1/2 frequency divider, 10 ... Magnetic head, 11 ... Main playback head, 12 ... Auxiliary playback head, 13 ... FM demodulator, 14 ... Noise Remover, 16...1H delay line, 17...Adder, 18, 21...Subtractor, 1
9, 20... amplitude detection circuit, 26... head drive device.

Claims (1)

[Claims] 1 A modulation means that modulates the video signal itself to be recorded as a highly correlated signal before and after one horizontal scanning period, and a signal whose phase is inverted for each horizontal scanning period on the first recording track. The first recording track and the second recording track are arranged so that the second recording track adjacent to the first recording track has a signal whose phase is not inverted every horizontal scanning period. a recording means for recording so as to alternately record on a recording medium; and when a first reproducing head accurately scans over a recording track during reproduction, both an adjacent first recording track and a second recording track; a second reproducing head that simultaneously scans the second reproducing head; and separation for separating the reproducing signal from the first recording track and the reproducing signal from the second recording track from the signal reproduced by the second reproducing head. means for obtaining an error signal corresponding to a level difference between the separated signals; and means for moving the first and second reproduction heads in a direction perpendicular to the recording track in accordance with the error signal. An auto tracking device.