JPS6115491A - Color video signal recording device - Google Patents

Abstract

PURPOSE:To improve S/N of a color signal at the time of reproduction and to obtain a stable reproduced picture free from color unevenness by replacing a burst signal with a pseudo burst signal having a rectangular envelope and the same in phase and frequency with the burst signal, then recording the result. CONSTITUTION:Color signals 3 obtained from a recording BPF2 are supplied to an ACC circuit 4. An analog switch 40 for replacing a burst signal with a pseudo burst signal is provided between the ACC circuit and a main convertor 23. This analog switch 40 is switched and controlled by a signal 46 from a burst switching signal generating circuit, and a signal 17 of 3.58MHz from a VXO oscillating circuit 16 is supplied to the main convertor 23 as a pseudo burst signal only at the time of burst signal. After the burst signal is replaced with the pseudo burst signal, the analog switch 40 is switched to the terminal (a) side, and color signal component is supplied to the main convertor 23 as it is.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to automatic color saturation adjustment (ACC> Regarding circuits.

[Prior Art] A color signal recording/reproducing circuit of a conventional color video signal recording/reproducing apparatus (VTR) will be described.

FIG. 1 is a block circuit diagram of a color signal recording system of a conventional VTR. In FIG. 1, the recording system is roughly divided into an ACC block and a frequency conversion block.

The ACC block includes an ACC circuit 4 that keeps the level of the burst signal included in the color signal constant, a burst gate circuit 6 that extracts only the burst signal from the color signal 5 with a constant burst level output from the ACC circuit 4, and a burst It is composed of an ACC detection circuit 12 that peak-detects the burst signal @11 provided by the gate circuit 6 and provides its output to the ACC circuit 4.

The frequency conversion block includes an automatic phase 111J that detects the phase of the burst signal 11 extracted by the burst gate circuit 6.
III (APC>detection circuit 14 and APC detection circuit 14
A voltage controlled crystal oscillator oscillation circuit (VXO oscillation circuit) 17 that is controlled by the output signal from the burst signal 11 and generates a signal of the same frequency and in phase synchronization with the burst signal 11; A sub-converter 18 converts the frequency by receiving a signal from an automatic frequency control m (AFC) circuit 19 which outputs a signal for conversion, and a color signal 5 having a constant burst level output from the ACC circuit 4 and a signal from the sub-converter 18. The main converter 23 receives a signal and converts the frequency.

FIG. 2 is a diagram showing signal waveforms of various parts during recording. The operation of the color signal recording system will be described below with reference to FIGS. 1 and 2.

From the input color video signal 1 shown in FIG. 2, only the color signal component 3 shown in FIG. 2 is extracted by a recording band pass filter (hereinafter referred to as recording BPF) 2. Color signal 3 is A
The CC circuit 4 produces a color signal 5 with a constant burst level. This color signal 5 is created by the following circuit operation. A horizontal synchronization separation circuit 7 separates only the horizontal synchronization signal 8 from the input color video signal 1. The separated horizontal synchronizing signal 8 is applied as a timing signal to a burst gate pulse generating circuit 9. In response to the timing of the horizontal synchronizing signal 8, the burst gate pulse generation circuit 9 generates a burst gate pulse shown in FIG. 2 that is synchronized with the burst signal included in the color signal 3 and has the same width as the envelope of the burst signal. Generate 10. Since the burst gate circuit 6 passes the input signal only when a pulse is applied, it receives the burst gate pulse 10 and outputs the color signal 5.
Extract only the burst signal 11 from the ACC detection circuit 1
Give to 2. The ACC detection circuit 12 performs peak detection on the applied burst signal 11 and provides its output to the ACC circuit 4 . The ACC circuit 4 adjusts the level of the burst signal according to its input level and outputs it as a color signal 5 with a constant burst level. The main converter 23 receives the color signal 5 and the signal from the sub-converter 18 and performs frequency conversion to convert the color signal 5 to a low frequency range. This frequency conversion is performed by the following circuit operation. The burst signal 11 extracted by the burst gate circuit 6 is applied to the AGO detection circuit 10 and also to the APC detection circuit 14 at the same time. AP
The C detection circuit 14 performs phase detection on the burst signal 11 and provides the detection output to the xO oscillation circuit 16. (2) The xO oscillation circuit 16 has its oscillation frequency and phase controlled according to the APC detection output 15, and always provides a signal 17 that is in phase synchronization with the burst signal 11 and has the same frequency to the sub-converter 18. Further, the AI-C circuit inputs the horizontal synchronization signal 8 separated from the input color video signal 1 by the horizontal synchronization separation circuit 7 and the magnetic head switching signal 20.
Frequency 62 is obtained by multiplying the frequency and shifting the phase by 90 degrees for each head switching signal to eliminate crosstalk.
The output signal of 9KH2 is given to the sub-converter 18.

The sub-converter 18 receives the signal 17 with a frequency of 3.58 MH2 from the vxO oscillation circuit 16 and the signal with a frequency of 629 kHz from the AFC circuit 19, and converts the signal to 3.58+0.62.
9-Give a signal with a frequency of 4.209 MH2 to the main converter 23. The main converter 23 converts the color signal 5 whose subcarrier frequency is 3.58 MHz and the subconverter 18
4. Receive a signal with a frequency of 4.209MH2 from 4.
A signal 24 having a frequency component of 209±3.58 MH2 is recorded using a low-pass filter (hereinafter referred to as recording LPF) 25.
give to The recording LPF 25 receives 4.2 of its input signal.
Only the color signal 26 having a subcarrier frequency of 09-3.58-0.629MH2-629KH2 is passed.

The low-frequency conversion color signal 26 that has passed through the recording LPF 25 is mixed with a frequency-modulated luminance signal and then recorded on a magnetic tape through a magnetic head. The above is the operation of the color signal recording system. Next, the color signal reproduction system will be described.

FIG. 3 is a block circuit diagram of the reproduction system. In FIG. 3, the color signal reproduction system is also roughly divided into an ACC block and a frequency conversion block, similar to the color signal recording system.

The ACC block converts the reproduced low-pass converted color signal 29 that has been low-pass converted into the reproduced low-pass converted color signal 3 with a constant burst level.
ACC circuit 4 that converts the burst signal to 0, a burst gate circuit 6 that extracts the burst signal from the reproduced color signal 35, and an ACC detection circuit 12 that peak-detects the burst signal 36 extracted by the burst gate circuit 6 and supplies it to the ACC circuit 4. It consists of

The frequency conversion block receives signals from the burst signal 36 extracted by the burst gate circuit 6 and a 3.58 MHz oscillation circuit 37 that generates a reference signal 38 with a frequency of 3.58 MH2, and performs phase detection on the burst signal 36. circuit 14, a vxO oscillation circuit 16 that receives the signal 15 from the APC detection circuit 14 and generates a signal that is phase-synchronized with the reproduced burst signal 36 and has the same frequency, and for high-frequency conversion of the reproduced low-frequency conversion color signal. an AFC circuit 19 that provides a signal 21 of Receiving the signal 22 from the converter, the reproduced low-frequency conversion color signal 20 is converted into a high-frequency signal.

and a main converter 23 for converting into. The operation of the color signal reproduction system will be described below.

The reproduced color video signal containing the FM modulated luminance signal component first passes through the reproduced LPF 28. The reproduction LPF 28 passes only the reproduction low frequency conversion color signal 29 from the reproduction color video signal, and provides its output to the ACC circuit 4. A.C.C.
The circuit 40 receives the reproduced low-frequency converted color signal 29 and supplies the reproduced low-frequency converted color signal @30 with a constant burst level to the main converter 3. The main converter 23 receives the reproduced low-frequency converted color signal @30 with a frequency of 629KH2 for mm transmission and the signal with a frequency of 4.209MH2 provided by the sub-converter 18, and converts the reproduced low-frequency converted color signal 30 into a frequency of 4.209±. 0
．． The frequency is converted to a high frequency range of 629MH2. Regeneration BPF3
2 receives the reproduced color signal 31 that has been frequency-converted to this high frequency range, and converts the input signal 31 to a frequency of 4.209T0.62.
Only the color signal 33 consisting of a carrier wave of 9-3°58 MH2 is allowed to pass. This reproduced color signal @33 includes crosstalk components from adjacent tracks on the magnetic tape. This crosstalk component is removed by a comb-shaped filter 34 and becomes a reproduced color signal 35. This reproduced color signal @35 is mixed with a reproduced luminance signal processed through another path to become a reproduced video signal.

The output from the comb filter 34 is also provided to the burst gate circuit 6. The burst gate circuit 6 synchronizes with the pulse signal from the burst gate pulse generation circuit 9.
Only the burst signal 36 from the reproduced color signal 35 is allowed to pass through. The burst gate pulse generation circuit 9 generates a reproduced video signal 39
The horizontal synchronization signal 8 separated by the horizontal synchronization separation circuit 7 is given timing to generate a pulse that is synchronized with the burst signal and has the same width as the duration of the burst signal. Burst signal 3 passed through burst gate circuit 6
6 is given to the ACC detection circuit 12. The ACC detection circuit 12 peak-detects the burst signal 36 and provides the output signal 13 to the ACC detection circuit 4 . ACC circuit 4 is AC
Upon receiving the C detection output 13, the burst level of the reproduced low-pass converted color signal @29 is adjusted according to the level of the detected output 13, and outputted as a reproduced low-pass converted color signal 30 with a constant burst level. Further, the burst signal 36 extracted by the burst gate circuit 6 is also given to the APC detection circuit 14. The APC detection circuit 14 uses a signal 38 from a 3.58 MH2 oscillator (3°58 MHz O20>37) that generates a reference signal of the same frequency as the burst signal in order to cope with the frequency fluctuation of the burst signal @36 received during the recording/reproducing process. and the burst signal 36, the phase of the burst signal 36 is detected.Receiving the detection output 15 from the APC detection circuit 14, the VxO oscillation circuit 16 detects the phase of the reproduced burst signal 36 at the same frequency and phase as the reproduced burst signal 36. A synchronized signal with a frequency of 3.58 MH2 is given to the sub-converter 18. The sub-converter 18 receives the signal 17 with a frequency of 3.58 MH2 and the frequency of 629 KHz output by the AFC circuit 19.
After receiving the signal 21, frequency conversion is performed to obtain a frequency of 4.2.
A signal 22 of 0.09 MHz is given to the main converter 23. The AFC circuit 19 frequency-multiplies the horizontal synchronization signal 8 separated by the horizontal synchronization separation circuit 7, and outputs a signal with a frequency of 629KH2 by shifting its phase by 90 degrees for each magnetic head according to the head switching signal 20. conventional VTR
is configured to keep the amplitude of the burst signal constant as described above.

FIG. 4 is a waveform diagram of burst signals in the recording system and the reproduction system.

The amplitude level of the burst signal is essentially constant.

However, the envelope of the waveform of the burst signal 11 during recording is no longer a rectangular wave as shown in FIG. 4 due to the characteristics of a color signal transmission system such as a filter.

That is, the portion of the maximum burst level is only a part of the burst signal. Therefore, the amplitude of the low-frequency converted burst signal obtained by low-frequency converting the burst signal 11 is also not constant. A low frequency converted burst signal whose burst level is not constant and whose envelope is close to a triangular wave is recorded on the magnetic tape. When this low frequency conversion signal is reproduced, due to the frequency characteristics of the electromagnetic conversion system of the magnetic tape magnetic head and the band limitation by the filter included in the reproduction system, etc.
jf! As shown in FIG. 4, the envelope of the reproduction burst signal becomes closer to a triangular wave. In other words, the portion with the maximum burst level becomes even smaller.

As described above, the ACC detection circuit 12 peak-detects the burst signal and provides the signal to the ACC circuit 4. Therefore, if the burst signal, which has a small maximum portion, receives even a small amount of noise, the peak detection output will fluctuate, and the operation of the ACC circuit 4 will become unstable. As a result, amplitude fluctuations of the color signal occur, resulting in deterioration of the signal/noise ratio (S/N ratio) of the color signal, resulting in disadvantages such as color unevenness in the reproduced image.

[Summary of the Invention] The purpose of the present invention is to eliminate the above-mentioned drawbacks and to
An object of the present invention is to provide a magnetic recording/reproducing device that improves the N ratio.

In summary, the present invention records a burst signal by replacing it with a signal (pseudo burst signal) whose envelope has a rectangular shape that matches the frequency and phase of the original burst signal, and when reproducing the pseudo burst signal. This is a magnetic recording/reproducing device configured to perform ACC detection using the following.

The objects and other objects and features of the present invention will become more apparent from the detailed description given below with reference to the drawings.

[Embodiment of the Invention] FIG. 6 is a block circuit diagram of a color signal recording system of a VTR which is an embodiment of the invention.

FIG. 6 is a signal waveform diagram at each part of the circuit of FIG. 5. In FIG. 5, in addition to the conventional color signal recording system circuit shown in FIG. 1, an analog switch 40 is provided between the ACC circuit 4 and the main converter 23 for replacing the burst signal with a pseudo burst signal. This analog switch 40 generates a burst switching signal 46 in response to the timing of the horizontal synchronization signal 8 separated by the horizontal synchronization separation circuit 7. It operates based on a signal from the burst switching signal generation circuit 44. Further, as a pseudo burst signal, a signal 17 with a frequency of 3.58 MHz generated by the XO oscillation circuit 16 is applied to one side terminal (the opening in FIG. 5) of the analog switch 40 via the burst level adjustment volume 55. The operation of this circuit will be described below.

The ACC circuit 4 supplies a color signal 5 with a constant burst level to the main converter 23 as in the conventional device.

The circuit operation for keeping this burst level constant is similar to that of the conventional device shown in FIG. Color signal 5 is the main converter 23
The burst signal is replaced with a pseudo burst signal 17 immediately before being input to the burst signal. The operation for replacing this burst signal is as follows. Burst switching signal generation circuit 4
4 becomes active by the recording instruction signal 45. The burst switching signal generating circuit 44 responds to the timing of the horizontal synchronizing signal 8 and switches the analog switch 40 to the open side in FIG. 5 only when a burst signal is received. At this time, analog switch 4
A pseudo burst signal 17 which is in phase synchronization with the burst signal and has the same frequency is applied to the front side of FIG. This pseudo burst signal level matches the level of the burst signal included in the color signal 5. This level matching operation is performed in advance by the burst level adjustment volume 55. After the burst signal is replaced with a pseudo burst signal,
The analog switch 40 is a burst switching signal generation circuit 46
The switch is switched to the A side in Fig. 5 by the signal from .

As a result, the color information signal portion is directly supplied to the main converter 23. Therefore, the color signal 41 is the sixth
As shown in the figure, the pseudo burst signal with a constant burst level and the color information signal are subjected to low frequency conversion. Thereafter, it is mixed with the FM luminance signal and recorded on the magnetic tape.

FIG. 7 is a block circuit diagram of a color signal reproduction system of a VTR which is an embodiment of the present invention. In FIG. 7, unlike FIG. 3, an analog switch 40 is provided between the ACC circuit 4 and the main converter 23. This analog switch 40 receives a signal 4 from a burst switching generation circuit 44.
6, the circuit is switched to the ACC circuit (a side in FIG. 7) or the xO oscillation circuit (b side in FIG. 7). However, since the switching signal generating circuit 45 becomes active only when receiving the recording instruction signal 45, it does not operate during reproduction and does not generate a signal.

Therefore, analog switch 40 remains connected to ACC circuit 4. That is, the circuit operation of the reproduction system is the same as that of the conventional apparatus shown in FIG.

FIG. 8 is a waveform diagram of a reproduced burst signal and a reproduced pseudo burst signal.

As shown in FIG. 8, the reproduced pseudo-burst signal 54 extracted by the burst gate circuit 6 during reproduction has a longer portion with the highest burst level than the conventional reproduced burst signal. Therefore, the ACC detection output 13 of the peak detection type ACC detection circuit 12 is stabilized. As a result, A
The circuit operation of the CC circuit 4 is also stabilized, and amplitude fluctuations in the reproduced low frequency conversion color signal are also reduced. In other words, the S/N of the reproduced color signal
ratio is improved.

"Effects of the Invention" As described above, according to this invention, with a simple circuit configuration,
By recording the burst signal with a pseudo-burst signal whose envelope is rectangular and whose phase and nine frequencies are the same as the burst signal, the S/N ratio of the color signal during playback can be improved. Stable reproduced images without unevenness can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram of a color signal recording system of a conventional VTR. FIG. 2 is a signal waveform diagram at each part of the circuit of FIG. 1. FIG. 3 is a block circuit diagram of a color signal reproduction system of a conventional VTR. FIG. 4 is a waveform diagram of a burst signal and a reproduced burst signal in a conventional VTR. Fifth
The figure is a block circuit diagram of a color signal recording system of a VTR which is an embodiment of the present invention. FIG. 6 is a signal waveform diagram at each part of the circuit of FIG. 5. FIG. 7 is a block circuit diagram of a color signal reproduction system which is an embodiment of the present invention. FIG. 8 is a waveform diagram of a conventional reproduced burst signal and a reproduced pseudo burst signal by the circuit of FIG. 7. In the figure, 4 is an ACC circuit, 6 is a burst gate circuit, 9 is a burst gate pulse generation circuit, 12 is an ACC detection circuit, 14 is an APC detection circuit, 16 is a VxO oscillation circuit, 40 is an analog switch, and 44 is a burst switching signal Generation circuit, 55 is a burst level adjustment volume. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (3)

[Claims] (1) A color video signal recording device that records a color video signal consisting of a color signal including a burst signal and a color information signal, and a luminance signal while keeping the level of the burst signal constant, wherein the burst signal is converted from the color signal. burst signal extraction means for extracting the burst signal, phase detection means for detecting the phase of the burst signal extracted by the burst signal extraction means, and an oscillation frequency and phase of which are controlled in response to the phase detection output of the phase detection means. a reference signal generating means for generating a reference signal having a phase period with the burst signal and the same frequency as the burst signal; and a replacing means for replacing the burst signal and the reference signal. Recording device. (2) The color video signal further includes a horizontal synchronizing signal, and the replacing means includes: pulse signal generating means for generating a pulse signal having a pulse width corresponding to the duration of the burst signal in response to the horizontal synchronizing signal. and a switching means for switching between the burst signal and the reference signal in response to the pulse signal, and replacing the burst signal and the reference signal, the color video signal according to claim 1. Recording device. (3) The color video signal recording device comprises: a burst level adjustment means that receives the color signal and keeps the level of the burst signal included in the color signal constant; and a burst level adjustment means that receives the output signal from the burst level adjustment means. further comprising: frequency converting means for converting the frequency of the output signal, the switching means having one and the other input terminals, and provided between the burst level adjusting means and the frequency converting means; One terminal is supplied with the output signal from the burst level adjustment means, and the other terminal is supplied with the reference signal, and in response to the signal from the pulse signal generation means, the switching means selectively passes the reference signal. A color video signal recording device according to claim 1 or 2.