JPS62203495A - Video signal processing circuit in video tape recorder - Google Patents

Abstract

PURPOSE:To obtain a reproducing picture having high picture quality in which skew distortion is corrected by detecting the dislocation in phase between demodulated video signals based on a horizontal synchronizing signal, correcting the dislocation of the phase by two delay circuits and obtaining the continuous video signal through a switching circuit. CONSTITUTION:The first delay circuit 8 outputs the video signal from the first demodulating circuit 6 constituted of a fixed delay line by delaying with a prescribed time. The second delay circuit 9 is constituted of a variable delay line, for instance, a CCD (Charge Coupled Device) delay line and delays and outputs the video signal from the second demodulating circuit 7 based on a delay control signal from a delay control signal forming means 12. To a phase comparator 14, a head switching pulse is applied and it compares the phases between both horizontal synchronizing signals at the timing immediately before the switching of a head. The delay control signal forming means 12 detects the phase difference between both horizontal synchronizing signals, forms the delay control signal so as to make coincident the phase of the video signal outputted from the first delay circuit 8 with that of the video signal outputted from the second delay circuit 9 and supplies to the second delay circuit 9.

Description

[Detailed Description of the Invention] Technical Field> The present invention relates to a video signal processing circuit in a video tape recorder equipped with at least two rotating magnetic heads.
More specifically, the present invention relates to a video signal processing circuit for correcting skew distortion that occurs when switching cylindrical rotating magnetic heads.

<Prior Art> In a general home video tape recorder, two rotating magnetic heads sequentially record a video signal of one minute per field on each track, and during playback, each rotating magnetic head records one minute of video signal per field. Each video signal is alternately reproduced, and the reproduction output from each rotating magnetic head is alternately switched to obtain a continuous video signal. When switching the rotating magnetic head, the horizontal synchronizing signal becomes discontinuous due to changes in tape tension, etc., resulting in skew distortion. However, conventionally, video signals for one field are recorded on one track, so the joint of video signals due to head switching is recorded in an inconspicuous place on the playback screen, that is, during the vertical blanking period. This prevents the effects of skew distortion from appearing on the playback screen.

By the way, with the recent trend toward higher image quality, a method can be considered in which, for example, the number of rotations of the head drum is doubled to increase the relative speed to achieve higher image quality. In this case, assuming that the head configuration is the same, one rotating magnetic head can record only half a field of video signals on one track, and one rotation of the rotating head drum, that is, two
Video signals for one field are recorded on one track using two rotating magnetic heads. Therefore, in the same playback process as before, the switching point of the rotating magnetic head comes not only during the vertical blanking period but also from the center of the playback screen, and the image disturbance due to skew distortion occurs at the center of the playback screen. It will happen.

<Object of the Invention> The present invention has been made in view of the above-mentioned points, and is intended to correct the influence of skew distortion when the switching point of the rotating magnetic head is located in the center of the playback screen. The purpose is to maintain the continuity of the video signal.

<Configuration of the Invention> In the present invention, in order to achieve the above-mentioned object, at least two first. In a video signal processing circuit in a video tape recorder having a second rotary magnetic head, a first rotary magnetic head demodulates the playback output from each of the rotary magnetic heads.
a second demodulation circuit; a first delay circuit that delays the video signal from the first demodulation circuit for a predetermined time; a second delay circuit that delays the video signal from the second demodulation circuit based on a delay control signal; First and second synchronization separation circuits separate horizontal synchronization signals from each video signal respectively provided from the demodulation circuit, and the phase of each horizontal synchronization signal separated by each synchronization separation circuit is determined by head switching based on head switching pulses. forming a delay control signal for forming and outputting the delay control signal for matching the phases of the video signal output from the first delay circuit and the video signal output from the second delay circuit by comparing them at the immediately preceding timing; and a switching circuit that alternately switches the outputs of both the delay circuits and outputs them as continuous video signals.

With the above configuration, the playback output from each rotating magnetic head is demodulated by two demodulation circuits, and the phase shift between the demodulated video signals is detected based on the horizontal synchronization signal separated from both video signals. After this phase shift is corrected by two delay circuits, a continuous video signal is obtained via a switching circuit.

<Example> Hereinafter, an example of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of essential parts of an embodiment of the present invention. The video tape recorder equipped with the video signal processing circuit 1 of this embodiment, like a general home video tape recorder, has two first . The second rotary magnetic head is aligned. This video tape recorder has
In order to achieve high image quality, the number of rotations of the rotating head drum is doubled, and each rotating magnetic head is configured to alternately record or reproduce half a field of video signals on magnetic tape. .

The reproduction output from the first rotating magnetic head corresponding to channel l (ch −1) is given to the first input terminal 2,
The reproduction output from the second rotating magnetic head corresponding to channel (ch-2) is applied to the second input terminal 3. Each reproduced signal from each input terminal 2.3 is transmitted to the first . They are each amplified by the second head amplifier 4.5, and further amplified by the first head amplifier 4.5. The signal is supplied to a second demodulation circuit 6.7 and demodulated into a video signal.

FIG. 2 is a signal waveform diagram at each part in FIG. ．． The output of the second head amplifier 4.5, Fig. 2 (D) and (E) is the output of the first head amplifier 4.5. The respective outputs of the second υM circuits 6 and 7 are shown. In addition, in FIGS. 2(D) and (E>, only the horizontal synchronizing signal is shown for simplicity.As shown in FIG. 2, in each channel, the rising and falling edges of the head switching pulse Lost ID after Moe
There is a period A during which the reproduced signals overlap (tl is the horizontal scanning period).

In the present invention, the horizontal synchronizing signal in the period B immediately before head switching is extracted from the overlapping period A, the phase error is detected, and one video signal (the second demodulating circuit 7
In order to match the phase of the video signal (video signal from the first demodulation circuit 6) with the phase of the other video signal (video signal from the first demodulation circuit 6), the configuration is as follows.

That is, the first demodulator demodulates the reproduction output of each rotating magnetic head. The second demodulation circuit 6.7 and the second! A first delay circuit 8 that delays the video signal from the demodulation circuit 6 for a predetermined time, a second delay circuit 9 that delays the video signal from the second demodulation circuit based on a delay control signal, and each of the demodulation circuits 6.7. The first . The phase of each horizontal synchronization signal separated by the second synchronization separation circuits to, ti and each synchronization separation circuit 10.11 is compared at a timing immediately before head switching based on the head switching pulse, and the signal is output from the first delay circuit 8. a delay control signal forming means 12 for forming and outputting the delay control signal for matching the phases of the output video signal and the video signal output from the second delay circuit 9; and both delay circuits 8.9. It also includes a switching circuit 13 that alternately switches the output and outputs it as a continuous video signal.

The first delay circuit 8 is composed of a fixed delay line.
The video signal from the demodulation circuit 6 is delayed for a predetermined time and output. The second delay circuit 9 is a variable delay line, for example, a CCD (C
The video signal from the second decoupling circuit 7 is delayed and outputted based on the delay control signal from the delay control signal forming means 12.

The delay control signal forming means 12 includes a phase comparator circuit 14 that outputs a voltage corresponding to the phase difference between the horizontal synchronization signals from the first and second synchronization separation circuits to, 11, and a phase comparator circuit 14 that outputs a voltage corresponding to the phase difference between the horizontal synchronization signals from the first and second synchronization separation circuits to, 11, and an oscillation circuit that oscillates at a frequency corresponding to the input voltage. It consists of a voltage controlled oscillator (VCO). The phase comparison circuit 14 is supplied with a head switching pulse and is configured to compare the phases between both horizontal synchronizing signals at a timing immediately before head switching. This delay control signal forming means 12 detects the phase difference between both horizontal synchronizing signals, and based on this, the signal is output from the second delay circuit 9 in accordance with the phase of the video signal output from the first delay circuit 8. A delay control signal is formed so that the phases of the video signals match and is applied to the second delay 1 circuit 9.

FIG. 3 is a signal waveform diagram for explaining phase matching by the video signal processing circuit l of the present invention. FIG. 3(A) shows the horizontal synchronizing signal from the first synchronizing separation circuit 10, FIG.
) shows the horizontal synchronization signal from the second synchronization separation circuit 11, FIG. 3(C) shows the output of the first delay circuit 8, and FIG. 3(D) shows the output of the second delay circuit 9. In addition, Figure 3 (
In C) and (D), only horizontal synchronization signals are shown, and a to e indicate corresponding horizontal scanning periods, respectively.

The first one corresponds to both channels. The phase difference between the horizontal synchronization signals from the second synchronization separation circuit 10.11 is t, and the first
If the predetermined delay time by the delay circuit 8 is 1, then the second
The delay circuit 9 delays the video signal from the second demodulation circuit 7 by a delay ff1T-t based on the delay control signal from the delay control signal forming means 12 and outputs the delayed video signal. As a result, the phases of the mountain and gorge image signals outputted from both delay circuits 8.9 will match. In this way, the first . The video signals from the second delay circuits 8 and 9 are alternately switched by a switching circuit 13 to obtain continuous video signals. The timing of switching the mountain/gorge image signal by this switching circuit 13 is determined by the above-mentioned overlapping period A.
and is performed within the horizontal blanking period.

In this way, the reproduction output from the RAD is transmitted to each rotating magnetic field from the two first. The second demodulation circuit 6.7 demodulates the two demodulated mountain and gorge image signals, and detects the phase shift between the demodulated mountain and gorge image signals based on the horizontal synchronization signals separated from both video signals. ．． After correction by the second delay circuits 8 and 9, a continuous video signal is obtained via the switching circuit 13, so even if the switching point of the head comes to the center of the screen, the playback screen will not be disturbed. .

FIG. 4 is a diagram showing the effect of skew distortion correction by the video signal processing circuit of the present invention, in which (A) shows the playback screen before skew distortion is corrected, and (B) shows a reproduced screen after skew distortion has been corrected by the processing circuit of the present invention. Note that FIG. 4 shows an example in which an image of one straight line is displayed. As is clear from FIG. 4, the skew distortion is corrected by the processing circuit of the present invention, and image disturbance does not occur even in the center of both surfaces. Therefore, even in a video tape recorder in which the number of revolutions of the rotary head drum is doubled compared to conventional ones in order to achieve high image quality, it is possible to obtain high-quality reproduced images with skew distortion corrected. .

<Effects of the Invention> As described above, according to the present invention, at least two first.
In a video signal processing circuit in a video tape recorder equipped with a second rotating magnetic head, the playback output from each rotating magnetic head is demodulated by two demodulation circuits, and the phase shift between the demodulated mountain and gorge image signals is determined by Detection is performed based on horizontal synchronization signals that are separated from each signal, and after correcting this phase shift using two delay circuits, a continuous video signal is obtained via a switching circuit. The image will not be distorted even if the switching point of the head is reached at It becomes possible to obtain a high-quality reproduced image in which the image is corrected.

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG. 2 is a block diagram of an embodiment of the present invention.
FIG. 3 is a signal waveform diagram for explaining the operation of FIG. 1, and FIG. 4 is a diagram showing the effect of skew distortion correction by the video signal processing circuit of the present invention. 1... Video signal processing circuit, 6.7... 1st. 2nd demodulation circuit, 8.9...1st. Second delay circuit, 10.11
...First. Second synchronization separation circuit, 12...delay control signal forming means, 13... switching circuit.

Claims (1)

[Claims] (1) A video signal processing circuit in a video tape recorder including at least two first and second rotating magnetic heads, comprising: first and second demodulation circuits that respectively demodulate playback outputs from the respective rotating magnetic heads; A first circuit that delays the video signal from the demodulation circuit for a predetermined period of time.
a delay circuit; a second delay circuit that delays the video signal from the second demodulation circuit based on a delay control signal; A video signal outputted from the first delay circuit and a video signal output from the first delay circuit by comparing the phase of each horizontal synchronization signal separated by the two synchronization separation circuits at a timing immediately before head switching based on the head switching pulse. a delay control signal forming means for forming and outputting the delay control signal to match the phase with the video signal output from the two delay circuits; and alternately switching the outputs of both the delay circuits and outputting them as a continuous video signal. A video signal processing circuit in a video tape recorder, comprising a switching circuit.