JPS60140987A - Switching circuit of head output - Google Patents

Abstract

PURPOSE:To eliminate a deficiency of a vertical synchronizing signal even at a special reproducing mode in terms of tape speed and to prevent a switching point from fluctuation by detecting a equivalent pulse of a reproduced image signal of an amplifier circuit and a decoding circuit provided on plural rotational magnetic heads so as to switch a head output. CONSTITUTION:Signals reproduced by the 1st and 2nd rotational magnetic heads 8 and 9 from an image track recorded on a magnetic tape 1 are amplified by the 1st and 2nd amplifier circuits 10 and 11. Demodulating circuits 12 and 13 decode reproduced signals A and B to image signals, and reproduced image signals can be obtained. Equivalent pulse detection circuit 14 and 15 are set so that they can output equivalent pulse detection signals at a position of 1.25H from a start of an equivalent pulse; therefore vertical synchronizing signals will not be lacking at a two-fold speed mode, and moreover image signals recorded on the magnetic tape 1 can be reproduced without fluctuation of a switching point 7.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a head output switching circuit in a reproduction mode of a magnetic recording/reproducing apparatus (hereinafter referred to as VTR), and particularly to a head output switching circuit suitable for a special reproduction mode. be.

Conventional structure and its problems In recent years, in order to obtain high-quality images in VTRs, the video track width has been increased by increasing the tape speed, and in order to use the video track more effectively, the amount of tape wrapped around the rotating cylinder has been reduced. A method of reducing this is adopted. As a result, σH of the tape format increases, and the amount of overlap between video tracks decreases, resulting in a lack of vertical synchronization signals in the special playback mode.

Hereinafter, the special playback mode in the 7" 7-ohm as described above will be explained with reference to the drawings.

Figure 1 shows automatic scanning tracking (hereinafter referred to as AST) in which the magnetic tape 1 is run at twice the nominal speed and the rotating magnetic head is displaced in the direction perpendicular to the video track to automatically adjust the tracking. Shows how to scan.

When reproducing video tracks 4a, ab, 4c, and 4d recorded on magnetic tape 1 running in the direction of arrow 2 at a tape speed twice the nominal speed, a rotating magnetic head (not shown) that scans in the direction of arrow 3 is used. ) is fixed, the trajectories sa, sb
becomes. In this method, it is possible to scan the shaded areas 4b and 4d where the lack of a video signal occurs every time the video track changes. However, αH of the above tape format
A video signal missing portion 6 corresponding to 3.5 d is generated.

Furthermore, switching point 7 is 1.75 points before the vertical synchronization signal.
Since the vertical synchronization signal is H, the vertical synchronization signal is 1.7 as shown in Figure 2.
5d minutes are not played. This lack of a vertical synchronization signal has the disadvantage that correction by a time base correction device (TBC) becomes difficult.

To solve this problem, it is possible to control the jumping position of the rotating magnetic head or change the aH. For the former method, there is a method proposed in JP-A-55-11633, which is effective for tape formats that have a sync track such as 1-inch VTRs, but for tape formats that do not have a sync track, it is necessary to use a vertical synchronization signal. may be lacking. The latter is impractical because the tape format changes, and a solution is desired that has a simple structure and does not cause a lack of vertical synchronization signals in any special playback mode.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a head output switching circuit that does not cause the absence of a vertical synchronization signal in special reproduction mode by AST.

Structure of the Invention The head output switching circuit of the present invention includes a first amplifier circuit that amplifies the reproduction output signal of the first rotating magnetic head, a first demodulation circuit that demodulates the reproduction signal of 5 pages into a video signal, and a second demodulation circuit that demodulates the reproduction signal of 5 pages. a second demodulation circuit that demodulates the reproduction signal of the second amplifier circuit that amplifies the reproduction output signal of the rotating magnetic head into a video signal; and a first equivalent pulse detection circuit that detects the equivalent pulse of the first demodulation circuit. , which has a second equivalent pulse detection circuit that detects the equivalent pulse of the second demodulation circuit, and is configured to obtain a head output switching signal from the first equivalent pulse detection circuit and the second equivalent pulse detection circuit. , and this results in p
In the special playback mode using AsT, it is possible to obtain a video signal without missing parts of the vertical synchronization signal.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 shows a block diagram of a head output switching circuit in one embodiment of the present invention. 8 and 9 are rotating magnetic heads, 1o and 11 are amplifier circuits that amplify the reproduction output signal of the rotation magnetic head, 12 and 13 are demodulation circuits that demodulate the reproduction signal of the amplifier circuit into a video signal, and 14 and 16
The equivalent pulse detection circuit 16 detects an equivalent pulse from the video signal obtained by the demodulation circuit, and the head output switching signal circuit 17 creates a head output switching signal from the output signal of the equivalent pulse detection circuit.
is a switch that switches each reproduction signal of the amplifier circuit using a head output switching signal.

The operation of the head output switching circuit of this embodiment configured as described above will be explained below.

A signal reproduced from a video track recorded on the magnetic tape 1 by the first rotary magnetic head 8 and the second rotary magnetic head 9 is transmitted to the first amplification circuit 1o and the second amplification circuit 1.
1 to obtain reproduced signals A and B shown in FIG. The demodulation circuit 12 demodulates the reproduced signals A and B into video signals to obtain reproduced video signals C and D shown in FIG.

Note that during the period in which the reproduced signals A and B do not appear, the reproduced video signals C and D become noise C1. Detection pulses E and F are obtained from the reproduced video signals C and D by equivalent pulse detection circuits 14 and 15.

The head output switching signal circuit 16 generates a head output switching signal G for switching the switch 17 by raising the 7-pen head output switching signal G in response to the detection pulse E and lowering it in response to the detection pulse F. Note that the detection pulses E and F are set in advance so that they are output at the switching point 7 of the tape format. By switching the switch 17 to the head output switching signal G, the reproduced signals A and B are selected, and a combined reproduced signal H is obtained and supplied to a demodulation circuit or the like.

Next, an example will be explained in which the magnetic tape is run at twice the nominal speed and scanning is performed by AST.

FIG. 6 shows a tape pattern, in which 18 is a vertical synchronizing signal, and 19 is a positional relationship between the switching point 7 and the leading edge of the vertical synchronizing signal 18, which is 1.75H. 20 indicates the amount of overlap between the video tracks, which is 5H. FIG. 6 is a diagram showing the relationship between the video signal recorded on the magnetic tape 1 and the video signal reproduced by the rotating magnetic head, and FIG. 6 (,) shows the video signal recorded on the video track 4h. , FIG. 6 0)) is a video track 4h reproduced by the AST rotating magnetic head 8, and the shaded area is the rotating magnetic head 8.
is the part that is in contact with the magnetic tape 1. Figure 6(c)
is an equivalent pulse detection signal E that detects a position 1.26H from the beginning of the equivalent pulse of the reproduced video signal C, and FIG. 6(d) is a head output switching signal G raised by the equivalent pulse detection signal E. The figure (,) shows a video track 4f reproduced by the rotating magnetic head 9, and the shaded area is the portion where the rotating magnetic head 9 is in contact with the magnetic tape 1. FIG. 6(f) shows the video signal recorded on the video track 4f. Note that the equivalent pulse detection signal F is output at a position 1.25H from the beginning of the equivalent pulse of the reproduced video signal reproduced by the rotating magnetic head 9. The head output switching signal G is lowered by the equivalent pulse detection signal F.

When the rotary magnetic head 8 is fixed and scanned, the locus 6d is displaced in the vertical direction with respect to the video track, and when the video track 4h is scanned, the vertical synchronizing signal 18 is shifted as shown in the shaded area in FIG. 6(b). It will be played 3.25H before the front line. On the other hand, the rotating magnetic head 9 can reproduce the entire trailing edge video track overlap portion of the video track 4f, as shown by the hatched area in FIG. 6(e).

That is, in the tape format used in this embodiment, vertical synchronization is achieved even in double speed mode by setting the equivalent pulse detection circuits 14 and 16 to output the equivalent pulse detection signal at a position 1.25H from the beginning of the equivalent pulse. The video signal recorded on the magnetic tape 1 can be reproduced without signal loss and without changing the switching point 7.

As described above, according to this embodiment, since the head output switching signal is created by detecting the equivalent pulse of the reproduced video signal from the rotating magnetic head 8.9, the vertical synchronization signal is absent regardless of the tape speed in the special reproduction mode. A head output switching circuit is realized in which there is no change in the head switching point and the head switching point does not fluctuate.

Effects of the Invention As is clear from the above explanation, unlike the conventional method of creating a head output switching signal using a pulse signal (PG) corresponding to the rotational phase of a rotary cylinder, the vertical synchronization signal is In order to overcome the drawbacks such as lack of switching points or fluctuations in switching points, the present invention is configured to switch head outputs by detecting equivalent pulses of reproduced video signals in amplifier circuits and demodulation circuits provided in each of a plurality of rotating magnetic heads. Therefore, in the special playback mode at any tape speed, there is no loss of vertical synchronization signal and a reproduced image without fluctuation of the switching point can be obtained, which is an excellent effect.

[Brief explanation of drawings]

1 and 2 are diagrams explaining the reproduction method in the conventional special reproduction mode, FIG. 3 is a block diagram of a head output switching circuit according to an embodiment of the present invention, FIG. 4 is a timing diagram of the same, and FIG. This figure and FIG. 6 are diagrams for explaining the reproduction method in the same special reproduction mode. 1... Magnetic tape, 8, 9... Rotating magnetic head, 10.11... Amplifying circuit, 12.1
3...Demodulation circuit, 14.15...Equivalent pulse detection circuit, 16...Head output switching signal circuit, 17...Switch. 1st @ 2nd cause 31%il Fig. 4 Clause IIl group - Suga and) Mi 廼

Claims (1)

[Scope of Claims] A first rotary magnetic head and a second rotary magnetic head for reproducing video signals recorded on a magnetic tape;
a first amplification circuit that amplifies the reproduction output signal of the rotary magnetic head; a second amplification circuit that amplifies the reproduction output signal of the second rotary magnetic head; a first demodulation circuit that demodulates the signal, a second demodulation circuit that converts the reproduced signal of the second amplifier circuit into a video signal, and a second demodulation circuit that detects an equivalent pulse of the video signal of the first demodulation circuit. 1 equivalent pulse detection circuit, a second equivalent pulse detection circuit that detects the equivalent pulse of the video signal of the second demodulation circuit, and an output signal of the first equivalent pulse detection circuit and the second equivalent pulse. means for obtaining a head output switching signal from the output signal of the detection circuit; and means for obtaining a reproduction signal of the first amplifier circuit and a reproduction signal of the second amplifier circuit 2 based on the head output switching signal. 1. A head output switching circuit comprising switching means for switching the head output of a rotating magnetic head during reproduction.