JPH02103764A - Video tape recorder - Google Patents

Abstract

PURPOSE:To improve the quality gradation of reproducing pictures by detecting a regenerative high frequency signal level of a rotary magnetic head at the high speed reproducing time and controlling the traveling speed of a magnetic tape to keep a relative phase between the min. point of this detected level and a rotary reference signal constant. CONSTITUTION:The subject recorder is provided with a level detecting means 12 for detecting the level of a regenerative high frequency signal to be outputted from the rotary magnetic heads 1A and 1B and a phase comparing means 21 for comparing a detected output of this level detecting means 12 with the rotary reference signal of the rotary magnetic heads 1A and 1B in phase. Then, at the time of high speed reproducing, the traveling speed of the magnetic tape is controlled based on an output of this phase comparing means 21 in order to keep the relative phase between the min. point of the level of the regenerative high frequency signal and the rotary reference signal constant. By this method, fluctuation of a noise bar position to appear on a screen at the high speed reproducing time can be prevented, thus improving the quality gradation of the reproducing pictures.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a helical scan type video tape recorder.

[Summary of the invention]

The present invention detects the reproduction RF signal level of a rotating magnetic head during high-speed reproduction in a helical scan type video tape recorder, and maintains the relative phase between the minimum point of this detection level and a rotation reference signal constant. By controlling the running speed of the magnetic tape, it is possible to improve the quality of the reproduced image by preventing fluctuations in the position of the noise bar on the reproduction screen with a simple configuration and without using special signals. be.

[Conventional technology]

As is well known, in an 8 mm video type VTR, ATF type tracking control is performed using pilot signals of four frequencies.

The pilot frequency is, for example, f + = 6.5 f H' = 102.5 kHzf
2 = 1.5f H'i 119. OkHzf:
+ = 10.5 f l (# 165.2 kHz f
4 = 9.5 f ++ 'i 148.
7kHz, and as shown in FIG. 3, the frequency difference between both adjacent tracks is If, respectively.

3f, and is recorded repeatedly every four tracks.

During normal playback, the frequency difference component (1fH1) between the crosstalk components from both adjacent tracks and the local pilot signal
3f,) to detect a trunking error.

In addition, in other conventional helical scan VTRs,
a tracking control signal with a repetition frequency of 30 Hz;
A so-called CTl- signal is recorded on a dedicated track provided at the edge of a magnetic tape, and reproduced CT1. , tracking control is performed based on the signals.

Problem to be solved by the invention C] By the way, in a VTR, in order to search for a desired program that has already been recorded, video signals are sometimes played back while the magnetic tape is running at high speed in the forward or reverse direction. be.

For example, in the case of forward playback at 9x speed, in an 8 mm video VTR, the dashed lines 1+cd and 1. As shown in Cb, one rotary magnetic head scans upstream from the starting end of a certain track to the end of nine tracks, diagonally intersecting each track, and then the other rotary magnetic head scans the 10th track. Scan from the start of the trunk upstream to the end of the 18-grain track, diagonally intersecting each trunk.

The output of the re-rotating magnetic head is output at a switching period Ts (-16, 10 m) via a switch controlled by a switch pulse as shown in FIG.
5) are derived alternately. Similar scanning is repeated thereafter.

However, in high-speed playback as described above, each magnetic head scans tracks with different azimuths, so
As shown in Figure 4B, the reproduction RF signal level of each magnetic head decreases every other track, and the S/N of the reproduced video signal in that part decreases, causing so-called noise bars to inevitably appear in the reproduced image. appears.

If the position of the noise changes on the playback screen, there is a problem in that the playback image becomes extremely difficult to see.

In order to solve these problems, in conventional 8mm video VTRs, the high-speed playback magnification is selected to be an odd number, and the diagonal scanning of multiple tracks as described above is used to
As shown in No. 4 C, the local pilot signal was switched for each scanning track in response to the regenerated pilot signal that changed for each scanning trunk, as shown in the figure.

As a result, a tracking error is detected by comparing the levels of the frequency difference component (ifH, 3f++) between the cross component from both adjacent trunks and the local pilot signal, as in the case of normal playback.

By integrating this tracking error voltage for each scanning track and servo-controlling the capstan motor, the switching pulse shown in FIG.
As shown in Figure B, it is possible to match the minimum level points of the reproduced RF signals from each head, and
A so-called noise lock state is obtained in which the position of the noise bar corresponding to the minimum signal level does not change on the playback screen.

However, the above-mentioned ATF method has a problem in that the circuit configuration becomes complicated due to switching of the pilot frequency for each track, extraction of frequency difference components, level comparison, etc., and the cost increases.

Furthermore, in the CTL method, servo control can be performed to achieve a noise lock state based on the CTL signal.
A pulse generator for CTL signals and a recording/reproducing head are required, which increases costs. Furthermore, there is a problem in that a dedicated track is required on the magnetic tape, which hinders improvement in recording density.

In view of this, an object of the present invention is to improve the quality of reproduced images by preventing fluctuations in the position of noise bars that appear on the screen during high-speed reproduction with a simple configuration and without using special signals for control. The object of the present invention is to provide a video tape recorder that can be improved.

[Means for Solving the Problems] The present invention provides a video tape recorder in which a rotating magnetic head scans a recording track formed at an angle on a magnetic tape to obtain a playback signal. A level detection means (12) for detecting the level of the reproduced high-frequency signal to be outputted, and a phase comparison means (21) for comparing the phase of the detection output of the level detection means and the rotation reference signal of the rotating magnetic head, A video tape recorder that controls the running speed of the magnetic tape based on the output of the phase comparison means during high-speed playback so as to maintain a constant relative phase between the minimum level point of the playback high-frequency signal and the rotation reference signal. be.

[Function] According to this configuration, without using a special signal, fluctuations in the position of the noise bar appearing on the screen during high-speed reproduction are prevented, and the quality of the reproduced image is improved.

〔Example〕

Hereinafter, an embodiment in which the video tape recorder according to the present invention is applied to an 8 mm video VTR will be described with reference to FIGS. 1 and 2.

FIG. 1 shows the configuration of an embodiment of the present invention.

In FIG. 1, a pair of magnetic heads (18) and (IB
) is attached to the rotating drum (2), and a directly connected motor (
3). This motor (3) is fitted with a rotary phase pulse generator (so-called P C) (4) and a frequency signal generator (so-called FC) (5).

The running speed of the magnetic tape T wound around the rotating drum (2) within a predetermined range is controlled by a capstan (6).

A motor (7) is directly connected to this capstan (6), and an FC (8) is attached thereto.

111 (1/l), the RF multiplied signal from (1B), via the changeover switch SW and the amplifier (11),
It is commonly supplied to the envelope detector (12) and the FM demodulator (13), and the output of the demodulator (13) is sent to the sync separation circuit (14).
).

The output of the envelope detector (12) is sent to the waveform shaping circuit (15).
The signal is supplied to the frequency divider (16) via the frequency divider (16). This frequency divider (
16) is supplied with a vertical synchronization signal from the synchronization separation circuit (14) as a reset signal. Further, the frequency division ratio of the frequency divider is appropriately set depending on the forward or reverse high-speed reproduction magnification.

(20) is the system control and digital servo control circuit (
The output of the PC (4) and PC (5) attached to the rotating drum (2) and the output of the capstan FG (8) are supplied to the microcomputer (microcomputer). In the control circuit (20), a switching pulse is formed by converting the duty factor of the PC pulse to approximately 50%, and this switching pulse is applied to the head changeover switch SW.
supplied to

(21) is a phase comparator circuit, to which the output of frequency division 1 (16) is supplied, and also a switching pulse is supplied via a delay circuit (22). The delay time τ of the delay circuit (22) is also appropriately set according to the high-speed reproduction magnification. The output of the phase comparison circuit (2I) is a low-pass filter (23)
is supplied to the adder (24) via the control circuit (20
) is summed with the speed servo output from the drive amplifier (9).
is supplied to the capstan motor (7).

Note that the servo output of the control circuit (2o) is supplied to the drum motor (3), and normal drum servo control is performed.

Further, K1 and K2 are forward and reverse high speed playback operation keys.

Next, the operation of the embodiment shown in FIG. 1 in the case of 9x speed in the forward direction will be explained with reference to FIG.

When 1 is operated on the key and the VTR enters the 9x playback mode, the same as described above (as shown in Figure 2B), the playback RF signal 0 whose level changes periodically is sent from the amplifier (11) to the envelope. The signal is supplied to the detector (12), and as shown in FIG. The detected output ◎ is shaped by the waveform shaping circuit (13) into a rectangular wave with a duty factor of, for example, 50%, as shown in the figure, and then supplied to the frequency divider (16).

In the case of 9x speed playback, the frequency division ratio of the frequency divider (16) is controlled by the control circuit (20) and set to 1/4, and as shown in Figure E, the frequency division ratio is equal to that of the switching pulse. Then, the frequency-divided output [F] delayed by τ-T, ./1.6 is supplied to the phase comparison circuit (21).

Further, in this case, the delay time τ2□ of the delay circuit (22) is controlled by the control circuit (20), and the delay time τ2□-Ts-/1
6, and the switching pulse supplied to the phase comparator circuit (21) via this delay circuit (22) has the same phase as the output of the frequency divider (16).

The output of the phase comparison circuit (21) is added to the servo output of the control circuit (20) in an adder (24) to servo control the capstan motor (7). This results in
Phase synchronization can be achieved between the divided output [F] of the frequency divider (16) and the switching pulse ■. In other words, the frequency division specific force [F]
The reproduced RF signal 0, which is the source of , is in phase synchronization with the switching pulse, and a noise lock state is obtained in which the position of the noise bar does not change on the reproduced screen.

In addition, in the above-mentioned embodiment, a switching pulse was used as a reference signal for the phase comparator circuit (21), but a pseudo vertical drive pulse may be used as a reference signal. This pseudo vertical drive pulse is determined by the system control circuit (20) from the rising and falling edges of the switching pulse, for example, by 6.5
Since the signal is generated with a delay of H, the delay time τ22 of the delay circuit (22) is shortened by this delay. In this case, the frequency divider (16) is reset by the pseudo vertical drive pulse.

In addition, the functions of the frequency divider (16) and the phase comparison circuit (21) to the adder (24) in the above-described embodiment are controlled by the control circuit (20).
) and processed by software.

Although the present invention has been described above in a case where it is applied to an 8 mm video type VRT, it can be similarly applied to a normal helical scan type VRT.

〔Effect of the invention〕

As detailed above, according to the present invention, during high-speed playback,
The reproduction RF signal level of the rotating magnetic head is detected, and the running speed of the magnetic tape is controlled so as to keep the relative phase between the minimum point of this detection level and the rotational reference signal constant, so a special signal is used. Therefore, a helical scan type video tape recorder can be obtained that can prevent fluctuations in the position of the noise bar on the playback screen with a simple configuration and improve the quality of the playback image.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of a video tape recorder according to the present invention, FIG. 2 is a time chart for explaining the operation of an embodiment of the present invention, and FIGS.
The figure is a diagram for explaining the present invention. (IA) and (IB) are magnetic heads, (4) is a rotational phase signal generator (PG), (7) is a capstan motor,
(12) is an envelope detector, (14) is a synchronous separation circuit, (
15) is a waveform shaping circuit, (20) is a system control and digital servo control circuit (microcomputer), (2
1) is a phase comparison circuit. Agent Sadado Ito Hidemori Matsukuma

Claims (1)

[Scope of Claims] A video tape recorder in which a recording track formed at an angle on a magnetic tape is scanned by a rotating magnetic head to obtain a reproduction signal, in which a reproduction high-frequency signal outputted from the rotating magnetic head is provided. A level detection means for detecting the level, and a phase comparison means for comparing the phase of the detection output of the level detection means and the rotation reference signal of the rotating magnetic head are provided, and during high-speed reproduction, the output of the phase comparison means is used. A video tape recorder characterized in that the running speed of the magnetic tape is controlled so as to keep the relative phase between the minimum level point of the reproduced high-frequency signal and the rotation reference signal constant.