JPS56149193A - Digital color signal generating circuit - Google Patents

Abstract

PURPOSE:To generate a digital chroma signal by a simple logic circuit by storing the half-cycle components of a chromaticity carrier signal in ROMs and by adding the polarity code signals that correspond to sample phases to the output signals of those ROMs. CONSTITUTION:In ROMb and ROMc, the chroma levels of the half-cycle cmponents of a chroma signal are stored. Chroma-control variable resistor VR1 and A/D converter (a) are used for an address generator; and ROMb outputs the 1st chroma level, and ROMc the 2nd chroma level 90 deg. out of phase with the 1st one. Those 1st and 2nd chroma levels and a switching signal from counter (e) are supplied to switch (f), which outputs the 1st and 2nd chroma levels by turns in response to every clock. Next, adder-subtractor (h) adds or subtracts the chroma level signal of the digital chroma signal to and from the control signal of variable resistor VR2 for luminance control with a polarity code signal. Further, blanking gate circuit (i) holds a blanking section at the black level to obtain the required signal at terminal (j).