JPS60256293A - Method for preventing chrominance synchronization at upper part of screen in vtr - Google Patents

Abstract

PURPOSE:To prevent completely the disturbance of color synchronization at the upper part of a scope by applying effectively an automatic phase control circuit even during the vertical blanking period at reproduction of a color video signal. CONSTITUTION:An automatic phase control APC circuit 12 is activated by a sum signal g+h where (g) is a burst gate pulse generated from a synchronizing signal processing circuit 10 and (h) is an extracted pulse. Then the circuit 12 compares a signal generated by a crystal oscillator 13, a color burst signal CB in a color signal subject to frequency conversion and the phase of a continuous sinusoidal wave signal (d). Then the oscillated frequency of a voltage controlled crystal oscillator VXO13 is controlled minutely by an error signal (i) in response to the phase difference. Thus, since the circuit 12 is operated normally by using the reproducing signal of the continuous sinusoidal wave signal inserted and recorded even during the vertical blanking period in the reproducing system, even if the synchronism of the color signal is disturbed due to switching of the video head, the disturbance is converged soon.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a VTR (video tape recorder), and more specifically, it records color video No. 41 separately into a luminance signal and a color signal, and The present invention relates to a method for preventing color synchronization disturbance at the top of the screen caused by video head switching in a VTR in which head switching is performed during or before the vertical blanking period.

[Conventional technology]

VTRs generally have two rotating video heads (
The video signal is recorded and played back by alternately switching the recording/playback head (recording/playback head), but a reference signal is created from the vertical synchronization signal of the video signal so that the joint is at the bottom edge of the screen or at an out of sight position outside the screen. , thereby controlling the rotation of the video head so that the switching position of the video head is during or just before the vertical blanking interval.

When recording and playing back video signals on such a VTR, the video signal is generally separated into a luminance signal and a color signal and recorded, but during playback, the playback signal becomes discontinuous at the video head switching position. , due to noise,
This causes a disturbance in the color synchronization of the color signal.

In addition, since the color burst signal inserted for the purpose of synchronizing one color interval is missing at the video head switching position or the vertical blanking period that follows, the color synchronization that is disrupted at the video head switching position is No correction is made during the vertical blanking period.

Then, based on the color burst signal inserted after the vertical blanking period, automatic phase control (APC) of the VTR is performed.
Color synchronization is achieved by the circuit, but since the color burst signal is inserted into a portion of the color signal only a few cycles per horizontal scanning period (horizontal scanning period), the correction ability of the APC circuit is weak, and color synchronization may be disrupted. It may take several 101-1 times after the vertical blanking period ends before correction is made, which disrupts the color synchronization of the two parts of the screen, making it very unsightly.

In order to prevent such color interphase disturbances in the second part of the screen in a VTR, the following methods have conventionally been used.

(1) The reproduced and demodulated color (chroma) signal is detected by detecting the reversal of the hue of 3 and converting the phase by +80" to bring it into the normal phase relationship, or the color signal 90° I detects a 90° phase shift and converts the phase by 90” to bring it into the normal phase relationship.
Method D and a method that uses both methods together.

(2) The video head switching position in the playback power video signal shown in Figure 6 (a) is 12ia fVIIS power type standard. AP as shown in figure (b)
Stop the operation of the APC circuit by C stop No. 473,
During this time, the APC information (an error signal indicating a phase shift) immediately before the stop is held as shown in FIG.

[Problem to be solved by the invention J However, in the method (1) above: j, demodulation color = 3
= It takes several 11 hours to detect a color inversion or a 90° phase shift of one signal (it takes time to pull in from a state other than a 180° or 90° phase shift), and in reality there are many malfunctions. There was a problem that it could not be completely corrected.

In addition, with the method (2) above, it is not possible to completely retain APC information while the APC circuit is stopped, and there is no new APC information during the stopped period, so APC
There was a problem in that color synchronization was often disrupted due to noise shock when the circuit was restarted. This invention solves these problems and more effectively and reliably adjusts the color at the top of the screen than the above-mentioned conventional method. The purpose is to prevent interphase disturbances.

[Means to solve the problem]

In order to solve the above-mentioned problem, the method for preventing intercolor period disturbance 4 at the top of the screen in a VTR according to the present invention, when recording a color video signal, at least the period corresponding to the vertical blanking period of the separated color signal. A continuous sine wave 4-signal synchronized with the color burst signal is inserted into a portion of the video head. The color interperiod disturbance caused by switching is made to converge within the vertical blanking period.

(Example〕 An embodiment of the present invention will be described below with reference to the drawings.

First, a method for recording a color video signal in a VTR embodying the present invention will be explained with reference to the signal waveform diagram shown in FIG.

FIG. 1(a) shows the vertical blanking period of a normal color video signal (television signal) and the signal waveforms before and after the vertical blanking period.

In the part other than the vertical blanking period, a horizontal synchronizing signal (15,734 KHz) t(
S and color burst signal (3,58MHz) CB
and a video signal y in which the color signal C is superimposed on the luminance signal Y.
In the vertical blanking period, there is a vertical synchronization signal (59,94Hz) VS narrowed by the equalization pulse (1/2 period of the horizontal synchronization signal), followed by a color burst. There is a period in which only signal CB is inserted.

Such a color video signal is recorded separately into a luminance signal and a synchronization signal, and a color signal and a color first signal (hereinafter simply referred to as "color signal"), and Fig. 1 (b) shows the separated parts. Indicates color signal. No color burst signal CB is included in the equalization pulse and vertical synchronization signal periods within the vertical blanking period of this color signal.

Therefore, during this period, a sampling pulse h as shown in FIG. The signal shown in the same figure (e) is created by inserting the signal into the color signal shown in the figure (e). This is set to a low frequency (6 in the Vl-1s method).
29KHz) and record it.

The continuous sine wave signal synchronized with the color burst signal is 3,58M, which is created to perform frequency conversion.
It is sufficient to use the signal H7.

By recording the color signal in this way, during reproduction, the APC circuit can be operated even during the vertical blanking period by the continuous sine wave signal d included in the reproduced color signal. Even if the color synchronization is disrupted due to the video head switching just before, the normal phase relationship can be drawn (converged) within a short period of time within the vertical blanking period. This will no longer happen.

This continuous sine wave signal is like a color burst signal.
Since it can be inserted continuously instead of several cycles per H, the effective operating period of the APC circuit becomes longer, and color synchronization deviation can be powerfully corrected in a short time.

FIG. 2 shows an example of the configuration of a recording system of a VTR embodying the present invention, and FIG. 3 similarly shows an example of the configuration of its reproduction system. Note that there are many parts where the same circuit can be used for both the recording system and the reproducing system, and these parts are given the same reference numerals.

In Figure 2, a low-pass filter (+-P 1,
The FM modulator 2 and the bypass filter (113F) constitute a luminance signal recording system. Also, 7- band pass filter (BPF)4. The frequency converter 6 and the low-pass filter constitute the main path of the color signal recording system.

Then, the input color video signal is separated into a luminance signal Y (including a synchronization signal) and a color signal C (including a color burst signal) by a low-pass filter 1 and a band-pass filter 4.

The luminance signal Y separated by the low-pass filter 1 is
The color signal is FM modulated by the FM modulator 2 and passed through the bypass filter 3 to obtain the low frequency conversion frequency n of the color signal, which will be described later.
The band near f II is cut and sent to the mixer 8.

The color signal C with a carrier frequency f s =3.58 MHz separated by the band pass filter 4 is converted into a continuous sine wave signal of 3.58 MHz synchronized with the color burst signal by a continuous sine wave signal insertion circuit 5 during a vertical line erasure period. The frequency converter 6 converts the frequency of the carrier wave into nfH (n is an integer, for example, 40.fH is the frequency of the horizontal synchronizing signal). 8-15.734K I-1z) and sent to the mixer 8 through the low-pass filter 7.

The mixer 8 superimposes this color signal on the luminance signal to create a recording video signal, which is recorded on a magnetic tape by a video head (not shown).

Furthermore, this color signal recording system includes a synchronization signal separation circuit S, a synchronization signal processing circuit 10. APC circuit CAPC phase comparator) 121 Voltage controlled crystal oscillator (hereinafter abbreviated as vXOj) that generates a continuous sine wave signal of frequency fs 1
3. AFC circuit (AFC phase comparator 42 frequency n
Voltage controlled oscillator (hereinafter abbreviated as rVcOJ) that generates a sine wave signal of fH15. I/n frequency divider 161 frequency converter 17. and a bandpass filter 18 are provided.

The synchronization signal separation circuit 9 separates a synchronization signal (a composite synchronization signal including a horizontal synchronization signal, a vertical synchronization signal, and an equalization pulse) from the luminance signal Y as shown in FIG. 5(a).

For example, as shown in FIG. 4, the synchronous in-number processing circuit 10 includes a half I-1 killer circuit 101 and a tiller circuit 102 for generating a burst gate pulse from this composite synchronous signal.

[Half I] The killer circuit 101 removes the equalization pulse at the 11/2 position and takes out only the horizontal synchronization signal and the equalization pulse with the same period (1/fu) as that signal, as shown in FIG. 5(b). . It is slightly delayed by the tiller circuit 102 to produce the burst game 1-pulse g shown in FIG. 5(c) corresponding to the color burst signal position.

The synchronization signal processing circuit 10 further includes a re-readable one-shot multi 10!1. as shown in FIG. AN
D gates 104, 105. Timer counter 106. A circuit for generating a continuous sine signal extraction pulse consisting of a multi-channel 107 and an adder circuit 10 are provided.

The one-shot multi 106 is triggered by the horizontal synchronizing signal or the rising edge of the equivalent pulse, and keeps the output at high level l' for a set time slightly longer than H/2, and if there is no next input pulse during that time, the output is turned off. Low level 0
However, when the next pulse is input within the set time, it is triggered again.

Leave the output at 1 as shown in FIG. 5(d).

AND Kate 104 is this one shot multi 103
The output of the one-shot multi 103 and the composite synchronization signal are input, and only when the composite synchronization signal becomes 0 when the output of the one-shot multi 103 is 1', the output is set to 1 as shown in FIG. 5(E).

When this pulse signal is input to the timer counter 106 through the AND gate 105, the timer counter 106 starts counting by setting the output to 1, as shown in FIG. After counting, the output is returned to O, and at the falling edge, one-shot multi 107
Tori force.

As a result, the output of the one-shot multi 107 becomes the fifth
As shown in the figure (f), after the set time l'11- becomes 0, and the AND gate 105 is closed, the timer counter 10 is set at least during the vertical blanking period.
Block input of pulses to 6.

In this way, as the output of the timer counter 106,
At least a portion of the vertical blanking period (preferably as early as possible)
A sampling pulse h for inserting a continuous sine signal into is generated and output to the continuous sine wave signal insertion circuit 5, and g+h which is added to the burst pulse 8 by the adder circuit 108 is also output.

The APC circuit 12 operates only when the burst gate pulse g is input from the synchronization signal processing circuit 10, and compares the phase of the color burst signal CB in the color signal with the sine wave signal d generated by the VXO 13, and calculates the phase of the burst gate pulse g from the synchronization signal processing circuit 10. The excavation frequency of vxol3 is slightly controlled by outputting an error signal l corresponding to the phase difference, and its output signal d is synchronized with the color burst signal.

The output signal d of this VX○16 is input to the continuous sine wave signal insertion circuit 5, and introduced to the adder circuit 52 via the switch 51, which is turned on only when the above-mentioned extraction pulse h12- is at the river'. It is inserted into the color signal separated by the filter 4 as shown in FIG. 1(E).

On the other hand, the AFC circuit 14 divides the horizontal synchronization signal of frequency f II in the composite synchronization signal separated by the synchronization separation circuit 9 and the signal of frequency n f H generated by the VCO 15 into I/n frequency by the frequency divider 16. Then, the excavation frequency of the VCO 15 is controlled by the error j signal corresponding to the difference, and the frequency of the output signal is locked to n times the horizontal timing signal.

Frequency conversion 1
17, and from the obtained signal of frequency fg±n f If, the frequency fs-
The nfH component is removed, and the fs+n f If signal is further input to the frequency converter 6.

This frequency converter 6 converts the color signal of carrier frequency fs into (fs+nfH)±fs.

Only the n f II component is sent to the mixer 8 through the low-pass filter 7 .

Next, the reproduction system shown in FIG. 3 will be explained. What differs from the configuration of the recording system described above is a bypass filter that separates the reproduced video signal into a luminance signal Y and a color signal C.
()-IPF) 20 and low pass filter (LPF) 21
．． FM demodulator 22. Continuous sine wave signal removal circuit 23. and a crystal oscillator 24 that generates a fixed signal of 3.58 MHz.
That's it.

Then, the 1t luminance No. 43 Y (including the synchronization signal) separated by the bypass filter 20 is sent to the FM demodulator 221.
This demodulates the signal.

Color signal C separated by low-pass filter 21
(including color burst signal and continuous sine wave signal)
The carrier wave frequency n f 11 is converted by the frequency converter 6 to the difference f S (
3,58 M l-1z ).

In this way, the color signal restored to its original frequency is passed through a continuous sine wave signal removal circuit 23 consisting of a switch that turns off only when the extraction pulse h from the synchronization signal processing 10 is 1, as shown in FIG. As shown in e), the continuous sine wave signal d inserted into the vertical blanking period is removed, and the mixer 8 superimposes it on the luminance signal and sends it to the TV receiver as demodulated color video (No. 75). .

By the way, in this case, the APC circuit 12 is operated by the sum signal g+h of the burst gate pulse g and the extraction pulse h generated by the synchronization signal processing circuit 10 shown in FIG. The phases of the color burst signal co and the continuous sine wave signal d in the color signal frequency-converted by 6 are compared.

Then, by the error signal 1 corresponding to the phase difference, V
Finely control the oscillation frequency of the XO13.

That is, in this playback system, even during the vertical blanking period, the APC circuit 12 can be operated normally using the playback signal of the continuous sine wave signal inserted and recorded. Even if the color signal synchronization is disrupted, it can be quickly converged.

Note that insertion of the continuous sine wave signal at the time of recording is sufficiently effective even if it does not correspond to substantially the entire period of the vertical blanking period, as long as it is inserted for a sufficiently longer period than the color burst signal.

[Effects of the Invention] As explained hereinafter, according to this invention, VTR
When reproducing a color video signal, the APC circuit can operate extremely effectively even during the vertical blanking period, so that the disturbance in color synchronization caused by switching between 5 video heads is converged within the vertical blanking period, and the upper part of the screen is This completely prevents color synchronization from being disrupted.

[Brief explanation of the drawing]

FIG. 1 is a signal waveform diagram for explaining an embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of a recording system of a VTR implementing this invention, and FIG. FIG. 4 is a block diagram showing an example of the configuration of the synchronization (i) processing circuit 10 in FIGS. 2 and 3, and FIG. Waveform Diagram FIG. 6 is a signal waveform diagram for explaining an example of a method for preventing color synchronization disturbance on the screen in a conventional VTR. 5. Continuous sine wave signal insertion circuit 6. Frequency conversion Device 10... Synchronous signal processing circuit 12... Automatic phase control (APC) circuit 23... Continuous sine wave signal removal circuit

Claims (1)

[Claims] 1. In a VTR that records a color video signal separately into a luminance signal and a color signal, and switches the video head during or before the vertical blanking period, when recording the color video signal, the separated color signal is A continuous sine wave signal synchronized with the color burst signal is inserted into at least a part of the period corresponding to the vertical blanking period, and an automatic phase control circuit is provided that performs color synchronization using the color burst signal in the reproduced color signal during reproduction. The VT is characterized in that it is operated even during the vertical blanking period by the reproduced signal of the inserted and recorded continuous sine wave signal, so that color synchronization disturbance due to switching of the video head is converged within the vertical blanking period.
How to prevent color synchronization disturbance at the top of the screen in R.