JPH06101836B2 - Magnetic recording / reproducing device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording / reproducing apparatus such as a video floppy disk drive apparatus for recording and reproducing or reproducing a still image on a magnetic sheet.

Conventional Technology FIG. 3 shows a conventional example. This is a block diagram showing a demodulation and dropout correction unit of a video signal during reproduction.

The FM signal reproduced from the magnetic sheet (not shown) by the magnetic head 1 is amplified by the preamplifier 2 to an appropriate amplitude.
The amplified FM signal is demodulated into a video signal by the detector of the FM demodulation circuit 3 and the demodulation filter. Further, the FM signal is input to the dropout detector 4. The dropout detector 4 compares the reference voltage and the amplitude of the FM signal, and outputs a dropout signal if the FM signal is lower. The FM demodulated video signal is input to one input terminal of the video signal changeover switch 6, and the video that has passed through the dropout correction 1H (one horizontal scanning period) delay line 7 is also input to the other input terminal. A signal is being input. In playback mode,
The video signal changeover switch 6 is switched by the dropout signal from the dropout detector 4 and is switched to the 1H delay line 7 when the dropout occurs. as a result,
The video signal before 1H (before the dropout occurs) is output, and the dropout can be corrected.

However, the conventional dropout correction method detects dropout detection with the amplitude of the FM signal amplified by the preamplifier 2 and corrects it with the FM demodulated video signal. FM
The group delay time of the demodulation circuit 3 causes a time difference between the time of detection and the time of correction, and there is a drawback in that there is a period in which the correction cannot be performed accurately even though the dropout is detected.

Means for Solving the Problems The present invention is a dropout detector, a low-pass filter having the same delay time as the demodulation filter of the FM demodulation circuit, a delay means for delaying the demodulated video signal by 1H, The video signal changeover switch means is included.

With the above configuration, by switching between the demodulated video signal and the output of the 1H delay means with the dropout signal delayed by the low-pass filter at the time of dropout detection, the detection time and the correction time can be changed. The dropout can be effectively corrected by reducing the time difference between.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a specific configuration of the present invention, and FIG. 2 is a waveform diagram for explaining the operation.
In these figures, the FM signal a reproduced from a magnetic sheet (not shown) via the magnetic head 1 is the preamplifier 2
Is moderately amplified. The amplified FM signal b is demodulated into a video signal d by the FM detector and the demodulation filter of the video signal demodulation circuit 3. The FM signal b is detected by the dropout detector 4 for the presence or absence of dropout. When the dropout occurs in the FM signal b (g section), the dropout generator 4 generates the dropout signal c. The dropout signal c is delayed by the low pass filter 5,
The video signal changeover switch 6 is controlled as the delayed dropout signal f.

The video signal d is applied to one input terminal of the changeover switch 6.
However, the video signal e delayed by 1H by the 1H delay line 7 composed of a glass delay line or a charge transfer device (CCD) or the like is input to the other one input terminal.

Here, when a dropout occurs, the delayed dropout signal f is used to switch from the video signal d to f. There is a time difference between the dropout signal c and the video signal d due to the group delay time of the FM demodulation circuit 3, but the dropout signal c has the same delay time as that of the demodulation filter of the FM demodulation circuit 3 and is passed through the low-pass filter 5. You can eliminate the time difference by delaying with
A dropout-corrected video signal g is obtained.

Advantageous Effects of the Invention According to the present invention, when there is a time difference between the dropout detection unit and the correction unit, it is not necessary to adjust the dropout signal position in accordance with the dropout position of the video signal, and the adjustment position can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram of an essential part showing an embodiment of the present invention, and FIG.
FIG. 3 is a signal waveform diagram for explaining the operation of FIG. 1, and FIG. 3 is a block diagram showing a conventional magnetic recording / reproducing apparatus. 3 …… FM demodulator, 4 …… Dropout detector, 5 ……
Low pass filter, 6 ... Video signal selector switch.

Claims (1)

[Claims] 1. A magnetic recording / reproducing apparatus for recording and reproducing or reproducing a frequency-modulated video signal in units of one field on a recording track of a magnetic sheet, wherein dropout detection detects a missing portion of a reproduced video signal. Means and
A low-pass filter having the same delay time as the detection filter of the FM demodulation circuit, a delay means for delaying the demodulated video signal by one horizontal scanning period, and a video signal changeover switch means, and when a dropout is detected A magnetic recording / reproducing apparatus characterized in that the demodulated video signal and the output of the 1H delay means are switched by the dropout signal delayed by the low-pass filter to correct the dropout.