Digital color encoder with improved circuitry

Abstract

A digital encoder includes a matrix circuit for synthesizing chrominance signals R-Y and B-Y based on RGB signals sampled at a predetermined sampling frequency which is an integral multiple of a chrominance subcarrier; low-pass filters; a delay circuit; a switch circuit for reducing a frequency of an output from the low-pass filters; a digital modulator for subjecting a chrominance subcarrier to quadrature two-phase balanced modulation using an output signal from the switch circuit so as to output a chrominance signal having a sampling frequency 1/m that of the predetermined sampling frequency; a sampling frequency conversion circuit for multiplying the sampling frequency of the chrominance signal by a factor of m so as to output a chrominance signal having the predetermined sampling frequency; and an adder for computing a sum of the luminance signal delayed by the delay circuit, the chrominance signals output by the sampling frequency conversion circuit and a composite synchronizing signal so as to synthesize a composite video signal. In another construction, a digital color encoder of the present invention includes a matrix circuit for producing a luminance signal and chrominance signals by blending RGB signals using a predetermined ratio assigned to each color component; a trap filter for rejecting transmission of luminance signal components that correspond to a chrominance subcarrier frequency; a modulator for producing a chrominance signal having an arbitrary phase, based on the chrominance signals; an adder for producing a composite color signal by computing a sum of the luminance signal processed by the trap filter and the chrominance signal produced by the modulator.