Circuit with a comb filter for causing color difference signals to coincide on each scanning line.

摘要

A circuit for producing a chroma signal which includes both of a first (R-Y) and a second (B-Y) color difference signal on each of scanning lines in response to a line-sequential color difference signal in which a first and a second color difference signal appear alternately on consecutive scanning lines. A carrier generator (40, FIGS. 3 and 5) generates a first (SC2a) and a second (SC1a) color subcarrier which are different in phase from each other in synchronism with the line-sequential color difference signal. The first color subcarrier (SC2a) is subjected to balanced modulation at a first modulator (60) which uses the first color difference signal (R-Y) for the modulation while the second color subcarrier (SC1a) is subjected to balanced modulation at a second modulator (66, 68, 70) which uses the second color difference signal (B-Y). The outputs of the first (60) and second (66, 68, 70) modulators are added together by a first adder (74). A delay circuit (80) is provided for delaying an output of the first adder (74) by a period of time which is substantially equal to one horizontal scanning period. The output of the delay circuit (80) is added to the output of the first adder (74) by a second adder (82) to produce the chroma signal. The circuit eliminates the need for operations heretofore performed for bringing color difference signals into coincidence at the baseband and thereby the need for delay circuits, switching circuits and adjusting circuits which implement such operations.