JPS60253394A - Signal processing circuit of video signal recording and reproducing device - Google Patents

Abstract

PURPOSE:To coincide the shift between the center of a color signal and that of a luminance signal by constituting a drop-out compensating circuit so that the FM demodulated luminance signal is delayed by 1H in a normal mode by the drop-out compensating circuit and then by >=2H when a drop-out is produced respectively, and then the luminance signal is led to an output terminal. CONSTITUTION:The signal demodulated by an FM demodulator 8 is supplied to a drop-out compensating circuit 10'. A drop-out detection circuit 9 detects the drop-out of the luminance FM signal, and this detection output controls the open/close of a switch 222. The switch 222 makes an input terminal 223 and an output terminal 225 conduct in a normal reproduction mode i.e., when no drop- out is produced. While an input terminal 224 and an output terminal 225 conduct when a drop-out is detected. Therefore the switch 222 is changed over by the function of the circuit 9 when a drop-out is produced. The normal signal obtained earlier by 1H than the drop-out generation is applied to a 1H delay line 221. Therefore the noises of drop-out never emerges at the output of the line 221. Thus a reproduced picture is obtained with a high contrast.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a signal processing circuit of a video signal recording and reproducing device.
In particular, recording an NTSC color video signal on a medium,
The present invention relates to a signal processing circuit for a video signal recording/reproducing device suitable for reproduction.

[Background of the invention]

2. Description of the Related Art Conventionally, there are apparatuses for recording and reproducing color video signals on recording media such as optical disks or magnetic tapes that use a photosensitive thin film as a recording layer.

FIG. 1 shows an example of the configuration of a signal processing circuit used in such a conventional device. The operation of this signal processing circuit will be explained below based on the same figure.

A video signal applied to an input terminal 21 is input to a comb filter circuit 1 which separates a luminance signal component and a carrier color signal component. The quadruple filter circuit 1 includes a one horizontal scanning period (1H) delay line 101, such as a glass delay line, adders 102, 103, and a phase inversion circuit 104. The adder 102 adds the signal from the input terminal 21 and the output signal from the delay line 101. Carrier color signal is NTS
In the case of a C signal, the phase is inverted every 1H, and the adder 10
A luminance signal component obtained by removing the carrier color signal component from the input video signal is obtained at the output of No. 2.

On the other hand, the adder 106 inputs the input video signal and the delay line 101.
A signal whose phase is inverted by the phase inverting circuit 104 is added to the output. A carrier color signal is extracted from the output of adder 103. The frequency characteristics of the 1H delay line 101 range from 3 MHz to 42 MHz as an example when using a glass delay line.
(Lepros is selected as a transit zone.

Therefore, the low frequency component of the luminance signal remains in the output of the adder 106. Therefore, band pass filter (BP)
F) In step 4, remove the low frequency component of the luminance signal and extract only the carrier color signal component.

The luminance signal is subjected to FM modulation of the carrier signal in the 1M modulator 2. The carrier color signal is converted into a low-range color signal with a frequency lower than the frequency of the FM signal, which is suitable for recording on a recording medium (not shown in the figure), using a well-known technique such as the heterodyne method in the frequency conversion circuit 5. is converted to The luminance FM signal and the low-pass color signal that have passed through the low-pass filter (LPF) 6 are added together by an adder 3, and outputted to a terminal 22 as a recording signal to a recording medium (not shown).

On the other hand, multiple reproduction signals from the recording medium are input to the terminal 23,
It is added to a bypass filter (EPF) 7 and a low pass filter (LPF) 12. Bypass filter~7
An FM luminance signal is extracted from the output of the FM"4! modulator (FM") and demodulated to reproduce the luminance signal.

On the other hand, the output of bypass filter ~7 is applied to dropout detection circuit 4. Dropout detection port 9 is
This is provided for the purpose of detecting dropouts in the luminance FM signal caused by scratches, dust, etc. on the recording medium. By generating a positive pulse by triggering at the passing timing, and making the time constant of the monomultiple a little larger than the period of the lowest frequency of the luminance FM signal.
) When the FM signal arrives, a positive voltage is output, and when there is a drop, a single negative voltage is output, or when the FM signal is detected by saturation line detection and the detected output is above a certain level. This outputs only a positive voltage.

The output signal of the 1M demodulator 8 is sent to the dropout compensation circuit 10.
Enter.

The dropout compensation circuit 10 consists of a 1H delay circuit 201 and a switch 202. The signal from the 1M demodulator 4 is guided to one input terminal 203 of the switch 202, and the signal output from the FM demodulator ~8 is input to the other input terminal 204.
The signal passed through the delay circuit 201 is added.

The contact of the switch 202 is the dropout detection circuit W&-9.
Normally, the input terminal 203 and the output terminal 205 are electrically connected, and when a dropout occurs, the input terminal 204 and the output terminal 205 are electrically electrically connected. Therefore, when a dropout occurs, FM demodulation is possible! The noise generated in S-8 does not pass through the switch 202, and instead, the 1B previous luminance signal having a correlation with the missing portion is outputted to the output terminal 205.

On the other hand, the low-pass color signal extracted from the output of the low-pass filter 12 is restored to its original frequency in the frequency conversion circuit 13 in the same manner as during recording.

During frequency conversion, although not shown, the well-known AFC,
The APC process removes phase fluctuations in the color signal. The restored carrier color signal passes through a low-pass filter 14 and enters a comb filter circuit 15.

The comb filter circuit 15 includes a 1H delay line 301 and an adder 3.
It has well-known effects on signal generation, crosstalk removal, S/N improvement, etc. The luminance signal from the dropout compensation circuit 10 and the carrier color signal from the comb filter 15 are added by an adder 11 and outputted from an output terminal 24 as a color video signal.

There is another way to configure the dropout compensation circuit. That is, as shown in FIG. 2, the reproduced signal is guided to the input terminal 213 of the Sochi 212, and the signal that has passed through the 1B delay circuit 211 from the output terminal 215 is guided to the switch 214. The terminal 216 and the output terminal 215 are connected, and the input terminal 214 and the output terminal 215 are connected when a dropout occurs. The configuration shown in FIG. 2 has the advantage of being able to compensate for dropout occurrences lasting more than 1H.

The video signal recording and reproducing apparatus described above had the following drawbacks. That is, there is a problem in that the color signal is delayed more than the luminance signal, and the colors are shifted downward on the playback screen. FIG. 3 shows an example of an output image from the output terminal 24 of the device shown in FIG. The outline of the luminance signal α and the outline of the color signal d match when input, but on the playback screen, the outline of the color signal d is wider by two scanning lines, and the center position is also different from that of the color signal. The side is shifted downward by one scan. The cause of this will be explained below.

FIG. 4 shows the vertical positional relationship of the luminance signal and color signal in each part of the apparatus shown in FIG. 1, and lines A-A' in FIGS. 3 and 4 correspond to each other.

Further, in FIG. 4, the horizontal axis represents the signal level. α in FIG. 4 is a luminance signal, which is used as a reference for the vertical position. b is the input signal and is located at the same position as α. C is the color signal after the top of the comb filter 10 in the recording circuit, and it is added to the signal delayed by 1B, so the outline is one scanning line wider than the original signal, and the center position is also scanned downward. There is a shift of 172 lines.

Regarding the luminance signal, since the band of the 1B delay line 101 has such a characteristic that only the carrier color signal passes, no delay is observed in the low-frequency component of the main component of the luminance signal. d is the color signal in the reproduced output; the center position is further lowered by 1/2 scanning line (C) by the comb filter 15, so the color signal becomes The outline is two scanning lines wider than the outline of the luminance signal, and the center position of the color signal is moved one scanning line below the center of the luminance signal, so that the color is two scanning lines below. I'll share it with you.

[Purpose of the invention]

Therefore, an object of the present invention is to provide a video signal in which the center of a color signal and the center of a luminance signal coincide without deviation in a signal processing circuit of a video signal recording and reproducing apparatus using a comb filter in both recording and reproducing systems. It is an object of the present invention to provide a signal processing circuit for a recording/reproducing device.

[Summary of the invention]

In order to achieve the above object, in the present invention, when the reproduced luminance signal passes through the dropout compensation circuit of the reproduction system, 1
The dropout compensation circuit is configured so that the signal always passes through the B delay circuit at least once.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. FIG. 5 shows an example of the configuration of an optical video recording and reproducing apparatus in which the present invention is implemented.

In this figure, parts common to those of the apparatus in FIG. 1 are given the same numbers, and their operations are also similar to those described in connection with FIG. 1.

The device shown in FIG. 5 differs from the device shown in FIG. 1 in the way the dropout compensation circuit 10' is constructed. In FIG. 5, the signal demodulated by the FM demodulator ~8 enters the dropout compensation circuit 10' and enters the input terminal 22 of the switch 222.
Join 3. The output terminal 225 of the switch 222 is connected to the input terminal of the 1B delay circuit 221. 1B delay circuit 22
1 is connected to the adder 11 as the output of the dropout compensation circuit, and at the same time is connected to the input terminal 224 of the switch 222.

The dropout detection circuit ~9 detects the occurrence of a dropout of the luminance FM signal using the method described above, and the detection output controls the opening and closing of the switch 222.

The switch 222 is connected to the input terminal 223 and the output terminal 2 during normal playback, that is, when no dropout occurs.
25 becomes conductive, and when the occurrence of dropout is detected, the input terminal 224 and the output terminal 225 become conductive. Therefore, normally, the regenerated luminance signal input to the dropout compensation circuit 10' is output to the adder 11 after being delayed by 1B by the 1H delay line 221.

When a dropout occurs, the switch 222 is switched by the function of the dropout detection circuit ~9, and even when a dropout occurs, the normal signal from 1H before is switched to the 1H delay line 22.
Added to 1. Therefore, noise due to dropout does not appear in the output of the 1H delay line 221, and a clear reproduced image can be obtained. This effect is also effective for those with a dropout length of 1B or more.

As described above, in the optical taste image signal reproducing device shown in FIG. 5, the delay of the luminance signal is 11 greater than in the devices shown in FIGS. 1 and 2. On the other hand, regarding color signals, the apparatus shown in FIG. 5 and the apparatus shown in FIG. 1 perform exactly the same processing, so there is no difference in delay time.

FIG. 6 shows the vertical positional relationship between the luminance signal and the color signal at the input and output of the device shown in FIG. With respect to the input luminance signal α and the input color signal A whose vertical positions coincide with each other, the center of the output luminance signal - and the center of the output luminance signal B also coincide at a position delayed by 1H from the input. Figure 7 is the 5th
In the reproduced screen from the device shown in the figure, the center - of the luminance signal C and the center of the color signal d coincide, so that the colors do not protrude downward and give an unnatural impression.

In Figure 7, the color signal d protrudes above and below the luminance signal C by one scanning line, but this is one quarter of the normal level as shown in Figure 6 d, so the effect on visual perception is minor. be.

Note that in the configuration of the dropout compensator shown in FIG. 5, the luminance signal always passes through the 1H delay circuit 221, so the delay circuit must have performance that does not cause deterioration in signal resolution. Especially required. Since the frequency band of NTSC video signals is up to 4.2 MHz, one example of a delay circuit is a charge-coupled device (COD) with 910 stages.
, and set the clock frequency to 4 times the color subcarrier frequency (1
4.5 MHz), the above requirements can be fully satisfied.

〔Effect of the invention〕

As explained above, in the present invention, the FM demodulated luminance signal is normally delayed by 1H in the dropout compensation circuit,
When a dropout occurs, a dropout compensation circuit is configured such that the signal is delayed by 21 seconds or more before being routed to the output terminal.

This allows the chrominance signal seen with conventional devices to become a luminance signal)
It is possible to eliminate the disadvantage that the surface protrudes significantly downward. Moreover, it does not lose any of the other features of conventional devices and does not require any complexity in construction.

Further, the present invention is applicable to any type of recording medium as long as it uses a 5-comb filter.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a signal processing circuit of a conventional video signal recording/reproducing device, Fig. 2 is a block diagram showing another configuration of a conventional dropout compensation circuit, and Fig. 3 is a front view of an example of a playback output screen. 4 is a diagram showing the position of signals on the screen in each part of the circuit, FIG. 5 is a block diagram showing an embodiment of the present invention, and FIG. 6 is a circuit input/output part in an embodiment of the present invention. FIG. 7 is a front view of an example of a reproduced output screen when the present invention is implemented. Explanation of symbols 1...Comb filter 2...FM modulation circuit 3...
- Addition circuit 5... Frequency conversion circuit ~7... Bypass filter ~8... pm demodulation s~9... Dropout detection circuit 10, 10'... Dropout compensation circuit 11...
Output port K 12...Low pass filter 13...Frequency conversion circuit 15...Comb filter 221...
1H delay circuit 222...-switch 223.224.
...Input terminal 225...Output terminal Patent attorney Akira Takahashi Figure 1; [J Figure 2 Figure 3 Figure 47 (α) (b), l, C'') Figure = "-J Figure 6 Salary 71 yen]

Claims (1)

[Claims] 1) In the signal processing circuit of the video signal recording and reproducing device that uses a comb filter in both the recording and reproducing systems, the reproduced FM
A dropout detection circuit that detects and outputs signal loss, a switch having two input terminals and one output terminal whose opening/closing is controlled by the output signal of the dropout detection circuit, and an output signal of the switch. a delay circuit that delays the FM demodulation by one horizontal scanning period, leads the FM demodulated output to the first input terminal of the switch, and leads the output of the delay circuit to the second input terminal of the switch.
the dropout detection circuit leads to the input terminal of the FM
When no signal loss is detected, the first input terminal and output terminal of the switch are connected, and when the FM signal loss is detected, the second input terminal and output terminal of the switch are connected. A signal processing circuit for a video signal recording and reproducing device, characterized in that: