JPS5922433B2 - Video signal magnetic reproducing device - Google Patents

Description

[Detailed Description of the Invention] In a VTR (magnetic recording/reproducing device), a video signal is generally divided into fixed periods, and is sequentially supplied to a plurality of rotating magnetic heads for recording, and during playback, the output of the head is are sequentially switched and extracted using a switch circuit to obtain a continuous original video signal.

In this case, in a high-end VTR for broadcasting,
The same number of pulse generating means as the heads are provided on the rotating shaft of the head, and the head output is switched based on the pulses from these pulses.The regenerated horizontal synchronizing pulse is stabilized by an AFC circuit, and the horizontal synchronizing pulse is stabilized by the AFC circuit. The time point at which the head output is switched is fixed to the horizontal blanking period.

However, when doing this, the plurality of pulse generating means must be installed at precisely predetermined intervals, which requires mechanical precision.

Further, the AFC circuit is required to be sufficiently stable against temperature changes and fluctuations in power supply voltage, making it expensive and making adjustment complicated or difficult. In view of these points, the present invention is intended to require only one pulse generating means and to eliminate the need for an AFC circuit.

Let me explain one example below.

In this example, the VTR is of a so-called 1.5 head type. FIG. 1 shows the video signal reproduction system, in which a rotating magnetic head 1 for vertical synchronizing pulses and a rotating magnetic head 2 for video signals have a predetermined angular interval and step difference from each other, and , are installed on a tape guide drum 3 so that the head 1 is in front, and this drum 3 is driven by a motor 5 to rotate the drum 3 at a period equal to the field frequency of the video signal.
For example, it can be rotated 60 times per second.

Approximately three magnetic tapes 4 are placed on the circumferential surface of the drum 3.
It runs diagonally across 600 corners, and
This tape 4 is transported at a constant speed by a capstan 6 and a pinch roller 7. In this case, tape 4 has
A video signal converted into an FM signal is recorded with a magnetization pattern as shown in FIG.

That is, the first vertical synchronizing pulse (approximately 20 horizontal periods including the preceding and following) of one field of video signal (FM signal) is recorded diagonally to the running direction of the tape 4 as one magnetic track 1A. A signal (original luminance signal) during the vertical scanning period following this vertical synchronizing pulse is recorded as one magnetic track 2A in the same direction as the track 1A. Further, along the edge of the tape 4, a vertical synchronizing pulse is recorded along the tape 4 as a magnetic track 4A for tracking control during reproduction. And when playing,
A vertical synchronizing pulse is regenerated from the track 4A by the magnetic head 11, and the regenerated vertical synchronizing pulse is supplied to the servo circuit 13. Pulse generating means 12 is provided on the rotating shaft 8 of the drum 3, and from this One pulse is extracted for each revolution of the heads 1 and 2, and this pulse is supplied to the servo circuit 13.

Then, the rotation of the motor 5 is controlled by the output of the servo circuit 13, and tracking of the heads 1 and 2 is performed so that the heads 1 and 2 correctly scan the tracks 1A and 2A, respectively. As shown in FIG. 4A, an FM signal Sv based on a vertical synchronizing pulse is taken out, and as shown in FIG. In this case, by selecting the lengths of the signals Sv, Sy at the time of recording, the front and rear of the reproduced signals Sv, Sy overlap each other little by little. The signals Sv and Sy from the heads 1 and 2 are supplied to the switch circuit 23 through the reproduction amplifiers 21 and 22, respectively, and are also supplied to the switch circuit 23 from the control circuit 30 described below as shown in FIG.
A rectangular wave signal Sw as shown in FIG. This video signal is taken out to the output terminal 26.

On the other hand, the control circuit 30 is configured as shown in FIG. 2, for example.

In other words, the fourth
As shown in Figure D, the positive polarity reference horizontal synchronization pulse Ph is
It is supplied to the counter 32 as its counting power, and
The pulses from the pulse generating means 12 are supplied to the delay circuit 33 and are made into pulses Pg located at the beginning of each field as shown in FIG.
2 is supplied as a set pulse. Therefore, the counter 32 counts the pulses Ph and is reset by the pulse Pg, so that its contents change from the beginning of each field as shown in FIG. 4F. The contents of this counter 32 are then supplied to detection circuits 34 and 35, and in the detection circuit 34, when the contents of the counter 32 reach, for example, "17", this is detected and a detection pulse is generated as shown in FIG. 4G. Pr is taken out, and when the content of the counter 32 reaches, for example, [260], this is detected in the detection circuit 35, and a detection pulse Ps is taken out as shown in FIG. 4H.

These pulses Pr and Ps are supplied to the set terminal R and the set terminal S of the RS flip-flop circuit 36, and therefore, the pulse Pg is obtained from the output terminal Q of the flip-flop circuit 36 as shown in FIG. from 1
Falling at the position of the 7th horizontal synchronization pulse Ph, 26
A rectangular wave signal Sr rising at the position of the 0th horizontal synchronization pulse Ph is extracted. In this way, the pulse generating means 12
A signal that changes at a fixed position with respect to the pulse Pg was obtained, but the rising and falling points of this signal Sr were also synchronized with the horizontal synchronizing pulse in the reproduced video signal. , dropout and noise compensation is performed.

That is, the video signal from the demodulation circuit 25 is supplied to the synchronization separation circuit 41, and as shown in FIG. 4J, a horizontal synchronization pulse Pk (Ta is a dropout period, Tb is a noise period, and Sn is the noise) is taken out, and this pulse Pk is applied to a triggerable type monostable multivibrator (the trigger is a rising trigger, and the inversion period τ, is
42 (assuming that it is longer than one horizontal period and shorter than two horizontal periods), and from its output terminal Q, as shown in FIG. During periods Ta and Tb, a signal Sk that falls after a period τ from the rise of the last pulse Pk or noise Sn is formed, and this signal Sk is supplied to the AND circuit 43, and the synchronous separation circuit More pulse Pk
is supplied to the AND circuit 43, and the AND circuit 43 extracts a horizontal period pulse Pi except for periods Ta and Tb, as shown in FIG. 4L. Also multi vibrator 4
As shown in FIG. 4M, from the output terminal Q of 2, the signal Sk
A signal Sm that changes in the opposite direction to that of Sm is extracted, and this signal Sm
is supplied to the AND circuit 44, and at the same time, the external reference horizontal synchronizing pulse Ph is supplied from the terminal 31 to the AND circuit 44, and from the AND circuit 44, as shown in FIG.
A horizontal period pulse Pn is extracted only at a and Tb.

And the pulses Pi from these AND circuits 43 and 44
, Pn are supplied to the OR circuit 45, and the pulse PO as shown in FIG.
At Tb, a pulse PO with the pulse Ph supplemented is taken out, and this pulse PO is delayed and compensated by the delay circuit 46 and then supplied to the T terminal of the JK flip-flop circuit 47, and the signal Sr from the flip-flop circuit 36 is sent to the flip-flop circuit 47. It is supplied to the J terminal of 47, and
A signal that changes in the opposite direction to the signal Sr from the output terminal Q of the flip-flop circuit 36 is sent to the output terminal K of the flip-flop circuit 47.
Supplied to the terminal.

Therefore, as shown in FIG. 4P, the flip-flop circuit 47 generates a signal that is synchronized with the reproduced horizontal synchronizing pulse Pk and rises and falls at a fixed position relative to the pulse Pg from the pulse generating means 12. Sw is obtained. Furthermore, even if there is a dropout or noise Sn in the reproduced horizontal synchronizing pulse Pk at this time, the influence of these is small on the signal Sn. Thus, according to the present invention, even if two rotating magnetic heads 1 and 2 are used, the switching signal Sw can be formed based on the pulse of one pulse generating means 12, and therefore the pulse generating means 12 can be used as a reference. The attachment of the means 12 does not require mechanical precision.

Furthermore, there is no need for an AFC circuit, and all necessary circuits operate digitally, so they are stable and easy to adjust and maintain. FIG. 5 shows part of another example of a compensation circuit for dropout and noise, in which 51 and 52 are T flip-flop circuits, 53 is a JK flip-flop circuit, and 54 is an RS flip-flop circuit.

Signals are obtained from each part according to the relationship shown in FIG. 6. Therefore, even if there is a dropout in the reproduced horizontal synchronization signal Ps, the pulse PO from the OR circuit 45 is corrected by the reference synchronization pulse Ph. be done.

[Brief explanation of drawings]

1 and 2 are system diagrams of one example of the present invention, FIG. 3 is a diagram of its magnetization pattern, FIG. 4 is a waveform diagram for explaining the same, and FIG. 5 is an example of another example of the present invention. FIG. 6 is a waveform diagram for explaining the system diagram. 1 and 2 are rotating magnetic heads, 32 is a counter, 34, 35
is the detection circuit.

Claims (1)

[Claims] 1. A device having at least two rotating magnetic heads, which sequentially reproduces video signals recorded on a magnetic tape in a divided manner, and sends the reproduced video signals to a switch circuit. In the apparatus which supplies the external reference horizontal synchronizing pulse to the counter and extracts the original continuous video signal, the external reference horizontal synchronizing pulse is supplied to the counter as its counting input, and the pulse obtained as the rotating magnetic head rotates is supplied to the counter. When the count content of this counter reaches a predetermined value, it is detected by each detection circuit, and this detection output and the horizontal synchronization pulse obtained from the reproduced video signal are used to switch the A video signal magnetic reproducing device that controls circuit switching. 2. In the device according to claim 1, the presence or absence of a horizontal synchronizing pulse obtained from the reproduced video signal is detected, and when this horizontal synchronizing pulse is not obtained, the external A magnetic reproducing device for video signals, wherein switching of the switch circuit is controlled by a reference horizontal synchronizing pulse.