JPH09247630A - Dropout compensation circuit, video reproducing device and video recording and reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dropout compensation circuit in which excessive dropout compensation is prevented in advance so as to conduct accurately vertical synchronizing signal separation in a vertical synchronizing signal at a monitor side. SOLUTION: A comparator 110 compares a reference voltage VREF1109 with a detection voltage VDET inputted by its inverting input terminal and when a level of the detection voltage VDET is lower than the reference voltage VREF1109, the comparator 110 outputs a dropout pulse to a switch 105 in response to the switching operation of a switch 111. The switching operation of the switch 111 is controlled by a vertical synchronizing pulse from a vertical synchronizing signal separator circuit 112. The vertical synchronizing pulse has a width for synchronization for a vertical synchronizing signal period, and the switch 111 receiving the vertical synchronizing pulse is open for the width of the vertical synchronizing pulse so as to open a path through from the comparator 110 to the switch 105.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dropout compensation circuit for performing dropout compensation on a video signal reproduced from a recording medium, a video reproduction device provided with the dropout compensation circuit, and a video recording / reproduction device.

[0002]

2. Description of the Related Art Generally, in a magnetic recording / reproducing apparatus such as a VTR, a reproduced signal may not be taken out from the magnetic recording medium due to a scratch or the like on the surface of the magnetic recording medium. The reproduced signal portion which cannot be taken out is corrected. In order to do so, dropout compensation is performed to replace that portion with a similar signal of 1H before. This dropout compensation is performed on the luminance signal of the reproduced signal. In the dropout compensation on the color signal, it is necessary to perform phase correction processing on the color signal itself so as to match the format of the television signal. The out-compensation circuit scale is large, and drop-out compensation for normal color signals is not performed.

VT equipped with this dropout compensation circuit
R will be described with reference to FIG. FIG. 3 is a block diagram showing a main part of a conventional VTR dropout compensation circuit.

As shown in FIG. 3, the VTR has a reproduction signal input terminal 101 for inputting a reproduction RF signal reproduced from a magnetic recording medium such as a magnetic tape. The reproduction RF signal input to the reproduction signal input terminal 101 is taken into the reproduction image signal processing circuit 113.

The reproduced image signal processing circuit 113 has an FM detection circuit 102. The FM detection circuit 102 detects the FM-modulated luminance signal and extracts a luminance signal including a video signal portion and horizontal / vertical synchronization signal portions. This luminance signal is output to the image signal processing circuit 103 together with the color signal.

The image signal processing circuit 103 performs image processing such as noise reduction processing and dropout compensation, and outputs a color signal together with a luminance signal from the video signal output terminal 106 as a reproduced video signal.

The dropout compensation circuit for performing the above-mentioned dropout compensation delays the luminance signal by one horizontal time.
An H delay circuit 104, a switch 105 for connecting the 1H delay circuit 104 and the image signal processing circuit 103, and a dropout pulse generation circuit 114 for controlling the switching operation of the switch 105.

The switch 105 is normally connected to the contact a, and the connection to the contact a returns the luminance signal from the image signal processing circuit 103 to the image signal processing circuit 103 again without delay processing. Be done. On the other hand, at the time of dropout compensation, the switch 105 performs the switching operation so as to select the connection with the contact b, and the 1H delay circuit 1
The luminance signal from 0 to 1 horizontal time ago is the image signal processing circuit 1
03 is input. The input luminance signal one horizontal time before is replaced with the portion where dropout has occurred, and dropout compensation is performed.

The switching operation of the switch 105 is controlled by the dropout pulse output from the dropout pulse generation circuit 114. The dropout pulse generation circuit 114 has a detection circuit 107 that takes in the reproduction RF signal via the reproduction signal input terminal 101. The detection circuit 107 performs detection on the reproduction RF signal, and the AC component of the detection output is removed by the low-pass filter 108.

The output from the low-pass filter 108 is input to the negative input terminal of the comparator 110 as a detection voltage. The positive input terminal of the comparator 110 is
The reference voltage VREF1109 is input. This reference voltage VRE
The value of F1109 is set to the lowest level of the reproduction RF signal that allows the reproduction image signal processing circuit 113 to extract the luminance signal from the reproduction RF signal input to the FM detection circuit 102. The comparator 110 has a reference voltage VRE.
F1109 is compared with the detection voltage input to the negative input terminal, and when the detection voltage level is lower than the reference voltage VREF1109, the above-mentioned dropout pulse is output from the output terminal to the switch 105.

Next, the dropout compensation operation will be described with reference to FIG. FIG. 4 is a diagram showing a signal waveform processed by dropout compensation in the VTR of FIG.

The reproduction signal input terminal 101 is shown in FIG.
As shown in, the reproduction RF signal reproduced from the magnetic recording medium is input. A dropout portion (level lowering portion at the center in the figure) is generated in the reproduced RF signal due to a scratch on the magnetic recording medium, and the dropout portion extends to a position near the vertical synchronizing signal portion. And The reproduction RF signal is taken in by the reproduction image signal processing circuit 113, and the dropout pulse generation circuit 1
It is taken in by 14.

In the dropout pulse generation circuit 114, the detection RF circuit 107 detects the reproduced RF signal, and the AC component of the detection output is the low-pass filter 10.
Removed at 8. The detection voltage VDET obtained by removing the AC component of the detection output has a voltage level decreasing portion corresponding to the dropout portion of the reproduction RF signal, as shown in FIG. 4 (b). This detection voltage VDET is input to the comparator 110.

In the comparator 110, as shown in FIG. 4B, the reference voltage VREF1109 is compared with the detection voltage VDET, and the detection voltage VDET level is the reference voltage VREF1109.
When it is lower, as shown in FIG. 4C, a dropout pulse having a width of a period in which the detected voltage level is lower than the reference voltage VREF1109 is output from the output terminal to the switch 105.

This dropout pulse causes the switch 105 to switch the connection from the contact point a to the contact point b for 1H.
The luminance signal of one horizontal time before is input from the delay circuit 104 to the image signal processing circuit 103. As shown in FIG. 4D, the input luminance signal one horizontal time before is replaced with the portion where dropout has occurred, and dropout compensation is performed.

[0016]

As described above, in the conventional VTR, the dropout portion in the reproduction RF signal is detected by comparing the detection voltage level VDET with the reference voltage VREF1109, and the detection voltage VDET level is detected as the reference voltage VREF1109. A dropout pulse is generated to provide dropout compensation during the lower period.

However, the value of the reference voltage VREF1109 in the comparator 110 is equal to the value of the reproduced image signal processing circuit 113.
In the above, since the FM detection circuit 102 is set to the lowest level of the reproduction RF signal from which the luminance signal can be extracted from the input reproduction RF signal, when the level of the vertical synchronizing signal portion is lower than the set level, Even if the reproduction image signal processing circuit 113 can perform synchronous processing on the low-level vertical sync signal portion, a dropout pulse is generated in a period including the vertical sync signal portion period, that is, the vertical sync signal portion is referred to as a dropout portion. Considering this, the vertical sync signal portion having a low level may be replaced with another signal one horizontal time before. Therefore, excessive dropout compensation is performed over the vertical sync signal portion having a low level, and a normal video signal output including the vertical sync signal portion cannot be obtained.

As described above, the vertical synchronizing signal portion having a portion replaced with another signal is not accurately separated from the video signal by the vertical synchronizing signal separation circuit on the monitor side, and vertical synchronization of the monitor cannot be obtained, so that the screen It causes problems such as flowing.

An object of the present invention is to provide a dropout compensating circuit capable of preventing excessive dropout compensation in advance so that the vertical synchronizing signal separation in the vertical synchronizing signal circuit on the monitor side can be accurately performed. It is to provide a reproducing apparatus and a video recording / reproducing apparatus.

[0020]

According to the first aspect of the present invention,
In a dropout compensation circuit that performs dropout compensation on a video signal reproduced from a recording medium, the dropout compensation circuit is set to prohibit execution of the dropout compensation during a vertical synchronization period of the video signal.

According to a second aspect of the present invention, in a video reproducing apparatus which performs dropout compensation on a video signal reproduced from a recording medium, execution of the dropout compensation is prohibited during a vertical synchronization period of the video signal. It is characterized by being set.

According to a third aspect of the invention, in a video recording / reproducing apparatus for performing dropout compensation on a video signal reproduced from a recording medium, execution of the dropout compensation is prohibited during a vertical synchronization period of the video signal. It is set to.

[0023]

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

FIG. 1 is a block diagram showing the configuration of the main part of a VTR equipped with an embodiment of the dropout compensation circuit of the present invention.

In the VTR, a reproduced signal may not be taken out from the magnetic recording medium due to a scratch or the like on the surface of the magnetic recording medium. In order to correct the reproduced signal part which cannot be taken out, the portion is reproduced 1H before. Perform dropout compensation to replace the existing signal.

As shown in FIG. 1, this VTR has a reproduction signal input terminal 101 for inputting a reproduction RF signal reproduced from a magnetic recording medium such as a magnetic tape. The reproduction RF signal input to the reproduction signal input terminal 101 is taken into the reproduction image signal processing circuit 113.

The reproduced image signal processing circuit 113 has an FM detection circuit 102. The FM detection circuit 102 detects the FM-modulated luminance signal and extracts a luminance signal including a video signal portion and horizontal / vertical synchronization signal portions. This luminance signal is output to the image signal processing circuit 103 together with the color signal.

The image signal processing circuit 103 performs image processing such as noise reduction processing and dropout compensation, and outputs a color signal together with a luminance signal from the video signal output terminal 106 as a reproduced video signal.

The dropout compensation circuit for performing the dropout compensation described above delays the luminance signal by 1 horizontal time.
The H delay circuit 104, the switch 105 for connecting the 1H delay circuit 104 and the image signal processing circuit 103, the dropout pulse generation circuit 114 for controlling the switching operation of the switch 105, and the vertical synchronization signal separation circuit 11
And 2.

The switch 105 is normally connected to the contact a, and the brightness signal from the image signal processing circuit 103 is returned to the image signal processing circuit 103 again without being delayed by the connection with the contact a. Be done. On the other hand, at the time of dropout compensation, the switch 105 performs the switching operation so as to select the connection with the contact b, and the 1H delay circuit 1
The luminance signal from 0 to 1 horizontal time ago is the image signal processing circuit 1
03 is input. The input luminance signal one horizontal time before is replaced with the portion where dropout has occurred, and dropout compensation is performed.

The switching operation of the switch 105 is controlled by the dropout pulse output from the dropout pulse generation circuit 114. The dropout pulse generation circuit 114 has a detection circuit 107 that takes in the reproduction RF signal via the reproduction signal input terminal 101. The detection circuit 107 performs detection on the reproduction RF signal, and the AC component of the detection output is removed by the low-pass filter 108.

The output from this low pass filter 108 is DC
The component detection voltage VDET is input to the negative input terminal of the comparator 110. The reference voltage VREF1109 is input to the positive input terminal of the comparator 110.
The value of the reference voltage VREF1109 is set to the lowest level of the reproduction RF signal from which the reproduction image signal processing circuit 113 can extract the luminance signal from the reproduction RF signal input to the FM detection circuit 102. Comparator 110
Compares the reference voltage VREF1109 with the detection voltage VDET input to the negative input terminal, and when the detection voltage VDET level is lower than the reference voltage VREF1109, outputs the above-mentioned dropout pulse to the switch 105.

This dropout pulse switch 10
The output to 5 is controlled by the intermittent operation of the switch 111, and the intermittent operation of the switch 111 is controlled by the vertical synchronizing signal separation circuit 112.

More specifically, the vertical sync signal separation circuit 112.
Takes in the reproduced video signal from the image signal processing circuit 113 and detects the vertical synchronizing signal from this video signal. A vertical sync pulse having a width corresponding to the vertical sync period while synchronizing with the detected vertical sync signal is generated by a free-running circuit in the vertical sync signal separation circuit 112, and the vertical sync pulse is output to the switch 111. . Switch 1
When the vertical synchronizing pulse is applied, the reference numeral 11 suspends for a period of the vertical synchronizing pulse width, and the disconnecting operation opens the path from the comparator 110 to the switch 105. On the other hand, when the vertical synchronizing pulse is not input to the switch 111, the switch 111 performs the connecting operation during the period when the vertical synchronizing pulse is not input, and the connecting operation closes the path from the comparator 110 to the switch 105.

Next, the dropout compensation operation will be described with reference to FIG. FIG. 2 is a diagram showing a signal waveform processed by dropout compensation in the VTR of FIG.

The reproduction signal input terminal 101 is shown in FIG.
As shown in, the reproduction RF signal reproduced from the magnetic recording medium is input. A dropout portion (level lowering portion at the center in the figure) is generated in the reproduced RF signal due to a scratch on the magnetic recording medium, and the dropout portion extends to a position near the vertical synchronizing signal portion. And The reproduction RF signal is taken in by the reproduction image signal processing circuit 113, and the dropout pulse generation circuit 1
It is taken in by 14.

In the dropout pulse generation circuit 114, the detection RF circuit 107 detects the reproduced RF signal, and the AC component of the detection output is the low-pass filter 10.
Removed at 8. The detection voltage VDET obtained by removing the AC component of the detection output has a voltage level decreasing portion corresponding to the dropout portion of the reproduction RF signal, as shown in FIG. 2B. This detection voltage VDET is input to the comparator 110.

In the comparator 110, as shown in FIG. 2B, the reference voltage VREF1109 is compared with the detection voltage VDET, and the detection voltage VDET level is the reference voltage VREF1109.
When it is lower, the detected voltage level is VREF110
A dropout pulse having a width of a period shorter than 9 is output from the output terminal, and the width of the dropout pulse is restricted by the intermittent operation of the switch 111. Specifically, as shown in FIGS. 2C and 2F, the vertical synchronization signal separation circuit 112 synchronizes with the vertical synchronization signal detected from the reproduced video signal from the image signal processing circuit 113 to synchronize the vertical synchronization period. A vertical synchronizing pulse having a width corresponding to the
1 performs an interruption operation during the period of the vertical synchronizing pulse width, and this interruption operation causes the comparator 110 to switch 10
Since the paths up to 5 are opened, the width of the dropout pulse is regulated so as not to be included in the vertical synchronizing signal period.

As the connection of the switch 105 is switched from the contact point a to the contact point b by the dropout pulse, the brightness signal of one horizontal time before is input from the 1H delay circuit 104 to the image signal processing circuit 103. As shown in FIGS. 2D and 2E, the input luminance signal one horizontal time before is replaced with a portion where dropout has occurred except for the vertical synchronizing signal portion, and dropout compensation is performed.

As described above, the dropout pulse having the width over the period including the vertical synchronizing signal portion period is not output, and it is possible to prevent the vertical synchronizing signal portion from being replaced with another signal one horizontal time before, and the monitor A reproduced video signal capable of accurately performing vertical sync signal separation in the vertical sync signal circuit on the side is output from the video signal output terminal 106. Therefore, since the vertical sync signal separation circuit on the monitor side cannot accurately separate the vertical sync signal from the reproduced video signal, the vertical sync of the monitor cannot be achieved, and a problem such as a screen flow can be eliminated. .

[0041]

As described above, according to the dropout compensating circuit of the first aspect, execution of the dropout compensation is prohibited during the vertical synchronizing period of the video signal. Excessive dropout compensation can be prevented in advance so that the vertical synchronization signal separation in the vertical synchronization signal circuit can be accurately performed.

According to the video reproducing apparatus of the second aspect, since the execution of the dropout compensation is prohibited during the vertical synchronizing period of the video signal, the vertical synchronizing signal separation in the vertical synchronizing signal circuit on the monitor side is performed. Excessive dropout compensation can be prevented in advance so that can be performed accurately.

According to the video recording / reproducing apparatus of the third aspect of the present invention, it is set so that the execution of the dropout compensation is prohibited during the vertical synchronizing period of the video signal. Therefore, the vertical synchronizing signal in the vertical synchronizing signal circuit on the monitor side is set. Excessive dropout compensation can be prevented in advance so that the separation can be done accurately.

[Brief description of drawings]

FIG. 1 is a block diagram showing a main part configuration of a VTR equipped with an embodiment of a dropout compensation circuit of the present invention.

FIG. 2 is a diagram showing a signal waveform processed by dropout compensation in the VTR of FIG.

FIG. 3 is a block diagram showing a main part of a dropout compensation circuit of a conventional VTR.

4 is a diagram showing a signal waveform processed by dropout compensation in the VTR of FIG.

[Explanation of symbols]

 102 FM detection circuit 103 Image signal processing circuit 104 1H delay circuit 105, 111 Switch 107 Detection circuit 108 Filter 109 Reference voltage 110 Comparator 112 Vertical sync signal separation circuit 113 Reproduced image signal processing circuit 114 Dropout pulse generation circuit

Claims (3)

[Claims] 1. A dropout compensation circuit for performing dropout compensation for a video signal reproduced from a recording medium, wherein the dropout compensation circuit is set to prohibit execution of the dropout compensation during a vertical synchronization period of the video signal. Dropout compensation circuit characterized by. 2. A video reproducing apparatus for performing dropout compensation on a video signal reproduced from a recording medium, wherein the dropout compensation is prohibited during the vertical synchronization period of the video signal. Characteristic video playback device. 3. A video recording / reproducing apparatus for performing dropout compensation on a video signal reproduced from a recording medium,
A video recording / reproducing apparatus, which is set so as to prohibit execution of the dropout compensation during a vertical synchronization period of the video signal.