JPS62224190A - Video signal recording and reproducing device - Google Patents

Abstract

PURPOSE:To improve the S/N of a reproducing burst signal, to improve the detection accuracy of a time base error, and to improve the picture quality, by recording a burst signal in the band of a frequency modulation system. CONSTITUTION:A video signal inputted to a terminal is divided into an LPF 2 output signal BL and a BPF 3 output signal BH, and the signal BH is brought to a low frequency conversion by a frequency converting circuit 10 and becomes a signal B'H. To the signal BL, a burst signal from a burst signal generating circuit 8 is applied by an adder 6, and said signal is modulated by an FM modulating circuit 7 and becomes a signal B'L, added to a low frequency converting signal B'H by an adder 9, and recorded in a magnetic tape 17. A color burst and high frequency components the high frequency components of a chroma signal and a luminance signal) contained in an input video signal are contained in the BPF 3 output BH, the LPF 2 output BL becomes the low frequency components of a horizontal synchronizing signal and a luminance signal, and the burst signal is multiplexed to the output BL of the LPF 2 and recorded, by which no influence is exerted on the video signal and multiplexing can be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a video signal recording and reproducing device, and particularly to a video signal recording and reproducing device having a time axis correction device.

[Conventional technology]

Currently, the widely used home VTRs use video signals (
Generally, the NTSC color signal) is divided into two frequency bands, and the high frequency component (chroma signal) is frequency converted to the low frequency band.
The low frequency component (luminance signal) is frequency modulated, and these components are mixed and recorded on tape. A so-called low-pass conversion color process is performed. This color process is known from Japanese Patent Publication No. 45-28613.

Fluctuations in the time axis (timebase error) occur due to vibrations of the tape, vibration of the tape, fluctuations in the rotation of the head drum, etc.

(On the other hand, only the chroma signal is corrected using the APC method so that even if a time base error occurs, one color shift does not occur.

The luminance signal is not corrected in any way, causing distortion of one screen and deteriorating the image quality. As a method to prevent image quality deterioration due to this time base error, a time base collector (TBC) is used.
is proposed. The time base collector extracts the time base error from the reproduced signal, controls the variable delay element so as to eliminate the error, and similarly controls the analog-to-digital converter (A/D converter), RAM, digital-to-analog converter ( It uses a D/A converter) to correct time base errors. As shown in Japanese Patent Publication No. 55-24755, suitable for home VTRs are:
There is a system that corrects the 0 time axis by providing a TBC circuit in each of the low frequency conversion system and the FM modulation system.

In these TBCs, the overall performance is dominated by how accurately time base errors are detected.

[Problem that the invention seeks to solve]

In the TBCVC of the above-mentioned prior art, detection is performed from the horizontal synchronization signal of the time-based reproduced video signal. Since the bandwidth of home VTRs is limited, IC,
Changes in the rising and falling edges of the horizontal synchronization signal are relatively gradual, and there is also a noise component, which causes detection errors in the horizontal synchronization signal position, causing the problem of not being able to detect time base errors with a sufficient groove wheel. there were,.

Furthermore, even if the color boost signal (3.58 MHz burst wave of 8 to 12 waves) inserted into the video signal is used as a signal to detect time base errors,
In the low-band conversion color process, the reproduced color burst signal is low-band converted (VII S
In the system, there were only 1 to 2 waves at 629 KHz), and the S/N was good (it was difficult to detect time base errors).

An object of the present invention is to accurately detect time base errors in a VTR using the above-mentioned low frequency conversion color process.

[Means for solving problems]

The above purpose is to provide means for generating a burst signal to detect time base errors, and to
This problem can be solved by recording the signal in a band passing through the frequency modulation system and detecting the time base error using the burst signal during playback.

[Effect]

Burst signals for time-based detection.

Because it is recorded in the band of the frequency modulation system, the S/N of the reproduced burst signal is better than when recording and reproducing using a low-frequency conversion system. Furthermore, since it is not low-frequency conversion, the wave number of the burst signal is also large ( The TBC can accurately detect time base errors.

Image quality can be improved.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1st
In the figure, 1 is a video signal input terminal, 2 is a low-pass filter (LPF), 3 is a band-pass filter (BPF),
4 is a horizontal synchronization signal extraction circuit.

5 is a color burst extraction circuit, 6 is an addition circuit, 7 is a frequency modulation (FM modulation) circuit, 8 is a burst signal generation circuit for time base error detection, 9 is an addition circuit, 10.
11 is a frequency conversion circuit, 12.13 is a phase-locked loop (PLL) circuit, 14 is a recording amplifier, 15, 1
6 is a magnetic head, and 17 is a magnetic tape.

18 is a regenerative amplifier, 19 is a band pass filter (BPF)
).

20 is a hello pass filter (LPF), 21 is a frequency demodulation (FM demodulation) circuit, and 22 and 23 are time axis correction circuits.

24 is a write signal generation circuit, 25 is a phase-locked loop (PLL) circuit, 26 is a burst signal extraction circuit for time base error detection, 27 is a reference frequency signal generation circuit, 28 is a read signal generation circuit, 29.30 is a Write control signal, 31 and 32 are readout control circuits, 33 is a frequency conversion circuit, 34 is a synchronization signal and color burst signal extraction circuit, 35 is an addition circuit, 36 is a video signal output terminal, 37 is a crystal oscillator for generating a reference frequency. , 38 is a burst signal removal circuit.

The video signal to be recorded inputted to the video signal input terminal l (
For example, NTSC color signal) is LPF 2 and BrF
3 into two frequency bands. The signal (Bt, ) passing through LPF2 mainly contains a luminance signal, and Br
The signal (BH) passing through F3 mainly contains a chroma signal. Among them, the signal BH is low frequency converted by the frequency conversion circuit 10 as follows.

First, a horizontal synchronizing signal is detected from the input video signal by the horizontal synchronizing signal extraction circuit 4, and the next stage PLL circuit 12 extracts the horizontal synchronizing signal by, for example, 40 times the horizontal synchronizing signal (629 KHz in NTSC).
) signals are generated. On the other hand, a color burst signal is extracted by the color burst signal extraction circuit 5 at a certain time.
By the PLL circuit 13 at the next stage.

A continuous wave of 3.58 MHz color subcarrier signals is generated. The two signals thus generated are transmitted to the frequency converter 1.
1, a signal of 4.21■2 is generated, and the signal BH is further converted by the frequency converter 10 to become a signal B'H of I MHz band centered at 629K) Iz. . The band of course varies depending on the bandwidth of BrF3, but currently it is around IM11z.

On the other hand, the output signal BL of the LPF 2 is a burst signal generated by the burst signal generation circuit 8 using the horizontal synchronization signal obtained from the horizontal synchronization signal extraction circuit 4 as a reference time.
After being added by the adder 6, it is FM modulated by the FM modulation circuit 7 to become the signal BL, which is added together with the low frequency conversion signal BH by the adder 9, amplified to a predetermined level by the recording amplifier 14, and then magnetically transmitted by the magnetic head 15. It is recorded on tape 17.

The principle of burst signal insertion will now be explained in detail with reference to FIG. In FIG. 2, the waveforms of the outputs of each component are shown over approximately one horizontal scanning period. As shown in (α) in the figure, the input video signal is composed of a horizontal synchronizing signal, a color burst, a luminance signal, and a chroma signal. The signal passing through BrF3 and LPF 2 is shown in the same figure (b
l, shown in (C).

The color burst and high-frequency components of the input video signal (high-frequency components of the chroma signal and luminance signal) are included in the output of BrF3, and the output of LPF2 includes the horizontal synchronization signal and the low-frequency components of the luminance signal (slightly chroma signal and high-frequency components of the luminance signal). (part of the I signal)), and no signal is included in the position where the color burst signal was located, as shown in area A of FIG. Therefore, as shown in FIG. 8(d), the burst signal generation circuit 8
and by adder 6.

The burst signal is multiplexed and recorded on the output BL of the LPF2. By doing this, multiplexing can be performed without affecting the video signal in any way. Next, the frequency of this burst signal will be described. The frequency conditions for this burst signal are FM
It is a frequency that passes through a modulation system, and considering the case where it is demodulated by PLL, it is desirable that the number of waves be large, and that the frequency be as high as possible. Furthermore, the sampling frequency of the time base collector (3x fSC or 4x fSC)
), or because the VTR has an oscillator, the number of oscillators can be reduced.
It is convenient to multiply by m (m and fL are integers). Here, BL
Since the -3dB bandwidth of
/2fsc (1,79MHz) is selected. This frequency is obtained from the reference signal generation circuit within the VTR, but the output of the PLL 13 may be divided by two and used. By determining the recording position and frequency of the signal for detecting time base errors in this way, it is possible to record the frequency of the burst signal at a relatively high frequency (much higher than that of the horizontal synchronization signal). No interference occurs to the signal or chroma signal.

Now, the video signal added with the burst signal and recorded on the magnetic tape as described above is processed in the 8th order in the reproduction process. The video signal reproduced by the magnetic head 16 is amplified to a predetermined level by a reproduction amplifier 18, and a low frequency signal BL which is FM modulated by the BrF 19 and a chroma signal BH which is low frequency converted by the LPF 20 are separated.

Among these signals, the signal BL is converted to FM by the FM demodulation circuit 21.
It is demodulated and becomes a baseband signal BL. The baseband signal BL and low frequency conversion signal BH are applied to time base correction circuits 22 and 23, respectively, and time base errors are removed. What is the principle of this TBC?

The PLL circuit 25 obtains continuous pulses including time base errors from the burst signal extracted from the BL multiplied signal by the burst signal output circuit 26. In this embodiment, by including an 8 frequency divider in the PLL circuit, -1/2f
A continuous pulse of 4fsc is obtained from a burst signal of 3C. Time axis correction circuits 22 and 23 are A/DK converters and random access memories (RAM).

and an r>/A converter. The write signal generation circuit 24 generates a write control signal consisting of the sampling timing of the A/D converter, a write address for the RAM of the time axis correction circuits 23 and 22, and a write timing signal for the RAM from the continuous pulse including the time base error. 29 and 30 are generated. As a result, R, A to f of the time axis correction circuits 22 and 23 have 1M
Signal BL and signal BH are A/D converted and stored.

These data are based on the read address of the RAM of the time axis correction circuits 23 and 22 generated from the read signal generation circuit 28, the read timing for the same RAM, and the D/A.
Readout control signal 31 consisting of a timing signal for human conversion
and 32 for D/A conversion. The clock frequency for this readout is set to exactly four times fsc from the reference signal generation circuit 27. Therefore, the time base error can be removed by A/D converting a signal containing a time base error using a clock containing a time base error, and then performing D/A conversion using a clock containing no time base error.

The signal BL from which the time base error has been removed in this way is
The burst removal circuit 38 removes the burst signal multiplexed during recording. This is performed with timing created by the synchronization signal and the horizontal synchronization signal output from the color burst signal extraction circuit 34.

On the other hand, the signal BH from which the time base error has been removed is as follows.

The signal BH is converted to the original frequency by the frequency conversion circuit 33.
This is added to the signal BL by the adder circuit 35 to form the original video signal. The fsc signal also output from the reference signal generation circuit 27 is given to the 1-frequency conversion circuit 33. The frequency conversion circuit 33 controls the frequency of the color burst extracted from the output signal of the addition circuit 35 to be equal to fsc when mixing the output of the synchronization signal and burst signal extraction circuit 34 and the output of the time axis correction circuit 23. Control.

This is known as the APC process.

As described above, according to the embodiment shown in FIG. 1, it is possible to obtain a video reproduction signal from which time base errors have been removed.

FIG. 3 shows an example of a TBC with another configuration. Only the reproduction system is shown, and the recording is the same as in FIG. Components that are the same as those in FIG. 1 are denoted by the same component numbers and detailed explanations will be omitted. In Fig. 3, 39 is a time axis correction circuit, and the A/D
Consists of a converter, RAM, and D/A converter. 40 is a phase comparison circuit. In this embodiment, the TBC is connected to the regenerative amplifier 18.
Do it immediately after.

This has become possible due to the recent appearance of high-speed A/D converters and D/A converters. The operation will be explained. The reproduction signal (B'H and B
'L mixed signal) is input to the 0 time axis correction circuit 39. The output of the time axis correction circuit 39 is BPF1961
γto 1, () dowa(1[)-1+7
TI +X Medium 1 ff 41M--L
JW & + -lII II separation is performed. The signal BL is FM demodulated by the FM demodulation circuit 21 and becomes the signal BL.
becomes. A burst extraction circuit 26 extracts a burst signal for time base error detection from the signal BL.

The phase comparison circuit extracts the burst signal (
A signal of approximately L/2 fsc with a time base error) and an accurate I/2 signal output from the reference frequency signal generation circuit 27
The write signal generation circuit 24 is controlled by performing a phase comparison with the fsc signal. That is, when the phase of the burst signal is ahead of the reference signal, the write frequency (output frequency of the write signal generation circuit 24) is increased, and when it is delayed, the write frequency (output frequency of the write signal generation circuit 24) is controlled to be low (in this way, the time correction circuit 39 The video signal stored in the RAM of.

A video signal that is D/A converted with accurate cycle timing by the output of the read signal generation circuit 28 and has no time base error is output from the time axis correction circuit 39.

As shown in FIG. 1, the signal from which the time base error has been removed as described above is obtained by removing the burst signal from the signal BL, and converting the frequency of the signal BH and adding them together to form a video signal. In this example.

In order to directly A/D convert an FM modulated signal, the sampling frequency needs to be higher than the example shown in FIG. 1, depending on the FM carrier frequency and frequency shift.

Note that there are many variations to the method of configuring the TBC described above. For example, I used an A/D converter, RAM, and D/A converter as a time axis correction circuit.

A variable delay element (such as a CCD) may be used. Further, in the embodiments shown in FIGS. 1 and 3, the write timing is controlled according to the time base error, but the write timing may be kept constant and the read timing 11 (1) may be controlled.

〔Effect of the invention〕

According to the present invention, since a burst signal for detecting time base errors can be inserted into an area that does not interfere with the video signal and at a relatively high frequency, the accuracy of detecting time base errors can be improved. This improves the accuracy of TBC operation and reduces time base errors. Therefore.

The quality a of the video signal is improved, and two improvements in image quality can be realized.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is an explanatory diagram of burst signal insertion, and FIG. 3 is a block diagram of another example of the configuration of a TBC. 4...Synchronization signal extraction circuit. 8...Burst signal generation circuit. 22, 23, 39... time axis correction circuit. 24...Write signal generation circuit. 28... Read signal generation circuit. 38...Burst removal circuit. 40...Phase comparison circuit.

Claims (1)

[Claims] means for dividing a video signal including a color burst into at least two bands (B_L and B_H); means for frequency converting a high frequency component (B_H) of the divided signal to a low frequency; Of which, the low frequency component (B_L
), and an output of the frequency converting means (
means for mixing the output (B_H) and the output (B_L) of the frequency modulation means and recording it on a recording medium; means for detecting the signal recorded from the recording medium; A means for frequency converting the component (B_H) and a means for frequency converting the frequency modulated component (B_L) of the detected signal.
), an output (B_H) of the frequency conversion means of the reproduced signal, and an output (B_H) of the frequency demodulation means of the reproduced signal.
In a video signal recording and reproducing apparatus that is provided with a means for mixing and outputting L), a means for detecting a time base error from a reproduced signal, and a means for reducing the time base error based on the detected time base error, and means for multiplexing the time base burst signal into a video signal, and when recording, the time base burst signal is multiplexed with the frequency modulation component and recorded. Video signal recording and playback device.