JP2942067B2 - Magnetic recording / reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording / reproducing apparatus such as a VTR (Video Tape Recorder), and more particularly to a video tape dropout compensation.

[0002]

2. Description of the Related Art In a VTR, as shown in FIG. 4, during reproduction, an FM signal read from a video tape by a magnetic head 50 is amplified and waveform-shaped by a head amplifier / equalizer 51, and then RFAGC ( High-frequency automatic gain control circuit) 52 and frequency conversion circuit 56.

The output of the RFAGC 52 is supplied to an FM demodulation circuit 5
3 and input to the dropout detection circuit 55. The signal obtained by the FM demodulation circuit 53 is passed through an LPF (Low Pass Filter) 54, whereby a luminance signal is extracted. The luminance signal is supplied to a switch 6 for dropout compensation.
After passing through 3 and 64, it is input to the addition circuit 65. The switches 63 and 64 are switched by a signal from a dropout detection circuit 55. When the dropout detection circuit 55 detects a dropout, a dropout from a trap circuit 59 to be described later is used instead of a luminance signal. A luminance signal for compensation is input to the switch 64.

A frequency conversion circuit 56 converts a low-frequency-converted chroma signal at the time of recording into a high-frequency signal, and converts the original NTSC-type chroma signal (color subcarrier frequency (f _SC ) = 3.58).
(MHz). The converted chroma signal is mixed with the luminance signal in an adder 65 and then mixed with a comb filter circuit 66.
Is input to

The comb filter circuit 66 includes a 1H (horizontal scanning period) delay circuit 5 comprising a CCD (charge coupled device).
7, and an adder 67 for adding the signal delayed by 1H and the original signal, and a subtractor 68 for subtracting the signal delayed by 1H and the original signal, and cancels the crosstalk of the chroma signal. It has become.

The signal from the adder 67 is added by an adder 69 to a low-frequency luminance signal obtained by passing the output of the subtracter 68 through an LPF 58 (cutoff frequency: about 1 MHz).
After the luminance signal is extracted, the luminance signal is input to the luminance signal processing circuit 60, and processing such as noise cancellation is performed.

[0007] The signal from the subtractor 68 is input to a BPF (Band Pass Filter) 61, and after extracting a chroma signal, the signal is input to a chroma signal processing circuit 62, where processing such as burst de-emphasis is performed.

A luminance signal from the luminance signal processing circuit 60;
The chroma signal from the chroma signal processing circuit 62 is added to the adder 7
0 is mixed and output as a video signal.

The luminance signal for dropout compensation is output from the delay circuit 57 to the color subcarrier trap circuit 5.
9, and this signal is input to one terminal b of the switch 64.

As shown in FIG. 5, when the level of the FM signal from the RFAGC 52 drops to -15 dB, the dropout detection circuit 55 regards it as dropout and outputs a high-level signal. On the other hand, when the level of the FM signal recovers to -6 dB, it is considered that dropout has disappeared, and a low-level signal is output. The response speed is usually 15 to 20 μs.

As described above, the dropout detection circuit 5
By switching the switches 63 and 64 based on the signal from No. 5, compensation for dropout using the delay circuit 57 is performed, so that even if there is a dropout, the image is not interrupted. I have.

[0012]

However, in the above-mentioned conventional configuration, when a non-recording tape is reproduced, only the noise is output from the magnetic head 50. Therefore, RF
The gain of the AGC 52 is maximized to amplify noise.
As a result, countless dropout detection pulses are generated from the dropout detection circuit 55.
3, 64 are turned on and off little by little. As a result, the screen becomes unstable and has a problem of being unsightly.

[0013]

In order to solve the above-mentioned problems, a dropout compensation circuit according to the present invention determines that a dropout exists when the level of an FM signal read from a video tape is equal to or lower than a predetermined level. and drop-out detecting circuit for a magnetic recording and reproducing apparatus having a dropout compensation circuit for compensating a drop-out based on the determination result of the dropout detection circuit, a detection means for detecting a blank section of video tape, no recording Drop in part
In order not to perform the out-compensation, switch means is provided for preventing the detection result of the drop-out from being sent to the drop-out compensation circuit when the non-recorded portion is detected by the detection means. At
Detect the part where FM signal is not recorded for longer than the fixed time
Clogging detection means and
The recording signal and FM signal are recorded
Tracking control signal detection
Clogging detection means and tracking
Video based on the detection result of the control signal detection means
It is characterized in that a non-recorded portion of the tape is detected .

[0014]

According to the above arrangement, dropout compensation is not performed in a non-recorded portion of a video tape. As a result, in the non-recording portion, only white noise appears on the screen, and a stable screen can be obtained.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

The VTR of this embodiment is, as shown in FIG.
At the time of reproduction, the FM signal read from the video tape by the magnetic head 31 is amplified and waveform-shaped by the head amplifier / equalizer 1, and then input to the RFAGC (high-frequency automatic gain control circuit) 2 and the frequency conversion circuit 6. You.

The output of RFAGC 2 is supplied to FM demodulation circuit 3
, A dropout detection circuit 5, a clogging detection circuit 13 (detection means), and a tracking control signal detection circuit 14 (detection means). The signal obtained by the FM demodulation circuit 3 is passed through a low pass filter (LPF) 4 to extract a luminance signal. The luminance signal is input to the addition circuit 35 (dropout compensation circuit) via the switches 32 and 33 for dropout compensation (dropout compensation circuit).

The switches 32 and 33 are switched by a signal from the dropout detection circuit 5. Accordingly, when the dropout detection circuit 5 detects a dropout, a trap circuit 9 described later is used instead of the luminance signal.
The luminance signal for dropout compensation from the (dropout compensation circuit) is input to the adder 35.

The frequency conversion circuit 6 converts the low-frequency-converted chroma signal at the time of recording into a high-frequency signal, and converts the original NTSC-type chroma signal (color subcarrier frequency (f _SC ) = 3.58 M).
Hz). The converted chroma signal is mixed with the luminance signal by the adder 35 and then input to the comb filter circuit 36.

The comb filter circuit 36 is a 1H (horizontal scanning period) delay circuit 7 composed of a CCD (charge coupled device).
(Dropout compensation circuit), and an adder 37 for adding the signal delayed by 1H and the original signal, and a subtractor 38 for subtracting the signal delayed by 1H and the original signal. It is designed to cancel crosstalk.

The signal from the adder 37 is added to the low-frequency luminance signal obtained by passing the output of the subtracter 38 through the LPF 8 (cutoff frequency: about 1 MHz) by the adder 39, and the luminance signal is extracted. After that, the signal is input to the luminance signal processing circuit 10 and processing such as noise cancellation is performed.

The signal from the subtractor 38 is input to a BPF (Band Pass Filter) 11, and after extracting a chroma signal, the signal is input to a chroma signal processing circuit 12, where a process such as burst de-emphasis is performed.

A luminance signal from the luminance signal processing circuit 10;
The chroma signal from the chroma signal processing circuit 12 is added to the adder 4
0 is mixed and output as a video signal.

A luminance signal for dropout compensation is obtained by passing the output of the delay circuit 7 through the color subcarrier trap circuit 9, and this signal is input to one terminal b of the switch 33.

The above-mentioned dropout detection circuit 5 has an RF
When the level of the FM signal from the AGC 2 drops to -15 dB, it is regarded as dropout and a high-level signal is output. On the other hand, when the level of the FM signal recovers to -6 dB, it is considered that dropout has disappeared, and a low-level signal is output. Response speed is usually 15-20μ
s.

As described above, the dropout detection circuit 5
The switches 32 and 33 are switched on the basis of the signal from the controller to compensate for the dropout using the delay circuit 7, so that even if there is a dropout, the image is not interrupted. .

In the VTR of this embodiment, the signal from the dropout detection circuit 5 is sent to the switches 32 and 33 via the switch 34 (switch means). The switch 34 is switched by a signal from the AND circuit 15, and a signal from the dropout detection circuit 5 is not sent to the switches 32 and 33 in a non-recording portion on the video tape. . This makes it possible to prevent dropout compensation from working in the non-recorded portion.

The detection of the non-recorded portion on the video tape is performed by a clogging detection circuit 13, a tracking control signal detection circuit 14, and an AND circuit 15.

As shown in FIG. 2, the clogging detection circuit 13 comprises a dropout detection circuit 5, an LPF 16, and inverters 17 and 18, and outputs a dropout detection signal from the dropout detection circuit 5 to the LPF 16
To remove high frequency components. Thus, when the clogging detection circuit 13 detects the clogging of the magnetic head 31 or a non-recorded portion longer than several hundred ms on the video tape, the output goes high.

The output of the tracking control signal detection circuit 14 goes high when the level of the tracking error signal is below a predetermined level. That is, when a just tracking state is reached or a non-recorded portion on a video tape on which a tracking control signal is not recorded is detected, the level becomes a high level.

When the output of the clogging detection circuit 13 is at a high level and the output of the tracking control signal detection circuit 14 is at a high level, it is determined that the portion is a non-recording portion. As a result, the switch 34 is turned to the ground side (terminal b in the drawing). As a result, the signal from the dropout detection circuit 5 is not sent to the switches 32 and 33, and the switches 32 and 33 are fixed to the side where the luminance signal from the LPF 4 is input to the addition circuit 35 (to the terminal a in the figure). Is done. As a result, the dropout compensation does not work in the non-recording portion, so that only white noise appears on the screen, and a stable screen is obtained.

FIG. 2 shows an example of the configuration of an 8 mm standard VTR as an example of the tracking control signal detection circuit 14.

In the 8 mm standard, ATF (Auto-Track-Fin
ding System). ATF signals f _{1 to} f ₄
Are sequentially switched cyclically for each field as shown in FIG. 3, and are superimposed on the FM signal and recorded on the video tape. Frequency of the ATF signal f ₁ ~f ₄ is
When the horizontal synchronization frequency is f _H , f ₁ ≒ 6.5 f _H , f _1
2 ≒ 7.5f _H , f ₃ ≒ 10.5f _H , f ₄ ≒ 9.5f _H , and the ATF signal f ₁ between adjacent tracks
Frequency difference ~f ₄ has become f _H or 3f _H.
Thus, taking out the signal components of f _H and 3f _H, by comparing that level, the tracking error signal indicating the shift amount and shift direction from the track of the magnetic head 31 is obtained.

The signal from the RFAGC 2 is input to the balanced modulator 20 after high frequency components are removed by the LPF 19. In the balanced modulator 20, the reference signal (carrier) from the reference signal generator 21 is balanced-modulated by the reproduced signal. The reference signal generator 21 is a microcomputer 28
Is controlled by The output of the balanced modulator 20 is f
After being amplified by the tuned amplifier 24 _H tuning amplifier 22 and 3f _H of, is rectified and detected by the respective detection rectifier 23 and 23. The difference between these detection voltages is obtained by the comparator 25 and is taken out as a tracking error signal. Since the polarity of the tracking error signal is inverted for each field, a signal which is inverted by the inverter 26 and a signal which is not inverted are alternately extracted by the switch 41 which is switched for each field by the head switching pulse, and the polarity of the tracking error signal is obtained. Unify. The tracking error signal having the same polarity is supplied to the comparator 27 and the microcomputer 2 for controlling the tracking.
8 is input.

The output of the comparator 27 goes high when the level of the tracking error signal is lower than a predetermined level. That is, when a just tracking state is reached or a non-recorded portion on a video tape on which a tracking control signal is not recorded is detected, the level becomes a high level.

On the other hand, in a VHS standard VTR, a control track is provided on a video tape, and a control signal is taken out by a dedicated head.
The configuration of the tracking control signal detection circuit 14 is simpler than in the case of an 8 mm standard VTR. That is, the control signal is simply amplified, and if it is equal to or lower than the predetermined level, it may be determined that the portion is a non-recorded portion.

In the above, the switch 32 is provided for improving circuit performance such as prevention of noise leak.
If you think only about dropout compensation, you don't have to. Further, the dropout detection circuit 5 in the clogging detection circuit 13 may be configured so that the DC voltage obtained by envelope detection of the FM signal is compared by a comparator and the result is output. Good.

A VTR according to the present invention includes a dropout detecting circuit 5 for determining that there is a dropout when the level of an FM signal read from a video tape is lower than a predetermined level, and a determination result of the dropout detecting circuit 5. A VTR provided with a dropout compensation circuit (comprising a switch 33, an adder circuit 35, a delay circuit 7, and a track 9) for compensating for a dropout based on the video tape. A detection circuit 13, a tracking control signal detection circuit 14,
And a switch 34 for preventing the result of dropout from being sent to the dropout compensation circuit when the non-recording portion is detected by the detecting means. , No dropout compensation is performed. As a result, in the non-recording portion, only white noise appears on the screen, and a stable screen can be obtained.

[0039]

As described above, the magnetic recording / reproducing apparatus of the present invention detects the non-recording portion of the video tape and does not perform the dropout compensation in the non-recording portion.
And switch means for preventing the determination result of dropout from being sent to the dropout compensation circuit when the non-recorded portion is detected by the detection means.
Is the FM signal longer than the specified time on the video tape
Clogging detection means for detecting a portion where no data is recorded
And tracking control on videotape
Detect the part where the signal and FM signal are not recorded
Tracking control signal detection means,
Bar detection means and tracking control signal detection
The non-recorded part of the video tape
To detect. Therefore , in the non-recording portion, only white noise appears on the screen, and an effect is obtained that a stable screen can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a main part of a VTR according to the present invention.

FIG. 2 is a block diagram showing a configuration of a clogging detection circuit and a tracking control signal detection circuit in the VTR of FIG. 1;

FIG. 3 is an explanatory diagram showing a recording pattern of an ATF signal of 8 mm standard on a video tape.

FIG. 4 is a block diagram showing a configuration of a main part of a conventional VTR.

FIG. 5 is an explanatory diagram showing an operation of a dropout detection circuit in the VTR of FIG.

[Explanation of symbols]

Reference Signs List 5 dropout detection circuit 7 delay circuit (dropout compensation circuit) 9 trap circuit (dropout compensation circuit) 13 clogging detection circuit (detection means) 14 tracking control signal detection circuit (detection means) 15 AND circuit (detection means) ) 33 switch (dropout compensation circuit) 34 switch (switch means) 35 addition circuit (dropout compensation circuit)

Claims (1)

(57) [Claims] 1. A drop-out detection circuit for determining that a drop-out exists when the level of an FM signal read from a video tape is equal to or lower than a predetermined level, and compensating for the drop-out based on a determination result of the drop-out detection circuit. in the magnetic recording and reproducing apparatus having a dropout compensation circuit, and detecting means for detecting a blank section of the videotape, peeled
In order not to perform dropout compensation in the recorded part, switch means is provided to prevent the detection result of dropout from being sent to the dropout compensation circuit when the non-recorded part is detected by the detection means , and the detection means is provided with : , On videotape
Clogging to detect the part where FM signal is not recorded for a long time
Detection means and tracking code on the video tape.
Control signal and FM signal are not recorded
Tracking control signal detecting means for detecting
Clogging detection means and tracking control
Based on the detection result of the video signal detection means.
A magnetic recording / reproducing apparatus for detecting a recording portion .