SU1069191A1 - Colour channel of secam colour-television receiver - Google Patents

Description

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The invention relates to a color television technique, in particular to color television (.TV) receivers. A chromaticity channel is known for the color-TV receiver of the SECAM system, with a switch, an amplitude limiter and a frequency detector, which are connected in series with a serially connected switch. A color signal is sent to the first input of the switch, the second input is connected to the output of the reference frequency oscillator and to the control input of the switchboard iodans are lower pulse. For periods of retraction across the pages, the switch sends a reference sinusoidal signal to the chroma channel with a frequency equal to the frequency of the unmodulated subcarrier. Due to this, reference areas appear in the demodulated signal to fix the black level, which simplifies the requirements for the parameters of frequency detector 11.; The disadvantage of the device is a transient process caused by a phase jump upon the introduction of a reference signal. The transition process distorts both the site for fixation and the video signal at the beginning of the forward path in rows. The closest to the technical essence of the invention is the color channel of a color TV receiver of the SECAM system, containing a switch, the first input of which is a color signal input, the second input is connected to the output of the reference frequency generator, and the first amplitude connected to one of the switch outputs a limiter, a ne frequency detector, a first adder and a first level fixing unit, while the second input of the first adder is connected to the trigger output, the counting input of which is input ohm lowercase pulses 121 However in the known device no necessity to store in the storage tank potential corresponding to black level during the forward stroke .po field, which leads to distortion of m discharge Accumulate Tel'nykh capacitor. The objectives of the invention are to improve the accuracy of black level fixation. The goal is reached. With the SECAM system color TV receiver channel containing a switch, the first input of which is an input of a color signal, the second input is connected to the output of the reference frequency generator, and the first connected in series are connected to one of the switch outputs amplitude limiter first frequency detector,: the first adder and the first level fixing unit, while the second input of the first adder is connected to: trigger trigger, the counting input of which is the input of horizontal pulses The second amplitude limiter, the second frequency detector, the second adder and the second level fixing unit, as well as the control pulse driver, the first input of which is connected to the control input of the switch, the second input of the second adder and the trigger output, the counting input of which is connected to the second input of the control signal generator, the two outputs of which are connected respectively to the two inputs of each of the block fixing level n, while the input of the second amplitude limiter connected to the second input of the switch. FIG. 1 shows a structural electrical circuit of a chromaticity channel, a color TV receiver system SECLM, FIG. 2 - voltage diagrams. The device contains a switch 1, a reference frequency generator 2, the first 3 and second 4 amplitude limiters, the first 5 and second b frequency detectors, the first 7 and second 8 adders, the first 9 and second 10 level fixing blocks, the control pulse driver 11 and the trigger 12. The device works in the following way. I. Both outputs of switch 1 are sent to a chroma signal and a reference signal from generator 2, controlled by trigger 12, switch 1 redistributes its incoming signals so that, for example, in black lines, input a1 of the 3-limit limiter 3 receives a podnesuya modulated signal S -Y, and. in odd lines, the reference signal from generator 2. Then the second signal arrives at the input of the second amp limiter 4 in the even lines, and in the odd lines, the reference signal is received, and modulated by the B - Y signal in the odd lines. In other words, Switch 1 divides information ii-Y and & -Y in two color difference channels and in each channel the color subcarrier alternates with the reference signal. The first 5 and second b frequency detectors demodulate the signals and a color difference signal and a constant level determined by the frequency of the oscillator 2 are output through the line. The first 7 and second 8 adders are controlled

meander from trigger 12, provide a shift of these levels so that they coincide with the levels of black

in the signals. Note that with zero frequency drift, these levels move along with color difference signals, which reduces the stability requirements of frequency detectors mules. In the interval of even lines where the reference level is transmitted; fig, 20.) is superimposed on it by a transient phase when applying to the frequency detector frequency reference. On the interval S at the beginning of the odd lines Sfig. 2a) there is also a transient caused by the absence of a color subcarrier during the period of the horizontal sync pulse transmission. Both of these areas should be excluded from the signal and replaced by the potential for the interval (Fig. 2q.) With blocks 9 and 10 of fixation. These blocks pass a discharge signal at the output in the time interval (Fig. 2a) i and during periods y on the memory capacitors,

existing in fixation blocks 9 and 10, the steady state enters; At time intervals fV.-y-wji, this level is read and transmitted to-exit. The first 9 and second 10 blocks are controlled by a shaper 11, in which the input strings C.Fig. converted to a write control signal of one of the blocks, 9 and 10, Figures. 2q) and a control signal for the ejection of another of these blocks (Fig. 2d). Shaper 11 can

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be performed on two elements AND or OR-NOT.

Due to the action of the level fixing blocks and the control pulse generator at the outputs of the device, separated color difference signals alternate in rows with fixing levels strictly corresponding to the black levels in the signals. In order to recover the missing information, a delay unit is connected to the outputs of the device, which is made according to a known scheme on two CCD registers. Delay unit provides repeat

5 input color difference signals on the lines where they are missing. At the same time, on the reverse moves along the lines in the signals, stable levels corresponding to black levels remain.

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In the proposed device, an increase in the fixation accuracy is achieved due to the fact that the fixation potential is recorded not once per field, as in the well-known, but through the string. Therefore, the fluctuations of this potential caused by the discharge of the storage capacitor are significantly reduced. At the same time, parts of the signal distorted by transients are not allowed into the memory and at the outputs of the device. The chroma channel is also convenient for building a PAL / SECAM decoder with a delay block on CCD resistors,

5 because the PAL decoder and the proposed SECAM color channel require a delay block of the same design.

Claims (1)

(57} COLOR COLOR CHANNEL. SECAM SYSTEM RECEIVER, comprising a 'switch, the first' input of which is a color signal input, a second input connected to the output of the reference frequency generator, and a first amplitude limiter, a first frequency detector, connected in series to the output of the switch , the first adder and the first block fixing the level, while the second input of the first adder is connected to the output of the trigger, the counting input of which is the output of the horizontal pulses, characterized in that, with In order to improve the accuracy of fixing the black level, a second amplitude limiter, a second frequency detector, a second adder and a second level fixation unit, and a control pulse generator, the first input of which is connected to the control input of the switch, the second input of the second adder and the trigger output, are introduced in series the count input of which is connected to the second input of for- tors, _with the control signal output © two of which are connected respectively to the two inputs of each of the clamp blocks, etc. and the input of the second amplitude limiter is connected to the second input of the switch.