JPS5925514B2 - Video signal time axis fluctuation removal device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for removing time axis fluctuations (so-called jitter) of a color video signal detected from a rotating recording medium such as a so-called video disk.

When detecting video signals recorded on a rotating recording medium such as a video disk while rotating at a constant speed, the time axis of the obtained video signal may vary due to eccentricity of the rotating recording medium or uneven rotation of the rotating mechanism. It is well known that this has an adverse effect on reproduced images. Particularly when a video signal includes color information, the permissible range of frequency and phase fluctuations of subcarriers is very narrow, and such time axis fluctuations must be suppressed as much as possible. A method for correcting or removing time-axis fluctuations in the detected video signal is to detect the time-axis fluctuations in the detected video signal, convert this fluctuation into a mechanical signal using a transducer, and move the video signal pickup device to the rotating recording medium. There is a method in which the relative speed between the recording medium and the pickup is kept constant by moving in the rotational tangential direction.

There is also a method in which the detected video signal is passed through a variable delay line to remove time axis fluctuations. The former method has the disadvantages of poor response of the device, poor linearity of the transducer used, making the entire device expensive, and poor reliability; The disadvantage is that the wire is very expensive. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a low-cost video signal time axis fluctuation removing device that has good responsiveness, high stability, and a simple configuration.

An embodiment of the present invention will be described below with reference to the accompanying drawings.
In FIG. 1, an FM demodulator 1 is supplied with a high frequency signal modulated by a video signal detected by a pickup or the like from a rotating recording medium (not shown) such as a video disk.

The output of demodulator 1 is a demodulated video signal. This video signal is, for example, a composite video signal including color information configured according to the NTSC system, and can be reproduced as a video by a reproduction device such as a TV receiver as it is. However, when detecting a video signal while rotating a rotating recording medium such as a video disk, there may be problems such as eccentricity of the recording medium or turntable, speed fluctuations during recording, distortion during manufacturing of the recording medium, uneven rotation of the turntable drive motor, etc. Therefore, the obtained video signal usually includes time axis fluctuation (jitter), and the magnitude of the time axis fluctuation may be 0.5% or more.

If an image is reproduced from a video signal that still contains this time axis fluctuation, image fluctuations and color blurring will occur. In order to remove such time axis fluctuations, in this embodiment, the color burst signal in the detected video signal that has passed through the switch 2 is separated by the bandpass filter 3 and supplied to one input of the phase detector 4. do.

Note that the function of the switch 2 will be described later. The output of the reference signal oscillator 5 is connected to the other input of the phase detector 4 by 1/n.
The output of a frequency divider 6 is supplied. The phase detector 4 operates during the burst gate pulse indicating that the burst signal is in progress, and generates a voltage according to the phase difference between the input signals. The output of the phase detector 4 is supplied to a voltage controlled variable frequency oscillator 8 after high frequency components are removed by a low pass filter 7 . This oscillator 8 has the same configuration as a normal voltage-controlled variable frequency oscillator, except that an element made of lithium tantalate (LiTaO3) is used as the oscillator, and the frequency can be varied by ±0.5% or more of the center frequency. It has a range. Further, it is necessary that the frequency fluctuation in the set frequency of the oscillator 8 be 10<-4> or less in order to prevent color tone deviation of the obtained video signal. Oscillator 8
The output frequency changes according to the fluctuation component ΔFIIC due to the time-axis fluctuation of the color subcarrier frequency Fs of the detected video signal. Some methods of detecting such time axis fluctuation component Δf use horizontal synchronization pulses. In addition, lithium tantalate has high stability and a low resonance Q compared to crystal, and the frequency variable range of the oscillator 8 is relatively wide, so it can cope with large time axis fluctuations. Thus, the output of the oscillator 8 containing the time axis variation component causes the detected video signal to be subjected to high frequency conversion in the first frequency converter 9, resulting in a signal that does not include the time axis variation component.

This high-frequency signal is passed through the band-pass transducer 10 and frequency-converted again by the second frequency converter 11 to obtain a video signal from which time-axis fluctuation components have been removed, and this video signal is used by a TV receiver or the like. It can be monitored. With the above configuration, it is possible to correct or eliminate the time axis fluctuation of the detected video signal, but from a practical point of view it is desirable to combine a circuit that compensates for so-called dropout when it occurs. Here, dropout refers to a no-signal state in the detected video signal due to dust or the like on the video disk. In this embodiment, the output of the wave transmitter 10 is delayed by a horizontal scanning period (1H).
After being delayed by the delay circuit 12, the third frequency converter 13 converts the signal into a lower frequency and supplies it to the switch 2.

The output signal of the frequency converter 13 is one of the output signals of the demodulator 1.
This is a pre-H signal and also includes a color signal. The switch 2 supplies the output signal of the third frequency converter 13 to the frequency converter 9 and the filter 3 in response to a control signal from a dropout detection circuit DOS (not shown) when a dropout occurs. Here, it should be noted that in general, the passband of a delay circuit using a delay line is 1 if the center frequency is f.
/3f, and if you want to pass a video signal (bandwidth is 4.2MHz in the NTSC system) as in this embodiment, the center frequency f of the video signal should be, for example, 13Mhz.
The frequency must be converted to Hz. However, in the present invention, it is possible to simplify the dropout compensation circuit, which also serves as the frequency conversion means for removing jitter, and to convert the frequency of the video signal described above, thereby achieving cost reduction. If the passband of the 1H delay circuit is made to include the frequency of the color signal,
Dropout compensation including color signals is possible, but
If dropout compensation for only the brightness signal is sufficient, 1H
The passband of the delay circuit can also be selected so that only the brightness signal passes.

In the above embodiment, the second frequency converter 11 and the third frequency converter 13 are used to return the high frequency converted signal by the first frequency converter 9 to the original video signal, and a heterodyne system is used. A demodulator may be used to return the high frequency converted signal to the original video signal.

[Brief explanation of the drawing]

The figure shows an embodiment of the invention. Explanation of symbols of main parts, 4...Phase detector, 5
. . . Reference frequency oscillator, 8 . . . Voltage controlled variable frequency oscillator, 9, 11, 13 . . . Frequency converter.

Claims (1)

[Scope of Claims] 1. Video signal detecting means for reproducing a video signal recorded on a rotating recording medium while rotating the rotating recording medium, and time axis fluctuation of the detected video signal from the video signal detecting means. a voltage-controlled variable frequency oscillator that generates a signal with a frequency that corresponds to the voltage and has a frequency variable range of ±0.5% or more with respect to the center frequency; and the oscillator. a first frequency conversion means for frequency converting the detected video signal into a predetermined frequency video signal by the output of the reference frequency oscillator; and a reference frequency oscillator; a second frequency conversion means for converting and producing a reproduced video signal; a delay circuit for delaying the output of the first frequency conversion means by one horizontal scanning period; and a third frequency conversion means for converting the frequency of the output of the delay circuit. ,
A video signal time axis fluctuation removing device comprising: switch means for replacing the output of the video signal detecting means with the output of the third frequency converting means when a dropout of the detected video signal occurs. 2. The reproduced video signal time base fluctuation removing device according to claim 1, wherein the voltage controlled variable frequency oscillator has a vibrator made of lithium tantalate. 3. The detection means includes a bandpass filter that passes only a predetermined frequency component of the output of the reproduction means, a reference frequency generation circuit, and a detection means that detects a signal according to a phase difference between the output of the bandpass filter and the output of the reference frequency generation circuit. 2. The reproduced video signal time axis fluctuation removing device according to claim 1, further comprising a phase detector that generates a voltage.