PURPOSE: To obtain circuit constitution which does not require many high-speed gates by selecting chroma frequencies so that frequency division ratios of two frequency dividers necessary for PAL each have a one-digit prime number.
CONSTITUTION: A recording chroma frequency is set to (43-1/8)fh in the 1st fie of PAL and (43+1/8)fh in the 2nd field, or to (43-1/4)fh in the 1st and the 2nd fields of NTSC (where fh is horizontal synchronizing frequency). Therefore, a VCO4 oscillates at 343fh in the 1st field of PAL and 345fh in the 2nd field, or at 342fh in the fields of NTSC. A 1/343 frequency divider has a frequency division ratio of 1/7×1/7×1/7 and is divided into a 1/7 frequency divider 23 and a 1/49 frequency divider 24. A 1/345 frequency divider has 1/3×1/5×1/23 and is divided into a 1/3 frequency divider 22 and a 1/155 frequency divider 25. Therefore, the 1/3 frequency divider requires only 2 flip-flops for frequency division of 343∼345fh=5.4 MHz, and the 1/7 frequency divider 23 required four flip-flops.
AZEYANAGI TOMOMITSU
KOJIMA NOBORU
