JP2001128030A - Digital synchronizing signal separator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correctly display characters by preventing the characters from fluctuating from side to side in accordance with the timing change of a horizontal synchronizing signal when the character outputted on a screen with the horizontal synchronizing signal separated from a composite synchronizing signal as a reference. SOLUTION: This separator is provided with a first (is provided with a first) threshold calculation means calculating a first threshold from a digital signal having a synchronizing signal, a first threshold comparison means comparing a first threshold with the digital signal and outputting a first synchronizing signal a vertical synchronizing signal separation means separating a vertical synchronizing signal from the first synchronizing signal, a horizontal synchronizing signal separation means separating the horizontal synchronizing signal from the first synchronizing signal, a second threshold calculation means calculating a second threshold from the digital signal with the horizontal synchronizing signal as the reference, a selection means switching and outputting the first and second thresholds with the vertical synchronizing signal as the reference and a second threshold comparison means comparing the output of the selection means and the digital signal and outputting a second synchronizing signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital synchronizing signal separating apparatus for detecting a synchronizing signal from a signal having a synchronizing signal such as a reproduction signal from a video tape recorder.

[0002]

2. Description of the Related Art Conventionally, a digital synchronizing signal separating apparatus described in Japanese Patent Application Laid-Open No. 11-75085 is known.

FIG. 3 shows a conventional digital synchronizing signal separating apparatus.
Shown in FIG. 3 is a block diagram showing a conventional digital synchronizing signal separating apparatus. 3, 10 is an input terminal, 12 is a threshold comparing unit, 18 is an output terminal, 20 is a minimum value detecting unit, 21 is an adding unit, 22 is a threshold holding unit, 23 is a difference comparing unit, 24 is an increase / decrease calculating unit, 25 is a threshold value selection unit.

[0004] The operation of the conventional digital synchronizing signal separating apparatus constructed as described above will be described below taking the case of an NTSC signal as an example.

First, an 8-bit AD-converted digital signal having a synchronization signal is input from an input terminal 10. This digital signal takes a value from 0 to 255. The minimum value detector 20 detects the minimum value of the digital signal at intervals of, for example, 35 × 10 ⁻⁶ [s]. The addition unit 21 adds, for example, a constant value 20 to the minimum value. The value output from the adding unit 21 is D1. The value output from the threshold value holding unit 22 that holds the threshold value is D2. Then, the increase / decrease calculator 24 calculates (D2-1) when D1 <D2, (D2 + 1) when D1> D2, and D1
If = D2, D2 is output. This is D3.

On the other hand, assuming that the constants A = -15 and B = 15,
A difference value (D1-D2) is calculated, and this difference value is A <(D
1-D2) According to the output value of the difference comparison unit 23 that detects whether the difference is within the range of <B, the threshold value selection unit 25
The value of D1 or D3 is output to the threshold value holding unit 22. Specifically, when the result of the difference comparison unit 23 is in the range of A <(D1−D2) <B, D1 is output, and in other cases, D3 is output. Finally, the input digital signal is compared with the output value D2 of the threshold value holding unit 22 by the threshold value comparison unit 12, and the comparison result is output from the output terminal 18 as a composite synchronization signal.

[0007]

However, in the above-mentioned conventional digital synchronizing signal separating apparatus, the threshold value changes at intervals of 35 × 10 ^-6 [s], which is the minimum value detection period. As a result, the timing of the composite synchronization signal changes. For this reason, for example, when characters are output on the screen based on the horizontal synchronization signal separated from the composite synchronization signal, the characters swing right and left in accordance with the timing change of the horizontal synchronization signal, and there is a problem that the characters are not displayed correctly. Was. An example is shown in FIGS.

A digital signal 50 as shown in FIG.
Is assumed to have been input from the input terminal 10 of FIG. Here, the sync signal level of the normally input NTSC signal has a sync tip level of 8 and a pedestal level of 64.
It is. First, assuming that the time interval for the minimum value detection unit 20 to detect the minimum value is 35 × 10 ⁻⁶ [s], the output of each minimum value is as shown by 51 in FIG. However, a constant 20 is added by the adding unit 21. Therefore, in the minimum value detection period 52, the output of the threshold value holding unit 22 is D2 = 2
8. The output of the adder is D1 = 84, and the difference between the two is A <
(D1-D2) <B is not within the range, and D1
> D2, the threshold value is (D2 + 1) = 29. In the minimum value detection period 53, D2 = 29 and D1 = 28
And the difference is in the range of A <(D1-D2) <B, and since D1 <D2, the threshold value is (D2-1) = 28
Becomes Therefore, the threshold value finally changes at intervals of 35 × 10 ⁻⁶ [s], as indicated by 54 in FIG.

FIG. 5 shows how the threshold value fluctuates. For example, if the threshold value fluctuates from the threshold value 61 in FIG. 5 to the threshold value 62, the horizontal synchronization signal separated based on the threshold value is 63,
It looks like 64. When the character A is inserted at a position delayed by the time T with respect to these horizontal synchronization signals, the insertion position of the character is shifted by one horizontal synchronization by Δt as shown in FIG. That is, there is a problem that the character is shaken in accordance with the fluctuation of the horizontal synchronization signal.

An object of the present invention is to solve the above-mentioned conventional problems and to provide a digital synchronizing signal separating apparatus capable of detecting a synchronizing signal stably without occurrence of character fluctuation on a screen. .

[0011]

To achieve this object, a digital synchronization signal separating apparatus according to the present invention comprises: a first threshold value calculating section for calculating a first threshold value from a digital signal having a synchronization signal; A first threshold comparing unit that compares the digital signal with a threshold value and outputs a first synchronizing signal; a vertical synchronizing signal separating unit that separates a vertical synchronizing signal from the first synchronizing signal; A horizontal synchronization signal separator for separating the horizontal synchronization signal; a second threshold calculator for calculating a second threshold from the digital signal based on the horizontal synchronization signal; and a first threshold and a second threshold based on the vertical synchronization signal And a second threshold comparator for comparing the output of the selector with the digital signal and outputting a second synchronizing signal.

With this configuration, a digital synchronizing signal separating apparatus capable of detecting a synchronizing signal so that the position of a character on the screen does not shift can be obtained.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the first aspect of the present invention, a first threshold value calculating section for calculating a first threshold value from a digital signal having a synchronization signal, and comparing the first threshold value with the digital signal. A first threshold comparing section for outputting a first synchronization signal; a vertical synchronization signal separating section for separating a vertical synchronization signal from the first synchronization signal; and a horizontal section for separating a horizontal synchronization signal from the first synchronization signal. A synchronizing signal separating unit, a second threshold calculating unit for calculating a second threshold from the digital signal based on the horizontal synchronizing signal, and switching and outputting the first threshold and the second threshold based on the vertical synchronizing signal A selector, and a second threshold comparator for comparing the output of the selector with the digital signal and outputting a second synchronizing signal, wherein the signal is calculated correctly during the video signal period. To output the synchronization signal from the threshold Ri, the synchronization signal so as not to shift the position of the character on the screen has the effect that can be detected.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1) FIG. 1 is a block diagram showing a configuration of a digital synchronization signal separating apparatus according to an embodiment of the present invention. In FIG. 1, 10 is an input terminal, 11
Denotes a first threshold value calculating unit which is a first threshold value calculating means for calculating a first threshold value from a digital signal having a synchronization signal;
Reference numeral 2 denotes a first threshold comparing section which is a first threshold comparing means for comparing the first threshold with a digital signal and outputting a first synchronizing signal, and 13 separates a vertical synchronizing signal from the first synchronizing signal. A vertical synchronizing signal separating unit as a vertical synchronizing signal separating means, 1
Numeral 4 denotes a horizontal synchronizing signal separating unit which is a horizontal synchronizing signal separating means for separating the horizontal synchronizing signal from the first synchronizing signal. A second threshold value calculation unit as a means, 16
Is a selection unit which is a selection means for switching and outputting a first threshold value and a second threshold value based on a vertical synchronization signal, and 17 is a unit for comparing the output of the selection unit 16 with a digital signal and outputting a second synchronization signal. This is a second threshold value comparison unit that is a second threshold value comparison unit that performs the operation. 18 is an output terminal.

Reference numeral 30 denotes a first average value detection unit which is a first average value detection means for detecting an average value in a first period based on the horizontal synchronization signal and outputting the first average value, and 31 denotes a horizontal synchronization signal. A second average value detection unit, which is a second average value detection means for detecting an average value of the second period based on the signal and outputting a second average value, includes a first average value and a second average value. A third average value detecting means for averaging the average value and outputting a third average value;
Is an average value holding unit that is an average value holding unit that holds a third average value and outputs a second threshold value, and their configuration is a second value calculation unit that is a second threshold value calculation unit. Is provided in the threshold value calculation unit 15.

Reference numeral 20 denotes a minimum value detection unit which is a minimum value detection means for detecting the minimum value of the digital signal at predetermined time intervals in the signal input from the input terminal 10, and 21 denotes an addition for adding a predetermined value to the minimum value. An addition unit 22 is a threshold holding unit which holds a threshold and outputs a first threshold. A threshold holding unit 23 is a threshold holding unit which outputs a first threshold when a difference between the output of the addition unit 21 and the first threshold falls within a predetermined range. A difference comparing unit 24, which is a difference comparing unit for detecting whether or not there is a difference, is an increase / decrease calculating unit which is an increase / decrease calculating unit for adding or subtracting a predetermined value to / from the first threshold value based on a result of comparing the output of the adding unit 21 with the first threshold value. And 25, a threshold selection unit that is a threshold selection unit that selects one of the output of the addition unit 21 and the increase / decrease calculation unit 24 based on the output of the difference comparison unit 23 and outputs the selected value as a threshold. Calculation means It is provided on the first threshold value calculation unit 11.

The operation of the digital synchronizing signal separating apparatus according to the present embodiment configured as described above will be described below. Here, a case where the digital signal having the synchronization signal is an NTSC signal will be described as an example.

A first threshold value calculating unit 11, which is a conventional threshold value calculating unit, calculates a first threshold value. The first synchronization signal is separated by comparing the threshold with the input digital signal in the first threshold comparator 12. The vertical synchronization signal is separated from the first synchronization signal by the vertical synchronization signal separation unit 13 and the horizontal synchronization signal is separated by the horizontal synchronization signal separation unit 14.

Next, as shown in FIG. 2, in a sync tip period 42 and a pedestal period 43 generated based on the horizontal synchronizing signal 41, the first average value detector 30 averages the sync tip portion of the digital signal. The second average value detector 31 calculates the average value of the pedestal portion of the digital signal. For example, they are averaged for a period of 1 × 10 ⁻⁶ seconds, respectively. Due to this averaging, the output of the first average value detection unit 30 and the output of the second average value detection unit 31 become almost constant values in any period.

Next, the two average values are further averaged by a third average value detection unit 32, and the average value holding unit 33 holds this average value as a second threshold value. This second threshold value is a threshold value obtained from the second threshold value calculation unit 15, and the threshold value is set to the selection unit 16 according to the output value of the vertical synchronization separation signal obtained earlier.
Output from Specifically, the first threshold is output during the vertical blanking period, and the second threshold, which is a substantially constant value, is output during the other periods. The threshold value output from the selection unit 16 and the input digital signal are compared by a second threshold value comparison unit 17, and the comparison result is output from an output terminal 18 as a synchronization signal.

The synchronization signal output from the output terminal 18 is
For example, if it is used as a reference for character display, it is possible to accurately and stably detect a synchronization signal even from a signal in which a signal variation (sag) occurs due to repeated dubbing, and the vertical and horizontal movement of a character can be detected. No shaking occurs.

As described above, according to the present embodiment, a synchronization signal can be accurately and stably separated from a digital signal having the synchronization signal.

The constants used in the above description are reference values. Also, the NTSC signal has been described as an example.
According to the present invention, a stable synchronization signal can be separated from a video signal having a synchronization signal such as AL or SECAM.

[0025]

As described above, according to the present invention, there is obtained an excellent effect that it is possible to prevent the characters and the like displayed on the screen from swaying and perform accurate and stable synchronization separation.

[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 waveform chart showing an operation of the digital synchronization signal separation device of the embodiment.

FIG. 3 is a block diagram of a conventional digital synchronization signal separation device.

FIG. 4 is a signal waveform diagram showing the operation of a conventional digital synchronization signal separation device.

FIG. 5 is a waveform chart showing an operation when a character is displayed by a conventional digital synchronization signal separation device.

[Explanation of symbols]

 Reference Signs List 11 first threshold calculator 12 first threshold comparator 13 vertical synchronization signal separator 14 horizontal synchronization signal separator 15 second threshold calculator 16 selector 17 second threshold comparator

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Takuya Otsuki 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. F-term (reference) 5C020 AA04 AA05 AA09 BA02 BA07 BA09 BA11 BB07 CA20

Claims (5)

[Claims] 1. A first threshold value calculating means for calculating a first threshold value from a digital signal having a synchronization signal, and a first threshold value comparing the digital signal with the first threshold value and outputting a first synchronization signal. Threshold comparing means; vertical synchronizing signal separating means for separating a vertical synchronizing signal from the first synchronizing signal; horizontal synchronizing signal separating means for separating a horizontal synchronizing signal from the first synchronizing signal; A second threshold value calculating means for calculating a second threshold value from the digital signal based on the reference; a selecting means for switching and outputting the first threshold value and the second threshold value based on the vertical synchronization signal; A second synchronizing signal separating device for comparing the output of the digital signal with the digital signal and outputting a second synchronizing signal. 2. The first threshold value calculating means includes a minimum value detecting means for detecting a minimum value of the digital signal at predetermined time intervals, an adding means for adding a predetermined value to the minimum value, and holding a threshold value. Threshold holding means for outputting a first threshold value; difference comparing means for detecting whether a difference between the output of the adding means and the first threshold value is within a predetermined range; According to the result of comparing the threshold value of the first, the first
An increase / decrease calculating means for adding or subtracting a predetermined value to or from the threshold value, and a threshold value selecting means for selecting one of the output of the adding means and the increase / decrease calculating means based on the output of the difference comparing means and outputting as the threshold value. 2. The digital synchronization signal separation device according to claim 1, wherein 3. The first threshold value calculating means detects an average value of a first period based on a horizontal synchronizing signal, and outputs a first average value. A second average value detecting means for detecting an average value of a second period based on the first average value and outputting a second average value;
A third average value detecting means for averaging the average value of the second and the third average value and outputting a third average value, and an average value holding means for holding the third average value and outputting the second threshold value. 2. The digital synchronization signal separation device according to claim 1, wherein: 4. The first period is a sync chip period,
4. The digital synchronization signal separation device according to claim 3, wherein the second period is a pedestal period. 5. The selection means selects and outputs a first threshold during a vertical blanking period based on a vertical synchronization signal, and selects and outputs a second threshold during periods other than the vertical blanking period. 4. The digital synchronizing signal separating device according to claim 1, 2, or 3.