JPS60223279A - Chrominance signal processor - Google Patents

Abstract

PURPOSE:To attain the stable response by changing a demodulated color difference signal and a synthetic ratio of delay output of said color difference signal only for a period of a burst signal. CONSTITUTION:A reproduced low band converted carrier chrominance signal is supplied through an input terminal 30 and demodulated to two color difference signals by a demodulator 20. These signals are transmitted through comb-shaped filters 25 and 26 and modulated to carrier chrominance signals through a modulator 29. These color signals are delivered to an output terminal 31. The output of the filter 25 is sent to a burst gate 27, and an oscillator 33 is controlled by the output transmitted through an LPF28. Then the demodulator 20 is controlled for accurate demodulation. The filter 25 contains a delay line 21, amplifiers 22 and 23 and an adder 24. The amplification factors of both amplifiers 22 and 23 can be changed only in a burst period by a burst flag signal and supplied from a terminal 32 and showing the burst period. This prevents the unstable response.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to a processing device for a low frequency conversion carrier color signal used in a video tape recorder.

Conventional configuration and its problems The color signal processing circuit commonly used in consumer video tape recorders converts the frequency of the sub-carrier color signal into a low-frequency carrier color signal for recording, and converts the frequency again during playback. This is a method called color under which returns the color signal to the sub-carrying color signal and removes the jitter of the color signal caused by the jitter of the rotating cylinder at that time.

FIG. 1 shows an example of a reproduction system using a conventional analog circuit of color under type. In the figure, the reproduced low-pass converted color signal is frequency-converted into a subcarrier color signal through a balanced modulator 1, and a bandpass filter 2 removes unnecessary components generated during balanced modulation.

Comb filter 13 composed of delay line 3 and subtractor 12
Then, crosstalk from adjacent tracks is removed and output.

On the other hand, a burst signal is extracted from the output to a burst game (4), and its phase is compared by a reference oscillator (11) and a phase comparator (6). The phase error passes through a low-pass filter 6 to control a voltage controlled oscillator (hereinafter referred to as VCO) 7. The output of the VCO 7 is summed with the frequency multiplied by 40 by a horizontal synchronization signal (fH) Roughney's locked loop circuit (PLL) 10 by a balanced modulator 8, and then passed through a bandpass filter 9 to obtain a carrier for the balanced modulator 1. .

In this way, the circuit operates so that the output is always synchronized in phase with the reference oscillator 11.

However, in this configuration, when the gain of the loop is increased in order to quickly respond to the jitter of the low-pass conversion carrier color signal, there is a drawback that the response becomes unstable because the comb filter 13 is included in the loop. Another drawback is that if the comb filter 13 is removed, crosstalk components from adjacent tracks cannot be removed. Furthermore, the conventional method passes the carrier color signal through the comb filter, which has the disadvantage that the delay line used in the comb filter must operate at a high frequency. There is still a method of removing the comb filter only during the burst period in order to speed up the response, but this method has the disadvantage that the single phase comparator 6 malfunctions due to crosstalk.

Purpose of invention.

The purpose of the present invention is to demodulate a low-pass conversion carrier color signal into two color difference signals and pass each through a comb filter to remove crosstalk, by changing the characteristics of the comb filter only during the burst period. The response of the device can be made faster without becoming unstable, and malfunctions due to crosstalk are reduced. By passing the color difference signal through a comb filter, the delay line used in the comb filter can operate at a low frequency. An object of the present invention is to provide a color signal processing device that can use a delay line.

Structure of the Invention The color signal processing device of the present invention converts a low-frequency conversion carrier color signal into a first
and a second demodulator for demodulating two color difference signals;
and a first and second delay circuit that respectively delay the second color difference signal; a first arithmetic circuit that adds the output of the first delay circuit to the first color difference signal at a predetermined combination ratio; a second arithmetic circuit that adds the output of the second delay circuit to the second color difference signal at a predetermined synthesis ratio; and a burst signal of the output signal of either the first or second arithmetic circuit. The control circuit includes a control circuit that controls the demodulation axis of the demodulator based on the phase, and is configured to set the synthesis ratio of either the first or second arithmetic circuit to a different value only during the burst signal period. It is.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 2 is a block diagram showing the configuration of an embodiment of the present invention. In the figure, a low frequency conversion carrier color signal reproduced from a video tape recorder is inputted to an input terminal 3o, and demodulated into two color difference signals by a demodulator 2°. Each color difference signal passes through comb filters 25 and 26, is modulated into a carrier color signal by a modulator 29, and is output to an output terminal 31. The output of the comb filter 26 is sent to a modulator 29 while also being sent to a burst gate 27.

The signal during the burst period is extracted. For example, if the color difference signal input to the comb filter 26 is an RY signal, the level during the burst period will be zero since the RY axis is perpendicular to the burst. Therefore, Purst Gate 27
The output is passed through a low-pass filter 28, and the oscillator 33 is controlled by the output.

The output is feedback-controlled as a control signal for the demodulator 20, and demodulation can be performed accurately. Note that the burst gate is controlled by a burst flag input from the input terminal 32.

Next, the comb filter 25 will be explained. The comb filter 26 is connected to the delay line 21 . The configuration includes amplifiers 22° 23 and an adder 24, and the amplifiers 22° 23 are connected to the input terminal 3.
The amplification factor can be set to a different value only during the burst period by the burst flag signal representing the burst period input from 2. Here, for example, the amplification factors of each of the amplifiers 22 and 23 are set during periods other than the burst period. , 5 and 0.6
and 0.3 and 0.7 during the burst period. FIG. 3 (-) shows the frequency characteristics of the gain of the comb filter 26. The solid line shows the characteristics of periods other than bursts.

The dashed line shows the characteristics of the burst period. In addition, the signal acid content is n
The crosstalk component in fH is (n+H) fH (n is an integer)
The spectrum is concentrated in Further, FIG. 3 Φ) shows the time axis response of the phase of the output terminal 31 when a step phase change is applied to the input terminal 3o. The horizontal axis represents time, and the vertical axis represents the amount of change in phase. Note that the amount of phase change given to the input is 1. The solid lines are the responses when the gains of the amplifiers 22 and 23 are fixed to 0.5 and 0.6, respectively, and the broken lines are the responses when the gains of the amplifiers 22 and 23 are set to 0.3 and 0.7, respectively. . In this example, R-
Since the signal during the burst period of the Y color code is controlled to be zero, the response is the comb filter 2 during the burst signal period.
It is determined by the characteristics of 5. Therefore, in this embodiment, as shown in FIG.
) shows the dashed response.

On the other hand, since the conventional comb filter adds the output of the delay line and the output that does not pass through the delay line on a one-to-one basis, it responds as shown by the solid line in Figure 3(b). 9 In this embodiment, the response of the device is faster than in the conventional example. Furthermore, as can be seen from the broken line characteristics in Figure 3(a), the gain at the valley frequency is C14 times as much as the gain at the peak frequency, and the crosstalk component appears at the valley frequency, so it is 0.4 times the gain at the valley frequency. It is possible to suppress the Therefore, it is possible to improve the signal-to-noise ratio of the signal during the burst period compared to the case where the comb-shaped filter is removed. Further, the characteristics shown by the broken line in FIG. 3(a) are only shown during the burst period, and the characteristics shown by the solid line (-) are shown in other periods, that is, periods where the color information of the video signal is present.
A large losstalk removal effect can be obtained. Further, the comb filter 26 may be similar to a conventionally used filter. Therefore, the burst signal of the carrier color signal obtained at the output terminal 31 passes through a comb filter with a shallow gain at the valley frequency only for the R-Y component, but the B-Y component has a zero gain at the valley frequency. The average signal-to-noise ratio of the signals passing through the comb filter is improved for both color difference signals compared to when the comb filter is made shallower.

In this embodiment, the gains of the amplifiers 22 and 23 are set to 0.3 and 0.7 during the burst period, respectively.
This is an example and is not limited to this value.

Effects of the Invention As is clear from the above description, the present invention can speed up the response to phase fluctuations of the input signal by controlling the frequency characteristics of the comb filter to increase the gain at the valley frequency only during the burst period. It is possible. It also has the effect of eliminating crosstalk during the burst period.

It is possible to obtain a burst with a good SN ratio. Furthermore, in the present invention, since the low-pass conversion carrier color signal is demodulated into a color difference signal and then passed through a comb filter, a comb filter that operates at a low frequency can be used. It further raises the gain of the trough of the comb filter during the burst signal period.

This is done only for one of the color difference signals.

The burst signal-to-noise ratio of the output carrier color signal is improved for both color difference signals when the comb filter is made shallower.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a conventional example, FIG. 2 is a block diagram showing the configuration of an embodiment of the present invention, and FIG.
) is a characteristic diagram of a comb-shaped filter using a button according to an embodiment of the present invention,
FIG. 3(b) is a characteristic diagram showing the response of one embodiment of the present invention. 20... Demodulator, 21, group, delay line, 22, 2
3...Amplifier, 24...Adder, 25.
26...Comb filter.

Claims (2)

[Claims] (1) a demodulator that demodulates a low-pass conversion carrier color signal into two first and second color difference signals, and first and second delay circuits that delay the first and second color difference signals, respectively;
a first arithmetic circuit that combines the output of the first delay circuit with a first color difference signal at a predetermined combination ratio; and a first calculation circuit that combines the output of the second delay circuit with a second color difference signal at a predetermined combination ratio. and a control circuit that controls the demodulation axis of the demodulator according to the phase of the burst signal of the output signal of either the first or second arithmetic circuit, A color signal processing device characterized in that the synthesis ratio of one of the first and second arithmetic circuits is set to a different value only during a burst signal period. (2) What is the synthesis ratio of the first or second arithmetic circuit? The ratio is 1 to 1 in periods other than the burst period, and in the burst period, a to (1-a) (where d is a real number and is O(a x 1)), as stated in claim (1). color signal processing device.