JP2512479B2 - Color signal processing device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color signal processing device effective for use in a video tape recorder.

2. Description of the Related Art Conventionally, in the video signal processing method used in consumer video tape recorders, the luminance signal is FM-modulated during recording,
The frequency of the chrominance signal is converted to the low frequency range, and the luminance signal is FM during playback.
In general, demodulation and color signals are frequency-converted again to restore them.

FIG. 4 is a block diagram of a reproduction system of a conventional VHS type color signal processing device. In the figure, a reproduction signal input from an input terminal 1 is supplied to a low-pass filter (hereinafter referred to as LPF) 3 through an amplifier 2 and a low-pass conversion color signal is taken out. Next, the amplitude is limited in the automatic gain control circuit (hereinafter referred to as ACC) 4, and the frequency is converted in the balanced modulator 5. Further, unnecessary components are removed by a bandpass filter (hereinafter referred to as BPF) 6. Next, in the burst 6 dB down circuit, the color burst signal, which has been increased by 6 dB at the time of recording, is downed by 6 dB and returned to the original state, the adjacent crosstalk is removed by the comb type filter 8, and the color burst 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, a 2FM-modulated luminance signal is extracted, and an amplitude is limited by a limiter 11,
The FM demodulator 12 demodulates the luminance signal. From the demodulated luminance signal, only the horizontal synchronizing signal is taken out by the H separation circuit 13. A first burst gate pulse including a color burst signal period is created in the first pulse generation circuit 14 based on the extracted horizontal synchronizing signal. The second pulse generation circuit outputs a second burst gate pulse having a narrower pulse width before and after the first burst gate pulse.

The first burst gate pulse is used for the timing of reducing the color burst signal by 6 dB in the burst 6 dB down circuit 7 and the timing for extracting the color burst signal in the burst gate circuit 16. The color burst signal extracted from the burst gate circuit 16 is compared in phase with the output signal of the reference oscillator 21 in the phase comparator 20. The phase comparator 20 operates only during the second burst gate pulse period. The error signal from the phase comparator 20 passes through the LPF 22 and the adder 23, and the center frequency is 320 f _H.
A voltage controlled oscillator (hereinafter referred to as VCO) 24 (f _H is a horizontal scanning frequency) is controlled. The output signal of the VCO 24 is output to the 1/8 frequency divider 27. The 1/8 frequency divider 27 outputs four output signals having different phases by 90 degrees, and the selection circuit 28 selects one of them. The selected signal is supplied to the balanced modulator 29. The output signal of the reference oscillator 21 is used as the carrier of the balanced modulator 29, and the output signal of the balanced modulator 29 is BPF3.
It passes through 0 and becomes the carrier of the balanced modulator 5.

In this way, the time axis fluctuation of the carrier color signal at the time of reproduction is corrected. In addition, the frequency detector 25
Since it does not become a lock state except at 320f _H , the oscillation frequency of VCO 24 is detected and VCO 24 is controlled through LPF 26 and adder 23. The configuration described above is provided, for example, in Japanese Examined Patent Publication No. 59-1.
It is described in Japanese Patent No. 3484.

Problems to be Solved by the Invention One of the basic problems in reproducing the color signal of a video tape recorder is the instability of the hue at the upper part of the television screen. In the conventional configuration shown above, the output burst signal is not phase-synchronized with the signal of the reference oscillator 21 in the predetermined period after the vertical synchronization signal, so that the hue at the upper part of the television screen is not stable and the It had the drawback of being uncomfortable.

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 second pulse generating circuit for generating a second burst gate pulse having a pulse width narrower than that of the first burst gate pulse, and a head switch pulse switching or vertical synchronizing signal for switching a signal from the head. Circuit for generating a pulse of a predetermined period from the first burst gate pulse in the pulse period from the mono-multi circuit, and the second burst except the pulse period from the mono-multi circuit. A switch circuit that selects a gate pulse and outputs a burst gate pulse for correcting the time axis fluctuation during playback. It is equipped with.

According to the present invention, the burst gate pulse for correcting the time base fluctuation of the carrier color signal at the time of reproduction is changed to the pulse width during the switching of the head switch pulse or the predetermined period from the vertical synchronizing signal. By adopting the first burst gate pulse having a wide pulse width and using the second burst gate pulse having a narrow pulse width in other periods, the feedback period becomes high because the gate period becomes long when the first pulse is adopted. Therefore, it is possible to obtain quick stability of hue.

Embodiment Hereinafter, a color signal processing device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of an embodiment of the present invention. The difference from the conventional example of FIG. 4 is that the head switch pulse input terminal 17 and the mono-multi circuit
18 and switch circuit 19 are newly added.
Since the other functions are the same as those in FIG. 1, the description thereof will be omitted here.

The circuit including the newly added head switch pulse input terminal 17, mono-multi circuit 18 and switch circuit 19 is a circuit for a burst gate pulse indicating a period in which the phase comparator 20 is operated. A head switch pulse is input to the input terminal 17, and a pulse of 16H (H indicates a horizontal scanning period) period is generated by the mono-multi circuit 18 from the switching. The switch circuit 19 selects the wide first burst gate pulse during the 16H period and selects the narrow second burst gate pulse during the other periods.
During the burst gate pulse period from the switch circuit 19, the phase comparator 20 operates.

FIG. 2 shows the output signal (a) of the burst gate circuit 16,
The waveforms and timings of the first burst gate pulse (b) and the second burst gate pulse (c) are shown, respectively. FIG. 3 shows the output signal (d) of the amplifier 2,
The waveforms and timings of the head switch pulse (e) and the output pulse (f) of the mono-multi circuit 18 are shown.

As described above, the first pulse generation circuit 14 for generating the first burst gate pulse (b) including the color burst signal period based on the horizontal synchronizing signal and the first burst gate pulse (b) A second pulse generation circuit 15 for generating a second burst gate pulse (C) having a narrow pulse width
And a mono-multi circuit 18 that generates a pulse (f) of 16H period from the switching of the head switch pulse (e) that switches the signal from the head, and the first burst gate pulse in the pulse period from the mono-multi circuit 18. With the configuration including the switch circuit 19 for selecting (b) and selecting the second burst gate pulse (c) in other cases, the operation time of the phase comparator 20 is long during the 16H period from the head switch. Therefore, the feedback gain becomes high, and the hue becomes stable quickly.

In the above, the input terminal of the mono-multi circuit 18
Although a head switch pulse (e) for switching the signal from the head is supplied to 17, the same operation is performed when the vertical synchronizing signal is supplied to the input terminal 17.

EFFECTS OF THE INVENTION According to the above-described configuration, the present invention is caused by the instability of the hue on the upper part of the TV screen because the feedback gain is increased and the hue is quickly stabilized in the period corresponding to the upper part of the TV screen. It is possible to obtain an excellent effect that the discomfort of the user can be eliminated.

[Brief description of drawings]

FIG. 1 is a block diagram of a color signal processing apparatus according to an embodiment of the present invention, FIGS. 2 and 3 are waveform and timing diagrams in FIG. 1, and FIG. 4 is a block diagram of a conventional color signal processing apparatus. Is. 14 …… First pulse generating circuit, 15 …… Second pulse generating circuit, 16 …… Burst gate circuit, 17 …… Input terminal, 18
...... Mono-multi circuit, 19 ...... Switch circuit, 20 ...... Phase comparator.

Claims (1)

(57) [Claims] 1. A color signal processing device used in a video tape recorder for frequency-converting a carrier color signal for recording in a low frequency range and recording the carrier color signal at the time of reproduction. A first pulse generating circuit for generating a first burst gate pulse including a color burst signal period, and a second pulse generating circuit for generating a second burst gate pulse having a pulse width narrower than that of the first burst gate pulse. And a mono-multi circuit for generating a pulse of a head switch for switching a signal from the head or a pulse for a predetermined period from the vertical synchronizing signal, and the first burst gate pulse in the pulse period from the mono-multi circuit. The second burst gate pulse is selected in a period other than the pulse period from the mono-multi circuit to select the carrier color signal during reproduction. Color signal processing apparatus and a switch circuit for outputting a burst gate pulse for correcting between base fluctuations.