JPH0452031B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for compensating for signal defects (dropouts) during playback in a video disc playback device.

Generally, the video signal recording method for video discs is
This is an FM carrier wave recording method. One of the problems that can be seen in the video played back by this type of video disc playback device is that black and white dots or streaks appear intermittently in place of regular video information at irregular positions. It is about appearing. The duration, intensity, and persistence of this video information defect vary, and even if it does not destroy the video information as a whole, the fact that such video defects appear intermittently is This significantly impairs image quality.

Therefore, various dropout compensation circuits have been proposed to eliminate the unpleasantness of this image defect, but the conventional dropout compensation circuits
Because the dropout detection pulse was used as the dropout switching pulse of the dropout compensation switch, that is, because the same pulse was used to switch between the regular signal and the 1H delayed alternative signal, the dropout compensation switch For about a few microseconds, the dropout compensation switch may be in a free state (off or on), or a timing shift may occur due to variations in the thresholds of the switching elements, resulting in gaps in the video signal and the rising edge of the switching pulse. , the switching noise due to the slowing of the falling edge remains in the signal after compensation, and even on the screen it appears about.
Black dots of about 0.1 to 0.2 μsec sometimes remained before and after the dropout.

This cannot be ignored considering that many short dropouts (approximately 1 to 2 μsec) occur in video disc playback devices.

The present invention has been made in view of the above points, and relates to a signal defect compensation device suitable for use in a video disc playback device, and in particular provides a signal defect compensation device that is not affected by switching noise when detecting a dropout. It is something.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a circuit configuration diagram of an embodiment of the present invention, where 1 is an input terminal, 2 is an FM demodulation circuit, and 3 is a circuit configuration diagram of an embodiment of the present invention.
5 is a de-emphasis amplifier, 4 and 4' are dropout compensation switches formed by analog switches made of semiconductor switching elements, and 5 is a
1H delay circuit, 6 is an output terminal, 7 is a dropout detection circuit consisting of two retrigger one-shot multivibrators M ₁ , M ₂ and other resistors, capacitors, and diodes, 8 is two transistors Q ₁ , Q This is a switching pulse shaping circuit consisting of ₂ and other resistors, capacitors, and diodes.

Here, an FM signal detected by a pickup device (not shown) is supplied to the input terminal 1 via a preamplifier (not shown). After being detected and amplified by an FM demodulation circuit 2 and a de-emphasis amplifier 3, this signal is subjected to dropout compensation by two dropout compensation switches 4 and 4' and output from an output terminal 6.

That is, when there is no normal dropout, control signals of "H" and "L" are supplied from the switching pulse shaping circuit 8 to each switch control terminal of the dropout compensation switches 4 and 4', respectively. ' are in the on/off state, and at this time the regular video signal is sent to switch 4.
is led out to the output terminal 6 via.

However, a dropout has now occurred for some reason, and an FM signal as shown in Figure 2 a appears at input terminal 1.
When a signal (the rectangular parts on the left and right sides of Fig. 2a is a normal signal, and the waveform written in the middle of the normal signal indicates a dropout) is supplied,
2 retrigger one-shot multivibrators
The dropout detection circuit 7 composed of _M1 , _M2, etc. outputs a detection pulse as shown in Figure 2b (a waveform whose fall is delayed by the amount of time a normal signal is detected after a certain period of time). Then, the pulse shaping circuit 8 supplies control signals of "L" and "H", which are opposite to the previous ones, to the respective control terminals of the switches 4 and 4', and the switch 4 is turned off.
Also, the switch 4' is turned on. Therefore, at this time, the substitute signal f delayed by 1H in the 1H delay circuit 5 is delivered to the output terminal 6 via the switch 4', thus performing dropout compensation.

What is particularly important in this embodiment is that when a positive detection pulse as shown in FIG. 2b is derived from the dropout detection circuit 7, the switching pulse shaping circuit ₈
A negative switching pulse with a _slow fall and a relatively steep rise as shown in FIG. The second steep and slow fall of
A switching pulse of positive polarity as shown in FIG. d is supplied to the control terminal of switch 4'.
As a result, when a dropout occurs, the switch 4 turns off with a slow delay, similar to the speed at which the impedance of a semiconductor switching element changes, whereas the switch 4' turns on quickly, and when the dropout ends, the switch 4 turns off. Switch 4' turns on quickly.
turns off with a slow delay. switch 4
Or switch 4' normal signal (normally switch 4'
normal signal, switch 4' at dropout
By turning off the 1H delay substitute signal slowly and turning it on (replacement) quickly, the signal will not be lost and the switching noise caused by the delay from the control signal input in the switch circuit to the signal switching can be reduced. effects can be removed. In this case, the timing structure is such that the switch 4 is switched after the 1H delayed alternative signal is switched by the switch 4', so that switching noise can be removed. As a result, the output terminal 6 is connected to the normal video signal (including the dropout portion) obtained from the de-emphasis amplifier 3 as shown in FIG. A video signal free of switching noise as shown in FIG. 2g is derived.

In the above embodiment, the dropout detection circuit 7 is configured using two retrigger one-shot multivibrators M ₁ and M ₂ to detect that the picked-up FM signal has shifted to below a predetermined deviation range due to dropout. However, dropout detection may be performed using other methods of detection based on the FM wave level or detection using both frequency and level. The same applies to the switching pulse shaping circuit 8.
The circuit configuration is not limited to the one shown in the figure, but two control pulses having different rising and falling timings may be created based on the dropout detection pulse.

As described above, according to the signal defect compensation device of the present invention, the normal signal and the 1H delayed alternative signal can be switched.
When a dropout occurs and when a dropout returns, the two dropout compensation switches are configured to have a negative polarity switching pulse with a relatively steep rise, and a positive polarity switching pulse with a steep rise and a slow fall. Switching is controlled by control signals with different falling timings, so that when a dropout occurs, one switch slowly turns off, while the other switch quickly turns on, and when dropout ends, one switch turns off. The switch turns on quickly, while the other switch turns on slowly and with a delay. Normal signal of one switch or the other switch (usually switch 4
normal signal, switch 4' at dropout
By turning off the 1H delay substitute signal slowly and turning it on (replacement) quickly, the video signal will not be lost, and switching noise caused by the delay from the control signal input in the switch circuit to the signal switching can be avoided. Since the effects of switching noise can be removed, the effects of switching noise can be suppressed to the extent that they cannot be discerned on the playback screen.

[Brief explanation of the drawing]

Fig. 1 is a circuit configuration diagram of an embodiment of the present invention;
The figures are waveform diagrams of various parts in the same embodiment. 4, 4'...Dropout compensation switch, 5
...1H delay circuit, 7...Dropout detection circuit, 8...Switching pulse shaping circuit.

Claims (1)

[Claims] 1 1H delayed by 1H by regular signal and 1H delay circuit
It is equipped with two dropout compensation switches made of semiconductor switching elements that switch between a delayed alternative signal and a delayed alternative signal based on a control signal, and when there is no normal dropout, the normal signal is derived to the output terminal via the compensation switch of one dropout, and the dropout is also output. In a signal defect compensation device that performs dropout compensation by deriving a 1H delayed alternative signal to the output terminal via the other dropout compensation switch when a dropout compensation switch occurs, a dropout detection circuit that detects a signal defect and generates a detection pulse, and a dropout detection circuit that detects a signal defect and generates a detection pulse. Based on this, a negative polarity switching pulse with a slow fall and a relatively steep rise, and a positive polarity switching pulse with a steep rise and a slow fall, with different timings of rise and fall. A switching pulse shaping circuit generates two control signals, and a switching pulse of negative polarity among the two control signals generated by this switching pulse shaping circuit is applied to one of the dropout compensation switches, and a positive polarity switching pulse is applied to one of the dropout compensation switches. and an application circuit for applying a switching pulse of the same magnitude to the other dropout compensation switch.