JPH0720261B2 - Color signal processor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color signal processing device in a video tape recorder that records and reproduces a color video signal.

2. Description of the Related Art Conventionally, the video signal processing method used in consumer video tape recorders is such that the luminance signal is FM-modulated and the chrominance signal is frequency-converted into a low frequency band for recording. Is a method of converting the frequency again and restoring it.

FIG. 3 is a block diagram of a reproduction system of conventional VHS system color signal processing. In the figure, the reproduction signal input from the input terminal 1 is passed through an amplifier 2 and is passed through a low pass filter (hereinafter,
It is supplied to the LPF 3), the low-frequency conversion carrier color signal is taken out, and the automatic gain control circuit (hereinafter referred to as the ACC circuit).
The amplitude is limited at 4, the frequency is converted at the balanced modulator 5, and the bandpass filter (hereinafter referred to as BPF) 6 removes unnecessary components generated at the time of balanced modulation. Further, in the burst 6 dB down circuit 7, the color burst signal, which has been increased by 6 dB at the time of recording, is lowered by 6 dB and returned to the original state, the adjacent crosstalk is removed by the comb filter 8, and the signal is output from the output terminal 9.

On the other hand, the reproduction signal output from the amplifier 2 is supplied to a high-pass filter (hereinafter, referred to as HPF) 10 to extract an FM-modulated luminance signal, and the amplitude is limited by a limiter 11.
The FM demodulator 12 demodulates the luminance signal. Only the horizontal synchronizing signal is extracted from the demodulated luminance signal in the H separation circuit 13, and the third burst gate pulse that substantially coincides with the timing of the color burst signal in time is extracted based on the extracted horizontal synchronizing signal. A first burst gate pulse having a wider pulse width before and after the third burst gate pulse generated by the pulse generating circuit 32 and output from the third pulse generating circuit 32 in the first pulse generating circuit 14. Is output. The first burst gate pulse is used in the burst 6 dB down circuit 7 at the timing of reducing the color burst signal by 6 dB.

The third burst gate pulse is used in the burst gate circuit 20 'for extracting only the color burst signal from the output signal of the comb filter 8. The color burst signal extracted from the burst gate circuit 20 'is phase-compared with the output signal of the reference oscillator 21 in the phase comparator 22,
The error signal passes through an LPF 23 and an adder 24 to control a voltage controlled oscillator (hereinafter referred to as VCO) 25. Oscillation frequency of VCO25 is 320H in case of NTSC system (H is horizontal scanning frequency)
Oscillates at. The output signal of the VCO 25 is output to the 1/8 frequency divider 28, which outputs four output signals that are different in phase by 90 degrees. One of them is selected by the selection circuit 29, and the balanced modulator 30
Is supplied to. The output signal of the reference oscillator 21 is also supplied to the horizontal modulator 30, is output to the BPF 31, the unnecessary components are removed in the BPF 31, and is supplied as the carrier of the balanced modulator 5. The frequency detector 26 detects the oscillation frequency of VCO25 because VCO25 does not enter the block state except 320H.
VCO25 is controlled through PF27 and adder 24.

The above structure is described in, for example, Japanese Patent Laid-Open No. 59-13484.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the above-mentioned configuration, when dubbing in which the color video signal reproduced by the video tape recorder is further recorded by the video tape recorder is repeatedly performed, the timing of the luminance signal and the color signal is increased. Gradually shifts, and when a burst gate pulse is created based on the horizontal sync signal, the burst gate pulse shifts from the timing of the actual color burst signal, causing the phenomenon of color fading or color unevenness, It has a drawback that it is uncomfortable for the user.

Means for Solving the Problems In order to solve the above problems, a color signal processing device of the present invention generates a first burst gate pulse including a color burst signal period based on a horizontal synchronizing signal. A pulse generating circuit, a first burst gate circuit for extracting a color burst signal from a carrier color signal using a first burst gate pulse, and a voltage value of the color burst signal extracted by the first burst gate circuit A first level detection circuit for detecting a signal, a second pulse generation circuit for generating a second burst gate pulse by shaping an output signal of the first level detection circuit, and the first burst gate circuit And a second level detector for detecting that the color burst signal extracted by is less than a predetermined level, and an output signal of the second level detector. A selection circuit controlled by the selection circuit for selecting and outputting the first burst gate pulse and the second burst gate pulse; and the first burst gate pulse or the second burst gate output from the selection circuit. It is configured to include a second burst gate pulse circuit for extracting a color burst signal for correcting the time base fluctuation of the carrier color signal at the time of reproduction by using the pulse.

According to the present invention, since the burst gate pulse for extracting the color burst signal for correcting the time base fluctuation of the carrier color signal at the time of reproduction is created by the voltage level of the color burst signal with the above-described configuration, the dubbing is performed. As a result, the burst gate pulse matches the position of the color burst signal even if the timing of the luminance signal and the color signal is deviated, which makes it possible to strengthen the color fading and color unevenness during dubbing, and when the color burst signal is below a certain level. In addition, since the burst gate pulse generated based on the horizontal synchronizing signal is used for switching, it is possible to prevent color fading that occurs when the burst gate pulse generated from the color burst signal is always used.

Embodiment A color signal processing device according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a color signal processing device according to an embodiment of the present invention. The difference from the conventional example of FIG. 3 is that the pulse generation circuit 32 of FIG. 3 is eliminated and the first burst gate circuit 15, the first level detection circuit 16, the second pulse generation circuit 17, and the second level are provided. The detection circuit 18 and the switch 19 are newly added, and the burst pulse supplied to the second burst gate circuit 20 is different. The other functions are similar to those described with reference to FIG. Now, the carrier color signal that has passed through the comb filter 8 is
In the first burst gate circuit 15, the color burst signal is extracted from the first pulse generation circuit 14 at the timing of the first burst gate pulse. The first level detection circuit 16 detects the voltage level in the extracted period to output the detection signal in the period in which the color burst signal actually exists, and the second pulse generation circuit 17 shapes the waveform to output the detected signal. Create a burst gate pulse of. A concrete circuit configuration example of the first level detection circuit 16 and the second pulse generation circuit 17 is described in, for example, Japanese Patent Laid-Open No. 56-80979. The color burst signal extracted by the first burst gate circuit 15 detects the level of the color burst signal in the second level detection circuit 18, and outputs a detection signal when the level is below a predetermined level. Second
As a specific configuration of the level detection circuit of, the level detection circuit of the color burst signal used in the color killer circuit can be considered. Now, the burst gate pulse supplied to the second burst gate circuit 20 is supplied through the switch 19. The switch 19 selects the second burst gate pulse output from the second pulse generation circuit 17 in the normal state, but the second level detection circuit 18 detects that the color burst level is below a predetermined level. In this case, the first burst gate pulse output from the first pulse generation circuit 14 is selected. The reason for switching between the first burst gate pulse and the second burst gate pulse is that the second burst gate pulse is generated from the color burst signal itself. Therefore, when the color burst signal is smaller than a predetermined level, burst This is to prevent the gate pulse from being output and the system to be cut off in order to remove the phase error variation of the carrier color signal, thereby causing the color fading.

FIG. 2 shows the waveforms and timings of the color burst signal (a), the first burst gate pulse (b), and the second burst gate pulse (c). If (a)
When the time position of the color burst signal of is shifted to the left or right, the second burst gate pulse of (c) also follows within the range of the first burst gate pulse of (b), and the position of the color burst signal is changed. Matches

As described above, in a video tape recorder in which a carrier color signal is frequency-converted into a low frequency for recording and is inversely converted into a carrier color signal at the time of reproduction, a first burst including a color burst signal period based on a horizontal synchronization signal. A first pulse generating circuit 14 for generating a pulse, and a first for extracting a color burst signal from a carrier color signal using a first burst gate pulse.
Burst gate circuit 15, a first level detection circuit 16 for detecting the voltage value of the color burst signal extracted by the first burst gate circuit 15, and an output signal of the first level detection circuit 16 Second pulse generating circuit 17 for generating a second burst gate pulse by
And a second level detector 18 for detecting that the color burst signal extracted by the first burst gate circuit 15 is below a predetermined level, and an output signal of the second level detector 18. A selection circuit 19 controlled to select and output the first burst gate pulse and the second burst gate pulse, and a first burst gate pulse or a second burst gate pulse output from the selection circuit 19 are used. By including the second burst gate pulse circuit 20 for extracting the color burst signal for correcting the time base fluctuation of the carrier color signal at the time of reproduction, the timing of the color burst signal from the horizontal synchronizing signal can be improved. Even if they are deviated, the second burst gate pulse follows the deviated position, so that the second burst gate pulse can be strengthened against color disappearance and color unevenness.

EFFECTS OF THE INVENTION With the above-described configuration, the present invention prevents the timing shift of the color burst signal and the burst gate pulse due to the timing shift of the luminance signal and the color signal that occurs when the dubbing is repeated, and eliminates the color disappearance during the dubbing reproduction The user's discomfort caused by color unevenness can be eliminated, and when the color burst signal is below a predetermined level, the burst gate pulse created based on the horizontal sync signal is used to switch the color burst signal at all times. It is possible to obtain an excellent effect that it is possible to prevent color fading that occurs when a burst gate pulse created from is used.

[Brief description of drawings]

FIG. 1 is a block diagram of a color signal processing device according to an embodiment of the present invention, FIG. 2 is a timing diagram of FIG. 1, and FIG. 3 is a block diagram of a conventional color signal processing device. 1 ... Input terminal, 2 ... Amplifier, 3 ... LPF, 4 ... ACC
Circuit, 5 ... Balanced modulator, 6 ... BPF, 7 ... Burst 6
dB down circuit, 8 ... comb filter, 9 output terminal, 10 HPF, 11 limiter, 12 FM demodulator, 13
...... H separation circuit, 14 ...... First pulse generation circuit, 15 ……
First burst gate circuit, 16 ... First level detection circuit, 17 ... Second pulse generation circuit, 18 ... Second level detection circuit, 19 ... Switch, 20 ... Second burst gate Circuit, 21 …… Reference oscillator, 22 …… Phase comparator, 23 ……
LPF, 24 ... Adder, 25 ... VCO, 26 ... Frequency detector,
27 …… LPF, 28 …… 1/8 divider, 29 …… Selection circuit, 30 ……
Balanced modulator, 31 …… BPF.

Claims (1)

[Claims] 1. A video tape recorder for frequency-converting a carrier color signal into a low frequency band for recording, and for converting the carrier color signal into a carrier color signal for reproduction, a first burst including a color burst signal period based on a horizontal synchronizing signal. A first pulse generation circuit for generating a gate pulse, a first burst gate circuit for extracting a color burst signal from a carrier color signal by using a first burst gate pulse, and an extraction by the first burst gate circuit A first level detecting circuit for detecting a voltage value of the color burst signal thus generated, and a second pulse generating circuit for generating a second burst gate pulse by shaping an output signal of the first level detecting circuit. A second detecting that the color burst signal extracted by the first burst gate circuit is below a predetermined level
And a selection circuit controlled by the output signals of the second level detector to selectively output the first burst gate pulse and the second burst gate pulse, and output from the selection circuit. A second burst gate circuit for extracting a color burst signal for correcting the time base fluctuation of the carrier color signal at the time of reproduction by using the first burst gate pulse or the second burst gate pulse A color signal processing device comprising: