JPH0259533B2 - - 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 system.

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 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 a frequency divider 3 that divides the frequency by 58, 1/50, 1/36, and 1/40.

The 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 respectively α=15KHz,
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, superimposed on the video signal (chroma signal and luminance signal) VD, and recorded as the recording signal VA. After being amplified by amplifier 6,
The signal is supplied to the video head 8 via contacts a and c of the recording/playback switch 7 and recorded on the video tape 9.

As a result, on each video track of the video tape 9, as shown in FIGS. 2 and 3, a pilot signal _f3 is applied to track _T1 , a pilot signal _f4 is applied to track _T2 , and a pilot signal f4 is applied to track _T3 . pilot signal
The signal _f1 is recorded in a circular order, the pilot signal _f2 is recorded on track _T4 , the pilot signal _f3 is recorded on track _T5 , and so on.

In FIGS. 2 and 3, 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 VB from the reproduced amplifier 10 is input to a bandpass filter 11, where only the pilot signal included in the reproduced signal VB is extracted, and the reproduced pilot signal fm' is outputted to the 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 outputs a tracking 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 to a capstan control circuit (tracking servo system), not shown. do.

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

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 _T3 , the pilot signal _f1 is input from the pilot signal generator 1 to the mixer 12, and as the video head 8 shifts to the track _T2 side, the second trace of | _f4 - _f1 | The level of the signal of the second frequency difference β becomes larger, and as _the track _shifts toward the track _T4 , 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, when the video tape is played back by running it at high speed in the same direction as the normal playback direction, for example, when playing back at 5x speed, the video head is moved as shown in Fig. 2. 8 scanning traces C ₁ , C ₂ , C ₃ , C ₄ ...
... intersects with video track Tn.

Therefore, for example, at the time of scanning trace _C1 , the reproduced pilot signal fm' changes sequentially to _f1 , _f2 , _f3 , and _f4 .

Therefore, at this time, if, for example, the pilot signal f1 is output from the pilot signal generator ₁ to the mixer 12 as in the normal reproduction mode, the signal with the frequency difference contained in the mixed pilot signal fmm' will be A signal with a frequency difference α and a second frequency difference β
The signal will not be stable, but will also include a signal with a third or fourth frequency difference, which will be disturbed.

As a result, the tracking error signal TE output from the differential amplifier 17 also becomes unstable, and the tracking error signal makes it impossible to lock the capstan servo, causing the playback screen to become distorted. There is an inconvenience.

Also, in the review mode, in which the videotape is played back by running it at high speed in the opposite direction to the normal playback mode, for example, when playing at 5x speed,
As shown in FIG. 3, the scanning trace of the video head 8
C ₁ , C ₂ , C ₃ , C ₄ . . . intersect with the video track Tn, causing the problem that the playback screen is disturbed as in the queue mode.

Purpose This invention has been made in view of the above points, and an object thereof is to prevent the playback screen from being disturbed even during high-speed playback in a magnetic recording and playback device that performs tracking control using a pilot method.

Structure Therefore, the magnetic recording/playback device according to the present invention detects the minimum point position of the envelope waveform of the playback signal, and switches the pilot signal to be mixed with the playback pilot signal according to the detection result during high-speed playback. It is.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to FIG. 4 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, when the video head 8A is selected and when the video head 8B is selected, the directions of increase and decrease in the level of the signals of the first and second frequency differences α and β are opposite.

Therefore, the tracking error signal TE output from the differential amplifier 17 or the signal obtained by inverting this tracking error signal TE by the inverter 19 is
External control signal (rotation control circuit 2 described later)
The signal is selected by the switch 20 which is switched to the terminal a or terminal b side in response to a switching pulse SB) from SB), and is output as a tracking error signal TE'.

First, the dropout detection circuit 21
The minimum point position of the envelope waveform of the reproduced signal ENV is detected and a dropout detection pulse DOP is output.

This dropout detection circuit 21 can be configured, for example, by a normal dropout compensation circuit (DOC), and performs AN detection on the reproduced signal ENV using an AN detection circuit, and removes high frequency components of this detection output using a low-pass filter to form an envelope. It may be configured such that only the peak portion of an inverted envelope signal obtained by detecting the envelope signal and inverting the envelope signal with an inverter is clamped by a clamp circuit, and the output of this clamp circuit is outputted as the dropout detection pulse DOP.

Next, the mono-multi circuit 23 of the rotation control circuit 22 is triggered by the rising edge of the dropout detection pulse DOP from the dropout detection circuit 21, and from that time on, the monomulti circuit 23 is activated.
Outputs a rotation switching pulse RC with a pulse width of 1/2 of the DOP pulse interval.

The rotation control circuit 22 sends a switching pulse (head switching pulse) SWP between terminals a and c of a switch 24, and also receives a rotation switching pulse from the monomulti circuit 23.
Connect RC between terminals b and c of switch 24,
Each of them is directly output as a switching pulse SB to the rotation switching signal input terminal of the frequency divider 3 of the pilot signal generator 1, and is also output to the switch 20.

The switch 24 is controlled to be switched to the terminal a side or the terminal b side by an external switching control pulse SA according to the selected playback mode, and when the normal playback mode is selected, it is switched to the terminal a side,
When the high-speed reproduction mode, which is the queue mode or the review mode, is selected, the terminal is switched to the terminal b side.

The rotation control circuit 22 also controls the switching pulse SWP or the rotation switching pulse RC from the monomulti circuit 23 to the switch 24.
The switching pulse SWP or rotation switching pulse is input to the 1/2 frequency divider 25 via
The pulse obtained by dividing the RC frequency by 1/2 is sent directly to switch 2.
6 between terminals a and c, and the inverter 27
After being inverted, it is outputted to the rotation switching signal input terminal of the frequency divider 3 of the pilot signal generator 1 as a switching pulse SC via terminals b and c of the switch 26.

The switch 26 is a switching pulse
An edge detection signal is output from an edge detection circuit 28 that detects the rising edge of SWP via a switch 29 that is turned on only in high-speed playback mode.
Switching to terminal a side or terminal b side is controlled by PA.

This switch 26 is switched to the terminal a side in the normal playback mode, that is, when the switch 29 is in the off state, and the edge detection signal PA is inputted in the high speed playback mode, that is, when the switch 29 is in the on state. The terminal is alternately switched to the terminal a side or the terminal d side each time.

In this way, changing the phase of the 1/2 frequency divided pulse by controlling the switch 26 every time the switching pulse SWP rises in the high-speed reproduction mode is done by changing the rotation of the head drum in the high-speed reproduction mode. This is because the number of envelope signals per revolution of the head drum and the number of tracks to be traced on the video tape deviate from each other in order to match the horizontal synchronizing signals (take H alignment), and this must be corrected.

The pilot signal generator 1 also receives switching pulses SB, SB, and SB input to the rotation switching signal input terminal.
The pilot signals are sequentially switched and output according to the SC status (“L”, “H”), and the order of the output pilot signals is changed from f ₁ → f ₂ → f ₃ during normal playback mode and queue mode. → f ₄ → f ₁ , and in review mode, the running direction of the videotape is opposite to that in normal playback mode and queue mode, so f ₄ → f ₃ → f ₂ → f ₃ → f ₄ order.

Next, the operation of this embodiment configured as described above will be explained with reference to FIGS. 4 and 5.

First, in the normal reproduction mode, the switch 24 of the rotation control circuit 22 is switched to the terminal a side, and the switch 29 is turned off and the switch 26 is switched to the terminal a side.

Therefore, at this time, the switching pulse SWP is directly output as the switching pulse SB, and the pulse obtained by dividing this switching pulse SWP by 1/2 is output as the switching pulse SB to the pilot signal generator 1. switching pulse
SWP is output to switch 20 as switching pulse SB.

Thereby, the pilot signal generator 1 switches and outputs the pilot signal in accordance with the switching pulse SWP and the pulse obtained by dividing the switching pulse SWP by 1/2.

In addition, the switch 20 generates a switching pulse.
Depending on SWP, the tracking error signal TE from the differential amplifier 17 or the inverted signal of this tracking error signal TE is used as the tracking error signal.
Output to the tracking servo system as TE′.

Accordingly, tracking control is performed as described above.

On the other hand, in queue mode,
The switch 24 of the rotation control circuit 22 is switched to the terminal b side, the switch 29 is turned on, and the switch 26 is alternately switched to the terminal a side or the terminal b side according to the edge detection signal PA from the edge detection circuit 28. Change.

Therefore, every time the dropout detection pulse DOP is output from the dropout detection circuit 21, the rotation switching pulse RC output from the monomulti circuit 23 is directly used as the switching pulse SB, and this rotation switching pulse RC is divided by 1/2. The pulse is output to the pilot signal generator 1 as a switching pulse SC with a phase corresponding to the state of the switch 26.
At the same time, the rotation switching pulse RC is outputted to the switch 20 as a switching pulse SB.

Thereby, the pilot signal generator 1 switches the pilot signal fm according to the rotation switching pulse RC from the monomulti circuit 23 corresponding to the dropout detection pulse DOP and the pulse obtained by dividing this rotation switching pulse RC by 1/2. and output it.

Further, the switch 20 alternately switches to the terminal a side or the terminal b side every time the rotation switching pulse RC is input, and outputs the tracking error signal TE from the differential amplifier 17 as it is, or outputs the tracking error signal TE from the differential amplifier 17 as it is. A signal obtained by inverting TE is output to the tracking servo system as a tracking error signal TE'.

This operation will be explained with reference to FIGS. 2 and 5, taking 5x speed playback as an example.

First, when recording, for example, as shown in Figure 2,
Pilot signal f ₁ to _{f 4} to video track T ₇ to T ₁₈
is recorded.

Note that at this time, for example, the video head 8A
(CH1) tracks T ₈ , T ₁₀ , T ₁₂ , T ₁₄ ,
Pilot signals f ₂ , f ₄ , f ₂ , f ₄ , f ₂ , f ₄ at T ₁₆ and T ₁₈
are recorded, and pilot signals f ₁ , f ₃ , f ₁ , f ₃ , f ₁ , f are recorded on tracks T ₇ , T ₉ , T ₁₁ , T ₁₃ , T ₁₅ , T ₁₇ by video head 8B (CH2). Suppose that ₃ is recorded.

Under this condition, in the queue mode, the switching pulse SWP rises at time _t1 , falls at time _t5 , and rises at time _t9 , as shown in FIG. 5, for example, between times _t1 and _t5 . Now video head 8A
(CH1) is selected and the scanning trace C ₂ shown in Figure 2
Assume that the video head 8B (CH2) is selected between time points _t5 and _t9 , and the trace _C3 shown in FIG. 2 is traced.

As a result, _{the envelope} waveform _{of the reproduced} signal _ENV is, as shown in _FIG . ₄ of track T ₁₀ , time t ₄ to _{t 5} of track T ₁₁ , and time t ₅ to _{t 6} of track T ₁₃ .
The reproduced signal waveform is of track _T14 from _t6 to _t7 , of track _T15 from time _t7 to _t8 , and of track _T16 from time _t8 to _t9 .

Therefore _, as _shown in FIG.
Dropout detection pulse DOP is output at t ₆ and t ₈ .

And this dropout detection pulse DOP
Every time the mono multi-circuit 23 outputs a dropout detection pulse, as shown in FIG.
A rotation switching pulse RC with a pulse width of 1/2 of the DOP pulse interval is output, and this rotation switching pulse RC and this rotation switching pulse
Pulses 1/2 RC shown in FIG.

In this case, the pilot signal generator 1 generates the pilot signal when the switching pulses SB and SC are "0, 1".
When f ₂ is “1, 0”, the pilot signal f ₃ is
When it is "0,0", the pilot signal _f4 is "1,1"
Suppose that the pilot signal f ₁ is output when .

Therefore, for example, when the pilot signal f 2 is output from the pilot signal generator 1 at time t ₁ in FIG. 5, the pilot signals f ₃ , f ₄ , _{f 1 are} output at each time from t ₂ to t ₉ , f ₂ , f ₃ , f ₄ , f ₁ are output.

As a result, the reproduced pilot signal from the track Tn traced by the video heads 8A and 8B is
Since fm' and the pilot signal fm output from the pilot signal generator 1 substantially match, the output of the differential amplifier 17 is also stabilized, and disturbances in the reproduced screen are suppressed.

Also, the switching pulse in review mode
SWP, envelope waveform of playback signal ENV, dropout detection pulse DOP, rotation switching pulse RC, and 1/2 rotation switching pulse 1/2RC
For example, as shown in FIG. 6, the tracks traced by the video heads 8A and 8B are
Since the reproduced pilot signal fm' from Tn and the pilot signal fm output from the pilot signal generator 1 substantially match, the output of the differential amplifier 17 is also stabilized, and disturbances in the reproduced screen are suppressed.

In this way, in this magnetic recording apparatus, the pilot signal to be mixed with the reproduction pilot signal is switched when the minimum point position of the envelope waveform of the reproduction signal is detected during high-speed reproduction.

As a result, even during high-speed playback, the pilot signal to be mixed changes according to changes in the playback pilot signal, so the output of the differential amplifier can be stabilized and the capstan servo can be locked, eliminating disturbances on the playback screen. suppressed.

Effects As explained above, according to the present invention, the pilot signal to be mixed with the reproduced pilot signal is switched when the minimum point position of the envelope waveform of the reproduced signal is detected during high-speed reproduction. is suppressed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of the tracking control system of a conventional magnetic recording/playback device, and FIGS. 2 and 3 are examples of the relationship between the video track and the scanning trace of the video head in queue mode and review mode, respectively. FIG. 4 is a block diagram showing an example of a tracking system of a magnetic recording/reproducing apparatus embodying the present invention, and FIGS. 5 and 6 are
5A and 5B are waveform diagrams of signals in queue mode and review mode, respectively, for explaining the operation of FIG. 4; FIG. 1... Pilot signal generator, 8A, 8B...
Video head, 9... Video tape, 12... Mixer, 13, 14... Band pass filter, 1
5, 16...Detection circuit, 17...Differential amplifier, 2
0...Switch, 21...Dropout detection circuit, 22...Rotation control circuit.

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 and reproducing apparatus that detects the frequency difference signal from a signal and performs tracking control based on the detection result, there is provided a dropout detection means for detecting a minimum point position of an envelope waveform of a reproduction signal, and a dropout detection means for detecting a minimum point position of an envelope waveform of a reproduction signal; 1. A magnetic recording and reproducing apparatus comprising rotation control means for switching a pilot signal to be mixed with the reproduced pilot signal in accordance with a detection result of the detection means.