JPS63164778A - Magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To prevent the oscillation of a video signal by using a dropout signal subject to waveform shaping at a waveform shaping circuit so as to switch a reproduced video signal and a video signal subject to 1H delay. CONSTITUTION:If a dropout takes place in in FM-RF signal, a dropout detector 4 generates a dropout signal (b) of L level (logical value) only during, e.g., dropout period and the signal (b) is given to a waveform shaping circuit 7, from which a dropout correction signal (c) is generated. If the dropout is consecutive for a long time (3H or over), the generation of the signal is limited during the 3H period. The dropout correction signal (c) controls a video signal changeover switch 5. If a dropout takes place, since the video signal changeover switch 5 and a 1H delay line 6 constitute the feedback signal, the dropout is corrected for 3H at maximum. Thus, the oscillation of the video signal is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magnetic recording and reproducing device that is effective for use in a video floppy device that records/reproduces or reproduces still images on a magnetic sheet.

Conventional technology Conventional examples are shown in FIGS. 4 to 6.

FIG. 4 is a block diagram showing a video signal demodulation and dropout correction section during playback.

FM-RF multiplied signal reproduced from a magnetic sheet (not shown) via magnetic head 1, preamplifier 2 to a suitable amplitude
is amplified. The amplified FM-RF signal is demodulated into a video signal m by the FM detector 3.

Furthermore, the jM-RF multiplied signal is sent to the dropout detector 4
is input.

The dropout detector 4 has a reference voltage and the above FM-RF.
The signal amplitudes are compared, and a dropout signal l is output when the FM-RF signal amplitude decreases.

One input terminal of the video signal changeover switch 6 has F.
Similarly, the video signal n that has passed through a 1H (one horizontal scanning period) delay line 6 for dropout correction is input to the other input terminal of the M-demodulated video signal m.

Therefore, as a result, the video signal changeover switch 6 outputs the video signal from 1H before (before the dropout occurs), so that the dropout can be corrected.

Problems to be Solved by the Invention However, the above conventional dropout correction method
As shown in Figure 6, 1H delay for dropout correction@
The delay time of e is also longer than that of F, where a long signal dropout occurs.
When the M-RF signal r is reproduced, the video signal energy is attenuated in the feedback loop between the video signal changeover switch 6 and the 1H delay line 6, which is configured by the operation of the dropout signal 8 when a dropout occurs. Nevertheless, since a feedback loop is similarly constructed, a video signal p in which an oscillation phenomenon occurs on the TV screen due to a slight change in DC voltage is output.

In view of the above-mentioned problems, the present invention provides a magnetic recording and reproducing device that can prevent the oscillation phenomenon of video signals.

Means for Solving the Problems The present invention comprises means for detecting a dropout signal, a delay means for delaying a demodulated video signal by 1H period, a video signal changeover switch means, and a waveform shaping means. has been done.

Operation When a dropout is detected, the oscillation phenomenon of the video signal is prevented by switching between the reproduced video signal and the video signal delayed by 1H using the dropout signal whose waveform has been shaped by the waveform shaping circuit.

Example Hereinafter, the present invention will be explained using the drawings.

FIG. 1 is a block diagram showing a specific configuration of the present invention, FIG. 2 is a circuit configuration, and FIG. 3 is a waveform diagram thereof.

The FM-RF multiplied signal is reproduced from a magnetic sheet (not shown) via a magnetic head 1 and is appropriately amplified by a preamplifier 2. The amplified FM-RF multiplied signal is demodulated into a video signal d by the FM detector 3.

The FM-RF signal is also input to a dropout detector 4 to detect the presence or absence of dropout.

When FM-RF double signal dropout occurs, the dropout detector 4, for example, goes low only during the dropout period.
Generates a level (logical value) dropout signal.

A waveform shaping circuit 7 generates a dropout correction signal C from the dropout signal S.

For example, if dropout continues for a long time (3H or more), it is limited to a 3H period.

The dropout correction signal C controls the video signal changeover switch 5.

The reproduced video signal d is input to one input terminal of the Eirin signal changeover switch 6, and the 1H signal is input to the other input terminal.
The Eirin signal that has passed through the delay line is input.

When a dropout occurs, a return loop is formed between the video signal changeover switch 5 and the 1H delay line 6, so that the dropout is corrected for a maximum of 3H periods.

The period during which dropout can be corrected here is determined by the delay time of the delay line, and normally when using a 1H delay line,
The limit is around H.

Therefore, a dropout-corrected video signal f can be obtained, and even if dropout occurs for a long time, a video signal free from oscillation can be provided.

FIG. 2 shows a specific configuration of the waveform shaping circuit 7 described above.

The dropout correction signal C is obtained by AND (logical value) of the dropout signal, the delay time 9 of the monostaple multivibrator 8, and the dropout signal C, respectively, of the diodes D and D2.

Now, if the dropout is shorter than 3H (dot-line period of the dropout signal p), the video signal changeover switch 6 is activated by the dropout signal q via the diode D2.
operates and if the dropout is for a long time, the dropout correction is canceled by the time constant of the differentiating circuit.

Effects of the Invention According to the present invention, it is possible to prevent the oscillation phenomenon of the video signal that occurs when a dropout exceeding the correction limit of the dropout correction circuit occurs.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a specific configuration of a magnetic recording/reproducing apparatus according to an embodiment of the present invention, and FIG. 2 is a circuit configuration diagram showing a more specific circuit configuration of a waveform shaping circuit in the block diagram of FIG. 1. , FIG. 3 is a waveform diagram for explaining FIGS. 1 and 2, FIG. 4 is a block diagram showing a conventional example, and FIGS. 6 and 6 are waveform diagrams for explaining FIG. 4. be. 4...Dropout detector, 5...
Video signal changeover switch, 6...1H delay line, 7...waveform shaping circuit, 8...multivibrator, Dl and D2...diode. Name of agent: Patent attorney Toshio Nakao and one other person Ec
αCo-'-”-bimethod

Claims (1)

[Claims] A magnetic recording and reproducing device that records/reproduces or reproduces a frequency-modulated video signal in units of one field on a recording track of a magnetic sheet, the device comprising a dropout detection means for detecting a missing portion of the reproduced video signal, and a demodulated video signal. The present invention is characterized by comprising a delay means for delaying a video signal obtained by one horizontal scanning period, a video signal changeover switch means, and a waveform shaping means, and for canceling the dropout signal when a no-signal period continues to a moderate degree. Magnetic recording and reproducing device.