JPH0325855B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a magnetic recording and reproducing apparatus such as a VTR that performs tracking control using a four-frequency pilot method.

Prior Art Conventionally, in magnetic recording and playback devices such as VTRs,
There is one that performs tracking control using a four-frequency pilot system.

An example of such a magnetic recording/reproducing device will be explained with reference to FIG.

In this magnetic recording and reproducing apparatus, first, a pilot signal generator 1 includes an oscillator 2 that generates a signal of a predetermined frequency, and a signal from the oscillator 2 at a predetermined frequency division ratio, for example 1, in accordance with an external control signal. It consists of an automatic frequency control oscillator consisting of frequency dividers 3 and the like that divide the frequency by /58, 1/50, 1/36, and 1/40.

This pilot signal generator 1 generates four types of pilot signals, each having a predetermined first, second, third, and fourth frequency difference α, β, γ, and δ.
fm (f ₁ , f ₂ , f ₃ , f ₄ ) and outputs these pilot signals f ₁ to f ₄ in a circular order under the control of a head switching pulse (switching pulse) SWP.

That is, between the frequencies of these pilot signals f ₁ to f ₄ , |f ₁ −f ₂ |=|f ₃ −f ₄ |=α |f ₂ −f ₃ |=|f ₄ −f ₁ There is a relationship of |=β |f ₃ −f ₁ |=γ |f ₄ −f ₂ |=δ.

For example, f ₁ = 100KHz, f ₂ = 115KHz, f ₃ = 160K
Hz, f ₄ = 145KHz, and the above 1st to 4th
The frequency differences α, β, γ, and δ are α=15KHz, respectively.
β=45KHz, γ=60KHz, δ=30KHz.

During recording, the pilot signal fm from the pilot signal generator 1 is input to the adder 5 via the low-pass filter 4, where it is superimposed on the video signal (chroma signal and volatility signal) _VD to generate the recording signal V. After being amplified by a recording amplifier 6 as _A , the signal is supplied to a video head 8 via contacts a and c of a recording/reproduction switch 7 and is recorded on a video tape 9.

As a result, as shown in FIG. 2, each video track of the video tape 9 has a pilot signal _f1 on track _T1 , a pilot signal _f2 on track _T2 , and a pilot signal _f3 on track _T3. However, the pilot signal _f4 is recorded on track _T4 , the pilot signal _f1 is recorded on track _T5 , and so on, in a circular order.

In FIG. 2, arrow A indicates the running direction of the video tape 9, and arrow B indicates the tracing direction of the video head 8.

During playback, the pickup signal (video signal and pilot signal) obtained by picking up the signal recorded on the video tape 9 by the video head 8 is transferred to the contacts b-c of the record/playback switch 7.
The signal is input to the reproduction amplifier 10 via the signal line and is amplified.

The reproduced signal V _B from the reproduced amplifier 10 is input to the bandpass filter 11, and only the pilot signal included in this reproduced signal V _B is extracted.
This regenerated pilot signal fm' is output to mixer 12.

When the video head 8 is accurately tracing a regular track, this reproduced pilot signal fm' includes the pilot signals recorded on the track being traced as well as the pilot signals recorded on the tracks on both sides. Also includes signals.

On the other hand, at this time, the pilot signal fm recorded on the track to be traced by the video head 8 is input from the pilot signal generator 1 to the mixer 12, and this pilot signal fm and the reproduced pilot signal fm' are mixed. Then, a mixed pilot signal fmm' containing at least one of the first to fourth frequency difference signals α, β, γ, and δ is output.

Therefore, from the mixed pilot signal fmm' output from this mixer 12, the band pass filter 13
The bandpass filter 14 extracts a signal with a first frequency difference α, and the bandpass filter 14 extracts a signal with a second frequency difference β.

The respective levels of the first frequency difference α signal and the second frequency difference β signal are detected by the detection circuits 15 and 16, respectively, and the differential amplifier 1
7, and a tracking error signal T _E corresponding to the level difference between the signal of the first frequency difference α and the signal of the second frequency difference β is sent to a capstan control circuit (tracking servo system), not shown. Output.

The tracking error signal T _E output from the differential amplifier 17 is zero when the video head 8 is on the regular track, positive voltage when it is ahead of the regular track, and positive voltage when it is behind the regular track. When it is present, the voltage becomes negative.

Therefore, the capstan control circuit controls the signal level of the first frequency difference α and the second frequency difference β.
The capstan motor is controlled so that the signal levels are the same.

That is, for example, in the example shown in FIG.
When tracing T ₂ , the pilot signal f ₂ is input from the pilot signal generator 1 to the mixer 12 , and as the video head 8 shifts toward track T ₁ , the first signal of |f ₁ −f ₂ | The level of the signal of the second frequency difference α becomes larger, and as the track _shifts toward the track _{T 3} side, the level of the signal of the second frequency difference β becomes larger.

Therefore, by performing tracking so that the level of the signal with the first frequency difference α and the level of the signal with the second frequency difference β are the same, a normal track can be accurately traced.

By the way, in this magnetic recording/playback device,
A signal with a first frequency difference α and a signal with a second frequency difference β are detected from a mixed pilot signal obtained by mixing a reproduced pilot signal and a pilot signal of a regular track to be traced, and a signal with a first frequency difference α and a signal with a second frequency difference β are detected. I'm trying to apply a tracking servo.

Therefore, depending on the relationship between the frequency of the pilot signal (reproduced pilot signal) recorded on the track being traced by the video head and the frequency of the pilot signal generated by the pilot signal generator, the video head can be set to the normal The lock-in time of the tracking servo system required to position the object on the track changes.

In the case of the 4-frequency pilot method, the video track corresponding to the pilot signal from the pilot signal generator is 1/4, so it is
Record CTL signals and control tracking
In the worst case, it may require twice as much lock-in time as the CTL method.

That is, as mentioned above, first, the pilot signals f ₁ , f ₂ , f ₃ , and f ₄ are generated in a circular order from the pilot generator by a switching pulse and a pulse obtained by dividing the frequency of this switching pulse by 1/2. Output.

For example, when the pilot signal _f1 is being output from the pilot signal generator, if the video head is shifted by about one track, the reproduced pilot signal will be different from the pilot signal _f1 and the pilot signal.
Becomes f ₂ or f ₄ .

At this time, the first and second frequency difference signals α,
Since the level of β corresponds to the level of the reproduction pilot signal _f2 or _f4 from the track to which the video head is misaligned, the video head can be quickly moved to a relatively normal track.

However, especially when the motor is started or when switching from high-speed playback (forward or reverse direction) to normal playback, the video head may have a maximum There may be a shift of about two video tracks.

In this case, for example, if the pilot signal generator outputs the pilot signal _f1 , the reproduced pilot signal will be the pilot signal _f3 and the pilot signal _f2 or _f4 , and the pilot signal _f3
Since the level of the pilot signal f ₂ or f ₄ decreases as the percentage of the pilot signal f 2 or f 4 is located on the recorded track, the first frequency difference α or the second frequency difference β
level becomes smaller.

In other words, the more often the video head is located on the track where the pilot signal _f3 is recorded, the more the detection result will be that the amount of deviation is not small, even though the actual deviation is about two tracks. .

Therefore, the lock-in time required to move the video head relative to each other by about two tracks to achieve tracking becomes large.
Unable to track quickly.

Purpose This invention has been made in view of the above points, and an object thereof is to shorten the lock-in time required for tracking in a magnetic recording/playback device that performs tracking control using the four-frequency pilot method as described above. .

Configuration In order to achieve the above object, the present invention provides a magnetic recording and reproducing apparatus as described above, which includes an error detection means for detecting the third and fourth frequency difference signals; A gain switching means is provided for switching to increase the phase gain of the tracking servo system when a signal with a third or fourth frequency difference is detected.

Embodiment Hereinafter, an embodiment of the present invention will be described with reference to FIG. 3 of the accompanying drawings. Note that the same parts as in FIG. 1 are given the same reference numerals, and explanations of those parts will be omitted.

First, in this magnetic recording and reproducing apparatus, a video tape 9 is traced by two video heads 8A and 8B.

Therefore, first, the video heads 8A and 8B are selected during recording/reproduction by the head changeover switch 18 which is changed over by the switching pulse SWP.

Furthermore, the directions of increase and decrease in the levels of the signals of the first and second frequency differences α and β are opposite when the video head 8A is selected and when the video head 8B is selected.

Therefore, the tracking error signal T _E output from the differential amplifier 17 or the signal obtained by inverting this tracking error signal T _E by the inverter 19 is
It is selected by a switch 20 operated by a switching pulse SWP and output as a tracking error T _E '.

Then, the mixed pilot signal fmm' outputted from the mixer 12 is passed through bandpass filters 13 and 1.
In addition to 4, it is also input to bunt pass filters 21 and 22.

The bandpass filter 21 extracts a signal with a third frequency difference γ from the mixed pilot signal fmm', and the bandpass filter 22 extracts a signal with a fourth frequency difference δ from the mixed pilot signal fmm'. , are output to detection circuits 23 and 24, respectively.

This detection circuit 23 includes a bandpass filter 21
The detection circuit 24 detects the level of the signal of the third frequency difference γ from the bandpass filter 2.
The level of the signal of the fourth frequency difference δ from 2 is detected and outputted to the differential amplifier 25, respectively.

This differential amplifier 25 outputs to the hold circuit 26 a deviation signal S _A corresponding to the difference between the level of the signal of the third frequency difference γ and the level of the signal of the fourth frequency difference δ.

This hold circuit 26 holds the deviation signal S _A from the differential amplifier 25 and outputs an error signal S _E.

These bandpass filters 21, 22, detection circuits 23, 24, differential amplifier 25, and hold circuit 26 constitute an error detection means.

Then, the tracking error signal T _E ' output from the terminal c of the switch 20 is transferred between the terminals c and a of the switch 28 and the resistor 29, which is switched according to the error signal S _E from the hold circuit 26 of the gain switching circuit 27. Alternatively, it is output between terminals c and b of the switch 28 and via the resistor 30.

The switch 28 is connected to the terminal a when the error signal S _E from the hold circuit 26 is at a low level "L".
and the error signal S _E becomes high level “H”.
Switches to terminal b side when .

Further, the resistance value R ₁ of the resistor 29 and the resistance value R ₂ of the resistor 30 are set to have a relationship of R ₁ >> _{R 2} .

Then, the tracking error signal T _E ' outputted via the gain switching circuit 27 is inputted via the phase filter 31 to a differential amplifier 32 whose other input is the servo speed error signal Go SSE. A deviation signal from the differential amplifier 32 is output to a servo control circuit (not shown).

Next, the operation of this embodiment configured as described above will be explained with reference to FIG. 2 mentioned above.

First, it is assumed that the pilot signal f ₂ is output from the pilot signal generator 1 to the mixer 12 when tracing a track on which the pilot signal f ₂ is recorded.

At this time, video head 8A receives the pilot signal.
If f ₂ is roughly accurately traced to the recorded track, for example, track T ₂ in FIG.
The reproduced pilot signal fm' input to the track T 2 includes the pilot signal f ₂ and the tracks T ₁ ,
The pilot signals f ₁ and f ₃ recorded at T ₃ are included.

Therefore, the mixed pilot signal fmm' output from the mixer 12 includes a signal with a first frequency difference α of |f ₁ - ₂ | and a signal with a second frequency difference β of |f ₂ - f ₃ |. The signal is included, but the signal with the third frequency difference γ and the signal with the fourth frequency difference δ are not included.

Thereby, first, the signal with the first frequency difference α and the signal with the second frequency difference β are extracted by the bandpass filters 13 and 14, respectively, and the detection circuit 1
5 and 16, the level is detected and input to the differential amplifier 17.

Therefore, the differential amplifier 17 outputs a tracking error signal T _E corresponding to the level difference between the signal of the first frequency difference α and the second frequency difference β,
This tracking error signal T _E is sent to the switch 20.
Depending on the state of the tracking error signal T E ', the signal is output directly or inverted to the gain switching circuit 27 as a tracking error signal T _E '.

At this time, as mentioned above, the mixed pilot signal
Since fmm' does not include the signals of the third frequency difference γ and the fourth frequency difference δ, the differential amplifier 2
Therefore, the error signal S _E from the hold circuit 26 becomes low level "L", and the switch 2 _of the gain switching circuit 27
8 has been switched to the terminal a side.

Therefore, the tracking error signal T _E ′ is
Since the signal is outputted between terminals c and a of the switch 28 and via the resistor 29, the gain is determined according to the resistance value of the resistor 29.

Then, the pilot signal generated from the pilot signal generator 1 of the video head 8A or 8B
If the amount of deviation from the track where fm is recorded is within the maximum of one track, the above-mentioned operation is performed and tracking servo control is performed.

However, when the motor is started or when the high-speed playback state returns to the normal playback state, the video head 8
A or 8B may be shifted by about two tracks from the track on which the pilot signal fm output from the pilot signal generator 1 is recorded.

For example, when the pilot signal _f2 is being output from the pilot signal generator 1, the second
In the example shown in the figure, track T ₂ must be traced, but in reality, track T 2 must be traced.
I have traced T ₄ .

At this time, for example, video head 8A is
Assuming that most of track _T4 and a part of track _T3 are being traced, the reproduced pilot signal fm' input to the mixer 12 includes the pilot signal _f4 recorded on track _T4 and track _T3 . Contains the pilot signal _f3 recorded in

Thereby, the mixed pilot signal fmm' output from the mixer 12 includes a signal with a second frequency difference β of |f ₂ −f ₃ | and a signal with a fourth frequency difference β of |f ₄ −f ₂ | δ signal is included.

Therefore, the signal with the fourth frequency difference δ is extracted by the bandpass filter 22, and its level is detected by the detection circuit 24 and input to the differential amplifier 25.

As a result, the deviation signal S _A is output from the differential amplifier 25, and the error signal S _E output from the hold circuit 26 becomes high level "H", so that the switch 28 of the gain switching circuit 27 is switched to the terminal. Switches from the a side to the terminal b side.

Therefore, the tracking error signal T _E ′ is
Terminal c of the switch 28 of this gain switching circuit 27
-b and is output via the resistor 30.

In this case, the resistor 30 of this gain switching circuit 27
The resistance value R ₂ of the resistor 29 has a relationship of R ₂ <<R ₁ with respect to the resistance value R ₁ of the other resistor 29 .

Therefore, the tracking error signal T _E ' has a lower attenuation level than when it is output via the resistor 29.

In other words, the gain of the tracking servo system (phase system) is higher than when the amount of deviation of the video head is within the range of about one track.

Therefore, in this case, the speed at which the video head is moved relative to the track is
This will be faster than when the servo system gain is the same as normal, and the lock-in time will be shorter.

For example, in the example shown in FIG. 2, when the video head 8A is tracing the track _T3 while the pilot signal generator 1 is outputting the pilot signal _f1 , the pilot signal is output as the reproduced pilot signal fm'. Since f ₃ is included, mixer 12
The mixed pilot signal fmm′ output from |
A signal with a third frequency difference γ of f ₃ −f ₁ | is included.

Therefore, the signal of this third frequency difference γ is extracted by the bandpass filter 21, and its level is detected by the detection circuit 23 and input to the differential amplifier 25, so that the gain switching circuit 27 also The switch 28 is switched from the terminal a side to the terminal b side, and the gain of the phase system increases.

In this way, in this magnetic recording and reproducing apparatus, when a signal having the third or fourth frequency difference is detected from the mixed pilot signal, the gain of the phase system is increased.

Thereby, even when the deviation of the video head is about two tracks, the phase system can be quickly pulled in.

In the above embodiment, an example was described in which the frequency of the pilot signal was set so that the third frequency difference and the fourth frequency difference were different.
Even if the frequency of the pilot signal is set so that the frequency difference between the two and the fourth frequency are the same,
It can be implemented similarly.

Effects As explained above, according to the present invention, in a magnetic recording device that performs tracking control using a four-frequency pilot method, when a signal with a third or fourth frequency difference is detected, the phase gain of the tracking servo system is adjusted. I changed it to make it higher, so
Even when the amount of deviation of the video head is large, the lock-in time is shortened, and the servo system can be quickly pulled in.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing an example of a tracking control system in a conventional magnetic recording device, and Figure 2 is a circuit diagram showing an example of a tracking control system in a conventional magnetic recording device.
FIG. 3, which is an explanatory diagram showing patterns on a video tape for explaining the frequency pilot method, is a circuit diagram showing an example of a tracking control system in a magnetic recording/reproducing apparatus embodying the present invention. 1... Pilot signal generator, 8A, 8B...
Video head, 12...Mixer, 13, 14, 2
1, 22...Band pass filter, 15, 16,
23, 24...detection circuit, 17, 25...differential amplifier, 26...hold circuit, 27...gain switching circuit.

Claims (1)

[Claims] 1. Four types of pilot signals each having a predetermined first, second, third, and fourth frequency difference are recorded on four consecutive video tracks in a circular order and played back. In a magnetic recording and reproducing apparatus, the signal having the first and second frequency difference is detected from a mixed pilot signal obtained by mixing the pilot signal and a pilot signal of a video track to be traced, and tracking control is performed based on the detection result. , error detection means for detecting the third and fourth frequency difference signals from the mixed pilot signal; and a tracking servo system when the error detection means detects the third or fourth frequency difference signals. 1. A magnetic recording and reproducing device comprising: gain switching means for switching to increase a phase gain.