JPH037196B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a time axis error signal generating apparatus for reproduced signals, and more particularly to a time axis error signal generating apparatus for reproduced color video signals.

In playback devices such as VTRs (video tape recorders) and VDPs (video disc players), a time axis correction device is essential to obtain high-quality color playback images, and there is a configuration as shown in FIG. 1, for example. A burst signal in a reproduced color video signal is separated by a color burst separator 1, and a phase comparator 2 compares the phases of the reproduced color burst signal and a reference signal. Also, horizontal sync separator 3
The phase of the reproduced horizontal synchronization signal separated in is compared with the reference signal in a phase comparator 4, and the outputs of both phase comparators 2 and 4 are added and synthesized in an adder 5 to form a correction drive signal for a time axis correction device 6. becomes.

In such a system, since the DC and AC components of the phase error component of the reproduced horizontal synchronizing signal correspond to the frequency fluctuation and phase fluctuation of the reproduced video signal, by using the output of the phase comparator 4, It is possible to compress and correct time axis fluctuations in the reproduced video signal up to the horizontal synchronization signal period (635 μsec).

Furthermore, a phase comparator 2 for the reproduced color burst signal
By using the comparative output of , it is possible to similarly correct and compress Terama axis fluctuations in the reproduced video signal up to the burst period (270 nsec), and obtain a good color reproduced image.

However, because of the dual servo loop system, there is a drawback that the operation of one servo loop acts as a disturbance to the operation of the other servo loop. That is,
Because the fluctuation error of the reproduced horizontal synchronization signal and the fluctuation error of the reproduced burst signal are simply added and combined, especially in the frequency domain where both error components compete, the minute fluctuation error of the horizontal synchronization signal becomes the burst signal. The resulting burst signal fluctuation error is detected as an excessive change in the loop and acts as a large disturbance on the horizontal synchronization signal loop. Therefore, if the gain of the burst signal loop is increased, the entire system will operate in an unstable manner, and the loop gain of the burst signal loop cannot be increased. However, in order to properly compress and correct the time axis of the reproduced video signal up to the burst signal period, it is desirable to increase the loop gain of the burst signal loop and give priority to burst signal fluctuation errors, but the method shown in Figure 1 does not. countermeasures would be impossible.

Further, the reference signals of the horizontal synchronizing signal loop and the burst signal loop have no correlation with each other, and therefore, the addition of the error signals of these loops is one of the unstable factors in the servo system.

SUMMARY OF THE INVENTION An object of the present invention is to provide a time axis error signal generating device for a reproduced signal that can operate a time axis servo loop stably and effectively.

The time axis error signal generating device according to the present invention uses a reproduced burst signal (3.58MHz in the case of NTSC system).
average frequency signal generating means for generating a signal having a frequency equal to the average frequency while following the average frequency of the color burst signal of , means for detecting the phase difference between the average frequency signal and the reproduced burst signal and generating a burst phase error signal corresponding to the high frequency component of the phase difference output; and a means for detecting a phase difference between and generating a low frequency component of this phase difference output, and adding the burst phase error signal and the low frequency component to generate a time axis error signal of the reproduced signal. It is said that

The present invention will be explained below using the drawings.

FIG. 2 is a block diagram of an embodiment of the present invention,
The phase of the reproduced color burst signal is compared with the oscillation output of a VCO (voltage controlled oscillator) 12 in a phase comparator 11 . This VCO 12 uses the color burst signal frequency (3.58MHz) as a free-running oscillation frequency, and the comparison output from the phase comparator 11 is
It passes through an LPF (low-pass filter) 13 and becomes a control signal for the VCO 12. These phase comparator 11, VCO 12
and VPF13 is PLL (phase locked loop)
Therefore, the VCO 12 is controlled by the integrated value, ie, the average value, by the VPF 13 of the output of the phase comparator 11, which is a fluctuation error of the reproduced color burst signal. Therefore,
The VCO 12 follows the average frequency of the reproduced color burst signal and generates a frequency equal to the average frequency. Then, only the high-frequency component of the output of the phase comparator 11 is passed through the HPF (high-pass filter) 14.
is derived and becomes one input of the adder 15.

The output of the VCO 12 is frequency-divided by 2/455 by a frequency divider 16 and becomes a reference signal for a phase comparator 17, and the phase fluctuation of the reproduced horizontal synchronizing signal is detected by the comparator 17. The phase fluctuation component of this horizontal synchronization signal is
It is input to the LPF 18, and only its knowledge area component is derived and becomes the other input to the adder 15. This addition output passes through the equalizer 19 and becomes a drive signal for the time axis correction device 20.

In the time axis error signal obtained in such a configuration, the time axis error of the reproduced color burst signal is dominant in the high frequency component, and the time axis error of the reproduced horizontal synchronization signal is dominant in the low frequency component. This eliminates the frequency range where burst errors and horizontal synchronization errors conflict with each other.
Even if the loop gain of the burst signal loop is set high to increase the high-frequency characteristics of the servo loop, there will be no negative effect on the horizontal synchronization signal loop, and the period of the burst signal can be reproduced stably and effectively. It is possible to compress the time axis changes in the signal.

The response characteristic of VCO12 to 3.58MHz is several Hz
If you configure the PLL circuit as follows, the VCO
12 can track the average frequency of the reproduced burst signal, and even if the output of this VCO 12 is frequency-divided and used as a reference signal for the horizontal synchronization signal loop, horizontal synchronization that has a dominant frequency of 30 Hz, which is the eccentric component of the recording disk, for example. The time base error of the signal is sufficiently detectable in the phase comparator 17. In addition, since the horizontal synchronization signal loop requires only the low-frequency component of the time axis error of the reproduced horizontal synchronization signal, the division period 16 is set to a division ratio of 1/455 to 1/ _2H. ( _H is the period of the horizontal synchronizing signal) Comparing the phases of the signal allows sufficient error detection.

In this way, by creating a correlation between the reference signals in the burst signal loop and the horizontal synchronization signal loop, even if the reference signal fluctuates to some extent, the independent System stability is maintained compared to the reference signal.

FIG. 3 is a block diagram of an application example in which the circuit device of FIG. 2 is used for VDP, and the same parts as those in FIG. 2 are designated by the same reference numerals, and their explanation will be omitted.
A spindle motor 25 is provided to rotate a recording disk (not shown), and a spindle servo is used to control the rotation of this spindle motor. This is because the horizontal synchronization signal reproduced by the horizontal synchronization separator 3 and the 15.75KHz reference signal from a separately provided crystal oscillator (not shown) are compared by the phase comparator 21 and output as one input to the adder 23. There is.

Phase comparator 1 in the previous horizontal synchronization signal loop
7, a low frequency component from the LPF 22 is derived and used as another input to the adder 23. This addition output is passed through the equalizer 24 to the spindle motor 2.
5 drive control signal.

Incidentally, as the time axis correction device 30, an optical type
For VDP, it is a tangential mirror,
Further, a controlled delay device such as a variable delay line or a CCD (charge coupled device) may be used to compensate the time axis of the reproduced video signal.

In the above description, an NTSC color video signal has been described, but it is also applicable to a PAL color video signal, and in the latter case, a pilot burst signal or the like is used as the burst signal.

As described above, according to the present invention, the loop gain of the reproduced burst signal loop can be increased without any adverse effect on the reproduced horizontal synchronizing signal loop, so that stable and good time axis compensation is possible. Further, by making the reference signals of both loops have a correlation with each other, the stability of the system is further improved. Furthermore, since a PLL circuit is used, the PLL circuit operates stably during the dropout period due to the flywheel effect of the PLL circuit, making the circuit resistant to dropouts.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of a conventional time axis correction device, FIG. 2 is a block diagram of an embodiment of the present invention, and FIG. 3 is a diagram showing an application example of the block in FIG. 2. Explanation of symbols of main parts, 11, 17... Phase comparator, 12... VCO, 13, 18... LPF, 1
4... HPF.

Claims (1)

[Scope of Claims] 1. Average frequency signal generating means for generating a signal having a frequency equal to the average frequency while following the average frequency of the reproduced burst signal in the reproduced color video signal, and this average frequency signal and the reproduced burst signal. A means for detecting a phase difference with a burst signal and generating a burst signal phase error signal according to a high frequency component of the output of the phase difference, and a phase comparison between a signal based on the average frequency signal and a reproduced horizontal synchronization signal. and means for generating a low-frequency component of the comparison output, the burst signal phase error signal and the low-frequency component being added to form a time axis error signal of the reproduced signal. Axis error signal generator. 2. The average frequency signal generating means includes a voltage controlled oscillator whose free running frequency is the same frequency as the burst signal, and detects a phase difference between the output of the voltage controlled oscillator and the reproduced color burst signal, and determines the phase difference. and means for controlling the voltage controlled oscillator according to a low frequency component of the output, the output of the voltage controlled oscillator being the average frequency signal. Device.