JP2936723B2 - Color signal reproduction device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color signal reproducing apparatus used for a video tape recorder (hereinafter, abbreviated as VTR).

[0002]

2. Description of the Related Art In recent years, color signal processing of a color under system has been increasingly used in consumer VTRs.

[0003] An example of a color signal reproducing apparatus conventionally used in this type of VTR will be described below with reference to the drawings.

FIG. 3 is a block diagram showing an example of a color signal reproducing apparatus used in a conventional VTR circuit. In FIG. 3, a reproduced video signal is input to an input terminal 1 and applied to a low-pass filter 2 (hereinafter, referred to as LPF) and an automatic gain control circuit 3 (hereinafter, referred to as ACC). (Hereinafter referred to as BM), passed through a band-pass filter 5 (hereinafter referred to as BPF), applied to a selection circuit 6, and its output is applied to a burst gate 7.
On the other hand, a part of the output of the BPF 5 is transmitted to the composite comb filter 9, where the input signal is applied for one horizontal scanning period (hereinafter, 1).
Indicated as H. ), A first arithmetic circuit 906, a second arithmetic circuit 907,
After being applied to the first comb filter 908 and the second comb filter 909, it is output from the output terminal 10. On the other hand, a signal that has passed through the phase comparator 11 and the LPF 12 has a center frequency of 4 m · fs (m is a natural number; fs is a reduced conversion color subcarrier frequency).
Recorded as CO. ), And its output passes through a phase shift circuit 14 (hereinafter, referred to as a PS circuit) to output the BM1.
Added to 5. The output of the crystal oscillation circuit 16 (hereinafter, referred to as XOSC) oscillating at the color subcarrier frequency is B
After being applied to M15, its output is applied to BM4 through BPF17. On the other hand, the output of the burst gate 8 is compared with a reference voltage 18 by an amplitude comparator 19 and then applied to the ACC circuit 3 through an LPF 20.

The operation of the color signal reproducing apparatus used in the conventional VTR having the above-described structure will be described below.

The reproduced video signal input from the input terminal 1 passes through the LPF 2 to extract a low-frequency converted carrier color signal. This low-frequency conversion carrier color signal is subjected to automatic gain control of the amplitude in ACC3 and then frequency converted in BM4. The output signal of the BM 4 is removed by the BPF 5 from unnecessary components generated at the time of frequency conversion, and supplied to the composite comb filter 9. Then, the crosstalk from the adjacent track is removed by the composite comb filter 9 and is output from the output terminal 10 as a reproduced carrier color signal.

FIG. 2 shows the composite comb filter 9 shown in FIG.
This will be described with reference to FIG. FIG. 2 shows a first arithmetic circuit 906 and a second arithmetic circuit 907 constituting the composite comb filter 9.
And 1H delay circuits 904 and 905 and an adder circuit 91
7 is an example block diagram showing a configuration of an inversion circuit 918. The operation of the composite comb filter 9 configured as described above will be described with reference to FIG. MAX circuits 911, 912, and 916 that output the larger of the input signals, and MINs 913 and 91 that output the smaller of the input signals
4,915 are provided. Here, the first comb filter 908 is constituted by a portion surrounded by a broken line, and the second comb filter 909 is constituted by a portion surrounded by a chain line. The second comb-shaped filter 909 has a configuration in which the input signal is delayed by 1H, but color blur does not occur in the vertical direction of the screen. In the first comb filter 908, there is no signal delay, but color blur occurs in the vertical direction of the screen. Composite comb filter 9 described above
Are output from output terminals 902 and 903.

Next, the description will return to the conventional color signal reproducing apparatus shown in FIG. The selection circuit 6 outputs the BP
Select the output signal of F5
The output signal of the comb filter 908 is selected and supplied to the burst gate 7. A burst signal is extracted from the carrier chrominance signal by the burst gate 7, and the phase comparator 11 compares the phase of the burst signal with the reference signal of the color subcarrier frequency output from the XOSC 16. Phase comparator 1 whose phase is compared
The output signal of No. 1 is smoothed by the LPF 12 and becomes a control signal of the VCO 13. The output signal of the VCO 13 is subjected to frequency division and phase shift processing by the PS circuit 14 and
Supplied to Then, in the BM 15, the XOSC 16
, And is supplied to the BM 4 via the BPF 17 as a carrier for conversion of the reproduction frequency conversion. In this way, the burst signal of the carrier chrominance signal is
APC (automatic phase control) loop that synchronizes the phase with the output signal of the APC. On the other hand, when the output signal of the BPF 5 is selected by the selection circuit 6, the first comb filter 908 is outside the APC loop. Also,
When the output signal of the comb filter 908 is selected by the selection circuit 6, the comb filter 908 is in the APC loop. When the comb filter 908 is outside the APC loop, the response of the APC is faster and the S / N ratio is improved. I have. The reason that the selection circuit 6 does not select the second comb filter 909 during long-time mode reproduction is that the output signal of the second comb filter 909 is
This is because the APC response is delayed and the S / N is deteriorated because the signal is delayed by 1H from the output signal of the signal 08.

On the other hand, the burst gate 8 receives the carrier chrominance signal output of the first comb filter 908 and extracts the burst signal. The burst signal extracted from the burst gate 8 is supplied to an amplitude comparator 19, and the reference signal 1
8 is compared with the amplitude. The output signal of the amplitude comparator 19 is LP
The signal is smoothed by F20 and becomes a control signal of ACC3. Thus, the ACC loop is configured so that the amplitude of the burst signal of the carrier chrominance signal becomes the amplitude represented by the reference voltage 18.

[0010]

In such a conventional configuration, the first comb filter 908 and the second comb filter 909 have different comb filter characteristics, so that the respective output terminals 903 and 902 have different characteristics. The state in which adjacent crosstalk is removed is different, and the residual crosstalk component included in the output signals of the output terminals 903 and 902 is different. Therefore, when the amount of crosstalk contained between the head output channels of the reproduced video signal input from the input terminal 1 is different, the amplitude of the burst signal output from the output terminal 902 of the second comb filter 909 becomes It differs between head output channels. For this reason, the amplitude of the burst signal of the carrier chrominance signal at the output terminal 10 also differs between channels. As a result, the screen flickers on the TV screen,
That is, there is a problem that a flicker phenomenon occurs.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a color signal reproducing apparatus which solves the above-mentioned problem and does not cause a color fringing phenomenon in a vertical direction and also prevents a flicker phenomenon appearing on a screen. .

[0012]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention controls the amplitude of a reproduced low-frequency converted carrier color signal.
Controlling the automatic gain control circuit, and the output of the automatic gain control circuit.
A balanced modulator for frequency-converting the force signal into a carrier chrominance signal;
Band-pass filter that removes unnecessary components of the output signal of the balanced modulator.
Filter and the output signal of the bandpass filter
A first delay circuit that delays by a horizontal scanning period, a second delay circuit that delays the output signal of the first delay circuit by one horizontal scanning period, and an input signal to the first delay circuit > and to processing the output signal of said first delay circuit
And a first comb filter configured by the following formulas , and three signals of an input signal to the first delay circuit, an output signal of the first delay circuit, and an output signal of the second delay circuit are arithmetically processed. A second comb filter comprising:
A crystal oscillator that oscillates at a color subcarrier frequency;
The burst signal included in the output signal of the comb filter and the
A phase comparator for comparing the phase of the output signal of the crystal oscillator,
The balanced modulation is controlled by an output signal of the phase comparator.
By creating a carrier for frequency conversion in the
A voltage-controlled oscillator for controlling the phase of the reproduced carrier color signal;
The reference voltage and the output signal of the second comb filter
The amplitude of the burst signal is compared with the reference voltage,
By creating a control signal for the gain control circuit, the second
The amplitude of the burst signal output from the filter is constant
An amplitude comparator is provided .

[0013]

According to the present invention, since the comb filter in the APC loop processes two-line signals, the image quality is maintained as before, and the reproduced carrier chrominance signal is 3 bits.
Since it is obtained from a comb filter that processes the line signal, the color bleeding phenomenon in the vertical direction of the screen does not occur, and the comb filter in the ACC loop is the same as the comb filter for obtaining the reproduced carrier color signal. By using this, it is possible to eliminate the amplitude difference between the channels and prevent the flicker phenomenon appearing on the screen.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a color signal reproducing apparatus used in a VTR circuit according to the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention. FIG. 1 is substantially the same as the block diagram of FIG. 3 shown in the conventional example, so only the differences will be described, and the other will be omitted. The difference is that the input signal of the burst gate 8 is extracted not from the output signal of the first comb filter 908 but from the output signal of the second comb filter 909. . Others are the same.

The operation of the color signal reproducing apparatus having the above-described configuration will be described below, focusing only on differences from the conventional example. Conventionally, ACC control is performed so that the amplitude of the burst signal of the output signal from the first comb filter 908 becomes constant. However, in the configuration of FIG. 1 of the present invention, the output from the second comb filter 909 is used. ACC control is performed so that the amplitude of the burst signal of the signal becomes constant. For this reason, the burst signal of the reproduced carrier color signal is controlled to be the same even when the crosstalk amount is different between the channels, eliminating the amplitude difference between the channels, preventing the flicker phenomenon appearing on the screen, Since the conventional APC loop is employed, the image quality is maintained as before, and the output signal from the second comb filter 909 is used as the reproduced carrier color signal, so that the vertical color fringing phenomenon also occurs as before. No longer.

[0017]

As is apparent from the above embodiment, according to the present invention, the comb filter in the APC loop uses a signal obtained by processing a signal of two lines, and the reproduced carrier chrominance signal is a signal of three lines.
AC signal obtained from the comb filter that processes the line signal
By using the same comb filter in the C loop as the comb filter for obtaining the reproduced carrier color signal, the conventional S / N can be secured, and the color blur phenomenon in the vertical direction can also be achieved. It is an object of the present invention to provide a color signal generating apparatus having an excellent effect that a flicker phenomenon appearing on a screen can be prevented because the amplitude difference between channels can be eliminated without generating the same.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a block diagram of a composite comb filter used in the present invention.

FIG. 3 is a block diagram of a conventional example.

[Explanation of symbols]

 2 LPF 3 ACC 4 BM 5 BPF 6 Selection circuit 7 Burst gate 8 Burst gate 9 Composite comb filter 11 Phase comparator 16 XOSC 18 Reference voltage 19 Amplitude comparator 904 1H delay circuit 905 1H delay circuit 906 First arithmetic circuit 907 Second arithmetic circuit 908 First comb filter 909 Second comb filter

Claims (1)

(57) [Claims] 1. A carrier chrominance signal recorded by frequency conversion into low frequency, a reproducing circuit of a video tape recorder of the color subcarrier system back into carrier chrominance signal again frequency conversion during reproduction, the low-frequency reproduced Automatic control of the amplitude of the converted carrier color signal
A dynamic gain control circuit, and an output signal of the automatic gain control circuit.
A balanced modulator for performing frequency conversion to a carrier chrominance signal;
Bandpass filter to remove unnecessary components of the output signal of the modulator
A first delay circuit for delaying the output signal of the band-pass filter by one horizontal scanning period, a second delay circuit for delaying the output signal of the first delay circuit for one horizontal scanning period, An arithmetic operation is performed on an input signal to the first delay circuit and an output signal of the first delay circuit to perform a configuration.
A first comb filter formed and the first delay circuit
This arithmetically processing the three signals of the input signal and the first delay circuit output signal and the output signal of the second delay circuit to the
A second comb filter composed of
A crystal oscillator that oscillates at a wave frequency,
The burst signal included in the output signal of the
A phase comparator for comparing the phase of the output signal of the vibrator;
In the balanced modulator controlled by the output signal of the comparator
Regeneration carrier by creating carrier for frequency conversion
A voltage-controlled oscillator that controls the phase of the color signal, and a reference voltage
And a buffer included in the output signal of the second comb filter.
The amplitude signal is compared with the reference signal and the automatic gain control is performed.
By creating a control signal for the control circuit, the second comb-shaped
The amplitude of the burst signal of the filter output signal becomes constant.
A color signal reproducing apparatus including an amplitude comparator .