JPS59231988A - Correcting circuit of phase of chrominance signal - Google Patents

Abstract

PURPOSE:To attain correction of discontinuity of a phase of a chrominance signal by detecting the phase of a color burst signal at every other horizontal period and forming a control signal in response to the phase to apply phase control to the chrominance signal. CONSTITUTION:The color burst signal and a horizontal synchronizing signal (a) separated from a reproduced video signal are applied respectively to input terminals 1, 10. The color burst signal is applied to a color burst phase detecting circuit 2 to generate a pulse signal (b) constituting of the 1st positive pulse and the 2nd negative pulse in response to the phase. Further, a gate signal (e) is formed from the signal (a) by an oscillating circuit 11 and a frequency dividing circuit 12. Then an FF circuit 13 is reset in the period A where the 1st track is scanned for reproduction, no chrominance signal is subject to delay, the circuit 13 is set in the period B entering the 2nd track and the chrominance signal is delayed by 1H. The discontinuous point of the chrominance signal is detected by utilizing the relation of phase between the signals (b) and (e) at each change of track, the amount of delay of the chrominance signal is changed and the discontinuity of phase is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a ROMA position correction circuit suitable for use in a video tape recorder that records and plays back PAL color television signals.

[Background of the invention]

In general, diagonal scanning type two-head video table recorders employ a so-called azimuth recording method in which the magnetization directions are different between adjacent tags, thereby suppressing crosstalk during playback between adjacent tags. In addition, between tracks in the same magnetization direction, the recording position of the horizontal synchronization signal is perpendicular to the track, for example, so-called H arrangement is performed, and n1 still playback is performed. Even during special playback such as slow-motion playback or slow-motion playback, the reproduced image is prevented from having debris.

On the other hand, in recent years, in the video tape recorder mentioned above, several speeds have been made selectable during recording. For example, recording can be performed by running the tape at half the tape speed of the standard tape speed. By making the time twice the standard time and running the tape at 1/3 the tape speed, it became possible to make the recording time three times the standard time.

Therefore, by selecting the tape speed according to the program you are trying to record, you can
It is now possible to record on one tape.

However, when the tape speed can be switched over several stages in this way, H alignment is possible between predetermined tracks for a certain tape speed, but it is not possible for other tape speeds. Third, H alignment between predetermined tracks becomes impossible.

In other words, in a diagonal scanning system 2 to 9 video tape recorder, one horizontal period + 7) (odd number x 1/
2) Since twice as many video signals are recorded, in order to be able to perform an H arrangement between tracks with the same magnetization direction (i.e. every other track), it is necessary to record the two closest tracks with the same magnetization direction.
It is necessary that the distance between two tracks be an integer multiple of the recording length of one horizontal period in the longitudinal direction of the track. This amount of deviation is normally measured by a video tape recorder that records color television signals in the NTSC or PAL format.
It is set to six times the recording length of one horizontal period at standard tape speed.

In such a tape recorder, if the tape speed at the time of recording is 173 times the standard speed, between two tracks closest to each other with the same magnetization direction, there will be an amount of tapering equal to the recording length of one horizontal period. However, if the tape speed during recording is 172 times the standard, the amount is 1.5 times the recording length of one horizontal period, and H-alignment is no longer achieved. n disappears.

Therefore, when special playback is performed using a tape on which video signals are recorded at 172 times the standard tape speed, Hevdo will perform playback scanning across two or more tracks in the same magnetization direction. Therefore, when the head moves from the - track to the next track, a phase difference of 172 times one horizontal period will occur in the reproduced horizontal synchronizing signal, and as a result, Skew will occur in the reproduced image.

In order to prevent the occurrence of such skew, normally when the head moves from the - track to the next track, the video signal is played back from this next track.
The signal is delayed by twice as much to eliminate the above-mentioned phase fluctuation of the horizontal synchronizing signal. In other words, such ski uniform correction is
This means that the two closest parallel tracks with the same magnetization direction have an isometry that is twice the recording length of one horizontal period, and as a result, the phase of the reproduced horizontal synchronization signal is The discontinuity of is removed.

However, when looking at the reproduced video signal σ (gloma signal) after such skew correction, in the case of a PAL chroma signal, the phase of the color difference signal RY is reversed every horizontal period, and at the same time, the phase of the color burst signal is reversed every horizontal period. changes by 90 degrees, the phase of the skew-corrected PAL chroma signal is discontinuous when the head switches from one track to the other in the same magnetization direction, which is continuously scanned for reproduction. becomes. Therefore, when such a PAL chroma signal is supplied to a color television receiver, the color killer circuit is activated at the time of the above switching, and the reproduced image is displayed as a black and white image.

As mentioned above, in the conventional PNL type color tape recorder, when special playback is performed using a tape on which a color video signal is recorded at a tape speed different from the standard tape speed, The problem is that the H alignment is distorted, causing a skew in the reproduced image, and even if this skew is corrected, colors are not reproduced in the reproduced image.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a chroma phase correction circuit capable of correcting phase discontinuity of a PAL chroma signal while eliminating the drawbacks of the prior art described above.

[Summary of the invention]

To achieve this object, the present invention detects the phase of a color burst signal of a P, AL chroma signal every other horizontal period, and forms a control signal corresponding to the phase [PAL].
The feature is that the phase side of the system chroma signal can be processed.

[Embodiments of the invention]

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

FIG. 1 is a professional diagram showing an embodiment of the chroma phase correction circuit according to the present invention, in which 1 is an input terminal, 2 is a color burst phase detection circuit, 3.4 is a differentiation circuit, and 5.6 is an amplification circuit. 7 is an inverting circuit, 8 and 9 are gate circuits, 10 is an input terminal, 11 is an oscillation circuit, 12 is a frequency divider circuit, 13 is a 7-proflock circuit, and 14 is an output terminal.

FIG. 2 is a waveform diagram showing signals at various parts in FIG. 1, and signals corresponding to those in FIG. 1 are given the same symbols.

In FIGS. 1 and 2, a color burst signal of a PAL chroma signal reproduced from a tape (not shown) and skew corrected is detected by a color burst phase detection circuit 2.
supplied to the The color burst phase detection circuit 2 detects the phase of the color burst signal! The phase is detected, and when the color burst signal is in the first phase, a first pulse of positive polarity is generated, and when the color burst signal is in a second phase that is 90 degrees different from the first phase.

It generates a second pulse of negative polarity and thus a first pulse of positive and negative polarity depending on the phase of the color burst signal.
A pulse signal ■ consisting of a second pulse is generated.

This pulse signal (2) is supplied to the differentiating circuit 6.4. The differentiating circuit 6 separates a first pulse from the pulse signal ■, and this first pulse is amplified by the amplifier circuit 5 to become a negative polarity pulse. supplied. Further, the differentiating circuit 4 separates a second pulse from the pulse signal ■, and this second pulse is amplified by the amplifier circuit 6 and inverted to become a positive polarity pulse ■, which is supplied to the gate circuit 9. to snatch

On the other hand, the simultaneously reproduced and skew-corrected horizontal synchronizing signal (2) is supplied from the input terminal 10 to the oscillation circuit 11, from which the n1 noise is removed, and then supplied to the n''''c frequency dividing circuit 12. The frequency dividing circuit 12 divides the repetition frequency of the horizontal synchronizing signal by 172, and generates a gate signal (2) with a duty ratio of 50% and a period twice that of the horizontal synchronizing signal. This gate signal (2) is supplied to a gate circuit 8.9.

Therefore, the gate circuits 8 and 9 are connected to the gate signal
One horizontal period is opened at the same time every other horizontal period.

While the gate circuits 8 and 9 are open, when the inverting circuit 7 outputs a pulse ■, this pulse passes through the gate circuit 8 and is reset as a pulse ■ to the flip-flop circuit 1.
3, the free y1 flow I7 circuit 13 is reset and the Q output becomes, for example, a low level. Also, while the gate circuits 8 and 9 are open, the amplifier circuit 6 outputs a pulse ■, and this pulse ■ passes through the gate circuit 9 and is free as a set pulse ■! When the signal is supplied to the Pflovp circuit 16, the Pflov1 circuit 13 is set and the Q output becomes high level. Flipfu-70-) 1 circuit 13
The Q output (2) is supplied as a control signal from the output terminal 14 to a chroma signal delay means (not shown). This delay means is controlled by the IJ control signal. When the control signal (2) is at a low level, the delay amount is zero, and when it is at a high level, the delay amount is equal to one horizontal period.

Next, the operation of this embodiment will be explained.

Now, as explained earlier in the prior art, it is assumed that an NFC tape with no H alignment and a trough 9 formed therein is being run at high speed and search playback is being performed. As a result, the hesado performs reproduction scanning across tracks of the same number of grains in the same magnetization direction, but in FIG. 2, period A is a certain track (
First tiger 11. Period B is the reproduction scanning period of the track to be scanned next (second track), and time t is the time when the head changes from the first track to the second track.

Therefore, from the PAL color video signal reproduced from such Q1, a color burst signal and a horizontal synchronization signal ■
The separated n1 power error burst signal is supplied to input terminal 1, and the horizontal synchronization signal 2 is supplied to input terminal 10. The color burst signal is supplied to a color burst phase detection circuit 2, which generates a pulse signal (2) consisting of a first pulse of positive polarity and a second pulse of negative polarity in accordance with the phase of the color burst signal. Also, from the horizontal synchronization signal ■, the generator circuit 11,
The gate signal ■ is formed by the frequency dividing circuit 12, but
In this case, the phase relationship between the pulse signal (■) and the gate signal (■) is as follows in the period A during which the first track is scanned for reproduction.
The first pulse of the positive polarity of the pulse signal (2) is set so as to match the high level of the gate signal (2).

The pulse signal ■ is separated into a first pulse and a second pulse by differentiating circuits 3 and 4.
A positive pulse (■) representing a pulse of 1 is supplied to the gate circuit 8, and a pulse (2) of positive polarity representing a second pulse (2) is supplied to the gate circuit 9. In A, when the gate circuits 8 and 9 are open for a period when the gate signal ■ is at a high level, the pulse ■ (from the inverting circuit 7) (from the n1 amplifier circuit 6) is supplied to the gate circuit 8, and the pulse ■ is supplied to the gate circuit. 9, the pulse ■ passes through the gate circuit 8 and becomes the receptor pulse ■1.
The slip flow circuit 13 is reset.

As a result, during the period A, the Q output (2) of the 7-ridog70-vp circuit 13 is at a low level, the delay amount of the delay means (not shown) is set to zero, and the n1 chroma signal is not delayed.

Next, when the head completes the reproduction scan of the first track 9-'7 and starts the reproduction scan of the second track at time t (period B), the pulse signal ■ from the color burst phase detection circuit 2 and The phase relationship with the gate signal 0 is reversed, and the negative polarity σ) $2 of the pulse signal ■ matches the high level of the gate signal ■.

Therefore, the time is also the first pulse from the amplifier circuit 6
passes through the gate circuit 9, and sets the circuit 13 as a seven-digit signal.

For this reason, the Q output (2) of the flip-flop circuit 16 becomes high level, and the delay amount of the delay means (not shown) is set equal to one horizontal period. From then on, Sodo is the second tiger,
During the period B in which J/F is regenerated and scanned, the flip-flop circuit 45 maintains the set state, and the chroma signal is delayed by one horizontal period.

Next, when Hevdo moves from the second track to the third track, the phase relationship between the pulse signal ■ and the gate signal ■ is further reversed, and the Q output ■ of the 7-rep-buf-roup circuit 13 becomes a low level. Therefore, the delay amount of the delay means is set to zero.

In this way, the tiger that Hevdo regenerates scans.

Each time the chroma signal changes, a point of discontinuity in the phase of the chroma signal is detected from the phase relationship between the pulse signal (2) and the gate signal 0, and the amount of delay of the n1 chroma signal is changed to remove the discontinuity in the phase.

As described above, in this embodiment, a control signal for removing the phase discontinuity of the chroma signal is obtained, but as mentioned earlier, this control signal consists of the pulse signal ■ and the gate signal (2) It changes depending on the phase relationship with the chroma signal, and as this phase relationship changes, discontinuity in the phase of the chroma signal is detected. In this case, the pulse signal ■ is different 2
If the phase of the chroma signal is not discontinuous, the temporal arrangement of the two pulses will be mutual, but if the phase is discontinuous, the arrangement of the two pulses will be as follows:
Since the phase differs at discontinuous points, the chroma can be improved by extracting every other pulse from the pulse signal and distinguishing which of the two types of pulses the extracted pulse is. Discontinuities in the phase of the signal are what are detected.

Therefore, in this embodiment, using the gate signal ■ as a reference, the gate circuits 8 and 9 extract every other pulse from the pulse signal ■, and the differentiating circuit 3.4 extracts every other pulse.
This makes it possible to distinguish whether the fC pulse is the first pulse or the second pulse.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to reliably detect phase discontinuity in a PAL chroma signal,
The phase discontinuity can be removed, the color reproducibility of the reproduced image can be ensured, and the structure is simple, so it is possible to provide a ROMA phase correction circuit.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of a chroma phase correction circuit according to the invention, and FIG. 2 is a waveform diagram showing signals at various parts of FIG. 1. 2... Color burst phase detection circuit, 6.4... Differential circuit, 7... Inverting circuit, 8.9... Gate circuit,
12... Branch circuit, 1! 1... Frivub 70bup circuit.

Claims (1)

[Claims] In a chroma phase correction circuit configured to correct phase discontinuity of a reproduced PAL chroma signal, the PAL chroma signal
A color burst signal of the L type chroma signal is supplied, and a first . a color burst detection circuit that generates a pulse signal consisting of a second pulse; a pulse extraction circuit that extracts every other pulse from the pulse signal; and a pulse extraction circuit that is supplied with pulses from the pulse extraction circuit.
A 7-lead V770 pulse circuit is provided, and the 7-leave 70 pulse circuit is set by one of the eleventh second pulses and reset by the other. A chroma phase correction circuit characterized in that the output signal of the dropout circuit is used as a phase control signal for the PAL chroma signal.