JPS6364117B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is an apparatus for recording and reproducing color video signals such as a VTR, in order to more faithfully correct time axis fluctuations (jitter components) of color signals that occur during reproduction. The present invention relates to a signal processing circuit of a recording and reproducing apparatus that increases the level of a burst signal included in a recording and reproducing apparatus.

In VTR, magnetic tape is used for household use.
A high-density recording method is adopted from the viewpoint of economical use, and in order to improve the S/N ratio of the reproduced burst signal used to correct time axis fluctuations (jitter components) of the reproduced color video signal. A method has been used in which the level of the burst signal is increased by 6 _dB compared to the standard.

FIG. 1 is a block diagram showing a signal processing circuit for recording color video signals in this type of VTR. Of the color video signals input from terminal 1, the luminance signal that has passed through low-pass filter 2 is
The frequency is modulated by the frequency modulation circuit 3. On the other hand, the carrier color signal is separated by a band filter 7,
After the amplitude is controlled by the ACC circuit 8, only the burst signal is increased by _6dB by the burst signal increase circuit 9. The carrier color signal with the burst signal multiplied by _6dB is applied to the frequency conversion circuit 10, frequency-converted by the carrier signal _C from the bandpass filter 14, and outputted from the lowpass filter 11 at a low frequency of _40H ( _H is the horizontal scanning frequency). A color signal with a range of frequencies can be obtained.
The output signal of the low-pass filter 11 is mixed with a frequency-modulated luminance signal from the frequency modulation circuit 3 by a mixing circuit 4, and recorded on a magnetic tape (not shown) via a recording amplification circuit 5 and a magnetic head 6. be done. The burst signal increase circuit 9 is controlled by a pulse obtained by delaying the horizontal synchronization signal from the synchronization signal separation circuit 12 in a delay circuit 13 so that the timing almost coincides with the timing of the burst signal, and the ACC circuit 8 Only the level of the burst signal of the carrier chrominance signal from is increased _{by 6dB} over the standard.
Further, a carrier signal _C for converting a carrier color signal in which the burst signal is increased by _6dB into a color signal with a low frequency is created as follows.

In Figure 1, a variable frequency oscillator (hereinafter referred to as
A frequency dividing circuit 19 and a phase comparison circuit 20 form an AFC loop, and the VFO 18 oscillates at a frequency 160 times higher than the frequency _H of the horizontal synchronizing signal obtained from the synchronizing signal separation circuit 12. this
The output of the VFO 18 is input to the frequency dividing circuit 16,
The frequency is divided by 1/4 and becomes a _40H signal. This _40H output signal and the crystal oscillator 17 that oscillates at _S = 3.58MHz
A frequency conversion circuit 15 converts the frequency of the output signal, and a band filter 14 selects the sum frequency component to create a carrier signal _C = _40H + _S . Therefore, if this carrier signal _C = 40 _H + _S and the carrier color signal _S from the burst signal increase circuit 9 are frequency-converted by the frequency conversion circuit 10, and the difference component is selected by the low-pass filter 11, 40 _H. A color signal converted to a low frequency is obtained.

FIG. 2 shows a reproduction signal processing circuit for reproducing the signal recorded by the recording circuit shown in FIG. 1 into an original video signal. A signal recorded on a magnetic tape (not shown) is detected by a magnetic head 6 and sent to a preamplifier 2.
After being amplified by 1, the frequency-modulated luminance signal is supplied to a demodulation circuit 24 via a high-pass filter 22 and a limiter 23, where it is demodulated into the original luminance signal. On the other hand, the color signal converted to a low frequency is extracted by a low frequency filter 27, and the signal level is controlled by an ACC circuit 8, and then a frequency conversion circuit 10
added to. Since the carrier signal _C ' is input to the frequency conversion circuit 10, the difference frequency component is extracted by the band filter 28, and only the level of the burst signal is reduced to 6d _B by the burst signal reduction circuit 29.
By decreasing it, the original carrier color signal is restored. This carrier color signal and the luminance signal from the demodulation circuit 24 are mixed in a mixing circuit 25, and the original color video signal is reproduced at the output terminal 26.

Here, a signal processing circuit that creates a carrier signal _C ' for correcting time axis fluctuations (jitter components) of color signals will be explained. VFO1
8 is a reproduced burst signal from the burst gate circuit 30 and a crystal oscillator 17 that oscillates at _S ≒3.58MHz.
The oscillation frequency is controlled by the error voltage obtained by comparing the phase of the output signal with the output signal in the phase comparison circuit 31, and the oscillation frequency becomes a frequency of 160 _H ± _ΔO corresponding to the error voltage, centered around 160 _H. The output signal of the VFO 18 is divided into 1/4 by the frequency dividing circuit 16, inputted to the frequency conversion circuit 15, frequency converted using the signal _S from the crystal oscillator 17, and the sum frequency component is extracted from the band filter 14. A carrier signal _C ' is obtained which is applied to the frequency conversion circuit 10.

Now, the color signal reproduced from the magnetic head 6 and converted into a low frequency signal obtained at the output of the ACC circuit 8 via the low frequency filter 27 has time axis fluctuation (jitter component), and its frequency is 40 _H + If △ _I , the carrier signal applied to the frequency conversion circuit 10 is _C ′ = 40 _H + △ _I + _S , then the carrier color signal output to the band filter 28 becomes _S , and the jitter component △ _I is removed. will be done. In order for the carrier signal _C ' to become _C ' = 40 _H + △ _I + _S , the oscillation frequency of the VFO 18 must be 4 (40 _H + △ _I ).
It should be controlled so that This VFO18
The phase comparison circuit 31 compares the phases of the reference signal of the output _S ≈3.58MHz of the crystal oscillator 17 and the burst signal obtained from the burst signal of the reproduced carrier color signal by the burst gate circuit 30, and the error signal is used to controlled. Therefore, the burst gate circuit 30
If noise is mixed in the burst signal extracted by This means that you will not be able to do it.

FIG. 3 shows a waveform diagram of the burst signal processing circuit in the conventional reproduced signal processing circuit shown in FIG. FIG. 3a shows the reproduced carrier color signal obtained by the bandpass filter 28 in FIG. 2, with the burst signal _B increased by 6dB above the standard level. 3b shows the output pulse of the delay circuit 13 obtained by delaying the output of the synchronization signal separation circuit 12, FIG. 3c shows the output signal of the burst signal reduction circuit 29, and FIG. 3a shows the output signal of the burst signal reduction circuit 29.
3d is the output signal of the burst gate circuit ₃₀ , and FIG. 3d is the output signal of the burst gate circuit 30. This is a burst signal waveform extracted only during the pulse period of FIG. 3b from the carrier color signal of c. The width of the pulse shown in FIG. 3b applied to the burst signal reduction circuit 29 is preferably as wide as possible, since the burst signal can be reduced. However, if the pulse applied to the burst gate circuit 30 and the pulse applied to the burst signal reduction circuit 29 are shared as in the conventional example shown in FIG.
In addition to the burst signal, noise components C before and after the burst signal are also extracted from the output signal of 0, as shown in FIG. 3d. Therefore, there is a drawback that jitter correction of the reproduced color signal cannot be performed sufficiently due to this noise.

The present invention eliminates the above drawbacks and provides a new signal processing circuit that can reliably increase or decrease burst signals in order to reproduce faithful color signals, and can also sufficiently correct jitter in reproduced color signals. .

FIG. 4 is a block diagram of a reproduced signal processing circuit showing one embodiment of the present invention. In Figure 4, the second
Components having the same operations and functions as the reproduced signal processing circuit described in the conventional example shown in the figure are given the same reference numerals. Further, reference numerals 32 and 33 each represent a pulse generation circuit which generates a signal having a specific pulse width delayed by a certain period of time from the horizontal synchronization signal which is the output signal of the synchronization signal separation circuit 12. This pulse generating circuit 32,
The timing waveform of No. 33 will be explained using FIG. 5 is a waveform diagram of the burst signal processing circuit in the reproduction signal processing circuit according to the embodiment of the present invention shown in FIG. 4, and FIG. 5a is a reproduction carrier color obtained by the band filter 28 in FIG. 4. The burst signal _B is 6dB higher than the standard level. FIG. 5b shows an output pulse generated by the pulse generation circuit 32, which is supplied to the burst signal reduction circuit 29 and is used to reduce the level of the burst signal in the reproduced carrier color signal, which is the output of the bandpass filter 28, by _6dB . It will be done. FIG. 5c shows the carrier color signal reproduced to the standard level by reducing the level of the burst signal B by 6d _B , and FIG. 5d shows the pulse generating circuit 33.
The output pulses produced by the above are supplied to the burst gate circuit 30 and are used to extract only the burst signal B from the reproduced carrier color signal shown in FIG. 5c. The output pulses of the pulse generating circuits 32 and 33 are designed to have timings as shown in FIGS. 5b and 5d. That is, the output pulse of the pulse generation circuit 33 (FIG. 5d) has a timing and pulse width that almost coincide with the burst signal of the reproduced carrier color signal, and the output pulse of the pulse generation circuit 32 has a timing and pulse width that almost coincides with the burst signal of the reproduced carrier color signal. Pulse (5th
Compared to Figure b), both before and after are slightly (0.3μs to 1.0μs
degree) is designed to generate a wide pulse. Therefore, as explained in FIGS. 4 and 5, by using another pulse for gating the burst signal, which is different from the pulse used to increase or decrease the level of the burst signal _by 6dB, the burst signal can be gated. Since the signal can be increased or decreased reliably, and the noise component C included in the burst signal extracted by the burst gate circuit 30 can also be reduced,
Jitter correction of reproduced color signals can also be performed accurately.

FIG. 6 is a specific configuration diagram showing one embodiment of the pulse generation circuits 32, 33, and FIG. 7 is a timing chart thereof. In Fig. 6, 34 is a terminal to which the horizontal synchronization signal (Fig. 7a) is input, 35, 36
are output terminals, respectively. Pulse generation circuit 33
is the first monostable multivibrator (hereafter
(referred to as MM). MM32-1 and second MM32-
2, and the pulse generating circuit 33 is composed of a third
It is composed of a MM33-1 and a fourth MM33-2. The operation will be explained using the timing chart shown in FIG. The first MM 32-1 is triggered by the rising edge of the horizontal synchronizing signal (FIG. 7a) input to the input terminal 34, and outputs a signal having a pulse width _t1 (FIG. 7b). Second MM32-
2 is triggered at the falling edge of FIG. 7b and outputs a signal with a pulse width t ₂ (FIG. 7c) to the output terminal 35, which is used to increase or decrease the burst signal. The third MM 33-1 is triggered at the rising edge of the horizontal synchronizing signal (FIG. 7a) and outputs a signal with a pulse width _t3 (FIG. 7d). Fourth MM33-2
is triggered at the falling edge of FIG. 7d and outputs a signal with a pulse width t ₄ (FIG. 7e) to the output terminal 36, which is used to extract a burst signal from the reproduced carrier color signal. Therefore, as shown in FIG. 6, the pulse generating circuits 32 and 33 delay the leading edge of the horizontal synchronizing signal by t ₁ and t ₃ , respectively, by using two monostable multivibrators, and generate pulses. Pulses of width t ₂ and t ₄ can be created.

As described above in the embodiments of the present invention, in a recording/reproducing apparatus such as a VTR that records a burst signal by increasing it by 6 _dB , the burst signal is used to correct the time axis fluctuation (jitter component) of the reproduced color signal. It has a first pulse generating circuit that generates a pulse to take out the burst signal, and a second pulse generating circuit that generates a pulse used to increase or decrease the burst signal, and horizontally synchronizes the output pulse of the first pulse generating circuit. The output pulse of the second pulse generation circuit is created based on the signal so that it almost coincides in time with the timing of the burst signal, and the output pulse of the second pulse generation circuit is slightly different from the output pulse of the first pulse generation circuit (0.3 μs to
By creating a wide pulse width (1.0 μs), the reproduced color video signal can be reproduced more faithfully.

[Brief explanation of drawings]

Figure 1 is a block diagram showing a signal processing circuit when recording a color video signal in a conventional VTR, Figure 2 is a block diagram during playback, and Figure 3 is a waveform of the burst signal processing section in Figure 2. Figure, 4th
5 is a waveform diagram of the burst signal processing section in FIG. 4, and FIG. 6 is a pulse generator that generates pulses for processing the burst signal. FIG. 7 is a block diagram showing a specific embodiment of the present invention, and is a timing chart in FIG. 6. 6...Magnetic head, 8...ACC circuit, 10,
15... Frequency conversion circuit, 12... Synchronization separation circuit, 14, 28... BPF, 16... Frequency division circuit,
17... Oscillator, 18... Variable frequency oscillator, 2
1... Preamplifier, 22... HPF, 23... Limiter, 24... Frequency demodulator, 25... Mixing circuit, 29... Burst signal reduction circuit, 30... Burst gate circuit, 31... Phase comparator circuit, 3
2, 33...Pulse generation circuit.

Claims (1)

[Claims] 1 Increase the level of the burst signal included in the carrier color signal, record it on a recording medium, return it to the original burst signal level during reproduction, extract the burst signal from the reproduced carrier color signal, and use this burst signal to In a color video signal recording and reproducing device that corrects time axis fluctuations of a reproduced carrier color signal, a first pulse generation device generates a burst gate pulse that temporally almost coincides with the timing of the burst signal based on a horizontal synchronization signal. circuit, and a second pulse generating circuit that generates a pulse having a wider pulse width both before and after the burst gate pulse, and the burst gate pulse of the first pulse generating circuit is used to generate a pulse with a time axis variation of the reproduced carrier color signal. The second
A color video signal processing circuit characterized in that the pulses of the pulse generating circuit are used to increase or decrease the level of the burst signal.