JP3543556B2 - Digital sync separator - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a digital sync separation apparatus for detecting a sync signal from a signal having a sync signal such as a signal reproduced by a video tape recorder.
[0002]
[Prior art]
Generally, in a video tape recorder (hereinafter abbreviated as VTR) that uses a magnetic tape as a recording medium and records and reproduces an analog signal having a synchronization signal, a signal level changes (hereinafter abbreviated as sag) by repeating dubbing. Occurs.
[0003]
This sag causes the digital sync separation device to malfunction and cause image quality degradation.
[0004]
Hereinafter, an example of a conventional digital sync separation device will be described with reference to the drawings. FIG. 2 is a block diagram showing a configuration of a conventional digital sync separation circuit device. In FIG. 2, a reproduction signal such as a VTR is input from an input terminal 30. In this conventional example, it is assumed that the reproduction signal of the VTR is an NTSC signal. The NTSC signal input from the input terminal 30 is input to the noise removal filter 31. The noise removal filter 31 is a low-pass filter that can pass frequency components of 100 kHz or less, and removes noise components. The output of the noise removal filter 31 is input to a threshold comparator 32 and compared with a threshold generated by a threshold constant generator 33. The comparison result from the threshold comparator 32 is output from the output terminal 34 as an NTSC composite synchronization signal. For example, Japanese Patent Application Laid-Open No. 2-260767 is known as a conventional technique as described above.
[0005]
[Problems to be solved by the invention]
However, the above-described conventional digital sync separation apparatus has a problem that when a signal in which sag is generated is input, the detection of the sync signal is incomplete. An example is shown in FIG. It is assumed that a signal in which sag occurs like the signal 40 in FIG. 3 is input from the input terminal 30 in FIG. Assuming that the threshold value generated from the threshold constant generator 33 in FIG. 2 is a threshold value 41 indicated by a broken line in FIG. 3, a signal 42 shown in FIG. 3 is output from the output terminal 34 in FIG. In this signal 42, there is a portion where the synchronization signal is not detected. That is, the detection of the synchronization signal is incomplete.
[0006]
SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, and provides a digital sync separation apparatus capable of detecting a sync signal even when a signal in which sag occurs is input.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, a digital synchronization separation apparatus according to the present invention includes a noise removal unit that removes a noise component of a digital signal having a synchronization signal and a minimum value of a signal from the noise removal unit at predetermined time intervals. Minimum value detecting means for detecting, adding means for adding a predetermined value serving as a reference threshold to a signal from the minimum value detecting means, register means for holding the threshold value, a signal from the adding means and a signal from the register means Difference comparing means for detecting whether or not the difference value of the signal falls within a certain range, and controlling the selection of a signal to be inputted to the register means based on the detection result; a signal from the adding means and a signal from the register means. compares the magnitude relationship between, 20 minutes of a predetermined value as a reference of the threshold value to a signal from the register means when the signal from the summing means is greater than the signal from the register means 1 value added value, and outputs the subtracted value to a value of one twentieth of a predetermined value as a reference of the threshold value to a signal from when the register means less, equal to the value of the signal from the register means, respectively In response to a signal from the difference comparing means, the difference calculating means includes a signal from the adding means when the difference value between the signal from the adding means and the signal from the register means is within a certain range. If the difference between the signal from the adding means and the signal from the register means is not within a certain range, the selector means outputs the signal from the increase / decrease calculating means to the register means, respectively, the signal from the register means and the noise removal. And a threshold comparing means for comparing with a signal from the means.
[0008]
Then, by changing the threshold level according to the detected minimum value, the threshold level operates so as to follow the level of sag, and a synchronization signal can be detected even from a signal in which sag is occurring.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a digital synchronization signal separation device according to an embodiment of the present invention will be described with reference to the drawings.
[0010]
FIG. 1 is a block diagram showing a configuration of a digital synchronization signal separation device according to the present embodiment. FIGS. 4 and 5 are waveform diagrams showing the operation of the digital sync separation apparatus of FIG. In FIG. 1, a digital signal having a synchronization signal is input from an input terminal 10. Here, an NTSC signal is used as a digital signal having a synchronization signal. In addition, the height of the synchronizing signal of the normally input NTSC signal is 8 in the lower part and 64 in the upper part in 8 bits. The noise removing filter 11 is a noise removing unit that removes a component of 100 kHz or more of the signal input from the input terminal 10. The minimum value detector 12 is a minimum value detection unit that detects the minimum value of the signal from the noise removal filter 11 at intervals of 60 μsec. The offset adder 13 is an adding unit that adds a constant 20 to the signal from the minimum value detector 12. The value output from the offset adder 13 is D1. The register 20 is register means for holding a threshold. The value output from the register 20 is D2. The difference comparator 17 calculates the difference value (D1−D2) assuming that the constants A = −15 and B = 15, and determines whether the difference value falls within the range of A <(D1−D2) <B. Is a difference comparing means for detecting The increase / decrease calculator 18 is an increase / decrease calculating unit that outputs (D2-1) when D1 <D2, outputs (D2 + 1) when D1> D2, and outputs D2 when D1 = D2. The value output from the increase / decrease calculator 18 is D3. The selector 19 is a selection unit that outputs the value of D1 or D3 to the register 20 according to a signal from the difference comparator 17. The selector 19 outputs D1 (terminal A) when the result of the difference comparator 17 is within the range of A <(D1-D2) <B, and outputs D3 (terminal B) otherwise. Is output. The threshold comparator 15 is a threshold comparing unit that compares the value from the register 20 with the value from the noise removal filter 11. The output terminal 16 outputs the comparison result from the comparator 15 as a synchronization signal.
[0011]
The operation of the digital synchronization separation apparatus configured as described above will be described below with reference to FIGS.
[0012]
First, FIG. 4 shows a case where an input video signal has a sag. The output of the noise removal filter 11 is a signal 50, and the output of the register 20 is a threshold 51 indicated by a broken line. In this case, it is assumed that the minimum value detected by the minimum value detector 12 at intervals of 60 μs satisfies A <(D1−D2) <B. As can be seen from FIG. 4, the level of the threshold 51 follows the level of sag. By this operation, the synchronization signal output from the output terminal 16 becomes the signal 52, which indicates that the synchronization signal has been correctly detected.
[0013]
FIG. 5 shows a case where the synchronization signal of the input video signal is missing for some reason. The output of the noise removal filter 11 is a signal 60, and the output of the register 20 is a threshold 61. In this case, since the minimum value detected by the minimum value detector 12 at intervals of 60 μs does not satisfy A <(D1−D2) <B in a range where the synchronization signal is missing, the threshold value output from the register 20 is used. Has only changed one at a time. The synchronizing signal output from the output terminal 16 is a signal 62. In a range where the synchronizing signal is missing, the synchronizing signal is a missing signal. By this operation, even in the range where the synchronization signal is missing, the signal of the video portion is not erroneously separated as the synchronization signal.
[0014]
With the configuration described above, a noise removing unit that removes a noise component of a digital signal having a synchronization signal, a minimum value detecting unit that detects a minimum value of a signal from the noise removing unit at a certain time interval, and a minimum value Adding means for adding a value to the signal from the detecting means, register means for holding a threshold value, and difference comparing means for detecting whether the difference between the signal from the adding means and the signal from the register means is within a certain range. An increase / decrease calculating means for adding or subtracting a value from a signal from the register means according to the result of comparing the magnitude relation between the signal from the adding means and the signal from the register means, and an addition according to a signal from the difference comparing means Selecting means for outputting either the signal from the means or the signal from the increase / decrease calculating means to the register means, the signal from the register means and the signal from the noise removing means By providing the threshold comparison means to compare, even from the signal occurring in the sag, it can be detected synchronization signal.
[0015]
Note that the frequency characteristics and constants used in the present embodiment are reference values, and appropriate values are set according to the level that follows the sag. Further, the method of the present invention can be applied to a case where a synchronization signal is separated from a digital signal whose DC level is not determined. In that case, the detection cycle of the minimum value detector 12 is set to be longer than the interval of the synchronization signal, and the threshold value calculator 14 in FIG.
[0016]
【The invention's effect】
As described above, the present invention provides a noise removing unit for removing a noise component of a digital signal having a synchronization signal, a minimum value detecting unit for detecting a minimum value of a signal from the noise removing unit at a certain time interval, and a minimum value detecting unit. Addition means for adding a value to a signal from the means, register means for holding a threshold, difference comparison means for detecting whether the difference between the signal from the addition means and the signal from the register means is within a certain range, Increase / decrease calculating means for adding or subtracting a value from the signal from the register means in accordance with the result of comparing the magnitude relationship between the signal from the adding means and the signal from the register means; and adding means in accordance with the signal from the difference comparing means The selector which outputs either the signal from the controller or the signal from the increase / decrease calculating means to the register means, compares the signal from the register means with the signal from the noise removing means. By providing the threshold comparison means for obtaining the synchronization signal, the synchronization signal can be accurately detected even from the signal in which the sag is generated. The synchronization signal can be detected at the same time.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a digital synchronization signal separation device according to an embodiment of the present invention; FIG. 2 is a block diagram showing a configuration of a conventional digital synchronization signal separation device; FIG. FIG. 4 is a waveform diagram showing the operation of the digital synchronization signal separation device of the present invention. FIG. 5 is a waveform diagram showing the operation of the digital synchronization signal separation device of the present invention.
DESCRIPTION OF SYMBOLS 10 Input terminal 11 Noise removal filter 12 Minimum value detector 13 Offset adder 14 Threshold calculator 15 Threshold comparator 16 Output terminal 17 Difference comparator 18 Increase / decrease calculator 19 Selector 20 Register

Claims (1)

Noise removing means for removing a noise component of a digital signal having a synchronization signal; minimum value detecting means for detecting a minimum value of the signal from the noise removing means at predetermined time intervals; and a signal from the minimum value detecting means. Adding means for adding a predetermined value serving as a reference threshold value, register means for holding the threshold value, and whether or not a difference value between a signal from the adding means and a signal from the register means is within a certain range. A difference comparing means for detecting and controlling selection of a signal to be inputted to the register means based on the detection result; and comparing a magnitude relation between a signal from the adding means and a signal from the register means. value signal obtained by adding a value of 1 for 20 minutes of a predetermined value greater than the signal to be a threshold of the reference to the signal from said register means from said register means from The value obtained by subtracting the value of 1 in 20 minutes when a small predetermined value that is a threshold value of the reference to the signal from said register means, equal to the increase and decrease calculation unit that outputs the value of the signal from said register means According to the signal from the difference comparing means, when the difference value between the signal from the adding means and the signal from the register means is in a certain range in the difference comparing means, the signal from the adding means, A selector unit for outputting a signal from the increase / decrease calculating unit to the register unit when a difference value between the signal from the adding unit and the signal from the register unit is not within a certain range; A digital synchronizing / separating device, comprising: a threshold comparing means for comparing a signal from the digital signal with a signal from the noise removing means.

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