JPS6154316B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dropout compensation circuit for a triple signal decoder.

A video disc player using the so-called TED method uses a stylus to press and scan the signal structure of a high-speed rotating video disc, detects the carved signal waveform as a pressure fluctuation, and converts it into an electrical signal using a piezoelectric element directly connected to the stylus. It is converted into .

However, dropouts may occur in the image due to inappropriate stylus pressure on the signal groove, dust on the video disk, scratches on the video disk surface, and other various causes. The color is completely different from the original color, and appears in the form of unsightly dots or lines on the reproduced image surface. In such a case, a method of compensating by inserting the waveform of one horizontal scanning line before the signal waveform with dropout can be considered, but TED
In this type of video disc player, a three-line sequential method is adopted for processing color video signals, so it is not possible to simply correct the waveform of one horizontal scanning line before. In other words, in the 3-wire sequential system, 1
Red (R), green (G), and blue (B) are recorded in order for each horizontal scanning line, and R, G, and B are detected in that order during playback as well. Therefore, if a dropout occurs in the R signal, the B signal one horizontal scanning line before
If the signal is supplemented as it is, a completely different color will be obtained, so it is necessary to supplement the signal three horizontal scanning lines before, which are in color synchronization.

The present invention has been made in view of the above points, and has three horizontal scanning lines (3H) which are controlled to open and close by a dropout detection pulse at the downstream stage of the video demodulator.
A switch circuit is provided to feed back and compensate for the delayed signal. Therefore, the color synchronization is consistent, and a corrected waveform that is extremely similar to the actual waveform can be obtained. However, in general, when the pickup leaves the disk and a dropout occurs, a squelch signal is output to cut off the video signal, but this cannot compensate for the dropout. Therefore, it is necessary to prohibit the squelch signal from occurring even if there is a momentary dropout. However, even when no signal is detected from the pickup for a long time, if the squelch signal is still prohibited, a signal delayed by 3H will be fed back in phase, causing an oscillation phenomenon. Therefore, a squelch signal inhibition gate circuit is inserted between the switch circuit and the 1H delay line to prevent the dropout correction signal delayed by 3H from being supplied to the 1H delay line while the video disc breaker is not operating. It's getting old.

An embodiment of the present invention will be described below based on the drawings.

1 is the input terminal for the FM signal detected by the pickup from the video disc, and this input terminal 1 is
FM video signal demodulator 3 via preamplifier 2
It is connected to the. A luminance signal line 4 containing high-frequency components, which is one line on the output side of the video demodulator 3, includes a delay line 5 for compensating for a delay caused by a low-pass filter 10, which will be described later, a dropout compensation switch circuit 6, and a luminance signal line 4 that includes a high-frequency component. The adder 7 is sequentially coupled to the low frequency component of the signal and connected to the output terminal 8.

The other line on the output side of the video demodulator 3, a line 9 for processing the low frequency components of the luminance signal, includes:
A modulator 1 connected to a low-pass filter 10 for obtaining low-frequency components and an oscillator 11 for color subcarrier (3.58MHz for NTSC system, 4.43MHz for PAL system)
2. Dropout correction switch circuit 13; gate circuit 14 that inhibits the squelch signal even when instantaneous dropout occurs as well as when no dropout occurs; 1H delay lines 15, 16 that provide a time delay of one horizontal scanning line; 17 are sequentially combined, and the OH (no delay), 1H, 2H, and 3H delayed signals are added to the adder 7 via the adder 18, and the 3H delayed signal is added to the switch circuit 6. , 13.

The preamplifier 2 includes a dropout detector 1.
9 is coupled, and the output side of this dropout detector 19 is coupled to the switch circuits 6, 13 and the time constant circuit 20. This time constant circuit 20
is output when dropout continues for a predetermined period of time, and is coupled to the video demodulator 3 and the squelch signal inhibition gate circuit 14.

Next, the operation of this circuit will be explained.

The FM signal detected by the pickup is amplified by a preamplifier 2 and demodulated by a video demodulator 3 into a triple pulse signal. The low-frequency component of this triple pulse signal is extracted by a low-pass filter 10 on line 9 that processes the low-frequency component of the luminance signal, and amplitude-modulated by a modulator 12 using a carrier wave of 3.58 MHz or 4.43 MHz. This modulated signal is sent as it is to the squelch signal inhibition gate circuit 14 via the switch circuit 13 if there is no dropout and the pickup is operating. This squelch signal inhibition gate circuit 14 remains closed not only when there is no dropout, but also when a momentary dropout occurs. Therefore, the modulated signal is sent to 1H delay lines 15, 16, 17, and the 0H, 1H, 2H and 3H delayed signals are added to adder 18 and averaged.

In the luminance signal line 4 containing the high-frequency component, the luminance signal passes through a delay line 5 for correcting the delay time caused by the low-pass filter 10, and if there is no dropout, is sent directly to the adder 7 via the switch circuit 6. Then, it is added with the low frequency component from the adder 18 and sent to the output terminal 8.

Here, when a dropout occurs in the detection signal, it is detected by the dropout detector 19 and a dropout detection pulse is obtained, and the switch circuits 6 and 13 are controlled by this pulse. A 3H delayed signal is sent from the 1H delay line 17 to the switch circuits 6 and 13. At this time, the squelch signal inhibition gate circuit 14 is not cut off by the instantaneous dropout detection pulse and remains closed. In this way, the low-frequency component luminance signal that has undergone dropout compensation in the switch circuit 13 passes through the squelch signal inhibition gate circuit 14 to the next stage 1H delay lines 15, 16, 17.
The signal is then sent to and processed. The brightness signal including the high frequency component which has been dropout compensated by the switch circuit 6 is sent to the adder 7, where it is combined with the brightness signal of the low frequency component which has been dropout compensated and signal processed.

Next, when the video disc player stops and no signal is detected from the pickup for a predetermined period of time, the output of the dropout detector 19 is fed back to the switch circuit 13 as a 3H delayed signal with an amplitude of 1 and the same phase. oscillation phenomenon. However, if the dropout continues for a predetermined period of time or more, the time constant circuit 20 outputs an output signal that shuts off the squelch signal inhibition gate circuit 14 and stops the oscillation.

As described above, in line-sequential color video processing, when a dropout occurs in a video signal detected by pickup, the present invention provides a signal from three horizontal scanning lines (3H) earlier, that is, a signal whose color synchronization matches and which is the closest. is compensated, no dots or lines appear on the playback screen, and the color synchronization of the compensated screen is the same as the dropout signal.
The reproduced screen does not change color to other colors and is compensated for in an extremely natural state. In addition, if the dropout continues for a predetermined period of time, such as when the pick-up stops, the gate circuit that prohibits the squelch signal will be disabled, cutting off the closed circuit and preventing the returned 3H delayed signal from being sent again. ,
It is possible to prevent noise from occurring on the playback screen due to oscillation. Furthermore, since independent switch circuits are provided for the luminance signal line containing high-frequency components and the line for low-frequency components, the time difference between the 3H delayed signal for dropout compensation and the output signal of the video demodulator is completely equalized. This allows for more accurate dropout compensation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a dropout compensation circuit according to the present invention. 1... Input terminal, 2... Preamplifier, 3... Video demodulator, 4... Luminance signal line containing high frequency components, 5... Delay line, 6, 13... Switch circuit,
7, 18... Adder, 8... Output terminal, 9... Luminance signal low frequency component signal processing line, 10... Low pass filter, 11... Oscillator, 12... Modulator, 14... Squelch signal prohibited Gate circuit, 1
5, 16, 17...1H delay line, 19...dropout detector, 20...time constant circuit.

Claims (1)

[Claims] 1. In a decoder that demodulates a video signal into a tripal signal using a video demodulator, processes the signal using a luminance signal line containing a high frequency component and a luminance signal line containing a low frequency component, and then adds the signals to obtain an output. A dropout compensation switch circuit provided separately for the luminance signal line containing the high-frequency component and the luminance signal line for the low-frequency component, and a dropout compensation switch circuit provided behind the switch circuit provided for the luminance signal line containing the low-frequency component. A gate circuit that inhibits the squelch signal at the time of detection, a delay line provided behind the squelch signal inhibit gate circuit to obtain a 3-horizontal scanning line delay signal and feed it back to the two switch circuits, and dropout detection from the video signal. A dropout detector detects a pulse and controls the two switch circuits, and a time constant circuit is coupled to the dropout detector and outputs an output when the dropout condition continues for a predetermined period or more to shut off the squelch signal inhibition gate circuit. A dropout compensation circuit for a triple pulse signal decoder, characterized in that: