JPH0332179A - Time axis correction device - Google Patents

Abstract

PURPOSE:To detect a time axis error with high accuracy and to obtain a stable video output by sampling a burst signal after an excess frequency band component for a period near the burst signal is eliminated. CONSTITUTION:The device is provided with a band stop filter 18 blocking the frequency component other than that near the burst signal in an input video signal 21, a selector 19 applying time division multiplex to a video signal 25 passing through the band stop filter 18 and the input video signal and a burst gate pulse generating circuit 17 applying a gate pulse 27 to the selector 19. Then the time axis error is detected by using the video signal 25 improving the S/N near the burst signal. The video signal in response to the time axis error is stored in the memory, thus, the time axis error is corrected by reading the video signal from the memory based on a reference synchronizing signal to obtain a stable video signal.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a time axis correction device, particularly a time axis correction device for removing time axis fluctuations from a video signal having time axis fluctuations such as a VTR playback signal. It is related to.

[Prior Art] FIG. 3 is a block diagram showing a configuration example of a conventional time axis correction device.

In the same figure, an analog-to-digital converter (hereinafter referred to as A/
D converter) (1), memory (2), digital
Analog converter (hereinafter referred to as D/A converter) (3),
A write clock generation circuit (4), a read clock converter (5), a video signal input terminal (6), a video signal output terminal (7), and an external reference synchronization signal input terminal (8) are shown.

Next, the operation of the above configuration will be explained.

Video signal input terminal (6) for video signals with time axis fluctuations
When inputted manually to the write clock generation circuit (4), it outputs a write clock that matches the time axis fluctuation of the video signal. Using this write clock, the A/D converter (1) samples the human video signal and converts it into PCM, and the sampled value is written into the memory (2).

On the other hand, the read clock generation circuit (5) creates a clock for reading the sampling data from the memory (2) based on the external reference synchronization signal inputted from the external reference synchronization signal input terminal (8), The sampling data is read from the memory (2) in synchronization with this read clock, and the read sampling data is converted back into an analog signal by the D/A converter (3).

Through the above process, time axis fluctuations are removed from the human input video signal, and an output video signal whose time axis is stabilized in synchronization with the external reference signal is obtained.

By the way, there are various means for generating the write clock as described above, and as an example, Japanese Patent Laid-Open No. 124385/1985 detects time axis fluctuations based on a burst signal included in a human-powered video signal and calculates the time. A means for rapidly responding to shaft variations is disclosed.

Figure 4 is a waveform diagram for explaining the principle of detecting sampling point shifts due to time axis fluctuations.If the period of the sine wave forming the burst signal is four times the sampling period, the burst signal can be sampled. As shown in the figure, four sample points are obtained per period.

The levels of each sample point are (Xl), (X2), (
X3), (X4), X1=B+As1nθ x2-B+As1n (θ+90@) −B +Ac
osθX3-B+Asin (θ+180°)-B-
Asin θ X4-B+As1n (θ+ 270')-B-A
cos θ. Here, the amplitude of the burst signal is (A), the DC level is (B), and the phase of the sampling point corresponding to the sampling point level (Xl) is (θ).

Therefore, Xl-X3-2A sin θ

If θ-0 is used as a reference for the sampling point, the deviation of the sampling point from the reference position can be found by calculating the phase (θ) of the sampling point. Therefore, by changing the phase of the sampling block according to the phase (θ) of the sampling point, a write clock corresponding to time axis fluctuations can be obtained.

FIG. 5 is a waveform diagram showing the timing when referring to the burst signal included in the input video signal. In FIG. 5, (9) is a human video signal, and a synchronization signal (10) separated from this input video signal (9) and a sampling period (11) of the burst signal are shown. Here, the horizontal synchronization signal is represented by negative polarity, and the sampling period of the burst signal is represented by positive polarity.

Furthermore, the portion (12) in the figure is a portion of the input video signal (9) that represents video information.

FIG. 6 is a spectrum diagram showing the frequency spectrum of the human-powered video signal (9). In Figure 6, (13)
represents the entire frequency spectrum of the human input video signal (9), and (14) and (15) represent the frequency spectra when focusing only on the sampling period of the burst signal shown in FIG.

The part (14) consists of the burst signal frequency fB and its vicinity, and the part (15) consists mainly of the DC component and the horizontal synchronization frequency component.

[Problems to be Solved by the Invention] Conventional time axis correction devices have the above-mentioned configuration, so even during the period near the burst signal, it is possible to sample the burst signal without particularly limiting the frequency band. As a result, noise in a frequency band other than the spectrum in the period near the burst signal may reduce the accuracy of detecting a forging phase shift at the sampling point, which is an issue that needs to be solved.

This invention was made to solve this problem, and suppresses noise during sampling of burst signals.
It is an object of the present invention to provide a time axis correction device that improves the accuracy of detecting phase shifts of sampling points.

[Means for Solving the Problems] A time axis correction device according to the present invention includes a band-elimination filter that blocks frequency components other than the vicinity of the burst signal waveform in a human-powered video signal, and a video signal that has passed through the band-elimination filter. a selector for multiplexing the human-powered video signal;
It has means for applying and storing a phase human input video signal corresponding to the time axis error detected through these, and for reading it out using a reference synchronization signal clock.

[Function] According to the present invention, components in the extra frequency range are blocked in the period near the burst signal of the human-powered video signal, so the phase shift of the burst signal can be detected with high precision, and stable detection can be achieved. You can expect it to work.

[Example] Hereinafter, an example of the present invention will be described based on the drawings.

FIG. 1 is a block diagram of a time axis correction device according to an embodiment of the present invention, in which an A/D converter (1),
Digital memory (2), D/A converter (3), write clock generation circuit (4), read clock generation circuit (
5), synchronous separation circuit (16), burst gate pulse generation circuit (17), band ejection filter (18), 2-man power 1-output selector (19), video signal input terminal (6), video signal output terminal (7) ), an external synchronization signal (8), and a delay line (20) are shown.

Next, the operation will be explained.

A human input video signal (21) having time axis fluctuation is input from the video signal input terminal (6), but in this invention, a band rejection filter (18 ) to pass.

Here, an example of the frequency-gain characteristic curve (22) of the band-elimination filter (18) is shown in FIG. Same figure (23), (
24) The frequency-gain characteristic is such that components in bands other than the frequency components included in the period near the burst signal indicated by diagonal lines are blocked.

Note that since frequency components higher than the burst signal frequency fn are limited in advance by the overall band fc, there is no need to provide them with attenuation characteristics.

After giving the input video signal (21) a delay time equal to the delay of the burst signal portion by the music rejection filter (18) in the delay line (20) shown in FIG. By time-division multiplexing with the filtered signal (25) that has passed through the band-elimination filter (18), a video signal (26) with an improved S/N ratio near the burst signal is obtained.

A timing signal for performing this time division multiplexing, that is, a burst gate pulse (27), is generated in a burst gate pulse generation circuit (17) based on a synchronization signal (28) separated by a synchronization signal separation circuit (16).

The above burst gate pulse (27) and synchronization signal (28)
The relationship between the timings of is shown in Figure 5 (11) and (10), respectively.
) is equivalent to the relationship.

The write clock generation circuit (4) generates a write clock (29) for A/D conversion and memory writing based on the separated synchronization signal (28). The video signal (30) converted into digital data by the A/D converter (1) is written into the memory (2) in synchronization with the write clock (29).

On the other hand, in the read clock generation circuit (5), a read clock (32) for memory reading and D/A conversion is generated based on an external reference synchronization signal (31) manually inputted from an external reference synchronization signal input terminal (8). The digital data is read out from the memory (2) in synchronization with this read clock (32), and the D/A converter (3)
It is returned to an analog signal (33).

Through the above process, time axis fluctuations are removed from the human input video signal, and an output video signal with a stable time axis in synchronization with the external reference signal is obtained.

As mentioned above, according to this embodiment, the input video signal (21)
A band-elimination filter (18) that blocks frequency components other than the vicinity of the burst signal in the band-elimination filter (18);
); a selector (19) for time-division multiplexing the video filtered signal (25) passed through the input video signal; and a burst gate pulse generation circuit (17) for supplying a gate pulse (27) to the selector (19). , the selector (19)
An analog-digital converter (1) that converts the output of the analog-digital converter (1), a memory (2) that stores the video signal output from the analog-digital converter (1), and a A time axis correction device comprising a write clock generation circuit (4) that stores a video signal in phase, and a read clock generation circuit (5) that reads the video signal from the memory (2) based on an external reference synchronization signal. By configuring this, the noise near the burst signal can be removed by the band rejection filter (18), the time axis error of the input video signal can be detected, and the video signal can be accurately stored in the memory according to the time axis error. Therefore, by reading video No. 73 from the memory based on the reference synchronization signal, a stable video signal with time axis errors corrected can be obtained.

[Effects of the Invention] According to the present invention, as explained above, after removing the extra frequency band components in the period near the burst transmission,
Since I configured it to sample the burst signal,
The time axis error can be detected with high precision, and the effect of being able to obtain stable video output can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a time axis correction device according to an embodiment of the present invention, FIG. 2 is a characteristic diagram showing an example of frequency-gain characteristics of a band rejection filter, and FIG. 3 is a conventional time axis correction device. Jif
Figure 4 is a waveform diagram for explaining the principle of detecting sampling point shifts due to time axis fluctuations; Figure 5 is a waveform diagram showing the timing when referring to burst signals; FIG. 6 is a spectrum diagram showing the frequency spectrum of a human-powered video signal. In the figure, (1) is an A/D converter, (2) is a memory,
(3) is a D/A converter, (4) is a write clock generation circuit, (5) is a read clock generation circuit, (6) is a video signal input terminal, (7) is a video signal output terminal, (8) ) is the input terminal for the external reference synchronization signal, (9) is the input video signal,
(1o) is the synchronization signal, (11) is the sampling period, (
12) is the video information part, (13) is the frequency spectrum,
(14) is the burst signal frequency spectrum, (15) is the DC horizontal synchronization frequency spectrum, (16) is the synchronization separation circuit, (17) is the burst gate pulse generator, (18)
) is a band rejection filter, (19) is a two-man output selector, (2o) is a delay line, (21) is an input video signal, (2
2) is a frequency-gain characteristic curve, (23) and (24) are burst signals, (25) is a filtered signal, (26) is a video signal, (27) is a burst gate pulse, (28) is a domei signal, (29) is a write clock, (3o) is a video signal, (31) is an external reference synchronization signal, (32) is a read clock, and (33) is an analog signal. In addition, the same symbols in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] A band rejection filter that blocks frequency components other than those near the burst signal in the input video signal, a selector that time-division multiplexes the video filtered signal that has passed through the band rejection filter and the input video signal, and a gate pulse applied to the selector. A burst gate pulse generating circuit to supply, an analog-to-digital converter for converting the output of the selector, a memory for storing the video signal output from the analog-to-digital converter, and a phase input signal to the memory according to the time axis error. A time axis correction device comprising: a write clock generation circuit that stores a video signal in the memory; and a read clock generation circuit that reads the video signal from the memory based on an external reference synchronization signal.