JPH0339988Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a time axis correction device, and more particularly to an apparatus for correcting a time axis error in a reproduced signal during reproduction of color video information.

In a color video information reproducing device, it is necessary to correct time axis errors in order to obtain stable and high quality color images. As a device to correct this time axis error, for example, it detects the timing of occurrence of a specific point (specific zero cross point) of the reproduced color burst signal, generates a timing signal, and adjusts the phase of this signal with a reference horizontal synchronization signal provided separately. There is already a known device that performs a comparison and generates a phase difference signal as a time axis error signal to perform time axis correction.

Here, since the subcarrier signal frequency in the NTSC television system is generally an odd multiple of 1/2 that of the horizontal synchronization signal, the color burst signal superimposed on the back porch of the horizontal synchronization signal in about 8 cycles is Each period of the synchronization signal is superimposed with a phase difference of 180 degrees with respect to the horizontal synchronization signal (see FIG. 2A). Therefore,
In the above-mentioned time axis error correction device, the phase of the reproduced color burst signal is inverted every other cycle of the horizontal synchronization signal and output, so that the phase of each color burst signal with respect to the reproduced horizontal synchronization signal has a constant relationship. It is set in advance, and the phase difference between the specific point of the color burst signal obtained in this manner and the reference signal is detected every horizontal synchronization.

In conventional time axis correction devices, color correction is caused by so-called drop-outs, which cause noise in the composite video signal obtained by FM demodulating the RF signal due to dropouts in the RF signal due to scratches or dust on the recording medium. There was a drawback that the timing of occurrence of a specific point of the burst signal was detected incorrectly, resulting in incorrect time axis correction. As a result, phase fluctuations occur in the obtained reproduced signal, resulting in color unevenness in the reproduced image lines, and the reproduced audio signal is also adversely affected.

Therefore, an object of the present invention is to provide a time axis correction device that can reduce the influence of dropout.

The time axis correction device according to the present invention includes a prohibition means for prohibiting new generation of a time axis error signal in response to a dropout detection signal generated when the occurrence of dropout of an RF signal read from a recording medium is detected, When a dropout detection signal is present, the time axis correction is performed using a time axis error signal immediately before the dropout detection signal is generated.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In Figure 1, the RF read from the recording medium
The signal is converted into a composite video signal a in a demodulator 1. The composite video signal a output from the demodulator 1 is supplied to a burst gate 2, a sync separation circuit 3, and a color phase corrector 4. The color burst signal b is separated from the composite video signal a by the burst gate 2 and applied to a limiter 5 for waveform shaping, and noise components such as amplitude fluctuations are removed. The output of this limiter 5 is directly supplied to one input terminal of an analog switch 6 for signal selection, and simultaneously supplied to the other input terminal of the analog switch 6 via a phase inverter 7. For switching control of the analog switch 6, a reference horizontal synchronization signal c output from a reference horizontal synchronization generator 8 is used. That is, the reference horizontal synchronization signal c is
The frequency is divided by 1/2 by the flip-flop 9, and the analog switch 6 is switched and controlled every horizontal synchronization. Therefore, the color burst signal and its phase inverted signal are alternately and selectively derived to the output terminal of the analog switch 6 every horizontal synchronization.

On the other hand, the synchronization separation circuit 3 separates the composite synchronization signal d from the composite video signal a to form a monostable multivibrator (hereinafter abbreviated as monostable multi).
10 trigger input terminals. The monostable multi 10 is formed to be triggered at the falling edge of the composite synchronization signal d and to be in an inverted state for a time slightly longer than 1/2 of 1H (one horizontal synchronization period). The Q output e of the monostable multi 10 is supplied to the trigger input terminal of the monostable multi 11 and to the phase comparator 12. Monostable multi 11 has Q output e
Triggered at the rising edge of This monostable multi 1
The Q output f of 1 is the trigger input of the monostable multi 13. The monostable multi 13 is triggered when the Q output f falls. The Q output of this monostable multi 13 is supplied to one input terminal of an AND (logical product) gate 14. The output g of the analog switch 6 is supplied to the other input terminal of the AND gate 14. The output h of this AND gate 14 is supplied to the trigger input terminal of the monostable multi 15. The monostable multi 15 is triggered when the output h falls and outputs a positive pulse i from the Q output terminal. This positive pulse i is supplied to the clear input terminal of the monostable multiplier 13, and is also supplied as a sampling pulse to the sample and hold circuit 17 via the gate circuit 16 as inhibiting means.
The gate circuit 16 consists, for example, of an AND gate to which a pulse i is supplied to one input terminal. The other input terminal of this gate circuit 16 is supplied with a dropout detection signal k output from a dropout detector 18. The dropout detector 18 is configured to drive a retriggerable mono-multivibrator with a predetermined time constant (for example, 207 ns) using one of positive or negative pulses obtained in synchronization with the zero cross of the RF signal as a trigger. Can be configured. At this time, if the time constant corresponds approximately to the maximum period of the RF signal,
When the RF signal is lost, the retriggerable mono multivibrator inverts and can detect dropouts. An example of this type of dropout detection device is the one described in Japanese Patent Application Laid-open No. 1395065/1983.

The sample and hold circuit 17 includes a trapezoidal wave generator 1.
A trapezoidal wave signal l whose level gradually increases (gradually decreases) is supplied as a time axis error detection signal outputted from 9. The trapezoidal wave generator 19 is configured such that when the output m of the pulse generation circuit 20 is at a high level, the output level decreases, and when the output m is at a low level, the output level increases with a predetermined slope. . The pulse generation circuit 20 generates a reference horizontal synchronization signal c
The configuration is such that a positive pulse is output for a predetermined period of time from the falling edge of . Then, the trapezoidal wave signal l is sampled in response to the generation timing of the pulse i in the sample and hold circuit 17, and the sampled trapezoidal wave signal l is held until the pulse i as the next sampling pulse is generated. . This sampling hold circuit 1
7 is used as a time axis error signal.

That is, the output n of the sample hold circuit 17 is supplied to the amplifier 22 and the color phase corrector 4 via the equalizer 21. The output of the amplifier 22 is sent to the mirror transducer 2 via a mirror stopper 23 for preventing excessive rotation of the tangential mirror.
4. Mirror transducer 24
The apparatus is configured to drive a tangential mirror in accordance with the input signal, thereby converting the input signal into a movement of a laser beam serving as a reading pickup in the tangential direction of the recording track. Further, the color phase collector 4 is constructed in the same manner as the device already devised by the inventors and disclosed in Japanese Patent Application No. 126880/1983. That is, the color phase collector 4 has a variable impedance element, and a transmission circuit network is provided in which the amplitude transfer characteristic is approximately constant regardless of this impedance element and the phase transfer characteristic depends on this variable impedance element. The configuration is such that the impedance of the impedance element is controlled according to the output n as a time axis error signal. This color phase corrector 4 corrects phase fluctuations of the composite video signal a.

Further, the phase comparator 12 compares the phases of the reference horizontal synchronizing signal c and the Q output e of the monostable multi 10. The output of this phase comparator 12 becomes a drive signal supplied to a drive circuit 26 that drives a spindle motor 25.

In the above configuration, when a composite video signal a as shown in FIG. 2A is outputted from the demodulator 1 over a continuous 2H period, a color burst signal b as shown in FIG. 2B is outputted from the burst gate 2. Then, the output g of the analog switch 6 becomes a pulse controlled to have the same phase relationship with each horizontal synchronizing signal as shown in FIG. On the other hand, synchronous separation circuit 3
As a result, a composite synchronization signal d as shown in FIG. When the composite synchronization signal d falls, the monostable multi 10 is triggered, and the Q output e is shown in the figure E.
remains at a high level for slightly longer than 1/2 of 1H. Since the monostable multi 11 is triggered when this Q output e becomes high level, the triggering of the monostable multi 11 due to the equivalent pulse inserted in the vertical synchronization signal period and the 3H before and after it is prevented. Become.

Here, the Q output f of the monostable multi 11 is F
As shown in the figure, the level remains high from the falling edge of the horizontal synchronization signal to almost the center of the 8-cycle sine wave signal that forms the color burst signal, and the inversion time of the monostable multi 13 is equal to the period of the color burst signal. The values of the capacitors and resistors for time setting of the monostable multis 11 and 13 are respectively set so that they are sufficiently long compared to .

Then, the output h of the AND gate 14 becomes a signal having the same waveform as the output g of the analog switch 6 after the Q output f returns to a low level as shown in FIG. When this output h becomes a low level, the monostable multi 15 is triggered and
A positive pulse i as shown in is output. The monostable multi 13 is cleared by this pulse i,
The output h of the AND gate 14 remains at a low level even when the output g becomes a high level.

On the other hand, when the reference horizontal synchronization signal c as shown in FIG. It becomes high level over time. Then, the trapezoidal wave signal l outputted from the trapezoidal wave generator 19 becomes as shown in FIG. An output n obtained by sampling and holding this trapezoidal wave signal l at the time of generation of a pulse i is output as a time axis error signal.

Next, as shown in FIG. 3A, when noise p is generated in the color burst signal included in the composite video signal a due to dropout, the noise p is also output from the burst gate 2 along with the color burst signal b, as shown in FIG. 3B. Ru. Therefore, the output g of the analog switch 6 becomes a signal whose transition point does not coincide with the zero-crossing point of the color burst signal b, as shown in FIG. Therefore, the composite synchronization signal d, monostable multi 1
0's Q output e and monostable multi 11's Q output f do not change in waveform even if dropout occurs, as shown in Figure D, Figure E, and Figure F, respectively.
The falling timing of the output h of the AND gate 14 no longer coincides with the zero-crossing point of the color burst signal b due to the occurrence of dropout, as shown in FIG. Therefore, as shown in H in the figure, the pulse i
Due to the occurrence of dropout, the generation timing of the color burst signal b does not coincide with the zero-crossing point of the color burst signal b.

However, when dropout occurs, the L
As shown in FIG. 3, a dropout detection signal k consisting of a low level signal is outputted from the dropout detector 18 and supplied to the gate circuit 16. Therefore, when dropout occurs, the supply of pulse i to sample hold circuit 17 is prohibited. On the other hand, the waveforms of the reference horizontal synchronizing signal c and the output m of the pulse generation circuit 20 do not change even if a dropout occurs, as shown in FIGS. It doesn't change even though. Therefore, this trapezoidal wave generating circuit 1
The trapezoidal wave signal l outputted from 9 is as shown in K in the same figure. That is, the trapezoidal wave signal l does not become as shown by the dashed line in FIG. 1K, but as shown by the solid line. At the same time, the sampling and holding operation of the trapezoidal wave signal l in the sample and hold circuit 17 is no longer performed, and the output n of the sample and hold circuit 17 becomes constant at the level immediately before the dropout occurs, as shown by the solid line in FIG. Generation of an erroneous time axis error signal as shown by the dashed line in FIG. M can be prevented.

In the above embodiment, the time axis correction is performed by supplying a time axis error signal to the color phase collector 4 and the mirror transducer 24. The time base correction may be performed by supplying a time base error signal to the variable delay means.

Above, we have explained the case in which time axis correction is performed using a time axis error signal obtained using a color burst signal in a reproduced signal. The present invention can also be applied to the case where time axis correction is performed using a time axis error signal obtained using a pilot burst signal.

As described in detail above, the reproduction signal time axis correction device according to the present invention is configured to prevent the generation of an erroneous time axis error signal due to dropout by continuously outputting the time axis error signal immediately before the dropout occurs. Therefore, it is possible to reduce the effects of dropout, that is, the adverse effects such as the occurrence of color unevenness in the reproduced image and the deterioration of the S/N of the reproduced audio signal.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIGS. 2 and 3 are waveform diagrams showing the operation of the apparatus shown in FIG. Explanation of symbols of main parts, 16...gate circuit,
17... Sample hold circuit, 18... Dropout detector.

Claims (1)

[Claims for Utility Model Registration] Reading means for obtaining an information signal from a recording medium carrying an information signal carrying a composite video signal, demodulating means for demodulating the information signal to obtain the composite video signal, and the composite video signal a pulse generating means for generating a sampling pulse at a timing corresponding to the burst pulse generation timing in the above; a time axis error detection signal having a level that gradually increases (or gradually decreases) in synchronization with a reference horizontal synchronizing signal; and a time-base error signal generating means for receiving one of the sampling pulses, sampling the level of the time-base error detection signal, and storing this as a time-base error signal until receiving a sampling pulse subsequent to the first sampling pulse. A time axis correction device in an information signal reading device, comprising dropout detection means for generating a dropout detection signal when detecting a dropout of the read signal, and during the existence period of the dropout detection signal,
A time axis correction device comprising: means for prohibiting supply of the sampling pulse to the time axis error signal generating means.