JPS5937919B2 - Cross color/dot interference removal device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a color television signal that is transmitted by multiplexing a carrier chrominance signal onto the high frequency region of a luminance signal using the PAL system. The present invention relates to a device for eliminating cross-color and dot interference caused by mutual crosstalk.

In the PAL system, to transmit a color signal, a subcarrier is modulated with the color signal, and the signal is superimposed on the high frequency portion of the video band.

Therefore, there is crosstalk between the two, degrading the image quality. One is subcarrier dot interference and the other is cross color interference. The former is currently eliminated by inserting a subcarrier trap in the receiver's luminance channel to limit the bandwidth of the luminance channel. In the latter case, the high-frequency signal component of the luminance signal passes through the color channel of the image receiving circuit and is processed, and this component is unrelated to the original image component and appears as a change in chromaticity on the reproduced screen. Normally, no measures are taken in the receiver to deal with this cross-color interference. Currently, the methods for removing the two dot interference and cross color interference and separating and obtaining the high frequency components of the carrier color signal and the luminance signal are as follows:
Regarding the PAL system, for example, the Television Society of Japan, Television System Circuit Research Committee material "Y, C separation circuit" (
There is a method of using a delay line of two horizontal scanning periods (hereinafter referred to as 2H), as described in the 1976 issue of the 28th day of the 11th.

That is, the waveforms of television signals are very similar for each frame and for each scanning line. In other words, the vertical correlation is strong. Therefore, if fH is the horizontal frequency, the energy distribution of the image will be as shown in Figure 1a, and the luminance signal component Y has a peak for each fH as shown by the solid line.
It becomes smaller as it reaches higher harmonics. On the other hand, color difference signal components are also distributed at similar intervals, but these signals are transmitted by subcarriers modulated by the PAL system.

The frequency of the subcarrier is approximately 1/4 of the horizontal frequency fH.
Since it is selected to be a multiple of
C) The carrier signal of the blue color difference signal U, which is modulated without reversing its polarity, is f Ji 4
distributed apart by. Also, for each horizontal scan line,
The carrier color signal corresponding to the red difference signal V whose polarity is inverted and modulated is located exactly in the middle of the carrier color signal corresponding to the blue difference signal U, as shown by the broken line in FIG.
Moreover, it is distributed at a location FN/4 away from the luminance signal. In order to separate the PAL luminance signal and the carrier color signal transmitted in this way, a C-shaped comb filter for the color channel and a Y-shaped comb filter for the luminance signal are used, as shown in Figure 1B and c. All you have to do is implement a shaped filter.

To realize such a comb filter, a circuit as shown in FIG. 2 can be considered. In the same figure, 2H delay line 1
By subtracting or adding the H-delayed signal and the original signal in the subtraction circuit 2 or the addition circuit 3, a C-shaped comb filter or a Y-shaped comb filter is formed, respectively. Expressed as the following equations, O In order to actually realize the above circuit, conventionally 2H
An ultrasonic delay line was used as the delay line 1.

However, in this ultrasonic delay line, ultrasonic waves propagate in a glass medium, and in addition, inductance is required to cancel the capacitance of the electrical-mechanical converter at the input/output section, so it is difficult to integrate the integrated circuit. This is disadvantageous in terms of compatibility with
As a more advantageous element in terms of compatibility with the above-mentioned integrated circuit, it is conceivable to use a charge transfer element such as a well-known CCD or BBD. However, a charge transfer element samples its input signal using a clock signal, and sequentially transfers and delays the sampled values.Therefore, the frequency of the clock signal is based on the sampling theorem with respect to the frequency band of the input signal. must be satisfied. Further, the required number of bits of a charge transfer element is approximately determined by the product of clock frequency and delay time, and as the clock frequency increases, the number of bits, that is, the number of elements increases. Concomitantly, the driving power of the clock signal increases, and clock noise becomes more likely to occur. When trying to simply replace the 2H ultrasonic delay line of the above conventional example with a charge transfer element, the amount of 4.43M
For a carrier color signal with a subcarrier frequency of Hz, the clock frequency is a repetition frequency of 10 MHz or more,
The number of bits is also 1200 bits or more. This value is an amount that is extremely difficult to put into practical use for consumer television receivers in terms of analog signal transfer. The present invention does not apply a comb filter for separating color signals and luminance signals to the conventional carrier color signal band, but applies it to the color difference signal band to control the clock of the charge transfer element used as a 2H delay line. By greatly reducing the frequency and number of bits, and by inserting a subcarrier trap circuit controlled by the color difference signal into the luminance signal channel to eliminate the comb-filtered cross-color interference, the dot interference can be eliminated. The object of the present invention is to provide a device that makes it possible to obtain a wideband luminance signal without any interference.

The present invention will be explained below based on the embodiment shown in FIG. In the figure, a PAL color television signal detected by a video detector 11 enters a video amplifier 12 and is amplified, a part of the signal goes into a band amplifier 16, and the other part goes into a luminance signal delay line 13. A PAL carrier color signal is obtained at the output of the band amplifier 16, and the red difference signal demodulator 1
7 and the blue difference signal demodulator 18 . In this case, 1
It is also possible to separate the red difference signal and the blue difference signal into carrier color signals using a delay line of H, but this is not shown here. The red difference signal demodulator 17 and the blue difference signal demodulator 18 synchronously detect the carrier color signal to obtain a red difference signal V and a blue difference signal U. At this time, the red difference signal demodulator 17
A PAL switch operation is performed to restore the polarity reversed for each H. Since the synchronous wave can also be considered as a frequency shift of the signal, the spectral distribution of the color difference signal obtained as described above is distributed in a relationship similar to that explained in FIG. 1a. That is, the color signal and luminance signal, which are distributed with strong energy for each FH, do not overlap each other and are distributed with an interval of f/4. However, since the two red difference signals and the blue difference signal are modulated by mutually orthogonal carrier waves, they are separated by synchronous detection. That is, only the red difference signal and no blue difference signal appear in the output of the red difference signal demodulator 17. Similarly, the blue difference signal does not include the red difference signal. However, the Y component of the luminance signal, which is a cross color interference component, is f
It exists in a 4-separate spectrum distribution. The above two color difference signals can be separated in the region of the carrier color signal using the 1H delay line as described above, but even in this case, cross color components remain. In this way, a part of the red difference signal including the cross color component enters the 2H delay line 19 for the red difference signal constituted by a charge transfer element, where it is delayed by 2H,
Furthermore, it is added to the original signal in the sum calculation circuit 21 for the red difference signal. The output of the sum calculation circuit 21 includes a color difference signal and FV4.
Luminance signal components concentrated at distant locations are removed, and only the red signal component is obtained. Similarly, by the 2H delay line 20 for the red signal and the summation circuit 22 for the blue difference signal, which are constructed of charge transfer elements, only the blue difference signal component can be obtained as the output of the summation circuit 22. The two types of color difference signals obtained as described above are guided to the matrix circuit 24.

On the other hand, the output of the video amplifier 12 enters a luminance signal delay line 13, where the delay time difference with the chrominance signal processing circuit is compensated for, and then guided to a subcarrier trap circuit 14.

This subcarrier trap circuit 14 is connected to a control signal generation circuit 23.
It is controlled to stop or start its operation by a control signal from. The control signal generation circuit 23 uses color difference signals that do not include cross color components from the sum circuits 21 and 22 for red and blue difference signals, and when the level of one of the color difference signals exceeds a certain level. A control signal is generated such that the subcarrier trap circuit 14 is activated only when the subcarrier trap circuit 14 is activated, and the other subcarrier trap circuits are not activated. The threshold value of the level is determined from the detection limit of dot interference on the screen. In this way, only when a chrominance signal exists and there is a risk of dot interference occurring, the band of the luminance signal is limited and the dot interference component is eliminated, and when a chrominance signal is not present, a broadband luminance signal is generated without band limitation. Obtain the signal and send it to video output circuit 1
5 to the CRT. As is clear from the above description, according to the present invention, color difference signals are transferred by charge transfer elements.
Comb processing requires two two-bit delay lines compared to processing the carrier color signal band, but the total number of bits in the charge transfer element is significantly reduced and the clock frequency is also significantly lower. You can choose.

Therefore, it is very advantageous in terms of integration degree, operating frequency, transfer efficiency, etc. In addition, regarding the brightness channel, there is also the problem of dot interference that remains in areas that are not vertically related, which was a drawback of conventional comb-shaped filters, such as the color on the screen suddenly becoming colorless in the vertical direction. It also has the excellent feature of being able to solve problems.

[Brief explanation of the drawing]

Figures 1A, b, and c are energy distribution diagrams of PAL signals, amplitude versus wave number characteristics diagrams of C-type and Y-type comb filters, Figure 2 is a block diagram showing an example of the configuration of a comb filter, and Figure 3 1 is a block diagram of one embodiment of the present invention. 14...Subcarrier trap circuit, 17...
...Red difference signal demodulator, 18...Blue difference signal demodulator, 19, 20...2H (2 horizontal scanning periods)
Delay line, 21, 22... Sum calculation circuit.

Claims (1)

[Claims] 1 The color difference signal output from the color difference signal demodulator of the PAL signal receiving circuit is connected to the primary color difference signal and the color difference delayed by two horizontal scanning periods by a delay line of two horizontal scanning periods and a sum calculation circuit made up of a charge transfer element. The subcarrier trap circuit in the luminance signal processing circuit is operated only when the color difference signal not containing the luminance signal component has a certain amplitude or more. 1. A cross color dot interference removal device, characterized in that it is configured to remove a carrier color signal component in a luminance signal.