JPH0473680B2 - - Google Patents

Description

TECHNICAL FIELD The present invention relates to a time axis correction device, and more particularly to a time axis correction device for reproduced color video signals.

BACKGROUND ART One method for detecting time axis fluctuations in a reproduced color video signal is to directly compare the phases of a reference signal and a reproduced burst signal. A time axis error cannot be detected unless it is at or near the approximate center of the operating range of the phase comparator. In other words, this method cannot be used unless the frequency difference between the reference signal and the reproduced burst signal is zero and the phase difference is also within a certain range.

As another method, a method using a PLL (phase locked loop) circuit having a VCO (voltage controlled oscillator) is known. In this method, the feedback loop operates so that the phase of the VCO is locked to the phase of the reproduced burst signal, so if the time axis error is within the pull-in range of the PLL circuit, the error can be detected accurately. .

However, in this method using a PLL circuit, the stability of the PLL circuit is determined by the loop filter and loop gain, but if the filter characteristics and loop gain are set to make this PLL circuit stable and increase the pull-in range, Since the PLL circuit also responds to the low-frequency component of the time-axis variation of the reproduced burst signal, there is a disadvantage that the resulting time-axis error signal lacks the low-frequency component.

Therefore, Japanese Patent Application Publication No. 2004-110030 has proposed a device that can accurately detect time axis errors in reproduced color video signals regardless of the variation range of the burst phase of the reproduced color video signal and eliminates the above-mentioned problems regarding the loop stability of the PLL method. It is disclosed in Publication No. 58-134594.

In this device, a signal having the same frequency as the color burst signal and a phase equal to the average phase of the reproduced burst signal is generated based on a fixed oscillation output, and the phase difference between this signal and the reproduced color burst signal is The apparatus is configured to correct the time axis error of the reproduced color video signal according to the color video signal.

The device disclosed in Japanese Patent Application Laid-open No. 58-134594 has four multipliers, four LPFs (low pass filters), and a reference oscillation signal (subcarrier) of π/2.
A phase shifter and the like are required at a minimum, which complicates the configuration and also requires adjustment.

SUMMARY OF THE INVENTION An object of the present invention is to provide a time axis correction device that can generate an accurate time axis error signal by eliminating the need for adjustment, the complexity of the configuration, and the loss of low frequency components of the time axis error signal. It is to be.

The time axis correction device according to the present invention performs a phase comparison between a reproduced horizontal synchronization signal and a reference signal, and a phase comparison between a reproduced color burst signal and a reference signal, and corrects the phase error of the reproduced horizontal synchronization signal within a range. When the phase error of the reproduced color burst signal is settled, the gate means derives the phase error of the reproduced color burst signal and uses it as a correction signal for a fine adjustment time axis correction loop that finely adjusts the time axis of the reproduced color video signal. This configuration combines the phase error of the horizontal synchronization signal and uses the combined output as an error signal for a coarse time axis feedback loop that coarsely adjusts the time axis of the reproduced color video signal.

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

FIG. 1 is a circuit block diagram of an embodiment of the present invention. A PF (high frequency) signal read from a pickup (not shown) is converted into a color video signal by a demodulator 1, and the time axis of this color video signal is The reproduced color video signal is outputted via the time axis corrector 2, which makes fine adjustments, and is led out to the outside.

On the other hand, an oscillator 3 that generates an oscillation output of 7.16MHz as a reference signal is provided, and this oscillation output is divided into 1/2 and 1/455 by frequency dividers 4 and 12, respectively, to produce a color subcarrier. and each reference signal for the horizontal synchronization signal. In the phase comparator 13, the phase of this horizontal synchronization signal reference signal is compared with the horizontal synchronization signal in the reproduced video signal separated by the horizontal synchronization separator 9, and the comparison output is passed through the adder 14 and used as the reproduction signal. It drives a coarse adjustment time axis correction means consisting of equalizers 15 and 16, a tangential mirror 17, and a spindle motor 18, which perform coarse adjustment of the time axis of the color video signal.

On the other hand, the frequency-divided output from the frequency divider 4 is phase-compared with the reproduced color video signal in a phase comparator 5, and sampled and held for each burst by the next S/H (sample/hold) circuit 6. The output of this S/H circuit 6 becomes a control signal for the time base corrector 2 via a gate 7, and becomes one input of the adder 14 via an LPF 8, and is sent to the tangent along with the phase error of the horizontal synchronization signal. Sial mirror 1
7. It becomes a drive signal for the spindle motor 18.

The gate 7 is opened and closed by the output of a window comparator 11, which detects the level of the comparison output of the phase comparator 13 and opens the gate 7 only when this level is within a certain range. It is configured to be open.

In such a configuration, a phase error of the reproduced horizontal synchronizing signal with respect to the reference signal and a phase error of the reproduced color burst signal with respect to the reference signal are respectively detected, but the phase error of the reproduced horizontal synchronizing signal is within a certain range. Only then is the phase error of the reproduced color burst signal derived from the gate 7 and becomes the control signal for the time base corrector 2. Furthermore, the low-frequency error component of the output of the gate 7 that has passed through the LPF 8 is added and synthesized with the phase error of the horizontal synchronization signal by an adder 14, and becomes an error signal of the feedback loop for coarse adjustment time base correction. Therefore, when the phase error of the horizontal synchronization signal becomes small to a certain extent, the phase error of the color burst signal is gated and fine time axis correction is performed, so that the subcarrier phase jitter of the output video signal is removed, and this burst Since the low-frequency component of the phase error is combined and inserted into the feedback loop via the spindle motor 18 and tangential mirror 17, the phase difference between the reference subcarrier and the reproduced color burst signal at the phase comparator 5 is Since it operates so as to be centered within the comparison operation range, a stable time axis correction signal can always be supplied to the time axis corrector 2.

Incidentally, the time axis corrector 2 is, for example, disclosed in Japanese Patent Application Laid-open No. 1986-
A delay element such as that disclosed in the specification of No. 12688 or a CCD (charge coupled device) can be used.

The above example is for the NTSC system, but
In the PAL system, oscillator 3 and frequency divider 4 in Figure 1
and 12, as shown in FIG.
2' may be input to the phase comparator 13.

Furthermore, instead of the tangential mirror 17 in the feedback loop, a variable delay line such as a CCD may be used to detect the phase error of the reproduced horizontal synchronizing signal and the reproduced color burst signal at the output thereof. A block of the embodiment in the case shown in FIG. 3 is shown, and the output of the equalizer 15 is
It controls a VCO (voltage controlled oscillator) 17, and its oscillation output is inserted after the demodulator 1. CCD
I try to control 19. The other configurations are similar to the example shown in FIG.

Effects As described above, according to the present invention, the circuit configuration is simplified, which is advantageous in terms of cost, and also eliminates the need for adjustment. Also, NTSC and
There is also the advantage that it is easy to share both types with PAL.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a diagram showing a partial modification of the block in FIG. 1, and FIG.
The figure is a block diagram of another embodiment of the invention. Explanation of symbols of main parts, 2... Time axis corrector,
3... Reference signal generator, 5, 13... Phase comparator, 7... Gate.

Claims (1)

[Claims] 1. A first phase comparison means that performs a phase comparison between a reproduced horizontal synchronization signal separated from the reproduced video signal and a reference signal, and a second phase comparison means that performs a phase comparison between the reproduced color burst signal separated from the reproduced video signal and the reference signal. phase comparison means, and gate means for deriving the comparison output of the second phase comparison means when the comparison output of the first phase comparison means is within a predetermined range, and the gate output of the gate means A fine adjustment time axis correction loop is formed to finely adjust the time axis of the reproduced video signal, and the low frequency component of the gate output and the comparison output of the first phase comparing means are combined, and this combined output is used to adjust the reproduction. A time axis correction device comprising a coarse time axis correction feedback loop that roughly adjusts the time axis of a video signal.