JPS61168164A - Helical scan magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To speed up the phase acquisition operation of a PLL circuit after area switching by varying the phase of switching pulses when an area being reproduced is switched and correcting the rotating speed of a rotary head. CONSTITUTION:The PLL circuit 9 which generates a clock required to read an information signal recording in an area in synchronism with switching pulses for switching the rotary head. When the area is switched and the phase is unlocked from the PLL circuit 9, the output of an LPF11 increases above a specific value and a window comparator 21 detects that. At this time, a correcting means 22 generates a voltage for the number and direction of an area to which switching is performed and applies the voltage to a drum control circuit 5. Therefore, the rotating speed of the rotary head is varied and corrected forcibly. Thus, when the playback area is switched from, for example, C to D, the phase of switching pulses are varied and the rotating speed of the rotary head is corrected to stabilize the PLL circuit after the area switching speedily.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a helical scan magnetic recording/reproducing device such as a video tape recorder.

[Conventional technology]

When a magnetic tape is helically scanned by a rotating head, tracks are formed that are inclined at a predetermined angle with respect to the magnetic tape. In a normal video tape recorder, a video signal is recorded here, but the applicant divided the track formed on the magnetic tape 1 into a plurality of areas A to F, as shown in FIG. It was previously proposed to record information signals, such as PCM audio signals, in areas A to F (Japanese Patent Application No. 148190/1982). Such a system can be applied to, for example, a so-called 8m video tape recorder. In this case, PCM audio signals can be recorded in areas A to F and used as an audio-only magnetic recording and reproducing device.

In order to read a digital signal such as a recorded PCM audio signal, it is necessary to generate a clock signal synchronized with the reproduced digital signal. FIG. 3 is a block diagram of a possible circuit for generating such a clock signal. In the figure, reference numeral 2 denotes a rotating drum around which the magnetic tape 1 is wound, and a rotating head (not shown) is mounted thereon. Reference numerals 3 and 4 denote a pulse generator and a frequency generator, respectively, which output signals with a phase and frequency corresponding to the rotational position of the rotary head. The drum control circuit 5 is supplied with the outputs of the pulse generator 3 and the frequency generator 4, compares them with a blinding signal, and controls the rotational phase and frequency of the rotary drum 2 in response to the error signal. It looks like this. The output of the pulse generator 3 is input to a switching pulse generator 6, which generates a switching pulse for switching the rotary head. This switching pulse is supplied to the vertical drive (Vd) signal generation circuit 8 via the phase switching circuit 7, and 59,941(z(NTSC)
In this case, a vertical drive (Vd) signal is generated. The vertical drive signal is input to the PLL circuit 9, and a master clock signal synchronized with the switching pulse is generated. P L
The L circuit 9 includes a phase comparator 10 and a low-pass filter 1.
1, a voltage controlled oscillator (VCO) 12, and a frequency divider 13.

However, what about the spin chias A to 71 provided corresponding to the areas A to F that the phase switching circuit 7 has? For example, when switch 7A is selected and a signal recorded in area A is being reproduced, switch 7A is selected.
When B is selected and the region to be reproduced is switched to B, the phase switching circuit 7 generates a switching pulse (the fifth
The phase of figure (a)) is changed (delayed) (Figure 5 (b)).
Therefore, the phase of the vertical drive signal is also changed.

[Problem that the invention seeks to solve]

By the way, in such a circuit, in order to attenuate high-frequency noise and increase the S/N in the loop, a low-pass filter 1 is used.
1. The PLL circuit 9 is adjusted to have a narrow band by the integral effect of the voltage controlled oscillator 12 and the loop gain. Therefore, when the area is changed and the phase of the vertical drive signal changes, etc., PLT; Circuit 9
The disadvantage is that once the lock is released, it takes a considerable amount of time to lock it again.

[Means for solving problems]

FIG. 1 shows a block diagram of the clock signal generation port l^3 in the helical scan magnetic recording and reproducing apparatus of the present invention, and the parts corresponding to those in FIG. 3 are given the same reference numerals. Detailed description will be omitted. In the present invention, a window comparator 21 is provided as a means for detecting the locked state of the PLL circuit 9, and when it is detected that the area is changed and the PLL circuit 9 is unlocked, the drum A correction means 22 for outputting a signal to the control circuit 5 is provided. Other rotating drum 2
, pulse generator 3, frequency generator 4, drum control circuit 5
, switching pulse generator 6, phase switching circuit 7,
vertical drive signal generation circuit 8 and phase comparator 10,
Low-pass filter 1, voltage controlled oscillator (VCO) 1.
2 and a frequency divider 13 is the same as that shown in FIG.

[Effect]

The operation will be explained with reference to FIG.

As in the case described above, the drum control circuit 5 controls the rotation of the rotary drum 2 in response to signals from the pulse generator 3 and the frequency generator 4. Further, in response to a signal from the pulse generator 3, a switching pulse generator 6 outputs a switching pulse for switching the rotary head. The phase switching circuit 7 changes the phase of this switching pulse at a rate of 36 degrees per region, and outputs the switching pulse at a phase corresponding to the region being reproduced. This output signal is supplied to the vertical drive signal generation circuit 8, which generates a 59.94Hz vertical drive signal (Fig. 2(a)), which is used by the PLL.
It is input to the phase comparator 10 of the circuit 9. Therefore, the phase comparator 10, the low-pass filter 11, the voltage controlled oscillator (VC
The PLL circuit 9 consisting of the frequency divider 13 and the frequency divider 13 outputs a master clock signal synchronized with the vertical drive signal from its voltage controlled oscillator 12.

The phase switching circuit 7 changes the phase of the switching pulse to 1.
Varying at a rate of 36 degrees per area.

Therefore, if the region being reproduced is switched to the upper region in FIG. If you switch the playing area one area down (for example, change the switch from 70 to 7D, area C
If the switching pulse is switched to the vertical region), the phase of the switching pulse, and therefore the phase of the vertical drive signal, will advance by 36 degrees. When the region is switched and the PLL circuit 9 is unlocked, the output of the low-pass filter 11 increases to a predetermined value or more, and the window comparator 21 detects this. At this time, the correction means 22 generates a voltage corresponding to the number and direction of regions to be switched, and applies it to the drum control circuit 5. Therefore, the rotational speed of the rotating head is forced to be corrected. For example, when switching from area C to area I, the phase of the vertical drive signal is delayed by Δt (approximately 36 degrees), as shown in FIG. 2(b), and the phase comparison occurs as shown in FIG. 2(c). The output of the converter 10 (the phase difference between the vertical drive signal and the frequency-divided output from the frequency divider 13 of the voltage-controlled oscillator 12) changes by Δt□. However, this phase comparator]
The rotary head is forcibly driven and its speed is increased so that the change in the phase difference outputted by O is reduced, so that the change in the phase difference becomes Δt2 and gradually decreases.

Therefore, the rate of change in the period of the vertical drive signal gradually decreases from T1 to T4, and quickly returns to the original period (T, = 1
159.94). As a result, the phase pulling operation of the PLL circuit 9 is performed again legally, and the PLL circuit 9 is locked again. When the PT, L circuit 9 is locked, the output of the low-pass filter 11 becomes less than a predetermined value, the window comparator 21 detects this, the operation of the correction means 22 is stopped, and the speed of the rotating head is returned to the original speed.

When the region to be reproduced is switched downward (for example, from region C to region B), the phase of the switching pulse advances by 36 degrees, so the rotary head is forced to slow down. Other than that, the operation is the same as in the case described above.

The value of the speed change of the rotating head is determined based on the closed loop band and phase of the PLL circuit 9 within the range where the four-frequency tracking pilot signal recorded on each track can be reproduced and the tracking servo of the capstan does not go off. It can be set as appropriate in consideration of the pull-in speed and the like. Of course, the period during which the capstan is out of tracking is sufficiently short compared to the period during which the speed of the rotating head is corrected, and the PLL circuit 9
The speed of the rotary head may be varied until regeneration of the pilot signal is no longer possible, provided this does not adversely affect the phase pulling operation of the rotary head. Furthermore, the method for detecting the locked state of the PLL circuit 9 is not limited to the above-mentioned case. Furthermore, when the power of the device is turned on, a predetermined one of the switches 7A to 7F (for example, switch 7Δ to select the first area A along the direction of movement of the rotating head) is always selected. You can do it like this.

〔effect〕

As described above, in the present invention, a track formed by helically scanning a magnetic tape with a rotary head is divided into a plurality of areas, and in a helical scan magnetic recording and reproducing apparatus that records and reproduces information signals in the areas, the rotary head is switched. The clock necessary for reading the information signal recorded in the area is generated in synchronization with the switching pulse, and when the area being played back is switched, the phase of the switching pulse is changed and the rotation speed of the rotary head is changed. Since the switching pulse and the clock are corrected, it is possible to quickly synchronize the phases of the switching pulse and the clock, and the region can be stabilized more quickly after switching.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a clock signal generation circuit in a helical scan magnetic recording/reproducing device of the present invention, Fig. 2 is a timing chart thereof, Fig. 3 is a block diagram of a conventional clock signal generation circuit, and Fig. 4 is a block diagram of its magnetic recording/reproducing device. 1- on the tape
FIG. 5 is a plan view schematically showing the rack and its timing chart. 1... Magnetic tape 2... Rotating drum 3... Pulse generator 4... Frequency generator 5... Drum control circuit 6... Switching pulse generation circuit 7... Phase switching circuit 8. ...Vertical drive signal generation circuit 9...PLL circuit 21...Window comparator 22...More than correction means

Claims (1)

[Claims] (1) In a helical scan magnetic recording and reproducing device that divides a track formed by helically scanning a magnetic tape with a rotary head into a plurality of regions and records and reproduces information signals in the regions, a switching pulse that switches the rotary head is used. It is equipped with a PLL circuit that generates a clock necessary for reading the information signal synchronously recorded in the area, and when the area being reproduced is switched, the phase of the switching pulse is changed and the rotation of the rotating head is changed. A helical scan magnetic recording and reproducing device characterized by correcting rotational speed.