JPS62254583A - Skew correction circuit - Google Patents

Abstract

PURPOSE:To eliminate a skew distortion by changing a delay time according to the frequency of a synchronizing signal. CONSTITUTION:A luminance signal of reproduced video signals is delayed by the first variable delay means 5A, 5B and a chrominance signal is delayed by the second delay means 9A, 9B. Then, the first and the second variable delay means are driven by oscillating means 18A, 18B. The synchronizing signal included in the reproduced video signal is separated, a saw-tooth shaped wave having the inclination changed according to the frequency of the synchronizing signal is generated from control means 14-17 to control the oscillating means and the delay time of the first and the second variable delay means is changed according to the frequency of the synchronizing signal. Thereby, the discontinuity of a switch part due to the extension and contraction of a tape and the fluctuation in the frequency of the synchronizing signal are suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a skew correction circuit suitable for use in video tape recorders and the like.

[Summary of the invention]

This invention provides control means for controlling first and second variable delay means for respectively delaying a luminance signal and a chrominance signal in a reproduced video signal to generate a sawtooth wave whose slope changes according to the frequency of a synchronizing signal. driven by oscillation means controlled by
By changing the delay time according to the frequency of the synchronization signal, so-called skew distortion can be eliminated.

[Conventional technology]

In a video tape recorder that sequentially records information on diagonal tracks using a plurality of rotating heads, so-called H-alignment is performed so that the recording positions of horizontal synchronization signals are adjacent to each other between adjacent tracks. If the arrangement is misaligned, discontinuity will occur in the horizontal synchronizing signal interval at the head switching portion, and the reproduced screen will be distorted, resulting in so-called skew distortion.

On the other hand, in conventional high-end professional video tape recorders, a time axis correction circuit is connected to correct jitter, but if the switching section produces an extremely short horizontal synchronization signal in the output of the video tape recorder, this can be corrected. Can not. In addition, there are many cases in which the RF multiplied signal is lost due to switching transients, and a dropout compensation circuit is often in operation. In any case, normal demodulation is not performed. Therefore, in normal monitors, the switching point is set within vertical blanking to make screen distortion less noticeable.

In addition, a switching point is placed at the bottom of the screen for general business use, and at the equivalent pulse section for broadcast use, so that screen distortion is not noticeable.

[Problem that the invention seeks to solve]

However, in some cases, a so-called full-scan monitor, which is capable of monitoring areas other than the picture area, may be connected as a monitor to the video tape recorder. In such a case, even if the switching point is at vertical blanking, any skew distortion will appear on the screen, which is a problem.

The present invention has been made in view of the above, and an object thereof is to provide a skew correction circuit that can prevent skew distortion in any case.

[Means for solving problems]

The skew correction circuit according to the present invention includes a first variable delay means (5A
), (5B) and a second variable delay means (9A) for delaying the color signal in the reproduced video signal.

(9B), oscillation means (18A) for driving the first and second variable delay means; (18B); control means (14) to (17) for generating waves to control the oscillation means, and configured to change the delay times of the first and second variable delay means according to the frequency of the synchronization signal. are doing.

[Effect]

The luminance signal in the reproduced video signal is delayed by the first variable delay means (5A), (5B), and the color signal is delayed by the second variable delay means (9A), (9B).

These first and second variable delay means are driven by oscillation means (18A) and (18B). Further, the synchronization signal included in the reproduced video signal is separated, and the control means (14) to (17) generate a sawtooth wave whose slope changes according to the frequency of the synchronization signal to control the oscillation means. .

Then, the delay times of the first and second variable delay means are changed depending on the frequency of the synchronization signal. For example, when the frequency of the synchronization signal is low, the delay time is gradually shortened, and when the frequency of the synchronization signal is high, the delay time is gradually increased. This suppresses discontinuities in the switch section and fluctuations in the frequency of the synchronizing signal due to expansion and contraction of the tape.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail based on FIGS. 1 to 5.

FIG. 1 shows the circuit configuration of this embodiment. In the figure, (IA) and (IB) are playback heads,
The video signals reproduced by the heads (IA) and (IB) are supplied to bypass filters (3A) and (3B) via reproduction amplifiers (2A) and (2B), respectively, where the FM-modulated luminance signal is Extracted. This luminance signal is supplied to demodulators (4A) and (4B) and demodulated.

The demodulated luminance signal is transferred to a charge-coupled device (referred to as CCO) (5A) as a variable delay line.
5B) and after a predetermined delay as will be described later, is supplied to one input of an adder (7) via a switch (6). In addition, the switch (6) is set to 1.5 from the switching pulse SP for head switching shown in FIG.
Switching is performed by a pulse delayed by H (H is the horizontal frequency).

Furthermore, the video signals from the heads (iA) and (IB) that have passed through the playback amplifiers (2A) and (2B) are supplied to low-pass filters (8A) and (8B), respectively, where, for example, 688kHz low-pass conversion color A signal is extracted. This low frequency conversion color signal is supplied to, for example, CCDs (9A) and (9B) as variable delay lines, and after receiving a predetermined delay as described later, a switch (lO) is applied.
is supplied to the frequency conversion circuit (lla) constituting the APC circuit (11).

The APC circuit (11) includes a frequency conversion circuit (lla), a bandpass filter (llb), a phase detector (lie
).

Crystal oscillator (lid) that generates a 3.58MHz signal
.

A voltage controlled oscillator (LI) that generates a 4.27 MHz signal
e), the color burst signal obtained at the output side of the bandpass filter (llb) and the 3.58 MHz signal from the crystal oscillator (lid) are compared in phase with a phase detector (llc), and the phase error voltage is calculated. voltage controlled oscillator (lie
) is controlled and supplied to the frequency conversion circuit (lla) to perform frequency conversion, and the bandpass filter (lla)
A 3.58 MHz carrier color signal is obtained on the output side of b).

The 3.58 MHz carrier color signal is supplied to the other input side of the adder (7), added to the luminance signal supplied to the one input side, and taken out at the output terminal (12).

Further, a switch (13) for selectively taking out the output of the demodulators (4A) and (4B) is provided on the output side of the demodulators (4A) and (4B). This switch (13)
is switched by a switching pulse sp as shown in FIG. 3A for head switching. Demodulator taken out (4A)
, (4B) is supplied to a synchronization separation circuit (14), where the horizontal synchronization signal is separated.The horizontal synchronization signal separated by 0 is supplied to a frequency-voltage conversion circuit (15), which converts the frequency signal into a voltage signal. is converted to This frequency-voltage conversion circuit (15) has characteristics as shown in FIG. 2A,
Generates a voltage proportional to frequency. In other words, a voltage Vo is generated with respect to the standard frequency fo of the separated horizontal synchronization signal, but when the frequency of the horizontal synchronization signal becomes higher than the standard frequency fo and reaches fH (when the tape is compressed), the voltage increases in proportion to this. A voltage VH higher than Vo is generated, and conversely, when the standard frequency fo becomes lower than fL (the tape is stretched), a voltage VL lower than the voltage Vo is generated proportionally.

The voltage signal converted by the frequency-voltage conversion circuit (15) is supplied to the voltage-current conversion circuit (16), where the voltage signal is converted into a current signal. This voltage-current conversion circuit (16) has characteristics as shown in FIG. 2B, and generates a current proportional to the voltage. In other words, as the supplied voltage increases, a large current is generated, and as the supplied voltage decreases, a small current is generated.

The current signal converted by the voltage-current conversion circuit (16) is supplied to sawtooth wave generation circuits (17A) and (17B).

These sawtooth wave generation circuit (17A), (17B>) are a switch S- connected in series between the output side of the voltage-current conversion circuit (16) and the ground, a DC power supply E, and a constant voltage generator connected in parallel to this series circuit. Consists of a current source 1o and a capacitor C,
The constant current source Io is for creating a constant offset current by sucking a current corresponding to the standard frequency of the horizontal synchronizing signal. Further, the switch needle of the sawtooth wave generation circuit (17^) is turned on by a reset pulse RPI as shown in FIG. The switch S- is turned on by a reset pulse RP2 as shown in FIG. 3C, which is generated in synchronization with the falling edge of the switching pulse SP. Sawtooth wave generation circuit (17A)
.

From (17B), when the frequency of the horizontal synchronizing signal is lower than the standard frequency, that is, when the tape is stretched, a voltage of a certain level is generated at the time of generation of the reset pulse, and from this voltage gradually decreases until the next reset pulse. On the other hand, when the frequency of the horizontal synchronizing signal is higher than the standard frequency, that is, when the tape is shrinking, the level gradually increases from the point at which the reset pulse is generated. Then, a sawtooth wave Vc is generated which returns to the original level with the next reset pulse. In other words, when the frequency of the horizontal synchronizing signal is higher than the standard frequency, a sawtooth wave is generated in the opposite direction to that when the frequency is lower than the standard frequency.

The sawtooth wave generated in this way is generated by a voltage controlled oscillator (
18A) and (18B). The voltage controlled oscillators (18A) and (18B) have characteristics as shown in FIG. 2C, and generate a clock signal having a period proportional to the sawtooth voltage. That is, the lower the sawtooth voltage, the shorter the period of the generated clock signal, and conversely, the higher the sawtooth voltage, the longer the period of the generated clock signal.

Clock signal from voltage controlled oscillator (18A) is CCD
(5A), (9A), voltage controlled oscillator (
The clock signal from CCD (5B),
(9B). CCD (5A), (9
A), (5B), and (9B) have the characteristics shown in the second diagram, and are voltage controlled oscillators (18^).

A delay amount proportional to the period of the clock signal from (18B) is given to the input signal. That is, the shorter the period of the clock signal, the smaller the amount of delay, and conversely, the longer the period of the clock signal, the larger the amount of delay.

Next, as an example, we will explain how to correct when the tape stretches.
This will be explained with reference to the drawings and FIG.

Figures 4A and 4B show the state of signals that have been recorded and played back correctly. At the switching point indicated by the broken line, the horizontal synchronization signal intervals of both channels are continuous (that is, the phases are continuous). Figures 4C and D During playback, the tape is stretched more than during recording, and the frequency of the horizontal synchronization signal is played lower than the standard frequency (IH interval is long), and the horizontal synchronization signal interval of both channels becomes discontinuous at the switching point. Because of this, skew distortion occurs.

Therefore, a synchronization separation circuit (14) separates the horizontal synchronization signal, a frequency-voltage conversion circuit (15) converts the horizontal synchronization signal from a frequency signal to a voltage signal, and a voltage-current conversion circuit (16) converts it into a current signal. Convert and create sawtooth wave generation circuit (17
A), (17B). Sawtooth wave generation circuit (1
7A) and (17B) generate a sawtooth wave in which the voltage gradually decreases as shown in Figure 4, and the voltage controlled oscillator (18A
), (18B). Voltage controlled oscillator (18
A), (18B) generate a clock signal whose period gradually becomes shorter, and the CCD (5A), (9A)
(5B) and (9B). CCD (
5A), (9A), (5B), and (9B) gradually reduce the amount of delay (delay time) within one field according to the supplied clock signal as shown in FIG. That is, in Fig. 5, τ1 is CCD (5A)
, (9A) delay amount, τ is CCD (5B),
The delay amount (9B) is substantially the same, and τ0 is the delay amount at the time of reset.

As a result, as shown in FIGS. 4E and 4F, the horizontal synchronization signal intervals of both channels at the switching point become continuous, and fluctuations in the frequency of the horizontal synchronization signal are also suppressed.

In this way, in this embodiment, the variable delay line to which video signals of multiple channels are supplied is controlled with a monotonically increasing or monotonically decreasing sawtooth wave to perform time axis correction, and then switching is performed, thereby eliminating skew distortion. Prevented. In the above-described embodiments, the variable delay line is not limited to the CCO, and other delay means may be used.

〔Effect of the invention〕

As described above, according to the present invention, the variable delay means to which the video signal is supplied via the oscillation means is controlled by a sawtooth wave whose slope changes according to the frequency of the synchronizing signal, and I changed the delay time, so
Discontinuity in the phase of both channels at the switching point is prevented, and fluctuations in the frequency of the synchronizing signal are corrected, thereby reducing skew distortion during reproduction, and is particularly useful for full scan monitors.

Furthermore, mechanical skew adjustment, which was conventionally performed, becomes unnecessary. Furthermore, since the length of 1H is constant, color signal system APC
The load on the follow-up characteristics of the circuit can be reduced.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention, FIG. 2 is a characteristic diagram of each part, and FIGS. 3 to 5 are diagrams for explaining the operation of the present invention. (IA), (IB) are playback heads, (3A),
(3B) is a bypass filter, (4A), (
4B) is a 1lUl device, (5A), (5B),
(9A) and (9B) are charge coupled devices (CCD)
, (7) is an adder, (8A) and (8B) are low-pass filters, (11) is an NPC circuit, (14) is a synchronous separation circuit, (15) is a frequency-voltage conversion circuit, and (16) is a voltage-current conversion circuit. The circuits (17A) and (17B) are sawtooth wave generation circuits, and (18A) and (18B) are voltage controlled oscillators.

Claims (1)

[Scope of Claims] A first variable delay means for delaying a luminance signal in a reproduced video signal; a second variable delay means for delaying a color signal in a reproduced video signal; oscillation means for driving the second variable delay means; and control means for controlling the oscillation means by generating a sawtooth wave whose slope changes according to the frequency of a synchronization signal included in the reproduced video signal. A skew correction circuit, characterized in that the delay times of the first and second variable delay means are changed according to the frequency of the synchronization signal.