JPH0632467B2 - VTR recording / reproducing video signal jitter detection method - Google Patents

Description

Description: [Industrial field of application] The present invention is suitable for VTR recording applied to a recording / reproducing apparatus or the like in which a luminance signal and a chrominance signal are time-axis multiplexed for recording / reproduction. The present invention relates to a method for detecting jitter in a reproduced video signal.

[Prior Art] A video signal reproduced from a recording / reproducing apparatus or the like has time axis fluctuation, that is, jitter. There are phase jitter and frequency jitter in the jitter, and the latter causes the expansion and contraction of the horizontal period in principle.

However, even in a home video composed of a relatively simple mechanical system, the amount of expansion and contraction due to frequency jitter is very small when viewed on the playback screen. From this, the stability of the reproduced image can be ensured only by correcting the phase jitter of the normal reproduced video signal.

This also means reduction of random noise using field or frame correlation, special video processing such as synthesis with two-channel video signals or fade-in / fade-out, or high-definition television (eg, IDTV).
Even in the digital processing operation for double-speed scanning, there is almost no possibility of causing any trouble in signal processing simply by correcting the phase jitter.

Now, FIG. 5 shows an example of a jitter detecting circuit 20 for phase jitter correction used in such a recording / reproducing apparatus (hereinafter referred to as VTR).

This figure shows an example of a jitter detection circuit used in a VTR for broadcasting. A composite video signal of NTSC system, PAL system or the like is directly recorded by an FM recording system.

The reproduced video signal a of, for example, the NTSC system (FIG. 6A) supplied to the terminal 1 is supplied to the sync separation circuit 2 and the horizontal sync signal b (B in FIG. 6) is extracted and separated. A burst gate pulse (not shown) formed from this horizontal synchronizing signal b is supplied to the burst gate circuit 3, and the burst signal c (C in the same figure) is separated therefrom.

The burst signal c is supplied to the narrow band bandpass filter 4 to be a burst signal d having a high C / N shown in FIG.

On the other hand, the horizontal synchronizing signal b is supplied to the delay pulse generating circuit 5 to form the delay pulse e as shown in FIG. 6E, and the burst signal d which has passed through the narrow band bandpass filter 4 and the jitter pulse forming circuit 6 are formed. The jitter detection pulse f as shown in FIG.
The leading edge phase of the jitter detection pulse f is delayed from the horizontal synchronizing signal b.

The trailing edge phase of the jitter detection pulse f is obtained by detecting a specific zero cross point of the burst signal d, and the trailing edge phase of the time axis correction circuit (TBC) is based on the falling timing of the jitter detection pulse f. The write timing is determined.

If there is a time axis fluctuation in the reproduced video signal a, the time axis of a specific zero-cross point in the burst signal d also changes accordingly. Therefore, in the TBC, the video signal is synchronized with this reproduction jitter. You can write.

By the way, TCI (Time Com
When the pressed integration) method is adopted, there is no burst signal as in the case of direct recording.

FIG. 7 shows an MTCI (Modified Tim) of the TCI recording system in which band-compressed color signals are line-sequentially recorded.
The signal format of the e Compressed Integration) method is shown.

The compressed component color signals, for example, the red and blue color difference signals RY and BY are inserted and multiplexed in the horizontal blanking period as shown in FIGS.

Y indicates a luminance signal. Red and blue color difference signals R-Y, B-
Ys are inserted line-sequentially.

In the case of a video signal adopting such a signal format, a jitter detection signal is usually obtained by detecting the rising or falling of the horizontal synchronizing signal.

[Problems to be Solved by the Invention] By the way, in the case of the TCI recording method as described above,
Since the jitter detection signal is detected on the basis of the falling edge or the rising edge of the horizontal synchronizing signal, there is a drawback that sufficient jitter detection accuracy cannot be obtained.

A case where the jitter detection signal is formed with reference to the falling edge of the horizontal synchronizing signal will be described with reference to FIG.

Since the noise N having a normal phase and random level is superimposed on the horizontal synchronizing signal, even if the detection level is set to A, the detection timing fluctuates by ΔT depending on the phase of the superimposed noise N. This fluctuation amount (the amount of fluctuation on the time axis, that is, the amount of synchronization jitter) ΔT affects the jitter detection accuracy.

For example, the fluctuation amount ΔT at an intermediate level of a horizontal synchronizing signal having a signal band of 4 MHz and an S / N ratio of 40 dB will be roughly estimated.

As shown in FIG. 9, when the amplitude of the horizontal synchronizing signal is 1 V _PP , the effective value of the noise N superimposed on the horizontal synchronizing signal b having the amplitude of 0.3 V is about 10 mV. Also, assuming that the falling waveform of the horizontal synchronizing signal can be approximated by a 1/2 cycle of a 4 MHz sine wave, the level gradient K at its center
Is K = 125 ns / (0.3 (π / 2) V) = 265 ns / V.

Assuming that the peak-peak value of the superimposed noise N is 6 times the effective value, the PP value of the variation amount ΔT is ΔT _PP = 265 × 0.01 × 6 = 16 ns. That is, the degree of jitter detection is 1 due to noise.
It cannot be suppressed below 6 nsec.

In addition to this, the detection level may fluctuate from A to B. Even if the detection level changes, the jitter detection accuracy changes significantly. In order to suppress the fluctuation amount ΔT ′ to 20 nsec or less, the fluctuation of the detection level must be suppressed to 50 mV or less. However, when such accuracy is required, the cost of the detection level forming circuit is significantly increased. It is hard to say that it is a very good solution.

The fluctuation of the detection level is also caused by the fluctuation of the clamp level or the fluctuation of the amplitude of the video signal.

Since the above-mentioned estimated value is based on the assumption that the circuit is configured with high accuracy, it is considered that the fluctuation amount ΔT sometimes reaches about 100 nsec in consideration of a consumer VTR.

As described above, when the jitter detection signal is formed with the rise of the horizontal synchronizing signal as a reference, there is a problem that sufficient jitter detection accuracy cannot be obtained.

In view of this, the present invention solves the above-mentioned conventional problems and improves the jitter detection by a VTR.
It proposes a method for detecting a jitter of a recording / reproducing video signal.

[Technical Means for Solving Problems] In order to solve the above problems, in the present invention, a VTR recording / reproducing image in which a luminance signal and a chrominance signal are time-axis multiplexed for recording / reproduction. In the signal jitter detection method, when the video signal was recorded, the leading edge phase of the horizontal sync signal and the phase of the FM carrier corresponding to the sync peak value were recorded at each horizontal sync, and FM demodulated at the time of playback. It is characterized in that the jitter of the reproduced video signal is detected by detecting a specific zero-cross point of the FM carrier in a narrow band with reference to the trailing edge of the horizontal synchronizing signal.

[Operation] One of the greatest features of this jitter detection method is that the FM carrier is also used as a signal corresponding to a burst signal.

Therefore, at the time of FM recording of the video signal, the leading edge of the horizontal sync signal and the phase of the FM carrier corresponding to the sync peak value are recorded in synchronization with each horizontal sync. That is, for each horizontal sync,
The leading edge of the horizontal sync signal resets the FM carrier corresponding to the sync peak value.

The second feature of this jitter detecting method is that a delay pulse for detecting a zero-cross point is formed by the trailing edge of the horizontal synchronizing signal when the video signal is reproduced.

The trailing edge of the demodulated horizontal sync signal is less affected by phase fluctuations due to FM carrier phase fluctuations, and the sync jitter is equivalent to 1/2 cycle (for a 3.4 MHz carrier, 15
It can be made sufficiently smaller than 0 ns). As a result, the gate circuit generated by the delay pulse can always accurately detect the zero-cross point at the specific position of the FM carrier.

The feature of FIG. 3 is that the jitter is detected using the FM carrier that has passed through the narrow band filter (BPF).

By passing through a narrow band filter, the C / N of the FM carrier becomes high, which makes the time base fluctuation due to noise small, and since there is no DC component, there is no offset error, and reproduction jitter is detected with high accuracy. be able to.

[Embodiment] Next, an example of a method for detecting a jitter of a video signal according to the present invention will be described in detail with reference to FIG.

For convenience of explanation, a time axis correction apparatus including a jitter detection system will be described with reference to FIG.

In the figure, reference numeral 31 denotes a reference synchronizing board, of the composite synchronizing signals output from this, the horizontal synchronizing signal is phase-compared with the horizontal synchronizing signal reproduced by the horizontal phase comparing circuit 33, and the vertical synchronizing signal is the vertical phase. The comparison circuit 34 compares the phase with the reproduced vertical synchronizing signal.

The error signal obtained from each of them is used as the recording / reproducing circuit 1 of the VTR.
It is supplied to the capstan servo system and the drum servo systems 35 and 36 provided corresponding to 0 to perform the capstan servo and the drum servo.

The reproduced video signal is FM demodulated in the demodulator 32.
The demodulation output is A that constitutes the time base correction circuit (TBC) 40.
Is supplied to the / D converter 42, and the jitter detection circuit 2
0, the jitter of the reproduced video signal is detected.
The jitter detection signal is used as a trigger signal for the write clock generation circuit 41, and the write clock phase is reset in synchronization with the falling edge of the jitter detection signal.

The write clock is used as a sampling signal for the A / D converter 42 and also as a write address signal for the digital memory 43. Therefore, the reproduced video signal is written in the digital memory 43 with jitter.

Then, the reference clock from the reference synchronization board 31 is supplied to the read clock forming circuit 44 to form a read address signal, and the video signal is read in synchronization with the clock. The read video signal is converted into an analog signal in the D / A converter 45 supplied with the same clock.

Since the read clock is generated in a constant cycle, a video signal without fluctuation in the time axis is reproduced by this. That is, the video signal whose jitter has been corrected is reproduced.

According to the present invention, in a jitter detection method for a video signal in which a luminance signal and a chrominance signal are time-axis-multiplexed and recorded and reproduced, at the time of recording the video signal, the horizontal sync signal is added before the horizontal sync signal. Edge phase and F corresponding to the synchronous peak value
Recording is performed in synchronization with the phase of the M carrier. This causes the FM carrier to be reset at the leading edge of the horizontal sync signal every horizontal line.

During reproduction, the jitter of the reproduced video signal is detected by detecting a specific zero-cross point in the FM carrier in the narrow band with reference to the trailing edge of the FM-demodulated horizontal synchronizing signal.

The write clock phase of the digital memory 43 is reset by the jitter detection signal. Therefore, this reproduced video signal is sampled and written by the write clock whose time axis is changing in synchronization with the reproduced video signal. After that, by using a read clock whose time axis is constant, the video signal is sequentially read in pixel units, so that a video signal in which the jitter is corrected can be obtained.

FIG. 1 is a concrete example for realizing such a jitter detection method for a video signal.

FIG. 1A shows an example of the recording circuit 10A of the recording / reproducing circuit 10 described above.

It is assumed that the input video signal supplied to the terminal 11 has no jitter. The signal form is an NTCI signal in which a line-sequential component color signal is time-axis compressed and multiplexed with a luminance signal as shown in FIG.

The input video signal is FM-modulated by the FM modulator 12. In consideration of the case where the S / N of the input video signal is deteriorated, the horizontal sync frequency is stabilized in the AFC circuit 13 in this example. As a result, the jitter at the leading edge of the horizontal synchronizing signal is suppressed to at least a predetermined value (5 nsec in this example) or less.

The horizontal synchronizing signal output from the AFC circuit 13 is supplied to the reset pulse forming circuit 14 to form a reset pulse h (FIG. 3B) synchronized with the leading edge of the horizontal synchronizing signal.

This reset pulse h resets the FM carrier. That is, the FM carrier frequency corresponding to the sync peak value corresponding to the leading edge of the horizontal sync signal is reset. As a result, the rising edge of the horizontal synchronizing signal and the phase of the FM carrier are synchronized.

Generally, in magnetic recording, the low carrier FM system is used, and it is customary that the carrier generator and the FM modulator are integrated and indistinguishable. Since the phase information of the FM carrier FM-modulated by the video signal g is lost within the effective scanning period of the image because of the video signal FM modulation, the phase information needs to be added every horizontal period. is there.
Therefore, the FM carrier is reset by the reset pulse h every horizontal period.

The FM carrier frequency corresponding to the sync peak value differs depending on the VTR recording method. By the way, the so-called VHS method V
In TR, 3.4 MHz (5.4 in high resolution system)
(MHz) becomes the FM carrier of the synchronous peak value.

When the zero cross detection as shown in FIG. 6D is performed when the jitter phase is detected, the FM carrier may be reset at a phase of 0 ° or 180 °.

As a result, an FM signal i as shown in FIG. 3C is obtained from the FM modulator 12, and this is supplied to the rotary magnetic head 17 via the recording amplifier 16 for recording.

FIG. 1B shows an example of the reproducing circuit 10B.

The FM video signal i reproduced by the rotary magnetic head 17 (fourth
(A) is supplied to the FM demodulator 32 and the carrier gate circuit 22 constituting the jitter detection circuit 20 via the preamplifier 18.

The video signal j (B in the figure) demodulated by the FM demodulator 32 is supplied to the time axis correction circuit 40 as an input video signal having a jitter component, and is also supplied to the sync separation circuit 21 to be included in the video signal j. More horizontal synchronization signal k (Fig. C)
Are extracted and separated.

This horizontal synchronizing signal k is supplied as a gate signal to the carrier gate circuit 22, and FM in the horizontal synchronizing signal section is supplied.
The carrier (carrier corresponding to the horizontal sync peak value) is gated (D in the same figure). The gated FM carrier 1 is used as a conventional burst signal.

The FM carrier 1 is supplied to the narrow band pass filter 23 to improve the C / N. When 3.4 MHz is selected as the FM carrier of the horizontal sync peak value as described above, the pass band is 3.4 MHz in this example.
A filter selected for ± 0.1 MHz is used.

When such a narrow band filter is used, the noise level (effective value) mixed in the FM carrier is reduced to 1/4 or less. As a result, the synchronization jitter (fluctuation of the time axis) due to the noise of the FM carrier is also reduced to 1/4 or less.

Therefore, when the synchronization jitter before filtering is about 16 nsec, this filtering reduces the synchronizing jitter to about 4 nsec. The FM carrier m after filtering is shown in FIG.

The demodulated video signal j is further supplied to the delay pulse forming circuit 24, where the delay pulse n (F in FIG. 8) delayed from the trailing edge of the horizontal synchronizing signal k by a predetermined time is formed.

The delay pulse n and the FM carrier m which is the above-mentioned filter output are supplied to the jitter detection signal forming circuit 25. The forming circuit 25 is composed of an RS flip-flop, is set by the delay pulse n, and is reset by the zero cross point of the FM carrier m input after the setting.

Therefore, the jitter detection signal o, as shown in FIG.
The signal is output as a signal synchronized with the zero-cross point of a specified cycle on the carrier m.

The specific zero-cross point is a zero-cross point of a cycle in which the FM carrier m has the maximum amplitude. In the waveform shown in FIG. 4, the amplitude becomes maximum in a cycle delayed by about 1 μs from the trailing edge of the horizontal synchronizing signal k, so the delay time of the delay pulse n is selected to be about 1 μs.

If the zero-cross point can be detected in a cycle with good C / N,
This is because the influence of the superimposed noise is reduced and the detection accuracy is improved.

The reason why the delay pulse n is formed with reference to the trailing edge of the horizontal synchronizing signal is that the carrier leak during FM demodulation has a far smaller effect on the horizontal synchronizing signal at the trailing edge than at the leading edge. That is, even if there is a carrier leak,
The phase of the leak component is stable with less variation from the leading edge (phase reset point) to the trailing edge.
The detection timing accuracy of the delay pulse n is improved.

Here, when the frequency of the FM carrier m is 3.4 MHz, the zero-cross points exist approximately every 147 nsec. Therefore, when the sync jitter at the trailing edge of the horizontal sync signal k is within the range of 100 nsec at the maximum, depending on the SN ratio of the reproduced signal, if the SN ratio is about 40 db, the specific zero-cross point is 5 nsec or less. It becomes possible to detect with the accuracy of.

That is, the residual jitter of the reproduced video signal can be suppressed to 5 nsec or less.

Since the trailing edge phase jitter of the carrier reset demodulation horizontal synchronization signal cannot be more than 1/2 cycle of the FM carrier at maximum, a malfunction such as detecting a zero cross point other than a predetermined specific zero cross point by the delay pulse n Does not occur.

In the above description, the present invention is applied to a VTR that records and reproduces a video signal according to the MTCI method. However, the carrier recording band is narrowed and the chroma signal is converted into a low frequency band.
The jitter detection method according to the present invention can be applied to a narrow band luminance signal in which the luminance signal is FM recorded.

In addition to the above, the present invention can be applied not only to a video signal for high definition television (HDTV) but also to a MUSE signal which is one of satellite broadcasting systems. In this case, change the positive polarity to negative polarity synchronization before recording,
If you reset that sync peak as the reference burst,
Even if the MUSE signal has a very short horizontal blanking period,
The reference burst recording for several cycles is possible with the FM carrier, and highly accurate jitter detection is possible.

[Effects of the Invention] As described above, according to the present invention, at the time of recording a video signal, the leading edge of the horizontal synchronizing signal and the phase of the FM carrier corresponding to the phase synchronization peak value are recorded in synchronization with each horizontal period. Then
During reproduction, the jitter of the reproduced video signal is detected by detecting a specific zero-cross point of the FM carrier in a narrow band with reference to the trailing edge of the FM-demodulated horizontal synchronizing signal.

Therefore, according to the present invention, the specific zero-cross point of the FM carrier can be detected with high accuracy. According to this, it is possible to reduce the residual jitter of the reproduced video signal to a fraction of the conventional value.

This is an FM with a high C / N that has passed through a narrow band filter.
This is because the carrier is used like the conventional burst signal.

Further, since the jitter of the VTR reproduction signal can be detected with high accuracy, the detection accuracy of the phase error is high, and therefore the speed error accuracy which is the difference value thereof is improved, and the speed error correction is facilitated.

Therefore, the method for detecting the jitter of the video signal according to the present invention is very suitable when applied to the recording / reproducing system of the video signal according to the above-mentioned TCI method.

[Brief description of drawings]

FIG. 1 is a system diagram of a recording / reproducing circuit showing an example for realizing a method for detecting a jitter of a video signal according to the present invention, and FIG. 2 is a system diagram showing an example of a time axis correction device, FIGS. 3 and 4.
FIG. 5 is a waveform diagram for explaining the jitter detecting operation. FIG. 5 is a system diagram of a conventional jitter detecting circuit for explaining the present invention.
FIG. 6 is an explanatory diagram of its operation, FIG. 7 is an explanatory diagram of a video signal format of the MTCI system, and FIGS. 8 and 9 are explanatory diagrams of synchronization jitter. 10 --- Recording / reproducing circuit 10A-Recording circuit 10B-Reproducing circuit 20-Jitter detection circuit 21-Synchronous separation circuit 22-Carrier gate circuit 23-Narrow band pass filter 24-Delay pulse forming circuit 25 …… Jitter detection signal forming circuit 32 …… FM demodulator 40 …… Time axis correction circuit 41 …… Write clock generating circuit 43 …… Digital memory 44 …… Read clock forming circuit

Claims (1)

[Claims] 1. A method of detecting a jitter of a video signal, wherein a luminance signal and a chrominance signal are time-axis multiplexed and recorded / reproduced, wherein a leading edge phase of a horizontal synchronizing signal when FM recording the video signal, The phase of the FM carrier corresponding to the sync peak value is recorded in phase synchronization with each horizontal cycle, and at the time of reproduction, a specific zero cross of the FM carrier in the narrow band is set with reference to the trailing edge of the FM demodulated horizontal sync signal. A method for detecting jitter in a VTR recording / reproducing video signal, characterized in that the jitter in the reproducing video signal is detected by detecting a point.