JPH05244549A - Magnetic reproducing device for video signal - Google Patents

Abstract

PURPOSE:To improve the quality of an output video signal by resetting a servo reference signal at an edge of a drum pulse in the EE mode. CONSTITUTION:A drum pulse 6a is fed to an edge differentiation circuit 25, and an edge differentiation circuit output signal 25a obtained by extracting an edge of the drum pulse 6a is fed to one input of an AND circuit 29. Moreover, an OR circuit 28 receives an EE signal S3 at a high level in the EE mode only and at a low level for other period than the mode. Then an OR circuit output signal 28a is obtained and it is fed to the other input of the AND circuit 29. The AND circuit 29 gives a reset signal 29a obtained by gating the edge differentiation circuit output signal 25a with the OR circuit output signal 28a to a servo reference counter circuit 24. Thus, even when the usual reproduction mode is selected from the EE mode, no much time is required to lock the servo and an output video signal is not disturbed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal magnetic reproducing apparatus for reproducing or recording / reproducing a video signal.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram for explaining a conventional VTR, FIG. 2 is a diagram for explaining the arrangement of a magnetic head formed on a rotary drum, and FIG. 5 is a drum pulse signal and a servo reference signal. 3 is a timing chart for explaining the relationship between Hereinafter, a conventional technique will be described with reference to the drawings.

In recent years, along with the development of digital technology, a time axis correction circuit (hereinafter abbreviated as "TBC") using this has been incorporated, or an output video signal of a VTR is supplied to a monitor through the circuit. There are cases. FIG. 3 is a block diagram for explaining the main part of a VTR incorporating such a TBC.

In FIG. 1A, a pair of magnetic heads composed of first and second magnetic heads A1 and A2 and third and fourth magnetic heads.
The pair of magnetic heads B1 and B2 are formed on a rotary drum, which will be described later, and a signal reproduced from the magnetic tape T using either one of the pair is used in the reproducing system 1.
Are supplied to the respective video signals and are subjected to demodulation and the like, and reproduced video signals 1
Output a.

The reproduced video signal 1a is supplied to the memory 21 in the TBC 2, and this memory 21 uses the control signal 22a generated by the control circuit 22 based on the clock signal 23a output from the crystal oscillation circuit 23. Then, the output video signal 2a obtained by controlling the writing and reading is supplied to a transmission line (not shown).

Further, in order to synchronize the reproduction video signal 1a and the writing and reading of the memory 21, the clock signal 23a
Is supplied to the servo system 3 as a time reference for the servo, by using the servo reference signal 24a obtained by counting in the servo reference counter circuit 24. Since the servo reference counter circuit 24 constitutes a ring counter, the servo reference signal 24a becomes a signal having a fixed cycle.

The servo system 3 has a role of controlling the phase of the rotary drum and the like. That is, the drum motor 4 is compared by performing a phase comparison between a reference signal described later and the drum pulse 6a.
A drive signal 3a for driving (DM) is obtained. The drum pulse 6a detects a magnetic field generated by magnets (not shown) having an N pole and an S pole, which are arranged in the drum motor 4 and oppose each other by 180 degrees, and the pickup head 5 detects the magnetic field. ). On the other hand, the reference signal is a so-called E that does not record or reproduce the servo reference signal 24a in the normal reproduction mode.
In the E mode and during recording, the vertical sync signal 3b is supplied from a sync separation circuit (not shown). The phase control of the rotating drum is not performed in the special reproduction mode such as high speed reproduction.

[0008]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the above, there were the following problems when switching modes.

(1) Switching from EE mode which is a state before reproduction or recording after power is turned on to normal reproduction mode The phase of the rotary drum in EE mode is synchronized with the vertical synchronizing signal 3b. However, when the mode is switched to the normal reproduction mode, the phase of the rotary drum is synchronized with the vertical reference signal 3b and the irrelevant servo reference signal 24a, so it takes time to pull in the output video signal 2a.
Will be disturbed.

(2) Switching from special reproduction mode to normal reproduction mode The phase of the rotating drum in special reproduction mode is not synchronized with the reference signal. However, when the mode is switched to the normal reproduction mode, the phase of the rotary drum is the servo reference signal 24a.
Since it is synchronized with, the output video signal 2a is disturbed during this time.

(3) In the normal reproduction mode, the first and second magnetic heads A1 and A2 to the third and fourth magnetic heads B1 and B are used.
Switching to 2 In FIG. 4, since the first and second magnetic heads A1 and A2 and the third and fourth magnetic heads B1 and B2 are formed with a constant angle θ, they are used for reproduction. When the magnetic head is switched, the waveform shaping circuit 6 delays the time corresponding to the angle θ and outputs the drum pulse 6a. Therefore, when the magnetic head is switched, it is necessary to newly synchronize with the servo reference signal 24a, and it takes a long time to pull in, and the output video signal 2a is disturbed during this time.

This will be described in detail with reference to FIG. 5. Here, FIG. 5A shows the servo reference signal 24a, and the first and second magnetic heads A1 and A at the timing AA.
It is assumed that the second magnetic head is switched to the third and fourth magnetic heads B1 and B2. The drum pulse 6a shown in FIGS. 7B and 7C respectively shows the case where the first and second magnetic heads A1 and A2 and the third and fourth magnetic heads B1 and B2 are used. It was done. When this is switched at timing AA, the drum pulse 6a having a short high level period becomes short as shown in FIG. 7D, and the phase becomes discontinuous before and after timing AA, and the servo reference shown in FIG. This is a problem because it takes time to synchronize with the signal 24a.

[0013]

The present invention has been described above in (1).
The following configurations are provided to solve the problems (3) to (3).

An image having a time axis correcting means for correcting the time axis of the reproduced video signal obtained by reproducing the video signal recorded on the magnetic recording medium by using the magnetic head formed on the rotating drum based on the time reference signal. In the signal magnetic reproducing device,
A counting means for outputting a servo reference signal synchronized with the time reference signal; and a servo means for comparing the servo reference signal with a drum pulse representing the phase of the rotating drum to control the phase of the rotating drum, In the EE mode, the video signal magnetic reproducing apparatus is characterized in that the servo reference signal is reset at the timing of the drum pulse by the counting means.

An image having a time axis correction means for correcting the time axis of a reproduced video signal obtained by reproducing a video signal recorded on a magnetic recording medium by using a magnetic head formed on a rotating drum, based on a time reference signal. In the signal magnetic reproducing device,
A counting means for outputting a servo reference signal synchronized with the time reference signal; and a servo means for comparing the servo reference signal with a drum pulse representing the phase of the rotating drum to control the phase of the rotating drum, A video signal magnetic reproducing apparatus characterized in that the servo reference signal is reset by the counting means at a timing of the drum pulse during a predetermined period after switching from the special reproduction mode to the normal reproduction mode.

An image having a time axis correcting means for correcting the time axis of a reproduced video signal obtained by reproducing a video signal recorded on a magnetic recording medium by using a magnetic head formed on a rotary drum, based on a time reference signal. In the signal magnetic reproducing device,
A counting means for outputting a servo reference signal synchronized with the time reference signal; and a servo means for comparing the servo reference signal with a drum pulse representing the phase of the rotating drum to control the phase of the rotating drum, A video signal magnetic reproducing apparatus characterized in that, after switching from a certain magnetic head pair to another magnetic head pair, the servo reference signal is reset by the counting means at a timing of the drum pulse for a predetermined period.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram for explaining a main part of a time axis correction circuit according to the present invention, and FIG. 2 is a timing chart of FIG. An embodiment according to the present invention will be described below with reference to the drawings. In this embodiment, the servo reference counter circuit 24 is forcibly reset at a predetermined timing and the problems (1) to (3) described above are given. It is a solution to the problem.

In FIG. 1, the drum pulse 6a (see FIG.
(Shown in (A)) is supplied to the edge differentiating circuit 25, where the edge differentiating circuit output signal 25a (shown in FIG. 2B) obtained by extracting the edge of the drum pulse 6a is one of the AND circuits 29. Is supplied to the input of. In addition, the EE signal S that is high level only in the EE mode and is low level in the other period
3 (shown in FIG. 2C) is supplied to the OR circuit 28.

Further, the special reproduction signal S1 (see FIG. 2) is high level only in the normal reproduction mode and low level in other periods.
(Shown in (D)) is supplied to the first timing circuit, where it rises in synchronization with the rising edge of the special reproduction signal S1 and is at a high level for at least the time corresponding to 1/2 cycle of the drum pulse 6a, During the other periods, the first timing circuit output signal 26a (shown in FIG. 2E) which is at the low level is supplied to the OR circuit 28.

Further, the first and second magnetic heads A1 and A2
Is used for a low level while the third and fourth magnetic heads B1, B2 are used for a high level. A use head signal S2 (shown in FIG. 2F) is supplied to the second timing circuit 27. The second timing circuit output, which is high level at least for a time period corresponding to a half cycle of the drum pulse 6a and rises in synchronization with the rising edge of the use head signal S2, and is low level for the rest of the period. The signal 27a (illustrated in FIG. 2G) is supplied to the OR circuit 28.

The first and second timing circuit output signals 26a, 27a thus obtained and the EE signal S3 are logically summed by the logical sum circuit 28 to obtain a logical sum circuit output signal 28a.
Is obtained and supplied to the other input of the AND circuit 29, and the AND circuit 29 gates the edge differentiating circuit output signal 25a with the OR circuit output signal 28a to obtain a reset signal 29a (Fig. 2 (H) is supplied to the servo reference counter circuit 24.

Now, an embodiment will be described in association with the above problems.

(1) When switching from the EE mode to the normal reproduction mode The phase of the rotary drum in the EE mode is synchronized with the vertical synchronizing signal 3b, but the pulse P in the reset signal 29a supplied to the servo reference counter circuit 24 is used. The servo reference signal 24
a is synchronized with the vertical synchronizing signal 3b. Therefore, EE
Even when the mode is switched to the normal playback mode, it does not take time to pull in the servo, and the output video signal 2
There is no disturbance in a.

(2) Switching from special reproduction mode to normal reproduction mode The phase of the rotary drum in special reproduction mode is not synchronized with the servo reference signal 24a, but is reset after switching from special reproduction mode to normal reproduction mode. Signal 29a
Servo reference counter circuit 2 by pulse Q in
Since 4 is reset, the time until the servo is pulled in can be shortened and the output video signal 2a can be improved.

(3) From the first and second magnetic heads A1 and A2 to the third and fourth magnetic heads B1 and B in the normal reproduction mode
When switching to 2 The phase of the drum pulse 6a becomes discontinuous before and after the timing AA, but since the servo reference counter circuit 24 is reset by the pulse Q in the reset signal 29a, the time until the servo is pulled in should be shortened. The output video signal 2a can be improved.

It is needless to say that the servo reference counter circuit 24 in the time axis correction circuit 2 may be independent.

[0027]

As described above, according to the present invention, particularly in the EE mode, the counting means resets the servo reference signal at the edge of the drum pulse.
Even when the EE mode is switched to the normal reproduction mode, it takes no time until the servo is pulled in, and the quality of the output video signal can be improved.

As described above, according to the present invention, the servo reference signal is reset by the counting means at the edge of the drum pulse for a predetermined period after the special reproduction mode is switched to the normal reproduction mode. When switching from the reproduction mode to the normal reproduction mode, it takes no time to pull in the servo, and the quality of the output video signal can be improved.

As described above, the present invention is particularly configured to reset the servo reference signal by the counting means at the edge of the drum pulse for a predetermined period after switching from one magnetic head pair to another magnetic head pair. Because I did
When the pair of magnetic heads used for reproduction is switched, it takes no time to pull in the servo, and the quality of the output video signal can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining a main part of a time axis correction circuit according to the present invention.

FIG. 2 is a timing chart of FIG.

FIG. 3 is a block diagram for explaining a conventional VTR.

FIG. 4 is a diagram for explaining the arrangement of magnetic heads formed on a rotating drum.

FIG. 5 is a timing chart for explaining a relationship between a drum pulse signal and a servo reference signal.

[Explanation of symbols]

2 time axis correction circuit (time axis correction means) 3 servo means (servo system) 24 servo reference counter circuit (counting means) 1a reproduced video signal 6a drum pulse 23a clock signal (time reference signal) 24a servo reference signal T magnetic recording medium A1, A2 first and second magnetic heads B1, B2 third and fourth magnetic heads

Claims (3)

[Claims] 1. A time axis correction means for correcting the time axis of a reproduced video signal obtained by reproducing a video signal recorded on a magnetic recording medium by using a magnetic head formed on a rotary drum, based on a time reference signal. In a video signal magnetic reproducing apparatus having the counting means for outputting a servo reference signal synchronized with the time reference signal, the servo reference signal and a drum pulse representing the phase of the rotating drum are compared to determine the phase of the rotating drum. A video signal magnetic reproducing apparatus comprising: a servo unit for controlling; and, in the EE mode, the servo reference signal is reset at the timing of the drum pulse by the counting unit. 2. A time axis correcting means for correcting a time axis of a reproduced video signal obtained by reproducing a video signal recorded on a magnetic recording medium by using a magnetic head formed on a rotary drum, based on a time reference signal. In a video signal magnetic reproducing device having the counting means for outputting a servo reference signal synchronized with the time reference signal, the servo reference signal and a drum pulse representing the phase of the rotating drum are compared to determine the phase of the rotating drum. A video signal magnetic, comprising a servo means for controlling, wherein the counting means resets the servo reference signal at the timing of the drum pulse during a predetermined period after switching from the special reproduction mode to the normal reproduction mode. Playback device. 3. A time axis correcting means for correcting the time axis of a reproduced video signal obtained by reproducing a video signal recorded on a magnetic recording medium by using a magnetic head formed on a rotary drum, based on a time reference signal. In a video signal magnetic reproducing apparatus having the counting means for outputting a servo reference signal synchronized with the time reference signal, the servo reference signal and a drum pulse representing the phase of the rotating drum are compared to determine the phase of the rotating drum. A servo means for controlling, and after switching from one magnetic head pair to another magnetic head pair, the counting means resets the servo reference signal at the timing of the drum pulse for a predetermined period. Video signal magnetic reproducing device.