SU735199A3 - Decoder of colour tv receiver of pal system - Google Patents

Description

togs, phase modulator 7, sawtooth voltage generator 8, second output demodulator 9;

The device works as follows. ,

. The chroma signal is fed to the input of key 1 along with a selector impulse: catfish, which can be used as a beam reversal pulse. Key 1 is open for the duration of the continuation of the selector impulse to sweep the pulse in its single signal for synchronization of colors .

From the output of switch 1, the signal is applied to two phase detectors 2 and 5, phase detector 2 is connected to the reference frequency generator 3, which has a generation frequency f and a frequency that is equal to the frequency of the color subcarrier. Phase detector 5 is connected to the second generator 6, having a clock 2n - 1

fj ,, or torus generation. +2

2n - 1 /

f lowercase

Where

.L About W

Sci

frequency, ai p - integer number.

The phase modulator 7 modulates the output signal of the second generator 7 in phase with a sawtooth voltage that is supplied from r "generator 8. From the first generator 3, the output signal is fed directly to the output demodulator 4 along the BV axis, while 6 passes to the output demodulator 9 along the RV axis through the phase modulator. ,,.,

A closed loop, formed by phase detector 2 and generator 3, provides automatic phase control.

The output from generator 3 is provided to output demodulator 4 as a reference subcarrier that is in phase with the axis B-V to provide a demo component of the axis B-V.

 The phase modulator 7 functions in such a way that it captures the phase difference between the signals, with a frequency, for example, f. -Jij, H color subcarrier with frequency fgj. at 0 ° and for each varying sweep time. In order to accomplish this, a sawtooth voltage is supplied from the oscillator 8 to the phase modulator 7 for phase modulation. output signal from generator 6, as a result of which the phase undergoes. continuous change in relation

to the color polnesu1 1eP with a speed of 180 for the horizontal scanning period. This means that the output from phase modulator 7 can be used as a reference carrier for demodulating the chroma signal to extract the R-V component from it. However, since the proposed device contains two generators 3 and b, in order to demodulate the R-V component separately from the B-V component demodulation, a phase difference between the two reference subcarriers from ± 90 may drift due to different temperature coefficients.

5 and aging effects. To avoid this, the proposed device uses automatic phase adjustment to maintain the phase difference exactly between the reference subcarriers used in the B-V and R-V demodulation components.

Claims (1)

1. French patent number 2019316, cl. H 04 N 9/00, 1970 (prototype).