JPS60220695A - Chrominance signal processor - Google Patents

Abstract

PURPOSE:To minimize malfunctions caused by crosstalk and, at the same time, to make the response of a chrominance signal processor quicker, by setting the compositing ratio of an arithmetic circuit to a different value during the period of a burst signal. CONSTITUTION:Reproduced low-frequency conversion carrier chrominance signals inputted from a terminal 35 are converted into carrier chrominance signals at a balanced modulator 20 and inputted in a comb line filter 26 through a BPF21. The filter 26 is composed of a delay line 22, amplifiers 23 and 24, and subtractor 25 and the amplifiers 23 and 24 can change their amplification factors during a burst period only by means of a burst flag signal inputted from a terminal 37 and indicating a burst period. As easily understood from the characteristic shown by the broken line of the figure, the gain at the bottom of frequency is 0.4 time larger than that at the top of frequency and, therefore, a crosstalk component can be suppressed to 0.4 time since the crosstalk appears at the bottom of frequency.

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 passes through a balanced modulator 1, is frequency-converted into a subcarrier color signal, is removed by a bandpass filter 2, unnecessary components generated during balanced modulation, and is subtracted by a delay line 3. A comb filter 13 composed of a filter 12 removes crosstalk from adjacent tracks and outputs the result.

On the other hand, a burst gate 4 extracts a burst from the output, and a reference oscillator 11 and a phase comparator 5 compare the phases. 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 added to the frequency obtained by multiplying the horizontal synchronizing signal (fH) by 40 in a phase 0 locked loop (PLL) circuit 1o in a balanced modulator 8, and then passes through a bandpass filter 9 to the balanced modulator 1. Get a career. 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.

Furthermore, there is a drawback that if the comb filter 13 is removed, crosstalk components from adjacent tracks cannot be removed. There is also a method of removing the comb filter only during the burst period, but this method has the disadvantage that the phase comparator 6 tends to malfunction due to crosstalk.

OBJECTS OF THE INVENTION The purpose of the present invention is to reduce malfunctions due to crosstalk when converting a low-intensity conversion signal into a carrier color signal having a color subcarrier frequency and removing adjacent crosstalk using a comb filter. It is an object of the present invention to provide a color signal processing device that can perform the processing quickly without making the response of the device unstable.

Structure of the Invention The color signal processing device of the present invention includes a frequency converter that converts the frequency of a low-pass conversion carrier color signal, a delay circuit that delays the output of the frequency converter, and an output of the delay circuit and the frequency converter. an arithmetic circuit that synthesizes the output of the arithmetic circuit at a predetermined synthesis ratio; and a control circuit that controls the amount of frequency conversion of the frequency converter according to the phase of a burst signal among the output signals of the arithmetic circuit; The ratio is configured to be set to a different value only during the burst signal period.

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 same figure, the reproduced low-pass conversion carrier color signal inputted from the scar terminal 36 is processed by the balanced modulator 20 to produce the carrier color signal. and is input to the comb filter 26 through the band pass filter 21.

This output is output to an output terminal 36, while a burst portion is extracted by a burst gate 27, and the phase is compared with a reference oscillator 29 by a phase comparator 28. The error output passes through a low-pass filter 30 and controls vCO 31. VC
The output of O31(7) is frequency-combined with the output of the PLL circuit 34 by the balanced modulator 32, and then passed through the bandpass filter 33.
The burst phase of the signal which enters the balanced modulator 20 through the reference oscillator 20 and appears at the output terminal 36 of the device as a whole is
Feedback control is applied so that the phase is equal to that of 9.

Note that the PLL circuit 34 provides an output that is 40 times the horizontal synchronization signal, and may be an oscillator fixed to the ICU in principle.

Next, the comb filter 26 will be explained.

The comb filter 2e is connected to the delay line 22. Amplifier 23°24
and a subtracter 26, and the amplifiers 23 and 24 can change the amplification factor to a different value only during the burst period in response to a burst flag signal input from an input terminal 37 representing the burst period. here.

For example, the amplification factors of each of amplifiers 23 and 24.

The description will be made using 0.6 and 0.5 for periods other than the burst period, and 0.3 and 0.7 for the burst period. FIG. 3(a) shows the frequency characteristics of the gain of the comb filter 26. The solid line shows the characteristics of periods other than the burst, and the broken line shows the characteristics of the burst period. Note that the signal component is (n + 2) f
As a crosstalk component, the nfH (n is an integer) p spectrum is concentrated in H. Further, FIG. 3 shows the time axis response of the phase of the output terminal 360 when a step phase change is applied to the input terminal 36.

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 line is amplifier 2
The broken lines are the responses when the gains of the amplifiers 23 and 24 are set to α3 and α7, respectively. In this embodiment, as described above, control is applied so that the phase of the output burst signal is equal to the phase of the reference oscillator 29, so the response is determined by the characteristics of the comb filter 26 during the burst signal period. Therefore, in this embodiment, the response shown by the broken line in FIG. 5 (bl) is shown.

On the other hand, the conventional comb filter subtracts the output of the delay line and the output that does not pass through the delay line on a one-to-one basis.
The response shown in the figure (bl) is shown by the solid line.

As is clear from this figure, the response of the device is faster in this embodiment than in the conventional example. Also, as can be seen from the characteristics of the broken line in Figure 3 (→), the gain at the valley frequency is 0.4 times the gain at the peak frequency, and the crosstalk component appears at the valley frequency, so it is 0.4 Therefore, the SN ratio of the burst signal can be improved compared to when the comb filter is removed.

In addition, the characteristics indicated by the broken line in Figure 3 (→) are only shown during the burst period; other periods, that is, periods where the color information of the video signal is present, have the characteristics indicated by the solid line (-), and Lostalk removal effect can be obtained.

In this embodiment, the gains of the amplifier 23.2A are set to 0.3 and 0.7 during the burst period, but this is just an example and is not limited to these values.

Effects of the Invention As is clear from the above explanation, 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 of the valley frequency only during the burst period. It is possible. Further, since there is a crosstalk removal effect during the burst period, a burst signal with a good SN ratio can be obtained, and an even greater crosstalk removal effect can be obtained outside the burst period.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the configuration of a conventional example, Figure 2 is a block diagram showing the configuration of an embodiment of the present invention, and Figure 3 (→
3 is a characteristic diagram of a comb filter used in an embodiment of the present invention (the average is a characteristic diagram showing the response of an embodiment of the present invention. 22... Delay line, 23, 24 ......Amplifier, 26...Adder, 26...Comb filter.

Claims (1)

[Claims] (1) A frequency converter that converts the frequency of a low-pass conversion carrier color signal, a delay circuit that delays the output of the frequency converter, and an output of the delay circuit and an output of the frequency converter at a predetermined synthesis ratio. a control circuit that controls the phase of an oscillator that provides a frequency for operating the frequency converter according to the phase of a burst signal among the output signals of the arithmetic circuit; A color signal processing device characterized in that only a signal period is set to a different value. (→ The synthesis ratio of the arithmetic circuit is 1 except during the burst period.
1 vs. 1, and the burst period is d vs. (1-a) (however, a
The color signal processing device according to claim 1, wherein is a real number and o<a<1.