JPH0331038B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for generating a time axis error signal for a reproduced signal, and more particularly to an apparatus for generating a time axis error signal during reproduction of color video information.

A device for reproducing color video information is indispensable to have a device for time axis correction, and is therefore provided with a device for detecting time axis fluctuations of the reproduced signal. For example, this detects the timing of occurrence of a specific point (specific zero cross point) of a reproduced color burst signal, generates a timing signal, compares the phase of this signal with a reference horizontal synchronization signal provided separately, and generates a phase difference signal. is output as a time axis error signal.

Generally, the sub-carrier signal frequency in the NTSC television system is an odd multiple of 1/2 that of the horizontal sync signal, so the color burst signal superimposed on the back porch of the horizontal sync signal in several cycles is Each period of the signal is superimposed with a phase difference of 180 degrees with respect to the horizontal synchronizing signal (see FIG. 2A). Therefore, in the above-mentioned time axis error signal generation device, the phase of the reproduced color burst signal is inverted every other cycle of the horizontal synchronization signal and outputted, so that the phase of each color burst signal with respect to the reproduced horizontal synchronization signal is maintained in a constant relationship. The phase difference between the specific point of the color burst signal obtained in this way and the reference signal is detected every horizontal period.

FIG. 1 is a block diagram of a conventional example of such a time axis error signal generating device. A separator 1 consisting of a 358MHz bandpass filter is provided to extract a color burst signal from the reproduced composite video signal A, and this burst signal is applied to a limiter 2 for waveform shaping to remove noise components such as amplitude fluctuations. is removed. This limiter output is applied directly to an analog switch 4 for signal selection and via a phase inverter 5, respectively.

For switching control of the switch 4, the output of the reference synchronization signal generator 6 is used. This signal is equivalent to the horizontal synchronization signal, and the frequency of this signal is divided into 1/2 by the flip-flop 7 and is supplied as a selection command signal to the switch 4 for each horizontal synchronization to control switching. Therefore, the changeover switch 4 operates as a selection means, and the reproduced color burst signal and its phase inverted signal are alternately and selectively derived to the output D of the switch 4 every horizontal period.

On the other hand, a separator 8 is provided to separate the horizontal synchronization signal from the reproduced signal, and is triggered by the generation timing of the separated horizontal synchronization signal.
Triggered by MMV (monostable multivibrator) 9 and further by single output B of this MMV9
MMV10 is provided. This MMV10
An AND gate 11 is provided which takes the output C of the gate as a gate input, and the selection output D of the color burst signal is applied to the other inputs.

Further, a trapezoidal wave generator 12 is provided which generates a trapezoidal wave signal from a reference signal, and this trapezoidal wave signal F is applied to a sample and hold circuit 13. The output of the gate 11 triggers the MMV 14, and in response to the timing at which the single pulse E is generated by this trigger, the trapezoidal wave signal F is sampled in the sample hold circuit 13 and held until the arrival of the next sampling signal E. be done. This hold output is used as a time axis error signal. Therefore, the reference synchronization signal generator 6, the trapezoidal wave generator 12,
sample hold circuit 13, horizontal sync separator 8,
A circuit including MMVs 9, 10, 14 and gate 14 acts as a means for generating a time base error signal.

Note that the MMV10 for gate signal generation is cleared by the generation timing of the single output E of the MMV14, and the output C of this MMV10 is integrated by the integrator 17 to generate a signal corresponding to the width of the output pulse C of the MMV10 and is added. MMV9 via device 15
The pulse width is controlled. By doing this, the generation of the gate signal C by the MMVs 9 and 10 is always controlled to be constant regardless of changes over time and temperature, thereby making it possible to accurately detect a specific point of the reproduced color burst signal. Furthermore, in order to obtain a still image or a double-speed image, it is necessary to give a jump command to the pick-up to jump the recording track, but it is also possible to detect specific points of the color burst signal before and after this jump operation. To ensure accuracy, the flip-flop 16 is triggered in response to the jump command signal, and the pulse width of the output B of the MMV 9 is controlled to be alternately large and small for each jump command.

FIG. 2 is a waveform diagram showing the operation of the circuit shown in FIG. 1, and the same reference numerals in both figures indicate equivalent waveforms. As shown in Figure 2, the color burst signals of adjacent horizontal sections are all controlled to have the same phase relationship with each horizontal synchronization pair signal at the output of switch 4 (Figure D). .

Therefore, gate pulse C by MMV9,10
is the timing at which the second burst signal is gated, and therefore the phase difference (time difference) between the generation timing of this second falling point and the reference signal.
is detected every horizontal period and the objective is achieved.

Here, during the jump operation when obtaining a still image, the pick-up information detection point (spot) instantly shifts from the n-th recording track to the (n-1)th recording track to be jumped next. , the phase of the color burst signal is reversed at the track switching point. Converting this to the time axis corresponds to half the wavelength of the burst (140ns)
This means that it is off by just that. In this state, if you also gate the second falling point and detect the time axis error, the phase difference of the reproduced signal will be disturbed at the instant of switching.
It takes time to stabilize at a point shifted by 140 ns, which causes instability at the top of the screen and hue fluctuations.

Therefore, the flip-flop 16 is triggered by the jump command signal, and the output width of the MMV 9 is forced to alternately expand and shorten by about 140 ns, thereby changing the phase of the entire video signal that was being reproduced before the jump. , then jump to match the field you're going to.

However, with this method, it is difficult to accurately shift the pulse width of output B of the MMV9 by 140 ns, so the phase error between the reproduction burst on the recording track before the jump and the reference signal is greatly disturbed, which causes the reproduction after the jump. This is undesirable as it affects the upper part of the screen of the video signal. The detailed operation and function of the circuit shown in FIG. 1 are disclosed in Japanese Patent Application Laid-Open No. 56-84091 (Japanese Patent Application No. 161195-1982).

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a time axis error signal generating device for a reproduced signal, which generates a stable time axis error signal even during a jump operation and improves the quality of reproduced images.

A time axis error signal generating device according to the present invention includes a selection means for alternately and selectively guiding a reproduced color burst signal and its phase inverted signal each time a selection command signal synchronized with a horizontal synchronization signal is generated; This device has means for generating a time axis error signal according to the time difference between the generation timing of a specific point of the output waveform of the output waveform and the reference signal. The reason is that a signal corresponding to the selection command signal is forcibly generated during operation.

The present invention will be explained below with reference to the drawings.

FIG. 3 is a circuit diagram of one embodiment of the present invention, and parts equivalent to those in FIG. 1 are designated by the same symbols.
In still image reproduction or double speed reproduction, a jump command pulse is generated in response to the end of the white flag signal a (see FIG. 4A) in the reproduced video signal. Note that a white flag signal is a composite video signal signal that is part of a control code.
This refers to a specific signal that is inserted in the 11H interval or the 274th H interval and has a white level for approximately 1H interval. Therefore, this white flag signal a is detected by the detector 18, and at the falling edge of the white flag signal a, the jump pulse generator 19 generates a jump drive signal C of positive and negative levels depending on the jump in the forward and reverse directions. A jump drive signal is applied to a tracking mirror drive mechanism in, for example, an optical information reproducing apparatus in order to shift the information detection point of the pickup.

This drive signal also serves as one input of a logic circuit consisting of inverters 20, 21 and NAND gates 22-24, and a jump direction signal from a jump direction command generator 25 is applied to other inputs. This is such that high and low level signals are generated depending on the forward jump operation required in the playback mode, and the MMV 26 is triggered by the output of the gate 24. This output D serves as one input to the AND gate 27.

Output B of the MMV 28 triggered by the output of the reference horizontal synchronization signal generator 6 becomes a selection command signal for the color burst signal selection switch 4, but this output B is used as another input to the AND gate 27, and this gate output E is This serves as a trigger signal for the flip-flop 7 which generates the switch control signal F.
The output D of MMV26 is also the flip-flop 2
9 is triggered, and the analog switch 31 is controlled by this output, and the reproduced signal A or this signal A is output.
The delayed signal by the 140ns delay device 30 is selected and becomes the monitor output.

The rest of the configuration is the same as that shown in FIG. 1, except that the flip-flop 16 that responds to the jump command is not required, and its explanation will be omitted.

FIG. 4 is an operational waveform diagram of each part of the circuit of FIG. 3, and in both figures, the same reference numerals indicate waveforms of equivalent parts. When the white flag signal a included in the reproduced signal A is detected, its falling edge (time
_t1 ), a jump drive signal C is generated corresponding to the jump direction according to the reproduction mode, and a gate output D is generated from the output NAND gate 24 of the logic circuit at the end of the jump drive pulse C (time _t2 ). be done.

The pulse width _t1 to _t2 of the drive pulse C has a time width sufficient to shift the information detection point of the pickup from the current track to the next track,
For example, in the case of a pickup using a tracking mirror for deflection, this is necessary to rotate the mirror by a predetermined angle. This driving pulse disappears when the information detection point crosses the center between the tracks, and thereafter the detection point is shifted to the center of the next recording track due to the inertia of the mirror, and the jump operation is completed. Therefore, when the information detection point comes to the center between the tracks, that is, at time _t2 when the drive pulse C disappears, the MMV 26 is triggered to forcibly generate the signal D, and this is switched via the gate 27. 4 is used as a pseudo selection command signal. Therefore, at this time _t2 , the flip-flop 7 is forcibly triggered and its state is reversed, so that the selection switch 4 is forcibly switched.
Therefore, the phase of the first burst signal of the new track in the reproduced signal is inverted with respect to the phase of the last burst signal of the previous track. Output G
In this case, there is no inversion as shown in FIG. 4G, and the phase relationship with respect to the reproduced horizontal synchronizing signal does not change at all before and after the jump operation.
Note that this output G corresponds to the output D in FIG. As a result, the detection points of the specific points of the color burst signals in the preceding and succeeding recording tracks do not shift at all, and the phase of the second falling point can always be detected, thereby stabilizing the time axis servo.

On the other hand, in the playback video output, the APC (Auto Phase Control) circuit on the monitor side is disturbed after jumping, so the delay amount of the playback signal is switched at the timing of signal D to prevent image distortion and hue fluctuations at the top of the screen on the monitor. I've lost it. This delay control is performed for the same purpose in the conventional example shown in FIG. 1. For example, the output of the flip-flop 16 shown in FIG. It is what makes it work.

As described above, according to the present invention, it is possible to obtain a stable image by suppressing time axis fluctuations during jump with a simple configuration, and it is possible to reduce image blurring and hue fluctuations at the upper part of the screen.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional time axis error signal generator, FIG. 2 is a waveform diagram of each part showing the circuit operation of FIG. 1, FIG. 3 is a block diagram showing an embodiment of the present invention, and FIG. 4 is a waveform diagram of each part showing the operation of the circuit of FIG. 3. FIG. Explanation of symbols of main parts, 1...Color burst separator, 4...Signal selection switch, 5...Phase inverter, 9, 10, 14, 26, 28...MMV,
19...Jump drive pulse generator.

Claims (1)

[Claims] 1. Selection means for alternately and alternatively deriving a reproduced color burst signal and its phase inverted signal each time a selection command signal synchronized with a horizontal synchronization signal is generated, and an output waveform of the selection means. This is a reproduction signal time axis error signal generating device having a means for generating a time axis error signal according to the time difference between the generation timing of a specific point and a reference signal, and the apparatus comprises means for generating a time axis error signal according to the time difference between the generation timing of a specific point and a reference signal. An apparatus characterized in that it forcibly generates a pseudo selection command signal corresponding to the selection command signal. 2. The apparatus according to claim 1, further comprising means for generating a pseudo selection signal corresponding to the selection command signal in synchronization with the end of the recording track jumping drive signal at the information detection point.