SU1728984A1 - Method of decoding color signal in pal system - Google Patents

Abstract

This invention relates to color television. The purpose of the invention is to improve noise immunity. The essence of this method of decoding the chroma signal in the PAL system () is that after dividing the chroma signal into quadrature components, they are subjected to synchronous detection by the subcarrier signal, which is synchronized by the second harmonic of the color signal. Received after this blue and red color difference signals. (CRS) may have different polarities. However, the polarity of the output DSRs will correspond to the given one regardless of the possible double digit phase of the subcarrier signal and regardless of the phase change of the quadrature component of the red DSR from line to line. Because it does not require the subcarrier phase information to be extracted from the flash signal and the subcarrier signal phasing is not required for synchronous detection at the beginning of each row, and the system noise immunity will increase. 2 Il. (L

Description

The invention relates to the field of color television and can be used in the development of decoding devices of the PAL system ().

The purpose of the invention is to improve noise immunity.

Fig. 1 shows the electrical structure. a circuit diagram of an apparatus for implementing a method for decoding a chroma signal in a PAL system (PABc); in fig. 2 is an electrical block diagram of the control unit.

A method for decoding a chroma signal in a PAL system is as follows.

After dividing the chrominance signal into quadrature components, they are subjected to synchronous detection. In this case, the subcarrier signal, with which synchronous detection of color signals is carried out, is synchronized by the second harmonic of the color signal. The blue and red color-difference signals obtained after synchronous detection can have different polarities, since during synchronization of the subcarrier with the second harmonic of the color signal, the two-digit phase of the signal of the subcarrier appears; In addition, the polarity of the red color difference signal at the output of the synchronous detector changes due to the phase change of the corresponding quadrature component from line to line by 180P. Therefore, at the beginning of each line of the television image, the polarity of the color flash pulse in this line is compared with the specified polarity. If the mismatch is polar

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A color flash pulse with a given color signal is inverted to the beginning of the active part of the line. Thus, the polarity of the output color difference signals will correspond to the specified value regardless of the possible two-digit phase of the subcarrier signal and regardless of the phase change of the quadrature component of the red color difference signal from line to line. Since it does not require the separation of the information about the phase of the subcarrier from the flash signal and does not require the phasing of the signal of the subcarrier for synchronous detection at the beginning of each row, the noise immunity of the system is increased.

A device that implements a PALcB system for decoding a chroma signal (PALcB) (FIG. 1) comprises a quadrature selector 1, a doubler-adder 2, a subcarrier signal generator 3, a phase shifter 4, the first synchronous detector 5 and the first control unit 6 and serially connected the second synchronous detector 7 and the second control unit 8.

The output of the subcarrier signal generator 3 is connected to the first input of the second synchronous detector 7. The input of the quadrature selector 1 is the input of the chroma signal. The first output of the quadrature selector 1 is connected to the second input of the doubler-adder 2 and to the second input of the second synchronous detector 7. The output of the first control unit 6 is the output of the first color difference signal (for example, red). The output of the second control unit 8 is the output of the second color difference signal (e.g., blue). The second inputs of the first control unit 6 and the second control unit 8 are combined and are the input of clock pulses.

The first control block b (Fig. 2) is made similar to the second control block 8 and comprises an inverter 9 connected in series, a first switch 10, a second switch 11, a threshold unit 12, a trigger 13 and a third switch 14. The input of the inverter 9 is the first input of the control block and connected to the second input of the third key 14 .. The output of the latter is connected to the output of the first key 10. The second input of the second key 11 is the second input of the control unit. The second output of the trigger 13 is connected to the second input of the first key 10, the output of which is the output of the control unit.

The device works as follows.

The input to the quadrature selector 1 is provided with a chroma signal in the PAL system. On

its output is formed by two quadrature components which, after doubling and summing in doubler-adder 2, synchronize the generator 3 of the subcarrier signal. In addition, the resulting quadrature components are fed to the second inputs of the first and second synchronous detectors 5 and 7. A subcarrier signal is supplied to their first inputs, and to the second input

0 of the second synchronous detector 7 directly from the generator 3 output of the subcarrier signal, and to the second input of the first synchronous detector 5 through the phase shifter 4, which shifts the phase of the raised signal by 90 °. The color difference signals obtained at the outputs of the first and second synchronous detectors 5 and 7 are fed to the first inputs of the first and second control blocks 6 and 8, respectively.

0 In the control units (Fig. 2), the polarity of the color flash pulse is compared with the preset and, if necessary, inverted corresponding color difference signal. For

5 of this signal from the output of the control unit through the second key 11, which is opened by the sync pulses at the instants of the color flash, is compared in the threshold block 12c with a given polarity. If the polarity of the signal at the input of the threshold unit 12 does not coincide with the pulse given at its output, a pulse arrives at the counting input of trigger 13. This pulse switches trigger 13 and the first key 10 and third key respectively. As a result, the color difference signal at the output control unit is changed to the opposite, corresponding to the specified one.

Thus, at the outputs of the device

0 polarity of color difference signals will always correspond to the specified value regardless of polarity of color difference signals at the outputs of synchronous detectors, i.e. no matter which of the two

5 phase values will be set to the subcarrier signal generator 3 and which of the two possible phase values will the received quadrature component of the red color difference signal have.

Claims (1)

0 claims A method for decoding a chroma signal in a PAL system (), in which color-difference signals are generated by synchronously detecting a color signal by a subcarrier signal synchronized by a second harmonic of a color signal, characterized in that, in order to improve noise immunity, after forming the color difference signals from each color difference signal, R 517289846 pulses are produced, the corresponding flash the polarity of the color signal corresponding to the two subcarriers; compare the difference signal if there is a discrepancy The polarity of each selected polarity of the selected pulse is given from a given pulse with a given polarity and inverted polarity. five one