JPH0636615B2 - Time axis error detection circuit - Google Patents

Description

The present invention relates to a time axis error detection circuit used in a time axis correction device.

[Conventional technology]

An example of a time axis correction device configured to supply a reproduced color video signal from a video disk to a CCD delay circuit and remove a time axis fluctuation in the reproduced color video signal by controlling the delay time of the CCD delay circuit. It is shown in FIG.

In FIG. 4, a reproduced color video signal formed by being optically read from the video disc and FM-demodulated at an input terminal indicated by 31 is supplied. This reproduced color video signal is passed through the CCD delay circuit 32, and a stable color video signal (FIG. 5A) from which the time-axis fluctuation has been removed is taken out to the output terminal 33. CCD delay circuit 32
Is supplied with a clock pulse from the VCO 34. The oscillation frequency of the VCO 34 is controlled, and the delay time of the CCD delay circuit 32 is changed.

The output color video signal of the CCD delay circuit 32 is supplied to the sampling pulse generation circuit 35. The sampling pulse generating circuit 35 includes a bandpass filter 41 having a center frequency of 3.58 MHz for separating a burst signal in a color video signal, a waveform shaping circuit 42, a sync separating circuit 43, a mono-multi (monostable multivibrator). 44) and 45 and an AND gate 46.

The burst signal (FIG. 5B) separated by the bandpass filter 41 is shaped into a pulse signal (FIG. 5C) by the waveform shaping circuit 42. The mono-multi 44 is triggered by the leading edge of the horizontal sync signal (FIG. 5D) separated by the sync separation circuit 43, and the pulse signal shown in FIG. 5E is generated from the mono-multi 44. The trailing edge of the output pulse signal of this mono-multi 44 triggers the mono-multi 45,
A gate pulse (FIG. 5F) is generated at the output of the monomulti 45.

The gate pulse and the shaped burst signal are AND gate 46
And a predetermined one wave of the shaped burst signal is output as a sampling pulse to the output of the AND gate 46 (FIG. 5G).
Is taken out as. The output signal of the AND gate 46 has a phase indicating the time-axis variation of the output color video signal of the CCD delay circuit 32. This AND gate 4
The output signal of 6 is supplied to one input terminal of the phase comparison circuit 38 as a sampling pulse.

The trapezoidal wave from the trapezoidal wave generation circuit 39 is supplied to the other input terminal of the phase comparison circuit 38. Trapezoidal wave generation circuit 39
Generates a trapezoidal wave shown in FIG. 5I which is synchronized with the reference horizontal synchronizing signal (FIG. 5H) which is the reference of the time axis from the terminal 40. The phase comparison circuit 38 is configured as a sampling and holding circuit, and the inclined portion of the trapezoidal wave is gated by the sampling pulse. The phase error voltage (J in FIG. 5) generated at the output of the phase comparison circuit 38 is supplied to the control terminal of the VCO 34, and the oscillation frequency of the VCO 34 is controlled.

FIG. 6 shows the time axis correction operation of the above-described time axis correction device. In FIG. 6A, the waveform 47 indicated by the solid line is
FIG. 6B shows the time change of the error voltage, and FIG. 6B shows the time change of the difference between the actual error (the waveform 48 of the broken line in FIG. 6A) and the detected error. 1 step of error voltage is 1
Corresponds to the horizontal period.

[Problems to be solved by the invention]

The vertical blanking period in the color video signal includes a period in which the burst signal is not included. In FIG. 6A, the error voltage is held at the previous value as indicated by 49 during the period in which the burst signal does not exist, which is indicated by TB.
Therefore, as shown in FIG. 6B, the difference from the actual error is
This difference becomes very large at the beginning of the interval where the next burst signal is accumulated.

A large difference between the detected error voltage and the actual error must be absorbed from the beginning of the section where the burst signal located in the latter half of the vertical blanking period exists to the beginning of the video period. However, when the time-axis variation is large, this difference cannot be absorbed, and the time-axis variation remains at the upper part of the screen, the color synchronization of the monitor television receiver cannot follow, and color unevenness occurs.

Therefore, an object of the present invention is to eliminate the interruption of the time axis correction operation that occurs due to the absence of a burst signal, and to make it possible to continuously detect time axis fluctuations even in a section where there is no burst signal. It is to provide a detection circuit.

[Means for solving problems]

The present invention is a gate pulse having a pulse width larger than at least one cycle of a burst signal of an input color video signal, which is triggered by a horizontal synchronization signal separated from an input color video signal and, after a predetermined time with reference to the horizontal synchronization signal. Is generated with respect to the burst signal, and the monostable multivibrator (15) having the time constant switching means (20) and the output of the monostable multivibrator (15) are in a predetermined phase based on the horizontal synchronizing signal. From the trailing edge of the output of the monostable multivibrator (15), the gate means (16) for gating the burst signal, the reset means (23) for resetting the monostable multivibrator (15) with the output of the gating means (16) A sampling pulse generating means (22) for generating a sampling pulse, and a sampling pulse Comparing means (8) for generating an error output by comparing the pulse and the phase reference signal, and detecting the presence / absence of a burst signal in the input color video signal, and a monostable multivibrator (15) when the burst signal is not detected. And a control means (21) for controlling the time constant switching means (20) so as to shorten the time constant of (1).

[Action]

The presence or absence of the burst signal is detected by the envelope detection circuit 21. When the burst signal is present, a pulse signal having a leading edge delayed by a certain time from the leading edge of the horizontal synchronizing signal and having a trailing edge reset by a predetermined wave of the separated burst signal is generated by the monomulti 15. It is formed. A sampling pulse having the phase information of the color video signal is generated from the output signal of the monomulti 15. On the other hand, when the burst signal does not exist, the monomulti 15 is not reset, the time constant of the monomulti 15 is reduced, and the same sampling pulse as when the burst signal is present is formed by the monomulti 15.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of a time axis correction device to which the present invention can be applied.

In FIG. 4, a reproduction color video signal formed by being optically read from the video disc and being FM demodulated is supplied to an input terminal indicated by 1. This reproduced color video signal is passed through the CCD delay circuit 2 and output terminal 3
Then, a stable color video signal (FIG. 3A) from which the time-axis fluctuation is removed is taken out. In the CCD delay circuit 2,
A clock pulse is supplied from the VCO 4. This VCO
The oscillation frequency of 4 is controlled, and the delay time of the CCD delay circuit 2 is changed.

The output color video signal of the CCD delay circuit 2 is supplied to a sampling pulse generation circuit 5 described later. The sampling pulse generating circuit 5 forms a sampling pulse (J in FIG. 3) having a phase corresponding to the time-axis variation of the output color video of the CCD delay circuit 2. This sampling pulse is supplied to one input terminal of the phase comparison circuit 8.

The trapezoidal wave from the trapezoidal wave generation circuit 9 is supplied to the other input terminal of the phase comparison circuit 8. The trapezoidal wave generation circuit 9 generates a trapezoidal wave shown in FIG. 3L in synchronization with the reference horizontal synchronizing signal (FIG. 3K) which is the reference of the time axis from the terminal 10.
The phase comparison circuit 8 is configured as a sampling and holding circuit, and the sloped portion of the trapezoidal wave is gated by the sampling pulse. The phase error voltage (M in FIG. 3) generated at the output of the phase comparison circuit 8 is supplied to the control terminal of the VCO 4, and V
The oscillation frequency of CO4 is controlled.

The sampling pulse generating circuit 5 has the configuration shown in FIG. In FIG. 2, from the input terminal indicated by 6 to C
The output color video signal of the CD delay circuit 2 is supplied to the bandpass filter 11 and the sync separation circuit 13.

The bandpass filter 11 has a center frequency of 3.58 MHz. The burst signal separated by the band pass filter 11 (FIG. 3B) is shaped into a pulse signal (FIG. 3C) by the waveform shaping circuit 12. Sync separation circuit 1
Mono-multi (abbreviation of monostable multi-vibrator) 1 by the leading edge of the horizontal synchronizing signal (Fig. 3D) separated by 3
4 is triggered, and the pulse signal shown in FIG. 3E is generated from the monomulti 14. The trailing edge of the output pulse signal of the mono-multi 14 triggers the mono-multi 15 to generate a gate pulse (F in FIG. 3) at the output of the mono-multi 15.

The gate pulse and the shaped burst signal are AND gate 16
And a predetermined one wave of the shaped burst signal is taken out from the output of the AND gate 16 as shown in FIG. 3G. The output signal of the AND gate 16 is the monomulti 23
Is supplied to. The monomulti 23 is triggered by the trailing edge of the output signal of the AND gate 16 and generates a narrow reset pulse (FIG. 3H) which falls to a low level. This reset pulse is supplied to the reset terminal of the monomulti 15, and the monomulti 15 is reset at the leading edge of the reset pulse.

The gate pulse (FIG. 3F) generated at the output of the mono-multi 15 is supplied to the mono-multi 22. Mono Multi 22
Are triggered on the trailing edge of the gate pulse to generate the sampling pulse shown in FIG. 3J. This sampling pulse is taken out to the output terminal 7. The trailing edge of the gate pulse is defined by the burst signal and has the phase information of the color video signal.

The mono-multi 15 includes a capacitor 17 and a resistor 18, and has a time constant circuit in which a series circuit of a resistor 19 and a switch 20 is connected in parallel with the resistor 18. The switch 20 is controlled by the detection signal of the envelope detection circuit 21.

The envelope detection circuit 21 includes a bandpass filter 1
The burst signal generated is supplied to the output terminal of No. 1 and the envelope detection circuit 21 generates a detection signal having a level according to the presence or absence of the burst signal. The detection signal becomes high level when there is a burst signal, as shown in FIG. 3I,
It goes low when there is no burst signal. When the detection signal is high level, the switch 20 is turned off, and when the detection signal is low level, the switch 20 is turned on.

The time constant of the monomulti 15 when the switch 20 is off is
It is determined by the capacitor 17 and the resistor 18. The time constant of the capacitor 17 and the resistor 18 is
The pulse width of the output pulse is set to be slightly longer so as to include the position of a predetermined wave (FIG. 3G) of the burst signal, as indicated by the broken line in FIG. 3F.

The time constant of the monomulti 15 when the switch 20 is on is
It is determined by the parallel connection of the resistors 18 and 19 and the capacitor 17, and becomes smaller than the time constant when the switch 20 is off. When the switch 20 is on, the pulse width of the output pulse of the monomulti 15 is equal to the pulse width when the monomulti 15 is reset by a predetermined wave of the burst signal when the switch 20 is off. A value of 19 is chosen.

The first half of the waveform diagram shown in FIG. 3 is for when a burst signal is present, and the second half of this waveform diagram is for when there is no burst signal during the vertical blanking period or the like. When there is a burst signal, the envelope detection circuit 21
The detection signal (I in FIG. 3) becomes high level during the period of the burst signal. Therefore, the switch 21 is turned off, and G in FIG.
As shown in the first half of FIG. 3, a predetermined wave of the burst signal is generated at the output of the AND gate 16 and the reset pulse (FIG. 3H) of the monomulti 15 is generated.

When there is no burst signal, no pulse signal is generated at the output of the AND gate 16 and the envelope detection circuit 2
The detection signal of 1 becomes low level as shown in FIG. Therefore, the switch 20 is turned on, and the time constant of the monomulti 15 becomes short. Therefore, as shown in FIG. 3F, a gate pulse having the same pulse width as when the monomulti 15 is reset is generated. This gate pulse triggers the monomulti 22 to form the sampling pulse shown in FIG. 3J.

The leading edge of the gate pulse formed by the mono-multi 15 is delayed from the leading edge of the horizontal synchronizing signal by a fixed time defined by the mono-multi 14. Therefore, the leading edge of this gate pulse has the phase information of the color video signal indicated by the phase of the horizontal synchronizing signal. Therefore, even in the section where the burst signal does not exist, the sampling pulse (J in FIG. 3) having a phase substantially matching the actual time-axis fluctuation can be generated, and the time-axis error can be continuously detected.

[Effect of the Invention] According to the present invention, even in a vertical blanking period in which a burst signal does not exist, or in a period in which burst signals cannot be separated by dropout, a time axis error of Detection can be performed. Therefore, the difference between the actual time axis error and the detected time axis error becomes large, and it is possible to prevent color unevenness from occurring in the reproduced image.

[Brief description of drawings]

FIG. 1 is a block diagram of a time axis correction device to which the present invention can be applied, and FIG. 2 is a block diagram of an embodiment of the present invention.
The figure is a waveform diagram of each part used for explaining one embodiment of the present invention,
FIG. 4 is a block diagram of a conventional time axis correction device, FIG. 5 is a waveform diagram of each part for explaining the conventional time axis correction device, and FIG. 6 is a schematic view for explaining the conventional time axis correction device. It is a diagram. Description of main symbols in the drawings 1: Color video signal input terminal, 2: CCD delay circuit, 3: Output terminal, 4: VCO, 5: Sampling pulse generation circuit, 11: Bandpass filter, 13: Sync separation circuit, 14, 15, 22, 23: Mono-multi, 20:
Switch, 21: Envelope detection circuit.

Claims (1)

[Claims] 1. A pulse width which is triggered by a horizontal synchronizing signal separated from an input color video signal and which, after a predetermined time with reference to the horizontal synchronizing signal, is larger than at least one cycle of a burst signal of the input color video signal. Generating a gate pulse for the burst signal, and generating a monostable multivibrator having a time constant switching means, and a burst signal in a predetermined phase based on the horizontal synchronizing signal by the output of the monostable multivibrator. Gate means for gating, reset means for resetting the monostable multivibrator with the output of the gate means, sampling pulse generating means for generating a sampling pulse from the trailing edge of the output of the monostable multivibrator, and the sampling pulse Error is generated by comparing with the phase reference signal Comparing means for generating force and detecting the presence or absence of the burst signal in the input color video signal, and shortening the time constant of the monostable multivibrator when the burst signal is not detected,
And a control unit for controlling the time constant switching unit.