JPS5748887A - Chroma demodulator - Google Patents

Abstract

PURPOSE:To prevent the stoppage of a switch circuit and to obtain an R-Y color difference signal having correct polarity, by obtaining a burst detection output the porality of which is able to determine with the phase of a line switching signal in a half the frequency of a horizontal scanning frequency. CONSTITUTION:A carrier chrominance signal processed at a delay line matrix circuit is directly applied to an R-Y demodulator 1, the R-Y reference sub-carrier having 90 deg. in phase is applied to one input terminal of the 1st switch circuit 2, and sub- carrier through a 180 deg. phase shifter 3 is inputted to another input terminal B. The circuit 2 is controlled with an output of a multivibrator 4 producing a fH/2 line switching signal through 1/2 frequency division of the horizontal pulses, the output of the circuit 2 is inputted to an input terminal A of the 2nd switch circuit 5, and a signal inverted at a 180 deg. phase shifter 6 is inputted to another input terminal B. The circuit 5 is controlled with a control circuit 8 operated with the output of a phase discriminator 7, and one of the two signals inputted to an output terminal 9 of the circuit 5 is alternately outputted and inputted to a demodulator 1 to output the R-Y color difference signal with correct polarity.