JPH0259534B2 - - 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,
For example, there is a device that performs tracking control using a four-frequency pilot method.

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 transmits a signal of a predetermined frequency from an oscillator 2 to four frequency dividers 3A, 3B, 3C, and 3D.
Depending on the predetermined frequency division ratio, e.g. 1/58, 1/50, 1/3
The pilot signals f ₁ , f ₂ , f ₃ , f ₄ from these frequency dividers 3A to 3D are divided into head switching pulses (switching pulses) SWP and this switching pulse. Pulse 1/2 divided by 1/2
It is composed of, for example, an automatic frequency control oscillator that outputs an output via a changeover switch 4 that switches terminals a→b→c→d→a in the order of SWP.

In other words, 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 rotate these pilot signals f ₁ to _{f 4} in a circular order, e.g., f ₁ →f ₂ →f ₃ →f ₄ →
Output in f ₁ order.

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 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 respectively α=15KHz,
β=45KHz, γ=60KHz, δ=30KHz.

During recording, the pilot signal fm (f ₁ to _{f 4} ) from the pilot signal generator 1 is input to the adder 6 via the low-pass filter 5 and converted into a video signal (chroma signal and volatility signal) VD. After being superimposed and amplified by the recording amplifier 7 as a recording signal VA, contacts a-c of the recording/playback switch 8
The video head 10 is connected to the video head 10 via the head changeover switch 9 which is switched between
A and 10B and recorded on the video tape 11.

Thereby, each video track of the videotape 11 has a track T ₁ as shown in FIG.
The pilot signal _f4 is on the track T2, the pilot signal _f1 is on the track _T2 , the pilot signal _f2 is on the track _T3 , the pilot signal _f3 is on the track _T4 , the pilot signal _f4 is on the track _T5 , and so on. are recorded in circular order.

In FIGS. 2 and 3, arrow A indicates the running direction of the video tape 11, arrow B indicates the tracing direction of the video heads 10A and 10B, CH1 indicates the video head 10A, CH2 indicates the video head 10A, and CH2 indicates the video head 10A and CH2. means head 10B.

During playback, the pick-up signals (video signals and pilot signals) obtained by picking up the signals recorded on the video tape 11 by the video heads 10A and 10B are transferred between contacts b and c of the head changeover switch 9 and the recording/playback changeover switch 8. The signal is inputted to the reproduction amplifier 13 via the input signal and is amplified.

The reproduced signal VB from the reproduced amplifier 13 is input to a bandpass filter 14, where only the pilot signal included in the reproduced signal VB is extracted, and the reproduced pilot signal fm' is outputted to the mixer 15.

When the video heads 10A and 10B are accurately tracing a regular track, this reproduction pilot signal fm' includes the pilot signal recorded on the track that is being traced, as well as the pilot signal recorded on the tracks on both sides. Also includes pilot signals.

On the other hand, at this time, the pilot signal fm recorded on the track to be traced by the video heads 10A and 10B is input from the pilot signal generator 1 to the mixer 15.
and the reproduced pilot signal fm' are mixed, and the first
A mixed pilot signal containing at least one of the signals with frequency differences α, β, γ, and δ of ~4
fmm′ is output.

Therefore, from the mixed pilot signal fmm' output from the mixer 15, the band pass filter 16
A signal with a first frequency difference α is extracted by the bandpass filter 17, and a signal with a second frequency difference β is outputted by the bandpass filter 17.

The respective levels of the first frequency difference α signal and the second frequency difference β signal, which are the first frequency difference signals, are detected by the detection circuits 18 and 19, respectively, and the levels are detected by the detection circuits 18 and 19, respectively. input to the dynamic amplifier 20.

At this time, when the video head 10A is tracing and when the video head 10B is tracing, the directions of increases and decreases in the levels of the signals of the first and second frequency differences α and β are opposite, and the differential Amplifier 2
The phase of the 0 output also differs by 180° from head to head.

Therefore, an error signal TE corresponding to the level difference between the signal of the first frequency difference α and the signal of the second frequency difference β output from the differential amplifier 20 is applied to the terminals a and b by the switching pulse SWP. Directly or inverter 22 by alternately switching switch 21
It is inverted and output to a capstan control circuit (tracking servo system), not shown, as an error signal TE' with the same phase regardless of the video head being traced.

Note that the error signal output from the differential amplifier 20
TE is zero when the video heads 10A, 10B are on the regular track, a positive voltage when they are ahead of the regular track, and a negative voltage when they are behind the regular track.

Therefore, the capstan control circuit drives and controls the capstan motor so that the level of the signal of the first frequency difference α and the level of the signal of the second frequency difference β become the same.

That is, for example, in the example shown in FIG.
When tracing _T2 , the pilot signal _f1 is input from the pilot signal generator 1 to the mixer 15, so the video head 10A (CH
1) shifts toward track T ₁ , |f ₄ −f ₁ |
As the level of the signal of the second frequency difference β increases and shifts to the track T ₃ side, |f ₁ − _{f 2}
The level of the signal with the second frequency difference β of | increases.

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 a magnetic recording/playback device that switches between two video heads like this, there are slight variations in the characteristics of the two video heads, so the envelope waveform of the playback signal is not uniform and varies from one video head to another. The level of the playback signal will be different.

Therefore, as described above, the pilot signal is detected from the reproduced signal, and the level of the first and second frequency difference signals is detected from the mixed pilot signal generated by mixing the pilot signal with a predetermined pilot signal. , if tracking is controlled by an error signal according to the level difference,
When switching video heads for tracing, the level of the error signal may change.

Additionally, in general, magnetic recording and playback devices
Since a wide video head and a narrow video head are used to perform trick play, the level of the playback pilot signal from the adjacent track differs depending on the head being traced. The level of the error signal may also vary.

As described above, in magnetic recording and reproducing devices that perform tracking control using the conventional four-frequency pilot method, the error signal fluctuates with the period of the head switching pulse (switching pulse) that switches the video head, resulting in poor wow and flutter. There is a problem.

Purpose This invention has been made in view of the above points, and an object of the present invention is to suppress the deterioration of wow and flutter in a magnetic recording and reproducing apparatus that controls tracking using a four-frequency pilot method.

Configuration Therefore, the magnetic recording and reproducing apparatus according to the present invention outputs an error signal through a notch filter that removes the frequency component of the head switching pulse when the tracking servo system is stabilized, and eliminates the error signal generated every time the head is switched. This is designed to remove fluctuations in

Embodiments Hereinafter, embodiments of the present invention will be described with reference to FIG. 3 and subsequent figures of the accompanying drawings. Note that portions corresponding to those in FIG. 1 are designated by the same reference numerals, and explanations of those portions will be omitted.

FIG. 3 is a block diagram showing the main parts of a tracking control system of a magnetic recording/reproducing apparatus embodying the present invention.

In this magnetic recording/playback device, the hold circuit 25 is a lock detection means, and the differential amplifier 22
When the error signal TE is fluctuating, it becomes, for example, a high level "H", and when the error signal TE becomes constant, that is, when the tracking servo is locked, it becomes a low level "L". Outputs a lock detection signal PH.

On the other hand, the switching circuit 26 includes a notch filter (BEP) 27 that inputs the error signal TE' outputted through the switch 21 and removes the frequency component of the switching pulse SWP, and inputs the error signal TE' to the terminal a. Then, the error signal TN from the notch filter 27 is input to terminal b, and the hold circuit 25
Switches to terminal a side or terminal b side according to lock detection signal PH from terminal c, and error signal from terminal c.
It consists of a changeover switch 28 that outputs TEN.

The changeover switch 28 is connected to the terminal a when the lock detection signal PH from the hold circuit 25 is "H".
When the lock detection signal PH is "L", it switches to the terminal b side.

Next, the operation of this embodiment configured as described above will be explained.

First, the tracking servo is not locked, for example, when starting playback (when starting the motor) or when switching from high-speed playback mode to normal playback mode.

Therefore, as mentioned above, the first and second signals are output from the mixed pilot signal fmm' which is a mixture of the reproduced pilot signal fm' from the track being traced by the video head 10A or 10B and the pilot signal fm corresponding to the regular track. Frequency difference signal α,
β is extracted, and the error signal TE is output from the differential amplifier 20 according to the level difference between the two signals, and the error signal TE or the error signal The signal obtained by inverting TE is the error signal
It is output to the switching circuit 26 as TE'.

At this time, since the tracking servo is not locked, the voltage level of the error signal TE output from the differential amplifier 20 fluctuates, and therefore the lock detection signal PH output from the hold circuit 25 changes.
becomes “H”.

Thereby, the changeover switch 2 of the changeover circuit 26
8 is switched to the terminal a side, so the changeover switch 21
The error signal TE′ from
Output to the tracking servo system as TEN,
The rotational speed of the capstan roller is controlled according to the difference from the speed servo error signal, and tracking is performed.

That is, until the tracking servo is locked, in order to increase the dynamic range, the frequency component of the switching pulse corresponding to the switching period of the video head is mixed with the speed servo system while being included in the error signal TE.

On the other hand, when the tracking servo enters the servo lock state, the error signal TE output from the differential amplifier 20 becomes a constant voltage, so the lock detection signal PH output from the hold circuit 25 becomes "L".

Thereby, the switching switch 2 of the switching circuit 26
8 is switched to the terminal b side, and the error signal TN generated by passing the error signal TE' from the changeover switch 21 through the notch filter 27 is output to the tracking servo system as the error signal TEN, and tracking control is performed.

In other words, when the servo enters the lock state, the frequency component of the switching pulse corresponding to the switching period of the video head is filtered through a notch filter from the error signal TE' in order to prevent the frequency component of the switching pulse from affecting the wow and flutter. 27.

As a result, fluctuations in the error signal due to video head switching are removed, so that deterioration of wow and flutter can be suppressed.

FIG. 4 is a block diagram showing another embodiment of the invention.

In this magnetic recording and reproducing apparatus, an error signal from the differential amplifier 20 is generated by the tracing video head in the magnetic recording and reproducing apparatus shown in FIG.
A changeover switch 21 and an inverter 22 for correcting the phase of TE are omitted.

And instead, pilot signal generator 1
The pilot signal f ₂ from the frequency divider 3B is inputted to terminals b and d of the changeover switch 4 via switches 30b and 30a, respectively, and the pilot signal f ₄ from the frequency divider 3D is inputted via switches 31b and 31a. are input to terminals d and b of the changeover switch 4, respectively.

Those switches 30a, 30b, 31a, 3
1b are switches that interlock with each other; during recording, switches 30b and 31b are closed and switches 30a and 31a are open; during playback, switches 30b and 31b are open, and switches 30a and 31b are open;
The switch 31 becomes closed.

When the pilot signal generator 1 is configured in this way, the switches 30b and 31b are closed during recording, so the pilot signals f ₁ to _{f 4} are changed from f ₁ to f ₂
The signals are output in the circular order of →f ₃ →f ₄ →f ₁ and recorded on each track of the video tape 11, for example, as shown in FIG. 2 described above.

On the other hand, during playback, the switches 30a, 3
1a is in the closed state, the pilot signals f ₁ to _{f 4}
are output in the circular order f ₁ → f ₄ → f ₃ → f ₂ → f ₁ .

Therefore, for example, video head 10A (CH
When 1) traces track _T2 in Fig. 2, the pilot signal is added to the reproduced pilot signal fm'.
f ₁ is mixed.

As a result, video head 10A is tracked.
As the track shifts to the T ₁ side, the signal of the second frequency difference β of |f ₄ - f ₁ | increases, and as the track shifts to the T ₃ side, the signal of the second frequency difference β of |f ₂ - f ₁ | The signal of α increases.

In other words, as the video head 10A moves relatively on the video tape in the direction of arrow C in FIG. 2, the signal of the second frequency difference β increases;
As it moves in the direction of arrow D, the first frequency difference α
signal increases.

On the other hand, when the video head 10B traces, for example, the track _T3 in FIG. 2, the pilot signal _f4 is mixed with the reproduced pilot signal fm' as described above.

As a result, video head 10B is tracked.
As the track shifts to the T ₁ side, the signal of the second frequency difference β of |f ₄ - _{f 1} | increases, and as the track shifts to the T ₃ side, the signal of the first frequency difference of |f ₃ - f ₄ | The signal of α increases.

In other words, as the video head 10B moves relatively on the video tape in the direction of arrow C in FIG. 2, the signal of the second frequency difference β increases.
As it moves in the direction of arrow D, the first frequency difference α
signal increases.

In this way, regardless of whether the video head to be traced is video head 10A or 10B, the directions of increase and decrease of the signal with the first frequency difference α and the signal with the second frequency difference β are the same, and the differential amplifier 2
The phase of the error signal TE output from 0 also becomes the same.

Thereby, as mentioned above, the error signal TE
The inverter 22 and changeover switch 21 for inverting the phase of the current are not required.

Therefore, in this embodiment, the error signal TE from the differential amplifier 20 is directly input to the hold circuit 25, and is also input to the switching circuit 26, and the error signal TE is directly output as the error signal TEN until the servo lock state is reached. However, after entering the servo lock state, the error signal TE is generated via the notch filter 27 and the error signal TN is output as the error signal TEN.

Thereby, the same effects as in the previous embodiment can be obtained.

Effects As explained above, according to the present invention, when the tracking servo is in the locked state, the error signal is output via the notch filter, so fluctuations in the error signal due to video head switching can be eliminated. , it is possible to suppress the deterioration of wow-flat ivy.

[Brief explanation of drawings]

FIG. 1 is a main part block diagram showing an example of a tracking control system in a conventional magnetic recording/playback device.
FIG. 2 is a pattern diagram showing an example of a recording pattern on a videotape to provide an explanation of tracking control using the four-frequency pilot method. FIG. 3 is a block diagram of a main part showing an embodiment of the present invention. FIG. 2 is a main part block diagram showing another embodiment of the present invention. 1...Pilot signal generator, 10A, 10B
...Video head, 11...Video tape, 15
... Mixer, 16, 17 ... Band pass filter, 18, 19 ... Detection circuit, 20 ... Differential amplifier, 25 ... Hold circuit, 26 ... Switching circuit,
27...notch filter, 28...changeover switch.

Claims (1)

[Claims] 1 A mixed pilot in which four types of pilot signals, each having a predetermined frequency difference, are recorded on four consecutive video tracks in a circular order, and the reproduced pilot signals are mixed with the pilot signal of the video track to be traced. In a magnetic recording/reproducing device that detects a frequency difference signal from a signal and performs tracking control according to an error signal corresponding to a difference in signal level of two predetermined frequency differences, it is detected that a tracking servo is locked. A magnetic device characterized in that it is provided with a lock detection means for detecting the lock, and a switching means for outputting the error signal directly or via a notch filter for removing the frequency component of the head switching pulse depending on the detection result of the lock detection means. Recording and playback device.