RU1818708C - Secam chrominance channel compensator - Google Patents

Abstract

The invention relates to television technology and can be used, for example, as part of the receiving equipment of the SECAM system for correcting crosstalk of a color signal. The purpose of the invention is to increase the signal-to-noise ratio and suppress crosstalk such as brightness and color. The inventive device for the correction of high-frequency predistortions contains: a band-pass filter, a notch filter, a first delay element, a second electronic switch, a second delay unit, a high-frequency predistortion corrector, a third electronic switch, four limiters, a low-pass filter, an amplitude detector, a frequency detector, a low-frequency corrector predistortions, delay unit, first electronic switch, key, capacitor, trigger, clock. 2 ill.

Description

The invention relates to television technology and can be used, for example, as part of the receiving equipment of the SECAM system.

The purpose of the invention is to increase the signal-to-noise ratio and suppress cross-distortion such as brightness-color.

In FIG. 1 shows a structural and electrical diagram of a device; Fig. 2 is a timing chart illustrating the operation of the device.

The correction device for the color channel of the SECAM system (Fig. 1) comprises a band-pass filter 1, a notch filter 2, a second delay unit 3, a second electronic switch 4, a third delay unit 5, a high-frequency predistortion corrector 6. a third electronic switch 7, a second limiter 8, third limiter

9, a low-pass filter 10, an amplitude detector 11, a fourth limiter 12, a first limiter 13, a frequency detector 14, a low-frequency predistortion corrector 15, a first delay unit 16, a first electronic switch 17, a key 18, a capacitor 19. a trigger 20, a clock generator 21.

The device operates as follows.

At the input of the bandpass filter 1 (PF-1), the full television signal SECAM (In) is received, a color signal is allocated to PF 1 (Fig. 2, b) (row DB), PF 1 passes the components of the color signal in the band from-3 -6 MHz and suppresses components outside the specified band (Fig. 2, a). In this case, the components of the current color signal are output at the output

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PF 1 (Fig. 2, c), where as an example the change in the amplitude and frequency of the four components of the color signal is shown: green (3), red (K), rest signal (B-B) and blue (G). However, the frequency-modulated signal of the color subcarrier subjected to the interfering effect from the response of a step-like change in the brightness signal (Fig. 2d) and other types of interference / passes through PF 1, which ultimately leads to a violation of color reception during the occurrence of the response and interference (Fig.2, d). As is known, the signal-to-noise ratio at the output of the demodulator is equal to the signal-to-noise ratio at its input multiplied by the coefficient DR / PB p - (K2 is the modulation index. Therefore, additional measures must be taken in the SECAM system to increase the noise immunity of color channels For this purpose, the following principle is proposed for detecting interference and the frequency (low and high) of the color signal components, which are magnified by the magnitude of the frequency from the resting frequency: the color signal components (Fig. 2, c, e) simultaneously arrive at bedinenny entrance notch filter 2 and the second delay unit 3 and the fourth input of the limiter 12, the amplitude characteristic which is illustrated in Figure 2, e.

Next, the signal from the output of the fourth limiter 12 passes sequentially through the amplitude detector 11, a low-pass filter 10, the third limiter 9 and to the control input of the second electronic switch 4, where a two-period rectifier can be used as the amplitude detector 11. The signal at the output of the low-pass filter 10 is shown in Fig. 2.g, where the magnitude of the amplitude of the signal depends on the value of the frequency components of the color signal. The amplitude increases with the departure of the frequency of the component (left and right) from the rest frequency. The control signal at the output of the low-pass filter 10 also contains a constant component in areas corresponding to the resting frequency. To eliminate it, a third limiter 9 is used with an amplitude characteristic that looks like in FIG. 2, k, curve 1. In this case, a constant amplitude and polarity control signal is generated at the output of the limiter 9 (FIG. 2, l) . With a positive pulse level, the control signal of the second electronic switch 4 switches to the output of the notch filter 2, and at zero to the output of the first delay element 3. Thus, s, k, g components with interference are rejected by filter 2 (only those

components that differ in frequency from the resting frequency, they are notched), i.e. the frequency response of the notch filter 2 attenuates the noise power and interference from the luminance signal. The value of this attenuation is characterized by the area of the frequency response of this filter. But at a frequency of rest and components close to it, the signal passes the second block of delay 3, i.e. arrives at the output of the second electronic switch 4 unchanged. This is due to a decrease in the amplitude of the components of the resting frequency due to the notch on the transmitting side.

At the output of the bandpass filter 1, due to its wide passband, the interference from the luminance signal will have a large peak value (Fig. 2, e) and short duration. As a result of this, amplitude and frequency modulation of the color signal will occur. At the same time, at the output of the second limiter 8 (amplitude characteristic of Fig. 2, k; curve 2), a control signal from interference and from the lowest frequency components of the color signal (Fig. 2, m) appears. This is due, as indicated above, to an increase in signal amplitude; in this case, the output of the third switch 7 is connected to the output of the third delay unit 5, since the color signal has already been rejected in RF 2. Thus, when control signals are present at the control inputs of the second and third electronic switches 4 and 7, respectively, the color signal with output PF 1 passes sequentially notch filter 2, the second electronic switch 4, the third delay unit 5, the third electronic switch 7; and in the absence of control signals (in the presence of a resting frequency) at the control inputs of electronic switches 4 and 7, the color signal passes the second delay unit 3, the second electronic switch 4 h, the high-frequency predistortion corrector 6, the third electronic switch 7, i.e. in the first case, interference and noise are reduced, and in the second, the full recovery of the subcarrier will occur. Since the visual perception of noise and interference differ in images of different colors and have different durations (puffs) of color transitions when a signal with a high saturation transitions, this is especially true for cyan, magenta, and blue colors, in the notch filter 2, the notch level is different colors can be made accordingly changing.

Next, the color signal passes through the first limiter 13 in turn, which suppresses emissions due to switching of the switches 4, 7, the frequency detector 14 and the low-frequency distortion corrector 15, which provide the demodulation of the color signals and the extraction of color difference signals. The color signal is fed directly to the first input of the first electronic switch 17, and to the second input through the first delay unit 16, the control input of which is connected to the output of the clock 21. The first electronic switch 17 and key 18 are controlled by the voltage of the half-line frequency from the trigger 20 driven by lowercase pulses. The zero frequency of the detector is tuned by connecting on each second line with a key 18, an additional capacitor 19, so that the black level in alternating demodulated signals ER-Y I.E. B-Y becomes the same.

An advantage of the claimed device is that it provides automatic tuning of the reception mode of the constituent color signals depending on the magnitude of the frequency of the color signal. At the same time, the AFC of the device adaptively changes, which ensures the effective suppression of the energy of the interfering high-frequency components of the luminance signal and the noise penetrating the color channel. The latter ensures high quality reproduced color television image.

Claims (1)

The correction device for the color channel of the SECAM system, comprising a high-frequency predistortion corrector, a first limiter, a frequency detector, a low-frequency predistortion corrector, a first delay unit and a first electronic switch, a trigger, a key, a capacitor and a clock generator, wherein the output of the low-frequency corrector predistortion is connected to the second input of the first electronic switch, the outputs of which are the outputs of the color-difference signals of the device Twa, and the control input of the switch is connected through a series-connected switch and a capacitor to the control input of the frequency detector 0 and the trigger output, the input of which is an input for horizontal pulses, and the control input of the first delay unit is connected to the output of the clock generator, characterized in that, with 5, in order to increase the signal-to-noise ratio and suppress crosstalk such as brightness-color, a band-pass filter, a notch filter, a second delay unit, a second electronic switch are introduced; 0 third delay unit, third electronic switch, second limiter, third limiter and connected in series. ny fourth limiter, amplitude a detector and a low pass filter, 5, the input of the bandpass filter is the input of the device, and the output is connected to the input of the fourth limiter and the combined input of the notch filter and the second delay unit, the first and second outputs of which are the first and second information inputs of the second electronic switch, the control input of which is connected to the output third limiter, the input of which is connected to the output of the filter 5 low frequencies by the input of the second limiter, the output of which is connected to the control input of the third electronic switch, the first and second information inputs of which are connected respectively to the output of the third delay unit and the output of the high-frequency predistortion corrector, each of which is connected to the output of the second electronic switch, third exit 5 electronic switch connected to the input of the first limiter, Hlh & e Fig - /