JPS6059794B2 - dropout compensator - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a video tape recorder (hereinafter referred to as VTR).
In such video signal reproducing apparatuses, a lack of a video signal (hereinafter referred to as dropout) occurs due to a non-contact period between the recording medium and the signal pickup means during reproduction.

) is related to a dropout compensation device for compensating for a signal during the period. Generally, in a VTR, a playback video signal may be absent for a short period of time, which is called a dropout, and the length of this period is often from one horizontal period (hereinafter referred to as IH) to several hours.

Compensation for this dropout has conventionally been performed by making use of the vertical correlation of the video signal to compensate for the dropout period with the video J image signal before IH, and is configured as shown in FIG. Here, the frequency modulated wave (hereinafter referred to as FM) signal reproduced by the VTR head and amplified by the head amplifier is demodulated by the FM demodulator 2, and the direct video 5
The image signal and the video signal via the IH delay line 3 are applied to the video switch 4. On the other hand, a dropout detector detects a dropout based on the presence or absence of an FM signal carrier, and the video switch 4 detects a dropout during the dropout period. By switching to the 1H previous video signal via the 1H delay line 3, a dropout-compensated video signal is obtained. The dropout detector will now be described with reference to FIGS. 2 and 3. Conventional dropout detection means (first
Dropout detector 1) extracts the FM carrier component of waveform A from the tape playback signal using a bandpass filter 5, performs envelope detection using the w detection circuit 6, obtains a signal such as waveform B, and shapes the waveform. In circuit 7, waveform B
A dropout detection signal as shown in waveform C is obtained by switching at level v of . Note that waveform D is the output of the FM demodulator, and noise appears between b and d. As mentioned above, envelope detection is performed on the FM carrier, and there is a delay in detecting dropout (between A and c in Figure 2), and this period is the delay time in the FM demodulator (A and b in Figure 2). When the number of dropouts exceeds 100%), a period (between B and c in FIG. 2) in which dropout compensation is not performed occurs. Furthermore, in order to perform dropout compensation during this period (between B and c in Figure 2), it is possible to insert a delay line immediately after the FM demodulator, but in this case, even when dropout has not occurred, Since the delay line is interposed in the video signal circuit, the delay line must have good characteristics. However, delay lines with good characteristics are expensive and difficult to obtain. When performing wideband video recording and playback, it is necessary to widen the dropout compensation signal as well, but generally the dropout compensation signal has good characteristics.
With the H ultrasonic delay line, it is difficult to directly delay a baseband video signal, and it is common to convert it to an appropriate frequency and then delay it.

Therefore, when trying to reproduce a wideband video signal from a tape, the reproduced FM signal is directly delayed by 1H using an ultrasonic delay line, and the FM signal is delayed by 1H before FM demodulation. It is also possible to compensate for dropouts by However, in this case, the response speed of the dropout detector must be particularly fast. However, as mentioned above, if dropouts are detected by direct envelope detection of the carrier of the FM signal, there is a limit to the response speed due to the time constant of the envelope detection circuit, and dropout detection may be delayed. It was hot.

The present invention is intended to solve this problem, and a first embodiment of the present invention will be described below with reference to FIGS. 4, 5, and 6.

FIG. 4 is a block diagram showing the configuration, FIG. 5 is a diagram showing frequency distribution, and FIG. 6 is a waveform diagram for explanation.

During recording, the luminance signal separated from the color video signal is frequency-modulated, and the color signal is low-frequency converted and superimposed on this and recorded on the recording medium. During playback, the reproduced FM signal is passed through a high-pass filter (hereinafter referred to as H).・The luminance signal component is extracted and applied to the video switch 4 via the JP-F (referred to as JP-F) 8.

The output of the video switch 4 is applied to the FM demodulator 2 and also to one input of the video switch 4 via a 1H delay line 3. On the other hand, the dropout detector 1 detects a dropout based on the presence or absence of the carrier component of the previously mentioned DM signal, and normally the output of the H-P-F 8 is added to the FM demodulator 2 via the video switch 4. When a dropout is detected, the 1H delay line output is applied to the FM demodulator 2 via the video switch 4, thereby obtaining a dropout-compensated luminance signal. Here, the dropout detector 1 includes an oscillation circuit 10, a mixer circuit 11, and a bandpass filter (hereinafter referred to as B-P-F) 1.
2, a W detection circuit 13, and a Schmitt circuit 14. F in the oscillation circuit 10 as shown in FIG. to oscillate the FM signal carrier FO. Beat up to 2 and B
- The signal from which f♂ is extracted by P-Fl2 is envelope-detected by the M detection circuit 13, and there is an FM with dropout as shown in waveform A in Figure 6 (enlarged waveform A in Figure 2).
The signal carrier is beat-up as shown in waveform B in Figure 6.

Therefore, even though the time constant of the AM detection circuit 13 is relatively small in order to envelope-detect the beat-up FM signal carrier, the detection output (waveform C in FIG. 6) has few ripples. The Schmitts circuit 14 shapes the output signal (waveform C) of the AM detection circuit 13, and determines that there is no FM signal carrier at the level of waveform C (7) V2, and determines that there is an FM signal carrier at the level of 1. By providing a hysteresis characteristic, chattering due to ripples and noise is prevented. As described above, a dropout detection signal as shown in waveform D is obtained, and the dropout period (
between f-h in Fig. 6) with a slight delay (f-G, h-1 in Fig. 6)
(between). As described above, the present invention beats up a reproduced FM signal, performs AM detection on the carrier of the beat-up FM signal, and
Furthermore, since the AM detected signal is used as the dropout detection signal, dropouts can be detected with a small time delay, so the configuration of the dropout compensation circuit can be facilitated.

Next, a second embodiment of the present invention will be described with reference to FIGS. 7 and 8.

FIG. 7 is a diagram showing the frequency distribution of a recording signal, and FIG. 8 is a block diagram showing the configuration of a dropout compensation device according to the present invention.

In this embodiment, as shown in FIG. 7, both the luminance signal and the color signal are frequency modulated, frequency division multiplexed, and recorded and reproduced. The playback FM signal output of the head amplifier 21 is B4.
-P-F 22 and a low-pass filter (hereinafter referred to as L●P-F) 23, the signal is separated into an FM luminance signal and an FM color signal. The FM brightness signal is applied to the video switch 26 via the equalizer 24, and is switched between the 1H previous FM brightness signal obtained by the 1H delay line 28 and the video switch 26. In other words, dropout is detected and the dropout signal is switched. When the dropout detection signal is output from the generator 37, the luminance signal from 1H before is sent to the video switch 26.
Get it as output. The FM luminance signal, which has undergone dropout compensation in this manner, is demodulated by an FM demodulator 32 via a limiter 30 to obtain a luminance signal.

On the other hand, the FM color signal obtained from the L-P-F 23 is applied to the video switch 27 via the equalizer 25, and
The voltage is applied to the mixer 35. This mixer 35 mixes the output of the oscillator 34 with the B-P-F 36.
The carrier component of the beat-up FM color signal is extracted and applied to a dropout signal generator 37. In this dropout signal generator 37, dropout is detected by amplitude detection of the carrier component of the beat-up FM color signal. When there is no normal dropout, the FM color signal is directly applied to the FM demodulator 33 via the video switch 27 and the limiter 31, and when dropout is detected, the FM color signal is applied to the FM demodulator 33 via the video switch 27 and the 1H delay line 29. By switching to the FM color signal, a dropout-compensated color signal is obtained at the output of the FM demodulator 33. As mentioned above, in the recording and reproducing method that frequency-modulates and multiplexes the luminance signal and chrominance signal, the carrier of the FM chrominance signal with a narrow deviation is amplitude-detected at beat-up 1, which makes it relatively easy and has a fast response speed. A dropout detection circuit can be configured.

Also, when recording by superimposing the FM luminance signal and FM color signal,
Dropouts occur in the FM luminance signal and FM color signal at almost the same time, and the circuit configuration is efficient because the dropout in the FM color signal is detected and the luminance signal and chrominance signal are compensated for each other. ing. In the above explanation, a delay line is provided before the FM demodulator to compensate for dropouts in the FM signal state, but it is also possible to provide a delay line after demodulation to compensate for dropouts. It's possible.

Next, still another configuration example of the present invention will be described with reference to FIG.

As mentioned in the explanation of the second configuration, when recording and reproducing the superimposed signals after frequency modulating the luminance signal and the chrominance signal, dropout occurs almost simultaneously for the luminance signal component and the chrominance signal component. However, the period of dropout is very short and its period is random. Furthermore, during the period when the knockout occurs, both the FM demodulated luminance signal and color signal are noise themselves.
It is very noticeable on the receiver screen. Therefore, this configuration utilizes the characteristic of visual perception that the resolution for brightness is high and the resolution for color is low, and the luminance signal component is compensated with the luminance signal 1H before, and the output of the color signal component is stopped during the dropout period. This simplifies the circuit configuration. The reproduced FM signal from the head amplifier 21 is separated into an FM luminance signal and an FM color signal by a B-P-F 22 and an L-P-F 23, respectively. F
The M color signal passes through the equalizer 25 and limiter 31
The dropout signal generator 37 extracts the carrier component of the FM color signal that is applied to the M demodulator, mixed with the output of the oscillator 34 in the mixer 35, and beat up in the B-P-F 36. The carrier component of the M color signal is amplitude-detected and then waveform-shaped to generate a dropout detection signal. FM demodulator 3
The color signal demodulated in step 3 is blocked by a gate circuit 40 during a period in which a dropout detection signal is present. On the other hand, B-P-F2
The FM brightness signal extracted in step 2 is applied to the video switch 26 via the equalizer 24;
The output directly appears at the output of the video switch 26 and is applied via a limiter 30 to an FM demodulator 32 to obtain a luminance signal. When a dropout is detected and a dropout detection signal is applied to the video switch, the output of the video switch 26 will have an FMn degree signal via a 1H delay line, and during the dropout period, a dropout will occur.
Compensation is made using the FM luminance signal before H. Also in this configuration, a delay line for delaying one horizontal period is provided before the FM demodulator, but it can also be provided after the FM demodulator to compensate for dropouts.

As described above, according to the present invention, dropout detection can be performed relatively easily and the response speed can be increased, and dropout compensation can be easily performed.

Further, according to the second configuration of the present invention, dropout compensation for wideband signals can be performed relatively easily.
According to the configuration, dropout compensation for wideband signals can be performed at low cost.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a conventional dropout compensation device, FIG. 2 is a waveform diagram explaining the same operation, FIG. 3 is a block diagram showing the configuration of the main parts, and FIG. 4 is an embodiment of the present invention. A block diagram showing an example, FIG. 5 is a frequency distribution diagram of the reproduced signal, FIG. 6 is a waveform diagram for explaining the same operation, FIG. 7 is a frequency distribution diagram of the reproduced signal in the second embodiment, and FIG. 8 9 is a block diagram showing the second embodiment of the present invention, and FIG. 9 is a block diagram showing the third embodiment of the present invention.
It is a block diagram showing an example of. 2...FM demodulator, 3...1H delay line, 4...video switch, 8...H-
P-FllO...Oscillator, 11...Mixer circuit, 12...B-P・Fll3...
Store detection circuit, 14...Schmitt circuit.

Claims (1)

[Scope of Claims] 1. A demodulating means for demodulating a frequency modulated wave signal reproduced from a recording medium recorded by frequency modulating at least one of a luminance signal or a color signal, and a demodulating means for demodulating a frequency modulated wave signal reproduced from a recording medium recorded by frequency modulating at least one of a luminance signal or a color signal, and a delay means for delaying the video signal by one horizontal period; a switching means for switching the reproduced frequency modulated wave signal or the demodulated video signal to the output of the delay means for a dropout detection signal period; and a carrier for the reproduced frequency modulated wave signal. beat-up means for converting a component into a high frequency band; amplitude detection means for detecting the presence or absence of a carrier component of the frequency modulated wave signal subjected to the high frequency conversion; and waveform shaping of the output signal of the amplitude detection means to generate a dropout detection signal. A dropout compensator comprising a waveform shaping means for creating a dropout compensator. 2 The luminance signal and the color signal are each frequency modulated and recorded on a recording medium by frequency division multiplexing, and the reproduced signal is separated into a frequency modulated luminance signal and a frequency modulated color signal, and the frequency modulated color signal is transmitted to a bead up means. 2. The dropout compensation device according to claim 1, wherein the dropout detection signal is obtained by a waveform shaping means. 3 The luminance signal and the chrominance signal are each frequency modulated and recorded on a recording medium by frequency division multiplexing, and the reproduced signal is separated into a frequency modulated luminance signal and a frequency modulated chrominance signal, and the frequency modulated chrominance signal is transmitted to a bead up means. A dropout detection signal is obtained by the waveform shaping means, and the dropout detection signal controls the switching means to which the luminance signal is applied, and the period reproduction color signal component of the dropout detection signal is sent to the output terminal. The dropout compensating device according to claim 1, wherein the dropout compensating device cuts off the application of the dropout compensating device.